http://www.mdpi.com/journal/catalysts Latest open access articles published in Catalysts at http://www.mdpi.com/journal/catalysts http://www.mdpi.com/2073-4344/3/2/501 The photocatalytic degradation of acridine orange (AO) dye by NaBiO3 photocatalyst under visible light irradiation was investigated systematically. The NaBiO3 photocatalyst exhibited a higher photocatalytic activity compared to the P25 photocatalyst. After 160 min of photocatalytic reaction, the degradation rate of AO could reach to 99% in appropriate conditions. Factors, such as catalyst dosage, solution pH, initial AO concentration and the presence of anions, were found to influence the degradation rate. To scrutinize the mechanistic details of the dye photodegradation, the intermediates of the processes were separated, identified and characterized by the HPLC-ESI-MS technique. The analytical results indicated that the N-de-methylation degradation of AO dye took place in a stepwise manner to yield mono-, di-, tri- and tetra-N-de-methylated AO species generated during the processes. The probable photodegradation pathways were proposed and discussed. Catalysts 2013-05-21 3 2 Article 10.3390/catal3020501 501 516 2073-4344 2013-05-21 doi: 10.3390/catal3020501 Chung-Shin Lu Chiing-Chang Chen Ling-Kuen Huang Peir-An Tsai Hsiao-Fang Lai http://www.mdpi.com/2073-4344/3/2/486 A method for synthesis without protecting groups of bis(indolyl)methanes by the (η3-benzyl)palladium system generated from a palladium catalyst and benzyl alcohol in water is developed. This domino protocol involves C3–H bond activation/benzylation of indole–carboxylic acids and benzylic C–H functionalization. Mechanistic studies indicate that the (η3-benzyl)palladium(II) complex, which is formed via oxidative addition of benzyl alcohol 2 to a Pd(0) species, activates the C–H bond at the C3-position of indole 1. Notably, water plays an important role in our catalytic system for sp3 C–O bond activation and stabilization of OH− by hydration for the smooth generation of the activated Pd(II) cation species, as well as for nucleophilic attack of indoles to hydrated benzyl alcohols. Catalysts 2013-05-16 3 2 Article 10.3390/catal3020486 486 500 2073-4344 2013-05-16 doi: 10.3390/catal3020486 Hidemasa Hikawa Hideharu Suzuki Yuusaku Yokoyama Isao Azumaya http://www.mdpi.com/2073-4344/3/2/455 Semiconductors crystal facet engineering has become an important strategy for properly tuning and optimizing both the physicochemical properties and the reactivity of photocatalysts. In this review, a concise survey of recent results obtained in the field of specific surface-oriented anatase TiO2 crystals preparation is presented. The attention is mainly focused on the fluorine-mediated hydrothermal and/or solvothermal processes employed for the synthesis and the assembly of anatase micro/nanostructures with dominant {001} facets. Their peculiar photocatalytic properties and potential applications are also presented, with a particular focus on photocatalysis-based environmental clean up and solar energy conversion applications. Finally, the most promising results obtained in the engineering of TiO2 anatase crystal facets obtained by employing alternative, possibly more environmentally friendly methods are critically compared. Catalysts 2013-05-16 3 2 Review 10.3390/catal3020455 455 485 2073-4344 2013-05-16 doi: 10.3390/catal3020455 Maria Dozzi Elena Selli http://www.mdpi.com/2073-4344/3/2/444 The purpose of this study is to present an “environmental catalyst” possessing both thermocatalytic activity and visible-light activity for the decomposition of organic pollutants. Molecule-sized MnOx clusters are highly dispersed on the surface of TiO2 (anatase/rutile = 4/1 w/w, P-25, Degussa) by the chemisorption-calcination cycle technique using Mn(acac)3 complex as a precursor (MnOx/TiO2). The thermo- and photo-catalytic activities of MnOx/TiO2 were studied for the degradation of 2-naphthol used as a model water pollutant. In contrast to the FeOx/TiO2 system, MnOx/TiO2 exhibits high thermocatalytic activity exceeding those of bulk β-β-MnO2 and Mn2O3. Also, visible-light activity is induced by the surface modification of TiO2 with MnOx clusters, whereas its UV-light activity decreases. Catalysts 2013-04-23 3 2 Article 10.3390/catal3020444 444 454 2073-4344 2013-04-23 doi: 10.3390/catal3020444 Qiliang Jin Hiroshi Arimoto Musashi Fujishima Hiroaki Tada http://www.mdpi.com/2073-4344/3/2/418 This work demonstrates how formation of strongly chemiluminescent 3-hydroxyphthalic hydrazide by hydroxylation of non-chemiluminescent phthalic hydrazide can be applied as a selective reaction probe to obtain information on authentic hydroxyl radical, i.e., •OHaq, formation, in black light illuminated Degussa P25 TiO2 aerated suspensions in the pH range from 3 to 11. The •OHaq formation was found to be strongly pH dependent. At alkaline pH, the apparent quantum efficiency of •OHaq formation was estimated to be at the ~10−2 level whereas at acidic pH it was near zero. Addition of phosphate and fluoride ions substantially enhanced the •OHaq production in the acidic pH range. It is suggested that •OHaq-radical formation in TiO2 photocatalysis can occur by oxidation of hydroxyl ions in the water layer adsorbed on TiO2 surfaces. Catalysts 2013-04-16 3 2 Article 10.3390/catal3020418 418 443 2073-4344 2013-04-16 doi: 10.3390/catal3020418 Haidong Liao Torbjörn Reitberger http://www.mdpi.com/2073-4344/3/2/401 Several important enzymatic reactions occurring in nature, such as, e.g., the digestion of fat, proceed only at the interface of two immiscible phases. Typically, these systems consist of an organic substrate, dispersed in an aqueous continuous phase, with a specialized enzyme capable of working at the interface. For adopting such a system for organic synthesis, a stable heterophase system with a large interfacial area is required. These prerequisites can be found in so-called miniemulsions. Such liquid-liquid heterophase systems feature droplets with sizes smaller than 500 nm, and more importantly, these emulsions do not suffer from Ostwald ripening, as conventional emulsions do. Consequently, the droplets show long-term stability, even throughout reactions conducted in the droplets. In this review, we will briefly discuss the physicochemical background of miniemulsions, provide a comprehensive overview of the enzymatically catalyzed reactions conducted in miniemulsions and, as data are available, to compare the most important features to conventional systems, as reverse microemulsions, (macro)emulsions and solvent-based systems. Catalysts 2013-04-09 3 2 Review 10.3390/catal3020401 401 417 2073-4344 2013-04-09 doi: 10.3390/catal3020401 Clemens Weiss Katharina Landfester http://www.mdpi.com/2073-4344/3/2/378 This article reviews work done at authors’ laboratories about catalysts based on combinations between copper and ceria for preferential oxidation of CO in H2-rich streams (CO-PROX). The main focus of this review is the characterization of active sites for the process on the basis of spectroscopic analysis of the systems under reaction conditions (operando techniques). On such a basis, it is exposed the state of the art in this field in connection with results obtained in other laboratories. Catalysts 2013-04-08 3 2 Review 10.3390/catal3020378 378 400 2073-4344 2013-04-08 doi: 10.3390/catal3020378 Arturo Martínez-Arias Daniel Gamarra Ana Hungría Marcos Fernández-García Guillermo Munuera Aitor Hornés Parthasarathi Bera José Conesa Antonio Cámara http://www.mdpi.com/2073-4344/3/2/363 Sulfate-doped TiO2 was prepared from sol−gel systems containing titaniumalkoxide and sulfuric acid. The time needed for gelation of the systems was significantlyreduced by ultrasonic irradiation. The doped sulfate was observed by FTIR and XPSmeasurements. Some sulfate ions remained in the TiO2 even after heating at 300−600 °C.The UV and visible photocatalytic activities of the samples were confirmed by thedegradation of trichloroethylene (TCE). The activity of the photocatalyst samples duringthe UV irradiation strongly depended on their crystallinities rather than their specificsurface areas, i.e., adsorption ability. The degradation rate during the visible irradiationdepended on both the adsorption ability and visible absorption of the photocatalystsamples. The visible absorption induced by the sulfate-doping was effective for theTCE degradation. Catalysts 2013-04-08 3 2 Article 10.3390/catal3020363 363 377 2073-4344 2013-04-08 doi: 10.3390/catal3020363 Hiromasa Nishikiori Maki Hayashibe Tsuneo Fujii http://www.mdpi.com/2073-4344/3/1/338 Practical photocatalysis for degradation of organic pollutants must take into account the influence of other chemicals. Significant Al deposition on titania can occur at naturally occurring concentrations of dissolved Al. This paper reviews the author’s work on the influence of deliberately deposited hydrous oxides of aluminium on the behavior of a ~130 m2 g−1 rutile TiO2, and then compares the behavior of deposited alumina with that of deposited silica. On rutile some adsorbed nitrogen is infrared-active. Alumina and silica deposited on the rutile reduce, and ultimately eliminate, this infrared-active species. They also reduce photocatalytic oxidation of both propan-2-ol and dichloroacetate ion and the photocatalytic reduction of diphenyl picryl hydrazine. The surface oxides suppress charge transfer and may also reduce reactant adsorption. Quantitative measurement of TiO2 photogreying shows that the adsorbed inorganics also reduce photogreying, attributed to the capture of photogenerated conduction band electrons by Ti4+ to form Ti3+. The influence of adsorbed phosphate on photocatalysis is briefly considered, since phosphate reduces photocatalytic disinfection. In the context of classical colloid studies, it is concluded that inorganic species in water can significantly reduce photoactivity from the levels that measured in pure water. Catalysts 2013-03-21 3 1 Review 10.3390/catal3010338 338 362 2073-4344 2013-03-21 doi: 10.3390/catal3010338 Terry Egerton http://www.mdpi.com/2073-4344/3/1/324 The effect of nanostructured supports on the activity of Rh catalysts was studied by comparing the catalytic performance of nano- and bulk-oxide supported Rh/ZnO, Rh/SiO2 and Rh/TiO2 systems in 1-hexene hydroformylation. The highest activity with 100% total conversion and 96% yield of aldehydes was obtained with the Rh/nano-ZnO catalyst. The Rh/nano-ZnO catalyst was found to be more stable and active than the corresponding rhodium catalyst supported on bulk ZnO. The favorable morphology of Rh/nano-ZnO particles led to an increased metal content and an increased number of weak acid sites compared to the bulk ZnO supported catalysts. Both these factors favored the improved catalytic performance. Improvements of catalytic properties were obtained also with the nano-SiO2 and nano-TiO2 supports in comparison with the bulk supports. All of the catalysts were characterized by scanning electron microscope (SEM), inductively coupled plasma mass spectrometry (ICP-MS), BET, powder X-ray diffraction (PXRD) and NH3- temperature-programmed desorption (TPD). Catalysts 2013-03-21 3 1 Article 10.3390/catal3010324 324 337 2073-4344 2013-03-21 doi: 10.3390/catal3010324 Maija-Liisa Kontkanen Matti Tuikka Niko Kinnunen Sari Suvanto Matti Haukka http://www.mdpi.com/2073-4344/3/1/310 Photocatalytically active titanium dioxide (TiO2) is widely used as a self-cleaning and self-disinfecting material in many applications to keep environments biologically clean. Several studies on the inactivation of bacteria and viruses by photocatalytic reactions have also been reported; however, only few studies evaluated the spectrum of the microbicidal activity with photocatalysis for various species. There is a need to confirm the expected effectiveness of disinfection by photocatalysis against multidrug-resistant bacteria and viruses. In this study, microbicidal activity of photocatalysis was evaluated by comparing the inactivation of various species of bacteria and viruses when their suspensions were dropped on the surface of TiO2-coated glass. Gram-positive bacteria, e.g., methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus faecalis, and penicillin-resistant Streptococcus pneumoniae, were easily inactivated by photocatalysis, whereas some gram-negative bacteria, e.g., Escherichia coli and multidrug-resistant Pseudomonas aeruginosa, were gradually inactivated by photocatalysis. Influenza virus, an enveloped virus, was significantly inactivated by photocatalysis compared with feline calicivirus, a non-enveloped virus. The effectiveness of microbicidal activity by photocatalysis may depend on the surface structure. However, they are effectively inactivated by photocatalysis on the surface of TiO2-coated glass. Our data emphasize that effective cleaning and disinfection by photocatalysis in nosocomial settings prevents pathogen transmission. Catalysts 2013-03-21 3 1 Article 10.3390/catal3010310 310 323 2073-4344 2013-03-21 doi: 10.3390/catal3010310 Ryuichi Nakano Masayuki Hara Hitoshi Ishiguro Yanyan Yao Tsuyoshi Ochiai Kazuya Nakata Taketoshi Murakami Jitsuo Kajioka Kayano Sunada Kazuhito Hashimoto Akira Fujishima Yoshinobu Kubota http://www.mdpi.com/2073-4344/3/1/288 Gold nanostars of ~70 nm tip to tip distances were synthesized by a seed mediated method and covalently self-assembled on 1,5-pentanedithiol modified electrodes. Electron transfer kinetics at the AuNS/dithiol modified electrodes were studied as a function of AuNS surface density which was varied by increasing their self-assembly time from 8 h, 16 h, 24 h to 32 h. Excellent electrocatalytic properties of AuNSs were observed toward electrochemistry of [Fe(CN)6]4−/3− redox couple. The apparent heterogeneous electron transfer constant, ket, has progressively increased with the surface density of AuNSs bonded to the electrodes from 0.65 × 10−5 cm s−1 (8 h), 1.47 × 10−5 cm s−1 (16 h), 3.95 × 10−5 cm s−1 (24 h) to an excellent 85.0 × 10−5 cm s−1 (32 h). Electrochemical charging of nanostars was confirmed, for the first time, by 79 times increase of double layer capacitance, Cdl, from 0.34 µF (8 h) to 27 µF (32 h). The electrochemical charging of AuNSs had also a strong influence on the electron tunneling process through the 1,5PDT molecules being more efficient at dense layers of AuNSs. The tunneling parameter, β, has decreased from 1.13 Å−1 (16 h) to 0.50 Å−1 (32 h). The AuNSs were chemically stable toward [Fe(CN)6]4−/3− showing no change in shape after electrochemical measurements. Catalysts 2013-03-12 3 1 Article 10.3390/catal3010288 288 309 2073-4344 2013-03-12 doi: 10.3390/catal3010288 Mariana Chirea http://www.mdpi.com/2073-4344/3/1/276 A partially reduced TiO2 surface exhibits increasingly complex nature when forming various defects, whose stoichiometry, structure and properties are markedly different from those of bulk TiO2. Using scanning tunneling microscopy and density functional theory, we investigate different types of surface defects formed by Ti interstitials on TiO2 (110) and their reactivity toward deposited gold atoms. Sub-stoichiometric strands greatly enhance bonding of Au by transferring the excess charges from the reduced Ti3+ onto the strands. Thus the sub-stoichiometric strands behave as strong electron donor sites toward reactants. On the contrary, fully stoichiometric nanoclusters provide increased Au bonding through its 1-coordinated oxygen, which acts as a strong electron acceptor site. Specific interactions between Au and defects as well as the implication of electron donor/acceptor complexes for catalytic reactions are discussed. Catalysts 2013-03-08 3 1 Article 10.3390/catal3010276 276 287 2073-4344 2013-03-08 doi: 10.3390/catal3010276 Kenneth Park Vincent Meunier Minghu Pan Ward Plummer http://www.mdpi.com/2073-4344/3/1/261 A series of novel half-titanocene complexes CpTiCl2[S-2-R-6-(PPh2)C6H3] (Cp = C5H5, 2a, R = H; 2b, R = Ph; 2c, R = SiMe3) have been synthesized by treating CpTiCl3 with the sodium of the ligands, 2-R-6-(PPh2)C6H3SNa, which were prepared by the corresponding ligands and NaH. These complexes have been characterized by 1H, 13C and 31P NMR as well as elemental analyses. Structures for 2a–b were further confirmed by X-ray crystallography. Complexes 2a–b adopt five-coordinate, distorted square-pyramid geometry around the titanium center, in which the equatorial positions are occupied by sulfur and phosphorus atoms of the chelating phosphine-thiophenolate and two chlorine atoms, and the cyclopentadienyl ring is coordinated on the axial position. The complexes 2a–c were investigated as the catalysts for ethylene polymerization and copolymerization of ethylene with norbornene in the presence of MMAO or Ph3CB(C6F5)4/iBu3Al as the cocatalyst. All complexes exhibited low to moderate activities towards homopolymerization of ethylene. However, they displayed moderate to high activities towards copolymerization of ethylene with norbornene. Catalysts 2013-03-06 3 1 Article 10.3390/catal3010261 261 275 2073-4344 2013-03-06 doi: 10.3390/catal3010261 Xiao-Yan Tang Jing-Yu Liu Yue-Sheng Li http://www.mdpi.com/2073-4344/3/1/247 TiO2 nanostructured films were synthesized by an aerosol chemical vapor deposition (ACVD) method with different controlled morphologies: columnar, granular, and branched structures for the photocatalytic inactivation of Escherichia coli (E. coli) in water. Effects of film morphology and external applied voltage on inactivation rate were investigated. As-prepared films were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometry (XRD), and UV-VIS. Photocatalytic and photoelectrochemical inactivation of E. coli using as-prepared TiO2 films were performed under irradiation of UVA light (note: UVA has a low efficiency to inactivate E. coli). Inactivation rate constants for each case were obtained from their respective inactivation curve through a 2 h incubation period. Photocatalytic inactivation rate constants of E. coli are 0.02/min (using columnar films), and 0.08/min (using branched films). The inactivation rate constant for the columnar film was enhanced by 330% by applied voltage on the film while that for the branched film was increased only by 30%. Photocatalytic microbial inactivation rate of the columnar and the branched films were also compared taking into account their different surface areas. Since the majority of the UV radiation that reaches the Earth’s surface is UVA, this study provides an opportunity to use sunlight to efficiently decontaminate drinking water. Catalysts 2013-03-04 3 1 Article 10.3390/catal3010247 247 260 2073-4344 2013-03-04 doi: 10.3390/catal3010247 Jinho Park Eric Kettleson Woo-Jin An Yinjie Tang Pratim Biswas http://www.mdpi.com/2073-4344/3/1/232 Kraft pulp has to be bleached to eliminate the chromophoric structures, which cause a darkening of the pulp. In Nature, an equivalent role is assumed by ligninolytic enzymes such as lignin peroxidases, manganese peroxidases and laccases. The development of low molecular weight manganese peroxidase mimics may achieve environmentally-safe bleaching catalysts for the industry. Herein we report the synthesis and characterization of six manganese(III) complexes 1–6, incorporating dianionic hexadentate Schiff base ligands (H2L1-H2L4) and different anions. Complex 4, Mn2L22(H2O)2(DCA)2 was crystallographically characterized. Complexes 1–4 behave as more efficient mimics of peroxidase in contrast to 5–6. We have studied the use of these complexes as catalysts for the degradation of the lignin model compound veratryl alcohol. The biomimetic catalysts were used in conjunction with chlorine-free inexpensive co-oxidants as dioxygen or hydrogen peroxide. Yields up to 30% of veratryl alcohol conversion to veratraldehyde have been achieved at room temperature in presence of air flow using 0.5% of catalyst. Catalysts 2013-03-04 3 1 Article 10.3390/catal3010232 232 246 2073-4344 2013-03-04 doi: 10.3390/catal3010232 Gustavo González-Riopedre María Fernández-García Esther Gómez-Fórneas Marcelino Maneiro http://www.mdpi.com/2073-4344/3/1/219 Gas-solid heterogeneous photooxidation of toluene over TiO2 catalyst was studied to investigate the factors controlling the catalytic activities. The toluene photooxidation behavior on TiO2 was strongly affected by the formation and oxidation behavior of intermediate compounds on TiO2, and their accumulation decreased the reaction rate for toluene photooxidation. The formation and oxidation behavior of the byproduct compounds depended on the initial concentration of toluene and water vapor. In situ Fourier transform infrared (FTIR) studies revealed that water vapor promoted the cleavage of the aromatic ring and facilitated CO2 formation. At the reaction temperature of 300 K, the deposition of Pt on TiO2 suppressed CO formation, whereas catalytic activity was decreased due to the increase in the amount of intermediate compounds. On the other hand, Pt/TiO2 showed higher activity than TiO2 at 353 K, in spite of the increase of the intermediate compounds. Catalysts 2013-03-04 3 1 Article 10.3390/catal3010219 219 231 2073-4344 2013-03-04 doi: 10.3390/catal3010219 Hisahiro Einaga Keisuke Mochiduki Yasutake Teraoka http://www.mdpi.com/2073-4344/3/1/189 Semiconductor heterogeneous photocatalysis, the subject of this review, is a versatile, low-cost and environmentally benign treatment technology for a host of pollutants. These may be of biological, organic and inorganic in origin within water and air. The efficient and successful application of photocatalysis demands that the pollutant, the catalyst and source of illumination are in close proximity or contact with each other. The ability of advanced oxidation technology to remove low levels of persistent organic pollutants as well as microorganisms in water has been widely demonstrated and, progressively, the technology is now being commercialized in many areas of the world including developing nations. This review considers recent developments in the research and application of heterogeneous semiconductor photocatalysis for the treatment of low-level concentrations of pollutants in water and air using titanium dioxide as a “model” semiconductor. The review considers charge transport characteristics on the semiconductor surface, photocatalyst reactor design and organic degradation mechanistic pathways. The effects of photoreactor operating parameters on the photocatalytic process are discussed in addition to mineralization and disinfection kinetics. Catalysts 2013-03-01 3 1 Review 10.3390/catal3010189 189 218 2073-4344 2013-03-01 doi: 10.3390/catal3010189 Alex Ibhadon Paul Fitzpatrick http://www.mdpi.com/2073-4344/3/1/176 We synthesized polyethylene (PE), poly(ethylene-co-1-decene), poly(ethylene-co-p-methylstyrene) and poly(ethylene-ter-1-decene-ter-p-methystyrene) using a rac-Et(Ind)2ZrCl2 metallocene catalyst and a methylaluminoxane cocatalyst system. The materials were characterized using nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy. We compared and studied the kinetics, thermal properties and mechanical ones of these polymers. Tg was related to the amorphous phase of the polymers, whereas the tensile strength and storage modulus (E’) were related to the crystalline phase. We also found that PE has the highest crystallinity through differential scanning calorimetry and wide-angle X-ray scattering analysis. The polymerization rates of poly(ethylene-co-1-decene) and poly(ethylene-ter-1-decene-ter-p-methystyrene) were always higher than that of polyethylene. Catalysts 2013-02-22 3 1 Article 10.3390/catal3010176 176 188 2073-4344 2013-02-22 doi: 10.3390/catal3010176 Dong Yang Hyun Kim Dong Kim http://www.mdpi.com/2073-4344/3/1/157 This review summarizes recent results for ethylene/styrene copolymerization using half-titanocenes containing anionic donor ligands, Cp’TiX2(Y) (X = halogen, alkyl; Y = aryloxo, ketimide etc.)–cocatalyst systems. The product composition, the styrene incorporation and microstructures in the resultant copolymers are highly influenced by the anionic donor employed. A methodology for an exclusive synthesis of the copolymers even under high temperature and high styrene concentrations has been introduced on the basis of a proposed catalytically-active species in this catalysis. Catalysts 2013-02-18 3 1 Review 10.3390/catal3010157 157 175 2073-4344 2013-02-18 doi: 10.3390/catal3010157 Kotohiro Nomura http://www.mdpi.com/2073-4344/3/1/148 The effect of ligand and Al cocatalysts in ethylene polymerization, using V(N-1-adamantyl)Cl2(L) [L = 2-(2,6-Me2C6H3)NCH2(C9H6N), 8-(2,6-Me2C6H3)NCH2(C9H6N)] and V(N-2-MeC6H3)Cl2[2-(2,6-R'2C6H3)NCH2(C5H4N)] (R' = Me, iPr), has been explored. The reaction products in the presence of Et2AlCl or Me2AlCl cocatalyst were polyethylene whereas the reaction product of the 2-methylphenylimido analogues in the presence of MAO cocatalyst was 1-butene with high selectivity, suggesting that the catalyst/cocatalyst nuclearity effect plays a role in this catalysis. Catalysts 2013-02-07 3 1 Article 10.3390/catal3010148 148 156 2073-4344 2013-02-07 doi: 10.3390/catal3010148 Atsushi Igarashi Wenjuan Zhang Wen-Hua Sun Kotohiro Nomura http://www.mdpi.com/2073-4344/3/1/137 In heterogeneous Ziegler-Natta catalysts for olefin polymerization, isolation of a single type of active sites is a kind of ambition, which would solve long-standing questions on the relationship between active site and polymer structures. In this paper, polypropylene produced by TiCl3/MgCl2 model catalysts with minimum Ti heterogeneity was analyzed by combined solvent fractionation and the two-site statistical model. We found that the active sites of the model catalysts were classified into only three types, whose proportions were dependent on the Ti dispersion state. The addition of external donors not only newly formed highly isospecific sites, but also altered the stereochemical nature of the other active sites. Catalysts 2013-02-07 3 1 Article 10.3390/catal3010137 137 147 2073-4344 2013-02-07 doi: 10.3390/catal3010137 Shougo Takahashi Toru Wada Toshiaki Taniike Minoru Terano http://www.mdpi.com/2073-4344/3/1/125 Heterogeneous catalysts for production of linear α-olefins from ethylene were prepared by the direct reaction of the α-diimine ligand [L: R-N=C(R')-C(R')=N-R; R' = Me and R = 2,6-Me2Ph (L5), 2,5-Me2Ph (L1), 2-MePh (L2), or Ph (L3); R' = 1,8-naphth-diyl and R = Ph (L4)] and Ni2+ ion-exchanged fluorotetrasilicic mica. Only high molecular weight polyethylene was obtained in the reaction using the L5/Ni2+-Mica procatalyst activated by AlEt3 (TEA) as an activator, whereas the TEA-activated L1- and L2/Ni2+-Mica procatalysts afforded a mixture of a large amount of low-molecular weight polyethylene and a small amount of oligomers having 4-22 carbons. The procatalyst consisting of Ni2+-Mica and the L3 ligand that possesses non-substituted phenyl groups on the iminonitrogen atoms effectively promoted the oligomerization of ethylene after its activation with TEA, resulting in the fact that the ethylene oligomers were produced with a moderate catalytic activity (101 g-ethylene g-cat−1 h−1 at 0.7 MPa-ethylene) in the presence of TEA. When the backbone was varied from the butane moiety (L3) to acenaphthene (L4), the solid product dramatically increased. The weight percentage of the oligomers in the total products increased with the increasing reaction temperature; however, an insignificant increase in the oligomers was observed when the ethylene pressure was decreased. Catalysts 2013-02-06 3 1 Article 10.3390/catal3010125 125 136 2073-4344 2013-02-06 doi: 10.3390/catal3010125 Hideki Kurokawa Kazuki Miura Kazuhiro Yamamoto Tsutomu Sakuragi Takao Sugiyama Masa-aki Ohshima Hiroshi Miura http://www.mdpi.com/2073-4344/3/1/104 A synthetic scheme was developed for the large-scale preparation of a dimethylthiophene-fused and tetrahydroquinaldine-linked dimethylcyclopentadienyl titanium complex (2), which is a high-performance homogeneous Ziegler catalyst. 2,3,4,5-Tetramethyl-4,5-dihydrocyclopenta[b]thiophen-6-one was prepared without chromatography purification on the 40-g scale in a laboratory setting, from which the ligand precursor for 2 was obtained in 65% yield on a 50-g scale in a one-pot without the need for chromatography purification. Metallation was achieved in a high yield (78%) through reaction of the dilithiated compound with TiCl4. Many derivatives were prepared by employing the same synthetic scheme as applied for 2. Among them, the titanium complex prepared from 2-methyl-4,5-dimethyl-6-(2-n-butyl-2,3,4,5-tetrahydroquinolin-8-yl)-4H-cyclopenta[b]thiophene exhibited an exceptionally high activity. Under commercially relevant high-temperature polymerization conditions (160 °C), this compound showed a higher activity than 2 (126 × 106 g/molTi∙h versus 72 × 106 g/molTi∙h), albeit with the formation of a polymer of slightly lower molecular weight (Mw, 159,000 versus 218,000) and with a slightly lower 1-octene content (9.3 mol% versus 12 mol%). Catalysts 2013-02-06 3 1 Article 10.3390/catal3010104 104 124 2073-4344 2013-02-06 doi: 10.3390/catal3010104 Sung Kim Ji Park Bo Song Seung-Woong Yoon Min Go Junseong Lee Bun Lee http://www.mdpi.com/2073-4344/3/1/88 In this work, we studied how TiO2 and ZrO2 coatings enhance the CO oxidation performance of SiO2-supported Pt catalysts under conditions relevant to automotive emissions control. SiO2 was coated with metal oxides TiO2 or ZrO2 by sol-gel method and the subsequent Pt loading was done by incipient wetness method. The prepared catalysts Pt/TiO2-SiO2 and Pt/ZrO2-SiO2 were compared with Pt/SiO2 and Pt/Al2O3 in fresh, sulfated, and hydrothermally aged states. The structure of the catalysts was characterized with BET, XRD, TEM, EDS, EXAFS, XANES, TPD and TPR to help interpret the CO oxidation performance. Higher dispersion, stability, and oxidation state of Pt were achieved on TiO2-SiO2 and ZrO2-SiO2 supports due to stronger metal-support interaction leading to superior CO oxidation performance compared to Pt/SiO2 and Pt/Al2O3. TiO2 and ZrO2 coatings introduced surface acidity but negligible basicity, which is a likely reason for the weak and low adsorption of SO2. The results suggest that the sol-gel coating of SiO2 with metal oxides could be an attractive strategy for designing automotive oxidation catalysts with enhanced performance such as low-temperature activity, sulfur tolerance, and hydrothermal stability. Catalysts 2013-02-06 3 1 Article 10.3390/catal3010088 88 103 2073-4344 2013-02-06 doi: 10.3390/catal3010088 Mi-Young Kim Jae-Soon Choi Todd Toops Eun-Suk Jeong Sang-Wook Han Viviane Schwartz Jihua Chen http://www.mdpi.com/2073-4344/3/1/74 Analysis methods that require small volumes of aqueous samples can be of large benefit for applications when expensive chemicals are involved or available volumes are substantially small and concentrations are low. A new method is presented to allow microvolume liquid injections on TOC equipment using a special designed Shimadzu gas injection kit® in combination with a high precision syringe and Chaney adapter. Next to details on the methodology of microvolume TOC injections, the technique is shown to be beneficial to evaluate the efficiency of photocatalytic dye degradation on titania materials in terms of CO2 conversion simultaneously with classic UV-Vis analysis measurements within a lab scale photocatalytic test setup (volume <100 mL). The possibility to allow multiple microvolume samplings in short time intervals during several hours without a substantial decrease in volume/catalyst ratio is of particular value for the evaluation of photocatalysts. By combining both techniques at short time intervals, additional knowledge of the degradation process/mechanism, kinetics and the efficiency can be obtained in a direct way. Moreover, the developed μV-TOC analysis is specifically useful in those applications in which low sample volumes in combination with low concentrations are involved. For example, μV-TOC can similarly be put into service in a wide range of small volume setups, e.g., analytes from high-throughput screening, pharmaceutical applications and other advanced oxidation processes that formally could not be analyzed due to limited sample volumes and often low concentrations. Catalysts 2013-01-22 3 1 Article 10.3390/catal3010074 74 87 2073-4344 2013-01-22 doi: 10.3390/catal3010074 Monika Kus Stefan Ribbens Vera Meynen Pegie Cool http://www.mdpi.com/2073-4344/3/1/36 Brookite is the least studied TiO2 photocatalyst due to the difficulties usually encountered in order to obtain it as a pure phase. In this review, a comprehensive survey of the different methods available for preparing brookite powders and films is reported. Attention has been paid both to the most traditional methods, such as hydrothermal processes at high temperatures and pressures, and to environmentally benign syntheses using water soluble compounds and water as the solvent. Papers reporting the photocatalytic activity of pure and brookite-based samples have been reviewed. Catalysts 2013-01-18 3 1 Review 10.3390/catal3010036 36 73 2073-4344 2013-01-18 doi: 10.3390/catal3010036 Agatino Di Paola Marianna Bellardita Leonardo Palmisano http://www.mdpi.com/2073-4344/3/1/27 We report the first evidence of an enzyme-catalyzed transetherification of model alkoxysilanes. During an extensive enzymatic screening in the search for new biocatalysts for silicon-oxygen bond formation, we found that certain enzymes promoted the transetherification of alkoxysilanes when tert-butanol or 1-octanol were used as the reaction solvents. Catalysts 2013-01-18 3 1 Communication 10.3390/catal3010027 27 35 2073-4344 2013-01-18 doi: 10.3390/catal3010027 Vincenzo Abbate Kurt Brandstadt Peter Taylor Alan Bassindale http://www.mdpi.com/2073-4344/3/1/11 Vanadium phosphorous oxide (VPO) is traditionally manufactured from solid vanadium oxides by synthesizing VOHPO4∙0.5H2O (the precursor) followed by in situ activation to produce (VO)2P2O7 (the active phase). This paper discusses an alternative synthesis method based on sol-gel techniques. Vanadium (V) triisopropoxide oxide was reacted with ortho-phosphoric acid in an aprotic solvent. The products were dried at high pressure in an autoclave with a controlled excess of solvent. This procedure produced a gel of VOPO4 with interlayer entrapped molecules. The surface area of the obtained materials was between 50 and 120 m2/g. Alcohol produced by the alkoxide hydrolysis reduced the vanadium during the drying step, thus VOPO4 was converted to the precursor. This procedure yielded non-agglomerated platelets, which were dehydrated and evaluated in a butane-air mixture. Catalysts were significantly more selective than the traditionally prepared materials with similar intrinsic activity. It is suggested that the small crystallite size obtained increased their selectivity towards maleic anhydride. Catalysts 2013-01-16 3 1 Article 10.3390/catal3010011 11 26 2073-4344 2013-01-16 doi: 10.3390/catal3010011 Juan Salazar Keith Hohn http://www.mdpi.com/2073-4344/3/1/1 Sr2−xBaxTa3O10−yNz (x = 0.0, 0.5, 1.0) nanosheets were prepared by exfoliating layered perovskite compounds (CsSr2−xBaxTa3O10−yNz). The Sr1.5Ba0.5Ta3O9.7N0.2 nanosheet showed the highest photocatalytic activity for H2 production from the water/methanol system among the Sr2−xBaxTa3O9.7N0.2 nanosheets prepared. In addition, Rh-loaded Sr1.5Ba0.5Ta3O9.6N0.3 nanosheet showed the photocatalytic activity for oxygen and hydrogen production from water. The ratio of hydrogen to oxygen evolved was around two. These results indicate that the Rh-loaded Sr1.5Ba0.5Ta3O9.6N0.3 nanosheet is a potential catalyst for photocatalytic water splitting. Catalysts 2013-01-16 3 1 Article 10.3390/catal3010001 1 10 2073-4344 2013-01-16 doi: 10.3390/catal3010001 Shintaro Ida Yohei Okamoto Hidehisa Hagiwara Tatsumi Ishihara http://www.mdpi.com/2073-4344/2/4/572 Photocatalytic water treatment using nanocrystalline titanium dioxide (NTO) is a well-known advanced oxidation process (AOP) for environmental remediation. With the in situ generation of electron-hole pairs upon irradiation with light, NTO can mineralize a wide range of organic compounds into harmless end products such as carbon dioxide, water, and inorganic ions. Photocatalytic degradation kinetics of pollutants by NTO is a topic of debate and the mostly reporting Langmuir-Hinshelwood kinetics must accompanied with proper experimental evidences. Different NTO morphologies or surface treatments on NTO can increase the photocatalytic efficiency in degradation reactions. Wisely designed photocatalytic reactors can decrease energy consumption or can avoid post-separation stages in photocatalytic water treatment processes. Doping NTO with metals or non-metals can reduce the band gap of the doped catalyst, enabling light absorption in the visible region. Coupling NTO photocatalysis with other water-treatment technologies can be more beneficial, especially in large-scale treatments. This review describes recent developments in the field of photocatalytic water treatment using NTO. Catalysts 2012-12-19 2 4 Review 10.3390/catal2040572 572 601 2073-4344 2012-12-19 doi: 10.3390/catal2040572 Manoj Lazar Shaji Varghese Santhosh Nair http://www.mdpi.com/2073-4344/2/4/544 This review gives an overview on the principles of light-promoted homogeneous redox catalysis in terms of applications in CO2 conversion. Various chromophores and the advantages of different structures and metal centers as well as optimization strategies are discussed. All aspects of the reduction catalyst site are restricted to CO2 conversion. An important focus of this review is the question of a replacement of the sacrificial donor which is found in most of the current publications. Furthermore, electronic parameters of supramolecular systems are reviewed with reference to the requisite of chromophores, oxidation and reduction sites. Catalysts 2012-11-27 2 4 Review 10.3390/catal2040544 544 571 2073-4344 2012-11-27 doi: 10.3390/catal2040544 Richard Reithmeier Christian Bruckmeier Bernhard Rieger http://www.mdpi.com/2073-4344/2/4/532 We have studied the effect of ball milling on alumina mixed nickel, magnetite and Raney nickel on the reaction: 2NaOH(s) + CO (g) = Na2CO3 (s) + H2 (g) and determined the optimum particle size for the catalysts. The best performance was shown by a 2 h ball milled Raney nickel with average crystallite size of 209 Å. This reaction serves the dual purpose of carbon sequestration and yielding hydrogen gas. Catalysts 2012-11-27 2 4 Article 10.3390/catal2040532 532 543 2073-4344 2012-11-27 doi: 10.3390/catal2040532 Sushant Kumar Vadym Drozd Surendra Saxena http://www.mdpi.com/2073-4344/2/4/517 Tyrosinase-based biosensors containing a phthalocyanine as electron mediator have been prepared by two different methods. In the first approach, the enzyme and the electron mediator have been immobilized in carbon paste electrodes. In the second method, they have been introduced in an arachidic acid Langmuir-Blodgett nanostructured film that provides a biomimetic environment. The sensing properties of non-nanostructured and nanostructured biosensors towards catechol, catechin and phenol have been analyzed and compared. The enzyme retains the biocatalytic properties in both matrixes. However, the nanostructured biomimetic films show higher values of maximum reaction rates and lowest apparent Michaelis-Menten constants. In both types of sensors, the sensitivity follows the decreasing order catechol > catechin > phenol. The detection limits observed are in the range of 1.8–5.4 μM for Langmuir-Blodgett biosensors and 8.19–8.57 μM for carbon paste biosensors. In summary, it has been demonstrated that the Langmuir-Blodgett films provide a biomimetic environment and nanostructured biosensors show better performances in terms of kinetic, detection limit and stability. Catalysts 2012-11-09 2 4 Article 10.3390/catal2040517 517 531 2073-4344 2012-11-09 doi: 10.3390/catal2040517 Constantin Apetrei Jose Saja Javier Zurro Maria Rodríguez-Méndez http://www.mdpi.com/2073-4344/2/4/490 Hydrogen is the ideal fuel for the future because it is clean, energy efficient, and abundant in nature. While various technologies can be used to generate hydrogen, only some of them can be considered environmentally friendly. Recently, solar hydrogen generated via photocatalytic water splitting has attracted tremendous attention and has been extensively studied because of its great potential for low-cost and clean hydrogen production. This paper gives a comprehensive review of the development of photocatalytic water splitting for generating hydrogen, particularly under visible-light irradiation. The topics covered include an introduction of hydrogen production technologies, a review of photocatalytic water splitting over titania and non-titania based photocatalysts, a discussion of the types of photocatalytic water-splitting approaches, and a conclusion for the current challenges and future prospects of photocatalytic water splitting. Based on the literatures reported here, the development of highly stable visible–light-active photocatalytic materials, and the design of efficient, low-cost photoreactor systems are the key for the advancement of solar-hydrogen production via photocatalytic water splitting in the future. Catalysts 2012-10-17 2 4 Review 10.3390/catal2040490 490 516 2073-4344 2012-10-17 doi: 10.3390/catal2040490 Chi-Hung Liao Chao-Wei Huang Jeffrey C. S. Wu http://www.mdpi.com/2073-4344/2/4/466 Carbon xerogels characterized by different textural, structural and chemical properties were synthesized and used as supports for Pt catalysts for the application in polymer electrolyte fuel cells. Synthesis conditions were varied in order to synthesize carbon xerogels following the sol-gel method. These included the reactants ratio (precursor/formaldehyde), the catalyst concentration (precursor/catalyst ratio) and type (basic and acid), the precursor type (resorcinol and pyrogallol) and the solvent (aqueous or acetone based). Stoichiometric mixtures of resorcinol and formaldehyde yielded well polymerized gels and highly developed structures. Slow gelation, favored by the presence of acetone as solvent in the sol and low catalyst concentration, resulted in higher polymerization extent with a highly mesoporous or even macroporous texture and more ordered structure, as evidenced by XPS and Raman spectroscopy. Small Pt particles of ca. 3.5 nm were obtained by using carbon xerogels characterized by an ordered surface structure. The specific activity towards the oxygen reduction reaction, i.e., the limiting catalytic process in low temperature fuel cells, is significantly favored by highly ordered carbon xerogels due to a metal-support enhanced interaction. Nevertheless, surface defects favor the distribution of the metallic particles on the surface of carbon, which in the end influences the effectiveness of the catalyst. Accelerated degradation tests were conducted to evaluate catalyst stability under potential cycling conditions. The observed decay of performance was considerably lower for the catalysts based on ordered carbon xerogels stabilizing Pt particles in a higher extent than the other xerogels and the commercial carbon black support. Catalysts 2012-10-17 2 4 Article 10.3390/catal2040466 466 489 2073-4344 2012-10-17 doi: 10.3390/catal2040466 Cinthia Alegre David Sebastián Estela Baquedano María Elena Gálvez Rafael Moliner María Jesús Lázaro http://www.mdpi.com/2073-4344/2/4/447 Carbon xerogels were prepared by the polycondensation of resorcinol and formaldehyde using three different solution pH values and the gels were carbonized at three different temperatures. Results show that it is possible to tailor the pore texture of carbon xerogels by adjusting the pH of the initial solution and the carbonization temperature. Materials with different textural properties were obtained and used as catalysts for NO oxidation at room temperature. The NO conversions obtained with carbon xerogels were quite high, showing that carbon xerogels are efficient catalysts for NO oxidation. A maximum of 98% conversion for NO was obtained at initial concentration of NO of 1000 ppm and 10% of O2. The highest NO conversions were obtained with the samples presenting the highest surface areas. The temperature of reaction has a strong influence on NO oxidation: the conversion of NO decreases with the increase of reaction temperature. Catalysts 2012-10-17 2 4 Article 10.3390/catal2040447 447 465 2073-4344 2012-10-17 doi: 10.3390/catal2040447 Juliana P. S. Sousa Manuel F. R. Pereira José L. Figueiredo http://www.mdpi.com/2073-4344/2/4/434 Pristine complex quaternary hydride (LiBH4/2LiNH2) and its destabilized counterpart (LiBH4/2LiNH2/nanoMgH2) have recently shown promising reversible hydrogen storage capacity under moderate operating conditions. The destabilization of complex hydride via nanocrystalline MgH2 apparently lowers the thermodynamic heat values and thus enhances the reversible hydrogen storage behavior at moderate temperatures. However, the kinetics of these materials is rather low and needs to be improved for on-board vehicular applications. Nanocatalyst additives such as nano Ni, nano Fe, nano Co, nano Mn and nano Cu at low concentrations on the complex hydride host structures have demonstrated a reduction in the decomposition temperature and overall increase in the hydrogen desorption reaction rates. Bi-metallic nanocatalysts such as the combination of nano Fe and nano Ni have shown further pronounced kinetics enhancement in comparison to their individual counterparts. Additionally, the vital advantage of using bi-metallic nanocatalysts is to enable the synergistic effects and characteristics of the two transitional nanometal species on the host hydride matrix for the optimized hydrogen storage behavior. Catalysts 2012-10-17 2 4 Article 10.3390/catal2040434 434 446 2073-4344 2012-10-17 doi: 10.3390/catal2040434 Sesha S. Srinivasan Prakash C. Sharma http://www.mdpi.com/2073-4344/2/4/422 Carbon aerogels prepared at different carbonization temperatures and with varying mesopore volumes were used as supports for Pt catalysts to study the n-C4H10/H2 reaction. Mean Pt particle size depended on the mesopore volume of the support, showing a linear decrease when the mesopore volume increased. The turnover frequency (TOF) for hydrogenolysis was much higher than for isomerization in catalysts supported on carbon aerogels obtained at 900–950 °C. However, both TOF values were similar in catalysts supported on the carbon aerogel obtained at 500 °C. TOF for hydrogenolysis and isomerization were related to the mean Pt particle size in catalysts supported on carbon aerogels obtained at 900–950 °C. In addition, both reactions showed a compensation effect between the activation energy and pre-exponential factor, indicating that they have the same intermediate, i.e., the chemisorbed dehydrogenated alkane. Catalysts 2012-10-12 2 4 Article 10.3390/catal2040422 422 433 2073-4344 2012-10-12 doi: 10.3390/catal2040422 Carlos Moreno-Castilla Francisco Carrasco-Marín Marta B. Dawidziuk http://www.mdpi.com/2073-4344/2/4/412 The complex [(κ3-(N,N,O-py2B(Me)OH)Ru(NCMe)3]+ TfO− (1) is a catalyst for transfer dehydrogenation of alcohols, which was designed to function through a cooperative transition state in which reactivity was split between boron and ruthenium. We show here both stoichiometric and catalytic evidence to support that in the case of alcohol oxidation, the mechanism most likely involves reactivity only at the ruthenium center. Catalysts 2012-10-11 2 4 Communication 10.3390/catal2040412 412 421 2073-4344 2012-10-11 doi: 10.3390/catal2040412 Zhiyao Lu Brock Malinoski Ana V. Flores Brian L. Conley Denver Guess Travis J. Williams http://www.mdpi.com/2073-4344/2/3/400 The effect of extended H2 sorption cycles on the structure and on the hydrogen storage performances of MgH2 powders with 5 wt% of Fe particle catalyst is reported. MgH2 powders with and without Fe have been ball milled under Argon, the doped MgH2 nanocomposite has been cycled under hydrogen pressure up to a maximum of 47 desorption and absorption cycles at 300 °C. After acceleration during the first 10 cycles, the kinetics behavior of doped MgH2 is constant after extended cycling, in terms of maximum storage capacity and rate of sorption. The major effect of cycling on particle morphology is the progressive extraction of Mg from the MgO shell surrounding the powder particles. The Mg extraction from the MgO shell leaves the catalyst particles inside the hydride particles. Many empty MgO shells are observed in the pure ball milled MgH2 upon cycling at higher temperature, suggesting that this enhancement of the extraction efficiency is related to the higher operating temperature which favors Mg diffusivity with respect to the H ion one. Catalysts 2012-09-24 2 3 Article 10.3390/catal2030400 400 411 2073-4344 2012-09-24 doi: 10.3390/catal2030400 Amelia Montone Annalisa Aurora Daniele Mirabile Gattia Marco Vittori Antisari http://www.mdpi.com/2073-4344/2/3/386 Cobalt talc doped with iron (Fe/Co~0.1) and dispersed in SiO2 aerogel was prepared from silica alcogel impregnated with metal nitrates by supercritical drying. Catalytic honeycombs were prepared following the same procedure, with the alcogel synthesized directly over cordierite honeycomb pieces. The composite aerogel catalyst was characterized by X-ray diffraction, scanning electron microscopy, focus ion beam, specific surface area and X-ray photoelectron spectroscopy. The catalytic layer is about 8 µm thick and adheres well to the cordierite support. It is constituted of talc layers of about 1.5 µm × 300 nm × 50 nm which are well dispersed and anchored in a SiO2 aerogel matrix with excellent mass-transfer properties. The catalyst was tested in the ethanol steam reforming reaction, aimed at producing hydrogen for on-board, on-demand applications at moderate temperature (573–673 K) and pressure (1–7 bar). Compared to non-promoted cobalt talc, the catalyst doped with iron produces less methane as byproduct, which can only be reformed at high temperature, thereby resulting in higher hydrogen yields. At 673 K and 2 bar, 1.04 NLH2·mLEtOH(l)−1·min−1 are obtained at S/C = 3 and W/F = 390 g·min·molEtOH−1. Catalysts 2012-09-19 2 3 Article 10.3390/catal2030386 386 399 2073-4344 2012-09-19 doi: 10.3390/catal2030386 Montserrat Domínguez Elena Taboada Elies Molins Jordi Llorca http://www.mdpi.com/2073-4344/2/3/368 Tetraethoxy orthosilicate (TEOS) was used not only as a precursor of silica, but also as an agent which reinforces the skeleton of silica-gel to prepare an aerogel and resultant silica and silica-alumina with large pore size and pore volume. In this gel skeletal reinforcement, the strength of silica aerogel skeleton was enhanced by aging with TEOS/2-propanol mixed solution to prevent the shrink of the pores. When silica aerogel was reinforced by TEOS solution, the pore diameter and pore volume of calcined silica could be controlled by the amount of TEOS solution and reached 30 nm and 3.1 cm3/g. The results from N2 adsorption measurement indicated that most of pores for this silica consisted of mesopores. Silica-alumina was prepared by the impregnation of an aluminum tri-sec-butoxide/2-butanol solution with obtained silica. Mixed catalysts were prepared by the combination of β-zeolite (26 wt%) and prepared silica-aluminas with large mesopore (58 wt%) and subsequently the effects of their pore sizes on the catalytic activity and the product selectivity were investigated in catalytic cracking of n-dodecane at 500 °C. The mixed catalysts exhibited not only comparable activity to that for single zeolite, but also unique selectivity where larger amounts of branched products were formed. Catalysts 2012-09-13 2 3 Article 10.3390/catal2030368 368 385 2073-4344 2012-09-13 doi: 10.3390/catal2030368 Atsushi Ishihara Tadanori Hashimoto Hiroyuki Nasu http://www.mdpi.com/2073-4344/2/3/352 Alumina-supported manganese catalysts with cryptomelane and/or birnessite structure have been prepared using a simple method based on the thermal decomposition of potassium permanganate. The samples have been characterized by XRD, FTIR, TGA, DSC, N2 adsorption at −196 °C, SEM, H2-TPR and XPS, and their catalytic activity for soot combustion has been tested and compared to that of a reference Pt/alumina catalyst. The thermal decomposition of alumina-supported KMnO4 yields a mixture of supported birnessite and potassium manganate which is the most effective, among those prepared, to lower the soot combustion temperature. However, this material is not useful for soot combustion because the accelerating effect is not based on a catalytic process but on the oxidation of soot by potassium manganate. A suitable soot combustion catalyst is obtained after potassium manganate is removed by water washing, yielding only the birnessite phase on the γ-Al2O3 support. This birnessite phase can be transformed into cryptomelane by calcination at 600 °C. These two samples, γ-Al2O3-supported birnessite and cryptomelane are suitable catalysts for soot combustion in NOx/O2 mixtures, as their catalytic activity is based on the NO2-assited mechanism, that is, both catalysts accelerate the oxidation of NO to NO2 and NO2 promotes soot oxidation. The soot combustion temperatures obtained with these birnessite/cryptomelane alumina-supported catalysts are similar to that obtained with the reference Pt/alumina catalyst. Catalysts 2012-09-11 2 3 Article 10.3390/catal2030352 352 367 2073-4344 2012-09-11 doi: 10.3390/catal2030352 Maria-Eugenia Becerra Nayda-Patricia Arias Oscar-Hernan Giraldo Franz-Edwin López-Suárez Maria-Jose Illán-Gómez Agustin Bueno-López http://www.mdpi.com/2073-4344/2/3/344 We report a study on the desorption properties, crystallography and chemical state of MgH2 and 1 mol% Nb2O5 ball-milled composites. Desorption temperatures of the composites decreased with increase of ball-milling time. Size of MgH2 crystallites decreased during ball-milling. Reduction of Nb2O5 after ball-milling was confirmed by tracing the chemical state of Nb and was further supported by TEM observation. The reduced phases may act as more effective catalysts improving the desorption properties. Catalysts 2012-09-10 2 3 Article 10.3390/catal2030344 344 351 2073-4344 2012-09-10 doi: 10.3390/catal2030344 Tao Ma Shigehito Isobe Yongming Wang Naoyuki Hashimoto Somei Ohnuki http://www.mdpi.com/2073-4344/2/3/330 The kinetics of hydrogen absorption/desorption in magnesium can be improved without any catalysis assistance and MgO was found to be more effective than the best catalyst reported so far, i.e., Nb2O5. Herein, a quantitative analysis of the hydrogen kinetics in magnesium modified with MgO was performed in order to identify possible rate controlling mechanisms. While hydrogen absorption was found to be diffusion controlled as commonly reported, hydrogen desorption evolved from nucleation and growth to an interface controlled process depending on the desorption temperature. Comparison with the effect of Nb2O5 indicates that similar rate limiting steps occur regardless of the oxide additive. These findings are reconciled by considering the tribological effect of solid oxide additives, as a correlation between oxides electronegativity and improvement in hydrogen kinetics was found. Such a correlation clearly highlights the mechanical effect of solid oxides in facilitating the grinding and stabilisation of small magnesium particles for efficient and fast hydrogen kinetics. Catalysts 2012-08-13 2 3 Article 10.3390/catal2030330 330 343 2073-4344 2012-08-13 doi: 10.3390/catal2030330 José-Ramón Ares-Fernández Kondo-Francois Aguey-Zinsou http://www.mdpi.com/2073-4344/2/3/327 An overview of the development of photocatalysis with an identification of contemporary areas of interest. Photocatalysis is placed in the broad field of catalysis. Catalysts 2012-08-09 2 3 Editorial 10.3390/catal2030327 327 329 2073-4344 2012-08-09 doi: 10.3390/catal2030327 Cooper H. Langford http://www.mdpi.com/2073-4344/2/2/303 Fischer–Tropsch synthesis is a set of catalytic processes that can be used to produce fuels and chemicals from synthesis gas (mixture of CO and H2), which can be derived from natural gas, coal, or biomass. Biomass to Liquid via Fischer–Tropsch (BTL-FT) synthesis is gaining increasing interests from academia and industry because of its ability to produce carbon neutral and environmentally friendly clean fuels; such kinds of fuels can help to meet the globally increasing energy demand and to meet the stricter environmental regulations in the future. In the BTL-FT process, biomass, such as woodchips and straw stalk, is firstly converted into biomass-derived syngas (bio-syngas) by gasification. Then, a cleaning process is applied to remove impurities from the bio-syngas to produce clean bio-syngas which meets the Fischer–Tropsch synthesis requirements. Cleaned bio-syngas is then conducted into a Fischer–Tropsch catalytic reactor to produce green gasoline, diesel and other clean biofuels. This review will analyze the three main steps of BTL-FT process, and discuss the issues related to biomass gasification, bio-syngas cleaning methods and conversion of bio-syngas into liquid hydrocarbons via Fischer–Tropsch synthesis. Some features in regard to increasing carbon utilization, enhancing catalyst activity, maximizing selectivity and avoiding catalyst deactivation in bio-syngas conversion process are also discussed. Catalysts 2012-06-15 2 2 Review 10.3390/catal2020303 303 326 2073-4344 2012-06-15 doi: 10.3390/catal2020303 Jin Hu Fei Yu Yongwu Lu http://www.mdpi.com/2073-4344/2/2/299 For many years, gold has been regarded as a poor catalyst due to its chemical inertness towards reactive molecules such as oxygen and hydrogen. The interest in using gold in catalysis has increased during the last 20 years, since Haruta reported the surprisingly high activity in CO oxidation at low temperature for small (3–5 nm) gold particles supported on various oxides. [...] Catalysts 2012-05-29 2 2 Editorial 10.3390/catal2020299 299 302 2073-4344 2012-05-29 doi: 10.3390/catal2020299 Leonarda F. Liotta http://www.mdpi.com/2073-4344/2/2/281 This study proposes a gas-cleaning process for the simultaneous removal of sulfur compounds, tar, and particles from biomass-gasified gas using Fe-supported activated carbon and a water-gas shift reaction. On a laboratory scale, the simultaneous removal of H2S and COS was performed under a mixture of gases (H2/CO/CO2/CH4/C2H4/N2/H2S/COS/steam). The reactions such as COS + H2 → H2S + CO and COS + H2O → H2S + CO2 and the water-gas shift reaction were promoted on the Fe-supported activated carbon. The adsorption capacity with steam was higher than that without steam. On a bench scale, the removal of impurities from a gas derived from biomass gasification was investigated using two activated filters packed with Fe-supported activated carbon. H2S and COS, three- and four-ring polycyclic aromatic hydrocarbons (PAHs), and particles were removed and a water-gas shift reaction was promoted through the first filter at 320–350 °C. The concentrations of H2S and COS decreased to less than 0.1 ppmv. Particles and the one- and two-ring PAHs, except for benzene, were then removed through the second filter at 60–170 °C. The concentration of tar and particles decreased from 2428 to 102 mg Nm−3 and from 2244 to 181 mg Nm−3, respectively. Catalysts 2012-05-08 2 2 Article 10.3390/catal2020281 281 298 2073-4344 2012-05-08 doi: 10.3390/catal2020281 Toshiaki Hanaoka Kotetsu Matsunaga Tomohisa Miyazawa Satoshi Hirata Kinya Sakanishi http://www.mdpi.com/2073-4344/2/2/264 Magnesium nickel silicate (MNS) has been investigated as a catalyst to convert tars and light hydrocarbons to syngas (CO and H2) by steam reforming and CO2 reforming in the presence of H2S for biomass gasification process at NexTech Materials. It was observed that complete CH4 conversion could be achieved on MNS catalyst granules at 800–900 °C and a space velocity of 24,000 mL/g/h in a simulated biomass gasification stream. Addition of 10–20 ppm H2S to the feed had no apparent impact on CH4 conversion. The MNS-washcoated monolith also showed high activities in converting methane, light hydrocarbons and tar to syngas. A 1200 h test without deactivation was achieved on the MNS washcoated monolith in the presence of H2S and/or NH3, two common impurities in gasified biomass. The results indicate that the MNS material is a promising catalyst for removal of tar and light hydrocarbons from biomass gasified gases, enabling efficient use of biomass to produce power, liquid fuels and valuable chemicals. Catalysts 2012-04-17 2 2 Article 10.3390/catal2020264 264 280 2073-4344 2012-04-17 doi: 10.3390/catal2020264 Richard Q. Long Scott M. Monfort Gene B. Arkenberg Paul H. Matter Scott L. Swartz http://www.mdpi.com/2073-4344/2/2/244 The economic utilization of abundant lignocellulosic biomass as a feedstock for the production of fuel and chemicals would represent a profound shift in industrial carbon utilization, allowing sustainable resources to substitute for, and compete with, petroleum based products. In order to exploit biomass as a source material for production of renewable compounds, it must first be broken down into constituent compounds, such as sugars, that can be more easily converted in chemical and biological processes. Lignocellulose is, unfortunately, a heterogeneous and recalcitrant material which is highly resistant to depolymerization. Many microorganisms have evolved repertoires of enzyme activities which act in tandem to decompose the various components of lignocellulosic biomass. In this review, we discuss recent advances in the understanding of these enzymes, with particular regard to those activities deemed likely to be applicable in commercialized biomass utilization processes. Catalysts 2012-04-12 2 2 Review 10.3390/catal2020244 244 263 2073-4344 2012-04-12 doi: 10.3390/catal2020244 Matt D. Sweeney Feng Xu http://www.mdpi.com/2073-4344/2/2/223 Combustion of solid biomass fuels for heat generation is an important renewable energy resource. The major part among biomass combustion applications is being played by small-scale systems like wood log stoves and small wood pellet burners, which account for 75% of the overall biomass heat production. Despite an environmentally friendly use of renewable energies, incomplete combustion in small-scale systems can lead to the emission of environmental pollutants as well as substances which are hazardous to health. Besides particles of ash and soot, a wide variety of gaseous substances can also be emitted. Among those, polycyclic aromatic hydrocarbons (PAH) and several organic volatile and semi-volatile compounds (VOC) are present. Heterogeneous catalysis is applied for the reduction of various gaseous compounds as well as soot. Some research has been done to examine the application of catalytic converters in small-scale biomass combustion systems. In addition to catalyst selection with respect to complete oxidation of different organic compounds, parameters such as long-term stability and durability under flue gas conditions are considered for use in biomass combustion furnaces. Possible catalytic procedures have been identified for investigation by literature and market research. Experimental studies with two selected oxidation catalysts based on noble metals have been carried out on a wood log stove with a retrofit system. The measurements have been performed under defined conditions based on practical mode of operation. The measurements have shown that the catalytic flue gas treatment is a promising method to reduce carbon monoxide and volatile organic compounds. Even a reduction of particulate matter was observed, although no filtering effect could be detected. Therefore, the oxidation of soot or soot precursors can be assumed. The selected catalysts differed in their activity, depending on the compound to be oxidized. Examinations showed that the knitted wire catalyst showed better activity for the reduction of carbon monoxide, whereas the honeycomb induced a higher reduction of aromatic compounds. The properties of the two catalysts can be combined by integrating both together. The one drawback of the catalyst so far is the deactivation for the conversion of methane. Catalysts 2012-04-12 2 2 Article 10.3390/catal2020223 223 243 2073-4344 2012-04-12 doi: 10.3390/catal2020223 René Bindig Saad Butt Ingo Hartmann Mirjam Matthes Christian Thiel http://www.mdpi.com/2073-4344/2/1/191 More than 10 million tons of biodiesel fuel (BDF) have been produced in the world from the transesterification of vegetable oil with methanol by using acid catalysts (sulfuric acid, H2SO4), alkaline catalysts (sodium hydroxide, NaOH or potassium hydroxide, KOH), solid catalysts and enzymes. Unfortunately, the price of BDF is still more expensive than that of petro diesel fuel due to the lack of a suitable raw material oil. Here, we review the best selection of BDF production systems including raw materials, catalysts and production technologies. In addition, glycerol formed as a by-product needs to be converted to useful chemicals to reduce the amount of glycerol waste. With this in mind, we have also reviewed some recent studies on the utilization of glycerol. Catalysts 2012-03-22 2 1 Review 10.3390/catal2010191 191 222 2073-4344 2012-03-22 doi: 10.3390/catal2010191 Le Tu Thanh Kenji Okitsu Luu Van Boi Yasuaki Maeda http://www.mdpi.com/2073-4344/2/1/171 Waste cooking oil with a high-acid-value (28.7 mg-KOH/g-oil) was converted to bio-hydrogenated diesel by a hydrotreatment process over supported Ru catalysts. The standard reaction temperature, H2 pressure, liquid hourly space velocity (LHSV), and H2/oil ratio were 350 °C, 2 MPa, 15.2 h–1, and 400 mL/mL, respectively. Both the free fatty acids and the triglycerides in the waste cooking oil were deoxygenated at the same time to form hydrocarbons in the hydrotreatment process. The predominant liquid hydrocarbon products (98.9 wt%) were n-C18H38, n-C17H36, n-C16H34, and n-C15H32 when a Ru/SiO2 catalyst was used. These long chain normal hydrocarbons had high melting points and gave the liquid hydrocarbon product over Ru/SiO2 a high pour point of 20 °C. Ru/H-Y was not suitable for producing diesel from waste cooking oil because it formed a large amount of C5–C10 gasoline-ranged paraffins on the strong acid sites of HY. When Al-polyoxocation-pillared montmorillonite (Al13-Mont) was used as a support for the Ru catalyst, the pour point of the liquid hydrocarbon product decreased to −15 °C with the conversion of a significant amount of C15–C18 n-paraffins to iso-paraffins and light paraffins on the weak acid sites of Al13-Mont. The liquid product over Ru/Al13-Mont can be expected to give a green diesel for current diesel engines because its chemical composition and physical properties are similar to those of commercial petro-diesel. A relatively large amount of H2 was consumed in the hydrogenation of unsaturated C=C bonds and the deoxygenation of C=O bonds in the hydrotreatment process. A sulfided Ni-Mo/Al13-Mont catalyst also produced bio-hydrogenated diesel by the hydrotreatment process but it showed slow deactivation during the reaction due to loss of sulfur. In contrast, Ru/Al13-Mont did not show catalyst deactivation in the hydrotreatment of waste cooking oil after 72 h on-stream because the waste cooking oil was not found to contain sulfur-containing compounds. Catalysts 2012-02-14 2 1 Article 10.3390/catal2010171 171 190 2073-4344 2012-02-14 doi: 10.3390/catal2010171 Yanyong Liu Rogelio Sotelo-Boyás Kazuhisa Murata Tomoaki Minowa Kinya Sakanishi http://www.mdpi.com/2073-4344/2/1/139 The removal of mercury from flue gases in scrubbers is greatly facilitated if the mercury is present as water-soluble oxidized species. Therefore, increased mercury oxidation upstream of scrubber devices will improve overall mercury removal. For this purpose heterogeneous catalysts have recently attracted a great deal of interest. Selective catalytic reduction (SCR), noble metal and transition metal oxide based catalysts have been investigated at both the laboratory and plant scale with this objective. A review article published in 2006 covers the progress in the elemental mercury (Hgel) catalytic oxidation area. This paper brings the review in this area up to date. To this end, 110 papers including several reports and patents are reviewed. For each type of catalyst the possible mechanisms as well as the effect of flue gas components on activity and stability are examined. Advantages and main problems are analyzed. The possible future directions of catalyst development in this environmental research area are outlined. Catalysts 2012-02-13 2 1 Review 10.3390/catal2010139 139 170 2073-4344 2012-02-13 doi: 10.3390/catal2010139 Beatrice-Andreea Dranga Liliana Lazar Heinz Koeser http://www.mdpi.com/2073-4344/2/1/121 The effect of gold presence on carbon monoxide oxidation and ethanol steam reforming catalytic behavior of two Ce-Zr-Co mixed oxides catalysts with a constant Co charge and different Ce/Zr ratios was investigated. The Ce-Zr-Co mixed oxides were obtained by the pseudo sol-gel like method, based on metallic propionates polymerization and thermal decomposition, whereas the gold-supported Ce-Zr-Co mixed oxides catalysts were prepared using the direct anionic exchange. The catalysts were characterized using XRD, TPR, and EDXS-TEM. The presence of Au in doped Ce-Zr-Co oxide catalyst decreases the temperature necessary to reduce the cobalt and the cerium loaded in the catalyst and favors a different reaction pathway, improving the acetaldehyde route by ethanol dehydrogenation, instead of the ethylene route by ethanol dehydration or methane re-adsorption, thus increasing the catalytic activity and selectivity into hydrogen. Catalysts 2012-02-03 2 1 Article 10.3390/catal2010121 121 138 2073-4344 2012-02-03 doi: 10.3390/catal2010121 Julio Cesar Vargas Svetlana Ivanova Sébastien Thomas Anne-Cécile Roger Véronique Pitchon http://www.mdpi.com/2073-4344/2/1/101 Supported gold catalysts are highly active in oxidation reactions. Beside the most frequently studied CO oxidation, they are readily applied in the epoxidation of more or less complex olefinic compounds using air or oxygen directly or other oxidants like peroxides of various kinds. Less frequently though, the reverse reaction, ring opening with single or double C–O scission is also investigated. These and other ring making and breaking reactions are reviewed, and the catalytic roles of gold species are described. Catalysts 2012-02-01 2 1 Review 10.3390/catal2010101 101 120 2073-4344 2012-02-01 doi: 10.3390/catal2010101 Krisztián Csankó Pál Sipos István Pálinkó http://www.mdpi.com/2073-4344/2/1/85 Catalytic hydrogenation of anthracene was studied over Ni supported on Hβ-zeolite catalyst under supercritical carbon dioxide (sc-CO2) solvent. Hydrogenation of anthracene in sc-CO2 yielded 100% conversion at 100 °C, which is attributed to the reduced mass transfer limitations, and increased solubility of H2 and substrate in the reaction medium. The total pressure of 7 MPa was found to be optimum for high selectivity of octahydroanthracene (OHA). The conversion and selectivity for OHA increased with an increase in H2 partial pressure, which is attributed to higher concentration of hydrogen atoms at higher H2 pressures. The selectivity reduced the pressure below 7 MPa because of enhanced desorption of the tetrahydro-molecules and intermediates from Ni active sites, due to higher solubility of the surface species in sc-CO2. The selectivity of OHA increased with the increase in catalyst weight and reaction time. The rate of hydrogenation of anthracene was compared with that found for napthalene and phenanthrene. The use of acetonitrile as co-solvent or expanded liquid with CO2 decreased the catalytic activity. Catalysts 2012-01-30 2 1 Article 10.3390/catal2010085 85 100 2073-4344 2012-01-30 doi: 10.3390/catal2010085 Endalkachew Sahle-Demessie Venu Gopal Devulapelli Ashraf Aly Hassan http://www.mdpi.com/2073-4344/2/1/68 Direct catalytic valorization of bioethanol to 1-butanol over different alumina supported catalysts was studied. Thirteen (13) heterogeneous catalysts were screened in search for the optimal material composition for direct one-pot conversion of ethanol to 1-butanol. For the most promising catalyst, a 25% ethanol conversion with 80% selectivity (among liquid carbon products) to 1-butanol could be reached at 250 °C. Additionally, the reaction kinetics and mechanisms were further investigated upon use of the most suitable catalyst candidate. Catalysts 2012-01-13 2 1 Article 10.3390/catal2010068 68 84 2073-4344 2012-01-13 doi: 10.3390/catal2010068 Toni Riittonen Esa Toukoniitty Dipak Kumar Madnani Anne-Riikka Leino Krisztian Kordas Maria Szabo Andras Sapi Kalle Arve Johan Wärnå Jyri-Pekka Mikkola http://www.mdpi.com/2073-4344/2/1/56 Ethanol and pentose were produced from lignocellulosic napiergrass by the simultaneous saccharification and fermentation process (SSF) using hydrolytic enzyme and S. Cerevisiae. After the ethanol was removed, the pentose solution was subjected to photocatalytic hydrogen evolution with Pt-loaded TiO2 under UV-irradiation. This process converted 100 g of napiergrass into 12.3 g of ethanol and 1.76 g of hydrogen whose total combustion energy of (∆H) was 615 kJ. This was close to the ∆H (639 kJ) of the pentose (13.6 g) and hexose (27.4 g) obtained by the cellulose-saccharification of 100 g of napiergrass. Catalysts 2011-12-22 2 1 Article 10.3390/catal2010056 56 67 2073-4344 2011-12-22 doi: 10.3390/catal2010056 Tsutomu Shiragami Takayuki Tomo Hikaru Tsumagari Yasuyuki Ishii Masahide Yasuda http://www.mdpi.com/2073-4344/2/1/38 Base metal promoted gold/titania catalysts were synthesized, characterized and tested in CO oxidation reaction. Catalysts containing dopant metals in higher oxidation states exhibited higher activity than catalysts containing dopants in reduced states. The activity of fresh catalysts promoted by Cu, Fe and Ni was similar to the unpromoted one, but treatment in reducing and oxidizing atmospheres revealed the supremacy of the copper promoted catalyst. The sequential deposition method proved to be better than the co-deposition—precipitation method. An attempt to explain these differences using XPS, FTIR and H2 TPR was performed. Catalysts 2011-12-22 2 1 Article 10.3390/catal2010038 38 55 2073-4344 2011-12-22 doi: 10.3390/catal2010038 Jan Mizera Nika Spiridis Robert P. Socha Małgorzata Zimowska Ryszard Grabowski Katarzyna Samson Józef Korecki http://www.mdpi.com/2073-4344/2/1/24 Gold has been considered as an active catalyst only when suitable techniques of preparation provided high metal dispersion. A comprehensive survey of the different methods now available for preparing active gold catalysts is reported with particular attention to the role of the supporting material in determining catalyst characteristics. Catalysts 2011-12-21 2 1 Review 10.3390/catal2010024 24 37 2073-4344 2011-12-21 doi: 10.3390/catal2010024 Laura Prati Alberto Villa http://www.mdpi.com/2073-4344/2/1/1 A novel preparation method was developed for the preparation of gold/iron oxide supported catalysts using the bimetallic carbonyl cluster salts [NEt4]4[Au4Fe4(CO)16] and [NEt4][AuFe4(CO)16] as precursors of highly dispersed nanoparticles over different supports. A series of catalysts with different metal loadings were prepared and tested in the complete oxidation of dichlorobenzene, toluene, methanol and in the preferential oxidation of CO in the presence of H2 (PROX) as model reactions. The characterization by BET, XRD, TEM, H2-TPR, ICP-AES and XPS point out the way the nature of the precursors and the thermal treatment conditions affected the dispersion of the active phase and their catalytic activity in the studied reactions. Catalysts 2011-12-21 2 1 Article 10.3390/catal2010001 1 23 2073-4344 2011-12-21 doi: 10.3390/catal2010001 Rosa Bonelli Stefano Zacchini Stefania Albonetti http://www.mdpi.com/2073-4344/1/1/175 Low-temperature water-gas shift reaction (WGS) using gold catalyst is expected to be an attractive technique to realize an efficient on-site hydrogen production process. In this paper, Au/Fe3O4 catalysts for promoting the WGS below 150 °C were developed by a preliminary reduction of Au/iron oxide (Fe3+) catalyst utilizing high reactivity of Au nano-particles. The reduction was conducted under a CO, H2, or CO/H2O stream at either 140 or 200 °C, and the effect of reduction conditions on the characteristics of the Au/Fe3O4 catalyst and on the catalytic activity in WGS at 80 °C was investigated. The reaction progress during the pre-reduction treatment was qualitatively analyzed, and it was found that the iron oxide in Au/Fe2O3 calcined at 200 °C was easily reduced to Fe3O4 phase in all reduction conditions. The reduction conditions affected the characteristics of both Au and iron oxide, but all of the reduced catalysts had small Fe3O4 particles of less than 20 nm with Au particles on the surface. The surface area and content of cationic Au were high in the order of CO, H2, CO/H2O, and 140, 200 °C. In the WGS test at 80 °C using the developed catalysts, the activities of the catalysts pre-reduced by CO at 140 or 200 °C and by H2 at 140 °C were very high with 100% CO conversion even at such a low temperature. These results indicated that factors such as higher surface area, crystallized Fe3O4, and cationic Au content contributed to the catalytic activity. Catalysts 2011-12-09 1 1 Article 10.3390/catal1010175 175 190 2073-4344 2011-12-09 doi: 10.3390/catal1010175 Shinji Kudo Taisuke Maki Takashi Fukuda Kazuhiro Mae http://www.mdpi.com/2073-4344/1/1/155 Au-based catalysts supported on carbon materials with different structures such as graphite (G) and fishbone type carbon nanofibers (CNF-F) were prepared using two different methods (impregnation and gold-sol) to be tested in the water gas shift (WGS) reaction. Atomic absorption spectrometry, transmission electron microscopy (TEM), temperature-programmed oxidation (TPO), X-ray diffraction (XRD), Raman spectroscopy, elemental analyses (CNH), N2 adsorption-desorption analysis, temperature-programmed reduction (TPR) and temperature-programmed decomposition were employed to characterize both the supports and catalysts. Both the crystalline nature of the carbon supports and the method of gold incorporation had a strong influence on the way in which Au particles were deposited on the carbon surface. The higher crystallinity and the smaller and well dispersed Au particle size were, the higher activity of the catalysts in the WGS reaction was noted. Finally, catalytic activity showed an important dependence on the reaction temperature and steam-to-CO molar ratio. Catalysts 2011-12-09 1 1 Article 10.3390/catal1010155 155 174 2073-4344 2011-12-09 doi: 10.3390/catal1010155 Sonia Gil Amaya Romero Antonio de Lucas Paula Sánchez Fernando Dorado Ana Raquel de la Osa Jesús Manuel García-Vargas Jose Luis Valverde http://www.mdpi.com/2073-4344/1/1/97 Mesoporous silica materials (MSM) with ordered and controllable porous structure, high surface area, pore volume and thermal stability are very suitable catalyst supports, because they provide high dispersion of metal nanoparticles and facilitate the access of the substrates to the active sites. Since the conventional wet-impregnation and deposition-precipitation methods are not appropriate for the incorporation of gold nanoparticles (AuNPs) into MSM, considerable efforts have been made to develop suitable methods to synthesize Au/MSM catalysts, because the incorporation of AuNPs into the channel system can prevent their agglomeration and leaching. In this review, we summarize the main methods to synthesize active gold catalysts supported on MSM. Examples and details of the preparative methods, as well as selected applications are provided. We expect this article to be interesting to researchers due to the wide variety of chemical reactions that can be catalyzed by gold supported catalysts. Catalysts 2011-12-02 1 1 Review 10.3390/catal1010097 97 154 2073-4344 2011-12-02 doi: 10.3390/catal1010097 Luis-Felipe Gutiérrez Safia Hamoudi Khaled Belkacemi http://www.mdpi.com/2073-4344/1/1/83 The structural and functional design of metal nanoparticles has recently allowed remarkable progress in the development of high-performance catalysts. Gold nanoparticles (AuNPs) are among the most innovative catalysts, despite bulk Au metal being regarded as stable and inactive. The hybridization of metal NPs has attracted major interest in the field of advanced nanocatalysts, due to electro-mediated ligand effects. In practical terms, metal NPs need to be supported on a suitable matrix to avoid any undesirable aggregation; many researchers have reported the potential of polymer-supported AuNPs. However, the use of conventional polymer matrices make it difficult to take full advantage of the inherent properties of the metal NPs, since most of active NPs are imbedded inside the polymer support. This results in poor accessibility for the reactants. Herein, we report the topochemical synthesis of Au and palladium (Pd) bimetallic NPs over the surfaces of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibers (TOCNs), and their exceptional catalytic performance. Highly-dispersed AuPdNPs were successfully synthesized in situ on the crystal surfaces of TOCNs with a very high density of carboxylate groups. The AuPdNPs@TOCN nanocomposites exhibit excellent catalytic efficiencies in the aqueous reduction of 4-nitrophenol to 4-aminophenol, depending on the molar ratios of Au and Pd. Catalysts 2011-11-25 1 1 Article 10.3390/catal1010083 83 96 2073-4344 2011-11-25 doi: 10.3390/catal1010083 Akihiro Azetsu Hirotaka Koga Akira Isogai Takuya Kitaoka http://www.mdpi.com/2073-4344/1/1/69 Bimetallic nanoparticles have attracted significant attention as their electrochemical and catalytic properties being superior to those of the individual component nanoparticles. In this study, gold-silver hybrid nanoparticles (AuAgNPs) with an Aucore-Agshell nanostructure were successfully synthesized on zinc oxide (ZnO) whiskers. The as-prepared nanocatalyst, denoted AuAgNPs@ZnO whisker, exhibits an excellent catalytic efficiency in the aqueous reduction of 4-nitrophenol to 4-aminophenol; the turnover frequency was up to 40 times higher than that of each component nanoparticle. Their unique features were attributed to the electronic ligand effect at the bimetallic interface. In addition, the AuAgNPs were synthesized on a ZnO whisker-containing paper with a fiber-network microstructure, which was prepared via a papermaking technique. The paper-structured AuAgNPs composite possessed both a paper-like practical utility and a good catalytic performance. Furthermore, the on-paper synthesis process for these bimetallic nanocatalysts is facile. These easy-to-handle nanocatalyst hybrid composites are expected to find a wide range of applications in various chemical and catalytic processes. Catalysts 2011-11-25 1 1 Article 10.3390/catal1010069 69 82 2073-4344 2011-11-25 doi: 10.3390/catal1010069 Hirotaka Koga Yuuka Umemura Takuya Kitaoka http://www.mdpi.com/2073-4344/1/1/52 The present study tries to give an insight to the combination of the homogeneous and heterogeneous catalytic properties in a new class of materials. Well dispersed gold nanoparticles on an ionic liquid layer supported on a mineral carrier have been prepared. This work is concentrated on the characterizations and understanding of the interactions between all the components of the catalytic system. The application of the materials in the reaction of oxidation of carbon monoxide shows rather unexpected results—a good catalytic activity completely independent of the temperature. Catalysts 2011-11-25 1 1 Article 10.3390/catal1010052 52 68 2073-4344 2011-11-25 doi: 10.3390/catal1010052 Svetlana Ivanova Luis Francisco Bobadilla Anna Penkova Francisca Romero Sarria Miguel Angel Centeno Jose Antonio Odriozola http://www.mdpi.com/2073-4344/1/1/40 The adsorption energies and the activation energy barriers for a series of reactions catalyzed by gold surfaces and obtained theoretically through density functional theory (DFT) based calculations were considered to clarify the role of the low coordinated gold atoms and the role of doping in the catalytic activity of gold. The effect of the surface steps was introduced by comparison of the activation energy barriers and of the adsorption energies on flat gold surfaces such as the Au(111) surface with those on stepped surfaces such as the Au(321) or the Au(110) surfaces. It is concluded that the presence of low coordinated atoms on the latter surfaces increases the adsorption energies of the reactants and decreases the activation energy barriers. Furthermore, the increasing of the adsorption energy of the reaction products can lead to lower overall reaction rates in the presence of low gold coordinated atoms due to desorption limitations. On the other hand, the effect of doping gold surfaces with other transition metal atoms was analyzed using the dissociation reaction of molecular oxygen as a test case. The calculations showed that increasing the silver content in some gold surfaces was related to a considerable increment of the reactivity of bimetallic systems toward the oxygen dissociation. Importantly, that increment in the reactivity was enhanced by the presence of low coordinated atoms in the catalytic surface models considered. Catalysts 2011-11-21 1 1 Review 10.3390/catal1010040 40 51 2073-4344 2011-11-21 doi: 10.3390/catal1010040 José L. C. Fajín Maria Natália D. S. Cordeiro José R. B. Gomes http://www.mdpi.com/2073-4344/1/1/18 It is demonstrated that the support effects play a crucial role in the gold nanocatalysis. Two types of support are considered—the “inert” support of hexagonal boron nitride (h-BN) with the N and B vacancy defects and the “active” support of rutile TiO2(110). It is demonstrated that Au and Au2 can be trapped effectively by the vacancy defects in h-BN. In that case, the strong adsorption on the surface defects is accompanied by the charge transfer to/from the adsorbate. The excess of the positive or negative charge on the supported gold clusters can considerably promote their catalytic activity. Therefore gold clusters supported on the defected h-BN surface can not be considered as pseudo-free clusters. We also demonstrate that the rutile TiO2(110) support energetically promotes H2 dissociation on gold clusters. We show that the formation of the OH group near the supported gold cluster is an important condition for H2 dissociation. We demonstrate that the active sites towards H2 dissociation on the supported Aun are located at corners and edges of the gold cluster in the vicinity of the low coordinated oxygen atoms on TiO2(110). Thus catalytic activity of a gold nanoparticle supported on the rutile TiO2(110) surface is proportional to the length of the perimeter interface between the nanoparticle and the support. Catalysts 2011-11-17 1 1 Article 10.3390/catal1010018 18 39 2073-4344 2011-11-17 doi: 10.3390/catal1010018 Min Gao Andrey Lyalin Tetsuya Taketsugu http://www.mdpi.com/2073-4344/1/1/3 The emphasis of this review is atomically monodisperse Aun nanoclusters catalysts (n = number of metal atom in cluster) that are ideally composed of an exact number of metal atoms. Aun which range in size from a dozen to a few hundred atoms are particularly promising for nanocatalysis due to their unique core-shell structure and non-metallic electronic properties. Aun nanoclusters catalysts have been demonstrated to exhibit excellent catalytic activity in hydrogenation and oxidation processes. Such unique properties of Aun significantly promote molecule activation by enhancing adsorption energy of reactant molecules on catalyst surface. The structural determination of Aun nanoclusters allows for a precise correlation of particle structure with catalytic properties and also permits the identification of catalytically active sites on the gold particle at an atomic level. By learning these fundamental principles, one would ultimately be able to design new types of highly active and highly selective gold nanocluster catalysts for a variety of catalytic processes. Catalysts 2011-09-07 1 1 Review 10.3390/catal1010003 3 17 2073-4344 2011-09-07 doi: 10.3390/catal1010003 Yan Zhu Rongchao Jin Yuhan Sun http://www.mdpi.com/2073-4344/1/1/1 There is something intrinsically fascinating about catalysts. The thought that a material can speed up a reaction by hundreds or thousands of times without being consumed is truly amazing. I frequently have the pleasure of teaching undergraduate and graduate chemical reaction engineering courses that include sections on catalysts. I have found that students take an immediate interest in catalysts and are fascinated by how they work. I certainly have been captivated with catalysts myself, as I have devoted my entire academic career to studying their properties. [...] Catalysts 2011-05-09 1 1 Editorial 10.3390/catal1010001 1 2 2073-4344 2011-05-09 doi: 10.3390/catal1010001 Keith Hohn