Editorial

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Open AccessEditorial

Feature Papers to Celebrate the Landmarks of Catalysts

by Keith L. Hohn

Catalysts 2015, 5(4), 2018-2023; https://doi.org/10.3390/catal5042018 - 24 Nov 2015

Viewed by 3179

Catalysis is a critical scientific field that underpins much of the world’s chemical industry. For example, it is often quoted that catalysis plays a role in 90% of all industrial chemical products. This importance has led to numerous academic journals and specialized conferences [...] Read more.

Catalysis is a critical scientific field that underpins much of the world’s chemical industry. For example, it is often quoted that catalysis plays a role in 90% of all industrial chemical products. This importance has led to numerous academic journals and specialized conferences on the subject, as practitioners seek outlets to publish their cutting-edge research on catalysis. [...] Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

Research

Jump to: Editorial, Review

389 KiB

Open AccessArticle

Investigation of Room Temperature Synthesis of Titanium Dioxide Nanoclusters Dispersed on Cubic MCM-48 Mesoporous Materials

by Sridhar Budhi, Chia-Ming Wu, Dan Zhao and Ranjit T. Koodali

Catalysts 2015, 5(3), 1603-1621; https://doi.org/10.3390/catal5031603 - 18 Sep 2015

Cited by 8 | Viewed by 6126

Abstract

Titania containing cubic MCM-48 mesoporous materials were synthesized successfully at room temperature by a modified Stöber method. The integrity of the cubic mesoporous phase was retained even at relatively high loadings of titania. The TiO₂-MCM-48 materials were extensively characterized by a [...] Read more.

Titania containing cubic MCM-48 mesoporous materials were synthesized successfully at room temperature by a modified Stöber method. The integrity of the cubic mesoporous phase was retained even at relatively high loadings of titania. The TiO₂-MCM-48 materials were extensively characterized by a variety of physico-chemical techniques. The physico-chemical characterization indicate that Ti⁴⁺ ions can be substituted in framework tetrahedral positions. The relative amount of Ti⁴⁺ ions in tetrahedral position was dependent on the order of addition of the precursor. Even at relatively high loadings of titania, no distinct bulk phase of titania could be observed indicating that the titania nanoclusters are well dispersed on the high surface area mesoporous material and probably exist as amorphous nanoclusters. The TiO₂-MCM-48 materials were found to exhibit 100% selectivity in the cyclohexene oxidation at room temperature in the presence of tert-butylhydroperoxide (t-BHP) as the oxidant. The results suggest that room temperature synthesis is an attractive option for the preparation of TiO₂-MCM-48 materials with interesting catalytic properties. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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962 KiB

Open AccessArticle

Bismuth Molybdate Catalysts Prepared by Mild Hydrothermal Synthesis: Influence of pH on the Selective Oxidation of Propylene

by Kirsten Schuh, Wolfgang Kleist, Martin Høj, Vanessa Trouillet, Pablo Beato, Anker Degn Jensen and Jan-Dierk Grunwaldt

Catalysts 2015, 5(3), 1554-1573; https://doi.org/10.3390/catal5031554 - 10 Sep 2015

Cited by 37 | Viewed by 10827

Abstract

A series of bismuth molybdate catalysts with relatively high surface area was prepared via mild hydrothermal synthesis. Variation of the pH value and Bi/Mo ratio during the synthesis allowed tuning of the crystalline Bi-Mo oxide phases, as determined by X-ray diffraction (XRD) and [...] Read more.

A series of bismuth molybdate catalysts with relatively high surface area was prepared via mild hydrothermal synthesis. Variation of the pH value and Bi/Mo ratio during the synthesis allowed tuning of the crystalline Bi-Mo oxide phases, as determined by X-ray diffraction (XRD) and Raman spectroscopy. The pH value during synthesis had a strong influence on the catalytic performance. Synthesis using a Bi/Mo ratio of 1/1 at pH ≥ 6 resulted in γ-Bi2MoO6, which exhibited a better catalytic performance than phase mixtures obtained at lower pH values. However, a significantly lower catalytic activity was observed at pH = 9 due to the low specific surface area. γ-Bi2MoO6 synthesized with Bi/Mo = 1/1 at pH = 6 and 7 exhibited relatively high surface areas and the best catalytic performance. All samples prepared with Bi/Mo = 1/1, except samples synthesized at pH = 1 and 9, showed better catalytic performance than samples synthesized with Bi/Mo = 2/3 at pH = 4 and 9 and γ-Bi2MoO6 synthesized by co-precipitation at pH = 7. At temperatures above 440 °C, the catalytic activity of the hydrothermally synthesized bismuth molybdates started to decrease due to sintering and loss of surface area. These results support that a combination of the required bismuth molybdate phase and a high specific surface area is crucial for a good performance in the selective oxidation of propylene. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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8864 KiB

Open AccessArticle

Iron Fischer-Tropsch Catalysts Prepared by Solvent-Deficient Precipitation (SDP): Effects of Washing, Promoter Addition Step, and Drying Temperature

by Kyle M. Brunner, Baiyu Huang, Brian F. Woodfield and William C. Hecker

Catalysts 2015, 5(3), 1352-1374; https://doi.org/10.3390/catal5031352 - 24 Jul 2015

Cited by 9 | Viewed by 6912

Abstract

A novel, solvent-deficient precipitation (SDP) method for catalyst preparation in general and for preparation of iron FT catalysts in particular is reported. Eight catalysts using a 2³ factorial design of experiments to identify the key preparation variables were prepared. The catalysts were [...] Read more.

A novel, solvent-deficient precipitation (SDP) method for catalyst preparation in general and for preparation of iron FT catalysts in particular is reported. Eight catalysts using a 2³ factorial design of experiments to identify the key preparation variables were prepared. The catalysts were characterized by electron microprobe, N₂ adsorption, TEM, XRD, and ICP. Results show that the morphology of the catalysts, i.e., surface area, pore volume, pore size distribution, crystallite sizes, and promoter distribution are significantly influenced by (1) whether or not the precursor catalyst is washed, (2) the promoter addition step, and (3) the drying condition (temperature). Consequently, the activity, selectivity, and stability of the catalysts determined from fixed-bed testing are also affected by these three variables. Unwashed catalysts prepared by a one-step method and dried at 100 °C produced the most active catalysts for FT synthesis. The catalysts of this study prepared by SDP compared favorably in activity, productivity, and stability with Fe FT catalysts reported in the literature. It is believed that this facile SDP approach has promise for development of future FT catalysts, and also offers a potential alternate route for the preparation of other catalysts for various other applications. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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11061 KiB

Open AccessArticle

Effect of Microgravity on Synthesis of Nano Ceria

by Ilgaz I. Soykal, Hyuntae Sohn, Burcu Bayram, Preshit Gawade, Michael P. Snyder, Stephen E. Levine, Hayrani Oz and Umit S. Ozkan

Catalysts 2015, 5(3), 1306-1320; https://doi.org/10.3390/catal5031306 - 20 Jul 2015

Cited by 8 | Viewed by 6858

Abstract

Cerium oxide (CeO₂) was prepared using a controlled-precipitation method under microgravity at the International Space Station (ISS). For comparison, ceria was also synthesized under normal-gravity conditions (referred as control). The Brunauer-Emmett-Teller (BET) surface area, pore volume and pore size analysis results [...] Read more.

Cerium oxide (CeO₂) was prepared using a controlled-precipitation method under microgravity at the International Space Station (ISS). For comparison, ceria was also synthesized under normal-gravity conditions (referred as control). The Brunauer-Emmett-Teller (BET) surface area, pore volume and pore size analysis results indicated that the ceria particles grown in space had lower surface area and pore volume compared to the control samples. Furthermore, the space samples had a broader pore size distribution ranging from 30–600 Å, whereas the control samples consisted of pore sizes from 30–50 Å range. Structural information of the ceria particles were obtained using TEM and XRD. Based on the TEM images, it was confirmed that the space samples were predominantly nano-rods, on the other hand, only nano-polyhedra particles were seen in the control ceria samples. The average particle size was larger for ceria samples synthesized in space. XRD results showed higher crystallinity as well as larger mean crystal size for the space samples. The effect of sodium hydroxide concentration on synthesis of ceria was also examined using 1 M and 3 M solutions. It was found that the control samples, prepared in 1 M and 3 M sodium hydroxide solutions, did not show a significant difference between the two. However, when the ceria samples were prepared in a more basic medium (3 M) under microgravity, a decrease in the particle size of the nano-rods and appearances of nano-polyhedra and spheres were observed. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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11752 KiB

Open AccessArticle

Surface Reaction Kinetics of Steam- and CO₂-Reforming as Well as Oxidation of Methane over Nickel-Based Catalysts

by Karla Herrera Delgado, Lubow Maier, Steffen Tischer, Alexander Zellner, Henning Stotz and Olaf Deutschmann

Catalysts 2015, 5(2), 871-904; https://doi.org/10.3390/catal5020871 - 29 May 2015

Cited by 131 | Viewed by 19819

Abstract

An experimental and kinetic modeling study on the Ni-catalyzed conversion of methane under oxidative and reforming conditions is presented. The numerical model is based on a surface reaction mechanism consisting of 52 elementary-step like reactions with 14 surface and six gas-phase species. Reactions [...] Read more.

An experimental and kinetic modeling study on the Ni-catalyzed conversion of methane under oxidative and reforming conditions is presented. The numerical model is based on a surface reaction mechanism consisting of 52 elementary-step like reactions with 14 surface and six gas-phase species. Reactions for the conversion of methane with oxygen, steam, and CO₂ as well as methanation, water-gas shift reaction and carbon formation via Boudouard reaction are included. The mechanism is implemented in a one-dimensional flow field description of a fixed bed reactor. The model is evaluated by comparison of numerical simulations with data derived from isothermal experiments in a flow reactor over a powdered nickel-based catalyst using varying inlet gas compositions and operating temperatures. Furthermore, the influence of hydrogen and water as co-feed on methane dry reforming with CO₂ is also investigated. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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2174 KiB

Open AccessArticle

Real-Time Raman Monitoring during Photocatalytic Epoxidation of Cyclohexene over V-Ti/MCM-41 Catalysts

by Hsiang-Yu Chan, Van-Huy Nguyen, Jeffrey C.S. Wu, Vanesa Calvino-Casilda, Miguel A. Bañares and Hsunling Bai

Catalysts 2015, 5(2), 518-533; https://doi.org/10.3390/catal5020518 - 30 Mar 2015

Cited by 13 | Viewed by 9085

Abstract

A series of V- and/or Ti-loading MCM-41 catalysts are successfully synthesized with a hydrothermal method. The photocatalytic and thermal epoxidations of cyclohexene in the presence of tert-butyl hydroperoxide (t-BuOOH) were investigated with real-time monitored by NIR-Raman spectroscopy. It suggests that [...] Read more.

A series of V- and/or Ti-loading MCM-41 catalysts are successfully synthesized with a hydrothermal method. The photocatalytic and thermal epoxidations of cyclohexene in the presence of tert-butyl hydroperoxide (t-BuOOH) were investigated with real-time monitored by NIR-Raman spectroscopy. It suggests that both V- and Ti-loading can be responsible for the cyclohexene epoxidation. Moreover, the complementary behavior of V- and Ti-loading may be related to a similar role of activation. Interestingly, the progress of the photo-epoxidation on V_0.25Ti₂/MCM-41 photocatalyst was monitored by changes in intensity of the characteristic Raman bands without interference from the UV-light irradiation. The result, for the first time, reveals that cyclohexene was directly photo-epoxidized to 1,2-epoxycyclohexane by t-BuOOH during the reaction. A possible mechanism of cyclohexene photo-epoxidation is also proposed for this study. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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1156 KiB

Open AccessArticle

Structural Evolution under Reaction Conditions of Supported (NH₄)₃HPMo₁₁VO₄₀ Catalysts for the Selective Oxidation of Isobutane

by Fangli Jing, Benjamin Katryniok, Elisabeth Bordes-Richard, Franck Dumeignil and Sébastien Paul

Catalysts 2015, 5(1), 460-477; https://doi.org/10.3390/catal5010460 - 23 Mar 2015

Cited by 15 | Viewed by 7461

Abstract

When using heteropolycompounds in the selective oxidation of isobutane to methacrolein and methacrylic acid, both the keeping of the primary structure (Keggin units) and the presence of acidic sites are necessary to obtain the desired products. The structural evolution of supported (NH₄ [...] Read more.

When using heteropolycompounds in the selective oxidation of isobutane to methacrolein and methacrylic acid, both the keeping of the primary structure (Keggin units) and the presence of acidic sites are necessary to obtain the desired products. The structural evolution of supported (NH₄)₃HPMo₁₁VO₄₀ (APMV) catalysts under preliminary thermal oxidizing and reducing treatments was investigated. Various techniques, such as TGA/DTG (Thermo-Gravimetric Analysis/Derivative Thermo-Gravimetry), H₂-TPR (Temperature Programed Reduction), in situ XRD (X-Ray Diffraction) and XPS (X-ray Photoelectron Spectroscopy), were applied. It was clearly evidenced that the thermal stability and the reducibility of the Keggin units are improved by supporting 40% APMV active phase on Cs₃PMo₁₂O₄₀ (CPM). The partial degradation of APMV takes place depending on temperature and reaction conditions. The decomposition of ammonium cations (releasing NH₃) leads to the formation of vacancies favoring cationic exchanges between vanadium coming from the active phase and cesium coming from the support. In addition, the vanadium expelled from the Keggin structure is further reduced to V⁴⁺, species, which contributes (with Mo⁵⁺) to activate isobutane. The increase in reducibility of the supported catalyst is assumed to improve the catalytic performance in comparison with those of unsupported APMV. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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4980 KiB

Open AccessArticle

Activated Carbon, Carbon Nanofiber and Carbon Nanotube Supported Molybdenum Carbide Catalysts for the Hydrodeoxygenation of Guaiacol

by Eduardo Santillan-Jimenez, Maxime Perdu, Robert Pace, Tonya Morgan and Mark Crocker

Catalysts 2015, 5(1), 424-441; https://doi.org/10.3390/catal5010424 - 16 Mar 2015

Cited by 66 | Viewed by 8184

Abstract

Molybdenum carbide was supported on three types of carbon support—activated carbon; multi-walled carbon nanotubes; and carbon nanofibers—using ammonium molybdate and molybdic acid as Mo precursors. The use of activated carbon as support afforded an X-ray amorphous Mo phase, whereas crystalline molybdenum carbide phases [...] Read more.

Molybdenum carbide was supported on three types of carbon support—activated carbon; multi-walled carbon nanotubes; and carbon nanofibers—using ammonium molybdate and molybdic acid as Mo precursors. The use of activated carbon as support afforded an X-ray amorphous Mo phase, whereas crystalline molybdenum carbide phases were obtained on carbon nanofibers and, in some cases, on carbon nanotubes. When the resulting catalysts were tested in the hydrodeoxygenation (HDO) of guaiacol in dodecane, catechol and phenol were obtained as the main products, although in some instances significant amounts of cyclohexane were produced. The observation of catechol in all reaction mixtures suggests that guaiacol was converted into phenol via sequential demethylation and HDO, although the simultaneous occurrence of a direct demethoxylation pathway cannot be discounted. Catalysts based on carbon nanofibers generally afforded the highest yields of phenol; notably, the only crystalline phase detected in these samples was Mo₂C or Mo₂C-ζ, suggesting that crystalline Mo₂C is particularly selective to phenol. At 350 °C, carbon nanofiber supported Mo₂C afforded near quantitative guaiacol conversion, the selectivity to phenol approaching 50%. When guaiacol HDO was performed in the presence of acetic acid and furfural, guaiacol conversion decreased, although the selectivity to both catechol and phenol was increased. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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Open AccessArticle

Structural Evolution of Molybdenum Carbides in Hot Aqueous Environments and Impact on Low-Temperature Hydroprocessing of Acetic Acid

by Jae-Soon Choi, Viviane Schwartz, Eduardo Santillan-Jimenez, Mark Crocker, Samuel A. Lewis, Sr., Michael J. Lance, Harry M. Meyer III and Karren L. More

Catalysts 2015, 5(1), 406-423; https://doi.org/10.3390/catal5010406 - 13 Mar 2015

Cited by 15 | Viewed by 6252

Abstract

We investigated the structural evolution of molybdenum carbides subjected to hot aqueous environments and their catalytic performance in low-temperature hydroprocessing of acetic acid. While bulk structures of Mo carbides were maintained after aging in hot liquid water, a portion of carbidic Mo sites [...] Read more.

We investigated the structural evolution of molybdenum carbides subjected to hot aqueous environments and their catalytic performance in low-temperature hydroprocessing of acetic acid. While bulk structures of Mo carbides were maintained after aging in hot liquid water, a portion of carbidic Mo sites were converted to oxidic sites. Water aging also induced changes to the non-carbidic carbon deposited during carbide synthesis and increased surface roughness, which in turn affected carbide pore volume and surface area. The extent of these structural changes was sensitive to the initial carbide structure and was lower under actual hydroprocessing conditions indicating the possibility of further improving the hydrothermal stability of Mo carbides by optimizing catalyst structure and operating conditions. Mo carbides were active in acetic acid conversion in the presence of liquid water, their activity being comparable to that of Ru/C. The results suggest that effective and inexpensive bio-oil hydroprocessing catalysts could be designed based on Mo carbides, although a more detailed understanding of the structure-performance relationships is needed, especially in upgrading of more complex reaction mixtures or real bio-oils. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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Open AccessArticle

Influence of the Synthesis Method for Pt Catalysts Supported on Highly Mesoporous Carbon Xerogel and Vulcan Carbon Black on the Electro-Oxidation of Methanol

by Cinthia Alegre, María Elena Gálvez, Rafael Moliner and María Jesús Lázaro

Catalysts 2015, 5(1), 392-405; https://doi.org/10.3390/catal5010392 - 13 Mar 2015

Cited by 28 | Viewed by 6701

Abstract

Platinum catalysts supported on carbon xerogel and carbon black (Vulcan) were synthesized with the aim of investigating the influence of the characteristics of the support on the electrochemical performance of the catalysts. Three synthesis methods were compared: an impregnation method with two different [...] Read more.

Platinum catalysts supported on carbon xerogel and carbon black (Vulcan) were synthesized with the aim of investigating the influence of the characteristics of the support on the electrochemical performance of the catalysts. Three synthesis methods were compared: an impregnation method with two different reducing agents, sodium borohydride and formic acid, and a microemulsion method, in order to study the effect of the synthesis method on the physico-chemical properties of the catalysts. X-ray diffraction and transmission electron microscopy were applied. Cyclic voltammetry and chronoamperometry were used for studying carbon monoxide and methanol oxidation. Catalysts supported on carbon xerogel presented higher catalytic activities towards CO and CH₃OH oxidation than catalysts supported on Vulcan. The higher mesoporosity of carbon xerogel was responsible for the favored diffusion of reagents towards catalytic centers. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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Open AccessArticle

A Mechanistic Study of Direct Activation of Allylic Alcohols in Palladium Catalyzed Amination Reactions

by Yasemin Gumrukcu, Bas De Bruin and Joost N. H. Reek

Catalysts 2015, 5(1), 349-365; https://doi.org/10.3390/catal5010349 - 11 Mar 2015

Cited by 15 | Viewed by 7946

Abstract

We here report a computational approach on the mechanism of allylicamination reactions using allyl-alcohols and amines as the substrates and phosphoramidite palladium catalyst 1a, which operates in the presence of catalytic amount of 1,3-diethylurea as a co-catalyst. DFT calculations showed a cooperative [...] Read more.

We here report a computational approach on the mechanism of allylicamination reactions using allyl-alcohols and amines as the substrates and phosphoramidite palladium catalyst 1a, which operates in the presence of catalytic amount of 1,3-diethylurea as a co-catalyst. DFT calculations showed a cooperative hydrogen-bonding array between the urea moiety and the hydroxyl group of the allyl alcohol, which strengthens the hydrogen bond between the O-H moiety of the coordinated allyl-alcohol and the carbonyl-moiety of the ligand. This hydrogen bond pattern facilitates the (rate-limiting) C-O oxidative addition step and leads to lower energy isomers throughout the catalytic cycle, clarifying the role of the urea-moiety. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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Open AccessArticle

Ni-CeO₂/C Catalysts with Enhanced OSC for the WGS Reaction

by Laura Pastor-Pérez, Tomás Ramírez Reina, Svetlana Ivanova, Miguel Ángel Centeno, José Antonio Odriozola and Antonio Sepúlveda-Escribano

Catalysts 2015, 5(1), 298-309; https://doi.org/10.3390/catal5010298 - 06 Mar 2015

Cited by 23 | Viewed by 7998

Abstract

In this work, the WGS performance of a conventional Ni/CeO₂ bulk catalyst is compared to that of a carbon-supported Ni-CeO₂ catalyst. The carbon-supported sample resulted to be much more active than the bulk one. The higher activity of the Ni-CeO₂ [...] Read more.

In this work, the WGS performance of a conventional Ni/CeO₂ bulk catalyst is compared to that of a carbon-supported Ni-CeO₂ catalyst. The carbon-supported sample resulted to be much more active than the bulk one. The higher activity of the Ni-CeO₂/C catalyst is associated to its oxygen storage capacity, a parameter that strongly influences the WGS behavior. The stability of the carbon-supported catalyst under realistic operation conditions is also a subject of this paper. In summary, our study represents an approach towards a new generation of Ni-ceria based catalyst for the pure hydrogen production via WGS. The dispersion of ceria nanoparticles on an activated carbon support drives to improved catalytic skills with a considerable reduction of the amount of ceria in the catalyst formulation. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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Open AccessArticle

Selective Oxidation of Raw Glycerol Using Supported AuPd Nanoparticles

by Carine E. Chan-Thaw, Sebastiano Campisi, Di Wang, Laura Prati and Alberto Villa

Catalysts 2015, 5(1), 131-144; https://doi.org/10.3390/catal5010131 - 13 Feb 2015

Cited by 29 | Viewed by 6907

Abstract

Bimetallic AuPd supported on different carbonaceous materials and TiO₂ was tested in the liquid phase oxidation of commercial grade and raw glycerol. The latter was directly obtained from the base-catalyzed transesterification of edible rapeseed oil using KOH. The best catalytic results were [...] Read more.

Bimetallic AuPd supported on different carbonaceous materials and TiO₂ was tested in the liquid phase oxidation of commercial grade and raw glycerol. The latter was directly obtained from the base-catalyzed transesterification of edible rapeseed oil using KOH. The best catalytic results were obtained using activated carbon and nitrogen-functionalized carbon nanofibers as supports. In fact, the catalysts were more active using pure glycerol instead of the one obtained from rapeseed, where strong deactivation phenomena were present. Fourier transform infrared (FT-IR) and TEM were utilized to investigate the possible reasons for the observed loss of activity. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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Open AccessArticle

Supported Photocatalyst for Removal of Emerging Contaminants from Wastewater in a Continuous Packed-Bed Photoreactor Configuration

by Mª Emma Borges, Dulce María García, Tania Hernández, Juan Carlos Ruiz-Morales and Pedro Esparza

Catalysts 2015, 5(1), 77-87; https://doi.org/10.3390/catal5010077 - 02 Feb 2015

Cited by 50 | Viewed by 8366

Abstract

Water pollution from emerging contaminants (ECs) or emerging pollutants is an important environmental problem. Heterogeneous photocatalytic treatment, as advanced oxidation treatment of wastewater effluents, has been proposed to solve this problem. In this paper, a heterogeneous photocatalytic process was studied for emergent contaminants [...] Read more.

Water pollution from emerging contaminants (ECs) or emerging pollutants is an important environmental problem. Heterogeneous photocatalytic treatment, as advanced oxidation treatment of wastewater effluents, has been proposed to solve this problem. In this paper, a heterogeneous photocatalytic process was studied for emergent contaminants removal using paracetamol as a model contaminant molecule. TiO₂ photocatalytic activity was evaluated using two photocatalytic reactor configurations: Photocatalyst solid suspension in wastewater in a stirred photoreactor and TiO₂ supported on glass spheres (TGS) configuring a packed bed photoreactor. The surface morphology and texture of the TGS were monitored by scanning electron microscope (SEM). The influence of photocatalyst amount and wastewater pH were evaluated in the stirred photoreactor and the influence of wastewater flowrate was tested in the packed bed photoreactor, in order to obtain the optimal operation conditions. Moreover, results obtained were compared with those obtained from photolysis and adsorption studies, using the optimal operation conditions. Good photocatalytic activities have been observed and leads to the conclusion that the heterogeneous photocatalytic system in a packed bed is an effective method for removal of emerging pollutants. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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Open AccessArticle

Valorisation of Vietnamese Rice Straw Waste: Catalytic Aqueous Phase Reforming of Hydrolysate from Steam Explosion to Platform Chemicals

by Cao Huong Giang, Amin Osatiashtiani, Vannia Cristina Dos Santos, Adam F. Lee, David R. Wilson, Keith W. Waldron and Karen Wilson

Catalysts 2014, 4(4), 414-426; https://doi.org/10.3390/catal4040414 - 15 Dec 2014

Cited by 15 | Viewed by 6755

Abstract

A family of tungstated zirconia solid acid catalysts were synthesised via wet impregnation and subsequent thermochemical processing for the transformation of glucose to 5-hydroxymethylfurfural (HMF). Acid strength increased with tungsten loading and calcination temperature, associated with stabilisation of tetragonal zirconia. High tungsten dispersions [...] Read more.

A family of tungstated zirconia solid acid catalysts were synthesised via wet impregnation and subsequent thermochemical processing for the transformation of glucose to 5-hydroxymethylfurfural (HMF). Acid strength increased with tungsten loading and calcination temperature, associated with stabilisation of tetragonal zirconia. High tungsten dispersions of between 2 and 7 W atoms·nm⁻² were obtained in all cases, equating to sub-monolayer coverages. Glucose isomerisation and subsequent dehydration via fructose to HMF increased with W loading and calcination temperature up to 600 °C, indicating that glucose conversion to fructose was favoured over weak Lewis acid and/or base sites associated with the zirconia support, while fructose dehydration and HMF formation was favoured over Brönsted acidic WO_x clusters. Aqueous phase reforming of steam exploded rice straw hydrolysate and condensate was explored heterogeneously for the first time over a 10 wt% WZ catalyst, resulting in excellent HMF yields as high as 15% under mild reaction conditions. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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Open AccessArticle

Catalytic Glycerol Hydrodeoxygenation under Inert Atmosphere: Ethanol as a Hydrogen Donor

by Efterpi S. Vasiliadou and Angeliki A. Lemonidou

Catalysts 2014, 4(4), 397-413; https://doi.org/10.3390/catal4040397 - 15 Dec 2014

Cited by 16 | Viewed by 6774

Abstract

Glycerol hydrodeoxygenation to 1,2-propanediol (1,2-PDO) is a reaction of high interest. However, the need for hydrogen supply is a main drawback of the process. According to the concept investigated here, 1,2-propanediol is efficiently formed using bio-glycerol feedstock with H₂ formed in situ [...] Read more.

Glycerol hydrodeoxygenation to 1,2-propanediol (1,2-PDO) is a reaction of high interest. However, the need for hydrogen supply is a main drawback of the process. According to the concept investigated here, 1,2-propanediol is efficiently formed using bio-glycerol feedstock with H₂ formed in situ via ethanol aqueous phase reforming. Ethanol is thought to be a promising H₂ source, as it is alcohol that can be used instead of methanol for transesterification of oils and fats. The H₂ generated is consumed in the tandem reaction of glycerol hydrodeoxygenation. The reaction cycle proceeds in liquid phase at 220–250 °C and 1.5–3.5 MPa initial N₂ pressure for a 2 and 4-h reaction time. Pt-, Ni- and Cu-based catalysts have been synthesized, characterized and evaluated in the reaction. Among the materials tested, Pt/Fe₂O₃-Al₂O₃ exhibited the most promising performance in terms of 1,2-propanediol productivity, while reusability tests showed a stable behavior. Structural integrity and no formation of carbonaceous deposits were verified via Temperature Programmed Desorption of hydrogen (TPD-H₂) and thermogravimetric analysis of the fresh and used Pt/FeAl catalyst. A study on the effect of various operating conditions (reaction time, temperature and pressure) indicated that in order to maximize 1,2-propanediol productivity and yield, milder reaction conditions should be applied. The highest 1,2-propanediol yield, 53% (1.1 g_1,2-PDO g_cat⁻¹·h⁻¹), was achieved at a lower reaction temperature of 220 °C. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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Review

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8635 KiB

Open AccessReview

Acyclic Diene Metathesis (ADMET) Polymerization for Precise Synthesis of Defect-Free Conjugated Polymers with Well-Defined Chain Ends

by Tahmina Haque and Kotohiro Nomura

Catalysts 2015, 5(2), 500-517; https://doi.org/10.3390/catal5020500 - 30 Mar 2015

Cited by 21 | Viewed by 9611

Abstract

This accounts introduces unique characteristics by adopting the acyclic diene metathesis (ADMET) polymerization for synthesis of conjugated polymers, poly(arylene vinylene)s, known as promising molecular electronics. The method is more suitable than the other methods in terms of atom efficiency affording defect-free, stereo-regular (exclusive [...] Read more.

This accounts introduces unique characteristics by adopting the acyclic diene metathesis (ADMET) polymerization for synthesis of conjugated polymers, poly(arylene vinylene)s, known as promising molecular electronics. The method is more suitable than the other methods in terms of atom efficiency affording defect-free, stereo-regular (exclusive trans) polymers with well-defined chain ends; the resultant polymers possess better property than those prepared by the conventional methods. The chain ends (vinyl group) in the resultant polymer prepared by ruthenium-carbene catalyst(s) can be modified by treating with molybdenum-alkylidene complex (olefin metathesis) followed by addition of various aldehyde (Wittig type cleavage), affording the end-functionalized polymers exclusively. An introduction of initiating fragment, the other conjugated segment, and one-pot synthesis of end-functionalized block copolymers, star shape polymers can be achieved by adopting this methodology. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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Open AccessReview

B-Site Metal (Pd, Pt, Ag, Cu, Zn, Ni) Promoted La_1−xSr_xCo_1−yFe_yO_3–_δPerovskite Oxides as Cathodes for IT-SOFCs

by Shaoli Guo, Hongjing Wu, Fabrizio Puleo and Leonarda F. Liotta

Catalysts 2015, 5(1), 366-391; https://doi.org/10.3390/catal5010366 - 12 Mar 2015

Cited by 50 | Viewed by 11991

Abstract

Perovskite oxides La_1−xSr_xCo_1−yFe_yO_3–δ (LSCF) have been extensively investigated and developed as cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) due to mixed ionic–electronic conductivity and high electrooxygen reduction activity for [...] Read more.

Perovskite oxides La_1−xSr_xCo_1−yFe_yO_3–δ (LSCF) have been extensively investigated and developed as cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) due to mixed ionic–electronic conductivity and high electrooxygen reduction activity for oxygen reduction. Recent literature investigations show that cathode performances can be improved by metal surface modification or B-site substitution on LSCF. Although the specific reaction mechanism needs to be further investigated, the promoting effect of metal species in enhancing oxygen surface exchange and oxygen bulk diffusion is well recognized. To our knowledge, no previous reviews dealing with the effect of metal promotion on the cathodic performances of LSCF materials have been reported. In the present review, recent progresses on metal (Pd, Pt, Ag, Cu, Zn, Ni) promotion of LSCF are discussed focusing on two main aspects, the different synthesis approaches used (infiltration, deposition, solid state reaction, one pot citrate method) and the effects of metal promotion on structural properties, oxygen vacancies content and cathodic performances. The novelty of the work lies in the fact that the metal promotion at the B-site is discussed in detail, pointing at the effects produced by two different approaches, the LSCF surface modification by the metal or the metal ion substitution at the B-site of the perovskite. Moreover, for the first time in a review article, the importance of the combined effects of oxygen dissociation rate and interfacial oxygen transfer rate between the metal phase and the cathode phase is addressed for metal-promoted LSCF and compared with the un-promoted oxides. Perspectives on new research directions are shortly given in the conclusion. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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Open AccessReview

Fischer-Tropsch Synthesis on Multicomponent Catalysts: What Can We Learn from Computer Simulations?

by José L. C. Fajín, M. Natália D. S. Cordeiro and José R. B. Gomes

Catalysts 2015, 5(1), 3-17; https://doi.org/10.3390/catal5010003 - 09 Jan 2015

Cited by 20 | Viewed by 14395

Abstract

In this concise review paper, we will address recent studies based on the generalized-gradient approximation (GGA) of the density functional theory (DFT) and on the periodic slab approach devoted to the understanding of the Fischer-Tropsch synthesis process on transition metal catalysts. As it [...] Read more.

In this concise review paper, we will address recent studies based on the generalized-gradient approximation (GGA) of the density functional theory (DFT) and on the periodic slab approach devoted to the understanding of the Fischer-Tropsch synthesis process on transition metal catalysts. As it will be seen, this computational combination arises as a very adequate strategy for the study of the reaction mechanisms on transition metal surfaces under well-controlled conditions and allows separating the influence of different parameters, e.g., catalyst surface morphology and coverage, influence of co-adsorbates, among others, in the global catalytic processes. In fact, the computational studies can now compete with research employing modern experimental techniques since very efficient parallel computer codes and powerful computers enable the investigation of more realistic molecular systems in terms of size and composition and to explore the complexity of the potential energy surfaces connecting reactants, to intermediates, to products of reaction. In the case of the Fischer-Tropsch process, the calculations were used to complement experimental work and to clarify the reaction mechanisms on different catalyst models, as well as the influence of additional components and co-adsorbate species in catalyst activity and selectivity. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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