Catalysts, Volume 6, Issue 10 (October 2016) – 18 articles

A one-pot hydrothermal strategy was used to synthesize Pt/GNs (PAMAM) & Pt/GNs (CS) composites. Pt nanoparticles are deposited onto graphene sheets (GNs) via synchronous reduction of K₂PtCl₄ and graphene oxide (GO) under hydrothermal conditons without additional reducing agent. During the synthesis process, polyamidoamine (PAMAM) or chitosan (CS) was used as a template respectively to obtain shape controlled Pt particles on the surface of GNs, leading to the formation of flower-like Pt nanoclusters for Pt/GNs (PAMAM) and uniform spherical Pt nanoparticles for Pt/GNs (CS). PAMAM and CS are simultaneously served as intrinsic reducing agents to accelerate reduction process; ensuring excellent electrical conductivity of the composites. Electrochemical tests show that Pt/GNs (PAMAM) and Pt/GNs (CS) have much higher electrocatalytic activity and better stability toward methanol oxidation reaction (MOR) in comparison with counterpart Pt/GNs and the commercially available 20% Pt/C catalyst (Pt/C) due to their better dispersion of Pt particles, stronger interaction between Pt and substrate materials, and better electron transfer capability. Full article

Supported copper oxide nanoparticles are a potential candidate for replacing the rare and expensive precious metals within the automotive three-way catalyst. However, a well-designed dispersion method is necessary to allow a stable high loading of active material, compensating its lower intrinsic activity and stability. In this work, a CuO-loaded SBA-15 catalyst has been manufactured by two methods. The ammonia-driven deposition precipitation (ADP) and the molecular designed dispersion (MDD) methods are both considered as efficient deposition methods to provide well-dispersed copper oxide-based catalysts. Their morphology, copper dispersion and the chemical state of copper were characterized and compared. Due to the differences in the synthesis approach, a difference in the obtained copper oxide phases has been observed, leading to a distinct behavior in the catalytic performance. The structure-activity correlation of both catalysts has also been revealed for automotive exhaust gas abatement. Results demonstrate that various copper species can be formed depending on the precursor–support interaction, affecting selectivity and conversion during the catalytic reaction. Full article

In this study, the optical properties of a TiO₂ photocatalyst were enhanced with various impregnations of Er³⁺ and Ni²⁺ separately, using the impregnation method as photocatalysts for the direct solar photolysis degradation of chloroxylenol. The synthesized Er³⁺/TiO₂ and Ni²⁺/TiO₂ catalysts were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX), metal mapping, and ultraviolet visible (UV–Vis) spectroscopy. The results showed that the Er³⁺/TiO₂ and Ni²⁺/TiO₂ nano-particles have the same structures of TiO₂ nano-particles with little difference in particle size. The Er³⁺ and Ni²⁺ ions were well-distributed on the TiO₂ surface, and it was found that the maximum band gap decreased from 3.13 eV for intrinsic TiO₂ to 2.63 eV at 1.8 wt % Er³⁺/TiO₂ and to 2.47 eV at 0.6 wt % for Ni²⁺/TiO₂. The initial concentration of chloroxylenol, catalyst loading, and pH of the solution are the most important factors affecting the solar photocatalytic degradation efficiency that were optimized using Design Expert software (version 6.0.10, Minneapolis, MN, USA, 2003). The results showed that the optimal conditions for chloroxylenol degradation include a pH of 4, TiO₂ loading at 3 g/L, and a chloroxylenol concentration of 50 mg/L. These conditions resulted in a degradation efficiency of 90.40% after 60 min of direct solar irradiation, wherein the solar energy recorded during a clear sunny day is 1000 W/m². However, some experiments were conducted on a semi-cloudy day to cover all weather stated and to study the degradation kinetics. During semi-cloudy day experiments, using Er³⁺/TiO₂ and Ni²⁺/TiO₂ with a solar irradiation activity of 600 W/m² for a 60 min exposure at optimal conditions increased the degradation efficiency from 68.28% for intrinsic TiO₂ to 82.38% for Er³⁺/TiO₂ and 80.70% for Ni²⁺/TiO₂. Full article

Due to the continuously rising demand for C₃–C₅ olefins it is important to improve the performance of catalysts for dehydrogenation of light alkanes. In this work the effect of modification by SiO₂ on the properties of the alumina support and the chromia-alumina catalyst was studied. SiO₂ was introduced by impregnation of the support with a silica sol. To characterize the supports and the catalysts the following techniques were used: low-temperature nitrogen adsorption; IR-spectroscopy; magic angle spinning ²⁹Si nuclear magnetic resonance; temperature programmed desorption and reduction; UV-Vis-, Raman- and electron paramagnetic resonance (EPR)-spectroscopy. It was shown that the modifier in amounts of 2.5–7.5 wt % distributed on the support surface in the form of SiO_x-islands diminishes the interaction between the alumina support and the chromate ions (precursor of the active component). As a result, polychromates are the compounds predominantly stabilized on the surface of the modified support; under thermal activation of the catalyst and are reduced to the amorphous Cr₂O₃. This in turn leads to an increase in the activity of the catalyst in the dehydrogenation of isobutane. Full article

It is highly desirable to design functionalized supports in heterogeneous catalysis regarding the stabilization of active sites. Pd immobilization in porous polymers and henceforth its application is a rapidly growing field. In virtue of its’ scalable synthesis and high stability in reaction conditions, amorphous polymers are considered an excellent scaffold for metal mediated catalysis, but the majority of them are found as either agglomerated particles or composed of rough spheres. Owing to several important applications of hollow organic tubes in diverse research areas, we aimed to utilize them as support for the immobilization of Pd nanoparticles. Pd immobilization in nanoporous polymer tubes shows high activity in Suzuki cross coupling reactions between aryl halides and sodium phenyl trihydroxyborate in water, which deserves environmental merit. Full article

Low temperature fuel cells (LTFCs) are considered as clean energy conversion systems and expected to help address our society energy and environmental problems. Up-to-date, oxygen reduction reaction (ORR) is one of the main hindering factors for the commercialization of LTFCs, because of its slow kinetics and high overpotential, causing major voltage loss and short-term stability. To provide enhanced activity and minimize loss, precious metal catalysts (containing expensive and scarcely available platinum) are used in abundance as cathode materials. Moreover, research is devoted to reduce the cost associated with Pt based cathode catalysts, by identifying and developing Pt-free alternatives. However, so far none of them has provided acceptable performance and durability with respect to Pt electrocatalysts. By adopting new preparation strategies and by enhancing and exploiting synergetic and multifunctional effects, some elements such as transition metals supported on highly porous carbons have exhibited reasonable electrocatalytic activity. This review mainly focuses on the very recent progress of novel carbon based materials for ORR, including: (i) development of three-dimensional structures; (ii) synthesis of novel hybrid (metal oxide-nitrogen-carbon) electrocatalysts; (iii) use of alternative raw precursors characterized from three-dimensional structure; and (iv) the co-doping methods adoption for novel metal-nitrogen-doped-carbon electrocatalysts. Among the examined materials, reduced graphene oxide-based hybrid electrocatalysts exhibit both excellent activity and long term stability. Full article

To contribute to the search for an oxygen-free biodiesel from vegetable oil, a process based in the oleic acid hydrodeoxygenation over Ni/γ-Al₂O₃ catalysts was performed. In this work different wt % of Ni nanoparticles were prepared by wetness impregnation and tested as catalytic phases. Oleic acid was used as a model molecule for biodiesel production due to its high proportion in vegetable oils used in food and agro-industrial processes. A theoretical model to optimize yield of n-C₁₇ was developed using size, distribution, and wt % of Ni nanoparticles (NPs) as additional factors besides operational conditions such as temperature and reaction time. These mathematical models related to response surfaces plots predict a higher yield of n-C₁₇ when physical parameters of Ni NPs are suitable. It can be of particular interest that the model components have a high interaction with operation conditions for the n-C₁₇ yields, with the size, distribution, and wt % of Ni NPs being the most significant. A combination of these factors statistically pointed out those conditions that create a maximum yield of alkanes; these proved to be affordable for producing biodiesel from this catalytic environmental process. Full article

The “8th International Congress on Biocatalysis (biocat2016)” is part of a biennial conference series. Biocatalysis is a topic based on the edge of biology and chemistry, which brings together scientists from the life sciences, engineers and computer scientists. This international conference serves as a platform to meet researchers from all over the world, to find collaboration partners for future projects and to gain novel insights into modern topics and techniques. Biocat covers the most exciting aspects and the latest developments in biocatalysis, including enzyme discovery, evolution and application, bioprocess engineering, cascade reaction systems and nanobiotechnology. In 2016, we welcomed 367 expert delegates in the respective fields. Established and young scientists from academia and the industry presented 51 lectures, 37 lightning talks and 234 posters. In addition, the biocat award, which is among the most prestigious awards in the field of biotechnology, has been awarded for the sixth time in the categories “Science in academia”, “Lifetime achievement” and “Industry”. Full article

In this comprehensive review, the main aspects of using Au/CeO₂ catalysts in oxidation reactions are considered. The influence of the preparation methods and synthetic parameters, as well as the characteristics of the ceria support (presence of doping cations, oxygen vacancies concentration, surface area, redox properties, etc.) in the dispersion and chemical state of gold are revised. The proposed review provides a detailed analysis of the literature data concerning the state of the art and the applications of gold–ceria systems in oxidation reactions. Full article

Developing cheap electrocatalysts for cathodic oxygen reduction in neutral medium is a key factor for practical applications of microbial fuel cells (MFCs). Natural hematite was investigated as a low-cost cathode to improve the performance of microbial fuel cells (MFCs). With hematite-coated cathode, the cell current density stabilized at 330.66 ± 3.1 mA·m⁻² (with a 1000 Ω load) over 10 days under near-neutral conditions. The maximum power density of MFC with hematite cathode reached to 144.4 ± 7.5 mW·m⁻², which was 2.2 times that of with graphite cathode (64.8 ± 5.2 mW·m⁻²). X-ray diffraction (XRD), Raman, electrode potential analysis, and cyclic voltammetry (CV) revealed that hematite maintained the electrode activities due to the stable existence of Fe(II)/Fe(III) in mineral structure. Electrochemical impedance spectroscopy (EIS) results indicated that the cathodic electron transfer dynamics was significantly improved by using hematite to lower the cathodic overpotential. Therefore, this low-cost and earth-abundant natural mineral is promised as an effective cathode material with potential large-field applications of MFCs in future. Full article

Nano-porous anodic aluminum oxide (AAO) supported Ni-Ce mixed metal oxide catalysts were prepared and tested for dry reforming of propane to produce synthesis gas. The presence of Ce efficiently suppressed the nickel particle sintering and improved the reducibility of nickel oxide supported on the AAO. The prepared NiO-CeO₂/AAO catalyst was highly efficient for the dry reforming of propane (DRP) with CO₂ over a temperature range of 480–580 °C. The catalyst achieved the best reforming performance of 90%–97%, and a H₂/CO ratio close to 1.37 at 580 °C. The AAO supported NiO-CeO₂ catalyst can be a promising catalytic system for DRP. Full article

An innovative nanoscale ZnO/polybutadiene rubber composite (ZBRC) was developed as a valid alternative to TiO₂ particles or immobilized TiO₂ for the mineralization of chlorinated hydrocarbons without difficulties in the recovery of nanoscale photocatalyst particles. A synergistic increase in the removal of 1,1,2-trichloroethylene (TCE) through the coupled reaction processes (i.e., sorption, photolysis, and photocatalysis) was observed because sorption of TCE to the ultraviolet(UV)-transparent polybutadiene rubber occurred, and was coupled with the heterogeneous photocatalytic reactions with nanoscale ZnO particles on the surface of ZBRC. The removal rate of TCE decreased with an increase in the initial concentration of TCE because of both inhibited generation of electron–hole pairs and deficiency of photons to activate ZnO particles. Also, the TCE removal rate increased as the loading amount of ZBRC increased. Based on satisfactory linear regressions (R² ≥ 0.94) between the apparent degradation rate constant (K_app) and the initial concentration vs. the ZBRC loading amount, the K_app values can be estimated, a priori, without performing photocatalytic experiments. The removal efficiencies were more significantly affected by the changes in the initial concentration of TCE and the ZBRC loading amounts than by the changes in light intensity and pH in aqueous solutions. From the results of response surface analysis, the greater removal efficiencies of TCE were achieved with higher pH values, greater amounts of ZBRC, and greater intensity of light. Based on these results, newly-developed ZBRC with both high removal efficiency and low cost performs as a valid alternative to TiO₂ particles or immobilized TiO₂ for the mineralization of chlorinated hydrocarbons in various environmental and industrial matrices. Full article

Various porous binary oxides with elevated textural properties were obtained in this work. The as-synthesized solids were calcined or modified by reflux and extraction processes. Characterizations through SEM, nitrogen physisorption and TEM techniques demonstrated the formation of porous metal oxide networks over all solids. XRD, thermal analyses and FTIR measurements showed the existence of nanosized rutile TiO₂, tetragonal ZrO₂, SiO₂ and γ-Al₂O₃ phases on the solids. The structure and texture of the as-synthesized SiAl sol-gel derived solid resulted in the formation of well-dispersed nanoparticles on the support. The removal of the organic compounds by ethanol extraction or reflux from SiAl resulted in the presence of structures with defined hierarchy of pores. Among the solids studied, the catalytic results in the esterification of glycerol with acetic acid indicated that best performances were obtained over SiAl sample when submitted to extraction and reflux treatments. This was due to the creation of accessible pores, which facilitated the reaction occurrence at glycerol to acetic acid molar ratio = 1:3 and T = 80 °C for 20 h using 75 mg of catalyst. The solids can be reused three times without complete loss of their catalytic performance. Full article

Carbon-supported Pt–Ru alloys with a Pt/Ru ratio of 1:1 were prepared by NaBH₄ reduction at room temperature. X-ray diffraction (XRD) measurements indicate that the as-prepared Pt–Ru nanoparticles had a face-centered cubic (fcc) structure. X-ray photoelectron spectroscopy (XPS) analyses demonstrate that alloying with Ru can decrease the 4f electron density of Pt, which results in a positive binding energy shift of 0.2 eV for the Pt 4f peaks. The catalytic properties of the synthesized Pt–Ru alloy catalysts were compared with those of commercial Pt/C catalysts by linear sweep voltammetry (LSV). The results show that the mass activity of the oxygen reduction reaction (ORR) is enhanced by 2.3 times as much mass activity of Pt relative to the commercial Pt/C catalyst. Single-chambered microbial fuel cell tests also confirm that the Pt–Ru alloys as cathode catalysts have better performance than that of commercial Pt/C catalysts. Full article

Lipase from Aspergillus niger was “doubly immobilized” with SiO₂ nanoparticles in sol-gel powders prepared via the base-catalyzed polymerization of tetramethoxysilane (TMOS) and methyltreimethoxysilane (MTMS). The hydrolytic activity of the immobilized lipase was measured using the p-nitrophenyl palmitate hydrolysis method. The results showed that the optimum preparation conditions for the gels were made using a MTMS/TMOS molar ratio of 5, 60 mg of SiO₂ nanoparticles, a water/silane molar ratio of 12, 120 mg of enzyme supply, and 120 μL of PEG400. Under the optimal conditions, the immobilized lipase retained 92% of the loading protein and 94% of the total enzyme activity. Characteristic tests indicated that the immobilized lipase exhibited much higher thermal and pH stability than its free form, which shows great potential for industrial applications. Full article