Electro-oxidation of Ethanol on Carbon Supported PtSn and PtSnNi Catalysts

Even though platinum is known as an active electro-catalyst for ethanol oxidation at low temperatures (< 100 oC), choosing the electrode material for ethanol electro-oxidation is a crucial issue. It is due to its property which easily poisoned by a strong adsorbed species such as CO. PtSn-based electro-catalysts have been identified as better catalysts for ethanol electro-oxidation. The third material is supposed to improved binary catalysts performance. This work presents a study of the ethanol electro-oxidation on carbon supported Pt-Sn and Pt-Sn-Ni catalysts. These catalysts were prepared by alcohol reduction. Nano-particles with diameters between 2.5-5.0 nm were obtained. The peak of (220) crystalline face centred cubic (fcc) Pt phase for PtSn and PtSnNi alloys was repositioned due to the presence of Sn and/or Ni in the alloy. Furthermore, the modification of Pt with Sn and SnNi improved ethanol and CO electro-oxidation. Copyright © 2016 BCREC GROUP. All rights reserved Received: 10th November 2015; Revised: 1st February 2016; Accepted: 1st February 2016 How to Cite: Hidayati, N., Scott, K. (2016). Electro-oxidation of Ethanol on Carbon Supported PtSn and PtSnNi Catalysts. Bulletin of Chemical Reaction Engineering & Catalysis, 11 (1): 10-20. (doi:10.9767/bcrec.11.1.394.10-20) Permalink/DOI: http://dx.doi.org/10.9767/bcrec.11.1.394.10-2

Single-Site Vanadyl Species Isolated within Molybdenum Oxide Monolayers in Propane Oxidation

The cooperation of metal oxide subunits in complex mixed metal oxide catalysts for selective oxidation of alkanes still needs deeper understanding to allow for a rational tuning of catalyst performance. Herein we analyze the interaction between vanadium and molybdenum oxide species in a monolayer supported on mesoporous silica SBA-15. Catalysts with variable Mo/V ratio between 10 and 1 were studied in the oxidation of propane and characterized by FTIR, Raman, and EPR spectroscopies, temperature-programmed reduction, UV/vis spectroscopy in combination with DFT calculations, and time-resolved experiments to analyze the redox properties of the catalysts. Molybdenum oxide (sub)monolayers on silica contain mainly dioxo (Si–O−)2Mo(═O)2 species. Dilution of silica-supported vanadium oxide species by (Si–O−)2Mo(═O)2 prevents the formation of V–O–V bonds, which are abundant in the pure vanadium oxide catalyst that predominantly contains two-dimensional vanadium oxide oligomers. Existing single vanadyl (Si–O−)3V(═O) sites and neighboring (Si–O−)2Mo(═O)2 sites do not strongly interact. The rates of reduction in propane and of oxidation in oxygen are lower for single metal oxide sites compared to those for oligomers. The rate of propane oxidation correlates with the overall redox rates of the catalysts but not linearly with the chemical composition. Retarded redox behavior facilitates selectivity toward acrolein on single-site catalysts. The abundance of M–O–M bonds is more important in terms of activity and selectivity compared to the nature of the central atom (molybdenum versus vanadium)

The oxidation of toluene on various molybdenum-containing catalysts

The activities for the vapour-phase oxidation of toluene of various molybdenum-containing catalysts have been measured in a flow microreactor operating at 1 atm pressure. The catalysts comprised (a) unsupported crystalline MoO3, (b) Mo oxide monolayers on Al2O3, CeO2, TiO2, and ZrO2 supports, and (c) Al-, Ce-, and Zr-molybdate salts. The rates of oxidation of toluene per unit surface area on the monolayer catalysts are higher than those on the corresponding salts, but the selectivities for the partial oxidation products show the opposite trend. The catalytic behaviour of unsupported MoO3 resembles more closely that of the salts than that of the monolayer catalysts. The kinetic data for the oxidation of toluene on all catalysts can be interpreted on the basis of a reduction-oxidation mechanism. The energies of activation for the reduction and oxidation steps are correlated with the ionic potentials of the cations in the supports. Poisoning by pyridine of MoOx/TiO2 has a profound effect on the activity and selectivity of the monolayer catalyst and gives some information about the nature and concentration of the active sites

Wet-oxidation waste management system for CELSS

A wet oxidation system will be useful in the Closed Ecological Life Support System (CELSS) as a facility to treat organic wastes and to redistribute inorganic compounds and elements. However at rather higher temperatures needed in this reaction, for instance, at 260 deg C, only 80% of organic in a raw material can be oxidized, and 20% of it will remain in the liquid mainly as acetic acid, which is virtually noncombustible. Furthermore, nitrogen is transformed to ammonium ions which normally cannot be absorbed by plants. To resolve these problems, it becomes necessary to use catalysts. Noble metals such as Ru, Rh and so on have proved to be partially effective as these catalysts. That is, oxidation does not occur completely, and the unexpected denitrification, instead of the expected nitrification, occurs. So, it is essential to develop the catalysts which are able to realize the complete oxidation and the nitrification

Cu-Mg-Fe-O-(Ce) complex oxides as catalysts of selective catalytic oxidation of ammonia to dinitrogen (NH3-SCO)

Multicomponent oxide systems 800-Cu-Mg-Fe-O and 800-Cu-Mg-Fe-O-Ce were tested as catalysts of selective catalytic oxidation of ammonia to dinitrogen (NH3-SCO) process. Materials were obtained by calcination of hydrotalcite-like compounds at temperature 800 degrees C. Some catalysts were doped with cerium by the wet impregnation method. Not only simple oxides, but also complex spinel-like phases were formed during calcination. The influence of chemical composition, especially the occurrence of spinel phases, copper loading and impregnation by cerium, were investigated. Materials were characterized by several techniques: X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), low-temperature nitrogen adsorption (BET), cyclic voltammetry (CV), temperature programmed reduction (H-2-TPR), UV-vis diffuse reflectance spectroscopy and scanning electron microscopy (SEM). Examined oxides were found to be active as catalysts of selective catalytic oxidation of ammonia with high selectivity to N-2 at temperatures above 300 degrees C. Catalysts with low copper amounts (up to 12 wt %) impregnated by Ce were slightly more active at lower temperatures (up to 350 degrees C) than non-impregnated samples. However, when an optimal amount of copper (12 wt %) was used, the presence of cerium did not affect catalytic properties. Copper overloading caused a rearrangement of present phases accompanied by the steep changes in reducibility, specific surface area, direct band gap, crystallinity, dispersion of CuO active phase and Cu2+ accessibility leading to the decrease in catalytic activity.Web of Science102art. no. 15

Catalysts on Demand: Selective Oxidations by Laboratory-Evolved Cytochrome P450 BM3

Efficient catalysts for selective oxidation of C-H bonds using atmospheric oxygen are highly desirable to decrease the economic and environmental costs associated with conventional oxidation processes. We have used methods of directed evolution to generate variants of bacterial cytochrome P450 BM3 that catalyze hydroxylation and epoxidation of a wide range of nonnative substrates. This fatty acid hydroxylase was converted to a propane monooxygenase (PMO) capable of hydroxylating propane at rates comparable to that of BM3 on its natural substrates. Variants along the PMO evolutionary lineage showed broadened substrate scope; these became the starting points for evolution of a wide array of enzymes that can hydroxylate and derivatize organic scaffolds. This work demonstrates how a single member of enzyme family is readily converted by evolution into a whole family of catalysts for organic synthesis

Pyrolysis-catalytic reforming/gasification of waste tires for production of carbon nanotubes and hydrogen

The production of high-value carbon nanotubes and hydrogen from the two-stage pyrolysis catalytic-steam reforming/gasification of waste tires have been investigated. The catalysts used were Co/Al₂ O₃ , Cu/Al₂ O₃ , Fe/Al₂ O₃ and Ni/Al₂ O₃ . The pyrolysis temperature and catalyst temperature were 600 °C and 800 °C, respectively. The fresh catalysts were analysed by temperature programmed reduction and X-ray diffraction. The product gases, including hydrogen were analysed by gas chromatography and the carbon nanotubes characterized by scanning and transmission electron microscopy and Raman spectrometry. The results showed that the Ni/Al₂ O₃ catalyst produced high quality multiwalled carbon nanotubes along with the highest H₂ yield of 18.14 mmol g⁻¹ tire, compared with the other catalysts, while the Co/Al₂ O₃ and Cu/Al₂ O₃ catalysts produced lower hydrogen yield, which is suggested to be associated with the formation of amorphous type carbons on the surface of the Co/Al₂ O₃ and Cu/Al₂ O₃ catalyst

Applications of low temperature CO-oxidation catalysts to breathable gases

Modifications of tin oxide/precious metal catalysts described for use in CO2 lasers have also been developed for use in other applications; namely, as low temperature CO oxidation components in fire escape hoods/masks for mines, aircrafts, hotels, and offices and in sealed environments, such as hyperbaric chambers and submarines. Tin oxide/precious metal catalysts have been prepared on a variety of high surface area cloth substrates for application in fire escape hoods. These show high and stable CO oxidation capability (10 to the 4th power ppm CO reduced to 10 to the 1st power ppm CO) at GHSV of 37,000 h(-1) with water saturated inlet gas at body heat (37 C) and below. Water vapor plays an important role in the surface state/performance of tin oxide catalyst. Water-resistant formulations have been produced by the introduction of transition metal promoters. Tin oxide/precious metal catalysts have also been developed for CO oxidation in the North Sea diving environment. These are currently in use in a variety of hyperbaric chambers and diving vehicles. Ambient temperature operation and resistance to atmospheric water vapor have been demonstrated, and as a result, they offer a viable alternative to hopcalite or heated catalyst systems. A new range of non-tin oxide based low temperature CO oxidation catalysts is described. They are based on reducible metal oxides promoted with previous metals. Preliminary data on selected materials in the form of both cloth artifacts and shaped pellets are presented. They are expected to be applicable both to the breathable gas application area and to CO2 lasers

Nitrogen containing species as intermediates in the oxidation of ammonia over silica supported molybdena catalysts

The behaviour of ammonia and oxygen over silica supported molybdena catalysts has been studied by means of thermal analysis techniques, such as thermo-gravimetry and heat-flow calorimetry. The composition of the reactants and products was determined by means of mass spectrometric analysis. Nitrogen- and hydrogen-containing species were observed to be present on the catalyst surface after reduction of the catalysts by ammonia and subsequent flushing in helium. Additional evidence for the presence of these species was provided by experiments in which labelled molecules were used as well as by means of X-ray photo-electron spectroscopy. The nitrogen- and hydrogen-containing species could be removed from the surface by O2. or NO. The reaction products were found to be N2 and H2O

Development of covalent triazine frameworks as heterogeneous catalytic supports

Covalent triazine frameworks (CTFs) are established as an emerging class of porous organic polymers with remarkable features such as large surface area and permanent porosity, high thermal and chemical stability, and convenient functionalization that promotes great potential in heterogeneous catalysis. In this article, we systematically present the structural design of CTFs as a versatile scaffold to develop heterogeneous catalysts for a variety of chemical reactions. We mainly focus on the functionalization of CTFs, including their use for incorporating and stabilization of nanoparticles and immobilization of molecular complexes onto the frameworks