P.V. Snytnikov

On the Mechanism of CO and CO2 Methanation Over Ni/CeO2 Catalysts

The reactions of the CO and CO2 methanation in the excess of hydrogen were studied over Ni/CeO2 and Ni(Cl)/CeO2 catalysts prepared from nitrate and chloride precursors, respectively. Macrokinetic parameters of the CO and CO2 methanation over Ni/CeO2 and Ni(Cl)/CeO2 catalysts were determined. The nature of surface species during the CO and CO2 methanation over Ni/CeO2 and Ni(Cl)/CeO2 catalysts was studied by the Fourier transform infrared spectroscopy in situ technique. It was shown that the CO methanation proceeds similar ways over both Ni/CeO2 and Ni(Cl)/CeO2 catalysts via CO and H2 chemisorption on the surface of Ni particles. The CO2 methanation over Ni/CeO2 catalyst proceeds via the CO2 adsorption on the ceria surface and stepwise hydrogenation to methane through hydrocarbonate and formate intermediates by the hydrogen spilled over from Ni particles. With the Ni(Cl)/CeO2 catalyst, this reaction pathway is locked due to the ceria surface blockage by chlorine, to inhibit the CO2 methanation and therefore provide a high efficiency of Ni(Cl)/CeO2 catalyst in preferential CO methanation in the presence of CO2.

Template-Assisted Wet-Combustion Synthesis of Fibrous Nickel-Based Catalyst for Carbon Dioxide Methanation and Methane Steam Reforming

Efficient capture and recycling of CO2 enable not only prevention of global warming but also the supply of useful low-carbon fuels. The catalytic conversion of CO2 into an organic compound is a promising recycling approach which opens new concepts and opportunities for catalytic and industrial development. Here we report about template-assisted wet-combustion synthesis of a one-dimensional nickel-based catalyst for carbon dioxide methanation and methane steam reforming. Because of a high temperature achieved in a short time during reaction and a large amount of evolved gases, the wet-combustion synthesis yields homogeneously precipitated nanoparticles of NiO with average particle size of 4 nm on alumina nanofibers covered with a NiAl2O4 nanolayer. The as-synthesized core-shell structured fibers exhibit outstanding activity in steam reforming of methane and sufficient activity in carbon dioxide methanation with 100% selectivity toward methane formation. The as-synthesized catalyst shows stable operation under the reaction conditions for at least 50 h.

Избирательное окисление СО на биметаллических катализаторах Pt0,5M0,5 (M = Fe, Co, Ni), приготовленных из двойных комплексных солей

Nanopowders of Pt 0.5 M 0.5 (M = Fe, Co, Ni) alloys prepared by decomposition of complex binary salts [Pt(NH 3 ) 5 Cl][Fe(C 2 O 4 ) 3 ]·4H 2 O, [Pt(NH 3 ) 4 ][Co(C 2 O 4 )2(H 2 O) 2 ]·2H 2 O, [Pt(NH 3 ) 4 ][Ni(C 2 O 4 )2(H 2 O) 2 ]·2H 2 O, respectively, were studied in the reaction of selective CO oxidation. The bimetal catalysts were shown more active at low temperature than the Pt nanopowder. The catalyst activities decrease in the series of Pt 0.5 Co 0.5  Pt 0.5 Ni 0.5 > Pt 0.5 Fe 0.5 >>Pt. The observed high activity of bimetal Pt 0.5 M 0.5 catalysts at low temperature and considerable coverage of the Pt surface by adsorbed CO molecules may be accounted for by the activation of CO on the Pt atoms and O 2 on the second metal (Fe, Co, Ni) atoms and by the reaction localization on the Pt-M contacts on the alloy nanoparticle surface. The bimetal systems under study can be used for improving practically important catalysts for selective CO oxidation; they also are applicable for reburning of CO and hydrocarbons, hydrogenation, electrochemical reactions etc. The reported method for preparation of bimetal nanopowders based on the decomposition of complex binary salts is simple, does not need expensive reactants and can be easily adapted for synthesis of supported catalysts containing nanoparticles of metal alloys Pt 0.5 M 0.5 (M = Fe, Co, Ni).

Porous Nanocrystalline Silicon Supported Bimetallic Pd-Au Catalysts: Preparation, Characterization, and Direct Hydrogen Peroxide Synthesis

Bimetallic Pd-Au catalysts were prepared on the porous nanocrystalline silicon (PSi) for the first time. The catalysts were tested in the reaction of direct hydrogen peroxide synthesis and characterized by standard structural and chemical techniques. It was shown that the Pd-Au/PSi catalyst prepared from conventional H2[PdCl4] and H[AuCl4] precursors contains monometallic Pd and a range of different Pd-Au alloy nanoparticles over the oxidized PSi surface. The PdAu2/PSi catalyst prepared from the [Pd(NH3)4][AuCl4]2 double complex salt (DCS) single-source precursor predominantly contains bimetallic Pd-Au alloy nanoparticles. For both catalysts the surface of bimetallic nanoparticles is Pd-enriched and contains palladium in Pd0 and Pd2+ states. Among the catalysts studied, the PdAu2/PSi catalyst was the most active and selective in the direct H2O2 synthesis with H2O2 productivity of 0.5 mol gPd-1 h-1 at selectivity of 50% and H2O2 concentration of 0.023 M in 0.03 M H2SO4-methanol solution after 5 h on stream at −10°C and atmospheric pressure. This performance is due to high activity in the H2O2 synthesis reaction and low activities in the undesirable H2O2 decomposition and hydrogenation reactions. Good performance of the PdAu2/PSi catalyst was associated with the major part of Pd in the catalyst being in the form of the bimetallic Pd-Au nanoparticles. Porous silicon was concluded to be a promising catalytic support for direct hydrogen peroxide synthesis due to its inertness with respect to undesirable side reactions, high thermal stability, and conductivity, possibility of safe operation at high temperatures and pressures and a well-established manufacturing process.