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An A-site deficient perovskite with metallic Ni in exsolution, Ni–Sr0.9Mo0.9O3−δ, has been prepared, characterized and tested as an anode material in intermediate-temperature solid-oxide fuel cells (IT-SOFCs). It was obtained by reduction of a Ni-containing scheelite oxide, from which Ni is segregated to the surface as metal nanoparticles with average size of 30–35 nm, as demonstrated by high-resolution transmission electron microscopy (HR-TEM). An in situ neutron powder diffraction (NPD) study of the Sr0.9Mo0.9O3−δ matrix shows an oxygen deficient cubic perovskite, defined in the Pm3¯m space group; no crystalline transitions were detected in the tested temperature range up to 850 °C. Morphological observations using a scanning electron microscope (SEM) and pore size determinations by Hg porosimetry showed a highly porous material with macropores. The electrical conductivity gave a maximum value of 215 S cm−1 at 850 °C. A suitable thermal expansion coefficient, with values close to that of the electrolyte, showed no abrupt changes in its slope. Polarization curves and electrochemical impedance spectra (EIS) under open circuit were investigated. In single-cell tests, the materials generated outstanding output powers close to 1025 mW cm−2 at 850 °C using pure H2 as fuel. All these features make this novel A-deficient perovskite with exsolved Ni particles a perfect candidate as anode material in intermediate-temperature SOFCs (IT-SOFCs). [ABSTRACT FROM AUTHOR]

The design of an active, effective, and economically viable catalyst for CO 2 conversion into value-added products is crucial in the fight against global warming and energy demand. We have developed very efficient catalysts for reverse water-gas shift (rWGS) reaction. Specific conditions of the synthesis by combustion allow the obtention of macroporous materials based on nanosized Ni particles supported on a mixed oxide of high purity and crystallinity. Here, we show that Ni/La-doped CeO 2 catalysts─with the "right" Ni and La proportions─have an unprecedented catalytic performance per unit mass of catalyst for the rWGS reaction as the first step toward CO 2 valorization. Correlations between physicochemical properties and catalytic activity, obtained using a combination of different techniques such as X-ray and neutron powder diffraction, Raman spectroscopy, in situ near ambient pressure X-ray photoelectron spectroscopy, electron microscopy, and catalytic testing, point out to optimum values for the Ni loading and the La proportion. Density functional theory calculations of elementary steps of the reaction on model Ni/ceria catalysts aid toward the microscopic understanding of the nature of the active sites. This finding offers a fundamental basis for developing economical catalysts that can be effectively used for CO 2 reduction with hydrogen. A catalyst based on Ni 0.07 /(Ce 0.9 La 0.1 O x ) 0.93 shows a CO production of 58 × 10 -5 mol CO ·g cat -1 (700 °C, H -1 (700 °C, H 2 /CO 2 = 2; selectivity to CO > 99.5), being stable for 100 h under continuous reaction.

There is great economic incentive in developing efficient catalysts to produce hydrogen or syngas by catalytic partial oxidation of methane (CPOM) since this is a much less energy-intensive reaction than the highly endothermic methane steam reforming reaction, which is the prominent reaction in industry. Herein, we report the catalytic behavior of nickel-based catalysts supported on different oxide substrates (Al 2 O 3 , CeO 2 , La 2 O 3 , MgO, and ZrO 2 ) synthesized via wet impregnation and solid-state reaction. Furthermore, the impact of Rh doping was investigated. The catalysts have been characterized by X-ray diffraction, N 2 adsorptiondesorption at -196°C, temperature-programmed reduction, X-ray photoelectron spectroscopy, O 2 -pulse chemisorption, transmission electron microscopy, and Raman spectroscopy. Supported Ni catalysts were found to be active for CPOM but can suffer from fast deactivation caused by the formation of carbon deposits as well as via the sintering of Ni nanoparticles (NPs). It has been found that the presence of Rh favors nickel reduction, which leads to an increase in the methane conversion and yield. For both synthesis methods, the catalysts supported on alumina and ceria show the best performance. This could be explained by the higher surface area of the Ni NPs on the alumina surface and presence of oxygen vacancies in the CeO 2 lattice, which favor the proportion of oxygen adsorbed on defect sites. The catalysts supported on MgO suffer quick deactivation due to formation of a NiO/MgO solid solution, which is not reducible under the reaction conditions. The low level of carbon formation over the catalysts supported on La 2 O 3 is ascribed to the very high dispersion of the nickel NPs and to the formation of lanthanum oxycarbonate, through which carbon deposits are gasified. The catalytic behavior for catalysts with ZrO 2 as support depends on the synthesis method; however, in both cases, the catalysts undergo deactivation by carbon deposits.