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[EN] The design of active and durable catalysts for the H2O/O2 interconversion is one of the major challenges of electrocatalysis for renewable energy. The oxygen evolution reaction (OER) is catalyzed by SrRuO3 with low potentials (ca. 1.35 VRHE), but the catalyst’s durability is insufficient. Here we show that Na doping enhances both activity and durability in acid media. DFT reveals that whereas SrRuO3 binds reaction intermediates too strongly, Na doping of ~0.125 leads to nearly optimal OER activity. Na doping increases the oxidation state of Ru, thereby displacing positively O p-band and Ru d-band centers, weakening Ru-adsorbate bonds. The enhanced durability of Na-doped perovskites is concomitant with the stabilization of Ru centers with slightly higher oxidation states, higher dissolution potentials, lower surface energy and less distorted RuO6 octahedra. These results illustrate how high OER activity and durability can be simultaneously engineered by chemical doping of perovskites., This work was supported by the ENE2013–42322-R and ENE2016-77055-C3-3-R projects from the Spanish Ministry of Economy and Competitiveness (MINECO). M.R. thanks MINECO’s Juan de la Cierva program for a grant (FPDI-2013-17582). F.C.V. thanks the Spanish MICIU for a Ramón y Cajal research contract (RYC-2015-18996) and financial support through the program “Units of Excellence María de Maeztu” (grant MDM-2017–0767). We thank G. Cibin for useful discussions on XAS data treatment and analysis from experiments on beamline B18 Diamond Light Source. We also thank A. Figueroa for helping with data acquisition on beamline I10 and discussions on data interpretation. We thank Diamond Light Source for access to beamlines B18 and I10 that contributed to the results presented here. We thank D. Arroyo and N. López for ICPOES analyses.

A perspective is provided on our current understanding of the activation of hydrocarbons by protonic zeolites. One has to distinguish the proton affinity of a zeolite, measured in an equilibrium experiment, from proton activation that determines a kinetic catalytic result. The proton affinity depends on the heat of adsorption and the intrinsic protonation energy of a substrate. The heat of adsorption is strongly micropore size and shape dependent. Kinetic proton activation depends on the activation energy of the proton activated rate limiting step and also on the heat of reactant adsorption. Differences in catalytic performance between zeolites are often rather due to differences in heat of adsorption than to intrinsic proton property differences.

С целью оптимизации формулы катализатора для процесса АТР СH 4 исследована активность NiPd/Ce 0.5Zr 0.5O 2/Al 2O 3 и NiPd/La 2O 3/Ce 0.5Zr 0.5O 2/Al 2O 3 образцов при вариации содержания Ce 0.5Zr 0.5O 2 (10-30 масс.%) и La 2O 3 (5-20 масс.%) в составе носителя. Выявлен оптимальный состав катализатора NiPd/20La 2O 3/10Ce 0.5Zr 0.5O 2/Al 2O 3, характеризующийся стабильной работой в условиях реакции АТР СH 4 и обеспечивающий выход H 2 65% при конверсии СН 4 90-100% и температуре реакции 850 оС., To optimize the catalyst formula for ATP of CH 4 the catalytic activity of NiPd/Ce 0.5Zr 0.5O 2/Al 2O 3 и NiPd/La 2O 3/Ce 0.5Zr 0.5O 2/Al 2O 3 samples was studied at variation of Ce 0.5Zr 0.5O 2 (10-30 wt.%) and La 2O 3 (5-20 wt.%) content in the support. The optimal catalyst composition was established. NiPd/20La 2O 3/10Ce 0.5Zr 0.5O 2/Al 2O 3 catalyst was characterized by stable activity with time on stream and provides an H 2 yield of 65% at conversion of CH 4 of 90-100% and at reaction temperature of 850 oC.

A palladium–copper–zinc catalyst (PdO : CuO : ZnO = 2 : 28 : 70), prepared by sequential precipitation of the respective cations, was tested in the hydrogenation of CO2 at high pressure (conditions: 60 bar, CO2 : H2 = 1 : 3 (molar), W/F = 0.0675 kg h/m3, 453–513 K). The methanol yield was improved on using this Pd-containing catalyst at all temperatures with respect to the reference copper–zinc catalyst (CuO : ZnO = 30 : 70). This improvement was not due to an additional effect in which palladium was acting as an independent catalytic site but was caused by a synergetic effect of Pd on the active Cu sites. This effect was explained in terms of hydrogen spillover and an increased stability against CO2 oxidation of the surface copper. Therefore, the present contribution not only supports previous literature findings concerning the hydrogen spillover mechanism but also resulted in a complementary view regarding the role of palladium in Pd-modified CuO-ZnO-based catalysts.

A Cu–Zn–Al precursor was synthesized by coprecipitation of the corresponding cations with sodium carbonate at constant pH and temperature. CuO–ZnO–Al2O3 composite oxide support was obtained by calcination (673 K) of the Cu–Zn–Al precursor. Two palladium-modified CuO–ZnO–Al2O3 samples were prepared by impregnation of the mixed-oxide support and further calcination (673 K). The presence of remaining CO32– anions in the CuO–ZnO–Al2O3 mixed oxide, as a result of incomplete Cu–Zn hydrotalcite phase decomposition, and the hydrothermal-like treatment during the Pd impregnation step, allow the partial reconstruction of the Cu–Zn hydrotalcite-type structure (memory effect). In addition, an enhancement in the CuO crystallinity was obtained for the Pd-modified oxides. A detailed characterization revealed that the hydrotalcite restoration enhances the crystallinity of the copper oxide as a consequence of a crystalline rearrangement of this oxidic phase.

The partial oxidation of methane to formaldehyde (MPO) with molecular O2 has been investigated on various bare and Fe-doped commercial silica catalysts at 650 °C. The influence of the Fe loading (0.01–3.2 wt.%) on the catalytic pattern and steady-state properties of the catalysts have been evaluated. The dispersion and coordination symmetry of surface Fe3+ species have been investigated by EPR analysis. "Isolated Fe3+ ions", "small Fe2O3 clusters" and "Fe2O3 particles" are present on the surface of the FeOx/SiO2 catalysts, their relative concentration depending upon the loading. Iron species, irrespective of the state of aggregation, enable the reactivity of the silica surface, whilst the highest HCHO productivity is associated with an optimum surface Fe loading (0.05–0.1 Feat nm-2). The different reactivity of the various Fe-doped silica catalysts has been rationalised and normalised in terms of different concentration of "isolated Fe3+ species" and "aggregated Fe2O3 moieities".