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We investigate the effect of cerium and tungsten addition to optimize the deNOx activity of V2O5/TiO2 catalysts over a broad temperature range in the catalytic reduction of NOx with NH3 (NH3-SCR) with and without the presence of water. The catalysts were synthesized following co-impregnation of TiO2 with different loadings and varying content of V2O5, CeO2 and WO3 oxides as promoters. Based on surface and bulk characterization, we show that all catalysts undergo different structural changes depending on the chemical nature of the promoters. X-ray photoelectron spectra indicate a tendency for surface reduction after addition of CeO2, surface oxidation after addition of WO3, and after catalytic NH3-SCR. Promotion of V2O5/TiO2 catalysts with CeO2 and/or WO3 broadens the operation temperature window of the catalytic NH3-SCR reaction under both dry and wet conditions and improves the N2 selectivity at high temperatures. The thermal deactivation resistance of CeO2- and WO3-promoted catalysts improves with increasing amount of WO3. We tentatively relate this to suppression of the sintering of the active VOx component and increasing the amount of CeVO4. The latter, as a consequence of Ce-V interaction, detrimentally changes the surface composition of the catalysts and hides active V in the bulk structure inaccessible for reaction. Water slightly decreases the overall catalytic activity of SCR at low temperatures, while preventing the formation of N2O at elevated temperatures. Addition of CeO2 leads to a slight decrease in overall reducibility of the catalysts, while W causes an enhancement in quantitative H2 uptake. On the contrary, the sole addition of CeO2 leads to an enhancement of ammonia adsorption and the appearance of new acidic surface sites, which beneficially combine the reduced surface of the catalysts with an enhanced deNOx activity at low temperature. [ABSTRACT FROM AUTHOR]

The original article can be found online at https://doi.org/10.1038/s41467-020-18563-w. Correction to: I Nature Communications i , https://doi.org/10.1038/s41467-020-18563-w, published online 23 September 2020. [Extracted from the article]

Exsolution of metal nanoparticles from perovskite-type oxides is a very promising approach to obtain catalysts with superior properties. One particularly interesting property of exsolution catalysts is the possibility of electrochemical switching between different activity states. In this work, synchrotron-based in-situ X-ray diffraction experiments on electrochemically polarized La0.6Sr0.4FeO3-δ thin film electrodes are performed, in order to simultaneously obtain insights into the phase composition and the catalytic activity of the electrode surface. This shows that reversible electrochemical switching between a high and low activity state is accompanied by a phase change of exsolved particles between metallic α--Fe and Fe-oxides. Reintegration of iron into the perovskite lattice is thus not required for obtaining a switchable catalyst, making this process especially interesting for intermediate temperature applications. These measurements also reveal how metallic particles on La0.6Sr0.4FeO3-δ electrodes affect the H2 oxidation and H2O splitting mechanism and why the particle size plays a minor role. Exsolution, nanoparticle precipitation from oxide materials during reduction, offers a promising approach to heterogeneous catalysis. Here, authors examine the switching behavior between high and low activity and correlate the electro-catalytic activity to exsolved phases from complex oxides. [ABSTRACT FROM AUTHOR]

We investigate the effect of cerium and tungsten addition to optimize the deNOx activity of V2O5/TiO2 catalysts over a broad temperature range in the catalytic reduction of NOx with NH3 (NH3-SCR) with and without the presence of water. The catalysts were synthesized following co-impregnation of TiO2 with different loadings and varying content of V2O5, CeO2 and WO3 oxides as promoters. Based on surface and bulk characterization, we show that all catalysts undergo different structural changes depending on the chemical nature of the promoters. X-ray photoelectron spectra indicate a tendency for surface reduction after addition of CeO2, surface oxidation after addition of WO3, and after catalytic NH3-SCR. Promotion of V2O5/TiO2 catalysts with CeO2 and/or WO3 broadens the operation temperature window of the catalytic NH3-SCR reaction under both dry and wet conditions and improves the N2 selectivity at high temperatures. The thermal deactivation resistance of CeO2- and WO3-promoted catalysts improves with increasing amount of WO3. We tentatively relate this to suppression of the sintering of the active VOx component and increasing the amount of CeVO4. The latter, as a consequence of Ce-V interaction, detrimentally changes the surface composition of the catalysts and hides active V in the bulk structure inaccessible for reaction. Water slightly decreases the overall catalytic activity of SCR at low temperatures, while preventing the formation of N2O at elevated temperatures. Addition of CeO2 leads to a slight decrease in overall reducibility of the catalysts, while W causes an enhancement in quantitative H2 uptake. On the contrary, the sole addition of CeO2 leads to an enhancement of ammonia adsorption and the appearance of new acidic surface sites, which beneficially combine the reduced surface of the catalysts with an enhanced deNOx activity at low temperature. [ABSTRACT FROM AUTHOR]

Abstract: Electron-microscopy suitable In2O3 thin films prepared by thermal deposition of In2O3 powder in 10−2 Pa O2 at 600K and, for comparison, a commercial polycrystalline In2O3 powder catalyst were tested in methanol steam reforming and in both routes of the water–gas shift reaction as a function of reaction temperature. The effect of oxidative (1bar O2, 373–673K, 1h) and reductive (1bar H2, 373–673K, 1h) catalyst pre-treatments was assessed. The resulting structural and morphological changes occurring during catalyst activation and catalytic reaction were monitored by (high-resolution) transmission electron microscopy, scanning electron microscopy and surface area measurements by N2 adsorption according to BET. Both the In2O3 thin film and the powder sample were observed to be structurally stable under typical catalyst pre-treatments in oxygen and hydrogen at temperatures T ≤673K and T <673K, respectively, as well as under typical methanol steam reforming conditions at temperatures T ≤680K. No pronounced catalyst sintering was observed below 673K. Both In2O3 samples were found to be highly active and selective toward CO2 in methanol steam reforming over a broad temperature range (450< T <673K). Selectivities of >95% toward CO2 were usually observed, with at maximum 5% or less CO formed. No dependence of selectivity on either reaction temperature or oxidative/reductive pre-treatment was observed. No catalytic activity in both routes of the water–gas shift reaction as tested in the same temperature region where the catalysts exhibit high reforming activity and selectivity, could be observed. Therefore In2O3 based catalysts offer a broad range of temperature not influenced by unwanted CO formation via the inverse water–gas shift process. [Copyright &y& Elsevier]

[Display omitted] • Strong influence of the Cu-ZrO 2 interface dimensions on the CO 2 selectivity in MSR. • Variation of Cu loading shows intrinsic contributions of ZrO 2 and Cu surface fraction. • ZrO 2 is an active support in methanol steam reforming. • ZrO 2 influences all reaction channels of the overall reaction mechanism. • Cu-ZrO 2 interfacial dimensions are independent of structural effects. On Cu/ZrO 2 catalysts, variation of the Cu loading from 0.2 wt% to 80 wt% allows assessing the influence of the Cu-ZrO 2 interface on the methanol steam reforming (MSR) performance by steering Cu particle size and morphology, revealing the contribution of potential active sites at the interface and the intrinsic relative contributions of the support and Cu surface fraction. As ZrO 2 influences both CO 2 -selective and selectivity-spoiling MSR reaction channels, disentangling support-specific effects from the special phase-boundary reactivity and the intrinsic Cu° reactivity is possible by our approach. By choosing a broad range of Cu loadings, a comparison of the most extreme cases of strong predominance of bulk-like Cu sites (80 wt% Cu) vs. highly dispersed Cu (0.2 wt%), dominated by interfacial and support reactivity, becomes accessible. Cu (80 wt%)/ZrO 2 evolves as the best MSR catalyst by avoiding adverse support effects and providing a high number of support-wetting bulk-like Cu sites. [ABSTRACT FROM AUTHOR]

• La 2 NiO 4 exhibits remarkable kinetic metastability in the DRM mixture up to 800 °C. • Decomposition of La 2 NiO 4 yields mainly a Ni/La 2 O 3 composite. • Reaction-formed hydrogen aids the decomposition of La 2 NiO 4 at lower temperatures. • Considerable coking and encapsulation of exsolved Ni revealed by in situ XRD. We focus on the stability and bulk/surface structural properties of the Ruddlesden-Popper phase La 2 NiO 4 and their consequences for dry reforming of methane (DRM) activity. Fuelled by the appearance as a crucial intermediate during in situ decomposition of highly DRM-active LaNiO 3 perovskite structures, we show that La 2 NiO 4 can be equally in situ decomposed into a Ni/La 2 O 3 phase offering CO 2 capture and release necessary for DRM activity, albeit at much higher temperatures compared to LaNiO 3. Decomposition in hydrogen also leads to an active Ni/La 2 O 3 phase. In situ X-ray diffraction during DRM operation reveals considerable coking and encapsulation of exsolved Ni, yielding much smaller Ni crystallites compared to on LaNiO 3 , where coking is virtually absent. Generalizing the importance of intermediate Ruddlesden-Popper phases, the in situ decomposition of La-based perovskite structures yields several obstacles due to the high stability of both the parent perovskite and the Ruddlesden-Popper structures and the occurrence of parasitic structures. [ABSTRACT FROM AUTHOR]