Calcined silica-supported sodium decavanadate (Na6V10O28/SiO2) is more active for the oxidative dehydrogenation of propane (ODP) than the thermodynamically stable α-polymorph of sodium metavanadate (α-NaVO3/SiO2) and the silica-bound, site-isolated terminal vanadium oxo [VO4]/SiO2 benchmark catalyst. Calcination of Na6V10O28/SiO2 in air at 600 °C leads to a mixture of Na1+x V3O8, interacting with the silica support, and the metastable polymorph of sodium metavanadate, β-NaVO3. The formation of β-NaVO3 at this temperature is unexpected as β-NaVO3 supported on silica and calcined at the same conditions transforms into α-NaVO3. At 450 °C (temperature of the ODP reaction) in an inert atmosphere, Na6V10O28/SiO2 transforms predominantly to the reduced phase α′-NaV2O5 that displays poor activity in ODP. However, the deactivated material recovers the high activity of calcined Na6V10O28/SiO2 after ca. 3 h time on stream (TOS) or after 1 h in air (450 °C). This observation is consistent with the proposed link between the high catalytic activity in ODP and the reducibility of a V phase as neither the catalytic performance nor characteristic Raman bands of α-NaVO3/SiO2 and [VO4]/SiO2 change significantly in an inert atmosphere at 450 °C. Vanadium K-edge operando X-ray absorption near-edge structure (XANES) and in situ Raman mapping show that the oxidation of α′-NaV2O5 to a mixture of Na1+x V3O8 and β-NaVO3 occurs under ODP conditions within several minutes. In contrast, the initial activity recovers within hours (depending on the conditions), and it is explained mostly by slow redispersion of the Na1+x V3O8 phase on SiO2.

Zn-based Al2O3-suported materials have been proposed as inexpensive and environmentally friendly catalysts for the direct dehydrogenation of propane (PDH), however, our understanding of these catalysts' structure and deactivation routes is still limited. Here, we correlate the catalytic activity for PDH of a series of Zn-based Al2O3 catalysts with their structure and structural evolution. To this end, three model catalysts are investigated. (i) ZnO/Al2O3 prepared by atomic layer deposition (ALD) of ZnO onto γ-Al2O3 followed by calcination at 700 °C, which yields a core-shell spinel zinc aluminate/γ-Al2O3 structure. (ii) Zinc aluminate spinel nanoparticles (ZnxAlyO4 NPs) prepared via a hydrothermal method. (iii) A reference core-shell ZnO/SiO2 catalyst prepared by ALD of ZnO on SiO2. The catalysts are characterized in detail by synchrotron X-ray powder diffraction (XRD), Zn K-edge X-ray absorption spectroscopy (XAS), and 27 Al solid state nuclear magnetic resonance (ssNMR). These experiments allowed us to identify tetrahedral Zn sites in close proximity to Al sites of a zinc aluminate spinel phase (ZnIV-O-AlIV/VI linkages) as notably more active and selective in PDH relative to the supported ZnO wurtzite phase (ZnIV-O-ZnIV linkages) in ZnO/SiO2. The best performing catalyst, 50ZnO/Al2O3 gives 77% selectivity to propene (gaseous products based) at 9 mmol C3H6 gcat −1 h −1 space time yield (STY) after 3 min of reaction at 600 °C. On the other hand, the core-shell ZnO/Al2O3 catalyst shows an irreversible loss of activity over repeated PDH and air-regeneration cycles, explained by Zn depletion on the surface due to its diffusion into subsurface layers or the bulk. ZnxAlyO4 NPs gave a comparable initial selectivity and catalytic activity as 50ZnO/Al2O3. With time on stream, ZnxAlyO4 NPs deactivate due to the formation of coke at the catalyst surface, yet the extend of coke deposition is lower than for the ZnO/Al2O3 catalysts, and the activity of ZnxAlyO4 NPs can be regenerated almost fully using calcination in air.

Mo doped BiVO4's lower efficiency can be attributed in part to exciton recombination losses. Recombination losses during photoelectrochemical water oxidation can be eliminated by using glycerol as a hole acceptor....

The oxidative dehydrogenation of propane (ODP) proceeds catalytically on a gas-solid interface (heterogeneous reaction) and/or in the gas phase (homogeneous reaction) via a radical chain process. ODP may therefore combine interrelated contributions from the heterogeneous dehydrogenation and gasphase reactions, which can be initiated by a catalyst. This study demonstrates that relatively high propene and ethene selectivities (ca. 80 % and 10 %) and propane conversions (viz., 10 % at 500 °C) can be achieved with an empty quartz reactor, which is comparable to the performances of state-of-the-art ODP catalysts (boron-based or supported VO x ). Optimization of the post-catalytic volume of a h-BN catalyst bed tested at 490 °C allows to increase the conversion of propane from 9 % to 15 % at a propene selectivity of 77 %, highlighting this parameter as an important variable for improving catalytic ODP performances.

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Zn-based Al₂O₃-suported materials have been proposed as inexpensive and environmentally friendly catalysts for the direct dehydrogenation of propane (PDH), however, our understanding of these catalysts’ structure and deactivation routes is still limited. Here, we correlate the catalytic activity for PDH of a series of Zn-based Al₂O₃ catalysts with their structure and structural evolution. To this end, three model catalysts are investigated. (i) ZnO/Al₂O₃ prepared by atomic layer deposition (ALD) of ZnO onto γ-Al₂O₃followed by calcination at 700 °C, which yields a core-shell spinel zinc aluminate/γ-Al₂O₃ structure. (ii) Zinc aluminate spinel nanoparticles (Zn_xAl_yO₄ NPs) prepared via a hydrothermal method. (iii) A reference core-shell ZnO/SiO₂ catalyst prepared by ALD of ZnO on SiO₂. The catalysts are characterized in detail by synchrotron X-ray powder diffraction (XRD), Zn K-edge X-ray absorption spectroscopy (XAS), and ²⁷Al solid state nuclear magnetic resonance (ssNMR). These experiments allowed us to identify tetrahedral Zn sites in close proximity to Al sites of a zinc aluminate spinel phase (Zn_IV–O–Al_IV/VI linkages) as notably more active and selective in PDH relative to the supported ZnO wurtzite phase (Zn_IV–O– Zn_IV linkages) in ZnO/SiO₂. The best performing catalyst, 50ZnO/Al₂O₃ gives 77% selectivity to propene (gaseous products based) at 9 mmol C₃H₆ gcat−1 h⁻¹ space time yield (STY) after 3 min of reaction at 600 °C. On the other hand, the core-shell ZnO/Al₂O₃ catalyst shows an irreversible loss of activity over repeated PDH and air-regeneration cycles, explained by Zn depletion on the surface due to its diffusion into subsurface layers or the bulk. ZnxAlyO₄ NPs gave a comparable initial selectivity and catalytic activity as 50ZnO/Al₂O₃. With time on stream, Zn_xAl_yO₄ NPs deactivate due to the formation of coke at the catalyst surface, yet the extend of coke deposition is lower than for the ZnO/Al₂O₃ catalysts, and the activity of Zn_xAl_yO₄ NPs can be regenerated almost fully using calcination in air.<br>

To advance CaO‐based CO2 sorbents it is crucial to understand how their structural parameters control the cyclic CO2 uptake. Here, CaO‐based sorbents with varying ratios of Na2CO3:CaCO3 are synthesized via mechanochemical activation of a mixture of Na2CO3 and CaCO3 to investigate the effect of sodium species on the structure, morphology, carbonation rate and cyclic CO2 uptake of the CO2 sorbents. The addition of Na2CO3 in the range of 0.1–0.2 mol% improves the CO2 uptake by up to 80% after 10 cycles when compared to ball‐milled bare CaCO3, while for Na2CO3 loadings >0.3 mol% the cyclic CO2 uptake decreases by more than 40%. Energy dispersive X‐ray spectroscopy (EDX), transmission electron microscopy, X‐ray absorption spectroscopy (XAS), and 23Na MAS NMR, reveal that in sorbents with Na2CO3 contents <0.3 mol% Na exists in highly distributed, noncrystalline [Na2Ca(CO3)2] units. These species stabilize the surface area of the sorbent in pores of diameters >100 nm, and enhance the diffusion of CO2 through CaCO3. For Na2CO3 contents >0.3 mol%, the accelerated deactivation of the sorbents via sintering is related to the formation of crystalline Na2Ca(CO3)2 and the high mobility of Na.

The promotion of silica-supported vanadyl species [VO4]/SiO2 (1) by α-NaVO3 or β-NaVO3 enhances the specific rate of the propene formation in oxidative dehydrogenation of propane (ODP) by, respectively, 30 and...