Photocatalytic conversion of CO2 to reduction products, such as CO, HCOOH, HCHO, CH3OH, and CH4, is one of the most attractive propositions for producing green energy by artificial photosynthesis. ...Herein, we found that Ga2O3 photocatalysts exhibit high conversion of CO2. Doping of Zn species into Ga2O3 suppresses the H2 evolution derived from overall water splitting and, consequently, Zn‐doped, Ag‐modified Ga2O3 exhibits higher selectivity toward CO evolution than bare, Ag‐modified Ga2O3. We observed stoichiometric amounts of evolved O2 together with CO. Mass spectrometry clarified that the carbon source of the evolved CO is not the residual carbon species on the photocatalyst surface, but the CO2 introduced in the gas phase. Doping of the photocatalyst with Zn is expected to ease the adsorption of CO2 on the catalyst surface.
Doping of Zn species into Ga2O3 suppresses the undesirable H2 evolution derived from overall water splitting. Zn‐doped, Ag‐modified Ga2O3 exhibits higher selectivity towards CO evolution than bare, Ag‐modified Ga2O3 (see figure).
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The dehydrogenation of lower alkanes was investigated on Pt–Sn/SiO2 catalysts prepared by impregnation with different thermal treatments. The treatment atmosphere played an important role in both the ...catalytic performance and the catalyst structure. An ensemble containing several adjacent Pt and Sn atoms from Pt–SnO2 or Pt–Sn alloy nanoparticles acts as the active site for dehydrogenation of lower alkanes, which can be respectively induced by treatment in an inert atmosphere (N2) or reductive atmosphere (H2) at high temperature.
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•Pt-SnO2 SMSI in Pt–Sn/SiO2 can be constructed via thermal treatments.•An ensemble containing Pt and Sn atoms acts as the active site for dehydrogenation.•The geometric effect of Sn on Pt contributes to the superior catalytic performance.
The addition of tin (Sn) is commonly used as a design strategy for catalyst optimization of platinum-based catalysts. The mechanistic understanding of this class of systems is, however, obscured by the structural complexity. Herein, a series of catalyst characterization techniques including X-ray absorption fine structure (XAFS) and in-situ CO diffuse reflectance infrared fourier transform spectroscopy (CO-DRIFTS) were utilized to study the catalyst structure. It was found that the structure and catalytic properties are closely related with the interaction between Pt and SnO2 (specifically the Pt-SnO2 strong metal-support interaction (SMSI)), which can be continuously tuned by thermal treating the Pt-Sn/SiO2 precursor at different atmospheres and temperatures. The treatment in an oxidative atmosphere (O2) also can generate Pt-SnO2 SMSI, which became weak at higher temperatures and led to the growth of Pt nanoparticles (NPs). Pt-SnO2 SMSI became stronger when the oxygen atmosphere was changed to an inert (N2) atmosphere. Small metallic Pt NPs were formed and their dispersion was increased with increasing treatment temperature with inert gas. The catalyst presented a moderate activity in the dehydrogenation of lower alkanes. The treatment in a reductive atmosphere (H2) produced the strongest Pt-SnO2 SMSI and most active catalyst. Highly dispersed Sn surface-enriched Pt–Sn alloy NPs were formed on SiO2, in which Pt was most electron rich. The apparent activation energy in n-butane dehydrogenation is higher on Pt–Sn/SiO2_1073 K H2 than the corresponding one on Pt–Sn/SiO2_1073 K N2. The kinetic studies revealed that the extreme isolation of Pt on Pt–Sn/SiO2_1073 K H2 (geometrical effects) dominantly contributed to its superior catalytic performance. The present work highlights the effects of thermal treatment-induced Pt-SnO2 SMSI, providing a new insight into the structure of Pt–Sn bimetallic catalysts and the promotional role of Sn in the dehydrogenation of lower alkanes to olefins on Pt surfaces.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Pt/SiO2 reduced at 1073 K exhibited a high catalytic activity in propane dehydrogenation, primarily attributed to the electronic modification of Pt nanoparticles by a strong metal-support interaction ...(SMSI) effect. The SMSI was observed in the Pt/SiO2 system following direct reduction in H2 (>773 K), and was found to increase with increasing reduction temperature.
Chromium-based cocatalysts influence H2 evolution during the overall water splitting reaction in the photocatalytic conversion of CO2 in the presence of H2O as an electron donor. To clarify the ...mechanism by which chromium species promote or suppress H2 evolution, the reaction was carried out in the presence of α- and β-Ga2O3, NaTaO3, ZnTa2O6, and SrTa2O6 photocatalysts with the in situ addition of chromate ions. We found that chromate ions suppress H2 evolution during the photocatalytic conversion of CO2 by H2O when the surface of the photocatalyst is highly protonated.
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•Na2CrO4 suppressed the evolution of H2 over highly protonated photocatalysts.•Na2CrO4 enhanced the evolution of H2 over lowly protonated photocatalysts.•The formation of Cr(OH)3 was critical to the enhancement effect in H2 evolution.•Dissolved chromate affected the evolution of H2 to a large degree.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
We have explored a solvothermal method for synthesizing various metal oxides in alcohol or glycol media at temperatures around 300°C. This review summarizes our recent results on the solvothermal ...synthesis of metal-oxide nanoparticles and their catalytic and photoluminescence performances. We have described the principles of solvothermal processing by classifying solvothermal methods according to the type of solvent used as follows: alcohol, vicinal glycol and 1,4-butanediol. (1) Solvothermal reaction of metallic cerium in alcohol yields a colloidal solution containing CeO2 nanoparticles, and the pore structure of the CeO2 coagulate can be controlled by the choice of bases added to the colloidal solution. Furthermore, the solvothermally synthesized CeO2 nanoparticles show good redox properties and an improved performance as a catalyst support in the selective oxidation of benzyl alcohol to benzaldehyde. (2) Solvothermal method in vicinal glycol produces an inorganic–organic composite, which is an effective precursor for the synthesis of metal-oxide nanoparticles. Nb2O5 nanoparticles synthesized via a solvothermal reaction in ethylene glycol show high activities as photocatalysts for the selective oxidation of alcohol. (3) Solvothermal reactions in 1,4-butanediol can yield various mixed oxides directly. Mn-modified hexagonal YbFeO3 synthesized by the solvothermal method has a higher catalytic activity for hydrocarbon combustion when compared to noble metal catalysts.
Ammonia is an attractive energy carrier for the hydrogen economy, given its high hydrogen density and ease of liquefaction. A titanate oxyhydride has recently been demonstrated that can catalyze ...ammonia synthesis without Ru or Fe metal, despite titanium being regarded as an inert element. Here, the synthesis activity of ammonia is examined when Ru, Fe, and Co particles are supported onto the oxyhydride BaTiO2.5H0.5. The activity of BaTiO2.5H0.5 as support is significantly higher than BaTiO3. For example, the activity for Fe and Co increases by a factor of 70–400, making them more active than Ru/MgO, one conventional Ru catalyst. In terms of mechanism, for Ru, H/D isotope studies show participation of lattice hydride in the catalytic cycle, while kinetic analysis shows reduced H2 poisoning probably due to spillover. For Fe (and Co), the presence of hydride results in significantly lower activation energy and N2 reaction order, likely due to strong electron donation from the oxyhydride. This metal‐dependent support effect is further verified by N2 isotopic exchange experiments. These perovskite‐type oxyhydrides can be easily modified in terms of A‐ and B‐site (A = Ba, B = Ti); the high potential for compositional variation and morphologies will expand the search for efficient catalysts for ammonia synthesis.
The addition of hydride to an oxide support enhances the ammonia synthesis activity of Ru, Fe, Co‐based catalysts by orders of magnitude. The results provide convincing evidence of lattice hydride participating in the catalytic cycle, and the measured kinetic parameters/isotopic exchange experiments describe a novel metal‐dependent support effect from the oxyhydride supports.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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