No abstract

Glycerol is produced in large quantities as a byproduct of biodiesel, and among others hydroxyacetone (acetol) is an important commodity obtained from glycerol. Metallic Cu has been identified as active site for the dehydration of glycerol to hydroxyacetone and acid and metal sites are known to influence the catalytic performance.In this study, dehydration of glycerol over 5 wt.% copper supported on -Al2O3, ZrO2 and SiO2 was investigated. Catalysts were characterized by N2 physisorption, H2-TPR, NH3-TPD, N2O chemisorption, XPS, XRD, FTIR of pyridine adsorption. Cu/ZrO2 exhibited the highest hydroxyacetone yield at 20% of glycerol conversion and the highest apparent reaction rate.The superior activity of Cu/ZrO2 was attributed to the highly acidic, both Lewis and Brönsted acidic, nature of the support and positive roles of the interfacial sites. The Weisz-Prater (WP) criterion was applied to confirm the absence of intraparticle diffusion limitations. It was assumed spherical particles and first order reaction. The WP value obtained in the worst scenario was less than 0.3 ensuring no diffusion limitation.Complementary DFT study indicates that both glycerol and hydroxyacetone interact significantly stronger on Cu/-Al2O3 and Cu/ZrO2 compared to metallic Cu, suggesting that the active sites are at the interface of Cu particles and the acidic support.

TiO2 is an active material for photocatalytic CO2 reduction. Its performance is improved by the addition of metal or metal oxide as co-catalyst. The enhanced electron-trapping capability is widely attributed to the function of these co-catalysts, but their precise roles are not fully understood. Here, we report how Pt and Co co-catalysts boost formation of H2 and CH4 during photocatalytic CO2 reduction. More specifically, we used in situ diffuse reflectance infrared Fourier transformed spectroscopy (DRIFTS) and multivariate spectral analysis to identify (in)active surface intermediates. The surface formates were identified as the reactive intermediate common to all TiO2-based catalysts. The catalytic activity and product selectivity are determined by the unique function of the co-catalyst, which distinctly interacts with the TiO2 surface to produce and decompose formates to H2 or CH4. The evolution of the surface species also clarifies the transient nature of photocatalytic activities and how the TiO2 surface and co-catalysts are deactivated under photocatalytic conditions.

The photocatalytic water splitting activity of a wide-bandgap material, Ga2O3, is greatly boosted with the addition of a Zn and Rh-Cr co-catalyst at optimum loadings. To date, however, the exact roles of the co-catalysts and particularly the origin of their synergistic functions have not been clarified. Herein, we present how the optimum Zn loading on Ga2O3 leads to creation of a ZnGa2O4/Ga2O3 heterojunction favorable for charge separation through information on the occupied and unoccupied electronic states of Zn and Ga elucidated by X-ray absorption and emission spectroscopic methods. The function of Rh-Cr as an electron sink and reduction site was proven by photocatalytic experiments using an electron scavenger (Ag+) and by learning where Ag deposits and its effects on photocatalytic activity. Finally, perturbation of the Zn electronic structure by photoactivation was evidenced by modulation excitation X-ray absorption spectroscopy. Importantly, Rh-Cr markedly enhanced the level of the perturbation, serving as proof of the direct communication and synergy between the electronic states of Zn, present in ZnGa2O4, and Rh-Cr deposited on Ga2O3.