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Electrochemical water splitting for the oxygen evolution reaction (OER) requires highly active, long-durable, and cost-effective catalysts to meet the needs of large-scale hydrogen production in the future. Herein, we studied the OER performance of spinel MFe2O4 (M = Zn and Ni) and NiOx. These metal oxides showed markedly different activities, which were closely related to their charge-transfer resistance and electrochemical surface area, attributing to the amount of oxygen vacancies. Particularly, ZnFe2O4 exhibits superior OER activity with an overpotential of 318 mV at the current density of 10 mA cm−2 (η10) and a Tafel slope of 50 mV dec−1. Furthermore, ZnFe2O4 also presents outstanding long-term stability for 100 h with negligible decay even at a high current density of 800 mA cm−2. This work provides a fundamental insight into the oxygen vacancy and spinel structure to help for the design of OER catalyst toward highly efficient water splitting. [ABSTRACT FROM AUTHOR]

Highlights: [•] High acetol yields from cellulose, and also from glucose and fructose were obtained. [•] The mechanism of cellulose conversion to acetol on bimetallic Ni-SnO x /Al2O3 catalysts was studied. [•] SnO x facilitated the isomerizaiton of glucose to fructose and its subsequent C C bond cleavage. [•] The hydrogenation activity of the Ni-SnO x /Al2O3 catalysts depends on the Sn/Ni ratio. [ABSTRACT FROM AUTHOR]

Cellulose is the most abundant source of biomass in nature, and its selective conversion into polyols provides a viable route towards the sustainable synthesis of fuels and chemicals. Here, we report the marked change in the distribution of polyols in the cellulose reaction with the Sn/Pt atomic ratios in a wide range of 0.1–3.8 on the SnOx-modified Pt/Al2O3 catalysts. Such a change was found to be closely related to the effects of the Sn/Pt ratios on the activity for the hydrogenation of glucose and other C6 sugar intermediates involved in the cellulose reaction as well as to the notable activity of the segregated SnOx species for the selective degradation of the sugar intermediates on the Pt–SnOx/Al2O3 catalysts. At lower Sn/Pt ratios of 0.1–1.0, there existed electron transfer from the SnOx species to the Pt sites and strong interaction between the catalysts, as characterized by temperature-programmed reduction in H2 and infrared spectroscopy for CO adsorption, which led to their superior hydrogenation activity (per exposed Pt atom), and in-parallel higher selectivity to hexitols (e.g. sorbitol) in the cellulose reaction, as compared to Pt/Al2O3. The hexitol selectivity reached the greatest value of 82.7% at the Sn/Pt ratio of 0.5, nearly two times that of Pt/Al2O3 at similar cellulose conversions (∼20%). As the Sn/Pt ratios exceeded 1.5, the Pt–SnOx/Al2O3 catalysts exhibited inferior hydrogenation activity (per exposed Pt atom), due to the formation of the crystalline Pt–Sn alloy, which led to the preferential conversion of cellulose to C2 and especially C3 products (e.g. acetol) over hexitols, most likely involving the isomerization of glucose to fructose and retro-aldol condensation of these sugars on the segregated SnOx species, apparently in the form of Sn(OH)2. These findings clearly demonstrate the feasibility for rational control of the cellulose conversion into the target polyols (e.g. acetol or propylene glycol), for example, by the design of efficient catalysts based on the catalytic functions of the SnOx species with tunable hydrogenation activity. [ABSTRACT FROM AUTHOR]