Selective oxidation of C–H bonds under mild conditions is one of the most important and challenging issues in utilization of energy-related molecules. Molybdenum oxide nanostructures containing Mo5+ species are effective for these reactions, but the accurate identification of the structure of active Mo5+ species and the catalytic mechanism remain unclear. Herein, unsaturated penta-coordinated Mo5c5+ with a high fraction in MoOx fabricated by the hydrothermal method were identified as the active sites for low-temperature oxidation of dimethyl ether (DME) by the deep correlation of characterizations, density functional theory calculations, and activity results, giving a methyl formate selectivity of 96.3% and DME conversion of 12.5% at unreported 110 °C. Low-temperature electron spin resonance (ESR) and quasi in situ X-ray photoelectron spectra (XPS) with the designed experiments confirm that the Mo5c5+ species can be formed in situ. Molybdenum located at the pentachronic site is preferable to significantly promote the oxidation of the C–H bond in CH3O* at lower temperatures.
Shuo Cao,Zun Guan,Ying Ma,Bing Xu,Jun Ma,Wei Chu,Riguang Zhang,Giuliano Giambastiani,Yuefeng Liu
The design and synthesis of highly efficient and selective catalysts for CO2 thermal reduction remain a challenging issue of modern catalysis. Molybdenum carbide has attracted great interest in CO2-to-CO conversion (Reverse Water Gas Shift process, RWGS) because of its ability to dissociate CO2 and H2. However, single dominant Mo- or C-terminated facets of molybdenum carbide are unlikely to activate CO2 and H2 molecules simultaneously. Herein, we demonstrate how structural diversity of cogenerated molybdenum species (i.e., Mon nanoclusters and Mo2C nanoparticles) on the surface of an oxygen-enriched C-carrier boosts synergistically the chemoselective RWGS process with rates up to 581 μmolCO2·gMo–1·s–1 with CO selectivity > 99% already at 400 °C under an H2-rich environment. This catalytic outcome ranks among the highest reported so far for molybdenum carbide- or noble metal-based catalysts in the process, and it is up to 1.8 times higher than that measured on Mo2C-based nanoparticles. The enhanced reactivity of the structurally mixed catalyst has been ascribed to a synergistic modulation of the geometrical and electronic structure of different Mo sites that reduces the temperature at which CO production starts and facilitates the chemoselective CO desorption pathway. Experimental and in silico studies have also unveiled the existence of a linear correlation between the percentage of high-valence molybdenum species in the metal active-phase composition (Moδ+ %) and the increase in the RWGS rate.
Yupei Ding,Jie Zhu,Minxia Jiang,Xiaowan Zhan,Jinwen Qin,Xue Jiang,Shuaifeng Wang,Tao Meng,Minhua Cao
RuSe2 has been considered an efficient alkaline hydrogen evolution reaction (HER) electrocatalyst due to its fast water dissociation kinetics and lower price. However, its strong affinity to the adsorbed active intermediates blocks the active sites, hence largely falling short of its full activity potential. Herein, we report a feasible competitive adsorption strategy by introducing oxyphilic molybdenum (Mo) species into RuSe2 (Mo–RuSe2) to regulate the strong interaction between the Ru sites and HER intermediates, enabling highly efficient alkaline HER performance. In situ experimental and theoretical calculation results reveal that the oxyphilic Mo tailoring for RuSe2 can not only alleviate OHad blocking on the Ru sites by the competitive adsorption of OHad between the Ru and Mo sites, but also optimize the hydrogen adsorption Gibbs free energy, thus facilitating the OHad transfer and H2 release process, both of which synergistically promote the regeneration of Ru active sites. The optimized Mo–RuSe2 exhibits an overpotential at 10 mA cm−2 as small as 27 mV and a low Tafel slope of 39 mV dec−1, as well as remarkable long-term stability. This finding is expected to shed new light on developing highly efficient alkaline HER catalysts by regulating the adsorption strength between the active sites and intermediates.
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