The hydrolysis of ammonia borane (NH3BH3) on metal-based heterogeneous catalysts under light irradiation has been considered as an efficient technique for hydrogen (H2) generation, in which the activity of the catalyst can be improved by increasing the electron density of the active metal. However, studies focused on reducing the electron density of the active metal are rare. Here, we report an electron density manipulation strategy to prepare highly electron-deficient ultrathin Co nanosheets via transferring nanosheets to support mesoporous Cr2O3 by simple one-step in situ reduction (denoted as Co/Cr2O3). X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge structure (XANES) spectra confirm the formation of electron-deficient Co nanosheets and the Co–O–Cr bond due to electron transfer from the nanosheets to mesoporous Cr2O3. Importantly, the Co–O–Cr bond can work as a bridge to accelerate the electron transfer under light irradiation and then improve the electron-deficiency degree of Co nanosheets. As a result, the optimal Co/Cr2O3 exhibits a high intrinsic catalytic performance with the turnover frequency (TOF) value of 106.8 min−1 and significantly reduces the activation energy (Ea) to 16.8 kJ mol−1 under visible light irradiation, which make it among the best ever recorded monometallic Co-based catalyst with enriched electrons. The density functional theory (DFT) calculation results suggest that the electron-deficient Co nanosheets are responsible for the greatly decreased H2O activation and dissociation energy barriers and then the acceleration of the evolution of H2. The work provides a new perspective for designing high efficiency catalysts for H2 production, which is beneficial for relative energy conversion and storage catalysis.
Yang Yang,Guohua Yao,Xiaojuan Zhu,Meiqi Gao,Lili Wang,Shunlin Li,Xuerong Li,Xuezhi Duan,De Chen,Weimin Yang,Ying Wan
Selective hydrogenation of phenol is a sustainable alternative to cyclohexane oxidation for the production of cyclohexanone. However, over-hydrogenation of cyclohexanone to cyclohexanol is thermodynamically favorable, limiting its selectivity. Here, we report an unprecedented cyclohexanone selectivity (>99.9%) in continuous-flow phenol hydrogenation using an electron-deficient Pd catalyst. The Pd atom exists in a unique Pd–N 5 C 4 structure in which it is coordinated with four quasi-planar N atoms and one axial N atom in the first shell and an additional four C atoms in the second shell that lie on the curved surface of a pore in ordered mesoporous carbon. The Pd site has a d charge depletion of 1.18 e that prevents cyclohexanone adsorption, which is therefore exclusively produced. Bonding the Pd atom to a curved plane of carbon atoms is an effective way to control the d charge of Pd and increase its selectivity for the green synthesis of fine chemicals.
Rational design of catalytic sites to activate the C C bond is of paramount importance to advance acetylene hydrochlorination. Herein, Cu sites with electron-rich and electron-deficient states were constructed by controlling the impregnation solutions. The π electrons flowing from acetylene to Cu site are facilitated over the electron-deficient Cu sites, achieving high activation of C C bond. The contradiction between the increased activation of acetylene required for enhanced catalytic activity and the resistance of Cu site to reduction by acetylene required for maintaining catalytic stability can be balanced by establishing strong interactions of Cu site with pyrrolic-N species. The catalytic activity displays a volcano shape scaling relationship as a function of Cu particle size. Tribasic copper chloride is concomitantly generated with the construction of electron-deficient Cu sites. The H–Cl bond of HCl can be activated over the tribasic copper chloride, accelerating the surface reaction of vinyl chloride production. This strategy of inducing electron deficiency provides new insight into the rational design of catalysts for the synthesis of vinyl chloride with a high catalytic performance.
Electronic structure tuning is an effective strategy to activate transition metals. In this study, silica-promoted γ-Al 2 O 3 -supported Fe-based hydrodesulfurization catalysts of Fe species with electron loss were successfully prepared by transferring electrons from Fe to Si. The characterization results showed that the Fe-based hydrodesulfurization catalyst with the addition of silica modulated the structure and properties of the active metal, which not only improved the degree of sulfidation of the active metal but also promoted the generation of Fe(III)-S. The hydrodesulfurization rate of dibenzothiophene showed a remarkable rise from 38.4 to 83.2% at 673 K. Importantly, the formation of Fe(III)-S greatly stretched the bond length of Fe-S bonds, exhibiting an increase of approximately 21%, this facilitating the generation of coordinatively unsaturated active site. Finally, the HDS reaction performance of the Fe-based hydrodesulfurization catalysts was mainly influenced by the Fe(III)-S/Fe(II)-S ratio, with the most significant enhancement in the direct desulfurization reaction path. The results of this study provide a promising approach for the design and development of environmentally friendly and economical Fe-based catalysts in the field of clean fuels.
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