Alloying is a general and efficent strategy to boost the catalytic activity of Co catalysts toword alcohol oxidation (AHO) through electronic effects. Besides, vacancis also exhibit superior AHO acitivity because of their strong adsorption ability to alcohols. Thus, a combination of the alloying and vacnacies would be a promising method to futher fabricate excellent catalysts for AHO. However, The controlable synthesis of alloy with rich-vacancies remains challenging.
Recently, a research team led by Prof. Kai Yan from Sun Yat-Sen University, controllably designed a CoSi alloy with rich-vacancies (AM-CoSi) through a solvent-free arc-melting (AM) method wihin 5 mins for base- and solvent-free selective oxidation of alcohols. The results were published in Chinese Journal of Catalysis (https://doi.org/10.1016/S1872-2067(23)64418-3).
Firstly, X-ray absorption fine structure (XAFS), electron paramagnetic resonance (EPR), and aberration corrected high angle annular dark field scanning transmission electron microscope (AC HAADF-STEM) confirmed the successful synthesis of AM-CoSi alloy with both Co vacancy (Cov) and Si vancncy (Siv), in which Siv is in the majority. The formation of vacancies in AM-CoSi maybe due to the rapid cooling during preparation process. Besides, Co element in AM-CoSi is in the form of metallic state.
The as-prepared AM-CoSi alloy catalysts were ultilized for Benzyl alcohol (BAL) base- and solvent-free oxidation. By regulating the catalytic reaction temperature, benzaldehyde (BZH) and benzyl benzoate (BBE) can be selectivitly optimized as the main production. 84.7% selectivity to BZH at 54.8% conversion of BAL can be obtained at 140 °C under 5 bar O2 for 6 h. 70% selectivity to BBE with up to 99.9% conversion of BAL can be achieved at 220 °C under 9 bar O2 for 24 h, which is the highest value reported so far. 6 aromatic alcohols with electro-donating and electro-withdrawing groups were also base- and solvent-free oxidated to produced aldehydes using AM-CoSi alloy with high catalytic performance and excellent universality. Besides, CoSi alloy maintained high stability in the oxidation process. Moreover, the formation route of BBE was examined and BBE is obtained through the direct esterification of BAL with benzoic acid (BAD) in the aid of AM-CoSi at high temperature. BAD can be obtained at high temperature rather than at low temperature (< 140°C) through the further oxidation of BZH from BAL conversion.
The factors for AM-CoSi catalytic ability were also exploited. Compare with their monometallic Co, counterpart Si, and standard CoSi alloy (S-CoSi) for the base- and solvent-free oxidation, the CoSi alloyed structure improves the BAL oxidation. AM-CoSi exibits a superior performance for the formation of BBE because of the important roles of vacancy in AM-CoSi. Density functional theory (DFT) calculations further reveal that Si vacancies and the alloyed structure of AM-CoSi contribute to formation of BBE.
This work was supported by National Natural Science Foundation of China (21776324, 22078374), and the Scientific and Technological Planning Project of Guangzhou, China (202206010145).
About the Journal
Chinese Journal of Catalysis is co-sponsored by Dalian Institute of Chemical Physics, Chinese Academy of Sciences and Chinese Chemical Society, and it is currently published by Elsevier group. This monthly journal publishes in English timely contributions of original and rigorously reviewed manuscripts covering all areas of catalysis. The journal publishes Reviews, Accounts, Communications, Articles, Highlights, Perspectives, and Viewpoints of highly scientific values that help understanding and defining of new concepts in both fundamental issues and practical applications of catalysis. Chinese Journal of Catalysis ranks among the top two journals in Applied Chemistry with a current SCI impact factor of 12.92. The Editors-in-Chief are Profs. Can Li and Tao Zhang.
Manuscript submission https://mc03.manuscriptcentral.com/cjcatal