Glucose hydrogenation over promoted Co-B amorphous alloy catalysts

摘要

Glucose hydrogenation was carried out in a well-stirred, high-pressure batch reactor on the unpromoted and Cr- and W -promoted Co-B amorphous alloy catalysts in the form of ultrafine particles. These were prepared by chemical reduction of the metallic salt solution with borohydride in aqueous solution. The Co-B amorphous alloy exhibited higher activity than other Co-based crystalline catalysts, mainly owing to the structural modification and the electronic interaction between metallic Co and alloying B (electronic effect). Its activity was even higher than that of either the Ni-B amorphous alloy catalyst or the Raney Ni catalyst, possibly due to the stronger adsorption ability of Co for ~drogen compared to that of Ni. Suitable concentration of either Cr- or W -promoters could further enhance the hydrogenation activity of Co-B amorphous alloy, since these promoters when present in the low-valent state contacting with the Co active sites could act as Lewis adsorption sites for the oxygen atom of the carbonyl group, which was then polarized, and thus, more easily hydrogenated via a nucleophilic attack on carbon atom by the dissociated hydrogen atom on surface Co active sites. The W -promoter exhibited a stronger promoting effect than the Cr-promoter since the W4+ oxide was more active than cr3+ oxide. However, too large a concentration of either Cr- or W -promoters led to decrease in the activity of Co-B amorphous alloy, since too many Co active sites were covered by Cr~(3+) or W~(4+) oxides.