Selective hydrogenation of cinnamaldehyde to cinnamyl alcohol over the Co-La-B/SiO2 amorphous catalyst and the promoting effect of La-dopant

Abstract The La-doped Co-B/SiO 2 amorphous catalyst (Co-La-B/SiO 2 ) was prepared by chemical reduction of mixed Co 2+ and La 3+ ions deposited on a silica support with KBH 4 aqueous solution at room temperature. The catalyst was employed in the liquid phase hydrogenation of cinnamaldehyde (CMA) to cinnamyl alcohol (CMO). At suitable content, the La-additives exhibited promoting effects on both the activity and the selectivity to CMO. The optimum La-content ( χ La ) was determined as 0.014 (molar fraction), over which the CMO yield could reach 80%. Based on various characterizations, the promoting effect of the La-dopant on the selectivity to CMO was mainly attributed to the presence of La 2+ and La 3+ . These La-species were favorable for both the activation of the CO bond and the formation of H − species and thus, promoted the hydrogenation of CO bond. These roles also promoted the hydrogenation activity. Besides, the promoting effect of the La-dopant might also attributed to the presence of the La oxides which increased the surface Co active sites. At high χ La , the activity decreased again due to the coverage of the Co active sites by the inactive La-additives and also due to the too strong adsorption of carbonyl group induced by La 3+ and La 2+ . Such strong adsorption might hinder the competitive adsorption of hydrogen.