Visible-Light-Promoted Selective Hydrogenation of Crotonaldehyde by Au Supported ZnAl-Layered Double Hydroxides: Catalytic Property, Kinetics, and Mechanism Investigation

alpha,beta-Unsaturated alcohols are a group of important chemicals and have frequently been synthesized by catalytic hydrogenation method due to its low cost and environmental friendly nature. However, the synthesis of high reactivity and selectivity catalyst that Visible light favors C=O hydrogenation is very challenging. Many references have reported the results of selective hydrogenation of crotonaldehyde to crotonyl alcohol, which either have high conversion and low selectivity or high selectivity and low conversion. Herein, Au-supported ZnAl-layered double hydroxides (Au/ZnAl-LDHs) were synthesized and used on the hydrogenation reaction of crotonaldehyde (CDE) to crotonyl alcohol (COL) under the moderate reaction conditions supplied with light irradiation. The experimental results indicated that the reactivity of CDE hydrogenation and selectivity of COL both have been greatly improved under visible light irradiation, from 42% to 99% for conversion of CDE, from 59.5% to 96% for COL selectivity, of COL both have been greatly improved under visible light irradiation, from 42% to 99% for conversion of CDE, from 59.5% to 96% for COL selectivity, and from 101 to 272 h(-1) for TOF, compared with no irradiation. On the basis of the proposed kinetics equation, it can be concluded that irradiation can not only remarkably increase the reaction rate of selective hydrogenation of CDE to COL but also obviously decrease the activation energy of the reaction system. The enhancement of photocatalytic property of is exactly due to the support of Au, which can be proved by the dependence of the catalytic performance on the wavelength range of light as well as the UV-vis result. In addition, the possible CDE catalytic reaction mechanism was concluded based on the calculation of surface adsorption and hydrogenation reaction path using the DFT method, which is well explained and supports the experimental results.