Ternary Cu-ZnO-ZrO2 Nanostructures Prepared by Surface-Assisted Coprecipitation for Catalytic Hydrogenation of Dimethyl Adipate to 1,6-Hexanediol

A series of ternary Cu-ZnO-ZrO2 nanostructures was prepared containing either tetrapropylammonium hydroxide (TPAOH, TH), polyoxyethylene lauryl ether carboxylic acid (BRIJ35, B5), poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (P123 P3), decyltrimethylammonium bromide (DB), poly(vinylpyrrolidone) (PVP, PP), or no surfactant. First, based on the characterization results of XPS, H2-TPR, and other characteristics, the Cu species play vital roles in the process of dimethyl adipate (DMA) hydrogenation, and the Cu+ and Cu0 generated after reduction have a synergistic effect in the hydrogenation process. Results showed that changing the surfactant type and surfactant concentration in the catalyst synthesis has a great effect on the catalytic activity of the catalyst. In particular, the HDO selectivity of the CZZ-4-P3 (52%) catalyst treated with poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) was significantly improved compared to the untreated CZZ (29%) catalyst, which is related to the highest concentration and number of oxygen vacancies. The larger amount of Ovac might promote the hydrogenation of DMA through interaction with the carbonyl group and then weaken the C═O bond. On the other hand, it also has a more surface basic (strong basic) amount on the CZZ catalyst. This will provide more adsorption sites and thus adsorb more DMA molecule. Furthermore, it has a larger dispersion of the Cu and smaller catalyst particles. This may be more conducive to adequate contact between the feedstock and catalyst, reducing diffusion effects.