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, H-2-TPR, and other characteristics, the Cu species play vital roles in the process of dimethyl adipate (DMA) hydrogenation, and the Cu+ and Cu-0 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 O-vac 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.