The precise decoration of Pd nanoparticles with ZnO via atomic layer deposition for the selective hydrogenation of 1,4-butynediol

Abstract

The synthesis of 1,4-butenediol (BED) through the hydrogenation of 1,4-butynediol (BYD) is of great importance in the pharmaceutical and chemical industries. Nevertheless, side reactions originating from deep hydrogenation and isomerization of BED generally decrease the yield of BED in the hydrogenation of BYD. The modification of the geometric and electrical properties of Pd catalysts can efficiently inhibit the deep hydrogenation and isomerization of BED, thus promoting the selectivity of BED. In this study, a ZnO over-coating with an appropriate thickness was deposited via ALD to precisely decorate Pd nanoparticles supported on CNTs. DFT calculations and CO-DRIFTS indicated that the ALD ZnO over-coating layer was preferentially deposited on the low-coordination sites of Pd. Moreover, pretreatment at 300 °C under an H₂ atmosphere strengthened the interaction between Pd and ZnO, which facilitated the hydrogenation of BYD to BED. H₂-TPR confirmed that the strong interaction between Pd and ZnO could effectively suppress the formation of palladium hydride, preventing the further hydrogenation of BED catalyzed by palladium hydride. Moreover, the blocked low-coordinated Pd sites prevented the adsorption of the intermediate BED on the Pd surface, thereby improving the selectivity for BED. Compared with the parent 10Pd/CNT, 7ZnO/10Pd/CNT-H₂-300 increased the selectivity for BED from 12% to 97%, with the conversion of BYD maintained at 96%.