Promoting effects of residual poly(vinyl alcohol) capping agent on the activity and chemoselectivity of Pt/Al2O3 for catalytic hydrogenation

Abstract

Capping agents are key to the colloidal synthesis of size- and shape-controlled nanoparticles (NPs) for catalysis. The capping agents on the NP surface are generally removed after synthesis to expose the catalytically active sites. However, the total removal of the capping agents results in the loss of the ability of the capped NPs to regulate the adsorption mode of the reactants, which can, in some cases, decrease selectivity. Here, poly(vinyl alcohol) (PVA)-capped Pt/Al2O3 are prepared and the amount of PVA capping agent remaining on the NP surfaces is controlled by heat treatment to take full advantage of capped NPs. Compared to a surface-clean Pt catalyst, those covered in PVA residues having partially exposed metal sites show enhanced activity and selectivity for the hydrogenation of acetophenone to 1-phenylethanol. Detailed characterization reveals that the promoting effects of the residual PVA are attributed to the combined contributions of electronic modification of the Pt surface, selective exposure of highly active Pt defect sites, and steric hindrance with the aromatic ring of acetophenone. This study offers insights into the roles of residual capping agents in heterogeneous catalysis and provides a new strategy for enhancing the performance of nanocatalysts using capped NPs.