Impacts of Organic Stabilizers on Catalysis of Au Nanoparticles from Colloidal Preparation

Metal nanoparticles (NPs) from colloidal synthesis are advantageous in fundamental catalysis research because of their precisely controlled size and morphology but unfortunately are usually contaminated with residues from the organic stabilizer essentially required in the synthesis. These residues could modify the surface property and disturb the catalysis intrinsic to clean NPs. Herein, polyvinylpyrrolidone (PVP)-stabilized Au NPs (4.7 +/- 1.0 nm) from colloidal synthesis were immobilized on SiO2 support and subjected to ultraviolet-ozone (UVO) treatment to remove the residues. Hydrogenation reactions of p-chloronitrobenzene (p-CNB) and cinnamaldehyde (CAL) were conducted to probe consequences of the stabilizer removal on the catalytic properties of Au NPs. Measurements by FTIR and XPS revealed a controlled removal and degradation of PVP according to the UVO-treatment duration. Careful HRTEM analysis disclosed that both the size and morphology of Au NPs remained unchanged after the UVO-treatment. Residual PVP significantly improved the activity of Au NPs for p-CNB hydrogenation but lowered the activity for CAL hydrogenation. Continued selectivity changes of CAL hydrogenation to favor the reaction at the C-C bond were observed on increasing the removal degree of the residues. The UVO-cleaned Au NPs were also restabilized with PVP and other stabilizers by adsorption in aqueous solution. Comparison of the catalytic properties of these Au NPs involving different stabilizers with those of the UVO-cleaned ones enabled a comprehension of the stabilizer impacts on the hydrogenation catalysis of Au NPs.