Effect of Protective Agents upon the Catalytic Property of Platinum Nanocrystals

“Unprotected” Pt nanocrystals were modified with triphenylphosphine (PPh₃), octadecylamine (ODA), poly(vinylpyrrolidone) (PVP), poly(vinyl alcohol) (PVA), and dodecanethiol (DT) to investigate the effect of protective agents on the intrinsic catalytic property of Pt nanocrystals. By evaluating the catalytic performance of these model catalysts for the hydrogenation of para-chloronitrobenzene (p-CNB), it was found that direct or indirect interaction between nanocrystals and protective agents imposed a great impact on the catalytic performance of the nanocrystals. Protective agents with different electron-donating ability (PPh₃, ODA, PVP, and PVA) directly altered surface electronic state of Pt nanocrystals to bring the surface Pt atoms into an electron-rich state, which would exert influence on the hydrogenation course by changing the adsorption and the reactivity of reactant, intermediates, and products. In contrast, DT exerted an indirect influence on the Pt nanocrystals. The coordinated Pt atoms were oxidized by DT to generate cationic Pt species on the surface of nanocrystals, and the cationic species would simultaneously improve the hydrogenation rate and selectivity to para-chloroaniline by polarizing the N=O bond in the −NO₂ group of p-CNB and altering the electronic state of Pt nanocrystals, respectively. This work provided further insights into nanocatalysis, which is helpful for further design and application of highly efficient nanocrystal catalysts.