Size Effect of Spinel Co0.5fe0.5al2o4 Supported Pt Catalysts for the Selective Hydrogenation of Cinnamaldehyde

Abstract

Spinel Co0.5Fe0.5Al2O4 composites supported Pt catalysts with various Pt loadings were prepared by an impregnation method using H2PtCl6·6H2O as precursor and tested in the liquid-phase selective hydrogenation of cinnamaldehyde (CAL). The size of Pt nanoparticles was delicately tuned in the range of 1.6-3.4 nm by changing Pt loadings and thus affected the catalytic performance of the Pt/Co0.5Fe0.5Al2O4 catalysts. Regarding the loading of Pt, varied from 0.3 wt% to 5 wt%, the activity (TOF) of CAL hydrogenation was greatly promoted with the increase of Pt loadings from 0.19 s-1 to 2.70 s-1. Simultaneously, the selectivity toward cinnamyl alcohol (COL) was also improved from 68% to about 94% with the increase of Pt loadings. Kinetic analyses of the selective hydrogenation of CAL over the Pt/Co0.5Fe0.5Al2O4 catalysts with different Pt particle size revealed that the selective hydrogenation of CAL was indeed structure-sensitive over Pt nanoparticles. In-situ FT-IR and H2-TPR characterization results indicated that electron-different metallic Pt species on the Pt particles with different particle size adjusted the adsorption mode of CAL on the Pt sites, therefore greatly adjusting the chemisorption and activation of carbonyl group in CAL. Stronger interaction occurred between Pt particles and spinel Co0.5Fe0.5Al2O4 support, giving rise to electron-deficient Pt particles on the Pt/Co0.5Fe0.5Al2O4 catalysts with smaller Pt particle size, so that C=O bond and C=C bond could be adsorbed and activated simultaneously. By contrast, electron-rich metallic Pt species existed on the Pt/Co0.5Fe0.5Al2O4 catalysts with larger Pt particle size, which is beneficial for the activation of C=O bond to form COL preferentially.

Keywords: size effect, Pt catalyst, cinnamaldehyde, selective hydrogenation