PtMx/SBA-15 (M = Co, Cu, Ni and Zn) bimetallic catalysts for crotonaldehyde selective hydrogenation

Abstract

Herein, a series of the Pt-based bimetallic catalysts (PtMx/SBA-15) are gained by using ultrasonic incipient wetness impregnation method (M = Co, Cu, Ni or Zn). The experimental results show that the catalytic performance (including catalytic activity (turnover frequency-TOF), selectivity to crotyl alcohol) of PtCox/SBA-15 for catalyzing crotonaldehyde selective hydrogenation is the best among PtMx/SBA-15. Additionally, the ratio of Pt/Co in the PtCox/SBA-15 catalysts is changed to successfully synthesize PtCo/SBA-15, PtCo2/SBA-15, PtCo5/SBA-15. It demonstrates that the selectivity of the PtCox/SBA-15 catalysts for crotonaldehyde selective hydrogenation to crotyl alcohol is significantly improved with the increase of the Co content. The PtCo5/SBA-15 catalyst provides 83.8% conversion of crotonaldehyde, 94.3% selectivity to crotyl alcohol and TOF of 910.5 h−1 under mild reaction conditions (3.0 MPa H2, 80 °C and 2.0 h). And PtCo5/SBA-15 has much better catalytic performance (higher catalytic activity and selectivity to crotyl alcohol) than PtCu5/SBA-15, PtNi5/SBA-15 and PtZn5/SBA-15. The reasons are as follows: (1) PtCo alloy forms, which is conducive to crotonaldehyde adsorption and activation; (2) there is an appropriate synergy effect between Pt and Co, greatly improving the capacity of the catalyst activating hydrogen under mild conditions; (3) the electron transfers from Co to Pt, resulting in the increase of Pt electron density and decrease of Co electron density, then the Co sites are advantageous to CO group adsorption and activation and Pt sites for H2 adsorbing and activating; (4) with the increase of the Co proportion in PtCox/SBA-15, the synergy effect between Pt and Co in PtCo alloy strengthens and thus increases the selectivity of CO group hydrogenation.