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

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 per-formance (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 hydro-genation 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 degrees 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 C--O 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 C--O group hydrogenation.