Cen Tang,Fangru Zhou,Yang Wen,Yumeng Xu,Aiping Jia,Mengfei Luo,Jiqing Lu
A series of MoO x -promoted Ir/BN catalysts were tested for liquid phase selective hydrogenation of crotonaldehyde. The MoO x -promotion could significantly improve the reactivity up to 5-fold. Such improvement was mainly due to the formation of Ir-MoO x interfacial sites in the promoted catalyst, which accelerated the adsorption and activation of crotonaldehyde molecule as evidenced by a much lower activation energy (18.9 kJ mol −1 on the 0.3Mo-3Ir/BN versus 38.4 kJ mol −1 on the 3Ir/BN). The kinetic results revealed negative reaction order of crotonaldehyde (up to -1.1) and high reaction order of H 2 (up to 2.2), indicating the high coverage of crotonaldehyde on the catalyst surface suppressed the adsorption of H 2 due to its low solubility in the liquid phase. Therefore, the adsorption and activation of H 2 on the catalyst might be the rate determining step. However, the preferred adsorption of crotonaldehyde on the Ir-MoO x interface alleviated the suppression of H 2 adsorption, which was another reason for the higher activity.
Herein, a series of the Pt-based bimetallic catalysts (PtM x /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 PtCo x /SBA-15 for catalyzing crotonaldehyde selective hydrogenation is the best among PtM x /SBA-15. Additionally, the ratio of Pt/Co in the PtCo x /SBA-15 catalysts is changed to successfully synthesize PtCo/SBA-15, PtCo 2 /SBA-15, PtCo 5 /SBA-15. It demonstrates that the selectivity of the PtCo x /SBA-15 catalysts for crotonaldehyde selective hydrogenation to crotyl alcohol is significantly improved with the increase of the Co content. The PtCo 5 /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 H 2 , 80 °C and 2.0 h). And PtCo 5 /SBA-15 has much better catalytic performance (higher catalytic activity and selectivity to crotyl alcohol) than PtCu 5 /SBA-15, PtNi 5 /SBA-15 and PtZn 5 /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 H 2 adsorbing and activating; (4) with the increase of the Co proportion in PtCo x /SBA-15, the synergy effect between Pt and Co in PtCo alloy strengthens and thus increases the selectivity of C O group hydrogenation.
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