摘要
本文报导Rh_4(CO)_(12)/SiO_2催化剂的CO加氢反应及锰,锂的助剂作用。同传统的RhCl_3/SiO_2相比,负载原子簇催化剂具有更好的反应活性。锰促进了CO转化率提高一个数量级以上。锂降低了CO加氢活性。Rh_4(CO)_(12)-MnCl_2-LiCl/SiO_2催化剂既保持高的反应活性,又提高了C_2-含氧化物选择性。XPS和IR谱表明,锰稳定了低氧化态铑离子并通过与铑的联合作用,促进对CO分子的活化,因此改善了催化剂反应性能。ESR揭示了在Rh_4(CO)_(12)-MnCl_2/SiO_2中铑、锰的相互作用,初步地讨论了与此有关的CO加氢反应机理。
The hydrogenation of CO over SiO2-supported rhodium carbonyl cluster catalysts and the effect of Mn, Li on the reaction were studied with IR,XPS,ESR,pulse reaction technique and activity measurement .The supported cluster catalysts showed higher catalytic activities than the traditional RhCl3-based catalyst. Addition of MnCl2 enhanced the conversion of CO to more than 10 times and addition of LiCl inhibited the conversion, whereas catalyst Rh4 ( CO ) 1 2-MnCl2- LiCl/SiO2 remained high catalytic activity and improved selectivity for C2-oxy genates.The O2 pulse during CO hydrogenation also increased conversion of CO and the yields of oxygen-containing products. The results of XPS and IR spectra indicated that MnCl2 stabilized the rhodium cations of low oxidation state, and the oxygen, atom of the Rh-CO adsorption complex interacts with a contiguous manganese ion, leading to somewhat lower CO stretching frequency possibly due to the tilted orientation of the adsorbed η2-CO. The synergetic effect of Rh and Mn enhanced the reactive activity of CO, thus making Rh4 ( CO ) 12 -MnCl2 LiCl/SiO2 a good catalyst for synthesis of C2-oxygenates from CO and H2. The results of ESR spectra showed that there was some interaction between Rh and Mn in the catalyst Rh4(CO)1 2-MnCl2/SiO2 .The main steps in the reaction mechanism for CO hydrogenation are CO dissociation on the rhodium metal clusters and hydrogenation of surface carbon to give CHx species. Both rhodium metals and rhodium ions appear to play a role in the reaction mechanism. Mn promoted the activation of CO molecules and Rh ions are stabilized by the interaction with promoters, so that both conversion of CO and selectivity of C2-oxygenate are enhanced appreciably.
出处
《分子催化》
EI
CAS
CSCD
1991年第1期42-49,共8页
Journal of Molecular Catalysis(China)
基金
国家自然科学基金
