铑催化合成气转化为乙醇反应中甲酰基中间体的化学捕获

本文采用化学捕获法对铑基催化剂上合成气转化反应中的甲酰基中间体进行了化学捕获,在CO+2D_2反应后,用CH_3I进行的化学捕获反应中生成了CH_3CHO、CH_3CDO两种形式的乙醛;补充的Ar吹扫实验显示DCO的甲基化反应对生成的CH_3CDO有重要贡献。因此,甲酰基的确是合成气反应中的C_1含氧中间体。根据这一结果,初步探讨了合成气反应中CH_x物种的生成途径。

Chemical Trapping of Formyl Intermediate in Syngas Conversion to Ethanol over Rhodium-Based Catalysts

The expected formyl intermediate was trapped in syngas conversion to ethanol over rhodium-based catalyst by chemical trapping technique. In formyl trapping experiment, CO/D2(l/2) instead of CO/H2 was used as the reactant gas and CH3I as the trapping agent, and the expected trapping product would be CH3CDO. Two species of acetaldehyde, i. e. , CH3CHO and CH3CDO, were formed in the trapping reaction. When the blank trapping reaction with CH3I was carried out only in the presence of CO over Rh-Mn(l : 1)/SiO2 prereduced in flowing CO, CH3CHO was still formed. This indicates the occurrence of dehydrogenation of some of the CH3 to give H, which then reacted with the CH3 CO formed by cis-insertion of CO into the CH3 from CH3 I to form CH3CHO, or then reacted with ' CO to form H CO, which was converted into CH3CHO by methylation. This means that there are two" possible pathways for the formation of CH3CDO in formyl trapping reaction. One is methylation of D CO, the other is deuteration of CH3 CO formed by CO insertion into CH3. By investigating the effects of purging time of Ar on the percentage of CH3CDO in total acetaldehyde formed in the trapping reaction and on the corresponding relative concentration of D, it was shown that a considerable proportion of CH3CDO was actually derived from the methylation of D CO, indicating the existence of formyl intermediate in syngas conversion to ethanol. Based on this result, the mechanism for the formation of CMX (x = 2 or 3) adspecies in syngas conversion to ethanol over rhodium-based catalysts was discussed.