钼催化剂上甲醇直接气相羰基化活性与吸附的关系

 制备了一系列非负载的钼催化剂，考察了催化剂上甲醇直接气相rn羰化活性与反应物及产物吸附的关系．结果发现，催化剂的制备方法对rn甲醇直接气相羰化活性的影响很明显，以纯二硫化钼试剂制备的催化剂rn，甲醇转化率与羰化产物乙酸甲酯的选择性最低；以三氧化钼气相还原rn硫化制备的催化剂，其羰化活性较低；以钼酸铵溶液经硫化铵溶液或硫rn化氢气体硫化制得的催化剂，其性能明显优于前两种，尤以钼酸铵经硫rn化铵溶液硫化制得的催化剂的性能最佳．催化剂的羰化活性明显依赖于rn催化剂的吸附性能，羰化活性高的催化剂不仅吸附CO的量大，而且对甲rn醇和乙酸甲酯的吸附量也明显较大．

Relationship between Catalytic Activity and Adsorption of Mo Catalysts in Direct Vapor Phase Carbonylation of Methanol

A novel sulfided Mo/C catalyst has a high activity and selectivity in methanol vapor phase carbonylation to methyl acetate without addition of any promoter in the feed. In this paper, a series of non supported Mo catalysts were prepared. Their catalytic performance for methanol direct vapor phase carbonylation was compared, and the relationship between catalytic activity and adsorption was investigated. The results show that the effect of preparation method is very great. MS1 and MS2 catalysts, which were prepared from pure MoS 2 (activated with a flow of H 2 at 673 K) and MoO 3 (sulfidized with a flow of 5%H 2S H 2 at 673 K) respectively, give lower conversion of methanol and lower selectivity for methyl acetate. MS3 and MS4 catalysts, which were prepared from ammonium heptamolybdate solution by sulfiding in H 2S and (NH 4) 2S aqueous solution respectively and subsequently activated with a flow of H 2 at 673 K, have higher activity and selectivity. Especially, the carbonylation activity over MS4 is forty times higher than over MS1. The amorphous catalysts (MS3 and MS4) have high conversion of methanol and high selectivity for methyl acetate because the uptakes of CO, CH 3OH and AcOMe are high. MS5, which was prepared from ammonium heptamolybdate solution by sulfiding in (NH 4) 2S aqueous solution and subsequently treated with a flow of N 2 at 673 K, has lower catalytic activity than MS4 (treated by H 2). The lowest activation energy of desorption and smaller quantity of adsorption are observed on MS5. The result indicates that the catalyst activity is much affected by the pretreatment conditions. The surface composition of the catalysts was analyzed by electron probe microanalysis (EPMA). The results show that the molar ratio of S/Mo is 2 2 (MoS 2 2 ) for MS4, and 2 0 (MoS 2) for MS5. The significantly higher carbonylation activity on MS4 compared to MS5 is most likely due to the comparatively larger molar ratio of S/Mo.