甲醇气相羰基化非铑非卤素新催化体系研究Ⅴ.载体对催化剂气相羰基化性能的影响

Study on the halide-and rhodium-free catalytic system for vapor phase carbonylation of methanol Ⅴ. Effect of supports on catalyst performance in vapor phasa carbonylation

以活性炭、三氧化二铝、二氧化硅作载体制备了一系列负载的钼催化剂 ,并对甲醇常压下直接气相羰基化进行了研究 ,实验发现载体对催化剂的羰化性能非常敏感。活性炭是最佳的催化剂载体 ;Mo/γ Al2 O3 催化剂虽甲醇转化率高 ,但羰化产物选择性低 ;而Mo/SiO2 催化剂不仅甲醇转化率低、而且羰化选择性几乎为零。实验对催化剂的CO、NH3化学吸附与羰基化性能的关系进行了分析 ,结果表明 :催化剂的酸性对甲醇的转化十分重要 ,催化剂对CO的化学吸附是决定羰化反应选择性的关键。此外 。

A novel Mo/C catalyst has a high activity and selectivity for methanol vapor phase carbonylation to methyl acetate without addition of any promoter in the feed. In this paper, a series of Mo catalysts supported on activated carbon, γ Al 2O 3 and SiO 2 are prepared. The results show that the effect of supports on Mo catalyst for direct vapor phase carbonylation of methanol is very sensitive. Activated carbon is the best supports; Mo/γ Al 2O 3 has a high conversion of methanol, but the selectivity for carbonylation is very low; and Mo/SiO 2 catalyst has a less conversion of methanol, and the selectivity for carbonylation is nearly zero. Moreover, the relationships between adsorptions of NH 3 and CO and carbonylation of methanol are investigated. The results show that the amount of absorbed NH 3 is more on the Mo/C and Mo/γ Al 2O 3than Mo/SiO 2. Acidity of catalyst is necessary to activate methanol, and the conversion of methanol is determined by the amount of acidic sites. The order of the amount of CO chemisorption is as follows: Mo/C (1190 μmol·g -1 ) >>Mo/γ Al 2O 3 (198 μmol·g -1 ) >Mo/SiO 2 (100μmol·g -1 ). It is suggested that the adsorbed CO molecules migrate from metal sites to activated carbon (spillover), and then the amount of absorbed CO is enhanced. The result demonstrates that the effect of chemisorbed CO on the selectivity for carbonylation is significant. At the same time, the reaction mechanism of direct vapor phase carbonylation of methanol is presented. The initial step of this reaction is suggested to be the cleavage of methanol to form CH 3 +, followed by adsorbed CO insertion into the metal methyl bond, forming CH 3C(O) +, which further interacts with methanol to form methyl acetate.