Pd-Sn-K/SiO_2催化剂上甲苯气相氧乙酰化反应  

Gas-Phase Oxidative Acetoxylation of Toluene over Pd-Sn-K/SiO_2 Catalyst

作　　者：束庆宇[1] 王新平[1] 任素贞[1] 施维[1] 

机构地区：[1]大连理工大学精细化工国家重点实验室,辽宁大连116024

出　　处：《催化学报》2005年第10期869-873,共5页

摘　　要：在常规固定床流动反应体系中研究了Pd-Sn-K/SiO2催化剂上气/固相氧化条件下甲苯与乙酸一步合成乙酸苄酯的反应.结果表明,金属态钯是催化甲苯氧乙酰化合成乙酸苄酯的高活性组分,锡化合物的存在可明显提高催化剂的活性.催化剂的活性与制备方法密切相关,用H2将SiO2上负载的钯化合物还原之后再负载锡化合物所得催化剂的活性较高.XRD分析结果表明,钯还原前负载锡化合物所得催化剂的活性大幅度降低的原因在于Pd和Sn形成了金属间化合物.使用Pd/SiO2质量比为0.015,K∶Sn∶Pd摩尔比为27∶3∶1的Pd-Sn-K/SiO2催化剂,在反应温度为180℃,混合原料气甲苯∶乙酸∶氧气∶氮气摩尔比为1∶4∶1∶4以及空速为1 680 h-1的条件下,甲苯转化率可达25.3%,乙酸苄酯选择性为91%.以TiO2和ZrO2代替SiO2载体,或以其它变价金属氧化物代替Sn氧化物助剂或金属钯,均未发现有更好的催化效果.The gas-phase oxidative acetoxylation of toluene with acetic acid to benzyl acetate over the Pd-Sn-K/ SiO2 catalyst was investigated in a fixed-bed flow reactor. Palladium in the metallic state supported on SiO2 is the highly active component for the reaction. The presence of tin oxides in the catalyst drastically enhances the catalyst activity. The catalytic properties of the Pd-Sn-K/SiO2 catalyst have a close relation with preparation methods. Higher activity was obtained when the catalyst was prepared by hydrogen reduction of the palladium component on SiO2 before tin oxide loading. The XRD results reveal that when the reduction of palladium with hydrogen was performed after tin oxide loading, the intermetallic compounds of PdSn or Pd20Sn13 are formed in Pd-Sn-K/SiO2, leading to the catalyst with lower activity for the reaction. Under the reaction conditions of 180 ℃ , toluene ： acetic acid： O2 ： N2 molar ratio of 1 ： 4 ： 1 ： 4 and GHSV of 1 680 h^- 1, 25.3 % of toluene conversion with 91% of selectivity for benzyl acetate was achieved over the Pd-Sn-K/SiO2 catalyst with a K：Sn：Pd molar ratio of 27 ： 3 ： 1. On the other hand, lower activity and selectivity were obtained when TiO2 or ZrO2 was used as the support instead of SiO2, or other noble metals were used instead of palladium as the active components. No other valence-variable metal oxides were found to be better than tin oxides as promoters for the toluene oxidative acetoxylation.

关 键 词：甲苯 乙酸 氧乙酰化 乙酸苄酯 钯 负载型催化剂 

分 类 号：O621.251[理学—有机化学] O643.32[理学—化学]