载体和担载酸对乙烯直接氧化合成乙酸反应的影响

 在固定床流动反应器上研究了Pd－酸／载体体系催化乙烯直接氧\r\n化合成乙酸的反应，并对载体相同但担载酸强度不同的催化剂的催化活\r\n性进行了比较．结果表明，担载酸的强度明显影响催化剂的活性，酸强\r\n度越大其催化活性越高．用NH3－TPD和异丙醇脱水探针反应表征了二氧\r\n化硅、活性碳和酸性白土三种载体担载的Pd－H4SiW12催化剂的酸性，\r\n并测试了三种催化剂的催化活性．结果表明，载体通过影响担载酸的强\r\n度而影响催化剂的活性，载体上的强酸中心越多，催化剂的活性越高．\r\n测定了二氧化硅、活性碳和酸性白土三种载体担载的Pd－H4SiW12催化\r\n剂上Pd的分散度，并与其催化活性相关联．结果表明，决定乙烯直接氧\r\n化生成乙酸反应活性的主要因素是催化剂的酸强度而不是Pd的分散度．

Effect of Support and Acidity of Catalyst on Direct Oxidationof Ethylene to Acetic Acid

The direct oxidation of ethylene to acetic acid over Pd acid/support catalysts in a fixed bed reactor was studied. The results showed that when the phospho tungstic acid (H 3PW 12 ), phospho molybdic acid (H 3PMo 12 ), phosphoric acid, sulfuric acid, silicotungstic acid (H 4SiW 12 ) or its soldium salts were supported on Pd/SiO 2, the acid strength influences the catalytic activity strongly, and the catalyst with stronger acid strength has higher activity. The acidity of Pd H 4SiW 12 catalysts supported respectively on SiO 2, activated carbon (AC), and acid clay (ACy) was characterized by NH 3 TPD and i C 3H 7OH dehydration. The results showed that the supports affect the catalytic activity through influencing the acid strength. The more the strong acid sites on catalyst, the higher the catalytic activity. When the silica, AC or ACy was used as support, the influence of Pd dispersion determined by hydrogen adsorption on the catalytic activity can not be observed. Therefore, it can be deduced that the decisive factor to the activity of catalysts is the acid strength but not the Pd dispersion.