对苯二甲酸加氢精制Pd/C催化剂失活原因探讨

对取自扬子石油化工股份有限公司对苯二甲酸加氢反应器上、中、下部3种不同失活程度的Pd／C催化剂在模拟工业条件下进行了活性评价，采用ICP，XPS，XRD，TEM等分析手段对其进行表征，并与新鲜催化剂进行了比较。结果表明，失活催化剂的Pd含量比新鲜催化剂有了明显的下降，且上部催化剂下降更突出；失活催化剂的平均晶粒明显长大，分散度降低。说明造成本批催化剂失活的主要原因是Pd流失及催化剂表面Pd含量的降低、Pd晶粒的长大以及杂质Cr含量的增加。

DEACTIVATION OF Pd/C CATALYST FOR PURIFICATION OF TEREPHTHALIC ACID

The deactivation behavior of Pd/C catalyst was different in the various sites of the reactor of the terephthalic acid purification unit in Yangzi Petrochemical Company. Three catalyst samples collected from the upper, middle and lower parts of the reactor and a fresh catalyst sample were evaluated in an autoclave reactor simulating the commercial operating conditions. The samples were also investigated by ICP, XPS, XRD and TEM. The ICP results showed that the palladium contents of the samples collected from the upper, middle and lower parts were 0.33%, 0.38% and 0.46%, respectively. They were all lower than the palladium content of the fresh catalyst sample (0.5%), indicating there was loss of palladium during the operation. The XPS analysis showed an obvious decrease of palladium content on the surface of the deactivated catalyst sample, especially the sample collected from the upper part. The results of XRD and TEM showed that the metal dispersion of the deactivated catalyst samples was poor and the average crystal size of palladium increased significantly. In summary, the loss of palladium, the decrease of surface palladium content, the growth of palladium crystal size and the poor metal dispersion, as well as the increase of impurities, such as chromium, were the main reasons of the deactivation of Pd/C catalyst used in the terephthalic acid purification unit of Yangzi Petrochemical Company.