Co-Al_(2)O_(3)高效催化CO_(2)氧化乙苯脱氢制苯乙烯

Highly efficient Co-Al_(2)O_(3) catalysts for oxidative dehydrogenation of ethylbenzene to styrene with CO_(2)

采用溶胶-凝胶法制备了不同Co含量的nCo-Al_(2)O_(3)催化剂(n=2%、5%、10%、15%、20%),研究了Co含量对催化剂结构和CO_(2)氧化乙苯脱氢性能的影响。结果发现,nCo-Al_(2)O_(3)催化剂上孤立的Co^(2+)离子与催化活性具有良好的对应关系,表明孤立的四面体Co^(2+)物种是其活性位点。Co-Al_(2)O_(3)催化剂上的Co物种结构和催化性能与Co含量相关。Co含量较低(≤10%)时,催化剂上优先形成孤立的四面体Co^(2+)物种;随着Co含量的增加,孤立的Co^(2+)位点增加,催化剂活性随之提高。Co含量较高(>10%)时,催化剂上形成Co_(3)O_4晶体颗粒,导致孤立的Co^(2+)位点减少,催化剂活性降低。10Co-Al_(2)O_(3)表现出最佳催化性能,550℃下乙苯转化率达64.4%,苯乙烯选择性为99.3%,反应30 h后,催化剂仍无明显失活,表明孤立的Co^(2+)活性位点具有良好的结构稳定性和优异的抗积炭性能。

nCo-Al_(2)O_(3) catalysts with different Co contents(n=2%,5%,10%,15%,20%)were prepared by a sol-gel approach.The effect of Co content on the nCo-Al_(2)O_(3) catalyst structure and performance in the oxidative dehydrogenation of ethylbenzene to styrene by CO_(2) was investigated.The results showed that the isolated Co^(2+)ions on the nCo-Al_(2)O_(3) catalysts had a positive influence on the catalytic activity,where the isolated tetrahedral Co species were considered as the active sites.Co contents on the Co-Al_(2)O_(3) catalyst greatly affected the structure of Co^(2+) species and the catalytic performance.The isolated tetrahedral Co^(2+) species are preferentially generated on the resultant nCo-Al_(2)O_(3) catalyst when the content of Co(n)is less than 10%;as a result,an increase of Co content here 2 leads to the formation of more isolated Co^(2+) sites and then improves the catalytic activity of nCo-Al_(2)O_(3) in the dehydrogenation of ethylbenzene.When Co content exceeded 10%,crystalline Co_(3)O_(4) particles were obtained on the formed catalyst,which resulted in the decline of the isolated Co^(2+)sites and catalytic activity.Among various nCo-Al_(2)O_(3) catalysts,10Co-Al_(2)O_(3) exhibited the best catalytic performance,with 64.4%conversion rate for ethylbenzene and 99.3%selectivity for styrene at 550℃.This catalyst remained stable without obvious deactivation for 30 h of 2 reaction,which suggests that the isolated Co+species as active sites presented excellent structural stability and excellent anti-coke deposition.