Zn对Cu-Zn-Al催化乙酸甲酯加氢反应的影响

采用共沉淀法制备Cu-Zn-Al催化剂,采用XRD、N₂等温吸附-脱附、SEM、H₂-TPR、XPS和ICP-OES等手段对催化剂进行表征。结果发现,Zn的加入降低了Cu-Zn-Al催化剂颗粒的团聚程度,提高了活性中心Cu组分的分散度。并且Zn含量的改变可以影响Cu组分的价态分布,进而影响其催化性能。当n(Cu)/n(Zn)=2/3时,n(Cu⁺)/n(Cu⁰)为1.04,Cu-Zn-Al对乙酸甲酯(MA)加氢反应具有最优的催化性能。在反应温度为240℃、反应压力为3.0 MPa、n(H₂)/n(MA)=20的最优条件下,Cu-Zn-Al催化乙酸甲酯反应中乙酸甲酯转化率为98.8%,甲醇和乙醇选择性分别为99.4%和98.7%。对Cu-Zn-Al催化剂进行300 h寿命测试,乙酸甲酯转化率一直稳定在98%以上,甲醇和乙醇选择性则分别保持在99%和98%左右。

Effect of Zn on Catalytic Performance of Cu-Zn-Al in the Hydrogenation of Methyl Acetate

Cu-Zn-Al catalysts were prepared by co precipitation method and characterized by XRD, N2 isothermal adsorption-desorption, SEM, H2-TPR, XPS and ICP-OES. Results indicate that the agglomeration of catalyst particles is reduced by the addition of Zn, obtaining the highly dispersed Cu active sites. Furthermore, the valence of Cu species in Cu-Zn-Al catalysts was also changed with the increase of Zn content. When the molar ratio of Cu/Zn is 2/3, the molar ratio of Cu+/Cu0 in the catalyst is 1.04 with a high activity in methyl acetate (MA) hydrogenation. The reaction conditions were optimized over Cu-Zn-Al catalyst with 2/3 of Cu/Zn molar ratio, as listed in following: reaction temperature of 240 ℃, reaction pressure of 3.0 MPa, and H2/MA molar ratio of 20. Under the optimal conditions, MA conversion is 98.8%, and ethanol and methanol selectivity is 98.7% and 99.4%, respectively. Importantly, Cu-Zn-Al catalyst shows excellent catalytic activity and stability in MA hydrogenation reaction. After 300 h operation, MA conversion maintains more than 98% with the selectivity of ethanol and methanol above 98% and 99%, respectively.