Ce_(x)Zr_(1-x)O_(2)/Co/C-N催化CO_(2)加氢性能研究

The Study of CO_(2)Hydrogenation Activity over Ce_(x)Zr_(1-x)O_(2)/Co/C-N Catalysts

将不同比例的铈锆前驱体负载到ZIF-67,氮气气氛焙烧制备Ce_(x)Zr_(1-x)O_(2)/Co/C-N催化剂,对催化剂进行了XRD、H_(2)-TPR、XPS表征,并在固定床反应器评价其CO_(2)加氢制甲醇性能.XRD结果表明,在铈中加入适量锆形成铈锆固溶体,铈锆固溶体与钴物种较强的相互作用力可以阻止表面金属Co的氧化.但过量加入的锆又会削弱这一作用力,部分金属Co被氧化为Co_(3)O_(4).H_(2)-TPR结果表明适量的锆的加入改善催化剂的还原性能,催化剂还原温度降低.XPS证实了25%Ce_(0.67)Zr_(0.33)O_(2)/Co/C-N催化剂中含有更多的氧空穴及氮含量,氧空穴和碱性氮都有利于CO_(2)的解离吸附.优化后的25%Ce_(0.67)Zr_(0.33)O_(2)/Co/C-N催化剂在225℃,2 MPa,GHSV=6 L·g^(-1)_(cat)·h^(-1)反应条件下取得最高甲醇时空收率,为3.0 mmol·g^(-1)_(cat)·h^(-1).

A series of Ce_(x)Zr_(1-x)O_(2)/Co/C-N catalysts are prepared with calcination of ZIF-67 supported different ratio of Ce/Zr precursor at N_(2)atmosphere.The catalysts are characterized with XRD,H_(2)-TPR and XPS,and their methanol synthesis activity of CO_(2)hydrogenation is studied in a fixed bed reactor.Ce_(0.75)Zr_(0.25)O_(2)solid solution is formed when Zr is added into Ce.The strong interaction between Ce_(0.75)Zr_(0.25)O_(2)solid solution and Co prevents the oxidation of metal Co on the surface of catalysts,however,too much addition of Zr will weak this interaction,Co species will be oxidized into Co_(3)O_(4)again.H_(2)-TPR results confirm that the addition of Zr decreases the reduction temperature of catalyst and improves the catalyst activity.25%Ce_(0.67)Zr_(0.33)O_(2)/Co/C-N has the highest content of oxygen vacancies and nitrogen element from XPS results,which both take advantage of CO_(2)dissociative adsorption.The highest methanol space-time yield of 3.0 mmol/g_(cat)/h is obtained with 25%Ce_(0.67)Zr_(0.33)O_(2)/Co/C-N at the reaction condition T=225℃,P=2 MPa,GHSV=6 L/g_(cat)/h.