Ca对Cu/B/Ca/Al_2O_3结构及其催化醋酸仲丁酯加氢反应性能的影响

Effects of Ca on the Structure of Cu/B/Ca/Al_2O_3 and Its Catalytic Performance in the Hydrogenation of sec-Butyl Acetate

以γ-Al2O3为载体采用分步浸渍法制备了不同Ca O含量的Cu/B/Ca/Al2O3催化剂,并测试了其催化醋酸仲丁酯加氢制备仲丁醇的反应性能.Ca O含量对催化剂的结构、氧化还原性能、酸碱性和金属铜分散度的影响分别采用XRD、H2-TPR、XPS、NH3-TPD和N2O-H2氧化还原滴定实验进行分析.结果表明,适量氧化钙的引入对金属铜的分散度无明显影响,过量的氧化钙(>20%)降低催化剂的比表面积,进而导致金属铜分散度的降低;但钙作为给电子助剂能够补偿电子从铜向氧化硼之间的迁移,提高催化剂的酯加氢活性.同时,氧化钙的引入能够有效消除Cu/B/Ca/Al2O3催化剂表面的强酸性位点并降低催化剂的酸量,减少醋酸仲丁酯加氢反应中酸催化副产物以及催化剂表面积碳的生成.

A series of Cu / B / Ca / Al2O3 catalysts with different Ca O contents were prepared by the wet impregnation step by step and studied in the hydrogenation of sec-butyl acetate to sec-butanol. Effects of Ca O contents on the c atalyst structure,reducibility,acidity and the dispersion of metallic copper were evaluated by XRD,H2-TPR,XPS,NH3-TPD and N2O-H2 redox titration,respectively. It was shown that a low content of Ca O in the catalyst had little influence on the dispersion of copper,but the high loading of Ca O( > 20%) reduced the surface area of catalyst greatly and led to a worse dispersion of copper. However,calcium as an electron-denoting element could compensate effectively the electron withdrawing from copper to B2O3,improving the catalytic activity for the hydrogenation of esters. Moreover,addition of Ca O could eliminate the strong acid sites on the surface of Cu / B / Ca / Al2O3 and reduce its total amount of acid,resulting in the lower acid-catalyzed products,as well as the less carbon deposition on the catalyst surface.