CaO对Cu-ZnO-ZrO_2催化CO_2加H_2合成甲醇性能影响

Effect of CaO on the performance of Cu-ZnO-ZrO_2 catalyst for methanol synthesis from CO_2 and H_2

用CaO作为改性助剂,采用并流共沉淀法制备了CuO∶ZnO∶ZrO_2为5∶4∶1(物质的量比),CaO添加量为0、1%、2%、4%、8%、16%(摩尔分数)的六组催化剂。用X射线衍射(XRD)、微商热重(TG-DTG)、傅里叶红外(FT-IR)、N2吸附脱附(BET)、X射线光电子能谱(XPS)、氢气程序升温还原(H_2-TPR)、CO_2程序升温脱附(CO_2-TPD)、NH_3程序升温脱附(NH_3-TPD)对催化剂进行了表征。用自制固定床评价了催化剂活性。结果表明,添加CaO后,催化剂路易斯酸性和表面碱性增强;催化剂母体中高温碳酸盐含量增加,热稳定性增强,CuO颗粒粒径变小,Cu-Zn协同作用增强,Cu比表面积增大,分散性变好。催化剂活性受到表面酸碱性、铜比表面积、Cu-Zn协同作用和铜分散性共同影响。当CaO为2%时,铜比表面积为79.3 m2/g、铜分散度为34.8%、CO_2转化率为24.55%、甲醇选择性为19.01%、甲醇收率为0.044 g/(gcat·h),催化剂活性最好。过量CaO占据催化剂孔道和覆盖表面活性位,使催化剂路易斯酸性和表面碱性过强,CuO与H_2有效接触减少,CO_2难以脱附,催化活性下降。因此,适量CaO(2%)添加可促进CO_2加氢反应合成甲醇。

CuO ∶ Zn O ∶ Zr O2= 5 ∶ 4 ∶ 1（ molar ratio） catalysts were prepared with CaO doping of 0,1%,2%,4%,8%,16%（ molar fraction） by cocurrent-flowco-precipitation. X-ray diffraction（ XRD）,thermal analysis（ TG-DTG）,Fourier infrared（ FT-IR）,N2 adsorption desorption（ BET）,X-ray photoelectron spectroscopy（ XPS）,hydrogen temperature programmed reduction（ H_2-TPR）,CO_2 temperature programmed desorption（ CO_2-TPD） and NH_3 temperature programmed desorption（ NH_3-TPD） were used to characterize the catalysts.The catalyst activity was evaluated with a lab-made fixed bed reactor. Results showthat CaO doping enhances Lewis acid and surface alkaline of the catalyst,increases the amount of high temperature carbonate in the catalysts,improves the thermal stability,reduces the CuO particle size,enhances the synergistic effect of Cu-Zn,increases the Cu specific surface area and the Cu dispersion. The catalyst activity is influenced by the surface acidity,the specific surface area of copper,the synergistic effect of Cu-Zn and the dispersion of copper. When the doping amount of CaO is 2%,the copper specific surface area is 79.3 m2/ g,the dispersion degree of copper is 34.8%,the CO_2 conversion is 19. 01%,the selectivity of methanol is 24. 55% and the yield of methanol is0.044 g /（ gcat·h）,catalyst activity is the highest. With the amount of CaO increasing,the excessive CaO occupies the catalyst pore and covers the surface active sites,the Lewis acid and the surface alkaline of the catalysts become so strong that the effective contact of CuO and H_2 is reduced,CO_2 is difficult to desorb,resulting in decrease of catalytic activity. Therefore,the proper doping amount of CaO（ 2%） can promote the synthesis of methanol through CO_2 hydrogenation.