助剂对ZnO/ZrO_(2)物化性质及催化性能的影响

Effect of promoter on physicochemical properties and catalytic performance of ZnO/ZrO_(2)

CO_(2)加氢制甲醇是实现碳中和目标的有效途径。尽管已报道的ZnO/ZrO_(2)催化剂具有高活性和稳定性,但其催化性能仍有望进一步提高。采用浸渍法制备得到一系列不同元素掺杂的Ma-ZnO_(x)/ZrO_(2)催化剂,并通过评价发现只有Ga促进了ZnO/ZrO_(2)催化剂催化CO_(2)加氢制甲醇。其中,5%Ga-ZnO_(x)/ZrO_(2)催化剂表现出优异的催化性能,在反应条件:P=3 MPa、T=320℃、V(H_(2))∶V(CO_(2))=4∶1、气体质量空速(WHSV)=24 000 mL/(g·h)时CO_(2)转化率为7.2%,甲醇选择性为81.0%,甲醇时空产率可达410 mg/(g·h),是ZnO/ZrO_(2)的1.26倍,且在反应100 h内催化性能无明显衰减。X射线光电子能谱(XPS)和电子顺磁共振(EPR)表征发现,适量Ga助剂的掺入可以促进催化剂中氧空位的形成。H_(2)程序升温还原(H_(2)-TPR)、CO_(2)/H_(2)程序升温脱附(CO_(2)/H_(2)-TPD)结果表明,Ga助剂的掺入增强了ZnO/ZrO_(2)催化剂活性位点的活性,Ga-ZnO_(x)/ZrO_(2)催化剂表现出更强的CO_(2)和H_(2)吸附活化能力。原位漫反射傅里叶变换红外(in situ DRIFTS)结果表明,各催化剂合成甲醇均遵循甲酸盐-甲氧基路径,Ga助剂的掺入促进了甲醇中间体的形成,并且更有利于HCOO*物种向CH3O*物种的转化,从而提高甲醇产率。

CO_(2) hydrogenation to methanol is an effective way to achieve the goal of carbon neutrality.Although the reported ZnO/ZrO_(2) catalysts have high activity and stability,their catalytic performance are expected to be further improved.A series of Ma-ZnO_(x)/ZrO_(2) catalysts with different elements doping were prepared by the impregnation method,and it was found by evaluation that only Ga promoted the catalytic CO_(2) hydrogenation to methanol by ZnO/ZrO_(2) catalyst.Among them,5%Ga-ZnO_(x)/ZrO_(2) catalyst showed excellent catalytic performance.At the reaction conditions:P=3 MPa,T=320℃,V(H_(2))∶V(CO_(2))=4∶1 and gas weight hourly space velocity(WHSV)=24000 mL/(g∙h),the CO_(2) conversion of 5%Ga-ZnO_(x)/ZrO_(2) catalyst was 7.2%,the methanol selectivity was 81.0%and the methanol spacetime yield was up to 410 mg/(g∙h),which was 1.26 times higher than that of the ZnO/ZrO_(2).And there was no significant decay in the catalytic performance within 100 h of reaction.X-ray photoelectron spectrometry(XPS)and electron paramagnetic resonance(EPR)characterization showed that doping with the appropriate amount of Ga promoter could promote the formation of oxygen vacancies in the catalyst.H_(2) temperature programmed reduction(H_(2)-TPR),temperatureprogrammed desorption of the preabsorbed CO_(2)/H_(2)(CO_(2)/H_(2)-TPD)results showed that the doping of the Ga promoter enhanced the activity of the active sites of the ZnO/ZrO_(2) catalyst,and the Ga-ZnO_(x)/ZrO_(2) catalyst exhibited a stronger capacity for the adsorption and activation of CO_(2) and H_(2).The in situ diffuse reflectance infrared Fourier transform spectroscopy(in situ DRIFTS)results showed that the synthesis of methanol by each catalyst followed the formatemethoxy pathway,and the incorporation of Ga promoter facilitated the formation of methanol intermediates and was favorable for the conversion of HCOO*species to CH3O*species,thus improving the methanol yield.