镍催化剂的结构特征及其催化甲烷二氧化碳重整反应

Structural characterization of Ni catalyst and its catalytic performance for methane reforming with CO_2

采用超声辅助沉淀法制备了ZrO_2载体,并制备了一系列Ni/ZrO_2催化剂用于甲烷二氧化碳重整反应制合成气。利用XRD、N_2吸附、TPR和H_2-TPD等方法对催化剂进行了表征,并研究了催化剂还原过程中Ni物种结构的变化。实验结果表明,Ni/ZrO_2催化剂的最佳Ni负载量约为10%(w),过高或过低的Ni含量都不利于形成最大数量的活性Ni原子。还原态Ni/ZrO_2催化剂表面存在两种金属Ni活性中心,处于金属Ni外表面平台位置的活性中心转化甲烷分子的效率较低,处于金属Ni台阶或节点位置的活性中心转化甲烷分子的效率较高。在反应温度750℃、反应压力0.1 MPa、气态空速108 000 mL/(g·h)、n(CH_4)∶n(CO_2)=1∶1的条件下,Ni/ZrO_2催化剂上金属Ni活性中心转化甲烷分子的转化频率为12.2～13.5 s^(-1)。

A ZrO2 support was prepared by the method of ultrasonic-assisted precipitation,and then was used in the preparation of Ni/ZrO2 catalysts for CO2 reforming of methane(CRM)to syngas.The Ni/ZrO2 catalysts were characterized by means of XRD,N2 adsorption,H2-TPR and H2-TPD.The effects of the reduction process on the structural characteristics of the Ni species were researched.The results showed that the optimum Ni loading for the Ni/ZrO2 catalysts was about 10%(w)and more or less Ni loading was harmful for getting the maximum number of active Ni atoms.Two kinds of Ni active sites were discovered in the reduced Ni/ZrO2 catalysts.The first kind of active Ni atoms was located at the terrace of Ni particles,with low catalytic conversion efficiency in CRM reaction.The second kind of active sites was situated on the steps or kinks of the Ni particles,and could converse methane molecules efficiently.Under the reaction conditions of 750℃,0.1 MPa,n(CH4)∶n(CO2)1∶1 and GHSV 108 000 mL/(g·h),the turn-over-frequency of Ni active sites in the Ni/ZrO2 catalysts was in the range of 12.2-13.5 s^-1.