Preparation Of MgO-Nd₂O₃ Modified Ni/ZrO₂ Catalyst And Its Performance In Carbon Dioxide Methanation

The excessive utilization of fossil energy has promoted the development of modern chemical industry.At the same time,it emits a large number of greenhouse gases such as CO₂,which significantly increased the burden of the environment.Therefore,researchers have increasingly strengthened the investigation on the recovery and resource utilization of CO₂.Reducing CO₂into methane and other high value-added chemicals is an effective way to synthesize chemical raw materials.CO₂methanation can not only increase the fossil energy reserves,but also effectively reduce carbon emissions.Therefore,it has an important influence in the field of CO₂resource utilization.Nickel has become the most widely used active component in the catalytic reaction of CO₂methanation because of its good activity,less side reactions and low price of raw materials.However,due to the strong exothermic thermodynamic characteristic,high temperature is not conducive to the reaction,hence it is very necessary to design a catalyst with high activity at low temperature and excellent stability at high temperature.In this study,we chose nickel as the active component of the catalyst and zirconia as the carrier.Firstly,the ZrO₂prepared by sol-gel method was used as the carrier to prepare Ni/ZrO₂,which was prepared by impregnation sol-gel method.Simultaneous interpreting the preparation of Ni/ZrO₂with the traditional sol-gel method,the influence of the preparation method on the performance of the catalyst was compared.Subsequently,MgO-ZrO₂carrier was used to prepare Ni/MgO-ZrO₂by impregnation of composite sol-gel method.The effects of the introduction and amount of MgO on the performance of the catalyst were compared.Finally,the MgO-Nd₂O₃-ZrO₂was used as the carrier and the Ni/MgO-Nd₂O₃-ZrO₂prepared by impregnation sol-gel method was compared with Ni/MgO-ZrO₂,Ni/Nd₂O₃-ZrO₂and Ni/ZrO₂.The effects of the combination of MgO and Nd₂O₃ on the performance of the catalysts were compared.The stability and catalytic performance of the catalyst was tested and the catalyst have been characterized by physical and chemical means such as N₂adsorption,X-ray diffraction,scanning electron microscope and transmission electron microscopy.The conclusions are as follows:1.Compared with the Ni/ZrO₂ catalyst prepared by sol-gel method,the Ni/ZrO₂prepared by co-impregnation of Ni active components on the ZrO₂carrier showed better activity.The results showed that the CH₄selectivity and CO₂conversion of Ni/ZrO₂prepared by impregnation composite sol-gel method reached 95.6%and 66.8%respectively,in which the active component Ni was small in size and evenly dispersed.2.The optimum content of MgO and Nd₂O₃in Ni/ZrO₂catalyst prepared by impregnation composite sol gel method is 20 wt.%.The introduction of promoter MgO was conducive to increase the specific surface area,significantly increased the alkaline sites of the catalyst,formed a pore structure,thus increasing the CO₂conversion of NM₂-Z catalyst to 78.16%at 400℃.The promoter Nd₂O₃also affected the specific surface area of the catalyst,increased the weak alkaline sites improved the interaction between metals,and improved the activity of the catalyst f NN2-Z catalyst,so that the CO₂ conversion rate reached76.12%at 350℃.3.When MgO and Nd₂O₃ are introduced into Ni/ZrO₂catalyst simultaneously,not only the specific surface area is suitable,but also the weak and medium alkaline sites are obtained,which have enhanced the Ni dispersion and strong intermetallic interaction,which is beneficial for the CO₂adsorption and conversion,and greatly improve the low temperature conversion of CO₂and the conversion frequency TOF.At the same time,the composite modified catalyst has stable crystal structure.The CH₄selectivity and CO₂conversion are99.35%and 82.13%respectively at 350℃,and the CO₂conversion is stable at 77.0% at 400℃.