Preparation of highly dispersed Ru/Si3N4 catalysts and their application in CO2 hydrogenation
Silicon nitride is an excellent catalyst support with high hydrothermal and mechanical stability.The amino groups on its surface can effectively anchor metals,significantly enhancing metal dispersion.However,commercial silicon nitride has a relatively low surface area,limiting its effectiveness in metal dispersion.Therefore,high-surface-area self-prepared silicon nitride(Si3N4)was used as a support to prepare catalysts(0.5%Ru/Si3N4,1.0%Ru/Si3N4 and 2.0%Ru/Si3N4,respectively)with different Ru loadings(0.5%,1.0%,and 2.0%by mass fraction,respectively)via the impregnation method.Additionally,2.0%Ru/Si3N4-C catalyst was prepared using commercial silicon nitride(Si3N4-C)as a control.Physicochemical properties of the catalysts were characterized,and their activities in the CO2 hydrogenation reaction at 300℃and 0.1 MPa were tested.The results show that compared with Si3N4-C,Si3N4 has a higher surface area(502 m2/g),significantly improving metal dispersion and reducing metal particle size.Si3N4-based catalysts expose more active sites.The metal particle size of 0.5%Ru/Si3N4 is small,and the catalyst exhibits strong H2 adsorption capacity,and thus H is difficult to desorption,which inhibits the hydrogenation of CO intermediates to CH4.As the Ru loading increases,the metal particle size increases,and the CH4 selectivity of the catalysts is better.Among the Ru/Si3N4 catalysts,2.0%Ru/Si3N4 shows higher CH4 selectivity(98.8%).At a space velocity of 10000 mL/(g·h),the CO selectivity of 0.5%Ru/Si3N4 is 88.2%.Compared with 2.0%Ru/Si3N4,2.0%Ru/Si3N4-C has larger metal particle size,fewer active sites,and lower activity.The CO2 conversion rates of 2.0%Ru/Si3N4 and 2.0%Ru/Si3N4-C are 53.1%and 9.2%,respectively.Si3N4 effectively improves metal dispersion,enhancing the catalytic activity in CO2 hydrogenation.By adjusting the Ru loading to control the metal particle size of the catalyst,the selectivity of the product CO or CH4 can be controlled.
CO2 hydrogenationRu/Si3N4 catalystsCH4 selectivityCO selectivity
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