Study On The Reverse Water Gas Conversion Reaction Of Alkali Modified Molybdenum Disulfide Catalyst

The preparation of chemical raw materials and chemicals by CO₂hydrogenation can not only achieve carbon emission reduction,but also make effective use of cheap CO₂resources.It is of great interest to convert inert CO₂molecules into reactive CO molecules by using inverse hydrogas conversion reaction,and then prepare high value-added chemicals.In this study,S-vacancy-rich layered Mo S₂was prepared by hydrothermal method,and K-modified Mo S₂catalysts were synthesized after impregnation with alkali metals.The comparative evaluation of the performance of catalysts with different potassium loadings for the inverse water gas change reaction was carried out,and the effect of reaction conditions was studied.The crystal structure,composition,morphology,specific surface area and reduction properties of the catalysts were characterized by XRD,BET,ICP,OEA,TEM,XPS and hydrogen programmed temperature rise reduction（H₂-TPR）to reveal the conformational relationships of the catalysts.The mechanism of hydrogenation reaction was revealed by CO₂/CO programmed temperature rise desorption（CO₂/CO-TPD）,in situ diffuse reflectance Fourier infrared test（DRIFTS）,and density flooding theory calculation（DFT）.The main findings are as follows:1.In this paper,Mo S₂catalysts with K/Mo of 0,0.05,0.15,0.4,0.72 and 0.87 were prepared.After comparison experiments,it was found that at H₂:CO₂=3:1,4MPa,300°C and20,000 m L g^-1h^-1,the catalyst without K addition was mainly methane based with a selectivity of about 81%,and the catalyst with K addition was mainly CO,and the selectivity could reach more than 95%,indicating that the introduction of potassium regulated the product selectivity.The catalyst with K/Mo of 0.72 had the highest CO selectivity of 98.6%and the lowest reaction activation energy of 41.54 k J/mol,and the CO₂conversion reached36.9%under the reaction conditions of 4 MPa,400°C,and 20,000 m L g^-1h^-1.The stability experiments for 500 h showed that under the reaction conditions of high temperature and high pressure and high air velocity(450°C,4 MPa,180,000 m L g^-1h^-1),the CO₂conversion can be maintained above 41%and the CO selectivity above 95%,which portends good prospects for industrial applications;2.The characterization using XRD,BET,ICP,OEA,TEM,XPS,and hydrogen programmed temperature rise reduction（H₂-TPR）revealed that K modified the active center,which promoted the catalyst reduction and increased the crystalline plane spacing of Mo S₂.Among them,the potassium-modified catalysts with K/Mo of 0.72 exhibited the largest crystalline surface spacing and fewer stacking layers,which allowed the base planes to be fully exposed and activated,which was beneficial to improve the catalytic performance,but the introduction of K reduced the catalyst specific surface area and caused some Mo S₂to form Mo O₂,which reduced the number of active centers.However,Mo O₂can play the role of structural auxiliary,stabilizing the molybdenum sulfide phase and exhibiting high stability.K/Mo=0.72 catalyst thus exhibits high intrinsic activity,high selectivity and high temperature stability.3.The CO₂/CO programmed temperature desorption（CO₂/CO-TPD）,in situ diffuse reflectance infrared（DRIFTS）demonstrated that potassium loading promoted the activation of CO₂on the catalyst surface and reduced the adsorption capacity of CO,facilitating the conversion of CO₂,and the desorption of the product CO.Density flooding theory（DFT）calculations show that the base-plane S vacancy K modification lowers the reaction potential barrier,which facilitates the hydrogenation of carboxylate to CO and promotes the inverse water gas reaction,while the source of CH₄is more inclined to the hydrogenation of carboxylate.The results of the theoretical calculations reveal that the inverse water gas conversion reaction of potassium-modified molybdenum sulfide-based catalysts follows the intermediate species decomposition mechanism.