Study On The Structure-property Relationship Of Ni-based Catalysts For Catalytic Hydrogenation Of Carbon Monoxide

Mineral heat smelting is a metal smelting and non-metal smelting method commonly used in the metallurgical and chemical industries,with various smelting methods and complex waste gas characteristics,containing a variety of toxic and harmful gases,which is a high energy consumption and high pollution industry.Among them,metal and non-metallic metallurgy reduction smelting tail gas are rich in carbon monoxide（CO）,which can be used as the raw material gas for carbon mono-chemicals.CO hydrogenation to different chemicals such as alcohols,acids,and methane（CH₄）is among the promising routes for the conversion and utilization of reducing impurity gases.Among them,nickel-based catalysts have been widely used in hydrogenation experiments in recent years due to the advantages of good catalytic activity,simple preparation,and low price.However,impurity gases such as organic sulfur（mainly including carbon disulfide（CS₂）,carbonyl sulfide（COS）,and methanol sulfur（CH₃SH））coexisting in the exhaust gas can lead to the deactivation of Ni-based catalysts.Therefore,in this thesis,nickel-based catalysts were investigated to further investigate the toxic effects of organosulfur based on revealing the structure-property relationships of CO hydrogenation,and finally,the toxicity resistance of the catalyst was improved by the modification of rare earth metals.The conclusions of the study are as follows:Firstly,the effect of catalysts with different crystalline alumina on the hydrogenation effect of CO was experimentally investigated.It is shown that Ni/γ-Al₂O₃has the best effect on CO hydrogenation;Then the effect of different Ni loadings on the CO hydrogenation effect was experimentally investigated.The study showed an optimal value of Ni loading,the CO hydrogenation performance of 20%Ni/Al₂O₃is better,and the selectivity of C₂₊produced at 250℃is significantly higher than that of other catalysts.And when the Ni loading is further increased,the Ni O gradually agglomerates and too high loading will cover the active site,thus inhibiting the CO hydrogenation performance.Secondly,the experiments investigated the effect of pretreatment conditions on the hydrogenation effect of CO.After evaluating the cyclic experiments with fresh samples of Ni₂₀/Al₂O₃,CO conversion,CH₄selectivity and C₂₊selectivity were found to be significantly increased,and it was speculated that the morphology of nickel,the active component of the catalyst,might be changed due to hydrogen in the reaction gas,so the mechanism of the effect was investigated using hydrogen pretreatment at different temperatures（200°C,400°C,600°C and 800°C）,and the results showed that the catalyst with hydrogen reduction at 600°C had the best performance for CO hydrogenation.The characterization results by X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,and high-resolution transmission electron microscopy（HRTEM）revealed that after hydrogen reduction at different temperatures,different sizes of metallic nickel appeared on the catalyst,which affected the CO hydrogenation reaction pathway and ultimately the reaction activity and product selectivity.Finally,the toxic effect of the coexistence of organosulfur（CS₂）impurity components on the catalyst was investigated,and the catalyst resistance to poisoning was improved by the addition of the additive lanthanum.The results show that the addition of the additive La is beneficial to improve the activity and stability of the catalyst.By XPS characterization,the results show that La₂O₃can be partially reduced from La₂O₃to La₂O_x（x<3）during the preparation of the catalyst,and La₂O_xcan be used as an electron donor to transfer some electrons to nickel,which is a key factor to improve the catalytic activity.Studies on the mechanism of sulfur poisoning have shown that the metallic nickel in the deactivated catalyst disappears and is converted into sulfur-nickel compounds,which leads to the disappearance of the active center of the CO hydrogenation reaction and the hydrogenation reaction does not proceed properly.