Study On Non-noble Metal Catalysts For Catalytic Reduction Of CO₂

Since the 19th century,the development of steel,coal and other industries,as well as the application and promotion of internal combustion engine,need to consume a lot of fossil fuels to provide energy and power.With the rapid development of economy,a lot of carbon dioxide(CO2)has been emitted into the atmosphere,which brings huge burden to the environment and potential irreversible threat to human society.One way to achieve a closed carbon-loop is to capture carbon dioxide from the emission source and then convert it into chemical raw materials and fuels through thermal catalytic hydrogenation reduction or electrochemical reduction,which is feasible in practice.However,up to now,the equilibrium conversion rate and equilibrium selectivity of specific products of catalytic CO2 reduction technology are still not very ideal.Therefore,the key scientific problem of optimizing CO2 reduction technology is how to design a catalyst with high activity and high selectivity for catalytic conversion of CO2.This thesis focuses on the modified design of non-noble metal catalysts to study their effects on the catalytic activities of electrocatalysis CO2 reduction and CO2 hydrogenation.In this thesis,metal doping,in-situ formation of defects on the surface of the catalyst,synthesis of a single active site and other means are used to inhibit the occurrence of side reactions and improve the catalytic ability of the catalyst for CO2 conversion at the same time.The main contents of the research are as follows:(1)Sn doped CuO nanosheets(Sn-doped CuO(Vo))were prepared by adding Sn precursor during the synthesis of CuO nanosheets.The results of various characterizations in this paper showed that Sn was doped into the crystal lattice of CuO in the form of atoms and a large number of oxygen defects were found on Sn-doped CuO(Vo).The electrochemical activity of the catalysts before and after doping was tested,the Faraday efficiency of electrocatalytic reduction of CO2 to C2H4 on Sn-doped CuO(Vo)reached 48.5%± 1.2%,which was significantly better than that of commercial CuO,Cu2O,undoped CuO and Sn doped CuO without Vo(Sn-CuO).Compared with pure CuO,the C2H4 bias current density of Sn-doped CuO(Vo)is increased by 2.3 times,and had good stability.Sn doping on the surface of Sn-doped CuO(Vo)can reduce the dimer barrier of adsorbed reaction intermediate*CO and promote carbon-carbon coupling to produce ethylene,which was proved by the results of density functional theory calculation.(2)Using ammonium heptamolybdate as the precursor,the Mo single atoms riveted on 2D nitrogenous carbon materials catalyst(Mo-NC)was synthesized by a very simple method and used to catalytic CO2 hydrogenation.The results of various characterizations in this paper showed that Mo is uniformly distributed on the surface of 2D nitrogenous carbon materials as a single active site.The catalyst was loaded into a fixed bed reactor for CO2 hydrogenation.It was found that the catalyst had excellent catalytic effect on reverse water-gas shift(RWGS).Compared with molybdenum carbide(Mo2C),a common molybdenum based catalyst for RWGS,Mo single atom catalyst had better CO2 turnover frequency(TOF),reaching 1260 mmolCO2·molMo-1·min-1 at 500℃.In addition,Mo-NC can also inhibit the methanation of CO2,and the selectivity of CO product was close to 100%.After 68 h activity test,Mo-NC still maintained a good catalytic effect.