Preparation Of Copper-based Bimetallic Catalysts And Their Catalytic Performances For Carbon Dioxide Reduction

The increasing accumulation of carbon dioxide in the atmosphere has caused many environmental and ecological problems in the world,so it is very important to convert carbon dioxide into high value-added chemical raw materials.Carbon monoxide obtained by carbon dioxide reduction can be further used for methanol synthesis and Fischer-Tropsch synthesis.In addition,the adjustability of CO/H₂ ratio is critical to the Fischer-Tropsch reaction.Therefore,the researchers are committed to developing inexpensive catalysts for the easy activation and efficient conversion of carbon dioxide.Copper-based catalysts have been widely studied because of their low cost and excellent performance of carbon dioxide reduction.However,there still exist some problems,such as easy agglomeration at high temperature and competitive hydrogen evolution reaction during electrochemical CO₂ reduction reaction（CO₂RR）.Thus trational design and controllab le preparation of copper-based catalysts need to be further studied.In this master thesis,based on the support effect,the"limited"feature of the metal-organic framework,the additive effect,and the bimetallic synergy,carbon-coated copper-zinc bimetallic nanoparticles on the fumed silica and the co-precipitated copper-cadmium bimetallic oxide were prepared and investigated for carbon dioxide thermal reduction and electroreduction,respectively.Synthetic parameters and performance evaluation were optimized by combination of all kinds of measurements and catalytic performance testings.Finally,the relationship of catalyst structure and its activity was explored and t he catalytic mechanism of the catalyst for CO₂ reduction was revealed.The main research contents are as follows:（1）Cu/Zn O-based catalyst modified by trimesic acid and its performances for CO₂ hydrogenation reduction.Trimesic acid（H₃BTC）was used to assemble and regulate Cu and Zn O components in the catalyst via its abilities of coordination and acid etching.Firstly,C u-HKUST-1 was synthesized by the self-assembly of H₃BTC and copper ions,which limited the sintering and agglomeration of C u nanoparticles in the subsequent carbonization and self-reduction process.Secondly,H₃BTC as an organic acid could etch Zn O nanoparticles to form a complex of H₃BTC and Zn ions to redisperse Zn species.Under the dual action of H₃BTC,carbon-coated bimetallic nanoparticles with a size of 2～6 nm could be obtained on the fumed silica through pyrolysis at high temperature.The prepared C u@C-Zn O/Si O₂ catalyst can achieve31.4%CO₂ conversion and 99%CO selectivity for RWGS reaction in a fixed bed reactor at 400°C and 3 MPa.Besides,it was also found that the molar ratio of Cu/Zn,composition and the introducing order of H₃BTC all affected the catalytic activity.This study provides an excellent strategy for the design and synthesis of catalysts containing copper and zinc components.（2）Preparation of copper-cadmium bimetallic oxide catalyst and its performances for CO₂RR.In the optimized preparation conditions,a series of C u_xCd_1-x（x=1,0.9,0.7,0.5,0.3,0.1,0）bimetallic oxide catalysts were synthesized by a parallel flow co-precipitation method.When x=0.5,the prepared Cu_0.5Cd_0.5 catalyst displayed peanut shape with a relatively uniform size.The results showed that the peanut-shaped catalyst was composed of Cu O and Cd O,which was beneficial to increase the activity of electrochemical reduction of CO₂ to CO,and could achieve88.4%CO faradaic efficiency at-0.86 V.In addition,the molar ratio of CO/H₂ could be tuned in a wide range（0.07～10.00）at a certain constant voltages（-1.16 V～-0.56V）by controlling the molar ratio of C u to Cd elements,which was attributed to the synergistic effect between interfaces of Cu O and Cd O oxides.The testing results showed that the existence of Cd O could increase the alkaline sites of the catalyst to improve the selectivity of CO,while Cu O could provide a higher capacitance environment.The peanut-shaped copper-cadmium bimetallic oxide catalyst shows a big potential for CO₂RR to syngas with adjustable CO/H₂ ratio powered by renewable electricity.