Preparation And Properties Of Highly Active Cu-based Catalysts For Synthesis Gas To Methanol

Methanol is an important chemical product and a substitute for fossil energy.The key to methanol synthesis is the catalyst.Cu-based catalysts are the most widely used and studied catalysts due to their low production cost and high catalytic activity.However,the Cu-based catalyst has poor thermal stability and its activity needs to be further improved.Based on this,in order to improve the activity of Cu-based catalysts,in this paper,CeO₂ is used as an electronic promoter,and a series of Cu/ZnO/Al₂O₃/CeO₂catalysts with different CeO₂ addition amounts are prepared by co-precipitation method.In order to improve the thermal stability of Cu-based catalysts,the inverse micelle method and the collaborative self-assembly method were used to prepare Cu/ZnO@SiO₂ core-shell catalysts and Cu/ZnO@HMAN hollow core-shells catalysts with Cu/ZnO as the core and SiO₂and aluminosilicate(HMAN)as the shell.Characterize and analyze the catalyst structure and evaluate the activity of the catalyst for methanol synthesis.The specific research content is as follows:1.Study on the preparation of Cu/ZnO/Al₂O₃/CeO₂(CZAC)catalyst by co-precipitation method and the effect of CeO₂addition on methanol synthesis performance.The catalyst was characterized and evaluated by XRD,XPS,H₂-TPR,CO₂-TPD,TG,N₂ adsorption/desorption and high-pressure fixed-bed reactor.The results show that the addition of CeO₂ not only affects the Cu particle size and metal-metal interaction in the CZAC catalyst,but also affects the content of oxygen vacancies and strong basic sites on the catalyst surface.The CZAC-5 catalyst with 5%CeO₂ addition has the smallest Cu O particle size(8.9 nm),strong intermetallic interaction,more oxygen vacancy and strong basic sites.The space-time yield of methanol of CZAC-5 catalyst is the largest at 0.315 g _{Me OH}·h^-1·g^-1_cat,which is better than the activity of the company's RK-5 catalyst(the space-time yield of methanol is0.215 g _{Me OH}·h^-1·g^-1_cat).The optimal reaction conditions for CZAC-5 catalyst are reduction temperature of 260?,reaction temperature of 250?,reaction pressure of 3MPa,and volumetric space velocity of 6000 m L·g^-1_cat·h^-1.2.Study on the preparation of Cu/ZnO@SiO₂ catalyst by reversed micelle method and the effect of Cu nanoparticle size on methanol synthesis performance.The Cu nanoparticle size was adjusted by changing the concentration of the metal solution and the concentration of the surfactant polyethylene glycol monohexadecyl ether(Brij56).XRD,TEM,and N₂ adsorption/desorption were used to characterize the catalyst and its performance in methanol synthesis was measured.The results show that as the concentration of the metal solution increases(0.25 M?2 M),the size of Cu particles gradually increases(2.45 nm?10.43 nm).With the increase of surfactant concentration(0.13 M?0.21 M),the particle size of Cu particles decreases first and then increases.When the concentration of the metal solution is 1 M and the concentration of the surfactant is 0.174 M,the Cu nanoparticle size of Cu/ZnO@SiO₂catalyst is the smallest,which is 3.23 nm,provides the most effective active sites,and its methanol synthesis activity is the best.CO conversion rate,methanol selectivity and methanol space-time yield are 5.8%,60.1%and 0.111 g _{Me OH}·h^-1·g^-1_cat,respectively.3.Study on the preparation of Cu/ZnO@HMAN hollow core-shells catalyst by collaborative self-assembly method and the effect on methanol synthesis performance.The catalyst was characterized by XRD,TEM,and N₂ adsorption/desorption,and its performance in methanol synthesis was measured.The results show that the addition of CTAB affects the pore structure of Cu/ZnO@HMAN catalyst shell and the mass transfer process of reaction gas molecules,thereby affecting its catalytic activity.As the amount of CTAB increases exponentially(Cu Zn@SiO₂/CTAB=1:0.25?Cu Zn@SiO₂/CTAB=1:1),the specific surface area and shell micropore volume of Cu/ZnO@HMAN catalyst gradually increase,and the space-time yield of methanol also increase.When the addition amount of CTAB is constant,with the increase of the concentration of the metal solution(0.15 M?1 M),the size of Cu nanoparticles increases,and the specific surface area and the pore volume of the shell layer increase.When the metal solution concentration is 0.5 M and Cu Zn@SiO₂/CTAB=1:1,the Cu/ZnO@HMAN catalyst has the most suitable Cu nanoparticle size and shell pore structure.It can provide the most effective active sites and places that are most conducive to the mass transfer and diffusion of reaction gas molecules.Therefore,the catalyst has the highest methanol space-time yield of 0.157 g _{Me OH}·h^-1·g^-1_cat,which is86.9%higher than the Cu/ZnO-0.5@SiO₂ catalyst prepared by the reversed micelle method.4.Stability study results show that the space-time yields of methanol of Cu/ZnO@SiO₂ and Cu/ZnO@HMAN catalysts with core-shell structure remain unchanged during the reaction time and have good stability.Besides the hollow structure Cu/ZnO@HMAN core-shell catalyst effectively improves the catalytic activity and the utilization rate of Cu.