The Applied Research Of Core-Shell-Like Catalyst For Catalyzing Hydrogenation Of Carbon Dioxide

Carbon dioxide is one of the main greenhouse gases and the richest carbon sourcein the world. Exploiting and utilizing CO₂is one of the most promising studies inmodern industry technology. Catalytic hydrogenation of CO₂to form methanol anddimethyel ether （DME） is an important way, which not only can relieve thecontamination of CO₂, but also can obtain the valuable chemicals and fuels. Thissynthetic technology will surely bring a remarkable environmental and economicefficiency, especially to those chemical plants producing a large number ofby products of CO₂and H₂.Preparation of dimethyl ether by hydrogenation of CO₂is a complex chemicalprocess. In this paper, the catalyst for the hydrogenation of carbon dioxide tomethanol and dimethyl ether was studied, and the following works were done:1. The direct synthesis of capsule catalyst which possessed a special core shellstructure of a coprecipitated CuO/ZnO/Al₂O₃core enwrapped by one layer ofmetal doping amorphous silica alumina membrane was achieved by in situhydrothermal synthesis, which could be characterized by X ray powder diffraction（XRD）, thermogravimetric analysis （TGA）, scanning electronic microscopy （SEM）,transmission electron microscopy （TEM）, and nitrogen sorption measurement. Themetal oxides cores and membrane prepared by different precipitants,structure directing templates, and hydrothermal synthesis conditions, as well as thetemperature and the pressure effecting on the catalysis activities of the capsulecatalyst for the CO₂hydrogenation to dimethyl ether, were discussed. Under thereaction conditions that pressure at3.0MPa, space velocity （SV） at1800mL g_cat^-1h^-1,volume ratio of CO₂/H₂at1:3and temperature at266oC, the capsule catalyst whosecores were co precipitated by urea and using n butylamine as templating agents toenwrap amorphous silica alumina membrane had the excellent catalytic properties fordimethyl ether synthesis, that was the conversion of CO₂could be reached to47.12wt%, yield and selectivity of dimethyl ether were19.98and42.41wt%, respectively.2. A general method has been developed for the synthesis of homogeneoushollow core shell microspheres of composite metal oxide （CuO ZnO Al₂O₃） by using carbonaceous saccharide microspheres as template via a simple one pot synthesis.Various metal salts were dissolved together with glucose in water, and the mixtureswere heated to180°C in an autoclave. During the hydrothermal treatment, carbonspheres are formed with metal ions incorporated into their hydrophilic shell. Theremoval of carbon via calcinations yields hollow metal oxide spheres. The productswere characterized by XRD, SEM, TGA, TEM, EDS and BET analysis. Hollow metaloxides microspheres were tested as a carbon dioxide hydrogenation catalyst. Underthe reaction conditions that pressure at2.8MPa, space velocity （SV） at1800mL g_cat^-1h^-1, volume ratio of CO₂/H₂at1:3and temperature at262°C, the hollowmetal oxides spheres had the excellent catalytic properties for methanol synthesis, thatis the conversion of CO₂could be reached to51.7wt%, selectivity and yield ofmethanol are47.2and24.4wt%, respectively. Notably, activity loss during CO₂hydrogenation oxidation due to undesirable particle agglomeration can be drasticallysuppressed using the hollow microcapsules.