Study On Bifunctional Catalysts CuO-ZnO-ZrO₂/HZSM-5 For The Hydrogenation Of Carbon Dioxide

The emission of greenhouse gases especially for the emission of CO₂ is increasingly become the focus of all over the world,research shows that CO₂ has contributed more than 50% in terms of the greenhouse effect,higher than the sum of all the other greenhouse gases.Predictably,increasingly serious greenhouse effect will make the ecology of the whole world and the balance of carbon cycle of nature suffer devastation.Therefore,in order to ensure long-term development of the world,it is imperative to transform economic development way and reduce CO₂ emission.At the same time,many scholars tried to convert CO₂ into clean and efficient energy or products for its cheap and abundant features.One-step synthesis of dimethyl ether from CO₂ hydrogenation is an effective way which not only solve the environmental problems caused by excessive emission of CO₂,but ease the problems of the energy shortage.In this thesis,the influence of preparation conditions of catalysts including precipitant,ratio of copper and zinc,calcination temperature,ratio of hydrogenation component?CuO-ZnO-ZrO₂?and dehydration component?HZSM-5?,precipitation temperature and ultrasonic treatment on the physicochemical properties and catalytic performance of CuO-ZnO-ZrO₂/HZSM-5 catalyst were investigated systematically and characterized by XRD,H2-TPR,BET,NH3-TPD techniques.Under the same reaction conditions,results show that the activity of compound bifunctional catalyst is ideal on condition that the precipitant is anhydrous sodium carbonate,the ratio of Cu and Zn is 5:4,the calcination temperature is 350?,the ratio of two-component is 3:1,the precipitation temperature is 70? as well as the catalyst is pretreated by ultrasonic treatment before reaction,which exhibits the conversion of CO₂ is 27.87%,DME selectivity is 70.8 % and total yield of dimethyl ether is 19.73 %.And then,the effect of reation conditions including reaction space velocity?GHSV?,reaction temperature?T?and reaction pressure?P?on the performance of catalyst has been explored in micro fixed bed reaction device-gas chromatography and preliminarily determines T=250 ?,P=3.0 MPa,GHSV=2400 ml·gcat-1·h-1 as the optimum reaction condition of this system.In addition,the effects of adding additives?CeO₂,La2O3,Al2O3,TiO₂?on catalystic activity were researched and characterized by XRD,BET and H2-TPR,NH3-TPD,XPS,SEM,ICP techniques.It is found that,all additives,to a certain extent,can effectively promote the dispersivity of active component Cu,increase both the specific surface area and the distribution of catalytic acidity,which contributes to the improvement of catalytic activity.Among all kinds of additives,activity of composite bifunctional catalyst by adding TiO₂ is the best,which makes 30.81% of CO₂ conversion rate,71 % of DME selectivity and 21.87 % of yield of dimethyl ether.