Preparation Of CuO-ZnO-ZrO₂/HZSM-5 Via Solid-state Reaction And Its Catalytic Performance For CO₂ Hydrogenation To Dimethyl Ether

In recent years, the greenhouse effect caused by carbon dioxide is increasingly significant. CO₂ recycling is the focus of governments and the scientific research personnel. Dimethyl ether ?DME? is considered to be an ideal clean fuel and a starting material for the production of a range of chemicals. Direct synthesis of dimethyl ether ?DME? from the catalytic hydrogenation of the carbon dioxide is of great economical and environmental importance, not only to synthesize the useful chemical products and fuels, which will utilize carbon dioxide more efficiently, but also to reduce the greenhouse effect resulted from carbon dioxide. Solid-state reaction method is a simple, rapid, solvent-free, and energy-saving process and it has become the important methods for preparation of new type of solid material.Bifunctional CuO-ZnO-ZrO₂/HZSM-5 catalysts were prepared by a route of solid-state reaction and tested for one-step synthesis of dimethyl ether ?DME? from CO₂ hydrogenation. The mass ratio of CuO-ZnO-ZrO₂ and HZSM-5, different calcination temperature, different complexants were investigated for the bifunctional CuO-ZnO-ZrO₂/HZSM-5 catalysts prepared by the solid-state reaction. At last, the solid-state reaction was compared with other preparation methods. The main results are as follows:1. The effect of the mass ratio of CuO-ZnO-ZrO₂ and HZSM-5 on the CuO-ZnO-ZrO₂/HZSM-5 catalystsCuO-ZnO-ZrO₂ is methanol synthesis component and HZSM-5 is methanol dehydration component. With the increase of the mass ratio of the two components from 1:1 to 12:1, the CO₂ conversion and DME selectivity increased at first, reached a maximum at 10:1 and then decreased. The content of CuO-ZnO-ZrO₂ does not change the structure of HZSM-5, but affects the acidity distribution and acid strength of HZSM-5. HZSM-5 can influence the dispersion and reduction temperature of CuO.2. The effect of calcination temperature on the CuOZnO-ZrO₂/HZSM-5 catalystsThe CuO-ZnO-ZrO₂/HZSM-5 catalysts with the ratio of CuO-ZnO-ZrO₂ to HZSM-5 of 10:1 were calcined at the temperature of 300? to 600?. With the increase of calcination temperature, the catalytic activity decreased gradually. The catalyst has the largest Scu at the calcination temperature of 300?. The calcination temperature has certain influence on the surface acidity. In this series of catalysts, acid quantity is enough, so methanol synthesis component is the main factor affecting the catalytic performance of the bifunctional catalysts.3. The effect of complexants on the CuO-ZnO-ZrO₂/HZSM-5 catalystsThe bifunctional CuO-ZnO-ZrO₂/HZSM-5 catalysts were prepared by complexant of oxalic acid, citric acid, edetic acid ?EDTA? and tartaric acid. The results show that the texture and adsorption properties of the catalysts change with the different complexants, which can mainly be attributed to the augment of copper metal surface area ?SCu?, adsorption capacity for CO₂ and H₂, weak acidity. Oxalic acid as the complexant exhibits the highest catalytic performance.Compared with oxalate and ammonium carbonate co-precipitation precipitation mechanical mixing method and deposition precipitation, the CuO-ZnO-ZrO₂/HZSM-5 catalysts prepared by solid-state reaction method has better catalytic performance. Thus, the solid-state reaction method is an efficient method for the preparation of bifunctional catalysts.