Effect Of The Properties Of Catalyst Precursors On The Structure And Performance Over Catalyst For One-step Synthesis Of DME Prepared By Complete Liquid-phase Technology

With the shortage of resources, many countries have paid more and more attention to the energy problem. Our country is rich in coal but poor in oil and gas. So the conversion from synthesis gas to chemical products becomes the research focus. Dimethyl ether, with excellent properties and widespread applications, is regarded as one kind of new clean energy in the 21 st century. Today, the study of the preparation of Dimethyl ether from synthesis gas will be more and more popular.In the process of the one-step synthesis of dimethyl ether in slurry reactor, The greatest advantage is process flows short, low production costs. However, the catalyst prepared by the conventional preparation method is easy to be inactivated in slurry bed, which hinders its industrial application. Our group put forward an complete liquid phase preparation technology to solve the problem. In our preliminary results, complete liquid phase synthesis of Cu-Zn-Al catalyst was quite stable, and showed good prospects for the living problem. However, the activity of the catalyst and dimethyl ether selectivity remains to be improved.Results show that, the properties of catalyst precursor are the key to the performance of catalyst, and the properties of precursor depends on the hydrolysis rate of raw salt obviously. Only the hydrolysis rate of components is in good coordinate the gel precursor with uniform distribution could be prepared, eventually get the excellent performance of the catalyst. The hydrolysis rate can be realized by changing raw materials. This paper used different copper sources（copper citrate, copper acetic acid and cupric nitrate） and different zinc sources（zinc citrate, zinc acetate and zinc nitrate）, and homemade zinc propoxide as raw material, synthesized three series of Cu-Zn-Al catalyst by the complete liquid phase method. We explored the effect of the hydrolysis rate of different copper salt and zinc salt of catalyst precursor on the activity of catalysts and the selectivity of DME. At the same time, the influence of aging time on the precursor properties and the overall catalytic performance of the catalyst was investigated in the sol-gel method. The catalyst samples were characterized by the technology of XRD, H₂-TPR, NH₃-TPD, BET, XPS and TEM. We discussed the influence of the internal structure and the external properties of Cu-Zn-Al catalyst on the catalytic performance. The main conclusions of the study are as follows:1. The performance of the catalyst respectively used copper citrate, copper acetic acid and cupric nitrate as raw material is quite different. The one used copper citrate has the best activity and the selectivity of DME,and the CO conversion and DME selectivity were 66% and 63.4% respectively.2. Different copper sources had a significant effect on texture morphology and properties of catalyst. Copper citrate catalyst has small and uniform spherical particle, and the ratio of strong acid and weak acid is high on the surface. Besides, copper species disperse well and have strong interaction with other components, so the amount of the reducible Cu is more.3. Using zinc citrate and zinc acetate as raw material can significantly improve the performance of Cu-Zn-Al catalyst. The overall catalytic performance of zinc citrate catalyst is the best, CO conversion and DME selectivity are all highest, reaching 69.17% and 73.9% respectively.4. Using zinc citrate as raw material can significantly change the texture of the catalyst and the pore shape of the catalyst. The amount of reducible Cu is more, and the dispersion and stability of Cu⁺ is best.5. The influence of aging time on the performance of Cu-Zn-Al catalyst was significant. The study shows that the appropriate aging time is the key to improve the catalytic performance of the catalyst, aging 11 days is the best, its CO conversion and DME selectivity is up to 74.69% and 59.71% respectively.6. Use the homemade zinc propoxide as the zinc source can significantly improve the CO conversion, its CO conversion and DME selectivity can reach 60.80% and 60.51% respectively. Zinc propoxide can significantly change the texture properties of the catalyst, increase the specific surface area, obtain more reducible substances at the same time, and increases the dispersion and stability of Cu⁺.7. Regulation of the hydrolysis rate of three kinds of salt to get more uniform catalyst gel precursor is an important method to obtain high performance catalyst.