Influence Of Preparation Method And Conditions On Performance Of Copper-Based Catalysts For Methanol Synthesis

Methanol is an important chemical, and it’s not only an important fundamental material in C1 industries but also a potential cleaning fuel. Currently, accompanied by China’s modern coal chemical technology continues to mature more and more, the applications of methanol and its downstream product continue to expand due to the rise of international crude oil prices, coal derived methanol become a developing hot spot in China′s coal chemical industry. Although copper-based catalysts have been used for many years with high activity and selectivity, it still exist many drawbacks, such as poor tolerance to poisoning, low thermal stability and low mechanical strength.In this paper, the Cu/ZnO/Al₂O₃ catalysts were tested for methanol synthesis. The effect of different preparation methods and conditions of catalysts on its activity had been widely investigated. Characterizied by X-ray diffraction （XRD）, Thermogravimetry （TG-DTG）, N₂ adsorption （BET）,temperature programned reduction （TPR） and FT-IRet al, the effects of different preparation conditions on the precursor and properties of catalysts were discussed in details.Catalysts were prepared by co-precipitation method （CP）, two-stage-precipitation method （TP）, fractional-precipitation method （FP）, the results show that activity of the catalysts prepared by FP and TP is better than that of CP. The Catalysts and their precursors were studied by characterizations, and the results showed that precursors prepared by FP and TP have much more chance for the substitution of copper and zinc. Based on these, a large amount of （Cu, Zn）2（CO₃）（OH）2 and （Cu, Zn）5（CO₃）2（OH）6 was obtained, and little （Cu, Zn）6Al2（OH）16 CO₃·4H2O was obtained. And the large amount of CuO-ZnO solid solution and high temperature carbonate was formed in the calcined catalyst. Morphologies are ascribed to improvement in the specific activity. The aging pH value was a key factor for the ctalysts with high activity prepared by TP. Keep pH value at 7.0 for 20 min. （by dripping nitric acid solution to the precursors）, or reduce the Al salt precipitation pH value, the high activity catalyst could both be obtained.And the optimal preparation conditions for Al were obtained as follows: Al/Zn ratio was at 75:0, the precipitating temperature was 40℃, the pH value was 4.0, and the content of Al was 10 mol%. It was found that the unaged Al precursors mixed with the Cu-Zn precursors which aged for 15 min, preformed better in catalytic activity.