Preparation of copper-zinc based methanol catalysts synthesized by stepwise precipitation method and their performance study
Copper-zinc coprecipitation method is a commonly used method for preparing copper-zinc based methanol synthesis catalysts,but this method is difficult to achieve the construction and regulation of copper-zinc oxide interface active sites on the surface of catalysts.To solve this problem,a stepwise precipitation method was applied.Keeping the overall Zn content unchanged,a part of zinc was co-precipitated with copper to form a bulk core,while a part of zinc was coated on the particle surface to form copper-zinc oxide interface sites.The influence of Zn coated ratios on the catalyst performance was studied.X-ray diffraction(XRD),N2 adsorption/desorption,X-ray photoelectron spectroscopy(XPS)and H2 temperature programmed reduction(H2-TPR)were used to analyze the particle sizes,pore properties,valence and electronic properties and reducing abilities.The results show that the catalysts synthesized by stepwise precipitation method have smaller particle sizes,richer pore structures,stronger copper-zinc interactions,more stable low valent copper sites and greater reductive capacity,compared with the catalyst synthesized by co-precipitation method.The methanol synthesis results show that the initial activity and the activity after a thermal treatment of catalyst are optimal when 25%zinc is encapsulated under the reaction conditions of 5.0 MPa,250℃and the space velocity of 10000 h-1.The initial activity increases by 6%and activity after thermal treatment increases by 11%,compared with the catalyst synthesized by co-precipitation method.When 50%zinc is encapsulated,the activity degradation rate of the catalyst after thermal treatment is the lowest(14.1%),which is only 66%of that of the catalyst synthesized by co-precipitation method.The activity and thermal stability of catalysts synthesized by stepwise precipitation have been significantly improved.This method achieves effective regulation of the active sites on the methanol catalyst surface,so as to successfully improve the activity and thermal stability of the copper-zinc based methanol catalysts.
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