Study Of Methanol Dehydrogenation And Ethyl Acetate Hydrogenation Over Copper-based Catalysts

Methanol and acetic acid are two important coal chemical downstream chemicals.In recent years,producing methanol from coal and carbonylation of methanol to acetic acid technology have been mature.Blind expansion of production capacity led to serious production capacity excess and low price of methanol and acetic acid.Using low-cost methanol and acetic acid as raw materials and developing new catalytic technology to prepare high value-added downstream products has a great significance for the coal chemical industry and the entire national economy.Methanol dehydrogenation to methyl formate and ethyl acetate hydrogenation to ethanol are two promising routes.Supported copper-based catalysts are ideal catalysts for these two reactions.Enhancing the catalytic performance of catalysts and revealing the relationship between catalyst composition and catalytic performance is very worth studying.Therefore,this paper focuses on the effect of the composition of supported copper-based catalysts on the dehydrogenation of methanol and the hydrogenation of ethyl acetate.Copper-based catalysts were prepared by equal volume impregnation method using silica,hydroxyapatite and magnesia as supports.Cu/Si O₂ catalyst with low total basicities favors methanol dehydrogenation to methyl formate.However,the Cu/HAP and Cu/Mg O catalysts with high total basicities result in the rapid degredation of the methyl formate to CO and H₂,reducing the selectivity of methyl formate.The reaction activation energy Ea1 of methanol dehydrogenation to methyl formate on Cu?5?/Si O₂ catalyst was 58.3 k J mol-1,which is lower than that on Cu?5?/HAP and Cu?5?/Mg O catalysts.The reaction energy Ea2 of methyl formate degredation is 91.1k J mol-1,which is higher than that on Cu?5?/HAP and Cu?5?/Mg O catalyst.Copper-based catalysts were prepared by equal volume impregnation method using silica as support and La,Ce and Nd as additives.The addition of rare earth elements can obviously change the dispersibility of copper component on the support and enhance the interaction between the copper species and the support.The surface basicities of the catalysts were obviously affected by the rare earth elements,which in turn affected the catalytic performance of the catalysts.Cu/La₂O₃/Si O₂ catalysts with weak surface base sites can effectively improve the methanol conversion,while not make methyl formate degredation too violently.However,the Cu/Ce2O/Si O₂ and Cu/Nd2O3/Si O₂ surfaces have strong base sites and high toatal basicities,resulting in obvious decrease in the selectivity of methyl formate.To study the effect of supports and additives on the copper-based catalysts for hydrogenation of ethyl acetate,we used co-precipitation method to prepare Cu/Zn O/Si O₂,Cu/Zn O/Al2O3 and Cu/Zn O/Zr O₂ catalysts.The catalytic performance of the catalysts is significantly affected by the type of supports and the content of Zn O.The addtion of Zn O can obvious reduce the crystal size of Cu0 in the catalyst and significantly change the surface acidity of the catalyst,both of which had important effects on the catalytic activity of the catalyst.The smaller size Cu0 in the catalyst and the higher surface acidity are more favorable for the hydrogenation of ethyl acetate to ethanol.The activation energies of ethyl acetate hydrogenation on Cu/Zn O/Al2O3 were significantly lower than those on Cu/Zn O/Si O₂ and Cu/Zn O/Zr O₂ catalysts.The activation of the catalyst can better reveal the relationship between the catalytic activity of the catalyst and the catalyst composition.