Study On The Preparation And Performance Of Cu/MgO/Fe₂O₃ Catalyst For Low Temperature Methanol Synthesis

Low temperature methanol synthesis(LTMS)is a thermodynamically favorable reaction.However,the reaction speed is slow due to high activation energy.In spite of extremely high active,homogeneous catalysts are easily poisoned by trace amounts of CO2 and H2O in feedgas The reaction over current heterogeneous catalysts is far from equilibrium conversion.To improve the activity of Cu/MgO catalysts for LTMS,the preparation process and the reaction passway were scrutinized.Effects of preparation method,constitution,promoter,reaction conditions on the reaction behavior of CO/H2/CO2 and methanol selectivity were studied.By means of characterization of phase,morphology,surface area and adsorption,the effects of microscopic morphology and promoter on the catalytic performance were discussed.1 For Cu/MgO catalyst by co-precipitation method,using precipitating temperature of 60℃,with Cu/Mg molar ratio of 3,the activity was the highest at 150℃.The conversion of CO was 17.3%and the methanol selectivity was 100%.As the temperature was raised from 150℃ to 200℃,CO2 and ethyl formate were byproduced.The temperature of 175℃ was better for the reaction.2 For Cu/MgO(Cu/Mg=3)catalyst by sol-gel combustion method,when the sol pH was 7 and the molar ratio of metal ions to citric acid was 1,the activity was the highest at 150℃.CO and CO2 were synchronously converted in the conversion of 19.8%and 9.9%,respectively.The methanol selectivity was 100%.The Cu/MgO had honeycomb-like porous morphology with surface area of 76.3 m3/g,much higher than that prepared by co-precipitation.Furthermore,metallic copper was directly obtained through calcination of Cu/MgO xerogel in inert N2 atmosphere,without traditional reduction procedure.3 For Cu/MgO/Fe2O3(3/0.75/0.25)catalyst by co-precipitation and sol-gel combustion,the later showed better activity and stability at 150℃.The conversion of CO and CO2 was 22.3%and 37.1%,respectively,which was obviously higher than that of Cu/MgO by co-precipitation.The selectivity of methanol was 94.6%.Temperature programmed desorption indicated that Fe203 had stronger adsorption capacity,which promots CO2 transformation via the reverse-water-gas-shift reaction.In a whole,introduction of Fe2O3 into Cu/MgO improves the activity for LTMS,and the resistance against C02 and H20 poisoning.