Study On Effect Of Microstructure Modulation Of Copper Catalysts On Liquid Phase Low-temperature Methanol Synthesis

Methanol is an important chemical raw material and energy storage carrier in industrial society.As energy resources in the future change,it is expected that methanol will play an ever-increasing role.Methanol synthesis is favorable at low temperature,namely,the feedgas conversion is high at low temperature.But boosting the catalyst activity is challenging.Cu/ZnO is the active component for industrial methanol synthesis catalyst operating at(220-280℃).However,its activity at low temperature remains low in terms of the equilibrium conversion.In this work series of modified Cu/ZnO catalysts were prepared and applied to methanol synthesis at 150℃ and 4 MPa in ethanol media.The physicochemical properties of the catalysts were characterized using XRD(X-ray diffraction),SEM(scanning electron microscopy),TEM(transmission electron microscope),XPS(X-ray photoelectron spectroscopy),CO/CO2/H2-TPD(temperature programmed desorption)and N2O-titrition.The influence of Cu content,type/content of promotor and preparation method on the catalyst structure and catalytic performance was studied.The catalyst structure and active sites were correlated with catalytic activity for the liquid phase low-temperature methanol synthesis.Cu/ZnO catalysts with mass ratio X:1(X=1,2,3,4)were prepared using an oxalic acid aided solidphase grinding procedure.When the Cu:ZnO was 2:1,the total carbon conversion of the feedgas and methanol selectivity reached 43.7%and 94%,respectively.2Cu/ZnO exhibited better adsorption and activation capability for CO/H2 and the most numbers of weakly and moderately basic sites.For MnO2,CeO2 or ZrO2 modified Cu/ZnO obtained by the same procedure,Cu/ZnO/MnO2 exhibited better catalytic activity than Cu/ZnO/CeO2 and Cu/ZnO/ZrO2,with the highest total carbon conversion of 54.7%.Addition of modifiers tuned the ratio of Cu+/Cu0 and the concentration of the basic sites on the catalyst surface,and increased the dispersion and surface area of Cu.With increased higher Cu+/Cu0 ratio on the Cu/ZnO/MnO2 surface promoted the CO conversion.Cu/ZnO/CeO2 and Cu/ZnO/ZrO2 with increased moderately basic sites raised the methanol selectivity to 97%.MnO2 was added in Cu/ZnO with nMn/nCu=0,3%,6%,9%,12%,respectively.The catalytic activity first increased and then decreased with the increase in MnO2 content.At nMn/nCu of 6%,the best catalytic activity was achieved in a total carbon conversion of 54.7%.Cu/ZnO/MnO2 prepared using co-precipitation,sol-gel or solid-phase grinding procedure displayed distinct morphology.Cu/ZnO/MnO2 by solid-phase grinding method exhibited the highest activity due to higher low-temperature adsorption of H2 and numbers of weakly basic sites.Study on the effect of feedgas(CO/CO2/H2、CO/H2、CO2/H2)composition on the catalytic activity of Cu/ZnO/MnO2 indicated that CO and CO2 were hydrogenized concurrently and presence of CO2 promoted the conversion of CO.