The Study Of Cu Catalytic Performance In Methanol/Ethanol Cross-condensation And Hydrogen Transfer

Bioethanol can be converted into many important chemicals,among which an important chemical product isobutanol can be prepared by cross-condensation of bioethanol and methanol.Cross-condensation of ethanol and methanol to isobutanol experemces Guerbet condensation mechanism.Homogeneous system achieved only high selectivity of isobutanol by adding liquid alkali.In heterogeneous system without liquid alkali,selectivity of isobutanol remains low even though the reaction was taken place at high temperate and high ratio of methanol/ethanol.The catalyst should have both dehydrogenation-hydrogen transfer active center and Aldol condensation active center.The challenge in preparation of isobutanol by cross-condensation of methanol and ethanol is high-efficiency C-C bond cross-condensation and hydrogen transfer of aldehyde.Therefore it is essential to study catalytic performance in methanol/ethanol cross-condensation and hydrogen transfer to improving the selectivity of isobutanol.In this work,the highly dispersed copper based catalysts has been prepared by in-situ reduction of as-prepared layered double hydroxides(LDHs)under H2 atmosphere.Catalystic performance in methanol/ethanol cross-condensation and hydrogen transfer were explored by regulating Cu content,Cu particle size,acid sites and basic sites and ratio of Cu/Zn.The main work is displayed as follows:(1)Cu-Mg2Al1-LDO with different Cu content was prepared by in-situ reduction of Cu-Mg2Al1-LDHs under H2 atmosphere.The catalyst with different Cu content obtained ethanol conversion of>85.0%.3.0 wt%Cu-Mg2.0Al1-LDO achieved the highest initial activity(90.3%)and isobutanol selectivity(25.0%).With the content of Cu increasing,the ability of forming C-C bond and hydrogen transfer is increasing,the ability of forming C-O bond is decreasing and the selectivity of Iso-C4 is increasing.(2)Cu-MgxAl1-LDO with different Mg/Al(3/1,4/1)was prepared by in-situ reduction under H2 atmosphere from LDHs.Different size of Cu particle was obtained.With the decreasing of Cu particle size,the ability of forming C-C bond and hydrogen transfer is increasing,the ability of forming C-O bond is decreasing and the selectivity of Iso-C4 is increasing.(3)Different support with elemental composition was prepared by in-situ reduction of LDHs(CuMgGa-LDHs,CuMgAlCe-LDHs,CuZnMgAl-LDHs,CuZnAl-LDHs).Different quantity of base and acid site produces different product distribution.With the ratio of medium and strong basic content/Lewis acid content increasing,the ability of forming C-C bond and hydrogen transfer is increasing,the ability of forming C-O bond is decreasing and the selectivity of Iso-C4 is increasing.(4)The effect of Zn was investagted,it can stabilize the Cu particle by forming CuZn alloy.The CuZn-MgAl-LDO with different molar ratio of Cu/Zn was also prepared by in-situ reduction of as-prepared LDHs under H2 atmosphere.The 6.6 wt%Cu-Zn0.5Mg2.0AI1.0-LDO in which the molar ratio of Cu/Zn is 2 shows the highest catalytic performance.The conversion of ethanol is 90.3%,the selectivity of C-C cross-coupling is 72.5%and selectivity of hydrogen transfer is 67.7%on 6.6 wt%Cu-Zn0.5Mg2.0Al1-LDO.(5)The 0.3 wt%Ir/8.0 wt%Cu-Zn0.3Mg2.0Al1.0-LDO was prepared by in-situ reduction under H2 atmosphere from Ir4+adsorbed layered double hydroxides(LDHs).The effect of Ir on the catalyst was investagted.Ir on the 0.3 wt%Ir/8.0 wt%Cu-Zn0.3Mg2.0Al1.0-LDO improved the ability of forming C-C bond and hydrogen transfer than 8.0 wt%Cu-Zn0.3Mg2.0Al1.0-LDO.