Studies On Direct Transformation Of Syngas Into Ethanol Via Methanol And Acetic Acid Intermediates By Relay Catalysis

Ethanol can be used as alternative fuel or fuel additive and hydrogen carrier,as well as an important fundamental chemical.The direct conversion of ethanol from syngas(CO/H2)is highly attractive because it is an atom-economic reaction.The existence of multiple reaction channels on the surface of traditional catalysts and the complexity of the reaction system lead to ethanol selectivity below 56%.It is extremely challenging to improve ethanol selectivity from syngas by controllable C-C coupling.In this thesis,a relay catalytic route was constructed with the transformation of syngas to ethanol as the target reaction.A multifunctional catalyst was developed to control a single reaction channel to achieve a highly selective synthesis of ethanol.The key factors and structure-performance relationship of catalysts affecting the relay catalytic reaction were investigated.The main research results of this thesis are outlined as following:1.In order to control the reaction channel of syngas conversion process to produce ethanol with high selectivity in single-pass.This thesis designed a relay catalytic route of syngas→methanol→acetic acid→ethanol and developed a multifunctional catalyst consisting of K-modified ZnO-ZrO2(K+-ZnO-ZrO2),modified mordenite(HMOR-DA-12MR)and Pt-Sn/SiC system to achieve 71%ethanol selectivity at 7.0%CO conversion,breaking the selectivity limitation of conventional catalysts.It was found that more surface oxygen vacancies and weaker surface acidity of K+-ZnO-ZrO2 were the keys to the high selectivity of methanol production from syngas.The mordenite was responsible for carbonylation of methanol to acetic acid,where the acidic sites located in 8-membered ring is active for carbonylation.Selective dealumination in 12-membered ring can inhibit the conversion of methanol to hydrocarbons and improve the performance of carbonylation reaction.Pt-Sn/SiC hydrogenated acetic acid to ethanol,and the PtSn alloy formation was the key to obtain high selectively of ethanol.It was shown that methanol carbonylation was the key to achieve C-C coupling,and controlling the appropriate temperature and the desired CO/CH3OH ratio promoted efficient C-C coupling.The study revealed that the effective separation of different functional catalysts was required to obtain ethanol with high selectivity.The presence of H2 in the syngas can improve the stability of the methanol carbonylation reaction by suppressing coke formation.The introduction of Sn constructed Pt-based catalysts with resistance to CO poisoning and thus promotes the hydrogenation of acetic acid to ethanol.2.In previous studies we found that the yield of syngas to ethanol by relay catalysis is not high.In order to improve the yield of ethanol,this thesis developed a highperformance methanol carbonylation catalysts.The MOR modified with a small amount of Ir(0.1Ir/H-MOR-DA-12MR)was found to significantly improve the activity and selectivity of methanol carbonylation to acetic acid,and reduce the required CO/CH3OH ratio for carbonylation reaction.At a CO/CH3OH ratio of only 4.0,the methanol conversion was 100%and the acetic acid/methyl acetate selectivity reached 98%over the O.1Ir/H-MOR-DA-12MR catalyst.The results indicated that Ir was atomically dispersed and located in the pore channel of mordenite,which promotes the activation of CO adsorption in the carbonylation process.And Ir synergized with the acidic sites in the 8-membered ring of MOR to improve the performance of carbonylation.Subsequently,the Ir-modified MOR was used for relay catalytic reaction of syngas to ethanol.The catalyst combination of Cu-Zn-Al oxide for syngas to methanol,0.lIr/H-MOR-DA-12MR for methanol carbonylation,and non-precious Cu-In/SiO2 for acetic acid hydrogenation was developed,and CO conversion of 28%and ethanol selectivity of 89%were achieved,which is significantly higher than the existing reported performances for syngas to ethanol.The study revealed that controlling the methanol synthesis in the first step under thermodynamically favorable conditions and synergistically matching the efficient carbonylation process in the second step are the keys to achieve high performances for ethanol production from syngas via relay catalysis.