The Application Of Zn-ligand Catalysts In Acetylene Hydration Reaction

Acetaldehyde is a common organic raw material with a wide range of applications.At present,countries with rich oil resources prefer the ethylene method,but the production cost of this method is relatively high.The production of acetaldehyde by the acetylene hydration method,in association with the current situation of abundant coal resources in China,still has a high research value.Hg-based catalysts are generally used in conventional gas-liquid phase catalytic systems,but Hg can pollute the ecological environment.At present,the gas-solid phase acetylene hydration reaction system mainly focuses on the research of carrier,Cd-based catalyst,Cu-based catalyst,Zn-based catalyst and reaction mechanism,but there are still some problems,such as Cd is a toxic metal;the divalent copper ion in Cu-based catalyst is easily reduced;the stability of Zn-based catalyst is poor,etc.This thesis investigates the application of Zn-ligand catalysts in acetylene hydration reactions,focusing on the following three aspects:（1）The effect of trifluoromethanesulfonic acid ligands on the performance of Zn-based catalysts for catalytic acetylene hydration reaction was investigated.The Zn-ligand catalysts were prepared by co-impregnation method and tested for their catalytic activity.Among them,the Zn-1.5Tf OH/AC ligand catalysts showed good activity with acetylene conversion and acetaldehyde selectivity of 96%and 72%,respectively,for 10 h.The addition of Tf OH significantly promoted the dispersion of Zn species,while offering additional surface acid site content and active catalytic sites,which are favorable for the acetylene hydration reaction.The Zn fraction is mainly present as a Zn-O4 coordination structure.The Tf OH ligand increases the relative content of（Zn OH）⁺species and alleviates the loss of Zn fraction and carbon accumulation.The results of DFT theoretical calculations indicate that the Tf O-Zn OH conformation with the lowest reaction energy barrier is more likely to be the coordination complex formed by Zn and Tf OH ligands.Additionally,the-OH in Tf O-Zn OH can directly participate in the reaction and be regenerated by dissociating H₂O,lowering the energy barrier.（2）The effect of phosphotungstic acid ligands on the performance of Zn-based catalysts for acetylene hydration reaction was investigated.A green and non-polluting solid heteropolyacid ligand-phosphotungstic acid（HPW）was used to improve the activity of Zn-based catalysts.HPW significantly improved the catalytic performance of the Zn-based catalysts,and the Zn-0.05HPW/AC ligand catalyst showed better activity,and after 10 h of reaction,the conversion of the Zn-0.05HPW/AC catalyst for acetylene was over 90%,while the selectivity of acetaldehyde could be maintained above 70%.Synchrotron characterization demonstrated that Zn was close to the coordination configuration of Zn-O4.HPW ligands promoted the distribution of the Zn fraction and reduced the clustering of Zn species,the loss of Zn fraction and the generation of carbon accumulation in the catalyst during the reaction.Py-FTIR and XPS characterization showed that HPW promoted the binding of B acid sites to Zn²⁺,which facilitated the formation of（Zn OH）⁺species.HPW reduced the apparent activation energy of the reaction,which in turn enhanced the activity of the acetylene hydration reaction.（3）The effect of zinc dihydrogen phosphate on the performance of the acetylene hydration reaction has been studied.The Zn/AC and Zn（H₂PO₄）₂/AC catalysts were prepared by the over-volume impregnation method using Zn Cl₂,Zn O as the zinc source,respectively,and used in the acetylene hydration reaction.After10 h of reaction,the acetylene conversion was 93.5%,while the acetaldehyde selectivity was 68.6%.Py-FTIR characterization showed a substantial increase in the acid content of the Zn（H₂PO₄）₂/AC catalyst.XPS characterization analysis demonstrated an increase in acid content,an increase in（Zn OH）⁺species content and a concomitant decrease in carbon accumulation.Zn（H₂PO₄）₂/AC has a lower apparent activation energy of the reaction,which has a facilitative effect on the reaction.