Cu/SiO₂ Catalyzed Conversion Of Dimethyl Oxalate To Ethylene Glycol Without Extraneous Hydrogen

Ethylene glycol is an important chemical intermediate and basic organic raw material.Combined with the current energy status of"rich coal and lean oil"in China,the route of syngas to ethylene glycol from coal has broad application prospects,but the process requires 2⁴ MPa hydrogen,which is expensive,difficult to transport and store,and inflammable and explosive.In order to solve the technological drawbacks of exogenous hydrogen,we have designed a new synthetic route,which is to convert dimethyl oxalate to ethylene glycol efficiently by using Cu/SiO₂ catalyst and methanol as hydrogen supply solvent without extraneous hydrogen.We have reported a method for preparing Cu/Cu₂O·SiO₂ catalyst by hydrothermal synthesis of copper silicate as precursor.By XRD,FT-IR,BET,TGA and CO-DRIFTS characterization,we found that the crystallinity and the difficulty of calcination decomposition of the copper silicate precursor prepared by KCl-assisted hydrothermal synthesis method are obviously decreased,oxygen defects appears on the surface,the crystal structure of the copper silicate precursor changes from a sheet into a small granular state,which is easier to be reduced,and the copper nanoparticles are smaller and have a higher dispersion.This is consistent with the characterization results from SEM and TEM.From the characterization results of XPS and XAES,it can be seen that the copper silicate prepared by KCl-assisted hydrothermal synthesis method has a large Cu⁰/Cu⁺ratio on the surface of the Cu/Cu₂O·SiO₂ catalyst,and the catalytic activity is also greatly improved,indicating that the small granular copper silicate is more easily reduced to Cu⁰ species,and the hydrogenation active site of dimethyl oxalate to ethylene glycol is Cu⁰.In addition,it can be seen from ICP and TEM-Mapping that the copper silicate precursor is substantially free of KCl,indicating that KCl only plays a role in inducing the transformation of the copper silicate structure during the hydrothermal process.In summary,KCl introduced in the hydrothermal synthesis process only acts to hinder the growth and crystallization of the flaky copper silicate,and induces the formation of a small granular copper silicate precursor which is uniformly dispersed,and generating more Cu⁰ species on the Cu/SiO₂ catalyst surface after reduction.Methanol is efficiently decomposed in the Cu₂O·SiO₂ site to generate hydrogen,then was transferred to the surface of Cu⁰ species through internal hydrogen transfer mechanism and was directly supplied to dimethyl oxalate for hydrogenation to ethylene glycol.Hydrogen production from methanol and hydrogenation of dimethyl oxalate were successfully coupled in a one-step process.In short,we developed a new one-pot method of producing ethylene glycol from dimethyl oxalate by using Cu/SiO₂ catalyst.This simple and green process is highly atom economy,and is in line with the definition of green chemistry and chemical process.