Preparation And Structure Analysis Of Cu/OMS Catalyst For Dimethyl Oxalate Hydrogenation

Ethylene glycol(EG)is an important raw chemical material in China,which is mainly used in the production of polyester,antifreeze,synthetic fiber and so on.Considering the characteristics of China's energy structure,the production of EG from syngas via dimethyl oxalate(DMO)hydrogenation has important strategic significance.The DMO hydrogenation is one of the important steps for this new technology.The study on the preparation of efficient catalyst with high activity,selectivity and stability is the crucial issue for this reaction.In order to improve the dispersion of the copper species and enhance the formation of Cu~+species,ordered mesoporous silica(OMS)was used as the support of copper species in this study.The as-synthesized Cu/OMS catalyst exhibited excellent catalytic performance in the hydrogenation of DMO to EG at lower temperature.Meanwhile,the structure evolution mechanism and fabrication strategy of the Cu/OMS catalysts were investigated.In this paper,a series of Cu/OMS catalyst with different copper loading and using OMS as the support were prepared through a modified ammonia evaporation method(AE method).The texture structure and catalytic activity of the catalysts were investigated in detail.The ordered mesoporous structure of the support was gradually destroyed with the increasing of the copper loading and the copper species was well dispersed in all the catalysts.20Cu/OMS exhibited the highest catalytic activity due to the largest Cu~0 and Cu~+surface areas.The space time yield of EG presented a positive correlation with both Cu~0 and Cu~+surface area,especially Cu~0 species.This indicated that the adsorption of hydrogen dissociation on Cu~0 shuold be the control step in the reaction on Cu/OMS.In order to further reveal the function of OMS,real-time sampling technique was employed to study the structure evolution mechanism of catalyst during the aging and evaporation step in the preparation process.It was found that the ordered mesoporous structure of OMS was reserved during the aging step,allowing the homogeneous distribution of copper ammonia in the mesopores.During the evaporation stage,copper phyllosolicate was formed via the reaction between copper species and surface silica,and the ordered mesoporous structure was nearly totally destroyed.Compared with the silica sol,OMS can promote the dispersion of the copper species due to its richer pore structure,leading to outstanding catalytic performance.In order to rationally fabricate the Cu/OMS catalysts with controllable structure and valence state of copper species,the influence of pH value in the preparation of Cu/OMS was studied.It was found that the mesopores of OMS was destroyed during the aging stage under the high pH value,so that the copper species precursor could not be well pre-distributed in the support,leading to the severe decrease of the copper dispersion.An appropriate pH value favor the high dispersion of copper species,resulting in excellent catalytic activity of Cu/OMS in DMO hydrogenation.