Preparation Of Ag-SBA-15 Catalyst And Its Application In DMO Hydrogenation To MG

Methyl glycolate(MG)is an important intermediate in chemical production process.The hydrolyzed glycolic acid can produce polyglycolic acid(PGA),which can be further used to yield medical materials and degradable plastics.The main work of this thesis is to prepare Ag-based catalysts for hydrogenation of dimethyl oxalate(DMO)to methyl glycolate using mesopore molecular sieve SBA-15 as the carrier.The factors influencing the structure-activity relationship of Ag-SBA-15 catalysts have been investigated in detail.The specific contents are described as following:(1)Based on previous works,SBA-15 with regular structure was successfully prepared.Also,the effect of Ag loading amount on the performance of Ag/SBA-15catalyst was investigated.The results showed that 10wt%Ag/SBA-15 catalyst exhibited the best performance in the hydrogenation of DMO to MG.(2)We investigated the effect of pH value of Ag salt precursors and impregnation solution on the surface structure,formation and dispersion of Ag species over the surface of Ag-SBA-15 catalyst prepared by impregnation method.The catalytic hydrogenation performance over different Ag salt precursors derived Ag-based catalysts was also investigated,and the factors affecting the structure-activity relationship of Ag-SBA-15catalysts were preliminarily studied.It suggests that pH value of impregnation solution and Ag salt precursors would affect the formation and dispersion of Ag species on the surface,thus affecting the catalytic hydrogenation performance of Ag-SBA-15 catalysts.The catalytic properties of Ag-SBA-15 catalyst were enhanced when the Ag salt precursors had a strong interaction with the silica hydroxyl groups in the channel of SBA-15,which was beneficial to increase the dispersion of Ag species on the surface and inhibit the aggregation of Ag species.(3)The hydrogenation performance of Ag-NH₃/SBA-15 catalyst preheated at different temperatures was further studied in this work.The results show that the preheating temperature play a significant role in the formation and dispersion of Ag species on the surface.Appropriate preheating temperature could not only remove the water in the catalyst system,but also enhance the silica hydroxyl interaction between Ag species and SBA-15,thus improving the dispersion of Ag species on the surface,and inhibiting the aggregation of Ag species in the reduction process.Therefore,the catalytic property of the catalyst is enhanced,which enables the DMO hydrogenation at a lower temperature to obtain high-yield MG product.In conclusions,the Ag-NH₃/SBA-15 catalyst with[Ag(NH₃)₂]⁺as precursor,pH value of impregnation solution of 9.3 and preheating treatment at 623 K exhibited the best performance.The DMO conversion rate and MG yield reached 97.9%and 94.9%at483 K,respectively,which reaches the optimal level reported at present.