The Design Of The New Type Of Silver Catalysts And Their Application In Dimethyl Oxalate Hydrogenation Reaction

Methyl oxalate （MG）, due to its unique molecular structure （both the hydroxyland the ester groups in the molecular）, is a very important refine chemicalintermediate. Because its chemical properties are similar to alcohol and ester, MG canundergo various reactions like carbonylation, hydrolyzation, oxidation, and so on.There are several routes to synthesizing MG; however, the most frequently used oneis oil route. As well known, there is a decrease in petroleum resources. Moreimportantly, over-consuming petroleum resources would bring us environmental andpolitical problems. Therefore, the development of a new and green catalytic syntheticprocedure from non-oil resources is a challenging project for us.In this thesis, we designed a series of silver-based catalysts and investigated theircatalytic properties by using the gas-phase dimethyl oxalate （DMO） hydrogenation asa probe reaction. The relationship of the catalytic activity to the structure wasestablished. According to this theme, our work had been carried out as follows in thetext:（1） A series of Ag-containing catalysts with different Ag particle size weresuccessfully synthesized by the ammonia-evaporation method. The Ag nanoparticleswere found highly homogeneously dispersed on support. The catalytic performancesof these catalysts were determined on the hydrogenation of DMO to MG undergas-phase fixed-bed conditions.97%conversion of DMO and95%selectivity to MGwere achieved over10.2wt%Ag/SiO₂catalyst at200℃and2.50MPa. Furtherincreasing Ag content did not increase activity, which might be due to the saturationof surface Ag when the Ag loading was up to10.2wt%.（2） Based on the abovementioned Ag/SiO₂catalyst, we studied the effect ofpromoters （such as Ni，Co，Pd，Pt，Cu） on the catalytic activity. The results revealedthat incorporation of Cu species greatly improved the hydrogenation activity and thecatalyst stability. With the characterization of XRD, TEM, and XPS, the catalystphase, morphology, and the electronic state were detected. The resultant CuAg wasidentified to be alloy, which maybe stabilize the Ag species, and on the other hand, change its surface electronic state, and thus improve the DMO hydrogen activity andstability.（3） To enhance the surface Ag content, SBA-15was used as support for Agcatalyst, and a series of Ag/SBA-15catalysts were successfully prepared throughdeposition-precipitation method. According to TEM, the resultant Ag particles wereidentified to be homogenously dispersed on the support and partial particles werelocated within the channels. We further studied the effect of calcination temperature,Ag loading, reactant content, and pore size on the reactivity. It was found that Agspecies would migrate from surface to bulk with increasing the calcinationtemperature, resulting in lower surface Ag content. When Ag loading was to11.4wt%,the calcination temperature was623K, a high activity and selectivity can be achievedat473K with a high LHSV （2.2h-1）. To the best of our knowledge, this is highercatalytic activity than all the reported results up to now. By several characterizations,the correlation of the catalytic performances to the structural properties has beententatively established.