Controllable preparation of sulfur-tolerant Pd catalysts under microwave irradiation and application of these catalystsin one-step synthesis of dimethyl ether

Abstract：According to the development of the direct syngas to DME（STD）technology,in this work,the hybrid catalyst preparation of Palladiuman（Pd） metal-supportfor DME synthesis by microwave technology was studied and developed,which has a good effect of sulfur tolerance.All research was divided into following three sections. Firstly,Pd metal-support catalystfor STD reaction was researched.Three series of Palladiuman catalysts supported on different carriers,γ-Al2O3,HZSM-5 and Al-MCM-41respectively,were prepared by impregnation.The properties of catalysts,such as surface phase structure and adsorption,reduction properties,surface acidity were controlled by changing calcination condition,Pd loading,or single and binary promoters and its added amount.The relationship between STD reactivity and the intrinsic characteristics of the catalyst were investigated. Secondly,the sulfur-tolerant mechanism of Pd catalysts was researched.The STD activity of catalysts after the process ofsulfur poisoning with H2S or thiophene and regeneration with syngas was investigated,the influence of carriers type and promoters type on thecatalysts＇ sulfur tolerance was analysis,the catalysts＇ structure and the reactants＇ chemical structureswere characterized based on various characterizations,and then the adsorption patterns and characteristics of sulfide on Pd metal active sides and acid active sides were revealed.Adsorption position of organic sulfur poisons and inorganic sulfur poisons on in CeO2-CaO-Pd/HZSM-5 catalyst was determined based on GC-MS,and thepossibletransformation mechanism of sulfides on catalyst were suggested. Finally,the kinetics of STD reaction over CeO2-CaO-Pd/HZSM-5 catalyst was researched.Because owing togood STD reactivity and sulfur tolerant,STD process conditions over CeO2-CaO-Pd/HZSM-5catalyst was further studied.The kinetic equations for STD reaction over CeO2-CaO-Pd/HZSM-5 catalyst in a fixed-bed reactor within the process conditions above were established.Statistical test shows the data calculated by the mechanism models are consistent with the experiments,so these modelsare reliable.