Catalytic Action Of Fe/ZSM-5 On Synthesis Of Dimethyl Ether From Methanol Dehydration

As a chemical product with superior performance,dimethyl ether is one of the research hotspots at home and abroad in recent years.At present,most of the catalysts for methanol dehydration to dimethyl ether are used to adjust or change the surface acidity by embedding other elements on HZSM-5 to improve the catalytic performance of methanol dehydration.However,modified HZSM-5 can only allow dehydration reaction at high temperature（≥220°C）and has low catalytic activity.In this paper,NaZSM-5 was modified by Fe³⁺solution by simple impregnation method,and its surface acidity and alkalinity were adjusted to prepare NaZSM-5supported Fe material.The morphology,composition and structure of the prepared composites were characterized by XRD,SEM,TEM,XPS,UV-vis,²⁹Si and ²⁷Al MAS NMR,ICP-OES,N₂ adsorption-desorption.The results showed that the composition of the catalyst was Fe/HNaZSM-5,and abundant acid and alkali active sites were distributed on the surface.The catalytic performance of the composite material was evaluated by experiments to determine the optimal reaction conditions.It was found that the conversion rate of methanol dehydration to dimethyl ether could be improved at a lower reaction temperature,and no by-products were generated during the reaction.At 180°C,the conversion of methanol can reach about 90%,and the selectivity of dimethyl ether is about 100%.The acidic and basic active sites on the catalyst surface were determined by NH₃-or CO₂-TPD,and the distribution of L acid and B acid sites on the catalyst surface was determined by pyridine infrared adsorption spectroscopy.The reaction mechanism of acid-base synergistic activation of methanol to produce CH₃⁺and CH₃O^-intermediates,and then the combination of the two to form dimethyl ether was determined.The adsorption behavior of the composite material for methanol was studied by in-situ infrared technology.The formation of CH₃⁺and CH₃O^-intermediates on the surface of the catalyst was confirmed.It was proved that the catalytic reaction was due to the synergistic reaction mechanism of surface acid and base,which improved the conversion rate of methanol dehydration reaction at a lower temperature.The stability of the catalyst was tested.The reaction was continuously operated for more than 500 h.The catalytic activity and selectivity remained unchanged,and no carbon deposition was produced during the reaction,indicating that the catalyst had extremely high operating stability.