Study On The Conversion Of Bio-ethanol To Propylene Catalyzed By Modified Nanoscale HZSM-5 Zeolites

The nanoscale HZSM-5 zeolite was modified by NaOH solution,magnesium,composite modification?NaOH solution and Mg modification?and P modification.Moreover,the modified HZSM-5 zeolites were used as catalyst in the selective conversion of bio-ethanol to propylene.All the catalysts were characterized by XRD,TEM,SEM,TG,N₂adsorption/desorption,NH₃-TPD,Py-IR,and ²⁷Al MAS NMR to investigate the influence of the physico-chemical properties of the nanoscale HZSM-5 zeolites on its catalytic performance for the conversion of bio-ethanol to propylene.In the condition of composite modification,since the NaOH solution alkali treatment will expand HZSM-5 zeolite pore radius and significantly increase the content of Br?nsted acid sites on the zeolite,so part of the magnesium acetate can enter into HZSM-5 zeolite after alkali treatment.In addition,in NaOH solution alkali-modifiedathe situation,the significant increation of Br?nsted acid sites also provide more space for the MgO modification process.Based on the results,we can obtain the pore size of the expanded complex modification HZSM-5,resulting in magnesium acetate entering into the tunnels,and interacting with strong acid sites,reducing its acid properties,and also improving molecular diffusion performance of the catalytic reaction and significantly reducing the average coke rate,eventually,significantly improving the catalytic performance of nano-HZSM-5 for bio-ethanol to propylene.A series of P modified HZSM-5 zeolite was prepared using?NH₄?₃PO₄·3H₂O as precursor.And we compared two SiO₂/Al₂O₃ ratio of HZSM-5 zeolite under the same condition of P modification.The results showed that with the increase of P content in HZSM-5 zeolites the surface acid strength weakened gradually.It is generally known that the strength of the acid on the surface of the HZSM-5 zeolites is the important factors,affecting the selectivity of propylene and the catalyst stability.Under the same conditions of P modification,the low SiO₂/Al₂O₃ ratio catalyst has higher acid density,and has the higher selectivity of propylene.The high SiO₂/Al₂O₃ ratio catalyst has lower acid density,which has the better stability.Therefore,it is of great importance to control the P content of the catalyst for increasing the selectivity of propylene and catalyst stability.After studying the relationship between P content and catalyst performance,we further researched the influence of different phosphorus source to the catalyst.The modified zeolites have the same surface acidity,and showed the same catalytic performance in the conversion of bio-ethanol to propylene.So,under the condition of the same P content,the kinds of inorganic P source have no significant effect on catalytic performance.