Conversion Of Ethanol To Propylene Catalyzed By Nanoscale HZSM-5Zeolites

Based on the comparison of catalytic performances of different crystal sizes HZSM-5zeolites for the conversion of ethanol to propylene, the effects of Si/Al ratio, NaOH solutiontreatment on the activity of the nanosized HZSM-5zeolite were studied. The preparedcatalysts were characterized by XRD, ICP-OES,27Al MAS NMR, N2adsorption/desorption,Py-IR, TG-dta to investigate the influence of the physico-chemical properties of the nanosizedHZSM-5zeolite on its catalytic performances for the conversion of ethanol to proplyene.The ZSM-5zeolites with different crystal sizes but the same Si/Al ratio were successfullysynthesized. With the crystallite size decreasing, the surface area, pore volume and porediameter of the HZSM-5zeolite increased, but the acidic properties of HZSM-5catalysts arevery similar. The small-sized HZSM-5showed higher propylene selectivity and betterstability than larger-sized HZSM-5during the ethanol conversion testing due to its larger porevolume and shorter channels.Four nanoscale ZSM-5zeolites with different Si/Al ratios were synthesized usinghydrothermal synthesis procedure. The crystal sizes and textual properties of the fourHZSM-5catalysts are very close, but their acidic properties are strongly influenced by theSi/Al ratio. The decreased Si/Al molar ratio of HZSM-5zeolite led to an increase both instrong acid sites and weak acid sites. During the ethanol conversion testing，the Si/Al ratios ofHZSM-5considerably affect the propylene selectivity and catalytic stability. The lower Si/Alratio nanoscale HZSM-5shows better stability.By treating nanoscale HZSM-5zeolites with appropriate concentration of NaOH solution(0.1M), their strong acid sites decrease, pore volume and pore diameter increase. Therefore,its propylene selectivity increased and lifetime prolonged. However, by treating HZSM-5zeolites with high concentration of NaOH solution, its medium acid sites increase and textualproperties get optimized, but catalysts frame structure is destroyed, resulting in a remarkabledecrease both in propylene selectivity and catalyst stability.