多级孔ZSM-5分子筛的制备及其丙烷脱氢制丙烯的催化性能

采用不同浓度的四乙基氢氧化铵(TEAOH)溶液处理HZSM-5分子筛,并通过XRD、XRF、H2化学吸附、吡啶红外吸附(FT-IR)和N2低温物理吸附对样品进行表征分析,考察有机碱溶液对载体和催化剂物化性能的影响。表征结果显示,低浓度的TEAOH溶液处理HZSM-5后形成介孔-微孔多级孔道结构,介孔容积和外比表面积明显增加,进而提高催化剂表面Pt金属裸露度;高浓度有机碱处理则能够明显增加分子筛表面酸性,同时引起催化剂表面Pt分散度下降。采用有机碱处理后的载体上制备了Pt-Sn-Na/HZSM-5催化剂,并在固定床反应器上考察了丙烷脱氢制丙烯的催化活性。结果表明,随着有机碱溶液的增加,丙烷初始转化率逐渐增加,丙烯选择性则逐渐下降,稳定性呈现出先增加后减少的趋势。以20 mol·L-1有机碱溶液处理HZSM-5分子筛为载体制备的催化剂用于丙烷脱氢活性评价显示,反应120 h后丙烷化率为34.93%,丙烯选择为98.67%,该催化剂脱氢活性和稳定性较佳。

Preparation of hierarchical ZSM-5 zeolite and its catalytic performance for propane dehydrogenation to propylene

HZSM-5 zeolites were treated by different concentrations of tetraethyl ammonium hydroxide(TEAOH).The effect of the organicalkali on the physicochemical properties of the suppot and catalysts was studied by means of XRD,XRF,H₂-chemisorption,FT-IR and N₂-adsorption.The results ofcharacterization showed that treating catalysts with low concentrations of organic base TEAOH facilitated the formation of meso-micro complex pores,and the mesoporous volume and outer specific surface area increased obviously.As a result,the degree of exposure of Pt species on the external surface of the catalyst increased.The treatment of high concentration organic base could significantly increase the surface acidity of zeolite and lead to the decrease of Pt dispersion.Pt-Sn-Na/HZSM-5 catalysts were prepared by using the treated zeolites.Their catalytic performance for propane dehydrogenation to propylene was evaluated in a fixed-bed reactor.The results showed that with the increase of organic alkali solution concentration,the initial conversion rate of propane gradually increased,the selectivity to propylene decreased gradually,and the stability increased first and then decreased.The catalyst for propane dehydrogenationwas evaluated,which was prepared with HZSM-5 zeolite treated by 2.0 mol·L^-1 organic base solution.The catalyst exhibited good activity and stability,propane conversion of 34.93% and the selectivity to propylene 98.67% were obtained after reaction for 120 h.