含锌HZSM-5催化剂的XPS表征与丙烷芳构化性能

XPS CHARACTERIZATION AND PROPANE AROMATIZATION OVER ZINC PROMOTED HZSM-5 CATALYSTS

用 XPS技术对离子交换法制备的 Zn/ HZSM-5和机械混合法制备的 Zn O/ HZSM-5两种丙烷芳构化催化剂进行了研究。结果表明 ,催化剂上的锌物种有两种形态 ,它们的 Zn(2 p)电子结合能差 (ΔEb=Eb(2 p3/2 ) -Eb(2 p1/2 ) )不同 ,Zn/ HZSM-5上主要锌物种的 ΔEb 比 Zn O/ HZSM-5上的高 1 .46 e V,分别对应于 [Zn(OH) ]+和Zn O。高温氢处理使 Zn/ HZSM-5的 ΔEb 减小 ,且锌含量有所降低 ,表明高温下锌物种与沸石质子酸位的可逆反应使 [Zn(OH) ]+和 Zn O相互间发生了转化。用 NH3-TPD方法对不同催化剂的酸性进行了测定 ,并对催化剂的丙烷芳构化反应性能进行了评价。结果表明 。

Zinc promoted(containing 2%)HZSM 5 catalysts were prepared by ion exchange (Zn/HZSM 5) as well as by physical mixing of ZnO with HZSM 5 (ZnO/HZSM 5) Two types of zinc species were recognized by XPS spectra,which have different electronic binding energy shift on Zn(2 p ),i e Δ E b= E b(2 p 3/2 ) - E b(2 p 1/2 ),and Δ E b=1 46 eV of main zinc species in Zn/HZSM 5 is greater than that in ZnO/HZSM 5 It is believed that the former corresponds to[Zn(OH)] + most likely located at zeolitic exchange positions and the latter to ZnO After treatment of hydrogen 20h at 560 ℃,Δ E b of Zn/HZSM 5 was slightly reduced and the zinc content decreased from 2 12% to 1 67% Results show that the transportation between[Zn(OH)] + and ZnO could be caused at higher temperatures by the reversible solid state reaction of zinc species with zeolitic proton acid The reactivity of propane converting to aromatics over catalysts was evaluated and the acidity of catalysts was measured by means of NH 3 TPD The results show that different zinc species on catalysts play different roles in propane aromatization