GaZSM-5分子筛的合成、表征及其在甲醇转化制烃(MTH)反应中的催化性能

Synthesis and characterization of GaZSM-5 with different Si/Ga molar ratio and its catalytic performance in the MTH reaction

通过水热合成法制得不同硅镓比的GaZSM-5分子筛,经酸交换后压片成型,得到甲醇转化制烃类的Ga ZSM-5催化剂。采用XRD、SEM、FT-IR、XPS、ICP、低温氮气吸附-脱附、NH_3-TPD和Py-FTIR技术对其进行了表征,并在连续流动固定床反应器上进行MTH反应性能评价。结果表明,分子筛中Ga物种主要以骨架Ga和骨架外表面游离态的Ga2O3两种状态存在。凝胶Si O2/Ga_2O_3配比为60合成所得GaZSM-5分子筛催化剂酸性适中,酸量为0.62 mmol NH_3/g,B酸和L酸比值为4.88,形成较大的晶间介孔孔容,达到0.51 cm^3/g;具有高的M TH活性稳定性,在相同评价条件下,催化剂寿命最高可达到456 h。与Al ZSM-5相比,Ga ZSM-5的酸性弱,能够抑制积炭生成;纳米GaZSM-5的晶间介孔改善了扩散性能,进一步提高反应活性稳定性,催化剂寿命延长120 h。

GaZSM-5 molecular sieve catalysts with different Si/Ga molar ratios were prepared with hydrothermal synthesis method followed by acid exchange and pelletization.The catalyst samples were characterized using XRD,SEM,FT-IR,XPS,ICP,low temperature N 2 physical adsorption and desorption,NH 3-TPD and Py-FTIR.The catalytic performance in the reaction of methanol to hydrocarbons was evaluated in a fixed bed reactor system.The results indicated that there were two kinds of gallium species,i.e.Ga in the framework Ga and Ga 2O 3 species on the crystal surface.The catalysts synthesized from SiO 2/Ga 2O 3(60/1)gel with modest acidity(0.62 mmol NH 3/g and the ratio of B/L 4.88)and large mesopore volume of 0.51 cm 3/g had the best catalytic stability.Under the same reaction conditions,the lifetime of GaZSM-5 catalyst was 456 h.The acid strength of GaZSM-5 was weaker than that of AlZSM-5,which could inhibit the coke formation.The intercrystalline mesopores of the nano GaZSM-5 crystal improved the diffusion property as well the catalyst stability.The GaZSM-5 lifetime was prolonged by 120 h.