薄片状PtZn@Silicalite-1分子筛的合成及催化丙烷脱氢性能研究

Synthesis of lamellar PtZn@Silicalite-1 zeolite and its catalytic properties for propane dehydrogenation

采用水热晶化法,以四甲基胍(TMG)为形貌调控剂,一步合成封装PtZn纳米合金的薄片状Silicalite-1分子筛(PtZn@Silicalite-1)。采用X射线衍射(XRD)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)等技术对样品进行表征分析,并考察了其丙烷脱氢催化性能。结果显示,加入TMG可有效调控Silicalite-1分子筛晶体的生长取向,晶体沿b轴的尺寸与TMG/SiO_(2)的比值呈反比。在550℃和纯丙烷气氛下,片状PtZn@Silicalite-1催化剂表现出优异的丙烷脱氢性能,经过20 h的连续反应,其失活常数仅为0.007 h^(-1),而常规PtZn@Silicalite-1催化剂为0.013 h^(-1)。结合表征结果,薄片状分子筛催化剂具有更大的外比表面积和更短的b轴直通道,这提高了脱氢活性位的可接近性,缩短了气体分子在孔道中的扩散路径,从而提升了催化剂的活性和稳定性。

The lamellar Silicalite-1 zeolite(PtZn@Silicalite-1)encapsulated PtZn nano-alloy was synthesized in one step by hydrothermal crystallization method with tetramethylguanidine(TMG)as morphology regulator.The catalysts were characterized by X-ray diffraction(XRD),transmission electron microscopy(TEM),and X-ray photoelectron spectroscopy(XPS),and their catalytic performance for propane dehydrogenation was investigated.The results show that the addition of TMG can effectively regulate the growth orientation of Silicalite-1 zeolite crystals,and the crystal size along the b-axis is inversely proportional to the ratio of TMG/SiO_(2).At 550℃and in pure propane atmosphere,the lamellar PtZn@Silicalite-1 catalyst showed excellent propane dehydrogenation performance.After 20 h of continuous reaction,its deactivation constant was only 0.007 h^(-1),while that of the conventional PtZn@Silicalite-1 catalyst was 0.013 h^(-1).Combined with the characterization data,the lamellar zeolite catalyst has larger external specific surface area and shorter b-axis through channel,which improves the accessibility of the dehydrogenation active site and shortens the diffusion path of gas molecules in the pore,thus improving the activity and stability of the catalyst.