One-Step Cyclohexane Nitrosation to e-Caprolactam over Metal Substituted AlPO-5

Abstract

Crystalline AlPO-5, SAPO-5, and metal substituted AlPO-5 (MeAlPOs) were prepared by the hydrothermal method and characterized by X-ray diffraction, N2 adsorption-desorption, scanning electron microscopy, particle size distribution, inductively coupled plasma (ICP) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, NH3 temperature-programmed desorption (TPD), H2 temperature-programmed reduction, and thermogravimetric-differential thermogravimetric (TG-DTG) analysis. All the samples crystallized with the AFI structure. TPD profiles showed that stronger Brønsted acid sites appeared and the number of Lewis acid sites increased when Si or a metal was introduced into the framework of AlPO-5. ICP, FT-IR spectra, and TG-DTG curves confirmed that Si or the metals were incorporated into the framework of the AlPO-5. The catalytic properties of the samples in cyclohexane nitrosation to e-caprolactam were studied. SAPO-5 with a larger BET surface area, more Lewis acid sites, and stronger Brønsted acid sites gave better activity and selectivity than AlPO-5. Among the MeAlPOs, CrAPO-5 with the larger BET surface area, more Lewis acid sites, and stronger Brønsted acid sites gave the better result with a conversion of 8.16% and e-caprolactam selectivity of 68.17%. 采用水热法制备了一系列结晶态的 AlPO-5 (磷酸铝分子筛), SAPO-5 (硅磷酸铝分子筛) 和 MeAlPOs (金属取代型磷酸铝分子筛) 催化剂, 利用 X 射线衍射、N2 吸附脱附法、扫描电镜、粒度分布、电感耦合等离子光谱、红外光谱、NH3 程序升温脱附、H2 程序升温还原和热重-微分热重分析对催化剂进行了表征, 并考察了其催化环己烷亚硝化一步法制备己内酰胺的反应活性. 结果表明, 随着 Si 或金属原子引入 AlPO-5 结构中, 催化剂的 Lewis 弱酸中心增加, 同时出现了 Brønsted 强酸中心. 相对于 AlPO-5, 具有较大比表面积和较多酸中心的 SAPO-5 和 CrAPO-5 表现出较好的环己烷亚硝化反应活性, 后者环己烷转化率为 8.16%, 己内酰胺选择性达 68.17%.