Radius of Curvature Effect on the Hydrotransformation of N-Heptane Over Mesoporous Al-Mcm-41

A series of both sodium-containing and sodium-free Al-MCM-41 samples with various pore sizes were hydrothermally synthesized using surfactant with different alkyl chain length (pore diameters ranging from 1.7 to 2.7 nm). They were extensively characterized by X-ray diffraction, N2 physisorption, the infrared spectra, the temperature-programmed desorption of ammonia, and solid-state NMR. Hydrotransformation of n-heptane was used as a model reaction to probe the pore wall surface curvature effect on catalytic performance. A distinct effect of radius of curvature on the hydroconversion occurs in this reaction system with and without the presence of sodium. It was speculated that the main reason for the pore diameter effect in this particular model system is that the formation of carbonium ions, also denoted as the transfer of proton, is affected by the local curvature of Al-MCM-41 since the steric effect or pore diffusion is not noticeable when the molecular size and pore dimension are compared.