Hydroconversion of n-heptane over Pt/Al-MCM-41 mesoporous molecular sieves

摘要

Pt/Al-MCM-41 samples with constant metal loading but various pore sizes were hydrothermally synthesized using cetyltrimethylammonium bromide (CTAB) surfactant with different alkyl chain length (pore diameters ranging from 1.7 to 2.7 nm). These samples were carefully characterized by X-ray diffraction, N2 physisorption, the infrared spectra, temperature-programmed desorption of ammonia, and solid-state MAS NMR. Hydroconversion of n-heptane was carried out over these Pt/Al-MCM-41 samples. It was found that the steric restrictions are negligible for this catalytic system and high catalytic activity and high isomer yield were achieved. Another finding was that the radius of curvature of pore wall surface had effect on the hydroconversion of n-heptane. It was speculated that the main reason for the curvature effect in this particular model system was that the formation of alkylcarbenium ions, also denoted as the transfer of proton, was affected by the distribution of acid sites on the pore wall surface.