Isopropylation of polynuclear aromatic hydrocarbons on Al-containing M41S mesoporous catalysts

MCM-48 with Al incorporated into the walls constructing its mesopores (Al-MCM-48) was synthesized by a hydrothermal method. Al-MCM-48 possesses almost the same surface area, thermal stability and pore size as MCM-48, and has an acidity equivalent to Al-MCM-41. However, in the isopropylation of naphthalene, Al-MCM-48 exhibits a higher activity than Al-MCM-41. This is attributed to its larger pore size and three-dimensional pore system, which is more advantageous for molecular diffusion than the relatively narrow and one-dimensional pore system of Al-MCM-41. Compared with the yields of 2,6-diisopropylnaphthalene on large-pore zeolites, those on A1-M41S (Al-MCM-41 and Al-MCM-48) are not high because of their fewer acid sites. Al-MCM-48 also shows a higher activity than Al-MCM-41 in the isopropylation of pyrene, and the activities on the mesoporous M41S materials were much higher than that on zeolite Y. Isopropylation of pyrene occurs inside the mesopores of M41S, while pyrene derivatives cannot be produced inside the micropores of zeolite Y. However, coke formation and adsorption of the reactant and/or product proceeded in the mesoporous channels and caused catalyst deactivation. The product distributions, especially the ratio of 2-isopropylpyrene/1-isopropylpyrene in pyrene isopropylation, indicate that shape selectivity occurs inside the regular mesopores of M41S.