Highly para-selective alkylation of toluene by methyl mercaptan over silylated ZSM-5 zeolite

• Toluene was efficiently alkylated by methyl mercaptan over H-ZSM-5 (E a = 80 kJ/mol) • Through a Friedel-Crafts mechanism, xylenes were the dominant products. • Over 12%SiO 2 /ZSM-5 catalyst, the para -selectivity was about 98% Friedel-Crafts alkylation of toluene with methyl mercaptan has been investigated in the presence of H-ZSM-5 and SiO 2 /H-ZSM-5 catalysts. The silica layers have been built on H-ZSM-5 zeolite by chemical liquid deposition of tetraethyl orthosilicate. The passivation with silica of the external surface of H-ZSM-5 zeolite has been confirmed by FT-IR spectroscopy and mesitylene isomerization, used as a model reaction. All catalysts exhibited notable behavior in the alkylation of toluene to xylenes. Efficiencies higher than 98 % in alkylation for both toluene and methyl mercaptan were obtained at 375 °C. In terms of para -selectivity, outstanding performance was revealed by the silylated zeolites. Thus, over 12 % SiO 2 /H-ZSM-5, at 375 °C and WHSV = 9.4 g toluene+CH3SH g cat -1 h −1 , the para -xylene selectivity was close to 100 %. The experimental apparent activation energy for the toluene alkylation with methyl mercaptan catalyzed by H-ZSM-5 was 80 kJ/mol.