t-Butylation of toluene with t-butyl alcohol over mesoporous Zn-Al-MCM-41 molecular sieves

Mesoporous Zn-Al-MCM-41 molecular sieves with Si/(Zn + Al) ratio equal to 75, 151, 228, 304 and 380 were synthesized using cetyltrimethylammonium (CTMA+) surfactants as template under hydrothermal conditions while the mesoporous materials were characterized using several instrumental techniques. The unitcell parameter, surface area, pore size, hydrothermal and thermal stability of Zn-Al-MCM-41 decreases with increasing metal-ions content. The acid sites in the Zn-Al-MCM-41 are higher than that of Al-MCM-41 [M. Selvaraj, A. Pandurangan, K.S. Seshadri, P.K. Sinha, K.B. Lal, Appl. Catal. A: Gen. 242 (2003) 347.] due to the aluminum ions non-framework by the introduction of zinc ions. The effect of reaction temperature, reaction time, t-butyl alcohol to toluene ratios and recyclability on the selectivity of 4-t-butyltoluene was studied. The Zn-Al-MCM-41(75) catalyst containing higher number of Bronsted acid sites was found to be more effective in the alkylation of alkyl aromatics, for example, in the production of 4-t-butyltoluene from toluene, using t-butyl alcohol as the alkylating reagent. The selectivity of 4-t-butyltoluene was obtained under varying experimental condition, viz. effect of reaction temperature, time and ratio of t-butyl alcohol to toluene for the various catalysts to follow the sequence Zn-Al-MCM-41(75) > Zn-Al-MCM-41(151) > Zn-Al-MCM-41(228) > Zn-Al-MCM-41(304) > Zn-Al-MCM-41(380).