Side-chain alkylation of toluene with methanol over cesium-ion-exchanged zeolite LSX and X catalysts

Abstract

A low-silica X (Si/Al = 1.01, LSX) zeolite was successfully synthesized through a two-step hydrothermal method. It was then modified with Cs⁺ using the ion-exchange method, and the obtained sample was tested as a catalyst in the side-chain alkylation of toluene with methanol. Compared with conventional CsX catalyst, the CsLSX catalyst exhibited improved reactivity in terms of toluene conversion. The toluene conversion was 8.50% on the CsLSX catalyst. One reason for this is that the CsLSX with a low Si/Al ratio had a stronger capacity for basic cation exchange. The greater amount of alkali cations promoted the dehydrogenation of methanol to formaldehyde, which was beneficial for the side-chain alkylation of toluene. Additionally, the higher number of aluminum atoms on the CsLSX catalyst allowed it to have more oxygen atoms with a negative charge (O^δ−) in the zeolite framework. These were more favorable for adsorbing toluene molecules and more effectively activated the C–H bond in the methyl side-chain of toluene. In addition, the CsLSX catalyst also exhibited improved catalytic stability, and enhanced selectivity toward styrene was obtained over CsLSX further modified with Na₂B₄O₇ or ZrB₂O₅.