Effects of Cesium Ions and Cesium Oxide in Side-Chain Alkylation of Toluene with Methanol over Cesium-Modified Zeolite X

The side-chain alkylation of toluene with methanol was studied on cesium-modified zeolite X prepared by ion-exchange and impregnation with different cesium precursors. The catalyst was characterized by X-ray diffraction, scanning electron microscopy, X-ray fluorescence spectroscopy, Ar physical adsorption-desorption, NH₃ temperature-programmed desorption (TPD), CO₂-TPD, thermogravimetric/differential thermal analysis, ultraviolet-Raman spectroscopy, energy-dispersive spectrometry, and X-ray photoelectron spectroscopy. Cesium hydroxide was found to be the most effective precursor for modifying zeolite X. Cesium ions bonded on the framework and cesium oxide formed in the pore were found to take different roles in this reaction. Cesium ions could adsorb and activate toluene or modify the basicity of framework oxygen, whereas cesium oxide could ensure the effective conversion of methanol to formaldehyde and inhibit the process of coke deposition. A possible reaction pathway for this reaction over cesium-modified samples was described. The synergistic effect of cesium ions and cesium oxide was proven to be important for the formation of styrene and ethylbenzene.