Effect of MFI Zeolite Crystal Size on Its Catalytic Performance in Toluene Disproportionation

The paper describes the physicochemical characterization and catalytic testing of MFI zeolites (both parent and P-modified) with crystal sizes varying from 0.15 to 6 μm. Their physicochemical properties were examined by X-ray diffraction analysis, X-ray fluorescence analysis, scanning electron microscopy, low-temperature nitrogen adsorption, IR spectroscopy, and ²⁷Al and ³¹P MAS NMR spectroscopy. Both the parent and P-modified MFI zeolites were then tested in toluene disproportionation. In the case of parent zeolites, a 15-fold reduction in the crystal size doubles toluene conversion but has no effect on p-selectivity. Phosphorus modification reduces the concentration of acid sites in the samples. In this case, increasing the crystal size to 3–6 μm enhances the p-selectivity up to 78.2%.