Preparation of graphitic carbon nitride g-C3N4-HMCM-22 composite catalysts and enhanced para-selectivity in m-xylene isomerization

A series of novel graphitic carbon nitride g-C 3 N 4 -HMCM-22 composite catalysts were successfully prepared. Their structure and acid properties were well characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), N 2 adsorption–desorption, Fourier transform infrared spectroscopy (TFIR), X-ray photoelectron spectroscopy (XPS), Scanning Electron Microscopy (SEM), and Py-FTIR. The prepared g-C 3 N 4 -HMCM-22 composite catalysts were then used for m-xylene (MX) isomerization. The effect of introduction of g-C 3 N 4 on catalytic performance was studied. Compared with parent HMCM-22 catalyst, g-C 3 N 4 -HMCM-22 composite catalysts exhibited an improved p-xylene (PX) selectivity in MX isomerization. Moreover, G1H1 composite catalyst showed the highest PX selectivity than other as-prepared composite samples. Correlating the catalyst performance with its physical and chemical properties uncovers that increasing amounts of Lewis acid sites and effectively inhibiting the external Brönsted acid sites of HMCM-22 would be the key to improving the selectivity of PX.