Effects of steam and TEOS modification on HZSM-5 zeolite for 2,6-dimethylnaphthalene synthesis by methylation of 2-methylnaphthalene with methanol

Shape-selective methylation of 2-methylnaphthalene (2-MN) over HZSM-5 catalysts modified by steam and tetraethoxysilane (TEOS) treatments was carried out in a fixed-bed reactor. Catalysts were characterized by XRD, NH3-TPD, BET, FT-IR spectra of pyridine adsorbed, and by adsorption of hexane and cyclohexane. The results show that the TEOS treatment can effectively passivate external active site and narrow pore mouth of catalyst, but it has less effect on the internal surface than steam modification. Hydrothermal treatment can effectively reduce both external and internal acid sites, and adjust channel of catalyst. Steam treatment can effectively increase the ratio of 2,6/2,7-DMN, but the ratio has no increasing trend on TEOS modified catalyst. So adjusting acidity property is more useful to increase the selectivity to 2,6-DMN and the ratio of 2,6/2,7-DMN than narrowing catalyst pore mouth. Tailoring acidic characteristics is more important than spatial control for distinguishing between 2,6-DMN and 2,7-DMN.