Impact of acidic properties of HBEA zeolite on isomerization of 1-methylnaphthalene

Selective isomerization of 1-methylnaphthalene was carried out in a fixed-bed reactor over HBEA catalysts modified by acid and tetraethoxysilane treatments, respectively. Catalysts were characterized by X-ray diffraction, NH3 temperature-programmed desorption, N2 physisorption, inductively coupled plasma analysis, thermogravimetric analysis and Fourier transform infrared spectrometry after adsorption of pyridine. The results demonstrated that tetraethoxysilane treatment successfully passivated external active sites of the zeolite, but had little effect on the selectivity of isomerization reaction and catalytic stability. Dealumination of HBEA zeolite by treatment with oxalic and hydrochloric acids can lead to higher surface area and pore volume. Sufficiently strong Brönsted acidic sites were found to be responsible for the isomerization activity. Furthermore, a decrease in the number of Lewis acidic sites in acid-modified zeolites were advantageous to suppress the hydride transfer and subsequent side reactions that form coke, leading to higher 2-methylnaphthalene selectivity and longer catalytic life.