Acidity and m-xylene isomerization activity of large pore, zirconium-containing alumino-silicate with BEA structure

Abstract

A large pore, zirconium-containing alumino-silicate with BEA structure, Zr–Al-¯ (SiO2/ZrO2D100 and 50; SiO2/Al2O3D25), has been synthesized hydrothermally using TEAOH as template and characterized by XRD, FTIR, and diffuse reflectance UV–visible spectral techniques to show that Zr4C ions are isolated and are probably linked to the framework of the aluminosilicate of BEA structure. The FTIR studies of adsorbed pyridine, evacuated at different temperatures show an increase in Lewis as well as Brønsted acidity of Zr–Al-¯ samples in comparison to Zr-free Al-¯ and Zrimpregnated Al-¯, having similar Al contents. The enhancement is probably the result of incorporation of Zr4C ions into the ¯ structure as Si¡O±¡ : : : Zr±C linkages. The catalytic activity of Zr–Al-¯ samples is demonstrated in the isomerization of m-xylene at atmospheric pressure in a fixed bed reactor. The additional acidity of Zr–Al-¯ catalyst has been correlated with a marginal increase in the isomerization activity as well as selectivity to the isomerization products rather than the disproportionation products, particularly at temperatures below 500 K.