Abstract: Catalytic properties of SiO2-supported ammonium metatungstate (AMT) catalysts calcined at different temperatures were investigated for the vapour-phase o-methylation of catechol with methanol. The catalysts calcined at 533 and 573 K showed relatively high catechol conversion (97%) and guaiacol selectivity (91%). The results of temperature-programmed desorption and infrared spectroscopy of adsorbed pyridine revealed that all the tested catalysts possessed weak acid-base sites, which might be the main active sites of the reaction. The stability of AMT/SiO2 calcined at 533 K was studied, and no obvious activity loss occurred within 46 h. With further increase of reaction time, the catalyst activity decreased gradually, but the selectivity for the main product remained almost steady. According to the results of scanning electron microscopy and TGA-DTA thermal analysis, it can be deduced that the coke deposited on the surface of AMT/SiO2 was the main reason for the catalyst deactivation. The catalytic properties of the catalyst could be partially recovered by calcining the used catalyst at a suitable temperature in air.

Key words: catechol, methanol, o-methylation, guaiacol, ammonium metatungstate, silicon dioxide, supported catalyst