Phenol methylation on acid catalysts: Study of the catalyst deactivation kinetics and mechanism

MARIA EUGENIA SAD; C. L. PADRÓ; C. R. APESTEGUÍA

APPLIED CATALYSIS A-GENERAL

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2014 vol. 475 p. 305 - 313

0926-860X

tThe kinetics and mechanism of coke formation and catalyst deactivation during the synthesis of cresolsfrom phenol methylation were investigated on SiO2?Al2O3, tungstophosphoric acid (HPA) supported onsilica, and zeolites HBEA, HZSM5, HMCM22 and HY. The nature, density and strength of surface acid siteswere probed by temperature programmed desorption of NH3coupled with infrared spectra of adsorbedpyridine. Coke formed on the catalysts during reaction was characterized by temperature programmedoxidation. All the samples deactivated on stream. A linear correlation was observed between the initialcatalyst deactivation and the amount of coke, thereby indicating that coke formation was responsiblefor the activity decay. Coking kinetic studies showed that a significant part of coke was rapidly formedfrom the reactants. When methanol was feeding alone, significant amounts of carbon were formed onthe catalysts (between 0.6% and 6.2%C), particularly on samples containing mainly strong Brønsted acidsites. Nevertheless, the coke amounts formed during phenol methylation were clearly higher (between3.7% and 14.9%C), which showed that phenol was also responsible for coke formation. More insight onthe role of phenol and methanol on coke formation was obtained by characterizing the coke natureusing infrared spectroscopy. Coked samples recovered after methanol decomposition reaction exhibitedIR absorption bands characteristics of olefinic species formed on Brønsted and Lewis acid sites. The IRspectra of coked samples recovered after phenol methylation showed the presence of phenolate, aromaticand polyaromatic species adsorbed mainly on Lewis acid sites.The kinetics and mechanism of coke formation and catalyst deactivation during the synthesis of cresolsfrom phenol methylation were investigated on SiO2?Al2O3, tungstophosphoric acid (HPA) supported onsilica, and zeolites HBEA, HZSM5, HMCM22 and HY. The nature, density and strength of surface acid siteswere probed by temperature programmed desorption of NH3coupled with infrared spectra of adsorbedpyridine. Coke formed on the catalysts during reaction was characterized by temperature programmedoxidation. All the samples deactivated on stream. A linear correlation was observed between the initialcatalyst deactivation and the amount of coke, thereby indicating that coke formation was responsiblefor the activity decay. Coking kinetic studies showed that a significant part of coke was rapidly formedfrom the reactants. When methanol was feeding alone, significant amounts of carbon were formed onthe catalysts (between 0.6% and 6.2%C), particularly on samples containing mainly strong Brønsted acidsites. Nevertheless, the coke amounts formed during phenol methylation were clearly higher (between3.7% and 14.9%C), which showed that phenol was also responsible for coke formation. More insight onthe role of phenol and methanol on coke formation was obtained by characterizing the coke natureusing infrared spectroscopy. Coked samples recovered after methanol decomposition reaction exhibitedIR absorption bands characteristics of olefinic species formed on Brønsted and Lewis acid sites. The IRspectra of coked samples recovered after phenol methylation showed the presence of phenolate, aromaticand polyaromatic species adsorbed mainly on Lewis acid sites.