Acylation of phenol on solid acids: Study of the deactivation mechanism

C.L. PADRO AND C.R. APETEGUÍA

CATALYSIS TODAY

Elsevier

Año: 2005 vol. 107 p. 258 - 265

0920-5861

The deactivation mechanism of the gas-phase synthesis of o-hydroxyacetophenone (o-HAP) via acylation of phenol with acetic acid was studied on Al-MCM-41 and zeolites HY, HBeta, and HZSM-5.  The o-HAP yield remained constant with time on stream on HZSM-5 but drastically decreased on the other samples because of coke formation.  The origin and nature of coke precursor species were studied by employing as reactants the key reaction intermediates and products involved in the phenol acylation reaction network.  It was found that coke precursors are formed from consecutive condensation reactions, and not from any ketene formation by phenyl acetate decomposition.  Specifically, it is proposed that o-acetoxyacetophenone (o-AXAP), which is formed by reaction between o-HAP and acetic acid, is the key intermediate specie responsible for the formation of carbonaceous deposits and, consequently, for the activity decay observed on Al-MCM-41, HY, and HBeta samples.  The narrow pore size structure of zeolite HZSM-5 would hinder the formation of bulky o-AXAP, thereby decreasing drastically the formation of coke.