Catalytic oxidation of toluene over CuNaHY zeolites - Coke formation and removal

Catalytic deep oxidation of toluene at low concentration in air, has been s tudied over CuNaHY zeolites with different copper contents. The reaction ha s been investigated in the course of time-on-stream, at temperatures betwee n 150 and 500 degreesC. The effect of copper content on the conversion of t oluene into CO2 and on the formation of carbonaceous deposits (coke) retain ed inside the zeolite pores has been analyzed as a function of the reaction temperature. The analysis of the coke extracted from the catalysts showed that it is mainly composed of aromatic hydrocarbons and oxygenated aromatic compounds, the latter being predominant at low temperature and preferentia lly formed on the catalysts containing more copper. A bifunctional mechanis m was proposed to explain the formation of coke over CuNaHY catalysts. Base d on the differences of the nature of coke formed on NaHY and CuNaHY cataly sts, and on a discussion about the coke formation and location, it was poss ible to conclude that copper sites are involved in both toluene and coke ox idation reactions. The increase of copper content from 1 to 8 wt.% promotes the oxidation of toluene and facilitates the removal of coke formed in the course of reaction. (C) 2001 Elsevier Science B.V. All rights reserved.