FACTORS AFFECTING THE DEACTIVATION OF VARIOUS ZEOLITES USED AS CATALYSTS FOR THE DIRECT PARTIAL OXIDATION OF BENZENE TO PHENOL

The way in which zeolites ZSM-5 and EU-1 deactivate when exposed to a mixture of benzene and nitrous oxide has been studied. The deactivation has been shown to be due to the deposition of carbonaceous material within the zeolite structure. It has been shown that upon exposure to the reaction mixture a substantial amount of the internal surface area of the zeolites is lost. The decrease in surface area accessible to the reactant molecules has been measured by the adsorption of nitrogen at -196 degrees C; polyaromatic molecules such as biphenyl and 2-phenoxyphenol are thought to be responsible for this decrease. This material has been found to be removable by treatment in nitrogen at 500 degrees C, causing the zeolites to be partially regenerated. In addition, it has been shown using the temperature-programmed desorption of ammonia that Bronsted acid sites are also blocked by polymeric carbonaceous material. This material is not removeable in nitrogen, the activity of the zeolites being totally regained after treatment in oxygen at 500 degrees C.