Reactivation of zeolite and oxide catalysts using nitrous oxide

Abstract

A novel procedure for the removal of carbonaceous deposits from catalysts using nitrous oxide is described. The general applicability of this method is demonstrated for zeolites H-Y and H-ZSM-5, acid-treated clinoptilolite and supported tungsten oxide as catalysts for hex-1-ene cracking and methanol conversion reactions. The method is particularly effective for acid-treated clinoptilolite as this material cannot be successfully reactivated using a standard oxygen method. Additionally with zeolite H-Y the procedure permits total removal of the carbonaceous deposits, which cannot be readily achieved using oxygen. For the catalysts investigated, nitrous oxide exhibited a marked variation in its reactivation activity (acid treated clinoptilolite > H-Y > H-ZSM-5 > 10% WO₃/Al₂O₃), a feature which is not observed with the standard oxygen reactivation procedure. Studies of N₂O decomposition of both coked and uncoked catalysts demonstrate that the main process occurring during N₂O reactivation is the direct oxidation of the coke deposit by molecular N₂O. The reactivation efficacy observed is expressed in terms of (a) the amount of coke deposited on the catalyst and (b) the structure of coke deposit which has been studied using solid-state ¹³C magic-angle spinning nuclear magnetic resonance spectroscopy.