In situ IR and catalytic studies of the regeneration of acid sites in coked zeolite Y

Abstract

The process of regeneration of zeolite catalyst by coke oxidation was followed by “in situ” experiments in which the coke deposition, and subsequently coke oxidation were carried out inside flow IR cell. The characterization of acid sites by ammonia sorption and desorption, as well as by CO sorption, was done also in the same IR cell without exposing the sample to the air. The information on the nature of OH groups was obtained by recording the spectra at low temperature (170 K) which narrows IR bands and improves resolution. The effect of coke deposition and regeneration on catalytic properties of zeolite was studied in the experiments in which coke deposition and zeolite regeneration were carried out inside IR cell (the properties of such zeolite were characterized by IR spectroscopy) and afterwards zeolite was transmitted to a pulse microreactor and catalytic test was realized. Coke deposition eliminated some hydroxyls (most acidic ones were eliminated the first): IR bands diminished, concentration and acid strength of OH groups decreased. As a consequence, catalytic activity in m-xylene reaction decreased too. Oxygen treatment at 720 K decreased IR bands of coke by ca. 40% but all protonic sites became able to protonate ammonia and became active in m-xylene reaction. However, OH bands which decreased by coke deposition restored their intensity only a little, suggesting that some protonic sites (of relatively low acidity) were “invisible” in IR spectra as OH groups, they were still able to protonate ammonia and to be active sites in m-xylene reaction.