In situ FTIR spectroscopy studies on CO and CO2 adsorption on NaX zeolites

Abstract

An infrared cell reactor is described for investigating surface species formed over self-supporting catalyst powder pellet. The cell has provision for <em>in situ </em>evacuation (static or dynamic vacuum upto 10^-5 torr) and pretreatment of a sample under inert or reactive gas medium at elevated temperatures upto 650 K. The cell can be used to investigate a variety of gas-solid interactions under high vacuum or at high pressure conditions as a part of closed system or in a flow through mode. The cell has been used to identify by FTIR spectroscopy surface species formed in the interaction of carbon monoxide and carbon dioxide gases with NaX zeolites at different pressures. In addition to the gaseous carbon monoxide encapsulated in zeolite cages, the CO molecules have been found to be bonded to both the charge balancing and the structural cations giving rise to multiple CO binding states over zeolites in agreement with our earlier thermal desorption spectroscopy studies [<em>J Catal</em><em>y</em><em>sis</em><em>, </em>113 (1988) 398, 120 (1989) 432]. Various carbonate type species and CO₂ adsorbed in different modes have also been detected, which are similar to the surface complexes formed in the interaction of CO₂ with NaX zeolites. The study reveals the sequence of surface processes occurring on exposing dehydroxylated zeolite X to CO.