AN INFRARED SPECTROSCOPIC STUDY OF THE REACTIONS OF CARBON MONOXIDE AND HYDROGEN WITH ZINC OXIDE

This infrared spectroscopic study of carbon monoxide and hydrogen coadsorption on zinc oxide was carried out with the following two objectives. First, the kinetics of the reactions of CO and H(,2) on zinc oxide were studied at room temperature. Secondly, the effects of differing pretreatments were examined to compare results in the literature which use different pretreatments for different types of experiments.; The adsorption was monitored transiently by a Fourier transform infrared spectrometer. Zinc oxide was pretreated either in oxygen, helium, or hydrogen to simulate several oxidation or reduction pretreatments.; The result of the adsorption depended greatly on the pretreatment used. CO and H(,2) adsorption on oxygen and helium treated zinc oxide resulted in a reversible CO species, a more strongly bound CO species, bidentate carbonates, formyl, formate, and methoxy. The hydrogen pretreatment resulted in the formation of hydroxyl groups on the zinc oxide. This modified the types and quantities of species observed.; A loss of surface area was found with each additional pretreatment. This also resulted in changes in the activity and selectivity for some of the reactions observed. The nonpolar zinc oxide plane is proposed to be the most stable plane by comparing the results with information from the literature.; Untreated zinc oxide was also examined. A previously unreported irreversibly adsorbed linear CO species was observed. This irreversible CO modified the subsequent decomposition of the untreated zinc oxide.; The interactions of CO with zinc oxide were found to be more complex than had been reported previously. A model was presented for the formation of bidentate carbonate from CO. It is proposed that CO reacts with two lattice oxygens of the zinc oxide. This strains the lattice resulting in a carbonate which is distinct from that formed from CO(,2). A model for the strongly bound CO species is also presented consisting of an interaction of CO with this strained carbonate complex.; Finally, the different pretreatments did not produce any shifts in the frequency of the linear CO species as was proposed in the literature.