Temperature programmed desorption (TPD) and X-Ray photoelectron spectroscopy (XPS) studies on clean polycrystalline graphite under Ultra High Vacuum conditions are described. The same three strongly bound oxygenated species are formed after O 2 , CO 2 and H 2 0 adsorption. They decompose to give CO at 973, 1093 and 1253 K. Small amounts of CO 2 are also produced after adsorption of these gases, with desorption temperatures at 463, 573, 693, 793 and 793 K. Attempts are made to ascribe these TPD features more precisely. After H 2 0 adsorption, some H2 is evolved at ca. 1300 K. Hydrocarbons (C l -C 6 ) are also produced, but is smaller amounts. A general mechanism is proposed for the gasification reactions of graphite with O 2 , CO 2 and H 2 0. Physical wetting of the clean graphite surface leads to a H 2 0 molecule re\'ersibly bound to the carbon surface. According to XPS data, a hydrate type of bond is proposed. Considerations on the non-catalytic as well as on the catalytic steam gasification of graphite are made. It is suggested that in both cases the reaction is not only controlled by the desorption of the products, i. e. the decomposition of the surface intermediates, but also by the sticking probability of the H 2 0 on the graphite edges.

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Temperature programmed desorption (TPD) results after chemisorption of carbon monoxide (CO) and carbon dioxide (C0 2 ) on polycrystalline graphite are presented. CO adsorbs onto graphite 'with a very low sticking coefficient « 10-12 ).After CO chemisorption, CO (mass 28 amu) desorbs in two temperature regions, between 400 and 700 K, and between 1000 and 1300 K, and CO 2 (mass 44 amu) des orbs below 950 K. The intensity of the CO 2 signal is less than one order of magnitude lower than the CO intensity. After CO 2 adsorption the major desorption product is CO at high temperatures (lOOO

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The adsorption of NO and NH3 on V205/Ti02 catalysts has been studied by ESR and XPS at temperatures and pressures close to those used for industrial tail gas cleanup from power plants and HNO, plants, using NO reduction with ammonia. The paper extends and confirms earlier studies on pure V20s and Ti02 samples.' The reduction of the vanadia sites by adsorbed NH3 occurs over the whole range of temperatures studied while NO adsorption is observed on the titania support. Reduction of NO to N2 occurs on the reduced vanadia sites, which are reoxidized in the process. The reduced vanadia sites, however, are blocked by chemisorbed NH,, preventing the reduction of NO which causes a drop in the NO molar conversion. The presence of oxygen (or water) in the reaction mixture plays a major role in the selectivity of the vanadium oxide catalyst since it interacts with NH, at the reduced vanadia sites, resulting in the elimination of the NH3 poisoning of the reduced surface sites at temperatures above 550 K. 1989, 55, 15 1. (14) Inomata, M.; Miyamoto, A.; Murakami, Y. J . C a r d 1980, 62, 40. (15) Odenbrand, C U. I.; Lundin, S. T.; Anderson, L. A. H. Appl. Carol.