Mechanistic studies of alkane partial oxidation reactions on nickel oxide by modern surface science techniques

Abstract

Publisher Summary The partial oxidation of alkanes is an important industrial reaction for the manufacturing of oxygenated hydrocarbons, such as alcohols, aldehydes, and ketones. In this chapter, the reaction of 2-propyl iodide with oxygen has been investigated on Ni(100) surfaces. The reaction of the resulting 2-propyl groups with oxygen on Ni(100) was characterized as a function of oxygen coverage by temperature-programmed desorption (TPD). A variety of products have been observed to desorb from the O/Ni(100) system and the selectivity among them is found to depend strongly on the coverage of oxygen. For low oxygen coverages, acetone is produced in addition to hydrogen, propane, and propene, but at oxygen surface concentrations close to monolayer saturation (0.50 ML) neither acetone nor hydrogen are detected and the amounts of propane and propene, produced from the iodide, are substantially reduced. Furthermore, high oxygen exposures lead to oxidation of the nickel surface, at which point no hydrocarbons desorb at all; only the products associated with total oxidation, namely, CO, CO2, and H2O, are observed. It has been also found that at temperatures slightly above 200 K some of the alkyl groups that remain on the surface migrate to the sites on top of the chemisorbed oxygen atoms, blocking the latter from the incoming probing ions. It is also suggested that acetone detection in the TPD experiments with the iodo alkane is reaction limited. Moreover, it has been observed that the formation of acetone, from 2-propyl groups, is enhanced by the presence of OH groups on the surface to the point of yielding TPD traces similar to those seen for the case of 2-propanol and some acetaldehyde are produced during the oxidation of ethyl groups, if hydroxide species are present on the surface.