Catalysis by Atomic-Sized Centers: Methane Activation for Partial Oxidation and Combustion
Technical Report,01 Apr 2012,31 Mar 2015
CALIFORNIA UNIV SANTA BARBARA SANTA BARBARA United States
Pagination or Media Count:
The overall goal of this work has been to find chemical and modifications of oxide surfaces that boost their catalytic performance for alkane conversion. Experimental work is done in collaboration with UCSB Professors Michael J. Gordon and Eric W. McFarland. We have examined a large number of modifications doping with higher-valence or lower-valence cations, halogenating the surface, delaminating some oxides to turn them in two-dimensional materials, creating submonolayers of oxides supported on other oxides or on metals, or promoting oxide catalytic chemistry by using molten salts. Based on calculations on a variety of oxide-molecule systems, we proposed a set of general rules that give guidance regarding which surface modifications will improve alkane activation by an oxide catalyst and reduce the number of calculations that need to be performed when analyzing a specific oxide catalyst for a specific alkane. For example, the presence of an acid on a surface will change the site to which a base will bind and will increase substantially the binding energy of the base. This strong acid-base interaction takes place through the oxide the base does not bind to the acid. The acid will influence the binding of the base even if the binding site is several lattice sites away. The same phenomena occur if an acid binds to a surface on which a base is present. Prior to this work it was assumed that in the presence of another species, a molecule will bind to the site to which it binds when it is alone on the surface this is not true if one molecule is an acid and the other is a base. These rules have been used to guide us in deciding which modifications of an oxide surface will increase the catalytic activity for alkane activation. Essentially we found that all lower-valence dopants will activate surface oxygen, making the Mars-van Krevelen mechanism for alkane partial oxidation more efficient.
- Physical Chemistry
- Atomic and Molecular Physics and Spectroscopy