The nature of the bonding within ceramic solids – non-noble metal or semi-metal oxides, carbides, nitrides, sulfides, phosphides, selenides, etc. – varies greatly from strongly ionic to mostly covalent. Likewise, their surface chemical reactivity varies equally as widely and in fundamental nature. Within this range of chemical reactivity lay materials that exhibit similar chemical reactivity as noble metals, but are constructed from non-noble metals and non-metals. Our aim is to develop a fundamental understanding of the bonding within these types of materials such that it may be connected with their surface chemical reactivity and catalytic activity. In this study, we have investigated the oxides, carbides, nitrides, sulfides, and phosphides of titanium (Ti), chromium (Cr), iron (Fe), and nickel (Ni) in the deoxygenation of guaiacol – a model reaction. By studying an extensive suite of first row transition metal ceramics, 20 materials in all, we were able to develop high-resolution trends that correlate surface chemical reactivity with orbital overlap, orbital population, and difference in element electronegativity (ionicity of bonding within solid). Specifically, we found that 1) the production of benzene, toluene, and xylene (BTX) can be enhanced by tuning the surface chemical reactivity towards oxygen such that phenolic oxygen removal is promoted; 2) the over hydrogenation of aromatic rings is diminished when surface bound atomic hydrogen is electron rich; and 3) innate surface chemical reactivity towards atomic carbon correlates well with the production of light hydrocarbon and coke formation. Finally, methylation of the aromatic ring to produce the more valued products toluene and xylene can be promoted by providing a reactive source of CHx groups, e.g., dimethyl carbonate.
See more of this Group/Topical: Catalysis and Reaction Engineering Division