A DFT study of graphite supported catalysts

Gold catalysed hydrochlorination of acetylene is a convenient alternative to the use of toxic mercury derivatives in large scale production of vinyl chloride. The catalytic performance of supported gold nanoparticles is highly dependent on a series of factors. Amongst them the catalyst support plays a fundamental role. Acid wash of carbonaceous supports has proven to influence the catalytic performances of gold nanoparticles. Atomic force microscopy revealed that after acid treatments the morphology of the graphite support presents spherical features. X-ray photoemission spectra detected the presence of hydroxyl and carbonyl groups which were formed at the surface sites after acid treatments. DFT calculations have been used to give an insight on the mechanisms of formation these features, functional groups and, to support the experimental data. In good agreement with the experiment, it has been found that when water molecules are intercalated within the interlayer space, the graphitic surface presents a curvature and the interlayer distance is largely increased. While pristine graphite is hydrophobic and inert to water, defective surfaces presenting under coordinated carbons show increased reactivity and are able to dissociate water also at room temperature. Pristine graphite surface has a poor particle adhesion but unsaturated carbons of defects or edges can chemisorb atoms and molecules to form strong bonds. Finally, in good agreement with the experiment, DFT results show that the interactions between gold nanoparticles and the hydroxyl groups are stronger than those between gold and carboxyl groups suggesting that the hydroxyls are better anchoring sites for gold nanoparticles than carbonyls