Origin of catalytic activity in sponge Ni catalysts for hydrogenation of carbonyl compounds

Computational results are presented from density function theory (DFT) that describe the reactivity of Al and early transition metal doped, sponge Ni catalysts. To develop an understanding of the catalytic activity of these materials, the direct reduction of acetaldehyde has been studied as a test system. Use of the scaling paradigm proposed by Norskov and co-worker shows the influence of dopant atoms upon the atomic adsorption energy of C and O and consequently adsorption energies of reaction intermediates. Construction of a simple kinetic model (parameterized from DFT) demonstrates that the presence of Al improves catalytic performance of carbonyl hydrogenation by increasing the reactivity towards O containing molecules, whilst at the same time decreasing the affinity towards C. Comparison is made to acetylene hydrogenation, where the activity is dependent on the C affinity of the catalysts. It is thus suggested that should one desire to selectively hydrogenate a carbonyl group in the presence of an alkene then the use of early transition metal dopants may facilitate this selectivity. Alternatively, one could use a dopant that is able to reduce the affinity for C but maintains a high O affinity. The origin of the activity change due to doping is shown to be the intrinsic electronic structure of the dopant rather than a perturbation of the lattice constant due to the dopant atom.