Catalysts Research Researcher Announce Breakthrough for Metal Catalyst Preparation
Catalyst researchers at IFP Energies nouvelles (IFPEN) have, for the first time, uncovered a molecular recognition phenomenon between cobalt-based catalyst precursors and the alumina support surface. The discovery could pave the way for future catalyst improvements, the anlysts believe...
Rueil-Malmaison/France – The interaction between transition metal complexes and oxide surfaces is a phenomenon used in a variety of fields like geochemistry, radioactive waste treatment or heterogeneous catalysis.
In the latter, this mainly concerns the preparation of supported metal catalysts, such as cobalt-based catalysts supported on alumina, used in numerous refining processes (hydrotreatment, Fischer-Tropsch synthesis) and chemical processes (conversion of molecules with a single carbon atom, in particular).
Obtaining Stable Grafts by Oxygen Integration
For these catalysts, ab initio quantum calculations, performed within IFP Energies nouvelles' Catalysis and Separation Division, have identified a molecular recognition phenomenon between cobalt-based catalyst precursors and the alumina support surface.
On theoretical gamma-alumina surface models, calculations based on Density Functional Theory (DFT) tend to demonstrate that the metal precursor coordination modes often invoked (coordination at surface hydroxyls) do not generate the octahedral cobalt species observed experimentally. The most stable grafts are obtained by the additional incorporation, in the metal coordination sphere, of oxygen atoms from the alumina network, resulting in a molecular recognition phenomenon, as illustrated in the figure.
In their recent publication, the authors propose a mechanism of epitactic cobalt hydroxide layer growth with the support, explaining the multiple experimental results, and predicting the geometry of the grafting sites together with the way these layers will be oriented with respect to the alumina support.
Passivation Effects and their Causes
A passivation effect of the silica is also demonstrated by calculation of the interaction of the same cobalt precursors with amorphous silica-alumina surface models developed at IFPEN. In fact, the amorphous nature of the surface limits the occurrences of the molecular recognition phenomenon.
These studies represent an advance in terms of the rationalization of the interface phenomena involved in the drying step, during the preparation of heterogeneous catalysts, and pave the way for new opportunities in terms of future investigations during the liquid medium impregnation steps.