Do happy catalyst supports work better? Surface coating of silica and titania supports with (poly)dopamine and their application in hydrotreating

In order to meet the demand for cleaner fuels, it is necessary to develop high performing hydrotreating catalysts. Although organic additives are often used to improve the performances of hydrotreating catalysts, bio-polymer additives have not yet been thoroughly investigated. We recently showed that dopamine, a neurotransmitter molecule, which is also frequently found in adhesive bio-polymers, efficiently coats the surface of an alumina carrier material and modifies the interaction with active components of hydrotreating catalysts, ie. cobalt and molybdenum. The catalytic performance of the CoMoS/Al2O3 catalysts could, thus, be improved. In the present paper we extend the strategy to other carrier materials (silica and titania). The catalysts prepared on (poly) dopamine (Pdop) coated silica showed enhanced activity for the hydrogenation of toluene reaction and the selective HDS of FCC gasoline model feed. Pdop coating lowers the MoS2 nanocrystallites' stacking on silica, thereby improving the accessibility of active edge sites. The origin of this increase in catalytic activity may be found in the higher capacity of Pdop's functional groups to interact with metallic precursors leading to a better dispersion of the active phase. On the contrary, when the interaction between the dopamine and the support is too strong (as observed for TiO2), the functional groups of Pdop are not available for interaction with Co and Mo species, resulting in decreased catalytic activity.