Insights into the structure of active sites in metal-doped solid acid catalysts

Based on our previous H/D exchange studies devoted to the quantification of the number of Brönsted acid sites in solid acids, we report here an innovative approach to determine both the amount and the localisation of different metal atoms inside zeolite materials, or deposited on solid acids. As a case study, the influence of Mo introduction in the MFI framework with different molybdenum loading and Si/Al ratio was investigated in details. Depending on the Si/Al ratio of the zeolite, i.e. the proximity of two Brönsted acid sites, the Mo-atoms substitute a different quantity of OH groups. Consequently, a chemical structure was proposed to ascertain the geometry of the Mo-complex in the channels of the ZSM-5 zeolite. An overview of the possibilities of this H/D exchange method was also given to show its versatility and flexibility to elucidate the structure and bonding of metal cations and oxides on different kinds of solid acids.

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