Highly dispersed Keggin phosphomolybdates as deoxydehydration catalysts

Details

Supervisors

Gaigneaux, Eric M.

Faculty

Faculté des bioingénieurs

Degree label

Master [120] : bioingénieur en chimie et bioindustries, à finalité spécialisée

Abstract

enThe realization that fossil fuel sources are finite have sparked a major research effort into the use of renewable biomass as a feedstock for chemicals and fuels. Deoxydehydration (DODH) appears to be an interesting reaction as it enables the conversion of biomass depolymerization products into highly functionalizable olefins. This work investigated the development of ammonium phosphomolybdate ((NH4)3PMo12O40 = NH4PMo) catalysts for the DODH of vicinal diols, exploring their potential as cost-effective and recyclable alternatives to rhenium-based catalysts. Through a systematic approach, the synthesis of both bulk and supported NH4PMo catalysts was optimized using a strategy involving the neutralization of phosphomolybdic acid (H3PMo12O40 = H3PMo) with NH3 and a subsequent posttreatment consisting of heating the sample at different temperatures after this neutralization. Posttreatment at 300°C was identified as critical for achieving the targeted product. PXRD, UV-Vis and IR spectroscopy, confirmed the structural integrity and chemical features of the synthesized catalysts. Bulk NH4PMo demonstrated recyclability, unlike H3PMo. However, the study also highlighted that the active phase primarily operates in a homogeneous manner, irrespective of the catalyst form. This behavior underscores a key limitation in realizing a fully heterogeneous system. TiO2 and SiO2 were evaluated as supports. TiO2 facilitated better dispersion of H3PMo and exhibited higher catalytic performance compared to SiO2, likely due to its amphoteric nature. Samples supported on SiO2 displayed evidence of leaching, with catalytic activity observed during cold filtration tests, further supporting the predominance of a homogeneous mechanism. Finally, further research is needed to detect the nature of the active catalyst phase and determine whether it can be reused and optimized to enhance its activity, minimize its leaching, and explore alternative support materials to maximize their industrial applicability.