Thesis of Roger Deplaze

defense of thesis Roger Deplaze - laboratory UCCS

Abstract :

The shift from fossil-based to renewable resources is crucial for mitigating climate change and environmental harm. While bio-based feedstocks are gaining importance, lignin - a complex and underutilised biopolymer - remains largely untapped as a source of renewable aromatics. A promising approach for its valorisation involves fast pyrolysis followed by catalytic hydrodeoxygenation (HDO) to reduce the oxygen content in the resulting oil. This thesis, conducted within the ANR project PYRODEOX, explores transition metal catalysts designed to selectively deoxygenate lignin-derived compounds without excessive hydrogenation.
Using m-cresol as a model molecule, SBA-15-supported bimetallic Ni-based catalysts were tested under gas-phase HDO conditions (300 °C, ambient pressure). The first part examined NiFe/SBA-15 catalysts with varying compositions and particle sizes. Increasing Fe content reduced activity and selectivity toward toluene, the target aromatic product. However, several NiFe catalysts, where alloying had been assured, achieved aromatic selectivities >= 90 %, demonstrating the potential of well-alloyed systems with optimised surface composition.
The second study focused on NiCu/SBA-15 catalysts prepared via glycine-assisted combustion impregnation. Partial substitution of Ni with Cu significantly enhanced both activity and aromatic selectivity. An optimal 1:1 Ni/Cu ratio achieved up to 94 %. Reaction pathway analysis suggested dynamic equilibria between m-cresol and its hydrogenated intermediates (m-OL and m-ONE), which probably acted as reversible reservoirs feeding into the DDO route - highlighting the influence of catalyst composition on mechanism.
The third study introduced a modified mesostructured silica synthesis using CTAB-based metallosurfactants to prepare single atom catalysts (SACs). A Ni-SAC showed three times the activity of the next best Ni catalyst and 91 % DDO selectivity, both attributed to the high metal dispersion. In contrast, the NiCu-SAC underperformed, illustrating the complex interplay of atomic structure and composition in SACs.
Overall, this work shows how nanoscale catalyst design - through control of composition, and dispersion - can effectively guide the HDO of lignin-derived compounds toward valuable aromatics, offering key insights for future biomass valorisation efforts.

Keywords: Heterogeneous Catalysis,Ni; Cu; Fe,HDO,m-cresol,SBA-15