Understanding stability, oligomerization and deactivation during catalytic lignin hydrodeoxygenation by mechanistic reaction micro-kinetics linked with 3D catalyst particle nanotomography

Lignin is an aromatics' natural source that can be converted into separate high value chemical compounds. Due to the highly-functionalised network structure of phenols, the mechanisms, activity and selectivity of the acidsupported transition metal rate catalyst (NiMo/Al2O3) for the hydrogenation, hydrodeoxygenation (HDO) and defunctionalisation of (l) phase model components (eugenol, guaiacol and 4-propylguaiacol) were investigated in this integrated experimental, characterisation and modelling study. Commercially available NiMo/Al2O3 intermediates exhibited strongly acidic properties that did little to promote the complete bond saturation of the allyl-benzenes to alkyl-benzenes, thermodynamically-favoured higher molecular weight compositions (e.g. dimers) formed instead, and deactivation followed. The condensation elementary steps for an independent system constituent were proposed, which is important for understanding, designing and optimizing an efficient valorisation industrial processes engineering. Interestingly, the stabilising steric hindrances of different defined representatives affected product functionality distribution, reactivity and stability. HDO promoted demethoxylation (reaction), while methoxy-phenols were more favourably de-methylated. In addition, NiMo/Al2O3 formulation was analysed to obtain the quantified surface, structural and morphological changes by NH3 activation temperature-programmed desorption (TPD), energy dispersive X-ray spectroscopy (EDS) mapping, Fourier transform infrared spectroscopy-attenuated total reflection (FTIR-ATR), nanometre computed tomography (nano-CT) and physi-sorption. Adsorbed carbonaceous species reduced its physicochemical interface, decreased by acidity.

Automated summary

The mechanisms, activity, and selectivity of the acid-supported transition metal rate catalyst (NiMo/Al2O3) for the hydrogenation, hydrodeoxygenation (HDO), and defunctionalization of lignin model compounds were investigated. The commercially available NiMo/Al2O3 intermediates showed strong acidity, which did not promote complete bond saturation but instead favored the formation of higher molecular weight compositions. The study provides insights for understanding and optimizing efficient valorization processes.