Understanding oligomerisation during catalytic lignin valorisation
We have recently published an open-access article on the kinetics of eugenol hydrodeoxygenation (HDO), with the aim of describing the stability of the process. In this study, the mechanisms, activity and selectivity of a NiMo/Al2O3 catalyst with acidic support for hydrogenation, HDO and defunctionalisation of model components (eugenol, guaiacol and 4-propylguaiacol) were investigated. The research integrated experimental study, characterization and modelling to gain insight into the process.
Commercially available NiMo/Al2O3 catalyst exhibited strong acidic properties, but had limited effectiveness in fully saturating the allylbenzenes to alkylbenzenes. Instead, higher molecular weight compositions, such as dimers, formed, leading to catalyst deactivation. The study suggested elementary steps for the condensation reaction of the individual system component, which are crucial for the design and optimization of efficient industrial processes for the valorisation of lignin. Interestingly, the presence of various steric hindrances affected the distribution, reactivity and stability of the products.
The NiMo/Al2O3 catalyst formulation was thoroughly analysed to determine surface, structural, and morphological changes by different techniques such as NH3 activation TPD, EDS-mapping, FTIR-ATR, physi-sorption and nanometre computed tomography (nano-CT). A result of a nano-CT image is a variation between blue (lowest X-ray absorption) and red (highest X-ray absorption) colour spectra. The observed variations in colourscale intensities indicated the irreversible binding of the carbonaceous species on the catalyst surface. The presence of adsorbed carbonaceous species reduced the physicochemical interface and acidity of the catalyst.
The proposed oligomerisation mechanism of the lignin model component provides excellent support for the development of catalysts and reaction processes for lignin valorisation, preventing condensation and the formation of undesirable products.
The authors of this research are Tina Ročnik Kozmelj, Matej Žula, Janvit Teržan, Blaž Likozar, Edita Jasiukaitytė-Grojzdek and Miha Grilc from the Department of Catalysis and Chemical Reaction Engineering (D13), Laura Činč Ćurić and Uroš Maver from the University of Maribor. The work is published in Journal of Cleaner Production (IF = 11.072).
Cover graphics: Scheme of oligomerisation and detected catalyst deactivation with 2D/3D Nanotomography