Chemically Activated Spruce Organosolv Lignin as a Carbocatalyst for Heterogeneous Oxidative Dehydrogenations in the Liquid Phase

Activated carbonsobtained from organosolv lignin by chemical activationwith KOH and oxidized with diluted HNO3 were studied ascatalysts for aerobic oxidative dehydrogenation (ODH) reactions. Thestructure/activity relationship was investigated through multipletechniques revealing the crucial role of oxygen functionality distributionin promoting two mechanistically archetypical ODH probe reactions:(i) the tetrahydroquinoline (THQ) aromatization, which representsODH triggered by hydride transfer, and (ii) the 2-phenyl indole homocouplingreaction, a model for single-electron transfer-promoted reactions.In particular, the catalytic activity, correlating with oxygen functionalitydistribution on the basis of X-ray photoelectron spectroscopy andtemperature-programmed desorption analysis, was associated with theC O surface functionalities, as confirmed by blocking experimentswith 2,2,2-trifluoroethyl hydrazine. Kinetic profiling tools wereemployed to assess THQ ODH product inhibition effects on the overallyield of the process as well as the extent of stoichiometric activityof the carbocatalyst. The breadth of the developed catalysts'applicability was explored through selected relevant ODH reactions.

Automated summary

Activated carbons obtained from organosolv lignin were used as catalysts for aerobic oxidative dehydrogenation (ODH) reactions. The relationship between structure and activity was investigated, and the distribution of oxygen functionality was found to play a crucial role. The catalytic activity was associated with C=O surface functionalities, which was confirmed by blocking experiments. The breadth of the catalysts' applicability was explored through selected relevant ODH reactions.