Hydrodeoxygenation (HDO) of lignin-derived model compounds at low temperature using perovskites

Hydrodeoxygenation (HDO) is a common upgrading strategy for the production of renewable transportation fuels and chemicals from lignocellulosic biomass by using H2 to selectively cleavage C-O bonds from the recalcitrant oxygenates found in bio-oil. Here, the perovskite lanthanum strontium cobaltite (La0.8Sr0.2CoO3) was, for the first time, used as catalyst for vapor-phase conversion of lignin-derived oxygenates, anisole and guaiacol, being effective at low temperature (473-623 K) and hydrogen pressures (PH2≤ 2 bar). In particular, selectivity toward C-O and C-C could be tuned: while C-O bond cleavage was achieved at lower temperatures and higher PH2, higher temperature and lower PH2 increased the selectivity toward C-C bond hydrogenolysis (Figure 1a,b). The complete set of results suggest that the hydrogenation/dehydrogenation mechanism plays an important role on perovskites, favoring the C-C bond hydrogenolysis pathway. In particular, the low selectivity towards hydrogenation products, i.e, cyclo-hexane from benzene and methoxycyclohexane from anisol, indicates that once they are formed they fast go to sequential hydrogenolysis. Characterization by X ray diffraction (XRD) and X ray photoelectron spectroscopy (XPS) (Figure 1c) showed that the appearance of metallic Co phase matches the change in selectivity. Comparison with the undoped perovskite, LaCoO3 , and cobalt oxides, showed: 1) the crucial role played by oxygen vacancies and Co2+in tuning the selectivity toward the HDO reaction, and 2) the importance of the peroviskte structure to stabilize the Co2+ phase at higher temperatures and PH2. This work was supported by BP. DZ acknowledges funding by FAPESP and CNPq.