One‐Pot Conversion of Lignin into Naphthenes Catalyzed by a Heterogeneous Rhenium Oxide‐Modified Iridium Compound

Abstract

The direct transformation of lignin into fuels and chemicals remains a huge challenge because of the recalcitrant and complicated structure of lignin. In this study, rhenium oxide‐modified iridium supported on SiO2 (Ir‐ReOx/SiO2) is employed for the one‐pot conversion of various lignin model compounds and lignin feedstocks into naphthenes. Up to 100 % yield of cyclohexane from model compounds and 44.3 % yield of naphthenes from lignin feedstocks are achieved. 2 D HSQC NMR spectroscopy before and after the reaction confirms the activity of Ir‐ReOx/SiO2 in the cleavage of the C−O bonds and hydrodeoxygenation of the depolymerized products. H2 temperature‐programmed reduction, temperature‐programmed desorption of NH3, IR spectroscopy of pyridine adsorption, X‐ray photoelectron spectroscopy, X‐ray absorption fine structure analysis, and control experiments reveal that a synergistic effect between Ir and ReOx in Ir‐ReOx/SiO2 plays a crucial role in the high performance; ReOx is mainly responsible for the cleavage of C−O bonds, whereas Ir is responsible for hydrodeoxygenation and saturation of the benzene rings. This methodology opens up an energy‐efficient route for the direct conversion of lignin into valuable naphthenes.

Deoxydehydration and Catalytic Transfer Hydrogenation: New Strategy to Valorize Tartaric Acid and Succinic Acid to γ-Butyrolactone and Tetrahydrofuran

“…It is also reported that ReO x NPs contain ammonium ion, which is probably a Brønsted acid site in the catalyst [22]. In addition to dehydration, the acid sites on [32]. The control test without catalyst under the same conditions (250 • C, 1 h) yielded ester compounds (Figure 1a).…”

Rhenium – A Tuneable Player in Tailored Hydrogenation Catalysis

“…A transformation of lignin into smaller units by a hydrogen source can lead either to complete reduction (cycloalkanes) or aromatic compounds (phenols, guaiacol, and syringols), depending on reaction conditions, such as H 2 pressure [50,57] . Occasionally, complete hydrogenation of lignin by H 2 is avoided for aromatic monomers production.…”

Advances in Versatile Nanoscale Catalyst for the Reductive Catalytic Fractionation of Lignin

“…IrÀ ReO x /SiO 2 with Lewis acid sites (Figure 8b, v˜= 1450 and 1490 cm À 1 ) and Brønsted acid sites (v˜= 1540 and 1490 cm À 1 ) showed an extraordinarily high catalytic activity in the one-pot hydrogenolysis of lignin feedstocks and lignin model compounds into naphthene. [117] The excellent activity of IrÀ ReO x /SiO 2 has mostly resulted in the synergistic effect between the hydrogenating sites on Ir 0 and acidic sites on ReO x /SiO 2 . Compared with noble metal Ir, mesoporous silica supported Ni-based catalysts are more common and economical in hydrogenolysis of lignin.…”

“…b) FTIR spectra of adsorbed pyridine on Ir/SiO 2 , ReO x /SiO 2 , and IrÀ ReO x /SiO 2 . [117] Reused with permission. Copyright 2020, Wiley-VCH.…”