**Ru-Catalyzed Oxidative Cleavage of Guaiacyl Glycerol-**β**-Guaiacyl Ether-a Representative** β**-O-4 Lignin Model Compound**

### **Mayra Melián-Rodríguez 1, Shunmugavel Saravanamurugan 1,2, Sebastian Meier 1, Søren Kegnæs 1 and Anders Riisager 1,\***


Received: 19 September 2019; Accepted: 30 September 2019; Published: 3 October 2019

**Abstract:** The introduction of e fficient and selective catalytic methods for aerobic oxidation of lignin and lignin model compounds to aromatics can extend the role of lignin applications in biorefineries. The current study focussed on the catalytic oxidative transformation of guaiacyl glycerol-β-guaiacyl ether (GGGE)–a β-O-4 lignin model compound to produce basic aromatic compounds (guaiacol, vanillin and vanillic acid) using metal-supported catalysts. Ru/Al2O3, prepared with ruthenium(IV) oxide hydrate, showed the highest yields of the desired products (~60%) in acetonitrile in a batch reactor at 160 ◦C and 5-bar of 20% oxygen in argon. Alternative catalysts containing other transition metals (Ag, Fe, Mn, Co and Cu) supported on alumina, and ruthenium catalysts based on alternative supports (silica, spinel, HY zeolite and zirconia) gave significantly lower activities compared to Ru/Al2O3 at identical reaction conditions. Moreover, the Ru/Al2O3 catalyst was successfully reused in five consecutive reaction runs with only a minor decrease in catalytic performance.

**Keywords:** aerobic oxidation; ruthenium; heterogeneous catalysis; lignin valorization; guaiacyl glycerol-β-guaiacyl ether
