From woody biomass extractives to health-promoting substances: Selective oxidation of the lignan hydroxymatairesinol to oxomatairesinol over Au, Pd, and Au–Pd heterogeneous catalysts

Aerobic selective oxidation of the naturally occurring lignan hydroxymatairesinol (HMR) to another lignan oxomatairesinol (oxoMAT) was carried out at 70 °C and atmospheric pressure over different gold and gold–palladium catalysts. Several groups of gold catalysts were prepared: Au ion-exchanged on Y-zeolites promoted by Cu, Ni, Fe; Au and Au–Pd supported via deposition–precipitation with urea – DPU on metal oxides (magnesia, alumina, ceria, zirconia, and lanthanum oxide); and Au on alumina, and alumina–ceria–zirconia mixed oxides prepared by the sol–gel method. The catalysts were characterized by ICP-AES, TEM, XPS and UV–Vis techniques. Acidity of supports was studied by an FTIR method using pyridine as a probe molecule. No catalytic activity was detected in case of gold catalysts based on zeolites. Au and Au–Pd catalysts supported on metal oxides showed different activity and selectivity in the HMR transformation depending on the support acidity/basicity and the active phase. The highest activity was reached over Au supported on alumina with big transport pores displaying 100% selectivity to oxoMAT.