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.