Catalytic oxidation of lignin model non-phenolic monomer Veratryl alcohol over iron containing mesoporous SBA-1

Abstract

Mesoporous solids possessing open framework, tunable pores, high surface area, and considerable thermal stability provide an ideal environment to be employed as solid catalysts, host material, adsorbent, etc. Herein, we report the study about the insertion of iron into the mesoporous silicate framework of SBA-1 and utilize the material as a potential heterogeneous catalyst for the selective oxidation of lignin model non-phenolic monomer, i.e. veratryl alcohol under mild reaction conditions. Veratraldehyde and veratric acid were obtained as the oxidation products. FeSBA-1 in combination with hydrogen peroxide was selective towards veratraldehyde, on the other hand, veratric acid was selectively obtained when tert-butyl hydroperoxide was used as the oxidant under identical reaction conditions. X-ray diffraction pattern of FeSBA-1 revealed the formation of a cubic, three-dimensional SBA-1 structure. HRTEM shows uniform and ordered pore structure having dimensions of ∽ 2.3 ̶ 3.4 nm and wall thickness of ∽ 3.5 nm. FESEM showed regular-shaped FeSBA-1 with spherical morphology having a dimension of ∽ 1.6 μm. BET surface area of 1337 m² g⁻¹ and pore diameter of ∽ 19 Å was determined by N₂ adsorption-desorption measurements. The mesoporous nature of FeSBA-1 was further supported by TGA studies. EPR studies indicated the presence of Fe(III) both in tetrahedral and octahedral coordination within the framework of FeSBA-1. DRUV-VIS studies revealed the presence of Fe(III) in both framework and extra-framework locations of the SBA-1 silicate network. IR studies supported the linkage of Fe–O–Si within FeSBA-1. The absence of the Fe₂O₃ phase was evidenced by Raman studies.