Photocatalytic reduction of levulinic acid using thermally modified niobic acid

Abstract

After the discovery that commercial niobic acid (H0) is able to reduce the levulinic acid in value added molecules, H0 was thermally treated at 200 °C, 400 °C, and 600 °C, generating the niobium oxides H1, H2 and H3 and the photocatalytic improvement towards reduction was investigated. Although the higher temperatures significantly decreased the specific surface area, it was important to remove surface hydroxyl groups and create the T and TT-Nb2O5 phase mixture in H3 which were responsible for its best performance (36.4% of conversion and almost 99% of selectivity for reduced products). To further improve the H3 photoactivity, an identical synthesis was performed in H2 flow to produce oxygen vacancies in the structure of the new photocatalyst (H3OV). This simple modification method increased ∼7% of products yield, which is the best photocatalytic result obtained for pure niobium oxides so far, and proved that it is possible to significantly increase photocatalytic performance without laborious modifications. The electronic and structural differences between H3 and H3OV were investigated by XRD Rietveld refinement, EPR, HR-TEM, DRS and SAED analyses.