Unveiling the catalytic active sites of iron-vanadium catalysts for the selective oxidation of methanol to formaldehyde

Abstract

Iron-Vanadium (FeV) catalyst showed a unique catalytic activity for the selective oxidation of methanol to formaldehyde; however, due to its complex compositions, the identification of catalytic active sites still remains challenging, inhibiting the rational design of excellent FeV-based catalysts. Here, in this work, a series of FeV catalysts with various compositions, including FeVO₄, isolated VO_x, low-polymerized V_nO_x, and crystalline V₂O₅ were prepared by controlling the preparation conditions, and were applied to methanol oxidation to formaldehyde reaction. A FeV_1.1 catalyst, which consisted of FeVO₄ and low-polymerized V_nO_x species showed an excellent catalytic performance with a methanol conversion of 92.3% and a formaldehyde selectivity of 90.6%, which was comparable to that of conventional iron-molybdate catalyst. The results of CH₃OH-IR, O₂ pulse and control experiments revealed a crucial synergistic effect between FeVO₄ and low-polymerized V_nO_x. It enhanced the oxygen supply capacity and suitable binding and adsorption strengths for formaldehyde intermediates, contributing to the high catalytic activity and formaldehyde selectivity. This study not only advances the understanding of FeV structure but also offers valuable guidelines for selective methanol oxidation to formaldehyde.