Moderate VOPO ₄ Modification Balances V ⁵⁺ /V ⁴⁺ Redox Sites for Efficient n‑Butane Oxidation to

ABSTRACT

The selective oxidation of n‑butane to maleic anhydride (MA) over vanadium phosphorus oxide (VPO) catalysts is critically dependent on the synergy between V ⁴⁺ ‑containing phases (VO) ₂ P ₂ O ₇ and V ⁵⁺ ‑containing phases VOPO ₄ . This reaction has long been hindered by a trade‑off between conversion and selectivity. In this study, ultrathin VOPO ₄ nanosheets with varying mass fractions (0.1–0.7 wt%) were attached to the VOHPO ₄ ·0.5H ₂ O precursor, enabling systematic control over the surface V ⁵⁺ /V ⁴⁺ ratio and lattice oxygen content in the V ⁵⁺ phase. An optimal VOPO ₄ loading of 0.3 wt% increased the lattice oxygen content in the V ⁵⁺ phase from 3.85 to 6.76 mmol/g, raising n‑butane conversion from 85.6% to 95.0% and achieving a MA yield as high as 56.0%. Structure–activity relationship studies indicate that the amount of lattice oxygen in the V ⁵⁺ phase is the primary factor regulating n‐butane conversion, and its effect on selectivity depends on whether the lattice oxygen in the V ⁴⁺ phase sites is over‐reduced. The balance between these two factors is fundamental to achieving high performance. However, excessive VOPO ₄ loading (≥ 0.5 wt%) leads to over‑reduction of V ⁴⁺ ‑associated lattice oxygen, thereby disrupting the selective oxidation pathway. This study provides theoretical guidance for optimizing VPO catalysts through precise regulation of the distribution state of V ⁵⁺ species.