Reactive lattice oxygen sites for C₄ hydrocarbon selective oxidation over β-VOPO₄

The role of lattice oxygen species in the catalytic oxidation of n-butane to maleic anhydride has been investigated using β-VOP0₄ labeled with ¹⁸0. The catalyst was prepared by stoichiometric reaction of (VO)₂P₂0₇ with ¹⁸0₂ using solid state preparation techniques. The β-VOPO _{7 2}¹⁸O _{1 2} was characterized using laser Raman and Fourier transform infrared spectroscopies: preferential incorporation at P-O-V sites was observed. A pulse reactor was used to react n-butane, 1-butane, 1,3-butadiene, furan, γ-butyrolactone, and maleic anhydride with the catalyst in the absence of gas-phase O₂. Incorporation of ¹⁸O into the products was monitored by mass spectrometry. Specific lattice oxygen sites could be associated with the reaction pathways for selective or nonselective oxidation. The results of this study also indicate that the initial interaction of n-butane with β-VOPO₄ is fundamentally different from the initial interaction of olefins or oxygenated species. The approach used in this research-referred to as Isotopic Reactive-Site Mapping-is a potentially powerful method for probing the reactive lattice sites of other selective oxidation catalysts.