Photothermal Catalytic Selective Oxidation of Isobutane to Methacrylic Acid over Keggin-Type Heteropolyacid

Thermal and photothermal catalytic selective oxidation of isobutane to methacrylic acid (MAA) are comparatively studied over a keggin-type Cs_2.9Cu_0.34V_0.49PMo₁₂O₄₀ heteropolyacid acid. An introduction of light was observed to enhance both the i-C₄H₁₀ conversion and the MAA selectivity, and consequently the MAA formate rate, particularly at low temperatures. Characterization results show that oxidation of methacrolein (MAL) to MAA is the rate-limiting step while UV light illumination promotes the oxidation of σ-bonded MAL with OH groups to σ-bonded MAA on the catalyst surface. These results demonstrate a synergistic effect of thermal catalysis and photocatalysis in selective oxidation of isobutane to MAA, which suggests photothermal catalysis as a promising strategy to catalyze the selective oxidation of higher hydrocarbons at relative mild reaction conditions.