Abstract:

A series of polyoxometalates(HPMoV) catalysts, H₄PMo₁₁VO₄₀(V1), H₅PMo₁₀V₂O₄₀(V2) and H₆PMo₉V₃O₄₀(V3), with different oxidizability were synthesized. Then Ru³⁺ was combined with HPMoV as Lewis acid cites. As a result, RuPMoV catalysts including Ru_4/3PMo₁₁VO₄₀(4-V1), Ru_5/3PMo₁₀V₂O₄₀(5-V2) and Ru₂PMo₉V₃O₄₀(6-V3) were prepared, which had both acidity and strong oxidizability. XRD, FT-IR, SEM, XPS and NH₃-TPD were used to characterize the structure of the catalysts. The catalytic performance, reaction factors and kinetics were investigated during the reaction of converting levulinic acid(LA) into γ-valerolactone(GVL) in formic acid/water(FA/H₂O) system, where FA was performed as hydrogen source. The results indicated that Ru³⁺ was introduced into the frame of polyoxometalates and the replacement of H⁺ in HPMoV by Ru³⁺, which did not change the structure of polyacid anions. The RuPMoV catalysts had the strong acidity and oxidizability. 5-V2 had the highest catalytic performance; at the condition of 0.1 g 5-V2, 6 mmol FA, 2.5 mmol LA, 5 mL H₂O, 160 ℃ and 8 h, the LA conversion was 98.1% and the GVL yield and selectivity were 97.1% and 99.0%, respectively. The yield of GVL could be up to 87.5% when the 5-V2 catalyst was reused for 5 times.The reaction kinetics exhibited a first-order reaction with the activation energy of 49.59 kJ/mol and the pre-exponential factor of 2.89×10⁵.

Key words: polyoxometalates, levulinic acid, γ-valerolactone, ruthenium