Synthesis and catalytic oxidation studies of a novel keggin-type complex catalyst [(CH2)5NH2]5PMo10V2O40

Abstract

Developing efficient and robust polyoxometalate catalysts is highly desirable for green organic oxidation. In this work, we synthesized a novel organic–inorganic hybrid Keggin-type complex, [(CH₂)₅NH₂]₅PMo₁₀V₂O₄₀, via the assembly of phosphomolybdovanadic acid and piperidine. Structural analyses using FT-IR and powder XRD confirmed the intact preservation of the parent [PMo₁₀V₂O₄₀]⁵⁻ framework, while the intercalation of piperidinium cations induced significant lattice expansion and structural rearrangement. Thermogravimetric analysis revealed a remarkable enhancement in thermal stability, with the hybrid resisting decomposition up to 433 °C. The practical utility of this complex was evaluated in the selective oxidation of benzaldehyde to benzoic acid using aqueous H₂O₂ under solvent-free conditions. Under optimal conditions (75 °C, 2.5 h), the catalyst achieved an isolated yield of over 86% with excellent selectivity. This enhanced catalytic performance is attributed to the synergistic V/Mo heterometallic effect combined with the unique hydrophobic microenvironment created by the organic cations.