H5PMo10V2O40 anchor by OH of the Titania nanotubes: Highly efficient heterogeneous catalyst for the direct hydroxylation of benzene

An efficient catalyst for the direct hydroxylation of benzene to phenol with H2O2 was prepared via the anchor of H5PMo10V2O40 (PMoV2) by OH of Titania nanotubes (TNT) via electrostatic interaction between the Keggin unit of PMoV2 and OH. The results of Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), solid-state 31P nuclear magnetic resonance (solid-state 31P NMR), X-ray photoelectron spectroscopy (XPS) and thermo gravimetric analysis (TGA) demonstrated that PMoV2 was successfully immobilized on the surface of Titania nanotubes by electrostatic interaction. The textural and morphology of PMoV2/Titania nanotubes were characterized by N2 adsorption-desorption, scanning electronic micrograph (SEM) and transmission electron microscope (TEM). PMoV2/Titania nanotubes shows excellent catalytic performance in the hydroxylation of benzene with a 27.3% benzene conversion and 99.1% selectivity to phenol. The results of contact angle and adsorption experiments demonstrate that excellent catalytic performance is attributed to the confinement effect of Titania nanotubes with the nanotube structure and hydrophobic microenvironment, which effectively disperse PMoV2 and concentrate the reactants as well as decrease intrinsic mass transfer resistance. The anchor effect of OH stabilizes and inhibits the leak of PMoV2, leading to good catalytic recyclability with almost unchanged catalytic efficiency after six recycling tests in the acid reaction condition.