Morphology-controlled preparation of heteropolyanion-derived mesoporous solid base

Heteropolyanion-derived mesoporous solid base catalysts were prepared by designing the basic ionic liquid (IL) N-3-[2-(2-aminoethylamino)ethylamino]-2- hydroxypropyl)pyridinium chloride ([TAHpy]Cl) to assemble with Keggin-structured sodium phosphotungstate (Na₃PW₁₂O₄₀) in the aqueous solution containing organic base diethylenetriamine (DETA). The obtained hybrids were characterized by various techniques such as thermogravimetric analysis, elemental analysis, Fourier transform infrared spectroscopy, scanning electron microscope, and nitrogen adsorption experiments. In the synthesis, the concentration of DETA was adjusted to control the morphology and mesostructure of the obtained basic hybrids, and concentrated DETA caused the formation of the mesoporous solid base. The structure analysis indicated that the obtained hybrid demonstrated a piece-like shape in macroscopical size, and these species were assembled by relative uniform small nanoellipsoids with the diameter of ∼50 nm, which forms a loosely packed structure. Assessed in the liquid-solid heterogeneous Knoevenagel condensation, the mesoporous solid base with a morphology of loosely packed nanoparticles presented superior activity, which was about 14 times higher than the nonporous analogues with large block morphology. A possible catalytic mechanism is proposed to explain the efficient catalytic performance.