Knoevenagel condensation reaction over acid–base bifunctional nanocrystalline CexZr1−xO2 solid solutions

Highly thermally stable three-dimensional spongelike mesoporous CexZr1−xO2 solid solutions consisting of nanometer size particles with different Ce/Zr compositions were synthesized by a modified sol–gel procedure using a triethanolamine/water mixture as a solvent to be used in liquid Knoevenagel condensation reaction. These materials were investigated in detail by means of X-ray diffraction (XRD), Raman spectroscopy, chemical analysis, X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), UV–Vis spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and adsorption microcalorimetry. The XRD, HRTEM and XPS studies proved the presence of nanocrystalline CexZr1−xO2 solid solutions. These solid solutions showed excellent chemoselectivity in the classical Knoevenagel reaction. The large pore sizes (around 10 nm) highlight the possibility of using CexZr1−xO2 as a support material for versatile catalytic systems. The results obtained from NH3 and SO2 adsorption microcalorimetry experiments successfully demonstrated the incorporation of ZrO2 into the CeO2 lattice resulting in both acidic and basic surface sites in a mixed oxide matrix.

Knoevenagel condensation reaction on ceria–zirconia (C/Z) catalysts was studied in the liquid phase to probe effects of acid-basic character of these materials on their catalytic and structural properties. No evident correlation was found between catalytic performances and the basic character of the samples, but the catalytic activity was clearly influenced by the ratio of basic to acidic sites. Lower basic to acidic sites ratio led to higher product yield.Figure optionsDownload high-quality image (104 K)Download as PowerPoint slide