Hierarchically porous zirconia through precursor-directed large-scale synthesis

Two new precursors, produced by modification of zirconium t-butoxide with 1-dimethylamino-propanol-2 (HDMAP), solid Zr-2(DMAP)(3)((OBu)-Bu-t)(5) (1), and liquid Zr-2(DMAP)(4)((OBu)-Bu-t)(4) (2), were obtained by reaction of 1.5 and 2 equivalents of HDMAP, respectively, in toluene on Zr((OBu)-Bu-t)(4). The produced compounds were characterized by Fourier-transform infrared spectroscopy, H-1 and C-13 nuclear magnetic resonance (NMR), and thermogravimetric analysis (TGA) to estimate their stability and volatility. Action of traces of water in solvents or contact with humid air transforms 1 and 2 into less soluble crystalline Zr-2(DMAP)(3)((OBu)-Bu-t)(4)(OH) (3). Molecular structures of compounds 1 and 3 were established using single-crystal X-ray studies and for 2, they were elucidated by applying 2D H-1-C-13-correlated NMR spectra. The crystals of 1 were subjected to hydrolysis via either storage in ambient atmosphere or immersion into boiling water and the resulting products were characterized by X-ray powder diffraction, TGA, scanning electron microscopy, and atomic force microscopy techniques. The product of hydrolysis in air, ZrO2-1, is essentially nonporous, while hydrolysis in boiling water results in ZrO2-2 with hierarchical macro-, meso-, and microporosity. Both materials are essentially X-ray amorphous with diffraction patterns appearing as oblique curves, resembling unresolved profiles of the monoclinic baddeleyite structure of ZrO2. Heat treatment at 200 and 400 degrees C does not affect essentially the morphology or porosity and leaves the phase composition unchanged, while that at 600 degrees C converts both samples into a tetragonal ZrO2 phase. The ZrO2-2 material is via this treatment losing microporosity and becoming macro-mesoporous with a well-defined pore size of about 3nm. Heat treatment at 900 degrees C results in collapse of pores and transformation into a well-defined monoclinic baddeleyite structure for both materials. [GRAPHICS] .