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Silica-pillared zirconium phosphate shows both micro- and mesoporous character, with an average pore dimension of 23 A after calcination at 480°C. Cu2+ coordinates in solution to the molecular precursor of the silica pillars, 2-aminoethyl-3-aminopropylsiloxane oligomers, and is carried into the interlayer region on contacting this solution with α-zirconium phosphate, where it serves as a probe for the evolution of the intercalated phase to a porous pillared solid on calcination. Electron paramagnetic resonance spectroscopy shows that the environment of Cu2+ changes from (4 + 2) nitrogen + oxygen to one containing oxygen only as the organic functions are eliminated. Above 400°C, (the temperature at which the material starts to exhibit appreciable surface area) and up to 600°C, the e.p.r. spectrum remains unchanged, and these limits define the temperature region in which the silica-pillared phosphate is stable. Two copper sites are identified in the pillared phase. These are considered to correspond to one in which copper is surrounded by oxygen atoms of the silica pillars, suggesting that part of the Cu2+ forms an integral part of the pillars, and a second related to Cu2+ occluded in the pores and accessible to incoming species such as water. |
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