Model silica-alumina acid catalysts for surface science and catalysis studies prepared by argon ion beam sputter deposition using HY-zeolite targets
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Thin films of silica-alumina were prepared by argon ion beam sputter deposition on gold foil using different HY-zeolites as targets. X-ray photoelectron spectroscopy (XPS) results on thin films (< 10 nm) revealed that the Si/Al ratio in the films initially decreases with deposition time, but later becomes very similar to that of the target zeolite. Similarly, the position of O 1s, Al 2p, Si 2p peaks converged to the binding energies for zeolite target used. Based on the line shape of the O KVV Auger transition, we find that there is no segregation of silica and alumina in the films. By scanning electron microscopy (SEM) and scanning Auger electron spectroscopy (SAE) the thin films appear homogeneous. X-ray diffraction (XRD) results on thicker films (∼ 1 μm) indicate that the silica-alumina layers are amorphous.
To test the catalytic activity cumene cracking was performed in a glass reactor. The sputter deposited thin silica-alumina films were active in cumene cracking at 573 K but at least a total of 20 cm2 macroscopic surface area was needed to easily distinguish the activity of the film from the background activity. Similar thin films prepared from alumina or silica or the a mixture of the two were inactive. Thus, the sputtered thin film retains some chemical memory of the target.
KeywordsZeolite thin films sputter deposition of zeolites ion beam deposition of zeolites model acid catalysts
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