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• W1567232061 abstract "A series of amorphous AlPO4-Al2O3 (APA1-A) catalysts were prepared to contain various A1PO4/Al2O3 weight ratios (Al2O3: 5–15 wt.%). The effect of the weight ratio and calcination temperature (at 773–1273 K, for 3 h) on the structure and texture of the resultant catalysts were determined. The samples were characterized by nitrogen adsorption-desorption, thermogravimetric analysis, differential thermal analysis. X-ray diffraction, high resolution 27Al and 31P MAS NMR and diffuse reflectance infrared Fourier transform spectroscopy. The presence of Al2O3 greatly affected the surface properties of AlPO4 upon heating, exerting a protective effect against sintering, and delaying the crystallization process. The thermal stability of the texture of the APAl-A systems was found to be considerably improved, in comparison with the AlPO4 catalyst, by the stabilization of the amorphous structure in the APA1-A systems, which was found to be fully retained, in the presence of Al2O3, upon calcination up to 1073 K. Calcination at 1273 K develops AlPO4 crystallinity in the α-cristobalite polymorph (which is greater as the Al2O3 content increases) but AlPO4 inhibits both the crystallization of the γ-Al2O3 phase and the γ- to α-Al2O3 phase transition. In particular, incorporation of 5 wt.-% Al2O3 resulted in an APAl-A system with remarkable thermal stability, after calcination, over the entire range of temperatures studied (773–1273 K). Amorphous APA1-A systems contain both tetrahedral and octahedral aluminum (their ratio varies with the Al2O3 content and the calcination temperature) while phosphorus always remains in P(OAl)4 environments. After calcination at 1273 K, only tetrahedral aluminum was found. Two types of aluminum surface hydroxyl groups (at 3786 and 3728 cm−1) and only one type of phosphorus surface hydroxyl group (at 3670 cm−1) are found in the DRIFT spectra. Furthermore, bands at 1130 and 478 cm−1 are found in the skeletal region. These are due to the triply degenerate P-O stretching vibration v3 mode of tetrahedral (PO4)3− and to the triply degenerate O-P-O bending variations v4 mode of (PO4)3− tetrahedra, respectively. A band at 714 cm−1, due to the stretching vibrations of Al-O bonds in combination with P-O bonds, is also found. Therefore the diffuse reflectance infrared Fourier transform spectra substantiated the structural changes in the samples in agreement with XRD and 27Al and 31P MAS NMR." @default.
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• W1567232061 date "1993-03-01" @default.
• W1567232061 modified "2023-09-22" @default.
• W1567232061 title "A1P04-A12O3 catalysts with low alumina content" @default.
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• W1567232061 doi "https://doi.org/10.1016/0926-860x(90)80009-4" @default.
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