Nitrogen Sorptiometric Study of Phosphation and Dispersion of Lanthanum(III) Oxide on Alumina Catalysts

• Published in: Adsorption science & technology Vol. 29; no. 10; pp. 927 - 941
• Main Authors: Mekhemer, Gamal A.H., Bukhzam, Ali F., El-Towaty, Amal S., Zaki, Mohamed I.
• Format: Journal Article
• Language: English
• Published: London, England SAGE Publications 01.12.2011
• Subjects: Adsorption; Catalysis; Catalysts; Dispersions; Impregnation; Oxides; Surface chemistry; Three dimensional
• ISSN: 0263-6174; 2048-4038
• DOI: 10.1260/0263-6174.29.10.927

Alumina-supported lanthanum(III) oxide catalysts at loadings varying in the range 3–30 wt% La2O3 were prepared by wet impregnation and calcination at 920 K for 2 h. An analogous series of catalysts were phosphated by impregnation with up to 6 wt% PO43– from aqueous solutions of (NH4)H2PO4 and then calcined similarly. The catalysts thus obtained were characterized by X-ray diffractometry, infrared spectroscopy and nitrogen sorptiometry at 77 K. The adsorption data were analyzed by the BET method and the t-method. The results suggested that lanthanum(III) oxide loadings up to 30 wt% exist as high-dispersion two- and three-dimensional structures on the surface of alumina that are not XRD-detectable (particle size < 2 nm). Strong interactions not only at the liquid/solid interface established during impregnation, but also at the solid/solid interface established during drying and/or calcination, are suggested to be important events in the dispersion mechanism. Phosphation led to the improvement of the two-dimensional lanthanum(III) oxide dispersion (probably in monolayers) rather than the three-dimensional one, most likely through direct bonding of the phosphate groups to exposed La3+ sites. It is inferred that nitrogen adsorption data can provide valuable qualitative information on the dispersion of supported oxide materials.