Resumo

FILLIPE A. C, Garcia et al. Effect of cerium loading on structure and morphology of modified Ce-USY zeolites. J. Braz. Chem. Soc. [online]. 2011, vol.22, n.10, pp. 1894-1902. ISSN 0103-5053.  http://dx.doi.org/10.1590/S0103-50532011001000010.

This work describes comprehensibly the effect of cerium loading on the structure and morphology of NH₄USY zeolite. The Ce-USY (2-25 wt.% of CeO₂) was obtained by wet impregnation of CeCl₃ followed by calcination at 550ºC for 8 h. At low loadings (2-10%), cerium species are mainly located at ion exchange positions in the framework, whereas at higher loadings (15-25%), small aggregates were formed on the HUSY surface. X-ray diffractograms (XRD) exhibited only the reflections related to HUSY, demonstrating the high dispersion of cerium species, but Fourier transform Raman spectroscopy (FT-Raman) detected CeO_x for the materials above 10%. Reaction of CeCl₃ with NH₄USY produced NH₄Cl, which decomposed to form HCl, leading to framework dealumination. The materials showed an increased Lewis/Brønsted ratio with increasing cerium loadings due to the interaction between the excess cerium and the OH groups of USY, and the consequent formation of CeO_x species.

Palavras-chave : cerium USY zeolite; cerium oxide; ultra stable Y zeolite; solid-state ion exchange; ²⁷Al and ²⁹Si MAS NMR spectroscopy.