Navegando por Assunto "Espectroscopia de Al e Si MAS NMR"

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Effect of cerium loading on structure and morphology of modified Ce-USY zeolites
(2011-10) GARCIA, Fillipe Augusto da Costa; ARAÚJO, Daniel Ribeiro; SILVA, Júnia Chaves Marinho; MACEDO, Julio Lemos de; GHESTI, Grace Ferreira; DIAS, Sílvia Cláudia Loureiro; DIAS, José Alves; ROCHA FILHO, Geraldo Narciso da
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 CeOx 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 CeOx species.