✍ Scribed by Arnaldo C. Faro Júnior; Jean Guillaume Eon; Leonardo Nogueira; Renata F. da Silva; Victor de O. Rodrigues
No coin nor oath required. For personal study only.
H-ZSM5 zeolites were impregnated by the incipient wetness method with gallium amounts varying between 2 and 10 wt.%, and were submitted to reductive and oxidative pre-treatments. The samples were analyzed by XAFS spectroscopy; the 2, 5 and 10 wt.% catalysts were analyzed after ex situ reduction followed by oxidation, while the 3 wt.% catalyst was analyzed after impregnation and after each pre-treatment. Quantitative analysis of the XAFS spectra suggested the presence of three gallium species: (i) bulk b-Ga 2 O 3 probably located on the external surface of the grains; (ii) highly dispersed gallium species, probably dimers, located in the zeolite channels; (iii) gallium clusters, probably tetramers, also located in the zeolite channels. The results show that the increase in gallium content systematically increases the proportion of b-Ga 2 O 3 and tends to form larger clusters (tetramers). On the other hand, the reductive and oxidative pre-treatments reduce the proportion of b-Ga 2 O 3 and tend to generate smaller clusters (dimers). Catalytic activity depends on the proportions of these species.
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A series of H-ZSM-5 samples (Si/Al = 14) were modified by impregnation with phosphoric acid and consecutive calcination. The influence of this modification was investigated by FT-IR and 27 Al and 31 P MAS NMR spectroscopy, temperature-programmed desorption of ammonia with coupled in situ FT-IR. Pho