ACIDITY AND CATALYTIC ACTIVITY OF SILICA- ALUMINA GELS PREPARED BY COGELATION USING INSTANTANEOUS MIXING METHOD .2. AVERAGE COMPOSITION OF SILICA-ALUMINA GELS PREPARED BY COGELATION USING INSTANTANEOUS MIXING METHOD, AND SURFACE AND BULK COMPOSITIONS OF THEIR PRIMARY PARTICLES
H. Hirano et al., ACIDITY AND CATALYTIC ACTIVITY OF SILICA- ALUMINA GELS PREPARED BY COGELATION USING INSTANTANEOUS MIXING METHOD .2. AVERAGE COMPOSITION OF SILICA-ALUMINA GELS PREPARED BY COGELATION USING INSTANTANEOUS MIXING METHOD, AND SURFACE AND BULK COMPOSITIONS OF THEIR PRIMARY PARTICLES, Nippon kagaku kaishi, (6), 1995, pp. 440-447
Silica alumina gels with various compositions were prepared by cogelat
ion using instantaneous mixing of aqueous solutions of sodium silicate
and aluminium nitrate, followed by washing, drying at 30 degrees C fo
r 24 h and calcining at 500 degrees C for 2 h. The washing is composed
of the two processes: the first is dispersion of the hydrogel into io
n-exchanged water, and the second is separation by filtration of the d
ispersing element. The hydrogels and filtrates were sampled the whole
quantity in every washing through five times. The amounts of elution o
f Na, Si and Al ions from the cogels into their filtrates were examine
d through the repetitive washing process. The chemical compositions of
each gel and each filtrate obtained were determined by chemical analy
sis and ICPE spectroscopy. In order to know the effect on the surface
composition by the calcination, one of the cogels was calcined at the
temperatures up to 500 degrees C, and the alumina content of these sam
ples was examined by XRF analysis.As the results, the decrease of Na i
on content in these hydro-cogels due to repetition of washing could be
recognized. Further, the elution of Si was found to be more than that
of Al for all the cogels, and the elution occurs on the surface of pr
imary particles of the co-gels. It was known that the calcination enha
nces the surface alumina composition. The comparison of the alumina co
ntent of the cogels known by chemical analysis with that known by XRF
analysis showed that the former is the same as the stoichiometrical co
mposition, and the latter is larger than that. We concluded that the s
urface AI,OB composition of primary particles had become markedly high
er than the bulk composition through washing and calcining the hydroge
ls.