Effect of partially neutralized aluminum solutions on the texture and pore structure of silica

N-2 adsorption measurements at 77 K were performed on two types of silica of different porosities, and on their products obtained by soaking in partially neutralized aluminum solutions of varying R = [OH]/[Al] = 0.5-2.0 (PH 3-4). TG analysis showed that the Al taken by the mesoporous silica was accompanied by its hydroxyls, but with the predominantly microporous silica it was stripped of some of them, where a strong potential field in the narrow pores compensated for any charge differences. IR spectral analysis showed that for microporous silica the peak (due to Si-O stretching of surface OH) is located at 950 cm(-1) instead of approximately 970 cm(-1) in the case of mesoporous silica, which seems to result from the strong perturbation between hydroxyls at close range in the narrow pores. A reduction in this peak lakes place upon Al treatment that increases with R, with the probable formation of a surface complex of the type =Si-O-Al. Uptake of Al ions produced a narrowing of the pores, that increased with the increase in Al content. From pore structure analysis, the micropore fraction could be sorted into ultramicropores (less than or equal to 10 Angstrom) and supermicropores (10-20 Angstrom). The volume of the former is almost unaffected by any change in Al content. The sizes of the supermicropores and mesopores (greater than or equal to 20 Angstrom) are crucial to the Al uptake. Changes in pore sizes at R greater than or equal to 1.0 facilitate the initial attack of the large Al polymeric species