Characterization and catalytic properties of a saponite clay modified by acid activation

Abstract

A natural saponite was acid activated at room temperature or 90~ with different acid/clay ratios and the products were characterized by powder X-ray diffraction, infrared spectroscopy and thermogravimetry. The leaching of Mg from the octahedral sheets is enhanced by an increase in the acid/clay ratio and by an increase in temperature of activation. Textural properties are reported, and it appears that they are strongly correlated to the presence of a noncrystalline silica phase which is formed during the acid activation process. The resorption of cyclohexylamine indicates that for samples activated at 90~ the number of acid sites in the acidactivated saponites decreases following severe acid treatment. Infrared spectroscopy of adsorbed pyridine on samples after calcination at 500~ suggests that acid ae~2vation at 90~ produces a single type of Bronsted site but two types of Lewis sites whereas activation at room temperature results in only one type of Lewis site in addition to a Br~nsted site. The two Lewis sites are suggested to originate from residual A1 in the clay structure and to AI exsolved from the layers during activation. The dehydration of pentan-l-ol has been used as a further probe to measure acidity by monitoring the degree of conversion and selectivity for the different samples.

Effect of acid activation of Saudi local clay mineral on removal properties of basic blue 41 from an aqueous solution

“…Mg 2+ cations are the most readily removed cations from the octahedral layers (Kooli and Jones, 1997). In our case, the low content in MgO made it difficult to confirm this suggestion.…”

“…The values were expressed per mass of clay mineral at 290°C as to exclude any differences between the amount of physisorbed base or non-exchanged interlayer water (Kooli and Jones, 1997). The raw MtKhl exhibited an acidity of 0.45 mmole of H + /g of clay mineral.…”

Silica adsorbent prepared from spent diatomaceous earth and its application to removal of dye from aqueous solution

“…It is well known that useful modifications of the properties of clay minerals can be achieved by acid activation [9][10][11][12][13], resulting in an increase of surface area and adsorption capacity. This method was preliminarily tested by mixing 5 g of the SDE with common acids (including, sulfuric acid, phosphoric acid, hydrochloric acid, nitric acid, and acetic acid) under the same activation conditions (including temperature, acid concentration, and holding time), maintaining a ratio of solution and SDE: 20 ml g −1 .…”

Surface properties of kaolin and illite suspensions in concentrated calcium hydroxide medium

“…Sitesensitive bands in the Fourier transform infrared (FTIR) of adsorbed pyridine have been employed in the determination of ratios of Brönsted (or protonic) to Lewis (or coordinative) acid sites for various solid oxide surfaces including diatomite [16], zeolithes [17,18] and pillared clays [19][20][21]. Information related to these ratios is important in the evaluation of the potentiality of the clay surface to adsorb hydroxide ions.…”