Acid-Activated Organoclays:  Preparation, Characterization and Catalytic Activity of Acid-Treated Tetraalkylammonium-Exchanged Smectites

Abstract

The catalytic activity of acid-treated clays for reactions involving polar substrates is optimized when the acidity of the surface and the swelling ability of the catalyst are at a maximum. In contrast the activity for reactions using nonpolar substrates is best when the surface area is maximized and the catalyst presents an essentially hydrophobic surface which serves to attract the nonpolar reagents. We have investigated the catalytic ability of acid-activated organoclays (AAOCs) which should provide reasonable levels of acidity, hydrophobicity, and swelling ability for use with nonpolar reagents. A range of organoclays containing tetramethylammonium, dodecyltrimethylammonium, or octadecyltrimethylammonium cations at the 25, 50, or 100% exchange level were prepared and subjected to selected acid-leaching procedures at either 20 or 95 °C. The activity of these AAOCs for the conversion of R-pinene to camphene was investigated. The conditions used for acid leaching seldom removed extensive amounts of organocation, and the yields (40% conversion to camphene) compared favorably with those reported for pillared clays. Acid-leached tetramethylammonium clays were the most active with yields four times higher than those for the corresponding parent clay. Acid-leached dodecyltrimethylammonium and octadecyltrimethylammonium clays were only active when the organocations occupied 25% of the exchange sites.

Bleaching Properties of Alumina-Pillared Acid-Activated Montmorillonite

“…The acid activation of the clay framework is observed to further increase the hydrophobicity of the Al-pillared acid-activated montmorillonite (Schutz et al, 1987). Furthermore, studies on acid-activated organoclays (Breen et al, 1997) attributed their catalytic activity to the hydrophylic and hydrophobic character of the clay surface. The higher hydrophobicity makes the adsorption of an excess of chlorophyll and other pigments on the Al-pillared acid-activated materials easier, thereby concentrating a higher number of colored species on its surface.…”

Adsorption of acid dyes from aqueous solutions onto acid-activated bentonite

“…After acid treatment the Si-O-Al vibration was only observed at 474 cm −1 ; the bending vibration of Si-O-Si was not observed. It is the most sensitive indication of the remains of the layers after extensive acid dissolution [21][22][23][24][25].…”

Microwave synthesis of delaminated acid saponites using quaternary ammonium salt or polymer as template. Study of pH influence

“…Surface area and acidity of natural clays are low and acid treatment and delamination were used to increase surface area (Vaccari, 1999). Among clay minerals, smectites have comparatively high surface area, acidity and swelling capacities making them good adsorption and catalytic materials (Dentel et al, 1995;Breen et al, 1997;He et al, 2001;Alther, 2003).…”