Talc modified by milling and alkali activation: Physico-chemical characterization and application in base catalysis

The work aimed at the development of benign solid base catalysts as alternatives for presently used noxious liquid bases. Talc, possessing intrinsic basic properties, was chosen as a particularly attractive and cost-effective precursor. Activation of talc by grinding in a planetary mill followed by treatment with 2 M NaOH was employed as means for basicity enhancement. Such protocol enabled profound modification of talc structure, otherwise resistant to treatment with a basic solution. Deep changes, not addressed in the literature reports so far, took place in the course of combined mechanical and alkali treatment. The amorphized ground talc transformed to the magnesium silicate hydrate (MSH) phase and brucite. Treatment with NaOH led to significant enhancement of surface basicity with respect to the parent materials. The effect was particularly spectacular for alkali-treated, strongly ground talc samples, containing the MSH component. The materials were tested in a base-catalyzed reaction of aldol condensation of acetone. The trend of catalytic activity followed closely the order of surface basicity, which pointed to the key role of MSH as a catalytically active phase in the modified talc solids. Joint mechanical and alkali activation of talc proved to be a simple, yet promising way of developing solid base materials for catalytic applications.