Surface chemical heterogeneity of pillared hydrotalcites

Abstract

A series of pillared hydrotalcite-like structures has been synthesized via synthetic meixnerite, the hydroxide-exchanged form of a Mg,Al hydrotalcite-like precursor, by its anion-exchange reaction with decarbonated water solutions of molybdate or tungstate salts. The X-ray diffraction (XRD) patterns and IR spectra confirmed the formation of hydrotalcite-like compounds with incorporated transition-metal anions. The surface acidity of the modified pillared materials and their calcined intermediates was measured by inverse gas chromatography and potentiometric titration. The pK distributions evaluated from the titration data using a stable numerical method for a solution of the adsorption integral equation (SAIEUS) provided information to identify chemical species present on substrate surfaces and established the basis for assessing the number and strength of surface acidic centres as well as their changes after thermal treatment at 873 K.