SURFACE CHEMICAL HETEROGENEITY OF PILLARED HYDROTALCITES

A series of pillared hydrotalcite-like structures has been synthesized via synthetic meixnerite, the hydroxide-exchanged form of a Mg, Al hy drotalcite-like precursor, by its anion-exchange reaction with decarbo nated water solutions of molybdate or tungstate salts. The X-ray diffr action (XRD) patterns and IR spectra confirmed the formation of hydrot alcite-like compounds with incorporated transition-metal anions. The s urface acidity of the modified pillared materials and their calcined i ntermediates was measured by inverse gas chromatography and potentiome tric titration. The pK distributions evaluated from the titration data using a stable numerical method for a solution of the adsorption inte gral equation (SAIEUS) provided information to identify chemical speci es present on substrate surfaces and established the basis for assessi ng the number and strength of surface acidic centres as well as their changes after thermal treatment at 873 K.