Basicity and Porosity of a Calcined Hydrotalcite-Type Material from Nitrogen Porosimetry and Adsorption Microcalorimetry Methods

The hydrothermal transformation at 90−95 °C of a slurry of Al2O3/MgO/(CH3COOH)/H2O with molar oxide composition 1:4.4:2.2:1111 produced a hydrotalcite-like (HT) material free from phase impurities and having an approximate unit cell composition of Mg0.66Al0.33(OH)2(CHCOO)0.33. 13C NMR and 27Al NMR spectra have revealed that the air-dried solid contains acetate anions probably as charge-compensating anions in the HT interlamellar space and that all the aluminum is present in octahedral coordination. After calcination in air at 500 °C, the stacks of brucite layers that form the HT crystals exfoliate, forming a stable mesoporous “house-of-cards” structure with pore width in the range 2.5−20.0 nm, characterized by a DFT surface area of 254 m2/g and total pore volume of 0.33 cm3/g at 0.995 p/Po, that is available to sorption and catalysis. A 5-h exposure to 100% steam at 760 °C collapses the HT material forming a residue that contains a well-crystallized MgO and an Al spinel phase identified by XRD. At 30 °C, ...