关键词: 微量吸附热, 凹凸棒粘土, 表面酸碱性质

Abstract: Attapulgite with the composition of [MgAlFe]₅Si₈O₂₀(OH)₂(OH)₂(OH₂)₄₄H₂Ohas beenwidely used as catalyst or catalyst support in various catalytic reactions.The surface acidityand basicity of attapulgite should play an important role, in particular, in the acid/base cat-alyzed reactions.In this paper, a Tian-Calvet type microcalorimeter was used to measurequantitatively the number and strength of acid/base sites on the surface of attapulgite sam-ple.The acid/base properties of the sample were also investigated with infrared spectroscopyand test reaction of isopropanol dehydration.The results indicated that the attapulgite dis-played the acidity with initial differential NH₃ adsorption heat of 130kJ/mol and saturatedNHs coverge of 1.5 pmol/m².The strength distributions of surface acid sites on attapulgiteand the calorometric results suggested that the attapulgite possessed only a few(<0.1 μmol/m²) very weak base sites with CO₂ adsorption heat lower than 5kJ/mol.The infrared spec-troscopy revealed that the attapulgite had both Brdnsted and Lewis acid sites-Moreover, theLewis acid sites(1619 cm^-1 ) were stronger than 90kJ/mol characteric of the NH, adsorptionheat.In summary, the attapulgite was a weak solid acid without any basicity compared tothe γ-Al₂O₃。

Key words: Microcalorimetry, Attapulgite, Surface acidity and basicity