“…Various methods were proposed to determine the solid acidity of montmorillonite (Adams and Mccabe, 2006;Akcay, 2005;Belkhadem et al, 2008;Breen, 1991a,b;Breen et al, 1995;Flessner et al, 2001;Frenkel, 1974;Janek, and Lagaly, 2001;Neaman et al, 2003;Ravindra Reddy et al, 2007;Reddy et al, 2009;Singh et al, 2007;Tyagi et al, 2006;Wei et al, 2006) based on the solid acid-base theory (Tanabe, 1989). Hammett indicators (Adams and Mccabe, 2006;Benesi, 1957;Walling, 1950), n-butylamine back titration (Reddy et al, 2005), and microcalorimetry (Breen, 1991a,b;Jerónimo et al, 2007) were used to determine the amount of acid sites. The temperature-programmed desorption (TPD) of basic gas molecules (Adams and Mccabe, 2006;Arena et al, 1998;Azzouz et al, 2006;Okada et al, 2006) and the Hammett indicator technique (Benesi, 1957;Walling, 1950) were used to estimate the acid strength.…”