ABSTRACT

In the pursuit of environmentally conscious industrial processes for chemical production, catalysis plays a crucial role in generating sustainable chemicals. Nonetheless, finding appropriate and effective catalysts for various catalytic reactions remains a challenge. Solid acid catalysts are regarded as environmentally friendly catalysts for acid-catalyzed reactions compared to toxic and corrosive mineral acids. Zeolites, a type of solid acid catalyst, have gained considerable attention in diverse acid-catalyzed reactions, while clay, a structurally similar aluminosilicate material, has received less recognition. This study explores the treatment of natural clay obtained from Omialafara, Ifon Ose Local Government Area, Ondo State, Nigeria with 35% HCl and 5% NH₄Cl to enhance its acidic properties, thereby creating a sustainable solid acid catalyst capable of substituting mineral acids in acid-catalyzed reactions. The research methodology includes pretreating clay samples with varying concentrations of HCl and NH₄Cl, The acid strength of the treated and untreated clay samples were evaluated using Hammett's indicators; methyl red, crystal violet and neutral red were used. Gravimetric pyridine analysis ascertained total acidity. HCl-treated clay did not provide a result in gravimetric analysis due of an unsuccessful experiment; however, NH₄Cl-treated clay showed a higher positive value than the untreated samples stemming from its greater pyridine adsorption. Untreated clay tested negatively for each of the three indicators used, while HCl-treated clay tested positively for methyl red and crystal violet but negatively for neutral red. NH₄Cl-treated clay tested positively for all three indicators. The dissimilarities in acidity strength may be attributable to the different concentrations of HCl and NH₄Cl employed during the pretreatment process. A negative test shows that the clay sample’s pKa value was not in the range in which the indicator changes color, while a positive value indicated the sample’s pKa was in a range the indicator used changes color. FTIR analysis revealed distinct peaks for each sample. Untreated clay exhibited pyridine FTIR peaks at 3690, 3623, 2012, 1028, 913, 790, and 678 cm^-1. HCl-treated clay showed peaks at 3690, 2885, 1028, 909, 790, and 685 cm^-1, while NH₄Cl-treated clay exhibited peaks at 3693, 3652, 3623 2050, 1982, 1118, 1028, 913, 793, 752, and 678 cm^-1. These peaks represent specific molecular vibrations: the peak at 3693, 3690, 3652, 3623 cm^-1 indicates the presence of -OH stretching, peak at 2885cm^-1 represents C-H stretching, peaks around 2000-2200 cm^-1 correspond to C≡N stretching, peaks at 1028 cm^-1 indicate Si-O stretching, peaks at 913 cm^-1 correspond to Al-O stretching, peaks around 790-793 cm^-1 represent Si-O bending, and peaks around 678-685 cm^-1 indicate Si-O-Si bending vibrations. The shifts and intensities of these peaks suggest structural changes in the clay due to the different pretreatment methods.