ABSTRACT
Aluminosilicate materials, particularly zeolites, are widely employed as catalysts in various industrial processes due to their unique properties. Clay, despite being less recognized than zeolites, holds significant importance in catalysis due to its abundant active sites and high surface area. This study aims to assess the acidity of potential solid acid catalysts derived from aluminosilicate materials, specifically clay. Various objectives were established, including modifying natural clay gotten from a study site in Omialafara, Ifon Ose Local Government Area, Ondo State, Nigeria, assessing acid strength using the Hammett indicator test, determining total acidity through Pyridine-adsorption gravimetry, differentiating between Lewis and Bronsted acid sites using Pyridine FT-IR analysis, and comparing acidity levels between treated and untreated clay samples. The clay samples were treated 20% HCl and 35% NH4Cl for 24 hours at room temperature respectively. The acid strength for the treated and untreated clay samples were evaluated using selected Hammett indicators (methyl red, neutral red and crystal violet). For methyl red, showed a positive response with both treated clays, indicating pH dropping below pka levels, while neutral red and crystal violet did not change color with 35% NH4Cl-treated clay which suggests acid levels below their detectable thresholds indicating that the pH did not rise significantly above pKa. The pKa values of +4.8 for methyl red, +0.8 for crystal violet, and +6.8 for neutral red provided insights into the acidity strengths of the treatments. Next was the gravimetric pyridine absorption test where clay samples treated with 20% HCl and 35% NH4Cl results showed varying pyridine adsorption and total acidity levels: untreated clay (0.01 g, 1.264 mmol/g), 20% HCl-treated clay (0.03 g, 4.74 mmol/g), and 35% NH4Cl-treated clay (0.22 g, 25.28 mmol/g). These findings highlight the significant enhancement of surface acidity in clay treated with NH4Cl compared to untreated and HCl-treated clay and Pyridine FT-IR analysis was to the presence of acidic site (Bronsted and Lewis site). Pyridine FTIR spectra for untreated clay peaks are 3693.8 cm⁻¹, 2161.9 cm⁻¹, 1118.2 cm⁻¹, 1028.7 cm⁻¹, 913.2 cm⁻¹, 790.2 cm⁻¹, 682.1 cm⁻¹ this shows no acid site, Pyridine FTIR spectra peaks for 20% HCl are 3623.0 cm⁻¹, 3414.2cm-1 , 3026.6 cm⁻¹, 1580.4 cm⁻¹,1438.8 cm⁻¹, 700.7 cm⁻¹ where peaks 1580.4 cm⁻¹ and 1438.8 cm⁻¹ indicate the presence of both Bronsted and Lewis acid site and Pyridine FTIR spectra peaks for 35% NH4Cl are 3026.6 cm⁻¹, 1923.3 cm⁻¹,1580.4 cm⁻¹,1483.5 cm⁻¹,1438.8 cm⁻¹ respectively where 1580.4 cm⁻¹,1483.5 cm⁻¹,1438.8 cm⁻¹ indicate the presence of Bronsted and Lewis acid sites. Finally, the study investigated untreated clay and clay treated with 20% HCl and 35% NH4Cl, where in the Pyridine FT-IR analysis distinct alterations, particularly notable in the 35% NH4Cl treated sample, Pyridine adsorption tests showed heightened acidity in the NH4Cl-treated clay compared to other treatment and while using indicators, it was found that HCl generally increased acidity, while NH4Cl had no effects detected by some tests. Overall, the findings highlight the potential of chemical treatments to modify clay properties for various applications.
