Table 5. Acidity Determination of the Catalysts Using n-Butyl Amine Titration.

			acid strength of the catalysts (mmol/g)
entry	Hammett indicator	color of the indicator after addition in the catalyst test solution	FS-1	FP-1	FC-1	SiO2 + Al2O3 + Fe2O3 60% + 35% + 5%
1	methyl red (pKa = +4.8) red in acid forms yellow in the base form	red to all catalysts (+)	2.93	2.20	1.12	0.78
2	crystal violet (pKa = +0.8) yellow in acid forms blue in the base form	blue to all catalysts (−)	no color change	no color change	no color change	no color change
3	p-nitro chlorobenzene (pKa = −12.70) yellow in acid forms colorless in the base form	colorless to all catalysts (−)	no color change	no color change	no color change	no color change