The surface morphology of the catalyst was investigated by a field emission scanning electron microscope (FE-SEM) MIRA LMU (Tescan). FE-SEM was operated at 30.0 kV of an accelerating voltage.
Powder X-ray diffraction (XRD) patterns were recorded on an Ultima+ diffractometer using Cu Kα radiation at 40 kV and 20 mA (Rigaku). The samples were scanned in the range of 2θ of 5–60° at a scanning speed of 1°/min.
Total NU 7026 density of AC, ACPhSO3H and Amberlyst-15 were determined using acid-base back titration method  and . Typically, the 0.2 g of sample and aqueous solution of NaOH (30 ml, 0.1 M) were mixed (magnetic stirrer, 300 rpm) at 50 °C for 1 h in 50 ml Erlenmeyer flask. After adding all components, the flask was purged with argon. Then the sample was filtered and washed with deionized water (100 ml) several times. Obtained filtrate was diluted to 150 ml with deionized water. Afterwards, 15 ml of diluted filtrate was titrated with aqueous HCl (0.01 M) using phenolphthalein as an gonads indicator.