The crystalline phase of the catalyst sample was confirmed
using a powder X-ray diffractometer (Rigaku, Japan) coupled with
Cu Kα radiation. The BET surface area was measured by N2 adsorption–
desorption isotherm apparatus (BEL; BELSORP-max). The basic
strength of the catalyst was determined by the Hammett indicator
method. The indicators used were as follows: neutral red (H_ = 6.8),
bromothymol blue (H_ = 7.2), phenolphthalein (H_ = 9.8), 2, 4-
dinitroaniline (H_ = 15), and 4-nitroaniline (H_ = 18.4). Basicity of
the catalyst was measured by the method of Hammett indicator–
benzene carboxylic acid (0.02 mol L−1 anhydrous methanol solution)
titration. The FTIR spectra were recorded on a Shimadzu IR-Prestige-
21 spectrometer in the range of 500–4000 cm–1. The KBr pelletmethod
was used for the sample preparation. The SEM images and surface elemental
analysis were recorded on a Quanta 200 SEM system equipped
with EDS detector (FEI Company, Netherlands).