*2.2. Characterization*

The XRD patterns of the samples were recorded using a Bruker AXS D8 (MA, USA) diffractometer with Cu-Kα radiation (λ = 1.5418 Å) at 2θ = 3–50◦. The morphology of solids was studied with a FESEM microscope (Leo Supra 50VP, Oberkochen, Germany) operating at 20 kV. The average crystal size of solids was determined using ImageJ software by counting 50 crystals randomly throughout the FESEM images. The Si/Al and K/Al ratios of the solids were determined by using a Perkin Elmer's atomic absorption spectrometer (AAS, AAnalyst 400). Prior to analysis, the sample was dissolved in hydrofluoric acid solution (0.5 M) where boric acid was also added to minimize the fluoride interference. Meanwhile, five standard solutions of each Al, Si and K elements were also prepared for calibration study. The surface area of the samples was calculated by using the BET equation where the monolayer volume (Vmono) was first obtained from the nitrogen adsorption isotherm; the samples were first degassed (6 h, 300 ◦C) before the adsorption isotherms were recorded from a Micrometrics ASAP 2010 analyzer (Norcross, USA) at −196 ◦C. The surface basicity of MER zeolite samples was analyzed using a BELCAT-B temperature programmed desorption (TPD) instrument (Osaka, Japan). Initially, the solid sample (ca. 100 mg) was outgassed at 450 ◦C overnight before CO2 gas was introduced for adsorption. The excess CO2 was then evacuated at room temperature and CO2 desorption was performed from 40 to 500 ◦C at a heating rate of 10 ◦C /min. The TPD profile was plotted as TCD signal versus desorption temperature.
