2.2. Characterizations
The ash content of the catalysts was determined using thestandard ASTM D2866-94 method. The metal content in the synthe-sized samples was measured by inductively coupled plasma opticalemission spectroscopy (ICP-OES, Horiba Jobin-Yvon).The specific surface area (SBET) was determined using anAutosorb-iQ-MP gas sorption analyzer (Quantachrome Instru-ments, USA) via nitrogen adsorption at 77 K.The pH at the point of zero charge (pHPZC) of the catalyst wasmeasured according to the method developed by Brunelle [18].
Increasing amounts of solid were added sequentially to a 50 mL0.0005 M NaCl solution until the pH reached a plateau. The pH atthe plateau corresponds to the pHPZC.The chemical state of iron on the catalysts was followed by X-ray diffraction (XRD) using a D/max 2200 vpc Diffratometer (RigakuCorporation, Japan) with a Cu K radiation at 40 kV and 30 mA.Scanning electron microscopy (SEM) images were recordedusing a JEOL JSM-6330F field emission scanning electron micro-scope equipped with an energy-dispersive X-ray (EDX) detector(JED-2300).