Abstract
Catalytic oxidation of carbon monoxide (CO) gas over nanosized nickel ferrites prepared from fly ash has been investigated. X-ray diffraction analyses showed that pure crystalline nickel ferrite, NiFe2O4, phase can be obtained by thermal treatment of the precursors at temperature >800 degrees C for 120 min in the studied pH range, from 7 (neutral) to 12 (highly alkaline). In the temperature range 500 <= T <= 800 degrees C, impure low crystalline NiFe2O4 phase formed. The main impurities are FeO (OH) and Fe2O3 center dot H2O phases. Higher magnetization (32 emu/g) is obtained for a precursor precipitated at pH 10 and thermally treated at 1,200 degrees C for 120 min. The catalytic oxidation of CO over nanocrystalline NiFe2O4 powders was studied using quadrupole mass gas analyzer system. The main parameters as crystal size, surface area and firing temperature are used to clarify the efficiency of using NiFe2O4 powders in catalytic oxidation of CO. It was found that the efficiency of catalytic oxidation decreased by increasing firing temperature and crystallite size of the samples. The lower crystal size (2-8.5 nm), the higher surface area (25-55 m(2)/g) and the presence of impurities FeO(OH) phase enhanced CO adsorption and consequently its oxidation.