Synthesis and characterization of magnetic zinc and manganese ferrite catalysts for decomposition of carbon dioxide into methane

Abstract

Recently, carbon dioxide (CO2) has been regarded as the main source of greenhouse gases in the world with global warming potential. Decomposition or methanation of CO2 with flowing H2 over oxygen-deficient ZnFe2O4 and MnFe2O4 nanocatalysts at 300–400 °C and 1 atm was studied. Fine structures of Fe/Zn/Mn species in ZnFe2O4/MnFe2O4 were also investigated. Experimentally, as-synthesized ZnFe2O4/MnFe2O4 nanocatalysts were prepared by a hydrothermal method for CO2 decomposition or methanation. Oxygen deficiency of ZnFe2O4/MnFe2O4 was obtained by reduction in hydrogen gas. Decomposition of CO2 into C and O2 was carried out within few minutes when it comes into contact with oxygen-deficient ZnFe2O4/MnFe2O4 through incorporation of O2 into ferrites. Oxygen and carbon rather than CO were produced in the decomposition process. The complete decomposition of CO2 was possible due to higher degree of oxygen deficiency. The pre-edge XANES spectra of Fe atom in ZnFe2O4/MnFe2O4 exhibits an absorbance feature at 7115 eV for the 1s to 3d transition which is forbidden by the selection rule in case of perfect octahedral symmetry. The EXAFS data showed that ZnFe2O4 (MnFe2O4) catalyst had two central Fe atoms coordinated by primarily FeO with a bond distance of 2.07 ± 0.02 (1.95 ± 0.02) with a coordination number of 3.94 (4.07), respectively. CH4 was produced during the reactivation of ZnFe2O4/MnFe2O4 with H2. Moreover, kinetics and thermodynamics studies of CO2 decomposition and methanation over ZnFe2O4/MnFe2O4 at 300–400 °C and 1 atm were also calculated using pseudo first-order model and Arrhenius equation, respectively.