A laboratory scale investigation of N2O catalytic reduction over cobalt and iron catalysts
Keywords:
N2O cobalt species, iron species, catalytic decomposition.Abstract
The economy of Pakistan is strongly reliant on agricultural activities. Nitric acid plants are operating in different locations of the country for the production of ammonium nitrate fertilizers. Unfortunately, N2O is one of the by-products formed, particularly in older nitric acid plants. N2O is a potent greenhouse gas and has a higher global warming potential (GWP) than CO2 and CH4. Furthermore, it plays an important role in ozone (O3) layer depletion. At present, the production of nitric acid is a single largest source of N2O emissions. In order to minimize the hazardous effects of N2O, its dissociation into N2 and O2 is more favourable reaction. In the current work, a laboratory scale N2O dissociation reaction is examined over different cobalt and iron catalysts in a fixed bed tubular reactor. The temperature and pressure of the reactor were varied between 300 °C – 500 °C, and 1 bar – 10 bar, respectively. Surface characterization of the prepared catalysts was done through ICP, TPD, XRD, TGA, and N2 adsorption/desorption isotherms.
Experimental results suggest that the catalyst support plays a vital role in N2O conversion. H-ZSM-5 support is inactive in a studied range of temperature (300 °C – 500 °C). When cobalt was loaded on H-ZSM-5 support, by wet deposition method, the Co-ZSM-5 catalyst showed the highest activity among all other catalysts tested. The surface morphology of the catalysts changes with cobalt or iron loading, as indicated by the variation in Langmuir surface area (m2g-1). As a whole, the activity of H-ZSM-5 increases with cobalt or iron loading, however, every loaded metal is not active for the N2O dissociation reaction. Co2+ species seems to be highly active for the N2O activation.
Additionally, it was also observed that the mass of the Co-ZSM-5(W.D) decreases by 18 % due to the water desorption during catalyst activation process. The evidence for the formation of different surface species is also shown in the present work.
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