Nitric Oxide Reduction with Hydrogen over Carbon-Supported Copper-Iron Oxides Catalysts

Nitric oxide (NO) is an air pollutant generated during fuel combustion which is responsible for ground-level ozone, acid rain and smog formation. Current abatement technologies include reducing NO to nitrogen (N2) in the presence of a reductant, usually ammonia, and a catalyst. Replacing ammonia with a less-toxic reductant such as hydrogen (H2-SCR) requires the utilization of expensive precious metal as a catalyst supported on metal oxides. This study aims to evaluate the potential use of hydrogen as a renewable reductant; activated carbon as a sustainable catalyst support; and less-precious metals as a catalyst to selectively convert NO to N2. Mono- and bimetallic oxide catalysts were synthesized via incipient wetness method using copper, iron and manganese oxides supported over palm kernel shell activated carbon. Copper-based catalysts were proven to totally convert NO (100 %) in an oxidizing condition starting at 250 °C, while co-impregnating with iron oxide (PKSFeCu) improved N2 selectivity (eg. from 80 to 100 % at 200 °C) as well as lowering the carbon combustion rate (eg. from 3.1 to 2.3 μmol CO+CO2/s). The catalysts were characterized via elemental and metal content analyses, nitrogen adsorption-desorption, ammonia-temperature-programmed desorption, Fourier-Transform infra-red spectroscopy, hydrogen-temperature-programmed reduction, thermogravimetric analysis, and NO-temperature-programmed desorption. The conversion and selectivity were found to correlate strongly with the catalyst reducibility and acidity. Kinetic experiments revealed that the rate of reaction for H2-SCR using PKSFeCu obeys a power rate law with an order of 0.82 with respect to NO concentration. The stability test showed that the catalyst is susceptible to changes in physical properties under prolonged exposure to high temperatures and feed gas disturbance. Therefore, improvements in terms of catalyst stability should be the main focus of future work for this sustainable H2-SCR system to become an attractive alternative to NH3-SCR.