Passive Nitrogen Oxides Removal from a Diesel-engine Exhaust Gas using a Biomass-Carbon Catalyst

Nitrogen oxides (NOx) removal from a diesel-engine exhaust gas is limited to the utilization of ammonia/urea as a reducing agent (SCR) which arose environmental concerns over the use of this chemical. Therefore, this study explored the potential of a sustainable NOx removal system by replacing ammonia with intrinsic reductants present in the exhaust gas such as hydrocarbons and carbon monoxide, and by application of cost-effective carbon-supported transitional metals catalyst. Copper-cerium catalyst supported over palm kernel shell activated carbon (Cu-Ce/PKS) was synthesized via deposition-precipitation method. The characterization shows that the catalyst has a considerably high surface area (though lower than the support). The high NOx removal by Cu-Ce/PKS in a passive catalytic reaction is attributed to the surface area provided by the carbon support, the low copper reducibility giving the low optimum operating temperature, and the synergistic effect between Cu and Ce resulting in the wide temperature window at low-temperature range. It is concluded that Cu-Ce supported over palm kernel shell activated carbon can be further developed to reduce NOx in a passive catalytic removal for a sustainable and cost-effective SCR system.  

Computational study for the circular redox reaction of N2O with CO catalyzed by fullerometallic cations C60Fe+ and C70Fe<sup/>

We applied density functional calculations to study the circular redox reaction mechanism of N₂O with CO catalyzed by fullerometallic cations C₆₀Fe⁺ and C₇₀Fe⁺. The on-top sites of six-membered rings (η⁶) of fullerene cages are the most preferred binding sites for Fe⁺ cation, and the hexagon to pentagon migration of Fe⁺ is unlikely under ambient thermodynamic conditions. The initial ion/molecule reaction, N₂O rearrangement and N₂ abstraction on the considered fullerometallic cations are easier than those on the bare Fe⁺ cation in the gas phase. Generally, our results indicate that fullerometallic ions, C₆₀Fe⁺ and C₇₀Fe⁺, are more favorable substrates for redox reaction of N₂O with CO in comparison to the other previously studied carbon nanostructures such as graphene and nanotubes.

Catalytic enhancement in dissociation of nitric oxide over rhodium and nickel small-size clusters: a DFT study

We applied density-functional theory (DFT) to investigate the adsorption and dissociation of NO on Rh19 and Ni19 clusters with a double-icosahedral (DI) structure. The transition structures of the NO dissociating on the potential-energy surfaces were derived using the nudged-elastic-band (NEB) method. The adsorption energies of NO molecules on the rhombus-center region of DI clusters are -2.53 eV and -2.78 eV with the N-O bond elongated to 1.33 Å and 1.35 Å, respectively, on Ni19 and Rh19, compared to 1.16 Å of the gaseous NO counterpart. The barriers to dissociation of N-O on both DI-Rh19 (Ea = 0.24 eV) and DI-Ni19 (Ea = 0.42 eV) clusters are small, indicating that the rhombus-center region of DI metal clusters might activate the scission of the N-O bond. To understand the interaction between these nanocluster catalysts and their adsorbates, we calculated the electronic properties including the local densities of states, orbital evolution of the adsorbates and interaction energies; the results indicate that a profound catalytic behavior for bond scission is observed in this unique rhombus-center region of DI metal-nanoclusters.