(582bh) Development of a MICRO-Kinetic MODEL of NO-CO Reaction over Gold Catalyst and Validation

Anupam Abha¹ Vishnu S Prasad¹ and Preeti Aghalayam¹

¹Department of Chemical Engineering, Indian Institute of Technology madras

Corresponding author: preeti@iitm.ac.in

Nitrogen oxides are considered to be one of the most toxic pollutants in the atmosphere causing severe health problems and environmental hazards. The contribution of automobile exhausts to the NOx emissions is tremendous. In order to reduce the amount of NOx from the automobile exhaust intensive treatment is needed. One excellent method is selective catalytic reduction (SCR) of NOx. SCR selectively reduces NOx to nitrogen in the presence of a reductant over a catalyst, despite an overall oxidative environment in the gas-phase. Also, this method instills a huge scope of further development in this field. Research is going on to optimize the combination of reductant and catalyst in order to provide the best conversion and selectivity to N₂ formation. CO-HCR has its distinct importance in this field as it has the ability to simultaneously reduce NOx and oxidize CO over a catalyst using CO as the reductant. The choice of catalyst is crucial for a better performance. Gold nano-particles are known to be an excellent catalyst as they have shown extraordinary behaviors in various aspects such as high selectivity towards N₂, better high temperature activity of aged catalyst, and improved performance in the presence of O₂and moisture compared to other catalysts [1].

In this work we propose to develop a micro-kinetic model for NO-CO reaction over nano gold catalysts. The model is validated based on literature reported [2]. In order to develop the micro-kinetic model we have incorporated a reaction mechanism consisting of 16 elementary reactions for the gold catalyst, including adsorptions, desorptions, and surface reactions. The thermodynamic data such as activation energies and pre-exponential factors were calculated for each reaction. The activation energy was calculated using a semi-empirical method UBIQEP [3], the pre-exponential factors were assumed to be in the order of magnitude as per transition state theory, & sticking coefficients were given nominal values. Incorporating the micro-kinetic model, the perfectly stirred reactor model was simulated using the commercial software CHEMKIN-PRO. The results obtained from the simulations were compared with the reported experimental results.

The simulation data is in coherence with the experiments for CO oxidation. It showed that the CO oxidation occurs at a very low temperature and it attains a total conversion. The results obtained from simulations and the literature for NO reduction for different oxygen inlet conditions are also studied and compared.

Gold nano-particles exhibit extra-ordinary catalyst characteristics and have shown to give an exceptional performance even in the usual catalyst inhibiting conditions. We plan to justify the experimental results with our modeling and give a reasonable explanation for the behavior exhibited by gold nano-particles. In future we will extend our work to develop a model for NO-HC reaction system over gold catalysts.

References

1. A.Ueda, M.Haruta, Gold bulletin, 1999, Vol 32 (1)
2. A.Wang, J.A.Toledo, C.Angeles, M.R.S Symp.Proc.Vol 1279,2010
3.  E. Shustorovich , surface science (205), 1988, 492-585