(189g) Reduction of NO By CO in Platinum Monoliths: Effect of Inlet Concentrations On Conversions At Various Temperatures | AIChE

(189g) Reduction of NO By CO in Platinum Monoliths: Effect of Inlet Concentrations On Conversions At Various Temperatures

Authors 

Vandanapu, V. - Presenter, Indian Institute of Technology Madras
Aghalayam, P., IIT Madras



Reduction of NO by CO in Platinum monoliths: Effect of inlet
concentrations on conversions at various temperatures

 

 Vismayie
Vandanapu, Preeti Aghalayam*

Department
of Chemical Engineering, Indian Institute of Technology Madras, Chennai 600036,
India

*Corresponding Author; Email: preeti@iitm.ac.in

Key words: CFD simulations, NO, CO

Several
micro-kinetic models have been proposed in literature for the NO- CO reaction
on the Pt group metal catalysts. Typically, these articles propose ideal PFR
models for validation of experimental data. It is of considerable interest to
observe the effects of transport phenomena on the conversion profiles for this
system.  Hence, CFD simulations incorporating features of micro-kinetic models
are crucial. This work is aimed at studying transport effects on conversion
profiles for the NO-CO system on a Pt catalyst, which is of importance for
automotive after treatment applications. Since the engine exhaust usually
contains higher CO concentrations than NO, we deal with cases in which the
inlet concentration ratios of the species, NO/CO (R) are lower than one, in
this study.

(Mantri
et al., 2007) have proposed a micro-kinetic model for the NO-CO system and
carried out ideal PFR simulations for various R values. The importance of N2O
as a side product has been highlighted. (Ravikeerti et al., 2012) have proposed
a reduced rate expression based on the above micro-kinetic scheme, using
sensitivity analysis and the pseudo steady state assumption, for R~1. Rate
expressions for the formation of both N2 and N2O have
been provided. The PFR simulations carried out with this reduced rate
expression match with those obtained by using the micro-kinetic model. In this
paper, we extend this work and incorporate the reduced rate expressions in CFD
simulations for Pt monoliths.

Figure
1 shows the various outlet species concentrations as a function of the reactor
temperature, from literature experiments (Chambers et al., 2001) and our CFD
results using the reduced rate expressions. The results for the CFD simulations
are in agreement with the experimental results, at R~1, including the maximum in
N2O concentration at 315 OC.

Figure
2 depicts the CO conversion profiles obtained from CFD simulations at various R
values. The conversion of CO is seen to decrease as the inlet CO concentration
increases, as expected. Figure 3 shows the corresponding N2O outlet
concentration profiles from the CFD simulations. Despite the marked change in
CO conversion seen in figure 2, there is only marginal impact of changing R, on
N2O.

In
further work, the effects of mixture diffusivity and the pre-exponential of the
rate determining step, on the conversion profiles at various R values, will be
examined. The work will also be extended to study the effect of R on conversions
and selectivity, for Rh-based monoliths.

 

Figure
1
: Comparison of CFD simulations (3000
ppm NO + 3400 ppm CO) with the experimental data (Chambers et al., 2001). The
experimental data is shown in symbols while the CFD simulation results are in
lines. Excellent match between the two is observed.

 

 

 

 

 

 

 

Figure
2
: Effect of changing inlet CO
concentrations on the conversion profiles obtained in CFD simulations. The high
temperature conversion of CO is found to decrease with decrease in R value, as
expected

 

Figure
3
: N2O profiles for various R
values. Th maximum N2O concentration decreases
slightly and shifts towards higher temperature with a decrease in R value