Mathematical Modeling of Conversion CO To CO 2 in Batch Mode CO 2 Laser System.

The oxidation of carbon monoxide CO over supported noble metal catalyst is an important part of the catalytic control in sealed-off TEA CO2 laser system. In this model, the activities of supported noble metal catalysts (Pt/Al2O3 and Pd/Al2O3) separately in removal CO as CO2 gas phase are studied at isothermal conditions. A batch equation is used in this model to study the effect of reaction rate parameter k (sec 1 − ) on conversion processes at contact time t =2500 (sec) and to control the path of gases from and the reactor cavity to indicate the effect of contact time. These results are confirming that the dissociated gases are removed by using catalysts to regenerate CO2 molecules during the electrical discharge


1-Introduction
CO oxidation catalysts have a long history of applications, so it is instructive to first consider the special requirements of the laser application.The removal of CO as CO2 is accomplished via catalytic converter with the supported noblemetals Pt and Pd (i.e.Pt/Al2O3 and Pd/Al2O3 catalysts).The gas-solid form is a most important type of heterogeneous [1].In this regard, numerous studies of the kinetics as well as investigations of the effects of supports and additives on the kinetics of this reaction over supported catalysts have been reported.

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During oxidation of CO by O2, whether in the gas-phase (homogeneous) or over a catalyst surface (heterogeneous), two basic steps must occur: dissociation of the O2 molecule and formation of O-CO bond.These two steps usually occur in separate events.Over the surface of a catalyst, O2 must adsorb and dissociate and CO must adsorb next to and react with an O atom and replenish CO2 [6,7,8] as shown: Where "S" is a site or area on the metal surface that can adsorb one CO molecule or one O atom.
In literature, there are many authors investigated the conversion of CO to CO2 experimentally in CO2 laser system [9,10].On the other hand, there were few mathematical models in literature that describe the reaction kinetics for such system [11].
Therefore in this paper we report the behavior of first-order differential equation of CO oxidation over supported noble metal catalysts such as (Pt/Al2O3, Pd/Al2O3) and investigate the effect of reaction rate constant k (sec

2-Numerical modeling of Conversion CO to CO2 by Using Batch Equation in CO2 Laser
Systems.

1-Model assumption
For motivation a batch equation is used with analytical solutions for this purpose we assume the following: • Batch operation system  ).

3-Results and Discussion:
The simulation result of determining the activity of pt/Al2O3 and pd/Al2O3 in oxidizing the carbon monoxide, CO gas phase in sealed-off CO2 laser system, is shown in figures ( 1) and ( 2), respectively.From these figures it was found that the activity of pt/Al2O3 in conversion of CO to CO2 is more efficient than using pd/Al2O3 as a function of contact time t .From these figures, on the other hand, one can note that the conversion is increased approximately exponentially with increasing the reaction rate constant ) (sec 1 − k at the same contact time.These results are confirming that the removal of CO by using pt/Al2O3 catalyst is more efficient due to the thermal effects and trend of both CO and Pt to connect together as shown in figure (1).While removing CO with pd/Al2O3 catalyst is less active because of the trend of Pd surface to connect with O2 for the harmony of electronic distributions of both O2 and Pd as shown in figure (2).As shown from the results above the k is not truly a constant, but is merely independent of the concentration of the species involved in the reaction.It's almost always strongly dependent on temperature as shown in figures.This assumption is valid in most laboratory and industrial reaction and seems to work quite Weil.

4-Conclusions
The activity of supported noble metal catalysts such as (Pt/Al2O3 and Pd/Al2O3) depends on reaction rate

tx
time rate of change of component CO is only a function of the concentration of CO.Then equation (1) can be solved for isothermal operation, since CO C and t are separable, to find: is the space time (sec) Also, the equation (2) for constant volumetric flow rate (Q) is useful in determining the space-time t for reaction rates that depend only on the concentration of one species.Equation (3) can be represented as a function of conversion (x) for constant volume as shown: the conversion of CO at any time can be represented by: Eng.&Tech.Vol.26,No.8,2008Mathematical modeling of conversion CO to CO2 in Batch mode CO2 laser system. is conversion of CO to CO2 gas phase.t is contact time (sec) .

Figure 1 :Figure 2 :
Figure 1: Conversion of CO to CO2 with pt/Al2O3 catalyst as a function of contact time for different rate