Modeling of Selective Catalytic Reduction of NO with NH3 Process using Cu/ZSM-5 Nanocatalyst

Nitrogen oxides have been reported as one of the most serious pollutants. Selective catalytic reduction (SCR) of NOx by NH3 is an effective technology for reducing nitrogen oxide emissions. Despite the wide use of NOx reduction by SCR process, many aspects concerning the reaction mechanism are still not well understood [1]. The objective of our current research is to develop a reaction kinetic model of the proposed mechanism for the SCR of NO by NH3 over Cu/ZSM-5 nanocatalyst. The Cu/ZSM-5 nanocatalyst prepared via impregnation method then catalytic tests were carried out in a fixed bed reactor at different temperatures of 100 to 400˚C. An objective of the modelling was to estimate the kinetic parameters based on the experimental results. For parameter fitting purposes the Arrhenius equation was reformulated as: k_i=A_i exp⁡〖[(-E_ai)/R(1/T- 1/Tm〗)] (1) The model of the reactor was adopted from a heterogeneous model in which the reaction was assumed to occur in the solid catalytic bed. In this model, the space time of the feed (W/FFeed) is considered as independent variable and the weight fractions (ω_i) of chemical species is considered as dependent ones [2]. (dω_i)/d(W/F_Feed ) =∑_(j=1)^n▒r_j i=1,2,…,number of components (2) All reactions are assumed elementary and depending on each reaction it would be first, second or third order. r_j= k_j ∏_(i=1)^m▒ω_i j= 1,2,…,number of reactions (3) where k_j is the kinetic parameter of jth reaction. The method for estimation of the kinetic parameters was consisted of solving mass conservation equations for each component. By means of equation (2), the mass gradient relations can be written for each component. The differential equations corresponding to the mass conservation equation of each chemical species were solved and the kinetic parameters were estimated using hybrid genetic algorithm. The objective function which was used to minimize the deviation between experimental and calculated weight fractions of chemical species is according to the equation (4) OF= ∑_(i=1)^m▒∑_(j=1)^p▒(ω_(i,j)-ω_(i,j( calc.)) )^2 (4) Figure 1 represent the products distribution versus space time of reactor at reaction temperature 300℃. In this Figure, the experimental and calculated values were shown by points and lines respectively. As observed in the Figure, the results indicates a good agreement between experimental and calculated data obtained from kinetic model.