Naslov
Kinetic investigation of the NO decomposition over V-O-W/Ti(Sn)O2 catalyst

Autori
Banas, J. ; Najbar, M. ; Tomašić, Vesna

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
International symposium on air and water pollution abatement (AWPA 2007): abstracts / Najbar, M ; Grzybek, T. ; Nazimek, D. - Krakov : DEKA, 2007, 109-111

Skup
International symposium on air and water pollution abatement

Mjesto i datum
Zakopane, Poljska, 21.06.2007. - 23.06.2007

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
nitrogen oxides; kinetics of NO decomposition; rutile supported V-O-W catalyst

Sažetak
Nitrogen oxides (NOx) are hazardous air pollutants. Concern for environmental and health issues coupled with stringent NOx emission standards generates a need for the development of efficient low-cost NOx abatement technologies. The emission abatement of NOx may be achieved by the combustion modifications by the flue gas post-treatments, such as selective catalytic reduction (SCR), selective non-catalytic reduction (SNCR), adsorption, scrubbing and biological degradation [1-3]. This work reports on kinetics of NO decomposition over nanostructured V-O-W/Ti(Sn)O2 catalyst. Assuming that NO decomposition occurs as a result of electron transfer from the metal active site to antibonding  NO orbital, several kinetic models were derived and applied to describe the kinetics of reaction. Comparison of V-O-W/Ti(Sn)O2 with Cu/ZSM-5 zeolite was also made and some conclusions about potential catalyst for the NO decomposition are withdrawn. Experimental The rutile supported nanostructured V-O-W catalyst was obtained using sol-gel method. VO(C3H7O)3 (Johnson Matthey), WCl6 (Aldrich), SnCl4 (Aldrich), Ti(C3H7O)4 and C3H7OH (Aldrich) were applied as substrates. A detailed description of the catalyst preparation can be found elsewhere  4 . The Cu-containing pentasil zeolite (Cu/ZSM-5) was prepared by ion exchange of Na/ZSM-5 (Si/Al=54 ; Leuna Werke) with 0.01 mol dm-3 of aqueous solution of copper (II) acetate. Copper content was 1.99 wt%. The prepared catalysts were characterized by several techniques, such as XRD, surface measurements, thermal analysis (DSC/TG) and nitrogen adsorption/desorption measurement. The catalytic properties of a V-O-W/Ti(Sn)O2 (r) catalyst and metal containing ZSM-5 were investigated at the temperature range from 438 to 773 K and at atmospheric pressure. Steady-state NO decomposition rates were measured using a tubular fixed-bed reactor (6.5 mm I.D. and 150 mm length) at various reactor space times. The catalyst activity for NO decomposition was evaluated by conversion of NO into N2. Results and discussion This work was aimed at investigation the kinetics of NO decomposition over V-O-W/Ti(Sn)O2 catalyst. Taking into account the sequence of elementary steps in the overall reaction mechanism and assuming that one of those steps was the slowest one (or rate-determining step, rds) several rate equation were derived. The empirical power-low model was tested too. As was shown earlier [5] NO is adsorbed on metal atoms in vanadia-like surface species via nitrogen atom (ON-Me). Thus, mechanisms based on this fact were considered first of all. Experimental values for the reaction rate were obtained according to the model for tubular reactor. Reactor model was developed under the following assumptions: steady state and isothermal conditions, ideal gas flow and neglected pressure drop through the catalytic layer. Values of the space times were normalized by dividing with maximum value (tmax) in order to compare the mean square deviations obtained at different measurements. Differential equations obtained by inserting the proposed kinetic models into the reactor model were solved numerically by the 4th order Runge-Kutta algorithm under simultaneous assessment of the kinetic parameters (Nelder-Mead method of nonlinear regression). The selection of a suitable model was based on minimization of the squares of differences between experimentally obtained and predicted results. The best fit to the experimental data was achieved using the simple power-low model (mean SD = 2.111×10-2). However, this model has no practical importance and it can be used only as fast screening technique in discovery and study of various catalysts for the desired purpose. Thus, experimental data were correlated with several mechanistic Langmuir-Hinshelwoods (LH) models. The differences among them were in the type of interactions between the reactants and active sites on the catalyst surface, in the assumed oxygen (or nitrogen) desorption from the active sites, as well as in the number of reaction parameters. Satisfactory degree of correlation was established using LH kinetic model given by Eq. 1. This model was developed assuming NO adsorption as the rate-determining step. (1) The V-O-W-/Ti(Sn)O2 catalyst exhibited the enhanced catalytic properties in comparison to the metal containing ZSM-5 zeolite, especially at lower reaction temperatures. Moreover, V-O-W/Ti(Sn)O2 catalyst showed high activity even at temperature of 438 K, which is of great importance for its practical applications in the real conditions. As it was shown earlier [6] the oxygen interaction with the reduced catalyst surface causes oxidation of the vanadium atoms segregated on V-O-W bronze crystallites, resulting in the formation of the vanadia-like monolayer species. These species show high activity in NO decomposition. This beneficial influence of the oxygen on the catalyst activity in NO decomposition to N2 and O2 is, according to our knowledge, observed for the first time. References [1] H. Brauer, Y.B.G. Varma, Air Pollution Control Equipment, Springer-Verlag, Berlin (1981). [2] N. N. de Nevers, Air Pollution Control Engineering, McGraw-Hill, New , New York (1995). [3] C.D. Cooper, F.C. Alley, Air Pollution Control – A Design Approach, Waveland Press, Inc., Long Grove (2002). [4] M. Najbar, F. Mizukami, A. Białas, J. Camra, A. Wesełucha-Birczyńska, H. Izutsu and A. Góra, Top. Catal. 11/12 (2000) 131. [5] P. Kornelak, A. Michalak, M. Najbar, Catal. Today 101 (2005) 175. [6] J. Banaś, V. Tomašić, A. Wesełucha-Birczyńska, M. Najbar, Catal. Today 119(1-4)(2007) 199.

Izvorni jezik
Engleski

Znanstvena područja
Kemijsko inženjerstvo

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