Estudo cinético da reação de redução do NO pelo CO em catalisador de paládio suportado em alumina

• Autor(a) principal: Mello, Nathalli Meorlluw
• Data de Publicação: 2017
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da UERJ
• Texto Completo: http://www.bdtd.uerj.br/handle/1/12075
• topic: N2O; Kinetics; fixed bed; alumina; palladium; N2O; cinética; leito fixo; alumina; paládio; CNPQ::ENGENHARIAS::ENGENHARIA QUIMICA::TECNOLOGIA QUIMICA

The evolution of vehicle emissions legislation has required a continuous improvement in the quality of fuels and the technology used. The catalysts used nowadays are composed of noble metals, generally Pd, Pt and Rh. The reaction of NO and CO in these catalysts is of fundamental importance for the reduction of NOx emissions. In addition to the desired formation of the N2, it can also occur the formation of N2O, depending on the catalyst and the operating conditions employed. This work aims to evaluate, through a kinetic study, the performance of the Pd / Al2O3 catalyst in the NO and CO reaction, in the absence of oxygen. Thermodynamic studies indicate that the formation reactions of N2 and N2O are exothermic and may be considered irreversible in the usual temperature domain of automotive catalysts. It was evaluated the conversions of reagents along a temperature ramp, from an ambient temperature up to 500 ° C (light-off curves) in three reaction cycles. From the exploratory tests and as a function of the formation profile of N2O, the concentrations were evaluated at temperature levels, 350, 400 and 450°C. The results indicated that N2O has an intermediate product behavior, since its concentration passes through a maximum and a temperature range. At temperatures above 450 ºC, the N2O conversion is practically complete and the N2 selectivity approaches 100%. With the help of stable values at the levels, one can collect data in a narrower range to understand the mechanisms between the formation of N2O and N2 and to obtain experimental data for a kinetic evaluation. Assuming that the dissociation of the adsorbed NO is the limiting step, a first-order kinetics with respect to NO was considered. From the fixed bed model next to the kinetic model and the experimental data at levels for four spatial velocities, the set of equations was solved, providing the kinetic parameters. From these, the theoretical light-off curves can be obtained. The differences between the experimental and simulated light-off curves were attributed to the transient character of stabilization of the catalytic activity by increasing the reaction temperature. The modeling indicated that the rate of formation of N2 through the route through N2O is higher than that of direct formation of N2, suggesting that this stage is the dominant in this reaction scheme