Showing papers by "Sounak Roy published in 2008"

Low-Temperature Selective Catalytic Reduction of NO with NH3 over Ti0.9M0.1O2-δ (M = Cr, Mn, Fe, Co, Cu)

Abstract: The catalysts, Ti0.9M0.1O2-δ (M = Cr, Mn, Fe, Co, Cu), were synthesized in anatase phase by solution combustion. Selective catalytic reduction (SCR) of NO with NH3 was investigated over these catalysts. The reaction occurred at the lowest temperature over Ti0.9Mn0.1O2-δ, but the selectivity for N2 was highest over Ti0.9Fe0.1O2-δ. Therefore, both Mn and Fe were substituted in TiO2 (Ti0.9Mn0.05Fe0.05O2-δ). The reaction occurred at low temperature with a high selectivity over this catalyst. In order to understand the reaction mechanism and the nature of the active sites, temperature programmed desorption (TPD) of NH3 and hydrogen uptake studies were carried out. The relation between the Lewis acid sites and SCR window and the relation between Bronsted acid sites and low temperature was established. The order of the SCR reaction with respect to NO, NH3, and O2 was also investigated. It was also shown that the N2 selectivity of the SCR reaction has a strong inverse correlation with the oxidation of ammonia.

Low temperature NOx and N2O reduction by H2: Mechanism and development of new nano-catalysts

Abstract: The understanding of the mechanistic aspects and development of new catalysts for NOx reduction is a priority area of research. Precious metal substituted TiO2 (Ti0.99M0.01O2−δ, where M = Ru, Rh, Pd, Pt) catalysts have been synthesized and investigated for the catalytic reduction of NO by H2. These catalysts have higher activity compared to other catalysts reported in literature. The rate of NO reduction by H2 depends on the reducibility of the catalysts. Temperature programmed reduction experiments with H2 indicate that as the H2 dissociation temperature decreases (reflecting the reducibility of the catalysts), the rate of NO + H2 reaction increases. A new bi-functional reaction mechanism has been developed that accounts for NO adsorption on Mn+ and NO dissociation on the oxide ion vacancy. The kinetic parameters were determined by fitting the model to the experimental data. Consistent with the experimental results, it was found that NO reduction rate was dependent on the adsorption and dissociation of H2 on the metal.

Selective Catalytic Reduction of NOx: Mechanistic Perspectives on the Role of Base Metal and Noble Metal Ion Substitution

Abstract: Selective catalytic reduction (SCR) of NO by NH3 in presence of excess oxygen is an industrially and environmentally important reaction. Determining a suitable catalyst substituted with noble metals or base metal ions with a suitable reaction mechanism is important. In this study, ionically substituted Mn and Pd in TiO2 catalysts were synthesized by the solution combustion technique and examined for SCR activity. A seven-step reaction mechanism was proposed to incorporate the role of NH3 oxidation in the SCR reaction that shows minima in the NO concentration profile. Both modeling and experimental results show that the reduction of NO in SCR condition follows the order Ti0.9Mn0.1O2-δ > Ti0.89Mn0.1Pd0.01O2-δ > Ti0.99Pd0.01O2-δ. However, the hydrogen uptake study showed that the noble metal ion (Pd2+) substituted TiO2 has better reducibility than the base metal ion (Mn3+) substituted TiO2. The rate of ammonia oxidation by different catalysts followed the reverse order such as that of NO reduction. This clea...