Preeti Aghalayam

Bio: Preeti Aghalayam is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Underground coal gasification & Catalysis. The author has an hindex of 22, co-authored 59 publications receiving 1360 citations. Previous affiliations of Preeti Aghalayam include University of Delaware & University of Massachusetts Amherst.

Bifurcation analysis on PT and IR for the reduction of NO by CO

Abstract: Due to the importance of the NO-CO reaction in current catalytic converters, reduction of NO by CO on Pt group catalysts is important to study. Various reaction mechanisms have been proposed for the NO-CO reaction on Pt(100), which shows bifurcations, kinetic oscillations and multiple steady states under ultra high vacuum (UHV) conditions due to complex surface dynamics. Some experiments on supported Pt group catalysts reported in literature show oscillations and bistability under atmospheric conditions as well. Industrially relevant conditions require the modelling and detailed analysis of the system at atmospheric pressure. We have proposed a reaction mechanism for the NO-CO system on Pt group catalysts and coupled it with an isothermal PSR model to obtain solutions at atmospheric conditions with the continuation software CONTENT 1.5, at different operating conditions. Simulation results suggest that Pt(111) shows bifurcations at certain operating conditions while Ir(111) shows stable solutions at all the operating conditions studied here. En raison de l'importance de la reaction entre NO et CO dans les convertisseurs catalytiques habituels, il est important d'etudier la reduction de NO par le CO sur des catalyseurs du groupe Pt. Divers mecanismes de reaction ont ete proposes pour la reaction de NO-CO sur Pt(100), qui montre des bifurcations, des oscillations cinetiques et de multiples etats permanents dans des conditions de vide extreme en raison de la dynamique de surface complexe. Certaines experiences dans la litterature scientifique sur des catalyseurs de groupe Pt supportes montrent en outre des oscillations et une bi-stabilite dans des conditions atmospheriques. Des conditions industrielles pertinentes requierent la modelisation et l'analyse detaillee du systeme a la pression atmospherique. On a propose un mecanisme de reaction pour le systeme de NO-CO sur des catalyseurs de groupe Pt et on l'a couple avec un modele PSR isotherme afin d'obtenir des solutions dans des conditions atmospheriques avec le logiciel de continuation CONTENT 1.5, dans differentes conditions operatoires. Les resultats des simulations suggerent que Pt(111) montre des bifurcations a certaines conditions operatoires, tandis que l'Ir(111) montre des solutions stables a toutes les conditions operatoires etudiees ici.

Microkinetic Modeling of HC-SCR of NO to N2, N2O, and NO2 on Pt Catalysts in Automotive Aftertreatment

Abstract: One of the main pollutants in automobile engine exhausts is NO. Hydrocarbon-based selective catalytic reduction (HC-SCR) is one of the most preferred methods to reduce NO at the expense of unburned hydrocarbons, which are also present in automobile exhausts. In this study, we have developed a detailed kinetic model and analyzed the selectivity of NO reduction to various products (N2, N2O, and NO2). The optimal operating conditions for the maximum reduction of NO to N2 are also explored. Various phenomena including coking and the oxygen-rich nature of the catalyst surface are found to occur as the amount of oxygen in the inlet is varied. The influence of O2 and temperatures on the selectivity of NO reduction is discussed in detail.

Understanding Pt-Rh Synergy in a Three-Way Catalytic Converter

Abstract: NO reduction to N2 is the key reaction for effi- cient operation of a three-way catalytic converter (TWC). It is reported that metal catalysts Pt and Rh co-exist as individual metals in a TWC to give synergistic perfor- mance. In this article, we have studied the NO þ CO reaction for a 1:1 physical mixture of silica supported Pt and Rh catalysts using fixed bed experiments and micro- kinetic modeling. The microkinetic model (14) for the reaction on single metals Pt and Rh is simulated for the mixture case in CHEMKIN PRO ® . It is observed that the mixture maintains the activity while producing less N2O (by-product of NO þ CO reaction) thus enhancing N2 selectivity inspite of having only half amount of Rh. Analysis of surface coverages on individual metals in mixture shows that in the presence of Pt, CO poisoning of Rh is reduced at lower temperature leading to better overall conversion and selectivity. This has potential ben- efit in automotive catalysis, as it results in the formation of significantly lower amounts of N2O, an undesirable side-product and greenhouse gas; at a lower cost than if pure Pt/Rh catalysts were used.

Modeling the Effects of the Inlet Manifold Design on the Performance of a Diesel Oxidation Catalytic Converter

Abstract: The effect of inlet flow distribution on the performance characteristics of a catalytic converter is analyzed for two common inlet manifold designs. Three-dimensional steady-state computational flu...

A review of catalytic partial oxidation of methane to synthesis gas with emphasis on reaction mechanisms over transition metal catalysts

Abstract: Catalytic partial oxidation of methane has been reviewed with an emphasis on the reaction mechanisms over transition metal catalysts. The thermodynamics and aspects related to heat and mass transport is also evaluated, and an extensive table on research contributions to methane partial oxidation over transition metal catalysts in the literature is provided. Presented are both theoretical and experimental evidence pointing to inherent differences in the reaction mechanism over transition metals. These differences are related to methane dissociation, binding site preferences, the stability of OH surface species, surface residence times of active species and contributions from lattice oxygen atoms and support species. Methane dissociation requires a reduced metal surface, but at elevated temperatures oxides of active species may be reduced by direct interaction with methane or from the reaction with H, H2, C or CO. The comparison of elementary reaction steps on Pt and Rh illustrates that a key factor to produce hydrogen as a primary product is a high activation energy barrier to the formation of OH. Another essential property for the formation of H2 and CO as primary products is a low surface coverage of intermediates, such that the probability of O–H, OH–H and CO–O interactions are reduced. The local concentrations of reactants and products change rapidly through the catalyst bed. This influences the reaction mechanisms, but the product composition is typically close to equilibrated at the bed exit temperature.

An overview of spatial microscopic and accelerated kinetic Monte Carlo methods

Abstract: The microscopic spatial kinetic Monte Carlo (KMC) method has been employed extensively in materials modeling. In this review paper, we focus on different traditional and multiscale KMC algorithms, challenges associated with their implementation, and methods developed to overcome these challenges. In the first part of the paper, we compare the implementation and computational cost of the null-event and rejection-free microscopic KMC algorithms. A firmer and more general foundation of the null-event KMC algorithm is presented. Statistical equivalence between the null-event and rejection-free KMC algorithms is also demonstrated. Implementation and efficiency of various search and update algorithms, which are at the heart of all spatial KMC simulations, are outlined and compared via numerical examples. In the second half of the paper, we review various spatial and temporal multiscale KMC methods, namely, the coarse-grained Monte Carlo (CGMC), the stochastic singular perturbation approximation, and the τ-leap methods, introduced recently to overcome the disparity of length and time scales and the one-at-a time execution of events. The concepts of the CGMC and the τ-leap methods, stochastic closures, multigrid methods, error associated with coarse-graining, a posteriori error estimates for generating spatially adaptive coarse-grained lattices, and computational speed-up upon coarse-graining are illustrated through simple examples from crystal growth, defect dynamics, adsorption–desorption, surface diffusion, and phase transitions.