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

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

Effect of noble metals deposition on the catalytic activity of MAPO-5 catalysts for the reduction of NO by CO

Molecular sieves MAPO-5 (M: Co, Ti, Cr and Fe) with the AFI structure type were prepared by the hydrothermal method. Noble metals (Pd, Rh, Ir and Ru) were deposited on the molecular sieve supports using the homogeneous deposition precipitation method. The catalysts were characterized using XRD, TEM, DRUV-VIS, N(2) sorption, SEM, TG/DTA and ICP analysis techniques. The PdO and RhO(x) species demonstrated small particle sizes as compared with other noble metals. The catalysts were evaluated for their performance in the reduction of NO by CO at different temperatures (150-500 degrees C) for a GHSV of 44,000 h(-1). Among the palladium and noble metals deposited catalysts, the PdCoAPO-5 and RhCoAPO-5 showed excellent performance. For the RhCoAPO-5 (Rh loading = 2.98% and Rh particle size = 2.2 nm) catalyst, the temperature required for complete NO reduction was 210 degrees C, which is lower than that required for PdCoAPO-5 (Pd loading = 2.96% and Pd particle size = 4 nm) and IrCoAPO-5 (Ir loading = 2.89% and Ir particle size = 6.5 nm) under identical conditions. The Rh deposited CoAPO-5 catalyst effectively operated at lower temperatures as compared with the other noble metal deposited CoAPO-5 catalysts studied here.

Micro-kinetic study of reduction of NO on Pt group catalysts

Catalytic reduction using CO has significant potential for the control of NOx using Pt group catalysts as CO is already present in the exhausts and Pt group catalysts have high durability in the presence of SO2 and H2O. Different reaction mechanisms are given in the literature for this reaction based on NO dissociation, -NCO formation and so on, but the exact reaction mechanism capable of capturing experimentally observed features is as yet unavailable. To determine the kinetics and reaction mechanism, we propose here an elementary reaction mechanism based on NO dissociation applicable to Pt group catalysts and simulated with CHEMKIN 4.0.2 using single and multiple PSR (Perfectly Stirred Reactor) model. The activation energies of the elementary steps are found from the Unity Bond Index-Quadratic Exponential Potential (UBI-QEP) method. Excellent agreement between literature experiments and our simulation results are observed for the NO-CO reaction on Pt and Rh catalysts and for the NO-CO-O-2 reaction on Ir catalyst. The effect of temperature on the NO reduction activity is captured well by the model. Additionally the simulations can also point towards importance of particular reactions, selectivity to N-2, effects of surface coverage, effects of residence time and catalytic surface area on NO reduction

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

NO reduction to N-2 is the key reaction for efficient 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 performance. In this article, we have studied the NO + CO reaction for a 1:1 physical mixture of silica supported Pt and Rh catalysts using fixed bed experiments and microkinetic modeling. The microkinetic model [14] for the reaction on single metals Pt and Rh is simulated for the mixture case in CHEMKIN PRO (R). It is observed that the mixture maintains the activity while producing less N2O (by-product of NO + CO reaction) thus enhancing N-2 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 benefit 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

Platinum group metals substituted MCM-41 molecular sieves: Synthesis, characterization and application as novel catalysts for the reduction of NO by CO

Mesoporous MCM-41 molecular sieves with Si/M (molar) ratios of 100 containing platinum group metals (Pd, Pt, Rh. Ir) were synthesized by the hydrothermal method These catalysts were systematically characterized by various analytical a rid spectroscopic techniques, viz, XRD, TEM. DRUV-vis, N(2) sorption XRD analysis confirmed that the presence of platinum metals did not influence the parent structure and phase purity of the MCM-41 catalysts DRUV-vis spectral studies of MCM-41 indicate the presence of platinum metal ions The catalytic activities of these catalysts were evaluated for the reduction of NO by CO as a function of temperature The Study revealed that the catalytic activity is, in the order (Rh>Ir>Pd>Pt) Our experimental results are in good agreement with theoretical previous analysts based on the NO(center dot) dissociation activation energy. (C) 2009 Elsevier B V

A process model for underground coal gasification - Part-III: Parametric studies and UCG process performance

Underground gas gasification (UCG) is a clean coal technology which involves in-situ gasification of deep-seated underground coal. The process can be divided in two phases based on state of coal seam and direction of cavity growth. In phase-I, cavity grows mainly in vertical direction while in phase-II it grows in horizontal direction. The in-house simulator developed for both the phases of UCG has been reported earlier Samdani a al. (2016a,b). It incorporates reaction kinetics, flow patterns, spalling, heat and mass transfer effects. In this work, we take further insight and perform parametric studies to examine the effects of different operating conditions, coal properties and design parameters on key performance indicators i.e. exit gas quality, energy generation rates etc. The investigation revealed that the exit gas quality and rate of coal consumption are strong functions of spalling rates and kinetics of reactions; the coal having very low spalling tendency or less reactivity may not be favorable for the UCG process. An important parameter called critical spalling rate has emerged through this analysis. It is the property of given coal above which UCG is sustainable. In addition, model performance is also sensitive to inlet gas temperature, pressure and composition. Optimum performance of UCG is obtained at a steam to oxygen ratio of 2.5 and at the highest possible inlet gas temperature, operating pressure, and oxygen content in the feed. Among the design parameters, the length of outflow channel is very important as it strongly affects both the exit gas calorific value and its fluctuations with time. The predicted effects of different parameters are in accord with the observations during lab-scale UCG experiments and different field trials. This study demonstrates the importance of a process model to determine the best conditions for UCG process and to evaluate feasibility of the process for a coal seam under consideration

Process Analysis for Dimerization of Isobutene by Reactive Distillation

Alkylates are a class of probable replacements for MTBE as gasoline additives that can be produced by dimerization of isobutene (to isooctene) with subsequent hydrogenation. The characteristics of the dimerization reaction make it a potential candidate for reactive distillation. The dimer, being heavier than C-4, can be maintained at a low concentration level in the reactive zone by simultaneous distillation, thereby suppressing the subsequent oligomer-producing reactions. In this work, the influence of important design and operating parameters on the performance of the reaction in a hybrid reactive distillation column is studied through process simulations. the results show that a high selectivity toward diisobutene can be achieved along with adequate temperature control in the presence as well as absence of polar components. Multiple steady states are observed in some cases that introduce additional complexities in the determination of the optimal windows for certain parameters. The process seems economically attractive, as it is capable of utilizing the existing reactive distillation assets and the feedstock for MTBE production by suitable revamping