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Both a mechanistic model, which accounts for ammonia, nitrate, and ammonium nitrate storage, and a global model, which only accounts for ammonia storage and no nitrates, were calibrated to the same data collected across a Cu-CHA catalyst. Once calibrated, the models were directly applied to simulate various driving cycles (cold WHTC, hot WHTC, FTP, NRTC, ETC, and WNTE), with different catalyst layouts (i.e., washcoat loading and cpsi) as part of the model validation process. It was demonstrated that the mechanistic model provides a notable improvement in the prediction of the NOx conversions for colder cycles (i.e., cold WHTC, hot WHTC, and FTP) due to its inclusion of nitrates and ammonium nitrate. The quality of prediction of the hotter cycles (i.e., NRTC, ETC, and WNTE) was close to the same for both models, since no ammonium nitrate accumulates at these higher temperatures. Despite the additional reactions and surface species included in the mechanistic model, no significant increase in simulation time is observed compared to the global model. Finally, the mechanistic model is applied to calibrate a simple NH3 dosing strategy. The dosing strategy is compared to a constant NH3/NOx approach, where it was shown through simulations, and confirmed experimentally, that the dosing approach allows for an increase in NOx conversion. Overall, this demonstrated that the model accurately predicts the increase in NOx conversion and that the model is a valuable tool to establish the catalyst’s true potential during driving cycles.

This paper describes a computational study of a proposed recuperative catalytic converter intended for the catalytic combustion of lean methane streams. The design is based on the principle of alternating layers of washcoated monolith channels through which the fluid passes in counter-current flow. Heat transfer occurs continuously across the boundary separating the layers, thus the exiting hot gas exchanges energy with the incoming cold gas. Monoliths composed of cordierite and silicon carbide are compared, each of which had 12% by volume washcoat applied. The effects of layer thickness, monolith length and space time are compared. It is found that the monolith comprised of higher thermal conductivity material is more effective in enhancing the temperature in the reactor. Conversion of methane entering the reactor at relatively low temperatures can be oxidised with some added thermal energy.

This paper demonstrates that the use of a solution-mapping approach can accelerate the simulation of a dual-layer ammonia oxidation catalyst by several orders of magnitude. In a first step, a 1-D + 1-D model of the dual-layer catalyst is set up. The results of this model are compared to the numerical solution of a 2-D model, and it is shown that the 1-D + 1-D model provides an accurate approximation of the full 2-D solution. In a second step, spline interpolation functions are constructed that map the solution of the mass balance equations for one axial volume element of the 1-D + 1-D model as a function of the inlet concentrations, temperature and residence time. During the runtime of the simulation, concentration profiles can be computed by simple successive calls of the interpolation function without the need for a numerical solver. The 5-dimensional spline functions reproduce the output concentrations of a reactor model with 35 axial volume elements with an accuracy of better than 1.25%. The use of the solution mapping reduces the computation time for a steady-state solution of the monolith model from 97.5 s down to 10 ms.

A highly efficient single channel monolith reactor model for the oxidation of ammonia is implemented. A mechanistic model for ammonia oxidation on platinum is used, and all internal and external mass transfer effects are included. The model efficiency is derived from the use of pre-computed solutions of the mass balance equations. Spline interpolation functions are constructed from pre-computed solutions of the mass balances of one volume element of the reactor model. It is shown that these spline functions reproduce the exact outlet concentrations of the volume element with a relative error of less than 3%. This solution mapping approach allows computation of concentration profiles in the reactor by simple successive calls of the interpolation function without any numerical solution. Outlet concentrations of the complete reactor computed in this way show a relative error of less than 2%. Application of the solution mapping approach speeds up the solution of the concentration profiles by a factor of more than 3200, compared to the numerical solution of the mass balances. In this way one steady state concentration profile in an ammonia oxidation catalyst can be computed in less than 0.003 s, despite the fact that the model uses mechanistic surface kinetics and includes the radial diffusion in the washcoat.

This paper demonstrates how pre-computed rate data can be used to enable the numerically efficient implementation of mechanistic kinetics in a reactor model for an automotive ammonia slip catalyst. In a pre-processing step the source terms for the gas species are mapped as a function of gas composition and temperature. From this map (80,000 data points), a spline interpolation function is constructed. The spline function approximates the numerical steady state solution of the kinetic model with an average error of less than 1%. Application of the rate mapping procedure results in a speedup of about two orders of magnitude. The spline approximation is implemented in a 2-dimensional model of a monolith reactor channel that includes diffusion in the washcoat layer. Depending on the channel diameter and the washcoat thickness, diffusion limitations in the open channel and in the washcoat can have a significant influence on the NH 3 conversion. Surprisingly, the selectivity for the products N 2 , N 2 O and NO is not sensitive to diffusion effects in the gas phase or in the washcoat.

This paper presents experimental and modelling results for the oxidation of mixtures of hydrogen and carbon monoxide in a lean atmosphere. Transient light-off experiments over a platinum catalyst (80 g/ft 3 loading) supported on a washcoated ceramic monolith were performed with a slow inlet temperature ramp. Results for CO alone agree with earlier results that predict self-inhibition of CO; that is an increasing light-off temperature with increasing CO concentration. Addition of hydrogen to the feed causes a reduction in light-off temperature for all concentrations of CO studied. The most significant shift in light-off temperature occurs with the addition of small amounts of hydrogen (500 ppm, v/v) with only minor marginal enhancement occurring at higher hydrogen concentrations. Hydrogen alone in a lean atmosphere will oxidise at room temperature. In mixtures of hydrogen and CO, the CO was observed to react first until a conversion of about 50% was observed, at which point the conversion of hydrogen rapidly went from 0 to 100%. Simulations performed using literature mechanistic models for the oxidation of these mixtures predicted that hydrogen ignites first, followed by CO, a direct contradiction of the experimental evidence. Upon changing the activation energy between adsorbed hydrogen and oxygen, the CO was observed to oxidise first, however, no enhancement of light-off was predicted. The effect cannot be explained by the mechanistic model currently under discussion.

Diesel particulate filters composed of so-called wall-flow monoliths are well established devices for diesel particulate abatement. Recent improvements in production technology allow implementation of full-featured catalyst functionality in the filter walls. From a reactor engineering point of view such wall-flow reactors with wall-integrated catalyst show fundamental differences compared to conventional flow-through monoliths. The complex interactions of convection, diffusion and reaction in the wall-flow monolith are studied by means of numerical simulation. A two-dimensional model for the flow in one pair of inlet/outlet channels with a generic first order reaction in the catalytic filter wall is developed. Concentration profiles in the reactor and a conventional flow-through catalyst are compared. It is found that in the range of moderate reactor conversion concentration gradients along the inlet channel of the filter are small. Thus the reactor can be described by an approximate one-dimensional model, taking into account only the radial flux through the filter wall and assuming a constant inlet concentration in axial direction along the inlet channel. Light-off curves are computed for the wall-flow and for the conventional flow-through monolith. Significantly better conversion is found for the wall-flow configuration. This can be explained by mass transfer limitation in the conventional flow-through monolith.