When will fossil fuel reserves be diminished

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.

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

Microscale combustion: Technology development and fundamental research

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.

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An overview of spatial microscopic and accelerated kinetic Monte Carlo methods

Combustion characteristics and flame stability at the microscale: a CFD study of premixed methane/air mixtures

Effect of Exhaust Gas Recirculation in NOx Control for Compression Ignition and Homogeneous Charge Compression Ignition Engines

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-O2 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 N2, effects of surface coverage, effects of residence time and catalytic surface area on NO reduction.

Micro-Kinetic Study of Reduction of NO on Pt Group Catalysts

Combustion of premixed H 2 /air flames near inert surfaces was studied numerically using detailed chemistry and multicomponent transport. The roles of inlet composition, radiative loss from the surface, and thermal quenching by cold walls in NO x and fuel emissions were analyzed. It is shown that the bifurcation behavior in terms of extinguishability strongly determines the role of thermal quenching in emissions. For weak, extinguishable flames, thermal quenching at the surface effectively reduces NO x emissions, although at the cost of higher fuel emissions. Strong, nonextinguishable flames at low strain rates are practically unaffected by thermal quenching except for an increased NO 2 mole fraction near the surface.

NOx and fuel emissions in combustion of hydrogen/air mixtures near inert surfaces

Nitric oxides and unburned hydrocarbons from automotive engines are major atmospheric pollutants. A strategy based on the simultaneous reduction of NO and oxidation of hydrocarbon can be very effective in aftertreatment. In this study, the various regimes of operation of this selective catalytic reduction process using propene as a representative hydrocarbon, with and without the presence of oxygen, are delineated. Detailed kinetic modeling using quantitative microkinetics for Pt and Rh catalysts is performed. Interesting catalytic features including coking and oxygen poisoning are clearly identified. An optimal operating regime in which the complete conversion of NO and C3H6 occurs in the presence of small amounts of oxygen is highlighted.

Microkinetic Modeling of the Effects of Oxygen on the Catalytic Reduction of NO on Pt and Rh in Automotive Aftertreatment

The direct methane proton exchange membrane fuel cell was demonstrated for the first time. A Nafion membrane doped with phosphoric acid was used as the electrolyte. Pd/C, Pd-Ru/C and Pd-Au/C were studied as the anode catalysts with catalyst loading of 0.2mg/cm2. Selection of these catalysts for the studies was made based on the activation energy obtained by calculation using the UBI-QEP method. It was shown among these catalysts; Pd-Au/C anode exhibited a maximum open circuit voltage of 0.55V with current density of 30mA/cm2. It was also seen that by bleeding oxygen on anode side, open circuit voltage was 0.74V and current density was increased to 160mA/cm2.

Preeti Aghalayam

Papers

Effect of Exhaust Gas Recirculation in NOx Control for Compression Ignition and Homogeneous Charge Compression Ignition Engines

Micro-Kinetic Study of Reduction of NO on Pt Group Catalysts

NOx and fuel emissions in combustion of hydrogen/air mixtures near inert surfaces

Microkinetic Modeling of the Effects of Oxygen on the Catalytic Reduction of NO on Pt and Rh in Automotive Aftertreatment

Direct Methane Proton Exchange Membrane Fuel Cell