Over the past several years, cerium oxide and CeO2-containing materials have come under intense scrutiny as catalysts and as structural and electronic promoters of heterogeneous catalytic reactions. Recent developments regarding the characterization of ceria and CeO2-containing catalysts are critically reviewed with a special focus towards catalyst interaction with small molecules such as hydrogen, carbon monoxide, oxygen, and nitric oxide. Relevant catalytic and technological applications such as the use of ceria in automotive exhaust emission control and in the formulation of SO x reduction catalysts is described. A survey of the use of CeO2-containing materials as oxidation and reduction catalysts is also presented.

Catalytic Properties of Ceria and CeO2-Containing Materials

Numerical Initial Value Problems in Ordinary Differential Equations

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Studies in Surface Science and Catalysis

A detailed chemical kinetic mechanism has been developed to describe the oxidation of small hydrocarbon and oxygenated hydrocarbon species. The reactivity of these small fuels and intermediates is of critical importance in understanding and accurately describing the combustion characteristics, such as ignition delay time, flame speed, and emissions of practical fuels. The chosen rate expressions have been assembled through critical evaluation of the literature, with minimum optimization performed. The mechanism has been validated over a wide range of initial conditions and experimental devices, including flow reactor, shock tube, jet-stirred reactor, and flame studies. The current mechanism contains accurate kinetic descriptions for saturated and unsaturated hydrocarbons, namely methane, ethane, ethylene, and acetylene, and oxygenated species; formaldehyde, methanol, acetaldehyde, and ethanol.

A Hierarchical and Comparative Kinetic Modeling Study of C1 − C2 Hydrocarbon and Oxygenated Fuels

Chemical-looping combustion (CLC) for inherent CO2 separations—a review

Coal oxidation at low temperatures: oxygen consumption, oxidation products, reaction mechanism and kinetic modelling

Coal oxidation at low temperatures (i.e. <100 °C) is the major heat source responsible for the self-heating and spontaneous combustion of coal and is an important source of greenhouse gas emissions. This review focuses on the chemical reactions occurring during low-temperature oxidation of coal. Current understanding indicates that this process involves consumption of O 2, formation of solid oxygenated complexes, thermal decomposition of solid oxygenated complexes and generation of gaseous oxidation products. Parameters, such as mass change, heat release, oxygen consumption, and formation of oxidation products in the gas or solid phase, have been used to qualitatively and quantitatively describe the oxidation process. Reaction mechanisms have been proposed to explain the characteristics of consumption of O2, and formation of oxidation products in the gas and solid phases. Various kinetic models have also been developed to describe the rate of oxygen consumption and the rates of formation of gaseous oxidation products in terms of the rate parameters of the relevant reactions, oxidation time, temperature, and initial concentration of oxygen in the oxidising medium. Further research emphasis should be placed on the formation of the complete reaction pathways proceeding in the oxidation process and on the development of kinetic models applicable for predicting the self-heating and gas emission in a coal seam or stockpile.

Coal oxidation at low temperatures: oxygen consumption, oxidation products, reaction mechanism and kinetic modelling, Pages 487-513

Mechanisms for formation, chlorination, dechlorination and destruction of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs)

In this paper we develop a friction factor correlation to predict the pressure drop during pumping and induction of concentrates of fire fighting foams containing around 1% of xanthan gum. Such concentrates are highly elastic, display small yield stress and exhibit significant thinning upon shearing. We demonstrate that in the turbulent regime, the Blasius equation normally used for Newtonian fluids seems to correlate well the friction factor with the Metzner-Reed Reynolds number. Our development provides an example of how the methodology used to develop the friction factor correlation can be applied to analyse a set of experimental data to verify its internal consistency. The friction factors developed in the paper can be applied to other foam concentrates that include a similar content of xanthan gum in their formulation, to predict pressure drop as a function of a flow rate and pipe diameter, provided that there exists an appropriate viscosity model. Subsequently, the paper presents experimental measurements of apparent viscosity for one foam concentrate and develops relevant viscosity models. We observe that the rheology of the concentrate is governed by the behaviour of xanthan gum. Although, the foam concentrate considered in the article is yield pseudo plastic (i.e., it follows the Herschel-Bulkley model), for the shear stresses normally encountered during pipe flow, the viscosity of the material can be described by a power law model. Over the temperature range of between 0 and 40 o C, the apparent viscosity displays only a weak dependence on temperature. Subsequent calculations of pressure drop with temperature demonstrate minor variation in pressure drop with temperature, but only in the turbulent flow regime. This suggests that induction systems intended to operate under widely varying temperature conditions should be designed to function in the turbulent flow regime.

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Eric M. Kennedy

Papers

Coal oxidation at low temperatures: oxygen consumption, oxidation products, reaction mechanism and kinetic modelling

Coal oxidation at low temperatures: oxygen consumption, oxidation products, reaction mechanism and kinetic modelling, Pages 487-513

Mechanisms for formation, chlorination, dechlorination and destruction of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs)

Friction factors for pipe flow of xanthan-based concentrates of fire fighting foams

Analysis of the mechanism of the low-temperature oxidation of coal