Development of a spatially-resolved technique for the measurement of effective diffusions and Its application to the reaction modelling of deactivated washcoated catalytic monoliths

Abstract

After the energy crisis in 1970s, the impacts of increasing numbers of vehicles, including natural gas vehicles (NGVs), on global air quality has highlighted the demand to optimise existing vehicle aftertreatment systems. Increasingly stringent emission regulations in many countries lead to challenges for automobile manufacturers to meet carbon monoxide (CO), total hydrocarbon and nitrogen oxides emission standards, thus further optimisation of current aftertreatment technologies is essential. Optimisation of the three-way catalysts (TWCs) converters is a challenge due to the spatially-distributed and transient nature of the operation of vehicles. The conventional method of investigating catalysts properties by analysis of the chemical species at the reactor outlet (end-pipe analysis method) provides large amounts of valuable knowledge, but due to the lack of intra-catalyst data, limits the possibility of designing and optimising catalytic converters. Spatially-resolved experimental techniques provide a solution to this drawback, by accessing spatiotemporal intra-catalyst information to help in the construction in more accurate and predictive models. Using spatially and/or temporally mapping of aftertreatment reactions in structured catalysts provide a density of information which is crucial for the optimisation of kinetics modelling for engine operations, however, difficult to access using traditional end-pipe analysis methods. The main requirement of catalytic converters modelling is to accurately predict their performance through mathematical expressions, representing physiochemical processes of these aftertreatment systems. These processes include mass transfer and surface reactions associated with the chemistry of interest. As mass transfers from the gas phase to the catalyst surface have significant influences in determining the kinetics of the reactions, the accuracy in describing these processes is crucial. The aim of the present work is to develop a novel methodology to determine, experimentally, the mass transfer coefficients in monolith catalysts using a spatially-resolved approach.