Catalytic Emission Abatement and Gas Separation

Doctoral thesis, 2006

Air pollution is still today a major health problem. Emissions from mobile and stationary sources are regulated, but economical considerations limit the implementation of the most efficient abatement systems. To improve urban air quality, there is therefore a need to develop simple, durable and cost efficient emission control methods. In this thesis, methods to limit the emissions of ozone generating compounds, i.e. nitrogen oxides (NOx) and volatile organic compounds (VOCs), have been studied. The addition of ozone in order to initiate CO oxidation was studied over one Pt/alumina catalyst using flow reactor experiments and through mean-field simulations. Ozone reacted rapidly with CO already at room temperature. An Eley-Rideal mechanism between adsorbed CO and colliding ozone is suggested. The reduction in bulk CO concentration decreases the CO self-poisoning and consequently cause an earlier catalyst light-off. The addition of SO2 has been shown to promote the total oxidation of propane, ethanol and ethyl acetate over Pt/alumina catalysts. The dominating reason for the promoting effect is associated with the formation of a sulfur species at the Pt/alumina interface. The interface species desorbed at 670-720 K, and the promotion was therefore lost. At higher temperatures, residual promotion or deactivation was found depending on the sample initial dispersion. Continuous lean NOx reduction over three physical mixtures of zeolites was investigated. When propene was used as the reducing agent, the reduction efficiency was determined purely by the small pre zeolite, while both zeolites influenced the results when isooctane was used. The efficiency was in both cases dependent on the selectivity for the NO2 reduction to N2 compared to NO. The use of a CO2 selective zeolite membrane in the shift reactor has the potential to improve the H2 yield for a diesel reformer in a fuel cell APU system. The selective adsorption of CO2 from a gas mixture of CO, CO2 and H2 was studied experimentally and through molecular simulations. CO2 adsorption was favored under all conditions, but the selectivity increased at low temperature and high pressure.