Enhanced Methane Oxidation Catalysis Through Feed Modulation And Oxygen Storage

The elimination of uncombusted CH4 from Natural Gas Vehicle emissions is necessary to meet future greenhouse gas regulations, requiring the development and optimization of novel methane oxidation catalyst. In this project, the catalytic oxidation of methane is examined under lean and stoichiometric conditions across several catalysts and how feed modulations can enhance catalyst performance. In the first section of this project, the effects of reductive H2 pulses were examined for Pd-Pt/Al2O3 and Pd-Pt/ CeO2 ZrO2-Y2O3-La2O3 catalysts. Alternating H2/O2 pulses resulted in significant and sustained methane oxidation activity, even when large quantities of H2O were present in the feed. The second part of the project involves the design and optimization of novel Four-Way Catalysts – bimetallic Pt/Pd catalysts supported on Al2O3 and augmented by mixed-metal oxides, otherwise known as spinels. We initially demonstrate the enhancements resulting from the combination of spinels and modulating feed conditions. Next, we optimize catalyst performance by examining the impact of different feed modulation parameters such as oscillation frequency, amplitude, and average lambda. Optimal catalyst performance was determined to occur under slightly rich, near-stoichiometric feed conditions, under high oscillation amplitudes and slow oscillation frequencies. Methane conversion enhancement is linked to its nonmonotonic dependence on O2. The project concludes with the modelling of methane oxidation over a Pt-Pd/Al2O3 catalyst, in preparation of future Four-Way Catalyst modelling efforts. A global kinetic model for total oxidation of methane, steam methane reforming, and the reversible water gas shift reaction was created and modelled in a simple PFR model and a low-dimensional, dual-phase, washcoat model. Both models were fit to collected experimental data. We conclude with proposals for further research based on the results of this project.