Theoretical investigation of axially non-uniform catalytic monoliths for methane combustion

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A two-dimensional mathematical model was formulated to investigate the effect of axially non-uniform catalyst distribution on temperature and concentration gradients in catalytic monoliths for typical steady state and transient methane combustion conditions. It was observed that exponentially decreasing catalyst distributions initiated light-off at the entrance of the monolith and temperature gradients were lower as compared to monoliths with uniform catalyst distribution under steady state conditions. Bulk fluid temperature suitable for homogeneous reactions initiation was reached further upstream. For transient conditions, non-uniform distributions alleviated axial temperature gradients but at the expense of temporal gradients. As temperature gradients are linked to thermal stresses, this work indicates that non-uniform distributions can affect monolith thermal stability.