Catalytic reactors are well-suited for hydrocarbon combustion in gas-turbine-based mesoscale (up to 1 kW electric) power generation applications. A platinum-coated, propane-fueled catalytic monolithic reactor has been investigated for portable gas-turbine-based power generation, its design being part of a recent Swiss initiative. Detailed parametric numerical studies were conducted for two reactor types, with ceramic and metallic monolithic structures, and combustion efficiencies were assessed at different inlet velocities and equivalence ratios. A 2-D elliptic numerical code was employed, with full treatment of all relevant heat transfer mechanisms inside the reactor channel. An operating scenario was chosen with a moderate mixture compression at p = 2.5 bar, fuel-to-air equivalence ratios up to φ = 0.40 and preheat temperature T_IN = 750 K (achievable in recuperated mesoscale gas turbine devices). Predicted gas-phase ignition delay times have initially affirmed the operational safety for the chosen operating parameters. Power output curves and combustion efficiencies have been calculated for different inlet velocities, equivalence ratios, and solid thermal conductivities. It was shown that, for a given reactor length, metallic materials were more favorable regarding maximum power output and combustion efficiency. Reactors with high solid thermal conductivity displayed increased fuel conversion at high inlet velocities, due to reduced light-off distances and the larger surfaces exposed to high temperatures compared to reactors with low wall thermal conductivities. Metallic reactors benefited from more robust construction (thicker solid walls) when operated under fuel-leaner conditions, while ceramic reactors profited only by increased equivalence ratios. Finally, metallic reactors yielded more uniform outlet gas properties over a wider operational range compared to ceramic ones.