Enhancement of hydrogen reaction in a micro-channel by catalyst segmentation

The paper addresses the combustion characteristics of multi-segment catalysts in a micro-reactor by numerical simulation with detailed heterogeneous and homogeneous chemistries. The effect of multi-segment catalyst is delineated in terms of different catalyst dispositions, different flow conditions and different reactor properties. With a fixed total catalyst length (1 cm), multi-segment catalyst reveals better performance than single catalyst. The space between catalyst segments reduces the inhibition of homogeneous reactions by catalyst and promotes homogeneous reactions in this region since the neighboring catalysts help to maintain a high wall temperature. Therefore, homogeneous combustion can shift upstream with the multi-segment catalyst. The results of different catalyst dispositions show that more catalyst segments has better performance but the catalyst space distance has no obvious effects due to the fast reaction rate of hydrogen. For different flow conditions, the results indicate multi-segment catalyst disposition has better conversion ratio even though there is no homogeneous combustion in the fluid region for fuel-lean condition. The results for different inlet velocities show that multi-segment catalyst has no obvious benefit on lower inlet velocity. However, it can extend the blowout velocity. Finally different reactor dimension and wall material are simulated. Although heterogeneous reactions strengthen in small channel, multi-segment catalyst still has obvious benefit. The results of different wall thermal conductivity do not have obvious difference for multi-segment catalyst. These results can be used in the design of a catalytic micro-reactor for hydrogen/air reactions.