Microreactors hold great promise for novel chemical process routes as well as for fundamental studies of existing reactions. A unique advantage of micromachined over conventional reactors is their large surface-to-volume ratio which makes such reactors particularly attractive for catalytic reactions.

We have previously demonstrated in experimental and theoretical investigations of hydrogen oxidation in a micromachined catalytic reactor that this spatial confinement of a chemical reaction biases the overall reaction behaviour towards catalytic conversion, and can ultimately lead to a complete suppression of homogeneous reactions.

Here, we present a significant extension of this previous study. We find that by varying the catalyst coverage on the microchannel walls in sufficiently small reaction channels, both reaction pathways (i.e. homogeneous as well as heterogeneous reactions) can be weakened to a point where ignition and/or conversion along either pathway is sufficiently delayed to suppress any reactive conversion over an extended microchannel length. The catalyst thus turns into a reaction inhibitor rather than the normally observed reaction promoting behaviour. The mechanism of this surprising “total quenching” will be discussed in detail and generalized mathematical formulas will be presented.