There has been significant recent interest in the development of low-temperature fuel cells for portable power generation because of their potentially very high efficiency and ultrahigh density of power generation. In many cases, hydrogen is a preferred fuel for use in fuel cells, because of its very high energy density. In this paper, we report the first experimental evidence that autothermal reverse-flow operation of a microreactor results in up to a 5% increase in reaction selectivity toward hydrogen, a 200 degreesC decrease in the oxidation ignition temperature, and a reactor "skin" temperature below 60 degreesC for many hours of stable autothermal operation. Finally, the critical issues in the design of portable catalytic microreactors for small-scale power generation are discussed, leading to the proposed novel, highly integrated planar reactor design aimed at optimal functionality, manufacturability, and low cost.