A heat exchange reactor including a housing, a plurality of tubes mounted in the housing and configured to carry a first fluid, and a baffle having a plurality of holes receiving the tubes. The baffle is configured to guide a second fluid provided within the housing to flow in a direction generally perpendicular to the tubes. The reactor includes various configurations for minimizing adverse effects of thermal expansion of the baffle and the tubes. The reactor is configured to minimize mechanical interference between the baffle and the tubes in both an operational state and a non-operational state, for example, by shaping the holes in the baffle to take into account thermal expansion. The reactor also includes a thermal insulator along a length of the tubes at a large temperature gradient zone within the reactor. The reactor further includes a heat transfer fin in contact with only one of the tubes.