Catalyst structure for a rapid reaction

A compact catalytic reactor comprising:

• a channel for a rapid reaction having an inlet in fluid communication with a gas mixture including hydrogen to undergo the rapid reaction, wherein the rapid reaction comprises combustion of hydrogen;
• and
• a first catalyst structure within the channel in the vicinity of the inlet and a second catalyst structure within the channel further from the inlet, such that a gas mixture supplied to the inlet flows past the first catalyst structure and the second catalyst structure;
• the first catalyst structure comprising an oxidized aluminum-containing ferritic steel alloy with an adherent alumina oxide surface, without incorporation of any additional catalytic material;
• the second catalyst structure having catalytic activity for the rapid reaction but the first catalyst structure having less catalytic activity for the rapid reaction;
• the second catalyst structure comprising a ceramic coating on a metal substrate, and a catalytically active material, the catalytically active material being platinum and/or palladium;
• the catalytic activity of the first catalyst structure for the rapid reaction being in the range from 0.1 to 0.2 times that of the second catalyst structure, wherein in a test in which the catalytic activity of catalyst structures of length 150 mm are compared by passing the hydrogen-containing gas mixture over the catalyst structures while holding the temperature at the wall of the channel at 100° C., the proportion of hydrogen that undergoes combustion over the first catalyst structure is between 0.1 and 0.2 times the proportion of hydrogen that undergoes combustion over the second catalyst structure;
• wherein the activity of the first catalyst structure for other reactions is no more than the activity for the rapid reaction.