Catalyst system for a flow reactor, and method for the catalytic oxidation of ammonia

A catalyst system for a flow reactor, comprising at least three catalyst gauze groups arranged one behind the other in the flow direction,

• each catalyst gauze group being formed from at least one catalyst gauze composed of at least one noble metal wire in each case, and
• the first catalyst gauze group comprising at least one catalyst gauze composed of at least one first noble metal wire made of a platinum alloy, the platinum alloy of the first noble metal wire consisting of, in addition to impurities, 80-98 wt. % platinum, 2-20 wt. % rhodium, and 0-15 wt. % palladium,
• the second catalyst gauze group comprising at least one catalyst gauze composed of at least one second noble metal wire made of a platinum alloy, the platinum alloy of the second noble metal wire consisting of, in addition to impurities, 75-98 wt. % platinum, 1-16 wt. % rhodium, and 1-20 wt. % palladium, and
• the third catalyst gauze group comprising at least one catalyst gauze composed of at least one third noble metal wire made of a palladium alloy, the palladium alloy of the third noble metal wire consisting of, in addition to impurities, 70-97 wt. % palladium, 0-10 wt. % rhodium, and 3-30 wt. % of at least one further metal, the at least one further metal being selected from the group consisting of nickel, tungsten, platinum and gold,
• wherein
• the rhodium content of the noble metal wires of the catalyst gauze groups decreases or remains constant in the flow direction and
• the palladium content of the noble metal wires of the catalyst gauze groups increases in the flow direction.