Catalyst for oxidising ammonia

A catalyst article for oxidizing ammonia, the catalyst article comprising a selective catalytic reduction (SCR) catalyst and a composite heterogeneous extruded honeycomb having longitudinally extending parallel channels, which channels being defined in part by channel walls having a total longitudinal length, wherein the channel walls comprise a cellular ceramic and open pore structure including a periodic arrangement of porous cells, each porous cell defined by a cell wall comprising a catalytically active interface layer, with adjacent catalytically active interface layers being joined to one another to form the cellular ceramic and open-pore structure, wherein the cellular ceramic and open-pore structure is embedded in an inorganic matrix component, wherein

• at least some of which porous cells are defined at least in part by a cell wall comprising a catalytically active interface layer of a catalytically active material comprising a precious metal supported on particles of a support material, and
• wherein the inorganic matrix material component is at least substantially free of the catalytically active material of the catalytically active interface layers.