An apparatus and method for treating diesel exhaust gases are described. The system consists of two functionalities, the first being a selective catalytic reduction (SCR) catalyst system and the second being a capture material for capturing catalyst components that have appreciable volatility under extreme exposure conditions. The SCR catalyst component is typically based on a majority phase of titania, with added minority-phase catalyst components comprising of one or more of the oxides of vanadium, silicon, tungsten, molybdenum, iron, cerium, phosphorous, copper and/or manganese vanadia. The capture material typically comprises a majority phase of high surface area oxides such as silica-stabilized titania, alumina, or stabilized alumina, for example, wherein the capture material maintains a low total fractional monolayer coverage of minority phase oxides for the duration of the extreme exposure. The method involves treatment of hot exhaust streams by both the catalyst material and capture material, wherein the capture material can be in a mixture with the catalyst material, or can be located downstream thereof, or both, but still be maintained at the extreme temperatures. Volatile catalyst components such as vanadia are thus removed from the vapor phase of the exhaust gas.