Abstract: A gas treatment device, comprises a substrate disposed within a shell. The substrate comprises a catalyst composition comprising a support, a catalyst, and a sufficient amount of SMSI material such that, upon exposure to a gas stream (at a gas treatment device operating temperature), less than or equal to about 35 wt % of hydrocarbons in the gas stream are burned. A method for forming a gas treatment device, comprises applying a slurry to a substrate, wherein the slurry comprises a support and a sufficient amount of SMSI material such that, upon exposure to a gas stream at a gas treatment device operating temperature, greater than or equal to about 50 wt % of hydrocarbons in the gas stream are cracked to a light fraction; applying a catalyst to the substrate; calcining the catalyst; and disposing the calcined substrate into a shell, with a retention material disposed between the shell and the calcined substrate.