A catalyst composition is provided having a CHA crystal structure; about 0.5 to about 5.0 mol % phosphorus; and SiO2 and Al2O3 in a mole ratio of about 5 to about 40. The catalyst composition is capable of NOx conversion at elevated temperatures. A catalytically active washcoat includes such catalyst compositions and one or more promoters or stabilizers, and may be applied to a monolith substrate to produce a catalytically active article. Methods of reducing NOx employing the catalyst compositions are also provided.