Provided is an improved catalyst for treating exhaust gas, particularly for selectively reducing NOx, and methods for using the same, wherein the catalyst includes a blend of a transition metal promoted zeolite and an un-promoted zeolite, wherein both zeolites have the same framework type. Such crosslinked polymers may be used to make polymer electrolyte membranes that may be used in electrolytic cells such as fuel cells. A detachable connecting element secures the coupling to the shaft at different positions along the shaft.