The present invention is directed to a metal-promoted zeolite beta
catalyst useful in the selective catalytic reduction of nitrogen oxides
with ammonia in which the zeolite beta is pre-treated so as to provide
the zeolite with improved hydrothermal stability.The stabilized beta
zeolite is provided by incorporating into the zeolite structure
non-framework aluminum oxide chains. The aluminum oxide chains can be
incorporated into the zeolite structure by a unique steaming regimen or
by treatment with rare earth metals, such as cerium. The treatment
process is unlike well-known methods of dealuminizing zeolites for the
purpose of increasing the silica to alumina ratio. In the present
invention, the non-framework aluminum oxide is characterized by FT-IR by
a peak at 3781.+-.2 cm.sup.-1, which when present, stabilizes the zeolite
against further dealumination such as under oxidizing and harsh
hydrothermal conditions.