Activity of Pd loaded on zeolite for the methane combustion was examin
ed using various kinds of mordenite and ZSM-5 zeolites with different
compositions of aluminum and cation. The activity strongly depended on
the composition as well as on the structure of zeolites. Among tested
catalysts, the highest and durable activity was found on the catalyst
which was prepared from an ion exchange with palladium amine complex
on the H-type siliceous mordenite such as Pd/H-mordenite (Si/Al-2=145)
. Reaction orders with respect to the partial pressures of methane and
oxygen indicated that the oxidized form of palladium was the active s
pecies. Characterization using TEM and XPS showed the high dispersion
of palladium in the framework of zeolite. TPR using methane as a reduc
tant showed that the high activity of Pd on the siliceous H-mordenite
could be explained qualitatively and quantitatively; i.e., Pd was affe
cted by the qualitative alteration caused by the induced effects by Al
and Na cations, whereas the number of active oxygens on Pd was quanti
tatively enhanced in the zeolite, particularly mordenite. The micropor
es of zeolite may have a role in preventing the sintering into large p
articles to stabilize the activity. (C) 1997 Elsevier Science B.V.