Af. Ahlstromsilversand et Cui. Odenbrand, COMBUSTION OF METHANE OVER A PD-AL2O3 SIO2 CATALYST, CATALYST ACTIVITY AND STABILITY/, Applied catalysis. A, General, 153(1-2), 1997, pp. 157-175
Palladium supported on Si-stabilised alumina has been demonstrated to
be an active and durable catalyst for the combustion of methane. Si is
more effective in stabilising alumina than La or Ba when the elements
are added through an impregnation technique. Multiple stabilisation w
ith combinations of La, Ba and Si does not increase further the stabil
ity against sintering. The stability increases logarithmically with th
e amount of Si added (0.5-8 atomic%). The rate of sintering is not aff
ected by an increase of the water vapour content of the atmosphere fro
m 1 to 20 vol.%. Doping palladium with rhodium or platinum increases t
he activity of the catalyst for methane combustion. The high-temperatu
re stability of pure Pd is however superior to the stabilities of the
Rh- and Pt-doped catalysts. Addition of La or Ce to the Pd-catalyst in
creases its stability against thermal deactivation but leads to an ove
rall decrease in activity. The activity of the as-prepared catalysts a
re affected by the Pd-content below a value corresponding to 5% of the
monolayer capacity. Thermally deactivated catalysts show a stronger a
ctivity dependence of the Pd-content than as-prepared catalysts. The c
ombustion reaction is first order with respect to methane and zero-ord
er with respect to oxygen (>2 vol.% of oxygen). Carbon dioxide has no
inhibitory effects on the combustion. The activity of the Pd-catalyst
is decreased by a factor of 5 through deactivation at 1473 K for 768 h
. The decrease in activity is linearly correlated to the decrease in s
pecific surface area.