Overlayer for Catalyst
Publication Date: 2003-Oct-13
The IP.com Prior Art Database
Overlayer for Catalyst
It is well known to add an overlayer to a catalyst that is used in, for example, a reformer
catalyst brick of a fuel processor for a motor vehicle.
In general, the overlayer is a coating on the catalyst that protects the catalyst from
reaching high temperatures, the high temperatures can be caused by exothermic reactions.
The overlayer is designed not to impact the light-off performance of the catalyst at low
flow rates, but does limit the reaction rate of the catalyst at high flow rates. By limiting
the reaction rate at high flow rates, the maximum temperature observed in the brick is
limited. This limitation protects the catalyst from thermal deactivation.
The overlayer is shown covering a catalytic layer which is supported by a
substrate. The loading of the overlayer can range between about 0.5 g/in3 to about 2
g/in3. The overlayer is deposited onto the catalyst in any suitable manner, such as
standard washcoating techniques that deposit a slurry containing the overlayer material
onto a substrate having a catalyst. The catalyst is placed on the substrate by any suitable
The overlayer comprises a porous, chemically inert material, such as alumina,
silica, ceria-zirconia, natural zeolites, or synthetic zeolites. The catalyst can be any
suitable catalyst for the reaction, such as platinum. It is to be appreciated that certain
inert materials may function better with certain catalysts. The substrate that supports the
catalyst can be any suitable carrier structure. For example, a monolithic structure used in
fuel processors that generally has a body and a plurality of channels running through the
Referring to Figs. 1 - 3, baseline primary reactor performance tests were run
employing the overlayer. The Primary Reactor design was a catalyst coated on 600/4
ceramic monolith (90mm diameter x 70 mm length) at 2 g/in3. The reactor was assumed
to adiabatic with uniform flow through all channels.
The feed conditions for the low flow rate and the high flow rate are provided in
Table 1 below. The conditions are based on a nominal 30kWth Gasoline Fuel Processor
for more realistic space velocities.
Condition Baseline value High Flow value
Feed flow rate (as C1) 3.6 mol/min 36 mol/min
H20:C 1:1 1:1
02:C 0.365 0.365
GHSV 29,000 hi 290,000 hi
Many reactions occur in the Primary Reactor during operation. For the purposes
of this study, it was considered sufficient to approximate the partial oxidation reaction of
hydrogen and carbon and steam reforming reaction of hydrogen and carbon. Fig. 1
illustrates the estimated light-off performance of the catalyst under the baseline
conditions. Fig. 2 shows the performance of the catalyst for partial oxidation. Fig. 3
shows the performance of the catalyst for steam reforming. Partial oxidation is an
exothermic reaction which converts fuel and air to carbon monoxide and pure hydrogen.
Steam reforming is an endothermic reaction which converts fuel and steam to carbon