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Overlayer for Catalyst

IP.com Disclosure Number: IPCOM000019948D
Publication Date: 2003-Oct-13

Publishing Venue

The IP.com Prior Art Database

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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.

Table 1

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

monoxide an...