Method for the treatment of a methanol reforming catalyst

A method for the treatment of a methanol reforming catalyst includes pre-aging the catalyst by baking it out in a dry atmosphere in order thereby to complete its inherent initial loss of volume before the start of the methanol reforming reaction. The method may be used for methanol reforming reactors in fuel-cell-operated motor vehicles.

BACKGROUND AND SUMMARY OF THE INVENTION 
This application claims the priority of German Patent Document No. 197 25 
009.2, filed Jun. 13, 1997, the disclosure of which is expressly 
incorporated by reference herein. 
The present invention relates to a method for the treatment of a methanol 
reforming catalyst. Such catalysts are known in various compositions. See, 
for example, patent applications DE 35 31 757 A1 and EP 0 201 070 A1. 
Usually the catalyst material is placed in the form of a charge of 
catalyst pellets into the reforming reaction chamber of a methanol 
reforming reactor. Such reactors serve, for example, for the production of 
hydrogen for the fuel cells of a fuel-cell-operated motor vehicle by the 
hydrogen reforming of liquid methanol carried by it. 
Various methods have been proposed for sustaining a high catalytic activity 
and for the achievement of a long life of the methanol reforming catalyst. 
Thus, in patent application JP 4-141234 (A) a special formulation of 
different metal oxides is given for obtaining a catalyst with a long life 
and high activity and selectivity. 
In patent application JP 63-310703 (A) the catalyst material is subjected 
in the reforming reaction chamber of a methanol reforming reactor to a 
reduction reaction prior to the start of the operation of the reforming 
reaction, leading to a reduction of the volume of the catalyst. A 
compression spring-loaded, movable cover plate keeps the catalyst material 
that has been placed in the reaction chamber in the form of a charge of 
pellets compressed in a tight pack. The reduction reaction is a process 
necessary for the operation of a copper catalyst. The shrinkage that 
occurs is definitely less than the shrinkage that occurs during the normal 
reforming operation. 
In patent application JP 63-315501 (A) it is proposed to place an air 
chamber between a burner and a reforming reaction chamber, through which 
air can be fed in a controlled manner in order to keep the catalyst 
temperature at a given level. 
In a process disclosed in patent application DE 33 14 131 A1, to prolong 
the life of the methanol reforming catalyst, the methanol is freed of any 
chlorine compounds contained therein, before it is brought into contact 
with the catalyst. 
In patent application GB 2 132 108 A it is known, in starting up a methanol 
reforming reactor to heat the catalyst material present in the reaction 
chamber rapidly by burning methanol with a stoichiometric or less than 
stoichiometric oxygen content and passing the combustion exhaust gases 
both through a tempering chamber in thermal contact with the reaction 
chamber and also through the reaction chamber itself. Water can be sprayed 
into the combustion gas stream that is fed into the reaction chamber in 
order to prevent overheating. As soon as the desired reforming temperature 
is reached the heating process is terminated and the reforming process is 
started. This is the case typically within less than a minute. 
In patent application DE 1 246 688 a methanol reforming reactor is 
disclosed that contains a nickel catalyst and a zinc-copper catalyst. In 
use, the reforming reaction is periodically interrupted for catalyst 
treatment phases which comprise a regenerating phase and optionally a 
subsequent nickel catalyst reactivation phase. In the regenerating phases 
the reactor is flushed out with a gas containing free oxygen at a 
temperature between 150.degree. C. and 450.degree. C., while in the nickel 
catalyst reactivation phases a purging is performed with a gas containing 
free hydrogen. The manufacturing process for the nickel catalyst prior to 
its use in the methanol reformation includes at the end a treatment of a 
nickel foreproduct in a reducing atmosphere for reduction to metallic 
nickel for several hours at temperatures between 150.degree. C. and 
600.degree. C. For the zinc-copper catalyst, at the end of the process by 
which it was made, provision can be made for heat treatment at 250.degree. 
C. for four hours to remove any granulating aid that may have been used. 
A known fact of virtually all current methanol reforming catalysts is that 
in the first hours of the operation of methanol reforming they undergo a 
marked loss of volume that results in a corresponding lessening of the 
performance of a methanol reforming reactor containing the catalyst. 
The present invention is addressed to the technical problem of devising a 
method for treating a methanol reforming catalyst such that, in the first 
hours of operation, a methanol reforming reactor containing the catalyst 
will exhibit no marked loss of performance caused by any lessening of 
specific catalytic activity due to the catalyst's loss of volume.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
The present invention solves this problem by the following method for the 
treatment of a methanol reforming catalyst. The treatment involves several 
hours of baking out the methanol reforming catalyst in a dry atmosphere, 
which is oxidizing or inert, at a sufficiently high temperature for the 
purpose of preaging it. The result of the pre-aging treatment is that 
during this process, and hence prior to its use in the methanol reforming 
operation, the catalyst undergoes its typical initial loss of volume. The 
parameters of the process are accordingly so chosen that this desired 
pre-aging effect is achieved, so that at the end of the pre-aging 
treatment the methanol reforming catalyst is in a substantially completely 
shrunken form in which, when used afterward in the methanol reforming 
operation, it shows no marked additional shrinkage. To achieve this, the 
time and temperature of the pre-aging treatment are appropriately adapted 
to the catalyst material in question which can be made with any of the 
conventional compositions. 
As an example representative of many additional embodiments of the present 
invention, a conventional Cu/ZnO/Al.sub.2 O.sub.3 methanol reforming 
catalyst will be considered, in which the Cu/ZnO material forms the 
catalytically active component, which is suitable for catalyzing the water 
vapor reforming of methanol in a corresponding methanol reforming reactor. 
FIG. 1 shows a block diagram of a methanol reforming reactor 1 having a 
reaction space 2 with catalyst material 3. The catalyst material is made 
usually in the form of pellets and loaded in bulk into the reforming 
reaction chamber of the methanol reforming reactor. 
To prevent the performance of the reactor, i.e., the conversion, from 
decreasing markedly in the first hours of the reforming reaction, the 
methanol reforming catalyst is previously subjected to a pre-aging 
treatment. 
This pre-aging of the catalyst can take place outside of the reforming 
reaction chamber before the catalyst is put into it, or alternatively 
within the reforming reaction chamber, catalyst material being added in 
the latter case several times during the aging process to compensate for 
the shrinkage that occurs. The process for the pre-aging treatment of the 
catalyst material involves baking out the conventionally made catalyst 
material in a dry atmosphere at the appropriate temperature. "Dry," in 
this connection, means a moisture content of less than one volume-percent. 
If the manufactured catalyst material is in unreduced form, the pre-aging 
baking-out process can be performed in air. If the catalyst material is in 
reduced form due to previous use in a reducing reaction, the baking out is 
performed in an inert atmosphere, e.g., a nitrogen or argon atmosphere. 
The type and temperature of the baking-out process are adapted to the 
catalyst material involved. Typically, the temperature is in the range of 
the temperatures commonly used for the later methanol reforming reaction, 
e.g., of the order of 300.degree. C. or higher. Typical baking-out time is 
in the range of several hours. Due to the pre-aging treatment, the 
catalyst material undergoes the typical initial shrinkage. At the same 
time, it appears that the process conditions chosen for this treatment 
assure that the pre-aged catalyst present at the end of the treatment has 
largely shrunk, i.e., during its subsequent use in catalyzing the methanol 
reforming reaction it no longer markedly decreases in volume. Preferably, 
the treatment parameters are selected such that the catalyst material 
shrinks to the smallest achievable volume. 
After the pre-aging process ends, the pre-aged methanol reforming catalyst 
can be loaded into the reforming reaction chamber of a methanol reforming 
reactor if it was not already pre-aged therein. If the pre-aged catalyst 
material is not immediately needed, it can be preserved in a closed 
container, and this enables the aging effect to be sustained over a fairly 
long period of storage. 
The methanol reforming catalyst treated by this process, which has 
undergone its inherent shrinkage during the pre-aging, no longer shows any 
substantial shrinkage even in the first hours of a subsequent reforming 
reaction. Accordingly, its specific activity, and the conversion achieved 
by a methanol reforming reactor in whose reforming reaction chamber the 
catalyst is contained, are largely preserved from the very beginning of 
the reforming reaction process. 
An additional advantage of the pre-aged methanol reforming catalyst that is 
present in the reforming reaction chamber is that, for the reforming 
reaction process that follows, no appreciable amounts of discardable 
catalyst components are created which otherwise could result in harm to 
reactor components that follow. 
The method of the invention is especially suitable for the. preparation of 
a methanol reforming catalyst for use in a methanol reforming reactor of a 
fuel-cell-operated motor vehicle in order to catalyze therein the water 
vapor reforming of liquid methanol for the production of hydrogen for the 
fuel cells. 
The foregoing disclosure has been set forth merely to illustrate the 
invention and is not intended to be limiting. Since modifications of the 
disclosed embodiments incorporating the spirit and substance of the 
invention may occur to persons skilled in the art, the invention should be 
construed to include everything within the scope of the appended claims 
and equivalents thereof.