The invention relates to a process for pretreating a catalyst material for catalysing a chemical reaction in a corresponding reactor, for example a reforming catalyst material for catalysing a methanol reforming reaction to obtain hydrogen in a motor vehicle operated by fuel cells.
A known fact about most common reforming catalyst materials, specifically those based on Cu and/or Zn, is that they undergo a marked decrease in volume and mass both during the initial forming and during the first operating hours during subsequent reforming reaction operation. If the catalyst material is consequently introduced into the reforming reactor and formed there, i.e. activated in its catalytic effect, without pretreatment, to be available subsequently for catalysing the reforming reaction, the decrease in volume and mass leads to the reactor volume of the catalyst material no longer being fully utilized in the operation of the reforming reactor. A corresponding decrease in the specific activity of the catalyst material, and consequently in the performance of the reforming reactor, occurs. This effect reduces the actual conversion capacity of the reactor with respect to its rated conversion capacity. A further difficulty of this phenomenon arises specifically in the case of reforming reactors with a heat exchanger structure. In the case of such reactors, used for example for reforming water vapour from methanol in motor vehicles operated by fuel cells, a first reaction chamber of two reaction chambers in heat exchanging connection is provided with a reforming catalyst material, while the second reaction chamber serves as a heating chamber, in which heat is provided, for example by a combustion process. If a reduction in volume of the reforming catalyst material then occurs in the first reaction chamber, to this extent no endothermic reforming reaction occurs any longer, so that the heat dissipation from the second reaction motor vehicles operated by fuel cells, a first reaction chamber of two reaction chambers in heat exchanging connection is provided with a reforming catalyst material, while the second reaction chamber serves as a heating chamber, in which heat is provided, for example by a combustion process. If a reduction in volume of the reforming catalyst material- then occurs in the first reaction chamber, to this extent no endothermic reforming Reaction occurs any longer, so that the heat dissipation from the second reaction chamber is reduced. As a consequence of this, overheating effects can occur and may lead to the reactor being damaged or even failing.
In German patent application No. 197 25 006.8 there is a description of a process for treating a reforming catalyst material suitable for catalysing a methanol reforming reaction in which the said material is pre-aged before it is introduced into the reforming reactor, in that it is treated in a methanol-water atmosphere at temperatures between approximately 240xc2x0 C. and approximately 350xc2x0 C. and with a charge between approximately 0.5 m3H2/h and approximately 50 m3H2/h per litre of catalyst material.
In German patent application No. 197 25 009.2 there is a description of a process for pretreating a reforming catalyst material for catalysing a methanol reforming reaction in which the said material is pre-aged before it is introduced into the reforming reactor, in that it is baked in a dry atmosphere. If the catalyst material is in unreduced form, the baking may be performed in air for example. If, on the other hand, it is in reduced form as a result of prior application of a reducing reaction, the baking is performed in an inert atmosphere, for example a nitrogen or argon atmosphere. The baking is typically performed over several hours at temperatures of the order of 300xc2x0 C. and more.
In laid-open patent application EP 0 192 289 A2 there is a description of a process for pretreating a crystalline silicate catalyst material after its production and before its use as a catalytically active substance, the pretreatment process comprising a two-step redox treatment in which the catalyst material is subjected in a first step for at least 15 minutes to a hydrogen-containing reducing gas at a temperature of between 350xc2x0 C. and 700xc2x0 C. and in a second step for at least 15 minutes to an oxygen-containing, oxidizing gas at a temperature of between 350xc2x0 C. and 700xc2x0 C. In the case of an SiO2/Ga2O3 catalyst material, the redox treatment cycle is preferably carried out no more than three times if the molar ratio in the crystalline silicate is at least 110, and between three and ten times if the molar ratio lies between 110 and 130, while in the case of molar ratios of between 130 and 220 the silicate is previously subjected to a calcining treatment at a temperature of between 600xc2x0 C. and 1000xc2x0 C. and then the redox treatment cycle is performed between three and ten times. The reducing treatment preferably takes place with a hydrogen content of the reducing gas of at least 20% by volume, the oxidizing treatment preferably takes place with an oxygen concentration of at least 5% by volume.
In the case of a methanol reforming reactor disclosed in laid-open patent application JP 63-310703 (A), measures are taken to maintain a dense packing of the catalyst charge introduced, in spite of the initial decrease in its volume and mass. For this purpose, after it has been introduced into the reforming reactor and before the reforming reaction operation begins, the catalyst material is subjected to a necessary reducing reaction, which leads to the decrease in volume of the catalyst material. A movable cover plate loaded by a compression spring keeps the catalyst material compressed as a densely packed charge.
The invention is based on the technical problem of providing a process for pretreating a catalyst material in such a way that, by use of the catalyst material pretreated in this way in a corresponding reactor, a marked decrease in the reactor conversion rate does not also occur in the first operating hours of the reaction operation and, in the case of the reactor mentioned above with a heat exchanger structure, harmful overheating effects are avoided.