Methanol reforming catalyst having a reduced volume shrinkage
View Patent ↗A methanol reforming catalyst containing passivated copper and zinc oxide and/or alumina can be prepared by (1) precipitating or spray-drying a mixture of catalyst precursor components dissolved or suspended in a diluent in order to form a solid catalyst precursor in the form of powder or granules, (2) calcining and reducing the solid catalyst precursor obtained in stage (1), (3) passivating the reduced catalyst precursor obtained in stage (2) and (4) shaping the passivated catalyst precursor obtained in stage (3) to form the catalyst. A reduction in the volume shrinkage and an increase in the mechanical hardness during operation of the methanol reforming catalyst are achieved by the preparation process.
1. A methanol reforming motor vehicle catalyst consisting of passivated copper and zinc oxide and/or alumina, which is obtained by
(1) precipitating or spray-drying solutions or suspensions of zinc-, aluminum-, and/or copper salts dissolved or suspended in a diluent, to form a solid catalyst precursor in the form of powder or granules,
(2) calcining and reducing the solid catalyst precursor obtained in stage (1),
(3) external (surface) passivating the reduced catalyst precursor obtained in stage (2) and
(4) shaping the passivated catalyst precursor obtained in stage (3) to form the catalyst.
2. A catalyst as claimed in claim 1 , wherein the shaping in stage (4) forms layers, extrudates, monoliths, strands, pellets, tablets or chips.
3. A catalyst as claimed in claim 1 , wherein the calcination and the reduction are carried out in succession in stage (2), and the calcined catalyst precursor obtained from stage (2) is optionally comminuted prior to the reduction.
4. A catalyst as claimed in claim 1 , wherein the catalyst contains alumina in addition to passivated copper and zinc oxide, and solutions and suspensions of zinc, aluminum and copper salts are precipitated simultaneously or in any desired sequence in stage (1).
5. A catalyst as claimed in claim 4 , wherein stages (1) and (2) are carried out as follows:
(a) precipitating a solution of zinc and aluminum salts, the Zn:A1 atomic ratio being from 3:1 to 1:3, with an alkali metal carbonate or hydroxide solution at a pH of from 5 to 12 and a temperature of from 20 to 100° C.,
(b) isolating and washing the precipitate to remove alkali metal ions,
(c) drying the precipitate,
(d) calcining the precipitate at a temperature of from 250 to 800° C. to obtain a mixed oxide,
(e) dispersing the mixed oxide in an acidic solution of copper and zinc salts, the Cu:Zn atomic ratio in the solution being from 1:5 to 20:1,
(f) precipitating the dispersion with an alkali metal carbonate or hydroxide solution at a pH of from 6 to 9 and a temperature of from 20 to 100° C.,
(g) repeating steps (b) to (d) once to form a catalyst precursor,
(h) reducing the catalyst precursor obtained in stage (g) with a gas containing free hydrogen,
wherein the solutions in steps (a) and/or (e) additionally to contain salts or oxides of one or more elements selected from the group consisting of the platinum metals, of groups 4, 5 and 11 and of the lanthanides of the Periodic Table of the Elements.
6. A process for the preparation of a catalyst as claimed in claim 1 , which process comprises:
(1) precipitating or spray-drying solutions or suspensions of zinc-, aluminum-, and/or copper salts dissolved or suspended in a diluent, to form a solid catalyst precursor in the form of powder or granules,
(2) calcining and reducing the solid catalyst precursor obtained in stage (1),
(3) external (surface) passivating the reduced catalyst precursor obtained in stage (2), and
(4) shaping the passivated catalyst precursor obtained in stage (3) to form the catalyst.
7. A process for reducing the volume shrinkage and for increasing the mechanical hardness during operation of methanol reforming catalysts, wherein the methanol reforming catalyst is prepared by a process as claimed in claim 6 .
8. A process for steam-reforming methanol by reacting methanol and water over a catalyst, as claimed in claim 1 , at from 0.5 to 10 bar and from 150 to 450° C.