DE577628C - Process for the production of molybdenum and tungsten catalysts - Google Patents

Description

It is known that metallic molybdenum and tungsten or their compounds as Contact masses for certain catalytic reactions, e.g. B. for the synthesis of ammonia or pressure hydrogenation of carbonaceous materials, due to their good catalytic properties Effectiveness are very suitable. The production of such catalysts in a form that they meet all requirements in in terms of catalytic effectiveness and at the same time a high mechanical Having resilience, however, presents considerable difficulties.

It has now been found that excellent molybdenum and tungsten catalysts, which also have excellent strength properties, if you get decomposable or volatile in the heat, in particular oxygen-containing compounds of molybdenum and / or and tungsten under pressure, on their own or in a mixture with others, expediently catalytically active substances heated to sintering or melting. After cooling, you get coarse to finely crystalline, very hard masses, which may be another post-treatment, e.g. B. with gases or solvents are subjected can. As the starting material, oxygen-containing compounds such as Moylbdic acid and tungstic acid or the lower oxides or hydroxides of these metals, also decomposable or volatile molybdates and tungstates are suitable. But there are also oxygen-free compounds of the two metals, e.g. B. alkali molybdenum cyanides, Sulfides, etc., into consideration. These substances can be used alone or in a mixture with one another or can be used with additives in particular of a catalytically or activating type. Mixtures with metals, eg. B. zinc, aluminum, magnesium, Chromium, preferably in powder form, or with oxides or salts of these metals, and also mixtures with metalloids, such as Silicon, boron, sulfur or selenium.

The temperatures required depend on the type of material used. In the case of molybdic acid, for. B. a temperature of about 900 ° is required, with partial decomposition of the acid, melting occurs. In the case of tungstic acid, a temperature of about 1500 ^{0 is} required. In the presence of metals, e.g. B. zinc or aluminum, the formation of complex compounds of molybdenum or tungstic acid with the resulting oxides of the metals may occur. It may be useful to maintain a greater excess pressure when heating. A pressure increase can, for. B. easily arise by splitting off oxygen; in many cases, however, it is also useful to

*) The patent seeker stated as the inventor:

Dr. Josef König in Uerdingen.

increased pressure by pressing in or passing an inert or chemical with the Catalyst to produce reacting gas. The effectiveness of the masses can possibly by treatment with gases, e.g. B. hydrogen, ammonia or hydrogen sulfide, or with solvents or other liquids such as acids and the like. It may be useful in some circumstances

ίο be the catalyst masses on carrier substances, z. B. pumice stone, porous gels of clay, iron oxide, silica, active charcoal, chamotte grains and the like. To apply. This can be B. done in such a way that carriers mixed with the to be treated Starting materials are heated, which during the heating either coat the surface of the support or penetrate the pores in the melt flow.

ao The catalytically active compounds can also be deposited or generated in the pores of the carrier prior to heating.

For special purposes, e.g. B. for the production of very dilute catalysts, the Finished highly effective catalyst also ground together with carrier substances and optionally shaped with binders.

The catalyst prepared by itself or on supports can optionally also itself serve as a catalytically active carrier for other contact substances and in this case be coated with other catalytically active metals or compounds.

example 1

100 parts by weight of molybdic acid are placed in a ceramic insert Metal cylinder, which carries an electrical heating coil on the outside, insulated. Of the The metal cylinder is surrounded by a jacket made of pressure-resistant material, which according to Art an autoclave can be closed. A hole in the cylinder is used to equalize the pressure between the heating and reaction space. After nitrogen up to a pressure of 30 atm. pressed into the oven is, is heated to about 900 °, whereby the molybdic acid with elimination of oxygen melts. The pressure increases to about 80 atm. After cooling down, you get a hard, dark-colored, crystalline mass that is still crushed to the desired grain size will. The mass can be transformed into a particularly hard metallic material by treatment with hydrogen at an elevated temperature Molybdenum of the same structure or z. B. by treatment with hydrogen sulfide Gases are completely or partially converted into molybdenum sulfide.

Example 2

100 parts by weight of molybdic acid preheated to 400 ° for a short time, are mixed with 20 parts by weight of zinc powder and 2 parts by weight of selenium, whereupon the The whole thing is heated to 900 ° in the autoclave. This creates a pressure of around 30 atm. The product obtained after cooling is a hard, brown-violet, very finely crystalline one Mass, which is characterized by excellent catalytic effectiveness in splitting and hydrogenation of oils and the like.

Example

A mixture consisting of 100 parts by weight of sharply dried molybdic acid and 20 parts by weight of tungstic acid is in the furnace specified in Example 1 under a nitrogen pressure of 50 atm. on heated about 1000 °.

The product obtained after cooling is a hard, blackish, crystalline, catalytically highly effective mass.

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Example 4

Vitreous, highly porous alumina gel in granular form is mixed with a concentrated solution soaked in ammonium molybdate and then treated with hydrochloric acid vapors, whereby molybdic acid is deposited in the pores will. After a short wash, the material prepared in this way becomes the one described above Apparatus heated to 900 °. After cooling, a catalyst is obtained which consists of a hard carrier material, in whose pores lower molybdenum oxides in are deposited catalytically particularly effective form. "

Example 5

Potassium molybdenum cyanide is in the manner described in Example ι at a nitrogen pressure of 10 atm. ^{heated to 100 0} for ι hour, the mass melts. After cooling, a gray-black product of great hardness is obtained, which is particularly suitable as a catalyst for hydrogenation reactions.

Example 6

In a furnace described in example ϊ with platinum as the heating coil and one off Tungstic acid is used in existing hard-to-melt ceramic material Presence of nitrogen at about 10 atm. Pressure heated to 1500 ° for a short time. the Tungstic acid is decomposed with the formation of a hard, dark gray, finely crystalline one Product that has a very favorable catalytic ^ effectiveness in cleavage and hydrogenation reactions shows.

Claims (1)

Claim:
Process for the production of molybdenum and tungsten catalysts, characterized in that decomposable or volatile compounds, in particular oxides, of molybdenum and / or tungsten are heated under pressure, alone or in a mixture with other substances, to sintering or melting .