CZ307583B6 - A method of preparing a molybdenum-nickel catalyst for catalytic hydrogenation of carbon dioxide with hydrogen to methane - Google Patents

Abstract

The present invention relates to a boehmite catalyst at 500 ° C in a muffle furnace containing 7% by weight of molybdenum and 4% by weight of nickel, the preparation of which comprises impregnating the catalyst with 20% by weight of nickel. solutions of hexa-ammonium heptamolybdate tetrahydrate and nickel nitrate hexahydrate, which is applied to the carrier with a residence time of at most 10 minutes, followed by firing at 500 ° C with a temperature gradient of 10 ° C / minute.

Description

Process for the preparation of a molybdenum - nickel catalyst for the catalytic hydrogenation of carbon dioxide with hydrogen to methane

Field of technology

The present invention relates to a process for the preparation of a nickel-molybdenum catalyst for the catalytic hydrogenation of carbon dioxide with hydrogen to methane and water.

Prior art

The catalytic hydrogenation of carbon dioxide with hydrogen to methane and water is also referred to as methanation or Sabatier reaction. This reaction is expressed by the equation:

CO ₂ + 4H ₂ θ CH. + 2H ₂ O

The reaction temperature ranges from 190 ° C to 800 ° C depending on the catalyst used. Catalysts whose activity decreases are used for the reaction: Ru> Ni> Co> Os> Pt> Fe> Mo> Pd> Ag. Of these metals, ruthenium, nickel, cobalt, iron and molybdenum are the most widely used. The mechanism of catalytic hydrogenation of carbon dioxide with hydrogen is relatively complex. The reaction takes place on the surface of the catalyst, so that its mechanism is significantly influenced by a particular catalyst. There are differing views on which intermediates appear during methane formation. By simplification, possible mechanisms can be divided into two basic types. The first idea assumes the conversion of carbon dioxide to carbon monoxide and the subsequent methanation of carbon monoxide. The second option is the direct hydrogenation of carbon dioxide without the formation of carbon monoxide as an intermediate.

One way to use the catalytic hydrogenation of carbon dioxide to methane is in a process known as Power-to-Gas. This concept of synthetic natural gas production uses surpluses of electricity produced from renewable energy sources. With this electrical energy, hydrogen can be produced by electrolysis. Carbon dioxide would then be separated from flue gases from fossil power plants. Using carbon dioxide and hydrogen, methane and water can be produced by catalytic hydrogenation of carbon dioxide. In the mentioned case, however, the flue gases contain a considerable amount of simulants, which act as a catalytic poison. One of the catalysts that has resistance to sulfur is molybdenum. The use of a mixed catalyst based on molybdenum nickel will allow its use for catalytic reactions in a wide range of high conversion temperatures.

The essence of the invention

The present invention provides a process for applying a molybdenum-nickel catalyst useful for the catalytic hydrogenation of carbon dioxide with hydrogen to methane and water, the steps comprising impregnating the porous surface of the support with hexaammonium (NH ₄ ) ₆ (Mo ₇ O ₂ ) .4H ₂ O heptamolybdate tetrahydrate solutions. of nickel nitrate hexahydrate Ni (NO ₃ ) ₂ .6H ₂ O on the porous surface of the fired boehmite. This catalyst preparation process differs from other patent processes (e.g. U.S. Pat. The catalyst support impregnated with catalytically active elements is no longer calcined. It is carried out by converting the catalytically active compounds into active form by reducing them with hydrogen at 450 DEG C. for 5 hours. The use of such a catalyst will allow the use of flue gases (as a source of carbon dioxide for methanation) with a minimum content of sulfur dioxide, which acts on the nickel catalyst as a catalytic poison. The catalyst thus prepared is active over a wide temperature range because nickel is a low temperature catalyst and molybdenum is a high temperature catalyst.

- 1 CZ 307583 B6

When placing the support in solutions (20% by weight), a residence time of a maximum of ten minutes must be observed, so the impregnation of the support must take place relatively quickly. This is due to the stability of hexaammonium heptamolybdate tetrahydrate. From 20 wt. solution of this substance with standing in air or heating begins to release ammonia and precipitate the compound as a solid tetrahydronium dihydrogen hexamolybdate pentahydrate (NH ₄ ) ₄ H 2 (Mo ₆ O ₂ ) .5H ₂ O. This substance is also known as ammonium polymolybdate and prevents the catalyst from being deposited. molybdenum-based on the surface of the support.

Example of an embodiment of the invention

This example describes the preparation of a catalyst according to the present invention containing molybdenum and nickel.

Boehmite fired in a muffle furnace at 500 ° C (minimum 6 hours) was used as catalyst support. At this temperature, the boehmite AIO (OH) converts to γ-alumina Al2O3. In this case, a boehmite having the shape of rings measuring 8x5 mm with a total inner surface area of 250 to 256 m ² / g and a pore volume of 0.45 ml / g was used, with 78% of the pores being below 6 nm in size.

For impregnation, 20 wt. aqueous solutions of hexaammonium heptamolybdate tetrahydrate (ΝΗ ₄ ) ₆ (Μθ7θ2 ₄ ) .4Η ₂ Ο and nickel nitrate hexahydrate Ni (NO ₃ ) 2.6H ₂ O. The solutions were mixed and 400 ml of this solution was used for subsequent impregnation. A pre-fired support was added to the solution at 500 ° C (γ-alumina). The residence time of the carrier in solution was a maximum of ten minutes. Subsequently, the catalyst support was separated from the solution by means of a Buchner funnel at atmospheric pressure. The supported supported catalyst was then placed in an oven heated to 110 ° C where it was left for 16 hours. After this time, the dried supported catalyst was placed in a muffle furnace where it was heated to a final temperature of 500 ° C with a temperature gradient of 10 ° C / minute. After heating the muffle furnace to 500 ° C, this temperature was maintained for 6 hours. During the firing of the catalyst, the hexaammonium heptamolybdate tetrahydrate and nickel nitrate hexahydrate were oxidized to the corresponding metal oxides. In this way, a content of 7% by weight can be achieved by impregnation. of molybdenum and 4 wt. nickel in the catalyst. Before using the catalyst, it is necessary to reduce the oxides of said elements with hydrogen. This reduction is performed at temperatures of about 450 ° C for 5 hours.

Industrial applicability

The process of the invention can be used to prepare a molybdenum-nickel catalyst for the catalytic methanation of carbon dioxide with hydrogen. This catalyst provides a higher resistance to sim compounds, in the case of using carbon dioxide from the flue gas for the catalytic hydrogenation of carbon dioxide with hydrogen, it is sulfur dioxide. A wide temperature range can be used in the methanation process due to the use of molybdenum-nickel catalyst elements, with the conversion of reactants to methane being high over the entire temperature range.

Claims (2)

PATENT CLAIMS A process for the preparation of a molybdenum-nickel catalyst for the methanation of carbon dioxide with hydrogen, characterized in that the fired boehmite at 500 ° C is impregnated with 20% by weight. solutions of hexaammonium heptamolybdate tetrahydrate and nickel nitrate hexahydrate with a holding time of the support in solution of a maximum of ten minutes at room temperature, after removing the solution it is dried at 110 ° C for 16 h and then heated in a muffle furnace to 500 ° C with a temperature gradient 10 ° C / minute. -2GB 307583 B6 Process according to Claim 1, characterized in that, after heating in a muffle furnace at 450 ° C for 5 hours, the oxides of molybdenum and nickel in the hydrogen stream are converted into catalytically active elements.