JP2768971B2 - Ammonia production catalyst - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a catalyst suitable for synthesizing ammonia from nitrogen and hydrogen.

[Conventional technology]

Conventionally, to synthesize ammonia, iron is the main component,
An iron-based catalyst to which alumina, potassium oxide, etc. is added as a co-catalyst is used, but the ammonia synthesis activity of this catalyst is not exhibited at low temperatures, so that the operating reaction temperature in industrial equipment is disadvantageous in terms of equilibrium theory. Regardless of 400 ~ 500 ℃
I have to use the high temperature. Therefore, in the existing ammonia production method, the recirculation ratio of the reaction gas is set large,
It is necessary to increase the space velocity and the power accompanying this,
The increase in operating costs such as heat transfer is remarkable.

It has already been reported that a lanelle ruthenium catalyst is effective as a catalyst for ammonia production, and that addition of potassium metal further promotes ammonia synthesis activity, and shows higher ammonia synthesis activity than conventional iron and ruthenium-based catalysts. Have been.

<< JOURNAL OF CATALYSIS 54 , P52-56 (1978) >> [Problems to be Solved by the Invention] However, addition of metallic potassium to the lanelle ruthenium catalyst promotes ammonia synthesis activity, but during preparation, metallic potassium is easily ignited in moisture. There is a certain problem in handling such as that it is necessary to avoid moisture in order to use.

An object of the present invention is to further improve the above-described catalyst for ammonia production using a Raney ruthenium catalyst, to provide a catalyst for ammonia production that is easy to prepare and has a higher ammonia synthesis activity.

[Means for solving the problem]

The catalyst for producing ammonia according to the present invention is obtained by adding an alkali metal compound to a lanelle ruthenium alloy and hydrocracking the alkali metal compound-added lanerthenium alloy.

The Raney ruthenium catalyst is prepared by a well-known method. For example, a ruthenium metal and an aluminum metal are mixed in a weight ratio.
It is advisable to mix them at a ratio of 1: 1 and first prepare a lannel ruthenium alloy by an arc melting method in an argon stream, and then develop it with an alkali hydroxide.

As the alkali metal in the alkali metal compound, sodium, potassium, rubidium, and cesium can be used. Particularly, cesium has high activity, and then rubidium, potassium, and sodium are preferred in this order. As the alkali metal compound, a nitrate is preferable, but an acetate, a carbonate, a cyanate, a hydroxide, or the like may be impregnated with the Raney ruthenium catalyst in the form of an aqueous solution.

The second feature of the present invention is that the amount of the alkali metal compound added to the Raney ruthenium catalyst is 1 to 20 mol%. It has been found that the activity is high, and when the amount is 1 mol% or less, or 20 mol% or more, the ammonia synthesis activity sharply decreases.

After the addition of the alkali metal compound to the Raney ruthenium catalyst, the system is evacuated at room temperature and subsequently reduced with hydrogen at 100 ° C to 350 ° C, preferably 250 ° C to 350 ° C. If this is high, oxides or metals generated by hydrocracking will vaporize,
Agglomeration occurs at a low temperature in the upper part of the reaction tube, not on the catalyst, which causes a problem that the amount added and the amount on the catalyst do not match. Since ammonia production is performed in a hydrogen atmosphere, the hydrogen reduction treatment may be omitted when preparing the catalyst, and the catalyst may be prepared only by vacuum evacuation means.

The reaction temperature in the ammonia synthesis reaction is preferably a low temperature and a high pressure in terms of equilibrium theory. However, the catalyst of the present invention is used at 100 ° C. to 350 ° C., preferably 150 ° C. to 500 ° C., and the reaction pressure is preferably 1 to 300 atm. Can be. Since the catalyst of the present invention has a low-temperature activity and a high concentration of ammonia is obtained, liquefaction and separation are easy.

[Action]

The catalyst for producing ammonia of the present invention is obtained by adding an alkali metal compound to a lanelle ruthenium alloy. In general, in ammonia synthesis, it is considered that the aluminum component remaining on the surface of the Raney ruthenium catalyst plays a role in maintaining a high specific surface area structure and also cleaves nitrogen molecules on the ruthenium surface. In the present invention, an alkali metal compound is further added to the lanerthenium-based compound, whereby an alkali metal or an alkali metal oxide formed during hydrogenolysis or ammonia synthesis is adsorbed to activate the catalyst surface, and the alkali It is considered that the ammonia-synthesizing activity is promoted by the electron donating property of a metal or the like.

When the amount of the alkali metal compound added is examined, the present invention is characterized in that the alkali metal compound is added in an amount of 1 to 20 mol% with respect to ruthenium. Alkali metals also cover the active adsorption site,
It is thought that the number of sites that adsorb and decompose nitrogen molecules is reduced, and as a result, ammonia synthesis activity is reduced.

Hereinafter, the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

〔Example〕

(Preparation of Raney ruthenium catalyst) Ruthenium (≧ 99.9%, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.)
Using aluminum (≧ 99.9%, manufactured by Kanto Chemical Co., Ltd.)
An alloy having a weight ratio of Ru / Al = 1/1 was prepared by an arc melting method in a stream of argon gas. Grind the prepared alloy, 1g alloy powder
Was stirred at 100 ° C. until hydrogen evolution was no longer observed. 5N-KOH aqueous solution 5
After adding 0 ml and stirring for 1 hour, the mixture was washed with distilled water until the pH reached 7, and developed.

When the reaction was performed without adding an alkali metal compound, the catalyst in the distilled water was subsequently transferred to a reaction tube having a closed circulation system in a nitrogen gas stream, the upper portion of the reaction tube was sealed, and the reaction tube was evacuated at room temperature. After that, while heating the catalyst, helium,
Then, after circulating nitrogen, it was used for the reaction.

(Addition of alkali metal compound) The Raney ruthenium catalyst which has been developed as described above is transferred to a reaction tube together with water, and each aqueous solution of sodium nitrate, potassium nitrate, rubidium nitrate, cesium nitrate, and the like is dissolved in a mole% of alkali metal to ruthenium. 0, 1, 6, 10, 2
The mixture was added so as to be 0 and 50, the upper portion of the reaction tube was sealed, and the inside of the reaction tube was evacuated at room temperature. After evacuation, hydrogen was introduced little by little and the temperature was raised to 300 ° C. and maintained until no decrease in hydrogen was observed through a liquid nitrogen trap to prepare a catalyst of the present invention.

(Ammonia synthesis activity) In ammonia synthesis, a glass tube with an inner diameter of 6 mm was filled with about 0.5 g of the present Laneruthenium catalyst (as starting alloy).
1g) Filling, while heating the catalyst layer from the outside, introduce 600 Torr into the system at a mixing ratio of nitrogen and hydrogen of 1: 3, and circulate through a liquid nitrogen trap at a reflux rate estimated to be about 80 ml / min. Was. The ammonia synthesized at this time was accumulated in the liquid nitrogen trap, and the production amount was calculated from the volume reduction in the system maintained at a constant pressure.

Further, the synthesis rate (mmol g ⁻¹ h ⁻¹ ) was determined at a predetermined reaction temperature by measuring the amount of production at regular intervals and when the amount of production became constant.

[Comparative Example 1] Ammonia synthesis was carried out in the same manner as in the above example, using the Raney ruthenium catalyst prepared in the above example without adding an alkali metal compound.

[Comparative Example 2] The Raney ruthenium catalyst prepared in the above example was treated with potassium vapor in a helium stream at 300 ° C for 30 hours to prepare a metal potassium-added catalyst, and ammonia synthesis was performed in the same manner as in the above example. Was. The potassium content is 11 mol% with respect to ruthenium.

(Ammonia synthesis reaction) For the catalysts prepared in the above Examples and Comparative Examples,
FIG. 1 shows the relationship between the ammonia synthesis rate and the reaction temperature. The amount of alkali nitrate added in FIG. 1 is 6 to 7 mol% based on ruthenium. The ammonia synthesis rate is represented by mmol g ⁻¹ h ⁻¹ .

That is, the effect of promoting alkali synthesis by the addition of an alkali metal compound in the Raney ruthenium catalyst of the present invention is greatest for cesium, followed by rubidium, potassium, and sodium, corresponding to the degree of electron donation of the alkali metal. It should be noted here that the cesium-added Raney ruthenium catalyst has a reaction activity at 300 ° C. that is two orders of magnitude higher than that of the Raney ruthenium catalyst of Comparative example 1, and the Raney ruthenium-potassium catalyst prepared in Comparative example 2. It can be understood that the catalysts to which the alkali metal compound is added in the examples have the same or higher ammonia synthesis activity as compared to

FIG. 2 shows the measurement results of the dependence of the amount of cesium nitrate added on the ammonia synthesis activity. In the figure, the reaction temperature is 300 ° C. and a nitrogen-hydrogen mixture at 600 Torr (weight ratio 1: 1).
The reaction was carried out in 3), and the catalyst used was one subjected to a hydrogen reduction treatment at 350 ° C. with 600 Torr of hydrogen.

That is, it can be seen that the change in the ammonia synthesis activity depending on the amount of cesium nitrate has a maximum value when the amount of ruthenium is 6 to 10 mol%.

Next, the relationship between the hydrogenolysis temperature of the cesium nitrate-added Raney ruthenium catalyst and the activity when used in ammonia synthesis is shown in FIG. Ammonia synthesis reaction conditions are a reaction temperature of 250 ° C. and a nitrogen-hydrogen mixture of 600 Torr (weight ratio 1: 3).

That is, it can be seen that the hydrogenolysis temperature of the cesium nitrate-added Raney ruthenium catalyst gives the highest ammonia synthesis activity at 300 ° C.

Next, the surface area and chemical adsorption characteristics of the catalysts obtained in the above Examples and Comparative Examples are shown in FIG. 4, and the valence states of the component elements of each catalyst obtained by X-ray electron photometry are reflected. Is what you do. Electron binding energy (unit
/ eV) is shown in FIG. 5, and the peak area ratio of each component element obtained by X-ray electron spectroscopy, which shows the concentration of the component element on the surface of each catalyst, is shown in FIG.

The BET surface area shown in FIG. 4 was obtained by evacuation of the catalyst layer at the pretreatment temperature for 2 hours before gas adsorption, and from the nitrogen adsorption amount at the liquid nitrogen temperature. The amount of hydrogen chemically adsorbed is at 0 ° C., and the amount of carbon dioxide adsorbed is at −77 ° C.

The X-ray electron spectrometry shown in FIGS. 5 and 6 was measured by moving the catalyst used in the reaction into a measuring device (Shimadzu ESCA 750) in the presence of an inert gas, and the binding energy was measured. Are all corrected with the Au 4f7 / 2 peak due to gold deposition being 83.3 eV.

That is, from the results of FIG. 4, when the alkali nitrate is added,
It can be seen that the BET surface area decreases to some extent.

From the result of the binding energy of Ru3d _5/2 in FIG. 5,
The addition of an alkali reduces the binding energy. That is, electron donation from ruthenium to alkali has occurred,
This is considered to be data directly related to promotion of the activity of ammonia synthesis.

The results in FIG. 6 show that aluminum, nitrogen and alkali are present on the ruthenium surface during the synthesis reaction.

〔The invention's effect〕

The ammonia production catalyst of the present invention is obtained by adding an alkali metal compound to a lannel ruthenium alloy and subjecting it to hydrogenolysis, wherein the alkali metal compound is added in an amount of 1 to 20 mol% based on ruthenium. Because it does not use alkali metal alone, it is conventional
Compared with an alkali metal catalyst, the preparation of the catalyst is extremely easy and can be used as a catalyst for producing ammonia, which exhibits extremely high ammonia synthesis activity.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the ammonia synthesis rate of each catalyst and its reaction temperature, FIG. 2 is a diagram for explaining the dependency of the amount of cesium nitrate added on the ammonia synthesis activity, and FIG. 3 is cesium nitrate. FIG. 4 is a diagram for explaining the relationship between the hydrocracking temperature and the ammonia synthesis activity of the added lanthanum ruthenium catalyst, FIG. 4 is a diagram showing the adsorption characteristic value of each catalyst, and FIG. FIG. 6 is a diagram showing the binding energy (unit / eV) of the element by X-ray electron spectrometry, and FIG. 6 is a diagram showing the result of the peak area ratio of the surface element by X-ray electron spectrometry in the working state of each catalyst.

Claims (2)

(57) [Claims] 1. A catalyst for ammonia production obtained by adding an alkali metal compound to a lanerthenium alloy and hydrocracking the alkali metal compound-added lanerthenium alloy. 2. The method according to claim 1, wherein said alkali metal compound is added in an amount of 1 to 20 mol% based on ruthenium.
The catalyst for producing ammonia according to the above.