JP6573494B2 - Composition for ammonia synthesis catalyst, method for producing the same, and method for synthesizing ammonia - Google Patents

Description

  The present invention relates to a composition for an ammonia synthesis catalyst, a method for producing the same, and a method for synthesizing ammonia.

  Hydrogen production technology from hydrocarbons and hydrogen utilization technology such as fuel cells are actively researched and developed. On the other hand, ammonia, which is a colorless gas with an irritating odor, dissolves well in water, shows alkalinity, and is easily liquefied by compression, is produced worldwide by 160 million tons (2010). Most of them have been used as raw materials for fertilizers, chemicals, chemical fibers and refrigerants. Ammonia is high in hydrogen content; easy to store and extract hydrogen; no carbon, so no carbon dioxide is generated when used; handling technology, safety management, medical law is established, transportation and storage process is easy There are features such as. Old production facilities for the purpose of using ammonia are aging and declining. Recently, the use of ammonia as new hydrogen energy has attracted attention. That is, in recent years, especially in the continent of Africa, ammonia is produced based on solar energy, and after safe and efficient storage and transportation, it can be obtained directly or modified in areas, homes, cars, etc. The development of a high yield ammonia synthesis catalyst is expected with the renewal of the ammonia synthesis plant in the future due to the provision of hydrogen.

  Ammonia has long been produced by the Harbor Bosch process using an iron-based catalyst. However, since the Harbor Bosch method needs to carry out the reaction under a high pressure of about 200 atm, it has problems such as equipment investment, increased power consumption, and complicated manufacturing processes.

  In recent years, a method for producing ammonia under a low pressure condition of about 10 atm using a ruthenium catalyst has been reported for the above problem. By using this catalyst, not only ammonia can be produced under low pressure conditions, but also ammonia synthesis inhibition by carbon monoxide and water can be reduced, and the ammonia yield is improved. In ammonia production using a ruthenium catalyst, the ruthenium catalyst may be supported on a carrier. As a carrier for supporting ruthenium, alumina generally used as a catalyst carrier is widely used. Recently, it has been disclosed that the amount of ruthenium used can be reduced and the reaction temperature can be lowered by using a rare earth oxide as a support instead of alumina (Patent Document 1). However, in the above ammonia production method, the ammonia yield when producing ammonia under a lower pressure condition is not sufficient.

  Therefore, the present inventors have recently aimed to provide a composition capable of producing ammonia in a high yield under low pressure conditions, and a method for producing ammonia using the composition. Ruthenium; lanthanoid; It has been found that a composition containing a promoter and / or a porous metal complex is used as an ammonia synthesis catalyst (Patent Document 2). This composition was prepared by an impregnation method in an aqueous solution, but its ammonia synthesis activity was insufficient, and the development of a highly active catalyst was demanded.

JP-A-6-79177 JP 2013-111562 A

  An object of the present invention is to solve the above-mentioned problems and to provide a composition for an ammonia synthesis catalyst having further improved ammonia synthesis activity, a method for producing the same, and a method for synthesizing ammonia.

In order to solve the above problems, the present invention provides the following inventions.
(1) A. Ruthenium or an alloy thereof, or a compound containing ruthenium, B. Compounds containing lanthanoids, and C.I. A composition for an ammonia synthesis catalyst obtained by physically mixing a basic promoter.
(2) The composition for an ammonia synthesis catalyst according to the above (1), wherein the compound containing a lanthanoid is a lanthanoid oxide.
(3) The composition for an ammonia synthesis catalyst according to the above (1) or (2), wherein the basic promoter is an alkali metal oxide or hydroxide, or an alkaline earth metal oxide or hydroxide. .
(4) The composition for an ammonia synthesis catalyst according to any one of the above (1) to (3), wherein the physical mixing is dry milling mixing not containing water.
(5) A method for synthesizing ammonia, characterized in that ammonia is produced by reacting nitrogen and hydrogen using the composition for ammonia synthesis catalyst according to any one of (1) to (4) as a catalyst.
(6) A. Ruthenium or an alloy thereof, or a compound containing ruthenium, B. Compounds containing lanthanoids, and C.I. A method for producing a composition for ammonia synthesis catalyst, comprising physically mixing a basic promoter to obtain a composition for ammonia synthesis catalyst.
(7) The method for producing an ammonia synthesis catalyst composition as described in (6) above, wherein the composition for ammonia synthesis catalyst obtained by physical mixing is subjected to a reduction reaction.

  ADVANTAGE OF THE INVENTION According to this invention, the composition for ammonia synthesis catalysts which further improved ammonia synthesis activity, its manufacturing method, and the synthesis method of ammonia can be provided.

The figure which compared the ammonia production | generation activity of each catalyst composition of Example 1, the comparative example 1, and the comparative example 2 is shown. The figure which compared the composition for catalysts of Examples 1-4 and the ammonia production | generation activity of the comparative example 1 is shown.

  In the present invention, physical mixing is so-called dry milling mixing, in which two or more different raw materials in a solid state are mixed as they are without using an aqueous solution or using a dry organic solvent other than water. To obtain a homogeneous composition. As this physical mixing means, for example, a dry grinding and mixing method using various grinding devices such as a mortar, ball mill, and bead mill can be applied.

  In the case of physical mixing, in the case of grinding and mixing using a dry organic solvent other than water, the mixing efficiency is improved. As the dry organic solvent, for example, an appropriate amount of toluene, acetone, dehydrated alcohol or the like is added. Also good.

  The composition for an ammonia synthesis catalyst of the present invention comprises A. Ruthenium or an alloy thereof, or a compound containing ruthenium, B. Compounds containing lanthanoids, and C.I. A basic promoter is blended by physical mixing.

  In the ruthenium or its alloy or the compound containing ruthenium which is the component A of the catalyst component, these may be used in combination of two or more. As the metal element other than ruthenium contained in the alloy, for example, at least one selected from the group consisting of iron, molybdenum and nickel is preferable, and iron is most preferable because it is industrially used for ammonia synthesis. In this case, nonmetallic elements such as carbon and silicon may be further contained. The ruthenium-containing compound is not particularly limited as a ligand other than ruthenium, and may be a neutral ligand or an ionic ligand. Specific examples include ruthenium chloride, ruthenium acetylacetonate, potassium ruthenium cyanate, sodium ruthenate, potassium ruthenate, ruthenium oxide, dodecacarbonyl triruthenium, ruthenium nitrate and the like. In the case of an alloy containing ruthenium or a compound containing ruthenium, the content ratio of ruthenium in the alloy or compound is preferably 1% by mass to 99% by mass, and 50% by mass to 95% by mass is easy to ensure reactivity. % Is more preferable. The blending ratio of the component A in the composition is not particularly limited as long as it has a good catalytic ability, but is preferably 0.01 to 15% by mass, preferably 0.1 to 13% by mass. %, More preferably 1 to 10% by mass.

  Moreover, when A component is ruthenium, it is preferable that the mixture ratio of ruthenium is 0.005-15 mass%, It is more preferable that it is 0.05-13 mass%, 0.5-10 mass% More preferably.

  In the composition of the present invention, the B component serves as a carrier for supporting the A component.

  The compound containing lanthanoid is not particularly limited, and may be a compound containing any of 15 lanthanoids, but is a compound containing any of lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, dysprosium, and terbium. It is preferable that lanthanum, cerium, praseodymium, and terbium are more preferable because they are strongly basic and therefore provide good electron supply to ruthenium and ammonia synthesis.

  In addition, examples of the compound containing lanthanoid include a compound containing a lanthanoid oxide such as a lanthanoid oxide, a lanthanoid sulfide, a lanthanoid hydroxide, and a lanthanoid sulfate, and a group 16 element (chalcogen); And compounds containing a group element (halogen). And since A component can be carry | supported favorably, the lanthanoid oxide which is a lanthanum oxide, a cerium oxide, or a praseodymium oxide is preferable, Most preferably, it is a praseodymium oxide.

  When the B component which is a lanthanoid oxide is produced, for example, a commercially available lanthanoid compound (lanthanoid nitrate, lanthanoid nitrate hydrate, etc.) is dispersed in an alkaline solution and obtained after obtaining a solid by a precipitation method. It can be produced by firing a solid. Since the lanthanoid oxide thus obtained has a stable crystal structure, it can support the component A well. As an alkaline solution, 5-50 mass%, More preferably, 15-35 mass% ammonia water is preferable. The solid can be obtained by filtering the precipitate. Firing can be performed at 250 to 900 ° C, more preferably 300 to 750 ° C. Moreover, you may perform temporary baking at lower temperature than baking before baking. The pre-baking temperature is preferably 200 to 400 ° C. (lower temperature than baking).

  The blending ratio of the B component in the composition is not particularly limited as long as it can support the A component satisfactorily, but is preferably 40 to 99.98% by mass, and preferably 50 to 99.8. It is more preferable that it is mass%, and it is further more preferable that it is 70-98 mass%.

  Moreover, it is preferable that the mixture ratio of A component with respect to the sum total of A component and B component is 0.1-15 mass%, and it is more preferable that it is 1-10 mass%. By setting it to 0.1% by mass or more, good catalytic activity can be obtained, and by setting it to 15% by mass or less, it is possible to balance catalyst activity and cost.

  In the composition of the present invention, the basic co-catalyst as the C component is used for improving the catalytic efficiency of the A component. In the present invention, the basic co-catalyst means an electron-donating substance that can promote catalytic ability when used together with the A component and the B component. The component C can promote the reaction by donating an electron to the ruthenium of the component A.

  The basic cocatalyst is not particularly limited, but a compound containing an alkali metal or a compound containing an alkaline earth metal is preferable, and an alkali metal oxide or hydroxide, or an alkaline earth metal oxide or More preferred are hydroxides, and alkali metal oxides or hydroxides are most preferred.

  As precursors used as raw materials for alkali metal oxides or hydroxides, or alkaline earth metal oxides or oxides, specifically, alkali metal or alkaline earth metal nitrates, sulfates, phosphates, And carbonates.

  As the alkali metal and alkaline earth metal, lithium, sodium, potassium, rubidium, cesium, beryllium, magnesium, calcium, strontium, and barium are preferable. And cesium is more preferred, and cesium is most preferred.

  Although the compounding ratio of the C component in the composition is not particularly limited, it is preferably 0.01 to 15% by mass, more preferably 0.1 to 13% by mass, and 1 to 10% by mass. Is more preferable. Moreover, it is preferable that the mixture ratio of C component is the quantity from which the atomic ratio with respect to A component will be 0.01-20 mass%. This is because the catalyst activity can be particularly improved by setting it to the lower limit value or more, and the decrease of the catalyst activity due to the presence of an excessive basic promoter can be prevented by setting the upper limit value or less.

  The mixing order of the components A to C is not particularly limited, and any addition method may be used simultaneously or sequentially. However, after adding the component A to the component B and grinding and mixing, the component C is further added. It is preferable to mix sequentially.

  Moreover, it is not always necessary to mix all components A, B, and C by grinding, and grinding mixing can be used only for mixing any one of the components. For example, the component A may be supported by wet impregnation and calcination with the supply source of the component A, and then the component C may be ground and mixed.

  As long as the effect of this invention is not impaired, components other than A-C component may be mix | blended with the composition of this invention.

  In the ammonia synthesis method of the present invention, ammonia is produced by reacting nitrogen and hydrogen using the composition for ammonia synthesis catalyst as a catalyst. The method for synthesizing ammonia is not particularly limited. For example, ammonia can be produced by supplying a raw material gas composed of hydrogen gas and nitrogen gas into a reaction vessel filled with a composition for ammonia synthesis catalyst. The reaction temperature is preferably 200 ° C to 600 ° C, more preferably 250 ° C to 500 ° C, and further preferably 300 ° C to 450 ° C. The pressure in the reaction vessel is preferably a low pressure of 1 to 50 atm, more preferably 1 to 40 atm, and further preferably 1 to 30 atm.

  According to the composition for an ammonia synthesis catalyst of the present invention, the ammonia yield is, for example, Cs / Ru: 1 to 5, 390 ° C., 9 atm, 4.5 to 5.5%, which is higher and more stable than the conventional catalyst. can get. In general, the ammonia synthesis reaction tends to increase the ammonia yield as the pressure is increased. Therefore, by using the composition for an ammonia synthesis catalyst of the present invention, a high yield can be obtained even under a high pressure condition of about 30 atmospheres or over 30 atmospheres. Expected to be obtained.

Yield is the ratio of the amount of substance actually obtained (yield) to the maximum amount of substance that can theoretically be obtained (theoretical yield) in a chemical process for obtaining a substance. One of the indicators of whether the process is good. For example, in a reaction of synthesizing ammonia from hydrogen and nitrogen, theoretically 2 mol of ammonia can be obtained from 1 mol of nitrogen and 3 mol of hydrogen (N ₂ + 3H ₂ → 2NH ₃ ). If 1 mol of ammonia is actually obtained when ammonia is synthesized from 1 mol of nitrogen and 3 mol of hydrogen, the yield is ammonia yield (1 mol) / theoretical yield of ammonia (2 mol) = 50%. Further, when the reaction as is supplied at the same rate as the stoichiometric ratio of the reaction, the theoretical yield (2 mol) = supply amount of a reaction product (in H ₂ 3 mol) × reaction formula of the product Coefficient (stoichiometric coefficient, 2) / stoichiometric coefficient of a reactant (3 in H ₂ ) holds, so use this to calculate the yield from the reactant feed rate and chemical reaction equation Can do. If this reaction is performed with 2 mol of nitrogen and 3 mol of hydrogen, theoretically, 1 mol of nitrogen is obtained, and 2 mol of ammonia is obtained. In this way, when reactants are supplied at a rate different from the stoichiometric ratio of the reaction, only the reactant (referred to as a limited reactant) having the smallest reactant coefficient in the reactant supply rate / reaction equation. Is completely consumed in theory. In this example, hydrogen is theoretically completely consumed, so hydrogen is the limiting reactant. In such a case, the theoretical yield = limited reactant supply amount x product stoichiometry coefficient / limited reactant stoichiometry coefficient, which is used to calculate the yield for the limited reactant only. can do.

  As described above, the composition for an ammonia synthesis catalyst of the present invention comprises A.I. Ruthenium or an alloy thereof, or a compound containing ruthenium, B. Compounds containing lanthanoids, and C.I. It is obtained by blending a basic promoter with the above physical mixing to obtain a composition for an ammonia synthesis catalyst.

  In the present invention, the catalytic activity can be improved by subjecting the composition for ammonia synthesis catalyst obtained by blending by the physical mixing to a reduction reaction to reduce ruthenium to a metallic state. The reduction can suitably be performed by hydrogen reduction, for example, 100 to 700 ° C., preferably 300 to 600 ° C., in a hydrogen-containing atmosphere for 0.5 to 20 hours.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to the Example shown here. Table 1 summarizes the compositions for ammonia synthesis catalysts described as examples and comparative examples.

1． Production Example 1 of Composition for Ammonia Synthesis Catalyst
A mixed solution obtained by adding 0.25 liter of an 8% aqueous solution of praseodymium nitrate to 0.25 liter of 28% ammonia water was stirred at room temperature for 11 hours. The resulting praseodymium hydroxide precipitate was separated, washed with room temperature water, filtered, and dried overnight at 70 ° C.

  The dried praseodymium hydroxide was converted to praseodymium oxide by a stepwise calcination treatment at 300 ° C. for 3 hours, then at 550 ° C. for 3 hours, and then at 700 ° C. for 5 hours.

  Subsequently, 4 g of praseodymium oxide cooled to room temperature was added to a 0.2 liter tetrahydrofuran solution in which 0.46 g of ruthenium carbonyl was dissolved, and stirred overnight. Next, the tetrahydrofuran was removed from the solution by evaporation, followed by baking at 350 ° C. for 5 hours in an atmosphere in which helium gas circulated to decompose ruthenium carbonyl and remove the organic ligand. Thus, a composition in which ruthenium (A) was supported on praseodymium oxide (B) was prepared. At this time, the loading of ruthenium on praseodymium oxide was 5% by mass.

Subsequently, the powdery ruthenium-oxide praseodymium composition thus prepared was ground for 5 minutes using an alumina mortar. 2 g of the ground ruthenium-praseodymium composition was weighed and added to another agate mortar. To this was added 0.17 g of cesium carbonate powder, and the mixture was further ground for 10 minutes. The resulting milled mixed composition was shaped and then crushed into 250-500 μm pellets. After that, the pellet is filled in an ammonia production apparatus described later, and hydrogen reduction is performed at 500 ° C. for 1 hour to decompose cesium carbonate to obtain a composition for catalyst composed of cesium oxide-ruthenium-praseodymium. It was. The ratio of cesium / ruthenium in this catalyst composition was 1/1 (mol / mol).
Examples 2-3
A cesium-ruthenium-praseodymium oxide composition having a ruthenium loading of 5 wt% and a cesium / ruthenium ratio of 0.1 / 1 / -5 / 1 (mol / mol) was obtained in the same manner as in Example 1.
Comparative Example 1
A mixed solution obtained by adding 0.25 liter of an 8% aqueous solution of praseodymium nitrate to 0.25 liter of 28% ammonia water was stirred at room temperature for 11 hours. The resulting praseodymium hydroxide precipitate was separated, washed with room temperature water, filtered, and dried overnight at 70 ° C.

  The dried praseodymium hydroxide was converted to praseodymium oxide by a stepwise calcination treatment at 300 ° C. for 3 hours, then at 550 ° C. for 3 hours, and then at 700 ° C. for 5 hours.

Subsequently, 4 g of praseodymium oxide cooled to room temperature was added to a 0.2 liter tetrahydrofuran solution in which 0.46 g of ruthenium carbonyl was dissolved, and stirred overnight. Next, the tetrahydrofuran was removed from the solution by evaporation, followed by baking at 350 ° C. for 5 hours in an atmosphere in which helium gas circulated to decompose ruthenium carbonyl and remove the organic ligand. Thus, a composition in which ruthenium (A) was supported on praseodymium oxide (B) was prepared. This composition was not subjected to grinding treatment, and the amount of ruthenium supported on praseodymium oxide was 5% by mass. The ratio of cesium / ruthenium in this catalyst composition was 1/1 (mol / mol).
Comparative Example 2
A ruthenium-praseodymium oxide composition having a ruthenium loading of 5% by mass was prepared in the same manner as in Comparative Example 1. 2 g of the ruthenium-praseodymium oxide composition after pulverization was added to 100 mL of purified water in a beaker and stirred. Cesium carbonate 0.17g was added here, and after stirring and impregnation, it was evaporated to dryness using a hot stirrer. The mixed composition after evaporation to dryness is shaped and crushed without grinding into 250-500 μm pellets, which are then filled into an ammonia production apparatus described later and subjected to hydrogen reduction at 500 ° C. for 1 hour. As a result, a catalyst composition comprising cesium oxide-ruthenium-praseodymium was obtained. The ratio of cesium / ruthenium in this catalyst composition was 1/1 (mol / mol).
2. Measurement of ammonia production activity of catalyst composition A fixed bed flow tubular reactor was used as the ammonia production apparatus. In a normal pressure experiment, a quartz reactor having an inner diameter of 7 mm was used. As a pretreatment for ammonia production, the reactor was filled with the composition (catalyst) used for the study, and hydrogen reduction was performed at 400 ° C. for 1 hour, or at 500 ° C. for 1 hour. Subsequently, the temperature was lowered to 310 ° C. as the reaction temperature while performing Ar purge, and when the temperature was stabilized, supply of the reaction gas was started and the temperature was raised to 350 ° C. The reaction gas was N ₂ / H ₂ = 1/3 (SV = 18000 ml / (h · g)). The reaction formula is as shown below.
N ₂ + 3H ₂ → 2NH ₃
(Reaction conditions)
Composition (catalyst amount): 0.2 g
Activation treatment conditions: under H ₂ flow, 10 mL / min, 500 ° C., 1 hour, reaction temperature: 310 to 430 ° C.
Reaction pressure: 0.9 MPa
Reaction gas: N ₂ 15 mL / min, H ₂ 45 mL / min Space velocity: 18000 mLh ⁻¹ g ⁻¹
Analysis of generated gas: electric conductivity meter The reaction temperature was 310 ° C to 430 ° C, and sampling was performed for 30 minutes. A schematic diagram of the ammonia sampling method is shown in FIG. The reactor outlet gas (ammonia, hydrogen, nitrogen) was passed through a 0.001 M or 0.01 M sulfuric acid solution as an ammonia trap to collect only ammonia. The reaction formula at this time is as shown below.
2NH ₃ + H ₂ SO ₄ → 2NH ₄ ⁺ + SO ₄ ²⁻
Ammonium ions and sulfate ions are produced from the ammonia in the outlet gas of the reaction tank and the sulfuric acid solution in the trap. The decrease in electrical conductivity in this reaction was monitored, and the activity of the catalyst for ammonia synthesis was measured.
3. Ammonia Production Activity FIG. 1 shows the results of comparing the ammonia production activities of the catalyst compositions of Example 1, Comparative Example 1, and Comparative Example 2. In either case, the activity was compared after hydrogen reduction at 500 ° C. for 1 hour. The catalyst composition of Example 1, which was physically mixed by adding cesium carbonate to the catalyst composition of Comparative Example 1, showed higher ammonia production activity than the catalyst composition of Comparative Example 1 at 350 ° C. or higher. In particular, the ammonia yield was about 5.3% at 390 ° C. In contrast, the catalyst composition of Comparative Example 2 in which Cs was prepared by a conventional evaporation to dryness showed a lower ammonia yield than the catalyst composition of Comparative Example 1. From this, it has been found that the effect of improving the activity can be obtained by adding Cs in the present invention and the above-mentioned physical mixing, and that the catalytic activity is rather lowered in the conventional impregnation method.

  FIG. 2 is a graph comparing the ammonia-forming activity of each catalyst composition of Examples 1 to 4 and Comparative Example 1. It can be seen that the ammonia production activity is improved by adding Cs and grinding. In particular, in the temperature range up to 350 ° C, the composition for the catalyst with Cs addition amount of Cs / Ru = 0.1 / 1 (mol / mol), and in the temperature range of 350 ° C or more, the addition amount of Cs is Cs / Ru = It was found that 1 to 5 (mol / mol) of the catalyst composition showed a high ammonia yield and a high acceleration effect was obtained.

  ADVANTAGE OF THE INVENTION According to this invention, the composition for ammonia synthesis catalysts which further improved ammonia synthesis activity, its manufacturing method, and the synthesis method of ammonia can be provided. That is, it is possible to provide a highly activated catalyst necessary for synthesizing ammonia, which is essential as a hydrogen carrier for hydrogen storage / transport technology, with a high yield and a method for producing the catalyst.

Claims (6)

A composition in which ruthenium or an alloy thereof or a ruthenium-containing compound (A) is supported on a compound (B) containing a lanthanoid and a basic promoter (C) are physically mixed , and hydrogen gas is applied without applying a voltage. A method for producing an ammonia synthesis catalyst composition, comprising obtaining an ammonia synthesis catalyst composition for synthesizing ammonia from nitrogen gas . The method for producing a composition for an ammonia synthesis catalyst according to claim 1, wherein the compound containing the lanthanoid is a lanthanoid oxide. The method for producing a composition for an ammonia synthesis catalyst according to claim 1 or 2, wherein the basic promoter is an alkali metal oxide or hydroxide, or an alkaline earth metal oxide or hydroxide. The method for producing a composition for an ammonia synthesis catalyst according to any one of claims 1 to 3, wherein the physical mixing is a dry milling mixture containing no water. A method for synthesizing ammonia, comprising producing ammonia by reacting nitrogen and hydrogen using the composition for an ammonia synthesis catalyst according to any one of claims 1 to 4 as a catalyst . The method for producing a composition for ammonia synthesis catalyst according to claim 1 , wherein the composition for ammonia synthesis catalyst obtained by physical mixing is subjected to a reduction reaction.