WO2019017399A1

WO2019017399A1 - Ammonia synthesis catalyst

Info

Publication number: WO2019017399A1
Application number: PCT/JP2018/026953
Authority: WO
Inventors: 政康西; 英行高木
Original assignee: 国立研究開発法人産業技術総合研究所
Priority date: 2017-07-19
Filing date: 2018-07-18
Publication date: 2019-01-24
Also published as: JPWO2019017399A1; JP6736073B2

Abstract

Provided is an ammonia synthesis catalyst having a configuration in which a catalytic component and a promoter component are supported on a carrier. The ammonia synthesis catalyst is characterized in that: the catalytic component is ruthenium, and the promoter component is an alkali metal or an alkaline-earth metal; and the carrier is a carbon material, in which an inter-layer distance between 002 planes derived from the carbon lamination structure is in the range of 0.339-0.375 nm, the specific surface area is in a range of 150-1400 m2/g, and the average pore diameter is in the range of 8-20 nm, the foregoing all being determined by X-ray diffraction analysis.

Description

Ammonia synthesis catalyst

The present invention relates to an industrially available catalyst used for the direct synthesis of ammonia from hydrogen and nitrogen, and more particularly to a ruthenium catalyst using mesoporous carbon as a carrier.

The chemical reaction for directly synthesizing ammonia from nitrogen and hydrogen is an exothermic reaction with a decrease in the number of moles (standard heat of formation is -46.1 kJ · mol ^-1 ) represented by the following chemical reaction formula, and is equilibrium theory The reaction is more favored by lower temperature and higher pressure.

Iron-based catalysts used in conventional ammonia synthesis have low catalytic activity at low temperatures of 300-400 ° C., and the reaction must be carried out at high temperatures of 400-600 ° C., which is equilibrium disadvantage in the above chemical reaction Absent. For this reason, there is a need to increase the recirculation ratio of the reaction gas and to increase the SV value (space velocity), etc., and there is a problem that the operating cost increases.
On the other hand, Akiha and Ozaki et al., In Non-Patent Documents 1 to 3 and Patent Documents 1 to 4, when ruthenium is used as a catalyst, high catalytic activity is obtained even at a low temperature of 200 to 400 ° C. , And reported that operating costs can be reduced.
Akiha, Ozaki et al., Non-Patent Document 2, Non-Patent Document 3, Patent Document 1, Patent Document 4 and Patent Document 5 for this ruthenium catalyst-supporting carrier, when activated carbon is used as the carrier, a highly active catalyst is obtained. Is reported to be Furthermore, in Non-Patent Document 4 and Patent Document 6, if the activated carbon is reduced in advance in a hydrogen atmosphere before ruthenium is supported, impurities such as S, N, O, Cl existing on the activated carbon surface can be removed, and the catalyst activity is improved. It also reports that it does.
Zbigniew Kowalczyk et al., Non-Patent Document 5 and Non-Patent Document 6, and Xiaoling Zheng et al., Non-Patent Document 7 heat treatment of activated carbon in an inert atmosphere reduces specific surface area and reduces catalytic activity, After that, when activated by CO ₂ or steam, partially graphitized carbon with a high specific surface area is obtained, and it is reported that the catalytic activity is improved.
Also, Ichikawa et al., Patent Document 7 and Patent Document 8, Alan Iper Foster et al., Patent Document 9, Forni-Luchio et al., Patent Document 10, a ruthenium catalyst carrier having a high specific surface area as a catalyst. Report that high catalytic activity can be obtained using
Furthermore, in recent years, research and development of mesoporous carbon having mesopores has been advanced (Non-patent document 8, Patent document 11, Patent document 12 etc.), Zhou Yaping et al. The use of mesoporous carbon with SiO ₂ as a template is proposed.
On the other hand, sufficient catalytic activity can not be obtained only by using a carbon material such as activated carbon or graphite as a ruthenium catalyst carrier, and in Non-Patent Documents 1 to 8 and Patent Documents 1 to 10, an alkali is used as a promoter. It is reported that high catalytic activity can be obtained by using metals and alkaline earth metals, and it is also reported that the effect is remarkable when Cs is used among alkali metals and Ba is used among alkaline earth metals. ing.

Japanese Patent Publication No. 48-23800 Japanese Patent Application Laid-Open No. 48-00184 Japanese Patent Application Laid-Open No. 48-00185 Japanese Patent Publication No. 51-44509 Japanese Patent Publication No. 54-37592 Japanese Patent Laid-Open No. 9-168739 Japanese Patent Application Laid-Open No. 47-14085 Japanese Patent Publication No.49-16037 Japanese Patent Application Laid-Open No. 53-57193 Japanese Patent Application Publication No. 2005-511278 Japanese Patent Application Laid-Open No. 2006-62954 JP, 2010-208887, A

Conventional carbon-based supports used in ruthenium catalysts used for direct synthesis of ammonia have several challenges.
Impurities consisting of S, N, O, Cl, etc. exist on the surface of activated carbon, which is a factor that inhibits the catalytic reaction. When activated carbon is heat-treated in a hydrogen stream, the impurities are removed and the catalytic activity becomes high. It is dangerous because it needs to be treated with hydrogen at high temperature, and it is not suitable for industrial mass production of catalysts.
In addition, activated carbon has low crystallinity of carbon, so resistance against methanation is low, and there is also a problem that heat resistance of the catalyst is poor. In order to solve these problems, when activated carbon is heat-treated at high temperature in an inert atmosphere to improve the crystallinity of carbon, narrowing and clogging of the pores proceed and the specific surface area is greatly reduced, and the catalytic activity is remarkably It causes another problem of falling. For this reason, activated carbon with enhanced crystallinity is activated again to recover the specific surface area to improve the catalytic activity, but a two-step process of performing activation operation in addition to heat treatment at high temperature is required It is not suitable for industrial mass production of catalysts.
On the other hand, graphite with a high specific surface area has high resistance to methanation and is excellent in the heat resistance of the catalyst, but has a smaller specific surface area compared to activated carbon, and the catalytic activity remains comparable to activated carbon to improve catalytic activity. It can not solve the essential problem of that.
Furthermore, mesoporous carbon produced using SiO ₂ as a template has a fundamental problem that the catalytic activity at low temperature is lower than when using activated carbon, and additionally, SiO ₂ is produced with hydrofluoric acid at the time of production. It is not suitable for industrial mass production of catalysts because the removal cost is high in terms of manufacturing equipment and environmental load.

In view of the above problems of the prior art, the present invention provides a ruthenium catalyst for ammonia synthesis with improved ammonia synthesis activity and improved heat resistance using a carrier material suitable for industrial mass production. To be an issue.

The present inventors use a carbon material obtained by heat-treating mesoporous carbon prepared using MgO as a template at a temperature of 1200 ° C. or more and 2500 ° C. or less in an inert atmosphere as a support, using a ruthenium catalyst and a support therefor. It was found that by supporting an alkali metal or alkaline earth metal as a catalyst, it is possible to obtain an ammonia synthesis catalyst in which the ammonia synthesis activity is improved and the heat resistance is improved. The present carbon material is characterized in that it can maintain a relatively high specific surface area while maintaining graphitization of carbon by heat treatment, and can maintain the pore structure of the original mesoporous carbon. Do.

Unlike mesoporous carbon prepared using MgO as a template (see, for example, JP-A-2010-208887), it is necessary to use a strong acid such as hydrofluoric acid in the manufacturing process, unlike mesoporous carbon prepared using SiO ₂ as a template. Rather, they are low cost in terms of manufacturing equipment and are friendly industrial raw materials in terms of environmental impact. For this reason, mesoporous carbon produced using MgO as a template is a material very suitable for industrial mass production of a catalyst, and it is possible to use the mesoporous carbon produced using SiO ₂ used in Non-Patent Document 9 as a template Are of completely different industrial value.

In general, when a carbon material having a high specific surface area is heat-treated at high temperature in an inert atmosphere, the specific surface area is significantly reduced along with the improvement of crystallinity, as confirmed in Example 4 to be described later. Although unknown, mesoporous carbon produced using MgO as a template has the property of being able to maintain a high specific surface area even when heat-treated in an inert atmosphere.
That is, mesoporous carbon produced using MgO as a template improves the crystallinity of carbon when heat-treated at 1200 ° C. or higher, and the interlayer distance of the 002 plane derived from the laminated structure of carbon by X-ray diffraction analysis is 0.375 nm or less It approaches 0.3354 nm which is the theoretical value of the interlayer distance of graphite. When the temperature for heat treatment is 1500 ° C., the interlayer distance is 0.368 nm, and at 1800 ° C., 0.355 nm, and at 2100 ° C., 0.340 nm, which is closer to the theoretical value of the interlayer distance. On the other hand, mesoporous carbon produced using MgO as a template has a specific surface area of 1200 m ² / g and an average pore diameter of 10 nm at a heat treatment temperature of 1500 ° C., 900 m ² / g at 11 000 ° C, 11 nm and 2100 ° C. As the heat treatment temperature rises, the specific surface area decreases and the average pore diameter tends to increase to 280 m ² / g and 14 nm, but even if the heat treatment temperature is 2500 ° C., the specific surface area as high as 150 m ² / g And an average pore diameter close to that of the original mesoporous carbon of 20 nm.
Thus, while heat treating the mesoporous carbon produced by using MgO as a template at a temperature of 1200 ° C. or more and 2500 ° C. or less in an inert atmosphere, on the other hand, the graphitization of the carbon material contributing to the catalytic activity proceeds On the other hand, by maintaining a high specific surface area and an average pore diameter close to that of the original mesoporous carbon, the supported amount of the catalyst component and the cocatalyst component when supporting the ruthenium catalyst and the cocatalyst on the obtained carbon material Since the ammonia synthesis activity is improved and the heat resistance is improved, a ruthenium catalyst for ammonia synthesis can be obtained.
The present invention has been made based on these findings obtained by the present inventors.

Such an effect is an effect obtained by using, as a catalyst support, a carbon material obtained by heat-treating mesoporous carbon prepared using MgO as a template at the above temperature, and it is used in Non-Patent Document 5 etc. It is a novel effect not found in activated carbon. In addition, Non-Patent Document 9 describes using mesoporous carbon produced with SiO ₂ as a template as a support, but the catalytic activity at a low temperature of 300 to 400 ° C. is equivalent to or less than that using activated carbon The heat treatment of mesoporous carbon in an inert atmosphere has not been described in advance, and the above-mentioned effects according to the present invention are far from predictable.

That is, this application provides the following invention.
(1) An ammonia synthesis catalyst comprising a catalyst component and a cocatalyst component supported on a carrier, wherein the catalyst component is ruthenium, the cocatalyst component is an alkali metal or alkaline earth metal, and the carrier is The interlayer distance of the 002 plane derived from the laminated structure of carbon by X-ray diffraction analysis is in the range of 0.339 nm to 0.375 nm, and the specific surface area is in the range of 150 m ² / g to 1400 m ² / g, average pore size An ammonia synthesis catalyst characterized in that it is a carbon material having a diameter of 8 nm or more and 20 nm or less.
<2> The interlayer distance of the carrier is in the range of 0.340 nm to 0.368 nm, the specific surface area is in the range of 280 m ² / g to 1200 m ² / g, and the average pore diameter is 10 nm to 14 nm The ammonia synthesis catalyst according to <1>, which is in the range of
<3> The ammonia synthesis catalyst according to <1> or <2>, wherein the supported amount of ruthenium is 1% or more and 15% or less in mass% with respect to the mass of the carrier.
<4> The ammonia synthesis catalyst according to any one of <1> to <3>, wherein the promoter component is an alkali metal.
<5> The ammonia synthesis catalyst according to <4>, wherein the supported amount of alkali metal is 1.5 or more and 15 or less in molar ratio to ruthenium.
<6> The ammonia synthesis catalyst according to <4> or <5>, wherein the alkali metal is at least one selected from the group consisting of sodium, potassium, rubidium and cesium.
<7> The substance mass of ammonia generated per unit time of reaction per unit mass of the catalyst is 3.4 mmol · g ⁻¹ · h ⁻¹ or more, <4> to <6> The ammonia synthesis catalyst as described in any one.
<8> The ammonia synthesis catalyst according to any one of <1> to <3>, wherein the co-catalyst component is an alkaline earth metal.
<9> The ammonia synthesis catalyst according to <8>, wherein the supported amount of alkaline earth metal is 0.5 or more and 10 or less in molar ratio to ruthenium.
<10> The ammonia synthesis catalyst according to <8> or <9>, wherein the alkaline earth metal is at least one selected from the group consisting of calcium, strontium and barium.
<11> The amount of ammonia produced per unit time of reaction per unit mass of the catalyst is 5.7 mmol · g ⁻¹ · h ⁻¹ or more, <8> to <10> The ammonia synthesis catalyst as described in any one.
<12> The support is prepared by heat-treating mesoporous carbon prepared using MgO as a template at a temperature of 1200 ° C. or more and 2500 ° C. or less in an inert atmosphere, and ruthenium and an alkali metal or alkaline earth metal are supported thereon A method for producing an ammonia synthesis catalyst according to any one of <1> to <11>, characterized in that
<13> The heat treatment temperature is in the range of 1500 ° C. to 2100 ° C., the interlayer distance of the support is in the range of 0.340 nm to 0.368 nm, and the specific surface area is in the range of 280 m ² / g to 1200 m ² / g The method for producing an ammonia synthesis catalyst according to <12>, wherein the average pore diameter is in the range of 10 nm to 14 nm.

According to the present invention, the amount of ammonia produced per unit time of reaction per unit mass of catalyst is 3.4 mmol · g ⁻¹ · h ⁻¹ or more using an alkali metal as a cocatalyst, alkali as a cocatalyst An ammonia synthesis catalyst is obtained which has an extremely high ammonia synthesis activity of 5.7 mmol · g ⁻¹ · h ⁻¹ or more using a rare earth metal and is excellent in heat resistance.

The contrast diagram of the methanation reactivity of the catalyst which uses the catalyst of this invention, and activated carbon as a support. The solid line shows the catalyst of the present invention, and the broken line shows a catalyst with activated carbon as a carrier.

The present invention is an ammonia synthesis catalyst comprising a catalyst component and a cocatalyst component supported on a carrier, wherein the catalyst component is ruthenium, the cocatalyst component is an alkali metal or an alkaline earth metal, and the carrier is The interlayer distance of the 002 plane derived from the laminated structure of carbon by X-ray diffraction analysis is in the range of 0.339 nm to 0.375 nm, and the specific surface area is in the range of 150 m ² / g to 1400 m ² / g. It is a carbon material having a pore diameter in the range of 8 nm or more and 20 nm or less, and is a content of an ammonia synthesis catalyst.
In the catalyst of the present invention, the amount of ammonia produced per unit time of reaction per unit mass of catalyst is 3.4 mmol · g ⁻¹ · h ⁻¹ or more using an alkali metal as a cocatalyst, and alkali as a cocatalyst It has extremely high ammonia synthesis activity of 5.7 mmol · g ⁻¹ · h ⁻¹ or more using a rare earth metal.
In the carrier, the interlayer distance is in the range of 0.340 nm to 0.368 nm, the specific surface area is in the range of 280 m ² / g to 1200 m ² / g, and the average pore diameter is in the range of 10 nm to 14 nm. Is more preferable.

If the average pore diameter of the support used in the present invention is less than 8 nm, the pores are easily clogged by a ruthenium catalyst or a cocatalyst, high catalytic activity can not be obtained, and if the average pore diameter exceeds 20 nm The average pore diameter of the support used in the present invention is preferably 8 nm to 20 nm, and more preferably 10 nm to 14 nm, because the specific surface area and the pore volume decrease, leading to a decrease in catalyst activity due to a decrease in the catalyst loading amount. It is more preferable that

The range of the supported amount of the ruthenium catalyst used in the present invention is not particularly limited as long as high catalytic activity can be obtained, but if the amount by mass based on the mass of the support is less than 1%, the supported amount of the catalyst is insufficient and sufficient catalyst The activity is not obtained, and if it exceeds 15%, the catalyst activity is lowered due to clogging of pores by the ruthenium catalyst and aggregation of the ruthenium catalyst, so it is preferably 1% or more and 15% or less, preferably 2.5% or more and 10% or less It is more preferable that
In addition, conventionally known methods such as a impregnation method, a mechanochemical method, a vacuum evaporation method can be adopted for supporting the ruthenium catalyst used in the present invention, and ruthenium chloride, ruthenium nitrate, nitosilol are used as raw materials of the ruthenium catalyst. Conventionally known materials such as ruthenium nitrate, potassium ruthenate, ruthenium acetylacetonate complex, ruthenium carbonyl complex and the like can be adopted.

The range of the supported amount of the cocatalyst used in the present invention is not particularly limited as long as high catalytic activity can be obtained, but when the cocatalyst is an alkali metal, the supported amount of catalyst is insufficient when the molar ratio to ruthenium is less than 1.5 Sufficient catalyst activity can not be obtained, and if it exceeds 15, it causes blockage of the pores of the support and aggregation of the cocatalyst, so that the catalyst activity is lowered, so 1.5 or more and 15 or less is preferable, and 2.5 or more and 10 or less It is more preferable that When the promoter is an alkaline earth metal, if the molar ratio to ruthenium is less than 0.5, the supported amount of the catalyst is insufficient and sufficient catalytic activity can not be obtained, and if it exceeds 10, pore clogs of the support and aggregation of the promoter occurs. In order to reduce the catalyst activity, it is preferably 0.5 or more and 10 or less, and more preferably 1 or more and 5 or less.
In addition, conventionally known methods such as impregnation method, heating and melting method, vacuum evaporation method, metal hydride adsorption decomposition method can be adopted for supporting the cocatalyst used in the present invention, and existing materials for cocatalyst can be used. Alkali metal salts or alkaline earth metal salts may be employed.
In addition, the alkali metal used for the co-catalyst of the present invention may be at least one or more selected from the group consisting of sodium, potassium, rubidium and cesium, and among them, cesium has a remarkable effect as a co-catalyst So most preferred. In addition, the alkaline earth metal used for the co-catalyst of the present invention may be at least one selected from the group consisting of calcium, strontium and barium, and among these, barium has a remarkable effect as a co-catalyst. Most preferred.

The support used in the present invention can be prepared by heat-treating mesoporous carbon produced using MgO as a template in an inert atmosphere at a temperature of 1200 ° C. or more and 2500 ° C. or less.
The mesoporous carbon prepared using MgO as a template improves the crystallinity of carbon when heat-treated at 1200 ° C. or higher, and the interlayer distance of the 002 plane derived from the laminated structure of carbon by X-ray diffraction analysis becomes 0.375 nm or less It is preferable because it improves, and the interlayer distance is 0.368 nm or less at 1500 ° C. or more, which is more preferable because the catalytic activity is further improved.
On the other hand, mesoporous carbon prepared using MgO as a template can maintain a high specific surface area of 150 m ² / g and a large average pore diameter of 20 nm even at a heat treatment temperature of 2500 ° C., and support catalyst components and cocatalyst components It is preferable because high catalytic activity can be maintained without significantly reducing the amount, and when the heat treatment temperature is 2100 ° C. or less, the specific surface area is 280 m ² / g or more, the average pore diameter is 14 nm or less, and the catalytic activity is further enhanced. So more preferable.

The gas used to form the inert atmosphere when performing the heat treatment in the present invention is not particularly limited, but high purity nitrogen gas, high purity argon gas, high purity helium gas, etc. are available at cost and availability. Preferred in terms of ease.

EXAMPLES The present invention will next be described in more detail by way of examples, which should not be construed as limiting the invention thereto.

Example 1
MgO-based mesoporous carbon (Toyo Carbon Co., Ltd., C Novel P (3) 010, BET specific surface area 1600 m ² / g, average pore diameter 10 nm) is heat-treated at 1500 ° C. for 1 hour in high purity nitrogen gas atmosphere And obtained MPC (1500). The interlayer distance of the 002 plane derived from the laminated structure of carbon by X-ray diffraction analysis of MPC (1500) was 0.368 nm, the specific surface area was 1200 m ² / g, and the average pore diameter was 10 nm.
A ruthenium solution is prepared by diluting a nitrosyl ruthenium (III) nitrate solution (Wako Pure Chemical Industries, Ltd.) to a predetermined concentration. Separately, a predetermined amount of cesium carbonate (Wako Pure Chemical Industries, Ltd.) is dissolved in water to prepare a cesium solution.
Take 1 g of MPC (1500) and add to 100 mL of ruthenium solution and impregnate with stirring for 30 minutes. Subsequently, the solvent is removed using an evaporator and dried at 110 ° C. for 1 hour. Thereafter, heat treatment is performed at 400 ° C. for 1 hour in an inert atmosphere to obtain Ru / MPC (1500) which is ruthenium-supported mesoporous carbon.
Next, 1 g of Ru / MPC (1500) is collected, added to 100 mL of the cesium solution, and impregnated while stirring for 30 minutes. Subsequently, the solvent is removed using an evaporator and dried at 110 ° C. for 1 hour. Thereafter, the catalyst was heat-treated at 450 ° C. for 10 hours in a hydrogen stream to prepare ruthenium-cesium-supported mesoporous carbon catalyst 10Ru-2.5Cs / MPC (1500). The amount of Ru supported was 10 wt%, and the Cs / Ru ratio was 2.5.

(Example 2)
The same mesoporous carbon as in Example 1 was heat-treated at 1800 ° C. for 1 hour in an inert atmosphere to obtain MPC (1800). The interlayer distance of MPC (1800) was 0.355 nm, the specific surface area was 900 m ² / g, and the average pore diameter was 11 nm. Except for this, the same operation as in Example 1 was performed to prepare Ru / MPC (1800) and 10Ru-2.5Cs / MPC (1800). The amount of Ru supported was 10 wt%, and the Cs / Ru ratio was 2.5.

(Example 3)
The same mesoporous carbon as in Example 1 was heat-treated at 2100 ° C. for 1 hour in an inert atmosphere to obtain MPC (2100). The interlayer distance of MPC (2100) was 0.340 nm, the specific surface area was 280 m ² / g, and the average pore diameter was 14 nm. The same operation as in Example 1 was carried out except for the above, to prepare 10Ru-2.5Cs / MPC (2100). The amount of Ru supported was 10 wt%, and the Cs / Ru ratio was 2.5.

(Comparative example 1)
Instead of mesoporous carbon, AC, which is obtained by treating activated carbon (Large Gas Chemicals Co., Ltd., HG15-119) in a hydrogen stream at 500 ° C. for 3 hours, is used. The interlayer distance of AC was 0.382 nm, the specific surface area was 1700 m ² / g, and the average pore diameter was 0.9 nm. The same operation as in Example 1 was followed except that Ru / AC and 10Ru-2.5Cs / AC were prepared. The amount of Ru supported was 10 wt%, and the Cs / Ru ratio was 2.5.

(Example 4)
The characteristics of the catalysts of Examples 1 to 3 of the present invention and the carriers used therefor, and the catalysts of Comparative Example 1 of the prior art and the carriers used therein were measured by the following methods.
(Method 1) Method of measuring catalyst activity 0.2 g of catalyst was placed in a quartz reaction tube with an inner diameter of 30 mm, the flow rate of mixed gas of H ₂ and N ₂ was set to SV = 9000 h ⁻¹ , and the temperature was raised to the catalyst activity measurement temperature Warm up. Ammonia synthesis reaction is performed in a state where the mixed gas flows, the gas at the outlet of the reaction tube is collected, and the ammonia concentration is quantitatively analyzed by a gas chromatograph. The H ₂ / N ₂ molar ratio of the reaction gas was 3, the pressure was 0.99 MPa, and the catalyst activity was measured at 350 and 400 ° C. The catalyst activity is represented by the amount of substance of ammonia (mmol · g ⁻¹ · h ⁻¹ ) produced per unit time of reaction per unit mass of catalyst.
(Method 2) Measurement Method of Specific Surface Area of Carrier and Interlayer Distance of 002 Plane Derived from Laminated Structure of Carbon The specific surface area of the carrier was measured by BET method using N ₂ as an adsorption gas.
The interlayer distance of the 002 plane derived from the laminated structure of carbon of the carrier was determined from the value of 2θ of the peak corresponding to the 002 plane in X-ray diffraction analysis.
(Method 3) established a carrier 30mg only was supported Ru in a quartz reaction tube of the measuring method the inner diameter 10mm methanation temperature of the catalyst, while raising the temperature at a rate of 10 ° C. / min up to 900 ° C. with H ₂ gas stream Then, methane contained in the gas at the outlet of the reaction tube was analyzed by a mass spectrometer.

The results of measuring the catalyst activity of the ammonia synthesis of the catalysts of Examples 1 to 3 and the catalyst of Comparative Example 1 are shown in Table 1.

Examples 1 to 3 show 11 times to 17.5 times higher catalytic activity as compared with Comparative Example 1, and the catalyst of the present invention has an effect that the catalytic activity is largely improved as compared with the catalyst of the prior art. . Moreover, Examples 1 to 3 differ from Comparative Example 1 in that they show high catalytic activity at 350 ° C. lower than 400 ° C., and the catalyst of the present invention is higher at a lower temperature than the catalyst of the prior art. There is also an effect that catalytic activity can be obtained and energy consumption in ammonia synthesis can be reduced.

The interlayer distance, specific surface area and average pore diameter of the 002 plane derived from the layered structure of carbon in the X-ray diffraction analysis of the carrier used in Examples 1 to 3 and Comparative Example 1 are shown in Table 2.

From the physical properties of each support shown in Table 2, the difference in ammonia synthesis activity of each catalyst shown in Table 1 is considered as follows.
The interlayer distance of the 002 plane of mesoporous carbon prepared using MgO as a template approaches 0.3354 nm which is the theoretical value of the interlayer distance of graphite as the heat treatment temperature in an inert atmosphere increases, and the carbon crystal as the heat treatment temperature increases. Sex is improving. As the crystallinity of carbon improves, the number of delocalized π electrons in the support increases and the number of electrons donated from the support to the ruthenium catalyst increases, so the amount of ammonia produced per unit surface area of the support is It is considered to increase. On the other hand, although the specific surface area of mesoporous carbon produced using MgO as a template decreases as the heat treatment temperature in the inert atmosphere increases, it can maintain a relatively high value of 280 m ² / g at 2100 ° C. On the other hand, the average pore diameter can maintain a relatively large value of 14 nm before heat treatment. It is considered that, due to the combined effects, high ammonia synthesis catalytic activity was obtained at a heat treatment temperature in the range of 1500 to 2100 ° C.
On the other hand, since activated carbon has an interlayer distance of 0.382 nm and the crystallinity of carbon is very low, the number of electrons donated from the support to the ruthenium catalyst is extremely small, and although the specific surface area is large, the average pore diameter It is considered that the catalytic activity of ammonia synthesis is low due to the fact that the micropores are smaller.

Next, the state of methane formation when Ru / MPC (1800) and Ru / AC obtained in the process of catalyst preparation of Example 2 of the present invention and Comparative Example 1 were heated to 900 ° C. in a hydrogen stream, It is shown in FIG. The solid line shows the catalyst of the present invention, and the broken line shows a catalyst with activated carbon as a carrier.
Ru / AC in which ruthenium is supported on activated carbon, which is used as a carrier in the catalyst of the prior art, starts to produce methane from around 300 ° C. and produces a very large peak around 625 ° C. Ru / MPC (1800) in which ruthenium is supported on a support obtained by heat-treating, in an inert atmosphere, mesoporous carbon prepared using MgO used as a support as a template in advance in a inert atmosphere, produces very slight methanation from around 550 ° C Is only observed. That is, the catalyst according to the present invention is extremely excellent in heat resistance as compared with the catalyst of the prior art.

In addition, mesoporous carbon produced using MgO as a template for the catalyst of the present invention as a template does not require the use of a strong acid such as hydrofluoric acid at the time of production, and only by heat treatment once in advance in an inert atmosphere It is a support material suitable for industrial mass production of catalysts, as compared to supports used in prior art catalysts, in that it can be a support from which highly active catalysts can be obtained.

In Examples 1 to 4, an example was shown using cesium which is an alkali metal as a co-catalyst. Examples 5 to 8 below show cases where barium, which is an alkaline earth metal, is used as a co-catalyst.

(Example 5)
MgO-based mesoporous carbon (Toyo Carbon Co., Ltd., C Novel P (3) 010, BET specific surface area 1600 m ² / g, average pore diameter 10 nm) is heat-treated at 1500 ° C. for 1 hour in high purity nitrogen gas atmosphere And obtained MPC (1500). The interlayer distance of the 002 plane derived from the laminated structure of carbon by X-ray diffraction analysis of MPC (1500) was 0.368 nm, the specific surface area was 1200 m ² / g, and the average pore diameter was 10 nm.
A ruthenium solution is prepared by diluting a nitrosyl ruthenium (III) nitrate solution (Wako Pure Chemical Industries, Ltd.) to a predetermined concentration. Separately, a predetermined amount of barium nitrate (Wako Pure Chemical Industries, Ltd.) is dissolved in water to prepare a barium solution.
Take 1 g of MPC (1500) and add to 100 mL of ruthenium solution and impregnate with stirring for 30 minutes. Subsequently, the solvent is removed using an evaporator and dried at 110 ° C. for 1 hour. Thereafter, heat treatment is performed at 400 ° C. for 1 hour in an inert atmosphere to obtain Ru / MPC (1500) which is ruthenium-supported mesoporous carbon.
Next, 1 g of Ru / MPC (1500) is collected, added to 100 mL of barium solution, and impregnated while stirring for 30 minutes. Subsequently, the solvent is removed using an evaporator and dried at 110 ° C. for 1 hour. Thereafter, the catalyst was heat-treated at 450 ° C. for 10 hours in a hydrogen stream to prepare ruthenium, a barium-supported mesoporous carbon catalyst 10Ru-1.8Ba / MPC (1500). The amount of Ru supported was 10 wt%, and the Ba / Ru ratio was 1.8.

(Example 6)
The same mesoporous carbon as in Example 5 was heat-treated at 1800 ° C. for 1 hour in an inert atmosphere to obtain MPC (1800). The interlayer distance of MPC (1800) was 0.355 nm, the specific surface area was 900 m ² / g, and the average pore diameter was 11 nm. Except for this, the same operation as in Example 5 was performed to prepare Ru / MPC (1800) and 10Ru-1.8Ba / MPC (1800). The amount of Ru supported was 10 wt%, and the Ba / Ru ratio was 1.8.

(Example 7)
The same mesoporous carbon as in Example 5 was heat-treated at 2100 ° C. for 1 hour in an inert atmosphere to obtain MPC (2100). The interlayer distance of MPC (2100) was 0.340 nm, the specific surface area was 280 m ² / g, and the average pore diameter was 14 nm. The same operation as in Example 5 was carried out except for the above, to prepare 10Ru-1.8Ba / MPC (2100). The amount of Ru supported was 10 wt%, and the Ba / Ru ratio was 1.8.

(Comparative example 2)
Instead of mesoporous carbon, AC, which is obtained by treating activated carbon (Large Gas Chemicals Co., Ltd., HG15-119) in a hydrogen stream at 500 ° C. for 3 hours, is used. The interlayer distance of AC was 0.382 nm, the specific surface area was 1700 m ² / g, and the average pore diameter was 0.9 nm. Except for this, the same operation as in Example 1 was performed to prepare Ru / AC, 10Ru-1.8Ba / AC. The amount of Ru supported was 10 wt%, and the Ba / Ru ratio was 1.8.

(Example 8)
With respect to the catalysts of Examples 5 to 7 and the catalyst of Comparative Example 2 which is the prior art, the catalyst activity of ammonia synthesis of the catalyst was measured by the same catalyst activity measuring method as used in Example 4.
The results are shown in Table 3.

Examples 5 to 7 show 1.2 to 2.0 times higher catalytic activity as compared to Comparative Example 2, and the catalyst of the present invention has an effect that the catalytic activity is largely improved as compared with the catalyst of the prior art. . Further, Examples 5 to 7 are different from Comparative Example 2 showing substantially the same catalytic activity at either temperature, in that they show high catalytic activity at 380 ° C. lower than 400 ° C. Compared with the prior art catalysts, high catalytic activity can be obtained at lower temperatures, and also has the effect of being able to reduce energy consumption in ammonia synthesis.
As described above, also in the case of using an alkaline earth metal as the cocatalyst, the same excellent effect as in the case of using an alkali metal as the cocatalyst is obtained.

As described above, the present invention provides a ruthenium catalyst for ammonia synthesis, which has improved ammonia synthesis activity and improved heat resistance using a carrier material suitable for industrial mass production. Value is extremely large.

Ammonia is a compound widely used in the chemical industry, such as being used as one of the raw material compounds in synthesis reactions of various compounds, and the present invention can be widely used in the field of the chemical industry.

Claims

An ammonia synthesis catalyst comprising a catalyst component and a promoter component supported on a carrier, wherein the catalyst component is ruthenium, the promoter component is an alkali metal or an alkaline earth metal, and the carrier is X-ray diffraction The interlayer distance of the 002 plane derived from the laminated structure of carbon by analysis is in the range of 0.339 nm to 0.375 nm, the specific surface area is in the range of 150 m 2 / g to 1400 m 2 / g, and the average pore diameter is 8 nm An ammonia synthesis catalyst characterized in that it is a carbon material in the range of not less than 20 nm.
The interlayer distance of the carrier is in the range of 0.340 nm to 0.368 nm, the specific surface area is in the range of 280 m 2 / g to 1200 m 2 / g, and the average pore diameter is in the range of 10 nm to 14 nm. The ammonia synthesis catalyst according to claim 1, characterized in that
The ammonia synthesis catalyst according to claim 1 or 2, wherein the supported amount of ruthenium is 1% or more and 15% or less in mass% with respect to the mass of the carrier.
The ammonia synthesis catalyst according to any one of claims 1 to 3, wherein the cocatalyst component is an alkali metal.
The ammonia synthesis catalyst according to claim 4, wherein the supported amount of alkali metal is 1.5 or more and 15 or less in molar ratio to ruthenium.
The ammonia synthesis catalyst according to claim 4 or 5, wherein the alkali metal is at least one selected from the group consisting of sodium, potassium, rubidium and cesium.
The substance amount of ammonia generated per unit time of the reaction per unit mass of the catalyst is 3.4 mmol · g -1 · h -1 or more, The method according to any one of claims 4 to 6, Ammonia synthesis catalyst as described.
The ammonia synthesis catalyst according to any one of claims 1 to 3, wherein the cocatalyst component is an alkaline earth metal.
The ammonia synthesis catalyst according to claim 8, wherein the supported amount of the alkaline earth metal is 0.5 or more and 10 or less in molar ratio to ruthenium.
The ammonia synthesis catalyst according to claim 8 or 9, wherein the alkaline earth metal is at least one selected from the group consisting of calcium, strontium and barium.
11. The method according to any one of claims 8 to 10, wherein the amount of ammonia produced per unit time of reaction per unit mass of the catalyst is 5.7 mmol · g −1 · h −1 or more. Ammonia synthesis catalyst as described.
The support is prepared by heat-treating mesoporous carbon prepared using MgO as a template at a temperature of 1200 ° C. or more and 2500 ° C. or less in an inert atmosphere, and supporting this with ruthenium and an alkali metal or alkaline earth metal The method for producing an ammonia synthesis catalyst according to any one of claims 1 to 11, characterized in that
The heat treatment temperature is in the range of 1500 ° C. to 2100 ° C., the interlayer distance of the carrier is in the range of 0.340 nm to 0.368 nm, and the specific surface area is in the range of 280 m 2 / g to 1200 m 2 / g. The method for producing an ammonia synthesis catalyst according to claim 12, wherein the average pore diameter is in the range of 10 nm to 14 nm.