JPH0761449B2 - Molybdenum sulfide catalyst for carbon dioxide reduction - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon dioxide reducing catalyst for reducing carbon dioxide to convert it into carbon monoxide and using it as a raw material or fuel for chemical products.

[0002]

2. Description of the Related Art In recent years, environmental pollution on a global scale has been widely highlighted as a problem that threatens the survival of humankind. Among them, the most difficult problem to address is global warming due to carbon dioxide. Unlike nitrogen oxides and sulfur oxides, which have been problematic so far, carbon dioxide is not toxic in itself, but it emits a huge amount of about 20 billion tons per year worldwide, and it is released into the atmosphere. With the increase of carbon dioxide concentration in the environment, climate change due to greenhouse effect will occur, and it is threatened that tens of millions of environmental refugees will occur. In order to prevent this, the suppression of carbon dioxide emissions through energy substitution and energy saving is being promoted as a policy, but since carbon dioxide emissions are closely related to economic and social development, the Suppression is an extremely difficult situation. Therefore, in order to prevent the global warming caused by carbon dioxide, the development of carbon dioxide reduction / immobilization technology is indispensable.

The carbon dioxide reduction / immobilization method by catalytic hydrogenation reaction in which carbon dioxide gas is reacted with hydrogen for reduction is compared with photochemical reaction method, electrochemical reaction method, polymer synthesis method, organic synthesis method and the like. The ability to reduce and immobilize carbon dioxide per unit time and unit area is large, and a large amount of carbon dioxide can be processed. In addition, existing Fischer-Tropsch hydrocarbon synthesis technology can be applied, and since it is a gas phase reaction, it also has the advantage of easy separation of products. Until now, a method using a noble metal catalyst such as ruthenium or rhodium has been studied as a reduction / immobilization method of carbon dioxide gas by a catalytic hydrogenation reaction (for example, F. Solymosi
and A. Erdohelyi, J. Mol. Catal., Vol.8, 471 (198
0)).

However, in this method, 1) the catalyst used is expensive, and it is easily poisoned by sulfur compounds such as hydrogen sulfide and sulfurous acid gas, and the catalytic activity is drastically reduced.
2) Carbon dioxide gas is reduced to methane in this reaction, but since this reaction is an exothermic reaction in which the energy of the product is lower than that of the raw material, the energy yield is poor. 3) The reaction does not proceed well unless the pressure is high. 4) Generally, the reaction is carried out at a high temperature, and since fossil fuel is used for obtaining the temperature, there is a drawback that carbon dioxide emission is not substantially suppressed.

On the other hand, molybdenum sulfide is widely distributed in the crust as molybdenite, and is an inexpensive and low-toxic substance commercially available as a lubricant or the like. Molybdenum sulfide catalysts are used as hydrodesulfurization catalysts and carbon monoxide methanation catalysts, but they do not require expensive precious metals and are not poisoned by sulfur compounds such as hydrogen sulfide or sulfurous acid gas, which makes them durable. It has the characteristic that However, almost no research has been conducted so far using molybdenum sulfide catalysts for carbon dioxide reduction, and it was reported that molybdenum sulfide has low activity for carbon dioxide reduction (M.Saito and RB). Anderson, J. Catal.,
Vol. 67, 296 (1981)).

[0006]

In view of the above points, the present invention addresses the global warming problem caused by carbon dioxide gas, is not poisoned by sulfur compounds, is durable, economical, and has low temperature and normal temperature. An object of the present invention is to provide a molybdenum sulfide catalyst for reducing carbon dioxide, which can selectively reduce carbon dioxide to carbon monoxide under mild conditions such as pressure.

[0007]

The catalyst for carbon dioxide reduction of the present invention is a molybdenum sulfide catalyst characterized by adding nickel or cobalt to molybdenum sulfide, or a sulfide characterized by supporting it on a carrier. It is a molybdenum catalyst. The catalyst of the present invention reacts carbon dioxide gas with hydrogen gas to efficiently reduce carbon monoxide.

As a result of intensive studies to achieve the above object, the present inventors have found that molybdenum sulfide alone has a low activity for reducing carbon dioxide, but when molybdenum sulfide is added with nickel or cobalt, the activity for reducing carbon dioxide is reduced. It was found that the activity was significantly improved, and by further supporting it on a carrier, the activity was dramatically improved.

The carrier used in the present invention includes alumina, silica, activated carbon, zeolite, activated clay, iron oxide,
Examples thereof include zirconia, titania, ferrite, yttria, thoria, lanthania, neodymia and mixtures thereof. It is preferable that these carriers have a large surface area such as porous and fine particles. Further, the alumina is most preferably γ-alumina.

The catalyst for reducing carbon dioxide of the present invention is an ammonium tetrathiomolybdate aqueous ammonia solution obtained by saturating an aqueous solution of ammonium molybdate with hydrogen sulfide or ammonium sulfide, or its acidity with nitric acid, hydrochloric acid, sulfuric acid or the like. Add nickel salt or cobalt salt to the solution, or add porous or fine particles,
It is prepared by adding a carrier such as a sol with stirring, drying it, and then heating it at a temperature of 400 to 700 ° C. in a stream of hydrogen, nitrogen, or an inert gas such as argon or helium. In addition, molybdenum sulfide such as molybdenum disulfide or molybdenum trisulfide or molybdenum sulfide supported on a carrier is heated at 400 ° C. to 70 ° C. in a stream of hydrogen, nitrogen, or an inert gas such as argon or helium.
It is also prepared by heating at a temperature of 0 ° C., adding to a nickel salt solution or a cobalt salt solution and drying. Further, it is also prepared by adding nickel or cobalt to molybdenum sulfide or molybdenum sulfide supported on a carrier and heating. The heating temperature at that time is preferably 600 ° C to 900 ° C.

The molybdenum sulfide supported on the carrier is added to an aqueous solution of ammonium molybdate while stirring the carrier in a state of porous, fine particles or sol, and saturated with hydrogen sulfide or ammonium sulfide, and then hydrochloric acid or sulfuric acid. Neutralized with acid, filtered, and filtered under nitrogen or an inert gas atmosphere 1
It is obtained by heating and drying at 00 to 150 ° C. overnight. In addition, a carrier in the form of porous particles, fine particles, or sol is added to an ammonium sulfide solution of ammonium molybdate solution or an aqueous ammonia solution while stirring and dried, and then heated in an oxygen stream, and then hydrogen sulfide or hydrogen and hydrogen sulfide. It can also be obtained by heating to 350 to 600 ° C. in a mixed gas stream.

The content of nickel and cobalt in the carbon dioxide reduction catalyst of the present invention is Ni / Mo or Co /
The Mo molar ratio is preferably 0.0001 to 2. When the contents of nickel and cobalt in the catalyst are higher than that, the surface area of the catalyst becomes small and the catalytic activity decreases. The amount of the catalyst of the present invention supported on the carrier is preferably 0.001 to 35% by weight.

By passing a gas containing carbon dioxide and hydrogen through the catalyst of the present invention thus obtained, carbon dioxide reacts with hydrogen on the catalyst and is converted into carbon monoxide with a selectivity of about 100%. It At this time, the reaction gas may contain an inert gas such as argon or helium, a nitrogen gas, or hydrogen sulfide. Even if an inert gas or nitrogen is contained, the reaction is hardly affected, and when hydrogen sulfide is contained, the catalytic activity is improved. Further, the molar ratio of carbon dioxide gas / hydrogen in the reaction gas is preferably close to 1. Carbon monoxide, which is a reaction product, can be used as a fuel as it is, and recently, using the existing methanol production process from synthesis gas (carbon monoxide and hydrogen) and C1 chemical technology, it has recently been used as a fuel for automobiles. It can also be used by converting it into the raw material for methanol and chemical products that are being bathed. Since the reaction for converting carbon dioxide gas into carbon monoxide is an endothermic reaction, the energy yield is good, and carbon monoxide as a product has stored heat from a heat source such as solar energy or waste heat.

[0014]

EXAMPLES Among the examples of the present invention, particularly representative ones are shown below.

Example 1 Nickel nitrate hexahydrate (40 mol% with respect to ammonium tetrathiomolybdate) in an aqueous ammonia solution of ammonium tetrathiomolybdate and fine powder of titania as a carrier (with respect to ammonium tetrathiomolybdate) (400% by weight) was added with stirring, and the mixture was vacuum dried at room temperature and then heated in a hydrogen stream at 450 ° C. for 1 hour. 500 mg of the obtained catalyst (Ni / Mo molar ratio = 0.4) was filled in a quartz U-shaped reaction tube having a diameter of 1 cm, and a mixed gas of carbon dioxide gas and hydrogen 1: 1 was passed at a flow rate of 20 ml / min. The reaction product was analyzed by using a gas chromatograph. As a result, at 200 ℃ 1.8%, 300
8.5% at ℃, 19.5% at 400 ℃, 30 at 500 ℃
% Carbon dioxide was converted to carbon monoxide. No reaction products other than carbon monoxide were found.

Comparative Example 1 500 mg of commercially available molybdenum disulfide (MoS2) was charged into a quartz U-shaped reaction tube having a diameter of 1 cm, and a mixed gas of carbon dioxide gas and hydrogen 1: 1 was added in an amount of 20 ml / in the same manner as in Example 1. m
The reaction product was analyzed by using a gas chromatograph. As a result, the conversion rate of carbon dioxide gas to carbon monoxide was 0% at 200 ° C and 30%.
It was 0% at 0 ° C, 0.3% at 400 ° C, and 4% at 500 ° C.

Example 2 Cobalt nitrate hexahydrate (60 mol% with respect to ammonium tetrathiomolybdate) in an aqueous ammonia solution of ammonium tetrathiomolybdate and γ-alumina fine powder (as ammonium tetrathiomolybdate) as a carrier. 600% by weight) was added with stirring, dried in vacuum at room temperature, and then heated in a hydrogen stream at 500 ° C. for 1 hour.
The obtained catalyst (Co / Mo molar ratio = 0.6) 500 m
g in the same manner as in Example 1, carbon dioxide and hydrogen 1:
The mixed gas of 1 was circulated at a flow rate of 20 ml / min to cause reaction, and the reaction product was analyzed using a gas chromatograph. As a result, 1.3% at 200 ° C and 7% at 300 ° C
%, 18% at 400 ° C. and 28% at 500 ° C. were converted to carbon monoxide. No reaction products other than carbon monoxide were found.

Example 3 Nickel nitrate hexahydrate (70 mol% with respect to ammonium tetrathiomolybdate) in an aqueous ammonia solution of ammonium tetrathiomolybdate and silica fine powder as a carrier (with respect to ammonium tetrathiomolybdate) (800% by weight) was added with stirring, dried in vacuum at room temperature, and then heated in a hydrogen stream at 500 ° C. for 50 minutes. Obtained catalyst (Ni / Mo molar ratio = 0.70) 500 mg
In the same manner as in Example 1 using carbon dioxide gas and hydrogen 1: 1
The mixed gas of was flowed at a flow rate of 20 ml / min to cause reaction, and the reaction product was analyzed using a gas chromatograph. As a result, 0.9% at 200 ° C, 5% at 300 ° C,
Carbon dioxide gas of 13% at 400 ° C. and 21% at 500 ° C. was converted into carbon monoxide. No reaction products other than carbon monoxide were found.

Example 4 Cobalt nitrate hexahydrate (100 mol% based on ammonium tetrathiomolybdate) in an aqueous ammonia solution of ammonium tetrathiomolybdate and fine powder of zirconia as a carrier (based on ammonium tetrathiomolybdate) (700 wt%) was added with stirring, and the mixture was vacuum dried at room temperature and then heated at 450 ° C. for 1 hour in a hydrogen stream.
Obtained catalyst (Co / Mo molar ratio = 1.0) 300 m
In the same manner as in Example 1 , using 1 g, a mixed gas of carbon dioxide gas and hydrogen at a flow rate of 20 ml / min was caused to flow and reacted, and the reaction product was analyzed using a gas chromatograph. As a result, 1.2% at 200 ° C., 6.8% at 300 ° C., 16% at 400 ° C. and 25% at 500 ° C. were converted into carbon monoxide.

Example 5 Molybdenum trisulfide was heated in an argon gas stream at 520 ° C. for 55 minutes. 1 g of the solution was added to 5 ml of a 10% aqueous solution of nickel nitrate hexahydrate and dried in a nitrogen stream with stirring overnight. Obtained catalyst (molar ratio of Ni / Mo
= 0.28) Using 300 mg, a mixed gas of carbon dioxide gas and hydrogen 1: 1 was added at 20 ml / min in the same manner as in Example 1.
The reaction product was analyzed by using a gas chromatograph. As a result, at 200.degree.
7%, 4.6% at 300 ° C, 12% at 400 ° C, 500
At 0 ° C., 20% of carbon dioxide was converted into carbon monoxide.

Example 6 Ammonium tetrathiomolybdate was added in a hydrogen stream,
Heated at 550 ° C. for 45 minutes. 1 g of the solution was added to 4 ml of a 20% aqueous solution of cobalt nitrate hexahydrate, and dried with stirring in a nitrogen stream overnight. Obtained catalyst (Co / M
Molar ratio of o = 0.44) Using 300 mg, Example 1
20 m of mixed gas of carbon dioxide gas and hydrogen 1: 1 in the same manner as
It was circulated at a flow rate of 1 / min for reaction, and the reaction product was analyzed using a gas chromatograph. As a result, 20
0.5% at 0 ° C, 4.2% at 300 ° C, 10% at 400 ° C
%, 18% of carbon dioxide at 500 ° C. had been converted to carbon monoxide.

Example 7 Molybdenum trisulfide supported on 80% by weight of activated carbon of molybdenum trisulfide was heated at 400 ° C. for 1 hour and 20 minutes in an argon stream. 1 g thereof was added to 7 ml of a 10% aqueous solution of cobalt nitrate hexahydrate, and the mixture was dried with stirring in a nitrogen stream overnight. Obtained catalyst (molar ratio of Co / Mo
= 0.71) 300 mg was used, and a mixed gas of carbon dioxide gas and hydrogen 1: 1 was added at 20 ml / min in the same manner as in Example 1.
The reaction product was analyzed by using a gas chromatograph. As a result, at 200.degree.
6%, 5.5% at 300 ° C, 14% at 400 ° C, 500
23% of carbon dioxide gas was converted into carbon monoxide at 0 ° C.

Example 8 Molybdenum trisulfide supported on iron trioxide (75 mol% of molybdenum trisulfide) in a helium gas stream at 550 ° C.
Heated at half an hour. 1 g of the solution was added to 4 ml of a 20% aqueous solution of nickel nitrate hexahydrate and dried in a nitrogen stream with stirring overnight. Obtained catalyst (mol of Ni / Mo
Ratio = 2.0) Using 300 mg, as in Example 1, mixed gas of carbon dioxide gas, hydrogen and argon of 4: 4: 1 was added.
The reaction product was circulated at a flow rate of 0 ml / min for reaction, and the reaction product was analyzed using a gas chromatograph. as a result,
2.2% at 200 ° C., 8.8% at 300 ° C., 19.8% at 400 ° C., and 31% at 500 ° C. were converted into carbon monoxide.

Example 9 Nickel nitrate hexahydrate (110 mol% with respect to ammonium tetrathiomolybdate) in a nitric acid aqueous solution of ammonium tetrathiomolybdate and zeolite fine powder as a carrier (with respect to ammonium tetrathiomolybdate) (300% by weight) was added with stirring, and vacuum drying was performed at room temperature, followed by heating in a nitrogen stream at 500 ° C. for 1 hour. Using 500 mg of the obtained catalyst (Ni / Mo molar ratio = 1.1) , carbon dioxide gas, hydrogen, and nitrogen were prepared in the same manner as in Example 1:
A 1: 1 mixed gas was passed at a flow rate of 30 ml / min to cause a reaction, and the reaction product was analyzed using a gas chromatograph. As a result, 1% at 200 ° C and 6% at 300 ° C
%, 15% at 400 ° C. and 24% at 500 ° C. were converted into carbon monoxide.

Example 10 In an aqueous solution of ammonium tetrathiomolybdate, cobalt nitrate hexahydrate (60 mol% with respect to ammonium tetrathiomolybdate) and neodymia fine powder as a carrier (750 with respect to ammonium tetrathiomolybdate)
(% By weight) was added with stirring, dried and then heated at 500 ° C. in a hydrogen-hydrogen sulfide stream. The resulting catalyst (Co
/ Mo molar ratio = 0.6) Using 500 mg, a mixed gas of carbon dioxide gas, hydrogen and argon 2: 2: 1 was circulated at a flow rate of 30 ml / min for reaction in the same manner as in Example 1 to react. The product was analyzed by gas chromatography.
As a result, 0.8% at 200 ° C, 5% at 300 ° C, 40%
Carbon dioxide gas of 13% at 0 ° C and 22% at 500 ° C was converted into carbon monoxide.

Example 11 Nickel nitrate hexahydrate (110 mol% relative to ammonium tetrathiomolybdate) in an aqueous solution of ammonium tetrathiomolybdate and ferrite fine powder (80 relative to ammonium tetrathiomolybdate) as a carrier.
(0% by weight) was added with stirring, vacuum-dried at room temperature, and then heated at 550 ° C. for 45 minutes in a nitrogen stream. Using 500 mg of the obtained catalyst (molar ratio of Ni / Mo = 1.1) , carbon dioxide gas, hydrogen, and nitrogen in the same manner as in Example 1:
A mixed gas of 2: 1 was caused to flow at a flow rate of 30 ml / min for reaction, and the reaction product was analyzed using a gas chromatograph. As a result, carbon dioxide of 1.7% at 200 ° C., 6.5% at 300 ° C., 17% at 400 ° C. and 26.5 at 500 ° C. was converted into carbon monoxide.

Example 12 Molybdenum trisulfide supported on thoria of 90% by weight of molybdenum trisulfide was heated in a hydrogen stream at 430 ° C. for 1 hour and 20 minutes. 1g of it is 10% of nickel nitrate hexahydrate
The solution was added to 8 ml of the aqueous solution, and dried with stirring in a nitrogen stream overnight. Obtained catalyst (molar ratio of Ni / Mo = 0.
87) Using 500 mg, a mixed gas of carbon dioxide gas, hydrogen and nitrogen 3: 3: 1 was added at 30 ml / m in the same manner as in Example 1.
The reaction product was analyzed by using a gas chromatograph by circulating the reaction product at a flow rate of in. As a result, 1.1% at 200 ° C., 6.5% at 300 ° C., 17.5 at 400 ° C.
%, 28% of carbon dioxide at 500 ° C. had been converted to carbon monoxide.

Example 13 Cobalt nitrate hexahydrate (100 mol% relative to ammonium tetrathiomolybdate) in an aqueous ammonia solution of ammonium tetrathiomolybdate and activated clay (70 relative to ammonium tetrathiomolybdate) as a carrier.
(0% by weight) was added with stirring, dried in vacuum at room temperature, and then heated at 470 ° C. for 50 minutes in a mixed gas stream of hydrogen and argon. The resulting catalyst (Co / Mo molar ratio = 1.
0) Using 1 g, a mixed gas of carbon dioxide gas, hydrogen and helium 2: 2: 1 was caused to flow at a flow rate of 20 ml / min for reaction in the same manner as in Example 1, and the reaction product was analyzed using a gas chromatograph. did. As a result, 0.4 at 200 ℃
%, 3.9% at 300 ° C, 9.5% at 400 ° C, 500
At 6.5 ° C., 16.5% of carbon dioxide had been converted to carbon monoxide.

Example 14 Nickel nitrate hexahydrate (60 mol% with respect to ammonium tetrathiomolybdate) was added to an aqueous ammonia solution of ammonium tetrathiomolybdate, and yttria fine powder was used as a carrier (with respect to ammonium tetrathiomolybdate). (600% by weight) was added with stirring, dried in vacuum at room temperature, and then heated in a hydrogen stream at 500 ° C. for 50 minutes.
Obtained catalyst (Ni / Mo molar ratio = 0.6) 500 m
g in the same manner as in Example 1, carbon dioxide and hydrogen 1:
The mixed gas of No. 1 was circulated at a flow rate of 30 ml / min to cause reaction, and the reaction product was analyzed using a gas chromatograph. As a result, 1.0% at 200 ° C and 5.% at 300 ° C.
2%, 13.5% at 400 ° C., and 22.5% at 500 ° C. were converted to carbon monoxide.

Example 15 Molybdenum trisulfide supported on lanthanum at 85% by weight of molybdenum trisulfide was heated at 550 ° C. for 45 minutes in a mixed gas stream of hydrogen sulfide and hydrogen at a ratio of 1: 1. Add 1 g of it to 4 ml of 20% aqueous solution of nickel nitrate hexahydrate,
It was dried in a nitrogen stream with stirring overnight. The obtained catalyst
(Ni / Mo molar ratio = 0.82) Using 1.5 g,
While flowing a mixed gas of carbon dioxide gas and hydrogen at a flow rate of 1 ml / min at a flow rate of 1 ml / min, the sunlight was condensed by a Fresnel lens with a diameter of 1.5 m to irradiate and react with the obtained reaction product. Was analyzed using. As a result, about 6% of carbon dioxide was converted into carbon monoxide.

Example 16 To a fine powder of molybdenum disulfide, 18% by weight of nickel fine powder was added and mixed well, and the mixture was mixed in an argon stream at 800
Heat at 45 ° C. for 45 minutes. The resulting catalyst (Ni / Mo model)
(Ratio = 0.47) Using 1.5 g, while irradiating a mixed gas of carbon dioxide gas and hydrogen at a flow rate of 1 ml / min with a flow rate of 1 ml / min, irradiate sunlight collected by a Fresnel lens with a diameter of 1.5 m The reaction product obtained was analyzed using a gas chromatograph. As a result, about 4% of carbon dioxide was converted to carbon monoxide.

[0032]

As described above, the present invention is not poisoned by sulfur compounds, is durable and economical, and selectively reduces carbon dioxide to carbon monoxide under mild conditions of low temperature and atmospheric pressure. The present invention provides a molybdenum sulfide catalyst for reducing carbon dioxide gas. Molybdenum sulfide is commercially available as a lubricant, is an inexpensive and low-toxic substance, and has no problem in terms of resource supply. With the catalyst of the present invention, carbon dioxide gas undergoes a reverse water gas shift reaction and is selectively reduced to carbon monoxide, but since this reaction is a gas phase reaction, it is possible to treat a large amount of carbon dioxide gas and endothermic reaction. Therefore, the energy yield is good, and if solar heat or waste heat is used as a heat source, the product carbon monoxide will have stored those heats and can also be used as a heat pump. Further, carbon monoxide, which is a reaction product, can be used as a fuel as it is, or it can be used by converting it into a raw material for methanol or a chemical product, which is in the limelight as an automobile fuel, by using the existing C1 chemical technology. Therefore, it is very effective in terms of global environment conservation and energy measures.

Claims (3)

[Claims] 1. A molybdenum sulfide catalyst for reducing carbon dioxide, which is obtained by adding at least one of nickel and cobalt to molybdenum sulfide. 2. A carrier loaded on at least one carrier selected from alumina, silica, activated carbon, zeolite, activated clay, iron oxide, zirconia, titania, ferrite, yttria, thoria, lanthania and neodymia. The molybdenum sulfide catalyst according to claim 1, which is for reducing carbon dioxide. 3. Ni / Mo or Co / Mo in the catalyst
The molybdenum sulfide catalyst for carbon dioxide gas reduction according to claim 1 or 2, wherein the molar ratio is 0.0001 to 2.