CN113492010A - Carbon dioxide reduction catalyst - Google Patents

Carbon dioxide reduction catalyst Download PDF

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Publication number
CN113492010A
CN113492010A CN202110291141.3A CN202110291141A CN113492010A CN 113492010 A CN113492010 A CN 113492010A CN 202110291141 A CN202110291141 A CN 202110291141A CN 113492010 A CN113492010 A CN 113492010A
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Prior art keywords
carbon dioxide
reduction catalyst
catalyst
dioxide reduction
methanol
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Inventor
山本修身
増田翔平
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Honda Motor Co Ltd
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Honda Motor Co Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/76—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/83—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with rare earths or actinides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/46—Removing components of defined structure
    • B01D53/62—Carbon oxides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C29/00—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring
    • C07C29/15—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring by reduction of oxides of carbon exclusively
    • C07C29/151—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring by reduction of oxides of carbon exclusively with hydrogen or hydrogen-containing gases
    • C07C29/153—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring by reduction of oxides of carbon exclusively with hydrogen or hydrogen-containing gases characterised by the catalyst used
    • C07C29/154—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring by reduction of oxides of carbon exclusively with hydrogen or hydrogen-containing gases characterised by the catalyst used containing copper, silver, gold, or compounds thereof
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/105—General auxiliary catalysts, e.g. upstream or downstream of the main catalyst
    • F01N3/108—Auxiliary reduction catalysts
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/50—Carbon oxides
    • B01D2257/504—Carbon dioxide
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2258/00—Sources of waste gases
    • B01D2258/01—Engine exhaust gases
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/50—Improvements relating to the production of bulk chemicals

Abstract

The invention provides a carbon dioxide reduction catalyst which can reduce carbon dioxide contained in exhaust gas of an internal combustion engine according to hydrogenation reaction to generate methanol. A carbon dioxide reduction catalyst (10) for hydrogenating carbon dioxide contained in exhaust gas of an internal combustion engine to reduce the carbon dioxide and produce methanol, wherein the carbon dioxide reduction catalyst (10) comprises: a carrier 11 containing an oxygen occlusion and release material that occludes and releases oxygen; and a catalyst metal 12 supported by the carrier 11 and made of a transition metal.

Description

Carbon dioxide reduction catalyst
Technical Field
The present invention relates to a carbon dioxide reduction catalyst.
Background
The present applicant is advancing the development of the following technologies: on-board vehicles (automobiles), carbon dioxide contained in exhaust gas from an internal combustion engine is hydrogenated to produce methanol, and the produced methanol is used as a fuel for the internal combustion engine. Here, as a catalyst for synthesizing methanol from a mixed gas of carbon dioxide and hydrogen, for example, a catalyst composed of Cu, Zn, and alumina has been proposed (for example, see patent document 1).
[ Prior art documents ]
(patent document)
Patent document 1: japanese examined patent publication No. 45-16682
Disclosure of Invention
[ problems to be solved by the invention ]
However, the present applicant has found that when a methanol synthesis catalyst in which a catalytic metal such as Cu or Zn is supported on a carrier such as alumina or silica as in patent document 1 is applied to a hydrogenation reaction of carbon dioxide contained in an exhaust gas of an internal combustion engine, the catalytic metal such as Cu or Zn is oxidized by oxygen contained in the exhaust gas, and thus the catalytic activity is not sufficiently exhibited, methanol is not produced, and carbon monoxide is produced as a by-product.
The present invention has been made in view of the above circumstances, and an object thereof is to provide a carbon dioxide reduction catalyst capable of reducing carbon dioxide contained in an exhaust gas of an internal combustion engine by a hydrogenation reaction to produce methanol.
[ means for solving problems ]
(1) The present invention provides a carbon dioxide reduction catalyst (for example, a carbon dioxide reduction catalyst 10 described later) for hydrogenating carbon dioxide contained in an exhaust gas of an internal combustion engine (for example, an engine 1 described later) to reduce the carbon dioxide and generate methanol, the carbon dioxide reduction catalyst comprising: a carrier (for example, a carrier 11 described later) containing an oxygen occlusion and release material that occludes and releases oxygen; and a catalytic metal (for example, catalytic metal 12 described later) supported on the carrier and composed of a transition metal.
(2) In the carbon dioxide reducing catalyst of (1), the oxygen-occluding and releasing material may be an oxide containing Ce (cerium).
(3) In the carbon dioxide reducing catalyst of (1) or (2), the oxygen occlusion and release material may be CeO2。
(4) In the carbon dioxide reduction catalyst according to any one of (1) to (3), the number of moles of the oxygen occlusion and release material in the carbon dioxide reduction catalyst may be equal to or greater than the number of moles of the catalyst metal in the carbon dioxide reduction catalyst.
(5) In the carbon dioxide reduction catalyst according to any one of (1) to (4), the catalyst metal may be composed of at least one of Cu and Zn.
[ Effect of the invention ]
The carbon dioxide reduction catalyst of the present invention comprises an oxygen storage/release material to form a carrier, and the carrier carries a catalyst metal made of a transition metal such as Cu or Zn. Accordingly, the oxygen storage/release material stores oxygen in accordance with a change in valence due to oxygen contained in the exhaust gas of the internal combustion engine, and thus can suppress oxidation of the catalyst metal made of a transition metal such as Cu or Zn. Therefore, the metal state of the catalyst metal can be maintained, and therefore, the catalyst activity can be sufficiently exhibited, and the production of carbon monoxide as a by-product can be suppressed, and methanol can be efficiently produced. Therefore, according to the present invention, it is possible to provide a carbon dioxide reduction catalyst capable of reducing carbon dioxide contained in exhaust gas of an internal combustion engine by hydrogenation reaction to produce methanol. In addition, in the conventional catalyst, it is expected that the catalytic activity is deactivated by oxidation of the catalyst metal, and an excessive amount of the catalyst metal is required.
Drawings
Fig. 1 is a diagram showing a configuration of a vehicle on which a carbon cycle system according to an embodiment of the present invention is mounted.
Fig. 2A is a schematic diagram showing the structure of a conventional carbon dioxide reduction catalyst.
Fig. 2B is a schematic diagram showing the structure of the carbon dioxide reduction catalyst of the present embodiment.
FIG. 3 is a diagram showing CuO/CeO2A graph showing the relationship between the molar ratio and the diameter of the CuO crystallites.
Fig. 4 is a graph showing the hydrogen saturation adsorption amounts of the carbon dioxide reduction catalysts of example 1 and comparative example 1.
Fig. 5 is a graph showing the relationship between the pressure of the carbon dioxide reduction catalyst, the carbon dioxide conversion rate, and the methanol selectivity in example 1 and comparative example 1.
Fig. 6 is a graph showing the relationship between the pressure and the methanol production rate of the carbon dioxide reduction catalysts of example 1 and comparative example 1.
Detailed Description
Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
The carbon dioxide reduction catalyst of the present embodiment is a catalyst capable of hydrogenating carbon dioxide contained in exhaust gas of an internal combustion engine to reduce the carbon dioxide and produce methanol. Therefore, the carbon dioxide reduction catalyst of the present embodiment will be described below by taking an example of application to a vehicle equipped with a carbon cycle system that separates, recovers, and reuses carbon dioxide.
Fig. 1 is a diagram showing a configuration of a vehicle V on which a carbon cycle system S of the present embodiment is mounted. The vehicle V includes an internal combustion engine 1 (hereinafter, referred to as "engine") that converts thermal energy generated by burning liquid hydrocarbon fuel into mechanical energy, and travels by driving wheels (not shown) using the mechanical energy obtained by the engine 1.
The vehicle V includes: an engine 1; a fuel supply device 2 that supplies fuel to the engine 1; CO 22A recovery device 3 for recovering carbon dioxide (CO) from an exhaust gas flowing through an exhaust pipe 16 of the engine 12) (ii) a An exhaust gas purification device 4 that purifies exhaust gas flowing in the exhaust pipe 16; a reactor 5 consisting of CO2The carbon dioxide recovered by the recovery device 3 is converted into methanol (CH)3OH) synthesis gas; a hydrogen supply device 6 for supplying hydrogen (H) to the reactor 52) (ii) a And, a condenser 7 fromMethanol is recovered from the synthesis gas discharged from the reactor 5. Furthermore, from CO2The recovery device 3, the reactor 5, the hydrogen supply device 6, and the condenser 7 constitute a carbon cycle system S.
The engine 1 is, for example, a multi-cylinder reciprocating engine, and includes: a plurality of gas cylinders; a piston provided to be movable in a reciprocating manner in each cylinder; an ignition plug provided in a combustion chamber partitioned by a piston in each cylinder; and a crankshaft rotated according to the reciprocating motion of the piston. These ignition plugs are ignited in response to a command from a control device, not shown, and burn a mixture of fuel and air supplied to the respective air cylinders.
The intake pipe 15 is a pipe for connecting an intake port communicating with each cylinder of the engine 1 to the outside of the vehicle and guiding air outside the vehicle to each cylinder. The exhaust pipe 16 is a pipe connecting an exhaust port communicating with each cylinder of the engine 1 to the outside of the vehicle. An exhaust gas purification device 4 and CO are provided in the exhaust pipe 16 in this order from the exhaust upstream side to the downstream side2And a recovery device 3. Exhaust gas generated by combustion of a gas mixture in each cylinder of the engine 1 passes through the exhaust gas purifying device 4 and CO2The recovery device 3 is discharged to the outside of the vehicle.
The fuel supply device 2 includes: a fuel tank 20 that accumulates fuel; a fuel injection valve 21 provided in an intake port communicating with each cylinder of the engine 1; and a fuel supply pipe 24 connecting the fuel tank 20 and the fuel injection valve 21.
The fuel tank 20 stores liquid hydrocarbon fuel such as gasoline, methanol, or a mixed fuel obtained by mixing such gasoline and methanol. The fuel supply pipe 24 compresses the fuel stored in the fuel tank 20 by a high-pressure pump, not shown, and supplies the compressed fuel to the fuel injection valve 21. The fuel injection valve 21 is opened in response to a command from a control device, not shown, and injects fuel supplied from the fuel supply pipe 24. An air-fuel mixture in which the fuel injected from the fuel injection valve 21 is mixed with the air supplied from the intake pipe 15 is supplied to each cylinder of the engine 1.
The exhaust gas purification device 4 includes an exhaust gas purification catalyst (for example, a three-way catalyst), and purifies unburned Hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NOx), and the like contained in the exhaust gas of the engine 1 by the action of the exhaust gas purification catalyst.
CO2Recovery unit 3 passing CO2The pipe 31 is connected to the reactor 5. CO 22The recovery device 3 recovers carbon dioxide from the exhaust gas flowing through the exhaust pipe 16 and passes the carbon dioxide through CO2The pipe 31 is supplied to the reactor 5. More specifically, CO2The recovery device 3 separates the exhaust gas flowing through the exhaust pipe 16 into a recovery gas containing carbon dioxide as a main component and nitrogen (N)2) CO removal as a main component2Waste gas, to CO2Discharging from the pipe 31 to remove CO2The exhaust gas is discharged to the outside of the vehicle through a tail pipe not shown.
CO2The recovery apparatus 3 is based on the use of CO, for example2Adsorbing material to separate the exhaust gas of the engine 1 into a recovered gas and CO removal2Exhaust gas of the aforesaid CO2The adsorbent selectively adsorbs carbon dioxide in the exhaust gas flowing through the exhaust pipe 16 under a predetermined adsorption condition, and desorbs the adsorbed carbon dioxide under a predetermined desorption condition. With respect to CO2For the adsorbent, for example, a lithium composite oxide can be used.
CO of the present embodiment2The recovery unit 3 is not limited to the use of CO2The adsorption/desorption characteristics of the carbon dioxide by the adsorbent separate the exhaust gas of the engine 1 into a recovered gas and a desorbed CO2The case of exhaust gas. CO 22The recovery device 3 may have the following configuration: by using CO selectively permeating carbon dioxide in the exhaust gas flowing through the exhaust pipe 162A separation membrane, thereby separating the exhaust gas of the engine 1 into a recovered gas and CO removal2And (4) exhaust gas.
The hydrogen supply device 6 includes: high pressure H2A tank 61 that stores high-pressure hydrogen; h2A pipe 63 for introducing high pressure H2Tank 61 is connected to reactor 5; and, an adjuster 64 provided at H2And a pipe 63. The regulator 64 will deliver a high pressure H2The hydrogen stored in the tank 61 is depressurized to a predetermined pressure and then passed through the hydrogen tank via the hydrogen gas2The pipe 63 is supplied to the reactor 5.
Further, the hydrogen supply device of the present embodiment6 is not limited to high pressure H2The hydrogen stored in the tank 61 is supplied to the reactor 5. The hydrogen supply device 6 may be configured to supply hydrogen generated from water by the electrolysis device to the reactor 5, or may be configured to supply hydrogen generated from ammonia to the reactor 5.
Reactor 5 for the removal of CO from the reaction mixture2Carbon dioxide contained in the recovered gas supplied from the pipe 31 and the secondary gas H2The hydrogen supplied from the pipe 63 is hydrogenated at a predetermined ratio in the reaction cylinder, thereby reducing carbon dioxide and synthesizing methanol.
More specifically, the reactor 5 includes: a reaction cylinder introduced from CO2A recovery gas supplied from the pipe 31; h2An injector for injecting the secondary stream H into the reaction cylinder2Hydrogen supplied from the pipe 63; a carbon dioxide reduction catalyst provided in the reaction cylinder; a heating device for heating the gas in the reaction cylinder; a compression device for compressing the gas in the reaction cylinder; and a synthesis gas pipe 51 connecting the reaction tube and the condenser 7.
The heating device heats the gas in the reaction tube to a temperature required for the hydrogenation reaction of carbon dioxide by using waste heat of the engine 1, that is, a part of heat energy generated by burning fuel in the engine 1. The compression device compresses the gas in the reaction cylinder to a pressure required for the methanol synthesis reaction by using a part of mechanical energy obtained by burning fuel in the engine 1, more specifically, power of a crankshaft of the engine 1. Further, with respect to the detailed structure of the carbon dioxide reduction catalyst, it will be explained in detail hereinafter.
In the reactor 5 as described above, CO is introduced2The piping 31 introduces a predetermined amount of the recovered gas into the reaction cylinder, and hydrogen is measured from H so that the ratio of carbon dioxide to hydrogen in the reaction cylinder becomes a predetermined ratio2The injector is injected into the reaction cylinder, and then the gas in the reaction cylinder is heated and compressed by the heating device and the compression device. Thus, the hydrogenation reaction of carbon dioxide is carried out in the reaction tube by the action of the carbon dioxide reduction catalyst (see the following formula (1)), and methanol is produced. And at the same time, since the twoThe action of the carbon oxide reduction catalyst also causes a reverse water gas shift reaction (see the following formula (2)) and a hydrogenation reaction of carbon monoxide (see the following formula (3)), thereby producing a methanol-containing synthesis gas.
CO2+3H2→CH3OH+H2O (1)
CO2+H2→CO+H2O (2)
CO+2H2→CH3OH (3)
The synthesis gas generated in the reaction tube in the above-described procedure is supplied to the condenser 7 through the synthesis gas pipe 51. The synthesis gas discharged from the synthesis gas pipe 51 contains not only methanol produced by the methanol synthesis reaction but also unreacted carbon dioxide or CO2Nitrogen and the like in the recovery gas are mixed into the recovery apparatus 3 without being completely separated.
The condenser 7 recovers methanol from the synthesis gas supplied from the reactor 5 and supplies the recovered methanol to the fuel tank 20. More specifically, the condenser 7 condenses the synthesis gas discharged from the reactor 5 by heat exchange, separates the synthesis gas into a liquid phase containing methanol as a main component and a gas phase containing unreacted carbon dioxide and nitrogen as main components, discharges the liquid phase from a liquid phase port and discharges the gas phase from a gas phase port.
The liquid port of the condenser 7 is connected to the fuel tank 20 by a liquid pipe 71. Therefore, the liquid phase discharged from the liquid phase port of the condenser 7 is guided into the fuel tank 20 by the liquid phase pipe 71. The exhaust gas purifying device 4 and CO in the gas phase port of the condenser 7 and the exhaust pipe 162The recovery devices 3 are connected to each other by a gas-phase pipe 72. Therefore, the gas phase discharged from the gas phase port of the condenser 7 is guided to CO by the gas phase pipe 722And a recovery device 3.
The flow of carbon in the vehicle V having the carbon cycle system S as described above will be described. First, when a mixture of the hydrocarbon fuel stored in the fuel tank 20 and the air introduced from the intake pipe 15 is combusted in the engine 1, exhaust gas containing nitrogen, carbon dioxide, and water as main components is discharged from the engine 1. The carbon dioxide in the exhaust gas is composed of CO2The recovery device 3 recovers the reaction product and supplies the recovered product to the reactor 5. In the reactor 5, a synthesis gas containing methanol is produced by reacting carbon dioxide with hydrogen. The methanol in the synthesis gas is recovered by the condenser 7 and is accumulated as fuel in the fuel tank 20. Furthermore, unreacted carbon dioxide contained in the synthesis gas is again separated from CO2The recovery device 3 recovers the reaction product and supplies the recovered product to the reactor 5. In this way, the vehicle V having the carbon cycle system S mounted thereon introduces carbon dioxide from the outside air while introducing carbon into the fuel tank 20, the engine 1, and the CO2The recovery device 3, the reactor 5, and the condenser 7 are circulated, thereby reducing the amount of carbon dioxide discharged from the tail pipe to the outside of the vehicle.
Next, the structure of the carbon dioxide reduction catalyst of the present embodiment will be described in detail.
Here, fig. 2A is a schematic diagram showing the structure of a conventional carbon dioxide reduction catalyst. Fig. 2B is a schematic diagram showing the structure of the carbon dioxide reduction catalyst 10 of the present embodiment.
As shown in fig. 2A, for alumina (Al)2O3) Or silicon dioxide (SiO)2) In the conventional carbon dioxide reduction catalyst 10A in which the carrier 11A made of an oxide such as Cu or Zn carries the catalyst metal 12A made of a transition metal such as Zn, Cu or Zn constituting the catalyst metal 12A is oxidized by oxygen contained in the exhaust gas of the engine 1, and is changed to copper oxide (CuO) or zinc oxide (ZnO). That is, the catalytic metal 12A is in a state of an oxide which cannot exhibit catalytic activity without maintaining a metallic state, and as a result, methanol is not produced, and carbon monoxide is produced as a by-product.
In contrast, as shown in fig. 2B, the carbon dioxide reduction catalyst 10 of the present embodiment includes: a carrier 11 containing an oxygen occlusion and release material (OSC material) that occludes and releases oxygen; and a catalyst metal 12 supported by the carrier 11 and made of a transition metal.
The carrier 11 may contain an oxygen occlusion and release material, and may contain an oxide such as alumina or silica and an oxygen occlusion and release material in combination, but is preferably composed of only an oxygen occlusion and release material. As the oxygen occlusion and release material, it is preferable to use Ce-containing oxidationA compound (I) is provided. Specifically, except for CeO2In addition, a composite oxide of Ce and Zr (zirconium) may be mentioned. Among them, CeO is more preferably used2。
The catalyst metal 12 is made of a transition metal, and among them, a catalyst metal containing at least one of Cu and Zn is preferably used. More preferably, a catalyst metal containing Cu and Zn in a predetermined preferable ratio is used. The preferred molar ratio of Cu to Zn is 1: 1-2: 1, in the above range.
The carbon dioxide reduction catalyst 10 of the present embodiment having the above-described structure can be produced by a conventionally known production method. Specifically, for example, the carrier 11 containing the oxygen storage/release material is impregnated into a slurry containing the catalyst metal 12 made of a transition metal such as Cu or Zn, thereby impregnating the carrier 11 with the catalyst metal. Subsequently, the carbon dioxide reduction catalyst 10 is obtained by carrying the catalytic metal 12 on the carrier 11 by heating and drying.
In the carbon dioxide reduction catalyst 10 of the present embodiment having the above-described structure, CeO is present as shown in fig. 2B2The oxygen storage and release material stores oxygen in accordance with a change in valence due to oxygen contained in the exhaust gas of the engine 1. That is, since oxygen in the exhaust gas is introduced into the oxygen storage/release material, oxidation of the catalyst metal made of a transition metal such as Cu or Zn can be suppressed. Therefore, the metal state of the catalyst metal can be maintained, and therefore, the catalyst activity can be sufficiently exhibited, and the production of carbon monoxide as a by-product can be suppressed, whereby methanol can be efficiently produced. In addition, although it is expected that the catalytic activity of the conventional catalyst is deactivated by oxidation of the catalyst metal and an excessive amount of the catalyst metal is required, the amount of the catalyst metal used can be reduced by the carbon dioxide reduction catalyst 10 of the present embodiment.
Here, FIG. 3 shows CuO/CeO2A graph showing the relationship between the molar ratio and the diameter of the CuO crystallites. FIG. 3 shows the following results: for only the CeO as the oxygen occlusion and release material2The carrier constituted was changed in the supporting amount (molar ratio) to support only CuO, and each of the obtained catalysts was subjected to X-ray diffraction measurement to examine CuOThe diameter of the fine crystal of (1). In FIG. 3, the horizontal axis represents CuO/CeO2The vertical axis represents the CuO crystallite diameter.
As shown in FIG. 3, it is found that in CuO/CeO2Region B having a molar ratio of more than 1, i.e., CeO2In the region B where the number of moles of CuO is smaller than that of the CuO, the diameter of the CuO crystallites increases. The increase in the diameter of the CuO crystallites means that the CuO itself is agglomerated. Therefore, in this region B, CeO, which is an oxygen occlusion and release material, is not necessarily said2The effect of introducing oxygen from CuO is good.
In contrast, the above results show that in CuO/CeO2Region A having a molar ratio of 1 or less, i.e., CeO2In the region a where the number of moles of CuO is equal to or more than the number of moles of CuO, the CuO crystallite diameter does not change greatly. That the crystallite diameter of CuO does not vary greatly means that CeO2Oxygen is taken out from CuO and occluded, and thereby, the aggregation of CuO itself is suppressed. That is, in the region a, CeO, which is an oxygen occlusion and release material, may be referred to as2The effect of introducing oxygen from CuO is good.
Therefore, in the carbon dioxide reduction catalyst 10 of the present embodiment, the number of moles of the oxygen occlusion and release material in the carbon dioxide reduction catalyst 10 is preferably equal to or greater than the number of moles of the catalyst metal 12 in the carbon dioxide reduction catalyst 10. This more reliably produces the oxygen storage/release material CeO2The effect of the carbon dioxide reduction catalyst 10 of the present embodiment described above is more reliably obtained with respect to the effect of introducing oxygen. Further, the number of moles here means the total number of moles in the case of using a plurality of oxygen-occluding and releasing materials or the case of using a plurality of catalyst metals, respectively.
The present invention is not limited to the above-described embodiments, and variations and modifications within a range that can achieve the object of the present invention are included in the present invention.
[ examples ]
Next, examples of the present invention will be described, but the present invention is not limited to these examples.
[ example 1]
A rotary evaporator was used to make a slurry containing predetermined amounts of copper nitrate, zinc nitrate and CeO2Evaporating and concentrating the mixed solution of the powder and the ion exchange water,thereby making CeO2Impregnated with Cu and Zn. Next, after drying by heating at 200 ℃ for 2 hours, it was calcined at 500 ℃ for 2 hours, thereby obtaining CeO2A carbon dioxide reduction catalyst in which Cu and Zn are supported. The mass% of each component of the obtained carbon dioxide reduction catalyst was: 12% by mass of Cu, 6% by mass of Zn, and CeO2The content was 82 mass%. Namely, CeO2The number of moles of (C) is equal to or more than the total number of moles of Cu and Zn.
Comparative example 1
A rotary evaporator was used to make the solution contain predetermined amounts of copper nitrate, zinc nitrate and SiO2Evaporating and concentrating the mixed solution of the powder and the ion-exchanged water to thereby obtain SiO2Impregnated with Cu and Zn. Then, after heating and drying at 200 ℃ for 2 hours, it was calcined at 500 ℃ for 2 hours, thereby obtaining SiO2A carbon dioxide reduction catalyst in which Cu and Zn are supported. The mass% of each component of the obtained carbon dioxide reduction catalyst was: cu 12 mass%, Zn 6 mass%, SiO2The content was 82 mass%.
[ evaluation ]
The carbon dioxide reduction catalysts of example 1 and comparative example 1 were examined for the relationship between the hydrogen saturation adsorption amount and pressure, the carbon dioxide conversion rate and methanol selectivity, and the relationship between the pressure and methanol production rate. The results are shown in
Figure BDA0002981985880000091
(hydrogen saturation adsorption amount)
Using 100% H at 300 deg.C250mg of each catalyst obtained in example 1 and comparative example 1 was subjected to reduction treatment, and after cooling to 50 ℃, the temperature was measured at 50 ℃ and 100% H2Hydrogen saturation adsorption capacity of the catalyst under ambient conditions. The gas flow rate was set to 30 cc/min. The unit a.u (arbitrary unit) means a relative unit indicating the hydrogen saturation adsorption capacity of example 1 when the hydrogen saturation adsorption amount of comparative example 1 is 1.
(carbon dioxide conversion rate)
Using a fixed bed flow type reactor, 2cc of each catalyst obtained in example 1 and comparative example 1 was charged in the reactor. Next, carbon dioxide and hydrogen were passed through the reactor at 25NL/h and 75NL/h, respectively, and a catalytic reaction test was carried out at a temperature of 250 ℃ and a pressure of 2 MPa. Gas chromatographic analysis is carried out on the gas composition before and after the catalysis, and the carbon dioxide conversion rate is calculated according to the carbon dioxide concentration before and after the catalysis.
(methanol selectivity)
The methanol selectivity means how much of the converted carbon dioxide is converted into methanol, which is determined based on the carbon dioxide conversion rate. Here, it is considered that carbon monoxide is also generated as a product of the reaction between carbon dioxide and hydrogen in addition to methanol. Therefore, the methanol selectivity was calculated by measuring the methanol concentration after the catalytic reaction by gas chromatography.
(methanol formation Rate)
The methanol production rate is obtained by multiplying the carbon dioxide conversion rate by the methanol selectivity. That is, the methanol production rate was calculated from the following formula (4).
Methanol yield (carbon dioxide conversion rate x methanol selectivity) (4)
[ examination ]
Fig. 4 is a graph showing the hydrogen saturation adsorption amounts of the carbon dioxide reduction catalysts of example 1 and comparative example 1. As shown in fig. 4, it was found that the hydrogen saturation adsorption amount of the carbon dioxide reduction catalyst of example 1 is particularly larger than that of the carbon dioxide reduction catalyst of comparative example 1. It is considered that this means that the hydrogenation reaction of carbon dioxide proceeds efficiently in the carbon dioxide reduction catalyst of example 1.
Fig. 5 is a graph showing the relationship between the pressure of the carbon dioxide reduction catalyst, the carbon dioxide conversion rate, and the methanol selectivity in example 1 and comparative example 1. As is clear from fig. 5, it is found that the carbon dioxide reduction catalyst of example 1 is particularly high in methanol selectivity as compared with the carbon dioxide reduction catalyst of comparative example 1. It was also found that the methanol selectivity of the carbon dioxide reduction catalyst of example 1 was significantly improved by increasing the pressure. This is a characteristic feature that has not been found in the case of conventional carbon dioxide reduction catalysts.
Further, it was also found that the carbon dioxide conversion rate did not differ greatly between the carbon dioxide reduction catalyst of example 1 and the carbon dioxide reduction catalyst of comparative example 1, but only the carbon dioxide conversion rate of the carbon dioxide reduction catalyst of example 1 was improved by increasing the pressure. This is also a characteristic feature not seen in the case of the conventional carbon dioxide reduction catalyst.
Fig. 6 is a graph showing the relationship between the pressure and the methanol production rate of the carbon dioxide reduction catalysts of example 1 and comparative example 1. As is clear from fig. 6, the carbon dioxide reduction catalyst of example 1 has a higher methanol production rate than the carbon dioxide reduction catalyst of comparative example 1. In particular, it was found that the carbon dioxide reduction catalyst of example 1 has a particularly higher methanol production rate than the carbon dioxide reduction catalyst of comparative example 1 by increasing the pressure.
From the above results, it was confirmed that the carbon dioxide reduction catalyst of the present embodiment can reduce carbon dioxide contained in the exhaust gas of the engine 1 by hydrogenation reaction to produce methanol.
Further, the mechanism for increasing the methanol production rate by increasing the pressure may be as follows. That is, when the pressure is increased, the equilibrium of the reaction of the following formula (1) described above, which produces methanol from carbon dioxide and hydrogen, tends to shift to the side (right side) where methanol is produced.
CO2+3H2→CH3OH+H2O (1)
As shown in formula (1), the left side reactant side is 1+ 3-4 mol, while the right side product side is 1+ 1-2 mol. In this case, according to the Le Chatelier's principle, the partial pressure on the reactant side becomes high as the pressure becomes high, and thus the reaction is promoted to the product side of as little as 2 moles to stabilize. Therefore, the methanol production rate increases as the pressure is increased.
Reference numerals
10: carbon dioxide reduction catalyst
11: carrier
12: catalyst metal

Claims (5)

1. A carbon dioxide reduction catalyst for hydrogenating carbon dioxide contained in exhaust gas of an internal combustion engine to reduce the carbon dioxide and produce methanol, the carbon dioxide reduction catalyst comprising:
a carrier containing an oxygen occlusion and release material occluding and releasing oxygen; and a process for the preparation of a coating,
and a catalyst metal supported by the carrier and composed of a transition metal.
2. The carbon dioxide reducing catalyst according to claim 1, wherein the oxygen-occluding and releasing material is an oxide containing Ce.
3. The carbon dioxide reducing catalyst according to claim 1, wherein the oxygen occlusion and release material is CeO2。
4. The carbon dioxide reduction catalyst according to claim 1, wherein the number of moles of the oxygen occlusion and release material in the carbon dioxide reduction catalyst is equal to or greater than the number of moles of the catalyst metal in the carbon dioxide reduction catalyst.
5. The carbon dioxide reduction catalyst according to claim 1, wherein the catalyst metal is composed of at least one of Cu and Zn.
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