JP3482459B2 - Catalyst for producing hydrogen by partial oxidation of methanol and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a novel CuZn.
The present invention relates to an Al oxide catalyst, a method for producing the same, and a method for producing hydrogen by a partial oxidation reaction of methanol using the catalyst. More specifically, in the method for producing hydrogen by a partial oxidation reaction of methanol, CO A new CuZnAl oxide catalyst capable of producing hydrogen gas containing no or very little CO,
The present invention relates to a method for producing this catalyst from a hydrotalcite-like layered double hydroxide, and a method for producing hydrogen gas with high selectivity using this catalyst. The present invention relates to a novel CuZnAl oxide catalyst, a method for preparing this catalyst by thermal decomposition of hydrotalcite-like layered double hydroxide, and a method for producing hydrogen by partial oxidation reaction of methanol using this catalyst in the presence of air. I will provide a.

[0002]

2. Description of the Related Art With the fear of depletion of fossil fuels, today,
Hydrogen is drawing attention as a new energy source that can replace fossil fuels. Hydrogen serves as fuel for the fuel cell and is converted into electrical energy. In this case, the only waste after power generation is water, which is a clean energy source from the viewpoint of global warming countermeasures. In addition, it does not emit nitrogen oxides, sulfur oxides, hydrocarbons, etc., which have an impact on the environment, and is an environmentally friendly energy source. There are both large and large output fixed type fuel cells and small and lightweight mobile type fuel cells, but the latter type is the fuel cell that is being considered for use in automobiles and the like. The problem here is how to obtain hydrogen. One of the solutions is to obtain hydrogen from methanol by any of the following reactions using a catalyst. (1) Decomposition reaction of methanol CH ₃ OH ⇔ 2H ₂ + CO △ H = + 92.0kJ / mol (2) Steam reforming reaction of methanol CH ₃ OH + H ₂ O ⇔ 3H ₂ + CO ₂ △ H = +49.4 kJ / mol (3) Partial oxidation reaction of methanol CH ₃ OH + (1/2) O ₂ ⇔ 2H ₂ + CO ₂ △ H = −192.2 kJ / mol △ H: Heat of reaction

The hydrogen obtained by the above reaction is introduced into a fuel cell.
When entering and converting to electricity, CO traces in the gas (20p
pm) is included in the Pt electrode of a fuel cell.
The damage to the output and the output drops sharply
is there. Therefore, make sure that hydrogen gas does not contain CO.
And is desired. However, in the reaction of (1), along with hydrogen
A large amount of CO is generated, and the reaction of (2) is almost the same as that of (1).
Although not so much, 100 ppm or more of CO is produced. Well
Also, in the reaction of (3), several tens of ppm of CO was produced,
As it is, it cannot be used as fuel for fuel cells. hydrogen
Introduce water vapor to remove CO in the gas, water
Water-gas shift reaction
(WGSR) (4) or oxidation reaction (5) is carried out,
Along with that, the new equipment will increase in size and cost.
Another problem arises. The reaction formulas of (4) and (5) are
Shown below. (4) Water gas shift reaction of CO CO + H₂O ⇔ H₂  + CO₂ (5) CO oxidation reaction CO + (1/2) O₂  ⇔ CO₂

Therefore, the development of new catalysts is awaiting a hydrogen production method that does not generate CO. By the way, as a method for producing hydrogen by a partial oxidation reaction of methanol, there is a method using a CuOZnO catalyst (T. Hua
ng and S. Wang, Appl. Catal., Vol.24, (1986) p.287.
). This method has a Cu: Zn (wt%) ratio = 82: 1.
As a result of performing the test at 8 to 7:93, Cu: Zn = 4
The 0:60 catalyst showed the highest activity at the reaction temperature of 220 to 290 ° C. However, the activity deterioration of the catalyst occurred rapidly within 1 hour. Also, the CO concentration increased as the oxygen / methanol ratio increased.

Further, a method using a CuZn oxide or a CuZnAl oxide catalyst (L. Alejo, R. lago, MA Pena an
d JLG Fierro, Appl. Catal., Vol. 162 (1997) p.
281.) This CuZn-oxide catalyst is Cu: Z
n = 20: 80-40: 60 and CuZnAl oxide-catalyst is Cu: Zn: Al = 40: 55: 15. Here, the catalyst precursor: Zn ₅ (CO ₃ ) ₂ (O
H) ₆ , Cu ₂ (CO ₃ ) (OH) ₂ , Zn ₃ Cu ₂
After the mixture of (CO ₃ ) ₂ (OH) ₆ is heated, ZnO, Cu
O mixture. The reaction temperature is 200 to 230 ° C.,
The oxygen / methanol ratio is 0.06. Furthermore, a method using a Pd-supported ZnO catalyst (ML Cubeiro and JLG
Fierro, J. Catal., Vol.179 (1998) p.150.). The Pd concentration of this Pd-supported ZnO catalyst is 1 to 5 wt%
And the reaction temperature is 230-270 ° C. But,
This method uses a very high concentration (20-40 mol%) of C.
O is a byproduct. Thus, various methods for producing hydrogen by the partial oxidation reaction of methanol have been reported so far.
A hydrogen production method that does not generate O has a problem to be further improved, and its development is strongly required.

[0006]

Under these circumstances, the present inventors have aimed to develop a high-selectivity hydrogen production method by a partial oxidation reaction of methanol in view of the above-mentioned prior art. As a result of earnest research, (1) a method for preparing a CuZnAl oxide catalyst by producing a hydrotalcite-like layered double hydroxide by a coprecipitation method and heating it at about 450 ° C., (2) This CuZn
When a partial oxidation reaction of methanol was carried out using an Al oxide catalyst, hydrogen gas containing no CO at all or very little CO was successfully produced, and the present invention was completed. That is, the object of the present invention is to provide a novel CuZnAl oxide catalyst used for hydrogen production by a partial oxidation reaction of methanol. It is another object of the present invention to provide a method for producing hydrogen gas that does not generate CO, using this catalyst.

[0007]

[Means for Solving the Problems] To solve the above problems
The present invention comprises the following technical means. (1)As a starting material,Cu, Zn, AlEach nitrate
Of Cu, Zn, AlMixing each nitrate solution
objectToNaOH aqueous solution and NaCO₃Aqueous solutionpH is about 9
Add so that it becomes constant withA precipitate is formed,
Aging thisShi,filtrationrear,until pH is 7WashingShi
After, A layer of dried CuZnAl layered double hydroxide
A medium precursor is prepared and then pyrolyzed in an air atmosphere.
ShiProduction of hydrogen by partial oxidation of methanol
forCuZnAl oxide catalystUsing methanol to air
Conversion to hydrogen gas by partial oxidation reaction in the coexistence
Therefore, CO is not contained at all, or very little CO is contained.
Hydrogen gas characterized by producing hydrogen gas not containing
Manufacturing method. (2) The molecular ratio of Cu, Zn and Al in the starting solution is (Cu
+ Zn) / Al = 2 to 5, as described in (1) above.water
Elementary gasManufacturing method. (3)About 10 ℃ min from room temperature ^-1 Up to about 450 ℃
Hydrogen gas according to (1) above, which is maintained for about 5 hours after the temperature is raised.
Manufacturing method. (Four) Oxygen / methanol (molar ratio) is 0.20 to 0.5
0, the above (1) The method for producing hydrogen gas according to [4]. (5) The reaction temperature is 200 to 245 ° C., the above (1)
The method for producing hydrogen gas according to 1.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below. The novel catalyst of the present invention consists of CuZnAl oxide. This CuZnAl oxide catalyst is manufactured as follows. Starting materials include Cu, Zn, Al
Prepare each nitrate salt of. The mixture of the respective aqueous solutions of nitrates of Cu, Zn and Al is reacted with the aqueous solution of NaOH and the aqueous solution of NaCO ₃ to produce a precipitate by the coprecipitation method. In this case, while stirring the above-mentioned mixture, an aqueous solution of NaOH, an aqueous solution of NaCO ₃ or an aqueous solution of NaOH and N
A mixed solution of aCO ₃ aqueous solution is added little by little, and a precipitate is formed by a coprecipitation method. The NaOH aqueous solution and the NaCO ₃ aqueous solution may be added individually or simultaneously, and the addition method thereof is not particularly limited. C in the starting solution
The molecular ratio of u, Zn and Al is (Cu + Zn) / Al = 2
It is preferably 5.

Next, the precipitate is aged at, for example, about 65 ° C., filtered, washed with deionized water or the like until the pH of the filtrate becomes neutral, and dried to form CuZnAl.
A catalyst precursor composed of a layered double hydroxide (hydrotalcite-like layered double hydroxide) is prepared. Next, the catalyst precursor composed of this hydrotalcite-like layered double hydroxide is thermally decomposed in an air atmosphere, for example, at 450 ° C. to form CuZnAl.
Prepare the oxide. Preferable examples of the thermal decomposition method and conditions include a method in which the catalyst precursor is placed in an electric furnace, heated from room temperature to about 450 ° C. at about 10 ° C. min ^{−1 and} then held for about 5 hours. However, for these, the heating temperature and the heating time at which the catalyst precursor is thermally decomposed may be adopted,
There is no particular limitation. Next, in the method of the present invention, the CuZnAl oxide catalyst produced by the above method is used to generate hydrogen gas without generating CO by converting methanol into hydrogen gas by a partial oxidation reaction in the presence of air. . In this case, the oxygen / methanol (molar ratio) is preferably 0.20 to 0.50, and hydrogen gas is produced with a high CO ₂ selectivity in this range. The reaction temperature is 200 to 245 ° C, and more preferably 200 to 230.
℃.

[0010]

EXAMPLES Next, the present invention will be described more specifically by way of examples, but the present invention is not limited to the following examples. Example 1 In this example, a catalyst precursor / catalyst was prepared. 1) Method A mixture of Cu, Zn, and Al nitrate aqueous solutions (Cu, Z
Aqueous NaOH solution (concentration; concentration; n, Al mixed so that the molecular ratio is (Cu + Zn) / Al = 2-5)
2M), an aqueous solution of NaCO ₃ (concentration: about 0.3M), or a mixed solution of an aqueous solution of NaOH (concentration: about 2M) and an aqueous solution of NaCO ₃ (concentration: about 0.3M) at room temperature and a pH of about 9M.
It was added little by little so as to be constant, and a precipitate was obtained.
Next, the precipitate was aged at 65 ° C. for 30 minutes with stirring, and after filtration, the precipitate was diluted with deionized water to adjust the pH of the filtrate to 7
It was washed several times (3 to 5 times) until it became, and dried at 70 ° C. to prepare CuZnAl-layered double hydroxide (catalyst precursor, this layered double hydroxide is referred to as LDH). next,
This CuZnAl-layered double hydroxide (catalyst precursor) is heated at 450 ° C. for 5 hours in an electric furnace in an air atmosphere to form CuZ.
An nAl-oxide (catalyst of the invention) was prepared.

2) Results Table 1 shows the chemical composition and XRD phase of the catalyst precursor (after drying at 70 ° C. and before heating) synthesized in this example. In this table,
LDH means layered double hydroxide. In addition, Table 2 shows the physical and chemical characteristics of the catalyst (after heating at 450 ° C.) synthesized in this example. Further, FIG. 1 shows an X-ray diffraction diagram (before heating and after heating at 450 ° C.) of the catalyst precursor and the catalyst synthesized in this example.

[0012]

[Table 1]

[0013]

[Table 2]

Example 2 (Hydrogen Gas Production by Partial Oxidation Reaction of Methanol) 1) Apparatus FIG. 2 shows a partial oxidation reaction catalyst experimental apparatus used in the catalyst experiment of this Example. This device has the following configuration. Structure: Small electric furnace 7, quartz glass reaction tube (diameter: 4m
mφ) 8, micro feeder (methanol supply device)
5, gas chromatography (gas analyzer) 10, recorder (recording the output of gas chromatography) 11, argon gas cylinder 1, air (oxygen concentration; 20.2%, nitrogen concentration; 79.8%) cylinder 2, Temperature controller 9,
Ribbon heater 6, flow rate regulators 3, 4

2) Experimental conditions and method Experimental conditions are shown below. (A) Experimental method: The experiment was carried out under the following conditions by a fixed pressure fixed bed flow system. Amount of catalyst used: 100 mg, catalyst particle size: 0.25 to 0.30 mmφ, reaction temperature: 200 to 245 ° C. (b) Reduction method: The CuZnAl-oxide catalyst was reduced prior to measurement. That is, hydrogen was added to 100 mg of CuZnAl-oxide catalyst packed in a quartz glass reaction tube.
While flowing at 0 cm ³ min ^-1 , set the catalyst temperature from room temperature to 3
The temperature was raised to 00 ° C. at 5 ° C. min ⁻¹ . After holding at 300 ° C. for 2 hours, the temperature was lowered to the measurement temperature and the measurement was started. (C) Measuring method: Methanol (liquid) was introduced into the catalyst layer at a ratio of 1.5 or 2.0 cm ³ h ^-1 using a micro feeder. Air (oxygen; 20.2 vol%, nitrogen;
(79.8 vol%) was introduced at 10 to 20 cm ³ min ^-1 , and argon gas as a carrier gas was introduced at 40 cm ³ min ^-1 . The concentration of methanol in air and argon gas is 2
It was suppressed to 0 vol% or less. The reaction product was analyzed by two gas chromatographs (with TC detector) connected online. The first gas chromatograph was equipped with a 2 m long column packed with Polapack Q, and water, methanol, formaldehyde, methyl formate,
Dimethyl ether was analyzed. The second gas chromatograph was equipped with a 2 m long column packed with molecular sieves 13X and analyzed for hydrogen, air, carbon monoxide, carbon dioxide and methane. The measurement data used was 5 to 7 hours after the start of the reaction.

3) Catalyst CuZnAl-2LDH _cal catalyst was used. After carrying out the reduction operation, the measurement was started. As a result of measuring the partial oxidation reaction of methanol by changing the reaction temperature and the flow rates of argon and air, the catalyst exhibited high activity at 200 ° C. The main products were hydrogen and carbon dioxide, the by-products were carbon monoxide (a small amount), and other substances were not detected. The effect of methanol space velocity (WHSV) * on catalyst performance is shown in FIG.
It was measured at oxygen / methanol = 0.25 (molar ratio) **.

The conversion of methanol is 0.20 to 0.35 m
olh^-1g^-1Decrease with increasing WHSV and
Above (0.42 molh^-1g^-1There was no change until).
On the other hand, of products (hydrogen, carbon dioxide, water, carbon monoxide)
The methanol space velocity did not affect the selectivity. hydrogen
And carbon dioxide selectivity is 0.20 to 0.42 molh
^-1g^-1Is almost 100% over the entire measured range of
It was The selectivity of water and carbon monoxide was almost 0%.
It was *: Methanol supply rate (molh^-1) / Catalyst weight
(G) = molh^-1g^-1 **: Partial oxidation reaction of methanol; CH₃ OH + (1/2) O₂ ⇔ 2H₂ + CO₂ Oxygen / methanol = 0.5 mol / 1
It should be mol = 0.5 (molar ratio).

The effect of oxygen / methanol (molar ratio) on the catalytic performance is shown in FIG. WHSV = 0.30 molh
^It was measured at ⁻¹ g ⁻¹ and reaction temperature = 200 ° C. The conversion of methanol increased from 27 to 40% as the oxygen / methanol (molar ratio) increased from 0.20 to 0.42. In this range, carbon monoxide was not produced and the carbon dioxide selectivity was 100%. When the oxygen / methanol ratio increases above 0.28, the selectivity of water gradually increases,
Along with that, the selectivity of hydrogen decreased. This is because the generated hydrogen reacts with excess oxygen. H ₂ + (1/2) O ₂ ⇔ H ₂ O

Example 3 (Effect of reaction temperature on catalyst performance) The effect of reaction temperature on catalyst performance was examined under the following conditions. Reaction temperature: 200 to 245 ° C., catalyst: CuZnAl-2LDH _cal , CuZnAl-3
LDH _cal , CuZnAl-4LDH _cal , CuZnA
l-42LDH _cal WHSV = 0.30 molh ⁻¹ g ⁻¹ , oxygen / methanol = 0.29 (molar ratio) The results are shown in FIG. The conversion of methanol is CuZn
Al-2LDH _cal , CuZnAl-3LDH _cal , C
With uZnAl-4LDH _cal , it improved with the increase of the reaction temperature. The reaction rate of methanol of CuZnAl-4LDH _cal at 245 ° C. was about 80%. However, CuZnA
With l-42LDH _cal , the rate of increase was small and decreased at 245 ° C. (Fig. 5 (a))

The selectivity of the reaction product also depends on the reaction temperature (200 to
245 ° C.). The hydrogen selectivity increased with the increase of the reaction temperature, and was 90 mol% or more in the range of 200 to 245 ° C. in all the catalysts. In particular, CuZnAl
-4LDH _cal and CuZnAl-42LDH _cal were 98 mol% at 200 ° C and 100 mol% at 215 ° C or higher. (Fig. 5 (b))

On the other hand, the carbon dioxide selectivity is 200 ° C.
CuZnAl-3LDH_cal , CuZnAl-4
LDH_cal , CuZnAl-42LDH_cal Is 100m
ol%, CuZnAl-2LDH_cal Is 98 mol%
Yes, and decreased with increasing reaction temperature. Carbon monoxide is 2
It was not produced at 00 ° C, but it was contained in the product.
The proportion of carbon oxide increased with increasing reaction temperature. this
Is the following reaction; CO + H₂ O ⇔ H₂+ CO₂ Reverse water gas shift (reverse water-g)
As shift reaction (reaction from right to left) is high
Due to what happens at the reaction temperature (Fig. 5 (c)).

Example 4 (Catalyst stability) The stability of the catalyst was examined under the following conditions. Reaction temperature: 200 ° C., reaction time: 4 to 24 hours Catalyst: CuZnAl-2LDH _cal , CuZnAl-3
LDH _cal , CuZnAl-4LDH _cal , CuZnA
l-42LDH _cal WHSV = 0.35 molh ⁻¹ g ⁻¹ , oxygen / methanol = 0.29 (molar ratio)

The results are shown in FIG. The conversion of methanol tends to decrease gradually with time, but CuZn
Al-4LDH _cal was almost unchanged. (Fig. 6
(A)) Hydrogen selectivity is CuZnAl-2L 4 hours after the start of the reaction.
DH _cal , CuZnAl-3LDH _cal , CuZnAl
-4LDH _cal is 98 mol%, 87-9 after 24 hours
It was 2 mol%. Also, CuZnAl-42LDH
_{The cal} was 90 to 95 mol%. (FIG. 6 (b)) The carbon dioxide selectivity is 95 to 10 in the range of 4 to 24 hours.
0 mol% and carbon monoxide selectivity were 0 to 5 mol%. CuZnAl-4LDH _cal , CuZnAl
Both traces of -42LDH _cal produced trace amounts of carbon monoxide below 50 ppm. (FIG. 6 (c)) From the above results, it was confirmed that there was no problem with the stability of the catalyst.

[0024]

As described above in detail, the present invention relates to a hydrogen production catalyst by a partial oxidation reaction of methanol, a method for producing the same, and a method for producing hydrogen gas by a partial oxidation reaction of methanol using this catalyst. According to the present invention, it is possible to provide 1) a novel CuZnAl oxide catalyst for hydrogen production by a partial oxidation reaction of methanol.
2) Using this catalyst, hydrogen gas can be produced without generating CO by carrying out a partial oxidation reaction of methanol. 3) CO is not contained at all by the partial oxidation reaction of methanol, or a very small amount of CO is produced. Effects such that hydrogen gas containing only CO can be generated, 4) a new production method of hydrogen gas as a new energy source can be provided, and the like are exhibited.

[Brief description of drawings]

FIG. 1 shows an XRD pattern of a catalyst precursor (upper stage) / catalyst (lower stage) according to the present invention.

FIG. 2 is an explanatory diagram of an apparatus used in Examples.

FIG. 3 shows the effect of methanol space velocity (WHSV) on catalyst performance.

FIG. 4 shows the effect of oxygen / methanol (molar ratio) on the catalytic performance.

FIG. 5 shows the effect of reaction temperature on catalyst performance.

FIG. 6 shows the results of examining the stability of the catalyst.

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-3-72951 (JP, A) JP-A-11-169714 (JP, A) JP-A-7-163870 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) B01J 21/00-38/74 C01B 3/32 C01B 3/40 H01M 8/06

Claims (5)

(57) [Claims] As claimed in claim 1 starting material, Cu, Zn, each of Al
Nitrate was prepared, the Cu, Zn, an aqueous solution of NaOH and NaCO ₃ aqueous solution to the mixture of the aqueous nitrate solution of Al p
H was added at a constant level of about 9 to form a precipitate, which was aged and filtered to a pH of 7 after filtration.
In After washing, the catalyst precursor dried consisting CuZnAl layered double hydroxide is prepared, then this is due to thermal decomposition and partial oxidation reaction of the resulting methanol in an air atmosphere
Using CuZnAl oxide catalyst for hydrogen production , methanol
Is converted to hydrogen gas by partial oxidation reaction in the presence of air
CO is not included at all, or very little
Characterized by producing hydrogen gas containing only CO
Method for producing hydrogen gas . 2. The method for producing hydrogen gas according to claim 1, wherein the molecular ratio of Cu, Zn, and Al in the starting solution is (Cu + Zn) / Al = 2 to 5. 3. From room temperature to about 45 ° C. at about 10 ° C. min ⁻¹
The water according to claim 1, which is kept for about 5 hours after being heated to 0 ° C.
Raw gas manufacturing method. 4. Oxygen / methanol (molar ratio) is 0.20
The method for producing hydrogen gas according to claim 1 , wherein the hydrogen gas is about 0.50. 5. The method for producing hydrogen gas according to claim 1 , wherein the reaction temperature is 200 to 245 ° C.