JP2730111B2 - New water photolysis catalyst - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a novel heterogeneous catalyst used for producing hydrogen by photolyzing water.

[Conventional technology]

Since the oil crisis, the depletion of fossil energy such as oil and coal has been seriously discussed, and the use of hydrogen as an alternative energy source for fossil energy and a clean energy source that does not pollute the air has been proposed.

As a method for producing hydrogen, a method for producing water by decomposing water (photolysis) with sunlight is considered to be promising. In extreme terms, this method merely irradiates water with sunlight, and does not require any additional energy such as electricity or heat.
The chemical formula of the decomposition is as follows.

H ₂ O → H ₂ + 1 / 2O ₂ ↑ However, when an easily oxidizable substance such as an alcohol or another organic substance is present, oxygen is not generated.

However, photodecomposition of water requires an appropriate catalyst (photocatalyst), and for example, TiO ₂ and SrTiO ₃ particles have been proposed.

[Problems to be solved by the invention]

However, although TiO ₂ particles have both strong reducing power and oxidizing power, generation of hydrogen and oxygen is hardly recognized unless a noble metal such as Pt or RuO ₂ is supported to form active sites.
Therefore, there is a disadvantage that the production process of the catalyst is two-stage in order to support a noble metal such as Pt or RuO ₂ , and that the production cost is high because an expensive raw material such as a noble metal is used. Also, SrTiO ₃ particles cannot produce hydrogen and oxygen unless NiO or Rh is supported, and have the disadvantages of high production cost and not very high hydrogen generation activity.

Therefore, an object of the present invention is to eliminate the need for a process for supporting precious metals and other supporting components, and to reduce the production cost because no precious metals are used. To provide a "heterogeneous catalyst".

[Means for solving the problem]

The present inventors have conducted intensive studies and found that the compounds described below are extremely useful as target catalysts, and have accomplished the present invention.

Accordingly, the present invention provides a compound represented by the following general formula I: [A _n-1 B _n O _{3n + 1} ] ^-u (where A is an alkali metal element, an alkaline earth metal element, a rare earth metal element and a transition metal element) B is one or more atoms selected from Ti, Nb or Ta, n is an integer of 1 to 7, and u is One or two selected from the group consisting of a layered anion atom group represented by the following formula: and hydrogen, an alkali metal element, an alkaline earth metal element and a group 3B element existing between layers. At least one kind of cation M, and as a whole, a compound having a laminated structure represented by a molecular formula: M _m [A _n-1 B _n O _{3n + 1} ]. provide.

Here, m is 1 or 2, and the product of valence of cation M and m is equal to u.

[Action]

As the element selected from the group consisting of the alkali metal element, the alkaline earth metal element, the rare earth metal element and the transition metal element represented by A in the general formula I, specifically, for example, Na, Ca, Sr, La, Nd, Er, Cr, Fe, Co or Ni are included.

Further, the element of the cation M specifically includes, for example, H, Li, Na, K, Rb, Cs, Sr, Tl, and the like.

Among the catalysts of the present invention represented by the molecular formula: M _m [A _n-1 B _n O _{3n + 1} ], those in which M is hydrogen are particularly preferred because of their high activity.

The compound represented by the molecular formula: M _m [A _n-1 B _n O _{3n + 1} ] is a compound known per se, but an example of its production will be described below.

Oxides, carbonates or nitrates of each element are weighed according to the atomic ratio of the target compound and mixed in an alumina mortar. The mixture is calcined in a platinum crucible at 1000-1300 ° C. for 5-30 hours in air. This calcined product is pulverized and mixed in an alumina mortar. When this is further refired under the above conditions, the desired product is obtained.

The target product thus obtained was confirmed to be a layered compound by powder X-ray diffraction.

Further, the compound synthesized by the solid phase reaction as described above,
By performing ion exchange with an aqueous acid or nitrate solution, the compound can be converted (synthesized) into another compound while maintaining the layered structure. The method of ion exchange is, for example, a method in which an aqueous solution containing ions not exchanging the original compound and having an appropriate concentration is stirred at room temperature or under heating for 10 hours to 10 days.

The shape of the compound used in the present invention should be particles having a large surface area in order to make effective use of light, and the particle size is preferably as small as possible. It is difficult. Therefore, in general, 0.1 to 10 µm, preferably 0.1 to 1 µm is appropriate.

Particles can be easily crushed by using a conventional crushing means such as a ball mill.

If the increase in the production cost is acceptable, the catalyst particles of the present invention may support the above-mentioned noble metals such as Pt and Rh. In such a case, the photocatalytic activity may be further increased in some cases.

The catalyst of the present invention is used for photodecomposing water. In this case, the water may contain organic substances or inorganic substances such as manure, organic waste, and organic sludge in addition to water.

Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto.

[Example 1] 7.08 g of K ₂ CO ₃ , 16.70 g of La ₂ O ₃ and 27.25 g of Nb ₂ O ₅ were weighed respectively, and they were mixed in a mortar. Firing at 20 ° C. for 20 hours.

The fired product was pulverized and mixed in an alumina mortar, and fired again under the above conditions.

 The obtained calcined product was ground in a mortar to a particle size of 10 μm or less.

The powder thus obtained was analyzed by powder X-ray diffraction to obtain K [La
Nb ₂ O ₇ ].

Example 2 6.19 g of K ₂ CO ₃ , 17.94 g of CaCO _3, and 35.72 g of Nb ₂ O ₅ were weighed and mixed in a mortar, then put in a platinum crucible, and placed in air at 1200 ° C. Fired for 10 hours.

The fired product was pulverized and mixed in an alumina mortar, and fired again under the above conditions.

 The obtained calcined product was ground in a mortar to a particle size of 10 μm or less.

The powder thus obtained was analyzed by powder X-ray diffraction to obtain K [Ca
₂ Nb ₃ O ₁₀ ].

Example 3 11.16 g of K [Ca ₂ Nb ₃ O ₁₀ ] powder of Example 2 and NaNbO ₃
After weighing out 3.28 g each and mixing them in a mortar, they were put into a platinum crucible and fired at 1300 ° C. in air for 10 hours.

The fired product was pulverized and mixed in an alumina mortar, and fired again under the above conditions.

 The obtained calcined product was ground in a mortar to a particle size of 10 μm or less.

The powder thus obtained was analyzed by powder X-ray diffraction to obtain K [Na
Ca ₂ Nb ₄ O ₁₃ ].

Example 4 5 g of K [Ca ₂ Nb ₃ O ₁₀ ] powder of Example 2 was taken, and
The mixture was added to 5 ml of 5N nitric acid aqueous solution, stirred at room temperature for 20 hours, and ion-exchanged.

 The ion-exchanged product was filtered and dried.

The powder obtained in this way has a layered structure retained H
[Ca ₂ Nb ₃ O ₁₀ ] was identified by powder X-ray diffraction.

Other than that, the catalysts shown in Table 1 below were prepared.

[Review of the catalyst]

50 ml of methanol, 300 ml of water and 1 g of catalyst in a 500 ml flask
While stirring with a magnetic stirrer.
Light was irradiated with a 0 W high-pressure mercury lamp.

After irradiation, the amount of generated hydrogen was measured every hour by gas chromatography to determine the steady-state activity. The results are shown in Table 1 below.

In this case, although methanol is added to water,
This is because the activity of the catalyst can be easily evaluated.

[Effects of the Invention] As described above, according to the present invention, a catalyst having high activity can be obtained without supporting a noble metal such as Pt or RuO _{2 and the} like, and therefore, the production cost of the catalyst can be reduced, and therefore, water Hydrogen can be produced at low cost.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Akira Tanaka 1773 Asamizodai, Sagamihara City, Kanagawa Prefecture Nikon Sagamihara Works Co., Ltd. (56) References JP-A-62-74452 (JP, A)

Claims (2)

(57) [Claims] 1. A compound of the general formula I: [A _n-1 B _n O _{3n + 1} ] ^{-u wherein} A is one or more atoms containing at least a rare earth metal element, and B is Ti, One or two or more atoms selected from Nb or Ta, n is an integer of 1 to 7, and u is the valence of the atomic group.) It consists of one or more cations M selected from the group consisting of hydrogen, alkali metal elements and alkaline earth metal elements present between the layers, and has a molecular formula: M _m [A _n-1 B _n O _{3n + 1} ]. A water photolysis catalyst comprising a compound having a laminated structure represented by the following formula: 2. The photocatalytic catalyst for water according to claim 1, wherein said M is hydrogen.