Chemistry of inorganic compounds – Hydrogen or compound thereof – Elemental hydrogen
Reexamination Certificate
2000-12-14
2003-02-11
Silverman, Stanley S. (Department: 1754)
Chemistry of inorganic compounds
Hydrogen or compound thereof
Elemental hydrogen
C502S306000, C502S307000, C502S324000, C502S326000, C502S328000, C502S329000, C502S345000, C502S347000, C502S349000, C502S353000, C502S355000
Reexamination Certificate
active
06517806
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a photocatalyst for hydrogen production and preparation thereof and a method for producing hydrogen by use of the same, more particularly, to a photoreaction in which hydrogen can be efficiently and economically produced from water in the presence of a CdZnMS photocatalyst according to the present invention.
BACKGROUND ART
Hydrogen is generally used to produce ammonia and methanol and is applied to produce saturated compounds as an essential element. Also, it plays a pivotal role in hydrotreating processes, including hydrogen addition, desulfurization, denitrogenation, demetallization and especially the hydrogenation of carbon dioxide, which causes global warming. Furthermore, hydrogen is viewed as a pollution-free energy source and a substitute for existing fossil fuels.
There are many different kinds of conventional methods for producing hydrogen, which include extraction from fossil fuels, such as naphtha, modification of natural gas, a reaction of vapor with iron at a high temperature, a reaction of water with alkaline metal, and an electrolysis of water, etc.
However, these techniques are economically unfavorable because immense heat or electric energy is required and, particularly, in the modification of fossil fuels, a large quantity of carbon dioxide is generated as a by-product. For an electrolysis of water, problems including a short electrode lifetime and a by-product generated such as an oxygen should be solved. Thus, it has heretofore been economically unfavorable to solve these problems due to the huge cost for a hydrogen production facility.
Hydrogen gas can readily escape from the gravity of the earth because it is of low specific gravity, and most of it exists in water or inorganic forms. For these reasons, only a small amount of hydrogen exists in the atmosphere. It is also very difficult to purify hydrogen existing in an inorganic form. Even though hydrogen purification is practically possible, it is also economically unfavorable. Therefore, the development of technique for a high-purity hydrogen from water is very important for solving the urgent problem of exploiting substitute energy sources.
Recently, hydrogen producing techniques in which a photocatalyst is used to decompose water into hydrogen and oxygen have been developed. However, there is little published prior art relating to photocatalysts for producing hydrogen. Representative prior art is exemplified by Japanese Pat. Laid-Open Publication Nos. Sho 62-191045 and Sho 63-107815 and applications of present inventors as below.
Japanese Pat. Laid-Open Publication No. Sho 62-191045 shows that hydrogen is generated from a photolysis reaction of an aqueous Na
2
S solution in the presence of a rare-earth element compound. Also, the rare-earth element compound as a catalyst has an advantage of exhibiting an optical activity in the range of the visible light.
Japanese pat. Laid-Open Publication No. Sho 63-107815 describes a photolysis reaction in which a composite oxide of niobium and alkali earth metal is used as a photocatalyst to generate hydrogen from a methanol solution in water. Likely, this photocatalyst has an advantage of being optically active in a visible light.
However, the noted prior art is disadvantageous in that the amount of hydrogen generated is so small and the rate of hydrogen production is only 10 mL/0.5 g hr.
There are also Korean Pat. Appl'n. No.95-7721, No.95-30416 and No.96-44214, which are able to solve the above problems.
Korean Pat. Appl'n No. 95-7721 suggests a photocatalyst represented by the following general formula I:
Cs(
a
)/K
4
Nb
6
O
17
I
In the presence of the photocatalyst of formula I, this technique has little affect on the environment and can generate hydrogen at room temperature. However, the oxygen-containing organic compounds acting as a hydrogen-generating promoter to produce hydrogen make an interruption to reuse the reactants.
Korean Pat. Appl'n No.95-30416 suggests a photocatalyst represented by the following formula II:
Cs(
a
)M(
c
)/S(
b
) II
This technique also has little affect on the environment and can generate hydrogen without an oxygen-containing organic compound acting as a hydrogen-generating promoter at room temperature but has some problems with the lifetime and stability of said photocatalyst of formula II. For example, when alkali metal, such as cesium (Cs), is impregnated in a photo-carrier, the amount of hydrogen generated is outstandingly increased but the catalyst stability is decreased.
Korean Pat. Appl'n No. 96-44214 describes a photocatalyst represented by the following formula III:
Pt(
a
)/Zn[M(
b
)]S III
This technique likewise has little affect on the environment. Although depending on electron donors and reducing agents, the photocatalyst of formula III is superior in simplicity of preparation, stability, and lifetime, as well as optical activity in the range of visible light, compared with previously-noted prior arts. But the amount of produced hydrogen is still economically unfavorable.
Korean Pat. Application No. 98-37179 suggests a photocatalyst represented by the following formula IV:
Pt(
a
)/Zn[M(
b
)]S IV
This technique also has little affect on the environment and the said photocatalyst of formula IV has an optical activity in some degree in the range of visible light. The preparation of the said photocatalyst is much simpler and by-products are much less produced. However, the amount of generated hydrogen is still not enough economically.
To solve the above mentioned problems, Korean Pat. Application 98-37180 by present inventors suggests a photocatalyst represented by the following formula V:
m
(A)/Cd[M(B)]S V
The said photocatalyst of formula V shows an optical activity in the range of visible light adjusted by light filter as well as in the sunlight. The amount of generated hydrogen is much larger and the lifetime of the said photocatalyst is semi-infinitive. By introducing various doping metals and promoters and other new methods, said prior art overcomes the restricted activity in the light sources and suggests more simple method of preparation. Likewise, the lifetime of photocatalyst is also longer and the amount of generated hydrogen from water is remarkably larger than that of prior art. However, this technique shows limited hydrogen activity only to one reducing agent.
To solve the above mentioned problems economically, Korean Pat. Application 99-22954 by present inventors suggests a photocatalyst represented by the following formula VI:
m
(
a
)/Cd[M(
b
)]S VI
In this prior art, the technique relates to novel CdS photocatalyst (photocatalyst system), preparation thereof and construction of new reduction system with a sulfite to generate hydrogen economically. However, the rate of producing hydrogen is still not satisfied in the economic point of view.
DISCLOSURE OF THE INVENTION
Therefore, it is an object of the present invention to overcome the above problems encountered in prior arts and to provide a novel photocatalyst for producing hydrogen with an optical activity in both visible and uv lights.
It is another object of the present invention to provide a photocatalyst with high activity in a reductant and sunlight, with a high yield of hydrogen, and with an infinite lifetime.
It is further object of the present invention to provide a preparation method for photocatalyst with a high degree of photocatalytic activity.
BEST MODE FOR CARRYING OUT THE INVENTION
The photocatalyst of the present invention is characterized by the following general formula VII:
m
(
a
)/Cd
x
Zn
y
M
z
S VII
wherein ‘m’ represents a doped metal element as an electron acceptor selected from the group consisting of Ni, Pt, Ru or the oxidized compound of these metals; ‘a’ represents a percentage by weight of m, ranging from 0.10 to 5.00; ‘M’ is at least one catalyst element selected from the group consisting of Mo, V, Al, Cs, Mn, Fe, Pd, Pt, P, Cu, Ag, I
Baeg Jin-Ook
Park Dae-Chul
Jacobson & Holman PLLC
Korea Research Institute of Chemical Technology
Medina Maribel
Silverman Stanley S.
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