Chemistry: electrical and wave energy – Processes and products – Processes of treating materials by wave energy
Reexamination Certificate
2001-02-07
2002-09-10
Wong, Edna (Department: 1741)
Chemistry: electrical and wave energy
Processes and products
Processes of treating materials by wave energy
C423S102000, C423S141000, C423S142000
Reexamination Certificate
active
06447650
ABSTRACT:
TECHNICAL FIELD
The present invention relates, in general, to a method for preparing a photocatalyst for hydrogen production and a method for producing hydrogen by use of the same, more particularly, to a method for preparing a CdS photocatalyst for the use of hydrogen production and to a photoreaction in which hydrogen is efficiently produced from water in the presence of the CdS photocatalyst.
BACKGROUND ART
In general, hydrogen is used to produce ammonia and methanol in the chemical industry. Hydrogen is also an essential material for hydrogenation in which unsaturated compounds are converted into saturated ones and for hydrotreating processes, including hydrogen addition, desulfurization, denitrogenation and demetallization. Another example for the use of hydrogen is contact hydrogenation of carbon dioxide which causes global warming. In addition, hydrogen is viewed as a pollution-free, clear energy source substituting for existing fossil fuels.
Conventional techniques for obtaining hydrogen include extraction from fossil fuels, such as naphtha, modification of natural gas, reaction of vapor with iron at a high temperature, reaction of water with alkaline metal, electrolysis of water, etc.
However, the said conventional methods are not economically favorable because immense heat or electric energy is required. Regarding modification of fossil fuels, the conventional methods have another disadvantage of generating a large quantity of by-products, such as carbon dioxide. In case of electrolysis, problems, such as a short electrode lifetime and generation of by-products, should be solved to purify hydrogen more easily. Thus the cost of facilities for hydrogen production is economically unfavorable due to the noted problems.
In the nature, some of hydrogen exists, in various compounds forms, particularly in inorganic forms but most of it exists in water. Only a small quantity of hydrogen exists in the atmosphere because it is of low specific gravity. It is also very difficult and economically unfavorable to purify hydrogen existing in inorganic forms.
Therefore, a method to produce hydrogen from water will be a very. meaningful technique in near future. Recently, hydrogen producing techniques have been developed in which photocatalysts are used to decompose water into hydrogen and oxygen. However, little has been published in prior art relating to photocatalysts for producing hydrogen. Representative examples are Japanese Pat. Laid-Open Publication Nos. Sho 62-191045 and Sho 63-107815 and a couple of Korean Patent applications by the present inventors as described as below.
Japanese Pat. Laid-Open Publication No. Sho 62-191045 relates to generating hydrogen from an aqueous Na
2
S solution in the presence of a rare earth element compound by a photolysis reaction. The rare earth element compound has an advantage of exhibiting optical activity in the range of visible light Japanese Pat. Laid-Open Publication No. Sho 63-107815 concerns a photolysis reaction in which a composite oxide of niobium and alkaline earth metal is used as a photocatalyst to generate hydrogen from a methanol solution in water. This photocatalyst likewise has an advantage of being active in the range of visible light.
However, both of the said prior arts are disadvantageous because the amount of hydrogen generated is as little as 10 ml/0.5 g hr.
Korean Pat. Application No. 95-7721 applied by the present inventors solve the above problems to some degree by suggesting a photocatalyst represented by the following formula I:
Cs(
a
)/K
Nb
6
O
7
I
This technique has little affect on the environment and generates hydrogen at room temperature but the oxygen-containing organic compounds is needed as hydrogen-generating promoters.
Korean Pat. Application No. 95-30416 suggests a photocatalyst represented by the following formula II:
Cs(
a
)H(
c
)/S(
b
) II
This technique has little affect on the environment and generates hydrogen without an oxygen-containing organic compounds as a hydrogen-generating promoter at room temperature, but encounters a problem with the life time and the stability of the photocatalyst. For example, when an alkali metal, such as cesium, is impregnated into a photo-carrier, the amount of generated hydrogen is increased outstandingly but the stability of the catalyst is decreased.
Similarly, Korean Pat. Application No. 96-44214 suggests a photocatalyst represented by the following formula III:
Pt(
A
)/Zn[M(
B
)]S III
This technique also has little affect on the environment. This compound shows not only the optical activity of photocatalyst in some degree but also the preparation is relatively simple and the stability of photocatalyst is superior. The life time of said compound is longer which depends on electron donors and reducing agents and the amount of generated hydrogen is larger than that of prior arts. When doping with Pt instead of Cs, the stability of the catalyst is improved but still the amount of generated hydrogen is not enough in the economic point of view.
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 has optical activity in some degree in the range of visible light. The preparation of the said photocatalyst is more simpler and by-products are much less produced.
To solve the above problem, 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 shows an optical activity in the range of visible light adjusted by light filter as well as sun light. The amount of generated hydrogen is much larger and the life time of the said photocatalyst is semi-infinitive. By introducing various doping metals and promoters and other new methods, the said application solves the restricted activity to the light source and suggests more simple preparation process. Likewise, the life time 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.
DISCLOSURE OF THE INVENTION
Therefore, it is an object of the present invention to overcome the previously-noted problems encountered in prior art, and to provide economical reduction system which remarkably improves the restricted activity of photocatalysts of prior art.
It is an another object of the present invention to provide that the preparation of the photocatalyst in the present invention is more simple and has little affect on the environment.
It is an another object of the present invention to provide that the photocatalyst in the present invention has an optical activity in the range of visible light adjusted by light filter as well as sun light and thus the amount of generated hydrogen is much larger.
It is an further object of the present invention to provide the life time of the photocatalyst in the present invention being semi-infinitive.
BEST MODE FOR CARRYING OUT THE INVENTION
A photocatalyst in accordance with the present invention represented by the following formula VI:
m
(
A
)/Cd[M(
B
)]S VI
wherein m represents a doped metal element as an electron acceptor selected from the group of Ni, Pd, Pt, Fe, Ru, Co or an oxidized compound of these metals; A represents a percentage by weight of m, ranging from 0.10 to 5.00; M is a promoter selected from the group consisting of V, Cr, Al, P, As, Sb and Pb; B represents mole% of M/(M+Cd), ranging from 0.001 to 20.00.
A method for preparing the said photocatalyst of formula VI, comprising the steps of: dissolving Cd-containing and M-containing compounds in water in such an amount that the mol % of M ranges from 0.001 to 20.00; adding H
2
S or Na
2
S as a reactant in the solution with stirring to precipitate Cd[M]S; washing the precipitate with water and
Baeg Jin-Wook
Park Dae-Chul
Jacobson & Holman PLLC
Korea Research Institute of Chemical Technology
Wong Edna
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