Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
2000-02-23
2001-10-09
Gorgos, Kathryn (Department: 1741)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
C502S326000, C204S157520
Reexamination Certificate
active
06300274
ABSTRACT:
TECHNICAL FIELD
The present invention relates, in general, to a photocatalyst for hydrogen production and, more particularly, to a photoreaction in which hydrogen can be efficiently and economically produced from water in the presence of a CdS photocatalyst. Also, the present invention is concerned with a method for preparing the photocatalyst and a method for producing hydrogen by use of the same.
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 warning. 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 a naphtha, modification of natural gas, the reaction of vapor with iron at a high temperature, the reaction of water with alkaline metal, 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. With electrolysis, problems, such as the short electrode lifetime and oxygen generated as a by-product, need to be solved. Thus, it has heretofore been economically unfavorable to solve these problems due to the huge cost of facilities for hydrogen production.
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 quantity of hydrogen exists in the atmosphere. Also, it is very difficult to purify hydrogen existing in an inorganic form. If possible, it is also not economically favorable. Thus, the development of techniques whereby high-purity hydrogen can be efficiently obtained from water is very important for solving the urgent problem of exploiting substitute energy sources.
Recently, hydrogen producing techniques have been developed in which a photocatalyst is used to decompose water into hydrogen and oxygen. 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.
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 the visible light range.
However, the noted prior art is disadvantageous in that the amount of hydrogen generated is small, and the rate of production is 10 ml/0.5g hr.
There are Korean Pat. Appl'n. No. 95-7721, No.95-30416 and No.96-44214, which are believed 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, UV light is irradiated onto an aqueous solution mixed with oxygen-containing organic compounds, such as formaldehyde and alcohol, acting as a hydrogen-generating promoter, to produce hydrogen. 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 it impossible to reuse the reactants.
Korean Pat. Appl'n No. 95-30416 suggests a photocatalyst represented by the following formula II:
Cs(a)H(c)/S(b) II
This technique also has little affect the environment and can generate hydrogen without the oxygen-containing organic compound as a hydrogen-generating promoter at room temperature but has some problems with the lifetime and stability of the 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.
In addition, 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 m is superior in simplicity of preparation, stability, and lifetime, as well as optical activity in the visible light range, compared with previously-noted inventions. But the amount of produced hydrogen is economically unfavorable.
DISCLOSURE OF THE INVENTION
Therefore, it is an object of the present invention to overcome the above problems encountered in prior art and to provide a novel photocatalyst for producing hydrogen with an optical activity in the range of visible light adjusted by a light filter, with a high yield of hydrogen and with an infinite lifetime of the photocatalyst.
In accordance with an aspect of the present invention, there is provided a photocatalyst represented by the following general formula V:
m(A)/Cd[M(B)]S V
wherein m represents a doped metal element as an electron acceptor selected from the group of Pt, Ru, Ir, Co, Rh, Cu, Pd, Ni, or an oxidized compound of these metals; A represents a percentage by weight of m, ranging from 0.10 to 2.50; M is a promoter selected from the group consisting of V, Cr, Al and P; B represents mole % of M/(M+Cd), ranging from 0.05 to 20.00.
The preparation of photocatalyst in the present invention is characterized by the doping procedure as the following steps of: dissolving Cd-containing and M-containing compounds in water in such an amount that the % by weight of M ranges from 0.05 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 until the pH of the wash water reaches 7 and vacuum-drying the precipitate in a nitrogen atmosphere; adding a liquid m-containing compound to this precipitate in such an amount that the % by weight of m ranges from 0.10 to 2.50.
In accordance with a further aspect of the present invention, there is provided a method for producing hydrogen, in which visible light adjusted by light filter or sunlight is irradiated onto a suspension of the photocatalyst in water to which Na
2
S (as an electron donor) and NaH
2
PO
2
(as a reducing agent) are added.
BEST MODE FOR CARRYING OUT THE INVENTION
Acting as an electron acceptor, the doping metal, m, in the photocatalyst of the present invention is an element selected from the group consisting of Pt, Ru, Ir, Co, Rh, Cu, Pd, and Ni or an oxide thereof and is used preferably at such an amount that the % by weight of m ranges approximately from 0.10 to 2.50. For example, if the amount of m ingredient is below 0.10% by weight, the amount of hydrogen generated is decreased and the stability of photocatalyst is also decreased. On the other hand, if the amount of m ingredient is over 2.50 % by weight, the amount of hydrogen generated is decreased and the production cost is not economically favorable.
In the photocatalyst of the present invention, M is selected from the group consisting of V, Cr, Al, and P, and B represents a mole % of M/(M+Cd), ranging from 0.05 to 20.00. If the value of B is less than the lower limit, the activity of photocatalyst will be decreased. On the other hand, if the value
Baeg Jin-Ook
Park Dae-Chul
Gorgos Kathryn
Jacobson & Holman PLLC
Korea Research Institute of Chemical Technology
Tran Thao
LandOfFree
CdS photocatalyst for hydrogen production, preparation... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with CdS photocatalyst for hydrogen production, preparation..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and CdS photocatalyst for hydrogen production, preparation... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2615875