Ordinary-temperature purifying catalyst

Details Ordinary-temperature purifying catalyst Ordinary-temperature purifying catalyst

2000-03-29

2002-12-10

Silverman, Stanley S. (Department: 1754)

Catalyst, solid sorbent, or support therefor: product or process

Catalyst or precursor therefor

Metal, metal oxide or metal hydroxide

C502S326000, C502S327000, C502S332000, C502S333000, C502S334000, C502S336000, C502S337000, C502S338000, C502S339000, C502S066000, C502S074000, C423S213500, C423S239100, C423S245100, C423S247000

Reexamination Certificate

active

06492298

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ordinary-temperature purifying catalyst, which can purify and remove an environmental loading material, such as carbon monoxide (CO), odorants, nitrogen oxides (NO
x
) and hydrocarbons (IC), formaldehyde which often generates in houses, and an ethylene gas which causes to deteriorate the freshness of foods, at an ordinary temperature (e.g., room temperature).
2. Description of the Related Art
Conventionally, in order to remove odorants and harmful gases, adsorbents, such as activated carbon and zeolite, have been used so far. However, the adsorbents require means for processing the adsorbed components.
Further, in order to purify carbon monoxide, one of harmful gases, the performance is required which purifies and removes carbon monoxide in a lower temperature range and in a shorter period of time. However, conventional catalysts have been still insufficient in the purifying ability at an ordinary temperature. Accordingly, a further improvement is required in the purifying performance.
The influences of formaldehyde to human bodies are irritating actions to the eyes, nose and throat. For example, the influences accompany syndromes, such as discomfort feelings, tearing, sneezing, coughing, vomiting and difficult breathing. The sources of the generation in the housing spaces are believed to be cigarette smoking, usages of heating apparatuses, home appliances, pieces of furniture and building materials. The formaldehyde is used as urea-formaldehyde adhesives in a large amount, is a raw material for adhesives for plywoods and particle boards, and is used as antiseptics for adhesives for wall papers. Accordingly, the Japanese Health and Welfare Ministry presents that the reference value of the formaldehyde concentration be 0.1 mg/Nm 3 (=80 ppb) or less in a room.
Recently, the formaldehyde has been regarded as one of the materials which cause the sick-house syndromes. Accordingly, the material makers and the housing makers try to construct houses with materials, which do not generate the formaldehyde, and to age houses so as to reduce the formaldehyde concentration before they hand over the houses to the customers. However, it cannot be said that the aforementioned treatments necessarily satisfy the reference values of the Japanese Health and Welfare Ministry.
Whilst, in order to remove the volatile formaldehyde, adsorbents, such as activated carbon and zeolite, have been used. However, the adsorbents have limited longevity. Accordingly, it is necessary to regularly replace the adsorbents, and to spend economical expenses. Further, it is necessary to provide means for processing the components adsorbed on the adsorbents anew.
As means for removing thee indoor odorants, etc., at an ordinary temperature, air purifiers have been known generally into which activated carbon is incorporated. Further, air purifiers have been commercially available which utilize photocatalysts.
In addition, the following have been put in markets: namely; methods for removing the odorants, etc., with ozone; methods by using photocatalysts therefor; apparatuses therefor; and filters therefor. However, regarding ozone, it is necessary to exceed the regulatory value of the ozone concentration in order to exhibit the advantages. Further, it is necessary to provide a catalyst for removing the ozone. Concerning the photocatalytic system, it is necessary to provide an artificial light source which excites the photocatalysts. Further, it is necessary to spend expenses for electricity when the light source always irradiates the photocatalysts. Hence, the costs go up.
In Japanese Unexamined Patent Publication (KOKAI) No. 6-219,721, a catalyst is disclosed. The catalyst includes metallic oxide particles, in which noble metal particles are mixed uniformly, and which are composed of CeO
2
. The metallic oxide can be at least one member selected from the group consisting of CeO
2
, ZrO
2
, TiO
2
and SnO
2
This catalyst is made by coprecipitating the metallic oxide, which is composed of the noble metal particles for purifying carbon monoxide to carbon dioxide. The catalyst has anionic holes in the surface so that it exhibits a high reactivity without a hydrogen reduction treatment. However, the publication discloses that the purifying performance was evaluated under the temperature condition of 150° C. or more, and does not refer to the purifying activity in a room temperature range.
Whilst, a specific catalyst is proposed as a method for oxidizing and decomposing odorants or harmful gases in air. For instance, Japanese Unexamined Patent Publication (KOKAI) No. 10-296,087 discloses that a catalyst,, which requires zirconia or ceria as an indispensable component and at least one member selected from the group consisting of Ag, Pd, Pt, Mn and Rh is loaded thereon, can be used to oxidize and decompose trimethylamine. However, in this case as well, the disclosed catalyst was simply examined for the purifying activity under the temperature condition of 200° C. in the examples. Further, the publication does not set forth the oxygen defect of the oxide used in the catalyst. Therefore, it is not believed that the catalyst keeps a sufficient ability of decomposing trimethylamine at a room temperature.
In a publication of the PCT applications, e.g., No. WO-91/01,175, a catalyst is disclosed which oxidizes oxydants in a low temperature range. The catalyst includes at least one reducing metallic oxide selected from the group consisting of iron oxide, ceria, zirconia, copper oxide, rare-earth element oxide, manganese oxide, vanadium oxide and chromium oxide, and a noble metal loaded on the metallic oxide. According to the publication, the catalyst oxidizes oxydants whose molecular weight is 50 or less at a temperature of up to 30° C. When paying attention to the reduction temperature as one of the production conditions of this catalyst, the publication sets forth that the reduction treatment was carried out at room temperature. However, it is impossible to introduce an oxygen defect, which exhibits a function of the present invention, into the aforementioned metallic oxides at room temperature.
In Japanese Unexamined Patent Publication (KOKAI) No. 7-51,567, a catalyst is disclosed. The catalyst is made by suspending activated carbon in an aqueous solution, in which molybdenum or cerium and platinum are solved, and by loading the molybdenum or cerium and the platinum on the activated carbon with heat or a reducing agent. However, the publication does not refer to subjecting the catalyst to a certain treatment after the loading.
Generally speaking, air cleaner filters using activated carbon effect the deodoring ability by physically adsorbing the odorants on the activated carbon. However, the activated carbon exhibits an upper limit of the adsorption, and does not effect the deodoring performance more than the saturated adsorption. Accordingly, the filters have short lives. Hence, it is essential to regenerate the filters for a long period of usage. When the regenerating is not carried out, it is indispensable to replace the filters.
In the filters using photocatalysts, it is indispensable to irradiate a light to actuate the photocatalysts in order to purify harmful substances. In order to carry out this, it is necessary to use a light source, such as a mercury lamp. Therefore, there arises a drawback in that the air cleaners, which employ the filters using the photocatalysts, are remarkably expensive in terms of the equipment costs and the running costs.
An ethylene gas contained in air is believed to degrade the freshness of fruit and vegetables by facilitating the physiological actions of fruit and vegetables and by developing the additional aging thereof. Accordingly, in order to preserve the freshness of perishables, the following methods are proposed: namely; decomposing the ethylene with ozone or hydrogen peroxide; and adsorbing the ethylene.
However, in the aforementioned methods, the adsorbing method exhibits the shortened durati

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