Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Patent
1995-02-02
1997-12-09
Caldarola, Glenn A.
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
502353, 423329, B01J 2322, B01J 2106
Patent
active
056960492
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a catalyst for the decomposition of nitrogen oxides contained in a waste gas, etc., in particular, a catalyst of titanium oxide-vanadium type for the decomposition of nitrogen oxides, having a high denitrification activity at a relatively low temperature, and a method for denitrification using the catalyst.
BACKGROUND TECHNIQUES
Waste gases formed by combustion of various fossil fuels contain nitrogen oxides (hereinafter referred to as "NOx"), resulting in one cause of air pollution. NOx includes NO, NO.sub.2, N.sub.2 O.sub.3, N.sub.2 O.sub.4, N.sub.2 O, etc. and the most part of NOx contained in waste gases formed by combustion of various fossil fuels such as petroleums, coals, etc. is NO. A number of proposals have been made as a method of treating NOx in waste gases. In the so-called catalytic reduction denitrification method comprising contacting a waste gas with a catalyst in the presence of ammonia (NH.sub.3) as a reducing agent to reduce and decompose NOx in the waste gas to N.sub.2 and to render it harmless, the reduction and decomposition of NOx selectively proceed even in the co-existence of oxygen. This is an effective method as a waste gas denitrification method.
As a catalyst for advancing such reduction and decomposition of NOx, a number of catalysts have been proposed, one of which is a titanium oxide-vanadium type catalyst. For example, Japanese Patent Laid-Open Publication No. 51966/1975(Japanese Patent Publication No. 2912/1979) discloses a method comprising contacting nitrogen oxides with a catalyst comprising vanadium supported on titanium oxide in the presence of ammonia at a temperature of 150.degree. to 650.degree. C. and thereby decomposing the nitrogen oxides into nitrogen and water. The catalyst used in this method has excellent properties, for example, a very high activity for the reduction reaction of NOx at a high temperature, e.g. at least 170.degree. C. In this case, the temperature at which NOx is contacted with the catalyst is in the range of 150.degree. to 650.degree. C., but the specific surface area of the catalyst comprising vanadium supported on titanium oxide is ordinarily at most about 50 m.sup.2 /g and the denitrification activity is markedly lowered at a reaction temperature of at most 170.degree. C. to largely lower the decomposition capacity of NOx.
As described above, catalyst comprising vanadium supported on titanium oxide has hitherto been proposed, but the catalyst of this type has the problem that a practically high denitrification capacity is hardly obtained unless a waste gas is contacted with the catalyst at a temperature of 200.degree. to 500.degree. C. In the case of using the catalyst, furthermore, there arises a problem that N.sub.2 O regarded as a causal material for breaking the ozone layer and warming the earth is by-produced in a proportion of 5 to 10% based on NOx, thus resulting in possibility of the secondary pollution.
In the titanium oxide-vanadium type catalyst, a catalyst having a relatively high specific surface area and specified pore ratio has been proposed. In Japanese Patent Laid-Open Publication No. 86845/1990, for example, a catalyst for denitrification is disclosed in which a metal oxide catalytic component such as vanadium pentoxide is deposited on anatase-type titania as a support. In this catalyst, the pore distribution of the anatase-type titania used as a support is controlled in such a manner that the porosity of pores (pores of at most 60 nm in diameter) is in the range of 0.05 to 0.5 cc/cc, the porosity of macro pores (pores of at least 60 nm in diameter) is in the range of 0.05 to 0.5 cc/cc and the total porosity is at most 0.80 cc/cc to raise the denitrification property. Furthermore, Japanese Patent Laid-Open Publication No. 130140/1985 discloses a catalyst for the denitrification of a waste gas comprising titanium oxide, tungsten oxide and vanadium oxide as catalytic active components and having a specific surface area of 80 to 200 m.sup.2 /g, pore volume of 0.1 to 0.5 cc/g a
REFERENCES:
patent: 4833113 (1989-05-01), Imanari et al.
patent: 4929586 (1990-05-01), Hegedus et al.
patent: 4975256 (1990-12-01), Hegedus et al.
patent: 4977127 (1990-12-01), Rikimaru
Adachi Masatosi
Ikeyama Nobuhide
Iwanaga Yutaka
Torikai Yuji
Caldarola Glenn A.
Ghyka Alexander G.
Mitsui Mining Co. Ltd.
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