Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Patent
1998-03-26
2000-05-23
Griffin, Steven P.
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
502326, 502330, 502331, 502338, 502345, 4232135, 4232391, 423604, 423605, B01J 2300, B01J 802, B01J 800, C01G 302, C01G 4502
Patent
active
060665904
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a harmful gas removing agent used for removing harmful gas including nitrogen oxides (NO.sub.x) such as nitrogen monoxide (NO), nitrogen dioxide (NO.sub.2), carbon monoxide (CO), and ozone (O.sub.3) contained in exhaust gases ventilated from motor tunnels, underground parking and the like to prevent air pollution.
BACKGROUND ART
Exhaust gases ventilated from motor tunnels, underground parking, and indoor spaces equipped with apparatus which produces harmful gases, are largely different from flue gases ventilated from incineration apparatus in that exhaust gases have normal temperature and low NO.sub.x concentration, and the NO.sub.x concentration drastically varies in an instant. Flue gases have been treated by a selective catalytic reduction process (NH.sub.3 reductive denitration process) for removing NO.sub.x therefrom. In the selective catalytic reduction process, NO.sub.x is reduced to nitrogen (N.sub.2) using ammonia (NH.sub.3) as a reducing agent with a presence of titania (TiO.sub.2) as a catalyst. However, the selective catalytic reduction process is not directly applicable for removing NO.sub.x from exhaust gases. For this reason, it has been considered that for the exhaust gas, after the NO.sub.x concentration is increased by passing the exhaust gas through an appropriate NO.sub.x adsorbent to adsorb NO.sub.x and heating and desorbing the adsorbent, the aforementioned NH.sub.3 reductive denitration process is adopted. The following adsorbents have been known as NO.sub.x adsorbents used for the process.
1) Activated alumina (Al.sub.2 O.sub.3) type NO.sub.x adsorbent (disclosed in Japanese Unexamined Patent Publication No. 4-367707). This adsorbent includes oxides of sodium and calcium, and in addition thereto oxides of manganese, iron or copper, thereby having an enhanced gas adsorption ability.
2) Low-concentration NO.sub.x adsorbent (disclosed in Japanese Unexamined Patent Publication No. 5-123568). This adsorbent includes anatase-type TiO.sub.2, used as a carrier, and ruthenium supported on the anatase-type TiO.sub.2.
3) An adsorbent for NO.sub.x, and especially NO.sub.2 (disclosed in Japanese Unexamined Patent Publication No. 7-88363). This adsorbent includes a carrier, and at least one precious metal selected from the group consisting of platinum, gold, ruthenium, rhodium, and palladium or a compound thereof, and if necessary, a metallic oxide of metals such as manganese, iron, cobalt, nickel, copper, and zinc supported on the carrier.
4) An NO.sub.x oxidizing and adsorbing agent (disclosed in Japanese Unexamined Patent Publication No. 8-173796). This agent contains .gamma.-MnO.sub.2-x (where 0.ltoreq..times..ltoreq.0.1) having a specific surface area of 100 m.sup.2 /g or more as a main component.
On the other hand, examples of known catalysts conventionally used for oxidizing CO into CO.sub.2 at normal temperature include a metallic oxide containing a copper oxide and a manganese oxide in a mixed state as main components (hopcalite catalyst), activated charcoal including platinum or palladium, and alumina. Also known as catalysts are a mixture of palladium or a compound thereof and activated manganese dioxide (Japanese Examined Patent Publication No. 63-33419), and a catalyst which includes alumina, and palladium salt, copper salt, and nickel salt supported on the alumina (Japanese Unexamined Patent Publication No. 60-7942).
Examples of known O.sub.3 removing agent capable of removing O.sub.3 at normal temperature include a catalyst containing a manganese oxide or a nickel oxide and an aluminum oxide as active ingredients (Japanese Unexamined Patent Publication No. 6-154601), a manganese dioxide catalyst (Japanese Unexamined Patent Publication No. 7-246335), a catalyst which includes a composite silica.multidot.boria.multidot.alumina, amorphous manganese oxide and amorphous palladium oxide supported on the compound oxide, and preferably further containing oxide of silver, iridium, rare-earth metals and/or transition metals (Japanese Unexa
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Horii Yuji
Inoue Toshinori
Shibano Hidetaka
Tomiyama Yoshiyuki
Yamashita Takeshi
Griffin Steven P.
Nguyen Cam N.
Sued-Chemie Nissan Catalysts Inc.
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