WO1997041948A1 - Catalytic reactor for the decomposition of ozone - Google Patents

Catalytic reactor for the decomposition of ozone Download PDF

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Publication number
WO1997041948A1
WO1997041948A1 PCT/US1997/007841 US9707841W WO9741948A1 WO 1997041948 A1 WO1997041948 A1 WO 1997041948A1 US 9707841 W US9707841 W US 9707841W WO 9741948 A1 WO9741948 A1 WO 9741948A1
Authority
WO
WIPO (PCT)
Prior art keywords
ozone
core structure
metal alloy
catalytically
air
Prior art date
Application number
PCT/US1997/007841
Other languages
French (fr)
Inventor
Stan C. Pollitt
Robert Tom
William Westelaken
Stephen T. Homeyer
Sarah J. Mikolajczyk
Original Assignee
Alliedsignal Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Alliedsignal Inc. filed Critical Alliedsignal Inc.
Priority to JP09540222A priority Critical patent/JP2000510039A/en
Priority to EP97924632A priority patent/EP0906147A1/en
Publication of WO1997041948A1 publication Critical patent/WO1997041948A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/50—Catalysts, in general, characterised by their form or physical properties characterised by their shape or configuration
    • B01J35/56—Foraminous structures having flow-through passages or channels, e.g. grids or three-dimensional monoliths
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/86—Catalytic processes
    • B01D53/8671—Removing components of defined structure not provided for in B01D53/8603 - B01D53/8668
    • B01D53/8675—Ozone
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/86—Catalytic processes
    • B01D53/88—Handling or mounting catalysts
    • B01D53/885—Devices in general for catalytic purification of waste gases
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J15/00—Chemical processes in general for reacting gaseous media with non-particulate solids, e.g. sheet material; Apparatus specially adapted therefor
    • B01J15/005—Chemical processes in general for reacting gaseous media with non-particulate solids, e.g. sheet material; Apparatus specially adapted therefor in the presence of catalytically active bodies, e.g. porous plates
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B01J23/48—Silver or gold
    • B01J23/50—Silver
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/89—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals
    • B01J23/8933—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals also combined with metals, or metal oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/8953—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals also combined with metals, or metal oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with zinc, cadmium or mercury
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B64—AIRCRAFT; AVIATION; COSMONAUTICS
    • B64D—EQUIPMENT FOR FITTING IN OR TO AIRCRAFT; FLIGHT SUITS; PARACHUTES; ARRANGEMENT OR MOUNTING OF POWER PLANTS OR PROPULSION TRANSMISSIONS IN AIRCRAFT
    • B64D13/00—Arrangements or adaptations of air-treatment apparatus for aircraft crew or passengers, or freight space, or structural parts of the aircraft
    • B64D13/06—Arrangements or adaptations of air-treatment apparatus for aircraft crew or passengers, or freight space, or structural parts of the aircraft the air being conditioned
    • B64D2013/0603—Environmental Control Systems
    • B64D2013/0685—Environmental Control Systems with ozone control

Definitions

  • the present invention relates generally to catalytic reactors, and more particularly, to a catalytic reactor for the decomposition of ozone in air.
  • the application of the catalytic reactor of the present invention includes, but is not limited to, the decomposition of ozone present in the conditioned air supplied to aircraft cabins.
  • Aircraft environmental control systems supply pressurized and conditioned air to the aircraft cabin.
  • the temperature, pressure and relative humidity must be controlled to provide for the comfort of the flight crew and passengers within the aircraft.
  • Modern commercial jet aircraft are typically designed for fuel-efficient operation at relatively high altitudes of 25,000 feet or more above sea level where the ozone content of the air is relatively high Accordingly, dunng operation at high altitudes the air supplied to the aircraft cabin from the environmental control system may contain ozone at a level of 1 - 3 ppmv
  • the presence of ozone in the air within the aircraft cabin can cause lung and eye irritation, headaches, fatigue and/or breathing discomfort
  • present Federal Aviation Agency (FAA) regulations limit ozone concentrations on commercial flights to 0 1 ppmv dunng a three hour time pe ⁇ od and 0 25 ppmv maximum at any time.
  • FAA Federal Aviation Agency
  • catalytic converters to reduce or eliminate undesirable ozone in the air supplied to aircraft cabins, in situations where relatively high ozone levels are expected, is known in the art
  • An example of a commonly known type of catalytic converter is illustrated in U S Patent 4,405,507 which discloses a ceramic (cordie ⁇ te) monolithic support structure having a high surface area washcoat applied to the monolithic support, with the washcoat being used to carry the catalyst (in this case a platinum group metal and a non-precious Group VLTI metal oxide or aluminate)
  • the washcoat is subject to att ⁇ tion when exposed to continued vibration and thermal cycling, such as that which may be expenenced when a converter is used in an aircraft application
  • the washcoat and the catalyst carried by the washcoat may be washed off of the ceramic monolithic support structure during routine maintenance cleaning
  • catalytic reactors of this type typically include
  • Patent Applications 08/271,922 and 08/494,656 each disclose improved catalytic ozone converters of compact size and lightweight construction.
  • Each of the co-pending applications discloses an aluminum or aluminum alloy support structure which comprises one or more plate-fin elements disposed within a converter housing.
  • Each of the plate-fin elements includes a plurality of fins ananged in an axial succession of off-set fin rows between the inlet and outlet ends of the housing.
  • the configuration of the plate-fin elements results in a relatively high mass transfer between the ozone-containing air and the ozone carried by the plate-fin elements for purposes of ozone decomposition
  • the plate-fin elements have an integral anodized surface layer at least two microns thick, with the cataiyst disposed on and within the anodized surface layer.
  • one or more Group VIII noble metals and optionally base metals from Groups VII, Ilia, and VTIa are disposed on and within the anodized surface layer of the plate-fin elements.
  • the anodizing steps required in each disclosure are relatively expensive
  • the catalysts which are disposed on and in the surface layer may be at least pamallv removed dunng routine maintenance cleaning
  • the catalytic reactor compnses a core structure constructed from a catalytically-active metal alloy
  • the core support structure has an inlet end effective for receiving a flow of ozone-containing air and an outlet end effective for discharging the ozone-containing air therefrom
  • the catalytically-active metal alloy is effective for decomposing at least a portion of the ozone present m the ozone-containing air as the ozone-containing air flows between the inlet and outlet ends of the core structure
  • the catalytically-active metal alloy compnses a silver- containing metal alloy, and may have a composition including silver and copper
  • the catalytically-active metal alloy may have a composition comp ⁇ sing, on a weight basis, about 55% silver, about 39% copper, about 5% zmc and about 1% nickel
  • the catalytically-active metal alloy may be
  • the core support structure is configured so as to define a plurality of tortuous flowpaths for the flow of the ozone-containing air between the inlet and outlet ends of the core structure so that the flow of the ozone-containing air is substantially turbulent between the inlet and outlet ends.
  • the core structure may comp ⁇ se at least one plate-fin element, with each of the plate-fin elements having a plurality of fins which are ananged in an axial succession of rows of the fins between the inlet and the outlet ends of the core structure
  • Each of the rows of fins defines a plurality of flow channels, and the fins of each of the rows are laterally off-set relative to the fins of axially adjacent ones of the rows so as to define the plurality of tortuous flowpaths for the flow of the ozone-containing air between the inlet and the outlet ends of the core structure
  • Each of the fins may have a generally rectangular cross- section
  • an alternative to p ⁇ or catalytic reactors is accomplished by providing a method for decomposing ozone in air
  • the method compnses the steps of constructing a core structure from a single, catalytically-active metal alloy, with the core structure having an inlet end and an outlet end.
  • the method may further comp ⁇ se the step of thermally activating the catalytically-active metal alloy, with the activating step comp ⁇ sing the step of heating the catalytically-active metal alloy to a temperature ranging from about 300°F to about 420°F for a period of time rangmg from about 30 minutes to about 60 minutes
  • the heating step comprises the step of calcining the alloy to the stated temperature for the stated period of time
  • the method may also comp ⁇ se the step of configu ⁇ ng the core structure so as to define a plurality of tortuous flowpaths for the flow of the ozone-containing air between the inlet end and the outlet end of the core structure
  • the catalytically-active metal alloy may be as desc ⁇ bed with respect to the first aspect of the invention
  • a mam advantage of the apparatus and method of the present invention is the provision of a light, compact and cost efficient catalytic converter for the decomposition of ozone in air, with the reactor bemg substantially mass-transfer limited
  • Fig 1 is a fragmentary isometnc view illustrating a po ⁇ ion of a core structure, comp ⁇ sing a plate-fin element, which may be incorporated in the catalytic converter of the present invention
  • Fig 2 is an elevational view taken along line 2-2 in Fig 1
  • Fig. 3 is an ozone destruction curve for the catalytically-active alloy of the present invention and illustrates the effects of thermally activating the alloy
  • Fig. 4 is a se ⁇ es of graphs illustrating the effect of temperature on the surface composition of the catalytically-active metal alloy of the present invention
  • Fig 5 is photo micro-graph of the surface of the catalytically-active metal alloy of the present invention in an as-received condition.
  • Fig 6 ts a photo micro-graph of the surface of the catalytically-active metal alloy of the present invention after thermal activation
  • Fig. 7 is an ozone destruction graph illustrating the ability of the catalytically- active metal alloy of the present invention to recover after temporary exposure to a sulfur dioxide contaminated, ozone-contatmng feed air.
  • Fig. 1 is a fragmentary isometric view illustrating a portion of a core structure 10 of a catalytic reactor for the decomposition of ozone in air. according to a prefened embodiment of the present invention
  • the core structure 10 includes at least one plate-fin element 12, with a portion of one of the plate-fin elements 12 being illustrated in Figs. 1 and 2.
  • the core structure 10 comprises a plurality of the plate-fin elements 12 mounted within a generally cylindrical housing (not shown), with the plate-fin elements ananged in a tightly packed cylindrical configuration, as a plurality of generally concentric annular rings
  • the center of the cylindrical space defined by the housing may be occupied by a small diameter support tube containing a short plate-fin element strip.
  • the core structure 12 includes an inlet end 14 which is effective for receiving a flow of ozone-containing air, indicated by flow anows 16, and an outlet end 18 effective for discharging the ozone-containing air 16 from the core structure 10
  • the catalytic reactor of the present invention provides a relatively lightweight and compact device for reducing the ozone content within the ozone-containing air 16, which may be supplied to an environmental control system for aircraft cabin pressurization and/or conditioning. When used in such an aircraft application, the catalytic reactor of the present invention may be mounted inside a conduit in se ⁇ es flow relationship with the aircraft environmental control system.
  • the ozone-containing air 16 may be supplied to the catalytic reactor from a compressor stage of a gas turbine engine of the aircraft, or alternatively may be provided from other sources such as ram air and/or a combination of engine compressor bleed and ram air In typical aircraft applications, the temperature of the ozone-containing air 16 may range from about 300°F ( 149°C) to about 420°F (216°C).
  • each of the plate-fin elements 12 compnses a plurality of fins 20 which are ananged in an axial succession of rows 22 of the fins 20 between the inlet end 14 and the outlet end 18 of the core structure 10
  • Three of the rows 22 of fins 20 are illustrated in Fig. 1 and designated as 22 A, 22B, and 22C Rows 22 A and 22B are further illustrated in the elevation view shown in Fig.
  • Each of the rows 22 includes a plurality of the fins 20 and defines a plurality of flow channels 24
  • the fins 20 of each of the rows 22 are laterally off-set by a distance x (Fig. 2) relative to the fins 20 of axially adjacent ones of the rows 22
  • the fins 20 of row 22B are laterally off-set with respect to the fins 20 of rows 22A and 22C Consequently, each plate-fin element 12 of the core structure 10 is configured so as to define a plurality of tortuous flowpaths for the flow of the ozone-containing air 16 between the inlet end 14 and the outlet end 18 of core structure 10
  • This results m a substantially turbulent flow of the ozone-containmg air 16 between the inlet end 14 and the outlet end 18 of core structure 10 which in turn results in a relatively high mass transfer between the ozone-contammg air 16 and the subsequently described catalyst, from which each plate-fin element 12 is constructed
  • Fig. 2 Each of the rows 22 includes a pluralit
  • each of the fins 20 has a generally rectangular cross-section in a prefened embodiment, as seen in an axial view, and includes a height H, a thickness t, a pair of flats F, and an axial depth
  • Each fin 48 approximates a full sine-wave shape as illustrated in brackets in Fig.
  • each fin row 22 has a lateral fin density which may also be va ⁇ ed with application
  • each fin 20 may alternatively have other geomet ⁇ c shapes such as a generally t ⁇ angular cross-section, or a generally trapezoidal cross-section
  • Each of the plate-fin elements 12 is constructed, or fabricated from a catalytically-active metal alloy which comprises a central feature of the present invention
  • the catalytically-active metal alloy may be shaped by conventional means such as stamping so as to form the plurality of fins 20
  • the catalytically-active metal alloy compnses a silver-containing metal alloy and, in a prefened embodiment, has a composition including silver and copper as p ⁇ nciple constituents
  • An example of an alloy which the inventors have determined to be acceptable for use in the present invention has a composition comprising, on a weight basis, about 55% silver, about 39% copper, about 5% zmc and about 1% nickel.
  • composition conesponds to the following atomic ratios- Ag.Cu.Zn:Ni -*30:36 4 5 1
  • the catalytically-active metal alloy of the present invention must comp ⁇ se a silver-containing metal alloy
  • the alloy is extremely active for ozone decomposition, providing mass-transfer- limited performance at temperatures as low as 212°F ( 100°C) Accordingly, for low temperature applications, i e temperatures in which the ozone-contaming air 16 is less than about 300°F ( 149°C) the silver-containing metal alloy must be activated by calcining, or heating the alloy in au ⁇ to a temperature ranging from about 300°F (149°C) to about 420°F (216°C) for a penod of time ranging from about 30 minutes to about 60 minutes For higher temperature applications, i e. those in which the ozone-containing air 16 is at least 300°F (149°C) the thermal activation step may be omitted
  • thermodynamic analysis of the surface composition of the plate-fin element 12 as a function of temperature was performed Again, the composition of the silver- containing metal alloy conesponded to atomic ratios of: 30 36 4 5 1
  • the results of the thermodynamic analysis illustrated graphically in Fig. 4, show that the surface composition of the silver-containing metal alloy (which is exposed to air) varies with temperature At ambient temperature, the equilibrium surface composition is a mixture of CuO, Ag 2 O, ZnO and NiO As shown in Fig.
  • a laboratory-scale reactor was assembled to include a section of a plate-fin element having 2 rows of fins, with each row of fins including 8 fins.
  • Measured fin dimensions were approximately as follows fin height (H in Fig 2) was 181 in. (4 60 mm), fin thickness was 0.0036 in ( 091 mm), and fin axial depth was 177 in. (4 50 mm)
  • the lateral fin density in each row was 16 fins/in
  • the plate- fin section was constructed from a silver-containing metal alloy having a composition comprising about 55% Ag, about 39% Cu, about 5% Zn and about 1% Ni.
  • the section of the plate-fin element was mounted in the laboratory-scale reactor and air containing 2 3 ppm by volume ozone was flowed through the plate-fin element, so as to contact multiple surfaces of the silver-containing metal alloy, at 1 x 10 ⁇ GHSV at STP and at the following five temperatures.
  • Table 1 provides a reference value for compa ⁇ son with the actual conversion as measured expe ⁇ mentally
  • the calculation assumes that the catalyst is able to convert any ozone which reaches it, that is, the chemical reaction is not limiting. The calculation then is based on the reaction rate which should be observed if mass transfer of the reactants and products to and from the catalyst is limiting (L Hegedus,
  • the "as-received" surface of the silver-containing metal alloy had a "white- copper” sheen.
  • the "as-received” metal alloy surface was relatively smooth in appearance with sub-micron size surface striations (possibly due to milling of the alloy during manufacture).
  • the activated silver-containing metal alloy surface had a dull gray appearance which was observed immediately after thermal activation.
  • the surface of the activated silver-containing metal alloy is roughened with particles which are about 1-10 microns in diameter.
  • Further analysis of both the "as-received” and activated fin samples using EDX confirmed that the "particles" observed on the surface of the activated silver- containing metal alloy contained high concentrations of silver. In contrast, copper and oxygen were found in extremely low concentrations. This result supported the thermodynamic analysis discussed previously in conjunction with Fig. 4, verifying that silver metal is the active site for ozone decomposition.
  • a laboratory reactor was assembled to a test section of a plate-fin element, having the same number of rows and fins, and made from the same alloy, as that described in Example 1. Durability testing was conducted to determine the ability of the silver-containing metal alloy to recover from a temporary poisoning with SO 2l as follows.
  • a "clean" feed air containing 2.3 ppm by volume of ozone was flowed through the plate-fin element at 1 x IO 6 GHSV at STP and at the following temperatures: 212°F, 302°F, 392°F, 482°F (100°C, 150°C, 200°C and 250°C)
  • 1 ppm by volume SO 2 was added to the ozone-containing air for a pe ⁇ od of 5 hours, after which the aforementioned "clean" feed was used for an additional 75 hours, at each temperature.
  • the ozone conversion was measured after 1 hour. 5 hours.
  • Catalyst poisoning by surface adso ⁇ tion of SO 2 can be reversible depending on the strength of the cataiyst-adsorbate bond.
  • the rapid recovery in catalyst performance after SO 2 removal shown in Table 2 and Fig. 7 demonstrates that this poisoning was reversible over the temperature range tested Accordingly, the temporary performance attenuation observed was due to "masking" of the catalyst sites by SO 2
  • the present reactor is cost reduced relative to prior reactors since it is not necessary to apply a washcoat to, or anodize, a metallic substrate. Additionally, since the alloy itself comprises the active catalyst, the catalyst will not be removed during routine maintenance cleaning.
  • the use of the silver-containing metal alloy of the present invention in conjunction with the prefened embodiment inco ⁇ orating the plate-fin elements, provides relatively high mass transfer between the ozone and the silver catalyst, and accordingly permits the use of a compact, lightweight reactor While the foregoing description has set forth the prefened embodiments of the invention in particular detail, it must be understood that numerous modifications, substitutions and changes can be undertaken without departing from the true spirit and scope of the present invention as defined by the ensuing claims.
  • the catalytic reactor of the present invention has been illustrated to include at least one plate-fin element in a prefened embodiment, other turbulent-producing structures may also be used, provided that the structure is made from the silver-containing alloy of the present invention.
  • the use of a turbulent-producing structure is prefened, the silver-containing metal alloy of the present invention may be advantageously utilized for ozone decomposition in structures which experience laminar flow conditions. The invention is therefore not limited to specific prefened embodiments as described, but is only limited as defined by the following claims.

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Abstract

A catalytic reactor is provided for the decomposition of ozone in air. The reactor comprises a core structure (10) having an inlet end effective for receiving a flow of ozone-containing air and an outlet end effective for discharging the ozone-containing air therefrom. The core structure is made of a catalytically-active metal alloy which is effective for decomposing at least a portion of the ozone present in the air as the ozone-containing air flows between the inlet end and outlet end of the core structure. The catalytically-active alloy comprises a silver-containing metal alloy and may comprise an alloy having silver and copper as the principle constituents. The catalytically-active alloy may optionally be thermally activated for use in low temperature applications. The core structure may be configured so as to provide a plurality of tortuous flowpaths between the inlet and outlet ends of the core structure to promote turbulent flow of the ozone-containing air.

Description

CATALYTIC REACTOR FOR THE DECOMPOSITION OF OZONE
CROSS-REFERENCES
The subject application is related to the following co-pending and commonly assigned U.S. Patent Applications which are expressly incoφorated by reference herein: Serial No. 08/271,922 filed on July 7, 1994 entitled "Catalytic Converter With Metal Monolith Having An Integral Catalyst"; Serial No. 08/494,656 filed on June 26. 1995 entitled "Catalytic Converter With Metal Monolith Having An Integral Silver Catalyst"
BACKGROUND OF THE INVENTION
1.0 Field of the Invention
The present invention relates generally to catalytic reactors, and more particularly, to a catalytic reactor for the decomposition of ozone in air. The application of the catalytic reactor of the present invention includes, but is not limited to, the decomposition of ozone present in the conditioned air supplied to aircraft cabins.
2.0 Related Art
Aircraft environmental control systems supply pressurized and conditioned air to the aircraft cabin. The temperature, pressure and relative humidity must be controlled to provide for the comfort of the flight crew and passengers within the aircraft.
Modern commercial jet aircraft are typically designed for fuel-efficient operation at relatively high altitudes of 25,000 feet or more above sea level where the ozone content of the air is relatively high Accordingly, dunng operation at high altitudes the air supplied to the aircraft cabin from the environmental control system may contain ozone at a level of 1 - 3 ppmv The presence of ozone in the air within the aircraft cabin can cause lung and eye irritation, headaches, fatigue and/or breathing discomfort As a result, present Federal Aviation Agency (FAA) regulations limit ozone concentrations on commercial flights to 0 1 ppmv dunng a three hour time peπod and 0 25 ppmv maximum at any time.
The use of catalytic converters to reduce or eliminate undesirable ozone in the air supplied to aircraft cabins, in situations where relatively high ozone levels are expected, is known in the art An example of a commonly known type of catalytic converter is illustrated in U S Patent 4,405,507 which discloses a ceramic (cordieπte) monolithic support structure having a high surface area washcoat applied to the monolithic support, with the washcoat being used to carry the catalyst (in this case a platinum group metal and a non-precious Group VLTI metal oxide or aluminate) While catalytic converters, or reactors, of this type have found widespread use, they are subject to the following limitations In the first instance, the washcoat is subject to attπtion when exposed to continued vibration and thermal cycling, such as that which may be expenenced when a converter is used in an aircraft application Secondly, the washcoat and the catalyst carried by the washcoat may be washed off of the ceramic monolithic support structure during routine maintenance cleaning Additionally, catalytic reactors of this type typically include a plurality of spaced flow channels which are formed in the support structure along an axially extending axis, and through which the ozone-containing air flows under laminar conditions Catalytic reactors of this type are typically mass-transfer limited, I e the efficiency of the reactor may be limited by the ability of the ozone molecule to diffuse to the surface of the catalyst This requires laminar-flow reactors to be much larger, and consequently heavier, than those which may employ turbulent flow of the ozone-containing air through the reactor Co-pending and commonly assigned U.S. Patent Applications 08/271,922 and 08/494,656 each disclose improved catalytic ozone converters of compact size and lightweight construction. Each of the co-pending applications discloses an aluminum or aluminum alloy support structure which comprises one or more plate-fin elements disposed within a converter housing. Each of the plate-fin elements includes a plurality of fins ananged in an axial succession of off-set fin rows between the inlet and outlet ends of the housing. The configuration of the plate-fin elements results in a relatively high mass transfer between the ozone-containing air and the ozone carried by the plate-fin elements for purposes of ozone decomposition In each disclosure the plate-fin elements have an integral anodized surface layer at least two microns thick, with the cataiyst disposed on and within the anodized surface layer. In Application Serial No. 08/271,922, one or more Group VIII noble metals and optionally base metals from Groups VII, Ilia, and VTIa are disposed on and within the anodized surface layer of the plate-fin elements. In one of the disclosed embodiments of Application Serial No. 08/494,656, silver is disposed on and within the anodized surface layer of the plate-fin elements, with this embodiment being prefened for relatively low temperature applications. The catalytic convener disclosed in each of the referenced co-pending applications represent a significant improvement over the then-existing prior art since the integral anodized surface layer is not subject to attntion, unlike washcoats of prior ceramic monolithic conveners, and the turbulent flow and resulting high mass transfer rate promoted by the plate-fin element configuration (due to the tortuous paths created by the off-set fin rows), permits the convener to be more compact than pπor designs The compactness of the disclosed conveners, coupled with the use of aluminum or aluminum alloy supports results in a lighter converter as compared to those employing ceramic monoliths. However, notwithstanding the aforementioned advantages of the inventions disclosed in the referenced co-pending applications, the anodizing steps required in each disclosure are relatively expensive Additionally, although the integral anodized surface layer is not subject to attntion. the catalysts which are disposed on and in the surface layer may be at least pamallv removed dunng routine maintenance cleaning
The foregoing illustrates limitations known to exist in present catalytic converters, or reactors Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter
SUMMARY OF THE INVENTION
In one aspect of the present invention, this is accomplished by providing a catalytic reactor for the decomposition of ozone in air According to a prefened embodiment, the catalytic reactor compnses a core structure constructed from a catalytically-active metal alloy The core support structure has an inlet end effective for receiving a flow of ozone-containing air and an outlet end effective for discharging the ozone-containing air therefrom The catalytically-active metal alloy is effective for decomposing at least a portion of the ozone present m the ozone-containing air as the ozone-containing air flows between the inlet and outlet ends of the core structure In other embodiments, the catalytically-active metal alloy compnses a silver- containing metal alloy, and may have a composition including silver and copper Even more particularly, the catalytically-active metal alloy may have a composition compπsing, on a weight basis, about 55% silver, about 39% copper, about 5% zmc and about 1% nickel The catalytically-active metal alloy may be thermally activated by heating the alloy to a temperature ranging from about 300°F to about 420°F for a penod of time ranging from about 30 minutes to about 60 minutes
In other embodiments, the core support structure is configured so as to define a plurality of tortuous flowpaths for the flow of the ozone-containing air between the inlet and outlet ends of the core structure so that the flow of the ozone-containing air is substantially turbulent between the inlet and outlet ends. The core structure may compπse at least one plate-fin element, with each of the plate-fin elements having a plurality of fins which are ananged in an axial succession of rows of the fins between the inlet and the outlet ends of the core structure Each of the rows of fins defines a plurality of flow channels, and the fins of each of the rows are laterally off-set relative to the fins of axially adjacent ones of the rows so as to define the plurality of tortuous flowpaths for the flow of the ozone-containing air between the inlet and the outlet ends of the core structure Each of the fins may have a generally rectangular cross- section According to a second aspect of the present invention an alternative to pπor catalytic reactors is accomplished by providing a method for decomposing ozone in air According to a prefened embodiment, the method compnses the steps of constructing a core structure from a single, catalytically-active metal alloy, with the core structure having an inlet end and an outlet end. flowing ozone-containing air between the inlet end and the outlet end of the core structure so that at least a portion of the ozone-containing air is in direct contact with the catalytically-active metal alloy According to other embodiments, the method may further compπse the step of thermally activating the catalytically-active metal alloy, with the activating step compπsing the step of heating the catalytically-active metal alloy to a temperature ranging from about 300°F to about 420°F for a period of time rangmg from about 30 minutes to about 60 minutes The heating step comprises the step of calcining the alloy to the stated temperature for the stated period of time The method may also compπse the step of configuπng the core structure so as to define a plurality of tortuous flowpaths for the flow of the ozone-containing air between the inlet end and the outlet end of the core structure The catalytically-active metal alloy may be as descπbed with respect to the first aspect of the invention
A mam advantage of the apparatus and method of the present invention is the provision of a light, compact and cost efficient catalytic converter for the decomposition of ozone in air, with the reactor bemg substantially mass-transfer limited
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other aspects of the present invention will become more apparent from the subsequent Detailed Descnption of the invention when considered in conjunction with the accompanying drawings wherein
Fig 1 is a fragmentary isometnc view illustrating a poπion of a core structure, compπsing a plate-fin element, which may be incorporated in the catalytic converter of the present invention,
Fig 2 is an elevational view taken along line 2-2 in Fig 1 , Fig. 3 is an ozone destruction curve for the catalytically-active alloy of the present invention and illustrates the effects of thermally activating the alloy, Fig. 4 is a seπes of graphs illustrating the effect of temperature on the surface composition of the catalytically-active metal alloy of the present invention,
Fig 5 is photo micro-graph of the surface of the catalytically-active metal alloy of the present invention in an as-received condition.
Fig 6 ts a photo micro-graph of the surface of the catalytically-active metal alloy of the present invention after thermal activation,
Fig. 7 is an ozone destruction graph illustrating the ability of the catalytically- active metal alloy of the present invention to recover after temporary exposure to a sulfur dioxide contaminated, ozone-contatmng feed air.
DETAILED DESCRIPTION
Refernng now to the drawings, Fig. 1 is a fragmentary isometric view illustrating a portion of a core structure 10 of a catalytic reactor for the decomposition of ozone in air. according to a prefened embodiment of the present invention The core structure 10 includes at least one plate-fin element 12, with a portion of one of the plate-fin elements 12 being illustrated in Figs. 1 and 2. In a prefened embodiment, the core structure 10 comprises a plurality of the plate-fin elements 12 mounted within a generally cylindrical housing (not shown), with the plate-fin elements ananged in a tightly packed cylindrical configuration, as a plurality of generally concentric annular rings The center of the cylindrical space defined by the housing may be occupied by a small diameter support tube containing a short plate-fin element strip. For further details of the aforementioned structural configuration of the prefened catalytic reactor, the reader may refer to commonly assigned European Patent No. 653,956, granted April 24, 1996, which is expressly incoφorated by reference herein in its entirety The core structure 12 includes an inlet end 14 which is effective for receiving a flow of ozone-containing air, indicated by flow anows 16, and an outlet end 18 effective for discharging the ozone-containing air 16 from the core structure 10 The catalytic reactor of the present invention provides a relatively lightweight and compact device for reducing the ozone content within the ozone-containing air 16, which may be supplied to an environmental control system for aircraft cabin pressurization and/or conditioning. When used in such an aircraft application, the catalytic reactor of the present invention may be mounted inside a conduit in seπes flow relationship with the aircraft environmental control system. The ozone-containing air 16 may be supplied to the catalytic reactor from a compressor stage of a gas turbine engine of the aircraft, or alternatively may be provided from other sources such as ram air and/or a combination of engine compressor bleed and ram air In typical aircraft applications, the temperature of the ozone-containing air 16 may range from about 300°F ( 149°C) to about 420°F (216°C). However, m certain aircraft applications, the temperature of the ozone-containing air 16 may be much cooler and lower temperature catalytic activity may be required, which is achievable with the catalytic reactor of the present invention as subsequently discussed in greater detail Each of the plate-fin elements 12 compnses a plurality of fins 20 which are ananged in an axial succession of rows 22 of the fins 20 between the inlet end 14 and the outlet end 18 of the core structure 10 Three of the rows 22 of fins 20 are illustrated in Fig. 1 and designated as 22 A, 22B, and 22C Rows 22 A and 22B are further illustrated in the elevation view shown in Fig. 2 Each of the rows 22 includes a plurality of the fins 20 and defines a plurality of flow channels 24 The fins 20 of each of the rows 22 are laterally off-set by a distance x (Fig. 2) relative to the fins 20 of axially adjacent ones of the rows 22 For instance, the fins 20 of row 22B are laterally off-set with respect to the fins 20 of rows 22A and 22C Consequently, each plate-fin element 12 of the core structure 10 is configured so as to define a plurality of tortuous flowpaths for the flow of the ozone-containing air 16 between the inlet end 14 and the outlet end 18 of core structure 10 This results m a substantially turbulent flow of the ozone-containmg air 16 between the inlet end 14 and the outlet end 18 of core structure 10 which in turn results in a relatively high mass transfer between the ozone-contammg air 16 and the subsequently described catalyst, from which each plate-fin element 12 is constructed As shown in Fig. 2, each of the fins 20 has a generally rectangular cross-section in a prefened embodiment, as seen in an axial view, and includes a height H, a thickness t, a pair of flats F, and an axial depth Each fin 48 approximates a full sine-wave shape as illustrated in brackets in Fig. 2 The off-set x, as well as the overall size of the fins 20 may be vaπed to achieve the desired flow characteπstics through each plate-fin element 12 for a particular application Each fin row 22 has a lateral fin density which may also be vaπed with application Although each fin 20 preferably has a generally rectangular shape, the fins 20 may alternatively have other geometπc shapes such as a generally tπangular cross-section, or a generally trapezoidal cross-section
Each of the plate-fin elements 12 is constructed, or fabricated from a catalytically-active metal alloy which comprises a central feature of the present invention The catalytically-active metal alloy may be shaped by conventional means such as stamping so as to form the plurality of fins 20 The catalytically-active metal alloy compnses a silver-containing metal alloy and, in a prefened embodiment, has a composition including silver and copper as pπnciple constituents An example of an alloy which the inventors have determined to be acceptable for use in the present invention has a composition comprising, on a weight basis, about 55% silver, about 39% copper, about 5% zmc and about 1% nickel. This composition conesponds to the following atomic ratios- Ag.Cu.Zn:Ni -*30:36 4 5 1 As subsequently discussed in greater detail, the inventors have identified silver as the active catalyst and accordingly, the catalytically-active metal alloy of the present invention must compπse a silver-containing metal alloy However, it is considered to be within the scope of the present invention to utilize metals other than copper as a principle constituent in combination with silver
Dunng initial testing of a portion of one of the plate-fin elements 12, which had been constructed using the catalytically-active metal alloy having the aforementioned atomic ratios of 30 36.4 5.1, the inventors observed that the silver-containing metal alloy was not catalytically active at low temperatures, as shown in the "ramp up" portion of Fig. 3 However, upon further testing, the inventors determined that the silver-containing metal alloy became catalytically-active for ozone decomposition after bemg thermally activated, as evidenced in the "ramp down" portion of Fig 3 It is noted that the test results shown in Fig. 3 conesponded to an ozone concentration of 2 36 ppmv and a flow rate of 1,000,000 GHSV (STP) As shown in Fig. 3, after the silver-containing metal alloy has been thermally activated, the alloy is extremely active for ozone decomposition, providing mass-transfer- limited performance at temperatures as low as 212°F ( 100°C) Accordingly, for low temperature applications, i e temperatures in which the ozone-contaming air 16 is less than about 300°F ( 149°C) the silver-containing metal alloy must be activated by calcining, or heating the alloy in au¬ to a temperature ranging from about 300°F (149°C) to about 420°F (216°C) for a penod of time ranging from about 30 minutes to about 60 minutes For higher temperature applications, i e. those in which the ozone-containing air 16 is at least 300°F (149°C) the thermal activation step may be omitted
In an effort to gain an increased understanding of this phenomena, a detailed thermodynamic analysis of the surface composition of the plate-fin element 12 as a function of temperature was performed Again, the composition of the silver- containing metal alloy conesponded to atomic ratios of: 30 36 4 5 1 The results of the thermodynamic analysis, illustrated graphically in Fig. 4, show that the surface composition of the silver-containing metal alloy (which is exposed to air) varies with temperature At ambient temperature, the equilibrium surface composition is a mixture of CuO, Ag2O, ZnO and NiO As shown in Fig. 4, this composition changes with temperature As the temperature increases, Ag2O decomposes, forming Ag° and O2 There is a strong conelation between the activation temperature required to obtain high ozone destruction activity and the predicted change in equilibπum surface composition. The results shown in Fig. 4 confirm that Ag° metal is the species which is catalytically-active for ozone decomposition These results were further verified in the subsequently discussed Examples and the associated examination of an as-received silver-containing metal alloy surface and an activated silver-containing metal alloy surface which was operated for greater than 300 hours in ozone air feeds at a vanety of temperatures The following examples are provided to demonstrate some of the benefits which may be achieved by following the teachings of this invention EXAMPLE 1
A laboratory-scale reactor was assembled to include a section of a plate-fin element having 2 rows of fins, with each row of fins including 8 fins. (Refer to Figs. 1 and 2) Measured fin dimensions were approximately as follows fin height (H in Fig 2) was 181 in. (4 60 mm), fin thickness was 0.0036 in ( 091 mm), and fin axial depth was 177 in. (4 50 mm) The lateral fin density in each row was 16 fins/in The plate- fin section was constructed from a silver-containing metal alloy having a composition comprising about 55% Ag, about 39% Cu, about 5% Zn and about 1% Ni. The section of the plate-fin element was mounted in the laboratory-scale reactor and air containing 2 3 ppm by volume ozone was flowed through the plate-fin element, so as to contact multiple surfaces of the silver-containing metal alloy, at 1 x 10δ GHSV at STP and at the following five temperatures. 122°F, 212T, 302T, 392°F and 482°F (50°C, 100°C, 150°C, 200°C, and 250°C) The ozone conversion was measured, after 60 hours of operation using a PCI Ozone Monitor (Model LC) before and after the laboratory reactor The results are presented in Table 1 Additionally, SEM-EDX analysis was performed on the surface of an "as-received" sample of the silver- containing metal alloy, as well as the surface of an aged sampie The low magnification (500x) SEM images of the "as received" and aged, or activated silver- containing fin surfaces are shown in Figs. 5 and 6, respectively
TABLE 1
Ozone Destruction Performance
1,000,000 GHSV (STP); 2.3 ppmv Ozone
Figure imgf000014_0001
* note mass transfer-limited calculations may have an error as great as +/-3% conversion in this range The column labeled "Predicted Mass Transfer Limited Conversion" shown in
Table 1 provides a reference value for compaπson with the actual conversion as measured expeπmentally The calculation assumes that the catalyst is able to convert any ozone which reaches it, that is, the chemical reaction is not limiting. The calculation then is based on the reaction rate which should be observed if mass transfer of the reactants and products to and from the catalyst is limiting (L Hegedus,
Ameπcan Chemical Society, Chicago Meeting, August, 1973, pgs 487-502) This method is for straight channel monoliths and has been modified by the inventors to account for the off-set fin design. If the actual conversion measured is the same as that which the mass transfer-limited calculation predicts, then it follows that mass transfer is limiting in fact and that the catalyst activity is not. Conversely, if the conversion is lower than the mass transfer limited conversion, then the catalyst activity is limiting. It may be seen from the results shown in Table 1 that mass transfer was limiting except at the temperature of 122°F (50°C).
The "as-received" surface of the silver-containing metal alloy had a "white- copper" sheen. As shown in Fig. 5, the "as-received" metal alloy surface was relatively smooth in appearance with sub-micron size surface striations (possibly due to milling of the alloy during manufacture). In contrast, the activated silver-containing metal alloy surface had a dull gray appearance which was observed immediately after thermal activation. As shown in Fig. 6, the surface of the activated silver-containing metal alloy is roughened with particles which are about 1-10 microns in diameter. Further analysis of both the "as-received" and activated fin samples using EDX confirmed that the "particles" observed on the surface of the activated silver- containing metal alloy contained high concentrations of silver. In contrast, copper and oxygen were found in extremely low concentrations. This result supported the thermodynamic analysis discussed previously in conjunction with Fig. 4, verifying that silver metal is the active site for ozone decomposition.
EXAMPLE 2
A laboratory reactor was assembled to a test section of a plate-fin element, having the same number of rows and fins, and made from the same alloy, as that described in Example 1. Durability testing was conducted to determine the ability of the silver-containing metal alloy to recover from a temporary poisoning with SO2l as follows. Initially, a "clean" feed air containing 2.3 ppm by volume of ozone was flowed through the plate-fin element at 1 x IO6 GHSV at STP and at the following temperatures: 212°F, 302°F, 392°F, 482°F (100°C, 150°C, 200°C and 250°C) After 20 hours of testing with the "clean" feed, 1 ppm by volume SO2 was added to the ozone-containing air for a peπod of 5 hours, after which the aforementioned "clean" feed was used for an additional 75 hours, at each temperature. The ozone conversion was measured after 1 hour. 5 hours. 20 hours, and 60 hours of exposure to the ozone- containing air The results of the test are shown in Table 2 and Fig. 7 SEM-EDX analysis of a poisoned alloy was conducted for comparison. Our spectroscopic analysis was in agreement with the hypothesis that the catalytically active sites were poisoned with silver SEM-EDX of a poisoned catalyst showed that the sulfur was associated with regions which were high in silver content; in contrast, areas which were high in copper were relatively free of sulfur
TABLE 2
Ozone Destruction Performance
1,000,000 GHSV (STP); 2.3 ppmv Ozone
Figure imgf000017_0001
It is well documented that sulfur can act as a catalyst poison, attenuating performance by either "masking" sites or by converting the active material into an inactive compound. Using the present silver-containing metal alloy, SO2 can either adsorb on the surface of the Ag particles ("masking" the sites) or the Ag and SO2 can react in this oxidizing environment to form catalytically inactive Ag2 SO4, which is extremely stable when formed As illustrated in Table 2 and Fig 7 (which conesponds to the 392°F test), a dramatic attenuation in performance was observed as soon as the SO2 was introduced. However, as shown in both Table 2 and Fig. 7, a rapid recovery to mass-transfer-limited performance was observed. This behavior was observed for each temperature range. Catalyst poisoning by surface adsoφtion of SO2 can be reversible depending on the strength of the cataiyst-adsorbate bond. The rapid recovery in catalyst performance after SO2 removal, shown in Table 2 and Fig. 7 demonstrates that this poisoning was reversible over the temperature range tested Accordingly, the temporary performance attenuation observed was due to "masking" of the catalyst sites by SO2 These results demonstrate that the silver-containing metal alloy is not ineversibly poisoned by sulfur contaminates in ozone-containing air feeds The use of the silver containing metal alloy in the catalytic reactor of the present invention provides a cost efficient, and relatively maintenance free, catalytic reactor for the decomposition of ozone in air. The present reactor is cost reduced relative to prior reactors since it is not necessary to apply a washcoat to, or anodize, a metallic substrate. Additionally, since the alloy itself comprises the active catalyst, the catalyst will not be removed during routine maintenance cleaning. The use of the silver-containing metal alloy of the present invention in conjunction with the prefened embodiment incoφorating the plate-fin elements, provides relatively high mass transfer between the ozone and the silver catalyst, and accordingly permits the use of a compact, lightweight reactor While the foregoing description has set forth the prefened embodiments of the invention in particular detail, it must be understood that numerous modifications, substitutions and changes can be undertaken without departing from the true spirit and scope of the present invention as defined by the ensuing claims. For instance, although the catalytic reactor of the present invention has been illustrated to include at least one plate-fin element in a prefened embodiment, other turbulent-producing structures may also be used, provided that the structure is made from the silver-containing alloy of the present invention. Furthermore, although the use of a turbulent-producing structure is prefened, the silver-containing metal alloy of the present invention may be advantageously utilized for ozone decomposition in structures which experience laminar flow conditions. The invention is therefore not limited to specific prefened embodiments as described, but is only limited as defined by the following claims.

Claims

18
1 A catalytic reactor for the decomposition of oone in air comprising a core structure constructed from a catalytically-active metal alloy, wherein said core structure has an inlet end effective for receiving a flow of ozone-containing air and an outlet end effective for discharging the ozone-containmg air therefrom, said catalytically-active metal alloy is effective for decomposing at least a portion of the ozone present in the ozone-containing air as the ozone-containing air flows between said inlet end and said outlet end of said core structure
2 The catalytic reactor as recited in claim 1 , wherein said catalytically-active metal alloy comprises a silver-containing metal alloy
3 The catalytic reactor as recited in claim 1 , wherein said catalytically-active metal alloy has a composition including silver and copper
4 The catalytic reactor as recited in claim 1 , wherein said catalytically-active metal alloy has a composition comprising, on a weight basis, about 55% silver, about 39% copper, about 5% zinc, and about 1 % nickel
5 The catalytic reactor as recited in claim 1 , wherein said catalytically-active metal alloy is thermally activated by heating said alloy to a temperature ranging from about 300°F to about 420°F for a period of time ranging from about 30 minutes to about 60 minutes
6 The catalytic reactor as recited in claim 1 , wherein
Said core structure is configured so as to define a plurality of tortuous flowpaths for the flow of the ozone-containmg air between said inlet end and said outlet end of said core structure so that the flow of the ozone-containmg air is substantially turbulent between said inlet end and said outlet end of said core structure
7 The catalytic reactor as recited in claim 6, wherein said core structure comprises at least one plate-fin element, each said plate-fin element having a plurality of fins which are arranged in an axial succession of rows of said fins between said inlet end and said outlet end of said core structure, each of said rows of said fins defines a plurality of flow channels, said fins of each of said rows are laterally off-set relative to said fins of axially adjacent ones of said rows so as to define said plurality of said tortuous flowpaths for the flow of the ozone-containing air between said inlet end and said outleet end of said core structure
8 The catalytic reactor as recited in claim 7, wherein each of said fins has a generally rectangular cross-section
PCT/US1997/007841 1996-05-09 1997-05-09 Catalytic reactor for the decomposition of ozone WO1997041948A1 (en)

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Citations (6)

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US4014657A (en) * 1972-05-25 1977-03-29 Vladimir Mikhailovich Gryaznov Catalytic-reactor for carrying out conjugate chemical reactions
US4261863A (en) * 1979-11-05 1981-04-14 Dart Industries Inc. Ozone control catalyst compositions
EP0367574A2 (en) * 1988-10-31 1990-05-09 Sakai Chemical Industry Co., Ltd., Ozone decomposition catalyst and method
EP0398765A1 (en) * 1989-05-19 1990-11-22 Sakai Chemical Industry Co., Ltd., Ozone decomposition
WO1994009903A1 (en) * 1992-10-28 1994-05-11 Allied-Signal Inc. Catalytic converter with metal monolith having an integral catalyst

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Publication number Priority date Publication date Assignee Title
US4014657A (en) * 1972-05-25 1977-03-29 Vladimir Mikhailovich Gryaznov Catalytic-reactor for carrying out conjugate chemical reactions
DE2362066A1 (en) * 1972-12-15 1974-06-27 Shell Int Research METHOD OF MANUFACTURING A SILVER CATALYST CONTAINING A CARRIER MATERIAL AND USE OF THIS CATALYST TO MANUFACTURE ETHYLENE OXIDE
US4261863A (en) * 1979-11-05 1981-04-14 Dart Industries Inc. Ozone control catalyst compositions
EP0367574A2 (en) * 1988-10-31 1990-05-09 Sakai Chemical Industry Co., Ltd., Ozone decomposition catalyst and method
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WO1994009903A1 (en) * 1992-10-28 1994-05-11 Allied-Signal Inc. Catalytic converter with metal monolith having an integral catalyst

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