WO2000013790A1

WO2000013790A1 - Ozone destroying compositions comprising manganese oxide

Info

Publication number: WO2000013790A1
Application number: PCT/US1999/017608
Authority: WO
Inventors: Jeffrey B. Hoke; Ronald M. Heck
Original assignee: Engelhard Corporation
Priority date: 1998-09-08
Filing date: 1999-08-03
Publication date: 2000-03-16
Also published as: AU5253199A

Abstract

The morphology of catalysts is demonstrated to have a significant effect on the durability of catalyst activity. Comparatively speaking, catalytic materials of larger median particle size appear and are believed to be more resistant to the masking and fouling effects of particulate material present in the air than catalytic materials of lower median particle size. The present application discloses a catalyst and a method of treating the atmosphere with an ozone decomposition composition of improved catalytic durability comprising contacting the atmosphere with a composition comprising a manganese oxide of median particle size diameter equal to or greater than about 2.0 micrometers.

Description

OZONE DESTROYING COMPOSITIONS COMPRISING MANGANESE OXIDE

BACKGROUND OF THE INVENTION

1.1 Field of the Invention 0 The present invention is directed toward compositions and methods of treating the atmosphere. More particularly, the morphology of ozone destroying manganese oxides are demonstrated to have significant effects on the durability of manganese oxides to decompose ozone.

5 1.2 Related Art

Co-pending, commonly assigned patent applications, 08/588,972, 08/589,030, 08/589.032, 08/589,182, 08/682,174, 08/695,687, 09/046,103, the disclosures of which are incorporated by reference, address various aspects of atmospheric pollutant treatment. However, these applications do not address the problem of long term 0 catalyst activity in view of the fouling and masking effects of particulate materials on catalytic materials, particularly manganese dioxides.

References are known which disclose proactively cleaning the environment, wherein the environment contains pollutants which may adversely affect performance of a catalyst used to clean the environment. 5 U.S. Patent No. 3,738.088 discloses an air filtering assembly for cleaning pollution from the ambient air by utilizing a vehicle as a mobile cleaning device. A variety of elements are disclosed to be used in combination with a vehicle to clean the ambient air as the vehicle is driven through the environment. In particular, there is disclosed ducting to control air stream velocity and direct the air to various filter 0 means. The filter means can include filters and electronic precipitators. Catalyzed postfilters are disclosed to be useful to treat nonparticulate or aerosol pollution such as carbon monoxide, unburned hydrocarbons, nitrous oxide and/or sulfur oxides, and the like. While US 3,738.088 discloses a filter to remove particulate material within the range of about 1 micron up to about 100 microns and higher and electronic precipitating means to remove finer particulate material in the range of 0.01 up to 1 micron, it does not address the masking and fouling of the particulate material on the catalyst as U.S. 3,738,088 appers to intend to remove particulates from the air stream before the air contacts the catalyst. Of the foregoing, commonly assigned patent applications, 09/046,103 is concerned with the intraparticle pore (i.e., micropore) characteristics of catalytic materials of sufficient average pore size and surface area to prevent or at least substantially reduce capillary condensation of water vapor into the micropores of the catalytic particle. The subject matter of the ' 103 application is different than the present application as the present application is concerned with particulate masking and fouling effects of interparticle formed pores which are at least several orders of magnitude larger than the micropores.

Applicants' invention provides a significant advance in providing catalytic compositions of improved durability. While not wishing to be bound to any particular theory, it is believed that compositions of this invention are of improved tolerance to the masking and fouling effects of particulate material such as dirt and dust. Such improved catalytic performance is achieved without providing additional devices or filters and is achieved by providing compositions with adjusted catalyst particle size.

SUMMARY OF THE INVENTION

The present invention relates to compositions and methods of improving the catalytic longevity or durability of catalytic compositions, particularly catalytic compositions comprising manganese oxides. One embodiment of this invention comprises an ozone decomposition composition of improved catalytic durability comprising a manganese oxide of median particle size diameter equal to or greater than about 2.0 micrometers.

Another embodiment of this invention comprises a method of treating the atmosphere with an ozone decomposition composition of improved catalytic durability comprising contacting the atmosphere with a composition comprising a manganese oxide of median particle size diameter equal to or greater than about 2.0 micrometers.

Yet another embodiment of this invention provides a method of improving the catalytic longevity of manganese oxide catalysts comprising the steps of providing: (a) a manganese oxide of median particle size diameter equal to or greater than about 2.0 micrometers,

(b) a polymeric binder, and

(c) admixing (a) and (b) to form a resulting composition with a morphology of interparticle pores sufficiently large enough to lessen the fouling or masking effects of particles present in the air when compared to compositions containing binder and a manganese oxides of lower median particle size than in (a).

Advantages of the compositions of this invention include improved catalytic durability of compositions without having to provide additional devices or filters to improve catalyst durability and merely requires providing compositions of adjusted catalyst particle size to achieve improved catalyst durability.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The compositions and methods of this invention relate to catalytic compositions of a moφhology which relate to improved ozone destruction durability.

The present invention will become more apparent from the following definitions and accompanying discussion.

The catalytic materials which can be employed in the present invention can vary widely but generally include platinum group metals, base metals, alkaline earth metals, rare earth metals and transition metals.

The platinum group metals include platinum, palladium, iridium, rhodium, silver and gold. The base metals include manganese, copper, nickel and cobalt. The alkaline earth metals include beryllium, magnesium, calcium, strontium, barium, and radium. The rare earth metals include cesium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. Early transition metals include scandium, yttrium, lanthanum, tympanum, zirconium, and hafnium.

Examples of such catalytic materials are disclosed in U.S. Patent 5,139,992, U.S. Patent No. 5,128,306, U.S. Patent No. 5,057,483, U.S. Patent No. 5,024,981, U.S. Patent No. 5,254,519, and U.S. Patent No. 5,212,142, each of which is incoφorated herein by reference.

The most preferred catalytic materials for use in the present invention are those which contain manganese and particularly those which contain manganese dioxide as explained in detail hereinafter. Such catalytic materials are especially suitable for treating ozone.

Useful ozone treating catalyst compositions comprise manganese compounds including manganese dioxide, non stoichiometric manganese dioxide (e.g., XMnO_{(1 5.} ₂₀₎), and/or XMn₂O₃ wherein X is a metal ion, preferably an alkali metal or alkaline earth metal (e.g. sodium, potassium and barium). Variable amounts of water (H₂O, OH^") can be incoφorated in the structure as well. Preferred manganese dioxides, which are nominally referred to as MnO₂ have a chemical formula wherein the molar ratio of manganese to oxide is about from 1.5 to 2.0. Up to 100 percent by weight of manganese dioxide MnO₂ can be used in catalyst compositions to treat ozone. Alternative compositions which are available comprise manganese dioxide and compounds such as copper oxide alone or copper oxide and alumina.

Useful and preferred manganese dioxides are alpha-manganese dioxides nominally having a molar ratio of manganese to oxygen of from 1 to 2. Useful alpha manganese dioxides are disclosed in U.S. Patent No. 5,340,562 to O'Young, et al.; also in O'Young, Hydrothermal Synthesis of Manganese Oxides with Tunnel Structures presented at the Symposium on Advances in Zeolites and Pillared Clay Structures presented before the Division of Petroleum Chemistry, Inc. American Chemical Society New York City Meeting, August 25-30, 1991 beginning at page 342; and in McKenzie, the Synthesis of Birnessite, Cryptomelane, and Some Other Oxides and Hydroxides of Manganese, Mineralogical Magazine, December 1971, Vol. 38, pp. 493-502. For the puφoses of the present invention, the preferred alpha- manganese dioxide is selected from hollandite (BaMn₈O_l6.xH₂O), cryptomelane (KMn_gO|₆.xH₂O), manjiroite (NaMn₈O₁₆.xH₂O) or coronadite (PbMn₈O₁₆.xH₂O).

The composition preferably comprises a binder as of the type described below with preferred binders being polymeric binders. The composition can further comprise precious metal components with precious metal components being the oxides of precious metal, including the oxides of platinum group metals and oxides of palladium or platinum also referred to as palladium black or platinum black. The amount of palladium or platinum black can range from 0 to 25%, with useful amounts being in ranges of from about 1 to 25 and 5 to 15% by weight based on the weight of the manganese component and the precious metal component. It has been found that the use of compositions comprising the cryptomelane form of alpha manganese oxide, which also contain a polymeric binder can result in greater than 50%, preferably greater than 60% and typically from 75-85% conversion of ozone in a concentration range of up to 400 parts per billion (ppb).

The preferred cryptomelane manganese dioxide can be calcined at a temperature range of from 250°C to 550°C and preferably below 500°C and greater than 300° for least 1.5 hours and preferably at least 2 hours up to about 6 hours.

The preferred cryptomelane can be made in accordance with methods described and incoφorated into U.S. Patent Application Serial No. 08/589,182 filed January 19, 1996 (Attorney Docket No. 3777C), incoφorated herein by reference. The cryptomelane can be made by reacting a manganese salt including salts selected from the group consisting MnCl₂, Mn(NO₃)₂, MnSO₄ and Mn (CH₃COO)₂ with a permanganate compound. Cryptomelane is made using potassium permanganate; hollandite is made using barium permanganate; coronadite is made using lead permanganate; and manjiroite is made using sodium permanganate. It is recognized that the alpha-manganese dioxide useful in the present invention can contain one or more of hollandite, cryptomelane, manjiroite or coronadite compounds. Even when making cryptomelane minor amounts of other metal ions such as sodium may be present. Useful methods to form the alpha-manganese dioxide are described in the above references which are incoφorated herein by reference. The preferred alpha-manganese dioxide for use in accordance with the present invention is cryptomelane. The preferred cryptomelane is "clean" or substantially free of inorganic anions, particularly on the surface. Such anions could include chlorides, sulfates and nitrates which are introduced during the method to form cryptomelane. An alternate method to make the clean cryptomelane is to react a manganese carboxylate, preferably manganese acetate, with potassium permanganate. It is believed that the carboxylates are burned off during the calcination process. However, inorganic anions remain on the surface even during calcination. The inorganic anions such as sulfates can be washed away with the aqueous solution or a slightly acidic aqueous solution. Preferably the alpha manganese dioxide is a "clean" alpha manganese dioxide. The cryptomelane can be washed at from about 60°C to 100°C for about one-half hour to remove a significant amount of sulfate anions. The nitrate anions may be removed in a similar manner. The "clean" alpha manganese dioxide is characterized as having an IR spectrum as disclosed in U.S. Patent Application Serial No. 08/589,182 filed January 19, 1996.

A preferred method of making cryptomelane useful in the present invention comprises mixing an aqueous acidic manganese salt solution with a potassium permanganate solution. The acidic manganese salt solution preferably has a pH of from 0.5 to 3.0 and can be made acidic using any common acid, preferably acetic acid at a concentration of from 0.5 to 5.0 normal and more preferably from 1.0 to 2.0 normal. The mixture forms a slurry which is stirred at a temperature range of from 50°C to 110°C. The slurry is filtered and the filtrate is dried at a temperature range of from 75°C to 200°C. The resulting cryptomelane crystals have a surface area of typically in the range of at least 100 m²/g.

Other useful compositions comprise manganese dioxide and optionally copper oxide and alumina and at least one precious metal component such as a platinum group metal supported on the manganese dioxide and where present copper oxide and alumina. Useful compositions contain up to 100, from 40 to 80 and preferably 50 to 70 weight percent manganese dioxide, and 10 to 60 and typically 30 to 50 percent copper oxide. Useful compositions include hopcalite (supplied by, for example, Mine Safety Applications, Inc.) which is about 60 percent manganese dioxide and about 40 percent copper oxide; and Carulite^® 200 (sold by Cams Chemical Co.) which is reported to have 60 to 75 weight percent manganese dioxide, 1 1 to 14 percent copper oxide and 15 to 16 percent aluminum oxide. The surface area of Carulite^® 200 is reported to be about 180 m²/g. Calcining at 450°C reduces the surface area of the Carulite^® by about fifty percent (50%) without significantly affecting activity. It is preferred to calcine manganese compounds at from 300°C to 500°C and more preferably 350°C to 450°C. Calcining at 550°C causes a great loss of surface area and ozone treatment activity. Calcining the Carulite^® after ball milling with acetic acid and coating on a substrate can improve adhesion of the coating to a substrate. Other compositions to treat ozone can comprise a manganese dioxide component and precious metal components such as platinum group metal components. While both components are catalytically active, the manganese dioxide can also support the precious metal component. The platinum group metal component preferably is a palladium and/or platinum component. The amount of platinum group metal compound preferably ranges from about 0.1 to about 10 weight percent (based on the weight of the platinum group metal) of the composition. Preferably, where platinum is present it is present in amounts of from 0. 1 to 5 weight percent, with useful and preferred amounts on pollutant treating catalyst volume, based on the volume of the supporting article, ranging from about 0.5 to about 70 g/ftΛ The amount of the palladium component preferably ranges from about 2 to about 10 weight percent of the composition, with useful and preferred amounts on pollutant treating catalyst volume ranging from about 10 to about 250 g/ft³. Useful amounts of the catalytic material can range from 70 to 95, preferably from 75 to 90 weight percent of the catalytic coating based on dry weight of the catalytic coating.

The pollutant treating compositions of the present invention preferably comprise a binder which acts to adhere the composition and to provide adhesion to the atmosphere contacting surface. It has been found that a preferred binder is a polymeric binder used in amounts of from 3 to 20, more preferably from 5 to 15 percent by weight of binder based on the weight of the composition. Preferably, the binder is a polymeric binder which can be a thermosetting or thermoplastic polymeric binder. The polymeric binder can have suitable stabilizers and age resistors known in the polymeric art. The polymer can be a plastic or elastomeric polymer. Most preferred are thermosetting, elastomeric polymers introduced as a latex into a slurry of the catalyst composition, preferably an aqueous slurry. Upon application of the composition and heating the binder material can crosslink providing a suitable support which enhances the integrity of the coating, its adhesion to the atmosphere contacting surface and provides structural stability under vibrations encountered in motor vehicles. The use of preferred polymeric binder enables the pollutant treating composition to adhere to the atmosphere contacting surface without the necessity of an undercoat layer. The binder can comprise water resistant additives to improve water resistance and improve adhesion. Such additives can include fluorocarbon emulsions, silicone polymers and petroleum wax emulsions. Useful polymeric compositions include polyethylene, polypropylene, polyolefin copolymers, polyisoprene, polybutadiene, polybutadiene copolymers, chlorinated rubber, nitrile rubber, polychloroprene, ethylene-propylene-diene elastomers, polystyrene, polyacrylate, polymethacrylate, polyacrylonitrile, poly(vinyl esters), poly(vinyl halides), polyamides, cellulosic polymers, polyimides, acrylics, vinyl acrylics and styrene acrylics, poly vinyl alcohol, thermoplastic polyesters, thermosetting polyesters, poly(phenylene oxide), poly(phenylene sulfide), fluorinated polymers such as poly(tetrafluoroethylene) polyvinylidene fluoride, poly(vinylfluoride) and chloro/fluoro copolymers such as ethylene chlorotrifluoroethylene copolymer, polyamide, phenolic resins and epoxy resins, polyurethane, and silicone polymers.

Preferred binders are selected from the group consisting of polymers and copolymers of acrylics, vinyl acrylics, styrene acrylics, ethylene vinyl acetates, vinyl acetates, fluorinated polymers and silicones.

Particularly preferred polymers and copolymers are vinyl acrylic polymers and ethylene vinyl acetate copolymers. A preferred vinyl acrylic polymer is a cross linking polymer sold by National Starch and Chemical Company as Xlink 2833. It is described as a vinyl acrylic polymer having a Tg of -15°C, 45% solids, a pH of 4.5 and a viscosity of 300 cps. In particular, it is indicated to have vinyl acetate CAS No. 108-05-4 in a concentration range of less than 0.5 percent. It is indicated to be a vinyl acetate copolymer. Other preferred vinyl acetate copolymers which are sold by the National Starch and Chemical Company include Dur-O-Set E-623 and Dur-O-Set E- 646. Dur-O-Set E-623 is indicated to be an ethylene vinyl acetate copolymer having a Tg of 0°C, 52% solids, a pH of 5.5 and a viscosity of 200 cps. Dur-O-Set E-646 is indicated to be an ethylene vinyl acetate copolymer with a Tg of -12°C, 52% solids, a pH of 5.5 and a viscosity of 300 cps. A useful and preferred binder is a crosslinking acrylic copolymer sold by National Starch and Chemical Company as X-4280. It is described as a milk white aqueous emulsion having a pH of 2.6; a boiling point of 212°F, a freezing point of 32°F; a specific gravity of 1.060; a viscosity of 100 cps. Polymeric dispersants may be added to enhance or promote slurry stability between the binder and catalyst. Binder/catalyst compatibility may be achieved by adding a polymeric acrylate derived dispersant (ca. 3% solids basis). The dispersant can be added during the ball milling operation or after. Despite generating a large negative charge on the catalyst particles, not all dispersants work equally as well. Preferred dispersants comprise polymers containing carboxylic acid groups or derivatives thereof such as esters and salts. Preferred dispersants include Accusol 445 (from Rohm & Haas) and Colloid 226/35 (from Rhone-Poulenc). Useful dispersants and a review of dispersion technology are presented in, Additives for Dispersion Technology, published by Rhone-Poulenc, Surfactants & Specialties hereby incoφorated by reference. Useful polymeric dispersants include but are not limited to polyacrylic acid partial sodium salts (i.e., at least partially contains a sodium salt of a polyacrylic acid) and anionic copolymer sodium salts sold by Rhone-Poulenc as Colloid ™ polymeric dispersants. Again, although surface charge is an important factor in determining catalyst/binder compatibility, it is not the only factor. In general, the dispersant (particularly Colloid 226) does a good job of stabilizing the slurry since a greater variety of latex binders (e.g. acrylics, styrene acrylics, and EVA's) are compatible. Long term compatibility problems may be addressed by increasing the quantity of dispersant, raising the pH somewhat, or both.

Useful amounts of dispersant range from 2 to 10, preferably from 2 to 6 weight percent of dispersant based on the dry weight of the composition.

The polymeric slurries of the present invention, particularly polymer latex slurries, can contain conventional additives such as thickeners, biocides, antioxidants, antifoamants and the like. The pollutant treating composition can be applied to the atmosphere contacting surfaces by any suitable means such as spray coating, powder coating, or brushing or dipping the surface into a catalyst slurry.

Milling of the catalytic composition may be done in any of a number of conventional particle milling devices in order to reach the desired particle size . One suitable device is a ball mill. The degree of particle milling can conveniently be measured by devices using light scattering techniques and the milling is stopped once the desired particle size is reached. One such suitable particle size measuring device is the Horiba LA-500 Laser Diffraction Particle Size Distribution Analyzer. The particle size referred to in the following examples and in the claims in the median particle size is based on the total number of particles in the measured sample.

The invention will become more apparent with reference to the accompanying examples.

EXAMPLES

Preparative Examples C-l

6000g of high surface area MnO₂ (220-250 m²/g cryptomelane) is combined in a 9 gallon ball mill with 9000g of deionized water and 514.3g of Rhone-Poulenc Colloid 226/35 polyacrylate dispersant (3% solids based on MnO₂ weight). The resulting mixture is milled for approximately 22 hours to a median particle size <1.0 μm. An additional 342.8g of Colloid 226 dispersant (2% solids based on MnO₂ weight) is added, the slurry is rolled for 10 minutes, and the mill is drained into a suitable mixing container. The resulting slurry is reduced to 25% solids overall with the addition of deionized water. Using an overhead stirrer, 13% of National Starch x- 4280 acrylic latex binder, 3.5% of Rohm & Haas RM-8W polymeric thickener, and 0.25% of Nopco NXZ defoamer are added sequentially with mixing (percentage amounts added are calculated on a solids basis compared to weight of MnO₂). The mixture is stirred a minimum of 30 minutes. The final slurry pH is approximately 5.5. The resulting composition contained approximately 82.3 % MnO₂, 4.1% dispersant, and 10.7 % latex binder, and 2.9 % thickener based on dry weight of the composition. E-l lOOOg of high surface area MnO₂ (220-250 m²/g cryptomelane) is combined in a 1 gallon ball mill with 1500g of deionized water and 50g of acetic acid (5% solids based on MnO₂ weight). The resulting mixture is milled for approximately 15 minutes to a median particle size approximately 3.5 μm. The slurry is drained from the mill, and the solids are reduced to 25% with the addition of deionized water. Using an overhead stirrer, 288.5g of National Starch E-646 EVA latex binder (15% solids based on MnO₂ weight) are added with stirring. The mixture is stirred a minimum of 30 minutes. The final slurry pH is approximately 4.5. The resulting composition contained approximately 83.3% MnO₂, and 12.5% latex binder and 4.2% acetic acid residue (e.g., in the form of acetate) based on dry weight of the composition.

In each of the foregoing examples, catalyst particle size was measured with a Horiba LA-500 Laser Diffraction Particle Size Distribution Analyzer. Specifically each catalytic material was ultrasonicated in the analyzer test chamber for approximately 20-30 seconds prior to the particle size measurement. The particle size is reported as a median based on the total number of particles in the measured sample. In other words, the smallest 50% of particles in the entire distribution have a particle size less than the median particle size value. Reproducibility in the measurement due to variability in the sampling is on the order of +/-0.1 μm.

Comparative Examples

E-l and C-l separately were applied to a 1997 Ford Contour radiator in coating weights of approximately 0.35 g/in³. These coated radiators were subsequently exposed to continuous air flow at 600,000/h space velocity for 650 hours (27 days). During this period the radiator exhaust air temperature was maintained at 70°C. Additionally, for 536 of the total 650 hours, the air stream contained approximately 100-200 ppb ozone. At the end of the aging period, ozone conversion data were collected at a space velocity of 600,000/h, a radiator exhaust air temperature of 75°C, and an ozone concentration of approximately 200-250 ppb ozone.

Comparative ozone conversion results for E-l and C-l catalyst coatings after 650 hours of continuous aging under simulated radiator operating conditions on a full- scale radiator test rig are summarized below:

75°C 45°C

E-l 84.9% 63.4%

C-l 66.4% 30.6%

The results indicate that after continuous aging in the presence of ozone, the ozone conversion performance of C-l coating is worse than that of E-l . This is particularly apparent at the lower 45°C test temperature where deactivation effects are more pronounced. Since the two coatings contain the same MnO₂ (cryptomelane) and roughly the same level of latex binder, the difference in "aging" performance is most likely attributed to the difference in particle size of the two coatings. The E-l coating contains catalyst particles with an average particle size of approximately 3.5 μm whereas the C- 1 coating contains catalyst particles with an average size of approximately 1.0 μm. The effect of this particle size difference is believed to give the E-l coating a much more porous inteφarticle moφhology relative to C-l . Mercury porosimetry measurements confirm that the E-l coating contains significantly larger pores (ca.7,50θA pore radius) compared to C-l (ca. l,50θA pore radius). These larger pores in turn possess a larger overall pore volume.

While not wishing to be bound by any particular theory, it is believed that because the C-l coating is of smaller median particle size than the E-l coating, is more densely packed, has smaller pores, and overall less pore volume than the E-l coating, it is likely that the C-l coating becomes more easily "fouled" or "masked" by solid contaminants in the ambient air (i.e., dirt particles). These masking components block the small pores of the C-l coating and thereby inhibit passage of ozone to the catalyst surface within the pores. This in turn reduces the ozone destroying efficiency of the catalyst coating. In order to improve the long term ozone destruction performance, catalyst particles greater than 1 μm average particle size should be utilized. This concept is not obvious based on standard coating technology (e.g. paint, paper, and textile coatings) where small particles (i.e. < 1 μm average particle size) are required in order to achieve the desired rheological and coating properties (e.g., uniformity, density, toughness, light scattering, tight packing, minimal void or pore formation, etc.). A typical example is latex based paint systems which utilize TiO₂ pigments of less than 1.0 μm average particle size (typically 0.1 μm). In the case of catalytic coatings, long term performance requirements dictate the use of larger particles.

Subsequent moφhology data generated using the C-l formulation as a basis and varying the median particle size revealed the following via mercury porosimetry:

Median Particle Size Inteφarticle Pore Radius 0.7 μm 1,500 A

1.8 μm 1,750 A 2.7 μm 5,800 A

3.3 μm 7,500 A

Referring to the foregoing data, it is reasonable to conclude that a 1.8 μm median particle size containing formulation would be expected to behave similarly to the 0.7 μm particle formulation as the pore radius of the 0.7 and 1.8 μm particles are essentially the same. However, when the median particle size is above 2.0 μm (i.e., 2.7 μm) the pore radius measured is significantly closer to the pore radius of the 3.3 μm particle. Therefore, it is reasonable to conclude that the 2.7 μm particles would behave more closely to the behavior of 3.3 μm particles and that effective catalytic durability is achieved at or above a 2.0 μm median particle size.

The principles, preferred embodiments, and modes of operating of this invention have been described in the foregoing specification. However, the invention which is intended to be protected herein is not to be construed as limited to the particular forms disclosed, since they are to be regarded as illustrative rather than restrictive. Variations and changes may be made by those skilled in the art without departing from the spirit of the invention.

Claims

What is claimed is:

1. An ozone decomposition composition of improved catalytic durability comprising a manganese oxide of median particle size diameter equal to or greater than about 2.0 micrometers.

2. The composition of claim 1, wherein the particle size diameter is in the range of about 2.7 to about 3.5 micrometers.

3. The composition of claim 1 or 2, further comprising platinum or palladium and a binder.

4. The composition of claim 1 or 2, wherein the binder is a polymeric binder.

5. The composition of claim 4, wherein the binder is selected from the group consisting of polymers and copolymers of acrylics, vinyl acrylics, styrene acrylics, ethylene vinyl acetates, vinyl acetates, fluorinated polymers and silicones.

6. The composition of claim 5, wherein the manganese oxide comprises from 70 to 95 weight percent of the composition based on dry weight.

7. The composition of claim 6, wherein the binder is from 3 to 20 weight percent of the composition based on dry weight.

8. The composition of claim 7 further comprising a polymeric dispersant in an amount from 2 to 10 weight percent of the compostion based on dry weight.

9. The composition of claim 8, wherein the manganese oxide is an alpha-manganese dioxide.

10. The composition of claim 9, wherein the alpha-manganese oxide is cryptomelane.

11. The composition of claim 10, wherein the cryptomelane comprises from 75 to 90 weight percent of the composition, the binder is an acrylic polymer or an ethylene vinyl acetate copolymer comprising from 5 to 15 weight percent of the composition, and the dispersant is a polymer containing carboxylic acid groups or derivatives thereof such as esters and salts comprising from 2 to 6 weight percent of the composition.

12. The composition of claim 11 , wherein the dispersant comprises at least a partial sodium salt of a polyacrylic acid.

13. The composition of claim 12, further comprising platinum or palladium.

14. The method of treating the atmosphere with an ozone decomposition composition of improved catalytic durability comprising contacting the atmosphere with a composition comprising a manganese oxide of median particle size diameter equal to or greater than about 2.0 micrometers.

15. The method of claim 14, wherein the median particle size diameter is in the range of about 2.7 to 3.5 micrometers.

16. The method of claim 15, wherein the manganese oxide is cryptomelane.

17. A method of improving the catalytic longevity of manganese oxide catalysts comprising the steps of providing:

(a) a manganese oxide of median particle size diameter equal to or greater than about 2.0 micrometers,

(b) a polymeric binder, and

(c) admixing (a) and (b) to form a resulting composition with a mo╧åhology of inte╧åarticle pores sufficiently large enough to lessen the fouling or masking effects of particles present in the air when compared to compositions containing binder and a manganese oxides of lower median particle size than in (a).

18. The method of claim 17, wherein the inte╧åarticle pores have a pore radius greater than about 1,750A as measured by mercury porosimetry.

19. The method of claim 18, wherein the inte╧åarticle pores are in the range of about 5,800 to 7,50╬╕A.

20. The method of claim 19, wherein the inte╧åarticle pores are about 7,50╬╕A.