System and method for treating a gas mixture comprising ozone and volatile organic compounds

Abstract

The present disclosure relates to a catalyst system for treating a gas mixture including ozone and volatile organic compounds, the catalyst system being in fluid flow communication with the gas mixture, the catalyst system comprising: a first catalyst comprising at least one platinum group metal, the first catalyst being utilised to predominantly oxidise the volatile organic compounds in the gas mixture; and a second catalyst comprising at least a manganese (Mn) component; the second catalyst being utilised to predominantly reduce the ozone in the gas mixture; wherein the first catalyst and the second catalyst are substantially discrete relative to each other. The present disclosure further relates to a method of treating a gas mixture and to an aircraft environmental control system.

Description

[0001] P101311W001

[0002] System and Method

[0003] FIELD OF THE INVENTION

[0004] This invention relates to a catalyst system suitable for treating a gas mixture comprising ozone and volatile organic compounds. In particular this invention relates to a catalyst system comprising a first catalyst and a second catalyst that are distinct relative to each other for the selective oxidation of volatile organic compounds and reduction of ozone respectively, in the gas mixture, preferably air, more preferably bleed air in an aircraft, which air is circulated into the interior of the aircraft.

[0005] BACKGROUND TO THE INVENTION

[0006] Breathable gas mixtures such as air include airborne contaminants such as, inter alia, bacteria, viruses, volatile organic compounds (VOCs), ozone (depending on the level thereof) and molecules creating distinct odours. Air containing these contaminants may be harmful to humans and animals and / or may cause discomfort to them and may cause headaches, irritation of the eyes, nose and throat and chest pains.

[0007] VOCs include more than 300 types of the carbon-based chemicals that share the common characteristics of low boiling point, high vapor pressure, and strong reactivity. Amongst the VOC species of greatest concern to human health and the environment are the aromatics, whose representative species include benzene, toluene, ethylbenzene and xylene (BTEX). BTEX species are carcinogens and mutagenic to humans.

[0008] There are many components that may be utilised in the purification of gas mixtures such as air, and the abatement of contaminants therein. For example, high efficiency particulate air filters (HEPA) are used to remove particles such as dust, allergens, bacteria and viruses. Disinfection systems such as ultraviolet lights may also be used. Gaseous filtration may also be employed to remove gaseous pollutants such as VOCs, odours and ozone but, in some cases, do not provide breathable air that complies with requisite air quality standards. P101311W001

[0009] The harm that contaminants in the air may cause to humans or animals is exacerbated in closed spaces where stale air is treated and / or combined with air from a source outside of the enclosed space which may contain contaminants. This is well exemplified by the bleed air used in an aircraft to refresh stale cabin air.

[0010] It will be appreciated that in an aircraft there is a continual replacement of stale cabin air with bleed air that has been treated. Usually, fresh air is taken from the atmosphere through the engine(s) of the aircraft and / or the auxiliary power unit (APU) of the aircraft. The resultant air is referred to as bleed air. Bleed air may be used for several purposes in aircraft such as engine start, wing anti-ice systems, water system pressurisation and air conditioning, wherein stale air is mixed with the bleed air (heated to an acceptable air cabin temperature and pressurised and put through a purification control system (environmental control system)) to remove pollutants including VOCs and ozone.

[0011] Aviation regulatory authorities, such as the Federal Aviation Administration (FAA) in the United States and the European Aviation Safety Agency (EASA) in Europe, have strict standards for cabin air quality. Purification systems are necessary to ensure compliance with these regulations and to maintain a safe and healthy environment for passengers and crew.

[0012] With respect to aircraft, flying at altitudes above about 40 000ft, the concentration of ozone becomes significant and even more so when ozone plumes are encountered. The FAA, in terms of its guideline, Advisory Circular AC 25-21 , advises that the concentration of ozone in breathable air should not exceed 0.25ppm over a period of 4 hours or less. The EASA regulations advise that the concentration of ozone in breathable air in cabin air should not exceed 0.1 ppm when measured over a period of 8 hours.

[0013] Aircrafts may now include a catalyst system as part of the pollution control system for the abatement of ozone and / or VOCs. The pollution control system is usually provided in the underbody of the aircraft. In providing such systems which contain, inter alia, a P101311W001 catalyst system, it is to be noted that ozone is a powerful oxidant which will deactivate many catalytic materials after a short time of exposure.

[0014] Numerous materials have been reported in the literature to be active for the catalytic decomposition of ozone. These include moisture (H2O), silver, platinum, manganese dioxide (MnC ), sodium hydroxide, soda lime, bromine, chlorine and nitrogen pentoxide. Of these, manganese dioxide is particularly prominent in terms of its catalytic activity towards decomposing ozone.

[0015] W02004096435A1 discloses a catalyst for decomposing ozone at temperatures up to about 150°C. In particular, a manganese-containing catalyst is disclosed which may include at least one precious metal selected from the group consisting of platinum group metals, silver and gold. The platinum group metal may be selected from platinum, palladium and rhodium. It is preferred however that the catalyst contains no precious metals.

[0016] While manganese (Mn) is known to effectively decompose ozone, it is not known to be particularly effective in decomposing VOCs. It is however known that platinum group metals are effective as active catalytic components in catalysts used to treat VOCs. Hence, homogeneous compositions comprising Mn and a platinum group metal have been used. The disadvantage of such compositions is that the Mn poisons the platinum group metal catalyst thus impairing the catalytic activity thereof and reducing its ability to oxidise the VOCs effectively. To counter the poisoning effect and achieve the effective oxidation of the VOCs, a higher loading of the platinum group metal is required, thus making such catalysts expensive.

[0017] US10392980 discloses a method for the treatment of emissions (which include NOXand various carbon oxides) from a diesel combustion engine using a diesel oxidation catalyst wherein a washcoat of a platinum group metal (and a support) and a washcoat of at least one base metal such as Co, Cu, Ce, Mn, NiO, Fe, Mo and W is provided. The platinum group metal (exemplified by reference to Pd in the specification) is applied on top of the base metal washcoat. Alternatively, the former is deployed upstream from the base metal catalyst. P101311W001

[0018] OBJECT OF THE INVENTION

[0019] The object of the invention is to provide a catalyst system which effectively removes VOCs and ozone in a gas mixture, wherein a first catalyst oxidises the VOCs and a second catalyst reduces ozone, wherein the first catalyst and second catalyst are substantially discrete relative to each other in order to considerably minimise the poisoning of the first catalyst by the second catalyst.

[0020] SUMMARY OF THE INVENTION

[0021] According to the present invention, there is provided a catalyst system for treating a gas mixture including ozone and volatile organic compounds, the catalyst system being in fluid flow communication with the gas mixture, the catalyst system comprising:

[0022] (i) a first catalyst comprising at least one platinum group metal, the first catalyst being utilised to predominantly oxidise the volatile organic compounds in the gas mixture; and

[0023] (ii) a second catalyst comprising at least a manganese (Mn) component; the second catalyst being utilised to predominantly reduce the ozone in the gas mixture; wherein the first catalyst and the second catalyst are substantially discrete relative to each other.

[0024] The gas mixture may further be treated prior to, during and / or after the removal of ozone and the VOCs.

[0025] The first catalyst may be arranged and configured, relative to the second catalyst, such that, in use, the gas mixture contacts the first catalyst prior to contact with the second catalyst.

[0026] The gas mixture to be treated may be air, preferably bleed air in an aircraft which may be used for the air conditioning of the cabin air in the aircraft. It will be appreciated that the bleed air may additionally be used for other purposes too.

[0027] The catalyst system may form part of an environmental control system of an aircraft. The catalyst system may be provided in a housing having an air intake, for receiving P101311W001 the air containing ozone and VOCs, such as the bleed air, and an outlet for discharging air that has been treated. The discharged air, or at least a portion thereof, may be cycled into the air conditioning of the aircraft.

[0028] Reference to “the catalysts” herein means both catalysts. Reference to “a catalyst” or “the catalyst” refers to either of the first catalyst or the second catalyst. The term “provided on or within” as used herein with reference to a substrate may encompass that the relevant catalyst is disposed on the substrate, such as in the form of a layer or coating, and / or that the catalyst is present in the substrate, such as in the form of an extruded catalyst. The term “disposed on” as used herein with reference to a substrate may encompass either that the relevant catalyst is directly disposed on the substrate, i.e. with no intervening material, and / or indirectly disposed on the substrate, i.e. with intervening material. If the substrate is porous, then the term “disposed on” may also encompass having the catalyst disposed therein, for example within the pores of the substrate, i.e. wherein the catalytic composition is disposed thereon and / or therein, for example, as a coating.

[0029] The first catalyst and the second catalyst of the invention are each disposed on or within a single substrate or on or within separate substrates. Preferably, the first catalyst and second catalyst are each disposed in the form of coatings on a single substrate or on separate substrates.

[0030] It will be appreciated that any combination of catalysts and their presence within or on a substrate is contemplated. For example, the first catalyst and the second catalyst may be disposed on or within the same substrate in a first zone and a second zone respectively. Alternatively, the first catalyst may disposed on a substrate and the second catalyst being disposed within the same substrate.

[0031] Alternatively, the first catalyst and second catalyst may be disposed on or within separate substrates.

[0032] Irrespective of the manner in which the catalysts are provided on or within a substrate, the first catalyst and the second catalyst are preferably arranged in use such that the P101311W001 gas mixture contacts the first catalyst prior to it making contact with the second catalyst.

[0033] The platinum group metal of the first catalyst may be either of platinum or palladium or a combination of both. In a preferred form of the invention, the first catalyst comprises Pt, Pt being the catalytically active component. The first catalyst may comprise Pt and be substantially free of Pd.

[0034] As used herein in relation to the catalysts, a “catalytically active” component is one that directly participates in the catalytic treatment of ozone and / or VOCs; and a “catalytically inactive” component is one which does not directly participate in the catalytic reduction of ozone and VOCs.

[0035] Where the first catalyst is disposed on the substrate, for example a monolith substrate, in the form of a coating, the PGM loading may be in the range of 20 to 300 g / ft3, for example, 30 to 250 g / ft3, such as 30 to 100 g / ft3, or 35 to 60g / ft3or 100 g / ft3to 300 g / ft3, such as 150 g / ft3to 250 g / ft3.

[0036] The term “loading” as used herein and by convention defines a concentration quantity of a component present in a catalyst layer on a substrate. The units of loading are generally expressed in g / ft3or g / in3and relate to the volume of the substrate that is used.

[0037] The second catalyst includes at least Manganese (Mn) as a catalytically active component. It may further include catalytically active components such as copper or magnesium. The second catalyst is preferably free of any platinum group metal.

[0038] Where the second catalyst is disposed on a substrate, for example a monolith substrate, in the form of a coating, the manganese loading may be in the range of 100 g / ft3to 2000 g / ft3, preferably, 100 to 1000 g / ft3, more preferably 120 g / ft3to 500 g / ft3.

[0039] The catalysts of the invention may further comprise a support material such as an inorganic oxide, on which, in the case of the first catalyst, the PGM is supported and, in the case of the second catalyst, the Mn is supported. Suitable supports include P101311W001 ceria and / or alumina optionally doped with one or more further elements, such as rare earth metals. Preferred supports preferably have a surface area in the range 10 to 1500 m2 / g, pore volumes in the range 0.1 to 4 mL / g, and pore diameters from about 10 to 1000 Angstroms. High surface area inorganic oxides having a surface area greater than 80 m2 / g are particularly preferred, e.g. high surface area ceria or alumina.

[0040] The support for the first catalyst comprising PGM, for example Pt, and the second catalyst comprising at least Mn may be independently selected from the group consisting of alumina, ceria silica-alumina, alumino-silicates, alumina-zirconia, alumina-ceria, alumina-lanthanum and ceria-zirconias. Suitable supports are well known in the art. Preferably the high surface area support has a surface area of at least 70 m2 / g, for example at least 80m2 / g, at least 150 m2 / g or at least 200 m2 / g.

[0041] The first catalyst and / or or the second catalyst may further comprise other components, particularly catalytically inactive components such as binders and other additives. The specific binders or additives employed may depend on the form of the finished catalyst.

[0042] The catalysts may be prepared according to methods known in the art. Where a catalyst is disposed on a substrate as a layer or coating, it may be applied to the substrate in the form of a washcoat. A washcoat typically comprises a liquid and a catalytic material. The washcoat may take the form of a solution, slurry or suspension of catalytic material in a solvent. Once coated onto the substrate, the washcoat typically undergoes a calcination step, to remove solvent and to fix the catalytically active material to the substrate.

[0043] Reference herein to “coating” or “coat” means the dried and calcined washcoat.

[0044] Where the first catalyst is applied to a substrate in the form of a washcoat, the washcoat may comprise PGM in the form of a salt, for example in the form of a nitrate salt, an acetate salt, a carbonate salt, a hydroxide salt or a carboxylate salt. Where the PGM comprises Pt, preferably the Pt is present in the washcoat in the form of a Pt(IV) nitrate salt. Where the PGM comprises Pd, preferably the Pd is present in the washcoat in the form of a nitrate salt, an acetate salt, a carbonate salt, a hydroxide salt or a carboxylate salt. P101311W001

[0045] Where the second catalyst is applied to a substrate in the form of a washcoat, the washcoat may comprise Mn in the form of a salt, for example in the form of a nitrate salt, an acetate salt or a carboxylate salt, preferably a Mn acetate salt.

[0046] Where a catalyst is provided within the substrate, the active substrate may be prepared by including the catalytically active component in a composition whose rheological properties have been set so as to be suitable for an extrusion process. This composition is a plastic (i.e. easily shaped or mouldable), viscous composition. To set the desired rheological properties of the composition and also the mechanical properties of the extrudate, binders or additives are typically added to the composition. This plastic composition is then subjected to an extrusion process for preparing, for example, a honeycomb body. The so-called “green” body thus obtained is then subjected to a high temperature calcination treatment to form the finished extruded catalyst body.

[0047] Where washcoats of catalysts are used, the washcoating is preferably performed by first slurrying finely divided particles of the catalyst materials (or precursors thereof) in an appropriate solvent, preferably water, to form a slurry (i.e. a washcoat). The slurry preferably contains between 5 to 70 weight percent solids, more preferably between 10 to 50 weight percent. Preferably, the particles are milled or subject to another comminution process in order to ensure that substantially all of the solid particles have a particle size of less than 20 microns in an average diameter, prior to forming the slurry. Additional components, such as stabilizers or promoters may also be incorporated in the slurry as a mixture of water soluble or water-dispersible compounds or complexes.

[0048] The substrate(s) may then be coated one or more times with the slurry such that there will be deposited on the substrate the desired loading of the catalyst materials.

[0049] After the substrate has been coated with the washcoat slurry, the coated substrate is dried and / or calcined, to form the final catalytic coating. Suitable drying and calcination conditions depend on the washcoat composition and the type of substrate. Such P101311W001 conditions are known in the art. Preferably, the coated substrate is calcined at 400 to 600°C for approximately 1 to 8 hours.

[0050] The coating may have a washcoat loading of between 1 to 4 g / in3, preferably between 2 to 3 g / in3. The term “washcoat loading” refers to the total mass of all components present in the final catalyst coating per unit volume of substrate.

[0051] Any suitable substrate may be employed for purposes of the invention.

[0052] The substrate(s) may be any of those materials typically used for preparing catalysts and will typically comprise a ceramic or metal monolith structure (also referred to as honeycomb substrates).

[0053] Each substrate has a fluid inlet and a fluid outlet and an axial length. For the avoidance of doubt, the inlet is the upstream end of the monolith substrate which, when arranged in a gas mixture treatment system, receives the gas mixture to be treated. The outlet is the downstream end of the monolith substrate which releases the treated gas mixture.

[0054] Monolith substrates have a honeycomb structure, having fine, parallel gas flow passages extending therethrough from an inlet or an outlet end of the substrate, wherein the passages are open to fluid flow therethrough (referred to herein as flow- through substrates). The passages, which are essentially straight paths from their fluid inlet to their fluid outlet, are defined by walls on which the catalytic material may be coated so that the gas mixture flowing through the passages contact the catalytic material. Alternatively, the monolithic substrate may be in the form of a wall-flow filter. The flow passages of the monolithic substrate are thin-walled channels, which can be of any suitable cross-sectional shape and size such as trapezoidal, rectangular, square, sinusoidal, hexagonal, oval, circular, etc.

[0055] Such monolithic substrates may contain up to about 900 or more flow passages (or “cells”) per square inch of cross section, although far fewer may be used. For example, the substrate may have from about 7 to 600, more usually from about 100 to 400, cells per square inch (“cpsi”). The cells can have cross sections that are rectangular, square, circular, oval, triangular, hexagonal, or are of other polygonal shapes. The P101311W001 monolithic substrate(s) may be made of any suitable refractory material, e.g., cordierite, cordierite-alumina, silicon nitride, or silicon carbide, or the substrates may be composed of one or more metals or metal alloys.

[0056] The first and second catalysts of the present invention may each be disposed on ceramic (e.g. cordierite) monolith substrates. Alternatively, the first and second catalysts of the present invention are each disposed on metallic monolith substrate.

[0057] Preferably the metallic monolith substrate comprises a FeCr alloy.

[0058] The catalysts and substrate configurations suitable for the invention are described as follows:

[0059] In an embodiment of the invention, in which the catalysts are provided on or within the same substrate, the first catalyst may be provided in an upstream zone of the substrate and the second catalyst may be provided in a downstream zone of the substrate. In this embodiment, the first catalyst may be disposed on the substrate as a coating extending from the fluid inlet for less than the axial length and the second catalyst may be disposed on the substrate as a coating extending from the fluid outlet for less than the axial length.

[0060] The coating comprising the first catalyst may extend from the fluid inlet of the substrate up to 75% of an axial length thereof, for example 25% to 75%, preferably 40% to 60% of the axial length of the substrate.

[0061] The coating comprising the second catalyst may extend from the fluid outlet of the substrate up to 75% of an axial length thereof, more preferably between 25% to 75%, preferably 40% to 60% of the axial length of the substrate.

[0062] The total axial length of the upstream zone and the downstream zone may be equal to 100% of the axial length of the monolith substrate, however during manufacturing a small overlap may be obtained as the layer coated last overlaps the layer coated first. It will be appreciated that the upstream zone and downstream zones are substantially discrete relative to each other, notwithstanding the small overlap. P101311W001

[0063] Alternatively, and in the embodiment wherein the catalysts are provided on or within the same substrate, the first catalyst may be provided as a layer coated on top of the second catalyst such that the gas mixture contacts the first catalyst prior to contacting the second catalyst. The first catalyst may be disposed on the substrate as a coating on top of a coating comprising the second catalyst.

[0064] The coating comprising the first catalyst may extend the full axial length of the substrate monolith or may extend less than 100% of the axial length of the substrate. For example, the coating comprising the first catalyst may extend from the inlet end for 25% to 75% of the axial length of the substrate, preferably 40% to 60% of the axial length of the substrate.

[0065] The coating comprising the second catalyst may extend the full axial length of the substrate monolith or may extend less than 100% of the axial length of the substrate. For example, the coating comprising the second catalyst may extend from the inlet end for 25% to 75% of the axial length of the substrate, preferably 40% to 60% of the axial length of the substrate.

[0066] In another embodiment, one or the other of the first catalyst and second catalyst may be incorporated within the substrate itself, in the form of an extruded, all-active catalyst. In particular, the substrate may be an active substrate comprising an extrusion of either of the catalysts while the other may be disposed on the active substrate as a coating or vice-versa. The coating comprising the first catalyst (or second catalyst) may extend the full axial length of the active substrate or may extend less than 100% of the axial length, for example 40% to 60% thereof.

[0067] In an embodiment of the invention the first catalyst, irrespective of whether it is coated onto the substrate or is in the substrate, is arranged and configured such that the gas mixture makes contact therewith prior to the second catalyst.

[0068] In an alternate embodiment of the invention, and wherein the first catalyst and second catalyst are provided on or within separate substrates, the first catalyst may be provided on or within a first substrate having axial length L1 and the second catalyst P101311W001 may be provided on or within a second substrate having axial length L2, wherein the first substrate is arranged upstream of the second substrate with respect to the gas mixture to be treated flowing through the catalyst system. The first and second substrates may be arranged in series and may be adjacent to and in contact with each other or may be separated by a specific distance.

[0069] The first and second substrates may be of equal axial length.

[0070] Alternatively, the first and second substrates may have different axial lengths. For example, the ratio of the axial length of the first substrate to the axial length of the second substrate (i.e. L1 to L2) may be at least 1 .5 to 1 or at least 2:1 , such as at least 3:1 , at least 5:1 , at least 6:1 and may be less than 10:1 , such as less than 8:1. Preferably, the ratio of the axial length of the first substrate to the axial length of the second substrate(i.e. L1 :L2) is in the range of 4:1 to 5:1 or in the range of 6:1 to 7:1 . The ratio of the axial length of the first substrate to the axial length of the second substrate (i.e. L1 :L2) may be about 5:1 or about 6.5:1 .

[0071] In a preferred form of the invention L1 :L2 is 1 :1 .

[0072] The first catalyst may be disposed on the first substrate as a coating. The coating comprising the first catalyst may extend the full axial length L1 of the first substrate or may extend for less than 100% of the axial length L1 .

[0073] Alternatively, the first catalyst may be incorporated within the first substrate itself, in the form of an extruded, all-active catalyst. In particular, the first substrate may be an active substrate comprising an extrusion of the first catalyst.

[0074] The second catalyst may be disposed on the second substrate as a coating. The coating comprising the second catalyst may extend the full axial length L2 of the second substrate or may extend for less than 100% of the axial length L2.

[0075] Alternatively, the second catalyst may be incorporated within the second substrate itself, in the form of an extruded, all-active catalyst. In particular, the second substrate may be an active substrate comprising an extrusion of the second catalyst. P101311W001

[0076] In an alternative embodiment, the first substrate is an active substrate comprising an extrusion of the first catalyst and the second substrate is an active substrate comprising an extrusion of the second catalyst and the axial length L1 of the first substrate is less than the axial length L2 of the second substrate. Preferably, the ratio of the axial length of the first substrate to the axial length of the second substrate (i.e. L1 : L2) is at least 2:1 , preferably 1 :1.

[0077] According to another aspect of the invention there is provided a method of treating a gas mixture including ozone and volatile organic compounds, the method comprising contacting the gas mixture with the catalyst system as hereinbefore described.

[0078] In use, the catalyst system operates at an operating temperature of between 25°C and 300°C, preferably between 100°C and 250°C, more preferably from 120°C and 170°C.

[0079] The method may include treating a gas mixture, preferably air, more preferably bleed air from one or more engines of an aircraft and / or from the auxiliary power unit (APU) of an aircraft.

[0080] The method may include the step of passing the gas mixture through an environmental control system to remove contaminants. The catalyst system of the invention may be provided separately from or as part of an environmental control system.

[0081] In an embodiment of the invention the catalyst system is provided within a housing, the housing having a gas mixture inlet and an exhaust outlet. The catalyst system may be disposed within the housing such that its periphery is hermetically sealed to inner walls of the housing such that all the gas mixture passing through the inlet is forced through the catalyst system.

[0082] The catalyst system is preferably arranged and configured within the housing such that the gas mixture passing through the gas mixture inlets contacts the first catalyst of the catalyst system prior to contacting the second catalyst such that the VOCs are substantially oxidised before the ozone, in the gas mixture, is reduced by the second catalyst.

[0083] The resultant treated gas mixture passes through the exhaust outlet.

[0084] The method may include the treatment of bleed air from an aircraft, before, during or after the removal of ozone and VOCs in the air. P101311W001

[0085] The method as described herein may include the step of circulating the exhausted air from the exhaust outlet into the air conditioning system of an aircraft.

[0086] BRIEF DESCRIPTION OF THE FIGURES

[0087] Figure 1 : is a comparison of catalysts comprising various components and their catalytic conversion of ozone, at a temperature range of 20 to 150°C.

[0088] Figure 2: is a comparison of catalysts comprising various components and their catalytic conversion of a VOC, namely propylene, at a temperature range of 0°C to 300°C.

[0089] Figure 3: is a comparison of catalysts comprising various components and their catalytic conversion of a VOC, namely toluene, at a temperature range of 0°C to 300°C.

[0090] DETAILED DESCRIPTION OF THE INVENTION

[0091] The invention will now be further described with reference to the following examples, which are illustrative, but not limiting of the invention.

[0092] Catalysts (i) to (iv) and (vi) to (vii) were prepared by dispersing a particulate alumina support material and precursor salts of the applicable catalytic metals in water to form a slurry with a solids content of less than 50%. The slurry was then coated onto ceramic honeycomb substrates via a conventional washcoating technique (such as that described in WO99 / 47260). The coated substrate was then dried and calcined to produce the final catalysts.

[0093] Core samples of the prepared catalysts each having diameter of 17.5mm, a cpsi of 400 and a length of 3 inches were then tested for ozone performance in a synthetic catalytic activity test (SCAT) apparatus using the following inlet gas mixture at selected inlet gas temperatures: 5 ppm ozone, 20% O2 remainder N2 with a flow rate of 50L / min.

[0094] A sample of each catalyst was crushed, pelletised, ground and sieved and tested for VOC performance by exposing the samples in a SCAT apparatus to a flow of gas having an inlet composition comprising 40ppm propylene, 15ppm toluene and 17% O2. The flow rate of the gas was 2L / min. Sieved fractions of 355-250um were used for testing. A total of 0.2g of sieved material per sample was tested. P101311W001

[0095] Catalyst (v) was prepared by dispersing a particulate alumina support material platinum salt in water to form a slurry. The slurry was then dried and calcined. The resulting powder was also pelletised ground and sieved before VOC testing.

[0096] The composition and metal loadings for each catalyst prepared are shown in Table 1 below.

[0097] Table 1

[0098] Figure 1 shows the results of the ozone testing. As can be seen from the results, PGM catalysts do not perform as well as Mn for ozone conversion. Further, whilst the ozone performance of PGM catalysts is improved by mixing with Mn, a Pd / Mn mixture does not perform as well as Mn alone at lower temperatures, and a Pt / Mn mixture provides no improvement over Mn alone.

[0099] Figures 2 and 3 show the results of the VOC testing: propylene conversion is shown in Figure 2 and toluene conversion is Figure 3. As can be seen from the results, Mn does not perform well for VOC conversion at lower temperatures and has a detrimental effect on PGM performance when combined therewith.

[0100] Thus, as can be seen from the results herein, the use of a catalyst system comprising separate, discrete PGM and Mn catalysts for the treatment of a gas stream comprising ozone and VOCs is more efficient than the use of a single PGM catalyst, a single Mn catalyst or a catalyst comprising a mixture of Mn and PGM.

Claims

P101311W001Claims:

1. A catalyst system for treating a gas mixture including ozone and volatile organic compounds, the catalyst system being in fluid flow communication with the gas mixture, the catalyst system comprising: i. a first catalyst comprising at least one platinum group metal, the first catalyst being utilised to predominantly oxidise the volatile organic compounds in the gas mixture; and ii. a second catalyst comprising at least a manganese (Mn) component; the second catalyst being utilised to predominantly reduce the ozone in the gas mixture; wherein the first catalyst and the second catalyst are substantially discrete relative to each other.

2. The system of claim 1 , wherein the first catalyst is substantially free of manganese.

3. The system of claim 1 or 2 wherein the first catalyst comprises platinum.

4. The system of claim 3 wherein the first catalyst is substantially free of palladium.

5. The system of any preceding claim, wherein the second catalyst is free of any platinum group metal.

6. The system of any preceding claim, wherein the first catalyst is arranged and configured, relative to the second catalyst, such that, in use, the gas mixture contacts the first catalyst prior to contact with the second catalyst.

7. The system of any preceding claim, wherein the gas mixture is bleed air from the engines and / or auxiliary power unit of an aircraft.P101311W0018. The system of any preceding claim, wherein the first catalyst is disposed on a substrate in the form of a first coating and the second catalyst is disposed on a substrate in the form of a second coating.

9. The system of claim 8, wherein the first coating has a PGM loading of between 20 g / ft3to 300 g / ft3, 20 to 250 g / ft3, 30 to 100 g / ft3, 35 to 60g / ft3, 100 g / ft3to 300 g / ft3or 150 g / ft3to 250 g / ft310. The system of claim 8 or 9, wherein the second coating has a Mn loading of between 100 g / ft3and 2000 g / ft3, 100 to 1000g / ft3or 120 g / ft3to 500 g / ft3.11 . The system of claim 8, 9 or 10, wherein the first and second catalysts are disposed on the same substrate and wherein the first coating and second coating are arranged side-by-side or one on top of the other such that, in use, the gas mixture comes into contact with the first coating prior to contacting the second coating.

12. The system of claim 11 , wherein the first coating extends to between 25% and 75%, or between 40% to 60% of an axial length of the substrate and the second coating extends to between 25% and 75% or between 40% and 60%, of the axial length of the substrate.

13. The system of claim 8, 9 or 10, wherein the first catalyst is coated on a first substrate and the second catalyst is coated on a second substrate.

14. A method of treating a gas mixture including ozone and volatile organic compounds the method comprising contacting the gas mixture with the catalyst system of any one of the preceding claims.

15. The method of claim 14 wherein the gas mixture is contacted with the catalyst system at a temperature of between 25°C and 300°C, preferably between 100°C and 250°C, more preferably from 120°C and 170°C.

16. The method of claim 14 or 15 wherein the gas mixture is bleed air from the engines and / or auxiliary power unit of an aircraft.P101311W00117. An aircraft environmental control system comprising: a housing having a gas mixture inlet and an exhaust outlet, wherein the catalyst system of any one of claims 1 to 13 is disposed in the housing; wherein the gas mixture is bleed air from the engines and / or auxiliary power unit of an aircraft; and wherein ozone- and VOC-reduced air exits the housing via the exhaust outlet and passes into the air conditioning system of the aircraft.

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