Apparatus for reducing NOx and method for preparing a catalyst for reducing NOx

Abstract

The present invention relates to an apparatus for reducing NOx in air and a method for preparing a catalyst for reducing NOx in air, the catalyst being for use in the apparatus. The apparatus includes a catalyst, the catalyst including Pt, PtCu, PtCo, PtNi, Pd, PtPd and / or PdCu. The apparatus further includes a reaction chamber for receiving the catalyst, the reaction chamber including an inlet for air and a reducing agent and an outlet. A heater is configured to heat the catalyst to a temperature between 20°C and 100°C. The apparatus also includes a reducing agent source, the reducing agent source being connected to the inlet. The method includes step a) of mixing a support material with a stabilizing polymer in water to form an aqueous solution. Step b) includes adding a first metal compound to the aqueous solution formed in step a) and stirring the solution. Step c) includes adding a reducing agent to the solution formed in step b) to form metal nanoparticles. Step d) includes adding an acid to the solution formed in step c). Step e) includes stirring the solution formed in step d) followed by filtering and drying to form supported metal nanoparticles.

Description

[Technical field]

[0001] The present invention relates to an apparatus for reducing (or reducing / reduction) nitrogen oxides (NOx) in the air, a method for reducing NOx in an enclosed space using the apparatus, and a method for producing a catalyst for reducing NOx. [Background technology]

[0002] Nitrogen oxides are a group of gases hereafter collectively referred to as "NOx", including nitric oxide (NO) and nitrogen dioxide (NO2). NO makes up the majority of NOx gases and combines with oxygen to form NO2. NOx is released into the atmosphere in a variety of ways. The main sources of NOx emissions are the combustion of fuels at high temperatures above 1200 °C, for example by road transport, the energy industry including power stations, manufacturing including industrial boilers, and non-road transport (including aviation, rail and shipping). In 2019, it was estimated that up to 80% of the NO2 concentration in the UK was NOx emissions from road transport (https: / / www.gov.uk / government / statistics / emissions-of-air-pollutants / emissions-of-air-pollutants-in-the-uk-nitrogen-oxides-nox). During fuel combustion, NOx is formed by the reaction of nitrogen (either in the air or in the fuel) with atmospheric oxygen. NOx is also produced naturally by lightning and by microbial processes in the soil.

[0003] NOx is an environmental pollutant that reacts to form acid rain and smog. NOx can negatively impact biodiversity and habitats by causing changes in soil chemistry. NOx can also form ozone by reaction with volatile organic compounds. Ozone can cause environmental problems by oxidizing vegetation and crops. Additionally, ozone can cause and exacerbate airway problems such as asthma attacks and cause eye, nose and throat irritation. NO2 is also particularly harmful to health, and can cause inflammation and infection of the respiratory system. NO2 can also worsen existing conditions such as asthma, as well as other lung and heart conditions.

[0004] Attempts have been made to reduce NOx emissions resulting from human activities. Selective catalytic reduction (SCR) systems convert NOx in an exhaust or flue gas stream into nitrogen gas and water by reacting the NOx with a reducing agent. SCR systems are widely used commercially, for example in power plants, boilers, gas turbines, and diesel engines for marine and road vehicles. Known SCR catalysts typically contain active catalytic components based on zeolites, precious metals or oxides of metals such as vanadium, tungsten, and molybdenum. Studies of precious metal SCR for the reduction of NOx emissions are e.g., Surface Science [online: http: / / dx.doi.org / 10.1016 / j.susc.2009.05.031] Vol. 603, 12 June 2009, K Okumura et al., "Effect of combinations of precious metals and metal oxide supports on the catalytic reduction of NO with H2", pp. 2544-2550; and Angewandte Chemie International Edition [online: https: / / doi.org / 10.1002 / anie.200500919] Vol. 44, 8 July 2005, S Zhou et al., "Pt-Cu core-shell and alloy nanoparticles for heterogeneous NOx reduction: unusual stability and reactivity of core-shell nanoparticles".

[0005] A commonly used reductant is liquid or aqueous ammonia. Despite the relatively high NOx conversion efficiency, a problem with known SCR systems is that the required effective temperature range is typically 177°C to 593°C (R.M. Heck et al., "Operating Characteristics and Commercial Operating Experience with High Temperature SCR NOx Catalysts," Environmental Progress Vol 13(4), November 1994, pp. 221-225). The specific temperature required depends on a variety of factors, including catalyst material and geometry. Thus, the environments in which known SCR systems can be used are limited. Reduction of NOx concentrations can also proceed via an oxidative pathway. NOx abatement catalysts that proceed via an oxidative pathway are susceptible to nitrates, such as nitric acid, which poison the catalyst surface and thus deactivate it.

[0006] An alternative method to reduce NOx emissions is selective non-catalytic reduction (SNCR), which involves reacting NOx with a reductant to form nitrogen and water. Reductants such as urea or ammonia may be used. Due to the absence of a catalyst, temperatures in the range of 850°C to 1100°C are required, depending on the reductant used. Such temperatures are higher than those required for SCR, and lower NOx conversion efficiencies are achieved compared to SCR. Therefore, SNCR systems are only suitable for relatively small installations in environments with low NOx emissions.

[0007] Further methods of reducing NOx emissions include the use of NOx sorbents, which include a catalyst support coated with a material that reversibly adsorbs, i.e. binds or "traps," NOx particles (conventionally known as lean NOx traps (LNTs)). Typical sorbents are zeolites or carbonates. When the sorbent becomes saturated with NOx, it is regenerated, for example, by injecting diesel fuel to desorb the NOx from the zeolite and react with the hydrocarbons contained in the diesel fuel to produce nitrogen gas and water. The problem is that NOx sorbents have a higher affinity for sulfur oxides than NOx, so periodic high-temperature desulfurization is required to remove the sulfur oxides and restore the activity of the sorbent. Absorption techniques are also used to remove NOx. For example, sulfuric acid reacts with NOx at high pressure and relatively low temperature (35°C). However, NOx conversion efficiency is low, corrosive chemicals are required, and relatively large areas are needed to accommodate the necessary equipment.

[0008] NOx absorbers are known to reduce NOx indoors. NOx absorbers are a component of mechanical ventilation heat recovery (MVHR) systems. Such systems may include disposable high efficiency particulate absorption (HEPA) filters and carbon filters to absorb NOx. Such systems are used domestically and commercially. HEPA and carbon filters can reduce NOx by 90%, but typically require replacement every 12 months (https: / / www.dyson.com / air-treatment / purifier-accessories). DISCLOSURE OF THEINVENTION [Problem to be solved by the invention]

[0009] Known methods for producing supported metallic, nanoparticle catalysts for NOx concentration reduction suffer from large particle size distributions and have been shown to cause a high degree of alloying between the metal components of the catalyst, which in some circumstances can adversely affect the catalytic activity of the supported metallic nanoparticles.

[0010] The aim of the present invention is to at least mitigate the above mentioned drawbacks. [Means for solving the problem]

[0011] According to a first aspect of the present invention, there is provided an apparatus for reducing NOx in air, the apparatus comprising a catalyst. The catalyst comprises Pt, PtCu, PtCo, PtNi, Pd, PtPd and / or PdCu. The apparatus further comprises a reaction chamber for receiving the catalyst. The reaction chamber comprises an inlet for air and a reducing agent, and an outlet. The reaction chamber further comprises a heater configured to heat the catalyst to a temperature between 20°C and 100°C, and a reducing agent source, the reducing agent source connected to the inlet.

[0012] Advantageously, the device facilitates the reduction of NOx concentration in the air at a lower temperature than conventional catalytic systems for reducing NOx concentration via a reduction catalytic pathway. Thus, the device is more energy efficient than conventional systems. Due to the use of relatively low temperatures, the device is also safer than conventional systems. This means that the device can be installed in a wider variety of locations, such as inside a building, and does not require evacuation of personnel from inside the building. Furthermore, the use of relatively low temperatures prevents the production of ammonia as a by-product of the reduction reaction. Advantageously, the by-products of the reduction of NOx are nitrogen and / or NO, both of which are inert gases at temperatures between 20°C and 100°C. The device of the present invention also does not suffer from build up of nitrates or nitric acid on the surface of the catalyst.

[0013] Preferably, the reducing agent is hydrogen. Hydrogen is cheap, readily available, and assists the catalyst in reducing NOx (or assists the catalyst in reducing NOx) at relatively low temperatures compared to conventional systems. Hydrogen also poses no environmental risks.

[0014] Preferably, the device further comprises a source of a substance to provide the reducing agent (i.e. an indirect source of reducing agent). The reducing agent, such as hydrogen, may be generated by reforming another substance or chemical. The substance may be a pollutant, a pollutant being a substance that has an undesirable effect on the environment. Formaldehyde is an example of a substance that is a pollutant that may advantageously provide hydrogen as a reducing agent. During use of the device, formaldehyde is only present at background levels, meaning that any harmful environmental risks are minimal.

[0015] Preferably, the heater (or heater) is configured to heat the catalyst to a temperature of 20° C. to 25° C. The device has been observed to reduce NOx particularly efficiently and safely in this temperature range.

[0016] Preferably, the reductant source comprises an electrolyser for producing the reductant, which allows the reductant, such as hydrogen, to be quickly and easily generated on demand and in situ, for example by splitting water, thereby preventing the reductant, e.g. hydrogen, from being wasted.

[0017] Preferably, the reducing agent is hydrogen, which is present in a concentration between 0.05% v / v and 4% v / v, advantageously within this concentration range good conversion of NOx to nitrogen and / or NO is observed, without posing a risk of ignition.

[0018] Preferably, hydrogen is present at a concentration of 0.05% v / v to 1% v / v, which is particularly effective when the catalyst is 0.1 wt% Pt-TiO2.

[0019] Preferably, the device comprises a flow controller to increase or decrease the flow rate of the reductant. Depending on the composition of the catalyst, the flow rate of hydrogen may be adjusted to achieve optimal reduction of NOx.

[0020] Preferably, the flow controller is configured to increase the flow rate of the reducing agent for a period of 5 to 15 seconds. Thus, the flow controller is configured to increase the flow rate of the reducing agent from a first flow rate to an increased second flow rate. The increased second flow rate of the reducing agent is maintained for a period of 5 to 15 seconds. After this period has elapsed, the flow controller is configured to decrease the flow rate of the reducing agent from the increased second flow rate back to the first flow rate. The temporary increase in the flow rate of the reducing agent, such as hydrogen, creates a pulsing effect. By pulsing the reducing agent in the presence of the catalyst, the catalytic activity of the catalyst is effectively regenerated. Thus, advantageously, the catalyst requires replacement less frequently, which provides cost savings. Furthermore, the regeneration of the catalyst can be performed in situ, making maintenance of the device quicker and easier.

[0021] Preferably, the catalyst is supported on a support. Advantageously, the support maximizes the specific surface area of ​​the catalyst to improve the activity of the catalyst. Typical supports include graphitic carbon nitride (gC3N4), silica, titanium dioxide, activated carbon and / or alumina.

[0022] Preferably, the catalyst is present in an amount of 0.1 wt% to 10 wt% based on the combined weight of the catalyst and the support. Particularly efficient reduction of NOx concentration is observed when the catalyst is used in this concentration range. Preferably, the catalyst is PtCu, the support is gC3N4, and PtCu is present in an amount of 0.1 wt% to 10 wt% based on the combined weight of PtCu and gC3N4.

[0023] Preferably, the device comprises at least one gas detector in communication with the outlet, the at least one gas detector being configured to detect nitric oxide (NO) and / or nitrous oxide (NO) in the gas leaving the reaction chamber. Advantageously, detection of NO and NO allows an operator to monitor the performance of the device and can indicate whether the device requires maintenance. By monitoring NO and NO concentrations, the nitrogen concentration can be deduced therefrom. Thus, the NOx detector can provide a user with information regarding the NOx concentration level. In response to this information, the flow controller can be adjusted to optimize the flow of reductant (e.g., hydrogen) to the device.

[0024] Preferably, the at least one gas detector comprises a chemiluminescence detector for detecting nitric oxide (NO) and / or nitrogen dioxide (NO2). Advantageously, the chemiluminescence detector has a wide NO detection range of 0.5 ppb to 20 ppm and is therefore more sensitive to NO than conventional NO detectors. An alternative detector is an electrochemical detector, which is advantageously small and low cost.

[0025] Preferably, the at least one gas detector includes an infrared detector for detecting nitrous oxide (NO). Although NO is inert in the temperature range operated by the device, depending on the environment in which the device is located, it may be desirable to monitor NO levels.

[0026] According to a second aspect of the invention, there is provided a system for monitoring NOx concentrations in air in a plurality of enclosed spaces, comprising a plurality of devices according to the first aspect of the invention. Each of the plurality of devices comprises at least one gas detector in communication with the outlet, the at least one gas detector configured to detect nitric oxide (NO) in gas leaving the reaction chamber, each of the plurality of devices being disposed in each of the plurality of enclosed spaces. Such a system allows a comparison of NOx concentrations to be made between different regions in the enclosed spaces. This assists an operator in determining whether the devices are functioning correctly and / or whether operating parameters such as temperature and / or catalyst concentration require adjustment.

[0027] According to a third aspect of the present invention, there is provided a method for reducing NOx in an enclosed space, the method comprising the steps of: providing an apparatus for reducing NOx according to the first aspect of the present invention; pumping air from within the enclosed space into the reaction chamber through the inlet; introducing a reducing agent into the reaction chamber such that the reducing agent, air and catalyst are exposed to each other; heating the reaction chamber to a temperature in the range of 20°C to 100°C; and pumping gas from the reaction chamber into the enclosed space through the outlet.

[0028] According to a fourth aspect of the present invention, there is provided a method for preparing a catalyst for reducing NOx in air, comprising the steps of: a) combining a support material with a stabilizing polymer in water to form an aqueous solution; b) adding a first metal compound to the aqueous solution formed in step a) and stirring the solution; c) adding a reducing agent to the solution formed in step b) to form metal nanoparticles; d) adding an acid to the solution formed in step c); e) stirring the solution formed in step d) followed by filtering and drying to form supported metal nanoparticles. Advantageously, this method provides an easy way to prepare catalysts with narrow particle size distribution. The catalyst prepared by this method has been observed to efficiently reduce the concentration of NOx in a device according to the first aspect of the present invention at low temperature range, especially when hydrogen is used as the reducing agent.

[0029] Preferably, the first metal compound comprises platinum or palladium. Advantageously, platinum and palladium catalysts have been shown to provide effective catalysts for NOx reduction at relatively low temperatures.

[0030] Preferably, the method further comprises adding a second metal compound to the aqueous solution formed in step a), the first metal compound being different from the second metal compound. Advantageously, the method can be used to produce bimetallic nanoparticles, which are particularly effective as NOx reduction catalysts in the device according to the first aspect of the invention.

[0031] Preferably, the first metal compound comprises platinum and the second metal compound comprises one of copper, cobalt or nickel. Advantageously, such a combination of metal elements provides a bimetallic NOx reduction catalyst that effectively converts NOx to inert products.

[0032] Preferably, the first metal compound comprises palladium and the second metal compound comprises copper. Catalysts containing palladium and copper may be readily prepared using the methods described above.

[0033] Preferably the second metal compound is a nitrate of copper, nickel or cobalt. Such materials are readily available and easy to handle and are particularly suitable for use in the method according to the fourth aspect of the invention.

[0034] According to a fifth aspect of the invention there is provided a catalyst for reducing NOx in air prepared by the method according to the fourth aspect of the invention for use in an apparatus according to the first aspect of the invention.

[0035] Where numerical ranges are recited herein, such ranges should be interpreted as including and disclosing the endpoints of the range. [Brief description of the drawings]

[0036] Various embodiments and aspects of the present invention are described below, without limitation, with reference to the accompanying drawings.

[0037] [Figure 1] FIG. 1 shows a schematic diagram of an apparatus for reducing NOx in air.

[0038] [Diagram 2] FIG. 2 shows a flow chart of a method for reducing NOx in an enclosed space using the device shown in FIG.

[0039] [Diagram 3] FIG. 3 shows the activity plot of the 1 wt% PtCu-gC3N4 catalyst used in the apparatus of FIG.

[0040] [Figure 4] FIG. 4 shows the activity plot of 0.1 wt% Pd-TiO2 used in the apparatus of FIG.

[0041] [Diagram 5] FIG. 5 shows the activity plot of 0.1 wt% Pd-TiO2 used in the device of FIG.

[0042] [Figure 6] FIG. 6 shows the ATR (attenuated total reflectance) spectra of 0.1 wt % Pd-TiO2 before and after use in the apparatus of FIG.

[0043] [Figure 7] FIG. 7 shows the activity plot of 0.1 wt% Pt-TiO2 used in the device of FIG.

[0044] [Figure 8] FIG. 8 shows the activity plot of the 0.05 wt % Pt 0.05 wt % Pd-TiO2 catalyst used in the apparatus of FIG.

[0045] [Figure 9a] 9a and 9b show activity plots of a 1 wt% PtCu-gC3N4 catalyst, synthesized by a method outside the scope of the present invention, used in the apparatus of FIG. 1. [Figure 9b] 9a and 9b show activity plots of a 1 wt% PtCu-gC3N4 catalyst, synthesized by a method outside the scope of the present invention, used in the apparatus of FIG. 1.

[0046] [Figure 9c] Figures 9c and 9d show the activity plots of the 1 wt% PtCu-gC3N4 catalyst synthesized by the method according to the present invention and used in the apparatus of FIG. 1. [Figure 9d] Figures 9c and 9d show the activity plots of the 1 wt% PtCu-gC3N4 catalyst synthesized by the method according to the present invention and used in the apparatus of FIG. 1.

[0047] [Figure 10] Figure 10 shows a flowchart for preparing a catalyst by the method according to the present invention.

Mode for Carrying Out the Invention

[0048] The present invention generally relates to reducing NOx in air. More specifically, aspects of the present invention relate to a reaction chamber and an apparatus including the reaction chamber, the reaction chamber having an interior for accommodating a catalyst therein and reducing the amount of NOx from air taken in from outside the reaction chamber. Other aspects include a method for preparing a catalyst for reducing NOx in air.

[0049] The apparatus of the present invention is for reducing the NOx concentration in air in a relatively low temperature range as compared with known systems. Therefore, the present apparatus is safer and more energy-efficient than known systems. The method for preparing a catalyst for reducing NOx in air provides a metal catalyst having a narrow particle size distribution, which is suitable for use in the apparatus of the present invention. <NOx Reduction Device>

[0050] Described herein is an apparatus 1 for reducing NOx (including nitric oxide (NO) and nitrogen dioxide (NO2)) in the atmosphere. In a preferred embodiment, the apparatus 1 may be deployed in a confined space. The confined space may be inside a building, for example, in a room, stairwell, or hallway of a building. The term "building" includes outdoor buildings such as a garage or cabin. The phrase "confined space" includes, for example, indoor environments such as a room with an opening that can be opened or closed, a stairwell, a hallway, a garage, or a cabin. For example, the phrase "confined space" includes a room with an entrance that can be opened and closed by a door, and / or a window that can be opened and closed. "Confined space" includes, for example, a room with an open or closed window.

[0051] The apparatus 1 includes a catalyst 20 selected from the group including Pt, PtCu, PtCo, PtNi, Pd, PtPd and / or PdCu. The catalyst 20 is supported by a support 22. The apparatus 1 further includes a reaction chamber 10 for receiving the catalyst 20, the reaction chamber 10 including an inlet 101 for air and a reducing agent, and an outlet 105. The apparatus 1 further includes a heater 12 configured to heat the catalyst to a temperature between 20°C and 100°C. The apparatus 1 may also include a temperature detector 18, but this is not required. The apparatus 1 includes a reducing agent source 14 including a reducing agent, which is connected to the inlet 101 for delivering the reducing agent into the reaction chamber 10. An inlet pipe 1011 is connected to the inlet 101 for delivering air and the reducing agent into the reaction chamber 10. In a preferred embodiment, air is directed through an air inlet pipe 1012, as shown in FIG. 1. The reducing agent source 14 and the air inlet pipe 1012 are connected to each other by a tube 103. In an alternative embodiment, the device 1 may comprise two inlets, one for air and the other for the reducing agent. An outlet tube 1051 is connected to the outlet 105 and is configured to allow the cleaned gas to leave the reaction chamber 10.

[0052] The apparatus 1 includes a heater 12 for heating the contents of the reaction chamber 10, including the catalyst 20, to a temperature in the range of 20°C to 100°C. The apparatus thus facilitates the reduction of NOx at a relatively low temperature range. The operating temperature range of the reaction chamber 10 is therefore at room temperature (i.e., 20°C) or slightly above room temperature. The operating temperature is in any case substantially lower than the effective temperature range of known SCR systems and is therefore safer. The apparatus described herein may therefore safely improve air quality inside an enclosed space, such as within a building, by reducing NOx in the air inside the enclosed space. Alternatively, the apparatus may be used to reduce NOx in the air outside the enclosed space. For example, the apparatus may be deployed in a road tunnel.

[0053] In a preferred embodiment, the heater 12 is configured to heat the catalyst 20 to a temperature of 20° C. to 25° C. This temperature range is advantageous when a Pt catalyst 20 (Pt-TiO2) supported on a titanium dioxide support 22 is used in the apparatus, with the Pt having a concentration of 0.1 wt% based on the combined weight of the Pt catalyst and titanium dioxide support. When operating in this temperature range with a 0.1 wt% Pt-TiO2 catalyst, the conversion of NOx gases is about 33% N2O and about 66% N2.

[0054] In an alternative embodiment, the catalyst 20 is bimetallic. In one embodiment, the catalyst 20 is PtCu and the support 22 is graphitic carbon nitride (gC3N4), i.e., PtCu-gC3N4. The PtCu may be present in a concentration of 0.1 wt% to 10 wt%, based on the combined weight of the catalyst 20 and the support 22. Relatively high NOx reduction is observed when a 0.1 wt% PtCu-gC3N4 or 1 wt% PtCu-gC3N4 catalyst / support system is used in the device.

[0055] The catalyst 20 may be combined with any suitable support 22. An example of a catalyst 20 and support 22 combination is PtCu-gC3N 4、 Pt-TiO 2、 Pd-TiO 2、 and PtPd-TiO2.

[0056] In alternative embodiments, the catalyst may be PtCo, PtNi, or PdCu. The two metals in the bimetallic catalyst may be present in a molar ratio of 1:1 to 1:3. In some examples, the PtCo, PtNi, or PdCu is present in a weight percent range of 0.1 wt % to 10 wt %, based on the combined weight of the catalyst 20 and the support 22.

[0057] In an alternative embodiment, the heater is configured to heat the catalyst 20 to a temperature between 65° C. and 75° C. In this temperature range, when the catalyst 20 is Pd and the support 22 is titanium dioxide (Pd—TiO2), and the Pd has a concentration of 0.1 wt % based on the combined weight of the Pd catalyst and the titanium dioxide support, the NOx gases are converted to 100% N2 with no trace of N2O.

[0058] The apparatus 1 may include a pump 107 for drawing air into the reaction chamber 10 from outside the apparatus 1, such as from the environment in which the apparatus 1 is located. In some embodiments, the pump 107 is inside an air inlet pipe 1012 connected to the air inlet 101. In some configurations, the pump 107 may be located in an outlet pipe 1051 to draw air and reducing agent through the reaction chamber 10. The reducing agent source 14 is connected to the reaction chamber 10 via the pipe 103 and the inlet pipe 1011. Preferably, the connection between the reducing agent source 14 and the pipe 103 is sealed so that the reducing agent can be directed to the interior of the reaction chamber 10 without being lost to the atmosphere.

[0059] In a preferred embodiment, the inlet 101 comprises a flow controller 1013 for increasing or decreasing the flow rate of the reducing agent from a first flow rate. In use, a user may repeatedly and periodically increase the flow rate of the reducing agent. For example, the first flow rate of the reducing agent may be increased to a second flow rate for a period of 10 seconds by activating the flow controller 1013. This creates a pulsing effect. By pulsing the reducing agent onto the catalyst 20, the catalytic activity of the catalyst 20 is effectively regenerated. Once the 10 second period has elapsed, the flow controller 1013 is configured to decrease the flow rate of the reducing agent from the increased second flow rate back to the first flow rate. This pulsing of the reducing agent may be repeated at intervals during operation of the device 1.

[0060] In a preferred embodiment, the reducing agent is hydrogen. The reducing agent source 14 may include an electrolytic cell for converting water to hydrogen. The water may be provided to the device 1 or may be extracted from the atmosphere. Alternatively, the reducing agent source 14 may be a canister or cylinder containing a mixture of hydrogen and an inert carrier gas. In an alternative embodiment, the device 1 further includes a source of material for providing the reducing agent (i.e., an indirect source of the reducing agent). For example, the device 1 may include a source of formaldehyde that provides the hydrogen. The source of material for providing the reducing agent (e.g., hydrogen) may be considered to be the reducing agent source 14. In one embodiment, the hydrogen is present at a concentration of 0.05% to 4% v / v. In an alternative embodiment, the hydrogen is present at a concentration of 0.05% to 1% v / v. Such a concentration of hydrogen does not pose a risk of ignition.

[0061] The catalyst 20 is supported on a carrier 22 and housed inside the reaction chamber 10. The arrangement of the catalyst 20 and the carrier 22 is not limited to that shown in Fig. 1. Any structural arrangement of the catalyst 20 and the carrier 22 that allows air and a reductant to contact the catalyst 20 is preferred. In a preferred embodiment, the catalyst 20 is coated on the carrier 20 in the form of a multi-channel monolith or beads packed in a tube.

[0062] The reaction chamber 10 is an enclosed space where a reducing agent (e.g., hydrogen) drawn from outside the reaction chamber 10 and air are mixed and exposed to the catalyst 20. The catalyst 20 promotes the reaction of nitric oxide (NO) with hydrogen to form nitrogen (N2) and / or nitrous oxide (N2O). Nitrogen (N2) and nitrous oxide (N2O) are inert gas products. In use, purified air containing nitrogen (N2) and nitrous oxide (N2O) exits the reaction chamber 10 via outlet 105 and is released into the atmosphere. Advantageously, the device 1 does not suffer from the build-up of nitrates or nitric acid on the surface of the catalyst 20 because the reaction proceeds via a reduction pathway rather than an oxidation pathway. Studies have shown that the catalyst 20 has a lifespan of at least two years. Thus, the device 1 has a long lifespan compared to known devices that use catalytic oxidation to minimize NOx.

[0063] The device 1 may include a light source for illuminating the catalyst, which is particularly useful when the device 1 is not exposed to natural light.

[0064] In some embodiments, the device 1 includes a gas detector 30 in communication with the outlet 105. In the embodiment shown in FIG. 1, the gas detector 30 is connected to the outlet 105 of the reaction chamber 10 by an outlet tube 1051. In some embodiments, the gas detector 30 may be directly connected to the outlet 1050. The gas detector 30 is configured to detect the concentration of nitrogen oxide (NO) and / or nitrogen dioxide (NO2) and / or nitrous oxide (N2O). The gas detector 30 may include a chemiluminescence detector that detects the concentration of NO in the first gas stream. Advantageously, the chemiluminescence detector has a wide NO detection range of 0.5 ppb to 20 ppm and is therefore more sensitive to NO than conventional NO detectors. An alternative to the chemiluminescence detector is an electrochemical detector, which is advantageously small and low cost. In the separate second gas stream, the NO2 is converted to NO. The NO concentration in the separate second gas stream is measured to provide a total NOx concentration. The NO2 concentration may be determined by the difference between the total NOx concentration and the NO concentration. The gas detector 30 may additionally or alternatively comprise an infrared detector for detecting the concentration of N2O. The infrared detector advantageously has an N2O detection range of 20 ppb to 50 ppm.

[0065] In some embodiments, if the chemiluminescence detector 30 detects that the amount of NO and / or NO2 exiting the reaction chamber 10 is above a first predetermined threshold, a control signal can be sent via the controller 16 to the heater 12 to increase the temperature to increase the reaction rate in the reaction chamber 10, resulting in cleaner air exiting the reaction chamber 10. Additionally or alternatively, a control signal can be sent from the controller 16 to the reducing agent source 14 to increase or decrease the concentration of the reducing agent (e.g., hydrogen). Additionally or alternatively, a control signal can be sent via the controller 16 to the pump 107 to decrease the flow of air into the reaction chamber 10, resulting in a decrease in the volume of air passing through the reaction chamber 10, thereby increasing the time for the reaction to occur and ensuring that the air exiting the reaction chamber 10 is cleaner. Similarly, if the detector 30 indicates that the amount of NO and / or NO2 is below a second predetermined threshold, a control signal can be sent via the controller 16 to the heater to reduce the temperature and improve the energy efficiency of the reaction chamber, and / or a control signal can be sent via the controller 16 to the pump 107 to increase the flow of air through the reaction chamber 10 and improve the amount of air purified in a given time.

[0066] The temperature detector 18 may provide the controller 16 with information regarding the temperature of the device 1. The controller 16 may then send a signal to the heater 12 to increase or decrease the temperature of the device 1, and thus the temperature of the catalyst 20.

[0067] By heating the materials in the reaction chamber 10 to temperatures between 20° C. and 100° C., the reaction chamber 10 and the apparatus 1 including the reaction chamber 10 may be used in a variety of situations where the use of conventional configurations operating at higher temperatures is not possible. For example, the apparatus 1 may be included in a building to provide cleaner air within the building. Multiple NOx reduction devices 1 may be included in a single building, if desired. Each enclosed space (room, hallway, stairwell, etc.) of a building may have one or more NOx reduction devices 1 to suit the needs of that enclosed space. For example, a garage may require multiple devices 1, while an office above the garage may require one device 1. Some enclosed spaces in a building may not require NOx reduction devices.

[0068] In some examples, the device 1 is included in a forced air central heating system. In other examples, the device 1 is included in an air conditioning system. Alternatively, the device 1 may be integrated into a vehicle such as an aircraft (e.g., the cockpit or fuselage). <Using the device in an enclosed space>

[0069] Next, a method for reducing NOx in an enclosed space such as a building will be described. Referring to FIG. 2, a first step 201 includes providing an apparatus 10 for reducing NOx as described above. Once the apparatus is installed, in step 203, air can be led into the reaction chamber 10 via the air inlet 101. In the configuration shown in FIG. 1, air is led to the air inlet 101 via the air inlet pipe 1012 and the inlet pipe 1011. Air may be led into the reaction chamber 10 with the aid of a pump 107. The pump 107 may be located in the air inlet pipe 1012 or in the air outlet pipe 1051. In some configurations, the pump 107 is not required in the apparatus 1 when the flow of air can be provided by the apparatus (or device) to which the apparatus 1 is connected. For example, if the outlet 105 is connected to an air conditioning unit, the means for drawing air through the air conditioning unit can also draw air through the reaction chamber 10.

[0070] Simultaneously with step 203, in step 205, a reducing agent may be introduced into the reaction chamber. The reducing agent, air, and catalyst 20 are exposed to each other in the reaction chamber. While the reducing agent, air, and catalyst 20 are exposed to each other, the reaction chamber 10 is maintained at a temperature in the range of 20°C to 100°C. In step 209, gas (purified air) is exhausted from the reaction chamber 10. The gas exiting the reaction chamber 10 has less NOx than the air entering through the air inlet 101. The gas exiting the reaction chamber 10 may be conducted through the outlet 105 directly to an enclosed space (e.g., a building), preferably via an outlet pipe 1051. Alternatively, the gas exiting the reaction chamber 10 may be conducted to a separate device. The separate device may adjust one or more properties of the air, such as temperature and / or humidity. For example, the device may be an air conditioning unit, a dehumidifier, or a forced air heating system.

[0071] The above-described method may be implemented, for example, to improve air quality inside enclosed spaces such as rooms, stairwells, or hallways in buildings. The method is particularly useful where gas-fueled equipment such as cookers, boilers, and / or log burners are installed. Similarly, it is beneficial to reduce the amount of NOx in buildings near sources of fossil fuel combustion (e.g., but not limited to, busy roads, bus depots, airport hangars, diesel train cabins, etc.). Thus, there is a need to be able to safely remove NOx from inside enclosed spaces, for example, in buildings.

[0072] In some embodiments, the reducing agent source is hydrogen. The above method is advantageous because the reduction of NOx occurs at relatively low temperatures (in the range of 20° C. to 100° C.) compared to the prior art. The use of such temperatures allows the method to be carried out safely inside an enclosed space, for example in a building, and does not prevent personnel from entering the enclosed space while the reaction proceeds. <System for monitoring NOx in multiple enclosed spaces>

[0073] A system for monitoring NOx in a plurality of enclosed spaces is described. The plurality of enclosed spaces can be a plurality of areas within one or more buildings. The system comprises a plurality of devices 1 each including a gas detector 30 as described above, and a receiver configured to receive data regarding NOx levels recorded by each of the plurality of devices. In the configuration of FIG. 1, the gas detector 30 is shown as sending a signal to the controller 16. The controller 16 may send a control signal to the pump 107 and / or the heater 12 of the device 1. The gas detector 30 of each device 1 can communicate with a central control device. In some configurations, a central control device is provided in addition to the controller 16 associated with each device 1. The central control device can send a control signal to each device 1 associated with the central control device to control the pump 107 and / or the heater 12. The central control device can analyze signals from each of the devices 1 associated with the central control device and can adjust the pump 107 and / or the heater 12 of those devices 1 individually or collectively.

[0074] In an alternative embodiment, the device 1 may include a temperature detector 18. The temperature detector 18 within each device can supply information regarding the temperature of the device to the controller 16 of each device. The temperature detector 18 can communicate with the central control device, and as a result, the central control device can analyze signals from each of the devices 1 associated with the central control device and can adjust the temperature of the heater 12 of those devices 1 individually or collectively. <Method for manufacturing a supported catalyst for reducing NOx>

[0075] Referring now to FIG. 10, a method (100) for making a supported catalyst for reducing NOx in air is described. The supported catalyst 20 is suitable for use in the reaction chamber 10, as described above. In step 1001, a support material is combined with a stabilizing polymer in water to form an aqueous solution. The support material is any material that preferably has a point zero charge between 5 and 7. For example, the support material can be graphitic carbon nitride (gC3N4), silica, alumina, or titanium dioxide, or a combination thereof. The stabilizing polymer (also known as a capping agent) can be polyvinyl alcohol.

[0076] In step 1003, a first metal compound is added to the aqueous solution. In a preferred embodiment, although not required, a second metal compound is added to the aqueous solution formed in step 1001. The stabilizing polymer binds to the metal compound to prevent agglomeration of the resulting nanoparticles and limit particle size. The aqueous solution to which the first metal compound has been added may then be stirred to mix the first metal compound into the aqueous solution. In a preferred embodiment in which a second metal compound is present, the first metal compound is different from the second metal compound.

[0077] The first metal compound is preferably (Pt(NH3)4(NO3)2). (Pt(NH3)4(NO3)2) is relatively less toxic than many other platinum compounds. In another embodiment, the first metal compound comprises palladium. The palladium compounds PdCl2 and K2PdCl4 have been found to be particularly advantageous. The second metal compound preferably comprises copper, such as the nitrate of copper, i.e., Cu(NO3)3.H2O. In another configuration, the first metal compound is HPtCl6. HPtCl6 is widely available and commonly used in metal (e.g., platinum) colloid preparation methods. In some configurations, the second metal compound comprises one of cobalt nitrate or nickel nitrate. In a preferred embodiment, the first metal compound comprises platinum, the second metal compound comprises copper, and the support material comprises graphitic carbon nitride (gC3N4). In a further preferred embodiment, the first metal compound comprises platinum, the second metal compound comprises palladium, and the support material comprises titanium dioxide.

[0078] Once the first (or first and second) metal compounds are mixed in the aqueous solution, a reducing agent is added to the aqueous solution in step 1005. The reducing agent reduces the metal salts in the solution. The reduced metals form metal nanoparticles. Any suitable known reducing agent may be used. However, it is preferred that sodium borohydride is used as the reducing agent. Sodium borohydride is a strong and fast-acting reducing agent. In step 807, an acid is added to the aqueous solution formed in step 1005. The acid reduces the pH of the solution to a range of pH 1-2 and provides an electronic charge to the support. Thus, the metal nanoparticles are immobilized on the support material. For example, the acid may be one of sulfuric acid or acetic acid. The aqueous solution formed in step 1007 is then stirred, filtered and dried in step 1009 to produce the supported catalyst 20.

[0079] As noted above, by first combining the support material with a stabilizing polymer to form an aqueous solution in step 1007, the supported catalyst resulting from this method, as noted above, provides a higher conversion of NO to NO than supported catalysts prepared by conventional sol immobilization methods.

[0080] In alternative embodiments, a single (first) metal compound may be used in the manner illustrated in FIG. 10 to prepare a monometallic catalyst. In these embodiments, the first metal compound may include platinum or palladium. In a preferred embodiment, the first metal compound is (Pt(NH3)4(NO3)2), PdCl 2、 It can be either K2PdCl4 or H2PtCl6. In an alternative embodiment, the first metal compound comprises palladium or platinum and the support material comprises titanium dioxide. <Solution preparation>

[0081] In a preferred embodiment of the method, the support material is dispersed and stirred in deionized water, for example by sonication. The support material in this preferred embodiment is graphitic carbon nitride (gC3N4). As mentioned above, other support materials can also be used.

[0082] The dispersed graphitic carbon nitride (gC3N4) is combined with a stabilizing polymer. The stabilizing polymer is preferably polyvinyl alcohol. Other stabilizing polymers such as polyethylene glycol (PEG) or polyvinylpyrrolidone (PVP) may also be used.

[0083] The first metal compound (or first and second metal compounds) is then added to the solution of dispersed support material (graphitic carbon nitride in a preferred embodiment) and stabilizing polymer (polyvinyl alcohol in a preferred embodiment). When the supported catalyst is PtCu-gC3N4, the first metal compound can be Pt(NH3)4(NO3)2, and in embodiments where a second metal compound is present, the second metal compound can be Cu(NO3)3.H2O.

[0084] The solution is stirred until the first metal compound, or the first and second metal compounds, are thoroughly mixed. In a preferred embodiment, the solution is stirred for 5 minutes (e.g., exactly 5 minutes, at least 4 minutes 45 seconds to 5 minutes 15 seconds). The solution may be stirred for longer depending on circumstances.

[0085] A reducing agent, such as sodium borohydride, is added dropwise to the solution to prevent localized regions of high reducing agent (or high localized reducing agent concentrations). In alternative embodiments, the reducing agent can be one of ferrous sulfate, formic acid, or ascorbic acid. The solution is stirred, for example, for 1 hour (e.g., exactly 1 hour, at least 45 minutes to 1 hour 15 minutes), or until Pt(NH3)4(NO3)2 and Cu(NO3)3.H2O react together to form bimetallic (PtCu) nanoparticles. In embodiments where only the first metal compound is present, the solution is stirred until metal nanoparticles are formed. The solution may be stirred longer, depending on circumstances. An acid, such as sulfuric acid, is subsequently added to the solution to lower the pH of the solution to within the range of pH 1 to pH 2 (the endpoints of pH 1 and pH 2 are included in this range) to electronically charge the graphitic carbon nitride such that PtCu nanoparticles (or monometallic nanoparticles) are immobilized on the surface of the graphitic carbon nitride. When an acid is added to the solution and the pH is lowered, a solution is formed in which the bimetallic nanoparticles are immobilized on the support material. In the above discussion, the acid is shown as sulfuric acid. Other acids, such as acetic acid, may be used instead of sulfuric acid. <Filtration>

[0086] Once formed, the solution is filtered. This can be done by any known method. For example, a Buchner funnel with filter paper and a vacuum pump is provided. With the pump running, the solution is poured onto the filter paper, and the supernatant passes through the filter paper, leaving the material on the filter paper. Depending on the scale of production, different filtration techniques can be applied. For example, the material may be filtered through the filter paper, relying only on gravity to separate the material from the supernatant (instead of a vacuum pump). <Drying>

[0087] The material is dried to form the catalyst. The material may be dried by any known method. In some configurations, the material is dried at room temperature overnight and then dried in a muffle furnace at 120° C. for 4 to 12 hours (wherein the 4 hour and 12 hour endpoints are included in the range). In other configurations, the material may be dried in a kiln or oven. <Grinding>

[0088] Preferably, the catalyst particles are in the form of a powder. To obtain the powder, the dried supported catalyst material may be ground. Before using the catalyst in the device, the powder may be pressed and sieved to obtain a particle size in the range of 100 to 250 μm. Use of catalysts in devices for reducing NOx in air

[0089] A 1wt% PtCu-gC3N4 supported catalyst was prepared. To synthesize 1wt% PtCu-gC3N4, the first metal compound used was (Pt(NH3)4(NO3)2), and the second metal compound used was Cu(NO3)3.H2O. Polyvinyl alcohol was used as the stabilizing polymer and sodium borohydride was used as the reducing agent.

[0090] The supported catalyst was placed in a device according to the first embodiment of the present invention and the reaction was carried out at room temperature (20°C). Figure 3 shows the activity plot of 1 wt% PtCu-gC3N4 in the presence of NO at a concentration of 0.5 ppm and a flow rate of 2 mL / min; and air at a flow rate of 95.5 mL / min. Hydrogen (reductant) is introduced into the device along with air (at a concentration of 4 v / v% and a flow rate of 2.5 mL / min). The reaction gas is stabilized through a bypass before switching to the PtCu catalyst. At about 18 minutes, NOx is completely mitigated and N2O and N2 are produced. As can be seen from the plot shown in Figure 3, at about 18 minutes, the NOx concentration decreases and N2O increases. Thus, the 1 wt% PtCu-gC3N4 supported catalyst achieves the effect of reducing NOx emissions.

[0091] Figure 4 shows the activity plot of the 0.1 wt% Pd-TiO2 catalyst used in Apparatus 1. The 0.1 wt% Pd-TiO2 catalyst used in Apparatus 1 is a monometallic catalyst prepared using a method within the scope of the present invention. The 0.1 wt% Pd-TiO2 was exposed to NO at a concentration of 0.5 ppm at a flow rate of 2 mL / min and hydrogen at a concentration of 0.1 v / v% at a flow rate of 2.5 mL / min. The flow rates were up to a total flow rate of 100 mL / min in air. At 120 minutes the temperature was increased to 70°C and a decrease in NO was observed. N2 was produced as a by-product with almost no NO.

[0092] FIG. 5 shows a further activity plot of the 0.1 wt% Pd-TiO2 catalyst used in Unit 1. The catalyst was heated to 80° C. and exposed to NO at a concentration of 0.5 ppm and hydrogen at a concentration of 3.6 v / v%. No air / oxygen was introduced at the start of the reaction. In the absence of oxygen, NOx is mitigated. The main product of NOx mitigation in the absence of oxygen is N2O. Referring to the plot shown in FIG. 5, when the catalyst is exposed to oxygen, N2O and N2 are produced as reduction reaction by-products. Thus, exposing the catalyst to oxygen increases the selectivity towards N2 as a by-product.

[0093] FIG. 6 shows the ATR spectra of a 0.1 wt% Pd-TiO2 catalyst before and after use in the apparatus 1. The "fresh" sample of 0.1 wt% Pd-TiO2 is the spectrum obtained before exposing the catalyst to NOx, air and heat in the apparatus 1. The "used" sample of 0.1 wt% Pd-TiO2 is after exposing the catalyst to NOx, air and heat in the apparatus 1. The "used" sample was heated for 4 hours and exposed to 10 v / v% hydrogen and 2.5 ppm NO in air. Regarding the ATR spectrum of the "used" sample of 0.1 wt% Pd-TiO2, there are no visible peaks characteristic of adsorbates. This advantageously confirms that there is no formation of nitrites, nitrosamines, ammonia or ammonium nitrate during the catalytic reaction. The surface of the catalyst is therefore not poisoned by adsorbates. This converts NOx directly to nitrogen and / or NO.

[0094] FIG. 7 shows an activity plot of the 0.1 wt% Pt-TiO2 catalyst used in Apparatus 1. The 0.1 wt% Pt-TiO2 catalyst used to generate this plot was prepared using a method within the scope of the present invention and exposed to NO at a concentration of 0.5 ppm at a flow rate of 2 mL / min along with air and hydrogen at 98 mL / min. For FIG. 7, the 0.1 wt% Pt-TiO2 catalyst was exposed to hydrogen at a concentration of 0.05 v / v% at a flow rate of 1.3 mL / min, air (oxygen concentration 20.5 v / v%), and NO at a concentration of 0.5 ppm at a flow rate of 2 mL / min, at a total flow rate of 100 mL / min. The catalyst was heated to a temperature of 20° C. Under these conditions, the 0.1 wt% Pt-TiO2 catalyst reduced the concentration of NOx in 8.5 hours. Hydrogen is pulsed over the catalyst using a flow controller to regenerate the catalyst activity for an additional 8 hours.

[0095] Figure 8 shows the activity plot of the 0.05wt%Pt0.05wt%Pd-TiO2 catalyst used in the device 1. The catalyst was exposed to NO at a concentration of 0.5ppm and a flow rate of 2mL / min, hydrogen at a concentration of 0.1v / v%, and oxygen at a concentration of 20.5v / v%. As can be seen from Figure 8, the catalyst exposed to a temperature of 20°C can reduce the concentration of NOx. <Comparative experiment>

[0096] Experiments were conducted to compare the catalytic behavior of 1 wt% PtCu-gC3N4 supported catalyst prepared by a conventional sol-immobilized preparation method (i.e., Method 1) with that prepared by a method within the scope of the present invention (i.e., Method 2).

[0097] The above catalyst was used in the device 1 according to the present invention. The 1 wt% PtCu-gC3N4 catalyst reduces the NOx concentration in air via a reduction pathway. The catalyst was exposed to NO at a concentration of 5000 ppm. In the presence of a reducing agent (hydrogen in this example), the catalyst reduces NO to form NO and nitrogen. The NO to NO conversion and particle size of PtCu for 1 wt% PtCu-gC3N4 prepared via methods 1 and 2 are shown in Table 1. TIFF2024532608000002.tif112169

[0098] From the results in Table 1 (and Figures 9a-9d below), it can be seen that 1 wt% PtCu-gC3N4 prepared by Method 2 achieves higher conversion of NO to NO in the presence of heat and in the presence of heat and oxygen compared to 1 wt% PtCu-gC3N4 prepared by Method 1 under the same conditions. Thus, 1 wt% PtCu-gC3N4 prepared by Method 2 provides improved NOx reduction effect over 1 wt% PtCu-gC3N4 prepared by conventional Method 1.

[0099] As shown in Table 1, conventional method 1 produces larger PtCu particles (diameter 3-4 nm), while method 2 produces smaller PtCu particles (diameter 2-3 nm). Therefore, the higher conversion of NO to NO by 1 wt% PtCu-gC3N4 obtained by method 2 can be attributed to the increased surface area to volume ratio of PtCu particles (compared to the PtCu particles obtained by method 1) and the reduced alloying between platinum and copper.

[0100] Figures 9a and 9b show activity plots of 1 wt% PtCu-gC3N4 obtained by conventional preparation method 1. To simulate atmospheric conditions, the catalyst was exposed to a flow of NO. Referring to the plot shown in Figure 9a, 1 wt% PtCu-gC3N4 was exposed to 1% v / v NO in helium at a flow rate of 10 ml / min and 4% v / v hydrogen (reductant) in helium at a flow rate of 10 ml / min in the presence of heat (50 °C). NO was observed as a by-product of the catalytic reaction between hydrogen and NO, and the conversion of NO to NO was 20% for 1 wt% PtCu-gC3N4 prepared by method 1.

[0101] Referring to Figure 9b, 1 wt% PtCu-gC3N4 was exposed to 1% v / v NO in helium at a flow rate of 7 ml / min, 4% v / v hydrogen (reductant) in helium at a flow rate of 7 ml / min, and 10% v / v oxygen in helium at a flow rate of 7 ml / min. The catalyst was also exposed to heat (50°C). No production of NO was observed. Thus, in the presence of oxygen, 1 wt% PtCu-gC3N4 prepared by method 1 did not show any NOx reduction activity. In other words, NO was not converted to NO.

[0102] Figures 9c and 9d show activity plots of 1 wt% PtCu-gC3N4 obtained by method 2 (i.e., the method of the present invention). Figure 9c shows activity plots of 1 wt% PtCu-gC3N4 exposed to 1% v / v NO in helium at a flow rate of 10 ml / min and 4% v / v hydrogen (reductant) in helium at a flow rate of 10 ml / min. The conversion of NO to NO in the presence of heat (50°C) was 50%.

[0103] Figure 9d shows the activity plot of 1 wt% PtCu-gC3N4 exposed to 1% v / v NO in helium at a flow rate of 7 ml / min, 4% v / v hydrogen (reductant) in helium at a flow rate of 7 ml / min, and 10% v / v oxygen in helium at a flow rate of 7 ml / min. Upon exposure to heat (50 °C), a 12% conversion of NO to NO was observed.

[0104] Therefore, it can be inferred that 1 wt% PtCu-gC3N4 prepared by Method 2 provides a more effective NOx reduction catalyst than 1 wt% PtCu-gC3N4 prepared by Method 1.

[0105] Many other variations and embodiments will be apparent to those skilled in the art, and all of these are intended to be included within the scope of the invention, whether or not covered by the claims as filed. Protection is sought for any and all novel subject matter disclosed herein and combinations thereof.

Claims

1. 1. An apparatus for reducing NOx in air, said apparatus comprising: a catalyst comprising Pt, PtCu, PtCo, PtNi, Pd, PtPd and / or PdCu; a reaction chamber for receiving the catalyst, the reaction chamber having an inlet and an outlet for air and a reducing agent; a heater configured to heat the catalyst to a temperature of between 20°C and 100°C; a reducing agent source connected to the inlet.

2. The apparatus of claim 1 , wherein the reducing agent is hydrogen.

3. The apparatus of claim 1 further comprising a source of material for providing said reducing agent.

4. The apparatus of claim 1 , wherein the heater is configured to heat the catalyst to a temperature of between 20°C and 25°C.

5. The apparatus of claim 1 , wherein the reducing agent source comprises an electrolytic cell for producing the reducing agent.

6. 2. The device of claim 1, wherein when the reducing agent is hydrogen, the hydrogen is present at a concentration of 0.05% v / v to 4% v / v.

7. 7. The device of claim 6, wherein the hydrogen is present at a concentration of 1% to 4% v / v.

8. The apparatus of claim 1 further comprising a flow controller for increasing or decreasing the flow rate of the reducing agent.

9. The apparatus of claim 8 , wherein the flow controller is configured to increase the flow rate of the reducing agent for 5 to 15 seconds.

10. The apparatus of claim 1 , wherein the catalyst is supported on a support.

11. 11. The apparatus of claim 10, wherein the catalyst is present in an amount of 0.1 wt % to 10 wt %, based on the combined weight of the catalyst and the support.

12. The catalyst is PtCu and the support is gC ３ N ４ and PtCu is PtCu and gC ３ N ４ 11. The device of claim 10, wherein the composition is present in an amount of 0.1 wt % to 10 wt % based on the combined weight of

13. and at least one gas detector in communication with the outlet, the at least one gas detector detecting nitric oxide (NO) and / or nitrous oxide (N) in the gas exiting the reaction chamber. ２ 0). The apparatus of claim 1, configured to detect

14. The at least one gas detector detects nitric oxide (NO) and / or nitrogen dioxide (NO ２ 14. The device of claim 13, comprising a chemiluminescence detector for detecting

15. The at least one gas detector detects nitrous oxide (N ２ 14. The apparatus of claim 13, further comprising an infrared detector for detecting O).

16. 1. A system for monitoring NOx concentrations in air in a plurality of enclosed spaces, comprising:

10. The apparatus of claim 1, wherein each of the plurality of apparatuses comprises at least one gas detector in communication with the outlet, the at least one gas detector detecting nitric oxide (NO) and / or nitrous oxide (N) in the gas exiting the reaction chamber. ２ O), wherein each of the plurality of devices is disposed in each of the plurality of enclosed spaces.

17. 1. A method for reducing NOx within an enclosed space, comprising: - providing a device for reducing NOx according to claim 1; - forcing air from inside the enclosed space through the inlet into the reaction chamber; - introducing a reducing agent into the reaction chamber so that the reducing agent, air and catalyst are exposed to each other; - heating the reaction chamber to a temperature in the range of 20°C to 100°C; - pumping gas from said reaction chamber through said outlet into said enclosed space.

18. A method for preparing a catalyst for reducing NOx in air, a) combining a carrier material with a stabilizing polymer in water to form an aqueous solution; b) adding a first metal compound to the aqueous solution formed in step a) and stirring the solution; c) adding a reducing agent to the solution formed in step b) to form metal nanoparticles; d) adding an acid to the solution formed in step c); e) stirring the solution formed in step d) followed by filtering and drying to form supported metal nanoparticles.

19. 20. The method of claim 18, wherein the first metal compound comprises platinum or palladium.

20. 20. The method of claim 18, wherein step b) further comprises adding a second metal compound to the aqueous solution formed in step a), wherein the first metal compound is different from the second metal compound.

21. 21. The method of claim 20, wherein the first metal compound comprises platinum and the second metal compound comprises one of copper, cobalt, or nickel.

22. 21. The method of claim 20, wherein the first metal compound comprises palladium and the second metal compound comprises copper.

23. 21. The method of claim 20, wherein the second metal compound is a nitrate of copper, nickel, or cobalt.

24. A catalyst for reducing NOx in air prepared by the method of any one of claims 18 to 23, for use in an apparatus according to any one of claims 1 to 15.

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