Bi-component catalyst for catalytic oxidation of gaseous pollutants as well as preparation method and application of bi-component catalyst

Abstract

The invention belongs to the technical field of catalysts, and particularly discloses a bi-component catalyst for catalytic oxidation of gaseous pollutants and a preparation method and application thereof.The bi-component catalyst is prepared by loading transition metal and precious metal step by step and comprises, by mass, 1-30% of transition metal, 0.05-10% of precious metal and the balance MOFs carrier. According to the bi-component catalyst for catalytic oxidation of gaseous pollutants and the preparation method and application of the bi-component catalyst, the problems that in the prior art, the catalytic efficiency is low, and the stability of the catalyst is poor are solved, the prepared catalyst can achieve efficient catalytic oxidation of high pollutant concentration at the low reaction temperature, and the catalytic oxidation efficiency is high. And the catalyst has relatively long service life and good catalytic stability.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, in particular to a two-component catalyst for catalytically oxidizing gaseous pollutants, and a preparation method and application thereof. Background Art

[0002] Industrial waste gas is widely sourced from various industries such as petrochemical, chemical, metallurgy, electronics, pharmaceutical, printing and dyeing, and food processing. The main components of these waste gases vary depending on the industry, but they generally include inorganic gas pollutants such as volatile organic compounds (VOCs), ammonia (NH3), and carbon monoxide (CO). VOCs and NO x Ozone and secondary organic aerosol (PM 2.5 ) precursors, easily forming photochemical smog and harming the ecosystem. When ammonia is released into the atmosphere, it will react with acidic gases (such as SO2, NO x ) reactions generate secondary fine particulate matter, which has a profound impact on atmospheric visibility and climate change. CO can cause acute poisoning, ammonia can irritate the respiratory tract and skin, and particulate matter can enter the bloodstream through the lungs and cause cardiovascular disease. Therefore, industrial waste gas treatment plays a vital role in the environmental protection industry, and its market demand is rapidly growing with global industrialization and the strengthening of environmental regulations.

[0003] Catalytic oxidation technology is widely used in industrial waste gas treatment and air purification because it can efficiently and environmentally friendly convert gaseous pollutants into harmless substances. However, existing catalysts still face some challenges in practical applications, such as insufficient catalytic activity, poor catalyst durability, and high catalyst costs. Especially in low-temperature catalytic oxidation, the efficiency of traditional catalysts is difficult to meet industrial needs. Precious metal catalysts (such as platinum and palladium) are often used as catalysts for the catalytic oxidation of gaseous pollutants due to their excellent catalytic activity. However, the high cost, scarcity of resources and sensitivity to reaction conditions of precious metal catalysts make them face many limitations in large-scale applications. To overcome this problem, researchers began to explore ways to improve catalytic performance by changing the structure and composition of the catalyst while reducing the use of precious metals.

[0004] Metal-organic frameworks (MOFs), a novel porous material, have garnered widespread attention in the field of catalysis in recent years. MOFs, composed of metal ions or metal clusters linked to organic ligands through coordination bonds, possess extremely high surface areas and tunable pore structures. MOFs are not only capable of efficiently loading active metals but, by manipulating their structure and composition, they can provide more catalytic sites, further enhancing the activity and selectivity of the catalysts. Therefore, MOFs have become ideal supports for precious metal catalysts.

[0005] Recent research has shown that introducing two different metal elements into a catalyst system, forming a bimetallic catalytic system, can significantly improve the catalytic performance of the catalyst. In particular, combining a noble metal (such as platinum, palladium, and silver) with a secondary metal (such as copper, manganese, and cobalt) can enhance the activity of the catalyst and optimize the reaction selectivity through electronic or geometric synergy between the metals. Specifically, the introduction of a secondary metal can modulate the electronic state of the noble metal, improving its catalytic efficiency while reducing the amount of noble metal used and the catalyst cost.

[0006] At present, bimetallic catalytic systems based on MOFs are still in the research stage. Although there are some studies on precious metals and transition metals (such as copper, nickel, etc.), there is still a lack of systematic research on the synergistic catalytic oxidation of gaseous pollutants by two components, especially in the catalytic oxidation of gaseous pollutants such as ammonia, VOCs and carbon monoxide.

[0007] To address the performance bottlenecks of existing catalysts, the present invention provides a dual-component catalyst based on MOFs loaded with precious metals and transition metals. This catalyst, through optimized synthesis methods, constructs a dual-component catalyst in which the precious metals and transition metals interact. Regulating the parameters of the preparation process can adjust the physicochemical properties, such as the electronic state, of the precious metals and transition metals in the catalyst, thereby enhancing the oxidation activity and selectivity of gaseous pollutants such as VOCs, carbon monoxide, and ammonia. Compared to traditional catalysts, the catalyst of the present invention exhibits higher catalytic activity, improved stability, and lower precious metal usage, and has broad prospects for industrial application. Summary of the Invention

[0008] The purpose of the present invention is to provide a two-component catalyst for catalytic oxidation of gaseous pollutants, a preparation method and application thereof, so as to overcome the problems of low catalytic efficiency and poor catalyst stability existing in the prior art. The prepared catalyst can achieve efficient catalytic oxidation at high pollutant concentrations at a lower reaction temperature, and has a long service life and good catalytic stability.

[0009] To achieve the above objectives, the present invention provides a two-component catalyst for catalytic oxidation of gaseous pollutants. The two-component catalyst is prepared by step-by-step loading of transition metals and precious metals, and includes the following raw material components in mass percentage: 1-30% transition metals, 0.05-10% precious metals, and the remainder MOFs carrier.

[0010] Preferably, the noble metal is one of platinum, silver or palladium.

[0011] Preferably, the transition metal is one of copper, manganese and cobalt.

[0012] Preferably, the MOFs carrier material is one of UiO-66, ZIF-67, and MIL-101.

[0013] Preferably, the mass ratio of the noble metal to the MOFs carrier is 0.01-0.1:1, and the mass ratio of the transition metal to the MOFs carrier is 0.1-0.3:1.

[0014] The present invention also provides a method for preparing a two-component catalyst for catalytically oxidizing gaseous pollutants, comprising the following steps:

[0015] S1. Prepare MOFs carrier, and synthesize MOFs carrier by solvothermal method or hydrothermal method according to MOFs carrier material;

[0016] S2, loading transition metals, dispersing the MOFs carrier in water, adding acetic acid to adjust the solution pH between 4-7, then adding transition metal salt solution, controlling the metal ion molar concentration to 0.001-0.1 mol / L, stirring evenly and ultrasonically treating at 80 ° C for 4-8 hours, further centrifuging and washing, dispersing the precipitate in acetone solution and standing for 12 hours, then centrifuging and repeating the above operation three times, centrifuging and drying, and finally calcining the precipitate at 150-300 ° C for 2-6 hours;

[0017] S3. Loading precious metals: Dispersing the inorganic salt of precious metals in aqueous solution, dissolving polyvinyl pyrrolidone in ethylene glycol, heating the ethylene glycol solution to 120-180°C, then adding the salt solution of precious metals to the ethylene glycol solution for reaction, further centrifuging, washing, and redispersing in N,N-dimethylformamide solution; dispersing the MOFs carrier in acetonitrile solution, adding the N,N-dimethylformamide dispersion of precious metals, ultrasonically treating for 1 hour, centrifuging, washing, and drying, and calcining the solid powder at 150-300°C for 2-6 hours.

[0018] The present invention also provides the use of a two-component catalyst for catalytically oxidizing gaseous pollutants, which is used to treat gaseous pollutants in industrial waste gas.

[0019] Preferably, the gaseous pollutant is one of carbon monoxide, ammonia, and volatile organic compounds, the volatile organic compounds include hydrocarbon organic compounds, oxygen-containing organic compounds, and nitrogen-containing organic compounds, the carbon monoxide concentration is 5000-20000 ppm, the ammonia concentration is 500-1000 ppm, and the volatile organic compound concentration is 500-1000 ppm.

[0020] The advantages and beneficial effects of the present invention using the above-mentioned two-component catalyst for catalytic oxidation of gaseous pollutants and its preparation method and application are:

[0021] 1. The present invention uses MOFs as carriers, which helps to uniformly disperse metal nanoparticles or metal ions. The metal nodes and organic ligands of MOFs regulate the chemical environment around the active components, optimize the physicochemical properties and reaction pathways of the active components, and reduce the reaction energy barrier. It also constructs a complex multi-component interface, promotes electronic interactions between metal carriers, and exerts the synergistic effect of precious metals and transition metals, thereby improving catalytic efficiency and selectivity.

[0022] 2. The catalyst of this invention features well-developed pores and a rich specific surface area, which increases the number of exposed active sites and facilitates the mass transfer of pollutant molecules. The pressure drop across the catalyst bed is minimal. The loading of precious metals and transition metals is optimized to achieve a balance between catalytic activity and cost-effectiveness, ensuring the catalyst's high efficiency in oxidation reactions.

[0023] 3. The dual-component catalyst of the present invention is suitable for the catalytic oxidation of gaseous pollutants in industrial waste gas. It can also be used in automobile exhaust treatment, air purification systems and environmental remediation. In particular, in the removal of VOCs, ammonia and carbon monoxide, the catalyst can efficiently remove harmful gases, improve air quality, and has broad industrial application prospects.

[0024] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 NH3 conversion curves of Examples 1 and 2 of the present invention;

[0026] Figure 2 1 is the CO conversion curve of Example 3 and Example 4 of the present invention;

[0027] Figure 3 5 is the toluene / DMF conversion curve of Example 5, Example 6 and Example 7 of the present invention;

[0028] Figure 4 : are the nitrogen selectivity curves in the corresponding reactions of Examples 1, 2, and 7 of the present invention;

[0029] Figure 5 1 is a graph showing the N2 adsorption-desorption isotherm test results of Examples 1, 2 and 3 of the present invention;

[0030] Figure 6 is a TEM image of the catalyst of Example 1 of the present invention;

[0031] Figure 7 This is a TEM image of the catalyst of Example 2 of the present invention. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0033] Unless otherwise defined, technical or scientific terms used in the present invention shall have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0034] Unless otherwise defined, the reagents and equipment used in the present invention are all commercially available.

[0035] This dual-component catalyst for the catalytic oxidation of gaseous pollutants is prepared by stepwise loading of a transition metal and a precious metal. The catalyst comprises the following raw materials, by weight percentage: 1-30% transition metal, selected from copper, manganese, and cobalt; 0.05-10% precious metal, selected from platinum, silver, or palladium; and the balance, a MOF support, selected from UiO-66, ZIF-67, or MIL-101. The mass ratio of the precious metal to the MOF support is 0.01-0.1:1, and the mass ratio of the transition metal to the MOF support is 0.1-0.3:1. The precious metal is primarily responsible for the high efficiency of the catalytic oxidation reaction, while the transition metal modulates the precious metal's electronic state, promoting the activation of oxygen molecules and thereby improving the overall efficiency of the oxidation reaction.

[0036] The preparation method of a two-component catalyst for catalytic oxidation of gaseous pollutants uses MOFs as a carrier and loads transition metals and noble metals in steps to construct a two-component catalyst. The two-component catalyst can completely convert VOCs, CO and ammonia into CO2, H2O and N2, including the following steps:

[0037] S1. Prepare the MOF support by synthesizing the MOF material using a solvothermal or hydrothermal method. The specific synthesis method depends on the selected MOF material. In this step, a metal salt (such as a zirconium or cobalt salt) and an organic ligand (such as terephthalic acid or an imidazole derivative) are dissolved in water or an organic solvent (such as N,N-dimethylformamide (DMF) or methanol). The reaction is carried out under controlled conditions to allow the nucleation and growth of MOF crystals. The desired MOF material is obtained through centrifugation, washing, and drying.

[0038] S2. Load the transition metal, disperse the MOFs carrier in water, add acetic acid to adjust the solution pH between 4-7, then add transition metal salt solution, control the metal ion molar concentration to 0.001-0.1 mol / L, stir evenly and ultrasonically treat at 80°C for 4-8h, further centrifuge and wash, disperse the precipitate in acetone solution and let it stand for 12h, then centrifuge and repeat the above operation three times, then centrifuge and dry, and finally calcine the precipitate at 150-300°C for 2-6h.

[0039] S3. Loading precious metals: Disperse the inorganic salt of precious metals in aqueous solution, dissolve polyvinyl pyrrolidone (PVP) in ethylene glycol, heat the ethylene glycol solution to 120-180°C, then add the salt solution of precious metals to the ethylene glycol solution for reaction, further centrifuge, wash, and redisperse in DMF solution; disperse the MOFs carrier in acetonitrile solution, add the DMF dispersion of precious metals, ultrasonicate for 1 hour, centrifuge, wash, and dry, and calcine the solid powder at 150-300°C for 2-6 hours.

[0040] The application of a two-component catalyst for catalytic oxidation of gaseous pollutants is applied to the treatment of gaseous pollutants in industrial waste gas. The gaseous pollutant is one of carbon monoxide, ammonia, and volatile organic compounds (VOCs). Volatile organic compounds include hydrocarbon organic compounds, oxygen-containing organic compounds, and nitrogen-containing organic compounds. VOCs include but are not limited to toluene, formaldehyde, acetaldehyde, DMF, acetone, ethylene, etc. The CO concentration is 5000-20000ppm, the reaction atmosphere is air, and the reaction temperature is 100-300°C. The NH3 concentration is 500-1000ppm, the reaction atmosphere is 10% oxygen / nitrogen, and the reaction temperature is 120-300°C. The VOCs concentration is 500-1000ppm, the reaction atmosphere is air, and the reaction temperature is 100-300°C.

[0041] In the above method, as a further embodiment, the reaction gas is 200-20000 ppm of gaseous pollutants (carbon monoxide, VOCs or NH3) and air, and the space velocity is 20000-120000 ml g -1 h -1 The reaction temperature is 100-300℃, under which conditions the complete conversion of gaseous pollutants can be achieved.

[0042] Example 1

[0043] The Pt / Cu / UiO-66 catalyst treats NH₃ gas. Using UiO-66 as a support, zirconium tetrachloride and terephthalic acid are dissolved in a DMF solution, hydrochloric acid is added and thoroughly mixed, and the mixture is allowed to react at 80-120°C for 12-24 hours. The resulting solution is filtered, washed, and dried to yield UiO-66. The UiO-66 is then loaded with transition metal Cu and precious metal Pt in separate steps. The Cu salt solution has a Cu ion concentration of 0.01 mol / L and a pH of 4-5. The mass ratio of Cu to support is 0.02:1, and the mass ratio of Pt to support is 0.002:1.

[0044] Reaction performance evaluation was conducted in a fixed continuous flow reactor, using custom-made cylinder NH3 gas at a concentration of 500 ppm. 0.1 g of the catalyst, after being pressed and sieved (40-60 mesh), was placed in a quartz reaction tube with an inner diameter of 6 mm. The total gas flow rate was 200 ml / min. The reaction activity was tested over a temperature range of 100 to 300°C. Reactants and products were monitored online using a GC-8890 gas chromatograph and a Fourier transform infrared spectrometer. The results showed that under a 10% oxygen reaction atmosphere, NH3 was completely converted at 200°C, with a nitrogen selectivity of 93%. The catalyst operated at 200°C for 100 hours without a significant decrease in activity, indicating good catalyst stability.

[0045] Example 2

[0046] The Cu ion concentration in the Cu salt solution was set to 0.006 mol / L, the solution pH was set to 6-7, and the rest of the contents were the same as in Example 1.

[0047] Experimental results show that ammonia is completely converted at 260°C with a nitrogen selectivity of 95%. The catalyst runs at 200°C for 100 hours with no significant decrease in activity, indicating the catalyst has good stability.

[0048] Example 3

[0049] The Pd / Co / UiO-66 catalyst was used to treat CO gas, using UiO-66 as a support. The preparation method was the same as in Example 1. Subsequently, the transition metal Co and the precious metal Pd were loaded stepwise on the UiO-66. The Co ion concentration in the Co salt solution was 0.007 mol / L, the mass ratio of Co to support was 0.05:1, and the mass ratio of Pd to support was 0.005:1.

[0050] Reaction performance evaluation was conducted using a reaction gas of 10,000 ppm CO (from a custom cylinder). The reaction was conducted under an air atmosphere with a gas flow rate of 100 ml / min. Other conditions were the same as in Example 1. The results showed that CO was completely oxidized at 150°C. The catalyst showed no significant decrease in activity after operating at 150°C for 100 hours, demonstrating the catalyst's excellent stability.

[0051] Example 4

[0052] The concentration of the Cu salt solution was set to 0.005 mol / L, the mass ratio of Cu to the carrier was 0.01:1, and the mass ratio of Pd to the carrier was 0.005:1. The remaining contents were the same as in Example 3 to prepare a Pd / Cu / UiO-66 catalyst. The prepared Pd / Cu / UiO-66 catalyst treated CO gas.

[0053] The reaction performance evaluation conditions were the same as those in Example 3. The results showed that CO was completely oxidized at 170°C. The catalyst was operated at 170°C for 100 hours without significant decrease in activity, indicating that the catalyst had good stability.

[0054] Example 5

[0055] The Pt / Mn / ZIF-67 catalyst was used to treat toluene gas. Using ZIF-67 as a support, cobalt nitrate and dimethylimidazole were dissolved in a methanol solution and reacted at room temperature for 12-24 hours. The reaction solution was filtered, washed, and dried to obtain ZIF-67. Subsequently, the transition metal Mn and the noble metal Pt were loaded onto ZIF-67 in a stepwise manner. The Mn salt solution had a Mn ion concentration of 0.05 mol / L, a pH of 5-6, and a mass ratio of Mn to support of 0.2:1 and a mass ratio of Pt to support of 0.01:1.

[0056] Reaction performance evaluation was conducted in an air atmosphere with a reaction gas concentration of 1000 ppm toluene at a gas flow rate of 50 ml / min. Other test conditions were the same as in Example 1. The results showed that toluene was completely oxidized at 170°C. The catalyst exhibited no significant decrease in activity after operating at 170°C for 100 hours, demonstrating the catalyst's excellent stability.

[0057] Example 6

[0058] The Pt / Mn / MIL-101 catalyst was used to treat toluene gas. Using MIL-101 as a support, chromium nitrate, terephthalic acid, and water were thoroughly mixed and stirred at room temperature for 0.5 hours. The mixture was then reacted at 180-220°C for 8-24 hours. The reaction solution was filtered, washed, and dried to obtain MIL-101. Mn and Pt were then loaded onto MIL-101 in a stepwise manner. The Mn salt solution had a Mn ion concentration of 0.07 mol / L, a pH of 4-5, and a Mn-to-support mass ratio of 0.3:1 and a Pt-to-support mass ratio of 0.01:1.

[0059] The reaction performance evaluation conditions were the same as those in Example 5. The results showed that toluene was completely oxidized at 140°C. The catalyst activity did not decrease significantly after operating at 140°C for 100 hours, indicating that the catalyst had good stability.

[0060] Example 7

[0061] Ag / Cu / UiO-66 was used to treat DMF gas, using UiO-66 as a carrier, and the preparation method was the same as in Example 1. Subsequently, transition metal Cu and precious metal Ag were loaded stepwise on UiO-66, with the Cu ion concentration in the Cu salt solution being 0.01 mol / L, the mass ratio of Cu to carrier being 0.1:1, and the mass ratio of Ag to carrier being 0.05:1.

[0062] Reaction performance was evaluated in an air atmosphere with a reaction gas concentration of 500 ppm DMF at a gas flow rate of 20 ml / min. Other conditions were the same as in Example 1. The results showed that DMF was completely decomposed at 200°C, with a nitrogen selectivity of 96%. The catalyst exhibited no significant decrease in activity after operating at 200°C for 100 hours, demonstrating the catalyst's excellent stability.

[0063] Figure 1 1 and 2 are NH3 conversion curves of Examples 1 and 2.

[0064] Figure 2 3 and 4 are the CO conversion curves of Examples 3 and 4.

[0065] Figure 3 It is the toluene / DMF conversion curve of Example 5, Example 6 and Example 7.

[0066] Figure 4 These are the nitrogen selectivity curves of Example 1, Example 2, and Example 7 in the corresponding reactions.

[0067] Figure 5 The N2 adsorption and desorption isotherm test results of Example 1, Example 2 and Example 3 are shown in the figure. The catalysts all have microporous structures, and their specific surface areas are 912.21, 978.28 and 613.35 m 2 / g, which is much higher than that of conventional oxide catalysts.

[0068] Figure 6 This is a TEM image of the catalyst of Example 1; the black particles with a diameter of about 3 nm in the image are Pt particles.

[0069] Figure 7 This is a TEM image of the catalyst of Example 2; the black particles with a diameter of about 3 nm in the image are Pt particles.

[0070] Therefore, the present invention adopts the above-mentioned two-component catalyst for catalytic oxidation of gaseous pollutants and its preparation method and application to overcome the problems of low catalytic efficiency and poor catalyst stability in the prior art. The prepared catalyst can achieve efficient catalytic oxidation at high pollutant concentrations at a lower reaction temperature, and has a long service life and good catalytic stability.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A two-component catalyst for catalytic oxidation of gaseous pollutants, characterized in that: The dual-component catalyst is prepared by loading transition metal and noble metal step by step, and comprises the following raw material components by mass percentage: 1-30% of transition metal, 0.05-10% of noble metal, and the rest of MOFs carrier.

2. The dual-component catalyst for catalytic oxidation of gaseous pollutants according to claim 1, characterized in that: The noble metal is one of platinum, silver or palladium.

3. The dual-component catalyst for catalytic oxidation of gaseous pollutants according to claim 1, characterized in that: The transition metal is one of copper, manganese and cobalt.

4. The dual-component catalyst for catalytic oxidation of gaseous pollutants according to claim 1, characterized in that: The MOFs carrier material is one of UiO-66, ZIF-67 and MIL-101.

5. The dual-component catalyst for catalytic oxidation of gaseous pollutants according to claim 1, characterized in that: The mass ratio of the noble metal to the MOFs carrier is 0.01-0.1:1, and the mass ratio of the transition metal to the MOFs carrier is 0.1-0.3:

1.

6. The method for preparing a dual-component catalyst for catalytic oxidation of gaseous pollutants according to any one of claims 1 to 5, characterized in that: The steps include: S1. Prepare a MOFs carrier, and synthesize the MOFs carrier using a solvothermal method or a hydrothermal method according to the MOFs carrier material; S2, loading transition metals, dispersing the MOFs carrier in water, adding acetic acid to adjust the solution pH between 4-7, then adding transition metal salt solution, controlling the metal ion molar concentration to 0.001-0.1 mol / L, stirring evenly and ultrasonically treating at 80°C for 4-8h, further centrifuging and washing, dispersing the precipitate in acetone solution and standing for 12h, then centrifuging and repeating the above operation three times, centrifuging and drying, and finally calcining the precipitate at 150-300°C for 2-6h; S3. Loading precious metals, dispersing inorganic salts of precious metals in aqueous solution, dissolving polyvinyl pyrrolidone in ethylene glycol, heating the ethylene glycol solution to 120-180°C, then adding the salt solution of precious metals to the ethylene glycol solution for reaction, further centrifuging, washing, and re-dispersing in N,N-dimethylformamide solution; dispersing the MOFs carrier in acetonitrile solution, adding N,N-dimethylformamide dispersion of precious metals, ultrasonically treating for 1 hour, centrifuging, washing, and drying, and calcining the solid powder at 150-300°C for 2-6 hours.

7. Use of a two-component catalyst for catalytic oxidation of gaseous pollutants as claimed in any one of claims 1 to 5, characterized in that: Used to treat gaseous pollutants in industrial waste gas.

8. Use of the dual-component catalyst for catalytic oxidation of gaseous pollutants according to claim 7, characterized in that: The gaseous pollutant is one of carbon monoxide, ammonia, and volatile organic matter, the volatile organic matter includes hydrocarbon organic matter, oxygen-containing organic matter and nitrogen-containing organic matter, the carbon monoxide concentration is 5000-20000ppm, the ammonia concentration is 500-1000ppm, and the volatile organic matter concentration is 500-1000ppm.

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