A spinel@CeO2 catalyst and its preparation method and application

Abstract

The present invention relates to the technical field of atmospheric pollution catalyst preparation, and in particular to a spinel@CeO2 catalyst, a preparation method and application thereof; wherein the preparation method comprises: S1, synthesizing MOFs with oxidizing metals; S2, synthesizing spinel@CeO2 by redox anchoring; and S3, preparing spinel@CeO2 heterojunction catalyst by confined pyrolysis; the present invention utilizes the oxidizing property, structural diversity and high dispersion of metal clusters of MOFs to drive them to undergo redox reaction with reductive Ce(OH)3, thereby achieving uniform anchoring of CeO2 in highly ordered oxidizing metal clusters in MOFs, and further achieving a catalyst modification strategy for improving the intrinsic activity of the catalyst by regulating the interaction between two components in the spinel@CeO2 heterojunction catalyst and the heterojunction interface, thereby preparing a catalyst for catalytic oxidation of VOCs with good low-temperature activity.

Description

Technical Field

[0001] The present invention relates to the technical field of air pollution catalyst preparation, and in particular to a spinel@CeO2 catalyst and a preparation method and application thereof. Background Art

[0002] Effective control of VOCs is of great significance to improving air pollution prevention and control. Among the many VOCs treatment methods, catalytic oxidation has many advantages, so the development of its efficient catalyst is of practical significance. To address the above problems, CeO2 has been favored by technicians in this field because of its good oxygen storage capacity. Based on CeO2, a variety of composite catalysts have been developed, such as:

[0003] The article "CeO2 from pyrolysis of MOFs for efficient catalytic combustion of VOCs" (DOI: 10.1016 / J.MCAT.2022.112857) discloses the preparation of CeO2 catalyst with MOF structure by pyrolysis of UiO-66 (Ce), and the improvement of catalytic performance for VOCs by the microporous structure of the catalyst.

[0004] The article "Catalytic Ozonation of Norfloxacin Using Co-Mn / CeO2 as a Multi-Component Composite Catalyst" discloses that the catalytic performance of the catalyst is improved by loading Co and Mn components on CeO2 to increase the active sites on the catalyst surface.

[0005] Unlike the aforementioned methods of using CeO2 as a framework to load transition metals or improving the structure of CeO2 itself, the present invention prepares a spinel@CeO2 catalyst using a completely new synthesis route. This catalyst has enhanced intrinsic catalytic activity due to the presence of a heterojunction structure between CeO2 and spinel. Furthermore, the present invention solves the following common problems existing in existing methods through this new synthesis route:

[0006] 1) Due to the large difference in the physical and chemical properties of spinel and CeO2, CeO2 is difficult to disperse on the spinel surface, which is not conducive to the formation of an active heterojunction interface;

[0007] 2) The spinel@CeO2 heterojunction catalyst constructed by traditional methods such as redox method has a small specific surface area, which is not conducive to the formation of active heterojunction interface;

[0008] 3) In spinel@CeO2 heterojunction catalysts constructed by traditional methods such as the template method, the interaction between CeO2 and spinel is weak, which is unfavorable for interfacial electron transfer and leads to limited improvement in the intrinsic activity of the catalyst. Summary of the Invention

[0009] To achieve the above objectives, the present invention utilizes MOFs to undergo a redox reaction with reductive Ce(OH)3, achieving uniform anchoring of CeO2 in highly ordered oxidizing metal clusters in MOFs. This further implements a catalyst modification strategy that improves the intrinsic activity of the catalyst by regulating the interaction between the two components and the heterojunction interface in the spinel@CeO2 heterojunction catalyst, ultimately preparing a VOCs catalytic oxidation catalyst with good low-temperature activity. The technical solution is as follows:

[0010] 1. Spinel@CeO2 catalyst,

[0011] The spinel@CeO2 catalyst designed in the present invention comprises spinel and CeO2 particles anchored on the spinel surface through an interfacial reaction, and has the following structural characteristics:

[0012] Spinel is obtained by confined pyrolysis of MOFs with oxidizing metals;

[0013] The interfacial reaction anchoring CeO2 process is through the interaction of MOFs with oxidizing metals and Ce under alkaline conditions. 3+ This is achieved by a redox reaction;

[0014] The oxidizing metal is a metal cyanide;

[0015] The spinel@CeO2 catalyst has a heterojunction structure and a specific surface area of ​​133-296g / m 2 , wherein the particle size of cerium dioxide is 2.1 to 16.2 nm.

[0016] 2. A method for preparing a spinel@CeO2 catalyst

[0017] The present invention provides a method for preparing a spinel@CeO2 catalyst, comprising the following steps:

[0018] S1. Synthesis of MOFs with oxidative metals by coprecipitation.

[0019] S2, under protective atmosphere and microwave heating, the surface of MOFs with oxidizing metals obtained in S1 is anchored with CeO2 particles through redox reaction to obtain MOFs@CeO2;

[0020] S3, pyrolysis of MOFs@CeO2 in S2 to generate spinel@CeO2 catalyst with heterojunction structure;

[0021] In S1, the solutions used in the coprecipitation method include solution A and solution B:

[0022] Solution A is an aqueous solution containing a transition metal salt, or an aqueous solution containing a transition metal salt and a surfactant; Solution B is an aqueous solution containing a metal cyanide;

[0023] The mixing method of solution A and solution B is as follows: under stirring, solution B is added dropwise to solution A, and stirring is continued for 0.2 to 3 hours;

[0024] The aging parameters of the coprecipitation method are: aging at room temperature for 5 to 24 h;

[0025] Explanation: The metal ions in metal cyanide are +3 and oxidizing. When they form MOFs with transition metal salts, they also inherit the oxidizing properties of metal cyanide, thereby driving redox reactions of reducing substances. At the same time, the metal clusters in MOFs are highly ordered, creating conditions for their atomic-level anchoring in the MOF space.

[0026] In S2, the reduced species in the redox reaction is:

[0027] Ce(OH)3 generated by the reaction of Ce(NO3)3·6H2O with NH3 release agent;

[0028] The parameters of microwave heating are as follows: microwave power of 400W to 500W, reaction temperature of 60°C to 70°C, and reaction time of 2h to 3h;

[0029] Note: Under nitrogen protection, the interference of oxygen in the preparation process is eliminated; the NH3 releaser in S2 is heated to produce NH3 and Ce 3+ It combines to form Ce(OH)3 with strong reducing properties, which can then undergo redox reactions with highly ordered oxidizing metal clusters in MOFs, causing CeO2 to be evenly anchored in the highly ordered oxidizing metal clusters in MOFs, thereby improving the interaction between CeO2 and MOFs and achieving atomic-level dispersion of CeO2, which is beneficial to the electron transfer at the interface between CeO2 and spinel in the derived spinel@CeO2 heterojunction catalyst, thereby improving the intrinsic activity of the catalyst; at the same time, the structural diversity of MOFs is beneficial to the formation of the heterojunction interface between CeO2 and spinel, and is also beneficial to the diffusion of VOCs, O2, and oxidation products on the catalyst surface; in addition, MOFs undergo reduction reactions, generating a large number of defects to maintain electrical neutrality, which is beneficial to the formation of oxygen vacancies during the thermal decomposition process. Oxygen vacancies are active sites in the catalytic oxidation process of VOCs and can improve the low-temperature activity of the catalyst.

[0030] In S3, the pyrolysis parameters are as follows: in air atmosphere, heating to 300°C to 400°C at a heating rate of 1°C / min to 2°C / min, and continuing calcination for 3-4h;

[0031] Note: The surface-anchored cerium dioxide can form a confinement effect, which is beneficial to preventing the MOFs structure from collapsing during the pyrolysis process, so that the spinel@CeO2 heterojunction catalyst inherits the MOFs morphology and pore structure.

[0032] Furthermore, the reaction system included in the preparation method is one of system A or system B:

[0033] In system A:

[0034] In S1: the transition metal salt is MnCl2·4H2O, and the metal cyanide is K3Co(CN)6;

[0035] In S2: the NH3 release agent is hexamethylenetetramine;

[0036] In system B:

[0037] In S1: the transition metal salt is Ni(NO3)2·6H2O, the surfactant is polypyrrolidone, and the metal cyanide is Na3Co(CN)6;

[0038] In S2: the NH3 release agent is ammonium chloride.

[0039] Furthermore, in system A:

[0040] In S1: the molar ratio of transition metal salt to metal cyanide is 10:28;

[0041] In S2: the mass ratio of MOFs, Ce(NO3)3·6H2O and NH3 releaser is 8:(2-3):4;

[0042] In system B:

[0043] In S1: the molar ratio of the transition metal salt, the surfactant and the metal cyanide is 40:1:30;

[0044] In S2: the mass ratio of MOFs, Ce(NO3)3·6H2O and NH3 releaser is 10:2:7.

[0045] Compared with the existing CeO2-based catalysts for decomposing VOCs, the beneficial effects of the present invention are:

[0046] (1) The present invention cleverly utilizes the oxidizing properties, structural diversity, and high dispersion of metal clusters of MOFs to drive their redox reaction with the reductive Ce(OH)3, achieving uniform anchoring of CeO2 in the highly ordered oxidizing metal clusters in MOFs, enhancing the interaction between CeO2 and MOFs, and achieving atomic-level dispersion of CeO2, which is beneficial to the electron transfer between CeO2 and the spinel heterojunction interface in the derived spinel@CeO2 heterojunction catalyst, thereby improving the intrinsic activity of the catalyst. At the same time, the structural diversity of MOFs is beneficial to the formation of the CeO2-spinel heterojunction interface and the diffusion of VOCs, O2, and oxidation products on the catalyst surface. In addition, the reduction reaction of MOFs generates a large number of defects to maintain electrical neutrality, which in turn facilitates the formation of oxygen vacancies during the pyrolysis process. Oxygen vacancies are active sites in the catalytic oxidation process of VOCs and can improve the low-temperature activity of the catalyst.

[0047] (2) CeO2 in the present invention is anchored on the surface of MOFs to form a confinement effect. The surface-anchored cerium dioxide can form a confinement effect, which is beneficial to prevent the MOFs structure from collapsing during the pyrolysis process, so that the spinel@CeO2 heterojunction catalyst inherits the morphology and pore structure of MOFs, solving the problem of easy structural collapse during the pyrolysis of MOFs materials.

[0048] (3) The spinel@CeO2 heterojunction catalyst prepared by the present invention has excellent low-temperature activity: the corresponding temperature T when the toluene conversion rate is 90% 90％ As a criterion for evaluating the catalyst activity, the T of 0.1 g spinel MOFs@CeO2 catalyst was calculated under the conditions of an initial toluene concentration of 1000 ppm and 5% vol water vapor. 90 % is 228℃, which greatly reduces the energy consumption compared with conventional catalysts. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 is the XRD pattern of CoMn-MOFs, CoMn-MOFs@CeO2 and CoMn@CeO2-0.2 in the present invention;

[0050] Figure 2 middle:

[0051] (a) SEM image of CoMn-MOFs;

[0052] (b) SEM image of CoMn@CeO2-0.2;

[0053] (c) HRTEM image of CoMn@CeO2-0.2;

[0054] (d) Mapping diagram of Mn, Co, Ce, and O in CoMn@CeO2-0.2. DETAILED DESCRIPTION

[0055] In order to further illustrate the method and effect achieved by the present invention, the technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0056] Example 1

[0057] Example 1 The spinel@CeO2 heterojunction catalyst CoMn@CeO2-0.2 was prepared according to the following steps.

[0058] (1) Synthesis of CoMn-MOFs with oxidizing metals: 5.95 g of MnCl2·4H2O was dissolved in 100 mL of water to form solution A, which was set aside. 3.1 g of K3Co(CN)6 was dissolved in 100 mL of water to form solution B. Solution B was then added dropwise to solution A under magnetic stirring. Stirring was continued for 0.5 h, then the stirring was stopped and the mixture was aged at room temperature for 5 h. The reaction product was washed with ethanol or water and dried to obtain CoMn-MOFs with oxidizing metals.

[0059] (2) Redox anchoring synthesis of CoMn-MOFs@CeO2: 0.8 g of CoMn-MOFs with oxidizing metals in (1) and 0.2 g of Ce(NO3)3·6H2O were ultrasonically separated in a mixed solution of 160 mL of water and 160 mL of ethanol, and then 0.4 g of hexamethylenetetramine was fully dissolved in the above solution. Subsequently, the above solution was placed in a microwave reactor under nitrogen protection and reacted at 70°C at a heating power of 400 W for 2 h. The reaction product was washed with ethanol or water and dried to obtain CoMn-MOFs@CeO2.

[0060] (3) Preparation of spinel@CeO2 heterojunction catalyst by confined pyrolysis: The MOFs@CeO2 in (2) was placed in a tubular furnace, and then heated to 400°C at a heating rate of 2°C / min in an air atmosphere and calcined for 3 h to obtain the spinel@CeO2 heterojunction catalyst CoMn@CeO2-0.2.

[0061] Depend on Figure 1 It can be seen that the XRD patterns of CoMn-MOFs, CoMn-MOFs@CeO2 and CoMn@CeO2-0.2 match the standard cards, indicating that the corresponding products were successfully prepared. Figure 2 (a) and (b) show that both CoMn@CeO2-0.2 and CoMn-MOFs are three-dimensional cubic, indicating that CoMn-MOFs plays a template role in the synthesis process of CoMn@CeO2-0.2. The three-dimensional cubic shape is conducive to the formation of the heterojunction interface between CoMn spinel and CeO2, and is also conducive to the diffusion of VOCs, O2, and oxidation products on the catalyst surface. Figure 2(c) It can be seen that CeO2 and CoMn spinel of the present invention form a heterojunction structure. Figure 2 (d) It can be seen that Mn, Co, Ce, and O are uniformly distributed in CoMn@CeO2-0.2. These results show that the method of the present invention can successfully prepare spinel@CeO2 heterojunction catalysts, and CeO2 is uniformly distributed on the spinel surface. At the same time, the catalyst can be effectively regulated by adjusting the morphology and structure of MOFs to achieve heterojunction interface regulation.

[0062] Example 2

[0063] Example 2 The spinel@CeO2 heterojunction catalyst CoMn@CeO2-0.3 was prepared according to the following steps.

[0064] (1) Synthesis of CoMn-MOFs with oxidizing metals: 5.95 g of MnCl2·4H2O was dissolved in 100 mL of water to form solution A, which was set aside. 3.1 g of K3Co(CN)6 was dissolved in 100 mL of water to form solution B. Solution B was then added dropwise to solution A under magnetic stirring. Stirring was continued for 0.5 h, then the stirring was stopped and the mixture was aged at room temperature for 5 h. The reaction product was washed with ethanol or water and dried to obtain CoMn-MOFs with oxidizing metals.

[0065] (2) Redox anchoring synthesis of CoMn-MOFs@CeO2: 0.8 g of CoMn-MOFs with oxidizing metals in (1) and 0.3 g of Ce(NO3)3·6H2O were ultrasonically separated in a mixed solution of 160 mL of water and 160 mL of ethanol, and then 0.4 g of hexamethylenetetramine was fully dissolved in the above solution. Subsequently, the above solution was placed in a microwave reactor under nitrogen protection and reacted at 70°C at a heating power of 400 W for 2 h. The reaction product was washed with ethanol or water and dried to obtain CoMn-MOFs@CeO2.

[0066] (3) Preparation of spinel@CeO2 heterojunction catalyst by confined pyrolysis: The MOFs@CeO2 in (2) was placed in a tubular furnace, and then heated to 400°C at a heating rate of 2°C / min in an air atmosphere and calcined for 3 h to obtain the spinel@CeO2 heterojunction catalyst CoMn@CeO2-0.3.

[0067] Example 3

[0068] Example 3 The spinel@CeO2 heterojunction catalyst CoNi@CeO2-0.2 was prepared according to the following steps.

[0069] (1) Synthesis of CoNi-MOFs with oxidizing metals: 0.632 g Ni(NO3)2·6H2O and 0.7 g polypyrrolidone were dissolved in 100 mL water to form solution A, which was set aside. 0.446 g Na3(Co(CN)6) was dissolved in 100 mL water to form solution B. Subsequently, solution B was added dropwise to solution A under magnetic stirring and stirring was continued for 1 h. Stirring was then stopped and the mixture was aged at room temperature for 24 h. The reaction product was washed with ethanol or water and dried to obtain CoNi-MOFs with oxidizing metals.

[0070] (2) Redox anchoring synthesis of CoNi-MOFs@CeO2: 1 g of CoNi-MOFs with oxidizing metals in (1) and 0.2 g of Ce(NO3)3·6H2O were ultrasonically separated in a mixed solution of 160 mL of water and 160 mL of ethanol, and then 0.7 g of ammonium chloride was fully dissolved in the above solution. Subsequently, the above solution was placed in a microwave reactor under nitrogen protection and reacted at 60°C at a heating power of 500 W for 3 h. The reaction product was washed with ethanol or water and dried to obtain CoNi-MOFs@CeO2.

[0071] (3) Preparation of spinel@CeO2 heterojunction catalyst by confined pyrolysis: The MOFs@CeO2 in (2) was placed in a tubular furnace, and then heated to 300°C at a heating rate of 1°C / min in an air atmosphere and calcined for 4 h to obtain the spinel@CeO2 heterojunction catalyst CoNi@CeO2-0.2.

[0072] Comparative Example 1

[0073] Comparative Example 1 Synthesis of CoMn spinel catalyst: The synthesis method is the same as that of Example 1, except that Ce(NO3)3·6H2O is not added during the synthesis process. The specific steps are as follows:

[0074] (1) Synthesis of CoMn-MOFs with oxidizing metals: 5.95 g of MnCl2·4H2O was dissolved in 100 mL of water to form solution A, which was set aside. 3.1 g of K3Co(CN)6 was dissolved in 100 mL of water to form solution B. Solution B was then added dropwise to solution A under magnetic stirring. Stirring was continued for 0.5 h, then the stirring was stopped and the mixture was aged at room temperature for 5 h. The reaction product was washed with ethanol or water and dried to obtain CoMn-MOFs with oxidizing metals.

[0075] (2) Synthesis of CoMn-MOFs-N: 0.8 g of CoMn-MOFs with oxidizing metals in (1) was ultrasonically separated in a mixed solution of 160 mL of water and 160 mL of ethanol, and then 0.4 g of hexamethylenetetramine was fully dissolved in the above solution. Subsequently, the above solution was placed in a microwave reactor under nitrogen protection and reacted at 70°C at a heating power of 400 W for 2 h. The reaction product was washed with ethanol or water and dried to obtain CoMn-MOFs-N.

[0076] (3) Preparation of CoMn spinel catalyst by pyrolysis: The CoMn-MOFs-N prepared in (2) was placed in a tubular furnace, and then heated to 400°C at a heating rate of 2°C / min in an air atmosphere and calcined for 3 h to obtain the CoMn spinel catalyst.

[0077] Comparative Example 2

[0078] Comparative Example 2 Synthesis of CeO2 catalyst: The synthesis method is the same as that of Example 1, except that no oxidizing MOFs are added during the synthesis process, and the oxidant is changed to oxygen; the specific steps are as follows:

[0079] 0.3 g of Ce(NO3)3·6H2O was ultrasonically dissolved in a mixed solution of 160 mL of water and 160 mL of ethanol, and then 0.4 g of hexamethylenetetramine was fully dissolved in the above solution. Subsequently, the above solution was placed in a microwave reactor under an oxygen atmosphere and reacted at 70°C for 2 h at a heating power of 400 W. The reaction product was washed with ethanol or water and dried to obtain a CeO2 precursor. The CeO2 precursor was placed in a tubular furnace and then heated to 400°C at a heating rate of 2°C / min in an air atmosphere and calcined for 3 h to obtain a CeO2 catalyst.

[0080] Catalyst performance evaluation

[0081] The catalysts synthesized in the examples and comparative examples were evaluated using a fixed-bed catalyst evaluation apparatus coupled with online gas chromatography. The specific steps were as follows: 0.1 g of the catalyst was accurately weighed and placed into a 5 mm quartz tube, which was then placed in a reactor. Under conditions of an initial toluene concentration of 1000 ppm and 5% vol water vapor, the outlet toluene concentration was measured at different temperatures. The temperature at which the toluene conversion rate reached 90% was used as the catalyst activity evaluation standard. The results are shown in Table 1.

[0082] Table 1 Catalytic energy consumption of toluene by different catalysts

[0083]

[0084] From Table 1, we can get the T of the experimental example 90％ The T of the CoMn@CeO2-0.2 catalyst prepared in Example 1 for toluene is significantly lower than that of the comparative example.90％ It can reach 228°C, that is, the catalyst prepared by the present invention can significantly reduce the energy consumption required for the reaction compared with conventional catalysts, indicating that the new preparation method designed by the present invention can significantly improve the low-temperature activity of the catalyst in catalytic oxidation of VOCs by effectively regulating the heterojunction interface, thereby achieving the purpose of greatly reducing the required energy consumption.

[0085] The specific surface area of ​​Example 1 is slightly lower than that of Comparative Example 1, indicating that MOFs act as a template during the synthesis process, and the high specific surface area of ​​MOFs can be used to increase the specific surface area of ​​the prepared catalyst; the particle size of CeO2 in Examples 1-3 is significantly lower than that of Comparative Example 2, indicating that the method of the present invention can effectively reduce the particle size of CeO2 and thereby increase the active sites at the heterojunction interface formed.

Claims

1. A spinel@CeO2 catalyst comprising spinel and CeO2 particles anchored on the spinel surface by an interfacial reaction, characterized in that: The spinel is obtained by confined pyrolysis of MOFs with oxidizing metals; The interface reaction anchoring CeO2 process is through the MOFs with oxidizing metals and Ce under alkaline conditions. 3+ This is achieved by a redox reaction; The oxidizing metal is a metal cyanide; The spinel@CeO2 catalyst has a heterojunction structure and a specific surface area of ​​133-296 g / m 2 , wherein the particle size of cerium dioxide is 2.1 to 16.2 nm.

2. A method for preparing a spinel@CeO2 catalyst, comprising the following steps: S1. Synthesis of MOFs with oxidative metals by coprecipitation. S2, under protective atmosphere and microwave heating, the surface of MOFs with oxidizing metals obtained in S1 is anchored with CeO2 particles through redox reaction to obtain MOFs@CeO2; S3, pyrolysis of MOFs@CeO2 in S2 to generate spinel@CeO2 catalyst with heterojunction structure; Its characteristics are: In S1, the solutions used in the coprecipitation method include solution A and solution B: Solution A is an aqueous solution containing a transition metal salt, or an aqueous solution containing a transition metal salt and a surfactant; Solution B is an aqueous solution containing a metal cyanide; The mixing method of the solution A and the solution B is as follows: adding the solution B dropwise to the solution A under stirring, and continuously stirring for 0.2 to 3 hours; The aging parameters of the coprecipitation method are: aging at room temperature for 5 to 24 hours; In S2, the reducing substance in the redox reaction is: Ce(OH)3 generated by the reaction of Ce(NO3)3·6H2O with NH3 release agent; The parameters of microwave heating are as follows: microwave power of 400W to 500W, reaction temperature of 60°C to 70°C, and reaction time of 2h to 3h; In S3, the pyrolysis parameters are: in an air atmosphere, heating to 300°C to 400°C at a heating rate of 1°C / min to 2°C / min, and continuing calcination for 3-4 hours.

3. The method for preparing a spinel@CeO2 catalyst according to claim 2, wherein: The reaction system included in the preparation method is one of system A or system B: In the system A: In S1: the transition metal salt is MnCl2·4H2O, and the metal cyanide is K3Co(CN)6; In S2: the NH3 release agent is hexamethylenetetramine; In the system B: In S1: the transition metal salt is Ni(NO3)2·6H2O, the surfactant is polypyrrolidone, and the metal cyanide is Na3Co(CN)6; In S2: the NH3 release agent is ammonium chloride.

4. The method for preparing a spinel@CeO2 catalyst according to claim 3, wherein: In the system A: In S1: the molar ratio of transition metal salt to metal cyanide is 10:28; In S2: the mass ratio of MOFs, Ce(NO3)3·6H2O and NH3 releaser is 8:(2-3):4; In the system B: In S1: the molar ratio of the transition metal salt, the surfactant and the metal cyanide is 40:1:30; In S2: the mass ratio of MOFs, Ce(NO3)3·6H2O and NH3 releaser is 10:2:

7.

5. The use of the spinel@CeO2 catalyst according to claim 1, characterized in that: It can be used for catalytic oxidation of toluene, and the catalytic effect is: 0.1g of the spinel@CeO2 catalyst in claim 1, with a corresponding temperature T of 90% for a toluene conversion rate 90％ As the catalyst activity evaluation standard, under the conditions of 1000ppm initial toluene concentration and 5%vol water vapor, its T 90 % is 228℃.

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