CN113908837A

CN113908837A - A kind of MOFs derivative denitration catalyst, its preparation method and application

Info

Publication number: CN113908837A
Application number: CN202111289495.0A
Authority: CN
Inventors: 韩小金; 秦国振; 黄张根; 郑剑锋
Original assignee: Shanxi Institute of Coal Chemistry of CAS
Current assignee: Shanxi Institute of Coal Chemistry of CAS
Priority date: 2021-11-02
Filing date: 2021-11-02
Publication date: 2022-01-11
Anticipated expiration: 2041-11-02
Also published as: CN113908837B

Abstract

The invention relates to the technical field of waste gas treatment, and particularly relates to a MOFs derivative denitration catalyst, and a preparation method and application thereof. The catalyst is FeO with a regular octahedral structure_xC; the preparation method comprises the following steps: mixing iron salt and a carbon source, dissolving in a solvent, reacting for a certain time at a certain temperature, washing, and drying to obtain a precursor MIL-101 (Fe); heating the precursor, introducing calcining gas for calcining to obtain the catalyst FeO_xC; the invention also provides application of the prepared catalyst in denitration. The catalyst can be used for denitration at low temperatureTo 80% conversion and on H₂O has certain resistance, and the catalyst does not influence the NO conversion rate and N under the condition of high water content in the flue gas₂And (4) selectivity.

Description

MOFs derivative denitration catalyst, preparation method and application thereof

Technical Field

The invention relates to the technical field of waste gas treatment, in particular to a MOFs derivative denitration catalyst, a preparation method and application.

Background

The nitrogen oxide NOx is one of main atmospheric pollutants in China, and in order to deal with serious harm brought by NOx emission, China sets up strict policy control emission aiming at various related industries. At present, the main denitration method at home and abroad is the Selective Catalytic Reduction (SCR) technology taking NH3 as a reducing agent. The industrially mature catalyst is V₂O₅-WO₃(MoO₃)/TiO₂The catalyst has high working temperature, poor high-temperature selectivity and biotoxicity. In view of the above problems, it is important to search for some novel catalyst materials.

The MOFs-based composite material with the metal organic framework generally consists of a continuous phase and a disperse phase, has the advantages of MOFs porosity and large comparative area, and retains the catalytic function of metal, so that the application of the MOFs-based composite material in denitration treatment can be discussed.

Disclosure of Invention

The invention aims to provide a preparation method of a MOFs derivative denitration catalyst, which can obtain a MOFs derivative with a controllable crystal face.

In order to achieve the above purpose, the technical scheme of the invention is as follows:

a preparation method of a MOFs derivative denitration catalyst comprises the following steps:

(1) mixing ferric chloride hexahydrate and terephthalic acid, dissolving in N, N-dimethylformamide, reacting at the temperature of 100 ℃ and 120 ℃ for 18-20h, washing with absolute ethyl alcohol and/or N, N-dimethylformamide, and drying at the temperature of 50-70 ℃ for 12-18h to obtain a precursor MIL-101(Fe) solid;

(2) heating the precursor prepared in the step (1) at the speed of 1-3 ℃/min, introducing a calcining gas, and calcining at the temperature of 450-550 ℃ for 2-3h to obtain the catalyst FeO_x/C。

Wherein the molar mass ratio of the ferric salt to the carbon source in the step (1) is 1:1-2: 1.

The calcining gas in the step (2) is CO and/or N₂。

Go toOf step (c) CO with N₂The volume ratio of (A) to (B) is 0.5:1 to 3: 1.

Further, the CO and N₂In a volume ratio of 0.95:1 to 1.05: 1.

CO in the calcining gas is used as a crystal face directing agent and is preferentially adsorbed on Fe₃O₄The growth speed of the crystal face is weakened by the adsorption effect, the growth speed of the nano crystal can be controlled during calcination, so that more crystal faces (111) are exposed on the surface of the nano crystal, the crystal face change of the catalyst is regulated and controlled, metal nano particles with controllable forms and fixed crystal faces are prepared, the obtained metal oxide has large specific surface area and high porosity, the dispersion of active components and the mass and heat transfer in the reaction process are facilitated, the surface acidity and the oxidizing capability of the catalyst are provided, and the adsorption and the conversion of the catalyst to reactants are improved. The high-performance catalyst with a specific active crystal face can be prepared by utilizing the strong interaction of the guiding agent and the specific crystal face.

The above-mentioned preparation method and the selection of reactants, solvents, desiccants, detergents and the like in the preparation step thereof, and the selection of reaction conditions such as temperature, time and the like are all preferable, are not limited to the above selection, and may be replaced or omitted as appropriate depending on the effect.

The invention also provides the prepared MOFs derivative denitration catalyst and application thereof in denitration.

The catalyst is FeO with a regular octahedral structure_xC, specific surface area of 260-300m²(ii)/g, the average pore diameter is 6.5-8.5 nm.

The catalyst surface is exposed to a high-activity (111) crystal face. (111) The crystal face increases the acidity of the catalyst surface, and can be better used for denitration application.

Compared with the prior art, the invention has the following advantages:

(1) the method can regulate and control the size and the shape of the crystal face by controlling the proportion of CO in the calcining atmosphere; the prepared MOFs derivative denitration catalyst has a specific active crystal face (111), a large specific surface area and a regular morphology, is beneficial to dispersion of active components and mass and heat transfer of reactants, and simultaneously generates rich acid sites on the surface to be beneficial to adsorption of ammonia species.

(2) The catalyst provided by the invention has the advantages of high catalytic activity, high selectivity, excellent resistance, strong stability, controllable form, fixed crystal face, capability of reaching 80% of conversion rate in low-temperature denitration, and capability of reacting on H₂O has certain resistance, and the catalyst does not influence the NO conversion rate and N under the condition of high water content in the flue gas₂And (4) selectivity.

Drawings

FIG. 1 is TEM and HRTEM images of catalysts prepared in examples 1-3 and comparative examples 1-2;

wherein (a) (b) the HRTEM image of comparative example 1,

(c) (d) is the HRTEM image of example 1,

(e) (f) is the HRTEM image of example 2,

(g) (h) is the HRTEM image of example 3,

(i) (j) is the HRTEM image of comparative example 2,

(k) (l) HRTEM image of precursor MIL-101 (Fe);

FIG. 2 is a graph of NH3-TPD characterization of catalysts made in comparative example 1 and examples 1-2;

FIG. 3 is a graph showing the nitrogen oxide conversion of catalysts prepared in examples 1-3 and comparative examples 1-2;

FIG. 4 is a graph showing the selectivity of nitrogen oxides for catalysts prepared in examples 1-3 and comparative examples 1-2;

FIG. 5 is an X-ray diffraction pattern of the catalysts prepared in examples 1-3 and comparative examples 1-2.

Detailed Description

The terms as used herein:

"prepared from … …" is synonymous with "comprising". The terms "comprises," "comprising," "includes," "including," "has," "having," "contains," "containing," or any other variation thereof, as used herein, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

When an amount, concentration, or other value or parameter is expressed as a range, preferred range, or as a range of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. For example, when the range "1 ~ 5" is disclosed, the ranges described should be construed to include the ranges "1 ~ 4", "1 ~ 3", "1 ~ 2 and 4 ~ 5", "1 ~ 3 and 5", and the like. When a range of values is described herein, unless otherwise stated, the range is intended to include the endpoints thereof and all integers and fractions within the range.

"and/or" is used to indicate that one or both of the illustrated conditions may occur, e.g., a and/or B includes (a and B) and (a or B).

The technical solutions of the present invention will be described in detail with reference to specific examples, but those skilled in the art will understand that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention.

Example 1

A preparation method of a MOFs derivative denitration catalyst,

(1) taking 1.35 g FeCl₃·6H₂O (5mmol) and 0.83g terephthalic acid (5mmol) were dissolved in 30ml N, N-Dimethylformamide (DMF), stirred well at room temperature for 30 minutes to ensure dispersion of the solution, the prepared mixed solution was transferred to 100ml stainless steel autoclave lined with Teflon, reacted at 100 ℃ for 18 hours, the product was washed with absolute ethanol and DMF and collected, dried at 50 ℃ for 12 hours to obtain MIL-101(Fe) as a solid.

(2) Introducing CO and N at a rate of 400ml/min₂The temperature of the calcining gas with the volume ratio of 0.5:1 is raised to 450 ℃ at the temperature rise rate of 1 ℃/min, and the calcining is carried out for 2h to obtain FeO_xa/C (VCO0.5) catalyst.

The prepared catalyst FeO_xThe specific surface area of the/C (VCO0.5) was 262m²In terms of/g, the mean pore diameter was 6.82 nm.

The prepared catalyst is applied to denitration by using FeO_xthe/C (VCO0.5) catalyst was charged in a fixed-bed reactor and used in the form of a composition of 500ppm NO, 500ppm NH₃，5％O₂Equilibrium gas N₂The flue gas test is carried out, the reaction temperature is 100-300 ℃, the reaction pressure is normal pressure, and the reaction airspeed is 30000h^-1。

As shown in fig. 3 and 4, the NO conversion at steady state at a temperature of 300 ℃ was 72.36% with selectivity 97.01%.

Example 2

A preparation method of a MOFs derivative denitration catalyst,

(1) taking 1.35 g FeCl₃·6H₂O (5mmol) and 0.55g terephthalic acid (3.33mmol) were dissolved in 30ml N, N-Dimethylformamide (DMF), stirred well at room temperature for 30 minutes to ensure dispersion of the solution, the prepared mixed solution was transferred to a 100ml stainless steel autoclave lined with polytetrafluoroethylene, reacted at 105 ℃ for 18.5h, the product was washed with absolute ethanol and DMF and collected, dried at 55 ℃ for 14h to obtain MIL-101(Fe) as a solid.

(2) Introducing CO and N at a rate of 400ml/min₂The temperature of the calcining gas with the volume ratio of 1:1 is raised to 480 ℃ at the temperature rising rate of 1.5 ℃/min, and the calcining is carried out for 2.2h to obtain FeO_xa/C (VCO1) catalyst.

The prepared catalyst FeO_xThe specific surface area of/C (VCO1) is 290m²In terms of/g, the mean pore diameter was 8.43 nm.

The prepared catalyst is applied to denitration by using FeO_xthe/C (VCO1) catalyst was charged in a fixed-bed reactor and used in the form of a composition of 500ppm NO, 500ppm NH₃，5％O₂Equilibrium gas N₂The flue gas test is carried out, the reaction temperature is 100-300 ℃, the reaction pressure is normal pressure, and the reaction airspeed is 30000h^-1。

The NO conversion at steady state at a temperature of 300 ℃ was 82.35% with a selectivity of 97.69%.

Example 3

A preparation method of a MOFs derivative denitration catalyst,

(1) taking 1.35 g FeCl₃·6H₂O (5mmol) and 0.415g terephthalic acid (2.5mmol) were dissolved in 30ml N, N-dimethylIn Dimethylformamide (DMF), the solution was sufficiently stirred at room temperature for 30 minutes to ensure dispersion, and the prepared mixed solution was transferred to a 100ml stainless steel autoclave lined with polytetrafluoroethylene, reacted at 110 ℃ for 19 hours, and the product was washed with absolute ethanol and DMF and collected, and dried at 60 ℃ for 15 hours to obtain MIL-101(Fe) as a solid.

(2) Introducing CO and N at a rate of 400ml/min₂The temperature of the calcining gas with the volume ratio of 2:1 is raised to 500 ℃ at the temperature rise rate of 2 ℃/min, and the calcining time is 2.5h, thus obtaining FeO_xa/C (VCO2) catalyst.

The prepared catalyst FeO_xThe specific surface area of the/C (VCO2) was 283m²In terms of/g, the mean pore diameter is 8.19 nm.

The prepared catalyst is applied to denitration by using FeO_xthe/C (VCO2) catalyst was charged in a fixed-bed reactor and used in the form of a composition of 500ppm NO, 500ppm NH₃，5％O₂Equilibrium gas N₂The flue gas test is carried out, the reaction temperature is 100-300 ℃, the reaction pressure is normal pressure, and the reaction airspeed is 30000h^-1。

The NO conversion at steady state at a temperature of 300 ℃ was 85.02% with a selectivity of 98.58%.

Example 4

A preparation method of a MOFs derivative denitration catalyst,

(2) Introducing CO and N at a rate of 400ml/min₂The temperature of the calcining gas with the volume ratio of 1:1 is raised to 480 ℃ at the temperature rising rate of 1.5 ℃/min, and the calcining is carried out for 2.2h to obtain FeO_xa/C (VCO1:1) catalyst.

The prepared catalyst FeO_xThe specific surface area of/C (VCO1:1) is 289m²In terms of/g, the mean pore diameter was 8.43 nm.

Preparation ofThe catalyst of (1) is applied to denitration by using FeO_xthe/C (VCO1:1) catalyst was charged in a fixed-bed reactor and used in the form of 500ppm NO, 500ppm NH₃，5％O₂，20％H₂O, balance gas N₂The flue gas test is carried out, the reaction temperature is 100-300 ℃, the reaction pressure is normal pressure, and the reaction airspeed is 30000h^-1。

The NO conversion at steady state at a temperature of 300 ℃ was 83.17% with a selectivity of 96.74%.

Comparative example 1

A preparation method of a MOFs derivative denitration catalyst,

(1) taking 1.35 g FeCl₃·6H₂O (5mmol) and 0.33g terephthalic acid (2mmol) were dissolved in 30ml N, N-Dimethylformamide (DMF), stirred well at room temperature for 30 minutes to ensure dispersion of the solution, the prepared mixed solution was transferred to a 100ml stainless steel autoclave lined with polytetrafluoroethylene, reacted at 115 ℃ for 19.5 hours, the product was washed with anhydrous ethanol and DMF and collected, dried at 65 ℃ for 16 hours to obtain MIL-101(Fe) as a solid.

(2) N was passed in at a rate of 400ml/min₂The temperature of the calcining gas is raised to 525 ℃ at the temperature rising rate of 2.5 ℃/min, and the calcining is carried out for 3h to obtain FeO_x/C(VN₂) A catalyst.

The prepared catalyst FeO_x/C(VN₂) Has a specific surface area of 206m²In terms of a/g, the mean pore diameter is 5.32 nm.

The prepared catalyst is applied to denitration by using FeO_x/C(VN₂) The catalyst was packed in a fixed bed reactor and used in the form of 500ppm NO, 500ppm NH₃，5％O₂Equilibrium gas N₂The flue gas test is carried out, the reaction temperature is 100-300 ℃, the reaction pressure is normal pressure, and the reaction airspeed is 30000h^-1。

The NO conversion at steady state at a temperature of 300 ℃ was 42.30% with a selectivity of 94.02%.

Comparative example 2

A preparation method of a MOFs derivative denitration catalyst,

(1) taking 1.35 g FeCl₃·6H₂O (5mmol) and 0.277g terephthalic acid (1.67mmol) was dissolved in 30ml N, N-Dimethylformamide (DMF), stirred well at room temperature for 30 minutes to ensure dispersion of the solution, the prepared mixed solution was transferred to a 100ml stainless steel autoclave lined with Teflon, reacted at 120 ℃ for 20 hours, the product was washed with absolute ethanol and DMF and collected, dried at 70 ℃ for 18 hours to give MIL-101(Fe) as a solid.

(2) Introducing CO calcining gas at a rate of 400ml/min, heating to 550 ℃ at a heating rate of 3 ℃/min, and calcining for 3h to obtain FeO_xa/C (VCO) catalyst.

The prepared catalyst FeO_xThe specific surface area of the/C (VCO) was 247m²In terms of/g, the mean pore diameter was 8.51 nm.

The prepared catalyst is applied to denitration by using FeO_xthe/C (VCO) catalyst was charged in a fixed-bed reactor and used in the form of a composition of 500ppm NO, 500ppm NH₃，5％O₂Equilibrium gas N₂The flue gas test is carried out, the reaction temperature is 100-300 ℃, the reaction pressure is normal pressure, and the reaction airspeed is 30000h^-1。

The NO conversion at steady state at a temperature of 300 ℃ was 83.68% with a selectivity of 98.46%.

From examples 1 to 3, it can be seen that as the volume fraction of CO in the calcination gas increases, the specific surface area and the pore size of the catalyst prepared by calcination increase, and the conversion rate and selectivity of nitrogen oxides increase. When CO and N are present₂After the volume ratio reaches 1:1, the CO content is increased, the performance of the catalyst is slightly influenced, and therefore, the CO and the N are preferably selected₂A calcining gas in a volume ratio of 0.95:1 to 1.05: 1.

It can be seen from comparative example 1 and examples 1-3 that when the calcination gas contains CO, the catalytic performance of the catalyst can be significantly improved, and CO, as a crystal plane directing agent, can well expose a high-activity (111) crystal plane to the catalyst, thereby preparing the catalyst with more excellent denitration performance.

From examples 2 and 4, it can be seen that the catalyst prepared by the method has stable activity and catalytic performance when the water content of the flue gas is high, and shows good water resistance.

Wherein, from FIG. 1To see that when the calcining gas had only N₂When the catalyst is prepared, the prepared catalyst has a (100) crystal face; when CO and N are in the calcining gas₂When the volume ratio is 0.5:1, the crystal faces of the prepared catalyst are (111) and (100) mixed; when CO and N are in the calcining gas₂When the volume ratio is 1:1, the prepared catalyst presents a typical regular octahedron shape, and the crystal lattice stripes are consistent with the (111) plane, which shows that the catalyst only has a high-activity (111) crystal plane; when CO and N are in the calcining gas₂When the volume ratio is 2:1 or only CO exists, the crystal face of the catalyst is not changed. I.e. when CO and N are present in the calcining gas₂When the volume ratio reaches 1:1, the catalyst has the best crystal face activity, the content of CO does not need to be additionally increased, and meanwhile, the damage of excessive CO to personnel, environment and the like can be avoided.

As can be seen from FIG. 2, as more (111) crystal planes are exposed on the surface of the catalyst, the acidity of the surface of the catalyst is continuously improved, and the content of basic NH is improved₃Adsorption and conversion are beneficial to SCR reaction.

As can be seen from the graphs in FIGS. 3 and 4, the catalyst prepared by the invention has excellent NH3-SCR performance, and can achieve a removal rate of nitrogen oxides of more than 70% within a temperature range of 250-300 ℃, a removal rate of more than 80 at 300 ℃ and a selectivity of nitrogen oxides of more than 95%.

XRD diffraction pattern of the catalyst corresponds to Fe₃O₄As can be seen from FIG. 5, as CO and N in the calcination gas flow, CO and N are mixed₂The volume ratio is increased, the crystallinity of the catalyst is improved when the ratio of CO to N is increased₂After the volume ratio reaches 1:1, the crystal structure of the catalyst cannot be changed by increasing the volume ratio of CO.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Furthermore, those skilled in the art will appreciate that while some embodiments herein include some features included in other embodiments, rather than other features, combinations of features of different embodiments are meant to be within the scope of the invention and form different embodiments. For example, in the claims above, any of the claimed embodiments may be used in any combination. The information disclosed in this background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

Claims

1. a preparation method of MOFs derivative denitration catalyst, is characterized in that, comprises the following steps:

(1) Dissolve the iron salt and the carbon source in a solvent, react at a certain temperature for a certain period of time, wash and dry to obtain the precursor MIL-101(Fe);

(2) heating the precursor prepared in the step (1) at a temperature, and passing in a calcining gas for calcination to obtain the catalyst FeO _x /C.

2. The preparation method of MOFs derivative denitration catalyst according to claim 1, wherein the iron salt in step (1) is ferric chloride hexahydrate; the carbon source is terephthalic acid; the iron The molar mass ratio of the salt and the carbon source is 1:1-3:1; the reaction temperature is 100-120°C, and the reaction time is 18-20h; the solvent is N,N-dimethylformamide, and the The detergent used for washing is absolute ethanol and/or N,N-dimethylformamide; the drying temperature is 50-70° C., and the drying time is 12-18 h.

3. the preparation method of MOFs derivative denitration catalyst according to claim 1, is characterized in that, the temperature rise rate of the temperature rise described in step (2) is 1-3 ℃/min, and the temperature of described calcination is 450-550 ℃ ℃, the calcination time is 2-3h.

4 . The preparation method of MOFs derivative denitration catalyst according to claim 1 , wherein the calcined gas in step (2) is CO and/or N ₂ . 5 .

5 . The preparation method of MOFs derivative denitration catalyst according to claim 4 , wherein the volume ratio of CO to N ₂ is 0.5:1-2:1. 6 .

6 . The method for preparing a MOFs derivative denitration catalyst according to claim 4 , wherein the volume ratio of the CO to N ₂ is 0.95:1-1.05:1. 7 .

7 . The MOFs derivative denitration catalyst prepared by the preparation method according to claim 1 , wherein the catalyst is FeO _x /C with a regular octahedral structure. 8 .

8 . The MOFs derivative denitration catalyst according to claim 7 , wherein the catalyst has a specific surface area of 260-300 m ² /g and an average pore diameter of 6.5-8.5 nm. 9 .

9 . The MOFs derivative denitration catalyst according to claim 7 , wherein the surface of the catalyst is exposed as a highly active (111) crystal plane. 10 .

10. The application of the MOFs derivative denitration catalyst according to any one of claims 7-9 in denitration.