CN113145108A

CN113145108A - MnO capable of adjusting oxygen species distributionxCatalyst, preparation method and application thereof

Info

Publication number: CN113145108A
Application number: CN202110454205.7A
Authority: CN
Inventors: 贺泓; 邓华; 潘婷婷; 陆宇琴; 单文坡
Original assignee: Institute of Urban Environment of CAS
Current assignee: Institute of Urban Environment of CAS
Priority date: 2021-04-26
Filing date: 2021-04-26
Publication date: 2021-07-23

Abstract

The invention provides MnO capable of adjusting oxygen species distribution_xThe preparation method comprises the following steps: (1) mixing manganese carbonate powder and a manganese nitrate solution to obtain a mixed precursor solution; (2) drying the mixed precursor solution obtained in the step (1) to obtain the MnO_xA catalyst; wherein, the molar ratio of the manganese element in the manganese carbonate powder in the step (1) to the manganese element in the manganese nitrate solution is recordedIs x: y, by adjusting x: y value modulation MnO_xOxygen species distribution of the catalyst. By changing the proportion of the precursor, the invention can regulate and control MnO in a large range_xDistribution of oxygen species, altering MnO_xPhysical and chemical properties to realize the purpose of treating various pollutants.

Description

MnO capable of adjusting oxygen species distributionxCatalyst, preparation method and application thereof

Technical Field

The invention belongs to the field of catalysts, and relates to MnO capable of adjusting oxygen species distribution_xA catalyst, a preparation method and application thereof.

Background

The increasing industrialization and urbanization of the air lead to the increase of the emission of Volatile Organic Compounds (VOCs) in the atmosphere year by year, and seriously threaten the ecological environment. Statistically, the emissions of man-made NMVOC increased from 9.76Tg in 1990 to 28.5Tg in 2017. The presence of volatile organic compounds in large amounts in the air can cause photochemical smog, severe haze, and formation of tropospheric ozone. Currently, tropospheric ozone is one of the most prevalent air pollution problems worldwide. As a high-activity oxidant, ozone can react with VOCs to generate more toxic oxidation products, which have serious harm to human health and crop production. The world health organization has set an index value for ozone (WHO2005) of 50ppb for an average of 8 hours per day. Therefore, the research on VOC and ozonolysis is an urgent necessity for the protection of the environment and human health. The catalytic oxidation technology is considered to be one of the most feasible technologies for removing VOCs due to the advantages of high efficiency, energy conservation, environmental protection and the like. Meanwhile, catalytic decomposition is also the most effective method for removing ozone at present. The development of the catalyst is the core of a catalytic oxidation method and catalytic decomposition, and the improvement of the activity of the catalyst and the reduction of the cost of the catalyst are hot spots in the research field of VOCs and ozone catalysis. The catalyst includes a noble metal and a transition metal oxide. Wherein, manganese oxide catalyst (MnO)_x) Has rich natural resources, low price and easy obtainment, has better oxidation capability and is a catalyst with very potential.

General preparation of MnO_xThe method comprises a hydrothermal method, a sol-gel method, a coprecipitation method and the like, and the manganese oxide crystal form is inevitably formed by high-temperature roasting and activation so as to have oxidation activity. The roasting process not only has high energy consumption, but also adds a die in the preparation processThe plate agent or other organic matters can also emit pungent smell to cause air pollution. In addition, anions such as chloride ions and sulfate ions in common manganese precursors (such as manganese chloride and manganese sulfate) are easily adsorbed on the surface of the catalyst, so that the capacity of the catalyst for adsorbing and decomposing pollutants is reduced, the catalyst needs to be fully washed and filtered by a large amount of deionized water, and the process not only consumes long time and high cost, but also consumes a large amount of clean water. Therefore, there is a need to develop an energy-saving, environment-friendly and simple-to-operate MnO_xA method of preparing the catalyst.

CN109395742A discloses an oxidation catalyst for catalyzing combustion of VOCs and a preparation method thereof. The oxidation type catalyst comprises a carrier, wherein a coating is coated on the carrier, the coating amount of the coating is 60-180 g/L, noble metal Pt and noble metal Pd are loaded in the coating, the loading amount of the noble metal is 0.2-5.0 g/L, the mass ratio of the noble metal Pt to the noble metal Pd is 0.1: 1-10: 1, and the coating comprises active alumina, a cobalt-cerium composite oxide and manganese oxide. The catalyst has the advantages of outstanding low-temperature VOCs ignition activity, high conversion efficiency and good thermal stability, but uses precious metals, has high manufacturing cost and is not beneficial to industrial production, and meanwhile, the catalyst has a single catalysis range and cannot catalyze the ozone decomposition.

CN111790374A discloses a MnZr catalyst for catalytic oxidation of VOCs (volatile organic compounds), and a preparation method and application thereof, wherein the catalyst takes nano zirconia as a carrier and takes MnOx as an active component; the chemical formula of which can be expressed as y MnO_x/ZrO₂-h, wherein h represents a catalyst structure comprising Mn-O-Zr bonds, y represents MnO_xThe value range of y is 5-15%, the balance is zirconia, and x represents manganese oxide compounds with different valence states; the formation of Mn-O-Zr bonds in the catalyst results from the Mn being linked to Zr-O after the fracture of the Mn-O bonds. The preparation method of the catalyst comprises the following steps: first, a method of impregnating is used to prepare lattice-doped MnO_x/ZrO₂The catalyst is modified by a hydrothermal method and finally modified by high-temperature steam, and the catalyst is complex in preparation method, single in catalysis range and incapable of catalyzing ozonolysis.

The scheme has the problems of using precious metals, complicated preparation method or single catalysis range, so that the development of a catalyst which is cheap and simple in preparation method, can catalyze VOC oxidation and ozone decomposition is urgently needed.

Disclosure of Invention

The invention aims to provide MnO capable of adjusting oxygen species distribution_xThe preparation method comprises the following steps: (1) mixing manganese carbonate powder and a manganese nitrate solution to obtain a mixed precursor solution; (2) drying the mixed precursor solution obtained in the step (1) to obtain the MnO_xA catalyst; wherein, the molar ratio of the manganese element in the manganese carbonate powder in the step (1) to the manganese element in the manganese nitrate solution is recorded as x: y, by adjusting x: y value modulation MnO_xOxygen species distribution of the catalyst. By changing the proportion of the precursor, the invention can regulate and control MnO in a large range_xDistribution of oxygen species, altering MnO_xPhysical and chemical properties to realize the purpose of treating various pollutants.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the invention provides MnO for adjusting oxygen species distribution_xA method for preparing a catalyst, the method comprising the steps of:

(1) mixing manganese carbonate powder and a manganese nitrate solution to obtain a mixed precursor solution;

(2) drying the mixed precursor solution obtained in the step (1) to obtain the MnO_xA catalyst;

wherein, the molar ratio of the manganese element in the manganese carbonate powder in the step (1) to the manganese element in the manganese nitrate solution is recorded as x: y, by adjusting x: y value modulation MnO_xOxygen species distribution of the catalyst.

The surface oxygen species are mainly divided into surface adsorbed oxygen and lattice oxygen, and the surface adsorbed oxygen has better fluidity than the lattice oxygen, thereby being beneficial to promoting electron transfer, pollutant adsorption and activation of oxygen molecules in air in the catalytic process. Thus the surface adsorbed oxygen/lattice oxygen ratioThe larger the catalyst activity, the better. On the other hand, oxygen vacancies generated by oxygen migration of the crystal lattice are active sites of the metal oxide to decompose VOC or ozone, and the stronger the fluidity and oxygen activation capability of the crystal lattice oxygen, the higher the oxidation property of the catalyst. By changing the proportion of the precursor, the invention can regulate and control MnO in a large range_xDistribution of oxygen species, altering MnO_xPhysical and chemical properties to realize the purpose of treating various pollutants.

Preferably, said x >0, for example: 0.1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, etc., y >0, e.g.: 0.1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc., and x + y is 10.

Preferably, the mass concentration of manganese nitrate in the manganese nitrate solution in the step (1) is 30-80 wt%, for example: 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%, or 80 wt%, etc.

Preferably, the total molar amount of manganese nitrate in the manganese carbonate powder and manganese nitrate solution in step (1) is 0.01-0.1 mol, for example: 0.01mol, 0.03mol, 0.05mol, 0.08mol, 0.1mol, or the like.

Preferably, the mixing of step (1) comprises magnetic stirring.

Preferably, the magnetic stirring time is 10-15 h, for example: 10h, 11h, 12h, 13h, 14h or 15h, etc.

Preferably, the drying temperature in the step (2) is 90-120 ℃, for example: 90 ℃, 100 ℃, 110 ℃ or 120 ℃, etc.

As a preferable scheme of the invention, the preparation method comprises the following steps:

(1) mixing manganese carbonate powder and a 30-80 wt% manganese nitrate solution to obtain a mixed precursor solution;

(2) drying the mixed precursor solution obtained in the step (1) at 90-120 ℃ to obtain MnO capable of adjusting oxygen species distribution_xA catalyst;

Preferably, the process of the invention does not require calcination and filtration.

In a second aspect, the invention provides MnO for adjusting oxygen species distribution_xA catalyst produced by the method of the first aspect.

Preferably, the surface of the catalyst adsorbs oxygen (O)_sur) Lattice oxygen (O)_latt) The variation range of the ratio is 0.48-8.72, for example: 0.48, 0.5, 0.8, 1, 2, 5, 8, or 8.72, etc.

In a third aspect, the invention provides MnO for adjusting oxygen species distribution as defined in the second aspect_xThe application of the catalyst is to the catalytic oxidation of volatile organic compound exhaust gas, and the catalyst can also be applied to the decomposition of ozone.

Preferably, the oxidized volatile organic compound off-gas comprises any one of ethyl acetate, toluene, or acetone, or a combination of at least two thereof.

Compared with the prior art, the invention has the following beneficial effects:

(1) the method of the invention can obtain MnO with high activity and reusability without roasting and filtering_xA catalyst. Simultaneously, MnO can be regulated and controlled in a large range by changing the proportion of the precursor_xDistribution of oxygen species, altering MnO_xPhysical and chemical properties to realize the purpose of treating various pollutants.

(2) The catalyst of the invention catalyzes and oxidizes T of ethyl acetate₅₀Can reach below 218.5 ℃ and T₉₀Can reach below 246.7 ℃, and 7-9# shows good ozone decomposition performance, and the ozone conversion rate can reach above 86.3% within 1 h.

Drawings

FIG. 1 is a graph comparing the catalytic conversion of ethyl acetate over the catalysts described in examples 1-9 and comparative examples 1-2.

FIG. 2 is a graph showing that catalysts described in examples 1-9 and comparative examples 1-2 catalyze the oxidation of ethyl acetate to produce CO₂The yield is compared with the figure.

Figure 3 is a graph of the catalytic toluene and acetone conversion of the catalyst described in example 5.

FIG. 4 is a graph showing the catalysis of the oxidation of toluene and acetone to CO by the catalyst described in example 5₂The yield chart.

FIG. 5 is a graph showing the comparison of the ozone decomposition rate at room temperature of the catalysts described in examples 1 to 9 and comparative examples 1 to 2.

FIG. 6 is a XPS comparison of catalysts described in examples 1-9 and comparative examples 1-2.

FIG. 7 is a graph comparing the catalytic ethyl acetate conversion after calcination at 500 ℃ for the catalysts described in examples 4-5, 7, 9, and comparative examples 1-2.

FIG. 8 is a graph comparing the catalytic ethyl acetate conversion after calcination at 800 ℃ for the catalysts described in examples 2, 4-5, 7, 9, and 1-2.

Detailed Description

The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitation of the present invention.

Example 1

This example provides a catalyst prepared as follows:

taking manganese carbonate powder and a 50 wt% manganese nitrate solution as precursors, wherein the total molar weight of the manganese carbonate powder and the 50 wt% manganese nitrate solution is 0.05mol, adding the precursors into a 50ml beaker according to the molar ratio of 1:9, stirring the mixture for 12 hours by using a magnetic stirrer, then drying the mixture in an oven at 100 ℃, and cooling the dried mixture to room temperature to obtain the catalyst, wherein the number of the catalyst is 1 #.

Example 2

This example provides a catalyst prepared as follows:

taking manganese carbonate powder and a 50 wt% manganese nitrate solution as precursors, wherein the total molar weight of the manganese carbonate powder and the manganese nitrate solution is 0.05mol, adding the precursors into a 50ml beaker according to the molar ratio of 2:8, stirring the mixture for 12 hours by using a magnetic stirrer, then drying the mixture in an oven at 100 ℃, and cooling the dried mixture to room temperature to obtain the catalyst, wherein the number of the catalyst is 2 #.

Example 3

This example provides a catalyst prepared as follows:

taking manganese carbonate powder and a 50 wt% manganese nitrate solution as precursors, wherein the total molar weight of the manganese carbonate powder and the 50 wt% manganese nitrate solution is 0.05mol, adding the precursors into a 50ml beaker according to the molar ratio of 3:7, stirring the mixture for 12 hours by using a magnetic stirrer, then drying the mixture in an oven at 100 ℃, and cooling the dried mixture to room temperature to obtain the catalyst, wherein the number of the catalyst is 3 #.

Example 4

This example provides a catalyst prepared as follows:

taking manganese carbonate powder and a 50 wt% manganese nitrate solution as precursors, wherein the total molar weight of the manganese carbonate powder and the manganese nitrate solution is 0.05mol, adding the precursors into a 50ml beaker according to the molar ratio of 4:6, stirring the mixture for 12 hours by using a magnetic stirrer, then drying the mixture in an oven at 100 ℃, and cooling the dried mixture to room temperature to obtain the catalyst, wherein the number of the catalyst is No. 4.

Example 5

This example provides a catalyst prepared as follows:

taking manganese carbonate powder and a 50 wt% manganese nitrate solution as precursors, wherein the total molar weight of the manganese carbonate powder and the 50 wt% manganese nitrate solution is 0.05mol, adding the precursors into a 50ml beaker according to the molar ratio of 5:5, stirring the mixture for 12 hours by using a magnetic stirrer, then drying the mixture in an oven at 100 ℃, and cooling the dried mixture to room temperature to obtain the catalyst, wherein the number of the catalyst is No. 5.

Example 6

This example provides a catalyst prepared as follows:

taking manganese carbonate powder and a 50 wt% manganese nitrate solution as precursors, wherein the total molar weight of the manganese carbonate powder and the 50 wt% manganese nitrate solution is 0.05mol, adding the precursors into a 50ml beaker according to the molar ratio of 6:4, stirring the mixture for 12 hours by using a magnetic stirrer, then drying the mixture in an oven at 100 ℃, and cooling the dried mixture to room temperature to obtain the catalyst, wherein the number of the catalyst is 6 #.

Example 7

This example provides a catalyst prepared as follows:

taking manganese carbonate powder and a 50 wt% manganese nitrate solution as precursors, wherein the total molar weight of the manganese carbonate powder and the 50 wt% manganese nitrate solution is 0.05mol, adding the precursors into a 50ml beaker according to the molar ratio of 7:3, stirring the mixture for 12 hours by using a magnetic stirrer, then drying the mixture in an oven at 100 ℃, and cooling the dried mixture to room temperature to obtain the catalyst, wherein the number of the catalyst is 7 #.

Example 8

This example provides a catalyst prepared as follows:

taking manganese carbonate powder and a 50 wt% manganese nitrate solution as precursors, wherein the total molar weight of the manganese carbonate powder and the 50 wt% manganese nitrate solution is 0.05mol, adding the precursors into a 50ml beaker according to the molar ratio of 8:2, stirring the mixture for 12 hours by using a magnetic stirrer, then drying the mixture in an oven at 100 ℃, and cooling the dried mixture to room temperature to obtain the catalyst, wherein the number of the catalyst is 8 #.

Example 9

This example provides a catalyst prepared as follows:

taking manganese carbonate powder and a 50 wt% manganese nitrate solution as precursors, wherein the total molar weight of the manganese carbonate powder and the 50 wt% manganese nitrate solution is 0.05mol, adding the precursors into a 50ml beaker according to the molar ratio of 9:1, stirring the mixture for 12 hours by using a magnetic stirrer, then placing the mixture into a 100 ℃ oven for drying, and cooling the mixture to room temperature to obtain the catalyst, wherein the number of the catalyst is 9 #.

Comparative example 1

This comparative example provides a catalyst prepared as follows:

adding 50 wt% of manganese nitrate solution serving as a precursor with the molar weight of 0.05mol into a 50ml beaker, stirring for 12 hours by using a magnetic stirrer, drying in an oven at 100 ℃, and cooling to room temperature to obtain the catalyst with the catalyst number of 0 #.

Comparative example 2

This example provides a catalyst prepared as follows:

adding manganese carbonate powder serving as a precursor with the molar weight of 0.05mol into a 50ml beaker, stirring for 12 hours by using a magnetic stirrer, drying in an oven at 100 ℃, and cooling to room temperature to obtain the catalyst, wherein the catalyst number is 10 #.

And (3) performance testing:

XPS tests were carried out on the catalysts obtained in examples 1 to 9 and comparative examples 1 to 2, and the results are shown in FIG. 6, and the respective simulated peak areas were calculated and the values are shown in Table 1.

The catalysts (40-60 mesh) obtained in examples 1-9 and comparative examples 1-2 were taken and placed in a catalyst activity evaluation apparatus, and activity evaluation was carried out in a fixed bed reactor. Simulated exhaust gas composition was 1000ppm ethyl acetate/toluene/acetone, 20% O₂，N₂The total flow rate is 300mL/min for balancing gas, the catalyst dosage is 0.2g, and the reaction space velocity is 90L/(g.h)^-1；

Simulated exhaust gas composition of 20% O₂(ii) a 42ppm ozone, RH 60%, N₂The total flow rate is 1200mL/min for balance gas, the catalyst dosage is 0.1g, and the reaction space velocity is 720L/(g.h)^-1. The results of the ozone decomposition rate test at room temperature and the ozone decomposition rate test on the conversion rates of ethyl acetate, toluene and acetone are shown in table 1:

TABLE 1

As can be seen from Table 1, from examples 1 to 9, the catalysts of the invention catalyze the oxidation of ethyl acetate T₅₀Can reach below 218.5 ℃ and T₉₀Can reach below 246.7 ℃, and 7# -9# shows good ozone decomposition performance, and the ozone conversion rate can reach above 86.3% within 1 h.

The catalysts described in examples 1-9 and comparative examples 1-2 catalyze ethyl acetate conversion and CO₂Yield comparison is shown in FIGS. 1-2, and the catalyst described in example 5 catalyzes the conversion of toluene and acetone and CO₂The yield is shown in FIGS. 3 to 4, and it can be seen from FIGS. 1 to 4 that 5# MnO was prepared at a molar ratio of 5:5 of manganese carbonate to manganese nitrate_xShows the optimal catalytic activity of ethyl acetate and CO₂Selectivity, at 230 ℃, the conversion rate of 1000ppm ethyl acetate is close to 100%, and CO is₂The selectivity reaches 100 percent. Meanwhile, the sample is applied to catalytic oxidation of toluene and acetone, shows excellent activity and achieves complete conversion at 275 ℃.

A comparison of the ozone decomposition rates at room temperature for the catalysts described in examples 1-9 and comparative examples 1-2 is shown in FIG. 5, and it can be seen from FIG. 5 that 7# MnO_xThe catalyst shows the highest activity when catalyzing and decomposing high-humidity ozone, and the ozone decomposition rate can reach 89.6% under the condition that RH is 60%.

The comparative graph of the catalytic ethyl acetate conversion rate after the catalysts described in examples 4-5, 7, 9 and 1-2 are calcined at 500 ℃ is shown in fig. 7, and the comparative graph of the catalytic ethyl acetate conversion rate after the catalysts described in examples 2, 4-5, 7, 9 and 1-2 are calcined at 800 ℃ is shown in fig. 8, which shows that the catalysts described in examples 7-8 have better high-temperature stability and still have better catalytic oxidation activity on ethyl acetate after being calcined at high temperature.

The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are within the scope and disclosure of the present invention.

Claims

1. MnO capable of adjusting oxygen species distribution_xA method for preparing a catalyst, characterized in that the method comprises the steps of:

2. The method of claim 1, wherein x >0, y >0, x + y is 10;

preferably, the mass concentration of the manganese nitrate in the manganese nitrate solution in the step (1) is 30-80 wt%.

3. The method according to claim 1 or 2, wherein the total molar amount of manganese nitrate in the manganese carbonate powder and the manganese nitrate solution in the step (1) is 0.01 to 0.1 mol.

4. The method of any one of claims 1-3, wherein the mixing of step (1) comprises magnetic stirring.

5. The preparation method according to claim 4, wherein the magnetic stirring time is 10-15 h.

6. The method according to any one of claims 1 to 5, wherein the temperature for the drying in the step (2) is 90 to 120 ℃.

7. The method of any one of claims 1 to 6, comprising the steps of:

8. MnO capable of adjusting oxygen species distribution_xCatalyst, characterized in that it is obtained by a process according to any one of claims 1 to 7.

9. MnO for tunable oxygen species distribution of claim 8_xCatalyst, characterized in that the surface of the catalyst adsorbs oxygen/lattice oxygenThe variation range of the ratio is 0.48-8.72.

10. MnO of claim 8 or 9 capable of adjusting oxygen species distribution_xThe application of the catalyst is characterized in that the catalyst is applied to catalytic oxidation of volatile organic compound exhaust gas, and the catalyst can also be applied to decomposition of ozone.