CN115212870A

CN115212870A - Cesium-doped sodium type layered manganese dioxide VOCs catalyst and preparation method and application thereof

Info

Publication number: CN115212870A
Application number: CN202210830634.4A
Authority: CN
Inventors: 程琰; 杨楠
Original assignee: Southwest Jiaotong University
Current assignee: Southwest Jiaotong University
Priority date: 2022-07-14
Filing date: 2022-07-14
Publication date: 2022-10-21
Anticipated expiration: 2042-07-14
Also published as: CN115212870B

Abstract

The invention discloses a cesium-doped layered manganese dioxide VOCs catalyst and a preparation method and application thereof. The XPS spectrum of Na1s for VOCs catalysts has characteristic peaks at 1070.9eV, and the XPS spectrum of Cs3d 722.8eV and 737.4 eV. The preparation method comprises the following steps: (1) obtaining a first solution, a second solution and a third solution; (2) Sequentially adding the second solution and the third solution into the first solution to form a first solid-liquid mixture; (3) Carrying out solid-liquid separation, and washing to be neutral to obtain a first precursor; (4) Dispersing the first precursor in a sodium hydroxide solution, and carrying out hydrothermal reaction to form a second solid-liquid mixture; (5) Carrying out solid-liquid separation, washing to be neutral, and drying to obtain a second precursor; (6) Calcining the second precursorAnd (4) firing to obtain the VOCs catalyst. The invention successfully dopes sodium and cesium in the layered manganese dioxide, so that the catalytic performance is obviously improved, and the invention also has higher stability and CO ₂ Selectivity and simple preparation process, so that the method is very suitable for removing VOCs by catalytic oxidation.

Description

Cesium-doped sodium type layered manganese dioxide VOCs catalyst and preparation method and application thereof

Technical Field

The invention relates to the technical field of VOCs catalysts, in particular to a cesium-doped sodium type layered manganese dioxide VOCs catalyst and a preparation method and application thereof.

Background

Volatile Organic Compounds (VOCs) are one of the main sources of atmospheric pollutants, and hazardous accidents caused by the VOCs are increasing year by year, so that the purification treatment technology of the VOCs becomes a research hotspot in the field of environmental catalysis. Currently, there are 300 types of VOCs identified, with the most common VOCs being benzene, toluene, styrene, ethane, ethylene, gasoline, and the like.

Due to the many advantages of catalytic oxidation technology, various catalysts for the catalytic oxidation of VOCs have been designed and synthesized. The noble metal is expensive and has poor stability, and the transition metal oxide in the non-noble metal catalyst has the advantages of high catalytic activity, low cost, poison resistance, good thermal stability and the like, so the transition metal oxide has the potential of replacing the noble metal catalyst which is commercially applied at present, and becomes a research hotspot in the field of catalysis. Manganese dioxide (MnO) ₂ ) Due to its unique physicochemical properties (such as multi-valence, polymorphism and non-stoichiometric composition), it has excellent catalytic activity and shows excellent performance in the catalytic oxidation of VOCs.

MnO ₂ Catalyst cause [ MnO ] ₆ ]The number of cells and the constructive pattern are different, forming different phase structures, which can be roughly divided into two main categories: (1) MnO with tunnel structure ₂ The common main crystal form is alpha-MnO ₂ 、β-MnO ₂ 、γ-MnO ₂ (ii) a (2) Of crystalline form containing a two-dimensional layered structure, i.e. delta-MnO ₂ 。MnO ₂ The structural morphology of the catalyst has obvious influence on the catalytic oxidation performance of the VOCs, and the manganese dioxide with a unique layered structure shows excellent catalytic oxidation activity of the VOCs.

Based on adjacent [ MnO ] ₆ ]The interlayer spacing, the concentration and distribution of manganese vacancies and the type of interlayer cations, the layered manganese dioxide can be divided into different subgroups, namely, the bessel ore, the birnessite (birnessite), the chalcopyrite and the thiospodumene. Among them, birnessite manganese dioxide has high ion exchange activity, has the characteristics of simple preparation and moderate interlayer spacing and layer charge density, and is easy to realize the exchange of interlayer cations, so that the birnessite manganese dioxide is widely researched.

Based on layered dioxygenDue to the excellent ion exchange performance of the manganese, different cations such as alkali metal ions, alkaline earth metal ions, transition metal ions and the like can be introduced into the interlayer of the layered manganese dioxide for modification so as to improve the catalytic performance. The interlayer of the layered manganese dioxide is filled with a large number of water molecules and metal cations, so that the stability of a layered structure is maintained, the structure collapse is prevented, and the specific surface area, the micro-morphology and the physicochemical property of the catalyst can be changed by adjusting the type and the concentration of the metal ions in the layer. The research in the field of doping of alkali metals and alkaline earth metals is also mainly around K, ca and other elements, and is mostly concentrated on alpha-MnO ₂ In the study of (2), the applicant has not found that the p-MnO is ₂ And (4) research of doping Na and Cs elements.

Disclosure of Invention

The invention aims to provide a cesium-doped layered manganese dioxide VOCs catalyst with excellent catalytic performance and simple preparation process, and a preparation method and application thereof.

In order to realize the purpose, the invention firstly provides a cesium-doped sodium type layered manganese dioxide VOCs catalyst, and the technical scheme is as follows:

the cesium-doped sodium type layered manganese dioxide VOCs catalyst has an XPS spectrum of Na1s with characteristic peaks at 1070.9ev, and an XPS spectrum of Cs3d with characteristic peaks at 722.8ev and 737.4 ev.

In order to achieve the purpose, the invention secondly provides a preparation method of the cesium-doped sodium type layered manganese dioxide VOCs catalyst, and the technical scheme is as follows:

the preparation method of the cesium-doped sodium type layered manganese dioxide VOCs catalyst comprises the following steps:

(1) Obtaining a first solution comprising a manganese salt; obtaining a second solution, wherein the second solution comprises an oxidant and sodium hydroxide; obtaining a third solution comprising a cesium salt;

(2) Sequentially adding the second solution and the third solution into the first solution to form a first solid-liquid mixture;

(3) Carrying out solid-liquid separation on the first solid-liquid mixture, and washing to be neutral to obtain a first precursor;

(4) Dispersing the first precursor into a sodium hydroxide solution, and then carrying out hydrothermal reaction to form a second solid-liquid mixture;

(5) Carrying out solid-liquid separation on the second solid-liquid mixture, washing to be neutral, and drying to obtain a second precursor;

(6) And calcining the second precursor to obtain the cesium-doped sodium type layered manganese dioxide VOCs catalyst.

As a further improvement of the above-mentioned preparation method: the manganese salt in the step (1) is manganese acetate, manganese sulfate, manganese nitrate or manganese chloride, the oxidant is hydrogen peroxide, and the cesium salt is cesium acetate, cesium sulfate, cesium nitrate or cesium chloride.

As a further improvement of the above-mentioned preparation method: and (3) in the step (2), starting to add the third solution within 3-10s after the second solution is added.

As a further improvement of the above-mentioned preparation method: and (3) carrying out solid-liquid separation by adopting vacuum filtration, and washing a filter cake to be neutral by adopting 600-3600 mL of water.

As a further improvement of the above-mentioned preparation method: the hydrothermal temperature in the step (4) is 120-180 ℃, and the time is 18-30 h.

As a further improvement of the above-mentioned preparation method: the drying temperature in the step (5) is 60-150 ℃, and the time is 8-16 h

As a further improvement of the above preparation method: the calcination time in the step (6) is 250-400 ℃ and 3-6 h.

As a further improvement of the above-mentioned preparation method: the molar ratio of cesium to manganese is between 0.05 and 0.2.

In order to achieve the above object, the present invention further provides a method for treating VOCs, the technical solution is as follows:

the VOCs catalyst is adopted in the treatment method of the VOCs, or the VOCs catalyst prepared by the preparation method is adopted.

Proved by verification, the cesium-doped layered manganese dioxide VOCs catalyst successfully dopes sodium and cesium in layered manganese dioxide, so that the performance of catalytic oxidation of VOCs is obviously improved, and the catalyst has high stability and CO ₂ Selectivity and simple preparation process, so that the method is very suitable for the technical field of removing VOCs by catalytic oxidation.

The invention is further described with reference to the following figures and detailed description. Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to assist in understanding the invention, and are included to explain the invention and their equivalents and not limit it unduly. In the drawings:

FIG. 1 shows XRD patterns of Na-600, na-1200, na-2000 and Na-3600.

FIG. 2 shows XPS spectra of Mn3s for Na-600, na-1200, na-2000, and Na-3600.

FIG. 3 shows XPS spectra of Mn2p for Na-600, na-1200, na-2000, na-3600.

FIG. 4 shows XPS spectra of O1s for Na-600, na-1200, na-2000, and Na-3600.

FIG. 5 shows XPS spectra of Na1s for Na-600, na-1200, na-2000, and Na-3600.

FIG. 6 shows H of Na-600, na-1200, na-2000, na-3600 ₂ -a TPR map.

FIG. 7 shows O of Na-600, na-1200, na-2000, na-3600 ₂ -a TPD profile.

FIG. 8 is a graph of the performance test data of Na-600, na-1200, na-2000, na-3600 catalytic oxidation toluene.

FIG. 9 is a graph showing the T50 and T90 of toluene catalytically oxidized by Na-600, na-1200, na-2000, na-3600, as a function of the amount of washing water.

FIG. 10 shows CO of Na-600, na-1200, na-2000, na-3600 ₂ And (5) selecting a test result.

FIG. 11 shows Arrhenius curves for Na-600, na-1200, na-2000, and Na-3600.

FIG. 12 is an XRD spectrum of Na-2000, cs-0.05, cs-0.1, cs-0.15, cs-0.2.

FIG. 13 shows Raman spectra of Na-2000, cs-0.05, cs-0.1, cs-0.15, and Cs-0.2.

FIG. 14 is an SEM photograph of Na-2000, cs-0.05, cs-0.1, cs-0.15 and Cs-0.2.

FIG. 15 is TEM and HRTEM photographs of Na-2000 and Cs-0.15.

FIG. 16 is an EDS map of Cs-0.15.

FIG. 17 shows N of Na-2000 ₂ Adsorption-desorption isotherms (a) and pore size distribution curves (b).

FIG. 18 shows Cs-0.05N ₂ Adsorption-desorption isotherms (a) and pore size distribution curves (b).

FIG. 19 shows Cs-0.1N ₂ Adsorption-desorption isotherms (a) and pore size distribution curves (b).

FIG. 20 shows Cs-0.15N ₂ Adsorption-desorption isotherms (a) and pore size distribution curves (b).

FIG. 21 shows Cs-0.2N ₂ Adsorption-desorption isotherms (a) and pore size distribution curves (b).

FIG. 22 shows XPS spectra of Mn3s for Na-2000, cs-0.05, cs-0.1, cs-0.15, and Cs-0.2.

FIG. 23 shows XPS spectra of Mn2p for Na-2000, cs-0.05, cs-0.1, cs-0.15, and Cs-0.2.

FIG. 24 shows XPS spectra of O1s for Na-2000, cs-0.05, cs-0.1, cs-0.15, and Cs-0.2.

FIG. 25 shows XPS spectra of Na1s for Na-2000, cs-0.05, cs-0.1, cs-0.15, and Cs-0.2.

FIG. 26 shows XPS spectra of Cs3d for Na-2000, cs-0.05, cs-0.1, cs-0.15, and Cs-0.2.

FIG. 27 shows H of Na-2000, cs-0.05, cs-0.1, cs-0.15, cs-0.2 ₂ -a TPR map.

FIG. 28 shows O of Na-2000, cs-0.05, cs-0.1, cs-0.15, cs-0.2 ₂ -a TPD profile.

FIG. 29 is a data chart of the performance test of Na-2000, cs-0.05, cs-0.1, cs-0.15, cs-0.2 catalytic oxidation toluene.

FIG. 30 shows CO of Na-2000, cs-0.05, cs-0.1, cs-0.15, cs-0.2 ₂ And (5) selecting a test result.

FIG. 31 is an Arrhenius curve of Na-2000, cs-0.05, cs-0.1, cs-0.15, cs-0.2.

Fig. 32 is a schematic configuration diagram of a catalyst activity evaluation device.

Detailed Description

The invention will be described more fully hereinafter with reference to the accompanying drawings. Those skilled in the art will be able to implement the invention based on these teachings. Before the present invention is described in detail with reference to the accompanying drawings, it is to be noted that:

the technical solutions and features provided in the present invention in the respective sections including the following description may be combined with each other without conflict.

Moreover, the embodiments of the present invention described in the following description are generally only some embodiments of the present invention, and not all embodiments. Therefore, all other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present invention without any creative effort shall fall within the protection scope of the present invention.

With respect to terms and units in the present invention. The terms "comprising," "having," and any variations thereof in the description and claims of this invention and in the related section are intended to cover a non-exclusive inclusion.

The first embodiment of the preparation method is to prepare the sodium-type layered manganese dioxide VOCs catalyst, and specifically comprises the following steps:

(1) Obtaining a first solution comprising a manganese salt; obtaining a second solution, wherein the second solution comprises an oxidant and sodium hydroxide;

(2) Adding the second solution to the first solution to form a first solid-liquid mixture;

(4) Dispersing the first precursor in a sodium hydroxide solution, and then carrying out hydrothermal reaction to form a second solid-liquid mixture;

(6) And calcining the second precursor to obtain the sodium type layered manganese dioxide VOCs catalyst.

The second embodiment of the preparation method is to prepare the cesium-doped sodium type layered manganese dioxide VOCs catalyst, and specifically comprises the following steps:

(1) Obtaining a first solution comprising a manganese salt; obtaining a second solution, wherein the second solution comprises an oxidant and sodium hydroxide; obtaining a third solution comprising a cesium salt; the molar ratio of cesium to manganese is 0.05 to 0.2, but is not limited to any one of values of 0.05, 0.08, 0.1, 0.12, 0.15, 0.17, and 0.2;

(2) Sequentially adding the second solution and the third solution into the first solution to form a first solid-liquid mixture; specifically, the addition of the third solution is started within 5s after the addition of the second solution is completed;

In the two embodiments described above:

the manganese salt in the step (1) is manganese acetate, manganese sulfate, manganese nitrate or manganese chloride, the oxidant is hydrogen peroxide, and the cesium salt is cesium acetate, cesium sulfate, cesium nitrate or cesium chloride.

Performing solid-liquid separation by adopting vacuum filtration, and washing a filter cake to be neutral by adopting 600-3600 mL of water; the water amount may be, but is not limited to, 600mL, 900mL, 1200mL, 1500mL, 1800mL, 2000mL, 2500mL, 2900mL, 3200mL, or 3600 mL.

The hydrothermal temperature in the step (4) is 120-180 ℃, and the time is 18-30 h; the hydrothermal temperature can be but is not limited to be any one of 120 ℃, 130 ℃, 140 ℃, 150 ℃, 160 ℃, 170 ℃ and 180 ℃, and the hydrothermal time can be but is not limited to be any one of 30h, 28h, 26h, 24h, 22h, 20h and 18 h.

The drying in the step (5) is specifically gradient drying, namely low-temperature drying (60-100 ℃ for 8-15 h) is carried out firstly, and then high-temperature drying (110-150 ℃ for 8-15 h) is carried out. Specifically, the temperature of the low-temperature drying may be, but is not limited to, any one of 60 ℃, 70 ℃, 80 ℃, 90 ℃ and 100 ℃, the temperature of the high-temperature drying may be, but is not limited to, any one of 110 ℃, 120 ℃, 130 ℃, 140 ℃ and 150 ℃, and the time lengths of the low-temperature drying and the high-temperature drying may be, but is not limited to, any one of 8h, 9h, 10h, 11h, 12h, 13h, 14h and 15 h.

The calcination time in the step (6) is 250-400 ℃, and the calcination time is 3-6 h; the calcination temperature can be, but is not limited to, any one of 250 ℃, 270 ℃, 300 ℃, 320 ℃, 350 ℃, 380 ℃ and 400 ℃, and the calcination time can be, but is not limited to, any one of 6h, 5.5h, 5h, 4.5h, 4h, 3.5h and 3 h.

The present invention is illustrated by the following specific examples.

Examples A1 to A4 are specific examples of the first embodiment, differing from the difference in the amount of washing water in step (3), the amounts of washing water in examples A1 to A4 were 600mL, 1200mL, 2000mL and 3600mL in this order, and the sodium-type layered manganese dioxide VOCs catalysts obtained were labeled Na-600, na-1200, na-2000 and Na-3600 in this order. The rest parameters are as follows: the manganese salt is manganese acetate tetrahydrate, the oxidant is hydrogen peroxide, the cesium salt is cesium nitrate, the hydrothermal temperature is 150 ℃, the hydrothermal time is 24 hours, the drying is drying at 60 ℃ and 150 ℃ for 12 hours respectively, the calcining time is 300 ℃, and the calcining time is 4 hours.

FIG. 1 shows XRD patterns of Na-600, na-1200, na-2000 and Na-3600.

As can be seen from FIG. 1, the diffraction peak positions of the four catalysts all appear in the vicinity of 12.3 °, 25 °, 36.5 ° and 65.5 °, corresponding to the (001), (002), (100) and (110) crystal planes of the layered manganese dioxide (PDF # 43-1456), respectively, which indicates that the four catalysts areThe chemical agents are all manganese birnessite type delta-MnO ₂ The change of the amount of washing water of the sodium-type layered manganese dioxide of the phase does not change the crystal phase structure of the catalyst.

FIG. 2 shows XPS spectra of Mn3s for Na-600, na-1200, na-2000, and Na-3600. FIG. 3 shows XPS spectra of Mn2p for Na-600, na-1200, na-2000, na-3600. FIG. 4 shows XPS spectra of O1s for Na-600, na-1200, na-2000, and Na-3600. FIG. 5 shows XPS spectra of Na1s for Na-600, na-1200, na-2000, and Na-3600.

The Average Oxidation State (AOS) of manganese can be obtained by the formula AOS =8.956-1.126 Δ Es, where Δ Es is the difference in binding energy between the two peaks of the XPS spectrum for Mn3s shown in fig. 2. The calculated AOS values for manganese for the four catalysts are shown in Table 1. The results show that the AOS values are sequentially Na-2000 > Na-1200 > Na-3600 > Na-600. The catalytic activity of the catalyst is in positive correlation with the AOS value of manganese, and the highest AOS value of the manganese in Na-2000 indicates that the surface of the Na-2000 is rich in manganese species with higher valence state.

As shown in FIG. 3, the Mn2p orbitals can be divided into asymmetric Mn2p3/2 and Mn2p3/2 spectra and deconvoluted into six sub-peaks, with the binding energies of 643.0eV and 654.3eV, 641.9eV and 653.4eV, 641.7eV and 652.0eV being attributable to the surface's Mn2p3/2 and Mn2p3/2 spectra, respectively ⁴⁺ 、Mn ³⁺ And Mn ²⁺ A substance. Mn of the four catalyst surfaces is calculated ⁴⁺ /(Mn ³⁺ +Mn ²⁺ ) The molar ratio is shown in Table 1. The results show that Mn ⁴⁺ /(Mn ³⁺ +Mn ²⁺ ) The ratio sequence is Na-2000 > Na-1200 > Na-3600 > Na-600. Higher Mn ⁴⁺ /(Mn ³ ⁺ +Mn ²⁺ ) The molar ratio indicates that the redox cycling of Mn ions is more, and therefore the catalytic oxidation activity is better, while the surface Mn ⁴⁺ The increase in (b) indicates that there are more vacancy defects on the surface of the catalyst, favoring the adsorption, activation and migration of oxygen.

In FIG. 4, the XPS spectrum for O1s was fit-split into peaks and deconvoluted into three peaks near the binding energies of 529.4eV, 531.5eV, and 533.1eV, respectively, due to lattice oxygen (O.sub. _lat ) Adsorbing oxygen (O) _ads ) And surface hydroxyl oxygen (O) _H2O ). O was calculated for four catalyst surfaces _lat /O _ads Mole ofThe ratios are shown in Table 1. O of four catalysts as shown in Table 1 _lat /O _ads The mol ratio is as follows: na-2000 > Na-1200 > Na-3600 > Na-600, indicating a suitable concentration of surface Na ⁺ Increase delta-MnO ₂ The oxygen content of the crystal lattice of (2) contributes to the catalysis.

As shown in fig. 5, a characteristic peak corresponding to Na1s was observed significantly at a binding energy of about 1070.9eV for each of the four catalysts. Belong to Na ⁺ The intensity of the characteristic peak of (A) decreased with the increase in the amount of washing water, indicating that the increase in the amount of washing water did decrease Na on the surface of the catalyst ⁺ And (4) content.

TABLE 1

FIG. 6 shows H of Na-600, na-1200, na-2000, na-3600 ₂ -a TPR map.

As shown in fig. 6, the reduction of the four catalysts occurs in the temperature range of 280-460 ℃, and four distinct reduction peaks, labeled α, β, γ, and δ, can be identified. By comparison, the four reduction peaks of Na-2000 all show the lowest reduction peak temperature, which means that the four reduction peaks have the strongest low-temperature reduction capability. Compared with Na-3600, has relatively moderate surface Na ⁺ The reduction peaks of the Na-1200 and the Na-2000 are sequentially shifted to the low temperature direction, which shows that the manganese ions of the compounds are gradually more easily reduced, thereby indicating that O _lat Gradually increases the activity of (c).

FIG. 7 shows O of Na-600, na-1200, na-2000, na-3600 ₂ -a TPD profile.

As shown in FIG. 7, each of the four catalysts had 3 oxygen desorption peaks, respectively labeled O _α (0～300℃)、O _β (300-500 ℃) and O _γ (> 500 ℃ C.). By comparison, O of Na-2000 _α The peak desorption peak temperature is lowest (86 ℃), which indicates that the surface chemical adsorption oxygen species activity is highest. Further, O of Na-2000 _γ The lowest temperature and highest intensity of the peak indicate the highest activity and mobility of the bulk lattice oxygen species.

FIG. 8 is a graph of the performance test data of Na-600, na-1200, na-2000, na-3600 catalytic oxidation toluene. FIG. 9 is a graph showing the T50 and T90 of toluene catalytically oxidized by Na-600, na-1200, na-2000, na-3600, as a function of the amount of washing water. Table 2 shows the data of the performance test of the catalytic oxidation of toluene by Na-600, na-1200, na-2000 and Na-3600.

As shown in fig. 8, each of the four catalysts exhibited a certain toluene removal performance, and the catalytic activity increased with an increase in the reaction temperature and then tended to be stable. As can be seen from the results of the T50 (temperature to 50% conversion) and T90 (temperature to 90% conversion) of the four catalysts as a function of the amount of wash water shown in fig. 9 and table 2, the four catalysts were active in the order: na-2000 > Na-1200 > Na-3600 and is approximately equal to Na-600, which shows that the moderate Na brought by the moderate washing water quantity ⁺ The content of the toluene has a promoting effect on the catalytic oxidation of the toluene.

TABLE 2

Catalyst and process for preparing same	T ₅₀ (℃)	T ₉₀ (℃)	Apparent activation energy (kJ/mol)
				Na-600	223	232	76.39
Na-1200	211	218	70.11
				Na-2000	202	212	66.53
Na-3600	224	230	82.09

CO converted after reaction of catalyst with toluene ₂ Continuously release CO if at high temperature ₂ The conversion rate can reach 100%, which shows that the toluene is completely decomposed and converted into H on the surface of the catalyst ₂ O and CO ₂ . As shown in FIG. 10, na-2000 can completely convert toluene to CO at temperatures below 230 deg.C ₂ And H ₂ O, no other by-products are produced, indicating better CO ₂ And (4) selectivity.

FIG. 11 shows Arrhenius curves for Na-600, na-1200, na-2000, and Na-3600.

The apparent activation energy (Ea) can be calculated from the slope of the Arrhenius curve, and in general, the lower the Ea, the easier the surface of the catalyst is activated and participates in the catalytic oxidation reaction. As shown in FIG. 11 and Table 2, the magnitude order of Ea values (in kJ/mol) of the four catalysts is: na-2000 (66.53) < Na-1200 (70.11) < Na-600 (76.39) < Na-3600 (82.09). As can be seen, na-2000 has the lowest Ea value, indicating that toluene is more readily catalytically oxidized at its surface.

(II) examples B1 to B4 are specific examples of the second embodiment, and are different in the molar ratio of cesium to manganese in step (1), the molar ratios of cesium to manganese in examples B1 to B4 are 0.05, 0.1, 0.15 and 0.2 in this order, and the catalysts corresponding to the obtained cesium-doped sodium type layered manganese dioxide VOCs are labeled Cs-0.05, cs-0.1, cs-0.15 and Cs-0.2 in this order. The rest parameters are as follows: the manganese salt is manganese acetate tetrahydrate, the oxidant is hydrogen peroxide, the cesium salt is cesium nitrate, the hydrothermal temperature is 150 ℃, the hydrothermal time is 24 hours, the drying is drying at 60 ℃ and 150 ℃ for 12 hours respectively, the calcining time is 300 ℃, the calcining time is 4 hours, and the amount of washing water in the step (3) is 2000mL.

FIG. 12 is an enlarged view of XRD patterns of Na-2000, cs-0.05, cs-0.1, cs-0.15 and Cs-0.2, wherein 2 theta of a is 5 to 80 DEG, and 2 theta of b is 10 to 15 deg.

As can be seen from FIG. 12a, the diffraction peak positions of the five catalysts all appear around 12.3 °, 24.9 °, 36.9 ° and 65.5 °, corresponding to the (001), (002), (100) and (110) crystal planes of Shui Na manganese ore-type layered manganese dioxide (PDF # 43-1456), respectively, indicating that the five catalysts are all layered structures, cs ⁺ Doping does not alter the crystalline phase structure of the catalyst. No characteristic diffraction peak of other crystal forms is detected, which indicates that the Cs ⁺ In MnO ² High degree of uniform dispersion. The relatively broader and weaker diffraction peaks exhibited by cs-0.15 compared to Na-2000, with poorer crystallinity, indicating that a large number of surface defects may be present on its surface, favoring adsorption and activation of VOCs. As can be seen from FIG. 12b, the diffraction peaks shift slightly with increasing Cs/Mn.

The interplanar spacing can be calculated by bragg diffraction formula 2d · sin θ = λ, wherein d (nm), θ (°), and λ (nm) are the interlayer distance, bragg angle, and X-ray wavelength, respectively, and the calculation results are shown in table 3. As can be seen from Table 3, as the doping amount of Cs increases, the interlayer spacing of the (001) plane gradually increases, indicating that Cs ⁺ The interlayer has been successfully embedded.

TABLE 3

FIG. 13 is a Raman spectrum of Na-2000, cs-0.05, cs-0.1, cs-0.15, cs-0.2.

As can be seen from FIG. 13, each of the five catalysts can be 630cm ^-1 The main characteristic peak which can be designated as sodium type layered manganese dioxide is observed in the vicinity. Cs-0.05, cs-0.1 and Cs-0.15 are positioned at 628cm ^-1 The near raman peak intensity is significantly reduced compared to Na-2000, which facilitates an increase in the number of vacancy defects, promoting catalytic oxidation of VOCs. The Raman peak intensity increased with increasing Cs/Mn, indicating that Cs ⁺ Successful insertion into delta-MnO ₂ Between the layers. The Raman peak of the Cs-doped catalyst was somewhat red-shifted compared to Na-2000, indicating that the incorporation of the Cs element resulted in a delta-MnO ₂ The local structure is modified, and the lattice distortion is generated to destroy the symmetrical structure. When the Cs/Mn reaches 0.15, the doping amount of the Cs is increased, the red shift degree of the Raman peak is reduced, and the excessive Cs is shown ⁺ Pile up on the surface of the catalyst and prevent more Cs ⁺ And entering the interlayer. Cs-0.15 at 556cm ^-1 Shows a new Raman peak, which indicates the Cs under the Cs/Mn doping ratio ⁺ A greater variety of lattice oxygens can be activated to participate in the catalytic oxidation of VOCs.

FIG. 14 is SEM photograph of Na-2000, cs-0.05, cs-0.1, cs-0.15, cs-0.2, where a, f belong to Na-2000, b, g belong to Cs-0.05, c, h belong to Cs-0.1, d, i belong to Cs-0.15, e, j belong to Cs-0.2.

As shown in FIG. 14, na-2000 has a nanosheet morphology with an average thickness of about 10nm, while Cs-0.05, cs-0.1 and Cs-0.15 exhibit smaller flower-like structures composed of the nanosheets, and the flower-like structures become progressively larger with increasing doping, with the thickness of the individual nanosheets ranging from about 15 to 20nm. Cs-0.2 exhibits large blocky morphology, probably due to Cs ⁺ Accumulation at the surface, this table shows that Na-2000 shows that Cs doping affects delta-MnO ₂ The morphology of (2).

FIG. 15 shows TEM and HRTEM photographs of Na-2000 and Cs-0.15, in which a and c belong to Na-2000, b and d belong to Cs-0.15.

As shown in FIG. 15, both catalysts showed significant lattice fringes, in which Na-2000 had lattice spacings of 0.7 and 0.35nm, close to those of the (001) and (002) crystal planes of the standard sample (PDF # 43-1456). Cs-0.15 has lattice fringes at 0.7nm, 0.35nm and 0.25nm corresponding to the (001), (002) and (110) crystal planes, indicating Cs ⁺ The introduction of (2) makes the exposure of crystal faces have larger difference. N is a radical ofThe exposed crystal faces of a-2000 are respectively (001) and (002), and Cs-0.15 simultaneously has three exposed crystal faces of (001), (002) and (110), so that the catalytic activity of the catalyst can be effectively improved. Cs-0.15 has a large number of severely blurred lattice fringes (the oval lines in the figure are highlighted), indicating that Cs ⁺ The introduction of (B) results in delta-MnO ₂ More crystal defects are generated which generally contribute to the formation of vacancy structures.

FIG. 16 is the EDS chart for Cs-0.15.

As shown in FIG. 16, mn, O, na and Cs are uniformly dispersed in Cs-0.15, which is beneficial to the transfer of electrons between different elements during the catalytic oxidation reaction and promotes the reaction.

FIG. 17 shows N of Na-2000 ₂ Adsorption-desorption isotherms (a) and pore size distribution curves (b). FIG. 18 is a photograph of Cs-0.05N ₂ Adsorption-desorption isotherms (a) and pore size distribution curves (b). FIG. 19 shows Cs-0.1N ₂ Adsorption-desorption isotherms (a) and pore size distribution curves (b). FIG. 20 shows Cs-0.15N ₂ Adsorption-desorption isotherms (a) and pore size distribution curves (b). FIG. 21 shows Cs-0.2N ₂ Adsorption-desorption isotherms (a) and pore size distribution curves (b). Table 4 shows pore structure data of Na-2000, cs-0.05, cs-0.1, cs-0.15 and Cs-0.2.

As shown in fig. 17-21, each of the five catalysts shows an IV-type nitrogen desorption isotherm with an H3-hysteresis loop, which indicates that each of the five catalysts is a mesoporous material and has a porous structure in the shape of a slit, which is favorable for the diffusion of VOCs molecules in the catalyst pore channels. As shown in Table 4, doped Cs ⁺ Then, the specific surface area of the catalyst is reduced, and the reduction of the Cs-0.20 specific surface area is particularly remarkable and is only 29.8m ² G, pore volume (0.135 cm) ³ /g) less than Na-2000 (0.145 cm) ³ /g) indicates Cs ⁺ Block delta-MnO ₂ Is partially porous.

TABLE 4

Catalyst and process for producing the same	Specific surface area (m) ² /g)	Aperture (nm)	Pore volume (cm) ³ /g)
				Na-2000	66.4	18.3	0.145
Cs-0.05	66.2	16.2	0.163
				Cs-0.10	65.8	12.9	0.163
Cs-0.15	53.5	12.2	0.145
				Cs-0.20	29.8	18.9	0.135

FIG. 22 is an XPS spectrum of Mn3s for Na-2000, cs-0.05, cs-0.1, cs-0.15, cs-0.2. FIG. 23 is an XPS spectrum of Mn2p for Na-2000, cs-0.05, cs-0.1, cs-0.15, cs-0.2. FIG. 24 is an XPS spectrum of O1s for Na-2000, cs-0.05, cs-0.1, cs-0.15, cs-0.2. FIG. 25 shows XPS spectra of Na1s for Na-2000, cs-0.05, cs-0.1, cs-0.15, and Cs-0.2. FIG. 26 shows XPS spectra of Cs3d for Na-2000, cs-0.05, cs-0.1, cs-0.15, and Cs-0.2.

Table 5 shows the AOS values, mn of manganese for the five catalysts obtained from FIGS. 22 to 24 ⁴⁺ /(Mn ³⁺ +Mn ²⁺ ) Molar ratio and O _lat /O _ads Quantitative analysis of the molar ratio. As shown in Table 5, the AOS value and Mn of manganese ⁴⁺ /(Mn ³⁺ +Mn ²⁺ ) Molar ratio and O _lat /O _ads The order of the mole ratio is Cs-0.15 > Cs-0.10 > Cs-0.05 > Cs-0.2 > Na-2000.

As shown in fig. 25, a characteristic peak corresponding to Na1s was observed significantly for each of the five catalysts at a binding energy of about 1070.9 eV. The Na1s peak of the Cs-doped catalyst was weaker compared to Na-2000, indicating that part of the surface of the catalyst was Na ⁺ Ions were also successfully exchanged. As shown in FIG. 26, a Cs3d3/2 peak (about 722.8 eV) and a Cs3d5/2 peak (about 737.4 eV) were observed on Cs-0.05, cs-0.1, cs-0.15, cs-0.2, indicating that surface Cs ⁺ Is present.

TABLE 5

The bulk elements of Na-2000, cs-0.05, cs-0.1, cs-0.15 and Cs-0.2 were analyzed by inductively coupled plasma (ICP-AES), the surface elements were analyzed by the XPS spectrum, and the molar ratios of the bulk elements and the surface elements obtained are shown in Table 6. As can be seen from Table 6, when the Cs/Mn ratio of the starting material was increased to 0.15, the increase of Cs/Mn in the bulk phase was not increased any more, and Cs in the bulk phase was increased ⁺ Saturation, excess Cs ⁺ More remained on the catalyst surface, which is consistent with the characterization results of SEM.

TABLE 6

FIG. 27 shows H with Na-2000, cs-0.05, cs-0.1, cs-0.15, cs-0.2 ₂ -a TPR map.

As shown in fig. 27, the four reduction peaks of Cs-0.15 each exhibited the lowest reduction peak temperatures of 258 ℃,307 ℃,377 ℃ and 436 ℃, respectively, meaning that they had the strongest low temperature reduction capability. The temperature sequence corresponding to the alpha peak is Cs-0.15 < Cs-0.10 < Cs-0.05 < Na-2000 < Cs-0.20, the integral area sequence corresponding to the beta peak is Cs-0.15 > Cs-0.10 > Cs-0.05 > Na-2000 ≈ Cs-0.20, and the result shows that the doped Cs is Cs ⁺ Mn of the post catalyst ⁴⁺ The content was increased, confirming proper Cs ⁺ The introduction of the catalyst reduces the strength of Mn-O bonds and provides more active lattice oxygen and H ₂ And (4) reacting.

As shown in FIG. 28, cs-0.05, cs-0.10, cs-0.15 of O was compared with Na-2000 _β Peak and O _γ The peak is obviously shifted to the low temperature direction, O _β The peak corresponding temperatures were reduced by 3 deg.C, 14 deg.C, 19 deg.C, O _γ The peak corresponding temperatures are reduced by 5 deg.C, 11 deg.C and 12 deg.C, respectively, which facilitates the catalytic oxidation of VOCs.

FIG. 29 is a data chart of the performance test of Na-2000, cs-0.05, cs-0.1, cs-0.15, cs-0.2 catalytic oxidation toluene. Table 7 shows the performance test data of Na-2000, cs-0.05, cs-0.1, cs-0.15 and Cs-0.2 catalytic oxidation of toluene.

As shown in FIG. 29, all five catalysts can realize complete catalysis of toluene at 225 ℃, and show the best catalytic performance. The low-temperature catalytic oxidation activity sequence of the toluene is as follows: cs-0.15 > Cs-0.10 > Cs-0.05 > Na-2000 > Cs-0.20, and the results show that Cs-0.15 shows the most excellent toluene catalytic combustion activity, and the T50 and T90 are 179 ℃ and 188 ℃ respectively, and are reduced by 23 ℃ and 24 ℃ respectively compared with Na-2000.

TABLE 7

Catalyst and process for preparing same	T ₅₀ (℃)	T ₉₀ (℃)	Apparent activation energy (kJ/mol)
				Na-2000	202	212	66.5
Cs-0.05	192	201	61.7
				Cs-0.10	183	192	54.6
Cs-0.15	179	188	41.1
				Cs-0.20	211	220	74.0

Cs-0.15 CO, as shown in FIG. 30 ₂ The selectivity was essentially synchronized with the catalytic activity, indicating that few by-products were produced during the removal of toluene. Compared with Na-2000 (98.3%), the selectivity of the carbon dioxide can reach 100% when the toluene is completely removed by Cs-0.15, which shows that the Cs ⁺ The doped catalyst more easily realizes the deep oxidation of the toluene.

FIG. 31 is an Arrhenius curve of Na-2000, cs-0.05, cs-0.1, cs-0.15, cs-0.2.

As shown in FIG. 31 and Table 7, the Ea value of Cs-0.15 was the lowest, indicating that toluene was more easily catalytically oxidized at its surface. The magnitude relationship of Ea values (in kJ/mol) of the five catalysts is as follows: cs-0.15 (41.11) < Cs-0.1 (54.57) < Cs-0.05 (61.72) < Na-2000 (66.53) < Cs-0.2 (74.03).

In summary, cs ⁺ The doping can effectively improve the catalytic combustion performance of the sodium type layered manganese dioxide catalyst on toluene, and the optimal doping ratio of Cs/Mn is 0.15.

An example of the method of treating VOCs of the present invention is to use the cesium-doped sodium layered manganese dioxide VOCs catalyst prepared in example B3.

In the above characterization:

SEM photographs were taken using a SIGMA500 scanning electron microscope.

TEM and HRTEM photographs are obtained by using a FEI Talos F200X transmission electron microscope; the sample treatment mode is as follows: the sample powder was sonicated in ethanol for 0.5h and then deposited on a carbon coated copper grid.

N ₂ The instruments and models used for the adsorption-desorption analysis are respectively full-automatic physical adsorption apparatus (BET) -N ₂ And Micromeritic ASAP2460; the pore diameter and the pore volume are calculated by a BJH (Barret-Joyner-Halenda) model, and the specific surface area is calculated by a BET (Brunauer-Emmett-Teller) model; vacuum degassing at 300 deg.C for 3 hr, measuring with high-purity nitrogen as adsorbate at 77K to obtain N ₂ Adsorption-desorption isotherms.

The XRD spectrum is obtained by adopting a Bruker D8 advance-wide angle XRD diffractometer, the radiation source is a monochromatic CuK alpha source, the lambda =0.1541nm, the scanning speed is 5 degrees/min, the scanning voltage is 40kV, and the current is 50mA.

Performing Raman test by using a LabRAM HR Evolution instrument, taking excitation light with the wavelength of 523nm as a laser source, and acquiring resolutions of 0.5cm ^-1 The diameter of a laser spot is 2 mu m, the power is 1.5mW, and the integration time is 30s.

XPS Equipment manufacturer is ThermoFisher, model Thermo Scientific NEXSA, X-ray source is monochromatic AlKa source (Mono AlKa) energy, and vacuum degree of the analysis chamber is about 5X 10-9mbar.

The experimental instrument adopted for the ICP-AES analysis is Agilent ICP-AES730.

Obtaining H ₂ TPR map and O ₂ The experimental apparatus of the TPD atlas is a TPD/TPR dynamic adsorption apparatus with the model of TP-5076.H ₂ Experimental operation of the TPR map as follows: (1) About 50mg of the sample was placed in a quartz tube and pretreated for 1 hour in a flowing nitrogen atmosphere; (2) The sample obtained by pretreatment is placed at 5%H with the flow rate of 50mL/min ₂ The temperature in the/Ar mixture is programmed from room temperature to 800 ℃ at a rate of 5 ℃/min. O is ₂ TPD profile experimental procedure as follows: (1) blowing helium gas for sample pretreatment for 1h at 300 ℃; (2) Cooling to 50 deg.C, introducing oxygen for 1h, purging with helium gas for 20min to complete adsorption process, moving base line under helium atmosphere, heating from 50 deg.C to 800 deg.C at 5 deg.C/min, cooling to 50 deg.C, and detecting desorbed oxygen by TCD.

As shown in FIG. 32, the evaluation apparatus was equipped with a GC-2000 II gas chromatograph equipped with a FID detector to detect the toluene content in the course of the catalytic reaction in real time.

(1) Conditions of the experiment

The length of the solid bed continuous flow quartz reactor is 70cm, and the inner diameter is 8mm; the particle size of the catalyst is 40-60 meshes; the flow rate of the carrier gas passing through the reactor is kept at 232mL/min, the concentration of the inlet toluene is about 1000ppm, the water content is 5 percent, and the gas mass space velocity (WHSV) is 30000 mL/(g.h); the chromatographic column is a special analytical column for benzene series; the temperature of the gasification chamber is 120 ℃; the temperature of the detector is 120 ℃; the temperature of the column box is 90 ℃; the carrier gas pressure was 0.3MPa (high purity nitrogen); the air pressure is 0.4MPa; the hydrogen pressure was 0.2MPa.

(2) Procedure of experiment

Before testing, at 50 ℃ under N ₂ And (3) pretreating the copper-manganese composite oxide VOCs catalyst in the atmosphere.

During the test, toluene (GAS 2) and water vapor (GAS 3) were both carried out by bubbling and mixed with air (GAS 1) in a mixer; regulating the flow of each path of gas through a mass flow controller to prepare mixed gas with required toluene concentration and water content; the mixed gas is catalyzed and degraded by a copper-manganese composite oxide VOCs catalyst in a catalyst bed layer of the reactor, the temperature of the catalyst bed layer is fed back in real time by a thermocouple and is regulated by program temperature control; the operation temperature of the catalyst bed layer is 140-300 ℃, and each temperature point is kept for half h; respectively using gas chromatograph and CO ₂ Online detector for detecting concentration of toluene and generated CO in real time ₂ Concentration, while recording when data at a fixed temperature point is stable.

The contents of the present invention have been explained above. Those skilled in the art will be able to implement the invention based on these teachings. All other embodiments, which can be derived by a person skilled in the art from the above description without inventive step, shall fall within the scope of protection of the present invention.

Claims

1. The cesium-doped sodium type layered manganese dioxide VOCs catalyst is characterized in that: the XPS spectrum for Na1s has characteristic peaks at 1070.9eV, and the XPS spectrum for Cs3d has characteristic peaks at 722.8eV and 737.4 eV.

2. The method of preparing the cesium-doped sodium layered manganese dioxide (VOCs) catalyst of claim 1, comprising the steps of:

3. The method of claim 2, wherein: the manganese salt in the step (1) is manganese acetate, manganese sulfate, manganese nitrate or manganese chloride, the oxidant is hydrogen peroxide, and the cesium salt is cesium acetate, cesium sulfate, cesium nitrate or cesium chloride.

4. The method of claim 2, wherein: and (3) in the step (2), starting to add the third solution within 3-10s after the second solution is added.

5. The method of claim 2, wherein: and (3) carrying out solid-liquid separation by adopting vacuum filtration, and washing a filter cake to be neutral by adopting 600-3600 mL of water.

6. The method of claim 2, wherein: the hydrothermal temperature in the step (4) is 120-180 ℃, and the time is 18-30 h.

7. The method of claim 2, wherein: the drying temperature in the step (5) is 60-150 ℃, and the time is 8-16 h.

8. The method of claim 2, wherein: the calcination time in the step (6) is 250-400 ℃ and 3-6 h.

9. The method of claim 2, wherein: the molar ratio of cesium to manganese is between 0.05 and 0.2.

A method for treating VOCs, comprising: a catalyst for VOCs as claimed in claim 1 or prepared by the method of any one of claims 2 to 9.