CN111203259A

CN111203259A - Preparation method of core-shell microwave catalyst and its application in hydrogen sulfide decomposition

Info

Publication number: CN111203259A
Application number: CN202010112405.XA
Authority: CN
Inventors: 徐文涛; 朱俊; 周继承; 陈佳楠
Original assignee: Xiangtan University
Current assignee: Xiangtan University
Priority date: 2020-02-24
Filing date: 2020-02-24
Publication date: 2020-05-29
Anticipated expiration: 2040-02-24
Also published as: CN111203259B

Abstract

The invention firstly provides a preparation method of a core-shell microwave catalyst, wherein the core-shell microwave catalyst comprises Mo₂C-core structure and BN-shell structure coated outside, i.e. Mo₂C @ BN catalyst, the preparation method comprising the steps of: uniformly mixing the powdery molybdenum dioxide with a solvent, adding boric acid and urea, reacting, and evaporating the solvent to obtain a precursor of the core-shell microwave catalyst; and roasting the precursor at 800-1200 ℃ in a nitrogen element-containing atmosphere to obtain the core-shell microwave catalyst. The invention also provides a core-shell catalyst and application thereof in microwave catalysis for directly decomposing H₂And (S) a method. The microwave catalyst provided by the invention has the advantages of low preparation cost and good wave-absorbing performance, and can realize efficient direct decomposition of hydrogen sulfide at a lower reaction temperature。

Description

Preparation method of core-shell microwave catalyst and application of core-shell microwave catalyst in hydrogen sulfide decomposition

Technical Field

The invention belongs to the technical field of catalysts, and particularly relates to a preparation method of a core-shell microwave catalyst and the catalyst.

Background

H₂S is a toxic, highly corrosive, polluting gas derived mainly from petroleum refining (e.g. hydrodesulfurization), natural gas processing, coal gasification, and the like. H contained in industrial exhaust gas₂The S gas can not only corrode equipment, but also seriously pollute the environment.

Industrially, H₂S is mainly treated by the Claus process, namely H₂S is oxidized into sulfur and water. Unfortunately, this process, although recovering sulfur, is H₂The hydrogen in the S is oxidized into water at high temperature, which causes serious waste of hydrogen resources. Meanwhile, the process treatment process causes secondary pollution, and the reaction temperature is high (> 1300K). H₂The demand of the energy-saving chemical industry is increasing as an important chemical raw material and a precious clean energy source. With the rapid development of economy and the increase of energy demand caused by environmental crisis, people are confronted with the secondary H₂Recovery of H from S₂And sulfur have generated a great deal of interest. Therefore, a sustainable and efficient direct decomposition technology of hydrogen sulfide is developed, and valuable H is extracted from harmful gases of hydrogen sulfide₂And elemental S are essential.

Unlike the Claus process, H₂S direct decomposition reaction can not only treat H₂S waste gas and H is obtained simultaneously₂And sulfur, two valuable commodities. Whereas the claus process can only recover sulphur. However, H₂The direct decomposition reaction of S faces the difficulties of kinetics and thermodynamics. Thermodynamically, H₂The S direct decomposition reaction is limited by thermodynamic equilibrium, even at temperatures up to 1000 ℃ H₂The conversion of S is also very low (only 20% and 30% at 1010 ℃ and 1130 ℃ respectively).

H₂The direct decomposition reaction kinetics of S is slow, and the apparent activation energy is up to 495.62 kJ/mol.

Due to H₂The direct decomposition reaction of S is limited by thermodynamic equilibrium, and generally, under the condition of low temperature, hydrogen sulfide is almostNo decomposition occurs. For example, Faraji et al have studied the pyrolysis method and found that when T < 1123K, almost no decomposition reaction of hydrogen sulfide occurs, and when T ═ 1273K, the decomposition rate of hydrogen sulfide is only 20%; directly decomposing H with a content of 1 vol% by catalytic thermal decomposition method in Nafi O.Guldal et al₂In the study of S, La was found_0.9Sr_0.1Cr_0.25Co_0.75O₃The catalyst has the decomposition rate of about 4.8 percent at 650 ℃ and 36.3 percent at 950 ℃, and needs to provide a large amount of heat for reaction, so that the energy consumption is overlarge; kraia et al at 20 wt.% Co/CeO₂As a catalyst, the conversion was only 15% at a reaction temperature of 700 ℃ and 35% even at 850 ℃.

Therefore, achieving efficient decomposition of hydrogen sulfide under low temperature conditions is a great challenge. If the hydrogen sulfide can be efficiently decomposed at a lower temperature, the method has great significance. For example: the reaction temperature is low, the operation condition is milder, and the energy consumption is saved. Thus, finding a suitable catalyst and a direct and efficient decomposition method is to achieve H₂The key of the low-temperature efficient direct decomposition of S.

Microwave irradiation is an efficient and rapid heating method. Under the microwave irradiation, the reaction rate can be remarkably accelerated, and the reaction selectivity can be changed, which is different from the traditional reaction mode. Compared with the traditional reaction mode, the microwave directly decomposes H₂S is more advantageous. Therefore, in order to better utilize the characteristics of microwave irradiation, it is very meaningful to develop a catalyst which has high activity and can be matched with microwaves at a lower reaction temperature.

Disclosure of Invention

The invention aims to solve the problem of high value of hydrogen sulfide resources, and provides a high-efficiency core-shell microwave catalyst and a low-temperature microwave catalyst for high-efficiency direct decomposition of H₂The S method not only solves the problem of environmental pollution, but also realizes high-value rational utilization of hydrogen sulfide, namely a technology for changing waste into valuable.

The invention provides a preparation method of a core-shell type microwave catalyst, and the core-shell type microwave catalyst is characterized in thatThe wave catalyst comprises Mo₂C-core structure and BN-shell structure coated outside, i.e. Mo₂C @ BN catalyst, the preparation method comprising the steps of: step A, preparing powdery molybdenum dioxide by taking ammonium molybdate as a raw material; b, uniformly mixing the powdery molybdenum dioxide with a solvent, adding boric acid and urea, reacting, and evaporating the solvent to obtain a precursor of the core-shell microwave catalyst; and roasting the precursor at 800-1200 ℃ in a nitrogen-containing atmosphere to obtain the core-shell microwave catalyst, wherein the solvent comprises water and/or ethanol, and the nitrogen-containing atmosphere contains nitrogen and/or ammonia.

In a specific embodiment, the roasting temperature in the step B is 900-1100 ℃, preferably 950-1050 ℃.

In a specific embodiment, the method for preparing powdered molybdenum dioxide in step a comprises: and uniformly mixing ammonium molybdate and ethylene glycol, adding nitric acid, continuously stirring, carrying out hydrothermal reaction at 120-180 ℃, washing the generated solid with water and ethanol, drying and roasting at 400-600 ℃ to obtain the powdery molybdenum dioxide.

In a specific embodiment, in the step B, the atomic molar ratio of the boron element in the boric acid to the molybdenum element in the molybdenum dioxide is 1:10 to 10:1, preferably 1:2 to 2: 1; the molar ratio of the boric acid to the urea is 1: 0.2-1: 30, preferably 1: 2-1: 6.

In a specific embodiment, in step B, ammonia gas is used as the nitrogen element-containing atmosphere during firing.

In a specific embodiment, the preparation method further comprises a step C: heating the core-shell microwave catalyst obtained in the step B to 300-800 ℃, wherein the core-shell microwave catalyst contains H₂S and H₂The activated core-shell microwave catalyst is obtained by carrying out sulfidation treatment on the mixed gas for 0.5-5 hours.

In a specific embodiment, in step C, H₂S and H₂H in the mixed gas of₂S and H₂The gas volume flow rate ratio of (1: 10) to (1: 1), preferably 1:4 to (1: 2).

A core-shell microwave catalyst prepared by the method.

The invention also provides a core-shell microwave catalyst, which comprises Mo₂C-core structure and BN-shell structure coated outside, i.e. Mo₂C @ BN catalyst.

The invention also provides a core-shell type catalyst for microwave catalytic direct decomposition of H₂S, characterized in that the catalyst comprises Mo₂C-core structure and BN-shell structure coated outside, i.e. Mo₂C @ BN catalyst; the method comprises arranging the core-shell type catalyst bed layer containing H in a microwave reactor₂Introducing the gas of S into a catalyst bed layer of a microwave reactor, and carrying out H reaction at the temperature of 550-700 DEG C₂S is directly decomposed into hydrogen and sulfur.

In one embodiment, microwave-catalyzed direct decomposition of H₂The reaction temperature of S is 600-680 ℃, preferably 630-650 ℃.

When the core-shell catalyst of the present invention is used, if the conversion of hydrogen sulfide can reach 99% at 650 ℃, the conversion of hydrogen sulfide is greater than or equal to 99% at a reaction temperature higher than 650 ℃, for example, 700 ℃. However, the lower the reaction temperature, the more energy-saving and environment-friendly, so the preferable microwave catalysis of the invention directly decomposes H₂The reaction temperature of S is 600-680 ℃, and more preferably 630-650 ℃.

In a specific embodiment, H is contained₂The content of hydrogen sulfide in the S gas is 1 to 50 vol%, preferably 10 to 20 vol%.

Compared with the prior art, the invention has the following advantages: the invention not only can directly decompose H with high efficiency₂S waste gas, and hydrogen resources and valuable sulfur can be obtained. The Mo provided by the invention₂The C @ BN microwave catalyst has extremely high catalytic activity at low temperature, and H is introduced when the reaction temperature is as low as 650 ℃ in a microwave catalytic reaction mode₂Standard gas with 15% S content, H₂The S conversion can be as high as 99.9%, indicating almost complete decomposition, and is significantly higher than the corresponding H in the conventional reaction mode₂S balance conversion rate. Hair brushThe microwave catalyst provided by the invention has low preparation cost and good wave-absorbing performance, and can realize efficient and direct decomposition of hydrogen sulfide at a lower reaction temperature.

Drawings

FIG. 1 shows Mo, a core-shell catalyst, in example 1₂C@BN-800,Mo₂C @ BN-900 and Mo₂XRD pattern of C @ BN-1000.

FIG. 2 shows Mo as a core-shell catalyst in example 1₂C @ BN-800 and Mo₂FT-IR plot of C @ BN-1000.

FIG. 3 shows Mo in example 1₂TEM image of C @ BN-1000 catalyst.

FIG. 4 shows Mo in example 1₂TEM image of C @ BN-800 catalyst.

FIG. 5 shows Mo catalyst in example 1₂C @ BN-1000, in particular B1 s.

FIG. 6 shows Mo catalyst in example 1₂C @ BN-800, in particular B1 s.

FIG. 7 shows Mo catalyst in example 1₂C @ BN-1000, in particular to N1 s.

FIG. 8 shows Mo catalyst in example 1₂C @ BN-800, in particular N1 s.

FIG. 9 shows Mo core-shell catalyst of example 1₂C@BN-800、Mo₂C @ BN-900 and Mo₂C @ BN-1000, under different temperatures and under the action of microwaves, is used for catalyzing the raw material conversion rate and equilibrium conversion rate of the decomposition of hydrogen sulfide.

Detailed Description

The present invention is described in detail below by way of examples, but the scope of the claims of the present invention is not limited to these examples. Meanwhile, the embodiments only give some conditions for achieving the purpose, and do not mean that the conditions must be met for achieving the purpose.

Example 1

This example shows a core-shell catalyst Mo according to the invention₂A preparation method and an activation method of C @ BN.

First of allStep one, 6g of ammonium molybdate tetrahydrate is weighed and added into 300mL of ethylene glycol to be stirred for 30 min. Then, 36mL of HNO was added with vigorous stirring₃Stirring was continued for 30 min. The mixed solution was then transferred to a 500mL autoclave. The reaction is kept at 160 ℃ for hydrothermal reaction for 14-24 h.

And step two, naturally cooling the reaction kettle in the step one, performing suction filtration, washing with distilled water and absolute ethyl alcohol for several times, and drying in a vacuum drying oven at 100 ℃ overnight.

Thirdly, putting the sample dried in the second step into a magnetic boat, putting the magnetic boat into a tube furnace, and then introducing N₂And roasting at 500 ℃ for 5 h. MoO is obtained after this step₂And (3) powder.

Step four, weighing 3.844g of MoO calcined in the step three₂Dispersing the powder sample in a mixed solvent of 225mL of distilled water and 225mL of absolute ethyl alcohol, firstly carrying out ultrasonic treatment for 30min, then stirring for 30min, then adding 1.85g of boric acid, continuing stirring for 30min, then adding 9g of urea, stirring for 36h in a 65 ℃ water bath kettle by using a preservative film for sealing, finally transferring to a 65 ℃ drying box, and evaporating the solvent for drying. Obtaining the precursor of the catalyst.

Fifthly, putting the sample dried in the fourth step into a magnetic boat, putting the magnetic boat into a tube furnace, and introducing NH₃And the sample was calcined at the target temperature for 2 hours. The calcination temperatures were 800, 900 and 1000 ℃. Is named Mo₂C@BN-800、Mo₂C @ BN-900 and Mo₂C @ BN-1000. In this step, core-shell Mo is obtained₂C @ BN catalyst.

Sixthly, vulcanizing the catalyst prepared in the fifth step for 2 hours at 450 ℃, and introducing H₂S and H₂The gas velocity is 40-60 mL/min and 120-160 mL/min respectively.

FIG. 1 shows Mo, a core-shell catalyst, in example 1₂C@BN-800,Mo₂C @ BN-900 and Mo₂XRD pattern of C @ BN-1000. Wherein three spectral lines from bottom to top respectively represent Mo₂C@BN-800,Mo₂C @ BN-900 and Mo₂C @ BN-1000. From XRD patterns, Mo appears in all three catalysts₂Diffraction peak of C, corresponding to α -Mo₂C(JCPDS Card No.35-0787)，Proves the MoO₂The carbonization reaction can occur at the calcining temperature higher than 800 ℃, and finally Mo is formed₂C. But because of Mo₂C @ BN-800 and Mo₂The BN shell layer of the two catalysts C @ BN-900 is thin, and the diffraction peak of the catalyst cannot be detected by XRD. And Mo₂C @ BN-1000 shows a BN diffraction peak, corresponding to BN (JCPDS Card No.18-0251), and due to the higher calcination temperature, the formed BN shell is thicker and has higher content, and can be detected by XRD.

FIG. 2 shows Mo as a core-shell catalyst in example 1₂C @ BN-800 and Mo₂FT-IR plot of C @ BN-1000. Wherein two spectral lines from bottom to top respectively represent Mo₂C @ BN-800 and Mo₂C @ BN-1000 FT-IR line. According to FT-IR, the h-BN structure is 1400 and 782cm^-1Two strong characteristic absorption bands exist nearby, and are respectively at Mo₂C @ BN-800 and Mo₂C @ BN-1000 was observed in the IR spectrum of the sample. Wherein, the thickness is 1400cm^-1Has a strong peak at 782cm^-1There is a weak zone due to the tensile vibration of B-N and the bending vibration of B-N-B, respectively. Indicating the formation of BN in the catalyst.

FIG. 3 and FIG. 4 are Mo in example 1, respectively₂C @ BN-1000 catalyst and Mo₂TEM image of C @ BN-800 catalyst. From the TEM image, Mo can be seen₂C @ BN-800 and Mo₂Mo in C @ BN-1000 catalyst₂C is coated by BN, and TEM proves that BN is generated. In addition, as can be seen from FIGS. 3 to 4, Mo is₂The C @ BN-800 catalyst forms a BN shell which is very few and very heterogeneous, and Mo₂The shell layer formed by the C @ BN-1000 catalyst is relatively uniform and is about 3-7 layers.

To further demonstrate the formation of BN in the core-shell catalysts of the invention, we conducted Mo on the catalyst₂C @ BN-1000 and Mo₂C @ BN-800 is subjected to XPS characterization. FIG. 5 shows Mo catalyst in example 1₂C @ BN-1000, in particular B1 s. FIG. 6 shows Mo catalyst in example 1₂C @ BN-800, in particular B1 s. FIG. 7 shows Mo catalyst in example 1₂C @ BN-1000, in particular to N1 s. FIG. 8 shows Mo catalyst in example 1₂C @ BN-800, in particular N1 s. In the B1s and N1s maps shown in FIGS. 5-8, BN formation was demonstrated in both catalysts.

Example 2

This example is to examine Mo in the core-shell catalyst described in example 1₂Application of C @ BN in microwave catalytic direct decomposition of H₂And (5) application effect of S.

In a laboratory, the method is specifically implemented, and H is₂S Standard gas is N provided by Dalianda Special gas Co.Ltd₂And H₂S in the mixture, wherein H₂The S content was 15 vol%.

Detection of H₂The gas chromatograph (2) model is Agilent GC 7890A.

The microwave catalysts prepared in example 1 were filled in a quartz tube reactor to form catalyst beds, respectively, with a filling amount of 2g and a mesh number of 20-60 mesh. Introduction of H₂S Standard gas (15 vol% H is used in the invention)₂S and 85 vol% N₂The mixed gas of (2) was subjected to an experiment) the flow rate was 60mL/min, and the reaction pressure was normal pressure. Regulating microwave power, changing the reaction bed temperature of the catalyst to maintain the bed temperature at 450 deg.C, 500 deg.C, 550 deg.C, 600 deg.C and 650 deg.C, respectively, and performing microwave catalysis to directly decompose H₂S experiments, the results are shown in Table 1, and Table 1 shows Mo at different temperatures₂C@BN-800、Mo₂C @ BN-900 and Mo₂H of C @ BN-1000 catalyst under microwave action₂Conversion of S direct decomposition.

TABLE 1

From the above table, it is understood that the decomposition rate of hydrogen sulfide increases with an increase in temperature. Mo at 650 deg.C₂H of C @ BN-1000 catalyst₂S conversion rate as high as 99.9%, indicating that H₂S is almost completely decomposed. Mo₂C @ BN-900 and Mo₂When the temperature of the C @ BN-800 catalyst bed is 650 ℃, H₂The S conversion rates are 67.4 percent and 47.1 percent respectively. It can be seen that the catalyst preparation forms a core-shell catalyst Mo₂In the process of C @ BN, the activity is highest when the calcining temperature is 1000 ℃.

FIG. 9 shows Mo core-shell catalyst of example 1₂C@BN-800、Mo₂C @ BN-900 and Mo₂C @ BN-1000, under different temperatures and under the action of microwaves, is used for catalyzing the raw material conversion rate and equilibrium conversion rate of the decomposition of hydrogen sulfide. As can be seen from FIG. 9, under microwave irradiation, Mo is present₂C@BN-800、Mo₂C @ BN-900 and Mo₂C @ BN-1000 catalyst for H₂The conversion rate of S decomposition reaction is far higher than that of H₂Thermodynamic equilibrium conversion of the S decomposition reaction. Thus, Mo₂The combined action of the C @ BN catalyst and the microwave can break H₂The chemical equilibrium of the S decomposition reaction greatly improves the conversion rate of the hydrogen sulfide.

According to other catalytic experiment conditions of the roasting temperature such as 1050 ℃, 1100 ℃ and 1200 ℃ and the spectrum representation conditions thereof, the roasting temperature in the key step of forming the core-shell type catalyst is preferably 900-1100 ℃, and more preferably 950-1050 ℃. Too low a calcination temperature during the formation of the core-shell type catalyst results in insufficient thickness of the BN shell, and thus the low temperature catalytic performance of the catalyst is limited. Too high a calcination temperature may also result in destruction of the catalyst structure.

Comparative example 1

This comparative example is a method for preparing and activating a non-core-shell molybdenum-containing catalyst powder.

In the first step, 6.000g of ammonium molybdate tetrahydrate is weighed into 300mL of ethylene glycol and stirred for 30 min. Then, 36mL of HNO was added with vigorous stirring₃Stirring was continued for 30 min. The mixed solution was then transferred to a 500mL autoclave. The reaction is kept at 160 ℃ for hydrothermal reaction for 14-24 h.

Thirdly, putting the sample dried in the second step into a magnetic boat, putting the magnetic boat into a tube furnace, and then introducing N₂And roasting at 500 ℃ for 5 h. Obtained after this stepMoO₂And (3) powder.

Fourthly, the sample obtained in the third step is put into a porcelain boat, the porcelain boat is put into a tube furnace, and then N is introduced₂And roasting at 1000 ℃ for 2 h. Obtaining the non-core-shell type molybdenum-containing catalyst powder.

Fifthly, vulcanizing the catalyst prepared in the fourth step at 450 ℃ for 2H, and introducing H₂S and H₂The gas velocity is 40-60 mL/min and 120-160 mL/min respectively. Obtaining a non-core-shell type molybdenum-containing catalyst sample.

Comparative example 2

This comparative example was conducted to examine the use of the non-core-shell molybdenum-containing catalyst described in comparative example 1 for microwave-catalyzed direct decomposition of H₂And (5) application effect of S.

The partially vulcanized non-core-shell molybdenum-containing catalyst microwave catalyst prepared in the comparative example 1 is filled in a quartz tube reactor to form a catalyst bed layer, the filling amount is 2g, and the mesh number is 20-60 meshes. Introduction of H₂S Standard gas (15 vol% H is used in the invention)₂S and 85 vol% N₂The mixed gas of (2) was subjected to an experiment) the flow rate was 60mL/min, and the reaction pressure was normal pressure. Regulating microwave power, changing the reaction bed temperature of the catalyst to maintain the bed temperature at 450 deg.C, 500 deg.C, 550 deg.C, 600 deg.C and 650 deg.C, respectively, and performing microwave catalysis to directly decompose H₂S experiment, the experimental results are shown in Table 2, and Table 2 shows the conversion rate of the non-core-shell type molybdenum-containing catalyst under the action of microwaves at different temperatures.

TABLE 2

From the above table, H is within the temperature range of 450-650 deg.C₂The S conversion increases with increasing bed temperature. The conversion was 26.3% at 450 ℃, 35.5% at 500 ℃, 44.5% at 550 ℃, 66.4% at 600 ℃ and only 79.5% at 650 ℃. In contrast, the conversion rate of the BN-coated Mo2C @ BN-1000 in the invention is as high as 99.9% at 650 ℃. It can be seen that the present inventionThe core-shell type catalyst has a structure corresponding to H₂The conversion of the S decomposition reaction is much higher than the uncoated catalyst in comparative example 1.

In addition, the non-core-shell type molybdenum-containing catalyst in the comparative example and the core-shell type catalyst in the invention have low conversion rate of hydrogen sulfide when being catalyzed at 450 ℃ and 500 ℃, and the reaction has no industrial application value. In addition, under the condition of keeping high conversion rate of raw materials, the lower the catalytic reaction temperature is, the more energy-saving and environment-friendly. Therefore, the reaction temperature for catalyzing the direct decomposition of the hydrogen sulfide corresponding to the catalyst is preferably 550-700 ℃, and more preferably 600-680 ℃.

Comparative example 3

It is known from the published data of the prior art that in the conventional reaction mode without using microwave heating, when hydrogen sulfide is directly decomposed without adding a catalyst, hydrogen sulfide is hardly decomposed at a temperature of 800 ℃ or lower.

Comparative example 4

Table 3 shows Mo at different temperatures₂C @ BN-1000 and prior art catalyst 30% NiS/30% gamma-Al₂O₃/40％BaMn_0.2Cu_0.8O₃The conversion under the action of microwaves was compared.

TABLE 3

The invention patent CN104437553A provides a microwave catalyst, which is a composite catalyst comprising an active component and a cocatalyst component, wherein the active component is nickel sulfide and/or cobalt sulfide, and the cocatalyst component is a perovskite catalyst component; the microwave catalyst also optionally comprises a carrier, wherein the carrier is one or more selected from gamma-Al 2O3, activated carbon, a ZSM-5 molecular sieve and a ZSM-11 molecular sieve; in the composite catalyst, the content of an active component is 10-60 wt%, the content of a carrier is 0-60 wt%, and the content of a cocatalyst component is 20-90 wt%. 30 percent NiS/30 percent gamma-Al prepared by the method provided by the invention₂O₃/40％BaMn_0.2Cu_0.8O₃The catalyst catalyzes the direct decomposition of hydrogen sulfide under the microwave condition to obtain H at different reaction temperatures₂Conversion of S. As can be seen from Table 3, under microwave irradiation, Mo provided in the present invention₂C @ BN-1000 core-shell type microwave catalyst for H₂The conversion rate of S decomposition reaction is obviously higher than 30 percent of NiS/30 percent of gamma-Al₂O₃/40％BaMn_0.2Cu_0.8O₃A catalyst. Thus, Mo₂The C @ BN-1000 core-shell type microwave catalyst is a high-effective direct decomposition of H₂S, microwave catalyst.

Comparative example 5

Table 4 shows the MoN at 650 ℃ reaction temperature_x@SiO₂、MoC_x@SiO₂、MoS₂@SiO₂、MoC_x-MoN_y@SiO₂And Mo₂C @ BN-1000 catalyst conversion rate under the action of microwave.

TABLE 4

The invention patent application CN109821564A previously published by the applicant provides a preparation method of a coated catalyst, the catalyst comprises a molybdenum-based compound core structure and a silicon dioxide shell structure coated outside, and the molybdenum-based compound core structure is one or more of molybdenum disulfide, molybdenum carbide and molybdenum nitride. MoN prepared by the method provided therein_x@SiO₂、MoC_x@SiO₂、MoS₂@SiO₂、MoC_x-MoN_y@SiO₂The four catalysts can catalyze the direct decomposition of hydrogen sulfide under the microwave condition, and the corresponding H corresponds to the reaction temperature of 650 DEG C₂The S conversion was 87.6%, 79.5%, 76.8%, 89.1%, respectively. Mo provided in the invention₂C @ BN-1000 catalyst is as high as 99.9% at 650 ℃. Mo to explain this patent₂The activity of the C @ BN-1000 core-shell type microwave catalyst at a lower reaction temperature (650 ℃) is higher than that of a coated catalyst in the prior art.

As can be seen from the comparison of the above examples and comparative examples, the Mo provided by the present invention₂The conversion rate of hydrogen sulfide of the C @ BN-1000 core-shell type microwave catalyst at a lower temperature of 650 ℃ can reach 99.9 percent, which shows that H₂S is almost completely decomposed. The combined action of the catalyst and the microwave can break the decomposition reaction balance of the hydrogen sulfide, greatly improve the conversion rate of the hydrogen sulfide and realize the purpose of efficiently decomposing the hydrogen sulfide at a lower reaction temperature.

The above embodiments are merely illustrative of the superiority of the present invention and do not limit the scope of the invention, and all modifications made within the scope of the disclosure or practical applications are within the scope of the present invention.

The foregoing is a more detailed description of the invention in connection with specific preferred embodiments and it is not intended that the invention be limited to these specific details. For those skilled in the art to which the invention pertains, several simple deductions and substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.

Claims

1. A preparation method of a core-shell microwave catalyst comprises Mo₂C-core structure and BN-shell structure coated outside, i.e. Mo₂C @ BN catalyst, the preparation method comprising the steps of:

step A, preparing powdery molybdenum dioxide by taking ammonium molybdate as a raw material;

b, uniformly mixing the powdery molybdenum dioxide with a solvent, adding boric acid and urea, reacting, and evaporating the solvent to obtain a precursor of the core-shell microwave catalyst; and roasting the precursor at 800-1200 ℃ in a nitrogen-containing atmosphere to obtain the core-shell microwave catalyst, wherein the solvent comprises water and/or ethanol, and the nitrogen-containing atmosphere contains nitrogen and/or ammonia.

2. The method according to claim 1, wherein the calcination temperature in step B is 900 to 1100 ℃, preferably 950 to 1050 ℃.

3. The method of claim 1, wherein the step a of preparing powdered molybdenum dioxide comprises: and uniformly mixing ammonium molybdate and ethylene glycol, adding nitric acid, continuously stirring, carrying out hydrothermal reaction at 120-180 ℃, washing the generated solid with water and ethanol, drying and roasting at 400-600 ℃ to obtain the powdery molybdenum dioxide.

4. The preparation method according to claim 1, wherein in the step B, the atomic molar ratio of the boron element in the boric acid to the molybdenum element in the molybdenum dioxide is 1:10 to 10:1, preferably 1:2 to 2: 1; the molar ratio of the boric acid to the urea is 1: 0.2-1: 30, preferably 1: 2-1: 6; preferably, ammonia gas is used as the nitrogen-containing atmosphere in the calcination in the step B.

5. The method according to any one of claims 1 to 4, further comprising a step C: heating the core-shell microwave catalyst obtained in the step B to 300-800 ℃, wherein the core-shell microwave catalyst contains H₂S and H₂Carrying out sulfidation treatment on the mixed gas for 0.5-5 hours to obtain an activated core-shell type microwave catalyst; preferably in step C, H₂S and H₂H in the mixed gas of₂S and H₂The gas volume flow rate ratio of (1: 10) to (1: 1), preferably 1:4 to (1: 2).

6. The core-shell microwave catalyst prepared by the method according to any one of claims 1 to 5.

7. A core-shell microwave catalyst contains Mo₂C-core structure and BN-shell structure coated outside, i.e. Mo₂C @ BN catalyst.

8. Core-shell type catalyst for microwave catalytic direct decomposition of H₂S method, characterized in thatIn that, the catalyst comprises Mo₂C-core structure and BN-shell structure coated outside, i.e. Mo₂C @ BN catalyst; the method comprises arranging the core-shell type catalyst bed layer containing H in a microwave reactor₂Introducing the gas of S into a catalyst bed layer of a microwave reactor, and carrying out H reaction at the temperature of 550-700 DEG C₂S is directly decomposed into hydrogen and sulfur.

9. The method of claim 8, wherein microwave-catalyzed direct decomposition of H₂The reaction temperature of S is 600-680 ℃, preferably 630-650 ℃.

10. The method of claim 8, comprising H₂The content of hydrogen sulfide in the S gas is 1 to 50 vol%, preferably 10 to 20 vol%.