A hollow nanotube catalyst and its preparation method and application

Abstract

The present invention provides a hollow nanotubular catalyst and its preparation method and application, which belong to the field of flue gas treatment technology. The catalyst has a uniform hollow nanotube structure with an outer diameter of about 9.0-10.0nm and an inner diameter of about 4.0-4.5nm. The active metal is dispersed on the hollow nanotube in an amorphous structure. The preparation method is to use Co-Mn / TiO2 as a precursor, mix it evenly with hexadecyltrimethylammonium bromide and an alkaline solution, and place it in a homogeneous reactor for hydrothermal treatment. The sample is collected by centrifugation, washed with deionized water, dilute nitric acid and ethanol to neutrality, dried, and calcined. The catalyst is applied to the field of synergistic denitrification and mercury removal, thereby improving the denitrification performance of the catalyst while having a high synergistic mercury oxidation removal performance, and has the potential for industrial application.

Description

Technical Field

[0001] The present invention belongs to the technical field of flue gas treatment, and in particular relates to a hollow nano-tubular catalyst and a preparation method and application thereof. Background Art

[0002] Coal-fired power plants are one of the main sources of anthropogenic emissions of air pollutants. Among these air pollutants, nitrogen oxides (NO x ) and mercury (Hg 0 ) has received widespread attention in recent years. x It will bring about a series of ecological problems such as acid rain, photochemical smog, and ozone layer depletion. Mercury is persistent, bioaccumulative, and highly toxic, which can seriously damage human health and the ecological environment. However, the separated Hg 0 and NO x The control technology has the disadvantages of large floor space, high equipment investment and high operating cost. Therefore, the NO removal is carried out in a purification device. x and Hg 0 It has important practical significance.

[0003] In the synergistic removal of NO x and Hg 0 During the process, NO is reduced on the catalyst, while Hg 0 is oxidized to HgO, thus achieving NO reduction in one purification device. x and Hg 0 The key issue for efficient removal of NO is to rationally improve the redox balance of the catalyst to achieve NO x and Hg 0 The morphology and structure of the catalyst usually affect its redox properties and thus change its catalytic performance. Based on this, by optimizing the morphology and structure to improve the redox balance of the catalyst, a highly efficient synergistic denitrification and mercury removal catalyst was developed for the synergistic removal of NO from flue gas. x and Hg 0 becomes particularly important.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide a hollow nanotube catalyst and a preparation method and application thereof to solve the above problems.

[0006] In order to achieve the above objectives, the present invention adopts the following technical solutions:

[0007] The present invention provides a hollow nanotube catalyst having a uniform hollow nanotube structure with an outer diameter of about 9.0-10.0 nm, an inner diameter of about 4.0-4.5 nm, and a specific surface area of ​​245-350 m 2 / g, and the active metal is dispersed on the hollow nanotubes in an amorphous structure. After the hollow nanotube catalyst is formed, the reaction rate of the reactant molecules on its surface is accelerated, and the enhanced surface acidity and abundant oxygen vacancies greatly improve the catalytic performance of the catalyst, thereby efficiently removing NO and Hg from the flue gas. 0 .

[0008] Furthermore, the active metals include cobalt and manganese.

[0009] The present invention also provides a method for preparing the hollow nanotubular catalyst: using Co-Mn / TiO2 as a precursor, mixing it evenly with cetyltrimethylammonium bromide (CTAB) and an alkaline solution, and then placing it in a homogeneous reactor for hydrothermal treatment, collecting the sample by centrifugation, washing it with deionized water, dilute nitric acid and ethanol in sequence until the pH value is neutral, and then drying and calcining to obtain the catalyst.

[0010] The hydrothermal precursor formed by Co-Mn / TiO2, hexadecyltrimethylammonium bromide and alkaline solution forms hollow nanotubes after hydrothermal treatment, and the addition of hexadecyltrimethylammonium bromide can make the hollow nanotubes more uniform.

[0011] Furthermore, the mass ratio of hexadecyltrimethylammonium bromide to Co-Mn / TiO2 is 0.05-0.15:1.

[0012] Furthermore, the temperature of the hydrothermal treatment is 130-160° C., and the time of the hydrothermal treatment is 20-26 hours.

[0013] Preferably, the alkaline solution comprises a sodium hydroxide solution. More preferably, the concentration of the sodium hydroxide solution is 8-10 mol / L.

[0014] More preferably, the alkaline solution comprises a mixed solution of sodium hydroxide and ammonia water. The addition of a small amount of ammonia water has been shown to enable hexadecyltrimethylammonium bromide to function stably in the hydrothermal precursor mixing process and the hydrothermal treatment process in the early stage of the reaction; however, if too much ammonia water is added, a large amount of gas will be generated during the hydrothermal treatment, causing safety hazards.

[0015] Furthermore, the Co-Mn / TiO2 is in the form of nanoparticles. By adding hexadecyltrimethylammonium bromide and hydrothermal treatment, the morphology and structure of the Co-Mn / TiO2 nanoparticles are changed. During this process, cobalt and manganese do not agglomerate, but only form a hollow tubular structure. Therefore, this method can make manganese and cobalt evenly dispersed, realizing the in-situ reconstruction of Co-Mn / TiO2 nanoparticles.

[0016] Furthermore, the calcination is carried out in an air atmosphere, the calcination temperature is 320-420° C., and the calcination time is 2-4 hours.

[0017] The present invention also provides an application of the hollow nanotube catalyst: the catalyst is used for coordinated denitration and demercuration.

[0018] Furthermore, the application includes: loading the catalyst into a fixed bed reactor, controlling the reaction temperature at 150-240°C, and simultaneously introducing NO, NH3, O2 and Hg 0 The reaction was carried out and the reaction space velocity was controlled at 3000h -1 -100000h -1 .

[0019] The hollow nanotube catalyst provided by the present invention has a uniform hollow nanotube structure with an outer diameter of about 9.0-10.0 nm, an inner diameter of about 4.0-4.5 nm, and a specific surface area of ​​245-350 m 2 / g, in which manganese and cobalt exist in an amorphous structure and are well dispersed on the hollow nanotubes. By constructing a hollow nanotube structure, the redox balance of the catalyst is rationally improved. Between 150-240 ° C, the NO conversion rate is above 98%, and Hg 0 The conversion rate approaches 100%, while maintaining N2 selectivity above 95%. This invention is the first to prepare a hollow nanotube Co-Mn / TiO2 catalyst for synergistic denitrification and mercury removal, achieving enhanced catalyst denitrification performance while also achieving high synergistic mercury oxidation removal performance, showing potential for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0021] Figure 1 This is a TEM image of the hollow nanotube catalyst of Example 1 of the present invention magnified 100,000 times;

[0022] Figure 2 This is a TEM image of the hollow nanotube catalyst of Example 1 of the present invention magnified 500,000 times;

[0023] Figure 3 This is a TEM image of the hollow nanotube catalyst of Example 1 of the present invention magnified 1,000,000 times;

[0024] Figure 4 This is a TEM image of the hollow nanotube catalyst of Example 1 of the present invention magnified 800,000 times;

[0025] Figure 5 for Figure 4 A local magnified view of a single nanotube;

[0026] Figure 6 This is an X-ray energy spectrum analysis diagram of cobalt, manganese, and titanium elements in the hollow nanotubes of Example 1 of the present invention;

[0027] Figure 7 This is an X-ray energy spectrum analysis diagram of the titanium element in the hollow nanotubes of Example 1 of the present invention;

[0028] Figure 8 This is an X-ray energy spectrum analysis diagram of manganese element in the hollow nanotubes of Example 1 of the present invention;

[0029] Figure 9 This is an X-ray energy spectrum analysis diagram of the cobalt element in the hollow nanotubes of Example 1 of the present invention. DETAILED DESCRIPTION

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0031] In the present invention, any unspecified ratio of substances should be understood as an arbitrary ratio; any unspecified unit of the ratio of substances should be understood as a mass ratio.

[0032] Example 1

[0033] A hollow nanotube catalyst, such as Figure 1-5 As shown, it has a uniform hollow nanotube structure with an outer diameter of about 9.6 nm, an inner diameter of about 4.2 nm, and a measured specific surface area of ​​296 m 2 / g. Figure 6-9As shown, manganese and cobalt exist in an amorphous structure and are well dispersed on the hollow nanotubes. Figure 7 It can be seen that the main structure of the hollow nanotubes is titanium and is evenly distributed. Figure 8 and Figure 9 It can be seen that manganese and cobalt elements are dispersed very evenly on the hollow nanotubes.

[0034] The preparation method of the hollow nanotube catalyst is as follows:

[0035] Co-Mn / TiO2 nanoparticles and CTAB were added to a mixed solution of 10 mol / L sodium hydroxide solution and ammonia water, with the mass ratio of sodium hydroxide solution to ammonia water being 99:1, the mass ratio of CTAB to Co-Mn / TiO2 nanoparticles being 0.09:1, and the feed ratio of Co-Mn / TiO2 nanoparticles to sodium hydroxide solution being 0.02 g / mL. The mixture was uniformly mixed by ultrasonic treatment for 1 h, and then transferred to a polytetrafluoroethylene-lined stainless steel autoclave and placed in a homogeneous reactor for hydrothermal treatment at 150°C for 24 h. After the autoclave was cooled to room temperature, the solid sample was collected by centrifugation and then washed with deionized water, dilute nitric acid, and anhydrous ethanol in sequence until neutral. The sample was then dried in a forced air drying oven at 80°C for 24 h and finally calcined at 400°C in air atmosphere for 2 h with a heating rate of 2°C / min to obtain hollow nanotubular Co-Mn / TiO2 catalyst. The catalyst was loaded into a fixed bed reactor, the reaction temperature was controlled at 150°C, and a simulated flue gas containing 500ppm NO, 500ppm NH3, 5% O2, 115μg / m 3 Hg 0 , N2 was used as the balance gas, and the reaction space velocity was controlled at 60000h -1 The conversion rate of NO in steady state is 99%, and Hg 0 The conversion rate was 100% and the N2 selectivity was 98%.

[0036] Example 2

[0037] A hollow nanotube catalyst with a uniform hollow nanotube structure, an outer diameter of about 9.1 nm, an inner diameter of about 4.0 nm, and a specific surface area of ​​278 m 2 / g. Its preparation method is as follows:

[0038] Co-Mn / TiO2 nanoparticles and CTAB were added to a mixed solution of 10 mol / L sodium hydroxide solution and ammonia water, with the mass ratio of sodium hydroxide solution to ammonia water being 99:1, the mass ratio of CTAB to Co-Mn / TiO2 nanoparticles being 0.12:1, and the feed ratio of Co-Mn / TiO2 nanoparticles to sodium hydroxide solution being 0.02 g / mL. The mixture was uniformly mixed by ultrasonic treatment for 1 h, and then transferred to a polytetrafluoroethylene-lined stainless steel autoclave and placed in a homogeneous reactor for hydrothermal treatment at 150°C for 24 h. After the autoclave was cooled to room temperature, the solid sample was collected by centrifugation and then washed with deionized water, dilute nitric acid, and anhydrous ethanol in sequence until neutral. The sample was then dried in a forced air drying oven at 80°C for 24 h and finally calcined at 320°C in air atmosphere for 4 h at a heating rate of 2°C / min to obtain hollow nanotubular Co-Mn / TiO2 catalyst. The catalyst was loaded into a fixed bed reactor, the reaction temperature was controlled at 210°C, and a simulated flue gas containing 500ppm NO, 500ppm NH3, 5% O2, 115μg / m 3 Hg 0 , N2 was used as the balance gas, and the reaction space velocity was controlled at 60000h -1 The conversion rate of NO in steady state is 100%, and Hg 0 The conversion rate was 100% and the N2 selectivity was 97%.

[0039] Example 3

[0040] A hollow nanotube catalyst with a uniform hollow nanotube structure, an outer diameter of about 9.6 nm, an inner diameter of about 4.2 nm, and a specific surface area of ​​296 m 2 / g. Its preparation method is as follows:

[0041] Co-Mn / TiO2 nanoparticles and CTAB were added to 8 mol / L sodium hydroxide solution, the mass ratio of CTAB to Co-Mn / TiO2 nanoparticles was 0.09:1, and the feed ratio of Co-Mn / TiO2 nanoparticles to sodium hydroxide solution was 0.02 g / mL. The mixture was uniformly mixed by ultrasonic treatment for 1 h, and then transferred to a polytetrafluoroethylene-lined stainless steel autoclave and placed in a homogeneous reactor for hydrothermal treatment at 140°C for 26 h. After the autoclave was cooled to room temperature, the solid sample was collected by centrifugation and then washed with deionized water, dilute nitric acid, and anhydrous ethanol in sequence until neutral. The sample was then placed in a forced air drying oven and dried at 80°C for 24 h. Finally, it was calcined at 380°C in air atmosphere for 3 h with a heating rate of 2°C / min to obtain a hollow nanotubular Co-Mn / TiO2 catalyst. The catalyst was loaded into a fixed bed reactor, the reaction temperature was controlled at 180°C, and a simulated flue gas containing 500ppm NO, 500ppm NH3, 5% O2, 115μg / m3 Hg 0 , N2 was used as the balance gas, and the reaction space velocity was controlled at 40000h -1 The conversion rate of NO in steady state is 98%, and Hg 0 The conversion rate was 100% and the N2 selectivity was 97%.

[0042] Example 4

[0043] A hollow nanotube catalyst with a uniform hollow nanotube structure, an outer diameter of about 9.6 nm, an inner diameter of about 4.2 nm, and a specific surface area of ​​296 m 2 / g. Its preparation method is as follows:

[0044] Co-Mn / TiO2 nanoparticles and CTAB were added to a 9 mol / L sodium hydroxide solution, with a mass ratio of CTAB to Co-Mn / TiO2 nanoparticles of 0.05:1 and a feed ratio of Co-Mn / TiO2 nanoparticles to sodium hydroxide solution of 0.025 g / mL. The mixture was uniformly mixed by ultrasonic treatment for 1 h, and then transferred to a polytetrafluoroethylene-lined stainless steel autoclave and placed in a homogeneous reactor for hydrothermal treatment at 160°C for 20 h. After the autoclave was cooled to room temperature, the solid sample was collected by centrifugation and then washed with deionized water, dilute nitric acid, and anhydrous ethanol in sequence until neutral. The sample was then placed in a forced air drying oven and dried at 80°C for 24 h. Finally, it was calcined at 400°C in an air atmosphere for 2 h with a heating rate of 2°C / min to obtain a hollow nanotubular Co-Mn / TiO2 catalyst. The catalyst was loaded into a fixed bed reactor, the reaction temperature was controlled at 180°C, and a simulated flue gas containing 500ppm NO, 500ppm NH3, 5% O2, 115μg / m 3 Hg 0 , N2 was used as the balance gas, and the reaction space velocity was controlled at 30000h -1 The conversion rate of NO in steady state is 98%, and Hg 0 The conversion rate was 100% and the N2 selectivity was 98%.

[0045] Example 5

[0046] The difference from Example 2 is that the alkaline solution does not contain ammonia. The test conditions are the same, and the conversion rate of NO in steady state is 98%, and the conversion rate of Hg 0 The conversion rate was 99% and the N2 selectivity was 95%.

[0047] Please note that the technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification. The above embodiments only express several implementation methods of the present application. The description is relatively specific and detailed, but it cannot be understood as a limitation on the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of this application, several variations and improvements can be made, which all fall within the scope of protection of this application. Therefore, the scope of protection of the patent in this application shall be based on the attached claims.

Claims

1. A hollow nanotube catalyst having a uniform hollow nanotube structure with an outer diameter of 9.0-10.0 nm and an inner diameter of 4.0-4.5 nm, wherein an active metal is dispersed in the hollow nanotube in an amorphous structure, characterized in that: The preparation method of the hollow nanotube catalyst comprises: using Co-Mn / TiO2 in the form of nanoparticles as a precursor, uniformly mixing it with hexadecyltrimethylammonium bromide and an alkaline solution, and then placing it in a homogeneous reactor for hydrothermal treatment, collecting the sample by centrifugation, washing it with deionized water, dilute nitric acid and ethanol in sequence until it is neutral, drying it, and calcining it to obtain the hollow nanotube catalyst; The mass ratio of hexadecyltrimethylammonium bromide to Co-Mn / TiO2 is 0.05-0.15:1; The alkaline solution includes a mixed solution of sodium hydroxide solution and ammonia water; The concentration of the sodium hydroxide solution is 8-10 mol / L; The mass ratio of the sodium hydroxide solution to the ammonia water is 99:

1.

2. The hollow nanotube catalyst according to claim 1, wherein The temperature of the hydrothermal treatment is 130-160° C., and the time of the hydrothermal treatment is 20-26 h.

3. The hollow nanotube catalyst according to claim 1, wherein The calcination is carried out in an air atmosphere at a temperature of 320-420° C. and for a time of 2-4 h.

4. A use of the hollow nanotube catalyst according to claim 1, characterized in that: The catalyst is used for coordinated denitrification and mercury removal.

5. The use of the hollow nanotube catalyst according to claim 4, characterized in that: The catalyst was loaded into a fixed bed reactor, the reaction temperature was controlled at 150-240 °C, and NO, NH3, O2 and Hg were introduced simultaneously. 0 The reaction was carried out with the reaction space velocity controlled at 3000 h -1 -100000 h -1 .

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