Nitrogen-doped porous carbon-TiO2 composite carrier, preparation method thereof and low-temperature denitration catalyst

Abstract

The invention provides a nitrogen-doped porous carbon-TiO2 composite carrier and a preparation method thereof and a low-temperature denitration catalyst.The nitrogen-doped porous carbon-TiO2 composite carrier comprises nitrogen-doped porous carbon and nano TiO2, the nitrogen-doped porous carbon is of a two-dimensional carbon sheet layered structure, contains open micropores and mesopores at the same time and is of a hierarchical pore structure, and the diameter of the nitrogen-doped porous carbon is larger than that of the nano TiO2. The nano TiO2 is uniformly dispersed on the surface of the two-dimensional carbon sheet layered structure; the content of the nano TiO2 is 75-90wt% by taking the total weight of the composite carrier as 100%. The nitrogen-doped porous carbon-TiO2 composite carrier has excellent specific surface area, porosity and titanium dioxide dispersibility, can realize complementary advantages of nitrogen-doped porous carbon and TiO2 carriers when being used as a low-temperature denitration catalyst loading substrate, and ensures effective combination of active components and good mass transfer and adsorption of reactants in a denitration reaction process; the adsorption performance, the low-temperature denitration performance and the stability of the catalyst are potentially improved.

Description

Technical Field

[0001] The present invention relates to a nitrogen-doped porous carbon-TiO 2 The invention relates to a composite carrier and a preparation method thereof and a low-temperature denitration catalyst, belonging to the technical field of environmental protection catalyst development and air pollutant control. Background Art

[0002] NH 3 Selective catalytic reduction (NH 3 -SCR) is the most widely used fixed source nitrogen oxide treatment technology. Commercial SCR catalysts are mainly V 2 O 5 -WO 3 / TiO 2 or V 2 O 5 -MoO 3 / TiO 2 The denitrification temperature of the system is generally 300-420°C. However, with the rapid iteration of synthetic heating devices used by refining and chemical enterprises, the flue gas temperature to be treated is often lower than 250°C, so the development of new low-temperature denitrification catalysts has become a top priority.

[0003] The carrier material of the denitrification catalyst is of great significance to ensure the stability of the catalyst, increase the specific surface area and mass transfer level of the catalyst, and improve the uniformity of the active components. 2 It has the advantages of high thermal stability, high mechanical strength and good sulfur resistance, and can be used as a carrier of various active components. 2 The raw material price is relatively low and environmentally friendly, and it is the most commonly used denitrification catalyst support material, such as VW-Ti, Mn-Ce-Ti and other systems. 2 The denitrification activity of the supported catalyst decreased significantly under low temperature conditions. This is partly due to the fact that TiO 2 The low surface area of ​​TiO limits the mass transfer level of the catalyst under low temperature conditions. 2 Due to the small particle size, they are easy to agglomerate during the synthesis process, which weakens the interface effect with the active components.

[0004] In order to improve the low-temperature activity of denitrification catalysts, carbon materials with high specific surface area and high chemical stability, such as activated carbon (AC), activated carbon fiber (ACF), carbon nanotubes (CNTs) and graphene (GR), have also been studied as carrier materials for low-temperature denitrification catalysts. In particular, carbon nanotubes and graphene have been shown to significantly improve the reductant NH 3 While adsorbing, it improves the redox ability of the active components of the catalyst. However, carbon materials used alone as denitrification catalyst carrier materials have always had problems such as poor water resistance and sulfur resistance.

[0005] Therefore, a new type of nitrogen-doped porous carbon-TiO is provided. 2 Composite carriers and preparation methods thereof and low-temperature denitration catalysts have become technical issues that urgently need to be solved in this field. Summary of the invention

[0006] In order to solve the above-mentioned shortcomings and deficiencies, an object of the present invention is to provide a nitrogen-doped porous carbon-TiO 2 Composite carrier.

[0007] Another object of the present invention is to provide the nitrogen-doped porous carbon-TiO 2 A method for preparing a composite carrier.

[0008] Another object of the present invention is to provide a low-temperature denitration catalyst, the carrier of which is the nitrogen-doped porous carbon-TiO 2 Composite carrier. The nitrogen-doped porous carbon-TiO 2 The composite support has excellent specific surface area, porosity and titanium dioxide dispersion. When used as a support substrate for low-temperature denitration catalysts, nitrogen-doped porous carbon and TiO 2 The two carriers complement each other in their advantages, ensuring effective binding of active components and good mass transfer and adsorption of reactants during the denitrification reaction, and have the potential to improve the adsorption performance, low-temperature denitrification performance and stability of the catalyst.

[0009] In order to achieve the above objectives, the present invention provides a nitrogen-doped porous carbon-TiO 2 Composite support, wherein the nitrogen-doped porous carbon-TiO 2 The composite support includes nitrogen-doped porous carbon and nano-TiO 2 The nitrogen-doped porous carbon is a two-dimensional carbon sheet structure and contains open micropores and mesopores, and has a multi-level pore structure. 2 Evenly dispersed on the surface of the two-dimensional carbon sheet structure;

[0010] Doping porous carbon-TiO with nitrogen 2 The total weight of the composite carrier is 100%, nano-TiO 2 The content is 75-90wt%.

[0011] The present invention does not make specific requirements on the nitrogen content of the nitrogen-doped porous carbon in the low-temperature denitration catalyst, which varies with the nitrogen source, ie, the polyamino compound.

[0012] As a specific embodiment of the composite carrier described above in the present invention, the nano-TiO 2 The particle size is 3-8nm.

[0013] As a specific embodiment of the composite carrier described above in the present invention, the nitrogen-doped porous carbon-TiO 2 The specific surface area of ​​the composite carrier is 180-400m 2 / g.

[0014] On the other hand, the present invention also provides the nitrogen-doped porous carbon-TiO 2 A method for preparing a composite carrier, wherein the preparation method comprises:

[0015] Step (1): uniformly mixing alkali metal salt of citrate and / or alkali metal salt of sorbate, a polyamino compound and aniline, placing the obtained solid-liquid mixture in a reactor for heterogeneous reaction, and after the reaction, performing a staged heat treatment on the obtained solid product in an inert atmosphere to obtain a nitrogen-doped porous carbon material;

[0016] Step (2): uniformly mixing the nitrogen-doped porous carbon material and the solid titanium salt, and then heat-treating the obtained solid mixture in an inert atmosphere to obtain nitrogen-doped porous carbon-TiO 2 Composite carrier.

[0017] The nitrogen-doped porous carbon-TiO provided by the present invention 2 The preparation method of the composite carrier is simple to operate and low in cost. The obtained nitrogen-doped porous carbon has a high specific surface area and a two-dimensional sheet structure, and the TiO2 loaded on the porous carbon sheet is 2 The particle size of nano-TiO 2 .

[0018] As a specific embodiment of the above-mentioned preparation method of the present invention, wherein the alkali metal citrate includes potassium citrate and / or sodium citrate, etc., and the alkali metal sorbate includes potassium sorbate, etc.

[0019] As a specific embodiment of the preparation method described above, the polyamino compound includes one or a combination of organic substances containing two or more amino groups and / or imino groups.

[0020] As a specific embodiment of the preparation method described above, the polyamino compound includes one or a combination of diphenylcarbazide, phenylenediamine and melamine.

[0021] As a specific embodiment of the above preparation method of the present invention, the mass ratio of alkali metal citrate and / or alkali metal sorbate to the polyamino compound is 2-5:1.

[0022] As a specific embodiment of the above preparation method of the present invention, 0.5-1.0 mL of aniline is added for every 1 g of alkali metal citrate and / or alkali metal sorbate.

[0023] As a specific embodiment of the above preparation method of the present invention, the temperature of the heterogeneous reaction is 160-200° C. and the time is 6-12 h.

[0024] As a specific embodiment of the preparation method described above in the present invention, the segmented heat treatment includes two stages of heat treatment, wherein the temperature of the first stage of heat treatment is 250-300°C, the holding time is 2-4h, and the temperature of the second stage of heat treatment is 650-800°C, the holding time is 2-3h.

[0025] As a specific embodiment of the preparation method described above in the present invention, step (1) also includes washing the product after the segmented heat treatment until the final filtrate is neutral, and then drying the washed product to obtain the nitrogen-doped porous carbon material. However, the present invention does not make specific requirements for the specific washing operation and the detergent used, and can be reasonably adjusted and selected according to the actual needs of the on-site operation, as long as the final filtrate is neutral. For example, in some embodiments of the present invention, the washing includes first washing the product after the segmented heat treatment with dilute HCl, and then washing with water and filtering multiple times until the filtrate is neutral. In addition, the present invention does not make specific requirements for the operation and conditions of the drying, and can be reasonably adjusted according to the actual needs of the on-site operation, as long as the product can be dried. For example, in some embodiments of the present invention, the drying is carried out in a vacuum drying oven at a temperature of 80°C and a time of 12h.

[0026] As a specific embodiment of the preparation method described above in the present invention, 12-30 g of solid titanium salt is added for every 1 g of nitrogen-doped porous carbon material.

[0027] As a specific embodiment of the preparation method described above in the present invention, the solid titanium salt includes one or a combination of titanium sulfate, titanium thiosulfate, titanium oxalate and titanyl sulfate.

[0028] As a specific embodiment of the preparation method described above of the present invention, in step (2), the temperature of the heat treatment is 400-600° C., preferably 500-550° C., and the time is 2-5 h.

[0029] The present invention does not make specific requirements on the inert atmosphere used in the above-mentioned preparation method step (1) and step (2), and can be reasonably selected according to the actual needs of the on-site operation. For example, in some embodiments of the present invention, the inert atmosphere can be a nitrogen atmosphere.

[0030] In another aspect, the present invention further provides a low-temperature denitration catalyst, wherein the carrier of the low-temperature denitration catalyst is the nitrogen-doped porous carbon-TiO 2 Composite carrier.

[0031] Compared with the prior art, the beneficial technical effects that can be achieved by the present invention include:

[0032] (1) The present invention is used to prepare nitrogen-doped porous carbon-TiO 2 A dual pore-forming system is adopted for composite carriers, wherein alkali metal salts of citrate and / or alkali metal salts of sorbate serve as carbon sources and activation salts. While polymerizing with the polyamino compounds, the alkali metal ions contained in them can generate corresponding metal oxides or metal atoms in situ during high-temperature heat treatment. The metal oxides or metal atoms have the function of pore-forming by the activation salt, thereby generating mesopores in the nitrogen-doped porous carbon material. The polyamino compounds serve as nitrogen sources and pore-forming agents, wherein the amino and / or imino groups, which are thermally unstable nitrogen-containing groups, can form micropores in the nitrogen-doped porous carbon material by thermal decomposition of some nitrogen-containing groups.

[0033] (2) The nitrogen-doped porous carbon-TiO provided by the present invention 2 The nitrogen-doped porous carbon in the composite carrier has a graphene-like two-dimensional carbon sheet structure, excellent specific surface area and multi-level pore structure (containing open micropores and mesopores at the same time), and the nitrogen atoms doped in the two-dimensional carbon sheet structure can increase the local electron cloud density, thereby improving the reducibility of the porous carbon material. Nano-TiO 2 Densely distributed and highly dispersed (uniformly dispersed) on the surface of the two-dimensional carbon sheet structure, it can solve the problem of nano-TiO 2 Problems of easy agglomeration and low specific surface area.

[0034] (3) The nitrogen-doped porous carbon-TiO 2 When the composite carrier is used as a carrier of a low-temperature denitrification catalyst, it helps to increase the effective contact area between the carrier and the active component and regulate the distribution of the active component, thereby reducing the sintering and aggregation of the active component during the reaction; it can also improve the adsorption capacity during the denitrification reaction and enhance the mass transfer of the reactants; in addition, since the nitrogen-doped porous carbon has excellent reducibility, by-products such as ammonium sulfate formed in the denitrification reaction will be preferentially reduced by NO on the nitrogen-doped porous carbon, thereby avoiding the reduction in activity of the active component due to the entrapment of ammonium sulfate. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the description of the embodiments will be briefly introduced below. 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 creative work.

[0036] Figure 1 The nitrogen-doped porous carbon-TiO provided in the embodiment of the present invention 2 Schematic diagram of the process for preparing the composite carrier.

[0037] Figure 2 PC-TiO provided in Example 1 of the present invention 2 -1. n-TiO provided in Comparative Example 1 2 And the pore size distribution diagram of P25 provided in Comparative Example 2.

[0038] Figure 3a and Figure 3b The PC-TiO 2 -1 and the n-TiO provided in Comparative Example 1 2 Transmission electron microscopy image of .

[0039] Figure 4 PC-TiO provided in Example 1 of the present invention 2 -1 and the n-TiO provided in Comparative Example 1 2 Raman spectrum.

[0040] Figure 5 PC-TiO provided in Examples 1 to 3 of the present invention 2 -1~PC-TiO 2 -3's XRD curve. DETAILED DESCRIPTION

[0041] It should be noted that the term "comprises" and any variations thereof in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0042] "Scope" disclosed in the present invention is given in the form of lower limit and upper limit. It can be one or more lower limits, and one or more upper limits respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower limit and upper limit define the boundaries of a particular range. All ranges defined in this way are combinable, i.e. any lower limit can be combined with any upper limit to form a range. For example, for a specific parameter, a range of 60-120 and 80-110 is listed, and it is understood that a range of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​listed are 1 and 2, and the maximum range values ​​listed are 3, 4 and 5, then the following ranges can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.

[0043] In the present invention, unless otherwise specified, the numerical range "ab" represents an abbreviation of any real number combination between a and b, where a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed in the present invention, and "0-5" is just an abbreviation of these numerical combinations.

[0044] In the present invention, unless otherwise specified, all embodiments and preferred embodiments mentioned in the present invention can be combined with each other to form a new technical solution.

[0045] In the present invention, unless otherwise specified, all technical features and preferred features mentioned in the present invention can be combined with each other to form a new technical solution.

[0046] In the present invention, if not specifically stated, the term "two" used in this specification means "at least two".

[0047] In the present invention, unless otherwise specified, all steps mentioned herein may be performed sequentially or randomly, but are preferably performed sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0048] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the attached table, drawings and examples. The following described embodiments are some embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention. If the specific conditions are not specified in the embodiments, they are carried out according to the normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified in the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0049] Figure 1 The nitrogen-doped porous carbon-TiO provided in the embodiment of the present invention 2 A schematic diagram of the preparation method of the composite carrier is shown in FIG. Figure 1 As shown, the preparation method comprises:

[0050] S100: uniformly mixing alkali metal salt of citrate and / or alkali metal salt of sorbate, polyamino compound and aniline, placing the obtained solid-liquid mixture in a reactor for heterogeneous reaction, and after the reaction, performing a staged heat treatment on the obtained solid product in an inert atmosphere to obtain a nitrogen-doped porous carbon material;

[0051] S200: uniformly mixing the nitrogen-doped porous carbon material and the solid titanium salt, and then heat-treating the obtained solid mixture in an inert atmosphere to obtain nitrogen-doped porous carbon-TiO 2 Composite carrier.

[0052] It should be noted that the present invention limits the combination of raw materials, that is, the three types of raw materials, alkali metal salts of citrate and / or alkali metal salts of sorbate, polyamino compounds and aniline, are mixed and reacted, and the number of reactants in any of the three types except aniline can be one or more. The present invention does not limit the order of adding raw materials, that is, the solid reactants including alkali metal salts of citrate and / or alkali metal salts of sorbate and polyamino compounds can be pre-mixed and ground first, and then aniline can be added, and then the heterogeneous reaction and staged heat treatment, that is, polymerization reaction and carbonization reaction, can be continued; alkali metal salts of citrate and / or alkali metal salts of sorbate, polyamino compounds and aniline can also be mixed and ground at the same time.

[0053] In S100 of a specific embodiment, the carbonization precursor of the nitrogen-doped porous carbon material is a polymer precursor formed by polymerization of oxygen-containing groups in alkali metal citrate and / or alkali metal sorbate with amino and / or imino groups in polyamino compounds and aniline. Wherein, the present invention uses excessive aniline, which can undergo self-polymerization during the heterogeneous reaction process of the reactor, so that the other two reactants, i.e., alkali metal citrate and / or alkali metal sorbate and polyamino compounds, can be coated and formed into a dense solid block product, which helps to reduce the decomposition of the polymer precursor during the carbonization reaction. However, if the amount of aniline is too much, it will affect the polymerization degree of the reactants, and a dense carbonization precursor (i.e., solid block product) cannot be formed, thereby affecting the carbonization reaction effect of the next stage. The oxygen-containing groups of alkali metal citrate and / or alkali metal sorbate themselves can polymerize with amino and / or imino groups in polyamino compounds. In addition, after the polyamino compound, aniline and alkali metal salt of citrate and / or alkali metal salt of sorbate react, the amino group and / or imino group can be fixed in the polymer, that is, the polyamino compound can also be used as a nitrogen source to complete nitrogen doping of porous carbon to obtain the nitrogen-doped porous carbon material.

[0054] The stepwise heat treatment in an inert atmosphere is to place the polymer precursor in an inert atmosphere for stepwise heat treatment, and the polymer precursor is paralyzed during the stepwise heat treatment. In the carbonization stage, the reaction that produces the pore-making effect is divided into two categories, one of which is the alkali metal ions contained in the alkali metal salt of citrate and / or the alkali metal salt of sorbate itself, such as potassium and / or sodium ions, which can generate corresponding metal oxides or metal atoms in situ during the carbonization stage, and the metal oxides or metal atoms have the effect of activating salt pore-making, thereby generating mesopores in the nitrogen-doped porous carbon material. On the other hand, the amino and / or imino groups in the polyamino compound are thermally unstable and are easily partially decomposed to produce a pore-making effect, thereby generating micropores in the nitrogen-doped porous carbon material. Therefore, the present invention can quantitatively control the specific surface area, pore structure, porosity, pore distribution and nitrogen doping amount of the nitrogen-doped porous carbon material by adjusting the mass ratio of the alkali metal salt of citrate and / or the alkali metal salt of sorbate and the polyamino compound and adding the volumetric dosage of aniline.

[0055] In a specific embodiment of S100, the segmented heat treatment includes two stages of heat treatment, wherein the temperature of the first stage of heat treatment is 250-300°C, and the holding time is 2-4h, and the temperature of the second stage of heat treatment is 650-800°C, and the holding time is 2-3h. The first stage of heat treatment, i.e., the low-temperature stage of heat treatment, can further stabilize the polymer and reduce the decomposition or structural collapse of the polymer. The temperature and time of the second stage of heat treatment, i.e., the high-temperature stage of heat treatment, can affect the porosity and specific surface area of ​​the porous carbon material formed. In this stage, the undecomposed nitrogen-containing groups, i.e., the amino groups and / or imino groups in the polyamino compounds are in-situ doped into the carbon sheet layered structure in the form of atoms, which can improve the reducibility of the porous carbon material.

[0056] In a specific embodiment of S200, the nitrogen-doped porous carbon material and solid titanium salt may be mixed and ball-milled. By controlling the mass ratio of the nitrogen-doped porous carbon material to the solid titanium salt during the ball-milling process, the dispersion degree and particle size of the formed nano-titanium dioxide may be adjusted.

[0057] Example 1

[0058] This embodiment provides a nitrogen-doped porous carbon-TiO 2 The composite carrier is prepared by a preparation method comprising the following specific steps:

[0059] Step (1): 1.0 g potassium citrate, 0.2 g diphenylcarbazide and 1.0 mL aniline are mixed and ground, and the homogenate (solid-liquid mixture) is placed in a reactor and reacted at 160° C. for 12 h; after the reaction, the obtained solid product is subjected to a segmented heat treatment reaction in a nitrogen atmosphere, first raised to 250° C. and maintained for 2 h, and then raised to 800° C. and maintained for 2 h; the solid product, i.e., the carbonized product, is washed with dilute HCl, and then washed with water several times and filtered until the filtrate is neutral; the washed product is then placed in a vacuum drying oven and dried at 80° C. for 12 h to obtain a nitrogen-doped porous carbon material.

[0060] Step (2): 5 mg of nitrogen-doped porous carbon material and 60 mg of titanium sulfate were mixed and ball-milled, and the resulting mixture was placed in a nitrogen atmosphere and heat-treated at 600 ° C for 2 h. After the heat treatment, nitrogen-doped porous carbon-TiO 2 Composite support, named PC-TiO 2 -1.

[0061] Example 2

[0062] This embodiment provides a nitrogen-doped porous carbon-TiO 2 The composite carrier is prepared by a preparation method comprising the following specific steps:

[0063] Step (1): 1.0 g potassium citrate, 0.2 g diphenylcarbazide and 1.0 mL aniline are mixed and ground, and the homogenate (solid-liquid mixture) is placed in a reactor and reacted at 160° C. for 12 h; after the reaction, the obtained solid product is subjected to a staged heat treatment reaction in a nitrogen atmosphere, first raised to 300° C. and maintained for 2 h, and then raised to 650° C. and maintained for 2 h; the solid product, i.e., the carbonized product, is washed with dilute HCl, then washed with water several times and filtered until the filtrate is neutral; the washed product is then placed in a vacuum drying oven and dried at 80° C. for 12 h to obtain a nitrogen-doped porous carbon material.

[0064] Step (2): 5 mg of nitrogen-doped porous carbon material and 60 mg of titanium sulfate were mixed and ball-milled, and the resulting mixture was placed in a nitrogen atmosphere and heat-treated at 400 ° C for 5 h. After the heat treatment, nitrogen-doped porous carbon-TiO 2 Composite support, named PC-TiO 2 -2.

[0065] Example 3

[0066] This embodiment provides a nitrogen-doped porous carbon-TiO 2 The composite carrier is prepared by a preparation method comprising the following specific steps:

[0067] Step (1): 1.0 g potassium citrate, 0.5 g diphenylcarbazide and 0.6 mL aniline are mixed and ground, and the homogenate (solid-liquid mixture) is placed in a reactor and reacted at 200° C. for 6 hours; after the reaction, the obtained solid product is subjected to a staged heat treatment reaction in a nitrogen atmosphere, first raised to 250° C. and maintained for 4 hours, and then raised to 750° C. and maintained for 3 hours; the solid product, i.e., the carbonized product, is washed with dilute HCl, and then washed with water several times and filtered until the filtrate is neutral; the washed product is then placed in a vacuum drying oven and dried at 80° C. for 12 hours to obtain a nitrogen-doped porous carbon material.

[0068] Step (2): 5 mg of nitrogen-doped porous carbon material and 60 mg of titanium sulfate were mixed and ball-milled, and the resulting mixture was placed in a nitrogen atmosphere and heat-treated at 600 ° C for 3 h. After the heat treatment, nitrogen-doped porous carbon-TiO 2 Composite support, named PC-TiO 2 -3.

[0069] Example 4

[0070] This embodiment provides a nitrogen-doped porous carbon-TiO 2 The composite carrier is prepared by a preparation method comprising the following specific steps:

[0071] Step (1): 1.0 g potassium citrate, 0.2 g melamine and 1.0 mL aniline are mixed and ground, and the homogenate (solid-liquid mixture) is placed in a reactor and reacted at 160° C. for 12 h; after the reaction, the obtained solid product is subjected to a staged heat treatment reaction in a nitrogen atmosphere, first raised to 250° C. and maintained for 2 h, and then raised to 800° C. and maintained for 2 h; the solid product, i.e., the carbonized product, is washed with dilute HCl, then washed with water several times and filtered until the filtrate is neutral; the washed product is then placed in a vacuum drying oven and dried at 80° C. for 12 h to obtain a nitrogen-doped porous carbon material.

[0072] Step (2): 5 mg of nitrogen-doped porous carbon material and 60 mg of titanium sulfate were mixed and ball-milled, and the resulting mixture was heat-treated at 600 °C in a nitrogen atmosphere for 2 h. After the heat treatment, nitrogen-doped porous carbon-TiO 2 Composite support, named PC-TiO 2 -4.

[0073] Example 5

[0074] This embodiment provides a nitrogen-doped porous carbon-TiO 2 The composite carrier is prepared by a preparation method comprising the following specific steps:

[0075] Step (1): 1.0 g of potassium sorbate, 0.2 g of diphenylcarbazide and 1.0 mL of aniline are mixed and ground, and the homogenate (solid-liquid mixture) is placed in a reactor and reacted at 160° C. for 12 hours; after the reaction, the obtained solid product is subjected to a staged heat treatment reaction in a nitrogen atmosphere, first raised to 250° C. and maintained for 2 hours, and then raised to 800° C. and maintained for 2 hours; the solid product, i.e., the carbonized product, is washed with dilute HCl, and then washed with water several times and filtered until the filtrate is neutral; the washed product is then placed in a vacuum drying oven and dried at 80° C. for 12 hours to obtain a nitrogen-doped porous carbon material.

[0076] Step (2): 5 mg of nitrogen-doped porous carbon material and 150 mg of titanium sulfate were mixed and ball-milled, and the resulting mixture was heat-treated at 500 °C for 3 h in a nitrogen atmosphere. After the heat treatment, nitrogen-doped porous carbon-TiO 2 Composite support, named PC-TiO 2 -5.

[0077] Comparative Example 1

[0078] The material provided in this comparative example does not include porous carbon material, which is a nano titanium dioxide catalyst. The specific preparation steps are: 150 mg of titanium sulfate is ball-milled and then heat-treated at 600 ° C in a nitrogen atmosphere for 2 h. After the heat treatment, a nano titanium dioxide catalyst is obtained, which is named n-TiO 2 .

[0079] Comparative Example 2

[0080] This comparative example uses a commercial titanium dioxide catalyst (P25, purchased from Aladdin Reagent Company) as a comparison.

[0081] Comparative Example 3

[0082] This comparative example provides a nitrogen-doped porous carbon-TiO 2 The preparation method of the composite carrier differs from that of Example 1 only in that:

[0083] Step (1): 1.0 g of potassium citrate and 0.2 g of diphenylcarbazide are mixed and ground, and the resulting solid mixture is placed in a reactor and reacted at 160° C. for 12 hours; after the reaction is completed, the obtained solid product is subjected to a staged heat treatment reaction in a nitrogen atmosphere, first raised to 250° C. and maintained for 2 hours, and then raised to 800° C. and maintained for 2 hours; the solid product, i.e., the carbonized product, is washed with dilute HCl, then washed with water several times and filtered until the filtrate is neutral; the washed product is then placed in a vacuum drying oven and dried at 80° C. for 12 hours to obtain a nitrogen-doped porous carbon material.

[0084] That is, compared with Example 1, no aniline was used in step (1) of Comparative Example 3.

[0085] Step (2): 5 mg of nitrogen-doped porous carbon material and 60 mg of titanium sulfate were mixed and ball-milled, and the resulting mixture was placed in a nitrogen atmosphere and heat-treated at 600 ° C for 2 h. After the heat treatment, nitrogen-doped porous carbon-TiO 2 Composite support, named PC-TiO 2 -6.

[0086] Comparative Example 4

[0087] This comparative example provides a nitrogen-doped porous carbon-TiO 2 The composite carrier is prepared by a preparation method comprising the following specific steps:

[0088] Step (1): 1.0 g potassium citrate, 0.2 g diphenylcarbazide and 1.0 mL aniline are mixed and ground, and the homogenate (solid-liquid mixture) is placed in a reactor and reacted at 160° C. for 12 h; after the reaction, the obtained solid product is subjected to a staged heat treatment reaction in a nitrogen atmosphere, firstly raised to 250° C. for 2 h, and then raised to 850° C. for 2 h; the solid product, i.e., the carbonized product, is washed with dilute HCl, and then washed with water for several times and filtered until the filtrate is neutral; the washed product is then placed in a vacuum drying oven and dried at 80° C. for 12 h to obtain a nitrogen-doped porous carbon material;

[0089] That is, compared with Example 1, the temperature of the second heat treatment in step (1) of Comparative Example 4 is 850°C, which is not within the range of 650-800°C claimed in the present application.

[0090] Step (2): 5 mg of nitrogen-doped porous carbon material and 60 mg of titanium sulfate were mixed and ball-milled, and the resulting mixture was placed in a nitrogen atmosphere and heat-treated at 600 ° C for 2 h. After the heat treatment, nitrogen-doped porous carbon-TiO 2 Composite support, named PC-TiO 2 -7.

[0091] Comparative Example 5

[0092] This comparative example provides a nitrogen-doped porous carbon-TiO 2 The composite carrier is different from the preparation method in Example 1 only in that:

[0093] Step (2): 5 mg of the nitrogen-doped porous carbon material obtained in step (1) was mixed with 200 mg of titanium sulfate and subjected to ball milling treatment. The resulting mixture was then heat treated at 600 °C for 2 h in a nitrogen atmosphere. After the heat treatment, nitrogen-doped porous carbon-TiO 2 Composite support, named PC-TiO 2 -8.

[0094] That is, compared with Example 1, in step (2) of Comparative Example 5, 40 g of titanium sulfate is added for every 1 g of nitrogen-doped porous carbon material, which is not within the range of adding 12-30 g of solid titanium salt for every 1 g of nitrogen-doped porous carbon material sought to be protected in the present application.

[0095] Characterization Test Example 1

[0096] This test example is respectively used for the PC-TiO 2 -1~PC-TiO 2 -5 and Comparative Examples 1 to 5 provide n-TiO 2 、P25、PC-TiO 2 -6~PC-TiO 2 -8 was subjected to physical adsorption test characterization, and the results were as follows:

[0097] PC-TiO 2 -1 The specific surface area of ​​the material is 262m 2 / g, and the total pore volume is 0.34cm 3 / g, of which the mesopore area is 152m 2 / g, the material presents a multi-level pore structure with coexistence of micropores and mesopores, among which PC-TiO 2 -1 The total weight of the material is 100%, TiO 2The content is 83.1%.

[0098] PC-TiO 2 -2 The specific surface area of ​​the material is 196m 2 / g, and the total pore volume is 0.28cm 3 / g, of which the mesopore area is 125m 2 / g, the material presents a multi-level pore structure with coexistence of micropores and mesopores, among which PC-TiO 2 -2 The total weight of the material is 100%, TiO 2 The content is 78.6%.

[0099] PC-TiO 2 -3 The specific surface area of ​​the material is 376m 2 / g, and the total pore volume is 0.36cm 3 / g, of which the mesopore area is 287m 2 / g, the material presents a multi-level pore structure with coexistence of micropores and mesopores, among which PC-TiO 2 -3 The total weight of the material is 100%, TiO 2 The content is 75.3%.

[0100] PC-TiO 2 -4 The specific surface area of ​​the material is 321m 2 / g, the total pore volume is 0.30cm 3 / g, of which the mesopore area is 111m 2 / g, the material presents a multi-level pore structure with coexistence of micropores and mesopores, among which PC-TiO 2 -4 The total weight of the material is 100%, TiO 2 The content is 77.5%.

[0101] PC-TiO 2 -5 The specific surface area of ​​the material is 185m 2 / g, and the total pore volume is 0.26cm 3 / g, of which the mesopore area is 124m 2 / g, the material presents a multi-level pore structure with coexistence of micropores and mesopores, among which PC-TiO 2 -5 The total weight of the material is 100%, TiO 2 The content is 87.2%.

[0102] n-TiO 2 The specific surface area of ​​the material is 104m 2 / g, and the total pore volume is 0.23cm 3 / g, of which the mesopore area is 95m 2 / g.

[0103] The specific surface area of ​​P25 material is 51m 2 / g, and the total pore volume is 0.12cm 3 / g, of which the mesopore area is 44m 2 / g.

[0104] PC-TiO 2 -6 The specific surface area of ​​the material is 123m 2 / g, and the total pore volume is 0.24cm 3 / g, of which the mesopore area is 103m 2 / g, PC-TiO 2 -6 The total weight of the material is 100%, TiO 2 The content is 91.5%.

[0105] PC-TiO 2 -7 The specific surface area of ​​the material is 168m 2 / g, the total pore volume is 0.25cm 3 / g, of which the mesopore area is 137m 2 / g, among which PC-TiO 2 -7 The total weight of the material is 100%, TiO 2 The content is 85.6%.

[0106] PC-TiO 2 -8 The specific surface area of ​​the material is 153m 2 / g, the total pore volume is 0.25cm 3 / g, of which the mesopore area is 98m 2 / g, among which PC-TiO 2 -8 The total weight of the material is 100%, TiO 2 The content is 94.9%.

[0107] The PC-TiO provided in Examples 1 to 5 was 2 -1~PC-TiO 2 -5 and Comparative Examples 1 to 5 provide n-TiO 2 、P25、PC-TiO 2 -6~PC-TiO 2 The specific surface area, mesoporous area and total pore volume data of PC-TiO-8 are tabulated and illustrated as shown in Table 1. 2 -1, n-TiO 2 The pore size distribution of P25 is shown in Figure 2 shown.

[0108] Table 1 Pore structure parameters of materials provided by Examples 1 to 5 and Comparative Examples 1 to 5

[0109]

[0110] According to Table 1, for the PC-TiO 2 -2 material, due to the decrease of carbonization temperature in the porous carbon synthesis stage, the specific surface area and pore volume of the overall material decreased, indicating that carbonization temperature is an important factor affecting the specific surface area and pore morphology of the material.

[0111] In Example 3, the amount of aniline in the porous carbon raw material was reduced, and the amount ratio of the polyamino compound was increased. 2 -3 The specific surface area of ​​the material is increased.

[0112] Example 4 The type of polyamino compound in the raw material was changed during the synthesis, and the final PC-TiO 2 -4 The specific surface area and pore volume of the material have changed significantly, with the specific surface area increasing to 321m 2 / g, but the mesopore area is reduced to 111m 2 / g, this is because different nitrogen-containing compounds, namely polyamino compounds, have different numbers and stabilities of nitrogen-containing groups, resulting in different degrees of decomposition during the carbonization process, and different pore morphologies formed in cooperation with potassium citrate. Therefore, the selection principle of polyamino compounds is that the porous carbon formed is a sheet-like structure with a suitable micro / mesopore ratio. This morphology and pore structure are conducive to the increase of titanium dioxide loading and the rapid transport of reactants in denitrification catalysis when used as a composite carrier.

[0113] In Example 5, potassium sorbate is used as both a carbon source and an activation salt, and the specific surface area of ​​the material is reduced. This is because different activation salts have different high-temperature decomposition mechanisms, and the proportion of mesopores in the formed porous carbon material is higher. Different activation salt raw materials can be selected according to the required pore distribution.

[0114] The n-TiO provided in Comparative Example 1 and Comparative Example 2 shown in Table 1 2 From the data of P25, it can be seen that the titanium dioxide not composited with nitrogen-doped porous carbon has a lower specific surface area and porosity, and a larger particle size of about 20-50nm.

[0115] like Figure 2 As shown in Figure 2, the P25 material is almost not distributed in the mesoporous section, while the n-TiO 2 The wide mesopore size distribution of the material is due to the narrow pores formed by the accumulation of nanoparticles. In Example 1 of the present invention, a composite carrier material is constructed by growing nano-titanium dioxide on nitrogen-doped porous carbon. The obtained PC-TiO 2 -1 The number of pores in the material is compared to n-TiO 2There is a significant improvement, and the number of micropores and mesopores has increased, which shows that the present invention can achieve the optimization of the specific surface area and porosity of the composite material at a lower porous carbon input.

[0116] In the preparation process of Comparative Example 3, aniline was not added. At this time, no encapsulated solid block product could be formed in the reactor. The polymerization product of potassium citrate and diphenylcarbazide was significantly thermally decomposed in the carbonization stage, so that the obtained nitrogen-doped porous carbon material and nitrogen-doped porous carbon-TiO 2 The specific surface area and total pore volume of the composite carrier decreased significantly.

[0117] In Comparative Example 4, the temperature of the second heat treatment in the preparation stage of nitrogen-doped porous carbon was too high, 850°C, resulting in pore collapse in the obtained nitrogen-doped porous carbon material, thus resulting in the final obtained nitrogen-doped porous carbon-TiO 2 The specific surface area and total pore volume of the composite support decreased.

[0118] In comparative example 5, the amount of titanium sulfate was increased, and the specific surface area and pore volume of the obtained material decreased. It was also found in the study that excessive titanium source would lead to the formation of nano-TiO 2 The size uniformity of TiO is reduced and the distribution on the carbon sheet is uneven, and a large amount of TiO 2 Reunion.

[0119] Characterization Test Example 2

[0120] This test example is respectively used for the PC-TiO 2 -1 and the n-TiO provided in Comparative Example 1 2 Transmission electron microscopy analysis was performed, and the obtained transmission electron microscopy images were as follows Figure 3a and Figure 3b As shown. Figure 3a It can be seen that PC-TiO 2 The nitrogen-doped porous carbon material used as the loading substrate in -1 presents a graphene-like sheet structure. The micro / mesopores on the sheet are the key to improving the catalyst adsorption capacity when the composite carrier is used as the loading substrate. Nano-TiO 2 During the heat treatment process, a large number of carbon nanotubes are generated and anchored on the carbon sheet. The particle size is about 3-5nm and the dispersion is high. This shows that the addition of nitrogen-doped porous carbon materials can reduce the agglomeration of titanium dioxide, thereby increasing the effective contact area when the material reacts with other active components. At the same time, due to the growth of the carbon layer on the surface of TiO 2 The confinement effect of the size results in a smaller nanoparticle size. Figure 3b It can be seen that the n-TiO 2 Among the materials, nano-TiO 2The particle size is about 10 to 20 nm, and the agglomeration is relatively serious. Using it as a loading substrate for a denitrification catalyst will affect the stability of the catalyst and the uniformity of the dispersion of the active components.

[0121] Characterization Test Example 3

[0122] This test example is respectively used for the PC-TiO 2 -1 and the n-TiO provided in Comparative Example 1 2 Raman spectroscopy analysis was performed, and the obtained Raman spectrum was as follows Figure 4 As shown. Figure 4 It can be seen that PC-TiO 2 -1 material has both the peak representing anatase titanium dioxide and the peak at 1320 cm -1 and 1580cm -1 The D / G peak representing the graphite structure indicates that the nitrogen-doped porous carbon material and nano-titanium dioxide form a composite structure.

[0123] Characterization Test Example 4

[0124] This test example is respectively used to test the PC-TiO 2 -1~PC-TiO 2 -3 for XRD analysis, the obtained XRD curve is as follows Figure 5 As shown. Figure 5 It can be seen that the diffraction peaks at 25.3°, 38.0°, 48.0°, 54.0° and 55.1° all correspond to anatase TiO 2 (JCPDF No.21-1272) (101), (004), (200), (105) and (211) crystal planes, which shows that the preparation method provided by the embodiment of the present invention can obtain anatase titanium dioxide with a high degree of crystallinity. Among them, the strong diffraction peak at 26° also shows that there is indeed a nitrogen-doped porous carbon component in the composite support material.

[0125] The above is only a specific embodiment of the present invention, and cannot be used to limit the scope of the invention. Therefore, the replacement of equivalent components, or equivalent changes and modifications made according to the protection scope of the patent of the present invention, should still fall within the scope of this patent. In addition, the technical features of the present invention can be freely combined with each other, with each other and with each other, and with each other.

Claims

1. A nitrogen-doped porous carbon-TiO 2 Composite carrier, It is characterized in that The nitrogen-doped porous carbon-TiO 2 The composite support includes nitrogen-doped porous carbon and nano-TiO 2 The nitrogen-doped porous carbon is a two-dimensional carbon sheet structure and contains open micropores and mesopores, and has a multi-level pore structure. 2 Evenly dispersed on the surface of the two-dimensional carbon sheet structure; Doping porous carbon-TiO with nitrogen 2 The total weight of the composite carrier is 100%, nano-TiO 2 The content is 75-90wt%.

2. The composite carrier according to claim 1, It is characterized in that Nano-TiO 2 The particle size is 3-8nm.

3. The composite carrier according to claim 1 or 2, It is characterized in that The nitrogen-doped porous carbon-TiO 2 The specific surface area of ​​the composite carrier is 180-400m 2 / g.

4. The nitrogen-doped porous carbon-TiO according to any one of claims 1 to 3 2 A method for preparing a composite carrier, It is characterized in that The preparation method comprises: Step (1): uniformly mixing alkali metal salt of citrate and / or alkali metal salt of sorbate, a polyamino compound and aniline, placing the obtained solid-liquid mixture in a reactor for heterogeneous reaction, and after the reaction, performing a staged heat treatment on the obtained solid product in an inert atmosphere to obtain a nitrogen-doped porous carbon material; Step (2): uniformly mixing the nitrogen-doped porous carbon material and the solid titanium salt, and then heat-treating the obtained solid mixture in an inert atmosphere to obtain nitrogen-doped porous carbon-TiO 2 Composite carrier.

5. The preparation method according to claim 4, It is characterized in that The alkali metal citrate includes potassium citrate and / or sodium citrate, and the alkali metal sorbate includes potassium sorbate.

6. The preparation method according to claim 4, It is characterized in that The polyamino compound includes one or a combination of organic substances containing two or more amino groups and / or imino groups.

7. The preparation method according to claim 6, It is characterized in that The polyamino compound includes one or a combination of diphenylcarbazide, phenylenediamine and melamine.

8. The preparation method according to claim 4, It is characterized in that The mass ratio of alkali metal citrate and / or alkali metal sorbate to the polyamino compound is 2-5:

1.

9. The preparation method according to claim 4 or 8, It is characterized in that For every 1 g of alkali metal citrate and / or alkali metal sorbate, add 0.5-1.0 mL of aniline.

10. The preparation method according to claim 4, It is characterized in that The temperature of the heterogeneous reaction is 160-200° C. and the time is 6-12 hours.

11. The preparation method according to claim 4 or 10, It is characterized in that The staged heat treatment includes two stages of heat treatment, wherein the temperature of the first stage of heat treatment is 250-300°C and the holding time is 2-4 hours, and the temperature of the second stage of heat treatment is 650-800°C and the holding time is 2-3 hours.

12. The preparation method according to claim 4, It is characterized in that For every 1g of nitrogen-doped porous carbon material, add 12-30g of solid titanium salt; Preferably, the solid titanium salt includes one or a combination of titanium sulfate, titanium thiosulfate, titanium oxalate and titanium oxysulfate.

13. The preparation method according to claim 4 or 12, It is characterized in that In step (2), the heat treatment temperature is 400-600°C, preferably 500-550°C, and the time is 2-5h.

14. A low-temperature denitration catalyst, It is characterized in that The carrier of the low-temperature denitration catalyst is the nitrogen-doped porous carbon-TiO 2 Composite carrier.

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