CN115970735A - Molecular sieve-multi-element oxide composite denitration catalyst and preparation method thereof - Google Patents

Abstract

The invention discloses a molecular sieve-multicomponent oxide composite denitration catalyst and a preparation method thereof, wherein the catalyst comprises a carrier and an active component; the carrier is a Silicalite-1 molecular sieve with an MFI pore structure, and the active components are oxides of copper and cerium, wherein the cerium surrounds the carrier, and the copper is concentrated in the central part of the carrier; based on the mass of the Silicalite-1 molecular sieve, the addition amount of the cerium element is 2 to 12 weight percent, and the addition amount of the copper element is 0.5 to 2.0 weight percent. According to the molecular sieve-multi-element oxide composite denitration catalyst and the preparation method thereof, the active components grow on the carrier in situ, the two active components are distributed on different areas of the surface of the carrier, the dispersion degree and the bonding strength of the active components on the surface of the carrier are improved, the synergistic effect among various metal active components is utilized, the denitration reaction temperature of the catalyst is effectively reduced, and the temperature window of the denitration reaction of the catalyst is widened.

Description

Molecular sieve-multi-element oxide composite denitration catalyst and preparation method thereof

Technical Field

The invention relates to the technical field of SCR denitration catalysts, in particular to a molecular sieve-multi-element oxide composite denitration catalyst and a preparation method thereof.

Background

With the rapid development of Chinese economy, nitrogen Oxides (NO) discharged to the atmosphere every year _x ) More and more, acid rain, haze, micro-particle pollution and the like appear in many areas, and the harm to human bodies, environment and ecology and the damage to social economy are huge. The removal of NO, an atmospheric pollutant, by Selective Catalytic Reduction (SCR) is an effective method. The SCR technology is characterized in that NH is sprayed into flue gas in the presence of a catalyst ₃ Urea or other nitrogen-containing reducing agent, with NO being selective _x Reaction to form N ₂ Instead of with O ₂ Non-selective oxidation occurs to achieve reduction of NO _x Reduction temperature, increase of NO _x The purpose of purification efficiency.

The industrial SCR catalyst with the best denitration effect and the most wide application is V ₂ O ₅ /TiO ₂ And V ₂ O ₅ -WO ₃ /TiO ₂ Catalysts, whose main advantages are represented by high activity and high sulfur resistance, but such catalysts need to be at higher temperatures: (>350 ℃) to avoid SO in the flue gas ₂ And NH ₃ NH formed by reaction ₄ HSO ₄ And (NH) ₄ ) ₂ S ₂ O ₇ Blocking the pore structure of the catalyst. However, in many cases, high temperature operation results in increased energy consumption and operating costs, and low temperature SCR units are more conducive to matching with most of the industrial boilers in China at present. Therefore, the low temperature of the SCR catalyst has attracted general attention. At present, although a plurality of low-temperature denitration catalysts have good denitration efficiency, the low-temperature denitration catalysts are easy to be subjected to SO ₂ The catalyst is difficult to be practically applied due to poisoning, and the catalyst is easy to cause poor dispersibility of active components on a carrier, narrow temperature window and poor stability due to a coprecipitation method and a sol-gel method. Therefore, there is a need to develop other low-temperature sulfur-resistant and water-resistant denitration catalysts.

Disclosure of Invention

The invention aims to provide a molecular sieve-multi-element oxide composite denitration catalyst and a preparation method thereof, and aims to solve the problems of high use temperature, poor sulfur resistance and water resistance, uneven distribution of active components, narrow temperature window and the like of the denitration catalyst.

In order to realize the aim, the invention provides a molecular sieve-multi-element oxide composite denitration catalyst and a preparation method thereof, wherein the catalyst comprises a carrier and an active component; the carrier is a Silicalite-1 molecular sieve with an MFI pore structure, and the active components are oxides of copper and cerium, wherein the cerium surrounds the carrier, and the copper is concentrated in the central part of the carrier; based on the mass of the Silicalite-1 molecular sieve, the addition amount of the cerium element is 2 to 12 weight percent, and the addition amount of the copper element is 0.5 to 2.0 weight percent.

A preparation method of a molecular sieve-multi-component oxide composite denitration catalyst comprises the following steps:

(1) Preparing a Silicalite-1 molecular sieve: dropwise adding ethyl silicate into a tetrapropyl ammonium hydroxide aqueous solution under the stirring condition, transferring the mixture into a reaction kettle after hydrolysis, centrifuging, washing and drying the mixture after hydrothermal in a drying oven to obtain a molecular sieve precursor, and transferring the molecular sieve precursor into a muffle furnace to calcine to obtain a Silicalite-1 molecular sieve;

(2) Preparation of the catalyst: firstly, dissolving copper salt and cerium salt in deionized water to form a mixed solution, then immersing the Silicalite-1 molecular sieve in the mixed solution, stirring at normal temperature, drying to obtain a catalyst precursor, grinding the catalyst precursor, transferring the ground catalyst precursor to a muffle furnace, and calcining to obtain Cu _n Ce _m A silicalite-1 catalyst.

Preferably, in the step (1), the ethyl silicate is dropwise added into the tetrapropylammonium hydroxide aqueous solution under the condition of constant magnetic stirring at 40 ℃, and after hydrolysis for 2 hours at 40 ℃, the silicon dioxide content in the ethyl silicate is 28-40%. 28% -40% represents ethyl silicate of different specifications purchased from the market.

Preferably, the hydrothermal temperature in step (1) is 160 ℃ and the hydrothermal time is 48 hours.

Preferably, the roasting in the step (1) is carried out for 6h at the temperature rising rate of 2 ℃/min to 550 ℃.

Preferably, in step (2), the temperature is raised to 100 ℃ to evaporate excess water, and the mixture is transferred to an oven at 80 ℃ for drying overnight.

Preferably, in the step (2), the mixture is roasted for 4 hours at the temperature rising rate of 5 ℃/min to 500 ℃ in the air atmosphere.

Preferably, the copper salt comprises one of copper nitrate, copper sulfate, copper acetate and copper chloride, and the mass of copper element in the copper salt accounts for 0.5-2.0% of the mass of the Silicalite-1 molecular sieve.

Preferably, the cerium salt comprises one of cerium nitrate, cerium chloride and cerium sulfate, and the mass of cerium element in the cerium salt accounts for 2-12% of the mass of the Silicalite-1 molecular sieve.

An application of a molecular sieve-multi-element oxide composite denitration catalyst is applied to the flue gas denitration with sulfur resistance and water resistance at the temperature of 135-270 ℃.

Therefore, the molecular sieve-multi-element oxide composite denitration catalyst adopting the structure and the preparation method thereof have the following beneficial effects:

1. the denitration catalyst disclosed by the invention uses the Silicalite-1 molecular sieve with an MFI pore diameter structure as a carrier, and compared with the method using titanium dioxide as the carrier in the prior art, the denitration catalyst has the advantages that the specific surface area is greatly increased, the catalyst is favorable for adsorbing and activating more flue gas, and the denitration efficiency is improved;

2. the preparation method of the denitration catalyst comprises the step-by-step synthesis of the carrier and the active components, wherein the active components grow on the carrier in situ, and the two active components are distributed in different areas on the surface of the carrier, so that the dispersion degree and the bonding strength of the active components on the surface of the carrier are improved, and the mechanical strength and the thermal stability of the catalyst are improved;

3. compared with the existing single-metal cerium-based or single-metal copper-based carrier, the carrier disclosed by the invention utilizes the synergistic effect among various metal active components, effectively reduces the denitration reaction temperature of the catalyst, widens the temperature window of the denitration reaction of the catalyst, and has higher denitration efficiency and wider temperature window;

4. good sulfur resistance and water resistance, environmental protection, low cost and simple operation.

The technical solution of the present invention is further described in detail by the accompanying drawings and embodiments.

Drawings

FIG. 1 is an SEM image of a Silicalite-1 molecular sieve prepared from different silicon sources of example 1-2;

FIG. 2 is a nitrogen sorption and desorption isotherm of the Silicalite-1 molecular sieve prepared in example 1-2;

FIG. 3 is a pore size distribution plot for the Silicalite-1 molecular sieve prepared in example 1-2;

FIG. 4 shows that CeO with different Ce contents is loaded in comparative example 1 _x The denitration performance of the catalyst;

FIG. 5 is CuO prepared in example 3 _x -CeO _x The denitration performance curve of the catalyst in a temperature region of 90-300 ℃;

FIG. 6 is H ₂ O to CuO _x -CeO _x Influence of catalyst denitration activity;

FIG. 7 is SO ₂ For CuO _x -CeO _x Influence of catalyst denitration activity;

FIG. 8 is a CeO supporting different Ce contents _x XRD spectrum of the catalyst;

FIG. 9 is CuO _x -CeO _x XRD spectrum of the catalyst;

FIG. 10 shows N of the vector ₂ Adsorption/desorption isotherms;

FIG. 11 is a pore size distribution curve of a support;

FIG. 12 is CuO _x -CeO _x N of catalyst ₂ Adsorption/desorption isotherms;

FIG. 13 is CuO _x -CeO _x Pore size distribution curve of the catalyst;

FIG. 14 is CuO _x -CeO _x TEM and HRTEM images of the catalyst ((a, b) Ce ₁₀ /Silicalite-1；(c,d)Cu _2.0 Ce ₁₀ /Silicalite-1；(e,f)Cu _2.0 /Silicalite-1)；

FIG. 15 is an XPS spectrum of catalyst ((a) CuO) _x -CeO _x A Ce3d fine spectrum in the catalyst; (b) CuO (copper oxide) _x -CeO _x Cu 2p fine spectrum in catalyst);

FIG. 16 is CuO _x -CeO _x A catalyst surface redox analysis chart;

FIG. 17 is CuO _x -CeO _x Analyzing a graph of acid sites on the surface of the catalyst;

FIG. 18 is NH ₃ At Ce ₁₀ Silicalite-1 and Cu _2.0 Ce ₁₀ In-situ infrared adsorption pattern of the surface of the Silicalite-1 catalyst.

Detailed Description

The present invention will be further described below, and it should be noted that the present embodiment is based on the technical solution, and a detailed implementation manner and a specific operation process are provided, but the present invention is not limited to the present embodiment.

Example 1

Preparation of Silicalite-1 molecular sieve

The preparation was carried out using a hydrothermal method in which tetrapropylammonium hydroxide (TPAOH) was used as the micropore template and ethyl silicate (TEOS, 28%) was used as the source of the hydrolyzed silicon. 12g TEOS were first added dropwise to 12.8g TPAOH aqueous solution under constant magnetic stirring at 40 ℃ and after 2h hydrolysis at 40 ℃ the mixture was transferred to a 50mL reaction vessel and heated in an oven at 160 ℃ for 48h. After the reaction kettle is cooled to room temperature, the mixture is centrifuged to obtain white precipitate, the white precipitate is washed for 3 times by deionized water and ethanol respectively, and the white precipitate is dried in an oven at 80 ℃ overnight. And finally, grinding the sample, transferring the sample to a muffle furnace, roasting for 6 hours at the temperature rise rate of 2 ℃/min to 550 ℃ in the air atmosphere, and marking the prepared sample as Silicalite-1-28%.

Example 2

Preparation of Silicalite-1 molecular sieve

The preparation of example 2 differs from that of example 1 in that ethyl silicate (TEOS, 40%) is used as the source of the hydrolyzed silicon and the prepared sample is labeled Silicalite-1-40%.

FIG. 1 is an SEM image of the Silicalite-1 molecular sieves prepared in examples 1-2 with different silicon sources, from which it can be seen that the Silicalite-1 molecular sieves have MFI pore size structures and the molecular sieve particle size is around 200nm, FIG. 2 is a nitrogen adsorption and desorption isotherm of the Silicalite-1 molecular sieves prepared in examples 1-2, FIG. 3 is a pore size distribution diagram of the Silicalite-1 molecular sieves prepared in examples 1-2, and from Table 1 it can be seen that the Silicalite-1 molecular sieves prepared with different silicon sources have specific surface area phaseIn contrast, the Silicalite-1 molecular sieve prepared in example 1 had a pore volume of 0.23cm ³ Per g, pore size 1.97nm, pore volume 0.48cm for the Silicalite-1 molecular sieve prepared in example 2 ³ G, pore diameter is 3.90nm.

TABLE 1 texture data for Silicalite-1-28% and Silicalite-1-40%

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Comparative example 1

Ce _m Preparation of a silicalite-1 catalyst:

preparation of supported CeO with Ce content of 2-12 wt% by impregnation method _x A catalyst. Firstly, dissolving a certain mass of cerium nitrate in 20mL of deionized water, then immersing the prepared Silicalite-1 molecular sieve powder into the mixed solution, magnetically stirring for 2 hours at normal temperature, raising the temperature to 100 ℃, evaporating excessive moisture, and transferring to an oven at 80 ℃ for drying overnight. And finally, grinding the sample, transferring the sample to a muffle furnace, and roasting the sample for 4 hours at the temperature rising rate of 5 ℃/min to 500 ℃ in the air atmosphere. The prepared sample is marked as Ce _m Silicilite-1 (i.e., ceO) _x Catalyst), wherein m represents the mass ratio of the Ce content to the carrier in the following feeds, namely Ce: silicalite-1= m. Specifically, m is 2, 4, 6, 8, 10, 12.

Comparative example 2

Cu _n Preparation of/Silicalite-1 catalyst:

the preparation method also utilizes an impregnation method to prepare the silica-1 molecular sieve which takes the silica-1 molecular sieve as a carrier and only contains CuO as an active component _x From 0.5 to 2.0 wt.% of Cu, respectively designated Cu _n Silicon alite-1 (i.e., cuO) _x Catalyst), wherein n represents the mass ratio of the Cu content to the carrier in the following feeds, namely Cu: silicalite-1= n. Specifically, n is 2.0.

Example 3

Cu _n Ce _m Preparation of/Silicalite-1 catalyst: respectively modifying Ce with the optimal denitration activity by 0.5-2.0 wt% of copper by using an impregnation method _m A silicalite-1 catalyst.

Firstly, dissolving a certain mass of copper nitrate and cerium nitrate in 20mL of deionized water, then immersing the prepared Silicalite-1 molecular sieve powder in the mixed solution, magnetically stirring for 2 hours at normal temperature, raising the temperature to 100 ℃, evaporating excessive water, and transferring to an oven at 80 ℃ for overnight drying. And finally, transferring the ground sample to a muffle furnace, and roasting for 4 hours at the temperature rise rate of 5 ℃/min to 500 ℃ in the air atmosphere. The prepared sample is marked as Cu _n Ce _m Silicilite-1 (i.e., cuO) _x -CeO _x Catalyst), wherein m and n represent the mass ratio of Ce and Cu content to the carrier in the following feeds, namely Cu: ce: silicalite-1= n.

Specifically, m is 10, n is 0.5, 1.0, 2.0.

Example 4

Catalyst NH ₃ SCR Activity test

NH of catalyst ₃ The SCR test was carried out in a fixed-bed reactor with a reaction gas composition of 500ppm NO,500ppm NH ₃ ,3vol％O ₂ ,6vol％H ₂ O and 50ppm SO ₂ (used in resisting water and sulfur reaction), N ₂ It is the balance gas. 200mg of catalyst (40-60 meshes) is transferred into a quartz reaction tube with the inner diameter of 6mm, and the reaction solution is subjected to N treatment at 200 DEG C ₂ Purging for 30min, cooling to room temperature, and carrying out reaction gas adsorption until the reaction gas is saturated. NH (NH) ₃ The SCR reaction is carried out at the temperature of 90-360 ℃ and the space velocity of 18000h ^-1 Under the conditions of (1). After the reaction has stabilized at a predetermined stability, NO and NO after the reaction ₂ The concentration was determined by a portable smoke analyser (Testo Pro 350). NO _x The conversion of (d) is calculated by the following formula:

wherein ([ NO) _x ]＝[NO]+[NO ₂ ])。

FIG. 4 shows comparative example 1CeO loaded with different Ce contents _x Denitration performance of the catalyst. As can be seen from the figure, ceO _x NO of catalyst _x Conversion efficiency increased significantly with increasing Ce content in the catalyst, however, when Ce loading increased from 10wt% to 12wt%, NO of the catalyst _x The conversion efficiency was rather reduced, which indicates that the optimum loading of Ce for the catalyst was 10wt%, with too much CeO loaded _x Instead, it will occupy the active sites on the catalyst surface, blocking the NH ₃ -the performance of the SCR reaction. However, it can be seen from the figure that even the activity of Ce is optimized ₁₀ Silicalite-1 at Low temperature section (C<200 ℃ C.) with less than 50% NO _x The conversion efficiency can only reach 80 percent of NO in a medium-high temperature section (200-300 ℃) _x The conversion efficiency is far from meeting the requirement of industrial denitration, so CeO is required _x Other metals are doped into the catalyst to form a multi-metal system to promote catalyst NH ₃ -activity of the SCR reaction.

FIG. 5 is CuO _x -CeO _x Denitration performance curve of the catalyst in the temperature range of 90-300 ℃. As can be seen from the figure, ce ₁₀ The denitration activity of the/Silicalite-1 catalyst is general, and can only reach 80 percent of NO even at 300 DEG C _x The conversion efficiency. When a small amount of CuO is incorporated in the catalyst _x After species, NO of the catalyst _x The conversion efficiency is obviously improved, wherein Cu _2.0 Ce ₁₀ the/Silicalite-1 catalyst can keep more than 80 percent of NO in a temperature range of 135-270 DEG C _x Denitration efficiency, denitration performance compare Ce ₁₀ the/Silicalite-1 catalyst is greatly improved. Furthermore, although Cu _2.0 the/Silicalite-1 catalyst also reached 80% NO after 165 deg.C _x Conversion efficiency, but the reaction activity of the catalyst is compared with the light-off temperature of Cu _2.0 Ce ₁₀ The temperature of the/Silicalite-1 catalyst is higher by 30 ℃. At the same time, cu _2.0 The reaction activity window of the/Silicalite-1 catalyst is narrow (165-225 ℃), and the application to actual flue gas denitration is difficult. However, with CuO _x -CeO _x CuO in catalyst _x Increased species content, NO of the catalyst in the high temperature zone _x The conversion efficiency decreases rapidly, mainly due toDoped CuO _x Species cause relatively many side reactions. In general, a small amount of CuO is incorporated _x CuO of a species _x -CeO _x Catalyst NH ₃ The catalytic activity of SCR is obviously improved, especially in the low-temperature stage below 200 ℃. Cu with optimal denitration activity _2.0 Ce ₁₀ Silicalite-1 catalyst vs. pure CuO alone _x And pure CeO _x The catalyst has higher low-temperature NO _x Conversion efficiency and broader activation temperature, which can be attributed to the interaction of the binary active metal components.

Because the actual flue gas contains a small amount of H ₂ O and SO ₂ Thus, H was selected to be considered at 210 ℃ respectively ₂ O and SO ₂ For CuO _x -CeO _x Influence of denitration activity of the catalyst. As can be seen from FIG. 6, H ₂ O to Ce ₁₀ /Silicalite-1，Cu _2.0 Ce ₁₀ Silicalite-1 and Cu _2.0 The influence of the denitration performance of the/Silicalite-1 catalyst is similar. When adding 6vol% to the reaction gas ₂ After O, NO of three catalysts _x The conversion efficiency is reduced by about 10 percent, but Cu is not enough _2.0 Ce ₁₀ NO of/Silicalite-1 catalyst _x The conversion efficiency can still be kept above 90%. When H is present ₂ NO of the catalyst after O is removed from the reaction gas _x The transformation efficiency rapidly increased to the original level, indicating that H ₂ The deactivation of the catalyst by O is reversible, the main reason for deactivation being H ₂ O and NH ₃ Competitive adsorption on the catalyst surface. FIG. 7 is SO ₂ Influence on the denitration performance of the three catalysts. When 50ppm SO was added to the reaction gas ₂ After, ce ₁₀ NO of/Silicalite-1 catalyst _x The conversion efficiency is firstly improved and then begins to decline, gradually stabilizing at about 50%. Ce ₁₀ The denitration efficiency of the/Silicalite-1 catalyst is improved by a small amount of SO ₂ The pretreatment of (2) helps to promote Ce ₁₀ The surface acidity of the/Silicalite-1 catalyst improves the denitration efficiency, but the SO is continuously introduced ₂ Will be mixed with CeO ₂ Sulfate species are formed on the surface, resulting in irreversible deactivation of the catalyst. Due to the fact thatCuO _x Is very easy to react with SO ₂ To form sulfate species, hence in SO ₂ In the presence of Cu _2.0 NO of/Silicalite-1 catalyst _x The conversion efficiency is only maintained at about 20 percent, while Cu _2.0 Ce ₁₀ SO resistance of/Silicalite-1 catalyst ₂ Performance and Ce ₁₀ the/Silicalite-1 catalyst is similar to the CuO catalyst, and can maintain the denitration activity of more than 50 percent _x The catalyst is greatly improved.

Example 5

The catalysts prepared in comparative examples 1-2 and example 2 were characterized.

(1) The catalyst prepared in comparative example 1 was subjected to ICP testing and XRD characterization, respectively.

The Ce content of all catalysts was characterized by ICP testing and the characterization results are shown in table 2. As can be seen from the table, when the Ce content in the catalyst is relatively low (6 wt% and below), the Ce content in the catalyst and the feeding amount are basically kept consistent; when the Ce content in the catalyst is higher (8 wt% and above), the Ce content in the catalyst is lower than the feeding amount by about 1-2 wt%, which shows that the catalyst with high Ce content has little loss of active components in the impregnation process, but the Ce content of each catalyst basically shows a linear increasing trend.

TABLE 2 different Ce _x Ce content in Silicilite-1 catalyst

FIG. 8 is a CeO supporting different Ce contents _x Powder XRD spectrum of catalyst. It can be seen from the figure that all catalysts show distinct characteristic peaks at 7.9 °,8.8 °,23.1 °,23.3 ° and 23.9 °, which can be attributed to MFI pore structure of the Silicalite-1 molecular sieve, indicating that the support still well maintains its unique pore structure during the impregnation process. At Ce ₂ Silicalite-1 and Ce ₄ The spectrum of the/Silicalite-1 was not found to be assigned to CeO ₂ Mainly because of the low Ce content in both catalysts, whereas in the other catalysts, both can be found at 28.6 °,47.5 ° and 56.3 ° to be assigned to CeO ₂ Characteristic peak of (a) indicating that minute CeO has been formed on the surface of the catalyst ₂ And (4) crystals.

(2) The catalysts prepared in comparative examples 1-2 and example 3 were characterized by ICP testing, XRD, TEM, BET, TEM, and EDS, respectively.

CuO prepared in example 3 _x -CeO _x The content of metal active components in the catalyst was determined by ICP and summarized in table 3. As can be seen from the table, the Ce content in each catalyst is substantially the same, and is around 8wt.%, and the loss compared with the feed amount (10 wt.%) is substantially the same. The Cu content in each catalyst is basically consistent with the feeding amount, and the obvious content difference is kept among the catalysts, so that the denitration performance of the catalyst is further researched.

Table 3 CuO prepared in example 3 _x -CeO _x Content of Metal component in catalyst

FIG. 9 is CuO _x -CeO _x Powder XRD spectrum of catalyst. As can be seen from the figure, all catalysts showed characteristic peaks ascribed to MFI channel structures at 7.9 °,8.8 °,23.1 °,23.3 ° and 23.9 °, indicating that the unique channel structure of the support was not affected during impregnation. In addition, in the XRD spectrum of the catalyst, it could be found at 28.6 °,47.5 ° and 56.3 ° to be assigned to CeO ₂ But is not found to be ascribed to CuO _x Mainly due to the fact that the loading of Cu is lower than the lowest detection concentration (5 wt%) of the instrument.

N of the vector ₂ The adsorption/desorption isotherms and pore size distribution curves are shown in FIGS. 10 and 11, cuO _x -CeO _x N of catalyst ₂ The adsorption/desorption isotherms and pore size distribution curves are shown in fig. 12 and 13, and the corresponding texture data for both are summarized in table 4. As can be seen from FIG. 12, all CuO _x -CeO _x N of catalyst ₂ The adsorption/desorption isotherms and the support were kept the same and both belong to the type i isotherm, indicating that all catalysts have a microporous structure, which is consistent with the pore size distribution results in fig. 13. All catalysts have obvious absorption peaks at 0.5-0.6 nm, which can be classified as the unique MFI pore channel structure of the carrier. Further, ce ₁₀ the/Silicalite-1 catalyst has a weak absorption peak near 10nm, and the absorption peak is along with CuO _x The increase in the amount of incorporation was shifted to the small pore diameter direction, which could be attributed to the CeO distributed on the surface of the catalyst ₂ Nanoparticles, consistent with analysis by powder XRD. As can be seen from Table 4, ceO was supported alone _x Ce of (1) ₁₀ The specific surface area and the pore volume of the/Silicalite-1 catalyst are 475.06m respectively ² G and 0.41cm ³ (ii)/g, and CuO alone _x Catalyst Cu of _2.0 the/Silicalite-1 is essentially identical (478.90 m ² G and 0.43cm ³ In terms of/g), but when the binary metal oxide is supported, there is a 5 to 10% reduction in both the specific surface area and the pore volume of the catalyst. However, in general, the specific surface area of the catalyst is 400m ² More than g, pore volume of 0.35m ² Above/g, so there is little difference in texture properties between the individual catalysts.

TABLE 4 Supports and CuO _x -CeO _x Texture data of the catalyst

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Selecting representative Ce ₁₀ /Silicalite-1、Cu _2.0 Ce ₁₀ Silicalite-1 and Cu _2.0 Silicalite-1 as a representative catalyst by TEM and EDS characterization the surface morphology of the catalyst was further investigated. FIG. 14 is CuO _x -CeO _x TEM and HRTEM images of the catalyst. As can be seen from the figure, in pure CeO _x In the supported catalyst, more dark spots appear at the edge of the carrier, belonging to CeO _x And (3) nanoparticles. In pure CuO _x In the loaded catalyst, the dark spots are mainly concentrated in the center of the carrier and have a size larger than that of CeO _x The nanoparticles are small. At the CuO _x -CeO _x In the catalyst, dark spots are distributed in the center and the periphery of the carrier. To further confirm the composition of dark spots on the surface of the carrier, the catalyst was subjected to test analysis by EDS mapping. In FIG. 14, the interplanar spacing of the dark spots at the edge of the carrier is approximately 0.32nm, corresponding to CeO ₂ The (111) crystal face of the crystal, which is consistent with the results in powder XRD. However, the dark spot size at the center of the support is small and the crystallinity is not high, and the interplanar spacing thereof cannot be accurately measured, but basically can be considered as dispersed CuO _x Species of the species.

Example 6

The denitration principle analysis was performed on the catalysts of example 3 and comparative examples 1 to 2.

(1)CuO _x -CeO _x Catalyst surface Structure analysis (XPS)

Ce was analyzed by XPS test ₁₀ /Silicalite-1，Cu _2.0 Ce ₁₀ Silicalite-1 and Cu _2.0 The atomic concentration and the atomic valence of the surface active metal of the/Silicalite-1 catalyst are shown in FIG. 15 and Table 5. Fig. 15 (a) is an XPS fine spectrum of Ce3d of the catalyst. The orbital peaks marked μ, μ ", μ '", v "and v'" in the figure are attributed to Ce ⁴⁺ While orbital peaks labeled μ 'and v' are ascribed to Ce ³⁺ Calculating Ce according to the peak area ³⁺ /(Ce ⁴⁺ +Ce ³⁺ ) The ratio of (a) to (b). As can be seen from Table 5, when CuO is added _x After speciation, ce on the surface of the catalyst ³⁺ The ratio of (A) to (B) is slightly reduced, indicating that CeO is present on the surface of the catalyst _x And CuO _x There may be interactions between them. FIG. 15 (b) is an XPS fine spectrum of catalyst Cu 2p, where Cu is _2.0 Ce ₁₀ The spectrum of Cu in the/Silicalite-1 catalyst can be determined by attributionFitting in 5 independent orbital peaks (peaks 932eV,933eV,952eV,953eV and 942 eV) respectively assigned to Cu 2p _1/2 And Cu 2p _3/2 Cu of (2) ⁺ And Cu ²⁺ And satellite peaks. As can be seen from Table 5, cu _2.0 Ce ₁₀ Silicalite-1 and Cu _2.0 The atomic concentrations of Cu species on the surface of the/Silicalite-1 catalyst are 0.25% and 0.11%, respectively, which is illustrated in the case of Cu _2.0 Ce ₁₀ More Cu species are exposed on the surface of the catalyst in Silicalite-1. At the same time, it can be found that _2.0 Almost all Cu species in the/Silicalite-1 catalyst are Cu ²⁺ In the form of _2.0 Ce ₁₀ Silicalite-1 catalyst, cu ⁺ /(Cu ⁺ +Cu ²⁺ ) The proportion of (A) is 12.48%. Cu ⁺ The increase in the ratio can be attributed to the redox reaction between the Cu and Ce species: ce ³⁺ +Cu ²⁺ →Ce ⁴⁺ +Cu ⁺ Thereby improving the oxidation-reduction property of the surface of the catalyst and being beneficial to improving low-temperature NH ₃ -the reactivity of the SCR.

TABLE 5 CuO _x -CeO _x Catalyst surface atomic concentration and valence state distribution

(2)CuO _x -CeO _x Analysis of the Redox Properties of the catalyst surface (H) ₂ -TPR)

Redox nature of the catalyst and its use in NH ₃ The catalytic activity in the SCR reaction is closely related, thus utilizing H ₂ The TPR technique evaluates the redox properties of the catalyst surface, the results of which are shown in FIG. 16 and Table 6. As can be seen from the figure, ce ₁₀ the/Silicalite-1 catalyst has only one reduction peak at 542 ℃ and can be classified as reduction of Ce species, which indicates that Ce ₁₀ The redox properties of the/Silicalite-1 catalyst surface are very weak. Cu _2.0 Ce ₁₀ the/Silicalite-1 catalyst has four reduction peaks in the temperature range from 100 to 600 ℃ with the reduction peaks marked I, II and III being associated with the reduction of Cu species (Cu ²⁺ →Cu ⁺ → Cu), the reduction peak marked as iv is associated with the reduction of the Ce species. Comparing the peak values of the reduction peaks of the three catalysts, cu can be found _2.0 Ce ₁₀ The reduction peak value of the/Silicalite-1 catalyst is found to be shifted to low temperature, which shows that Cu and Ce species in the catalyst become more active and are easy to reduce. The reduction peak areas in the figures were also integrated and summarized in table 6. From the table, it can be found that Cu _2.0 Ce ₁₀ The reduction peak area of the/Silicalite-1 catalyst is 1023a.u, which is close to Cu _2.0 2 times of the/Silicalite-1 catalyst is Ce ₁₀ Tens of times that of the/Silicalite-1 catalyst, which indicates the incorporation of CuO _x Of Cu _2.0 Ce ₁₀ The redox property of the/Silicalite-1 catalyst is greatly improved, so that the Cu _2.0 Ce ₁₀ the/Silicalite-1 catalyst can be used for NH at low temperature ₃ The optimum catalytic activity is shown in the SCR reaction.

TABLE 6 CuO _x -CeO _x H of catalyst ₂ Reduction peak to peak temperature and consumption

(3)CuO _x -CeO _x Catalyst surface acid site analysis (NH) ₃ -TPD)

The acidity of the catalyst surface determines the reaction gas NH ₃ The adsorption and activation capability on the surface of the catalyst directly influences the NH ₃ Activity in SCR reactions, thus by NH ₃ TPD experiment to evaluate the acidity, NH, of the catalyst surface ₃ The desorption curve and the integral calculation result of (a) are shown in fig. 17 and table 7, respectively. As can be seen from the figure, all three catalysts showed significant NH levels between 120 and 130 deg.C ₃ Desorption peak corresponding to NH adsorbed on weakly acidic site of carrier ₃ . In addition to that, cu _2.0 Ce ₁₀ Silicalite-1 and Cu _2.0 the/Silicalite-1 catalyst also has 2 and 1 NH respectively at 150-300 DEG C ₃ Desorption peaks, which can be attributed to Lewis acidic sites provided by the Cu species. Combined with the distribution of surface atomic valenceUnder the condition of Cu _2.0 Ce ₁₀ The new Lewis acid site on the surface of the/Silicalite-1 catalyst can be attributed to Cu ²⁺ And Cu ⁺ And Cu _2.0 Silicalite-1 catalyst only containing Cu ²⁺ ，Ce ₁₀ the/Silicalite-1 surface provides few Lewis acid sites. Thus, cu _2.0 Ce ₁₀ Surface acidity of/Silicalite-1 catalyst vs. pure CeO alone _x And pure CuO _x The catalyst is significantly strengthened so that NH is at low temperature ₃ Excellent catalytic activity in the SCR reaction.

TABLE 7 CuO _x -CeO _x NH of the catalyst ₃ Peak temperature of desorption peak and total amount of acid

To further understand the adsorption morphology of the reactive species on the catalyst surface, the reaction on NH ₃ And NO _x The adsorption condition of the species on the surface of the catalyst is studied by in-situ infrared. At NH ₃ /NO+O ₂ The infrared spectrograms of the catalyst surface are collected at different time points until the reaction gas is saturated on the catalyst surface. FIG. 18 is NH ₃ At Ce ₁₀ Silicalite-1 and Cu _2.0 Ce ₁₀ In-situ infrared adsorption pattern of the surface of the Silicalite-1 catalyst. For Ce in FIG. 18 (a) ₁₀ The catalyst is/Silicalite-1 with the center of 1570,1221 and 1081cm ^-1 Can be attributed to the coordinated NH adsorbed on the Lewis acid site ₃ Symmetrical and asymmetrical vibrations. Centered at 1740cm ^-1 Weak absorption peak and adsorption

NH at the acid position ₄ ⁺ Species related. Centered at 1395 and 1325cm ^-1 The strong absorption peak of (A) is mainly N ₂ H ₄ species-NH ₂ Oscillating vibration of the radicals. For Cu in FIG. 18 (b) _2.0 Ce ₁₀ Silicalite-1 catalyst, NH adsorbed on Lewis acid sites ₃ Absorption peak of (2) (1566 cm) ^-1 ) The remarkable enhancement is obtained while the length is 1439cm ^-1 Is subjected to existence of a catalyst belonging to NH ₄ ⁺ Absorption peak of (2), indicating Cu _2.0 Ce ₁₀ Lewis acidity and/or->

The acidity is enhanced, as is the NH before ₃ The TPD data are consistent. Cu _2.0 Ce ₁₀ The enhancement of the surface acidity of the/Silicalite-1 catalyst contributes to NH ₃ Adsorption of species, thereby increasing low temperature NH of the catalyst ₃ -SCR activity.

Therefore, according to the molecular sieve-multi-element oxide composite denitration catalyst and the preparation method thereof, with the structure, the active components grow on the carrier in situ, and the two active components are distributed in different areas on the surface of the carrier, so that the dispersion degree and the bonding strength of the active components on the surface of the carrier are improved, the mechanical strength and the thermal stability of the catalyst are improved, the synergistic effect among various metal active components is utilized, the denitration reaction temperature of the catalyst is effectively reduced, and the temperature window of the denitration reaction of the catalyst is widened.

Finally, it should be noted that: the above embodiments are only intended to illustrate the technical solution of the present invention and not to limit the same, and although the present invention is described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that: modifications and equivalents may be made to the invention without departing from the spirit and scope of the invention.

Claims (10)

1. A molecular sieve-multi-component oxide composite denitration catalyst is characterized in that: the catalyst comprises a carrier and an active component; the carrier is a Silicalite-1 molecular sieve with an MFI pore structure, and the active components are oxides of copper and cerium, wherein the cerium surrounds the carrier, and the copper is concentrated in the central part of the carrier; based on the mass of the Silicalite-1 molecular sieve, the addition amount of the cerium element is 2 to 12 weight percent, and the addition amount of the copper element is 0.5 to 2.0 weight percent.

2. The preparation method of the molecular sieve-multi-component oxide composite denitration catalyst according to claim 1, characterized by comprising the following steps: the method comprises the following steps:

(1) Preparing a Silicalite-1 molecular sieve: dropwise adding ethyl silicate into a tetrapropyl ammonium hydroxide aqueous solution under the stirring condition, transferring the mixture into a reaction kettle after hydrolysis, centrifuging, washing and drying the mixture after hydrothermal in a drying oven to obtain a molecular sieve precursor, and transferring the molecular sieve precursor into a muffle furnace to calcine to obtain a Silicalite-1 molecular sieve;

(2) Preparation of the catalyst: firstly, dissolving copper salt and cerium salt in deionized water to form a mixed solution, then immersing the Silicalite-1 molecular sieve in the mixed solution, stirring at normal temperature, drying to obtain a catalyst precursor, grinding the catalyst precursor, transferring the ground catalyst precursor to a muffle furnace, and calcining to obtain Cu _n Ce _m A silicalite-1 catalyst.

3. The preparation method of the molecular sieve-polyoxide composite denitration catalyst according to claim 2, characterized in that: dropwise adding the ethyl silicate into the tetrapropyl ammonium hydroxide aqueous solution under the condition of constant magnetic stirring at 40 ℃ in the step (1), and hydrolyzing for 2 hours at 40 ℃, wherein the content of silicon dioxide in the ethyl silicate is 28-40%.

4. The preparation method of the molecular sieve-polyoxide composite denitration catalyst according to claim 2, characterized in that: the hydrothermal temperature in the step (1) is 160 ℃, and the hydrothermal time is 48 hours.

5. The preparation method of the molecular sieve-polyoxide composite denitration catalyst according to claim 2, characterized in that: in the step (1), the mixture is roasted for 6h at the temperature rising rate of 2 ℃/min to 550 ℃.

6. The preparation method of the molecular sieve-polyoxide composite denitration catalyst according to claim 2, characterized in that: and (2) raising the temperature to 100 ℃, evaporating excessive water, and transferring to an oven at 80 ℃ for drying overnight.

7. The preparation method of the molecular sieve-polyoxide composite denitration catalyst according to claim 2, characterized in that: in the step (2), roasting for 4h at the temperature rising rate of 5 ℃/min to 500 ℃ in the air atmosphere.

8. The preparation method of the molecular sieve-polyoxide composite denitration catalyst according to claim 2, characterized in that: the copper salt comprises one of copper nitrate, copper sulfate, copper acetate and copper chloride, and the mass of the copper element in the copper salt accounts for 0.5-2.0% of the mass of the Silicalite-1 molecular sieve.

9. The preparation method of the molecular sieve-polyoxide composite denitration catalyst according to claim 2, characterized in that: the cerium salt comprises one of cerium nitrate, cerium chloride and cerium sulfate, and the mass of cerium element in the cerium salt accounts for 2-12% of the mass of the Silicalite-1 molecular sieve.

10. The use of the molecular sieve-polyoxide composite denitration catalyst as claimed in claim 1, wherein: the catalyst is applied to the flue gas denitration of resisting sulfur and water at the temperature of 135-270 ℃.

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