A composite oxide catalyst for catalytic decomposition of high-concentration N2O and a preparation method thereof

Abstract

A composite oxide catalyst for catalytically decomposing high-concentration N2O and a preparation method thereof, belonging to the technical field of air pollution control. The catalyst of the present invention is a composite oxide composed of nickel, niobium and cobalt, and the molecular formula is Ni x Nb y Co z O w , x / z=0-0.5, y / z=0-0.5, and further comprising an auxiliary metal oxide of an alkali metal or an alkaline earth metal. The catalyst can decompose most or all of the N2O in the pollution emission system into N2 and O2 when the space velocity is 1000-30000 / hour, the N2O concentration is 5-30%, the O2 concentration is 5-15%, the H2O concentration is 0-20%, and the reaction temperature is 450-500°C. The catalyst has high catalytic activity and good stability, and is particularly suitable for the removal of N2O in nitric acid plants and adipic acid plants.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental protection catalytic materials and air pollution control, and relates to a composite metal oxide catalyst and a preparation method thereof, which is particularly suitable for catalytically decomposing high-concentration N2O into O2 and N2 at a relatively low temperature under oxygen-rich and water-containing conditions. Background Art

[0002] N2O is commonly known as "laughing gas". It is not only a greenhouse gas, but also seriously pollutes the atmospheric environment. The global warming potential of N2O is about 310 times that of CO2 and 21 times that of CH4. It can be stable in the air for a long time and is very easy to destroy the ozone layer. With the rapid development of chemical synthesis industrial products such as adipic acid, nitric acid, and coal chemical industry in industry, the concentration of N2O in the atmosphere has continued to rise. Among them, the N2O emissions emitted by the adipic acid industry and the nitric acid industry are the largest, and the N2O emissions in the tail gas of adipic acid account for about 10% of the total global industrial production N2O emissions. However, the N2O emitted in the adipic acid industry and the nitric acid industry is often in a relatively high concentration and contains a certain proportion of O2 and H2O. General catalysts tend to reduce their activity or even lose their activity under oxygen-rich and water-containing conditions. The present invention will design and study catalysts for the practical problem of high concentrations of N2O and a certain proportion of O2 and H2O in the tail gas of the adipic acid and nitric acid industries.

[0003] The N2O decomposition and elimination catalysts reported in current research mainly include three categories: precious metal catalysts, metal oxide catalysts and molecular sieve catalysts.

[0004] Precious metal catalysts are a type of traditional catalyst that has been studied earlier. The most studied elements are Rh, Ir, Ru, Pd, Pt, etc. Their shortcomings are obvious. Patent CN102451683A discloses a catalyst with TiO2-modified Al2O3 as a carrier and Group VIII precious metals as active components. Due to its high market price, this catalyst is easily poisoned by impurity gases such as SO2, which greatly limits its application in complex industrial tail gas catalytic emission reduction.

[0005] Molecular sieve catalysts are mainly Co, Fe, Cu exchanged ZSM-5, BETA, FER and other molecular sieves, but compared with precious metal catalysts and metal oxide catalysts, molecular sieves of this type are expensive and easily blocked and deactivated. Patent CN102380410A is a catalyst that uses mordenite as a carrier and loads bimetallic composite oxides of cobalt and iron, which has a certain ability to resist water and oxygen poisoning. The disadvantage is that zeolite catalysts are expensive and easily blocked and deactivated.

[0006] Transition metal oxide catalysts, mainly oxides of Co, Ni, and Cu, as well as mixed oxides, oxide solid solutions or perovskites and spinel-type complexes formed by their combination in different proportions. In addition, many additives have been reported to improve the catalytic activity of N2O decomposition. Studies have shown that these additives are only effective in improving the N2O decomposition activity when they occupy a relatively small amount in the catalyst. Patent CN104624203A discloses a Pb-modified Co oxide-based N2O decomposition catalyst that has strong tolerance to impurity gases such as CO2 and SO2. However, the catalyst did not investigate the catalytic activity of N2O in oxygen-rich water-containing conditions. Patent CN101204657A discloses a cobalt-cerium composite oxide catalyst with the addition of alkali metals and its preparation method. The catalyst composition is Co3O4, CeO2 with Ce / Co=0-1 (molar ratio) and alkali metal (Li, Na, K, Rb, Cs) with M / Co=0.01-1 (molar ratio); at normal pressure, 260-370°C (furnace temperature), and a space velocity of 0.2 g·s·cm -3 Under the reaction conditions, in a fixed bed reactor, N2O with a concentration of 1000ppm is directly catalytically decomposed into N2 and O2. Patent CN104475112A discloses a catalyst with ZnAl2O4 as a carrier to load active components CuO and one or two active components of Fe, Co, Ni, Zr, Mg, Ca, and Ba oxides, which has a certain ability to resist water poisoning. The above catalysts catalytically decompose N2O with a low concentration and cannot meet the requirements for decomposing high-concentration N2O.

[0007] In view of the insufficiency of the development and application of domestic N2O removal catalysts, it is necessary to develop a catalyst with strong resistance to water and oxygen poisoning, low catalytic activity temperature, long service life, and good overall mechanical strength and thermal stability. This catalyst can provide a solution for this. Summary of the invention

[0008] The purpose of the present invention is to solve the problem of N2O tail gas emitted by the nitric acid industry and the adipic acid industry, and to provide a composite oxide catalyst for catalytically decomposing high-concentration N2O under oxygen-rich water-containing conditions. The catalyst can efficiently catalytically decompose N2O, realize the purification of industrial waste gas in nitric acid devices and adipic acid devices, and can significantly reduce the emission of N2O in industrial production. In particular, N2O can be 100% degraded under low temperature conditions.

[0009] The composite oxide catalyst provided by the present invention is used for catalytic decomposition of high-concentration N2O under oxygen-rich water conditions. The catalyst is a composite oxide composed of nickel, niobium and cobalt, and the molecular formula is Ni x Nb y Co z O w, x / z=0-0.5, y / z=0-0.5, y is not 0, and more preferably, both x and y are not 0, and the amount of O corresponding to w is used to supplement the negatively valent substance.

[0010] The composite oxide catalyst for catalytically decomposing high-concentration N2O under oxygen-rich water conditions provided by the present invention is x Nb y Co z O w The compound is also compounded with an oxide of metal M, wherein the oxide of metal M is a metal oxide of one, two, or a combination of two or more of alkali metals or alkaline earth metals, and the M metal is 0.5 to 10% of the molar fraction of cobalt, that is, the molecular formula is M a -Ni x Nb y Co z O w , where a / z = 0.005 to 0.1.

[0011] In the present invention, the alkali metal is Na, K, Rb or Cs; the alkaline earth metal is Mg, Ca, Sr or Ba.

[0012] The composite oxide catalyst for catalytically decomposing high-concentration N2O under oxygen-rich water conditions provided by the present invention comprises the following steps:

[0013] (a) The corresponding metal salts of each component are placed in deionized water to form a metal solution and stirred for 30 minutes. When the composite metal M contains an alkaline earth metal, a soluble alkaline earth metal salt is generally mixed and dissolved with the above metal salt to form an aqueous solution.

[0014] (b) Dissolve the precipitant in deionized water to form a precipitant solution and stir thoroughly. When the composite metal M contains an alkali metal, a soluble salt or base of the alkali metal is generally mixed and dissolved with the precipitant to form a precipitant solution.

[0015] (c) adding the precipitant solution dropwise into the metal solution to make the mixed solution pH>12, aging at room temperature for 1 hour, and collecting the precipitated material;

[0016] (d) drying the precipitated material at 80-120° C. for 12-24 hours, and calcining it in a muffle furnace at 300-750° C. for 3-10 hours to obtain a catalyst.

[0017] The precipitant is one or more of ammonia water, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, potassium carbonate, potassium bicarbonate and urea, the metal salt is nitrate, carbonate or acetate, the composite metal M can be salt or alkali, and the precipitate is collected by vacuum filtration, centrifugal collection, and rotary evaporation collection.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) The catalyst preparation method is simple, the raw materials are cheap and easily available, it is harmless to the human body and the environment, it is easy to industrialize and has good application prospects.

[0020] (2) The catalyst has a wide range of application conditions. Under normal pressure, space velocity of 1000-30000 / hour, reaction temperature of 450-500°C, it can achieve complete catalytic decomposition of 5-30% N2O under the conditions of 5-15% O2 and 0-20% H2O concentration. It can still maintain good catalytic activity at lower temperatures. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is the XRD pattern of the catalyst prepared under the conditions of Examples 1-5.

[0022] Figure 2 This is the curve of the conversion rate of N2O catalytic decomposition with different catalysts under the conditions of Examples 1-5.

[0023] Figure 3 It is the curve of the conversion rate of catalytic decomposition of N2O under different reaction conditions under the conditions of Example 5 and Example 6. DETAILED DESCRIPTION

[0024] The present invention is further described below by way of examples, but is not limited to the following examples.

[0025] Example 1 (Comparative Example)

[0026] The Co3O4 composite oxide catalyst was prepared as follows: 0.10 mol of cobalt nitrate was weighed and dissolved in 50 mL of distilled water. Then 0.2 mol of ammonia water was diluted to 50 mL, and the ammonia solution was added dropwise to the solution. After mixing completely, it was aged at room temperature for 1 hour. The solid product was collected by centrifugation and dried under ventilation at 80°C. After obtaining the dried mixture, it was heated and calcined in a muffle furnace at a heating temperature of 360°C. The heating rate was 5°C / min and the calcination time was 6 hours.

[0027] The prepared Co3O4 composite oxide catalyst is granulated and loaded into a quartz reaction tube, and the gas is mixed and then introduced into the reaction tube, and then enters the reactor for reaction. The concentration of N2O in the reaction system is 30%, O2 is 5%, and H2O is 10% (He is the balance gas). The N2O decomposition is carried out under the condition that the mixed gas hourly space velocity range is 30000 / hour. When the reaction temperature is within the range of 300-500℃, sampling is carried out every 50℃, and it is found that the N2O conversion rate can reach 83.98% at 350℃. The N2O conversion rate can reach 94.17% at 400℃. The N2O conversion rate can reach 97.41% at 450℃ and 98.54% at 500℃.

[0028] Example 2

[0029] Ni 0.1 CoO w The composite oxide catalyst was prepared as follows: 0.1 mol of cobalt nitrate and 0.01 mol of nickel nitrate were weighed and dissolved in 50 mL of distilled water. Then 0.22 mol of ammonia water was diluted to 50 mL, and the ammonia solution was added dropwise to the solution. After mixing completely, it was aged at room temperature for 1 hour. The solid product was collected by centrifugation and dried under ventilation at 80°C. After obtaining the dried mixture, it was heated and calcined in a muffle furnace at a heating temperature of 360°C. The heating rate was 5°C / min and the calcination time was 6 hours.

[0030] The prepared Ni 0.1 CoO w After the composite oxide catalyst is granulated, it is loaded into a quartz reaction tube, and the gas is mixed and then introduced into the reaction tube, and then enters the reactor for reaction. The concentration of N2O in the reaction system is 30%, O2 is 5%, and H2O is 10% (He is the balance gas). The N2O decomposition is carried out under the condition that the hourly space velocity of the mixed gas ranges from 30000 / hour. When the reaction temperature is within the range of 300-500°C, a sampling test is carried out every 50°C, and it is found that the N2O conversion rate can reach 93.41% at 350°C. The N2O conversion rate can reach 97.74% at 400°C. The N2O conversion rate can reach 99.17% at 450°C. The N2O conversion rate can reach 99.6% at 500°C.

[0031] Example 3

[0032] Nb 0.1 CoO wThe composite oxide catalyst was prepared as follows: 0.1 mol of cobalt nitrate and 0.01 mol of niobium oxalate were weighed and dissolved in 50 mL of distilled water. Then 0.22 mol of ammonia water was diluted to 50 mL, and the ammonia solution was added dropwise to the solution. After mixing completely, it was aged at room temperature for 1 hour. The solid product was collected by centrifugation and dried under ventilation at 80°C. After obtaining the dried mixture, it was heated and calcined in a muffle furnace at a heating temperature of 360°C. The heating rate was 5°C / min and the calcination time was 6 hours.

[0033] The prepared Nb 0.1 CoO w After the composite oxide catalyst is granulated, it is loaded into a quartz reaction tube, and the gas is mixed and then introduced into the reaction tube, and then enters the reactor for reaction. The concentration of N2O in the reaction system is 30%, O2 is 5%, and H2O is 10% (He is the balance gas). The N2O decomposition is carried out under the condition that the hourly space velocity of the mixed gas ranges from 30000 / hour. When the reaction temperature is within the range of 300-500°C, sampling is carried out every 50°C, and it is found that the N2O conversion rate can reach 90.2% at 350°C. The N2O conversion rate can reach 98.24% at 400°C. The N2O conversion rate can reach 99.77% at 450°C. The N2O conversion rate can reach 99.97% at 500°C.

[0034] Example 4

[0035] Ni 0.05 Nb 0.05 CoO w The composite oxide catalyst was prepared as follows: 0.1 mol of cobalt nitrate, 0.05 mol of nickel nitrate and 0.05 mol of niobium oxalate were weighed and dissolved in 50 mL of distilled water. Then 0.22 mol of ammonia water was diluted to 50 mL, and the ammonia solution was added dropwise to the solution. After mixing completely, it was aged at room temperature for 1 hour. The solid product was collected by centrifugation and dried under ventilation at 80 ° C. After obtaining the dried mixture, it was heated and calcined in a muffle furnace at a heating temperature of 360 ° C. The heating rate was 5 ° C / min and the calcination time was 6 hours.

[0036] The prepared Ni 0.05 Nb 0.05 CoO wAfter the composite oxide catalyst is granulated, it is loaded into a quartz reaction tube, and the gas is mixed and then introduced into the reaction tube, and then enters the reactor for reaction. The concentration of N2O in the reaction system is 30%, O2 is 5%, and H2O is 10% (He is the balance gas). The N2O decomposition is carried out under the condition that the gas hourly space velocity of the mixed gas ranges from 30000 / hour. When the reaction temperature is within the range of 300-500°C, a sampling test is carried out every 50°C, and it is found that the N2O conversion rate can reach 94.85% at 350°C. The N2O conversion rate can reach 99.53% at 400°C. The N2O conversion rate can reach 100% at 450°C. The N2O conversion rate can reach 100% at 500°C.

[0037] Example 5

[0038] Cs 0.02 -Ni 0.05 Nb 0.05 CoO w The composite oxide catalyst was prepared as follows: 0.1 mol of cobalt nitrate, 0.05 mol of nickel nitrate and 0.05 mol of niobium oxalate were weighed and dissolved in 50 mL of distilled water. Then 0.22 mol of ammonia water and 0.002 mol of cesium hydroxide were prepared into 50 mL of aqueous solution, and the aqueous solution was added dropwise to the solution. After mixing completely, it was aged at room temperature for 1 hour. The solid product was collected by centrifugation and dried under ventilation at 80°C. After obtaining the dried mixture, it was heated and roasted in a muffle furnace at a heating temperature of 360°C. The heating rate was 5°C / min and the roasting time was 6 hours.

[0039] The prepared Cs 0.02 -Ni 0.05 Nb 0.05 CoO w After the composite oxide catalyst is granulated, it is loaded into a quartz reaction tube, and the gas is mixed and then introduced into the reaction tube, and then enters the reactor for reaction. The concentration of N2O in the reaction system is 30%, O2 is 5%, and H2O is 10% (He is the balance gas). The N2O decomposition is carried out under the condition that the gas hourly space velocity range of the mixed gas is 30000 / hour. When the reaction temperature is within the range of 300-500°C, a sampling test is carried out every 50°C, and it is found that the N2O conversion rate can reach 97.4% at 350°C. The N2O conversion rate can reach 99.71% at 400°C. The N2O conversion rate can reach 100% at 450°C. The N2O conversion rate can reach 100% at 500°C.

[0040] Example 6

[0041] Repeat Example 5 to prepare Cs 0.02 -Ni 0.05 Nb 0.05 CoO w catalyst.

[0042] The prepared Cs 0.02 -Ni 0.05 Nb 0.05 CoO w After the composite oxide catalyst is granulated, it is loaded into a quartz reaction tube, and the gas is mixed and then introduced into the reaction tube, and then enters the reactor for reaction. The concentration of N2O in the reaction system is 30%, O2 is 15%, and H2O is 20% (He is the balance gas). The N2O decomposition is carried out under the condition that the hourly space velocity of the mixed gas ranges from 30000 / hour. When the reaction temperature is within the range of 300-500°C, a sampling test is carried out every 50°C, and it is found that the N2O conversion rate can reach 93.2% at 350°C. The N2O conversion rate can reach 99.2% at 400°C. The N2O conversion rate can reach 100% at 450°C. The N2O conversion rate can reach 100% at 500°C.

[0043] Experimental results: (1) Figure 1 : This is the XRD spectrum of the catalyst prepared under the conditions of Examples 1 to 5. It can be seen from the figure that the catalysts prepared by the coprecipitation method in Examples 2 to 5 do not have nickel, niobium and cesium oxide crystal phases, indicating that the nickel, niobium and cesium oxides are highly dispersed in Co3O4; the diffraction peak of Co3O4 becomes weaker and the half-peak width becomes wider, indicating that doping may make the Co3O4 grains smaller and the crystallinity lower.

[0044] (2) Figure 2 The curves of the conversion rate of N2O decomposition by different catalysts under the conditions of Examples 1 to 5 vary with temperature. It is proved that the N2O conversion rate of the catalysts with nickel oxide and niobium oxide added is higher than that of the catalysts without nickel oxide and niobium oxide added, and the N2O conversion rate is higher when both are added at the same time than when both are added separately. After adding cesium, the activity is significantly improved.

[0045] (3) Figure 3 The curves of the conversion rate of N2O catalytic decomposition under different reaction conditions under the same catalyst in Examples 5 and 6 are as a function of temperature. When the catalyst is in the presence of higher oxygen concentration and high water vapor, the conversion rate at 350°C only drops by 4%, and at 450°C, both conversion rates reach 100%. This proves that the catalyst has a high resistance to water and oxygen poisoning.

Claims

1. A composite oxide catalyst for catalytically decomposing high-concentration N2O under oxygen-rich water conditions, characterized in that: The catalyst is a composite oxide composed of two or three of nickel, niobium and cobalt, with a molecular formula of Ni x Nb y Co z O w , x / z=0~0.5, y / z=0~0.5, y is not 0, the amount of O corresponding to w is used to supplement the negatively valent substances; the oxides of nickel and niobium are highly dispersed in Co3O4.

2. A composite oxide catalyst for catalytically decomposing high-concentration N2O under oxygen-rich water conditions according to claim 1, characterized in that: Select x and y to be non-zero.

3. A composite oxide catalyst for catalytically decomposing high-concentration N2O under oxygen-rich water conditions according to claim 1, characterized in that: In Ni x Nb y Co z O w The compound is further compounded with an oxide of metal M, wherein the oxide of metal M is a metal oxide of one, two, or a combination of two or more of alkali metals or alkaline earth metals, and the molar fraction of metal M is 0.5-10% of cobalt, that is, the molecular formula is M a -Ni x Nb y Co z O w , where a / z=0.005~0.

1.

4. A composite oxide catalyst for catalytically decomposing high-concentration N2O under oxygen-rich water conditions according to claim 3, characterized in that: The alkali metal is Na, K, Rb or Cs; the alkaline earth metal is Mg, Ca, Sr or Ba.

5. A method for preparing a composite oxide catalyst for catalytically decomposing high-concentration N2O under oxygen-rich water conditions according to any one of claims 1 to 4, characterized in that: The following steps are involved: (a) placing the corresponding metal salts of each component in deionized water to form a metal solution and stirring the solution for 30 minutes; when the composite metal M contains an alkaline earth metal, mixing and dissolving the alkaline earth metal soluble salt with the above metal salt to form an aqueous solution; (b) dissolving a precipitant in deionized water to form a precipitant solution and stirring the solution thoroughly; when the composite metal M contains an alkali metal, mixing and dissolving a soluble salt or base of the alkali metal with the precipitant to form a precipitant solution; (c) adding the precipitant solution dropwise into the metal solution to make the mixed solution pH>12, aging at room temperature for 1 hour, and collecting the precipitated material; (d) drying the precipitated material at 80-120° C. for 12-24 hours, and calcining the precipitated material in a muffle furnace at 300-750° C. for 3-10 hours to obtain a catalyst; Wherein the precipitant is one or more of sodium hydroxide, potassium hydroxide, potassium carbonate, cesium hydroxide, potassium bicarbonate and urea, the metal salt is nitrate, carbonate or acetate, and the precipitate is collected by vacuum filtration, centrifugal collection or rotary evaporation collection; when the precipitant is sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, potassium carbonate or potassium bicarbonate, the precipitate can be collected by vacuum filtration, centrifugal collection or rotary evaporation collection. x Nb y Co z O w The base is compounded with an oxide of metal M.

6. Use of a composite oxide catalyst for catalytic decomposition of high-concentration N2O under oxygen-rich water conditions as claimed in any one of claims 1 to 4, for catalytic decomposition of high-concentration N2O under oxygen-rich water conditions.

7. The use according to claim 6, characterized in that Under normal pressure, space velocity of 1000~30000 / hour, reaction temperature of 450~500 °C, it can achieve complete catalytic decomposition of 5~30% N2O under the conditions of 5~15% O2 and H2O concentration of 0~20%.

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