CN111569953B - Preparation method of denitration catalyst - Google Patents

Preparation method of denitration catalyst Download PDF

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CN111569953B
CN111569953B CN202010368637.1A CN202010368637A CN111569953B CN 111569953 B CN111569953 B CN 111569953B CN 202010368637 A CN202010368637 A CN 202010368637A CN 111569953 B CN111569953 B CN 111569953B
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赵玉平
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Hunan Litai Environmental Engineering Co ltd
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Abstract

The invention provides high-load Ru-MnO X Preparation method of graphene denitration catalyst, wherein the catalyst is in a flake shape, and Ru metal is in MnO X The catalyst has the advantages of high dispersion of graphene, loading capacity of Ru of 10-15wt.%, high dispersion of Ru metal on the surface of the catalyst, no agglomeration phenomenon, particle size of 1-2nm, extremely high conversion rate and selectivity, and good SO 2/water resistance stability.

Description

Preparation method of denitration catalyst
Technical Field
The invention relates to a preparation method of a high-load Ru-MnOX/graphene denitration catalyst, belonging to the field of denitration catalysts.
Technical Field
Nitrogen oxides NOX are compounds consisting of only two elements, nitrogen and oxygen, and there are many kinds of nitrogen oxides, including nitrous oxide N2O, nitric oxide NO, nitrogen dioxide NO2, dinitrogen trioxide N2O3, dinitrogen tetroxide N2O4, dinitrogen pentoxide N2O5, and other compounds, and herein, except nitrogen dioxide, other NOX are extremely unstable, and become nitrogen dioxide and nitric oxide when exposed to light, humidity, or heat, and nitric oxide becomes nitrogen dioxide again. The main causes of atmospheric pollution are Nitric Oxide (NO) and nitrogen dioxide (NO 2). The sources of NO secondary pollutants in the atmosphere mainly comprise two aspects, namely a natural source and an artificial source. The artificial source of NOx is divided into a fixed source and a mobile source, wherein the fixed source is mainly from combustion of industrial boilers/kilns and fuels of coal-fired power plants and is a main source of NO two emission, and the mobile source mainly refers to emission of motor vehicle tail gas. In fact, whether it is a fixed source or a mobile source, the vast majority of the NO two emitted therein originates from the combustion process of fossil fuels, and the emission amount shows a trend of increasing with the increasing level of the development of the economic society.
At present, the main methods adopted by the flue gas denitration technology are a Selective Catalytic Reduction (SCR) method, a selective non-catalytic reduction (SNCR) method, an SCR/SNCR mixed method technology and the like. The SNCR has stronger temperature dependence and lower denitration rate (only 25-40%), and a Selective Catalytic Reduction (SCR) technology is widely applied to a plurality of countries with strict flue gas emission standards, can meet the NOx emission standards with higher requirements, and is considered as the most economic and reliable denitration technology at present.
The SCR denitration catalyst refers to the condition that the optimal active temperature interval of the denitration catalyst is in a low temperature region, namely an SCR system has a good denitration effect within the temperature range of 60-200 ℃. The low-temperature SCR technology has the advantages that (1) a catalyst bed layer is arranged at the tail end of the whole denitration device, the old boiler is relatively easy to reform, the investment cost can be greatly reduced, and (2) because NH3 is difficult to generate oxidation reaction at low temperature, the unnecessary NH3 loss is reduced, and the denitration operation cost is reduced. (3) The smoke concentration and SO2 concentration in the flue gas are very low, and especially, the elements such as alkali metal and alkaline earth metal K, ca, na, mg and the like are greatly reduced, SO that the catalyst is not easy to be poisoned, and the service life is prolonged. At present, the research on the low-temperature SCR flue gas tip removal technology mainly focuses on the development of low-temperature SCR catalysts, and the research on the active ingredients of the low-temperature tip removal catalysts mainly focuses on metal oxides such as CuO, fe2O3, mnOx, ceO2 and the like. The low-temperature SCR desorption catalyst is mainly divided into a TiO2 carrier catalyst, an AI2O3 carrier catalyst, an Activated Carbon (AC) carrier catalyst, a molecular hoof carrier catalyst and the like according to carrier materials. The carrier mainly functions to provide a large specific surface area and improve dispersion of the active material. The selection of the catalyst carrier firstly considers the specific surface area and the pore structure of the catalyst carrier and secondly considers whether the carrier can enhance the mechanical strength of the catalyst so as to ensure that the catalyst has a certain shape. Among the catalysts, metal oxide and carbon-based catalysts are successfully realized in industrial application, and the molecular sieve catalyst has high performance of removing NOx, so that the molecular sieve catalyst is an active research field. At present, most of coal-fired power plants adopt metal oxide catalysts as main de-confirmation catalysts, and carbon-based catalysts are widely applied in the aspects of simultaneous desulfurization and de-confirmation.
As for the Activated Carbon carrier, activated Carbon (AC) has a rich pore structure, a low cost, a large specific surface area, and a certain SCR denitration activity, and has been used for air or industrial exhaust gas purification treatment for a long time. In the treatment of NOx, it can be used as an adsorbent and a catalyst, and under the condition of low temperature, it is mainly used as adsorbent, and under the condition of high temperature, it is converted into catalyst [33]. The active carbon has higher application value in NOX treatment, has the biggest advantages of rich sources, low price and easy regeneration, and is suitable for the environment with lower temperature. The catalytic performance of the activated carbon as a catalyst is not ideal enough, and the catalytic activity is very low particularly under the condition of high space velocity. Different metal oxides are loaded on the carbon-based material and the modified material thereof, so that the denitration performance of the catalyst can be improved, and a few scholars at home and abroad have prepared the carbon-based material catalyst with good low-temperature catalytic activity. In the denitration reaction process, the catalytic activity of the activated carbon is also influenced by surface groups, the acid groups on the surface of the activated carbon adsorb NH3, the basic groups adsorb NOx, and the two substances on the adjacent adsorption sites can react with each other. Therefore, in practical applications, it is often necessary to perform a pre-activation treatment to increase surface acidic groups or basic groups, or to load some active components to improve the catalytic performance.
Regarding the manganese active component, mn-based oxide catalysts are receiving attention because of having an extremely high low-temperature denitration performance. The main reason for this may be that the Mn species has a rich variable valence state, being capable of providing free electrons as an active component. Electrons on a d orbit of Mn with different valence states in MnOX are in a half-filled state, an electron orbit of tetravalent Mn is 3d3, an electron orbit of divalent Mn is 3d5, and electrons on the d orbit are very easy to migrate to ammonia and oxygen, so that the catalyst has extremely strong low-temperature oxidation-reduction capability in NH3-SCR reaction. The MnOx is used as a catalyst, the SCR reaction can be promoted to start to occur at the time of less than 100 t, and a very good effect is achieved at the time of 100-200 ℃. Researches find that various factors such as the oxidation state, the crystal structure and the surface structure of MnOX jointly determine the catalytic performance of MnOX. The most significant disadvantages of MnOX catalysts are limited antitoxic ability and complex valence states of MnOX, which are difficult to control for indeterminate form of the hard oxides. The research of a large number of researchers shows the denitration performance of the single metal oxide catalyst component, provides a reliable experimental basis, and lays a foundation for the subsequent research of the low-temperature denitration catalyst.
With respect to the noble metal catalyst:
for example, CN 101518718A discloses a functional filter felt for purifying harmful components in flue gas, which comprises a fiber material and a functional catalyst with catalytic desulfurization and/or denitrification reactions, wherein the active component of the functional catalyst comprises one or more of noble metals and metal oxides, the noble metals are one or more of gold, silver or platinum group metals, the platinum group metals are ruthenium, rhodium, palladium, osmium, iridium or platinum, the metal oxides are one or more of CuO, cu2O, V2O5, coO, co2O3, mnO2, mn2O3, mn3O4, fe2O3, feO, fe3O4, moO3, WO3 and CeO2, namely, the active component comprises cerium oxide, manganese oxide and ruthenium oxide, the carrier of the active component is titanium dioxide, and the catalyst has extremely high NOx removal activity and good poisoning resistance at an ultralow temperature of 80-120 ℃.
CN 109718767A discloses a ruthenium series ultralow temperature denitration catalyst, which is prepared by sectional impregnation and roasting and comprises the following components in percentage by mass: 1.22 to 2.84 percent of cerium element, 10.42 to 11.7 percent of manganese element, 1.14 to 2.68 percent of ruthenium element and 45.84 to 47.02 percent of titanium element. Compared with the existing Ce-Mn/TiO2 catalyst, the catalyst disclosed by the invention has the advantages of realizing a good denitration effect at an ultralow temperature of 80-120 ℃, remarkably improving the poisoning resistance, being long in service life and the like.
CN 110368934A discloses a ruthenium system ultra-low temperature denitration catalyst, which is provided based on the problem that active components in the existing denitration catalyst are not easy to load on the surface of a metal material carrier, and comprises the following steps: (1) carrier etching; (2) impregnating, drying and roasting the carrier; the invention also provides the wire mesh SCR denitration catalyst prepared by the preparation method. The invention has the beneficial effects that: the wire mesh SCR denitration catalyst prepared by the invention has good denitration performance at 70-120 ℃, and the activity at 80 ℃ reaches more than 80%.
The above patents all mention the use of noble metals Ru and MnO2 as active components, but both have a serious problem of low-temperature catalytic activity, mainly because the loading of Ru is too low, it is known that Ru as a noble metal catalyst, like Rh, usually gives the catalyst extremely high low-temperature catalytic activity, but Ru as a noble metal catalyst, the loading is generally 0.1wt.% to 5wt.% during the loading process, when the loading is more than 5wt.%, serious agglomeration occurs, the particle size is more than 150nm as shown in fig. 7, and there is a technical solution that the loading of Ru is raised to more than 10wt.% and the Ru high dispersion state is maintained.
Disclosure of Invention
Based on the problems in the prior art, the invention provides a preparation method of a high-load Ru-MnOX/graphene denitration catalyst.
The method comprises the following steps:
(1) Pretreating graphene: placing 2-3g of graphene into a 100 mL flask, adding 98wt.% of H2SO4 and 65-67wt.% of HNO3, ultrasonically oscillating for 20-30 min, performing reflux treatment at 130-140 ℃ for 3-4H under the heating conditions of stirring and oil bath, filtering and washing with deionized water, and air-drying the filtrate at 60-80 ℃ for 12-24H to obtain the graphene base material subjected to mixed acid oxidation treatment.
(2) Hydrothermal preparation of MnOX/graphene material: and (2) placing the graphene substrate prepared in the step (1) in 0.2-0.5M Mn (NO 3) 2.6H2O aqueous solution, dropwise adding 0.5-1g of urotropine, stirring for 3-5min, placing in a hydrothermal reaction kettle, performing hydrothermal reaction at 95-100 ℃ for 9-10h, naturally cooling, washing with deionized water, filtering, drying in air, and roasting.
(3) Loading Ru metal: soaking the MnOX/graphene material prepared in the step (2) in 0.22-0.57M ethanol solution of ruthenium nitrosyl nitrate for 2-5h, condensing and drying in vacuum, and then roasting, washing and drying to obtain the high-load Ru-MnOX/graphene denitration catalyst.
Furthermore, the morphology of the Ru-MnOX/graphene is like a flower sheet.
Further, the pore size of the catalyst is intensively distributed in the range of 200-700nm.
Furthermore, the loading amount of Ru in the catalyst is 10-15wt.%, and Ru metal is highly dispersed on the surface of the catalyst, so that the catalyst is free from agglomeration and has a particle size of 1-2nm.
Further, the volume ratio of H2SO4 to HNO3 is 2-3, and the washing is stopped when the filtering solution pH =6.0-6.5 after filtering and washing.
Further, the roasting in the step (2) is muffle furnace roasting, and the roasting temperature programming parameters are as follows: heating to 300-330 deg.C at 10-15 deg.C/min, maintaining the temperature for 1.5-2h, and naturally cooling to room temperature.
Further, the roasting in the step (3) is muffle furnace roasting, and the roasting temperature programming parameters are as follows: raising the temperature to 300-330 ℃ at 1-2 ℃ per min, keeping the temperature for 30-40min, and naturally cooling to room temperature.
Further, the catalyst has NOx conversion rate higher than 80% and NOx selectivity higher than 90% in the temperature range of 75-200 ℃.
Further, the catalyst has stability of more than 300h under the condition of no SO 2/water.
Further, the catalyst has stability of more than 250h in the presence of SO 2/water.
The scheme of the invention has the following beneficial effects:
(1) The MnOX/graphene carrier is in a shape of a flower with pore channels intensively distributed at 200-700nm as shown in figure 2, in addition, 20-30nm graphene mesoporous pore channels exist, the carrier is high in specific surface area, and the MnOx crystal form is shown in figure 1.
(2) The loading amount of Ru in the Ru-MnOX/graphene catalyst is 10-15wt.%, and Ru metal is highly dispersed on the surface of the catalyst, so that the catalyst is free from agglomeration and has the particle size of 1-2nm.
(3) The denitration effect is good, the NOx conversion rate and the selectivity are extremely high, and the stability is more than 300h.
(4) The water resistance and sulfur resistance are strong, and the denitration efficiency of the catalyst is stabilized to be more than 99.9 percent at 105oC and Ru-MnOX/graphene.
Drawings
Fig. 1 is an XRD pattern of the inventive MnOx-graphene support.
Fig. 2 is a STEM map of a MnOX/graphene support of the present invention.
Fig. 3 is a STEM diagram of a 10wt.% Ru-MnOX/graphene support of the present invention.
Fig. 4 is a STEM map of a 12.5wt.% Ru-MnOX/graphene support of the present invention.
Fig. 5 is a STEM map of a 15wt.% Ru-MnOX/graphene support of the present invention.
FIG. 6 is a SEM-Mapping plot of a 10wt.% Ru-MnOX/graphene support of the invention.
FIG. 7 is a TEM agglomeration profile of a prior art Ru/SBS-15 catalyst with a loading of 5%.
Detailed Description
Example 1
A preparation method of a high-load Ru-MnOX/graphene denitration catalyst comprises the following steps:
(1) Pretreating graphene: placing 2g of graphene in a 100 mL flask, adding 98wt.% of H2SO4 and 65-67wt.% of HNO3, wherein the volume ratio of H2SO4 to HNO3 is 2
And ultrasonically oscillating for 20 min, then carrying out reflux treatment for 3h at 130 ℃ under the conditions of stirring and oil bath heating, filtering and washing by deionized water, and carrying out air drying on the filtered matter for 12 h at 60 ℃ to obtain the graphene base material subjected to mixed acid oxidation treatment.
(2) Hydrothermal preparation of MnOX/graphene material: placing the graphene substrate prepared in the step (1) in 0.2M Mn (NO 3) 2.6H2O aqueous solution, dropwise adding 0.5g of urotropine, stirring for 3min, placing in a hydrothermal reaction kettle, performing hydrothermal reaction at 95 ℃ for 9h, naturally cooling, washing with deionized water, filtering, drying with air, and roasting, wherein the roasting is muffle furnace roasting, and the temperature rise parameters of the roasting program are as follows: heating to 300 deg.C at 10 deg.C/min, maintaining the temperature for 1.5h, and naturally cooling to room temperature.
(3) Loading Ru metal: soaking the MnOX/graphene material prepared in the step (2) in 0.22M ethanol solution of ruthenium nitrosyl nitrate for 2h, condensing and drying in vacuum, then roasting, washing, drying, and highly loading the Ru-MnOX/graphene denitration catalyst, wherein the roasting temperature programming parameters are as follows: raising the temperature to 300 ℃ at a speed of 1 ℃/min, keeping the temperature for 30min, and naturally cooling to room temperature.
Example 2
A preparation method of a high-load Ru-MnOX/graphene denitration catalyst comprises the following steps:
(1) Pretreating graphene: placing 2.5g of graphene in a 100 mL flask, adding 98wt.% of H2SO4 and 65-67wt.% of HNO3, wherein the volume ratio of H2SO4 to HNO3 is 2.5, filtering and washing until the filtrate pH =6.25, stopping washing
And ultrasonically oscillating for 25 min, then carrying out reflux treatment at 135 ℃ for 3.5h under the conditions of stirring and oil bath heating, filtering and washing by deionized water, and carrying out air drying on the filtered matter at 75 ℃ for 18 h to obtain the graphene base material subjected to mixed acid oxidation treatment.
(2) Hydrothermal preparation of MnOX/graphene material: placing the graphene substrate prepared in the step (1) in 0.25M Mn (NO 3) 2.6H2O aqueous solution, dropwise adding 0.75g of urotropine, stirring for 4min, placing in a hydrothermal reaction kettle, performing hydrothermal reaction at 97.5 ℃ for 9.5h, naturally cooling, washing with deionized water, filtering, drying in air, and roasting, wherein the roasting is muffle furnace roasting, and the temperature rise parameters of the roasting program are as follows: raising the temperature to 300-330 ℃ at the speed of 12.5 ℃/min, keeping the temperature for 1.75h, and naturally cooling to room temperature.
(3) And (3) loading Ru metal: soaking the MnOX/graphene material prepared in the step (2) in 0.39M ethanol solution of ruthenium nitrosyl nitrate for 3.5h, condensing and drying in vacuum, then roasting, washing, drying, and highly loading the Ru-MnOX/graphene denitration catalyst, wherein the roasting temperature programming parameters are as follows: heating to 315 ℃ at the temperature of 1.5 ℃/min, keeping the temperature for 35min, and naturally cooling to room temperature.
Example 3
A preparation method of a high-load Ru-MnOX/graphene denitration catalyst comprises the following steps:
(1) Pretreating graphene: 3g of graphene was placed in a 100 mL flask, and 98wt.% H was added 2 SO 4 And 65-67wt.% HNO 3 ，H 2 SO 4 And HNO 3 The volume ratio of (1) is 3.
(2) Hydrothermal preparation of MnOX/graphene material: placing the graphene base material prepared in the step (1) in 0.5M Mn (NO 3) 2.6H2O aqueous solution, dropwise adding 1g of urotropine, stirring for 5min, placing in a hydrothermal reaction kettle, performing hydrothermal reaction at 100 ℃ for 10h, naturally cooling, washing with deionized water, filtering, drying with air, and roasting, wherein the roasting is muffle furnace roasting, and the roasting temperature programming parameter is as follows: raising the temperature to 330 ℃ at a speed of 15 ℃/min, keeping the temperature for 2 hours, and naturally cooling to room temperature.
(3) Loading Ru metal: soaking the MnOX/graphene material prepared in the step (2) in 0.57M ethanol solution of ruthenium nitrosyl nitrate for 5 hours, condensing and drying in vacuum, then roasting, washing, drying, and highly loading the Ru-MnOX/graphene denitration catalyst, wherein the roasting temperature programming parameters are as follows: raising the temperature to 300-330 ℃ at the speed of 2 ℃/min, keeping the temperature for 30-40min, and naturally cooling to room temperature.
Taking the preparation method of example 2 as a sample preparation method, by controlling the dosage of the MnOX/graphene material of step (3), the Ru content is effectively controlled to be 10wt.%, 12.5wt.%, 15wt.%, respectively, and the designations S-1, S-2, S-3 correspond to fig. 3, fig. 4, and fig. 5, respectively, in which Ru metal is highly dispersed on the surface of the base material, in which white dots are metal particles, and black portions are a substrate. In which S-1 was subjected to mapping test, as shown in fig. 6, it was further determined that the particles were in a highly dispersed state and the mass of Ru was 10.73wt.%, substantially in accordance with the calculation.
Test conditions of the catalyst, amount of catalyst used 500mg, test atmosphere of SCR 750ppm NO, 750ppm NH 3 ，5vol% O 2 Ar balance gas, space velocity 50000 h −1 。
Table 1 shows the effect of different temperatures on the performance of different supported catalysts (NOX conversion, N2 selectivity).
Figure DEST_PATH_IMAGE002
As is clear from table 1 above, each sample exhibited a tendency that the NOx conversion rate increased and then decreased with increasing temperature. The improvement of the conversion rate of the catalyst to NO is obvious from 50-75 ℃, for example, the conversion rate of the S-1 catalyst at 50 ℃ and 75 ℃ is 23.7% and 80.3% respectively, the temperature rise is particularly obvious for the conversion rate of 10wt.% Ru-MnOX/graphene catalyst NOx, the conversion rate of the S-2 catalyst at 50 ℃ and 75 ℃ is 45.2% and 85.2% respectively, the conversion rate of the S-3 catalyst at 50 ℃ and 75 ℃ is 55.6% and 93.7% respectively, the catalytic activity of the S-3 15wt.% Ru-MnOX/graphene catalyst at 75 ℃ can reach 93.7% along with the increase of the Ru content, the catalytic activity is far higher than that of the similar noble metal-MnOX catalyst, the noble metal-MnOX catalyst reported in the literature is usually 40-60%, the effective denitration can be lower than 1ppM level along with the continuous increase of the temperature, and the catalytic activity is reduced along with the continuous increase of the temperature.
In general, the Ru-MnOX/graphene catalyst of the invention has NOx conversion rate of more than 80% and NOx selectivity of more than 90% in the range of 75-200 ℃.
TABLE 2S-2 catalysts stability test (105 deg.C)
Figure DEST_PATH_IMAGE004
As shown in table 2 above, the S-2 catalyst was tested for stability, with test adjustments: the catalyst was used in an amount of 500mg, the SCR test atmosphere 750ppm NO, 750ppm NH 3 ，5vol% O 2 Ar balance gas, space velocity 50000 h-1.
It can be obviously found that the stability of the Ru-MnOX/graphene is more than 300h, and when 420h is satisfied, the conversion rate is reduced to 97.0%.
TABLE 2S-3 catalysts stability test (105 deg.C)
Figure DEST_PATH_IMAGE006
As shown in the above table 3, the stability of the S-2 catalyst was tested by the water and sulfur resistance test, and the test was adjusted as follows: the catalyst was used in an amount of 500mg, the SCR test atmosphere 750ppm NO, 750ppm NH 3 ，5vol% O 2 ，100 ppm SO 2 ，5 vol% H 2 Balance gas of O and Ar, space velocity of 50000 h −1 。
Under the test condition, the denitration efficiency of the catalyst is still stable to be more than 99.9% for 250h, which proves that the catalyst has stronger sulfur-resistant and water-resistant capabilities, but the catalytic activity of the catalyst is obviously reduced along with the time, and probably the main reason is water vapor, so that the Ru nanoparticles are subjected to migration and aggregation, and the catalytic activity is reduced.
Although the present invention has been described above by way of examples of preferred embodiments, the present invention is not limited to the specific embodiments, and can be modified as appropriate within the scope of the present invention.

Claims (3)

1. A preparation method of a denitration catalyst is characterized by comprising the following steps:
(1) Pretreating graphene: 2-3g of graphene was placed in a 100 mL flask, 98wt.% H was added 2 SO 4 And 65-67wt.% HNO 3 Said H is 2 SO 4 And HNO 3 The volume ratio of (A) is 2-3, ultrasonic oscillation is carried out for 20-30 min, then reflux treatment is carried out for 3-4 h at 130-140 ℃ under the conditions of stirring and oil bath heating, deionized water is filtered and washed until the pH of filtrate is =6.0-6.5, then washing is stopped, and the filtrate is air-dried for 12-24 h at 60-80 ℃ to obtain the graphene base material subjected to oxidation treatment;
(2) Hydrothermal preparation of MnO X Graphene material: putting the graphene substrate prepared in the step (1) in 0.2-0.5M of Mn (NO) 3 ) 2 . 6H 2 Adding 0.5-1g urotropine dropwise into the O aqueous solution, stirring for 3-5min, placing in a hydrothermal reaction kettle, carrying out hydrothermal reaction at 95-100 ℃ for 9-10h, naturally cooling, washing with deionized water, filtering, air drying, and roasting; the roasting in the step (2) is muffle furnace roasting, and the roasting temperature programming parameters are as follows: heating to 300-330 deg.C at 10-15 deg.C/min, maintaining the temperature for 1.5-2h, and naturally cooling to room temperature;
(3) Loading Ru metal: mnO prepared in the step (2) X Soaking the graphene material in 0.22-0.57M ethanol solution of ruthenium nitrosyl nitrate for 2-5h, vacuum condensing and drying, then roasting, washing and drying to obtain high-load Ru-MnO X A graphene denitration catalyst; the roasting in the step (3) is muffle furnace roasting, and the roasting temperature programming parameters are as follows: heating to 300-330 deg.C at 1-2 deg.C/min, holding the temperature for 30-40min, and naturally cooling to room temperature.
2. As claimed in claim1, the preparation method of the denitration catalyst is characterized in that the catalyst is free of SO 2 Under the anhydrous condition, the stability is more than 300h.
3. The method of claim 1, wherein the denitration catalyst comprises SO 2 And the stability is more than 250h under the condition of water.
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