CN101357328A - Monolithic catalyst for flue gas denitrification with silicon-based ceramics as carrier and preparation method thereof - Google Patents

Abstract

The invention relates to a monolithic flue gas denitrification catalyst with silicon-based ceramics as a carrier and a preparation method thereof, belonging to the fields of air pollution control technology and environmental protection catalytic materials. It is characterized in that silicon-based ceramics are used as the first carrier, active silica is used as the second carrier, and _CeO2 is added with one or more transition metal oxides such as Mo, W, Cu, Fe, Zr, and La as the active group. point. The preparation method adopted is to impregnate the silicon-based ceramics with aluminum sol, dry and roast to prepare the active silica coating, and then impregnate the Ce(NO ₃ ) ₃ solution to prepare the active CeO ₂ coating. Compared with the prior art, the invention not only improves the mechanical and thermal stability of the catalyst carrier, but reduces the load of active components; it is also environmentally friendly without secondary pollution, improves the activity of the catalyst, and expands the active temperature window.

Description

Monolithic catalyst for flue gas denitrification with silicon-based ceramics as carrier and preparation method thereof

technical field

The invention relates to an environmentally friendly, efficient and cheap flue gas denitrification monolithic catalyst and a preparation method thereof, belonging to the fields of air pollution control technology and environmentally friendly catalytic materials.

Background technique

Among the numerous flue gas denitrification methods, selective catalytic reduction (SCR) denitrification technology has been widely used because of its high denitrification efficiency. At present, the SCR denitrification equipment of large and medium-sized thermal power plants in my country is all imported, and the price is very expensive (the denitrification catalyst for a 600MW unit costs about 40 million and needs to be replaced every two years). Flue gas denitrification catalysts without independent intellectual property rights have become my country's environmental protection The "coreless pain" in the field. Commercial SCR denitration catalysts are mainly catalysts in which V ₂ O ₅ is the active component and TiO ₂ is the carrier. Using NH ₃ , CO or hydrocarbons (HC) as reducing agents, the NOx in the flue gas is reduced to N ₂ . V ₂ O ₅ is a highly toxic substance. It invades the human body through inhalation, ingestion, and skin absorption, causing serious damage to the human respiratory system and skin. Long-term exposure can cause bronchitis, visual impairment, and kidney damage. Therefore, pollution will be generated during the catalyst production process, and spent catalysts are difficult to dispose of. In recent years, the development of highly efficient, cheap and environmentally friendly catalysts for flue gas denitrification has become a research hotspot for scholars at home and abroad.

At present, there are few domestic patents related to flue gas denitrification catalysts. Among the existing patents, the three patents (CN1475305), (CN1777477), and (CN1792431) all use V ₂ O ₅ as the active component, and the V ₂ O ₅ -WO ₃ (MoO ₃ )/TiO ₂ catalyst has high denitrification activity, It has good anti-poisoning performance and is an integrated technology of foreign denitrification catalysts. Among them, the patent (CN1475305) is a self-contained honeycomb denitration catalyst prepared with activated carbon as a support body, and the catalyst has high activity at low temperature. The disadvantage is that the catalyst has poor sulfur resistance, and the support body is easy to pulverize. The patent (CN1777477) mainly describes the improvement of the V ₂ O ₅ -WO ₃ (MoO ₃ )/TiO ₂ catalytic system honeycomb monolithic denitration catalyst. The patent (CN1792431) is a monolithic catalyst with cordierite honeycomb ceramics as the support and V ₂ O ₅ -WO ₃ /TiO ₂ -Al ₂ O ₃ as the catalytic active system. The disadvantage is that the catalysts of patents 2 and 3 are expensive, mainly because the cocatalysts WO ₃ and MoO ₃ are added in large amounts, and the raw materials themselves are expensive and toxic. Both patents (CN1401416) and (CN1457920) use cordierite honeycomb ceramics as the support body, and the catalytic system is CuO/γ-Al ₂ O ₃ , which is environmentally friendly and has high catalytic activity. The disadvantage is that the catalyst is easy to pulverize and has poor wear resistance.

In view of the domestic flue gas denitrification catalyst development experience and insufficiency, the development of an efficient, cheap and environmentally friendly integral denitrification catalyst has become a major problem to be solved by Chinese environmental protection enterprises and various scientific research units.

Contents of the invention

The purpose of the present invention is to provide a flue gas denitrification integral catalyst with high denitrification efficiency, low cost, simple process, environmental protection and no secondary pollution. Another object of the present invention is to provide a preparation method of the above-mentioned catalyst.

The technical solution of the present invention is: the present invention proposes a monolithic flue gas denitrification catalyst with silicon-based ceramics as the carrier, which is characterized in that the catalyst uses silicon-based ceramics as the first carrier, and an active silica coating as the second Two carriers, CeO ₂ and doped metal oxides are active components; wherein based on the quality of the first carrier, the mass percentage of the second carrier active silica loading is 3 to 40%, and the active component loading The mass percentage content is 1～26%.

The above-mentioned loading amount of CeO ₂ is based on the mass of the first carrier, and its mass percentage is 1-20%. The doped metal oxide is one or more of Mo, W, Cu, Fe, Zr, La metal oxide; the loading amount of the doped metal oxide is based on the mass of the first carrier, and its mass percentage The content is 0-6%.

The aforementioned silicon-based ceramics are silicon oxide ceramics, ATS (Al ₂ TiO ₅ -TiO ₂ -SiO ₂ ) ceramics, mullite ceramics or cordierite ceramics.

The present invention also provides the method for above-mentioned catalyst, and its concrete steps are:

(1) Preparation of SiO ₂ sol

According to the molar ratio of tetraethyl orthosilicate (TEOS): ethanol: H ₂ O: H ⁺ =1: (5~7): (3~4): (0.08~0.09), firstly mix ethyl orthosilicate with Mix absolute ethanol thoroughly, then add the mixture of deionized water and acidic catalyst drop by drop under stirring, after the dropwise addition, stir and reflux the reaction mixture at a constant temperature of 65-80°C for 30-75min to obtain a stable SiO ₂ sol ;

(2) Coating of the second carrier layer of _SiO2

Immerse the pretreated silicon-based ceramics in the _SiO2 sol prepared in step (1), take it out, dry and roast, or repeat the dipping, drying and roasting for 1 to 4 times, that is, coat the second _SiO2 carrier layer, and Based on the mass of the first carrier, the mass percentage of active silicon dioxide loading is 3-40%;

(3) Preparation of active component impregnation solution

Dissolve Ce salt in distilled water until it is completely dissolved, then dope with metal salt or doped with metal crystalline hydrate to prepare a stable aqueous solution;

(4) Loading of active _CeO2

Immerse the sample that has been coated with SiO ₂ second carrier coating in step (2) in the solution prepared in step (3), blow off the residual solution in the channel after the immersion, dry and roast, or repeat immersion and drying And after roasting, the monolithic catalyst is obtained; wherein based on the mass of the first carrier, the mass percentage of _CeO2 is 1-20%, and the mass percentage of the doped metal oxide is 0-6. %.

Wherein said Ce salt and doping metal salt are nitrate, sulfate or phosphate of cerium and doping metal.

The drying method in the above steps (2) and (4) is natural drying in the shade or drying in a drying oven. When drying in the shade naturally, the drying time is 24 to 48 hours; 8 to 24 hours. The roasting temperature is 350-600°C, and the holding time is 1-3 hours. The soaking time in steps (2) and (4) is 15 to 60 minutes.

The acid catalyst described in the above step (1) is acetic acid, nitric acid, hydrochloric acid, sulfuric acid or phosphoric acid.

The pretreatment method in the above step (2) refers to boiling the aluminum-based or silicon-based ceramics with a nitric acid solution with a mass fraction of 3-10% for 10-30 minutes, then washing them with clear water, and drying them for later use.

The preparation method of the above-mentioned SiO ₂ sol can refer to the existing SiO ₂ sol technology, and can also be directly sold in the market, or self-made (the self-made sol is stable, and the fired active SiO ₂ has a large specific surface area).

Beneficial effect:

The catalyst prepared by the present invention is highly efficient, environmentally friendly, non-toxic, and low in cost (the price of commercially available silica gel is cheaper than that of aluminum glue), and has a widened activity window (the activity range of the mainstream commercial titanium vanadium catalyst system is 290-430 ° C, aluminum cerium The activity range of the catalyst system is 250-350°C, the activity range of the silicon cerium catalyst system of the present invention is 250-400°C), the active component has a large specific surface area and good dispersibility, the preparation process provided by the present invention is simple, and the catalyst is thermally stable Good, strong resistance to sulfur and water vapor.

Description of drawings

FIG. 1 is a graph showing the NO conversion rate of the catalyst prepared in Example 1 as a function of the reaction temperature.

Detailed ways

Example 1

(1) Preparation of SiO ₂ sol

Measure 100ml TEOS, 30ml ethanol and 80ml water with a graduated cylinder and put them into a round bottom flask, then add glacial acetic acid catalyst at 0.085 times the amount of TEOS substance, stir evenly with a glass rod, and put it into an electronic constant temperature water bath. Condensation and reflux at a constant temperature of 70°C for 50 minutes will produce a stable SiO ₂ sol.

(2) Coating of the second carrier layer of _SiO2

Immerse 8g of pretreated silica porcelain in the _SiO sol prepared in step (1) for 30min, take it out and dry it in the shade for 24 hours, then bake it in a muffle furnace at 500°C for 2 hours, repeat dipping, drying and roasting (drying) Roasting system is constant) 1 time, until the required carrier load is reached, that is, SiO is coated _The second carrier layer is based on the quality of the first carrier, and its mass percentage is 8%;

(3) Preparation of active component impregnation solution

Dissolve 10g Ce(NO ₃ ) ₃ .6H ₂ O in distilled water until completely dissolved to obtain a Ce(NO ₃ ) ₃ solution;

(4) Loading of active _CeO2

The sample that has been coated with _SiO in the step (2) The second carrier coating is immersed in the solution prepared in the step (3) for 30min, after the immersion finishes, the residual solution in the channel is blown out, and after 24 hours of natural drying in the shade, the The active component CeO ₂ coating was prepared by roasting in a Furnace at 500°C for 2 hours, and its mass percentage was 13.5% based on the mass of the first carrier.

The NOx removal efficiencies of the catalysts are shown in Table 1.

Example 2

(1) Preparation of SiO ₂ sol

Measure 100ml TEOS, 24ml ethanol and 84ml water into a round bottom flask with a graduated cylinder, then add nitric acid catalyst at 0.08 times the amount of TEOS, stir evenly with a glass rod, and put it into an electronic constant temperature water bath. Condensate and reflux at a constant temperature of 65°C for 50 minutes to obtain a stable SiO ₂ sol.

(2) Coating of the second carrier layer of _SiO2

Immerse 8g of pretreated ATS ceramics in the _SiO sol prepared in step (1) for 15min, take it out and dry it in a blast drying oven at 80°C for 10 hours, then heat it in a muffle furnace at 450°C for 2 hours and bake it. Cover the _SiO2 second carrier layer, based on the quality of the first carrier, its mass percentage is 5.1%;

(3) Preparation of active component impregnation solution

Dissolve 10g Ce(NO ₃ ) ₃ .6H ₂ O in distilled water until completely dissolved to obtain a Ce(NO ₃ ) ₃ solution;

(4) Loading of active _CeO2

Immerse the sample that has been coated with the _SiO2 second carrier coat in the step (2) in the solution prepared in the step (3) for 15 minutes, blow off the residual solution in the channel after the immersion, and dry it at 80 °C in a blast drying oven After 10 hours, it was baked in a muffle furnace at 450° C. for 2 hours to obtain an active CeO ₂ coating, with a mass percentage of 12.0% based on the mass of the first carrier.

Example 3

(1) Preparation of SiO ₂ sol

Measure 100ml TEOS, 33ml ethanol and 63ml water into a round bottom flask with a graduated cylinder, then add sulfuric acid catalyst at 0.08 times the amount of TEOS, stir evenly with a glass rod, and put it into an electronic constant temperature water bath. Condensate and reflux at a constant temperature of 75°C for 50 minutes to obtain a stable SiO ₂ sol.

(2) Coating of the second carrier layer of _SiO2

Immerse 8g of pretreated cordierite porcelain in the _SiO sol prepared in step (1) for 20min, take it out and dry it in a blast drying oven at 100°C for 9 hours, then bake it in a muffle furnace at 350°C for 3 hours, repeat Dipping, drying and roasting (drying and roasting system unchanged) 1 time, until reaching the required carrier load, that is, coating SiO _The second carrier layer is based on the quality of the first carrier, and its mass percentage is 9.4 %;

(3) Preparation of active component impregnation solution

Dissolve 10g Ce(NO ₃ ) ₃ .6H ₂ O in distilled water until completely dissolved to obtain a Ce(NO ₃ ) ₃ solution;

(4) Loading of active _CeO2

The sample that has been coated with _SiO in the step (2) The second carrier coat is immersed in the solution prepared in the step (3) for 20min, after the dipping finishes, the residual solution in the channel is blown out, after 24 hours of natural drying in the shade, the The furnace was kept at 350° C. for 3 hours and baked to obtain an active CeO ₂ coating. Based on the mass of the first carrier, its mass percentage was 13.8%.

Example 4

(1) Preparation of SiO ₂ sol

Measure 100ml TEOS, 28ml ethanol and 80ml water into a round bottom flask with a measuring cylinder, then add hydrochloric acid catalyst at 0.09 times the amount of TEOS, stir evenly with a glass rod, and put it into an electronic constant temperature water bath. Condensation and reflux at a constant temperature of 80°C for 50 minutes will produce a stable SiO ₂ sol.

(2) Coating of the second carrier layer of _SiO2

Immerse 8g of pretreated silica porcelain in the _SiO sol prepared in step (1) for 25min, take it out and dry it in a blast drying oven at 105°C for 8 hours, then bake it in a muffle furnace at 400°C for 3 hours, repeat Impregnation, drying and roasting (drying and roasting system unchanged) 1 time, until the required carrier load is reached, that is, SiO is coated _{The second} carrier layer is based on the quality of the first carrier, and its mass percentage is 10.5 %;

(3) Preparation of active component impregnation solution

Dissolve 10g Ce(NO ₃ ) ₃ .6H ₂ O in distilled water until completely dissolved to obtain a Ce(NO ₃ ) ₃ solution;

(4) Loading of active _CeO2

Immerse the sample that has been coated with SiO ₂ second carrier coat in the step (2) in the solution prepared in step (3) for 25min, blow off the residual solution in the channel after the immersion, and dry it in a drying oven at 60°C for 12 hours Afterwards, it was baked in a muffle furnace at 400° C. for 3 hours to obtain an active CeO ₂ coating. Based on the mass of the first carrier, its mass percentage was 15.3%.

Example 5

(1) Preparation of SiO ₂ sol

Measure 100ml TEOS, 33ml ethanol and 84ml water into a round bottom flask with a measuring cylinder, then add phosphoric acid catalyst at 0.09 times the amount of TEOS, stir evenly with a glass rod, and put it into an electronic constant temperature water bath. Condensation and reflux at a constant temperature of 70°C for 50 minutes will produce a stable SiO ₂ sol.

(2) Coating of the second carrier layer of _SiO2

Immerse 8g of pretreated mullite porcelain in the _SiO sol prepared in step (1) for 30min, take it out and dry it in a blast drying oven at 105°C for 8 hours, then bake it in a muffle furnace at 450°C for 3 hours. Repeat dipping, drying and roasting (drying and roasting system is constant) 4 times, until reaching the required carrier loading, that is, coating SiO _The second carrier layer is based on the quality of the first carrier, and its mass percentage is 25%;

(3) Preparation of active component impregnation solution

Dissolve 10g Ce(NO ₃ ) ₃ .6H ₂ O in distilled water until completely dissolved to obtain a Ce(NO ₃ ) ₃ solution;

(4) Loading of active _CeO2

Immerse the sample that has been coated with SiO ₂ second carrier coat in the step (2) in the solution prepared in step (3) for 30 minutes, blow off the residual solution in the channel after the immersion, and dry it in a drying oven at 60°C for 12 hours Afterwards, it was baked in a muffle furnace at 450° C. for 3 hours to obtain an active CeO ₂ coating. Based on the mass of the first carrier, its mass percentage was 16.1%.

Example 6

(1) Preparation of SiO ₂ sol

In 300 g of commercially available silica sol, 5 g of concentrated nitric acid was added dropwise to adjust the pH value of the sol to 0.6, and the solid phase content was 13%.

(2) Coating of the second carrier layer of _SiO2

Immerse 8g of the treated ATS ceramics in the _SiO sol prepared in step (1) for 40min, take it out and dry it in a blast drying oven at 105°C for 8 hours, then bake it in a muffle furnace at 500°C for 3 hours, that is, coating Good SiO _{The second} carrier layer is based on the quality of the first carrier, and its mass percentage is 15.2%;

(3) Preparation of active component impregnation solution

Dissolve 10g Ce(NO ₃ ) ₃ .6H ₂ O, 0.3g FeCl ₂ , 0.2g Cu(NO ₃ ) ₂ and 0.2g zirconium oxychloride in distilled water until completely dissolved to obtain a stable composite solution;

(4) Loading of composite active components

Immerse the sample that has been coated with SiO ₂ second carrier coat in the step (2) in the solution prepared in step (3) for 40 minutes, blow off the residual solution in the channel after the immersion, and dry it in a drying oven at 60°C for 12 hours After that, it was baked in a muffle furnace at 500° C. for 3 hours to obtain a coating of composite active components. Based on the mass of the first carrier, its mass percentage was 14.8%.

Example 7

(1) Preparation of SiO ₂ sol

In 300 g of commercially available silica sol, 8 g of concentrated nitric acid was added dropwise to adjust the pH value of the sol to 0.2, and the solid phase content was 14.5%.

(2) Coating of the second carrier layer of _SiO2

Immerse 8g of pretreated cordierite porcelain in the _SiO sol prepared in step (1) for 50min, take it out and dry it in a blast drying oven at 105°C for 8 hours, then bake it in a muffle furnace at 550°C for 2 hours, repeat Impregnation, drying and roasting (drying and roasting system unchanged) 1 time, until reaching the required carrier load, that is, coating SiO _The second carrier layer is based on the quality of the first carrier, and its mass percentage is 30.1 %;

(3) Preparation of active component impregnation solution

10g Ce(NO ₃ ) ₃ .6H ₂ O, 0.3g molybdenum 2-ethylhexanoate and 0.2g zirconium oxychloride were dissolved in distilled water until completely dissolved to obtain a stable composite solution;

(4) Loading of composite active components

Immerse the sample that has been coated with _SiO2 second carrier coat in step (2) in the solution prepared in step (3) for 50min, blow off the residual solution in the channel after the immersion, and dry it in a drying oven at 60°C for 12 hours After that, it was baked in a muffle furnace at 550° C. for 2 hours to obtain a coating of the composite active component. Based on the mass of the first carrier, its mass percentage was 17.3%.

Example 8

(1) Preparation of SiO ₂ sol

Into 300 g of commercially available silica sol, 8 g of concentrated nitric acid was added dropwise to adjust the pH value of the sol to 0.2, and the solid phase content was 16%.

(2) Coating of the second carrier layer of _SiO2

Immerse 8g of pretreated silica porcelain in the _SiO2 sol prepared in step (1) for 60min, take it out and dry it in a blast drying oven at 105°C for 8 hours, then bake it in a muffle furnace at 600°C for 2 hours, repeat Dipping, drying and roasting (drying and roasting system unchanged) 2 times, until reaching the required carrier load, that is, coating SiO _The second carrier layer is based on the quality of the first carrier, and its mass percentage is 40 %;

(3) Preparation of active component impregnation solution

10g Ce(NO ₃ ) ₃ .6H ₂ O, 0.3g tungsten nitrate, 0.2g lanthanum sulfate and 0.2g zirconium oxychloride were dissolved in distilled water until completely dissolved to obtain a stable composite solution;

(4) Loading of composite active components

Immerse the sample that has been coated with _SiO2 in the second carrier coat in the step (2) in the solution prepared in the step (3) for 60 minutes, blow off the residual solution in the channel after the immersion, and dry it in a drying oven at 60 ° C for 12 hours After that, it was roasted at 600°C for 2 hours in a muffle furnace, and then dipped, dried and roasted (the drying and roasting system remained unchanged) once until the required carrier load was reached, that is, the coating of the composite active component was prepared. Based on the mass of the first carrier, its mass percentage is 25%.

Catalyst denitrification activity test example

The nitrogen oxide removal efficiency of table 1 embodiment 1 catalyst

Test Conditions:

Quartz tube reactor, inner diameter d is 8mm;

Catalyst particle size: 1.25mm～12mm, accumulation length: 18cm;

The flue gas composition is: NO: 600ppm, NH ₃ : 600ppm, O ₂ : 5%;

Airspeed: 5000h ^-1 .

Claims (7)

1, a kind of is the flue gas denitrating integral catalyst of carrier with the silicon based ceramic, it is characterized in that described catalyst is is first carrier with silicon based ceramic, and the active oxidation silicon coating is second carrier, CeO ₂With blended metal oxide be active component; Wherein the quality with first carrier is a benchmark, and the load capacity quality percentage composition of second carrier is 3～40%, and the quality percentage composition of activity component load quantity is 1～26%.

2, catalyst according to claim 1 is characterized in that described CeO ₂Load capacity be benchmark with the quality of first carrier, its quality percentage composition is 1～20%; The load capacity of blended metal oxide is a benchmark with the quality of first carrier, and its quality percentage composition is 0～6%.

3, catalyst according to claim 1, it is characterized in that described blended metal oxide be at least Mo, W, Cu, Fe, Zr, La metal oxide in a kind of.

4, catalyst according to claim 1 is characterized in that described silicon based ceramic is silica porcelain, Al ₂TiO ₅-TiO ₂-SiO ₂Pottery, Mullite porcelain or cordierite porcelain.

5, a kind of Preparation of catalysts method as claimed in claim 1, its concrete steps are:

(1) SiO ₂The preparation of colloidal sol

According to ethyl orthosilicate (TEOS): ethanol: H ₂O: H ⁺=1: (5～7): (3～4): the molar ratio of (0.08～0.09), earlier ethyl orthosilicate is fully mixed with absolute ethyl alcohol, the mixture that under agitation dropwise adds deionized water and acidic catalyst again, after dropwising with reactant mixture behind 65～80 ℃ of constant temperature stirring and refluxing 30～75min, promptly make stable SiO ₂Colloidal sol;

(2) SiO ₂The coating of second carrier layer

Pretreated silicon based ceramic is immersed in the SiO that step (1) prepares ₂In the colloidal sol, take out the back drying and roasting, perhaps after repeated impregnations, drying and the roasting 1～4 time, control is benchmark with the silicon based ceramic quality, and the quality percentage composition of active silica load is 3～40%, obtains having applied SiO ₂Second carrier layer;

(3) preparation of activity component impregnation liquid

Ce salt is dissolved in the distilled water until dissolving fully, the more stable aqueous solution of doped metal salt or doping metals crystallization water compound preparation;

(4) active CeO ₂Load

To apply active SiO in the step (2) ₂The sample of second carrier coating is immersed in the solution of step (3) preparation, dipping finishes the residual solution in the most duct of after-blow, and dry, roasting perhaps promptly make integral catalyzer after repeated impregnations, drying and the roasting, be benchmark wherein with the first carrier quality, CeO ₂The quality percentage composition of load be 1～20%, the quality percentage composition of the load of blended metal oxide is 0～6%.

6, preparation method according to claim 5 is characterized in that described Ce salt and doped metal salt are nitrate, sulfate or the phosphate of Ce and doping metals.

7, preparation method according to claim 5 is characterized in that in the described step (2), (4) that drying mode is a nature when drying in the shade, 24～48 hours drying times; When common air dry oven was dry, baking temperature was 60～120 ℃, 8～24 hours drying times; Sintering temperature is 350～600 ℃, and temperature retention time is 1～3h.Dip time is 15～60min in step (2), (4).

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