CN111744468A - A kind of low temperature alkali metal SCR denitration catalyst and its preparation method and application - Google Patents

Abstract

The invention discloses a low-temperature alkali metal resistant SCR denitration catalyst and a preparation method and application thereof, wherein the catalyst takes an oxide of titanium as a carrier, an oxide of vanadium as an active component, and oxides of tungsten, molybdenum and rare metals as promoters; the rare metal is one or more of Eu, Nd, Ho or Sb; the mass ratio of the titanium to the vanadium to the tungsten to the molybdenum to the rare metal is 100: 1-4: 2-6: 0.5-4: 0.5-3. The preparation method comprises the following steps: respectively weighing titanium oxide, vanadium oxide, tungsten oxide precursor, molybdenum oxide precursor and rare metal oxide precursor; adding a precursor of vanadium oxide, a precursor of tungsten oxide, a precursor of molybdenum oxide and a precursor of rare metal into deionized water, slowly adding titanium dioxide in the stirring process, stirring and dipping the obtained solution, drying, grinding and calcining. The low-temperature alkali metal resistant SCR denitration catalyst has the characteristics of low denitration reaction temperature, wide catalytic reduction denitration activity temperature window, excellent alkali metal poisoning resistance and low cost.

Description

A kind of low temperature alkali metal SCR denitration catalyst and its preparation method and application

technical field

The invention relates to the field of catalysts, in particular to a low-temperature alkali-resistant SCR denitration catalyst and a preparation method and application thereof.

Background technique

The massive emission of nitrogen oxides is the key pollutant causing compound air pollution, and it has become an environmental problem that urgently needs to be solved. In recent years, biomass boilers have received extensive attention due to their unique advantages. Biomass boilers avoid the problems of "large smoke and dust pollution, insufficient combustion, large waste, and no energy saving" existing in coal-fired boilers, and have the characteristics of direct emission without smoke, dust, and sufficient combustion, which is an important development direction in the future. one. With the increasingly strict environmental protection standards, the NO _x treatment of biomass boilers is imminent. The current emission standard refers to the "Boiler Air Pollutant Emission Standard" GB13271-2014, and the special emission limit is 200mg/m ³ . In places with stricter requirements, the nitrogen oxide emission standard for biomass boilers is 150mg/m ³ , and the special emission standard is 50 mg/m ³ .

NH ₃ -SCR technology is currently one of the most widely used and mature flue gas denitrification technologies, and the catalyst is the core of the technology. At present, most commercial catalysts are V ₂ O5-WO ₃ /TiO ₂ catalysts, whose working temperature is generally in the range of 300-400 °C. They have been used in coal-fired power plant flue gas treatment for many years, and the technology is relatively mature. However, the flue gas of biomass boilers contains high concentrations of alkali metals such as sodium and potassium, and the activity of traditional V ₂ O5-WO ₃ /TiO ₂ catalysts will decrease rapidly or even completely deactivate under these conditions. The poor resistance to alkali metal poisoning of catalysts is a major obstacle to the conversion and utilization of biomass energy.

The currently published patents on low-temperature alkali-resistant SCR denitration catalysts generally have a high activation temperature and a narrow active temperature window, which cannot be applied to flue gas with large temperature fluctuations; at the same time, the content of active components is high, increasing the catalyst manufacturing cost. For example, the anti-alkali poisoning and efficient denitration catalyst disclosed in patent CN201810573766.7 has an activation temperature as high as 300°C, which greatly limits the application of this technology. The test temperature of the flat-plate anti-alkali metal and sulfur poisoning catalyst disclosed in Patent 201810048205.5 is as high as 350°C. In addition, patent CN201911015822.6 discloses a preparation process of a honeycomb low-temperature SCR catalyst. Although the activation temperature is as low as 130 °C, the activity decreases rapidly when the temperature is higher than 180 °C, and SO ₂ obviously leads to serious irreversible deactivation of the catalyst. At the same time, only the active component manganese has been added in an amount of more than 30%, which leads to excessive production costs.

It is of great significance to the development of biomass boilers and the emission reduction of nitrogen oxides to develop SCR low-temperature denitration catalysts with low temperature and high efficiency, wide active temperature window, excellent anti-alkali metal poisoning performance and low production cost.

SUMMARY OF THE INVENTION

Purpose of the invention: In order to overcome the deficiencies in the prior art, the purpose of the present invention is to provide a low-temperature alkali-resistant SCR denitration catalyst with low temperature efficiency, wide active temperature window, strong alkali metal poisoning resistance and low cost. Another object is to provide a preparation method of a low-temperature alkali-resistant SCR denitration catalyst with a simple preparation method and easy operation. Another object of the present invention is to provide a low-temperature alkali-resistant SCR denitration catalyst in the energy conversion of biomass boilers. Applications.

Technical scheme: The low-temperature alkali-resistant SCR denitration catalyst described in the present invention takes titanium oxide as carrier, vanadium oxide as active component, tungsten, molybdenum and rare metal oxide as co-catalyst; the rare metal is One or more of Eu, Nd, Ho or Sb; the mass ratio of titanium, vanadium, tungsten, molybdenum and rare metals is 100:1-4:2-6:0.5-4:0.5-3.

Oxides of vanadium are VO ₂ , V ₂ O ₅ or ammonium metavanadate. The precursor of tungsten oxide is ammonium tungstate, the precursor of molybdenum oxide is ammonium molybdate, the precursor of europium is one or more of europium nitrate, europium acetate or europium oxalate, and the precursor of neodymium is One or more of neodymium nitrate, neodymium carbonate or neodymium oxalate, the precursor of holmium is holmium nitrate, holmium oxalate or holmium acetate, and the precursor of antimony is one or more of antimony nitrate or antimony acetate.

Preferably, the precursor of europium is europium nitrate, the precursor of neodymium is neodymium nitrate, the precursor of holmium is holmium nitrate, and the precursor of antimony is antimony acetate.

The preparation method of the above-mentioned low-temperature alkali-resistant SCR denitration catalyst comprises the following steps:

In step 1, the oxides of titanium, the oxides of vanadium, the precursors of tungsten oxides, the precursors of molybdenum oxides, and the precursors of rare metal oxides are respectively weighed according to the element mass ratio;

Step 2: Add vanadium oxide precursors, tungsten oxide precursors, molybdenum oxide precursors, rare metal precursors and titanium dioxide into 50ml of deionized water, and the obtained solution is first used at a frequency of 20-60kHz. Ultrasonic immersion for 20~40min, then immersion for 3~5h with magnetic stirring at a rotational speed of 20~30r/s, then heat up to 50~70℃, stir until the water is completely evaporated to dryness, and after evaporation, put it in an oven at 100~120℃ Drying for 10-16 hours, grinding into powder, and calcining at 400-500° C. for 3-5 hours to obtain a low-temperature alkali-resistant SCR denitration catalyst.

The application of the above-mentioned low-temperature alkali-resistant SCR denitration catalyst in the energy conversion of biomass boilers.

Preparation principle: The ultrasonic-enhanced impregnation process is used to make the active components more uniform and dispersed on the surface of the TiO ₂ carrier. Molybdenum, antimony and various rare metal elements provide more additional acid sites, and at the same time improve the catalyst's low-temperature redox performance, thereby improving the catalyst's low-temperature activity and anti-alkali metal poisoning performance.

Beneficial effect: Compared with the prior art, the present invention has the following remarkable features:

1. Only a small amount of oxides of tungsten, molybdenum and antimony are added to the low-temperature alkali-resistant SCR denitration catalyst, and the mass ratio of vanadium, tungsten, molybdenum, and rare metal additives in the catalyst is reasonably set, and the auxiliary means of ultrasonic reinforcement is adopted. , The prepared low-temperature alkali metal SCR denitration catalyst has the characteristics of low denitration reaction temperature, wide catalytic reduction and denitration activity temperature window, excellent alkali metal poisoning resistance and low cost;

2. The activation temperature T50 of the low-temperature alkali-resistant SCR denitration catalyst is as low as 150°C, and the denitration efficiency can reach 90% at 180°C, and the denitration efficiency can be maintained above 90% in the temperature range of 180-380°C. ;

3. The surface of the low temperature alkali metal SCR denitration catalyst has more Lewis acid and Bronsted acid, which is more stable;

4. The doping of rare metal elements significantly improves the low-temperature redox performance of the catalyst;

5. The preparation method of the present invention is simple and easy to operate.

Description of drawings

Fig. 1 is the denitration performance curve diagram of the denitration catalyst of the present invention.

Fig. 2 is the performance curve of the denitration catalyst of the present invention after sodium poisoning.

Fig. 3 is the performance curve of the denitration catalyst of the present invention after potassium poisoning.

Figure 4 is an in-situ infrared test result of the denitration catalyst of the present invention.

Detailed ways

In the following examples, all raw materials are purchased and used.

Example 1

A preparation method of a low-temperature alkali-resistant SCR denitration catalyst, comprising the following steps:

(1) Weigh 5g titanium dioxide, 0.081g VO ₂ , 0.134g ammonium tungstate, 0.046g ammonium molybdate, 0.037g europium nitrate, 0.038g neodymium nitrate;

(2) Add VO ₂ , ammonium tungstate, ammonium molybdate, europium nitrate, and neodymium nitrate into 50 ml of deionized water, slowly add titanium dioxide during stirring, and immerse the obtained solution at Stir with magnetic force at 20r/s for 3h, then heat up to 50°C, stir and impregnate for 5h, evaporate to dryness, put it in an oven at 100-120°C for 10h, grind it through a 100-mesh sieve, and calcine the powder at 400°C for 3h.

Wherein, europium nitrate can be replaced with one or more of europium acetate and europium oxalate, and neodymium nitrate can be replaced with one or more of neodymium carbonate or neodymium oxalate.

Example 2

The preparation method of the low-temperature alkali-resistant SCR denitration catalyst comprises the following steps:

(1) Weigh 5g titanium dioxide, 0.357g V ₂ O ₅ , 0.413g ammonium tungstate, 0.368g ammonium molybdate, 0.201g holmium nitrate, 0.190g antimony nitrate;

(2) V ₂ O ₅ , ammonium tungstate, ammonium molybdate, holmium nitrate, and antimony nitrate were added to 50 ml of deionized water, and titanium dioxide was slowly added during the stirring process, and the obtained solution was first soaked with ultrasonic waves of 60 kHz frequency at 30° C. for 40 minutes After 5 hours of magnetic stirring with a rotating speed of 30r/s, the temperature was raised to 70°C, stirred and immersed for 8 hours, evaporated to dryness, dried in an oven at 120°C for 16 hours, ground through a 100-mesh sieve, and the powder was calcined at 500°C for 5 hours.

Wherein, holmium nitrate can be replaced with one or more of holmium oxalate and holmium acetate, and antimony nitrate can be replaced with antimony acetate.

Example 3

The preparation method of the low-temperature alkali-resistant SCR denitration catalyst comprises the following steps:

(1) Weigh 5g of titanium dioxide, 0.229g of ammonium metavanadate, 0.307g of ammonium tungstate, 0.184g of ammonium molybdate, 0.073g of europium acetate, 0.048g of europium oxalate, 0.063g of neodymium oxalate, and 0.063g of antimony nitrate;

(2) Add ammonium metavanadate, ammonium tungstate, ammonium molybdate, europium acetate, europium oxalate, neodymium oxalate, and antimony nitrate to 50 ml of deionized water, and slowly add titanium dioxide during stirring. Ultrasonic immersion at 40 kHz frequency for 30 minutes, followed by magnetic stirring at 25 r/s for 4 hours, then heated to 60 °C, stirring and immersion for 6.5 hours, evaporated to dryness, dried in a 110 °C oven for 13 hours, ground through a 100-mesh sieve, and powdered Calcined at 450°C for 4h.

Example 4

The preparation method of the low-temperature alkali-resistant SCR denitration catalyst comprises the following steps:

(1) Weigh 5g titanium dioxide, 0.081g VO ₂ , 0.115g ammonium metavanadate, 0.206g ammonium tungstate, 0.092g ammonium molybdate, 0.063g neodymium oxalate, 0.055g holmium acetate;

(2) Add VO ₂ , ammonium metavanadate, ammonium tungstate, ammonium molybdate, neodymium oxalate, and holmium acetate into 50 ml of deionized water, slowly add titanium dioxide during stirring, and use a Ultrasonic immersion for 25min, followed by magnetic stirring at 22r/s for 3.5h, then heated to 55°C, stirring and immersion for 6h, evaporated to dryness, placed in a 105°C oven for 11h, ground through a 100-mesh sieve, and the powder was heated at 410°C Calcined for 3.5h.

Example 5

The preparation method of the low-temperature alkali-resistant SCR denitration catalyst comprises the following steps:

(1) Weigh 5g of titanium dioxide, 0.268g of V ₂ O ₅ , 0.344g of ammonium tungstate, 0.276g of ammonium molybdate, and 0.180g of holmium oxalate;

(2) Add V ₂ O ₅ , ammonium tungstate, ammonium molybdate, and holmium oxalate into 50 ml of deionized water, and slowly add titanium dioxide during stirring. The obtained solution is first immersed with ultrasonic waves of 55 kHz frequency at 28° C. for 35 minutes, and then used Magnetic stirring at 28r/s for 4.5h, then heated to 65°C, stirring and immersing for 7h, evaporated to dryness, dried in a 115°C oven for 15h, ground through a 100-mesh sieve, and the powder was calcined at 490°C for 4.5h.

Example 6

The preparation method of the low-temperature alkali-resistant SCR denitration catalyst comprises the following steps:

(1) Weighing

(2) Dissolve 5g of titanium dioxide in 50mL of deionized water, add 0.229g of ammonium metavanadate, 0.344g of ammonium tungstate, 0.184g of ammonium molybdate, 0.126g of antimony acetate and 0.182g of europium nitrate; ultrasonically soak for 30min at 40kHz , stir evenly for 4 hours at room temperature, then heat up to 60 °C and continue stirring and immersion for 5 hours at 20 r/s, then after the water is evaporated to dryness, dry it in an oven at 110 °C for 12 hours, take it out and grind it to below 100 mesh, in a muffle furnace 500 ℃ calcination 5h.

Example 7

The preparation steps are the same as those in Example 6, except that the catalyst raw materials are: 5 g of titanium dioxide, 0.344 g of ammonium metavanadate, 0.344 g of ammonium tungstate, 0.184 g of ammonium molybdate, and 0.384 g of holmium nitrate.

Example 8

The preparation steps are the same as in Example 6, except that the catalyst raw materials are: 5 g of titanium dioxide, 0.287 g of ammonium metavanadate, 0.172 g of ammonium tungstate, 0.368 g of ammonium molybdate, and 0.304 g of neodymium nitrate.

Comparative ratio

The preparation steps are the same as in Example 6, except that the catalyst raw materials are: 5 g of titanium dioxide, 0.344 g of ammonium metavanadate and 0.344 g of ammonium tungstate.

Denitrification performance test

The catalysts prepared in Examples 6-8 and Comparative Examples were ground, tableted and sieved, and 300 mg of 40-60 mesh samples were used for catalytic activity testing experiments. Since about 90% of the NO _x in the flue gas is NO, NO _x is replaced by NO in the simulated flue gas, and the standard cylinder gas (where NO and NH ₃ are mixed with N ₂ as the balance gas) , the volume fraction of NO is 1.0%, and the volume fraction of NH ₃ is 1.0%) to simulate the flue gas, and the intake air composition is Φ(NO)=Φ(NH ₃ )=0.05%, Φ(O ₂ )=5%, and N ₂ is Equilibrium gas, the total flue gas volume is 100mL/min; each gas is gradually mixed through the mass flow meter and finally enters the air mixer for full mixing; the reactor is a quartz tube with an inner diameter of 7mm, which is provided by a vertical tubular heating furnace with a temperature control system The reaction temperature environment; the flue gas is analyzed by the Testo350-XL flue gas analyzer, and the analysis results are shown in Figure 1.

It can be seen from Figure 1 that the denitration catalyst prepared by the present invention has a lower activation temperature and a wider activation temperature window. Between ~380°C, denitration efficiencies of 90%, 80%, and 80% or more can be achieved, respectively.

It can be seen from Figures 2 and 3 that the denitration catalyst prepared by the present invention exhibits higher resistance to sodium and potassium poisoning. At 250 °C, the denitration efficiency after sodium and potassium poisoning was increased by 24% and 17%, respectively, compared with the vanadium-tungsten-titanium catalyst. Wherein, after potassium poisoning, the high-temperature activity of the vanadium-tungsten-titanium catalyst is almost completely lost, while the catalyst prepared by the present invention still has a certain activity.

It can be seen from Figure 4 that, compared with the traditional vanadium-tungsten-titanium catalyst, the acidity of the denitration catalyst prepared by the present invention is significantly enhanced, especially the B acid strength at 1440 cm ⁻¹ . This is beneficial to the improvement of catalyst activity and the improvement of anti-alkali metal performance. The XRF test results of the catalysts prepared in Examples 6-8 are summarized in Table 1, respectively, and it can be seen that the content of each component basically conforms to the preparation requirements.

Table 1 XRF test results of catalysts

V₂O₅ WO₃ Sb₂O₃ Eu₂O₃ Ho₂O₃ Nd₂O₃ MoO₃ TiO₂ Comparative Example 1 6.217 6.231 - - - - - 86.659 Example 6 4.507 6.570 1.366 1.6125 - - 3.547 81.78 Example 7 6.103 6.143 - - 3.651 - 3.520 79.773 Example 8 4.872 2.928 - - - 2.346 6,393 83.193

Claims (10)

1. A low-temperature alkali metal resistant SCR denitration catalyst is characterized in that: the method comprises the following steps of (1) taking an oxide of titanium as a carrier, an oxide of vanadium as an active component, and oxides of tungsten, molybdenum and rare metals as promoters; the rare metal is one or more of Eu, Nd, Ho or Sb; the mass ratio of the titanium to the vanadium to the tungsten to the molybdenum to the rare metal is 100: 1-4: 2-6: 0.5-4: 0.5-3.

2. The low-temperature alkali metal-resistant SCR denitration catalyst as recited in claim 1, wherein: the oxide of vanadium is VO₂、V₂O₅Or ammonium metavanadate.

3. The low-temperature alkali metal-resistant SCR denitration catalyst as recited in claim 1, wherein: the precursor of the tungsten oxide is ammonium tungstate, the precursor of the molybdenum oxide is ammonium molybdate, the precursor of europium is one or more of europium nitrate, europium acetate or europium oxalate, the precursor of neodymium is one or more of neodymium nitrate, neodymium carbonate or neodymium oxalate, the precursor of holmium is holmium nitrate, holmium oxalate or holmium acetate, and the precursor of antimony is one or more of antimony nitrate or antimony acetate.

4. The preparation method of the low-temperature alkali metal-resistant SCR denitration catalyst according to claim 1, comprising the steps of:

step one, respectively weighing titanium oxide, vanadium oxide, tungsten oxide precursor, molybdenum oxide precursor and rare metal oxide precursor according to the element mass ratio;

and secondly, adding a precursor of vanadium oxide, a precursor of tungsten oxide, a precursor of molybdenum oxide, a precursor of rare metal and titanium dioxide into deionized water, stirring and dipping the obtained solution, drying, grinding and calcining to obtain the low-temperature alkali-resistant SCR denitration catalyst.

5. The preparation method of the low-temperature alkali metal-resistant SCR denitration catalyst according to claim 4, wherein the method comprises the following steps: the ultrasonic dipping is carried out for 20-40 min, then the dipping is carried out for 3-5 h by magnetic stirring, and then the temperature is increased to 50-70 ℃ and the stirring is carried out until the water is completely evaporated.

6. The preparation method of the low-temperature alkali metal-resistant SCR denitration catalyst according to claim 5, wherein the method comprises the following steps: the ultrasonic frequency is 20-60 kHz.

7. The preparation method of the low-temperature alkali metal-resistant SCR denitration catalyst according to claim 5, wherein the method comprises the following steps: the rotating speed of the magnetic stirring is 20-30 r/s.

8. The preparation method of the low-temperature alkali metal-resistant SCR denitration catalyst according to claim 4, wherein the method comprises the following steps: and drying is carried out for 10-16 h at 100-120 ℃.

9. The preparation method of the low-temperature alkali metal-resistant SCR denitration catalyst according to claim 4, wherein the method comprises the following steps: the calcination is carried out for 3-5 h at 400-500 ℃.

10. The use of the low temperature alkali metal resistant SCR denitration catalyst of claim 1 in energy conversion of biomass boilers.

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