CN106238033A - Active carbocoal low-temperature denitration agent of Cerium Oxide Nanotubes and preparation method and application is modified on surface - Google Patents

Abstract

The invention belongs to the technical field of air pollution control, and relates to an active semi-coke low-temperature denitrification agent with surface-modified cerium oxide nanotubes, a preparation method and application thereof. The preparation method includes modifying the CeO2 nanotube _on the surface of the active semi-coke carrier by using a hydrothermal method. The invention synthesizes cerium oxide nanotubes on the surface of active semi-coke through a hydrothermal method, improves the specific surface and reactivity of the catalyst, and thus improves the low-temperature denitrification efficiency.

Description

Active semi-coke low-temperature denitrification agent with surface-modified cerium oxide nanotubes and preparation method thereof and application

technical field

The invention belongs to the technical field of air pollution control, and in particular relates to an active semi-coke low-temperature denitrification agent with surface-modified cerium oxide nanotubes and a preparation method and application thereof.

Background technique

In recent years, nitrogen oxides (NO _x ) have become the main air pollutants due to their serious environmental impacts such as acid rain, photochemical smog, ozone hole destruction, and greenhouse effect. The emission of NO _x in the atmosphere is increasing with the increase of coal-based energy consumption and the rapid increase of motor vehicle ownership. At present, ammonia selective catalytic reduction (NH ₃ -SCR) technology is the most effective, mature and widely used denitrification technology. The industrial catalyst of this technology is a vanadium-tungsten-titanium system (V ₂ O ₅ -WO ₃ /TiO ₂ ), but the operating temperature of the catalyst is high (300-450°C), and the active temperature window is narrow. In addition, catalysts are easily poisoned by ash, SO ₂ and H ₂ O in flue gas. Therefore, the development of low-temperature denitration catalysts has become a research hotspot.

Cerium (Cerium, Ce) has been widely studied in the denitrification process because of its good oxygen storage performance and redox performance. The most important property of CeO ₂ is as an oxygen storage source. Under oxidation and reduction conditions, the purpose of storing and releasing oxygen is achieved by changing the oxidation state of Ce ³⁺ and Ce ⁴⁺ . In addition, my country is a big country with rare earth reserves and output ranking first in the world, but my country's rare earth consumption only accounts for about 1/4 of the world's total, and there is still a problem of unbalanced rare earth utilization. The substantial increase in consumption has led to a large backlog of high-abundance elements such as cerium and lanthanum. Therefore, it is of great significance to vigorously develop rare earth catalytic materials to change the current imbalance in the use of rare earths in my country.

Contents of the invention

The purpose of the present invention is to address the deficiencies in the prior art, and propose an active semi-coke low-temperature denitrification agent with surface-modified cerium oxide nanotubes and its preparation method and application.

In order to achieve the above object, the present invention adopts the following technical solutions:

A method for preparing an active semi-coke low-temperature denitrification agent with surface-modified cerium _oxide nanotubes, comprising modifying CeO2 nanotubes on the surface of an active semi-coke carrier by a hydrothermal method.

Preferably, the active semi-coke carrier is an active semi-coke with ZnO nanorods grown on the surface.

Above-mentioned preparation method comprises the following steps:

1) Pulverizing the active semi-coke, putting it into zinc acetate colloid for ultrasonic treatment, drying the obtained sample after filtering, and calcining to obtain the active semi-coke with ZnO seed crystals pre-spread on the surface;

2) Prepare zinc nitrate and hexamethylenetetramine solutions of the same concentration, mix equal volumes to obtain a mixed solution, then put the active semi-coke with ZnO seeds pre-coated on the surface into the mixed solution, and react in a homogeneous phase Hydrothermal synthesis is carried out in a device to prepare active semi-coke with ZnO nanorods grown on the surface;

3) Put the active semi-coke with ZnO nanorods grown on the surface into a cerium nitrate solution, and perform a hydrothermal reaction in a homogeneous reactor to prepare an active semi-coke low-temperature denitrification agent with surface _- modified CeO2 nanotubes.

The above preparation method, wherein,

Preferably, step 1) crushes the active semi-coke to 10-20 mesh.

Preferably, the concentration of the zinc acetate colloid in step 1) is 0.005mol/L-0.1mol/L, more preferably 0.05mol/L.

Preferably, the ultrasonic treatment time in step 1) is 5-30 min, more preferably 5 min.

Preferably, the calcination condition in step 1) is calcination at 200-400° C. for 0.2-1 h, more preferably at 370° C. for 0.5 h.

Preferably, the concentrations of the zinc nitrate solution and the hexamethylenetetramine solution in step 2) are both 0.05mol/L-0.2mol/L, more preferably 0.1mol/L. Preferably, in step 2), in g/mL, the ratio of the added weight of active semi-coke pre-coated with ZnO seed crystals on the surface to the volume of the mixed solution is 1-5:30, preferably 2:30.

Preferably, the hydrothermal reaction temperature in step 2) is 80-120°C, and the time is 0.5-8h; preferably, the hydrothermal reaction temperature is 95°C, and the time is 1.5h.

Preferably, the rotational speed of the homogeneous reactor in step 2) is 5-40 rpm, more preferably 10 rpm.

Preferably, the concentration of cerium nitrate in step 3) is 0.0005mol/L-0.2mol/L, more preferably 0.01mol/L-0.1mol/L, even more preferably 0.05mol/L.

Preferably, the step 3) hydrothermal reaction temperature is 80-120°C, and the time is 0.5-4h; preferably, the hydrothermal reaction temperature is 95°C, and the time is 1h.

Specifically, the above-mentioned preparation method comprises the following steps:

1) Crush the active semi-coke to 10-20 mesh, put it into 0.05mol/L zinc acetate colloid and sonicate for 5min, filter and dry the obtained sample at 105°C for 1h (air blast drying oven can be used), and then put it into the muffle Calcined in a furnace at 370°C for 30 minutes to prepare active semi-coke with ZnO seeds pre-spread on the surface;

2) Prepare zinc nitrate and hexamethylenetetramine solutions with a concentration of 0.05 mol/L, mix them in equal volumes to obtain a mixed solution, and then put the above-mentioned active semi-coke with ZnO seeds pre-spread on the surface into the mixed solution, Carry out hydrothermal synthesis at 95°C for 1.5h in a homogeneous reactor to obtain active semi-coke with ZnO nanorods grown on the surface; the speed of the homogeneous reactor is 10rpm; the surface is pre-coated with ZnO crystals in g/mL The volume ratio of the weight of active semi-coke added to the mixed solution is 1-5:30, preferably 2:30;

3) Put the active semi-coke with ZnO nanorods grown on the surface into a 0.01mol/L-0.1mol/L cerium nitrate solution, and conduct a hydrothermal reaction at 95°C for 1 hour in a homogeneous reactor to prepare surface-modified CeO ₂ Nanotube active semi-coke low temperature denitrification agent.

The active semi-coke of the present invention can be prepared according to conventional methods in the prior art, or purchased commercially. In addition, the present invention provides a specific method for preparing active semi-coke, comprising the following steps: measuring 10 mL of nitric acid solution with a volume fraction of 30% in a 50 mL ground-neck Erlenmeyer flask. Weigh 4 g of the semi-coke sample, place it in a conical flask and shake it for 10 minutes, so that the semi-coke sample and the above nitric acid solution are evenly mixed. Then react in a constant temperature water bath at 80°C for 2h. The activated semi-coke was washed with deionized water until the pH was 7. The cleaned samples were dried in a blast drying oven at 105°C for 6h, and then calcined at 700°C for 2h under an argon atmosphere to obtain active semi-coke.

The invention also includes the active semi-coke low-temperature denitration agent of the surface-modified cerium oxide (CeO ₂ ) nanotube prepared by the above method.

The present invention also includes the application of the active semi-coke low-temperature denitrification agent with surface-modified cerium oxide (CeO ₂ ) nanotubes in air pollution control. The applications mainly include the treatment of _NOx in exhaust gas from coal-fired power plants, sintering plants, cement plants, etc. NO _x is a general term in the field, which means nitrogen oxides of different valence states or mixtures thereof.

The invention synthesizes cerium oxide nanotubes on the surface of active semi-coke through a hydrothermal method, improves the specific surface and reactivity of the catalyst, and thus improves the low-temperature denitrification efficiency.

Description of drawings

Fig. 1: SEM (scanning electron microscope) picture of the low-temperature denitration agent synthesized in embodiment 1;

Figure 2: SEM image of the low temperature denitrification agent synthesized in Example 2;

Fig. 3: SEM picture of the low-temperature denitration agent synthesized in Example 3;

Fig. 4: represent the denitrification efficiency of the CeO synthesized in Examples 1, ₂ , and 3 in the experimental example;

Figure 5: shows the NO conversion rates of cerium oxide nanotubes (Ce0.05/ASC, Example 2), CeO ₂ nanoparticles (CeO ₂ NP/ASC), and ZnO nanorods (ZnO/ASC) in the experimental example.

detailed description

The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention. If no specific technique or condition is indicated in the examples, it shall be carried out according to the technique or condition described in the literature in this field, or according to the product specification. The reagents or instruments used were not indicated by the manufacturer, and they were all conventional products that can be purchased through formal channels.

Example 1

A method for preparing an active semi-coke low-temperature denitrification agent with surface-modified cerium oxide nanotubes, comprising the following steps:

1) Crush the active semi-coke to 10-20 mesh, put it into 0.05mol/L zinc acetate colloid and sonicate for 5min, after filtering, dry the sample in a blast drying oven at 105°C for 1h, and then put it in a muffle furnace Calcined at 370°C for 30 minutes to pre-spread ZnO seeds on the surface of the active semi-coke.

2) Prepare zinc nitrate and hexamethylenetetramine solutions with concentrations of 0.05mol/L respectively, take 15mL of the two solutions respectively, then mix them in equal volumes, and then put 2g of active semi-coke that has been seeded with ZnO into the mixed solution , hydrothermally synthesized in a homogeneous reactor at 95°C for 1.5h to obtain active semicokes with ZnO nanorods grown on the surface (ie, ZnO nanorods, ZnO/ASC). The rotation speed of the homogeneous reactor was 10 rpm.

3) Put the active semi-coke with ZnO nanorods grown on the surface into a 0.01mol/L cerium nitrate solution, and perform a hydrothermal reaction in a homogeneous reactor at 95°C for 1 hour to obtain the low-temperature active semi-coke with surface _- modified CeO2 nanotubes Denitration agent (Ce0.01/ASC).

Example 2

The low-temperature denitrification agent (Ce0.05/ASC) was prepared according to the method of Example 1, the only difference being: Step 3) The concentration of the cerium nitrate solution was 0.05mol/L.

Example 3

The low-temperature denitrification agent (Ce0.1/ASC) was prepared according to the method of Example 1, the only difference being that in step 3) the concentration of the cerium nitrate solution was 0.1 mol/L.

Experimental example

The SEM (scanning electron microscope) images of the low-temperature denitration agent prepared in Examples 1-3 are shown in Figs. 1-3 respectively.

Catalyst performance evaluation: Take the low _- temperature denitrification agent prepared in Examples 1-3, CeO2 nanoparticles ₍ CeO2 NP/ASC, CeO2 nanoparticles are prepared by traditional impregnation method: immerse the ASC substrate in ₅ ml of cerium nitrate solution of appropriate concentration , taken out after a certain period of time and annealed at 300°C for 30min. This step was repeated several times until all the solutions were completely absorbed) and 1g each of ZnO nanorods (ZnO/ASC, prepared according to the method of Example 1), placed in a fixed-bed reactor . The experimental conditions are: 1000ppm NO, 1000ppm NH ₃ , 3% O ₂ , and the balance gas is N ₂ . The airspeed is 6000h ^-1 . (for carrying out the comparison of catalytic performance, embodiment 1-3 cerium _oxide nanotube, CeO Nanoparticle, ZnO nanorod should have identical cerium loading. Therefore the concentration of cerium nitrate solution is definite when cerium oxide nanoparticle is prepared. )

The experimental results are shown in Table 1, Figure 4 and Figure 5 (the abscissa is the temperature, and the ordinate is the NO conversion rate (%)).

Table 1

The results showed that cerium oxide nanotubes were successfully prepared on the surface of active semi-coke substrate by adjusting the reaction conditions and used to remove NO from power plant exhaust gas. The cerium loading of cerium oxide nanotubes prepared under the condition of cerium nitrate concentration of 0.05M is very low, only 0.62%. Figure 5 shows the NO conversion of ceria nanotubes (Ce0.05/ASC, Example ₂ ) and CeO2 nanoparticles ( _CeO2NP /ASC) and ZnO nanorods (ZnO/ASC). It can be clearly observed from Fig. 5 that the cerium oxide nanotubes exhibit better low _- temperature catalytic performance compared with ZnO nanorods and CeO2 nanoparticles. It can be seen from Table 1 that the cerium oxide nanotube (Ce0.05/ASC) catalyst exhibited the best denitrification performance, and the NO conversion increased from 60% at 90°C to 90% at 210°C. While for CeO2 nanoparticles, the efficiency is only 55 _% at 210 °C.

Although, the present invention has been described in detail with general description, specific implementation and test above, but on the basis of the present invention, some modifications or improvements can be made to it, which will be obvious to those skilled in the art . Therefore, the modifications or improvements made on the basis of not departing from the spirit of the present invention all belong to the protection scope of the present invention.

Claims (10)

1. a preparation method for the active carbocoal low-temperature denitration agent of surface modification Cerium Oxide Nanotubes, exists including using hydro-thermal method Active carbocoal carrier surface modifies CeO₂Nanotube.

Preparation method the most according to claim 1, it is characterised in that described active carbocoal carrier is growing ZnO nanorod Active carbocoal.

Preparation method the most according to claim 1 and 2, it is characterised in that comprise the following steps:

1) active carbocoal is pulverized, put into supersound process in zinc acetate colloid, after filtration, gained sample is dried, calcining, prepare Surface overlays the active carbocoal of ZnO crystal seed；

2) preparing zinc nitrate and the hexamethylenetetramine solution of same concentrations, equal-volume mixes to obtain mixed solution, then by described Surface overlays the active carbocoal of ZnO crystal seed and puts in described mixed solution, carries out Hydrothermal Synthesis in homogeneous reactor, prepares table The active carbocoal of face growing ZnO nanorod；

3) active carbocoal of described superficial growth ZnO nanorod is put in cerous nitrate solution, homogeneous reactor carries out water Thermal response, prepares surface and modifies CeO₂The active carbocoal low-temperature denitration agent of nanotube.

Preparation method the most according to claim 3, it is characterised in that step 1) active carbocoal is crushed to 10-20 mesh； And/or,

Step 1) in the concentration of zinc acetate colloid be 0.005mol/L-0.1mol/L, preferably 0.05mol/L；And/or,

Step 1) in sonication treatment time be 5-30min, preferably 5min；And/or,

Step 1) in calcination condition be 200-400 DEG C calcining 0.2-1h, preferably 370 DEG C calcining 0.5h.

Preparation method the most according to claim 3, it is characterised in that step 2) in zinc nitrate solution and hexamethylenetetramine The concentration of solution is 0.05mol/L-0.2mol/L, preferably 0.1mol/L；And/or,

Step 2) in hydrothermal temperature be 80-120 DEG C, the time is 0.5-8h；Preferably hydrothermal temperature is 95 DEG C, and the time is 1.5h；And/or,

Described step 2) in the rotating speed of homogeneous reactor be 5-40rpm, preferably 10rpm.

Preparation method the most according to claim 5, it is characterised in that step 2) in terms of g/mL described surface overlay ZnO The active carbocoal of crystal seed adds volume ratio 1-5:30 of weight and described mixed solution, preferably 2:30.

Preparation method the most according to claim 3, it is characterised in that described step 3) in the concentration of cerous nitrate be 0.0005mol/L-0.2mol/L, preferably 0.01mol/L-0.1mol/L, the most preferably 0.05mol/L；And/or,

Described step 3) hydrothermal temperature is 80-120 DEG C, the time is 0.5-4h；Preferably hydrothermal temperature is 95 DEG C, the time For 1.5h.

Preparation method the most according to claim 3, it is characterised in that comprise the following steps:

1) active carbocoal is crushed to 10-20 mesh, puts into ultrasonic 5min in the zinc acetate colloid of 0.05mol/L, filter gained Sample dries 1h in 105 DEG C, is then placed in Muffle furnace calcining 30min in 370 DEG C, and prepared surface overlays the activity of ZnO crystal seed Semicoke；

2) compound concentration is zinc nitrate and the hexamethylenetetramine solution of 0.05mol/L, and equal-volume mixes to obtain mixed solution, so After above-mentioned surface overlay the active carbocoal of ZnO crystal seed put in described mixed solution, in homogeneous reactor, 95 DEG C carry out water Thermal synthesis 1.5h, prepares the active carbocoal of superficial growth ZnO nanorod；The rotating speed of described homogeneous reactor is 10rpm；Described table Face overlays the active carbocoal addition of ZnO crystal seed and is preferably 2g, and liquor capacity is 30mL；

3) active carbocoal of described superficial growth ZnO nanorod is put in 0.01mol/L-0.1mol/L cerous nitrate solution, In homogeneous reactor, 95 DEG C carry out hydro-thermal reaction 1h, prepare surface and modify CeO₂The active carbocoal low-temperature denitration agent of nanotube.

9. the active carbocoal low-temperature denitration of Cerium Oxide Nanotubes is modified on the surface that method described in any one of claim 1-8 prepares Agent.

10. the active carbocoal low-temperature denitration agent of Cerium Oxide Nanotubes is modified on air contaminant treatment in surface described in claim 9 Application；Preferably, described application includes processing NO in waste gas_x。