CN113786842B - Catalyst for synthesizing ammonia from NO oxide, preparation method and application thereof - Google Patents

Catalyst for synthesizing ammonia from NO oxide, preparation method and application thereof Download PDF

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CN113786842B
CN113786842B CN202111069783.5A CN202111069783A CN113786842B CN 113786842 B CN113786842 B CN 113786842B CN 202111069783 A CN202111069783 A CN 202111069783A CN 113786842 B CN113786842 B CN 113786842B
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solution
tio
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CN113786842A (en
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戴文新
程刚
陈旬
付贤智
员汝胜
张子重
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Fuzhou University
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Abstract

The invention discloses a catalyst for synthesizing ammonia by NO oxide, a preparation method and application thereof, wherein Pd nano particles are loaded on Fe modified TiO with visible light absorption 2 And (3) preparing the supported Pd catalyst on a semiconductor carrier. By introducing the flexible LED lamp strip into the catalytic converter filled with the supported Pd catalyst, the efficient catalytic removal of CO and NO at low temperature is realized by utilizing the photo-thermal coupling effect, and meanwhile, NH with high added value can be generated 3 . Compared with the conventional thermocatalytic reaction, the photo-thermal coupling method can greatly reduce the use temperature of the denitration catalyst and obviously reduce the energy consumption required by the conventional ammonia synthesis reaction. In addition, NH generated during the reaction 3 Also helps downstream NH 3 The SCR reaction can be carried out with further reduced use of spray materials such as ammonia or urea. The method has great prospect in the aspects of denitration and purification of tail gas and development and utilization of a novel synthetic ammonia catalytic system.

Description

Catalyst for synthesizing ammonia from NO oxide, preparation method and application thereof
Technical Field
The invention belongs to the field of environmental protection and synthesis of NH by photo-thermal synergistic catalysis 3 The field, in particular to a supported Pd catalyst, a preparation method and application thereof, wherein the supported Pd catalyst not only can improve the catalytic removal effect on CO and NO through the photo-thermal synergistic effect, but also promotes the NH product with high industrial added value through the humidity existing in a reaction system 3 Is generated.
Background
With the development of socioeconomic performance, nitrogen oxides (NO x ) The excessive emission of (2) causes great harm to our living environment and human health, and the self-purification capability of the atmosphere is insufficient to degrade NO emitted by industrial fixed sources and mobile sources, so that the technology for continuously advancing pollution control, consolidating and expanding the guard warfare achievements in blue sky, controlling the emission of NOx, and continuously developing and researching the removal technology of nitrogen oxides is imperative. The current removal of NO mainly includes: 1) The control technology before combustion, namely, nitrogen content in fuel is reduced through a series of methods, such as improving the quality of gasoline and fuel gas and using clean energy, so that the possibility of generating NOx is reduced from the source; 2) The combustion process control technology mainly controls the combustion zone, namely controls the generation of NOx in the combustion process by various technical means such as reducing the residence time of fuel in the high-temperature combustion zone, creating a reduction zone in the combustion zone, properly reducing the oxygen concentration in the combustion zone, reducing the temperature of the combustion zone and the like, and mainly improves the internal structure and the working mode of a mobile source engine; 3) The combustion post-treatment technology mainly adopts the treatment of some aspects outside the engine or incinerator and other machines to reduce NO x The purpose of the discharge. Wherein, ammonia gas in the combustion post-treatment technologySelective catalytic reduction of NO (NH) 3 SCR) is the most widely used and mature technical means at present due to the rapid and efficient characteristics thereof, but NH 3 The production and transportation cost is higher, the problems of easy leakage and corrosive pipelines exist, and more importantly, the operation temperature area of the technology is narrow, and the technology only aims at NO discharged by a fixed source x Is performed by the processor. In recent years, the CO-SCR reaction derived from the three-way catalytic technology of automobile exhaust gas purification has been widely studied and used because there is a large amount of unburnt CO in the flue gas duct, which is also a polluting gas harmful to human body, and the reduction of NO by CO not only eliminates both pollutants simultaneously, converting them into CO2 and N2 (co+no=co 2 + 1/2N 2 ) Meanwhile, the technology also overcomes the defect that NH3-SCR can not remove NOx in a mobile source. At present, the research on catalyzing CO to reduce NO is gradually mature, but the low-temperature catalytic activity and N of the CO are 2 The selectivity of (c) remains to be improved.
While NH is 3 As an industrial raw material, has important value in the production and preparation of dyes, polymers, fertilizers and explosives, and is also a carbon neutral carrier with high energy density, but the traditional thermocatalytic synthesis of ammonia (N) 2 + 3H 2 = 2NH 3 ) Higher temperatures and pressures are often required, which results in excessive energy consumption. Although in recent years the synthesis of NH by electrocatalysis 3 （N 2 + H 2 O → NH 3 + O 2 ) Has been extensively studied and studied, but its catalytic activity and NH 3 The selectivity to (2) is still low and for trace NH 3 Also, there are great difficulties in detection. However sum N 2 NO has weaker bond energy than NO, is a chemically active polar molecule, and a number of studies have demonstrated that when H 2 When used as a reducing agent, the NO can be directly reduced to NH under the anaerobic condition and the action of a catalyst 3 （H 2 + NO → NH 3 + H 2 O). Whereas, previous studies focused mainly on how to reduce NO to N for reactions catalyzing CO to reduce NO 2 Direct reduction to NH is not studied 3 . In fact, the discharged flue gas is asUsually contains a certain amount of water, so we consider that on the basis of catalyzing CO to reduce NO, CO and H at low temperature are further regulated 2 The water gas shift reaction between O to produce H 2 （CO + H 2 O → H 2 + CO 2 ) Subsequent use of H 2 Further reducing NO to generate NH 3 . The technical method can obviously improve the efficiency of the denitration reaction, reduce the energy consumption required by the traditional synthetic ammonia reaction, and produce NH in the reaction process 3 Will also contribute to downstream NH 3 The SCR reaction proceeds, and therefore has important implications both in theoretical research and in practical applications.
Disclosure of Invention
The invention aims to overcome the following problems: 1) The defect of poor capability of removing CO/NO by pure thermocatalysis leads to the problem of poor low-temperature catalytic performance; 2) The traditional high energy consumption problem of thermal catalytic synthesis of ammonia provides a supported Pd catalyst, a preparation method and application thereof, wherein Pd is supported on a semiconductor carrier, so that the performance of the Pd catalyst for catalytic removal of CO/NO under the condition of containing a certain humidity is improved through photo-thermal coupling, and the NH of a reaction product is remarkably improved 3 Is selected from the group consisting of (1). Solves the problem that the conventional Pd supported catalyst and a simple carrier can catalyze CO/NO reaction only at a higher temperature, and promotes NH 3 The energy consumption of the traditional synthetic ammonia reaction is effectively reduced. The preparation method of the catalyst is simple and feasible, and is favorable for popularization and application.
In order to achieve the above purpose, the invention adopts the following technical scheme:
a supported Pd catalyst is TiO doped with Fe 2 （Fe-TiO 2 ) The Pd nano particles are high-dispersion supported catalyst composed of active components; wherein, the doping amount of Fe is 1.0% -10.0 at%, preferably 5.0 at%; the content of active component Pd in the catalyst was 1.0 wt%; the supported Pd catalyst can realize the removal of CO and NO and NH in tail gas at a lower temperature under the condition of introducing visible light 3 Is generated.
The preparation method of the supported Pd catalyst comprises the steps of preparing Fe doped by a sol-gel methodTiO of (C) 2 A carrier, and a deposition-precipitation method is used for preparing Fe-TiO 2 The active component Pd is loaded on the carrier; the method specifically comprises the following steps:
(1) Under ice water bath, rapidly adding isopropyl titanate into glacial acetic acid, vigorously stirring, and then dropwise adding a certain amount of deionized water to obtain a transparent solution A; weighing a certain amount of Fe (NO 3) 3.9H2O according to a proportion, and dissolving in deionized water to obtain a solution B; dropwise adding the solution B into the solution A to obtain a mixed solution C, continuously adding deionized water as a balance liquid, magnetically stirring 6 h, standing and ageing 12 h, and then adding the ageing liquid at 80 o C, slowly drying in an oil bath, and finally, adding the mixture into a muffle furnace by 2 o The temperature rising rate of C/min rises to 500 o C, calcining 1 h to obtain an Fe-TiO2 carrier, and defining a sample as x% of Fe-TiO2 according to different amounts of introduced Fe, wherein x% represents a theoretical molar ratio of Fe to Ti;
(2) In the Fe-TiO obtained 2 Addition of PdCl to the Carrier 2 Stirring the solution and deionized water for 30-60 min, ultrasonically treating for 15-30 min, and adding excessive NaBH containing NaOH 4 Stirring the solution at room temperature for 2-8 h, centrifuging, washing with deionized water, and performing 60-80 o And C, vacuum drying to obtain the supported Pd catalyst.
In the step (1), the volume ratio of isopropyl titanate to glacial acetic acid is 1:2. PdCl in step (2) 2 The concentration of the solution is 6.0 mg/mL, naBH containing NaOH 4 In solution, naBH 4 And NaOH solutions were each 0.1 mol/L in concentration.
The supported Pd catalyst can promote NH while realizing the photo-thermal coupling conversion of NO+CO in tail gas 3 Is generated. The application method is that a flexible LED lamp strip is introduced into a catalytic converter filled with a supported Pd catalyst, so that CO/NO removal and NH removal at a lower temperature are realized through photo-thermal coupling 3 An improvement in selectivity; the LED strip is introduced by being arranged around the reaction tube or packed in a catalyst bed inside the reaction tube. The reaction temperature is 60-210 DEG o C, performing operation; the humidity is 50% -75%.
The invention has the remarkable advantages that:
(1) The invention uses Fe doped TiO 2 （Fe-TiO 2 ) The catalyst is used as a carrier, fully exerts the performance of catalyzing and oxidizing at low temperature to remove CO and NO, and has a large amount of oxygen vacancies to CO, NO and H 2 The promoting effect of O adsorption activation is characterized; meanwhile, tiO after Fe doping 2 When Pd is loaded on the carrier, photo-generated electrons can be transferred from a semiconductor with a Fermi level to Pd metal with a low Fermi level, so that the electron density of the Pd surface of the active metal is improved, and the adsorption and activation of CO and NO are facilitated.
(2) Compared with the simple thermocatalytic reaction, the invention prepares the Pd supported catalyst by selecting the semiconductor with visible light response as the carrier and prepares the Pd supported catalyst according to NO+CO, CO+H 2 The characteristic of O reaction, the LED lamp strip is introduced to carry out visible light illumination in the reaction process, so that the performance of the catalyst for catalyzing and removing CO and NO and the reduction product NH are obviously improved by utilizing the photo-thermal coupling effect 3 The selectivity of the catalyst effectively reduces the reaction temperature and reduces the energy consumption.
(3) The preparation method and the application operation of the invention are simple and easy, and the preparation method and the application operation are hopeful to realize the effect of high-efficiency catalytic purification of NO and the generation of NH by utilizing waste through adding a section of photo-thermal coupling device in the tail gas purification system discharged by an industrial fixed source or a mobile source 3 Is suitable for popularization and application.
Drawings
FIG. 1 shows 1.0. 1.0 wt% Pd/5% Fe-TiO as obtained in example 1 2 Is a transmission electron microscope image of (a).
FIG. 2 shows 1.0. 1.0 wt% Pd/5% Fe-TiO as obtained in example 1 2 Is a XRD pattern of (C).
FIG. 3 shows the result of example 1, 1.0 wt% Pd/5% Fe-TiO 2 Ultraviolet-visible diffuse reflectance spectrogram of (c).
FIG. 4 is a schematic view of the structure of a catalyst performance evaluation reaction system.
Detailed Description
In order to make the contents of the present invention more easily understood, the technical scheme of the present invention will be further described with reference to the specific embodiments, but the present invention is not limited thereto.
EXAMPLE 1 Pd/Fe-TiO 2 Preparation of the catalyst
Under ice water bath, the isopropyl titanate precursor solution of 18 mL was rapidly added to glacial acetic acid of 36 mL with vigorous stirring, and then a certain amount of deionized water was dropwise added to obtain a transparent solution a. 1.212 and g of Fe (NO 3) 3.9H2O is weighed according to a proportion and dissolved in 65 mL of deionized water to obtain a solution B. The solution B was added dropwise to the solution a to obtain a mixed solution C, and then 100 mL of deionized water was continuously added thereto as a balancing solution. After magnetic stirring 6 h, standing and aging 12 h, and then aging the aging liquid at 80 o C, slowly drying in an oil bath, and finally, adding the mixture into a muffle furnace by 2 o The temperature rising rate of C/min rises to 500 o Calcining 1 h to obtain the Fe-TiO2 carrier with 5% Fe doping amount.
1.2 g of Fe-TiO2 solid powder is weighed and added with PdCl with the concentration of 2.0 mL of 6.0 mg/mL 2 Introducing 100 mL deionized water into the solution, stirring for 30 min, performing ultrasonic treatment for 15 min, adjusting the pH value of the solution to about 10.0, and slowly dripping NaBH with the concentration of 0.1 mol/L 4 And NaOH to reduce Pd fully, centrifugal washing with deionized water to ion concentration lower than 10 ppm, and final washing at 80 o Vacuum drying under C to obtain Pd/Fe-TiO with Pd content of about 1.0 wt% and Fe doping amount of 5.0 at% 2 A catalyst.
FIG. 1 shows the Pd/Fe-TiO composition 2 A transmission electron microscope of the catalyst and a Mapping graph of element distribution. It was found that the prepared samples exhibited an irregular scattered particle morphology, which may be conducive to mass transfer of the reactants and to some promotion of the adsorption of NO and CO. The EDX profile of the sample further verifies the presence of element Pd, O, ti, fe (see inset of fig. 1 a) and reflects an actual loading of 0.86% of the sample surface Pd. From the HRTEM image shown in FIG. 1 b, it can be seen that lattice fringes with interplanar spacings of 0.350 and 0.224, nm, respectively, tiO 2 And (101) and (220) faces of Pd. And the lattice fringes with the interplanar spacing of 0.184 nm belong to Fe 2 O 3 (024) surface of Pd-supported catalystAn amount of iron oxide species aggregates. The EDX-Mapping pictures shown in FIGS. 1 c-g also further demonstrate Pd/Fe-TiO 2 Uniform distribution of Pd, fe, ti, O elements in the sample.
FIG. 2 shows the obtained TiO 2 、Pd/TiO 2 、Fe-TiO 2 、Pd/Fe-TiO 2 XRD spectrum of the sample. And a carrier TiO 2 And Fe-TiO 2 In contrast, the diffraction peak of the Pd-loaded sample is not changed significantly, and the sample still shows a typical anatase crystal form. Diffraction peaks for Pd, fe and their oxides were also not observed in the loaded samples, probably due to the high dispersion of Pd and doped Fe species in the support.
FIG. 3 shows the obtained TiO 2 、Pd/TiO 2 、Fe-TiO 2 、Pd/Fe-TiO 2 Uv-vis diffuse reflectance spectrum of the catalyst. After Fe doping, tiO can be observed 2 The absorption band edge of (c) is significantly red shifted, so that the light absorption of the catalyst sample is enhanced in the range of 400-500 and nm. And after the noble metal Pd is loaded, pd/Fe-TiO is further promoted 2 The absorption of visible light shows that the supported catalyst can better utilize visible light and exert the photocatalysis effect.
Example 2 evaluation of catalyst Performance
The catalyst obtained in example 1 catalyzes the removal of CO/NO and the generation of NH 3 The performance evaluation of (2) was performed on a self-designed atmospheric continuous flow reactor. The normal pressure continuous flow device is shown in fig. 4, and comprises a gas distribution system, a photocatalytic reactor, a circulating oil bath temperature control system, a light source and an analysis system.
Wherein, the photocatalysis reactor is double-layer quartz glass, the inner layer of the reactor is filled with catalyst, and the outer layer can be filled with circulating silicone oil to control the temperature of the reaction process. The glass reactor is provided with a visible light emitting device (LED lamp strip) which can be used for exciting the catalyst to generate light response, and visible light emitted by the light emitting device can penetrate through the glass reactor to reach the surface of the catalyst.
In addition, the light-emitting device (especially the LED lamp strip) in the reaction system can be directly arranged between the catalysts in the reaction tube, the emitted visible light can directly irradiate the surfaces of the catalysts, the utilization rate is high, the flexible LED lamp strip can change the appearance along with the reaction tube, the vibration resistance is good, the catalyst can be heated by the heat emitted by the lamp strip, and the electric heating of the temperature required by the reaction is reduced.
Reaction conditions: the glass reactor was filled with 0.3. 0.3 g catalyst (20. 20 mm. Times. 20. 20 mm. Times. 1. 1 mm. In length and width) and the catalyst particle size was about 0.2 to 0.3mm (60 to 80 mesh). The reaction gas enters a glass reactor filled with catalyst particles through a gas inlet, a required temperature is provided for the reactor through a circulating oil bath controlled by temperature programming, and visible light is applied to the reactor. The CO and NO contents in the reaction gas were fixed to 0.30 vol.% and 0.15 vol.%, respectively, N 2 As an equilibrium make-up gas, the total flow rate of the reaction gas was about 100 mL/min (ghsv=30,000 h -1 ) The humidity was controlled at 75%. The visible light source adopts 10W LED lamp strips (10 small bulbs of 1W are connected together in series, the main light emitting wavelength is 450-550 nm), and the light intensity of the light irradiated on the surface of the catalyst is 182 mW/cm 2 . The gas outlet adopts a GASERA One type photoacoustic spectrometer (PAS) to analyze CO and CO in the atmosphere on line 2 、N 2 O、H 2 O、NH 3 The Testo 340 type flue gas analyzer analyzes the concentration change of the online detection NO, and the CO/NO conversion rate and NH are calculated by taking the result of the reaction for 2 hours 3 Is selected from the group consisting of (1). CO conversion, NO conversion and NH 3 The selectivity conversion calculation formula is as follows:
in the formula (1-1) [ CO ]] in And [ CO ]] out CO content (V%) in inlet gas and outlet gas respectively, formula (1-2) [ NO] in And [ NO ]] out NO content (V%) in the inlet and outlet gases, respectively, [ NH ] in the formula (1-3) 3 ] out For NH in effluent gas 3 Content (V%).
According to the method, the performance of the catalyst for catalyzing and removing CO/NO and NH under different conditions are respectively evaluated 3 The selectivity of (2) is shown in Table 1Shown.
TABLE 1 Pd/Fe-TiO before and after illumination 2 Performance of catalytic CO/NO removal and NH pair 3 Selectivity of (2)
The results in Table 1 show that the conversion of CO and NO, NH, after the introduction of visible light under the same conditions, are compared with the pure thermal reaction conditions 3 The selectivity of (a) is greatly improved. The visible light has obvious promoting effect on the performance of the catalyst.
The foregoing description is only of the preferred embodiments of the invention, and all changes and modifications that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims (8)

1. The application of the supported Pd catalyst is characterized in that: introducing a flexible LED lamp strip into a catalytic converter filled with a supported Pd catalyst, thereby realizing removal of CO and NO and NH at a lower temperature through photo-thermal coupling effect 3 Is generated; the reaction temperature is 60-210 ℃;
the catalyst is prepared by Fe-TiO 2 The Pd nano particles are high-dispersion supported catalyst composed of active components; wherein the content of active component Pd in the catalyst is 1.0-wt percent, and the content of doping element Fe in the carrier is 1.0-10.0-at percent.
2. The use according to claim 1, characterized in that: the preparation method of the supported Pd catalyst comprises the following steps: firstly, synthesizing Fe-TiO by using sol-gel method 2 A carrier; then depositing and precipitating the Fe-TiO to obtain 2 The active component Pd is loaded on the carrier.
3. The use according to claim 2, characterized in that: the preparation method of the supported Pd catalyst specifically comprises the following steps:
(1) In ice water bath, isopropyl titanate is rapidly added into glacial acetic acidAnd stirring vigorously, and then dropwise adding a certain amount of deionized water until a transparent solution A is obtained; weighing a certain amount of Fe (NO) 3 ) 3 ·9H 2 O is dissolved in deionized water to obtain solution B; dropwise adding the solution B into the solution A to obtain a mixed solution C, and then continuously adding deionized water into the solution C to serve as balance liquid; magnetic stirring 6 h, standing and aging 12 h, slowly drying the aging liquid in an oil bath at 80deg.C, and calcining 1 h in a muffle furnace at a heating rate of 2 deg.C/min to 500 deg.C to obtain Fe-TiO 2 The carrier, according to the quantity of Fe introduced, defines the sample as x% Fe-TiO 2 X% represents the theoretical molar ratio of Fe to Ti;
(2) In the Fe-TiO obtained 2 Addition of PdCl to the Carrier 2 Stirring the solution and deionized water for 30-60 min, ultrasonically treating for 15-30 min, and adding excessive NaBH containing NaOH 4 Stirring the solution at room temperature for 2 h, centrifuging, washing with deionized water, and vacuum drying at 60-80 ℃ to obtain the supported Pd catalyst.
4. A use according to claim 3, characterized in that: the volume of isopropyl titanate and glacial acetic acid in the step (1) is 1:2.
5. A use according to claim 3, characterized in that: pdCl in step (2) 2 The concentration of the solution was 6.0. 6.0 mg/mL.
6. A use according to claim 3, characterized in that: naBH containing NaOH in step (2) 4 In solution, naBH 4 And NaOH at a concentration of 0.1 mol/L.
7. The use according to claim 1, characterized in that: the LED strip is arranged around the reaction tube or packed in a catalyst bed inside the reaction tube.
8. The use according to claim 1, characterized in that: the humidity is 50% -75%.
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