CN117563656A - A diatomic symbiotic composite catalyst and its preparation method and application - Google Patents

Abstract

The invention discloses a diatomic symbiotic composite catalyst and a preparation method and application thereof. In the high-temperature heat-relieving process, the nitrogen-containing compound forms a nitrogen-doped carbon carrier; and palladium salt and zinc salt coordinate with nitrogen and carbon to be embedded into a carbon skeleton in the pyrolysis process to form Pd and Zn diatomic, thus obtaining the Pd and Zn diatomic symbiotic compound molecular sieve catalyst. The symbiotic composite catalyst is applied to the flue gas denitration process, the denitration efficiency reaches more than 90% under the medium-low temperature condition, and a feasible thought can be provided for solving the current increasingly serious environmental pollution.

Description

A diatomic symbiotic composite catalyst and its preparation method and application

Technical field

The invention belongs to the technical field of chemical synthesis. Specifically, it relates to a diatomic symbiotic composite catalyst and its preparation method and application.

Background technique

Nitrogen oxides (NOx) are important air pollutants in non-electricity industries such as coal-fired power generation and steel metallurgy, which seriously threaten the ecological environment and human health. As my country attaches increasing importance to environmental protection, relevant Chinese departments have launched and implemented the "Emission Standards for Air Pollutants from Thermal Power Plants (GB 13223-2011)" and the "Technical Specifications for Ultra-Low Emission Flue Gas Treatment Engineering for Coal-fired Power Plants", which clearly stipulate The NOx emission mass concentration in flue gas is ≤50mg/m3. Therefore, it is of great research significance and industrial value to explore and develop denitration technology that is green, environmentally friendly, and has great industrial development potential.

Currently in industrial applications, vanadium-titanium SCR catalysts have good removal performance for NOx in flue gas. However, they have shortcomings such as high reaction temperature (300-400°C), poor activity at medium and low temperatures, and easy poisoning. The expired vanadium-titanium catalyst is defined as hazardous waste, which brings difficulties to subsequent treatment. It is urgent to develop catalysts with superior denitrification performance and good sulfur resistance. In recent years, researchers have carried out a lot of research in the field of denitrification and catalysts and achieved a series of results. Among them, diatomic catalysts, as a new type of catalyst, have shown positive application value in many fields such as catalysis. More importantly, this type of catalyst has the advantages of clear structure and active center as well as high selectivity, which brings important opportunities for the development of denitration catalysts.

Contents of the invention

The purpose of the present invention is to provide a diatomic symbiotic composite catalyst and its preparation method and application, so as to solve the problems in the prior art that out-of-stock catalysts have poor reactivity in medium and low temperature environments, have higher requirements for reaction temperature, and are difficult to deal with after poisoning failure. question.

The object of the present invention can be achieved through the following technical solutions:

A method for preparing a diatomic cogeneration composite catalyst, including the following steps:

Precursor preparation: Add molecular sieve, palladium salt and zinc salt to the mixed solvent to form a uniform dispersion; then slowly add the nitrogen-containing compound into A and continue stirring; the stirred solid is filtered and vacuum dried to obtain the precursor body;

Pyrolysis: The prepared precursor is pyrolyzed in a tube furnace in an inert atmosphere to obtain a diatomic symbiotic composite catalyst.

Preferably, the mass ratio of molecular sieve, palladium salt and zinc salt is 1:0.1-1:0.1-6.

Preferably, the mixed solvent is a mixed solution of water and methanol in any ratio.

Preferably, the dosage ratio of molecular sieve to mixed solvent is 0.2-20 mg/ml.

Preferably, the molecular sieve is a mixture of one or more of titanium silicon molecular sieve, Beta molecular sieve and Y-type molecular sieve in any ratio.

Preferably, the nitrogen-containing compound is one of dimethylimidazole, dicyandiamide, melamine and urea.

Preferably, the pyrolysis includes the following steps:

Place the precursor in a tube furnace and perform carbonization treatment in an inert atmosphere: react the precursor at 400-700°C for 1-5 hours; then react at 800-1100°C for 1-10 hours.

Beneficial effects of the present invention:

1. The present invention uses molecular sieves as the matrix, palladium salts and zinc salts as metal salts, nitrogen-containing compounds as nitrogen sources and carbon sources, and adopts a stirring-pyrolysis strategy to prepare a Pd and Zn diatomic symbiotic composite catalyst. During the high-temperature depyrolysis process, nitrogen-containing compounds form nitrogen-doped carbon carriers; and during the pyrolysis process, palladium salts and zinc salts are coordinated with nitrogen and carbon and embedded into the carbon skeleton to form Pd and Zn diatoms, which can be prepared A Pd and Zn diatomic cogeneration composite molecular sieve catalyst was obtained. The preparation method has the advantages of simplicity, reliability, and easy availability.

2. The Pd and Zn diatomic symbiotic composite catalyst described in the present invention is used in the flue gas denitration process. The denitration efficiency reaches more than 90% under medium and low temperature conditions (150-250°C), which can solve the current increasingly serious environmental pollution. Provide a practical idea.

3. Compared with the existing technology, the method of preparing the Pd and Zn diatomic symbiotic composite catalyst prepared by the present invention is simple and has uniform morphology, avoids the use of toxic metals, reduces environmental hazards, and has low metal content, effectively reducing The use of metal salt reduces preparation costs.

Description of the drawings

The present invention will be further described below in conjunction with the accompanying drawings.

Figure 1 is the X-ray powder diffraction XRD pattern of Y-type molecular sieve;

Figure 2 is an X-ray powder diffraction XRD pattern of the diatomic intergenerational composite catalyst obtained in Example 1;

Figure 3 is a scanning electron microscope SEM photo of the diatomic intergrowth composite catalyst obtained in Example 1;

Figure 4 is the Pd high-resolution XPS spectrum of the diatomic intergeneration composite catalyst obtained in Example 1;

Figure 5 shows the Zn high-resolution XPS spectrum of the diatomic symbiotic composite catalyst;

Figure 6 is a denitration performance test chart of the diatomic symbiotic composite catalyst obtained in Example 1.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

Example 1

A method for preparing a diatomic cogeneration composite catalyst, including the following steps:

A. Dispersion: Weigh 100 mg Y-type molecular sieve, 60 mg palladium acetylacetonate, and 0.60 g zinc nitrate and disperse them in 20 mL of a mixed solvent of methanol and water with a volume ratio of 1:1;

B. Preparation: Add 0.7g dimethylimidazole to the dispersion of step A at room temperature and stir for 24 hours. The solid obtained by the reaction is filtered and dried in a vacuum drying oven at 40°C for 8 hours;

C. Pyrolysis: The precursor obtained in step B is first calcined at 500°C for 1 hour in an argon atmosphere, and then calcined at 900°C for 5 hours; finally, it is naturally cooled to room temperature to become a diatomic symbiotic composite catalyst.

X-ray powder diffraction patterns (Figures 1 and 2) show that the XRD diffraction peaks of the diatomic intergenerational composite catalyst are mainly Y-type molecular sieves without any impurity peaks; scanning electron microscopy (SEM, Figure 3) shows that molecular sieves and Pd, The Zn diatomic catalyst is uniformly mixed; (Figure 4 and Figure 5).

Denitrification performance test

The diatomic catalyst obtained in Example 1 was used in a tubular SCR reactor (see Figure 6) for denitration performance testing:

The catalyst filling amount is 500mg, and the flue gas composition is simulated by a steel cylinder. The flue gas includes NO, O ₂ , N ₂ , and NH ₃ is a reducing gas. The gas flow and composition are adjusted and controlled by a flow meter. The volume fractions of NO and NH ₃ are Both are 0.05%, the volume fraction of O ₂ is 5%, and the rest is N ₂ . The gas flow rate is 400ml·min ^-1 , the air speed is about 40000h ^-1 , the temperature is set to 200°C, and after the air flow is stable for 30 minutes, use German M60x cigarette The gas analyzer measured the denitrification rate at 90%.

Example 2

A method for preparing a diatomic catalyst, including the following steps:

A. Dispersion: Weigh 100 mg Beta molecular sieve, 30 mg palladium acetylacetonate, and 0.60 g zinc nitrate and disperse them in 20 mL of a mixed solvent of methanol and water with a volume ratio of 1:1;

B. Preparation: Add 1.0g of dicyandiamide to the dispersion of step A at room temperature and stir for 24 hours. The solid obtained by the reaction is filtered and dried in a vacuum drying oven at 40°C for 8 hours;

C. Pyrolysis: The precursor obtained in step B is first calcined at 500°C for 3 hours in an argon atmosphere, and then calcined at 900°C for 2 hours; finally, it is naturally cooled to room temperature, which is a diatomic catalyst symbiotic molecular sieve catalyst.

Denitrification performance test

The diatomic catalyst obtained in Example 2 was used in a self-made tubular SCR reactor for denitration performance testing:

The catalyst filling amount is 500mg, and the flue gas composition is simulated by a steel cylinder. The flue gas includes NO, O ₂ , N ₂ , and NH ₃ is a reducing gas. The gas flow and composition are adjusted and controlled by a flow meter. The volume fractions of NO and NH ₃ are Both are 0.05%, the volume fraction of O ₂ is 5%, and the rest is N ₂ . The gas flow rate is 400ml·min ^-1 , the air speed is about 40000h ^-1 , the temperature is set to 150°C, and after the air flow is stable for 30 minutes, use German M60x cigarette The gas analyzer measured the denitrification rate at 92%.

Example 3

A method for preparing a diatomic catalyst, including the following steps:

A. Dispersion: Weigh 100 mg Beta molecular sieve, 40 mg palladium acetylacetonate, and 0.60 g zinc chloride and disperse them in 20 mL of a mixed solvent of methanol and water with a volume ratio of 1:1;

B. Preparation: Add 1.0g melamine to the dispersion of step A at room temperature and stir for 24 hours. The solid obtained by the reaction is filtered and dried in a vacuum drying oven at 40°C for 8 hours;

C. Pyrolysis: The precursor obtained in step B is first calcined at 500°C for 5 hours in an argon atmosphere, and then calcined at 1000°C for 10 hours. Finally, it is naturally cooled to room temperature, which is a diatomic catalyst symbiotic molecular sieve catalyst.

Denitrification performance test

The diatomic catalyst obtained in Example 3 was used in a self-made tubular SCR reactor for denitration performance testing:

The catalyst filling amount is 500mg, and the flue gas composition is simulated by a steel cylinder. The flue gas includes NO, O ₂ , N ₂ , and NH ₃ is a reducing gas. The gas flow and composition are adjusted and controlled by a flow meter. The volume fractions of NO and NH ₃ are Both are 0.05%, the volume fraction of O ₂ is 5%, and the rest is N ₂ . The gas flow rate is 400ml·min ^-1 , the air speed is about 40000h ^-1 , the temperature is set to 250°C, and after the air flow is stable for 30 minutes, use German M60x cigarette The gas analyzer measured the denitrification rate at 91%.

The above contents are only examples and explanations of the present invention. Those skilled in the art may make various modifications or supplements to the described specific embodiments or substitute them in similar ways, as long as they do not deviate from the invention or exceed the rights of the present invention. The scope defined in the claims shall belong to the protection scope of the present invention.

Claims (10)

1. The preparation method of the diatomic symbiotic composite catalyst is characterized by comprising the following steps:

precursor preparation: adding a molecular sieve, palladium salt and zinc salt into a mixed solvent to form a uniformly dispersed dispersion liquid; then slowly adding the nitrogen-containing compound into the A, and continuously stirring; filtering the stirred solid and drying the solid in vacuum to obtain a precursor;

and (3) pyrolysis: and pyrolyzing the prepared precursor in a tube furnace in an inert atmosphere to obtain the diatomic symbiotic composite catalyst.

2. The preparation method of the diatomic symbiotic composite catalyst of claim 1 is characterized in that the mass ratio of molecular sieve, palladium salt and zinc salt is 1:0.1 to 1:0.1 to 6.

3. The method for preparing the diatomic symbiotic composite catalyst of claim 1 wherein the mixed solvent is a mixed solution of water and methanol in any ratio.

4. The method for preparing the diatomic symbiotic composite catalyst of claim 2 characterized by the fact that the dosage ratio of molecular sieve to mixed solvent is 0.2-20mg/ml.

5. The method for preparing the diatomic symbiotic composite catalyst of claim 1 wherein the molecular sieve is a mixture of one or more of titanium-silicon molecular sieve, beta molecular sieve and Y-type molecular sieve in any ratio.

6. The method for preparing the diatomic symbiotic composite catalyst of claim 1 characterized in that the nitrogen-containing compound is one of dimethylimidazole, dicyandiamide, melamine and urea.

7. The method for preparing the diatomic symbiotic composite catalyst of claim 1 wherein the pyrolysis comprises the steps of:

the precursor is placed in a tube furnace for carbonization treatment under inert atmosphere: reacting the precursor at 400-700 deg.c for 1-5 hr; then reacting for 1-10 hours at 800-1100 ℃.

8. The method for preparing a diatomic symbiotic composite catalyst according to claim 1, wherein the loading of Pd in the composite catalyst is 0.05-5.0 wt% and the loading of Zn is 0.05-12.0wt%.

9. A diatomic symbiotic composite catalyst characterized in that it is prepared according to the method of preparing a diatomic symbiotic composite catalyst according to any of claims 1 to 8.

10. The use of a diatomic symbiotic composite catalyst as claimed in claim 9 for the treatment of flue gases containing nitro-gases.