CN112264075B - High-efficiency demercuration photocatalyst suitable for medium-low temperature condition and preparation method thereof - Google Patents

Abstract

The invention discloses a high-efficiency mercury removal (Hg ⁰ ) photocatalyst suitable for medium and low temperature conditions and a preparation method thereof. The core-shell structure g‑C ₃ N ₄ @TiO ₂ was first prepared by TiO ₂ (001) with high exposure of the (001) crystal plane, and then CeO ₂ was highly dispersedly supported on g‑C ₃ N ₄ @TiO ₂ , The utilization efficiency of Ce atoms is significantly improved, thereby preparing CeO ₂ ‑g‑C ₃ N ₄ @TiO ₂ with high photocatalytic mercury removal activity. At 50-250°C, the catalyst exhibits excellent photocatalytic Hg ⁰ removal performance, and the catalytic performance remains stable for a long time. The preparation method of the photocatalyst in the present invention is simple and repeatable, the raw material is cheap and environmentally friendly, and has strong practical value and application potential.

Description

A kind of high-efficiency mercury removal photocatalyst suitable for medium and low temperature conditions and preparation method thereof

technical field

The invention relates to the technical field of catalysts, in particular to a catalyst for removing gaseous Hg ⁰ in flue gas.

Background technique

China is the country with the most serious atmospheric mercury (Hg _g ) pollution. Thermal power plants have become one of the main sources of Hg _g emissions due to their huge emissions. Gaseous elemental mercury, Hg ⁰ ), oxidized mercury (Hg ²⁺ ), and particulate bound mercury (Hg ^p ). Hg ²⁺ is easily absorbed by amine solutions, and Hg ^p is easily captured by cloth bags, electrostatic precipitators or fabric filters, however, Hg ⁰ is difficult to remove due to its high volatility and insolubility. At present, there are various techniques for removing Hg ⁰ from gas streams, such as wet deep oxidation, catalytic oxidation, photochemical oxidation, and adsorption. Using catalyst to catalyze the oxidation of Hg ⁰ in the exhaust gas to remove or convert the Hg ⁰ in the exhaust gas into Hg ²⁺ , and then use the relatively mature wet desulfurization technology and equipment for coal-fired power plants to remove the mercury, which is the most widely used coal-fired technology. It is a cost-effective and promising method in flue gas mercury removal technology. Therefore, it is necessary to develop efficient medium-low temperature environment-friendly catalysts.

SUMMARY OF THE INVENTION

In order to overcome the above-mentioned deficiencies of the prior art, the present invention provides a high-efficiency mercury removal photocatalyst suitable for medium and low temperature conditions and a preparation method thereof. The mercury removal photocatalyst is used in photocatalytic removal of Hg ⁰ , and can effectively remove gaseous elemental mercury Hg ⁰ in a gas including atmosphere, flue gas and the like under medium and low temperature conditions.

One of the technical solutions adopted by the present invention to solve its technical problems is:

A high-efficiency mercury removal (Hg ⁰ ) photocatalyst suitable for medium and low temperature conditions, which is gC ₃ N ₄ @TiO ₂ loaded with CeO ₂ , and the gC ₃ N ₄ @TiO ₂ has a core-shell structure, with gC 3 N 4 @TiO 2 ₃ N ₄ (graphitic carbon nitride) is the shell and TiO ₂ (001) is the core.

A high-efficiency degassing elemental mercury (Hg ⁰ ) photocatalyst suitable for medium and low temperature conditions of the present invention prepares gC ₃ N ₄ @TiO ₂ with core-shell structure through TiO ₂ (001) with high exposure (001) crystal plane. , and then CeO ₂ was highly dispersed on gC ₃ N ₄ @TiO ₂ to significantly improve the utilization efficiency of Ce atoms, thus preparing a catalyst CeO ₂ -gC ₃ N ₄ @TiO ₂ with high photocatalytic mercury removal activity.

Further, the application temperature range of the mercury removal photocatalyst is 50-250°C. The CeO ₂ -gC ₃ N ₄ @TiO ₂ photocatalyst exhibits excellent Hg ⁰ removal performance at 50-250 °C. Preferably, the effect of removing Hg ⁰ is best at 50-100°C.

Further, in the mercury removal photocatalyst, the relative content (mass percentage) of CeO ₂ is 1-7 wt %. Preferably, the relative content of CeO ₂ is 2-4 wt %.

The second of the technical solutions adopted by the present invention to solve its technical problems is:

A preparation method of a high-efficiency mercury removal (Hg ⁰ ) photocatalyst suitable for medium and low temperature conditions. Based on TiO ₂ (001), gC ₃ N ₄ @TiO ₂ with a core-shell structure was synthesized by an in-situ growth method, and then passed through an in-situ growth method. CeO ₂ is highly dispersed and supported on gC ₃ N ₄ @TiO ₂ by impregnation method, and CeO ₂ -gC ₃ N ₄ @TiO ₂ photocatalyst is obtained by calcination at high temperature (eg, 200-500 °C).

Further, the method further includes preparing TiO ₂ (001) by a hydrothermal method, mixing tetrabutyl titanate and HF in a volume ratio of 3-5:1, and performing a hydrothermal reaction at 190-210° C. for 22- 26h, after cooling, adjust the pH value to neutral, after drying, raise the temperature to 540-560°C at a heating rate of 1-3°C/min, and calcinate for 1-3h to obtain TiO ₂ (001). Among them, the preferred preparation parameters include, for example: 18-22 mL of tetrabutyl titanate and 4-6 mL of 47-49% HF are mixed, put into a high-pressure reactor, heated at 195-205 ° C for 23-25 h; cooled Then, the pH was adjusted to 6.8-7.2 with deionized water, and after drying, the temperature was raised to 545-555°C at a heating rate of 1.5-2.5°C/min, and calcined for 1.5-2.5h to obtain TiO ₂ (001).

Further, the preparation method of the gC ₃ N ₄ @TiO ₂ with a core-shell structure includes: dissolving urea and TiO ₂ (001) in water, thoroughly mixing in a vacuum, then solid-liquid separation, and drying, and the obtained The solid is heated to 510-530°C under N ₂ atmosphere at a heating rate of 4-6°C/min and annealed for 1-3h to obtain gC ₃ N ₄ /TiO ₂ with a core-shell structure. Among them, the optimization of the preparation parameters, for example, includes: dissolving urea and TiO ₂ (001) in different mass ratios in 25-35 mL of deionized water, and magnetically stirring them in a vacuum system for 0.5-1.5 h to fully mix them, and then adding Centrifuge at 4000-6000 r/min and dry; wrap the centrifuged solid with 2-4 layers of aluminum foil, and under _N2 atmosphere, raise the temperature to 515-525 ℃ at a heating rate of 4.5-5.5 ℃/min and anneal for 1.5-2.5 h, to obtain gC ₃ N ₄ /TiO ₂ with a core-shell structure.

Wherein, the mass ratio of urea and TiO ₂ (001) is 5:1 to 30:1. Preferably, the mass ratio of urea to TiO ₂ (001) is 18-22:1, and the prepared catalyst has better performance.

Further, the method for loading CeO ₂ on gC ₃ N ₄ @TiO ₂ includes: uniformly dispersing gC ₃ N ₄ @TiO ₂ with a core-shell structure in water, adjusting the pH to 8.8-9.2, and then Ce(NO ₃ ) ₃ ·6H ₂ O was added, and after the reaction was stirred at room temperature, filtered and washed until the pH value was neutral, and dried to obtain gC ₃ N ₄ @TiO _{2 loaded with CeO 2 ;}

Further, the method for obtaining a CeO ₂ -gC ₃ N ₄ @TiO ₂ photocatalyst by calcination includes: heating the CeO ₂ -loaded gC ₃ N ₄ @TiO ₂ at a rate of 3-5°C/min in an air atmosphere The speed is increased to 290～310℃, and calcined for 1～3h to obtain CeO ₂ -gC ₃ N ₄ @TiO ₂ photocatalyst.

Among them, the optimization of preparation parameters includes, for example: dispersing 0.40-0.60g core-shell gC ₃ N ₄ @TiO ₂ evenly in 70-80 mL deionized water, adding ammonia water to adjust the pH to about 8.9-9.1, and then adding in a certain proportion Ce(NO ₃ ) ₃ ·6H ₂ O, stirred at room temperature for 2 to 3 hours, filtered and washed to a pH of about 6.8 to 7.2, and dried. Finally, the mixture is raised to 295-305°C at a heating rate of 3.5-4.5°C/min under an air atmosphere, and calcined for 1.5-2.5h.

Preferably, in the above steps, the drying temperature is 60-80° C., and the drying time is 8-15 h, for example, 11-13 h.

In a preferred embodiment of the present invention, the prepared catalyst is used in photocatalytic removal of Hg ^0. At 50-250°C, the CeO ₂ -gC ₃ N ₄ @TiO ₂ photocatalyst has excellent Hg ⁰ removal performance.

The equipment, reagents, processes, parameters, etc. involved in the present invention, unless otherwise specified, are conventional equipment, reagents, processes, parameters, etc., and no further examples are given.

All ranges recited herein include all points within that range.

In the present invention, "about", "about" or "about" and the like can mean within ±20% of the stated range or value.

In the present invention, unless otherwise specified, % is mass percentage, and ratio is mass ratio.

In the present invention, the "normal temperature" refers to the normal ambient temperature, which can be 10-30°C. The "medium and low temperature" refers to 50 to 250°C.

Compared with the background technology, the technical solution has the following advantages:

1. In the present invention, gC ₃ N ₄ @TiO ₂ with a core-shell structure is prepared by TiO ₂ (001), and then CeO ₂ is dispersed and supported on gC ₃ N ₄ @TiO ₂ to obtain CeO ₂ -gC ₃ N ₄ @ _TiO2 photocatalyst can maintain excellent photocatalytic Hg ⁰ removal performance at medium and low temperature, has good stability and can be reused.

2. The catalyst prepared by the method of the present invention will not cause secondary pollution to the environment during use.

3. The operation process for preparing the catalyst of the present invention is simple and highly repeatable, and the catalyst preparation process only needs the help of conventional equipment and instruments, which is suitable for industrialized large-scale production.

Description of drawings

Figure 1 shows the photocatalytic Hg removal of 3% CeO ₂ ^-gC ₃ N ₄ @TiO ₂ and commercial TiO ₂ with different ratios of urea and TiO ₂ (001) prepared in the embodiment of the present invention at 50-250° C. Performance graph with temperature on the horizontal axis and removal rate of Hg ⁰ on the vertical axis.

Detailed ways

The technical solutions of the present invention will be further illustrated and described below through specific embodiments in conjunction with the accompanying drawings.

Example 1:

The prepared CeO ₂ -gC ₃ N ₄ @TiO ₂ catalyst was used for photocatalytic removal of Hg ⁰ in coal-fired flue gas. The specific implementation steps are as follows:

(1) 20 mL of tetrabutyl titanate and 5 mL of 48% HF were mixed and put into a high-pressure reactor, heated at 200 ° C for 24 h; The heating rate of °C/min was increased to 550 °C, and calcined for 2 h to obtain TiO ₂ (001).

(2) Dissolve 20 g of urea and 1 g of TiO ₂ (001) in 30 mL of deionized water, stir the uniform suspension magnetically in a vacuum system for 1 h, centrifuge at 5000 r/min, and dry for 12 h; wrap the solid with 3 layers of aluminum foil , and annealed at 520 °C for 2 h at a heating rate of 5 °C/min under N ₂ atmosphere to obtain gC ₃ N ₄ /TiO ₂ with a core-shell structure.

(3) Disperse 0.50g of gC ₃ N ₄ @TiO ₂ evenly in 75mL of deionized water, add ammonia water to adjust the pH to about 9, add a certain amount of Ce(NO ₃ ) ₃ ·6H ₂ O to make the CeO in the product ₂ The mass percentage is 3%, stirred at room temperature for 2.5 hours, filtered and washed to pH about 7, and dried for 12 hours. Finally, the mixture was heated to 300°C at a heating rate of 4°C/min under air atmosphere, and calcined for 2 hours to obtain a CeO ₂ -gC ₃ N ₄ @TiO ₂ catalyst, denoted as 3%CeO ₂ -gC ₃ N ₄ @TiO ₂ (20:1).

Example 2:

The prepared CeO ₂ -gC ₃ N ₄ @TiO ₂ catalyst was used for photocatalytic removal of Hg ⁰ in coal-fired flue gas. The specific implementation steps are as follows:

(1) 20 mL of tetrabutyl titanate and 5 mL of 48% HF were mixed and put into a high-pressure reactor, heated at 200 ° C for 24 h; The heating rate of °C/min was increased to 550 °C, and calcined for 2 h to obtain TiO ₂ (001).

(2) Dissolve 25 g of urea and 1 g of TiO ₂ (001) in 30 mL of deionized water, stir the uniform suspension magnetically in a vacuum system for 1 h, centrifuge at 5000 r/min, and dry for 12 h; wrap the solid with 3 layers of aluminum foil and annealed at 520°C for 2h at a heating rate of 5°C/min under N ₂ atmosphere to obtain core-shell gC ₃ N ₄ /TiO ₂ .

(3) Disperse 0.50g core-shell gC ₃ N ₄ @TiO ₂ evenly in 75mL deionized water, add ammonia water to adjust the pH to about 9, add a certain amount of Ce(NO ₃ ) ₃ ·6H ₂ O to make the The mass percentage of CeO ₂ is 3%, stirred at room temperature for 2.5 hours, filtered and washed to pH about 7, and dried for 12 hours. Finally, the mixture was heated to 300°C at a heating rate of 4°C/min under air atmosphere, and calcined for 2 hours to obtain a CeO ₂ -gC ₃ N ₄ @TiO ₂ catalyst, denoted as 3%CeO ₂ -gC ₃ N ₄ @TiO ₂ (25:1).

Example 3:

The prepared CeO ₂ -gC ₃ N ₄ @TiO ₂ catalyst was used for photocatalytic removal of Hg ⁰ in coal-fired flue gas. The specific implementation steps are as follows:

(1) 20 mL of tetrabutyl titanate and 5 mL of 48% HF were mixed and put into a high-pressure reactor, heated at 200 ° C for 24 h; The heating rate of °C/min was increased to 550 °C, and calcined for 2 h to obtain TiO ₂ (001).

(2) Dissolve 15 g of urea and 1 g of TiO ₂ (001) in 30 mL of deionized water, stir the uniform suspension magnetically in a vacuum system for 1 h, centrifuge at 5000 r/min, and dry for 12 h; wrap the solid with 3 layers of aluminum foil and annealed at 520°C for 2h at a heating rate of 5°C/min under N ₂ atmosphere to obtain core-shell gC ₃ N ₄ /TiO ₂ .

(3) Disperse 0.50g core-shell gC ₃ N ₄ @TiO ₂ evenly in 75mL deionized water, add ammonia water to adjust the pH to about 9, add a certain amount of Ce(NO ₃ ) ₃ ·6H ₂ O to make the The mass percentage of CeO ₂ is 3%, stirred at room temperature for 2.5 hours, filtered and washed to pH about 7, and dried for 12 hours. Finally, the mixture was heated to 300°C at a heating rate of 4°C/min under air atmosphere, and calcined for 2 hours to obtain a CeO ₂ -gC ₃ N ₄ @TiO ₂ catalyst, denoted as 3%CeO ₂ -gC ₃ N ₄ @TiO ₂ (15:1).

Examples 4 to 5

Using the method of Reference Examples 1 to 3, the mass ratio of urea and TiO ₂ (001) in step (2) was changed to be 30:1 and 10:1, respectively, to obtain catalyst 3% CeO ₂ -gC ₃ N ₄ @ _TiO2 (30:1) and catalyst ₃ %CeO2 _{- gC3N4} @ _TiO2 (10:1).

Take 0.20 g of the catalysts prepared in Examples 1 to 5 to carry out photocatalytic Hg ⁰ removal reaction. The reaction simulated flue gas is high-purity nitrogen as the carrier gas to carry Hg ⁰ into the mixer through the vapor generation device, and at the same time, another channel of air is introduced as a dilution gas to mix with the mercury vapor, and the total intake flow is 1L/min. Pass the simulated flue gas into a quartz reactor equipped with 0.20 g of catalyst, keep the reactors at 50 °C, 100 °C, 150 °C, 200 °C, 250 °C, and record the change of Hg ⁰ concentration at the outlet to calculate Hg ⁰ removal rate. The results obtained are shown in FIG. 1 . It can be seen from Fig. 1 that CeO ₂ -gC ₃ N ₄ @TiO ₂ has good photocatalytic Hg removal performance, and the Hg removal rate is stable ^at about 100% ^at 50 °C and 100 °C, and 250 °C The removal rate of Hg ⁰ was stable at around 58.2%, which was significantly higher than that of commercial TiO ₂ .

The above descriptions are only preferred embodiments of the present invention, so the scope of implementation of the present invention cannot be limited accordingly, that is, equivalent changes and modifications made according to the patent scope of the present invention and the contents of the description should still be covered by the present invention. within the range.

Claims (7)

1. The demercuration photocatalyst suitable for medium and low temperature conditions is characterized in that: which is loaded with CeO ₂ G to C of ₃ N ₄ @TiO ₂ And said g-C ₃ N ₄ @TiO ₂ Having a core-shell structure in g-C ₃ N ₄ As a shell, with TiO ₂ (001) Is a nucleus; in the demercuration photocatalyst, CeO ₂ The mass percentage of (A) is 1-7 wt%; the demercuration photocatalyst is prepared by the following method: with TiO as a carrier ₂ (001) Synthesizing g-C with core-shell structure by in-situ growth method on the basis ₃ N ₄ @TiO ₂ Then, CeO is added by dipping ₂ Loaded at g-C ₃ N ₄ @TiO ₂ CeO was obtained by calcination ₂ -g-C ₃ N ₄ @TiO ₂ A photocatalyst; g-C with core-shell structure ₃ N ₄ @TiO ₂ The preparation method comprises the following steps: mixing urea and TiO ₂ (001) Dissolving in water, mixing thoroughly in vacuum, solid-liquid separating, drying, and dissolving the obtained solid in N ₂ Heating to 510-530 ℃ at a heating rate of 4-6 ℃/min in the atmosphere, and annealing for 1-3 h to obtain g-C with a core-shell structure ₃ N ₄ /TiO ₂ 。

2. The demercuration photocatalyst as defined in claim 1, wherein: the application temperature range of the demercuration photocatalyst is 50-250 ℃.

3. The demercuration photocatalyst as defined in claim 1, wherein: the CeO obtained by calcination ₂ -g-C ₃ N ₄ @TiO ₂ In the process of the photocatalyst, the calcination temperature is 200-500 ℃.

4. The demercuration photocatalyst of claim 1, wherein: further comprising: preparation of TiO by hydrothermal method ₂ (001): mixing tetrabutyl titanate and HF according to a volume ratio of 3-5: 1, carrying out hydrothermal reaction at 190-210 ℃ for 22-26 h, cooling, adjusting the pH value to be neutral, drying, raising the temperature to 540-560 ℃ at a heating rate of 1-3 ℃/min, calcining for 1-3 h, and thus obtaining TiO ₂ (001)。

5. The demercuration photocatalyst as defined in claim 1, wherein: the urea and TiO ₂ (001) The mass ratio of (A) to (B) is 5: 1-30: 1.

6. The demercuration photocatalyst as defined in claim 1, wherein: the CeO is added ₂ Loaded at g-C ₃ N ₄ @TiO ₂ The method comprises the following steps: g-C with core-shell structure ₃ N ₄ @TiO ₂ Uniformly dispersing in water, adjusting the pH value to 8.8-9.2, and adding Ce (NO) ₃ ) ₃ ·6H ₂ O, stirring and reacting at normal temperature, filtering and cleaning until the pH value is neutral, and drying to obtain the CeO-loaded carrier ₂ G to C of ₃ N ₄ @TiO ₂ (ii) a The CeO obtained by calcination ₂ -g-C ₃ N ₄ @TiO ₂ The method of photocatalyst comprises: will be loaded with CeO ₂ G to C of ₃ N ₄ @TiO ₂ Heating to 280-320 ℃ at a heating rate of 3-5 ℃/min in an air atmosphere, and calcining for 1-3 h to obtain CeO ₂ -g-C ₃ N ₄ @TiO ₂ A photocatalyst.

7. The demercuration photocatalyst as defined in claim 1, 4 or 6, wherein: the drying temperature is 60-80 ℃, and the drying time is 8-15 h.

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