CN109985654A - A kind of alkali metal ion modified carbon nitride catalyst and its preparation method and application - Google Patents

Abstract

The invention belongs to the technical field of catalysts, and in particular relates to an alkali metal ion modified carbon nitride catalyst, a preparation method and application thereof. The catalyst is mainly composed of carbon nitride, the modified alkali metal ions include one or a combination of Na ⁺ , K ⁺ and Cs ⁺ , wherein the content of the alkali metal ions is 0.1-10 wt %; the The alkali metal ions in the catalyst are adsorbed on the deprotonated amino nitrogen of carbon nitride through electrostatic interaction. The catalyst of the present invention can be used as an organic sulfur hydrolysis catalyst, and exhibits good catalytic activity and stability.

Description

A kind of alkali metal ion modified carbon nitride catalyst and its preparation method and application

technical field

The invention belongs to the technical field of catalysts, and in particular relates to an alkali metal ion modified carbon nitride catalyst, a preparation method and application thereof.

Background technique

Carbonyl sulfide (COS), as the main form of organic sulfur, widely exists in fossil raw materials such as coal, natural gas and petroleum. A trace amount of COS in industrial production can easily cause catalyst poisoning and deactivation in the production process, corrosion of production equipment and instruments, and affect the quality of chemical products; in addition, untreated COS is discharged into the atmosphere, which will react with oxygen to form SO ₂ , which promotes photochemistry. The reaction will bring serious pollution to the environment and pose a threat to human health. Carbonyl sulfide has stable physical and chemical properties and is weakly acidic. Compared with H ₂ S, it is neither easy to dissociate nor liquefy. The methods generally used to remove H ₂ S cannot completely and effectively remove COS directly. At present, the main removal technologies of COS include hydrolysis, reduction, absorption, adsorption, photolysis and oxidation. Among them, hydrolysis to remove COS has been proved to be one of the most effective methods. The basic principle is that : COS reacts with water to convert into H ₂ S under the action of a catalyst, and then removes H ₂ S by other methods. The whole process is simple to operate and has low energy consumption. The key technology of hydrolysis is to develop efficient and economical catalysts.

Most of the current COS hydrolysis catalysts use metal oxides or activated carbons as carriers, and are prepared by loading active components on the metal oxides or activated carbons. Most of these supported COS hydrolysis catalysts contain transition metals, which are expensive, and have disadvantages such as complicated preparation process, easy detachment of active components from the carrier, and poor activity stability. Therefore, through the innovation of COS hydrolysis catalyst, it is novel to invent a COS hydrolysis catalyst that does not contain transition metals and has a strong interaction between active components and supports.

In recent years, carbon nitrides with graphitic-like structures composed of carbon- and nitrogen-rich elements have received extensive attention. Carbon nitride polymers have good heat and chemical resistance, non-toxic and inexpensive, good biocompatibility and semiconductor properties, and currently have very good application prospects in the fields of energy and catalysis. The carbon nitride surface has abundant unpolymerized amino groups, which can be used as an ideal base catalyst and supported catalyst carrier. The COS hydrolysis reaction is an alkali-catalyzed reaction, and the alkali metal ion-modified carbon nitride synthesized by the ionothermal method has strong basicity, and the alkali metal ions can be adsorbed on the carbon nitride support through electrostatic interaction, which is not easy to fall off and has good dispersibility. Therefore, alkali metal ion-modified carbon nitride is expected to be an efficient catalyst for a class of COS hydrolysis.

In the Journal of Catalysis, Jiang Jing et al. disclosed a comparative study of an alkali metal doped graphitic carbon nitride in visible light photocatalytic hydrogen production, which used alkali metal hydroxide to dope carbon nitride, but Due to the strong alkalinity of the alkali metal hydroxide, the main structure of the carbon nitride in the graphite phase and the alkali metal hydroxide is easily damaged during the high temperature treatment, resulting in a decrease in the crystallinity of the graphite phase carbon nitride. Therefore, the π-conjugated system decreases and the basicity is not high. In the present invention, in the synthesis of alkali metal ion-modified carbon nitride by ionothermal method, neutral alkali metal halide is used as ionic solvent to react with carbon nitride at high temperature, which greatly improves the crystallinity of carbon nitride and expands the π-conjugated system. Therefore, the synthesized alkali metal ion-modified carbon nitride has strong basicity.

SUMMARY OF THE INVENTION

In order to solve at least one aspect of the above problems and defects existing in the prior art, the present invention provides an alkali metal ion modified carbon nitride carbonyl sulfide hydrolysis catalyst and a preparation method thereof.

To achieve the above object, the present invention adopts the following technical solutions:

The first aspect of the present invention discloses a carbon nitride catalyst modified by alkali metal ions, the alkali metal ions include one or more of Na ⁺ , K ⁺ and Cs ⁺ , wherein the content of alkali metal ions is 0.1 ~10 wt%. The alkali metal ions in the catalyst are adsorbed on the deprotonated amino nitrogen of carbon nitride by electrostatic interaction.

The second aspect of the present invention discloses the preparation method of the alkali metal ion modified carbon nitride catalyst, which comprises the following steps:

(1) calcining nitrogen-containing organic compounds in air or nitrogen atmosphere at 450-650 ℃ for 2-4 hours to obtain carbon nitride;

(2) grinding and mixing the carbon nitride obtained in step (1) with the alkali metal chloride evenly;

(3) calcining the mixture obtained in step (2) at 550-650° C. for 2-4 hours in an inert atmosphere to generate alkali metal ion-modified carbon nitride;

(4) Mix the solid powder obtained in step (3) with deionized water, then filter to remove the alkali metal ions not adsorbed on the carbon nitride, and dry the obtained solid for at least 6 hours to obtain the alkali metal ion modification of carbon nitride catalysts.

The nitrogen-containing organic compound described in the above step (1) is one or more of cyanamide, dicyandiamide, melamine, amine thiocyanate, thiourea, guanidine carbonate and urea.

The alkali metal halide in the above step (2) is one or more of sodium chloride, potassium chloride, cesium chloride, sodium bromide, potassium bromide and cesium bromide. The mass ratio of carbon nitride to alkali metal halide is: 1:(0.5～50).

The third aspect of the present invention discloses the use of the alkali metal ion-modified carbon nitride catalyst for catalytic hydrolysis of COS.

The significant advantages of the present invention are:

(1) The synthesis method of the present invention is safe and environmentally friendly, the preparation process is simple, and the conditions are mild and controllable.

(2) The alkali metal ion-modified carbon nitride catalyst synthesized by the present invention does not contain transition metals, and the raw materials are cheap; the alkali metal ions are uniformly dispersed on the carbon nitride, have a strong interaction with the carbon nitride, and are not easy to fall off.

(3) The carbon nitride catalyst modified by alkali metal ions synthesized in the present invention can be used to catalyze the hydrolysis of COS. In the 10-hour catalytic reaction (70° C.) test, the COS conversion rate reaches 92%, and the activity does not change significantly , good stability.

Description of drawings

Fig. 1 is the X-ray powder diffraction pattern (XRD) of ionothermal synthesis of potassium ion-modified carbon nitride obtained in Example 1 and the synthesis of potassium ion-supported carbon nitride by impregnation method;

Fig. 2 is the infrared (FTIR) spectrum of ionothermal synthesis of potassium ion-modified carbon nitride obtained in Example 1 and the synthesis of potassium ion-supported carbon nitride by impregnation method;

3 is a transmission electron microscope (TEM) and mapping diagram of potassium ion-modified carbon nitride synthesized in Example 1;

4 is a graph showing the activity of the potassium ion-modified carbon nitride synthesized in Example 1 and the potassium ion-supported carbon nitride synthesized by the impregnation method for catalyzing (70° C.) COS hydrolysis.

Detailed ways

In order to make the content of the present invention easier to understand, the technical solutions of the present invention will be further described below with reference to specific embodiments, but the present invention is not limited thereto.

Example 1

First, 10 g of melamine was weighed and placed in an alumina crucible, and calcined at 550 °C for 4 h in an air atmosphere. After natural cooling, the sample was taken out and ground into powder to obtain carbon nitride powder. Weigh 2g of carbon nitride powder and 10g of alkali metal chloride (potassium chloride) and grind them uniformly, calcined at 600 °C for 2h in a nitrogen atmosphere, and the solid obtained after natural cooling is ultrasonically dispersed in water to remove free carbon nitride on the surface. The potassium ions are filtered and dried to obtain potassium ion-modified carbon nitride.

Example 2

First, 10 g of melamine was weighed, placed in an alumina crucible, and calcined at 550 °C for 2 h in an air atmosphere. After natural cooling, the sample was taken out and ground into powder to obtain carbon nitride powder. Weigh 2g of carbon nitride powder and 10g of alkali metal chloride (sodium chloride) and grind them uniformly, calcined at 600 °C for 2h in a nitrogen atmosphere, and the solid obtained after natural cooling is ultrasonically dispersed in water to remove free carbon nitride on the surface. The sodium ions are filtered and dried to obtain sodium ion-modified carbon nitride.

Example 3

First, 10 g of melamine was weighed and placed in an alumina crucible, and calcined at 550 °C for 4 h in an air atmosphere. After natural cooling, the sample was taken out and ground into powder to obtain carbon nitride powder. Weigh 2g of carbon nitride powder and 10g of alkali metal chloride (5g of sodium chloride and 5g of potassium chloride) and grind them uniformly, calcined at 600 °C for 2h in a nitrogen atmosphere, and the solid obtained after natural cooling is ultrasonically dispersed in water, remove Free sodium and potassium ions on the surface of carbon nitride are filtered and dried to obtain carbon nitride modified by sodium and potassium ions.

Comparative Example 1

First, 10 g of melamine was weighed and placed in an alumina crucible, and calcined at 550 °C for 4 h in an air atmosphere. After natural cooling, the sample was taken out and ground into powder to obtain carbon nitride powder. Weigh 2 g of carbon nitride powder and 286 mg of potassium chloride into 10 mL of water, stir for 10 min, and then control the temperature at 80 °C to evaporate the water to dryness to obtain potassium ion-supported carbon nitride.

Figure 1 is the X-ray powder diffraction pattern (XRD) of the potassium ion-modified carbon nitride synthesized by the ionothermal method and the potassium ion-supported carbon nitride synthesized by the impregnation method obtained in Example 1. It can be seen from the figure that the ionothermal method is synthesized The crystallinity of carbon nitride in the alkali metal ion modified carbon nitride is improved.

Fig. 2 is the Fourier transform infrared spectrogram (FT-IR) of the ionothermal synthesis of potassium ion-modified carbon nitride obtained in Example 1 and the synthesis of potassium ion-supported carbon nitride by impregnation method, as can be seen from the figure In the range of 800 cm ^-1 and 1200~1600 cm ^-1 , they correspond to the breathing vibration of the oxazine ring and the stretching vibration of the aromatic CN heterocycle, ^respectively . Caused by the bonded NH ₂ , NH, it was confirmed that the prepared product was a carbon nitride material.

3 is a high-resolution transmission electron microscope (TEM) and mapping image of the potassium ion-modified carbon nitride obtained in Example 1. From the figure, obvious lattice fringes can be seen, and the lattice fringe spacing is 0.31 nm. It can be seen from the mapping diagram that potassium ions are distributed uniformly.

Figure 4 is the activity diagram of the potassium ion-modified carbon nitride synthesized in Example 1 to catalyze the hydrolysis of COS. From the figure, we can draw that the potassium ion-supported carbon nitride synthesized by the impregnation method has basically no activity to catalyze the hydrolysis of COS, The potassium ion-modified carbon nitride synthesized by ionothermal method has high catalytic activity for COS hydrolysis. In the catalytic reaction for 10 hours, the COS conversion rate reaches 92%, and the activity does not change significantly, and the stability is good.

The above descriptions are only preferred embodiments of the present invention, and all equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention.

Claims (6)

1. a kind of carbon nitride catalyst of alkali metal ion modification, which is characterized in that the alkali metal ion of the modification includes Na⁺、 K⁺And Cs⁺One such or several combination, wherein the content of alkali metal ion is 0 .1~10wt%.

2. the carbon nitride catalyst of alkali metal ion modification according to claim 1, which is characterized in that the base catalyst In alkali metal ion be adsorbed on by electrostatic interaction on the ammonia nitrogen of carbonitride deprotonation.

3. a kind of method for the carbonitride base catalyst for preparing alkali metal ion modification as described in claim 1, feature exist In, comprising the following steps: (1) organic compounds containing nitrogen is obtained under air or inert atmosphere, 450-650 DEG C of calcining 2-4h Carbonitride；

(2) carbonitride and alkali halide ground and mixed obtained step (1) is uniform；

(3) mixture for obtaining step (2) generates alkali metal ion modification in 550-650 DEG C of calcining 2-4h of inert atmosphere Carbonitride；

(4) solid powder that step (3) obtains is mixed with deionized water, is then filtered, remove the free alkali on carbonitride Metal ion, by the dry carbonitride base catalyst modified to get the alkali metal ion of obtained solid.

4. preparation method according to claim 3, which is characterized in that organic compounds containing nitrogen described in step (1) is cyanogen One or more of amine, dicyandiamide, melamine, thiocyanic acid amine, thiocarbamide, guanidine carbonate and urea.

5. preparation method according to claim 3, which is characterized in that step (2) alkali halide be sodium chloride, One or more of potassium chloride, cesium chloride, sodium bromide, potassium bromide and cesium bromide；The quality of carbonitride and alkali halide Than are as follows: 1:(0.5~50).

6. a kind of carbon nitride catalyst of alkali metal ion modification according to claim 1 is in carbonyl sulfur COS hydrolysis Using.