CN117205940A - A CrMnCoLDH-H catalyst and its preparation method and application - Google Patents

Abstract

The invention provides a CrMnCoLDH-H catalyst and its preparation method and application, aiming to provide a ternary hydrotalcite catalyst with high oxidation performance for formaldehyde; its preparation method is simple, easy to operate, and easy to be produced in batches; The preparation method of Cr _0.2 MnCo-LDH is: 1) Prepare manganese salt separately, recorded as solution a; prepare cobalt salt, recorded as solution b; prepare chromium salt, recorded as solution c; 2) Prepare alkali with sodium hydroxide and sodium carbonate Solution d; 3) Add solution a, solution b, solution c and solution d into a polytetrafluoroethylene-lined hydrothermal kettle, and put the hydrothermal kettle into an electric constant temperature blast drying box for crystallization; 4) After the reaction is completed Cool to room temperature, centrifuge the reactants in the inner lining, wash, and finally dry to obtain the solid product Cr _0.2 MnCo-LDH; 5) Further reduce in a H ₂ /Ar gas mixture containing 5% H ₂ to obtain a sample; it is a thermal Catalytic materials and environmental protection technology fields.

Description

A CrMnCoLDH-H catalyst and its preparation method and application

Technical field

The invention belongs to the technical fields of thermocatalytic materials and environmental protection, and specifically relates to a CrMnCoLDH-H catalyst. The invention also relates to a preparation method of the CrMnCoLDH-H catalyst and a method for catalytically oxidizing formaldehyde with CrMnCoLDH-H.

Background technique

Since the beginning of urbanization and industrialization, the emission of volatile organic compounds (VOCs) has become a matter of concern due to its harmful effects on the human body. Among them, formaldehyde (HCHO), as one of the main VOCs, has been listed as I Class carcinogens, measures must be taken to reduce the emission of pollutants. Room temperature catalytic oxidation is considered to be one of the most promising technologies for removing HCHO because of its high efficiency, no secondary pollution during the treatment process, and the ability to completely convert HCHO into CO ₂ and H ₂ O.

Traditional formaldehyde degradation catalysts can be divided into precious metal catalysts and non-noble metal catalysts. Precious metal catalysts include, but are not limited to, platinum (Pt), palladium (Pd), gold (Au), silver (Ag), and rubidium (Rb). These metals have good low-temperature catalytic activity and have the advantages of long service life, low dosage, and anti-corrosion. However, precious metals have disadvantages such as being expensive, easy to sinter, and easy to be poisoned, which greatly limits their practical applications. Non-noble metal catalysts, on the other hand, have high catalytic activity and are widely available, cheap, stable and resistant to poisoning. This makes them stand out in HCHO catalytic oxidation. The development of a non-noble metal catalyst with a simple and easy preparation method to catalyze the oxidation of formaldehyde has great application prospects.

LDH (Layered double hydroxides) is a compound composed of a positively charged metal hydroxide layer and negatively charged anions filled between the layers. The general formula is M ^II _1-x M ^III _x (OH) ₂ ^z+ ( A ^n- ) _z/n ·mH ₂ O (M ^II and M ^III are divalent and trivalent metals respectively; A ^n- is an interlayer anion). Among them, the anions and metal ions are adjustable, have a unique layered structure, and are affected by the lattice positioning effect, making each metal element highly dispersed, and have been widely used as catalytic materials. Therefore, we used the positioning effect of hydrotalcite to synthesize a third metal-dispersed three-way catalyst through hydrothermal method, so that the catalyst has high formaldehyde catalytic efficiency.

Contents of the invention

The invention provides a CrMnCoLDH-H catalyst with high oxidation performance for formaldehyde.

The first object of the present invention is to provide a preparation method of CrMnCoLDH-H catalyst, which is simple, easy to operate and easy to produce in batches.

To this end, the first technical solution provided by the present invention is as follows:

A preparation method of CrMnCoLDH-H catalyst, including the following steps:

(1) Prepare manganese salts separately, and record them as solution a; prepare cobalt salts, and record them as solution b; prepare chromium salts, and record them as solution c;

(2) Prepare a mixed alkali solution d of sodium hydroxide and sodium carbonate;

(3) Add solution a, solution b, solution c and solution d into a polytetrafluoroethylene-lined hydrothermal kettle, and put the hydrothermal kettle into an electric constant-temperature blast drying box for crystallization;

(4) After the reaction is completed, cool to room temperature, centrifuge the reactants in the inner lining, wash, and finally dry to obtain the solid product Cr _0.2 MnCo-LDH;

(5) The above solid product is calcined and reduced in a H ₂ /Ar gas mixture containing 5% H ₂ at 100-300°C for 3-10 hours, and the resulting sample is represented as CrMnCoLDH-H;

In the present invention, the divalent manganese salt is preferably Mn(acac) ₂ or Mn(NO ₃ ) ₂ solution (50 wt.% in H ₂ O), more preferably Mn(NO ₃ ) ₂ solution (50 wt.% in H ₂ O);

The cobalt salt is a trivalent cobalt salt, and the trivalent cobalt salt is preferably Co(NO ₃ ) ₂ ·6H ₂ O or Co(acac) ₃ , and more preferably Co(NO ₃ ) ₂ ·6H ₂ O;

In the present invention, the molar ratio of manganese salt, cobalt salt and chromium salt is preferably 0.5:1:0.1-0.5, more preferably 0.5:1:0.2-0.4.

In the present invention, the molar ratio of NaOH to NaCO ₃ is preferably 1:0.2-1.2, and more preferably the molar ratio of NaOH to NaCO ₃ is 1:0.5-0.8.

In the present invention, the preferred crystallization temperature is 100-200°C, more preferably 120-150°C; the preferred crystallization time is 6-24h, more preferably 12-18h;

In the present invention, the preferred washing conditions are: washing with deionized water 3-5 times and washing with ethanol 3-5 times, more preferably washing with deionized water three times and washing with ethanol three times; the drying temperature is 60-80°C, and the drying time is 10-24h, more preferably the drying temperature is 60°C and the drying time is 24h.

In the present invention, the preferred reduction temperature is 100-300°C, the heating rate is 5°C/min, and the reduction time is 6-12h. More preferably, the reduction temperature is 150-200°C, the heating rate is 5°C/min, and the reduction time is 6-12h.

The second object of the present invention is to provide the application of the above-mentioned CrMnCoLDH-H catalyst to catalytically oxidize formaldehyde.

The CrMnCoLDH-H catalyst provided by the invention is used in the field of normal temperature thermal catalysis. The catalyst has a certain catalytic effect on monomer small molecular organic matter and can be used to degrade common organic pollutants in the air; the method of using the above-mentioned CrMnCoLDH-H catalyst to catalyze the oxidation of formaldehyde, the catalytic conditions are: formaldehyde concentration -30ppm, air The speed is 21,600mL/(g·h), the reaction temperature is 30°C, the reaction time is 1h, and the catalyst mass is 0.2g.

Compared with the existing technology, the beneficial effects achieved by the technical solution of the present invention are:

(1) The technical solution provided by the present invention selects non-noble metals as raw materials, which greatly reduces the cost of catalyst preparation;

(2) The CrMnCoLDH-H prepared by the technical solution provided by the present invention increases the lattice oxygen content through hydrogen reduction treatment, thereby improving its ability to oxidize formaldehyde;

(3) The technical solution provided by the present invention has low preparation cost, simple preparation conditions, convenient operation, and is convenient for large-scale production in industry.

Description of the drawings

Figure 1 is an X-ray crystal diffraction pattern (XRD) of the catalyst prepared in Example 3 and Comparative Example 1;

Figure 2 is a scanning electron microscope (SEM) of Cr _0.2 MnCoLDH-H3 prepared in Example 3;

Figure 3 is a scanning electron microscope (SEM) of CrMnCoLDH prepared in Comparative Example 1;

Figure 4 is the Fourier transform infrared spectrum (FTIR) of the catalyst prepared in Example 3 and Comparative Example 1;

Detailed ways

The technical solution of the present invention will be further described in detail below in conjunction with the specific embodiments, but this does not constitute any limitation on the present invention. A limited number of modifications made by anyone within the protection scope of the present invention will still be within the protection scope of the present invention. within.

Example 1

A ternary hydrotalcite catalyst provided in this embodiment is prepared by the following method:

In the present invention, the preferred crystallization temperature is 100-200°C, more preferably 120-150°C; the preferred crystallization time is 6-24h, more preferably 8-16h;

(1) Take 5mmol Mn(NO ₃ ) ₂ solution (50wt.% in H ₂ O) and dissolve it in 20mL deionized water, recorded as solution a; take 10mmol Co(NO ₃ ) ₂ ·6H ₂ O and dissolve it in 20mL deionized water. In water, it is recorded as solution b; 2mmol Cr(acac) ₃ is added to 20mL of deionized water, and it is recorded as solution c;

(2) Add 20mmol NaOH and 10mmol Na ₂ CO ₃ to 20mL of deionized water, and record it as mixed alkali solution d;

(3) Add solution a, solution b, solution c and solution d into a polytetrafluoroethylene-lined hydrothermal kettle, and place the hydrothermal kettle into a 120°C electric constant-temperature blast drying oven for crystallization for 8 hours;

(4) After the reaction is completed, cool to room temperature, centrifuge the reactant, wash 3 times with deionized water and 3 times with ethanol until the pH value of the supernatant is neutral, and dry the precipitate in an oven at 60°C for 24 hours to obtain the solid product Cr _0.2MnCoLDH ;

(5) The above solid product is calcined at 150°C for 6 hours in a 5% H ₂ /Ar mixed atmosphere, and the resulting sample is represented as Cr _0.2 MnCoLDH-H1.

Example 2

Another ternary hydrotalcite catalyst provided in this embodiment is prepared by the following method:

(1) Take 5mmol Mn(NO ₃ ) ₂ solution (50wt.% in H ₂ O) and dissolve it in 20mL deionized water, recorded as solution a; take 10mmol Co(NO ₃ ) ₂ ·6H ₂ O and dissolve it in 20mL deionized water. In water, it is recorded as solution b; 3mmol Cr(acac) ₃ is added to 20mL of deionized water, and it is recorded as solution c;

(2) Add 20mmol NaOH and 12mmol Na ₂ CO ₃ to 20mL of deionized water, and record it as mixed alkali solution d;

(3) Add solution a, solution b, solution c and solution d into a polytetrafluoroethylene-lined hydrothermal kettle, and place the hydrothermal kettle into a 150°C electric constant-temperature blast drying oven for crystallization for 10 hours;

(4) After the reaction is completed, cool to room temperature, centrifuge the reactant, wash 3 times with deionized water and 3 times with ethanol until the pH value of the supernatant is neutral, and dry the precipitate in an oven at 60°C for 24 hours to obtain the solid product Cr _0.2MnCoLDH ;

(5) The above solid product is calcined at 200°C for 6 hours in a 5% H ₂ /Ar mixed atmosphere, and the resulting sample is represented as Cr _0.3 MnCoLDH-H2.

Example 3

Another ternary hydrotalcite catalyst provided in this embodiment is prepared by the following method:

(1) Take 5mmol Mn(NO ₃ ) ₂ solution (50wt.% in H ₂ O) and dissolve it in 20mL deionized water, recorded as solution a; take 10mmol Co(NO ₃ ) ₂ ·6H ₂ O and dissolve it in 20mL deionized water. in water, recorded as solution b; 2mmol Cr(NO ₃ ) ₃ ·9H ₂ O was added to 20 mL of deionized water, recorded as solution c;

(2) Add 20mmol NaOH and 14mmol Na ₂ CO ₃ to 20mL of deionized water, and record it as mixed alkali solution d;

(3) Add solution a, solution b, solution c and solution d into a polytetrafluoroethylene-lined hydrothermal kettle, and put the hydrothermal kettle into a 130°C electric constant-temperature blast drying oven for crystallization for 12 hours;

(4) After the reaction is completed, cool to room temperature, centrifuge the reactant, wash 3 times with deionized water and 3 times with ethanol until the pH value of the supernatant is neutral, and dry the precipitate in an oven at 60°C for 24 hours to obtain the solid product Cr _0.2MnCoLDH ;

(5) The above solid product is calcined at 200°C for 6 hours in a 5% H ₂ /Ar mixed atmosphere. The obtained sample is represented as Cr _0.2 MnCoLDH-H3; its X-ray crystal diffraction pattern (XRD) is shown in Figure 1; scanning electron microscope (SEM) picture See Figure 2; Fourier transform infrared spectrum (FTIR) see Figure 4.

Example 4

Another ternary hydrotalcite catalyst provided in this embodiment is prepared by the following method:

(1) Take 5mmol Mn(NO ₃ ) ₂ solution (50wt.% in H ₂ O) and dissolve it in 20mL deionized water, recorded as solution a; take 10mmol Co(NO ₃ ) ₂ ·6H ₂ O and dissolve it in 20mL deionized water. in water, recorded as solution b; 3mmol Cr(NO ₃ ) ₃ ·9H ₂ O was added to 20 mL of deionized water, recorded as solution c;

(2) Add 20mmol NaOH and 16mmol Na ₂ CO ₃ to 20mL of deionized water, and record it as mixed alkali solution d;

(3) Add solution a, solution b, solution c and solution d into a polytetrafluoroethylene-lined hydrothermal kettle, and put the hydrothermal kettle into a 140°C electric constant-temperature blast drying oven for crystallization for 14 hours;

(4) After the reaction is completed, cool to room temperature, centrifuge the reactant, wash 3 times with deionized water and 3 times with ethanol until the pH value of the supernatant is neutral, and dry the precipitate in an oven at 60°C for 24 hours to obtain the solid product Cr _0.2MnCoLDH ;

(5) The above solid product is calcined at 150°C for 8 hours in a 5% H ₂ /Ar mixed atmosphere, and the resulting sample is represented as Cr _0.3 MnCoLDH-H4.

Example 5

Another ternary hydrotalcite catalyst provided in this embodiment is prepared by the following method:

(1) Take 5mmol Mn(NO ₃ ) ₂ solution (50wt.% in H ₂ O) and dissolve it in 20mL deionized water, recorded as solution a; take 10mmol Co(NO ₃ ) ₂ ·6H ₂ O and dissolve it in 20mL deionized water. in water, recorded as solution b; 4mmol Cr(NO ₃ ) ₃ ·9H ₂ O was added to 20 mL of deionized water, recorded as solution c;

(2) Add 20mmol NaOH and 10mmol Na ₂ CO ₃ to 20mL of deionized water, and record it as mixed alkali solution d;

(3) Add solution a, solution b, solution c and solution d into a polytetrafluoroethylene-lined hydrothermal kettle, and put the hydrothermal kettle into a 150°C electric constant-temperature blast drying oven for crystallization for 16 hours;

(4) After the reaction is completed, cool to room temperature, centrifuge the reactant, wash 3 times with deionized water and 3 times with ethanol until the pH value of the supernatant is neutral, and dry the precipitate in an oven at 60°C for 24 hours to obtain the solid product Cr _0.2MnCoLDH ;

(5) The above solid product is calcined at 200°C for 8 hours in a 5% H ₂ /Ar mixed atmosphere, and the resulting sample is represented as Cr _0.4 MnCoLDH-H5.

Comparative example 1

The ternary hydrotalcite catalyst provided in this case is prepared by the following method:

(1) Take 5mmol Mn(NO ₃ ) ₂ solution (50wt.% in H ₂ O) and dissolve it in 20mL deionized water, recorded as solution a; take 10mmol Co(NO ₃ ) ₂ ·6H ₂ O and dissolve it in 20mL deionized water. in water, recorded as solution b; 2mmol Cr(NO ₃ ) ₃ ·9H ₂ O was added to 20 mL of deionized water, recorded as solution c;

(2) Add 20mmol NaOH and 10mmol Na ₂ CO ₃ to 20mL of deionized water, and record it as mixed alkali solution d;

(3) Add solution a, solution b, solution c and solution d into a polytetrafluoroethylene-lined hydrothermal kettle, and put the hydrothermal kettle into a 150°C electric constant-temperature blast drying oven for crystallization for 16 hours;

(4) After the reaction is completed, cool to room temperature, centrifuge the reactant, wash 3 times with deionized water and 3 times with ethanol until the pH value of the supernatant is neutral, and dry the precipitate in an oven at 60°C for 24 hours to obtain the solid product Cr _0.2 MnCoLDH; see Figure 1 for the X-ray crystal diffraction pattern (XRD); see Figure 3 for the scanning electron microscope (SEM) pattern; see Figure 4 for the Fourier transform infrared spectrum (FTIR).

In order to better prove the advantages of the technical solution provided by this application, the activity evaluation results of the ternary hydrotalcite catalyst provided in Examples 1 to 5 and Comparative Example 1 of this application for the catalytic oxidation of formaldehyde are given below.

Reaction conditions:

Temperature: 30℃

Formaldehyde concentration: 30ppm

Airspeed: 21,600mL/(g.h)

Reaction stabilization time: 1h

Catalyst mass: 0.2g

Table 1 Activity evaluation results of CrMnCoLDH catalyst

As can be seen from the above table, the CrMnCoLDH-H catalysts in the examples have all undergone hydrogen reduction treatment, while the catalysts in the comparative examples have not been subjected to hydrogen reduction treatment. As can be seen from the table, the Cr content in the comparative example is the best ratio of 0.5:1:0.2 in the example. It is found that the conversion rate of formaldehyde catalyzed in the comparative example is significantly lower than that in the example; this shows that the hydrogen reduction treatment makes CrMnCoLDH-H Has good formaldehyde catalytic activity. Therefore, the embodiment is a type of thermal catalyst with excellent activity.

Claims (7)

1. The preparation method of the CrMnCoLDH-H catalyst is characterized by comprising the following steps of:

(1) Preparing manganese salt respectively, and marking the manganese salt as a solution a; preparing cobalt salt as a solution b; preparing chromium salt, and marking as a solution c;

the molar ratio of the manganese salt, the cobalt salt and the chromium salt is as follows: 0.5:1:0.1-0.5;

(2) Preparing a mixed alkali solution d of sodium hydroxide and sodium carbonate;

the NaOH and the NaCO ₃ The mol ratio of (2) is 1:0.2-1.2;

(3) Adding the solution a, the solution b, the solution c and the solution d into a polytetrafluoroethylene lining hydrothermal kettle, and putting the hydrothermal kettle into an electrothermal constant-temperature blast drying oven for crystallization;

the crystallization temperature is 100-200 ℃, and the crystallization time is 6-24 hours;

(4) Cooling to room temperature after the reaction is finished, centrifuging reactants in the inner lining, washing, and finally drying to obtain a solid product Cr _0.2 MnCo-LDH：

(5) The solid product contains 5%H ₂ H of (2) ₂ Calcining and reducing in Ar mixed gas at 100-300 ℃ for 3-10 hours, wherein the obtained sample is expressed as CrMnCoLDH-H.

2. The method for preparing CrMnCoLDH-H catalyst according to claim 1, wherein the manganese salt in step (1) is a divalent manganese salt, the cobalt salt is a trivalent cobalt salt, and the chromium salt is a trivalent chromium salt.

3. The method for preparing CrMnCoLDH-H catalyst according to claim 2, wherein the divalent manganese salt is Mn (NO ₃ ) ₂ Solution or Mn (acac) ₂ The method comprises the steps of carrying out a first treatment on the surface of the The trivalent cobalt salt is Co (NO) ₃ ) ₂ ·6H ₂ O or Co (acac) ₃ The method comprises the steps of carrying out a first treatment on the surface of the The trivalent chromium salt is Cr (NO) ₃ ) ₃ ·9H ₂ O or Cr (acac) ₃ 。

4. The method for preparing CrMnCoLDH-H catalyst according to claim 1, wherein the centrifugation parameters in step (4) are: 6000 rpm, 3min; the washing condition is that deionized water is adopted for washing 3-5 times, and ethanol is adopted for washing 3-5 times; the drying temperature is 60 ℃ and the drying time is 10-24 hours.

5. A CrMnCoLDH-H catalyst prepared by the method of any one of claims 1 to 4.

6. Use of a CrMnCoLDH-H catalyst according to claim 5 for the catalytic oxidation of formaldehyde.

7. A method for catalyzing and oxidizing formaldehyde by using a CrMnCoLDH-H catalyst is characterized in that the catalysis conditions are as follows: formaldehyde concentration was 30ppm, space velocity was 21, 600 mL/(g.h), reaction temperature 30 ℃, reaction time 1h, catalyst mass 0.2g.