A CrMnCoLDH-H catalyst, its preparation method and application

Abstract

This invention provides a CrMnCoLDH-H catalyst, its preparation method, and its application, aiming to provide a ternary hydrotalcite catalyst with high oxidation performance for formaldehyde; its preparation method is simple, easy to operate, and suitable for mass production; Cr 0.2 The preparation method for MnCo-LDH is as follows: 1) Prepare manganese salt, denoted as solution a; prepare cobalt salt, denoted as solution b; prepare chromium salt, denoted as solution c; 2) Prepare alkaline solution d using sodium hydroxide and sodium carbonate; 3) Add solutions a, b, c, and d to a polytetrafluoroethylene-lined hydrothermal reactor, and place the reactor in an electrically heated constant-temperature drying oven for crystallization; 4) After the reaction is complete, cool to room temperature, centrifuge the reactants in the liner, wash, and finally dry to obtain the solid product Cr. 0.2 MnCo-LDH; 5) Further reduction in H2 / Ar mixture containing 5% H2 to obtain the sample; belongs to the fields of thermocatalytic materials and environmental protection technology.

Description

Technical Field

[0001] This invention belongs to the field of thermocatalytic materials and environmental protection technology, specifically relating to a CrMnCoLDH-H catalyst. This invention also relates to a method for preparing the CrMnCoLDH-H catalyst, and a method for catalytic oxidation of formaldehyde using CrMnCoLDH-H. Background Technology

[0002] Since the beginning of urbanization and industrialization, the emission of volatile organic compounds (VOCs) has become a major concern due to their harmful effects on human health. Formaldehyde (HCHO), as one of the main VOCs, has been classified as a Group 1 carcinogen, necessitating measures to reduce its emissions. Room temperature catalytic oxidation, due to its high efficiency and lack of secondary pollution during the process, can completely convert HCHO into CO2 and H2O, and is considered one of the most promising technologies for HCHO removal.

[0003] Traditional formaldehyde degradation catalysts can be divided into noble metal catalysts and non-noble metal catalysts. Noble metal catalysts include, but are not limited to, platinum (Pt), palladium (Pd), gold (Au), silver (Ag), and rubidium (Rb). These metals exhibit good catalytic activity at low temperatures and have advantages such as long service life, low dosage, and corrosion resistance. However, noble metals also have disadvantages such as high price, easy sintering, and susceptibility to poisoning, which greatly limits their practical application. Non-noble metal catalysts, on the other hand, have high catalytic activity, are widely available, inexpensive, stable, and resistant to poisoning. This makes them stand out in the catalytic oxidation of HCHO. Developing a non-noble metal catalyst with a simple and easy-to-implement preparation method for the catalytic oxidation of formaldehyde has great application potential.

[0004] LDH (Layered Double Hydroxides) is a compound consisting of positively charged metal hydroxide layers and negatively charged anions filling the interlayer. Its general formula is M0. II 1-x M III x (OH)2 z+ (A n- ) z / n ·mH2O(M II and M III They are divalent and trivalent metals, respectively; A n- It is an interlayer anion. The anions and metal ions are tunable, possessing a unique layered structure. Influenced by the lattice positioning effect, the metal elements are highly dispersed, making it widely used as a catalytic material. Therefore, we utilize the positioning effect of hydrotalcite to synthesize a third-metal-dispersed ternary catalyst via a hydrothermal method, resulting in a catalyst with high formaldehyde catalytic efficiency. Summary of the Invention

[0005] This invention provides a CrMnCoLDH-H catalyst with high oxidation performance for formaldehyde.

[0006] The first objective of this invention is to provide a method for preparing a CrMnCoLDH-H catalyst that is simple, easy to operate, and suitable for mass production.

[0007] Therefore, the first technical solution provided by this invention is as follows:

[0008] A method for preparing a CrMnCoLDH-H catalyst includes the following steps:

[0009] (1) Prepare manganese salts separately, denoted as solution a; prepare cobalt salts separately, denoted as solution b; prepare chromium salts separately, denoted as solution c;

[0010] (2) Prepare a mixed alkaline solution d of sodium hydroxide and sodium carbonate;

[0011] (3) Add solutions a, b, c and d to a polytetrafluoroethylene-lined hydrothermal reactor, and place the hydrothermal reactor in an electric thermostatic drying oven for crystallization;

[0012] (4) After the reaction is complete, cool to room temperature, centrifuge the reactants in the liner, wash, and finally dry to obtain the solid product Cr. 0.2 MnCo-LDH;

[0013] (5) The above solid product was calcined and reduced in a H2 / Ar mixed gas containing 5% H2 at 100-300℃ for 3-10h. The resulting sample is denoted as CrMnCoLDH-H.

[0014] In this invention, the divalent manganese salt is preferably a Mn(acac)2 or Mn(NO3)2 solution (50 wt.% in H2O), more preferably a Mn(NO3)2 solution (50 wt.% in H2O);

[0015] The cobalt salt is a trivalent cobalt salt, preferably Co(NO3)2·6H2O or Co(acac)3, more preferably Co(NO3)2·6H2O;

[0016] In this invention, the molar ratio of manganese salt, cobalt salt, and chromium salt is preferably 0.5:1:0.1-0.5, and more preferably 0.5:1:0.2-0.4.

[0017] In this invention, the molar ratio of NaOH to NaCO3 is preferably 1:0.2-1.2, and more preferably 1:0.5-0.8.

[0018] In this invention, the crystallization temperature is preferably 100-200℃, more preferably 120-150℃; the crystallization time is preferably 6-24h, more preferably 12-18h.

[0019] In this 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℃ and the drying time is 10-24h, more preferably the drying temperature is 60℃ and the drying time is 24h.

[0020] In this invention, the preferred reduction temperature is 100-300℃, the heating rate is 5℃ / min, and the reduction time is 6-12h; more preferably, the reduction temperature is 150-200℃, the heating rate is 5℃ / min, and the reduction time is 6-12h.

[0021] A second objective of this invention is to provide the application of the above-mentioned CrMnCoLDH-H catalyst in the catalytic oxidation of formaldehyde.

[0022] The CrMnCoLDH-H catalyst provided by this invention is applied in the field of room-temperature thermocatalysis. The catalyst exhibits certain catalytic efficiency for small-molecule organic monomers and can be used to degrade common organic pollutants in the air. The method for catalytic oxidation of formaldehyde using the aforementioned CrMnCoLDH-H catalyst has the following catalytic conditions: formaldehyde concentration -30 ppm, space velocity 21,600 mL / (g·h), reaction temperature 30℃, reaction time 1 h, and catalyst mass 0.2 g.

[0023] Compared with the prior art, the beneficial effects achieved by the technical solution of this invention are as follows:

[0024] (1) The technical solution provided by the present invention selects non-precious metals as raw materials, which greatly reduces the cost of catalyst preparation;

[0025] (2) The CrMnCoLDH-H prepared by the technical solution provided by the present invention has its lattice oxygen content increased by hydrogen reduction treatment, thereby improving its ability to oxidize formaldehyde;

[0026] (3) The technical solution provided by the present invention has low preparation cost, simple preparation conditions, convenient operation, and is easy to scale up in industrial production. Attached Figure Description

[0027] Figure 1 These are X-ray diffraction (XRD) patterns of the catalysts prepared in Example 3 and Comparative Example 1.

[0028] Figure 2 The Cr prepared in Example 3 0.2 Scanning electron microscopy (SEM) of MnCoLDH-H3;

[0029] Figure 3 This is a scanning electron microscope (SEM) image of CrMnCoLDH prepared in Comparative Example 1;

[0030] Figure 4 The Fourier transform infrared (FTIR) spectra of the catalysts prepared in Example 3 and Comparative Example 1 are shown. Detailed Implementation

[0031] The technical solution of the present invention will be further described in detail below with reference to specific embodiments, but this does not constitute any limitation on the present invention. Any limited modifications made by anyone within the scope of protection of the present invention are still within the scope of protection of the present invention.

[0032] Example 1

[0033] The ternary hydrotalcite catalyst provided in this embodiment is prepared by the following method:

[0034] In this invention, the crystallization temperature is preferably 100-200℃, more preferably 120-150℃; the crystallization time is preferably 6-24h, more preferably 8-16h.

[0035] (1) Dissolve 5 mmol Mn(NO3)2 solution (50 wt.% in H2O) in 20 mL of deionized water and record it as solution a; dissolve 10 mmol Co(NO3)2·6H2O in 20 mL of deionized water and record it as solution b; add 2 mmol Cr(acac)3 to 20 mL of deionized water and record it as solution c;

[0036] (2) Take 20 mmol NaOH and 10 mmol Na2CO3 and add them to 20 mL of deionized water, and record it as mixed alkaline solution d;

[0037] (3) Add solutions a, b, c and d to a polytetrafluoroethylene-lined hydrothermal reactor and place the hydrothermal reactor in a 120℃ electric thermostatic drying oven for crystallization for 8 hours.

[0038] (4) After the reaction was completed, the mixture was cooled to room temperature, centrifuged, washed three times with deionized water, and then washed three times with ethanol until the pH of the supernatant was neutral. The precipitate was dried in an oven at 60°C for 24 hours to obtain the solid product Cr. 0.2 MnCoLDH;

[0039] (5) The above solid product was calcined at 150°C for 6 hours in a 5% H2 / Ar mixed atmosphere. The resulting sample was denoted as Cr. 0.2 MnCoLDH-H1.

[0040] Example 2

[0041] Another ternary hydrotalcite catalyst provided in this embodiment is prepared by the following method:

[0042] (1) Dissolve 5 mmol Mn(NO3)2 solution (50 wt.% in H2O) in 20 mL of deionized water and record it as solution a; dissolve 10 mmol Co(NO3)2·6H2O in 20 mL of deionized water and record it as solution b; add 3 mmol Cr(acac)3 to 20 mL of deionized water and record it as solution c;

[0043] (2) Take 20 mmol NaOH and 12 mmol Na2CO3 and add them to 20 mL of deionized water, and record it as mixed alkaline solution d;

[0044] (3) Add solutions a, b, c and d to a polytetrafluoroethylene-lined hydrothermal reactor and place the hydrothermal reactor in a 150℃ electric constant temperature drying oven for crystallization for 10 hours.

[0045] (4) After the reaction was completed, the mixture was cooled to room temperature, centrifuged, washed three times with deionized water, and then washed three times with ethanol until the pH of the supernatant was neutral. The precipitate was dried in an oven at 60°C for 24 hours to obtain the solid product Cr. 0.2 MnCoLDH;

[0046] (5) The above solid product was calcined at 200°C for 6 hours in a 5% H2 / Ar mixed atmosphere. The resulting sample was denoted as Cr. 0.3 MnCoLDH-H2.

[0047] Example 3

[0048] Another ternary hydrotalcite catalyst provided in this embodiment is prepared by the following method:

[0049] (1) Dissolve 5 mmol of Mn(NO3)2 solution (50 wt.% in H2O) in 20 mL of deionized water and record it as solution a; dissolve 10 mmol of Co(NO3)2·6H2O in 20 mL of deionized water and record it as solution b; add 2 mmol of Cr(NO3)3·9H2O to 20 mL of deionized water and record it as solution c;

[0050] (2) Take 20 mmol NaOH and 14 mmol Na2CO3 and add them to 20 mL of deionized water, and record it as mixed alkaline solution d;

[0051] (3) Add solutions a, b, c and d to a polytetrafluoroethylene-lined hydrothermal reactor and place the hydrothermal reactor in a 130℃ electric constant temperature drying oven for crystallization for 12 hours.

[0052] (4) After the reaction was completed, the mixture was cooled to room temperature, centrifuged, washed three times with deionized water, and then washed three times with ethanol until the pH of the supernatant was neutral. The precipitate was dried in an oven at 60°C for 24 hours to obtain the solid product Cr. 0.2 MnCoLDH;

[0053] (5) The above solid product was calcined at 200°C for 6 hours in a 5% H2 / Ar mixed atmosphere. The resulting sample was denoted as Cr. 0.2 MnCoLDH-H3; its X-ray diffraction (XRD) pattern is shown in [reference needed]. Figure 1 See scanning electron microscope (SEM) image for reference. Figure 2 For Fourier transform infrared spectroscopy (FTIR), please refer to [reference needed]. Figure 4 .

[0054] Example 4

[0055] Another ternary hydrotalcite catalyst provided in this embodiment is prepared by the following method:

[0056] (1) Dissolve 5 mmol of Mn(NO3)2 solution (50 wt.% in H2O) in 20 mL of deionized water, and record it as solution a; dissolve 10 mmol of Co(NO3)2·6H2O in 20 mL of deionized water, and record it as solution b; add 3 mmol of Cr(NO3)3·9H2O to 20 mL of deionized water, and record it as solution c;

[0057] (2) Take 20 mmol NaOH and 16 mmol Na2CO3 and add them to 20 mL of deionized water, and record it as mixed alkaline solution d;

[0058] (3) Add solutions a, b, c and d to a polytetrafluoroethylene-lined hydrothermal reactor and place the hydrothermal reactor in a 140℃ electric thermostatic drying oven for crystallization for 14 hours.

[0059] (4) After the reaction was completed, the mixture was cooled to room temperature, centrifuged, washed three times with deionized water, and then washed three times with ethanol until the pH of the supernatant was neutral. The precipitate was dried in an oven at 60°C for 24 hours to obtain the solid product Cr. 0.2 MnCoLDH;

[0060] (5) The above solid product was calcined at 150°C for 8 hours in a 5% H2 / Ar mixed atmosphere. The resulting sample was denoted as Cr. 0.3 MnCoLDH-H4.

[0061] Example 5

[0062] Another ternary hydrotalcite catalyst provided in this embodiment is prepared by the following method:

[0063] (1) Dissolve 5 mmol of Mn(NO3)2 solution (50 wt.% in H2O) in 20 mL of deionized water and record it as solution a; dissolve 10 mmol of Co(NO3)2·6H2O in 20 mL of deionized water and record it as solution b; add 4 mmol of Cr(NO3)3·9H2O to 20 mL of deionized water and record it as solution c;

[0064] (2) Take 20 mmol NaOH and 10 mmol Na2CO3 and add them to 20 mL of deionized water, and record it as mixed alkaline solution d;

[0065] (3) Add solutions a, b, c and d to a polytetrafluoroethylene-lined hydrothermal reactor and place the hydrothermal reactor in a 150℃ electric constant temperature drying oven for crystallization for 16 hours.

[0066] (4) After the reaction was completed, the mixture was cooled to room temperature, centrifuged, washed three times with deionized water, and then washed three times with ethanol until the pH of the supernatant was neutral. The precipitate was dried in an oven at 60°C for 24 hours to obtain the solid product Cr. 0.2 MnCoLDH;

[0067] (5) The above solid product was calcined at 200°C for 8 hours in a 5% H2 / Ar mixed atmosphere. The resulting sample was denoted as Cr. 0.4 MnCoLDH-H5.

[0068] Comparative Example 1

[0069] This case study provides a ternary hydrotalcite catalyst, which is prepared by the following method:

[0070] (1) Dissolve 5 mmol of Mn(NO3)2 solution (50 wt.% in H2O) in 20 mL of deionized water and record it as solution a; dissolve 10 mmol of Co(NO3)2·6H2O in 20 mL of deionized water and record it as solution b; add 2 mmol of Cr(NO3)3·9H2O to 20 mL of deionized water and record it as solution c;

[0071] (2) Take 20 mmol NaOH and 10 mmol Na2CO3 and add them to 20 mL of deionized water, and record it as mixed alkaline solution d;

[0072] (3) Add solutions a, b, c and d to a polytetrafluoroethylene-lined hydrothermal reactor and place the hydrothermal reactor in a 150℃ electric constant temperature drying oven for crystallization for 16 hours.

[0073] (4) After the reaction was completed, the mixture was cooled to room temperature, centrifuged, washed three times with deionized water, and then washed three times with ethanol until the pH of the supernatant was neutral. The precipitate was dried in an oven at 60°C for 24 hours to obtain the solid product Cr.0.2 MnCoLDH; X-ray crystal diffraction (XRD) pattern (see reference). Figure 1 See scanning electron microscope (SEM) image for reference. Figure 3 For Fourier transform infrared spectroscopy (FTIR), please refer to [reference needed]. Figure 4 .

[0074] To better demonstrate the advantages of the technical solution provided in this application, the following are the activity evaluation results of the ternary hydrotalcite catalyst for catalytic oxidation of formaldehyde provided in Examples 1 to 5 and Comparative Example 1 of this application.

[0075] Reaction conditions:

[0076] Temperature: 30℃

[0077] Formaldehyde concentration: 30 ppm

[0078] Air velocity: 21,600 mL / (gh)

[0079] Reaction stabilization time: 1 hour

[0080] Catalyst mass: 0.2g

[0081] Table 1. Activity evaluation results of CrMnCoLDH catalyst

[0082]

[0083] As can be seen from the table above, the CrMnCoLDH-H catalysts in the examples all underwent hydrogen reduction treatment, while the catalysts in the comparative examples did not undergo hydrogen reduction treatment. The table also shows that the Cr content in the comparative examples, selected at the optimal ratio of 0.5:1:0.2, was the best among the examples, and the formaldehyde conversion rate of the comparative example was significantly lower than that of the examples. This indicates that hydrogen reduction treatment endows CrMnCoLDH-H with excellent formaldehyde catalytic activity. Therefore, the examples represent a class of highly active thermal catalysts.

Claims

1. A method for the catalytic oxidation of formaldehyde using a CrMnCoLDH-H catalyst, characterized in that, The catalytic conditions were as follows: formaldehyde concentration of 30 ppm, space velocity of 21,600 mL / (g·h), reaction temperature of 30℃, reaction time of 1 h, and catalyst mass of 0.2 g. The catalyst was prepared by the following steps: (1) Prepare manganese salts separately, denoted as solution a; prepare cobalt salts separately, denoted as solution b; prepare chromium salts separately, denoted as solution c; The molar ratio of the manganese salt, cobalt salt, and chromium salt is 0.5:1:0.1-0.5; (2) Prepare a mixed alkaline solution d of sodium hydroxide and sodium carbonate; The molar ratio of NaOH to NaCO3 is 1:0.2-1.2; (3) Add solutions a, b, c and d to a polytetrafluoroethylene-lined hydrothermal reactor, and place the hydrothermal reactor in an electric thermostatic drying oven for crystallization; The crystallization temperature is 100-200℃, and the crystallization time is 6-24h; (4) After the reaction is complete, cool to room temperature, centrifuge the reactants in the liner, wash, and finally dry to obtain the solid product Cr. 0.2 MnCo-LDH; (5) The above solid product was calcined and reduced in a H2 / Ar mixed gas containing 5% H2 at 100-300℃ for 3-10h. The resulting sample is denoted as CrMnCoLDH-H.

2. The method for catalytic oxidation of formaldehyde using a CrMnCoLDH-H catalyst according to claim 1, characterized in that, The manganese salt mentioned 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 catalytic oxidation of formaldehyde using a CrMnCoLDH-H catalyst according to claim 2, characterized in that, The divalent manganese salt is Mn(NO3)2 solution or Mn(acac)2; the trivalent cobalt salt is Co(NO3)2·6H2O or Co(acac)3; the trivalent chromium salt is Cr(NO3)3·9H2O or Cr(acac)3.

4. The method for catalytic oxidation of formaldehyde using a CrMnCoLDH-H catalyst according to claim 1, characterized in that, In step (4), the centrifugation parameters are: 6000 rpm, time 3 min; the washing conditions are: washing with deionized water 3-5 times and washing with ethanol 3-5 times; the drying temperature is 60℃ and the time is 10-24 h.

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