Preparation of a MnCoOx composite catalyst and its application in catalytic oxidation of formaldehyde at room temperature

Abstract

The present invention discloses a MnCoO x The composite catalyst and its application in the catalytic oxidation of formaldehyde at room temperature include the following steps: dissolving a certain amount of manganese salt and cobalt salt in a certain amount of deionized water, then rapidly mixing with an oxalate aqueous solution, stirring and reacting at a certain temperature for a period of time to obtain a suspension, and centrifuging the suspension to obtain a precipitate MnCoO x The catalyst was washed with deionized water for several times and dried to obtain a powdered composite catalyst. x The catalyst has abundant oxygen vacancies and exhibits significantly better catalytic activity and water resistance than single-component MnO2 in the formaldehyde catalytic oxidation reaction at room temperature.

Description

Technical Field

[0001] The present invention relates to a MnCoO x The invention relates to a preparation method and application of a composite catalyst, belonging to the field of catalytic technology and environmental protection. Background Art

[0002] With the increasing diversification of home decoration, various decorative paints and wood furnishings are being widely used indoors. While home decorations are becoming more beautiful, indoor formaldehyde pollution is also becoming a growing problem. Formaldehyde, a major pollutant in interior decoration, is a colorless, toxic gas with a strong, irritating odor. It is released over a period of 3-15 years. According to a survey conducted by the China Association for Standardization, in modern society, people spend 90% of their lives indoors. Long-term exposure to formaldehyde can cause headaches, eye irritation, respiratory inflammation, pneumonia, and even cancer.

[0003] Strategies for indoor formaldehyde purification, including adsorption, biofiltration, photocatalytic oxidation, plasma degradation, and catalytic oxidation, have emerged over the past few decades. Among them, the room-temperature catalytic oxidation of formaldehyde to harmless carbon dioxide and water is considered the most promising approach. Considering that the key source of reactive oxygen species in formaldehyde oxidation is molecular oxygen in the air, and the activation site of molecular oxygen is oxygen vacancies, it is necessary to develop catalytic materials with abundant oxygen vacancies to achieve a continuous supply of reactive oxygen species. Due to the easy transition between multiple valence states of the element Mn, it has the advantage of adjustable oxygen vacancies, and MnO2 has been proven to be a very promising catalyst in the field of formaldehyde catalytic oxidation. However, the ubiquitous presence of moisture in indoor air and the increased humidity in rainy weather environments pose certain challenges to the catalytic performance of MnO2. Therefore, improving the activity of MnO2 also requires enhancing its water resistance.

[0004] Transition metal oxide CoO x The chemical bond between Co and O atoms is weak, and oxygen vacancies can be generated quickly even at low temperatures. 3+ With Co 2+ The rapid redox cycle between CoO and MgO makes it exhibit excellent catalytic performance in various oxidation processes, such as methane oxidation. x With excellent hydrothermal stability, MnCoO x Composite catalysts have great application potential in room temperature formaldehyde oxidation reaction. Summary of the Invention

[0005] The purpose of the present invention is to provide a MnCoO x A composite catalyst and its application in the catalytic oxidation reaction of formaldehyde at room temperature improve its activity and enhance its water resistance. In order to achieve the above-mentioned object, the technical solution of the present invention is as follows:

[0006] The present invention provides a MnCoO x A method for preparing a composite catalyst, comprising the following steps:

[0007] a. Dissolving a certain amount of manganese salt and cobalt salt in deionized water and stirring to dissolve at room temperature to obtain a manganese - cobalt precursor salt solution;

[0008] b The oxalate was dissolved in deionized water and added to the manganese obtained in a - cobalt precursor salt solution, and vigorously stirred at a certain temperature for a certain time to obtain a manganese - cobalt salt precipitate;

[0009] c. The precipitate obtained in step b was centrifuged, washed with deionized water several times until the upper liquid was clear and dried to obtain MnCoO x Composite catalyst.

[0010] In the above technical solution, further, the manganese salt and cobalt salt in step a are potassium permanganate and cobalt nitrate, and the molar ratio of the manganese salt to the cobalt salt is 1:1~5.

[0011] In the above technical solution, further, in step b, the oxalate is ammonium oxalate monohydrate, and the molar ratio of the manganese salt to the oxalate is 1 to 5:1.

[0012] In the above technical solution, further, the molar ratio of the manganese salt and the oxalate used in step a and step b is 1:1 to 5:1.

[0013] In the above technical solution, further, the volume ratio of the manganese-cobalt precursor salt solution in step a to the oxalate solution in step b is 1:2~3:1.

[0014] In the above technical solution, further, the stirring temperature and time in step b are 70-100° C. and 8-12 h, respectively.

[0015] The present invention also provides an application of the catalyst in a catalytic oxidation reaction of formaldehyde at room temperature.

[0016] The beneficial effects of the present invention are:

[0017] (1) The present invention directly prepares MnCoO by a one-pot oxidation-reduction method. x The method is simple, low-cost and economical; (2) The present invention innovatively obtains MnCoO with rich oxygen vacancies and hydrothermal stability through the optimized coupling of manganese-cobalt dual centers. x The composite catalyst further improves its catalytic activity and water resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 MnCoO prepared in Example 1x -ⅠSEM image of composite catalyst;

[0019] Figure 2 The catalyst water resistance test of Example 2 and Comparative Example 1 (MnCoO x -Ⅱ and MnO2-Ⅰ represent the catalysts prepared in Example 2 and Comparative Example 1, respectively). DETAILED DESCRIPTION

[0020] The embodiments of the present invention are described in detail below. The embodiments described below are illustrative and are only used to explain the present invention, and are not to be construed as limiting the present invention.

[0021] Unless otherwise specified, the materials used in the examples of the present invention can be obtained from commercial sources or prepared according to conventional methods well known to those skilled in the art.

[0022] The MnCoO x The composite catalyst was prepared by an oxidation-reduction method, and the specific operation details are shown in Examples 1, 2, and 3; the catalytic oxidation decomposition performance of formaldehyde at room temperature was used as the catalyst evaluation index, as shown in Examples 4 and 5.

[0023] Example 1

[0024] First, 5 g of potassium permanganate and 5 g of cobalt nitrate hexahydrate were dissolved in 100 mL of deionized water, and then 5 g of ammonium oxalate monohydrate was dissolved in 50 mL of deionized water. The two fully dissolved solutions were quickly mixed together and vigorously stirred at 90 °C for 10 h. Then, the obtained MnCoO x The precipitate was washed with deionized water several times until the upper liquid was clear, and then dried to obtain MnCoO x Composite catalyst, named MnCoO x -Ⅰ, its SEM photo is as follows Figure 1 shown.

[0025] from Figure 1 It can be seen that the MnCoO prepared in Example 1 x The composite catalyst exhibits an ultra-thin needle-like morphology, and the needle-like nanoparticles further aggregate to form spherical particles with a particle size of about 100 nm.

[0026] Example 2

[0027] First, 2.5 g potassium permanganate and 5 g cobalt nitrate hexahydrate were dissolved in 80 mL deionized water, and then 2.3 g ammonium oxalate monohydrate was dissolved in 50 mL deionized water. The two fully dissolved solutions were quickly mixed together and vigorously stirred at 90 ° C for 10 h. Then, the obtained MnCoO xThe precipitate was washed with deionized water several times until the upper liquid was clear, and then dried to obtain MnCoO x Composite catalyst, named MnCoO x -Ⅱ.

[0028] Example 3

[0029] First, 2.5 g potassium permanganate and 5 g cobalt nitrate hexahydrate were dissolved in 80 mL deionized water, and then 4.6 g ammonium oxalate monohydrate was dissolved in 50 mL deionized water. The two fully dissolved solutions were quickly mixed together and vigorously stirred at 90 °C for 10 h. Then, the obtained MnCoO x The precipitate was washed with deionized water several times until the upper liquid was clear, and then dried to obtain MnCoO x Composite catalyst, named MnCoO x -Ⅲ.

[0030] Comparative Example 1

[0031] 2.5 g of potassium permanganate and 2.3 g of ammonium oxalate monohydrate were dissolved in 75 mL of deionized water respectively. The two fully dissolved solutions were then quickly mixed and vigorously stirred at 90 °C for 10 h. The obtained MnO2 precipitate was then washed with deionized water several times until the upper liquid was clear and then dried to obtain a single-active component MnO2 catalyst, named MnO2-I.

[0032] MnCoO in Examples 1, 2, and 3 x The decomposition of the composite catalyst and the single-component MnO2 catalyst of Comparative Example 1 at different space velocities with a catalytic concentration of 100 ppm formaldehyde at room temperature (MnCoO x -Ⅰ, MnCoO x -Ⅱ、MnCoO x -Ⅲ and MnO2-Ⅰ represent the catalysts prepared in Examples 1, 2, 3 and Comparative Example 1, respectively) as follows:

[0033]

[0034] Example 4

[0035] The MnCoO in Examples 1, 2, and 3 were respectively x -Ⅰ, MnCoO x -Ⅱ、MnCoO x The MnO2-III composite catalyst and the MnO2-I catalyst in Comparative Example 1 were loaded into a self-made fixed-bed quartz reactor, and a mixed gas (100 ppm formaldehyde, 99.99% air) was introduced. The volumetric space velocity was adjusted to 50,000, 80,000, 110,000, and 170,000 h-1. -1During the test, the temperature of the test system was maintained at 25°C. Formaldehyde and carbon dioxide analyzers were used to detect the formaldehyde and carbon dioxide concentrations in the reaction tail gas in real time. Table 1 shows the test results after 30 minutes of reaction.

[0036] It can be seen from Table 1 that the MnCoO prepared in Examples 1-3 x The activity of the composite catalyst was significantly superior to that of the MnO2 catalyst in Comparative Example 1, indicating that the introduction of the Co element effectively increased the oxygen vacancies in the catalyst, thereby improving the catalyst's reactivity. Furthermore, a comparison of the reactivity of the catalysts prepared in Examples 2 and 3, each with the same Co and Mn contents, shows that the amount of the reducing agent, ammonium oxalate, also affects the reactivity at the same Co and Mn content; increasing the amount of ammonium oxalate increases the catalyst's activity.

[0037] Example 5

[0038] The composite catalyst MnCoO in Example 2 x The catalytic oxidation performance of formaldehyde in the presence of water was evaluated for the single-component catalyst MnO2-Ⅰ in Example 1 and the single-component catalyst MnO2-Ⅱ. The catalyst was loaded into a self-made fixed-bed quartz reactor and the introduced mixed gas consisted of 100 ppm formaldehyde, 5% water vapor and 94.99% air at a gas volume space velocity of 50,000 h -1 , other test methods and test conditions are consistent with Example 4.

[0039] from Figure 2 It can be seen that the composite catalyst MnCoO prepared in Example 2 x The activity and stability of -Ⅱ are significantly better than those of the MnO2-Ⅰ catalyst prepared in Comparative Example 1, which shows that the introduction of Co element not only improves the reaction activity of the catalyst, but also enhances the stability of the catalyst.

[0040] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of implementation. The scope of protection of the present invention shall be determined by the scope defined in the claims. Based on the above description, other variations or modifications may be made, and any obvious variations or modifications derived therefrom shall remain within the scope of protection of the present invention.

Claims

1. A MnCoO for room temperature formaldehyde catalytic oxidation x The preparation method of the composite catalyst is characterized by: The MnCoOx composite catalyst is prepared by an oxidation-reduction method, which comprises the following steps: a. Dissolving a certain amount of manganese salt and cobalt salt in deionized water and stirring to dissolve at room temperature to obtain a manganese - cobalt precursor salt solution; b The oxalate was dissolved in deionized water and added to the manganese obtained in a - cobalt precursor salt solution, and vigorously stirred at a certain temperature for a certain time to obtain a manganese - cobalt salt precipitate; c. The precipitate obtained in step b was centrifuged, washed with deionized water several times until the upper liquid was clear and dried to obtain MnCoO x Composite catalyst; The manganese salt and cobalt salt in step a are potassium permanganate and cobalt nitrate, and the molar ratio of the manganese salt to the cobalt salt is 1:1-5; In step b, the oxalate is ammonium oxalate monohydrate, and the molar ratio of the manganese salt to the oxalate is 1 to 5:1; The volume ratio of the manganese-cobalt precursor salt solution in step a to the oxalate solution in step b is 0.5-3:1; The temperature and stirring time in step b are 70-100° C. and 8-12 h, respectively.

2. MnCoO prepared by the preparation method according to claim 1 x Application of composite catalyst in catalytic oxidation of formaldehyde at room temperature.

Images