CN106693985B - Preparation method of flaky spinel-structured cobalt-manganese composite oxide - Google Patents
Preparation method of flaky spinel-structured cobalt-manganese composite oxide Download PDFInfo
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- MZZUATUOLXMCEY-UHFFFAOYSA-N cobalt manganese Chemical compound [Mn].[Co] MZZUATUOLXMCEY-UHFFFAOYSA-N 0.000 title claims abstract description 55
- 239000002131 composite material Substances 0.000 title claims abstract description 55
- 238000002360 preparation method Methods 0.000 title claims abstract description 17
- 239000000243 solution Substances 0.000 claims abstract description 45
- 238000003756 stirring Methods 0.000 claims abstract description 42
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims abstract description 20
- 238000000967 suction filtration Methods 0.000 claims abstract description 17
- 238000001035 drying Methods 0.000 claims abstract description 16
- GEVPUGOOGXGPIO-UHFFFAOYSA-N oxalic acid;dihydrate Chemical compound O.O.OC(=O)C(O)=O GEVPUGOOGXGPIO-UHFFFAOYSA-N 0.000 claims abstract description 15
- 238000000034 method Methods 0.000 claims abstract description 13
- 239000011259 mixed solution Substances 0.000 claims abstract description 11
- 238000005303 weighing Methods 0.000 claims abstract description 11
- MIVBAHRSNUNMPP-UHFFFAOYSA-N manganese(2+);dinitrate Chemical compound [Mn+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O MIVBAHRSNUNMPP-UHFFFAOYSA-N 0.000 claims abstract description 10
- 239000002244 precipitate Substances 0.000 claims abstract description 9
- 239000007864 aqueous solution Substances 0.000 claims abstract description 8
- QGUAJWGNOXCYJF-UHFFFAOYSA-N cobalt dinitrate hexahydrate Chemical compound O.O.O.O.O.O.[Co+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O QGUAJWGNOXCYJF-UHFFFAOYSA-N 0.000 claims abstract description 8
- 239000007787 solid Substances 0.000 claims abstract description 8
- MUBZPKHOEPUJKR-UHFFFAOYSA-N Oxalic acid Chemical compound OC(=O)C(O)=O MUBZPKHOEPUJKR-UHFFFAOYSA-N 0.000 claims description 19
- 238000010438 heat treatment Methods 0.000 claims description 11
- 239000011572 manganese Substances 0.000 claims description 6
- 235000006408 oxalic acid Nutrition 0.000 claims description 6
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 claims description 5
- 239000010941 cobalt Substances 0.000 claims description 5
- 229910017052 cobalt Inorganic materials 0.000 claims description 5
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 claims description 5
- 229910052748 manganese Inorganic materials 0.000 claims description 5
- UHOVQNZJYSORNB-UHFFFAOYSA-N Benzene Chemical compound C1=CC=CC=C1 UHOVQNZJYSORNB-UHFFFAOYSA-N 0.000 abstract description 42
- 230000000694 effects Effects 0.000 abstract description 8
- 239000000047 product Substances 0.000 abstract description 7
- 238000009826 distribution Methods 0.000 abstract description 4
- 229910052751 metal Inorganic materials 0.000 abstract description 4
- 239000002184 metal Substances 0.000 abstract description 4
- 239000002994 raw material Substances 0.000 abstract description 4
- 238000005406 washing Methods 0.000 abstract description 4
- 150000001768 cations Chemical class 0.000 abstract description 2
- 238000007254 oxidation reaction Methods 0.000 abstract description 2
- 150000003839 salts Chemical class 0.000 abstract description 2
- 238000006243 chemical reaction Methods 0.000 description 15
- 229910052596 spinel Inorganic materials 0.000 description 15
- 239000011029 spinel Substances 0.000 description 15
- 239000013078 crystal Substances 0.000 description 8
- 239000000463 material Substances 0.000 description 7
- 238000002485 combustion reaction Methods 0.000 description 6
- 230000000052 comparative effect Effects 0.000 description 5
- 230000003197 catalytic effect Effects 0.000 description 4
- 239000012855 volatile organic compound Substances 0.000 description 4
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 3
- 238000002441 X-ray diffraction Methods 0.000 description 3
- 239000003054 catalyst Substances 0.000 description 3
- 238000001027 hydrothermal synthesis Methods 0.000 description 3
- 229910021645 metal ion Inorganic materials 0.000 description 3
- 229910002091 carbon monoxide Inorganic materials 0.000 description 2
- 238000007084 catalytic combustion reaction Methods 0.000 description 2
- 238000000975 co-precipitation Methods 0.000 description 2
- UBEWDCMIDFGDOO-UHFFFAOYSA-N cobalt(II,III) oxide Inorganic materials [O-2].[O-2].[O-2].[O-2].[Co+2].[Co+3].[Co+3] UBEWDCMIDFGDOO-UHFFFAOYSA-N 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 238000001878 scanning electron micrograph Methods 0.000 description 2
- 229910016978 MnOx Inorganic materials 0.000 description 1
- YLYPAGJDBMPYKO-UHFFFAOYSA-N [Mn].[Mn].[Co].[Co] Chemical compound [Mn].[Mn].[Co].[Co] YLYPAGJDBMPYKO-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000007664 blowing Methods 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 238000006555 catalytic reaction Methods 0.000 description 1
- 150000001868 cobalt Chemical class 0.000 description 1
- XEUFSQHGFWJHAP-UHFFFAOYSA-N cobalt(2+) manganese(2+) oxygen(2-) Chemical compound [O--].[O--].[Mn++].[Co++] XEUFSQHGFWJHAP-UHFFFAOYSA-N 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 238000002425 crystallisation Methods 0.000 description 1
- 230000008025 crystallization Effects 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 239000002270 dispersing agent Substances 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 235000019441 ethanol Nutrition 0.000 description 1
- -1 ethylene, propylene Chemical group 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 229910052738 indium Inorganic materials 0.000 description 1
- APFVFJFRJDLVQX-UHFFFAOYSA-N indium atom Chemical compound [In] APFVFJFRJDLVQX-UHFFFAOYSA-N 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 238000011031 large-scale manufacturing process Methods 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 230000005291 magnetic effect Effects 0.000 description 1
- 150000002696 manganese Chemical class 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000002808 molecular sieve Substances 0.000 description 1
- 239000002114 nanocomposite Substances 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 239000012716 precipitator Substances 0.000 description 1
- 239000002243 precursor Substances 0.000 description 1
- 230000035484 reaction time Effects 0.000 description 1
- 238000005245 sintering Methods 0.000 description 1
- URGAHOPLAPQHLN-UHFFFAOYSA-N sodium aluminosilicate Chemical compound [Na+].[Al+3].[O-][Si]([O-])=O.[O-][Si]([O-])=O URGAHOPLAPQHLN-UHFFFAOYSA-N 0.000 description 1
- 238000003980 solgel method Methods 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 238000003786 synthesis reaction Methods 0.000 description 1
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
- B01J23/76—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
- B01J23/84—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
- B01J23/889—Manganese, technetium or rhenium
- B01J23/8892—Manganese
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J35/00—Catalysts, in general, characterised by their form or physical properties
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J35/00—Catalysts, in general, characterised by their form or physical properties
- B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/02—Impregnation, coating or precipitation
- B01J37/03—Precipitation; Co-precipitation
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
- F23G7/00—Incinerators or other apparatus for consuming industrial waste, e.g. chemicals
- F23G7/06—Incinerators or other apparatus for consuming industrial waste, e.g. chemicals of waste gases or noxious gases, e.g. exhaust gases
- F23G7/07—Incinerators or other apparatus for consuming industrial waste, e.g. chemicals of waste gases or noxious gases, e.g. exhaust gases in which combustion takes place in the presence of catalytic material
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Abstract
The invention provides a preparation method of a flaky spinel-structured cobalt-manganese composite oxide, which comprises the following steps: firstly, weighing an aqueous solution of cobalt nitrate hexahydrate and manganese nitrate, dissolving the aqueous solution in absolute ethyl alcohol, and stirring and dissolving to obtain a solution A; weighing excessive oxalic acid dihydrate, dissolving in absolute ethyl alcohol, and stirring to obtain a solution B; secondly, dropwise adding the solution B into the solution A while stirring, and continuously stirring to obtain a mixed solution; thirdly, after stirring, carrying out suction filtration on the obtained mixed solution, and then placing the precipitate obtained after suction filtration in a forced air oven for drying; and fourthly, placing the dried solid in a muffle furnace for roasting to obtain the flaky spinel-structured cobalt-manganese composite oxide. The method does not need to introduce other metal cations except necessary metal salts, has the advantages of cheap raw materials, simple operation, no need of washing, uniform product distribution and high purity, and the obtained product shows high activity to the complete oxidation reaction of benzene.
Description
Technical Field
The invention relates to a preparation method of a cobalt-manganese composite oxide, belongs to the technical field of material preparation and environmental protection, and particularly relates to a preparation method of a flaky spinel-structured cobalt-manganese composite oxide Co2 MnOx.
Background
The cobalt-manganese composite oxide is a novel material with wide application, and has great application prospects in the aspects of magnetics, electronics, catalysis, energy conversion, storage and the like because the cobalt-manganese composite oxide contains two different metal ions and has a special spinel crystal structure. With the recent development of various laws and regulations for the control of VOCs (volatile organic compounds), the application of cobalt-manganese composite oxides in the control of VOCs has been receiving attention.
The activity of the cobalt-manganese composite oxide catalyst on removing VOCs is related to the specific surface area, the dispersion degree of active components, the interaction among the components and the like; these factors are directly related to the preparation process, among others. The conventional methods for preparing cobalt-manganese composite oxides include a coprecipitation method, a sol-gel method, and the like. The cobalt manganese oxide obtained by the method is mainly granular, and generally has the defects of high impurity content, large grain size, uneven distribution and the like. Often exhibit lower catalytic performance.
The catalytic material is prepared into a sheet structure, so that the performance of the material can be greatly improved; after retrieval: in the patent CN105597769A, a hydrothermal method is adopted to synthesize a flaky-shaped nano composite metal oxide catalyst CeO2-Co3O4, and the prepared CeO2-Co3O4 has more flaky microscopic shapes with more advantageous exposed active crystal faces, so that the catalyst has higher activity and CO catalytic selectivity; in patent CN102303900A, the sheet indium trisulfide is synthesized by a hydrothermal method, and has good visible light degradation capability; in patent CN103011188A, a microwave heating method is adopted to synthesize a nano SAPO-34 molecular sieve with a sheet shape, which is prominent in the reaction of preparing low-carbon olefins such as ethylene, propylene and the like from methanol. In the preparation of the materials with the sheet shapes, a hydrothermal method usually needs high temperature and high pressure, and longer reaction time is needed. Microwave heating also needs to be carried out at a higher temperature, so the above method inevitably increases the cost and is difficult to realize mass production.
The synthesis of cobalt-manganese composite oxides with rod-shaped and flower-shaped morphology structures has been reported in the literature, but reports related to cobalt-manganese composite oxides with sheet morphology are not found.
Disclosure of Invention
In view of the above problems, the present invention aims to provide a method for preparing a cobalt-manganese composite oxide having a sheet structure, which has the advantages of abundant raw material sources, simple preparation method, suitability for large-scale production, and the like. The cobalt-manganese composite oxide prepared by the method has a flaky spinel structure, has the characteristic of high reaction activity, and can catalyze and combust benzene at a low temperature. The XRD result shows that the obtained cobalt-manganese composite oxide has a spinel structure; SEM shows that the cobalt manganese composite oxide is in a flaky shape.
The invention is realized by the following technical scheme:
a preparation method of a flaky spinel-structured cobalt-manganese composite oxide comprises the following steps:
firstly, weighing an aqueous solution of cobalt nitrate hexahydrate and manganese nitrate, dissolving the aqueous solution in absolute ethyl alcohol, and stirring and dissolving to obtain a solution A; weighing excessive oxalic acid dihydrate, dissolving in absolute ethyl alcohol, and stirring to obtain a solution B;
secondly, dropwise adding the solution B into the solution A while stirring, and continuously stirring to obtain a mixed solution;
thirdly, after stirring, carrying out suction filtration on the obtained mixed solution, and then placing the precipitate obtained after suction filtration in a forced air oven for drying;
and fourthly, placing the dried solid in a muffle furnace for roasting to obtain the flaky spinel-structured cobalt-manganese composite oxide.
Preferably, in the first step: the mass fraction of the manganese nitrate aqueous solution is 50%.
Preferably, the ratio of the total mole number of cobalt and manganese in the solution A to the mole number of oxalic acid dihydrate in the solution B is 1:1.2, and the molar concentration of the oxalic acid solution is 0.72 mol/L. Due to the spinel structure general formula of A2BO4, A is usually +3 valence metal ions, and B is usually +2 valence metal ions. The preferred condition of the present invention is a molar ratio of Co/Mn of 2:1, enabling Co2MnOx to be obtained with a perfect spinel structure. And a little excess of oxalic acid ensures that the cobalt salt and the manganese salt are completely precipitated according to the theoretical addition amount (2:1), and the flaky shape of the cobalt-manganese-cobalt-manganese composite oxide collapses due to the excess of the oxalic acid.
Preferably, in the second step, the stirring is continued for 4-6 h.
Preferably, in the third step: the temperature set by the air-blowing oven is 70-80 ℃. The temperature range has small influence on the precipitate obtained by suction filtration and is beneficial to the complete volatilization of the absolute ethyl alcohol. Preferably, the drying time in the blast oven is 10-12 h.
Preferably, in the fourth step: the roasting temperature is 300-500 ℃. The roasting temperature is favorable for obtaining a good crystal phase structure and a good cobalt-manganese composite oxide appearance, and further the material performance is improved. The flaky cobalt-manganese composite oxide with a perfect spinel structure can be obtained by roasting at a selected temperature (300-500 ℃), and the catalytic combustion of benzene shows the optimal performance.
Preferably, in the fourth step: the roasting time is 3-5 h, and the heating rate is 2 ℃/min.
The invention adopts conditions such as proper temperature, heating rate and the like to have important influence on obtaining Co2MnOx with a perfect spinel structure. Firstly, in order to obtain a good spinel structure and control the sheet shape of the cobalt-manganese composite oxide, the roasting temperature of the invention is too low, when the temperature is too low, the good spinel crystal phase structure can not be obtained, and when the temperature is too high, the sheet shape of the cobalt-manganese composite oxide can be damaged. The invention selects oxalic acid as a precipitator, and CO or CO can be generated in the decomposition process of the formed oxalate precursor2Gas, and drying temperature, heating rate, roasting temperature and time, etc. all affect CO or CO2The generation and release of gas, in turn, affects the crystalline phase structure and the microstructure of the product. The rate of temperature rise affects crystal crystallization, while the temperature and time affect grain growth and further affect the microstructure of the product. Further, since the atoms of cobalt and manganese are different in size, the crystal structure is easily deformed when the crystal grains grow up, which may promote the improvement of the performance on one hand, but may affect the microstructure and the crystal phase structure of the product on the other hand.
According to the invention, other metal cations except necessary metal salt are not required to be introduced, ethanol is used as a dispersing agent, oxalic acid is added for coprecipitation, washing is not required, and the prepared cobalt-manganese composite oxide is of a flaky cobalt-manganese spinel structure. The preparation method has the advantages of cheap raw materials, simple operation, no need of washing, uniform product distribution and high purity, and the obtained product has high activity for the complete oxidation reaction of benzene.
Compared with the prior art, the invention has the following advantages:
(1) the raw materials used in the invention are simple and have low cost.
(2) The preparation method is simple in preparation process, free of washing and suitable for large-scale preparation in large-scale actual working conditions.
(3) The material prepared by the invention has good reaction performance for benzene combustion reaction.
Drawings
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
FIG. 1 is an XRD pattern of a cobalt manganese composite oxide according to examples 1 to 3 of the present invention;
FIG. 2 is an SEM photograph of a cobalt manganese composite oxide according to example 1 of the present invention;
FIG. 3 is an SEM photograph of a cobalt manganese composite oxide according to example 2 of the present invention;
fig. 4 is an SEM image of the cobalt manganese composite oxide according to example 3 of the present invention.
Detailed Description
The following examples illustrate the invention in detail: the present embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments.
Example 1:
4.656g of cobalt nitrate hexahydrate and 2.860g of manganese nitrate solution (the mass fraction is 50%) are weighed and placed in a 500mL beaker, 200mL of absolute ethyl alcohol is added, and solution A is obtained after stirring and dissolving; weighing 3.620g of oxalic acid dihydrate, placing the oxalic acid dihydrate in a 100mL beaker, adding 50mL of absolute ethyl alcohol, and stirring and dissolving to obtain a solution B; dropwise adding the solution B into the solution A while stirring, and continuously stirring for 4-6 h; after stirring, carrying out suction filtration on the obtained mixed solution, and then placing the precipitate obtained after suction filtration in a blast oven at 70-80 ℃ for drying for 12h and drying; and (3) placing the dried solid in a muffle furnace for roasting at the roasting temperature of 300 ℃ for 4h at the heating rate of 2 ℃/min to obtain the flaky cobalt-manganese composite oxide.
As shown by SEM results in FIG. 2, the thickness of the sheet was 0.03. mu.m. The XRD pattern result of example 1 in fig. 1 shows that the oxide has a spinel structure.
Example 2:
4.656g of cobalt nitrate hexahydrate and 2.860g of manganese nitrate solution (the mass fraction is 50%) are weighed and placed in a 500mL beaker, 200mL of absolute ethyl alcohol is added, and solution A is obtained after stirring and dissolving; weighing 3.620g of oxalic acid dihydrate, placing the oxalic acid dihydrate in a 100mL beaker, adding 50mL of absolute ethyl alcohol, and stirring to dissolve to obtain a solution B; dropwise adding the solution B into the solution A while stirring, and continuously stirring for 4-6 h; after stirring, carrying out suction filtration on the obtained mixed solution, and then placing the precipitate obtained after suction filtration in a blast oven at 70-80 ℃ for drying for 12h and drying; and (3) placing the dried solid in a muffle furnace for roasting at 400 ℃ for 4h at the heating rate of 2 ℃/min to obtain the flaky cobalt-manganese composite oxide.
As shown by SEM results in FIG. 3, the thickness of the sheet was 0.02. mu.m. The XRD result of example 2 in fig. 1 shows that the oxide is of a spinel structure.
Example 3:
4.656g of cobalt nitrate hexahydrate and 2.860g of manganese nitrate solution (the mass fraction is 50%) are weighed and placed in a 500mL beaker, 200mL of absolute ethyl alcohol is added, and solution A is obtained after stirring and dissolving; weighing 3.620g of oxalic acid dihydrate, placing the oxalic acid dihydrate in a 100mL beaker, adding 50mL of absolute ethyl alcohol, and stirring to dissolve to obtain a solution B; dropwise adding the solution B into the solution A while stirring, and continuously stirring for 4-6 h; after stirring, carrying out suction filtration on the obtained mixed solution, and then placing the precipitate obtained after suction filtration in a blast oven at 70-80 ℃ for drying for 12h and drying; and (3) placing the dried solid in a muffle furnace for roasting at 500 ℃ for 4h at the heating rate of 2 ℃/min to obtain the flaky cobalt-manganese composite oxide.
As shown by SEM results in FIG. 4, the thickness of the sheet was 0.03. mu.m. The XRD result of example 3 in fig. 1 shows that the oxide is of a spinel structure.
Comparative example 1:
firstly, 4.656g of cobalt nitrate hexahydrate and 2.860g of manganese nitrate solution (the mass fraction is 50%) are weighed and placed in a 500mL beaker, 200mL of absolute ethyl alcohol is added, and solution A is obtained after stirring and dissolving; weighing 3.620g of oxalic acid dihydrate, placing the oxalic acid dihydrate in a 100mL beaker, adding 50mL of absolute ethyl alcohol, and stirring to dissolve to obtain a solution B;
dropwise adding the solution B into the solution A while stirring, and continuously stirring for 4-6 h;
after stirring, carrying out suction filtration on the obtained mixed solution, and then placing the precipitate obtained after suction filtration in a blast oven at 70-80 ℃ for drying for 12h and drying;
and (3) roasting the dried solid in a muffle furnace at 600 ℃ for 4h at the heating rate of 2 ℃/min to obtain the granular cobalt-manganese composite oxide.
Comparative example 2:
firstly, 4.656g of cobalt nitrate hexahydrate and 2.860g of manganese nitrate solution (the mass fraction is 50%) are weighed and placed in a 500mL beaker, 200mL of absolute ethyl alcohol is added, and solution A is obtained after stirring and dissolving; weighing 3.620g of oxalic acid dihydrate, placing the oxalic acid dihydrate in a 100mL beaker, adding 50mL of absolute ethyl alcohol, and stirring to dissolve to obtain a solution B;
dropwise adding the solution B into the solution A while stirring, and continuously stirring for 4-6 h;
after stirring, carrying out suction filtration on the obtained mixed solution, and then placing the precipitate obtained after suction filtration in a blast oven at 70-80 ℃ for drying for 12h and drying;
and (3) placing the dried solid in a muffle furnace for roasting at 700 ℃ for 4h at the heating rate of 2 ℃/min to obtain the granular cobalt-manganese composite oxide.
Evaluation of application effects:
the cobalt-manganese composite oxide has high reaction activity and good stability, and can be used for catalytic combustion at low temperature and maintaining long-term stability. The XRD patterns of the cobalt manganese composite oxides described in the different examples in fig. 1 indicate the spinel structure of the cobalt manganese composite oxides. The SEM images of FIGS. 2 to 4 show the sheet structure of the cobalt-manganese composite oxide.
Evaluation of catalytic Activity: the cobalt manganese composite oxides described in examples 1 to 3 and comparative examples 1 to 2 were reacted in a continuous flow fixed bed apparatus by introducing a mixed gas of benzene vapor and air; the reaction pressure is normal pressure to 1atm, the reaction space velocity is 30000 mL/(g.h), and the benzene concentration in the mixed gas of air and benzene vapor is 1000 ppm.
The results showed that the cobalt manganese composite oxide described in example 1 had a light-off temperature of 140 ℃ and a complete conversion temperature of 235 ℃ for the benzene combustion reaction. The ignition temperature of the cobalt manganese composite oxide for benzene combustion reaction in example 2 was 145 ℃ and the complete conversion temperature was 245 ℃. The ignition temperature of the cobalt manganese composite oxide for benzene combustion reaction in example 3 was 155 ℃ and the complete conversion temperature was 245 ℃.
The light-off temperatures of the cobalt manganese composite oxide for the benzene combustion reaction in comparative examples 1-2 were 175 ℃ and 180 ℃, respectively; while the complete conversion temperatures are 265 ℃ and 305 ℃ respectively.
The cobalt-manganese composite oxide of embodiments 1 to 3 of the present invention has a flaky spinel structure, uniform particle distribution, and low ignition temperature and complete conversion temperature for the combustion reaction of benzene, and the optimum cobalt-manganese composite oxide can realize complete conversion of benzene with a concentration of 1000ppm at 235 ℃. The cobalt-manganese composite oxide obtained in the comparative example is granular, is unevenly distributed, has lower reaction activity than the cobalt-manganese composite oxide obtained in the example, has higher ignition temperature and complete conversion temperature, is easy to inactivate, and has poor sintering resistance.
The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes and modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention.
Claims (7)
1. A preparation method of a flaky spinel-structured cobalt-manganese composite oxide is characterized by comprising the following steps:
firstly, weighing an aqueous solution of cobalt nitrate hexahydrate and manganese nitrate, dissolving the aqueous solution in absolute ethyl alcohol, and stirring and dissolving to obtain a solution A; weighing excessive oxalic acid dihydrate, dissolving in absolute ethyl alcohol, and stirring to obtain a solution B; in the solution A, the molar ratio of cobalt to manganese is 2:1, and the total molar concentration of cobalt and manganese is 0.12 mol/L; the ratio of the total mole number of cobalt and manganese in the solution A to the mole number of oxalic acid dihydrate in the solution B is 1: 1.2;
secondly, dropwise adding the solution B into the solution A while stirring, and continuously stirring to obtain a mixed solution;
thirdly, after stirring, carrying out suction filtration on the obtained mixed solution, and then placing the precipitate obtained after suction filtration in a forced air oven for drying;
and fourthly, placing the dried solid in a muffle furnace for roasting to obtain the flaky spinel-structured cobalt-manganese composite oxide, wherein the roasting temperature is 300-500 ℃, the roasting time is 3-5 h, and the heating rate is 2 ℃/min.
2. The method for preparing a flaky spinel-structured cobalt-manganese composite oxide according to claim 1, wherein the mass fraction of the manganese nitrate aqueous solution is 50%.
3. The method for preparing a flaky spinel-structured cobalt-manganese composite oxide according to claim 1, wherein the molar concentration of the oxalic acid solution is 0.72 mol/L.
4. The method for preparing a flaky spinel-structured cobalt-manganese composite oxide according to claim 1, wherein in the second step, the stirring is continued for 4 to 6 hours.
5. The preparation method of the flaky spinel-structured cobalt-manganese composite oxide according to claim 1, wherein in the third step, the temperature of the air-blast oven is 70-80 ℃.
6. The preparation method of the flaky spinel-structured cobalt-manganese composite oxide according to claim 5, wherein in the third step, the drying time in the forced air oven is 10-12 h.
7. A flaky spinel-structured cobalt manganese composite oxide prepared by the method according to any one of claims 1 to 6.
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