CN115676896B - Amorphous manganese oxide composite material and preparation method and application thereof - Google Patents
Amorphous manganese oxide composite material and preparation method and application thereof Download PDFInfo
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Abstract
The invention discloses an amorphous manganese oxide composite material, the chemical general formula of which is A x B y Mn z O v Wherein A is one or more of first transition metal elements without manganese, B is one or more of lanthanide metal elements, bi and Y, x is more than 0 and less than or equal to 1, Y is more than 0 and less than or equal to 5, z is more than 0 and less than or equal to 9, and v is more than 0 and less than or equal to 25. The manganese oxide composite material is of an amorphous structure and has a high specific surface area. Also discloses a preparation method of the amorphous manganese oxide composite material and application of the amorphous manganese oxide composite material in the fields of ozone purification, VOC degradation and the like. The amorphous manganese oxide composite material can efficiently degrade ozone and other pollutants in high-humidity, ultralow-temperature and high-temperature environments. The amorphous manganese oxide composite material has the advantages of wide raw material source, low cost, green and environment-friendly preparation method, high stability, long service life and easy realization of industrialization.
Description
Technical Field
The invention relates to the technical field of manganese oxide compounds, in particular to a preparation method and application of an amorphous manganese oxide composite material.
Background
Ozone (O) 3 ) Is a near-ground and commercial aviation pollutant which is ubiquitous in the world at present, and has obvious harm to both an ecosystem and human health. For humans, even with prolonged exposure to low concentrations of O 3 And can also lead to symptoms or diseases including cardiovascular, blood pressure, respiratory and pulmonary functions. It is reported that 104 to 123 thousands of people in the world in 2010 are exposed to O for a long time 3 Causing respiratory diseases and death (environ. Health pest, 2017, 125, 087021). Troposphere O 3 Is Nitrogen Oxides (NO) emitted by humans x ) The secondary pollutants produced by the reaction of Volatile Organic Compounds (VOCs) with sunlight are easily diffused into the room and endanger the safety of residents. In addition, electrical equipment (ultraviolet disinfection cabinet, film laminating machine, ozone washing machine, copying machine, commercial ozone generator, ozone air purifier and the like) with high-voltage discharge or ozone action can further improve indoor O 3 And (4) horizontal. Thus, whether from ozoneWhether the source is generated or indoor purification is required urgently 3 The removal method is used for guaranteeing the life health and safety of people.
For ozone gas in the atmosphere, including outdoor near-ground and indoor ozone gas, the existing technologies for efficiently catalyzing and purifying ozone at room temperature are rare, and the mainstream technologies for purifying ozone gas comprise an absorption method, an adsorption method, a direct combustion method, a catalytic combustion method, a photocatalytic method and the like. At present, most of catalysts used in the ozone purification market are manganese dioxide, and the purpose of removing ozone is achieved by adding low-temperature heating treatment. But there are many critical problems that need to be solved in the industry at present. Firstly, as heating or illumination treatment is required, the equipment cost and the operation risk are increased, and the use is hindered; secondly, because the specific surface area is lower, the manganese oxide catalyst is usually loaded on a carrier such as active carbon for use, so that the efficiency is reduced; finally, the ozone purification environments of all walks of life are not consistent, for example, the production of jeans needs an ozone washing technology, tens of thousands of ppm ozone needs to be introduced for bleaching and ageing treatment, and common activated carbon supported catalysts are extremely easy to ignite and can not be competent due to extremely high ozone concentration and severe exothermic reaction; in addition, in the commercial aviation field, the concentration of ozone in high altitude is about five times of that of near ground (simple and faithful analysis and research on ozone concentration in aircraft cabins [ J ] civil aircraft design and research, 2011 (1): 33-34.), and at low temperatures of forty ℃ below zero, the existing catalysts are difficult to degrade by ozone effectively so as to protect the safety of crewmembers and passengers. Therefore, the manganese oxide catalyst material which has low-temperature activation, high specific surface area, high temperature resistance, ultralow temperature resistance and independent intellectual property rights is designed and developed, and the application value is high.
In the related research at present, patent publication No. CN106512715A discloses that noble metal or transition metal oxide as an active component is combined with activated carbon, molecular sieve or organic metal framework material as an adsorption component for purifying ozone-removing gas in an aircraft cabin, and the design structure is novel, but the cost of the catalyst and the adsorbent is high; the patent with publication number CN108889116A loads europium on activated carbon, and the prepared formed catalyst is very portable and can be directly applied, but the preparation process is comparativelyComplicated and not completely ozone-removing within a certain time. The LaFeO is prepared by a citric acid sol-gel method in a patent with publication number CN107376926A 3 The perovskite type ozone catalyst can reach nearly 100 percent of ozone conversion rate under a room temperature drying environment, and does not reduce within 8 hours, but the test conditions are not harsh enough.
The prior art has poor service performance under the conditions of high humidity, extremely low temperature, extremely high temperature and large air volume, does not relate to the experiment of durability, has the defects of expensive raw materials, complex preparation method, difficult industrialization, low efficiency, short service life, instability, difficult regeneration, easy moisture absorption and the like, and urgently needs a catalyst which can effectively treat ozone at room temperature, has low price, can realize industrialized mass production and can meet the requirement of catalytically treating ozone at room temperature even in the environment of ultralow temperature, high temperature and high humidity.
Disclosure of Invention
The invention aims to solve the technical problems of overcoming the defects and the defects of the existing ozone decomposition catalyst such as catalytic efficiency, stability and applicable environment and providing an amorphous manganese oxide catalyst. The invention also aims to provide a preparation method of the amorphous manganese oxide catalyst. The invention also aims to provide the application of the amorphous manganese oxide catalyst in catalytic decomposition of ozone.
The above object of the present invention is achieved by the following technical solutions:
the amorphous manganese oxide composite material is amorphous, and the microscopic morphology of the amorphous manganese oxide composite material is an amorphous structure. Has extremely high specific surface area, and further, 475.4 m can be obtained through proper element proportion and experimental conditions 2 Specific surface area of/g and above. The high specific surface area has more oxygen defect sites, and provides more pore structures and active sites.
The amorphous manganese oxide composite material comprises a transition metal oxide component, a rare earth oxide component and a manganese oxide component.
The chemical general formula of the amorphous manganese oxide composite material is A x B y Mn z O v Wherein A is any one or more of first transition series transition metal elements (without manganese), B is any one or more of lanthanide series metal elements, bi and Y, wherein x is more than 0 and less than or equal to 1, Y is more than or equal to 0 and less than or equal to 5, z is more than 0 and less than or equal to 9, and v is more than 0 and less than or equal to 25. For example x is 0.1, 0.2, 0.3, 0.5, 0.8, 1.0, y is 0.2, 0.5, 1, 2, 3, 4, 5, z is 1, 1.25, 2, 2.5, 4, 6, 8, 9, v is 5, 6.3, 10, 15, 20, 25.
The amorphous manganese oxide composite material is characterized in that A is selected from any one or more of Ti, V, cr, fe, co, ni, cu and Zn, and preferably, A is selected from any one or more of Fe, co and Ni.
The amorphous manganese oxide composite material is characterized in that B is selected from any one or more of La, ce, pr, nd, pm, sm, eu, gd, tb, dy, ho, er, tm, yb, lu, bi and Y, and preferably B is selected from any one or more of Sm, gd and Y.
The amorphous manganese oxide composite material comprises manganese elements, the valence forms of the manganese elements comprise trivalent manganese and tetravalent manganese, and the valence change of the manganese elements provides redox catalytic activity for the composite material.
The amorphous manganese oxide composite material comprises transition metal oxides, provides extremely high specific surface area for the composite material, is higher than common transition metal oxides, and provides sufficient reaction sites and abundant oxygen vacancies for the decomposition of ozone on a catalyst. At the same time, a staggered interface is formed between different oxides, and strong interaction is probably formed. The strong interface effect can generally induce electron transfer between different mediums, thereby changing the catalytic performance of the metal nanoparticles. In addition, electron transfer between different valence states of the transition metal element and between the transition metal element and the manganese element provides more possibility for the decomposition of ozone on the catalyst.
The amorphous manganese oxide composite material comprises rare earth oxide, and plays roles of stabilizing the structure and enhancing the thermal stability through the coordination and blending of crystal fields between the rare earth oxide and crystal lattices of transition metal oxide and manganese oxide.
A preparation method of an amorphous manganese oxide catalyst comprises the following steps:
(1) Adding a rare earth metal precursor, a transition metal precursor, a divalent manganese precursor and a heptavalent manganese precursor into deionized water according to a certain proportion, and fully stirring and mixing for more than 0.5 hour;
(2) Slowly dripping the prepared alkaline solution into the solution until superfine precipitates are completely generated, keeping the pH of the solution at 8-14, and continuously stirring for more than 0.5 hour;
(3) Adding the mixed solution obtained by stirring into a reaction kettle, and heating in an oven;
(4) And filtering, washing, centrifuging or suction filtering and drying the heated filtrate to obtain the amorphous manganese oxide composite material.
Preferably, the anionic form of the transition metal precursor comprises NO 3 - 、Cl - 、SO 3 2- 、SO 4 2- 、OH - 、SiO 3 2- 、PO 4 3- 、CH 3 COO - 、CO 3 2- 、HCO 3 - 、C 2 O 4 2- Etc., more preferably NO 3 - 、Cl - 、CH 3 COO - One or more of (a) and (b).
Preferably, the anionic form of the rare earth metal precursor comprises NO 3 - 、Cl - 、SO 3 2- 、SO 4 2- 、OH - 、SiO 3 2- 、PO 4 3- 、CH 3 COO - 、CO 3 2- 、HCO 3 - 、C 2 O 4 2- Etc., more preferably NO 3 - 、Cl - 、CH 3 COO - One or more of (a) and (b).
Preferably, the anionic form of the divalent manganese precursor comprises NO 3 - 、Cl - 、SO 3 2- 、SO 4 2- 、OH - 、SiO 3 2- 、PO 4 3- 、CH 3 COO - 、CO 3 2- 、HCO 3 - 、C 2 O 4 2- Etc., more preferably NO 3 - 、Cl - 、CH 3 COO - One or more of (a) and (b).
Preferably, the heptavalent manganese precursor is permanganate, which is one or more of lithium permanganate, sodium permanganate, potassium permanganate, rubidium permanganate, magnesium permanganate, calcium permanganate and strontium permanganate, and is further preferably one or more of sodium permanganate and potassium permanganate.
Preferably, the molar ratio of the transition metal precursor to the rare earth precursor is 1.
Preferably, the molar ratio of the transition metal precursor to the divalent manganese precursor is 1.
Preferably, the molar ratio of the transition metal precursor to the heptavalent manganese precursor is 1 to 3, more preferably 2 to 3.
Preferably, the molar ratio of the divalent manganese precursor to the heptavalent manganese precursor is not less than 3.
Preferably, the alkaline solution is one or more of a NaOH solution, a KOH solution, a tetramethylammonium hydroxide solution, an aqueous ammonia solution, and the like, and further preferably a NaOH solution or a KOH solution.
Preferably, the solution has a pH of 8 to 14, more preferably 9 to 12.
Preferably, the heating temperature of the oven is 100-200 ℃, and further preferably 140-180 ℃.
Preferably, the heating time of the oven is 1 to 24 hours, and more preferably 3 to 8 hours.
The application of the amorphous manganese oxide composite material in catalytic decomposition of ozone is also within the protection scope of the invention.
Compared with the prior art, the invention has the beneficial effects that:
(1) The amorphous manganese oxide composite material of the invention provides a preparation method of a composite oxide with high specific surface area and rich pore channel structure.
(2) The amorphous manganese oxide composite material has strong oxidation-reduction capability and stability and catalytic oxidation activity through direct in-situ growth and mutual cooperation of transition metal oxide, rare earth oxide and manganese oxide.
(3) The amorphous manganese oxide composite material has a remarkable catalytic effect on ozone decomposition, and particularly has an excellent catalytic effect on ozone decomposition in the environments of high temperature, high concentration, ultralow temperature and high humidity which are troublesome in the field of ozone decomposition at present.
(4) The amorphous manganese oxide composite material has the advantages of wide raw material source, low cost, green and environment-friendly preparation method, high stability, long service life and easy realization of industrialization.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:
FIG. 1 is a graph of the concentration of ozone in an empty 20-hour tube used to explain the stability and accuracy of the concentration of ozone in the present specification;
FIG. 2 shows FeY, an amorphous manganese oxide composite obtained in example 1 of the present invention 2 Mn 2.5 O 9 X-ray diffraction pattern (XRD);
FIG. 3 is a schematic view of the apparatus for generating, reacting and detecting the mixed gas containing ozone according to the present invention;
FIG. 4 shows FeY, an amorphous manganese oxide composite obtained in example 1 of the present invention 2 Mn 2.5 O 9 Scanning Electron Micrographs (SEM);
FIG. 5 shows an amorphous manganese oxide composite FeY obtained in example 1 of the present invention 2 Mn 2.5 O 9 The BET adsorption/desorption curve of (1);
FIG. 6 shows an amorphous manganese oxide composite FeY obtained in example 1 of the present invention 2 Mn 2.5 O 9 The BJH pore size distribution test chart;
FIG. 7 shows an amorphous manganese oxide composite FeY obtained in example 1 of the present invention 2 Mn 2.5 O 9 Ozone degradation durability test (50 hours);
FIG. 8 shows FeY, an amorphous manganese oxide composite obtained in example 1 of the present invention 2 Mn 2.5 O 9 Benzene catalytic combustion test of (1);
FIG. 9 shows an amorphous manganese oxide composite FeY obtained in example 1 of the present invention 2 Mn 2.5 O 9 The propylene catalytic combustion test of (1);
FIG. 10 shows FeY, an amorphous manganese oxide composite obtained in example 1 of the present invention 2 Mn 2.5 O 9 CO catalytic oxidation test of (2).
Detailed Description
The following examples are intended to illustrate the invention, but not to further limit the scope of the invention. It should be noted that, in the present application, the embodiments and features of the embodiments may be combined with each other without conflict. The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.
The chemical general formula of the amorphous manganese oxide composite material is A x B y Mn z O v Wherein A is any one or more of first transition series transition metal elements (without manganese), B is any one or more of lanthanide series metal elements, bi and Y, x is more than 0 and less than or equal to 1, Y is more than 0 and less than or equal to 5, z is more than 0 and less than or equal to 9, and v is more than 0 and less than or equal to 25.
The A is selected from any one or more of Ti, V, cr, fe, co, ni, cu and Zn, and preferably the A is selected from any one or more of Fe, co and Ni.
In a preferred embodiment of the present application, the above-mentioned a must contain Fe, and the interaction between Fe and the rare earth metal element and the manganese element is more obvious, so that the catalytic ozone efficiency is more remarkably improved.
The B is selected from any one or more of La, ce, pr, nd, pm, sm, eu, gd, tb, dy, ho, er, tm, yb, lu, bi and Y, and preferably, the B is selected from any one or more of Sm, gd and Y.
In a preferred embodiment of the present application, the element B must contain Y, and the interaction between the element Y and the transition metal element and the manganese element is more significant, so that the improvement of the catalytic ozone efficiency is more prominent.
The invention provides an application of an amorphous manganese oxide composite material as a catalyst in catalytic decomposition of ozone. Has excellent catalytic effect of ozonolysis under the environment of high temperature, low temperature, high concentration and high humidity which is troublesome in the field of ozonolysis at present.
The invention mainly aims at a catalytic purification method, and through optimizing the design of a catalyst in the reaction process, the ozone pollutants can be efficiently treated and purified while the reaction temperature and the energy consumption are reduced, so that the method plays an extremely important role in pollution treatment of different industries, protection of atmospheric environment and guarantee of life health and safety of people.
The amorphous manganese oxide composite material contains Mn-O catalytic active sites, and strong p-d electron hybridization between Mn and O weakens the action of Mn and external O, so that the efficiency of small molecule oxidation is improved. Compared with the crystal manganese oxide, the amorphous manganese oxide has the characteristics of short-range order and long-range disorder, and metal ions in the short-range order structures can exert strong interaction at an atomic level, so that the catalyst shows extremely excellent catalytic performance; and Mn related to multi-valence manganese ions and with rich valence states of manganese elements 2+ /Mn 3+ Or Mn 3+ /Mn 4+ The redox cycle of (a) is more favorable for the enhancement of its redox performance.
Under proper conditions, the addition of the transition metal element enables the composite material to form amorphous more easily under certain conditions, the specific surface area and active sites of the catalyst are greatly improved, the active sites of manganese decomposition ozone are more exposed on the surface, and meanwhile, the amorphous transition metal oxide can realize the room temperature decomposition of ozone through rich valence state and valence change capability, so that the effect of '1 +1 > 2' is realized. In addition, compared with the combination of common crystalline manganese oxide and transition metal oxide, the catalyst has more possible exposed crystal faces and exchange electron (bonding) possibility at the 'mass' level; at the level of 'number', the larger specific surface area enables the surface of the catalyst to have more active sites and pore channel structures. Because each oxide is in an amorphous state, a large number of crystal faces are staggered, and the strong interface effect generated between the staggered crystal faces can generally induce the electron transfer between different media, thereby changing the catalytic performance of the metal nano particles. In addition, electron transfer between different valence states of the transition metal element and between the transition metal element and the manganese element provides more possibility for the decomposition of ozone on the catalyst. Therefore, compared with the combination of common crystalline manganese oxide and transition metal oxide catalysts, the catalyst disclosed by the invention can play a role in various scenes such as ultralow temperature, high humidity, large air volume, high ozone concentration and the like, and has excellent ozone purification effect and industrial application potential.
Furthermore, if rare earth elements are added, the physical and chemical properties of the composite material system are also greatly influenced. By adding rare earth elements, electrons and structures can be further stabilized, and the thermal stability of the material is enhanced. The introduction of rare earth elements greatly increases the electron exchange and crystal face exposure among active components, and further improves the catalytic decomposition effect of ozone.
The amorphous manganese oxide composite material has higher combination stability among the components than a physical loading mode, so the stability of catalyzing and purifying ozone by utilizing the amorphous manganese oxide composite material is higher, and the service life is longer; the amorphous manganese oxide composite material does not contain noble metal, so the cost is lower; meanwhile, the preparation method of the composite material is mature and simple, so that the mass production can be realized to better solve the problem in the existing ozone treatment field; furthermore, experiments prove that the composite material can play a good catalytic effect on ozone in high-low temperature, high-low humidity, high-low air volume and high-low concentration environments, so that the composite material can be suitable for ozone purification treatment in different industries.
The amorphous manganese oxide composite material has the advantages of small particle size, multiple pore channel structures, high specific surface area and multiple exposed active sites, and can catalyze ozone to decompose under severe conditions.
When the amorphous manganese oxide composite material is applied as a catalyst for catalytic purification of ozone, the powder of the amorphous manganese oxide composite material can be granulated and put into equipment for use. In order to reduce the cost of catalysis and to minimize catalyst loss during processing due to gas purging, it is preferred that the amorphous manganese oxide composite be mixed with a support to form a composite catalyst. For example, the solution and/or slurry of the amorphous manganese oxide composite material is coated on a carrier such as a carbon material, a ceramic material, a foam material or a solid acidic material, so that the carrier is used for immobilizing the amorphous manganese oxide composite material, thereby being beneficial to the passing of the gas to be treated and the contact with the catalyst on one hand, reducing the loss of the catalyst on the other hand, prolonging the service life of the catalyst and reducing the use cost of the catalyst; meanwhile, the specific surface area of the loaded integral composite catalyst can be increased, and the catalytic efficiency is further improved. It is further preferred that the support is ZrO 2 、TiO 2 、SiO 2 、WO 3 、Nb 2 O 5 、SnO 2 、Al 2 O 3 、Co 3 O 4 、CeO 2 、Fe 2 O 3 Activated carbon, graphene, clay, zeolite, metal organic framework, covalent organic framework, honeycomb ceramic, foamed ceramic, cermet, foam, sponge, polyurethane cotton, non-woven fabric. Of course, in addition to the above-mentioned carriers, carriers currently used for ozone treatment catalysts can be applied to the present application, and are not listed here.
When the compound is used as a catalyst for catalytic purification of ozone, the catalytic conditions, the process flow and the like of the compound are compatible with those of the prior art, for example, the amorphous manganese oxide composite material is used for replacing the prior catalyst, and other process parameters and equipment maintain original data.
In one embodiment of the present application, the above application comprises contacting the ozone-containing gas stream at a temperature in the range of-40 ℃ to 500 ℃ (preferably in the range of-20 ℃ to 50 ℃, more preferably in the range of 0 ℃ to 25 ℃), under the catalytic action of the amorphous manganese oxide composite. The temperature range does not mean that ozone gas can be treated only in the temperature range, but is obtained under certain catalyst and certain treatment conditions.
The advantageous effects of the present application will be further described below with reference to examples and comparative examples.
Aiming at the treatment of gas flow containing ozone, the performance of catalytic ozone when the amorphous manganese oxide composite material is used as a catalyst is tested by adopting a constant-temperature and constant-humidity environment, and specifically:
a certain amount of catalyst is taken to be pelletized (40-60 meshes) and then is placed in a reaction tube with the inner diameter of 4 mm, and air flow containing a certain amount of ozone gas is introduced. The ozone conversion device realizes intermittent temperature and humidity change through the constant-temperature and constant-humidity box, the air distribution device and the ozone generator, can adjust the flow and the concentration at the same time, is constant in a certain time, detects the ozone concentration in every two seconds through the ozone detector, and calculates the ozone conversion rate. Wherein the test time for each of the examples and comparative examples in the present invention is at least 10 hours, and the conditions are unchanged for 10 hours, and the ozone concentration per hour is defined as the sum of the average values of the ozone concentration data collected over the period. The final product of the catalyst-converted ozone is oxygen, and no other by-product gas is produced.
The design of the test refers to the national standard manganese series ozone decomposition catalyst activity test method (HG/T5419-2018), including filler, leakage detection, ozone concentration calculation methods and the like, and regarding ozone detection means, the test in the patent application directly adopts a calibrated commercial ozone detector (3S-J5000, ozone in the same forest) for testing, concentration determination can be carried out in real time, the commercial ozone detector conforms to the national ozone generator safety and sanitation standard (GB 28232-2011), the ozone concentration test is carried out by adopting the principle of an ultraviolet light absorption method, and the detailed content can refer to corresponding national standard. Aiming at the stability of the test, the standard HG/T5419-2018 requires that the analysis is carried out once every 0.5-1 hour under the same state, and if the extreme difference value of the ozone conversion rate of continuous 3 times of analysis is less than or equal to 1 percent, the experiment can be ended and the stability is determined. In the test of this patent application, each test lasts at least 10 hours, can guarantee the stability and the accuracy of test result. Wherein, the empty reaction tube was tested for ozone concentration for 20 hours, the graph of ozone concentration is shown in FIG. 1, the average value in 20 hours is 100 ppm, and the maximum deviation rate is less than 0.1%, therefore, the stability and accuracy of the test are determined. The ozone generating, reacting and detecting device is shown in fig. 2.
Example 1
Preparation of amorphous manganese oxide composite FeY 2 Mn 2.5 O 9 The method comprises the following steps:
(1) Adding 1 mmol of ferrous nitrate, 2 mmol of yttrium nitrate, 1.5 mmol of manganese nitrate and 1 mmol of potassium permanganate into 40 ml of deionized water, and fully stirring and mixing for 1 hour;
(2) Slowly dripping the prepared KOH solution into the solution until superfine precipitates are completely generated, wherein the pH of the solution is =10, and continuously stirring for 1 hour;
(3) Adding the mixed solution obtained by fully stirring into a 100 ml polytetrafluoroethylene lining, putting into a reaction kettle, and heating in an oven at 180 ℃ for 5 hours;
(4) Filtering, washing, centrifuging or suction filtering and drying the heated filtrate to obtain the amorphous manganese oxide composite material with the theoretical chemical formula of FeY 2 Mn 2.5 O 9 。
Example 1 amorphous manganese oxide composite FeY 2 Mn 2.5 O 9 The XRD test result shows that the crystal is in an amorphous phase structure, and is shown in figure 3; the morphology is nano-particle, the SEM test result is shown in figure 4, and the particle size of the microscopic nano-particle is between 25 and 45 nm; the BET and BJH test results are shown in FIGS. 5 and 6, respectively, and the specific surface area is 475.4 m 2 (ii) in terms of/g. The BET adsorption and desorption curves are a typical IV-type isothermal curve and an H3-type hysteresis curve, which show that the BET adsorption and desorption curves have a large amount of micropores and mesoporous structures. BJH pore size distribution curve is the same as that of the pore size distribution curveThe porous composite material can clearly see a large number of micropores and mesoporous structures, wherein the micropores are mainly distributed at about 0.4 nm, the mesopores are mainly distributed at about 3.2 nm, the abundant micropore structures provide a large number of specific surface areas and reaction active sites for the composite material, and the distribution of the hierarchical pore structures is beneficial to various reactions.
The obtained amorphous manganese oxide composite catalyst is used for decomposing ozone pollutants at room temperature, and the specific reaction conditions are as follows:
and (2) introducing an ozone mixed gas with the concentration of 100 ppm into the reaction tube, wherein the gas flow is 1.2L/min, in order to ensure that the test gas flow is smoother and the diffusion pressure is reduced, carrying out granulation treatment on the catalyst, and selecting particles with the particle size of 40-60 meshes for ozone catalysis. The specific dosage of the catalyst is 100 mg, and the reaction space velocity is 720000 ml/g -1 ·h -1 The reaction temperature was 25 deg.C (room temperature). The change in ozone concentration with time was recorded by an ozone detector, the test time was 10 hours, and the ozone conversion rate was represented by the ozone consumption rate.
After a plurality of tests, the results show that the catalyst has the capability of efficiently decomposing ozone at room temperature, and the test results and the corresponding specific surface area data are shown in table 1. The test time is prolonged to 50 hours, and the test result is shown in figure 7, which shows that the amorphous manganese oxide composite catalyst FeY 2 Mn 2.5 O 9 Has excellent catalytic stability for ozone decomposition.
In order to examine the stability and thermal shock resistance of the catalyst, the catalyst was subjected to a high-temperature treatment at 500 ℃ for 2 hours. The room temperature ozone pollutant decomposition experiment is carried out on the treated catalyst under the same conditions, the test result and the corresponding specific surface area data are shown in the table 2, and the catalytic effect can be still maintained although the specific surface area is slightly reduced.
Further, the catalyst was subjected to benzene oxidation, propylene oxidation, and CO oxidation experiments, as shown in fig. 8, 9, and 10, respectively. It can be seen that the catalyst has excellent performance in the fields of VOC, CO catalytic combustion and the like.
The experimental conditions are as follows:
benzene oxidation: the dosage of the catalyst is 100 mg; the particle size is 40-60 meshes; benzene concentration 250 ppm; carrying gas air; the gas flow is 40 mL/min; the reaction space velocity is 24000 mL/(g.h); the holding time for each temperature period was 40 minutes.
Oxidation of propylene: the dosage of the catalyst is 100 mg; the particle size is 40-60 meshes; the propylene concentration was 1000 ppm; carrying gas air; the gas flow is 40 mL/min; the reaction space velocity is 24000 mL/(g.h); the temperature is kept for 40 minutes at each temperature stage.
CO oxidation: the dosage of the catalyst is 100 mg; the particle size is 40-60 meshes; CO concentration 6662 ppm; carrying gas air; the gas flow is 100 mL/min; the reaction space velocity is 60000 mL/(g.h); the holding time for each temperature period was 40 minutes.
Example 2
Preparing amorphous manganese oxide composite CuY 2 Mn 2.5 O 9 The reaction mixture was used for room temperature ozonolysis reaction, the procedure was the same as in example 1 except that ferrous nitrate was changed to cupric nitrate.
The obtained amorphous manganese oxide composite CuY was processed in the same manner as in example 1 2 Mn 2.5 O 9 When the catalyst is used for room-temperature ozonolysis reaction, the result shows that the catalyst has high ozone decomposing capacity at room temperature, and the test result and the corresponding specific surface area are shown in the following table 1.
Example 3
Preparation of amorphous manganese oxide composite FeLa 2 Mn 2.5 O 9 The reaction mixture was used for room temperature ozonolysis reaction, the preparation procedure was the same as in example 1 except that yttrium nitrate was changed to lanthanum nitrate.
The amorphous manganese oxide composite material FeLa thus obtained was subjected to the same procedure as in example 1 2 Mn 2.5 O 9 When the catalyst is used for room-temperature ozonolysis reaction, the result shows that the catalyst has high ozone decomposing capacity at room temperature, and the test result and the corresponding specific surface area are shown in the following table 1.
Example 4
Preparation of amorphous manganese oxide composite FeYMn 1.25 O 5 Was used for the ozonolysis reaction at room temperature, and the preparation was the same as in example 1 except that the amount of ferrous nitrate was changed to 2 mmol.
The amorphous manganese oxide composite FeYMn thus obtained was subjected to the same procedure as in example 1 1.25 O 5 When the catalyst is used for room-temperature ozonolysis reaction, the result shows that the catalyst has high ozone decomposing capacity at room temperature, and the test result and the corresponding specific surface area are shown in the following table 1.
Example 5
Preparation of amorphous manganese oxide composite FeY 3 Mn 2.5 O 10.5 Was used for the ozonolysis reaction at room temperature, and the preparation was the same as in example 1 except that the amount of yttrium nitrate was changed to 3 mmol.
The amorphous manganese oxide composite FeY thus obtained was subjected to the same procedure as in example 1 3 Mn 2.5 O 10.5 When the catalyst is used for room-temperature ozonolysis reaction, the result shows that the catalyst has high ozone decomposing capacity at room temperature, and the test result and the corresponding specific surface area are shown in the following table 1.
In order to examine the stability and thermal shock resistance of the catalyst, the catalyst was subjected to a high-temperature treatment at 500 ℃ for 2 hours. The room temperature ozone pollutant decomposition experiment is carried out on the treated catalyst, the condition of example 1 is shown in the table 2, the test result and the corresponding specific surface area data are shown in the table 2, and the catalytic effect can be still maintained although the specific surface area is slightly reduced.
Example 6
Preparation of amorphous manganese oxide composite FeY 0.2 Mn 2.5 O 6.3 Was used for ozonolysis reaction at room temperature, and the preparation was the same as in example 1 except that the amount of yttrium nitrate was changed to 0.2 mmol.
The amorphous manganese oxide composite FeY thus obtained was subjected to the same procedure as in example 1 0.2 Mn 2.5 O 6.3 When the catalyst is used for room-temperature ozonolysis reaction, the result shows that the catalyst has high ozone decomposing capacity at room temperature, and the test result and the corresponding specific surface area are shown in the following table 1.
In order to examine the stability and thermal shock resistance of the catalyst, the catalyst was subjected to a high-temperature treatment at 500 ℃ for 2 hours. The treated catalyst is subjected to a room temperature ozone pollutant decomposition experiment, the condition of example 1 is shown in table 2, the test result and the corresponding specific surface area data are shown in table 2, the specific surface area is obviously reduced, and the catalytic effect is also reduced to a certain degree.
Example 7
Preparation of amorphous manganese oxide composite FeY 2 Mn 4 O 10.5 Was used for ozonolysis at room temperature, and the preparation was the same as in example 1 except that the amount of manganese nitrate was changed to 3 mmol.
The amorphous manganese oxide composite FeY thus obtained was subjected to the same procedure as in example 1 2 Mn 4 O 10.5 When the catalyst is used for room-temperature ozonolysis reaction, the result shows that the catalyst has high ozone decomposing capacity at room temperature, and the test result and the corresponding specific surface area are shown in the following table 1.
Example 8
Preparation of amorphous manganese oxide composite FeY 2 Mn 2.5 O 9 (100 ℃ C.) was used for the room-temperature ozonolysis reaction in the same manner as in example 1 except that the heating temperature in step (3) was changed to 100 ℃.
The amorphous manganese oxide composite FeY thus obtained was subjected to the same procedure as in example 1 2 Mn 2.5 O 9 The catalyst is used for room temperature ozonolysis reaction at 100 ℃, and the result shows that the catalyst has high ozone decomposing capacity at room temperature, and the test result and the corresponding specific surface area are shown in the following table 1.
Example 9
Preparation of amorphous manganese oxide composite FeY 2 Mn 2.5 O 9 (200 ℃ C.) was used for the ozonolysis reaction at room temperature in the same manner as in example 1 except that the heating temperature in step (3) was changed to 200 ℃.
The amorphous manganese oxide composite FeY thus obtained was subjected to the same procedure as in example 1 2 Mn 2.5 O 9 The catalyst is used for room temperature ozonolysis reaction at (200 ℃) and has high ozone decomposing capacity at room temperature, and the test result and the corresponding specific surface area are shown in the following table 1.
Example 10
Preparation of amorphous manganese oxide composite FeY 2 Mn 2.5 O 9 (12 hours) for room temperature ozonolysis reaction in the same manner as in example 1 except that the heating time in step (3) was changed to 12 hours.
The amorphous manganese oxide composite FeY thus obtained was subjected to the same procedure as in example 1 2 Mn 2.5 O 9 The catalyst is used for room temperature ozonolysis reaction (12 hours), the result shows that the catalyst has high ozone decomposing capacity at room temperature, and the test result and the corresponding specific surface area are shown in the following table 1.
Example 11
Preparation of amorphous manganese oxide composite FeY 2 Mn 2.5 O 9 (pH = 13) for room temperature ozonolysis reaction prepared as in example 1 except that more KOH was added to make the pH of the mixed solution =13.
The amorphous manganese oxide composite FeY thus obtained was subjected to the same procedure as in example 1 2 Mn 2.5 O 9 (pH = 13) was used in the room temperature ozonolysis reaction, and the results showed that the catalyst has high ozone decomposing ability at room temperature, and the test results and the corresponding specific surface area are shown in table 1 below.
Example 12
Preparation of amorphous manganese oxide composite FeY 2 Mn 2.5 O 9 (aqueous ammonia solution) for room temperature ozonolysis reaction, the procedure was the same as in example 1 except that the precipitant KOH solution was changed to an aqueous ammonia solution.
The amorphous manganese oxide composite FeY thus obtained was subjected to the same procedure as in example 1 2 Mn 2.5 O 9 (aqueous ammonia solution) is used for the room temperature ozonolysis reaction, the result shows that the catalyst has high ozone decomposing capacity at room temperature, and the test result and the corresponding specific surface area are shown in the following table 1.
Example 13
Preparation of amorphous manganese oxide composite FeY 2 Mn 2.5 O 9 (ferric sulfate) for room temperature ozonolysis reaction, the preparation process is the same as example 1, except that the precursor is changed from ferric nitrateIs ferric sulfate.
The amorphous manganese oxide composite FeY thus obtained was subjected to the same procedure as in example 1 2 Mn 2.5 O 9 The (ferric sulfate) is used for the room-temperature ozonolysis reaction, the result shows that the catalyst has high ozone decomposing capacity at room temperature, and the test result and the corresponding specific surface area are shown in the following table 1.
Comparative example 1
Preparation of crystalline manganese oxide composite FeY 2 Mn 2.5 O 9 (240 ℃ C.) was used for the ozonolysis reaction at room temperature in the same manner as in example 1 except that the heating temperature in step (3) was changed to 240 ℃.
The obtained crystalline manganese oxide composite FeY was subjected to the same procedure as in example 1 2 Mn 2.5 O 9 The catalyst has certain ozone decomposing capacity at room temperature, and the test results and the corresponding specific surface area are shown in the following table 1.
Comparative example 2
Chinese patent CN104084192A discloses manganese oxide, rare earth and transition metal composite oxide supported on activated carbon. For better comparison, a reference catalyst 1 was prepared according to the synthesis method disclosed in chinese patent CN104084192A, and the synthesis method of the reference catalyst 1 is as follows:
taking 50% manganese nitrate aqueous solution, cerium nitrate, ferric nitrate and honeycomb activated carbon as raw materials, preparing 1.5% solution according to the proportion that the loading amounts of manganese oxide, iron oxide and cerium oxide are 7.5%, 3.5% and 1%, drying the solution by excessive impregnation of the activated carbon, and calcining the dried solution in a tubular furnace for 8 hours in a nitrogen atmosphere at the temperature of 320 ℃ to obtain a reference catalyst MnCeFeO x /C。
The reference catalyst MnCeFeO x The result shows that the catalyst has certain capability of decomposing ozone at room temperature, and the test result and the corresponding specific surface area are shown in the following table 1.
Comparative example 3
Chinese patent CN110420636A discloses a lanthanum modified manganese oxide catalyst, its preparation method and its application. For better comparison, reference catalyst 2 was prepared according to the synthesis method disclosed in chinese patent CN110420636A, and the synthesis method of reference catalyst 2 is as follows:
(1) Dissolving manganese sulfate monohydrate and potassium permanganate in deionized water according to a molar ratio of 3;
(2) Carrying out hydrothermal treatment on the mixed solution obtained in the step (1), wherein the hydrothermal treatment condition is that the temperature is 90 ℃ and the time is 24 hours, and after the hydrothermal treatment is finished, sequentially washing, filtering and drying the obtained solid product by using deionized water to obtain a black solid;
(3) Preparing lanthanum nitrate hydrate into a solution with a certain concentration, adding the solution into the black solid obtained in the step (2), uniformly stirring the solution, and standing the mixture for a period of time to obtain a mixture A, wherein the mass ratio of La atoms in lanthanum salt to Mn atoms in the black solid is m La :m Mn ＝0.005:1；
(4) Drying the mixture A in an oven at 80 ℃ for 12 hours to obtain a mixture B;
(5) Placing the mixture B in a muffle furnace, heating from room temperature to 300 ℃ at the heating rate of 3 ℃/min, and roasting at constant temperature for 4 hours to obtain 0.5% -La-MnO 2 A lanthanum modified manganese oxide catalyst.
0.5% -La-MnO of reference catalyst 2 When the catalyst is used for room-temperature ozonolysis reaction, the result shows that the catalyst has certain capability of decomposing ozone at room temperature, and the test result and the corresponding specific surface area are shown in the following table 1.
TABLE 1 ozone decomposition test results at room temperature for different catalysts and corresponding specific surface area
TABLE 2 test results of ozone decomposition at room temperature after 500 deg.C treatment of different catalysts and corresponding specific surface areas
As can be seen from the results in Table 1 and FIG. 7, the amorphous manganese oxide composite FeY was prepared 2 Mn 2.5 O 9 Has excellent ozone catalytic degradation activity, and the effect is still maintained to be more than 99 percent in a durability test of 50 hours. Further, it can be seen that the catalytic effect of ozone degradation is affected by various factors such as the kind, content, specific surface area, degree of crystallization, etc. of the active component.
The kind and content of the active ingredient were changed by changing the element composition and element content (examples 1 to 7). When the transition metal element is changed from Fe to Cu, the specific surface area is greatly reduced, but the conversion rate is reduced from 99.6% to 83.5%, and the Fe with more valence-change spaces can be amorphous MnO x Providing more electron transfer and more active sites. When only the rare earth element Y is changed to La, the ozone conversion rate is not greatly different, but once the content of Y is increased, Y, which is relatively less effective, is relatively less effective 2 O 3 Space for the active material is squeezed, resulting in a decrease in catalytic performance.
The specific surface area (degree of crystallization) and the active species were varied by varying the heating time, heating temperature, pH, kind of precipitant, kind of precursor in the preparation conditions (examples 8 to 13). When the heating temperature is too low (or the reaction time is extremely short), there is not enough energy to allow the redox reaction to proceed, and a large amount of Fe and Mn will exist in a lower valence state, and although it is amorphous and has an extremely large specific surface area, the catalytic effect is significantly reduced due to too few active sites. By combining the analysis of the comparative example 1, when the heating temperature is higher or the reaction time is prolonged, the amorphous state is gradually changed into the crystalline state, the specific surface area is greatly reduced, the number of active sites is greatly reduced, and the catalytic effect is reduced; and each staggered crystal face further grows, the interface effect is reduced, more frequent electron transfer is lacked, the types and the number of active sites are reduced, and the ozone catalytic effect is further reduced. In addition, by selecting proper precipitator and precursor and adjusting proper pH value, the formation of amorphous state (namely, the increase of specific surface area and the enhancement of interface effect) can be promoted, and a better ozone catalytic degradation effect is achieved. When the precipitant is changed from ammonia water solution to KOH solution, or the transition metal precursor is changed from sulfate to nitrate, or the pH value of the solution is adjusted from 13 to 10, the specific surface area of the catalyst is reduced to different degrees, which corresponds to the reduction of the catalytic ozone activity of the catalytic material.
The catalysts synthesized in comparative examples 1, 2 and 3 have low specific surface area and no strong interface effect, so that the composite catalyst has limited catalytic effect, which is far lower than that of the amorphous catalyst FeY in example 1 2 Mn 2.5 O 9 。
Also, although the amorphous material has a high specific surface area, can provide a large number of active sites and produce a strong interface effect, upon the input of a large amount of energy from the outside (e.g., high-temperature heating), the catalyst is easily transformed from the amorphous state to the crystalline state, thereby losing a large number of active sites, resulting in a decrease in the effect (similar to comparative examples 1 to 3). Therefore, the supporting and stabilizing effects of the rare earth elements cannot be lost. As can be seen from Table 2, feY was also treated at 500 ℃ for 2 hours 2 Mn 2.5 O 9 And FeY 3 Mn 2.5 O 10.5 The catalytic effect of (A) is almost reduced, while FeY 0.2 Mn 2.5 O 6.3 The specific surface area and the catalytic effect are greatly reduced, which shows the supporting and stabilizing effects of the rare earth element on the composite catalyst to the material at high temperature.
The examples are provided to further illustrate the present invention, but it should be understood that the above description is only a preferred example of the present invention and is not intended to limit the present invention. It will be understood by those skilled in the art that various modifications and changes may be made without departing from the scope of the invention and are intended to be included within the scope of the invention.
Claims (9)
1. The amorphous manganese oxide composite material is characterized in that the chemical general formula of the composite material is A x B y Mn z O v Wherein A is one or more of first transition metal elements excluding manganese, B is one or more of lanthanide metal elements, bi and Y, x is more than 0 and less than or equal to 1, Y is more than 0 and less than or equal to 5, z is more than 0 and less than or equal to 9, and v is more than 0 and less than or equal to 25; a is selected from any one or more of Ti, V, cr, fe, co, ni and Zn,
the preparation method of the composite material comprises the following steps:
(1) Adding a rare earth metal precursor, a transition metal precursor, a divalent manganese precursor and a heptavalent manganese precursor into deionized water, and fully stirring, dissolving and mixing for more than 0.5 hour;
(2) Slowly dripping the prepared alkaline solution into the solution until superfine precipitates are completely generated, keeping the pH of the solution at 8-14, and continuously stirring for more than 0.5 hour;
(3) Adding the mixed solution obtained by stirring into a reaction kettle, and heating in an oven; the heating temperature of the oven is 100-200 ℃; the heating time is 1-24 hours;
(4) And filtering, washing, centrifuging or suction filtering and drying the heated filtrate to obtain the amorphous manganese oxide composite material.
2. The amorphous manganese oxide composite of claim 1, wherein a is selected from any one or more of Fe, co and Ni.
3. The amorphous manganese oxide composite of claim 1, wherein B is selected from any one or more of La, ce, pr, nd, pm, sm, eu, gd, tb, dy, ho, er, tm, yb, lu, bi and Y.
4. The amorphous manganese oxide composite of claim 1, wherein the specific surface area of the composite is in the range of 100-600 m 2 Between/g.
5. A method for preparing the amorphous manganese oxide composite material according to claim 1, comprising the steps of:
(1) Adding a rare earth metal precursor, a transition metal precursor, a divalent manganese precursor and a heptavalent manganese precursor into deionized water, and fully stirring, dissolving and mixing for more than 0.5 hour;
(2) Slowly dripping the prepared alkaline solution into the solution until superfine precipitates are completely generated, keeping the pH of the solution at 8-14, and continuously stirring for more than 0.5 hour;
(3) Adding the mixed solution obtained by stirring into a reaction kettle, and heating in an oven; the heating temperature of the oven is 100-200 ℃; the heating time is 1-24 hours;
(4) And filtering, washing, centrifuging or suction filtering and drying the heated filtrate to obtain the amorphous manganese oxide composite material.
6. The method according to claim 5, wherein in the step (1), the anion form of the transition metal precursor, the rare earth metal precursor, or the divalent manganese precursor includes NO 3 - 、Cl - 、SO 3 2- 、SO 4 2- 、OH - 、SiO 3 2- 、PO 4 3- 、CH 3 COO - 、CO 3 2- 、HCO 3 - 、C 2 O 4 2- One or more of (a); the heptavalent manganese precursor is permanganate, and the permanganate is one or more of lithium permanganate, sodium permanganate, potassium permanganate, rubidium permanganate, magnesium permanganate, calcium permanganate and strontium permanganate.
7. The preparation method according to claim 5, wherein the molar ratio of the transition metal precursor to the rare earth precursor in step (1) is 1 to 5; the molar ratio of the transition metal precursor to the divalent manganese precursor is 1 to 6 to 4; the molar ratio of the transition metal precursor to the heptavalent manganese precursor is 1; the molar ratio of the divalent manganese precursor to the heptavalent manganese precursor is not less than 3.
8. The method according to claim 5, wherein the alkaline solution in the step (2) is one or more of NaOH solution, KOH solution, tetramethylammonium hydroxide solution, and aqueous ammonia solution.
9. The amorphous manganese oxide composite material of claim 1, as a catalyst for catalytic reactions of catalytic decomposition of ozone, catalytic combustion of VOCs, degradation of formaldehyde, catalytic oxidation of CO, catalytic oxidation of nitrogen oxides, deodorization.
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