CN116060080A - Composite metal oxide catalyst and preparation method and application thereof - Google Patents

Composite metal oxide catalyst and preparation method and application thereof Download PDF

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CN116060080A
CN116060080A CN202310077484.9A CN202310077484A CN116060080A CN 116060080 A CN116060080 A CN 116060080A CN 202310077484 A CN202310077484 A CN 202310077484A CN 116060080 A CN116060080 A CN 116060080A
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metal oxide
composite metal
oxide catalyst
cerium
manganese
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安太成
何宇钊
彭洪根
刘宏利
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Guangdong University of Technology
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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
    • B01J29/00—Catalysts comprising molecular sieves
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/86—Catalytic processes
    • B01D53/8678—Removing components of undefined structure
    • B01D53/8687—Organic components
    • B01J35/56—
    • B01J35/615—
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/206—Rare earth metals
    • B01D2255/2065—Cerium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/207—Transition metals
    • B01D2255/2073—Manganese
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/40—Mixed oxides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/70—Organic compounds not provided for in groups B01D2257/00 - B01D2257/602
    • B01D2257/708—Volatile organic compounds V.O.C.'s
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
    • Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters

Abstract

The invention discloses a composite metal oxide catalyst, a preparation method and application thereof, and relates to the technical field of thermal catalytic treatment of organic pollutants. According to the invention, the manganese oxide and the cerium oxide are encapsulated in the silicon dioxide ball by improving the Stirling process, then the silicon dioxide is transformed into the all-silicon molecular sieve, the structure of the all-silicon molecular sieve, the contents of the manganese oxide and the cerium oxide and the proportion of manganese element and cerium element are controlled, so that the low-temperature thermal catalytic activity, the water resistance and the adsorption performance of the composite metal oxide catalyst are synchronously improved, and the composite metal oxide catalyst has the functions of adsorbing and enriching and in-situ catalytic degradation of VOCs.

Description

Composite metal oxide catalyst and preparation method and application thereof
Technical Field
The invention relates to the technical field of thermal catalytic treatment of organic pollutants, in particular to a composite metal oxide catalyst and a preparation method and application thereof.
Background
Volatile Organic Compounds (VOCs) have a certain toxicity and are one of the most important sources causing atmospheric pollution and ozone overstock. The catalytic oxidation technology can directly degrade VOCs into pollution-free CO 2 And water, have the advantages of energy conservation, high efficiency, no secondary pollutants, and the like, and are considered to be one of the most effective and cost-effective techniques for removing VOCs.
The main technical core of the catalytic oxidation method is to design and prepare a high-efficiency catalyst. The catalyst adopted by the current catalytic oxidation method is mainly commercial Pd/Al 2 O 3 However, the catalyst has poor water resistance, reduced catalytic activity under the condition of water content and weak adsorption performance, and the catalyst needs to show corresponding activity at a higher temperature, and can cause reduced catalytic activity due to sintering of the catalyst and aggregation of active metal centers under the condition of high temperature for a long time, and Pd belongs to noble metal and has high cost. The composite metal oxide catalyst is used for replacing the noble metal catalyst, so that the catalytic oxidation temperature and cost can be reduced to a certain extent, but the existing composite metal oxide catalyst has poor water resistance, active sites are easy to combine with water molecules, so that the catalytic capability of the catalyst on VOCs is reduced, and the adsorption performance is also poor.
The prior art discloses a low-temperature SCR catalyst, the carrier of the catalyst is a compound of titanium dioxide and silicon dioxide, active components comprise manganese oxide and pre-vulcanized cerium oxide, the catalyst has certain water resistance, but the specific surface area is low, and the adsorption performance of the composite metal oxide catalyst cannot be considered at the same time.
Disclosure of Invention
The invention aims to overcome the defect and the defect that the existing composite metal oxide catalyst cannot simultaneously give consideration to low-temperature catalytic activity, water resistance and adsorption performance, and provides the composite metal oxide catalyst which is prepared by packaging manganese oxide and cerium oxide in an all-silicon molecular sieve, controlling the content of active components, and simultaneously regulating and controlling the proportion of manganese element and cerium element.
Another object of the present invention is to provide a method for preparing the above composite metal oxide catalyst.
It is a further object of the present invention to provide the use of the above composite metal oxide catalyst for the treatment of volatile organic compounds.
The above object of the present invention is achieved by the following technical scheme:
the composite metal oxide catalyst comprises an active component and a carrier, wherein the active component of the composite metal oxide catalyst is manganese oxide and cerium oxide, and the carrier is an all-silicon molecular sieve;
the manganese oxide and the cerium oxide are encapsulated in an all-silicon molecular sieve;
the mass content of the active component in the composite metal oxide catalyst is 6-15%, wherein the mass ratio of manganese element to cerium element is (1-2) (2-1).
The following are to be described:
the carrier of the composite metal oxide catalyst is an all-silicon molecular sieve, and is obtained by carrying out crystal transformation on silicon dioxide spheres, so that the dispersion of active components is improved due to the rich pore channel structure and the high specific surface area, the active components are highly dispersed, and the adsorption performance of the composite metal oxide catalyst is improved. After the active components of manganese oxide and cerium oxide are highly dispersed in the all-silicon molecular sieve, the active sites of the composite metal oxide catalyst are increased, and the content of the active components is controlled, so that the influence of competitive adsorption of water vapor on the adsorption performance of the catalyst is small, the catalytic activity is increased, and the all-silicon molecular sieve belongs to a hydrophobic molecular sieve.
Specifically, in the active component, the total mass content of manganese oxide and cerium oxide encapsulated in the all-silicon molecular sieve is more than or equal to 50 percent.
When the content of the active component in the composite metal oxide catalyst is too low, active sites are reduced, and when the content of the active component in the composite metal oxide catalyst is too high, metal aggregation can be caused, and the catalytic activity and the water resistance can be reduced. Specifically, the content of the carrier all-silicon molecular sieve in the composite metal oxide catalyst is 85-94%.
In addition, the active components of the composite metal oxide catalyst, namely manganese oxide and cerium oxide, can form manganese-cerium metal composite oxide, such as manganese-cerium solid solution, oxidation-reduction coupling can be generated between manganese and cerium, such as tetravalent manganese is reduced to trivalent manganese, and trivalent cerium is oxidized to tetravalent cerium, and oxygen vacancies can be formed in the process, so that adsorption and activation of gaseous oxygen are provided, and further degradation of VOCs is promoted, so that the composite metal oxide catalyst still has good catalytic oxidation performance under low-temperature conditions. In addition, the adsorption of small amounts of water vapor onto the composite metal oxide catalyst may generate active oxyhydrogen species, further promoting catalytic oxidation efficiency. Therefore, the molar ratio of manganese element to cerium element in the active component is controlled to improve the low-temperature catalytic performance of the composite metal oxide catalyst, and the catalytic activity is further improved.
Specifically, the mass ratio of the manganese element to the cerium element may be 1:1, 2:1, 1:2, and preferably 1:1.
In the composite metal oxide catalyst, more than half of manganese oxide and cerium oxide are encapsulated in the whole silicon molecular sieve, and the rest is loaded on the surface of the whole silicon molecular sieve to achieve the effect of high dispersion, meanwhile, the whole silicon molecular sieve has a pore channel structure which can expose more active sites, and the adsorption of the whole silicon molecular sieve to VOCs can directly generate in-situ catalytic oxidation reaction, so that the catalytic activity and catalytic efficiency of the catalyst are improved.
Specifically, the mass content of the active component in the composite metal oxide catalyst may be 6%, 10%, 12%, 14%, 15%.
Preferably, the mass content of the active component in the composite metal oxide catalyst is 10 to 14%, more preferably 10 to 12%, still more preferably 12%.
Specifically, the specific surface area of the all-silicon molecular sieve is 300-450 m 2 /g, for example, may be 300m 2 /g、350m 2 /g、400m 2 /g、420m 2 /g、430m 2 /g、450m 2 /g。
Preferably, the specific surface area of the all-silicon molecular sieve is 400-430 m 2 /g, more preferably 420m 2 /g。
The specific surface area of the all-silicon molecular sieve is controlled, so that the high dispersion of the active components of manganese oxide and cerium oxide in the all-silicon molecular sieve is facilitated, and the adsorption of the catalyst is further improved.
The invention specifically protects a preparation method of the composite metal oxide catalyst, which comprises the following steps:
s1, adding lower alcohol and ammonia water into a mixed solution of manganese salt and cerium salt, and uniformly mixing to obtain a suspension; the volume ratio of the mixed solution of the lower alcohol, the manganese salt and the cerium salt to the ammonia water is (70-80) 3:4; the total concentration of manganese ions and cerium ions in the mixed solution is 0.1 mol/L-0.8 mol/L;
s2, adding a silicon source into the suspension obtained in the step S1, and drying the obtained suspension after the silicon source is completely hydrolyzed to obtain a precursor;
s3, adding tetrapropylammonium hydroxide into the precursor obtained in the step S2, uniformly mixing and crystallizing; the mass ratio of the tetrapropylammonium hydroxide to the precursor is (0.5-1.5): 1; the crystallization temperature is 100-200 ℃;
s4, roasting the product obtained by crystallization in the step S3 to obtain a composite metal oxide catalyst; the roasting temperature is 500-800 ℃.
The lower alcohol in the step S1 is a solvent, specifically one of methanol, ethanol, n-propanol and n-butanol, and the selection of the solvent can influence the particle size of the silica spheres obtained in the step S2.
The silicon source in the step S2 undergoes two reactions of hydrolysis and polycondensation in suspension, and the silicon dioxide balls formed by polycondensation are used in the subsequent process of converting silicon dioxide into an all-silicon molecular sieve; the hydrolysis and polycondensation reaction is a process of generating silicon dioxide by the reaction of a silicon source and water, in the process, the hydrolysis can be promoted by increasing the ratio of water to the silicon source (namely the water-silicon ratio), but the silicon bonds generated can be broken due to the fact that the water-silicon ratio is too large, silicon dioxide balls can not be formed, manganese ions and cerium ions can not be packaged, and the silicon dioxide can not be converted into an all-silicon molecular sieve, so that the balance of the hydrolysis reaction and the polycondensation reaction needs to be controlled in the process.
The ammonia water in the step S1 is used as an alkaline catalyst, can control the particle size of the formed silicon dioxide, can inhibit the hydrolysis of a silicon source in the reaction process, and is beneficial to the occurrence of polycondensation reaction, so that the silicon dioxide particles with regular shapes are formed.
Specifically, the mass fraction of the ammonia water is 5-25%.
The mass fraction of ammonia can affect the rate of hydrolytic polycondensation of the silicon source and thus the morphology of the silica.
In the step S1, the volume ratio of the mixed solution of lower alcohol, manganese salt and cerium salt to ammonia water can influence the morphology and pore channel structure of silicon dioxide generated by the reaction, and the excessive proportion of manganese salt and cerium salt can lead to the unsuccessful formation of an all-silicon molecular sieve structure, thereby influencing the catalytic activity and the adsorption performance of the composite metal oxide catalyst; controlling the concentration of manganese ions and cerium ions in the mixed solution is a key for controlling the content of active components in the composite metal oxide catalyst, and too low a concentration of the active components is insufficient, so that incomplete and even failure of silicon dioxide crystal transformation can be caused by too high a concentration, and an all-silicon molecular sieve carrier can not be formed.
Specifically, the volume ratio of the lower alcohol, manganese salt and cerium salt mixed solution to ammonia water may be 70:3:4, 75:3:4, 80:3:4.
In the step S2, whether the silicon source is hydrolyzed and condensed completely directly influences the structure of the catalyst; the drying process is to remove residual lower alcohol solution and ammonia water to make the precursor a dry solid.
Specifically, the volume ratio of the silicon source to the lower alcohol in S1 is 3 (70-80).
Specifically, the silicon source is one of ethyl orthosilicate, silica sol and water glass.
The silicon source hydrolysis process conditions are as follows: stirring at 20-95 deg.c and hydrolyzing for 0.5-48 hr.
Specifically, the drying temperature is 80-100 ℃ and the drying time is 0.2-12 h.
Specifically, the silicon dioxide obtained by polycondensation of the silicon source has a spherical structure.
The manganese ions and the cerium ions need to be packaged in silicon dioxide, then crystal transformation and roasting are carried out, the packaging belongs to core-shell packaging, and the adoption of spherical silicon dioxide is beneficial to the realization of the full-silicon molecular sieve core-shell packaging of manganese oxide and cerium oxide.
The tetrapropylammonium hydroxide added in the step S3 plays a role of a guiding agent and a template agent, and guides the silicon dioxide to be converted into the all-silicon molecular sieve in the crystallization process, and the mass ratio of the tetrapropylammonium hydroxide to the precursor directly influences whether the silicon dioxide can be converted into the all-silicon molecular sieve. In addition, in the step S3, the crystallization adopts a steam dry gel crystal transformation method, the crystallization temperature is also a key factor of whether silicon dioxide can be recrystallized into an all-silicon molecular sieve, the crystallization is incomplete or even fails due to the excessively high temperature, the pore channel structure and the encapsulation morphology of the all-silicon molecular sieve can be influenced, and the dispersity and the adsorption performance of manganese oxide and cerium oxide are reduced; specifically, the mass ratio of tetrapropylammonium hydroxide to precursor can be 0.5:1, 0.75:1, 1:1, 1.33:1, 1.5:1.
Preferably, the mass ratio of tetrapropylammonium hydroxide to precursor is (1-1.5): 1, more preferably 1.33:1.
The mixing of the tetrapropylammonium hydroxide and the precursor is carried out in a grinding mode, and the total grinding time is 10-20 min.
Specifically, the crystallization temperature may be 100 ℃, 110 ℃, 120 ℃, 130 ℃, 150 ℃, 160 ℃, 200 ℃.
The calcination time and temperature in step S4 affect the oxidation of manganese and cerium ions, as well as the resulting dispersibility of manganese and cerium oxides and the removal of tetrapropylammonium hydroxide. Too high a temperature can cause aggregation of the active components, decrease of active sites and decrease of catalytic activity; the temperature is too low to thoroughly remove tetrapropylammonium hydroxide, so that impurities exist on the surface of the all-silicon molecular sieve, and even manganese ions and cerium ions cannot be thoroughly oxidized, and the catalytic efficiency of the composite metal oxide catalyst is reduced.
Specifically, the firing temperature may be 500 ℃, 600 ℃, 650 ℃, 700 ℃, 750 ℃, 800 ℃, preferably 650 to 750 ℃, more preferably 700 ℃.
Specifically, the manganese salt in the step S1 is one or more of manganese nitrate, manganese chloride and manganese sulfate.
Specifically, the cerium salt in the step S1 is cerium nitrate or cerium sulfate.
Specifically, the preparation method of the mixed solution of manganese salt and cerium salt can be referred to as follows:
adding manganese salt and cerium salt into deionized water, and dissolving at 20-80 ℃.
Specifically, the total concentration of manganese ions and cerium ions in the mixed solution of the step S1 is 0.2mol/L to 0.6mol/L, preferably 0.4mol/L to 0.5mol/L.
Further controlling the total concentration of manganese ions and cerium ions can control the content of metal ions, which is beneficial to the encapsulation of the metal ions by the silica spheres.
Specifically, the crystallization time in the step S3 is 12 to 72 hours, preferably 40 to 50 hours, and more preferably 48 hours.
The structure of the silica all-silicon molecular sieve can be better controlled by matching the crystallization time and the crystallization temperature.
Preferably, the crystallization temperature in the step S3 is 110 to 130 ℃, more preferably 120h.
Specifically, the roasting time in the step S4 is 0.2 to 12 hours, preferably 3 to 5 hours, and more preferably 4 hours.
Through the collocation of roasting time and roasting temperature, the removal of tetrapropylammonium hydroxide can be better controlled, and meanwhile, the active components are ensured not to be aggregated.
The invention particularly protects the application of the composite metal oxide catalyst in the treatment of volatile organic compounds.
The active components in the composite metal oxide catalyst are highly dispersed, oxygen vacancies can be formed by oxidation-reduction coupling action between manganese and cerium, in-situ catalytic oxidative degradation of VOCs is promoted, and the catalyst has good low-temperature catalytic oxidative performance, and can further prevent the catalyst deactivation caused by aggregation of the active components in the catalytic process. In addition, the composite metal oxide catalyst has excellent water resistance, and the catalytic activity is not reduced or even improved under the condition of containing water vapor.
Specifically, the composite metal oxide catalyst is assembled in a VOCs regenerative catalytic combustion method device or a catalytic oxidation combustion device to be treated for application.
Compared with the prior art, the invention has at least the following beneficial effects:
the invention provides a composite metal oxide catalyst and a preparation method and application thereof, wherein manganese oxide and cerium oxide are encapsulated in silicon dioxide balls by an improved Stirling method, and a full silicon molecular sieve is formed by conversion, the content of manganese oxide and cerium oxide and the proportion of manganese element and cerium element are controlled, so that the composite metal oxide catalyst has the functions of adsorption enrichment and in-situ catalytic degradation of VOCs.
The composite metal oxide catalyst contains 10vol.% of H 2 The catalytic oxidation is carried out on VOCs under the condition of O (g) steam, when the conversion rate of the VOCs reaches 90%, the temperature is not more than 250 ℃, and the water resistance and the low-temperature catalytic performance are good; in addition, the composite metal oxide catalyst adsorbs VOCs, the time for the VOCs to penetrate the catalyst and release again is not less than 30 minutes, and the adsorption performance is good.
Drawings
Fig. 1 is an overall scanning electron microscope image of the composite metal oxide catalyst of example 1.
Fig. 2 is a partial scanning electron microscope image of the composite metal oxide catalyst of example 1.
FIG. 3 is a graph comparing the efficiency of the catalysts of example 1 and comparative example 1 to acetone degradation.
FIG. 4 is a graph comparing adsorption curves of the catalysts of example 1 and comparative example 1 to acetone.
Detailed Description
The invention will be further described with reference to the following specific embodiments, but the examples are not intended to limit the invention in any way. Raw materials reagents used in the examples of the present invention are conventionally purchased raw materials reagents unless otherwise specified.
Example 1
The composite metal oxide catalyst comprises an active component and a carrier, wherein the active component of the composite metal oxide catalyst is manganese oxide and cerium oxide, and the carrier is an all-silicon molecular sieve;
the specific surface area of the all-silicon molecular sieve is 420m 2 /g；
The manganese oxide and the cerium oxide are encapsulated in an all-silicon molecular sieve;
in the composite metal oxide catalyst, the mass content of an active component is 12%, wherein the mass ratio of manganese element to cerium element is 1:1; the mass content of the all-silicon molecular sieve is 88%.
The preparation method of the composite metal oxide catalyst can refer to the following steps:
s1, adding absolute ethyl alcohol and ammonia water into a mixed solution of manganese nitrate and cerium nitrate hexahydrate, and continuously stirring for 2 hours at 35 ℃ to completely precipitate manganese ions and cerium ions in the mixed solution, thereby obtaining a suspension; wherein the volume ratio of the mixed solution of the absolute ethyl alcohol, the manganese salt and the cerium salt to the ammonia water is 80:3:4;
s2, slowly dropwise adding 6mL of ethyl orthosilicate into the suspension obtained in the step S1, continuously stirring at 35 ℃ for 24 hours to hydrolyze the ethyl orthosilicate to obtain a silicon dioxide precipitate, obtaining a suspension, and drying the suspension in a 100 ℃ oven for 12 hours to obtain a precursor; the volume ratio of the absolute ethyl alcohol in the S1 to the tetraethoxysilane in the S2 is 80:3;
s3, adding tetrapropylammonium hydroxide into the precursor obtained in the step S2, grinding for 15min in a mortar, and adding into a polytetrafluoroethylene reaction kettle for crystallization; the mass ratio of tetrapropylammonium hydroxide to precursor is 1.33:1; the crystallization temperature is 120 ℃; the crystallization time is 48 hours;
s4, roasting the product obtained by crystallization in the step S3 to obtain a composite metal oxide catalyst; the roasting temperature is 700 ℃, and the roasting time is 4 hours;
the mixing step of the manganese nitrate and the cerium nitrate hexahydrate in the step S1 is as follows:
manganese nitrate and cerium nitrate hexahydrate are added into 6mL of deionized water, and are stirred and dissolved at 35 ℃ to obtain a mixed solution with the total concentration of manganese ions and cerium ions of 0.467 mol/L.
Examples 2 to 8
A composite metal oxide catalyst, the structure and composition of which are the same as in example 1, except for the differences shown in Table 1.
TABLE 1 structural parameters of composite Metal oxide catalysts
Figure BDA0004066626120000071
Figure BDA0004066626120000081
Note that: the mass content of all-silicon molecular sieves in the catalysts of each example in table 1 above = 1-mass content of active component.
The procedure for preparing the composite metal oxide catalyst of each example in Table 1 above is the same as that of example 1, except for the differences shown in Table 2.
TABLE 2 preparation parameters of composite Metal oxide catalysts
Figure BDA0004066626120000082
Example 9
A method for preparing a composite metal oxide catalyst, which has the same steps as those of example 1, except that manganese nitrate in step S1 is replaced with manganese sulfate.
Example 10
A preparation method of a composite metal oxide catalyst comprises the steps as in example 1, except that cerium nitrate hexahydrate in the step S1 is replaced with cerium sulfate tetrahydrate.
Example 11
The preparation method of the composite metal oxide catalyst in embodiment 1 is the same as embodiment 1, except that in step S3, the crystallization temperature is 100 ℃ and the time is 72 hours; the roasting temperature is 500 ℃ and the roasting time is 12 hours.
Example 12
The preparation method of the composite metal oxide catalyst in embodiment 1 is the same as that in embodiment 1, except that in step S3, the crystallization temperature is 110 ℃ and the time is 50 hours; the roasting temperature is 650 ℃ and the roasting time is 5 hours.
Example 13
The preparation method of the composite metal oxide catalyst in embodiment 1 is the same as embodiment 1, except that in step S3, the crystallization temperature is 130 ℃ and the time is 40h; the roasting temperature is 750 ℃ and the roasting time is 3 hours.
Example 14
The preparation method of the composite metal oxide catalyst in embodiment 1 is the same as embodiment 1, except that in step S3, the crystallization temperature is 200 ℃ and the time is 24 hours; the roasting temperature is 800 ℃ and the time is 1h.
Comparative example 1
A carrier-free manganese-cerium composite metal oxide catalyst, the manganese-cerium composite metal oxide catalyst has a plate aggregation structure.
The preparation method of the manganese-cerium composite metal oxide catalyst can refer to the following steps:
s1, dissolving cerium nitrate hexahydrate and manganese nitrate in 50ml of deionized water, wherein the ratio of manganese ions to cerium ions is 1:1, and then adding citric acid monohydrate (CA), wherein the molar ratio of CA/(Mn+Ce) is kept at 1.2;
s2, after the citric acid monohydrate is completely dissolved, heating the mixture to 80 ℃ in a water bath, and maintaining the temperature under stirring until gel is formed;
s3, drying the gel obtained in the step S2 in an oven at 120 ℃ overnight to obtain a spongy material, calcining the material in a muffle furnace at 200 ℃ for 2 hours, and then increasing the temperature to 700 ℃ at a speed of 2 ℃/min for 2 hours to obtain the unsupported manganese-cerium composite metal oxide catalyst.
Comparative example 2
A preparation method of a composite metal oxide catalyst is the same as in example 1, except that cerium nitrate hexahydrate is not added in the step S1.
Comparative example 3
A preparation method of a composite metal oxide catalyst is the same as in example 1, except that manganese nitrate is not added in the step S1.
Comparative example 4
The composite metal oxide catalyst has the structure and the components same as those in the embodiment 1, and is characterized in that in the active components of the composite metal oxide catalyst, the mass ratio of manganese element to cerium element is 1:3.
the preparation method of the catalyst is the same as in example 1.
Comparative example 5
A composite metal oxide catalyst having the same composition as in example 1 except that the carrier of the composite metal oxide catalyst is silica.
The preparation method of the catalyst was the same as in example 1, except that step S3 was not performed, and the calcination temperature in step S4 was 550 ℃.
Result detection
(1) Low temperature catalytic performance test:
the catalysts of the above examples and comparative examples were each 80mg and were each tested in a fixed bed continuous flow quartz reactor, and the catalysts were purged with air at 300 ℃ for 2 hours, dried and activated before testing. The composition of the reaction gas is as follows: the acetone gas with the mass space velocity of 60000mLg is obtained by bubbling acetone through air as diluent gas to obtain 1000ppm acetone gas cat. -1 h -1 。
The catalytic reaction is carried out at 100-300 ℃, the heating rate is 1 ℃/min, and the temperature T of the catalyst when the acetone reaches 90% conversion rate is recorded 90-1 Lower temperatures indicate better low temperature catalytic performance.
(2) And (3) water resistance test:
the specific test method is the same as (1) the low-temperature catalytic performance testThe test was carried out with the difference that 10vol.% H was introduced into the reaction gas 2 O (g) water vapor, the temperature T of the catalyst at which 90% conversion of acetone is achieved is recorded 90 The lower the temperature, the higher the catalytic activity of the catalyst in the presence of water vapor, i.e. the better the water resistance.
In addition, the catalyst of example 1 was subjected to water resistance tests of different water vapor contents, the specific test method being as above, except that 3vol.% of H was introduced into the reaction gas, respectively 2 O(g)、5vol.％H 2 O(g)、7vol.％H 2 O(g)、10vol.％H 2 Water vapor with O (g) content.
(3) Adsorption performance test:
80mg of each catalyst of each example and comparative example is placed in an acetone reaction tube which is communicated with 1000ppm and has the flow rate of 70ml/min, the time is started when the catalyst is switched from an empty reaction tube state to a reaction tube filled with the catalyst at the temperature of 30 ℃, meanwhile, the concentration of acetone at the tail end of the reaction tube is started to be collected on line until the concentration of the acetone is recovered to the initial concentration, the time is stopped, and the adsorption penetration time from the adsorption of the acetone by the catalyst to the release of the acetone is obtained; the mass space velocity during the reaction is 60000mLg cat. -1 h -1 . The longer the adsorption breakthrough time, the better the adsorption performance of the catalyst.
The results are shown in Table 3.
TABLE 3 catalytic Properties of composite Metal oxide catalysts
T 90-1 (℃) T 90-2 (℃) Adsorption penetration time (min)
Example 1 179 178 45
Example 2 225 220 30
Example 3 195 197 35
Example 4 185 182 40
Example 5 202 206 35
Example 6 210 212 32
Example 7 205 205 42
Example 8 198 198 42
Example 9 186 188 45
Example 10 180 182 45
Example 11 185 183 40
Example 12 182 184 42
Example 13 192 190 42
Example 14 204 208 42
Comparative example 1 209 240 15
Comparative example 2 255 250 30
Comparative example 3 272 270 32
Comparative example 4 240 242 34
Comparative example 5 342 354 22
As can be seen from Table 3, the composite metal oxide catalyst of the present invention has low temperature thermal catalytic performance at a temperature of less than 250 ℃ when reaching 90% conversion, and 10vol.% H is introduced into the reaction gas 2 After the water vapor of O (g), the temperature corresponding to the 90% conversion rate is basically unchanged, which proves that the composite metal oxide catalyst also has excellent water resistance; meanwhile, in the adsorption performance test, the penetration time of the acetone to the catalyst is more than 30 minutes, and the adsorption performance of the catalyst is good; in examples 11 to 14, the crystallization conditions and calcination conditions of the composite metal oxide catalyst described in example 1 were changed, and the final composite metal oxide catalyst was different in activity, i.e., low temperature, due to the difference in crystallinity of the final all-silica molecular sieve, the difference in pore structure, the difference in the number of exposed active sites, and the influence of the calcination temperature on the dispersibility of the active componentsThe catalytic performance and the water resistance are different; in the comparative example 2, which is a single manganese oxide, and in the comparative example 3, which is a single cerium oxide, the catalytic activity of the obtained catalyst is reduced, and in the low-temperature performance test and the water resistance performance test, the temperature corresponding to the 90% conversion rate is above 250 ℃; the mass ratio of manganese to cerium in comparative example 4 is beyond the scope of the technical scheme of the invention, and the catalytic activity of the catalyst is also reduced; the manganese-cerium composite metal oxide catalyst in comparative example 1 is a non-carrier manganese-cerium composite metal oxide catalyst, and CA is added only to adjust the structure of the catalyst so that the catalyst has gaps, cannot aggregate into stone blocks, but has plate blocks, but has poorer water resistance and adsorption performance than the composite metal oxide catalyst of the invention; the catalyst in comparative example 5 is silica, and is not converted into an all-silicon molecular sieve, and the final catalyst has low-temperature catalytic performance, water resistance and adsorption performance.
The catalytic efficiency results for the composite metal oxide catalyst of example 1 at different temperatures at different water vapor contents are as follows: in water vapour 3vol.% H 2 T at O (g) 90 Temperature is 169 ℃,5vol.% H 2 T at O (g) 90 Temperature is 172 ℃,7vol.% H 2 T at O (g) 90 Temperature is 175 ℃,10vol.% H 2 T at O (g) 90 At 178 ℃, T as the water vapor content increases 90 Although the temperature is increased to some extent, the amplitude is not more than 10 ℃, which further indicates that the composite metal oxide catalyst has good water resistance.
Fig. 1 is an overall scanning electron microscope image of the composite metal oxide catalyst of example 1, and fig. 2 is a stacked scanning electron microscope image of the composite metal oxide catalyst of example 1, and it can be seen from fig. 1 and 2 that the characteristic morphology of the catalyst with silicon-1 (all-silicon molecular sieve) shows that silicon dioxide is successfully transformed into all-silicon molecular sieve, and meanwhile, manganese-cerium composite metal oxide on the outer surface of the molecular sieve is uniformly distributed and does not aggregate, thus showing that metal is well dispersed.
FIG. 3 is a graph showing the comparison of the acetone degradation efficiency of the catalysts of example 1 and comparative example 1, from which it can be seen that the examples1 (black curve) at T to 90% conversion 90 The temperature was 179℃and the catalyst of comparative example 1 (gray curve) T 90 The temperature was 209 ℃, demonstrating that example 1 of the present invention has better low temperature catalytic activity compared to the catalyst of comparative example 1.
Fig. 4 is a graph comparing the adsorption curves of the catalyst of example 1 and comparative example 1 to acetone, and it can be seen from the graph that the adsorption penetration time of the catalyst of experimental example 1 (black line) is 45 minutes, which is far longer than the adsorption time of the catalyst of comparative example 1 (gray line) by 15 minutes, indicating that the composite metal oxide catalyst of example 1 of the present invention contains an all-silicon molecular sieve structure, and has better adsorption performance than the catalyst of comparative example 1 which does not contain an all-silicon molecular sieve structure.
It is to be understood that the above examples of the present invention are provided by way of illustration only and not by way of limitation of the embodiments of the present invention. Other variations or modifications of the above teachings will be apparent to those of ordinary skill in the art. It is not necessary here nor is it exhaustive of all embodiments. Any modification, equivalent replacement, improvement, etc. which come within the spirit and principles of the invention are desired to be protected by the following claims.

Claims (10)

1. The composite metal oxide catalyst comprises an active component and a carrier, and is characterized in that the active component of the composite metal oxide catalyst is manganese oxide and cerium oxide, and the carrier is an all-silicon molecular sieve;
the manganese oxide and the cerium oxide are encapsulated in an all-silicon molecular sieve;
the mass content of the active component in the composite metal oxide catalyst is 6-15%, wherein the mass ratio of manganese element to cerium element is (1-2) (2-1).
2. The composite metal oxide catalyst according to claim 1, wherein the mass content of the active component in the composite metal oxide catalyst is 10 to 14%.
3. The composite metal oxide catalyst according to claim 1, wherein the specific surface area of the all-silicon molecular sieve is 300 to 450m 2 /g。
4. The composite metal oxide catalyst according to claim 1, wherein the specific surface area of the all-silicon molecular sieve silicon is 400-430 m 2 /g。
5. A method for producing the composite metal oxide catalyst according to any one of claims 1 to 4, comprising the steps of:
s1, adding lower alcohol and ammonia water into a mixed solution of manganese salt and cerium salt, and uniformly mixing to obtain a suspension; the volume ratio of the mixed solution of the lower alcohol, the manganese salt and the cerium salt to the ammonia water is (70-80) 3:4; the total concentration of manganese ions and cerium ions in the mixed solution is 0.1 mol/L-0.8 mol/L;
s2, adding a silicon source into the suspension obtained in the step S1, and drying the obtained suspension after the silicon source is completely hydrolyzed to obtain a precursor;
s3, adding tetrapropylammonium hydroxide into the precursor obtained in the step S2, uniformly mixing and crystallizing; the mass ratio of the tetrapropylammonium hydroxide to the precursor is (0.5-1.5): 1; the crystallization temperature is 100-200 ℃;
s4, roasting the product obtained by crystallization in the step S3 to obtain a composite metal oxide catalyst; the roasting temperature is 500-800 ℃.
6. The method according to claim 5, wherein the total concentration of manganese ions and cerium ions in the mixed solution of step S1 is 0.2mol/L to 0.6mol/L.
7. The method according to claim 5, wherein the crystallization time in the step S3 is 12 to 72 hours.
8. The process according to claim 5, wherein the crystallization temperature in step S3 is 110 to 130 ℃.
9. The method according to claim 5, wherein the calcination time in the step S4 is 0.2 to 12 hours.
10. Use of a composite metal oxide catalyst according to any one of claims 1 to 4 for the treatment of volatile organic compounds.
CN202310077484.9A 2023-01-17 2023-01-17 Composite metal oxide catalyst and preparation method and application thereof Pending CN116060080A (en)

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB777233A (en) * 1953-12-24 1957-06-19 Union Carbide & Carbon Corp Crystalline synthetic zeolites
CN105797749A (en) * 2016-04-06 2016-07-27 金华科海检测有限公司 Preparation and application of magnetic nano-photocatalyst adopting multi-layer core-shell structure
CN109746025A (en) * 2017-11-03 2019-05-14 中国石油化工股份有限公司 A kind of denitrating catalyst and its preparation method and application
CN113198459A (en) * 2021-03-29 2021-08-03 上海中船临港船舶装备有限公司 Catalyst for low-temperature catalytic combustion and preparation method and application thereof

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB777233A (en) * 1953-12-24 1957-06-19 Union Carbide & Carbon Corp Crystalline synthetic zeolites
CN105797749A (en) * 2016-04-06 2016-07-27 金华科海检测有限公司 Preparation and application of magnetic nano-photocatalyst adopting multi-layer core-shell structure
CN109746025A (en) * 2017-11-03 2019-05-14 中国石油化工股份有限公司 A kind of denitrating catalyst and its preparation method and application
CN113198459A (en) * 2021-03-29 2021-08-03 上海中船临港船舶装备有限公司 Catalyst for low-temperature catalytic combustion and preparation method and application thereof

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