CN112023976A - Bimetallic modified MCM-41 molecular sieve catalyst, preparation method and application - Google Patents
Bimetallic modified MCM-41 molecular sieve catalyst, preparation method and application Download PDFInfo
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- B01J29/00—Catalysts comprising molecular sieves
- B01J29/03—Catalysts comprising molecular sieves not having base-exchange properties
- B01J29/0308—Mesoporous materials not having base exchange properties, e.g. Si-MCM-41
- B01J29/0316—Mesoporous materials not having base exchange properties, e.g. Si-MCM-41 containing iron group metals, noble metals or copper
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- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
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Abstract
A bimetal modified MCM-41 molecular sieve catalyst and a preparation method and application thereof, wherein a template agent, a diluent and acid are mixed, or the template agent, the diluent and alkali are mixed, then a silicon source is added, and the MCM-41 molecular sieve is obtained after uniform stirring, filtering, washing and drying; the metal nitrate and the MCM-41 molecular sieve are ball-milled, mixed evenly and then roasted to obtain the bimetallic modified MCM-41 molecular sieve catalyst. The preparation method is simple and easy to operate, and the bimetallic oxide species generated by decomposing the metal nitrate can be better dispersed on the MCM-41 molecular sieve, so that the agglomeration and sintering of active sites are effectively avoided; can effectively improve the activity of the toluene complete oxidation reaction and the like, reduce the reaction temperature window, and inhibit the stability of the generated catalyst of partial carbon deposition to ensure that the conversion rate of the toluene is unchanged after the reaction is carried out for 37 hours.
Description
Technical Field
The invention belongs to a catalysis technology for improving the activity of toluene catalytic oxidation reaction, and relates to a bimetallic modified MCM-41 molecular sieve catalyst, a preparation method and application thereof.
Background
VOCs (volatile organic compounds) are a general term for various organic compounds having a boiling point of 50 to 260 ℃ or a saturated vapor pressure of 10Pa or more at 20 ℃ at room temperature, according to the definition of the world health organization. VOCs are secondary organic aerosols and O in atmospheric environment3One of the important precursors of pollution, the emission reduction and treatment of VOCs have become the key work of the current atmospheric pollution prevention and treatment. Toluene (tolumene) is a typical VOCs, widely exists in waste gas and liquid in petrochemical industry, indoor furniture decorations and the like, and belongs to Harmful Air Pollutants (HAPs).
Effective toluene management is important for end management, in addition to source and process control. The end treatment techniques include absorption, combustion, condensation, adsorption, biological, and low-temperature plasma methods. The combustion method is a complete destruction method and comprises a direct combustion method and a catalytic combustion method, the direct combustion method is high in operation temperature (800-1200 ℃), high in process energy consumption, and dioxin and NO are easy to appear in combustion tail gasxAnd the like, and the range of application is gradually limited, and in order to improve thermal economy, researchers have accelerated the reaction, i.e., the catalytic combustion method (catalytic oxidation method), by improving a catalyst to lower the reaction temperature, changing the original reaction path, and lowering the reaction activation energy. The catalysts used in the method can be roughly classified into noble metal catalysts, transition metal oxide catalysts and rare earth composite oxide catalysts. The activity of the composite transition metal oxide catalyst is obviously higher than that of a single metal oxide catalyst, certain composite oxides can achieve the effect of a noble metal catalyst under certain conditions, and meanwhile, the supported transition metal oxide catalyst can effectively solve the problem of active site sintering at high temperature. Transition metal oxide catalysts are currently gaining wide attention as alternatives to noble metal catalysts.
At present, the literature and patents on the reaction catalyst and process research are increasing year by year, and most researchers have focused on the selection of an auxiliary agent and a carrier for a transition metal oxide catalyst and a preparation method thereof in order to obtain a catalyst which is excellent in catalytic activity, high in stability and low in price. The type and the property of the carrier have important influence on the supported cocatalyst, and the research generally comprehensively considers the carrier from the aspects of material specific surface area, pore structure, hydrophilicity and hydrophobicity and the like. The MCM-41 molecular sieve has high specific surface area, developed pore structure and adjustable hydrophilicity and hydrophobicity, and can effectively improve the dispersibility of the auxiliary agent. The existing MCM-41 supported catalyst has higher temperature window and large reaction energy consumption in the catalytic oxidation reaction of toluene.
Disclosure of Invention
The invention aims to improve the activity of the catalytic oxidation reaction of toluene, and provides a bimetallic modified MCM-41 molecular sieve catalyst, a preparation method and application thereof.
In order to achieve the purpose, the invention is realized by the following technical scheme:
the preparation method of the bimetallic modified MCM-41 molecular sieve catalyst comprises the following steps:
(1) mixing a template agent and a diluent with acid, or mixing the template agent and the diluent with alkali, then adding a silicon source, uniformly stirring, filtering, washing and drying to obtain the MCM-41 molecular sieve;
(2) the metal nitrate and the MCM-41 molecular sieve are ball-milled, mixed evenly and then roasted to obtain the bimetallic modified MCM-41 molecular sieve catalyst.
The further improvement of the invention is that the template agent is cetyl trimethyl ammonium bromide, cetyl triethyl ammonium bromide, cetyl pyridine bromide or 1-hexadecyl-3-methylimidazole bromide ionic liquid; the silicon source is tetraethoxysilane, sodium silicate, micro silicon powder or silica sol; the diluent is water; the acid is hydrochloric acid; the alkali is ammonia water.
The invention is further improved in that the mass concentration of the hydrochloric acid is 35 percent, and the mass concentration of the ammonia water is 29 percent.
The invention is further improved in that the mass ratio of the template agent, the silicon source, the diluent and the acid is 1 (2-7) to (305-1000) to (8-28), and the mass ratio of the template agent, the silicon source, the diluent and the alkali is 1 (2-7) to (305-1000) to (8-28).
The further improvement of the invention is that the molar ratio of the metal nitrate to the silicon in the MCM-41 molecular sieve is 1 (2-150).
The further improvement of the invention is that the metal nitrate is any two of ferric nitrate nonahydrate, cerium nitrate hexahydrate, manganese nitrate tetrahydrate, copper nitrate trihydrate, cobalt nitrate hexahydrate and silver nitrate; the rotating speed of ball milling is 500 r/min, and the time is 1-30 h;
the further improvement of the invention is that the roasting temperature is 350-600 ℃, and the roasting time is 4-7 h; heating from room temperature to 350-600 ℃ at a heating rate of 1-5 ℃/min.
A bimetallic modified MCM-41 molecular sieve catalyst prepared according to the method.
The bimetallic modified MCM-41 molecular sieve catalyst is applied to the catalytic oxidation reaction of toluene.
The further improvement of the invention is that 0.05-0.4 g of catalyst is added into a reaction container, then nitrogen, oxygen and toluene are introduced into the reaction container, the total space velocity of the nitrogen, the oxygen and the toluene is 10000 mL/(g.h) -100000 mL/(g.h), and the reaction is carried out at 150-400 ℃ to realize the catalytic oxidation of the toluene; wherein, the volume concentration of the toluene in the mixed gas of the nitrogen, the oxygen and the toluene is 0.05-1%.
Compared with the prior art, the invention has the beneficial effects that:
the invention takes MCM-41 molecular sieve as a carrier, adopts a simple ball milling method, and prepares a series of bimetal modified MCM-41 molecular sieve catalysts through the selection of different bimetal precursors, so as to obtain toluene catalytic oxidation catalysts with more excellent performance, wherein the reaction for catalyzing toluene is as follows:
C7H8+9O2→7CO2+4H2O
compared with the traditional impregnation method, the sol-gel method, the coprecipitation method and the ion exchange method, the preparation method has the advantages that the bimetallic oxide species generated by decomposing the metal nitrate can be better dispersed on the MCM-41 molecular sieve, so that the phenomenon that the bimetallic oxide species are effectively prevented from being generatedAgglomeration and sintering of active sites; meanwhile, due to the fact that bimetallic load is carried out, compared with the traditional molecular sieve catalyst, the catalyst can effectively improve the activity of the toluene complete oxidation reaction and the like, reduce the reaction temperature window, inhibit the generation of partial carbon deposit, and can reach T at 266 ℃ under the reaction space velocity of 0.1 percent of toluene and 30000 mL/(g.h) in volume concentration90The stability of the catalyst is such that the toluene conversion does not change after 37 hours of reaction. The catalyst of the invention is environment-friendly and has no pollution.
Drawings
FIG. 1 is a schematic representation of the N of a comparative example 1H-MCM-41 molecular sieve2Adsorption and desorption curves.
Figure 2 is an XRD spectrum of five samples of the bimetallic modified MCM-41 molecular sieve of example 7 and examples 10-13.
FIG. 3 is a graph of the catalytic oxidation activity of five samples of the bimetallic modified MCM-41 molecular sieve of example 7 and examples 10-13 in toluene.
FIG. 4 is O for five samples of the bimetal modified MCM-41 molecular sieve of example 7 and examples 10-132-TPD spectrum.
FIG. 5 shows Cu of example 71/60Ce1/15OzStability test results for the/MCM-41 sample.
Detailed Description
The technical scheme of the invention is further explained by combining specific examples.
The preparation method of the MCM-41 molecular sieve catalyst modified by different bimetal (Fe/Ce, Mn/Ce, Ag/Ce, Co/Ce and Cu/Ce) for catalytic oxidation of toluene comprises the following steps:
the catalyst is characterized in that different bimetal (Fe/Ce, Mn/Ce, Ag/Ce, Co/Ce and Cu/Ce) modified MCM-41 molecular sieve catalysts are adopted, MCM-41 molecular sieve catalysts synthesized under different acid-base conditions are adopted as carriers, different bimetal precursors are combined with the MCM-41 molecular sieve by a ball milling method, the molar ratio of the metal precursors to the carriers is 1: 150-1: 2, the treatment time is 1-30 h, the formed catalyst is excellent in activity and stability, and the molar ratio of the metal precursors to the carriers and the treatment time are preferably 1: 120-1: 4 and 2-24 h.
The preparation method comprises the following steps:
(1) preparing an MCM-41 molecular sieve: cetyl Trimethyl Ammonium Bromide (CTAB), cetyl triethyl ammonium bromide, cetyl bromopyridine (CPBr) or 1-hexadecyl-3-methylimidazole bromide ionic liquid is used as a template agent, Tetraethoxysilane (TEOS), sodium silicate, micro silicon powder or silica sol is used as a silicon source, water is used as a diluent, hydrochloric acid with the mass concentration of 35% is used under an acidic condition, and ammonia water (NH) with the mass concentration of 29% is used under an alkaline condition3·H2O), stirring for 1.5-48 h at room temperature, filtering, washing, and drying at 110 ℃ to obtain the MCM-41 molecular sieve.
The molar ratio of the template agent, the silicon source, the diluent and the acid/alkali is 1 (2-7): (305-1000): 8-28.
(2) And ball-milling the metal precursor and the MCM-41 molecular sieve, wherein the ball-milling speed is 500 r/min, and the time is 1-30 h. The metal salt is inserted between the template agent and the molecular sieve silicon wall by utilizing the action between the template agent and the molecular sieve silicon wall, and then the metal salt is roasted to obtain the bimetallic modified MCM-41 molecular sieve catalyst.
Wherein the molar ratio of the metal precursor to the MCM-41 molecular sieve is 1 (2-150).
The metal precursor is any two of ferric nitrate nonahydrate, cerous nitrate hexahydrate, manganese nitrate tetrahydrate, copper nitrate trihydrate, cobalt nitrate hexahydrate and silver nitrate. Nitrate is adopted to ensure that no impurity remains during roasting.
The roasting temperature is 350-600 ℃, and the roasting time is 4-7 h.
The catalyst is applied to the toluene catalytic oxidation reaction as follows: adding 0.05-0.4 g of catalyst into a reaction container, introducing nitrogen, oxygen and toluene into the reaction container, wherein the total space velocity of the nitrogen, the oxygen and the toluene is 10000 mL/(g.h) -100000 mL/(g.h), and reacting at 150-400 ℃ to realize the catalytic oxidation of the toluene; wherein, the volume concentration of the toluene in the mixed gas of the nitrogen, the oxygen and the toluene is 0.05-1%.
The following are specific examples.
Example 1
Preparing an MCM-41 molecular sieve: 2.7333g of CTAB is weighed in a 200mL beaker, 93mL of deionized water and 13.32mL of hydrochloric acid are weighed and added into the beaker, the mixture is stirred until the CTAB is completely dissolved, 8.4mL of TEOS is weighed and added into the beaker, the mixture is continuously stirred for 6 hours, filtered and washed to be neutral, and the mixture is dried overnight at 110 ℃, so that the MCM-41 molecular sieve carrier is obtained and is marked as H-MCM-41(4 and 200mL beakers are prepared simultaneously).
Preparing a bimetallic modified MCM-41 molecular sieve catalyst: weighing 2g of the H-MCM-41 molecular sieve, adding the H-MCM-41 molecular sieve into a 50mL agate ball milling tank, weighing 0.0842g of ferric nitrate nonahydrate and 0.0912g of cerous nitrate hexahydrate, adding the mixture into the tank, sealing, and carrying out ball milling at 500 revolutions per minute for 12 hours. After the ball milling is finished, heating the mixture from room temperature to 400 ℃ at the heating rate of 1 ℃/min in a muffle furnace, and roasting the mixture for 6 hours to finally obtain the bimetallic Fe/Ce modified MCM-41 molecular sieve, which is marked as Fe1/60Ce1/60Oz/H-MCM-41。
Example 2
Preparing an MCM-41 molecular sieve: the same as in example 1.
Preparing a bimetallic modified MCM-41 molecular sieve catalyst: weighing 2g of the H-MCM-41 molecular sieve, adding the H-MCM-41 molecular sieve into a 50mL agate ball milling tank, weighing 0.0842g of ferric nitrate nonahydrate and 0.1824g of cerous nitrate hexahydrate, adding the mixture into the tank, sealing, and carrying out ball milling at 500 revolutions per minute for 12 hours. After the ball milling is finished, the temperature is raised to 400 ℃ in a muffle furnace at the rate of 1 ℃/min, and the mixture is roasted for 6 hours to finally obtain the bimetallic Fe/Ce modified MCM-41 molecular sieve which is marked as Fe1/60Ce1/30Oz/H-MCM-41。
Example 3
Preparing an MCM-41 molecular sieve: the same as in example 1.
Preparing a bimetallic modified MCM-41 molecular sieve catalyst: weighing 2g of the H-MCM-41 molecular sieve, adding the H-MCM-41 molecular sieve into a 50mL agate ball milling tank, weighing 0.0842g of ferric nitrate nonahydrate and 0.3648g of cerous nitrate hexahydrate, adding the mixture into the tank, sealing, and carrying out ball milling at 500 revolutions per minute for 12 hours. After the ball milling is finished, the temperature is raised to 400 ℃ in a muffle furnace at the rate of 1 ℃/min, and the mixture is roasted for 6 hours to finally obtain the bimetallic Fe/Ce modified MCM-41 molecular sieve which is marked as Fe1/60Ce1/15Oz/H-MCM-41。
Example 4
Preparing an MCM-41 molecular sieve: the same as in example 1.
Preparing a bimetallic modified MCM-41 molecular sieve catalyst: weighing 2g of the H-MCM-41 molecular sieve, adding the H-MCM-41 molecular sieve into a 50mL agate ball milling tank, weighing 0.0842g of ferric nitrate nonahydrate and 0.5472g of cerous nitrate hexahydrate, adding the mixture into the tank, sealing, and carrying out ball milling at 500 revolutions per minute for 12 hours. After the ball milling is finished, the temperature is raised to 400 ℃ in a muffle furnace at the rate of 1 ℃/min, and the mixture is roasted for 6 hours to finally obtain the bimetallic Fe/Ce modified MCM-41 molecular sieve which is marked as Fe1/60Ce1/10Oz/H-MCM-41。
Example 5
Preparing an MCM-41 molecular sieve: the same as in example 1.
Preparing a bimetallic modified MCM-41 molecular sieve catalyst: weighing 2g of the H-MCM-41 molecular sieve, adding the H-MCM-41 molecular sieve into a 50mL agate ball milling tank, weighing 0.0842g of ferric nitrate nonahydrate and 1.0944g of cerous nitrate hexahydrate, adding the mixture into the tank, sealing, and carrying out ball milling at 500 revolutions per minute for 12 hours. After the ball milling is finished, the temperature is raised to 400 ℃ in a muffle furnace at the rate of 1 ℃/min, and the mixture is roasted for 6 hours to finally obtain the bimetallic Fe/Ce modified MCM-41 molecular sieve which is marked as Fe1/60Ce1/5Oz/H-MCM-41。
Comparative example 1
The sample in comparative example 1 was H-MCM-41 shown in example 1, calcined for 6H in a muffle furnace at a ramp rate of 1 ℃/min to 540 ℃, and the molecular sieve was not loaded with metal. FIG. 1 shows N in this sample2The adsorption and desorption curves show that the Langmuir IV isotherm with a hysteresis loop of H3 type shows that the sample is a typical mesoporous material.
Taking 0.1g of a catalyst sample (40-60 meshes) after tabletting and screening, reacting in a fixed bed reactor at the normal pressure and the temperature of 200-400 ℃, the volume concentration of the raw material toluene is 0.1%, and the total gas space velocity is 30000 mL/(g.h), and before the reaction, purging the catalyst for 3h by in-situ high-purity nitrogen. And (4) performing gas on-line chromatographic analysis on the product tail gas after heat preservation.
TABLE 1 modified Fe with different Fe/Ce contents1/60CeyOzThe result of the reaction of catalyzing toluene complete oxidation by the H-MCM-41
As can be seen from Table 1, the MCM-41 carrier has no catalytic oxidation activity of toluene, under the condition of a certain Fe content, the catalytic oxidation activity of toluene shows a volcanic type change trend along with the increase of the Ce content, when the Ce content is increased again, the activity is slightly improved, and compared with the loading amount, the improvement range is slightly low, so that the comprehensive consideration is that the Fe of the embodiment 3 has no catalytic oxidation activity of toluene1/60Ce1/15OzThe result of the/H-MCM-41 sample is better.
After the optimal metal loading capacity is determined, the influence of different double metals on the catalytic oxidation reaction performance of the toluene is continuously researched.
Example 6
In the case where the other experimental conditions were exactly the same as in example 3, the ferric nitrate nonahydrate was changed to manganese nitrate tetrahydrate.
Example 7
In the case where the other experimental conditions were exactly the same as in example 3, the ferric nitrate nonahydrate was changed to cupric nitrate trihydrate.
Example 8
In the case where the other experimental conditions were exactly the same as in example 3, the iron nitrate nonahydrate was changed to cobalt nitrate hexahydrate.
Example 9
In the case where the other experimental conditions were exactly the same as in example 3, the iron nitrate nonahydrate was changed to silver nitrate.
The final catalyst can obtain the optimal bimetal through activity test comparison.
TABLE 2 results of different bimetal modified H-MCM-41 catalyzed toluene complete oxidation reactions
As can be seen from Table 2, the Cu/Ce bimetal modified MCM-41 molecular sieve catalyst has the best toluene catalytic oxidation activity.
After the Cu/Ce bimetal modified MCM-41 molecular sieve is determined, the influence of different Cu/Ce contents on the reaction is continuously researched.
Example 10
Under otherwise identical experimental conditions as in example 7, the metal loading was fixed and the ratio of copper nitrate trihydrate and cerium nitrate hexahydrate was varied so that the molar ratio Cu/Ce was 0:5, yielding Cu0Ce1/12Oz/MCM-41。
Example 11
Under otherwise identical experimental conditions as in example 7, the metal loading was fixed and the ratio of copper nitrate trihydrate and cerium nitrate hexahydrate was varied so that the molar ratio Cu/Ce was 0.5:4.5 to yield Cu1/120Ce3/40Oz/MCM-41。
Example 12
Under otherwise identical experimental conditions as in example 7, the metal loading was fixed and the ratio of copper nitrate trihydrate and cerium nitrate hexahydrate was varied so that the molar ratio Cu/Ce was 2:3 to give Cu1/30Ce1/20Oz/MCM-41。
Example 13
Under otherwise identical experimental conditions as in example 7, the metal loading was fixed and the ratio of copper nitrate trihydrate and cerium nitrate hexahydrate was varied so that the molar ratio Cu/Ce was 5:0, yielding Cu1/12Ce0Oz/MCM-41。
The final catalyst can obtain the optimal bimetal content through activity test comparison.
TABLE 3 Cu of different Cu/Ce contentsxCeyOzMCM-41 catalyzed toluene complete oxidation reaction result
From table 3, it can be seen that, under the condition of a fixed loading amount, the toluene catalytic oxidation activity and the Cu content of the bimetallic modified MCM-41 molecular sieve catalyst with different Cu/Ce contents show a volcanic type change trend, and it can be found that the Cu/Ce content of example 7 is the optimal one. FIGS. 2-4 show XRD, reactivity and O for these five samples2-TPD map. From XIt can be seen from the RD results that when the Cu loading was too large, a distinct CuO crystalline phase appeared; the reaction activity diagram can visually show that the optimal Cu/Ce content exists for the catalytic oxidation reaction of the toluene, and the 90 percent conversion of the toluene can be realized at 266 ℃; o is2The TPD plots show that each sample exhibits a different oxygen profile. FIG. 5 shows the stability test results of the toluene catalytic oxidation reaction of the sample of example 7, which shows that the sample has excellent and stable reaction activity, and the activity is not changed under the condition of continuous reaction for 37 h.
Example 14
Preparing an MCM-41 molecular sieve: 2.7333g of CTAB is weighed in a 200mL beaker, 87mL of deionized water and 20mL of ammonia water are weighed and added into the beaker, the mixture is stirred until the CTAB is completely dissolved, 8.4mL of TEOS is weighed and added into the beaker, the mixture is continuously stirred for 6 hours, filtered and washed to be neutral, and the MCM-41 molecular sieve carrier is obtained after overnight drying at 110 ℃ and is marked as B-MCM-41.
Under otherwise identical experimental conditions as in example 7, the H-MCM-41 molecular sieve was changed to the B-MCM-41 molecular sieve. Namely the molecular sieve carrier obtained under alkaline conditions. The suitable carrier molecular sieve can be obtained by comparing activity tests.
TABLE 4 Cu under different support Synthesis conditions1/60Ce1/15OzMCM-41 catalyzed toluene complete oxidation reaction result
As can be seen from Table 4, the activity of the H-MCM-41 molecular sieve as a carrier in the catalytic oxidation of toluene is far better than that of the B-MCM-41 as a carrier, which shows that the MCM-41 carrier synthesized under acidic conditions is very important for the bimetallic supported catalyst obtained by the ball-milling method to be used in the catalytic oxidation reaction of toluene.
Example 15
In the case where the other experimental conditions were exactly the same as in example 7, the templating agent for preparing H-MCM-41 was changed to cetyltriethylammonium bromide.
Example 16
In the case of other experimental conditions identical to those of example 7, the templating agent for preparing H-MCM-41 was changed to cetylpyridinium bromide (CPBr).
Example 17
In the case of otherwise identical experimental conditions as in example 7, the templating agent used to prepare H-MCM-41 was changed to ionic liquid brominated 1-hexadecyl-3-methylimidazole.
Example 18
In the case of otherwise identical experimental conditions as in example 7, the silica source used in the preparation of H-MCM-41 was changed to sodium silicate.
Example 19
Under the same other experimental conditions as those of example 7, the silicon source for preparing H-MCM-41 was changed to silica fume.
Example 20
Under otherwise identical experimental conditions as in example 7, the silica source used in the preparation of H-MCM-41 was changed to silica sol.
TABLE 5 Cu under different H-MCM-41 synthesis conditions1/60Ce1/15OzMCM-41 catalyzed toluene complete oxidation reaction result
As can be seen from Table 5, the H-MCM-41 molecular sieve synthesized under different templates has less influence on the catalytic oxidation activity of toluene, and is preferred because CTAB has lower cost; the H-MCM-41 molecular sieve synthesized by different silicon sources is used as a carrier, and the catalytic oxidation activity of toluene is greatly influenced, which indicates that TEOS is preferred under the synthesis proportion.
Example 21
In the case where the other experimental conditions were exactly the same as in example 7, the calcination temperature was changed to 350 ℃.
Example 22
In the case where the other experimental conditions were exactly the same as in example 7, the firing temperature was changed to 500 ℃.
Example 23
In the case where the other experimental conditions were exactly the same as in example 7, the calcination temperature was changed to 600 ℃.
Example 24
In the case where the other experimental conditions were exactly the same as in example 7, the temperature increase rate was changed to 2 ℃/min.
Example 25
In the case where the other experimental conditions were exactly the same as in example 7, the temperature increase rate was changed to 5 ℃/min.
TABLE 6 Cu under different calcination conditions1/60Ce1/15OzMCM-41 catalyzed toluene complete oxidation reaction result
As can be seen from Table 6, the bimetallic modified MCM-41 molecular sieve obtained at different calcination temperatures or heating rates has a greater influence on the catalytic oxidation activity of toluene.
Comparing the above results, the catalyst was tested under the following experimental conditions: adding 0.2g of catalyst into a reaction container, then introducing nitrogen, oxygen and toluene into the reaction container, wherein the total space velocity of the nitrogen, the oxygen and the toluene is 30000 mL/(g.h), and reacting at the temperature of 200-; wherein, the volume concentration of the toluene in the mixed gas of the nitrogen, the oxygen and the toluene is 0.1 percent. Referring to fig. 3 and 5, it can be seen that 90% conversion of p-toluene can be achieved at 266 ℃ with better stability. The catalyst of the invention has low cost, simple preparation method and high activity, and has the prospect of realizing industrialization.
The catalyst of the present invention can be prepared by adjusting the process parameters according to the scheme described in the summary of the invention, and after the catalyst is tested by using the relevant characterization means, the catalyst basically shows the structure and performance consistent with the embodiments.
The invention has been described in an illustrative manner, and it is to be understood that any simple variations, modifications or other equivalent changes which can be made by one skilled in the art without departing from the spirit of the invention fall within the scope of the invention.
Claims (10)
1. The preparation method of the bimetallic modified MCM-41 molecular sieve catalyst is characterized by comprising the following steps:
(1) mixing a template agent and a diluent with acid, or mixing the template agent and the diluent with alkali, then adding a silicon source, uniformly stirring, filtering, washing and drying to obtain the MCM-41 molecular sieve;
(2) the metal nitrate and the MCM-41 molecular sieve are ball-milled, mixed evenly and then roasted to obtain the bimetallic modified MCM-41 molecular sieve catalyst.
2. The method for preparing the bimetallic modified MCM-41 molecular sieve catalyst of claim 1, wherein the template agent is cetyl trimethyl ammonium bromide, cetyl triethyl ammonium bromide, cetyl pyridinium bromide or 1-hexadecyl-3-methylimidazole bromide ionic liquid; the silicon source is tetraethoxysilane, sodium silicate, micro silicon powder or silica sol; the diluent is water; the acid is hydrochloric acid; the alkali is ammonia water.
3. The method for preparing the bimetallic modified MCM-41 molecular sieve catalyst as recited in claim 2, wherein the mass concentration of hydrochloric acid is 35% and the mass concentration of ammonia water is 29%.
4. The preparation method of the bimetallic modified MCM-41 molecular sieve catalyst as claimed in claim 1, wherein the mass ratio of the template agent, the silicon source, the diluent and the acid is 1 (2-7): (305-1000): 8-28), and the mass ratio of the template agent, the silicon source, the diluent and the alkali is 1 (2-7): 305-1000): 8-28.
5. The preparation method of the bimetallic modified MCM-41 molecular sieve catalyst as claimed in claim 1, wherein the molar ratio of the metal nitrate to the silicon in the MCM-41 molecular sieve is 1 (2-150).
6. The method for preparing the bimetallic modified MCM-41 molecular sieve catalyst of claim 1, wherein the metal nitrate is any two of ferric nitrate nonahydrate, cerium nitrate hexahydrate, manganese nitrate tetrahydrate, copper nitrate trihydrate, cobalt nitrate hexahydrate and silver nitrate; the rotating speed of the ball milling is 500 r/min, and the time is 1-30 h.
7. The preparation method of the bimetallic modified MCM-41 molecular sieve catalyst as claimed in claim 1, wherein the roasting temperature is 350-600 ℃ and the time is 4-7 h; heating from room temperature to 350-600 ℃ at a heating rate of 1-5 ℃/min.
8. The bimetallic modified MCM-41 molecular sieve catalyst prepared according to any one of claims 1-7.
9. Use of the bimetallic modified MCM-41 molecular sieve catalyst prepared according to any one of claims 1-7 in catalytic oxidation of toluene.
10. The application of the catalyst as claimed in claim 9, wherein 0.05-0.4 g of the catalyst is added into a reaction vessel, then nitrogen, oxygen and toluene are introduced into the reaction vessel, the total space velocity of the nitrogen, oxygen and toluene is 10000 mL/(g.h) -100000 mL/(g.h), and the reaction is carried out at 150-400 ℃ to realize the catalytic oxidation of the toluene; wherein, the volume concentration of the toluene in the mixed gas of the nitrogen, the oxygen and the toluene is 0.05-1%.
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