CN112108145B - Alumina-supported iridium cluster catalyst and preparation and application thereof - Google Patents
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Abstract
The invention relates to an alumina supported iridium cluster catalyst and preparation and application thereof. Specifically, the content of iridium is 0.1-5% of the total mass of the catalyst, the iridium is highly dispersed on alumina in the form of clusters, and the cluster size is 0.5-5 nm. The iridium cluster as the only catalytic activity center is suitable for room-temperature formaldehyde elimination and catalytic decomposition of NJ-DT-3, shows excellent catalytic activity, can completely catalyze and oxidize high-concentration formaldehyde (180 ppm) into carbon dioxide and water at room temperature, and has higher reaction rate when being used for the decomposition reaction of NJ-DT-3.
Description
Technical Field
The invention relates to an alumina supported iridium cluster catalyst, and preparation and application thereof, which can be used for room temperature elimination of formaldehyde which is a typical volatile organic pollutant and decomposition reaction of NJ-DT-3.
Background
Volatile Organic Compounds (VOCs) are the main air pollutants, and formaldehyde (HCHO) is one of the typical VOCs, and the problem of air pollution caused by the VOCs is becoming more serious and more important. On the one hand, outdoor formaldehyde is mainly derived from industrial exhaust gas and automobile exhaust emission. Recent research shows that the discharged formaldehyde can react with sulfur dioxide to generate hydroxymethanesulfonate, which is an important source of PM2.5, so that the formaldehyde is the main cause of haze weather in winter in China. On the other hand, indoor formaldehyde mainly comes from the release of building and decorative, finishing materials such as adhesives, plywood, paints, diluents, and the like. Formaldehyde is a highly toxic substance and is a main indoor air pollutant, and long-term exposure to formaldehyde can cause symptoms such as headache, nausea, allergy and the like, and even cause teratogenesis and carcinogenesis. Therefore, the elimination of formaldehyde, especially at room temperature, has important significance for effectively improving the air quality, solving the problem of air pollution and protecting the human health.
At present, the common methods for eliminating formaldehyde at room temperature mainly comprise an adsorption method, a photocatalysis method and a catalytic oxidation method [ ChemSusChem,2013,6,578-592 ]]. The adsorption method generally adopts porous materials as adsorbents, and carbon-based adsorbents (such as activated carbon, carbon fibers and the like) and porous oxides (such as activated alumina, silica gel and the like) are commonly used. Although the formaldehyde eliminating agent is cheap and has good adsorption capacity, the adsorption capacity is limited, and the formaldehyde eliminating agent is easy to reach saturation and cannot continuously eliminate formaldehyde. ZnO and TiO are mostly adopted for the photocatalysis method 2 The absorbed formaldehyde is oxidized into CO by the light irradiation of the photocatalyst 2 And H 2 However, the generation of CO and other by-products is often accompanied in the catalytic process, and the cost of the used ultraviolet light source is high and the service life is short, so that the wide application of the method is limited. The catalytic oxidation method uses metal or its oxide as catalyst, oxygen in air as oxidant, and converts formaldehyde into nontoxic CO 2 And H 2 And O. The method has the advantages of low energy consumption, high efficiency, environmental friendliness and the like, and is paid much attention by researchers.
In the formaldehyde oxidation reaction, a supported noble metal catalyst system generally shows excellent catalytic performance, and at present, pt, pd, au and the like are researched more frequently. He et al reported that alkali metal ion (Li, na, K) modified Pt/TiO 2 Catalyst, found 2% Na-1% 2 CatalysisThe catalyst has excellent catalytic performance in formaldehyde oxidation reaction, and can completely oxidize 600ppm formaldehyde at room temperature [ Angew. Chem. Int. Ed.,2012,51,9628-9632]. Zhou et al for CeO of different morphologies 2 The performance of the supported Pd catalyst in the formaldehyde oxidation reaction is compared and researched, and CeO is found 2 The catalytic activity of the supported noble metal Pd is higher than that of octahedron and rodlike CeO when the supported noble metal Pd is in a cubic shape and the exposed crystal face is a (100) crystal face 2 Has high activity of catalyzing formaldehyde oxidation when being used as a carrier [ Environ. Sci. Technol.2015,49,8675-8682]. Noble metal iridium, an important member of platinum group metals, exhibits excellent catalytic activity in PROX, water vapor shift, and the like, while being less studied in formaldehyde oxidation reactions. Recently, li et al prepared Ir/TiO via an excess impregnation process 2 The catalyst has lower activity in the catalytic formaldehyde oxidation reaction, the catalytic activity is greatly improved after the catalyst is further modified by Na ions, formaldehyde can be completely eliminated at room temperature, and the addition of the Na ions is considered to promote the reduction of titanium oxide at the metal-carrier interface, increase the oxygen vacancies on the surface of the carrier, promote the activation of water and further improve the catalytic performance [ ACS Catal.2018,8, 11377-11385-1138 ]]. Gao et al use hydrogenated TiO 2 (i.e., naBH) 4 Pre-reduction treatment) as a carrier, loading Ir and then catalyzing formaldehyde oxidation reaction to find hydrogenated TiO 2 The catalytic activity is obviously improved due to rich oxygen vacancies and surface hydroxyl groups, but the conversion rate at room temperature is still less than 20 percent, and the activity is lower [ New J.chem.,2018,42,18381-18387]. At present, reducible TiO is selected in all reported Ir catalyst systems 2 As a carrier, inert Al 2 O 3 The Ir-based catalyst loaded on the carrier is not reported to be used for formaldehyde oxidation reaction.
Propellants provide a source of energy for rocket engine thrust, have a direct effect on the flight performance of an aircraft, and are therefore important for rocket engines. Conventional propellants are largely divided into solid propellants and liquid propellants. The solid propellant exists in a rocket engine in a solid form, is easy to store and has high density, but has low specific impulse and poor controllability, and can not be repeatedly started and stopped, while the liquid propellant cannot be repeatedly started and stoppedThe flow is convenient to control, but leakage is easy to occur, and the safety factor is low, so that the solid propellant and the liquid propellant cannot completely meet the requirements on the safety and the efficiency of the propellant. In the continuous search for new propellants, gel propellants are produced, and are considered to be propellants with great application prospects in the field of future aerospace due to the advantages of both solid propellants and liquid propellants. The gel propellant can be rapidly decomposed under the action of the catalyst to generate a large amount of gas and release heat, so that the rapid conversion from chemical energy to kinetic energy is realized. At present, the most typical catalyst for catalyzing the decomposition of gel propellants is Al 2 O 3 Supported Ir catalysts, e.g. catalyst No. Shell405 U.S. Pat. No. 4,124,538]However, ir loadings of up to 20-40wt% were achieved. Ir as a rare noble metal and a high-grade strategic material needs to be optimized by a new catalyst synthesis method so as to reduce the dosage of Ir and reduce the dependence on Ir reserves. An effective method for dispersing the material into single atoms [ ZL201218006496.5 ]]However, during the decomposition of the propellant, it is possible for the Ir particles to grow together due to the higher specific surface energy of the monoatomic atoms [ angelw.chem., int.ed.2012,51,5929]. Hitherto, ir-based catalysts mainly adopt an impregnation method, precursors are primarily dispersed on the surface of a carrier in an ionic form, and the formation of catalytic centers with nonuniform dispersion is difficult to avoid in the post-treatment process [ Catalysis Today,2012,185,198]The proportion of effective components is low, and most Ir metal is wasted.
The invention firstly uses inert carrier Al 2 O 3 The supported Ir cluster catalyst with uniform size is applied to the catalytic decomposition of propellant NJ-DT-3.
Disclosure of Invention
The invention aims to provide an inert carrier Al 2 O 3 A supported cluster Ir catalyst and preparation and application thereof.
In order to achieve the purpose, the invention adopts the technical scheme that:
a cluster Ir catalyst, which is made of non-reducible Al 2 O 3 Is used as a carrier, noble metal Ir is used as an active component, the Ir content accounts for 0.1 to 5 percent of the total mass of the catalyst, al is added 2 O 3 The nano-particles are highly dispersed in a cluster form, and the cluster size is 0.5-5 nm.
The catalyst is prepared by a colloid formation-deposition loading two-step method, and the specific process comprises the following steps: ir sol is prepared by adopting a low-carbon alcohol reduction method as a precursor, and then the Ir sol is dropwise added into Al under the condition of violent stirring 2 O 3 And (3) reacting in the carrier suspension for 3h, standing and aging for 1h, filtering and washing while hot, and drying at 80 ℃ for 12h to obtain the target catalyst.
The Ir cluster sol is prepared by the low carbon alcohol reduction method, and the specific process comprises the following steps: dissolving chloroiridic acid in 50-100 mL of low-carbon alcohol to prepare L with the concentration of 3.9-39 mmol -1 Adding 50-100mL of 0.03-0.75 mol L of the solution -1 Stirring NaOH or KOH low-carbon alcohol solution at room temperature for 0.5 to 3 hours until the solution is uniformly mixed, transferring the solution into an oil bath at the temperature of between 100 and 160 ℃, and reacting for 1 to 3 hours under the protection of argon or nitrogen atmosphere to obtain the iridium cluster sol.
The lower alcohol is one or more of methanol, ethylene glycol, glycerol and 1, 4-butanediol.
The catalyst is reduced in a hydrogen atmosphere, the gas composition is 20 to 100vol% 2 He is balance gas, and reduction is carried out for 0.5-2 h at 200-300 ℃.
The catalyst can be used for catalyzing formaldehyde oxidation reaction at room temperature, and has the composition of 180ppm formaldehyde and 20vol.% O 2 He equilibrium feed gas, relative humidity 50%, at space velocity 3X 10 4 mL g cat -1 h -1 Introducing into a normal pressure fixed bed reactor filled with a catalyst, and testing the formaldehyde conversion rate within the range of 20-80 ℃.
The catalyst can be used for catalytic decomposition reaction of NJ-DT-3 propellant and has higher reaction rate.
Compared with the prior art, the invention has the substantive characteristics that:
1. the catalyst prepared by the method has the advantages that the active component Ir is dispersed in clusters with uniform size, and the catalytic activity of the catalyst is improved and the dosage of the noble metal Ir is reduced.
2. The carrier used for preparing the catalyst is inert alumina, the specific surface area is large, ir dispersion is facilitated, and Ir is taken as the only active center.
3. The Ir catalyst loaded by the inert carrier alumina has high activity, can completely oxidize high-concentration 180ppm formaldehyde at room temperature, and realizes the breakthrough of the performance of efficiently eliminating formaldehyde by taking the non-reducible oxide as the Ir-based catalyst loaded by the carrier for the first time.
4. The decomposition reaction rate of the cluster Ir catalyst catalyzed NJ-DT-3 propellant prepared by the method is higher than that of Ir/Al prepared by other preparation methods 2 O 3 A catalyst.
Drawings
FIG. 1 is a schematic representation of Ir/Al prepared in example 1 and comparative examples 1 and 2 2 O 3 XRD pattern of catalyst.
FIG. 2 is Ir/Al prepared in example 1 2 O 3 Catalyst HAADF-STEM diagram and particle size statistical diagram.
FIG. 3 is a graph of Ir/Al prepared in example 1 of the present invention and comparative examples 1 and 2 2 O 3 The catalytic performance of the catalyst for catalyzing formaldehyde oxidation is compared with a graph.
FIG. 4 is a graph of Ir/Al prepared in examples 1, 12, 13, 14 and 15 of the present invention 2 O 3 The oxidation performance of the catalyst catalyzing formaldehyde is shown in the test chart.
FIG. 5 is a graph of Ir/Al prepared in comparative example 3 of the present invention 2 O 3 The catalytic performance of the catalyst for catalyzing formaldehyde oxidation is compared with a graph.
FIG. 6 is a graph of Ir/Al prepared in example 1 of the present invention and comparative examples 1 and 2 2 O 3 Catalyst stability test chart.
FIG. 7 is a schematic view of Ir/Al prepared by different methods 2 O 3 The decomposition rates of the catalysts NJ-DT-3 are compared.
Detailed Description
The following examples are intended to illustrate the invention in more detail and are not intended to limit the scope of the invention.
Example 1:
dissolving 1.0g of chloroiridic acid in 50mL of ethylene glycol, wherein the concentration of metal iridium ions in the solution is 39mmol L -1 50mL of the solution was added at a concentration of 0.25mol L -1 Adding sodium hydroxide and glycol solution into the mixture, stirring the mixture for 0.5h at room temperature, transferring the mixture into an oil bath at 160 ℃,stirring and reacting for 1h under the protection of argon atmosphere to obtain Ir nanosol, measuring 4.0mL of Ir nanosol, and dropwise adding the Ir nanosol to the vigorously stirred Al with the particle size of 10-12 nm 2 O 3 Reacting in the carrier suspension at 80 ℃ for 3h, aging for 1h, filtering and washing while hot, and drying at 80 ℃ for 12h to obtain 1.5wt.% Ir/Al 2 O 3 Catalyst, labeled 1.5IrAl-NP. The catalyst was at 20vol.% H 2 /He(H 2 Volume fraction of 20%, he is equilibrium gas, hereinafter both expressed in this way) was reduced at 300 ℃ for 0.5h in an atmosphere and then subjected to XRD and STEM characterization, the results are shown in fig. 1 and 2. The XRD result shows that no diffraction peak of Ir species is found in the spectrogram, and the Ir species is on the carrier Al 2 O 3 A highly dispersed state is exhibited. From STEM electron micrographs, the Ir nanoparticles had an average particle size of 1.1nm, a narrow particle size distribution range (0.8 to 2 nm), and uniform size. 1.5IrAl-NP catalyst was used for evaluation of the formaldehyde oxidation reaction. The test conditions were that the amount of catalyst used was 100mg, and the composition of the reaction feed gas was 180ppm of HCHO,20vol.% of O 2 He is balance gas, relative humidity is 50%, and total flow is 50mL min -1 (STP) at a mass space velocity of 3X 10 4 mL g cat -1 h -1 And carrying out temperature programming activity test on the catalyst in a temperature range of 20-80 ℃. Catalyst before reaction testing at 20vol.% H 2 Reducing for 0.5h at 300 ℃ in a He atmosphere. The result is shown in figure 3, which shows that the 1.5IrAl-NP catalyst prepared by the method has excellent catalytic performance in formaldehyde oxidation reaction, and the formaldehyde conversion rate is kept at 100% in the temperature range of 20-80 ℃.
Examples 2 to 11: the preparation method is the same as example 1, and the specific conditions are shown in the following table:
example 13:
compared with example 1, except that the amount of Ir nanosol used was 2.7mL Ir nanosol, the remaining steps were consistent, and 1.0wt.% Ir/Al was obtained 2 O 3 Catalyst, labeled 1.0IrAl-NP.
Example 14:
compared with example 1, except that the amount of Ir nanosol used was 1.4mL Ir nanosol, the remaining steps were identical, and 0.5wt.% Ir/Al was obtained 2 O 3 Catalyst, labeled 0.5IrAl-NP.
Example 15:
compared with example 1, except that the amount of Ir nanosol used was 14mL Ir nanosol, the remaining steps were consistent, and finally 5wt.% Ir/Al was obtained 2 O 3 Catalyst, labeled 5IrAl-NP.
Example 16:
compared with example 1, except that the amount of Ir nanosol used was 0.28mL of Ir nanosol, the remaining steps were identical, and 0.1wt.% Ir/Al was obtained 2 O 3 Catalyst, labeled 0.1IrAl-NP.
Comparative example 1:
preparation of Al by deposition precipitation 2 O 3 A supported Ir catalyst. 1.0g of Al with the grain diameter of 10-12 nm 2 O 3 Dispersing in 100mL ultrapure water to form a suspension, and stirring vigorously for 3.0mL min -1 Was dropped into 91uL of 164mg mL -1 0.2mol L of chloroiridic acid -1 Adjusting the pH value to 9.2 with NaOH, reacting at 80 ℃ for 3h, aging for 1h, filtering and washing while hot, and drying at 80 ℃ for 12h to obtain 1.5wt.% Ir/Al 2 O 3 Catalyst, labelled 1.5IrAl-DP.
Comparative example 2:
al preparation by adopting isovolumetric impregnation method 2 O 3 A supported Ir catalyst. 91uL 164mg mL of chloroiridic acid solution was diluted to 0.6mL with ultrapure water, and 1.0g of Al having a particle diameter of 10 to 12nm was added dropwise 2 O 3 Mixing the powder with glass rod, drying in 80 deg.c oven for 12h 1.5wt.% Ir/Al 2 O 3 Catalyst, labelled 1.5IrAl-IMP.
Examples 17-20 were conducted to examine the effect of different influencing factors on the performance and stability of the catalysts prepared. And (3) carrying out formaldehyde elimination performance test on the catalyst by adopting a normal-pressure fixed bed micro-reaction evaluation device. The test conditions were that the catalyst dosage was 100mg, and the composition of the reaction feed gas was 180ppm HCHO，20vol.％O 2 He is balance gas, relative humidity is 50%, and total flow is 50mL min -1 (STP) at a mass space velocity of 3X 10 4 mL g cat -1 h -1 . And carrying out temperature programming activity test on the catalyst at a temperature range of 20-80 ℃. Catalyst before reaction testing at 20vol.% H 2 The reaction solution is reduced for 0.5h at 300 ℃ in a/He atmosphere, and then the He gas is blown to be reduced to room temperature. During the test, samples were taken every 20min, 1h at each temperature point, 3 times. The concentration of the reaction equilibrium gas was detected by FID detector in the chromatogram. Because the HCHO concentration in the feed gas is in the ppm level, trace CO is obtained 2 Before entering the FID detector, the hydrogen is hydrogenated by a nickel converter, and all the hydrogen is converted into CH 4 And then detecting.
The HCHO conversion was calculated as follows:
HCHO Conversion(％)＝[CO 2 ]/[CO 2 ] A ×100％
wherein: [ CO ] 2 ] A Completely converts formaldehyde in the raw material gas into CO 2 Time corresponding CH 4 Chromatographic peak area
[CO 2 ]For balancing CO in gas under different reaction temperature conditions 2 Corresponding CH 4 Chromatographic peak area.
Example 17: investigating the influence of the preparation method on the formaldehyde elimination performance of the catalyst
100mg of the catalyst prepared in example 1 and comparative examples 1 and 2 was packed in a quartz reaction tube, and the catalyst was at 20vol.% H before the reaction 2 Reducing for 0.5h at 300 ℃ under the atmosphere of/He, purging helium to room temperature, and using the pretreated catalyst for formaldehyde oxidation reaction evaluation. The results are shown in FIG. 3, which shows that the 1.5Ir/Al-NP catalyst prepared by the colloid-precipitation method in example 1 exhibits the highest formaldehyde elimination performance, the formaldehyde conversion rate is kept at 100% in the temperature test range of 20-80 ℃, while the 1.5Ir/Al-DP catalyst with the same Ir loading prepared by the precipitation method has the conversion rate of 57% at room temperature and 83% at 80 ℃, the 1.5Ir/Al-IMP catalyst prepared by the impregnation method has the worst formaldehyde elimination performance, and the formaldehyde conversion rate is still 4 at 80 DEG C0% or less. Therefore, the 1.5Ir/Al-NP catalyst prepared by the preparation method of the catalyst, namely the colloid-deposition method has obvious elimination performance advantage in the formaldehyde elimination reaction.
Example 18: investigating the influence of noble metal Ir loading on the formaldehyde elimination performance of the catalyst
The 100mg Ir load is 0.1 to 5.Wt% 2 O 3 The catalyst was packed in a quartz reaction tube at 20vol.% H before reaction 2 Reducing for 0.5h at 300 ℃ under the atmosphere of/He, purging helium to room temperature, and using the pretreated catalyst for formaldehyde oxidation reaction evaluation. The results are shown in fig. 4, which shows that the catalytic formaldehyde oxidation performance is increased with the increase of Ir loading, indicating that Ir nanoclusters are active centers for catalytic reaction in the catalytic formaldehyde elimination process.
Example 19: investigating the influence of the pretreatment atmosphere on the formaldehyde elimination performance of the catalyst
Different from example 1 is catalyst 1.5IrAl-NP at 20vol.% O 2 Pre-reducing for 0.5h at 300 ℃ under the atmosphere of/He, purging with helium to room temperature, and then evaluating the formaldehyde oxidation reaction. The results are shown in FIG. 5, which shows that the catalytic activity is greatly reduced after the treatment in the oxygen atmosphere, and the conversion rate at room temperature is less than 20%, thus showing that the pretreatment atmosphere of the catalyst has an important influence on the catalytic activity.
Example 20: investigating the influence of the preparation method of the catalyst on the stability of the catalytic formaldehyde oxidation reaction
80mg of the catalyst prepared in example 1 and comparative examples 1 and 2 was packed in a quartz reaction tube, and the catalyst was at 20vol.% H before the reaction 2 Reducing for 0.5h at 300 ℃ under the atmosphere of/He, blowing helium to room temperature, and using the pretreated catalyst for evaluating the oxidation stability of formaldehyde. The results are shown in fig. 6, which shows that the three catalysts prepared by the colloid-deposition method, the precipitation method and the equal-volume impregnation method all have stable reaction performance in the formaldehyde oxidation reaction, but the catalytic activities show obvious differences, the formaldehyde elimination performance is the highest on the 1.5Ir/Al-NP catalyst, the last time on the 1.5Ir/Al-DP and the worst on the 1.5Ir/Al-IMP catalyst, and the activity sequence is consistent with the results in fig. 3.
Example 21 catalytic NJ-DT-3 decomposition reaction Rate testing
Catalyst of example 1 and comparative examples 1 and 2 at 20vol.% H 2 Reducing the mixture for 0.5h at 300 ℃ in a hydrogen atmosphere of/He, then filling the mixture into a reactor, adding a certain amount of NJ-DT-3 raw material, and recording the reaction time after the test temperature is reached. The decomposition reaction rate of NJ-DT-3 can be expressed in TOF, i.e., the amount of reactant converted per unit time per unit active site, and is calculated by the following formula:
wherein, C DT-3 For the NJ-DT-3 conversion, t is the reaction time after reaching the reaction temperature, M Ir/DT-3 Is the molar ratio of Ir in the added catalyst to the raw material NJ-DT-3.
The results are shown in FIG. 7, which shows that the 1.5IrAl-NP catalyst prepared by the preparation method of the invention has higher reaction rate for catalyzing the decomposition of NJ-DT-3 than the catalyst prepared by the traditional deposition precipitation method and the equal volume impregnation method.
Claims (1)
1. The application of the iridium cluster catalyst loaded on alumina is characterized in that: the catalyst is used for formaldehyde elimination reaction, the dosage of the catalyst is 100mg, the composition of raw material gas for reaction is 180ppm HCHO, and 20vol.% O 2 He is balance gas, relative humidity is 50%, and total flow is 50mL min -1 STP, mass space velocity of 3' \ 10005Ohio 10 4 mL g cat -1 h -1 The testing temperature is 20 ℃; catalyst before reaction testing at 20vol.% H 2 Reducing for 0.5h at 300 ℃ in a/He atmosphere; the preparation method of the catalyst comprises the following steps of dissolving 1.0g of chloroiridic acid in 50mL of ethylene glycol, wherein the concentration of metallic iridium ions in the solution is 39mmol L -1 50mL of the solution was added at a concentration of 0.25mol L -1 Adding sodium hydroxide and ethylene glycol solution into the solution, stirring the solution at room temperature for 0.5h, transferring the solution into an oil bath at 160 ℃, stirring the solution for reaction for 1h under the protection of argon atmosphere to obtain Ir nano sol, measuring 4.0mL of the Ir nano sol, and dropwise adding the Ir nano sol into the Al with the particle size of 10 to 12nm which is stirred vigorously 2 O 3 Reacting in the carrier suspension at 80 ℃ for 3h, aging for 1h, filtering and washing while the solution is hot, and drying at 80 ℃ for 12h to obtain 1.5wt.% Ir/Al 2 O 3 A catalyst.
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