CN115945192A - Perovskite loaded Pd embedded methane combustion catalyst and preparation method thereof - Google Patents
Perovskite loaded Pd embedded methane combustion catalyst and preparation method thereof Download PDFInfo
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Abstract
The invention relates to a perovskite loaded Pd embedded methane combustion catalyst, a preparation method and application thereof. Firstly, a certain amount of perovskite precursor, active component precursor and complexing agent are simultaneously dissolved in deionized water. Evaporating the solvent at 80-100 ℃, transferring the solvent to 100-120 ℃ for foaming for 8-12 h, finally mashing the xerogel and roasting the xerogel for 3-5 h at 850-1000 ℃ in air atmosphere to obtain a sample. The key point of the invention is that the exposure degree of Pd species on the surface of the catalyst is regulated and controlled by controlling the use amount of A site element, and finally the perovskite loaded Pd embedded catalyst is invented. Compared with the prior art, the catalyst provided by the invention not only has good catalytic activity, but also has small activity loss after aging for 50h at 1000 ℃.
Description
Technical Field
The invention belongs to the technical field of catalysts, and relates to a perovskite loaded Pd embedded methane combustion catalyst and a preparation method thereof.
Background
Natural gas is one of the most commonly used fossil fuels at present, and its main component is methane (CH) 4 ) Gas, about 85%. The hydrogen-to-carbon ratio of methane is highest in all hydrocarbons, so the energy released by combustion of methane is highest in the same volume of hydrocarbons, and the only products of complete combustion are CO 2 And H 2 O, a clean, efficient and safe energy source. However, methane is a greenhouse gas with the greenhouse effect of CO 2 20 times higher, the greenhouse effect is exacerbated by the unorganized emission of methane in trace amounts that are incompletely combusted, resulting in more serious ecological problems.
The catalytic combustion of methane is a clean and efficient methane elimination method, however, because of the high symmetry of methane molecules, the dissociation of the first C-H bond requires higher energy, so the catalytic combustion reaction is often required to be carried out at higher temperature (> 500 ℃), and the catalyst is required to have good thermal stability. Noble metal Pd is one of the active components which are generally accepted to have the best catalytic combustion effect on methane, but the noble metal Pd is easy to agglomerate or sinter under the high-temperature reaction condition due to the lower Taman temperature, so that the loss of the active components of the catalyst and the reduction of the activity of the catalyst are caused.
Perovskite (ABO) 3 ) Is a composite metal oxide with high thermal stability, the A site is usually alkaline earth metal or rare earth metal with larger ionic radius, and the B site is usually transition metal element. In the application of perovskite in catalytic oxidation reaction, A site element generally has no catalytic activity, and active site is provided mainly by more active B site element, but most transition metal perovskites have poor catalytic activity and cannot meet the requirements of actual working conditions. Thus, the advantageous complementary effect can be achieved by combining the noble metal with the perovskite.
Literature (Nature, 2002,418eCoO 3 For CO-NOx conversion, it was found that the catalytic activity varies with the fluctuations in the composition of the reaction gas. In the oxygen-poor state, pd species will precipitate out of the perovskite lattice, providing sufficient active sites, while in the oxygen-rich state, pd species will re-enter the perovskite lattice, decreasing activity. The oxidation-reduction fluctuation enables the Pd species to be in a dynamic and stable state, and the sintering resistance of the Pd-based catalyst is effectively improved. However, the characteristic that Pd can be dissolved again under the oxygen-rich condition limits the relevant application of the catalyst in catalytic combustion under the oxygen-rich condition.
Literature (Applied Catalysis B: environmental,2018,239 3 And then, part of A site La elements on the surface are etched by a nitric acid solution post-treatment mode, more Pd active sites are exposed, and excellent activity is shown in methane catalytic combustion. However, the acid etching destroys the skeletal structure of the catalyst, and the catalyst surface is reformed under a long-term high-temperature reaction condition, resulting in a decrease in catalyst activity.
The catalysts in the reports have all advantages but still have disadvantages, and the design of the high-stability perovskite supported noble metal type catalyst aiming at the catalytic combustion reaction under the oxygen-rich condition has great practical application prospect.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, provides a perovskite-loaded Pd embedded methane combustion catalyst with good activity and stability and a preparation method thereof, and solves the problem that the supported Pd catalyst prepared by the traditional method is easy to sinter under the high-temperature reaction condition.
The purpose of the invention can be realized by the following technical scheme: a perovskite loaded Pd embedded methane combustion catalyst adopts perovskite as a substrate and noble metal Pd as an active component, wherein the A site element of the perovskite is La, and the B site element is Al.
The invention also provides a preparation method of the perovskite loaded Pd embedded methane combustion catalyst, which comprises the steps of dissolving a La source, an Al source, a Pd source and a complexing agent in deionized water according to a certain proportion, continuously stirring at 80-100 ℃, and evaporating water to form transparent gel; then transferring the gel to an oven at 100-120 ℃ for foaming, wherein the foaming period needs to last for 8-12 h; finally, the foamed xerogel is smashed and placed in a muffle furnace to be roasted for 3 to 5 hours at the temperature of 850 to 1000 ℃ to prepare the perovskite loaded Pd embedded catalyst.
According to the molar parts, 8-9 parts of La source, 9-10 parts of Al source and 0.5-1 part of Pd source, wherein the using amount of the La source is lower than the total molar parts of the Al source and the Pd source.
The La source is lanthanum nitrate hexahydrate or lanthanum acetate, the Al source is aluminum nitrate nonahydrate, and the Pd source is palladium nitrate, palladium chloride or palladium acetylacetonate.
Further, the Pd source is palladium nitrate, and the La source is lanthanum nitrate hexahydrate.
The complexing agent is one or more of citric acid, ethylene glycol and ethylenediamine tetraacetic acid.
The molar ratio of the metal total amount of the La source, the Al source and the Pd source to the complex is 1.
The invention also provides application of the perovskite loaded Pd embedded methane combustion catalyst in methane catalytic combustion.
The methane catalytic combustion adopts raw material gases of methane, oxygen and nitrogen, wherein the methane accounts for 0.8-1.2 vol.%, the oxygen accounts for 10-20 vol.%, and the nitrogen is balance gas.
The methane is subjected to combustion reaction under the action of a catalyst, the reaction temperature is 250-600 ℃, and the space velocity is 10000-30000 ml/(g.h).
Compared with the prior art, the invention has the beneficial effects that:
1. the invention utilizes the mode that Pd is doped into a perovskite substrate and then is precipitated in situ in the high-temperature roasting process, and regulates and controls the exposure degree of Pd species on the surface of the catalyst by controlling the using amount of an A site element, thereby preparing the perovskite loaded Pd embedded catalyst. The catalyst not only has good catalytic activity, but also has small activity loss after aging for 50h at 1000 ℃.
2. The invention adopts a simpler sol-gel method, realizes the control of the exposure degree of Pd particles on the surface of the catalyst by modulating the dosage of perovskite A site element, and obtains the perovskite loaded Pd embedded catalyst. The high-temperature resistance of the Pd component is improved while the Pd component can fully exert catalytic activity, and even after aging for 50 hours at 1000 ℃, the Pd particles are not sintered obviously and the activity loss is small.
Drawings
FIG. 1 shows CH in catalysts obtained in examples 1 to 5 of the present invention 4 A catalytic combustion activity map;
FIG. 2 shows CH in the catalysts of comparative examples 1 to 4 and example 2 4 A catalytic combustion activity map;
FIG. 3 is a TEM image of the catalyst of example 2 in the present invention.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments.
Example 1
3.03g of La (NO) 3 ) 3 ·6H 2 O,3.38g of Al (NO) 3 ) 3 ·9H 2 O,0.71g Pd (NO) 3 ) 2 The solution (Pd content 15 wt.%) and 3.93g citric acid were simultaneously dissolved in 30mL of deionized water. Evaporating water at 80 ℃ until the transparent gel is formed, then transferring the transparent gel into a 110 ℃ oven for foaming for 10 hours to obtain dry gel, finally smashing the dry gel and roasting the dry gel for 3 hours at 1000 ℃ in the air atmosphere to obtain La 0.7 Al 0.9 Pd 0.1 O 3 And (3) sampling.
Example 2
Adding 3.46g of La (NO) 3 ) 3 ·6H 2 O,3.38g of Al (NO) 3 ) 3 ·9H 2 O,0.71g Pd (NO) 3 ) 2 The solution (Pd content 15 wt.%) and 4.16g citric acid were simultaneously dissolved in 30mL of deionized water. Evaporating water at 80 deg.C until it is transparent gel, then transferring the transparent gel into 110 deg.C oven to foam for 10 hr to obtain dried gel, finally mashing the dried gel and roasting at 1000 deg.C in air atmosphere for 3 hr to obtain the final productTo La 0.8 Al 0.9 Pd 0.1 O 3 And (4) sampling.
Example 3
3.89g of La (NO) 3 ) 3 ·6H 2 O,3.38g of Al (NO) 3 ) 3 ·9H 2 O,0.71g Pd (NO) 3 ) 2 The solution (Pd content 15 wt.%) and 4.39g of citric acid were simultaneously dissolved in 30mL of deionized water. Evaporating water at 80 ℃ until the gel is transparent, then transferring the transparent gel into a drying oven at 110 ℃ for foaming for 10h to obtain dried gel, finally smashing the dried gel and roasting the dried gel for 3h at 1000 ℃ in air atmosphere to obtain La 0.9 Al 0.9 Pd 0.1 O 3 And (4) sampling.
Example 4
4.33g of La (NO) 3 ) 3 ·6H 2 O,3.38g of Al (NO) 3 ) 3 ·9H 2 O,0.71g Pd (NO) 3 ) 2 The solution (Pd content 15 wt.%) and 4.62g citric acid were simultaneously dissolved in 30mL of deionized water. Evaporating water at 80 ℃ until the gel is transparent, then transferring the transparent gel into a drying oven at 110 ℃ for foaming for 10h to obtain dried gel, finally smashing the dried gel and roasting the dried gel for 3h at 1000 ℃ in air atmosphere to obtain La 1.0 Al 0.9 Pd 0.1 O 3 And (3) sampling.
Example 5
The samples of examples 1 to 4 were placed in a muffle furnace and calcined at 1000 ℃ for 50h in an air atmosphere to obtain the corresponding high temperature aged samples (example-age).
Comparative example 1
Preparation of LaAlO by impregnation 3 A supported Pd catalyst. Firstly, laAlO is prepared by a sol-gel method 3 Specifically, 4.33g of La (NO) 3 ) 3 ·6H 2 O,3.75g of Al (NO) 3 ) 3 ·9H 2 O, and 4.62g citric acid were simultaneously dissolved in 30mL of deionized water. Evaporating water at 80 deg.C until it is transparent gel, then transferring the transparent gel into 110 deg.C oven to foam for 10 hr to obtain dried gel, finally mashing the dried gel and roasting at 1000 deg.C in air atmosphere for 3 hr to obtain LaAlO 3 And (3) sampling. Taking 1g LaAlO 3 With 0.33g Pd (NO) 3 ) 2 Mixing the solutions (Pd content of 15 wt.%), performing ultrasonic treatment for 10min, standing for 4-8 hr, evaporating water at 80 deg.C, and calcining at 1000 deg.C in air atmosphere for 3 hr to obtain Pd/LaAlO 3 And (3) sampling.
Comparative example 2
Preparation of Al by impregnation 2 O 3 A supported Pd catalyst. 1g of commercial Al was taken 2 O 3 (BASF) and 0.33gPd (NO) 3 ) 2 Mixing the solution (Pd content of 15 wt.%) uniformly, performing ultrasonic treatment for 10min, standing for 4-8h, evaporating water at 80 deg.C, and calcining at 1000 deg.C for 3h to obtain Pd/Al 2 O 3 And (3) sampling.
Comparative example 3
Preparation of CeO by the impregnation method 2 A supported Pd catalyst. Firstly, roasting nitric acid hexahydrate at 800 ℃ for 3 hours to prepare CeO 2 Taking 1g of CeO 2 With 0.33g Pd (NO) 3 ) 2 Mixing the solutions (Pd content of 15 wt.%), ultrasonic treating for 10min, standing for 4-8 hr, evaporating water at 80 deg.C, and calcining at 1000 deg.C in air atmosphere for 3 hr to obtain Pd/CeO 2 And (4) sampling.
Comparative example 4
And (4) placing the samples of the comparative examples 1-3 in a muffle furnace, and roasting for 50 hours at 1000 ℃ in an air atmosphere to obtain corresponding high-temperature aged samples (comparative example-age).
Test example
The catalysts 1 to 5 of examples according to the present invention and the catalysts 1 to 4 of comparative examples were subjected to activity evaluation using a fixed bed reactor as a methane catalytic combustion evaluation apparatus. The evaluation of the methane combustion activity was carried out at 150 to 600 ℃ at a temperature rise rate of 4 ℃/min in an evaluation atmosphere containing 1% CH 4 、20％O 2 And N 2 The equilibrium gas, the reactant gas flow rate was 50ml/min, the test mass space velocity was 15,000ml/(g.h), and the outlet product concentration was determined using a Gas Chromatography (GC) analyzer. The test results are shown in fig. 1 and 2.
As can be seen from the attached FIG. 1, the catalytic activity of example 2 on methane is the best, and the conversion rate of methane can reach 100% at about 400 ℃, and then the results are example 1, example 3 and example 4. Although the activity of the example 1 is reduced after being aged for 50h at 1000 ℃, the methane conversion of 100 percent can be achieved at about 450 ℃, and the activity loss of the examples 2, 3 and 4 after being aged at high temperature is smaller (only reduced by 5-10 ℃). It is clear that the catalysts prepared by the process of the present invention have a certain difference in activity, but most of them have good thermal stability, wherein example 2 has both excellent catalytic performance and good thermal stability.
As can be seen from FIG. 2, in one aspect, laAlO is impregnated with LaAlO 3 And common commercial carriers such as Al 2 O 3 And CeO 2 The catalysts prepared by loading Pd thereon have better activity than that of example 2, because the impregnation method used in the comparative example can completely disperse Pd on the surface of the carrier, while the sol-gel method used in the examples can cause part of Pd species to exist in the bulk of the catalyst, and relatively less Pd is exposed on the surface. On the other hand, for comparative examples 1, 2, 3 after aging at high temperature, none of them had the same activity as the invention after aging, further demonstrating the excellent thermal stability of the catalyst of the invention.
As can be seen from fig. 3, the Pd nanoparticles in the sample of example 2 are present in an embedded form on the surface of the perovskite substrate, and this embedded structure effectively prevents the migration and aggregation of Pd species during high temperature aging.
In conclusion, the methane combustion catalyst provided by the invention has good low-temperature activity, excellent heat-resistant stability, simple preparation method and easy industrial large-scale production.
The present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents and are included in the scope of the present invention. The above-mentioned embodiments only represent the embodiments of the present invention, but they should not be understood as the limitation of the scope of the present invention, and it should be noted that those skilled in the art can make several variations and modifications without departing from the spirit of the present invention, and these all fall into the protection scope of the present invention.
Claims (10)
1. The perovskite-loaded Pd embedded methane combustion catalyst is characterized in that perovskite is used as a substrate, and noble metal Pd is used as an active component, wherein the A site element of the perovskite is La, and the B site element of the perovskite is Al.
2. The preparation method of the perovskite supported Pd embedded methane combustion catalyst as claimed in claim 1, characterized in that La source, al source, pd source and complexing agent are dissolved in deionized water according to a certain proportion, and are continuously stirred at 80-100 ℃, and water is evaporated to form transparent gel; then transferring the gel to an oven with the temperature of 100-120 ℃ for foaming, wherein the foaming period needs to last for 8-12 h; finally, the foamed xerogel is smashed and roasted for 3 to 5 hours at the temperature of 850 to 1000 ℃ to prepare the perovskite loaded Pd embedded catalyst.
3. The preparation method of the perovskite supported Pd embedded methane combustion catalyst as claimed in claim 2, characterized in that, calculated by mole fraction, la source 8-9 parts, al source 9-10 parts, pd source 0.5-1 parts, wherein the amount of La source is lower than the total mole fraction of Al source and Pd source.
4. The method of claim 2, wherein the La source is lanthanum nitrate hexahydrate or lanthanum acetate, the Al source is aluminum nitrate nonahydrate, and the Pd source is palladium nitrate, palladium chloride or palladium acetylacetonate.
5. The method of preparing a perovskite supported Pd embedded methane combustion catalyst as claimed in claim 4, wherein the Pd source is palladium nitrate and the La source is lanthanum nitrate hexahydrate.
6. The method of preparing a perovskite supported Pd embedded methane combustion catalyst as claimed in claim 2, wherein the complexing agent is one or more of citric acid, ethylene glycol and ethylene diamine tetraacetic acid.
7. The method for preparing a perovskite supported Pd embedded methane combustion catalyst as claimed in claim 2, wherein the molar ratio of the total amount of metals of the La source, the Al source and the Pd source to the complex is 1.
8. Use of the perovskite supported Pd embedded methane combustion catalyst as claimed in claim 1, wherein the catalyst is used in methane catalytic combustion.
9. The preparation method of the perovskite supported Pd embedded methane combustion catalyst according to claim 8, wherein the raw material gas for methane catalytic combustion is methane, oxygen and nitrogen, wherein methane accounts for 0.8-1.2 vol.%, oxygen accounts for 10-20 vol.%, and nitrogen is balance gas.
10. The perovskite supported Pd embedded methane combustion catalyst as claimed in claim 1, wherein the methane is subjected to combustion reaction under the action of the catalyst, the reaction temperature is 250-600 ℃, and the space velocity is 10000-30000 ml/(g-h).
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