CN116571241A - Ultra-dispersed Ag-CeO 2 Catalyst and preparation method thereof - Google Patents
Ultra-dispersed Ag-CeO 2 Catalyst and preparation method thereof Download PDFInfo
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- 238000002360 preparation method Methods 0.000 title claims abstract description 20
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- 239000001301 oxygen Substances 0.000 claims abstract description 19
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- 239000000463 material Substances 0.000 claims abstract description 14
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- 229910000422 cerium(IV) oxide Inorganic materials 0.000 claims abstract description 3
- 229910045601 alloy Inorganic materials 0.000 claims description 51
- 239000000956 alloy Substances 0.000 claims description 51
- 238000003723 Smelting Methods 0.000 claims description 31
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims description 24
- 238000001354 calcination Methods 0.000 claims description 24
- 238000001035 drying Methods 0.000 claims description 15
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 12
- 239000002994 raw material Substances 0.000 claims description 12
- 238000011068 loading method Methods 0.000 claims description 10
- 238000002844 melting Methods 0.000 claims description 10
- 230000008018 melting Effects 0.000 claims description 10
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 8
- 238000001816 cooling Methods 0.000 claims description 8
- 229910052802 copper Inorganic materials 0.000 claims description 8
- 239000010949 copper Substances 0.000 claims description 8
- 238000002074 melt spinning Methods 0.000 claims description 8
- 230000008569 process Effects 0.000 claims description 8
- 238000010438 heat treatment Methods 0.000 claims description 7
- 239000010453 quartz Substances 0.000 claims description 7
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 7
- 229910052782 aluminium Inorganic materials 0.000 claims description 6
- 229910052786 argon Inorganic materials 0.000 claims description 6
- 230000001681 protective effect Effects 0.000 claims description 6
- 239000000126 substance Substances 0.000 claims description 6
- 229910052684 Cerium Inorganic materials 0.000 claims description 5
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- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 2
- 239000012300 argon atmosphere Substances 0.000 claims description 2
- GWXLDORMOJMVQZ-UHFFFAOYSA-N cerium Chemical compound [Ce] GWXLDORMOJMVQZ-UHFFFAOYSA-N 0.000 claims description 2
- 238000001291 vacuum drying Methods 0.000 claims description 2
- 238000005275 alloying Methods 0.000 claims 1
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- 230000009286 beneficial effect Effects 0.000 abstract description 2
- 229910000420 cerium oxide Inorganic materials 0.000 description 37
- BMMGVYCKOGBVEV-UHFFFAOYSA-N oxo(oxoceriooxy)cerium Chemical compound [Ce]=O.O=[Ce]=O BMMGVYCKOGBVEV-UHFFFAOYSA-N 0.000 description 37
- 230000000052 comparative effect Effects 0.000 description 13
- AFCARXCZXQIEQB-UHFFFAOYSA-N N-[3-oxo-3-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)propyl]-2-[[3-(trifluoromethoxy)phenyl]methylamino]pyrimidine-5-carboxamide Chemical compound O=C(CCNC(=O)C=1C=NC(=NC=1)NCC1=CC(=CC=C1)OC(F)(F)F)N1CC2=C(CC1)NN=N2 AFCARXCZXQIEQB-UHFFFAOYSA-N 0.000 description 10
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- YLZOPXRUQYQQID-UHFFFAOYSA-N 3-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)-1-[4-[2-[[3-(trifluoromethoxy)phenyl]methylamino]pyrimidin-5-yl]piperazin-1-yl]propan-1-one Chemical compound N1N=NC=2CN(CCC=21)CCC(=O)N1CCN(CC1)C=1C=NC(=NC=1)NCC1=CC(=CC=C1)OC(F)(F)F YLZOPXRUQYQQID-UHFFFAOYSA-N 0.000 description 4
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 description 4
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Classifications
-
- 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
- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
- B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
- B01J23/66—Silver or gold
-
- 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
- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/08—Heat treatment
Abstract
The invention discloses an ultra-dispersed Ag-CeO 2 Catalyst, ag-CeO 2 The catalyst is super-dispersed metal Ag loaded on CeO 2 The catalyst with the nano rod structure is prepared by dispersing Ag-CeO 2 No Ag characteristic peak exists in the XRD pattern of the catalyst, no Ag particles exist in a TEM pattern with a 5nm multiplying power, and Ag in a dispersed state exists in an energy spectrum distribution diagram; wherein Ag represents silver, ceO 2 Indicating ceria. The invention has the characteristics and beneficial effects that: the Ag-CeO material and the preparation method provided by the invention can be calcined at a lower temperature in an oxygen atmosphere to obtain an Ag-CeO with super-dispersion effect 2 The catalyst prepared by the method has the advantages of lower reduction temperature, more oxygen vacancies and excellent catalytic performance, and has important values in the fields of catalysis, energy sources, optics and the like.
Description
Technical Field
The invention relates to the technical field of nano materials, in particular to an ultra-dispersed Ag-CeO 2 A catalyst and a method for preparing the same.
Background
Recent studies have shown that supported catalysts have good catalytic activity. Ag-based catalysts are widely studied as more attractive metals than other noble metals due to their higher stability and lower cost, as well as unique catalytic properties for various catalytic reactions. Cerium oxide (CeO) 2 ) As an important rare earth oxide, it is highly stable, has excellent oxygen storage capacity, redox performance and strong metal-carrier interactionIs of great interest, is widely used as a high-efficiency and promising catalytic material, and shows excellent catalytic performance. The silver-supported nano-particle can better stabilize dispersed silver, so that stronger interaction occurs between metal and a carrier, and the geometrical and electronic interaction at the interface of the metal and the carrier influences the structure of the supported nano-particle, so that the supported nano-particle has high metal dispersibility and catalytic activity. Thus, ag-CeO 2 The catalyst is a very promising catalyst, has higher catalytic activity and lower cost commercial availability, and is widely applied to the fields of catalysis, energy sources, optics and the like.
Ag/CeO is currently widely known 2 The catalytic activity of (2) is mainly similar to the morphology of the carrier, the dispersity of Ag, ag and CeO 2 There is a correlation in the interactions between them. According to the prior researches, ceO with a nano rod structure 2 Exhibits excellent properties of activating surface lattice oxygen, generating more oxygen vacancies, and promoting Ag/CeO 2 Is a catalyst activity of (a). In addition, the smaller the particle size, the higher the dispersity, the higher the catalytic activity of the active component Ag, and Ag and CeO 2 The direction of electron transfer between the supports can also significantly affect the intrinsic catalytic activity of the catalyst. In the prior art, the catalytic activity of the catalyst can be obviously improved through heat treatment, but the high temperature easily causes the Ostwald ripening phenomenon of the active component of the catalyst, the sintering growth of the active component particles and the reduction of the catalyst activity. In most studies, ag-CeO 2 Ag in the composite material is loaded on CeO 2 On the support, although interfacial interactions can be enhanced, catalytic performance may be reduced due to sintering of Ag nanoparticles in a high temperature environment.
Disclosure of Invention
Aiming at the problems in the prior art, the invention discloses an ultra-dispersed Ag-CeO 2 Catalyst and preparation method thereof by designing Ag-Ce directly bonded Ag-CeO 2 The catalyst structure not only improves the silver loading (Ag mass, ag and CeO) 2 The mass ratio of the total mass) and overcomes the Ostwald ripening effect, and large-size Ag particles can be thinned into ultra-dispersed Ag, so that the atomic utilization rate is improved, and the catalytic activity is improved.
The invention is realized by the following technical scheme:
the invention provides an ultra-dispersed Ag-CeO 2 Catalyst, ag-CeO 2 The catalyst is super-dispersed metal Ag loaded on CeO 2 The catalyst with the nano rod structure is prepared by dispersing Ag-CeO 2 No Ag characteristic peak exists in the XRD pattern of the catalyst, no Ag particles exist in a TEM pattern with a 5nm multiplying power, and Ag in a dispersed state exists in an energy spectrum distribution diagram; wherein Ag represents silver, ceO 2 Indicating ceria.
The above design of the invention, ag-CeO of the invention 2 Ag in the catalyst can be super-dispersed and loaded on CeO 2 On the nano rod structure, on Ag-CeO 2 No characteristic peak of Ag is observed in XRD patterns of the catalyst, no stacking arrangement of silver atom particles is observed in TEM patterns at 5nm multiplying power, and Ag dispersing phenomenon can be observed in an energy spectrum analysis chart, which shows that Ag particles are dispersed in CeO 2 The obtained Ag is sufficiently dispersed, and the morphology, the size and the stacking degree are lower than those of XRD, which can be detected and observed, and TEM and HAADF prove that the Ag is super-dispersed to enable the Ag-CeO to be obtained 2 The catalyst has excellent catalytic performance.
Further, the Ag loading (in the present invention, ag loading means Ag mass, ag and CeO 2 The mass ratio of the total mass) is not higher than 14%. The Ag loading of the catalyst is higher than that of the prior art, the catalyst not only overcomes the aggregation of Ag possibly caused by the excessive loading, but also ensures that the Ag is in CeO 2 The catalyst is fully dispersed, and has better catalytic activity.
As a further scheme, the diameter of the nano rod is 10nm-20nm.
As a further proposal, the Ag-CeO 2 A catalyst having characteristic XRD diffraction peaks of 28 °, 34 °, 48 °, 57 °, 69 °, 77 °; the Ag-CeO 2 The XPS spectrum distribution diagram of the catalyst has characteristic peaks of 368.1eV and 374.1 eV. No characteristic diffraction peak of Ag was found in the XRD pattern, but the presence of Ag in the catalyst was confirmed in the spectrum pattern, so AgIs carried by CeO in ultra-dispersed way 2 And (3) upper part.
The invention also provides the Ag-CeO 2 A method of preparing a catalyst, the method comprising:
s1: preparation of Ce x Ag y Al z The alloy thin strip, wherein x, y and z respectively correspond to the atomic percentages of all alloy elements, ce represents cerium and Al represents aluminum, wherein x is more than or equal to 0.80 and less than or equal to 0.95, y is more than or equal to 0.05 and less than or equal to 0.2, z=4, and x+y+z=5;
s2: ce is prepared from x Ag y Al z Placing the alloy ribbon in 5-10 mol/L sodium hydroxide solution for chemical dealloying;
s3: ce is prepared from x Ag y Al z Taking out the powder product obtained after dealloying the alloy thin strip, cleaning and drying to obtain Ag-CeO with a nano rod-shaped structure 2 An intermediate;
s4: ag-CeO of the obtained nanorod-like structure 2 Calcining at the temperature of not higher than 350 ℃ in the oxygen atmosphere to obtain the ultra-dispersed Ag-CeO 2 A catalyst.
Under the combined action of the atomic percentage of each alloy element, the concentration of sodium hydroxide and the calcining temperature, the method promotes the generation of the ultra-dispersed Ag-CeO 2 A catalyst. Wherein the atomic percentage of the Al element is 4 times of the sum of the atomic percentages of the Ce element and the Ag element, and the atomic percentage of the Ce element is 4 to 19 times of the atomic percentage of the Ag element, which can promote the Ce x Ag y Al z The alloy ribbon can quickly form a proper channel suitable for oxygen to be introduced in the dealloying process of 5-10 mol/L sodium hydroxide, and simultaneously promote the partial oxidation of Ce to form CeO 2 And after drying, primarily forming powdered Ag-CeO with nano rod-shaped structure 2 Intermediate, ag-CeO with nano rod-shaped structure 2 The intermediate is favorable for obtaining CeO with better crystallinity when calcined in oxygen atmosphere 2 Meanwhile, ag-CeO 2 The microstructure of direct bonding of the medium Ag-Ce promotes the thinning and dispersion of Ag particles at low temperature (not more than 350 ℃), overcomes the Ostwald ripening phenomenon and obtains the Ag-CeO with super-dispersed nano rod-shaped structure 2 Catalyst, fromWhile Ag-CeO is improved 2 Catalytic activity of the catalyst. Compared with other methods, the dealloying method has the advantages of simplicity, convenience, low cost, suitability for mass preparation, more effective and controllable preparation process and capability of preparing Ag-CeO with nano rod structure 2 The catalyst material has high specific surface area and uniform structure.
As a further proposal, the Ce x Ag y Al z The preparation process of the alloy ribbon comprises the following steps of x Ag y Al z The method comprises the steps of weighing Ce, ag and Al element materials respectively according to target components, uniformly mixing to obtain smelting raw materials, smelting in an argon protective atmosphere, continuously smelting the smelting raw materials after smelting, stopping heating, cooling the alloy along with a crucible until solidification, turning over the alloy, repeatedly smelting, and cooling to obtain a mother alloy ingot with uniform components; breaking a master alloy ingot into small blocks, loading the small block alloy ingot into a quartz tube, and spraying molten alloy liquid on a copper roller in a vacuum melt-spinning device rotating at high speed under the argon atmosphere by utilizing the vacuum melt-spinning device to prepare Ce x Ag y Al z Amorphous alloy ribbon.
As a further proposal, the continuous smelting time after the raw materials are melted is 100s-140s, the smelting temperature is 1800-2200 ℃, the repeated smelting times are 3-5 times, and the vacuum degree of the vacuum melt-spinning equipment is not more than 9 multiplied by 10 -4 Pa, the linear speed of the copper roller is 2300r/min-2700r/min.
As a further scheme, in the S2, the chemical dealloying condition temperature is placed at 25-35 ℃ for 19-21 h.
In a further scheme, in the step S3, the drying condition is vacuum drying, the drying temperature is 65-75 ℃, and the drying time is 23-25 h. Drying is favorable for preliminary forming Ag-CeO with nano rod-shaped structure 2 Intermediate, ag-CeO for forming stable nano rod-shaped structure by low-temperature calcination 2 Providing a base condition.
The invention has the characteristics and beneficial effects that: the Ag-CeO material and the preparation method provided by the invention can be calcined at a lower temperature in an oxygen atmosphere to obtain an Ag-CeO with super-dispersion effect 2 Catalyst, preparation of the inventionThe catalyst has lower reduction temperature, more oxygen vacancies and excellent catalytic performance, and has important value in the fields of catalysis, energy sources, optics and the like.
Drawings
To more clearly illustrate Ag-CeO in the examples of the present invention 2 The catalyst, the following description of which will be briefly described below, or the drawings used in the description of the prior art, are merely some examples of the invention.
FIG. 1 is an XRD pattern of the alloy ribbon prepared in example 1 of the present invention.
FIG. 2 shows Ag-CeO prepared by the method of the present invention 2 XRD pattern of the catalyst after heat treatment in an oxygen atmosphere at calcination temperatures of 300℃and 500 ℃.
FIG. 3 shows Ag-CeO prepared in example 1 of the present invention 2 TEM image, HAADF image and energy spectrum of the material after 300 ℃ heat treatment of the catalyst; wherein FIG. 3a is Ag-CeO 2 -a TEM image of 300 catalyst; FIG. 3b is Ag-CeO 2 -HAADF map of 300 catalyst; FIGS. 3 c-3 f are diagrams of Ag-CeO 2 -300 elemental profile of the catalyst.
Fig. 4 is an XRD pattern of the catalyst of comparative example 1 of the present invention.
Fig. 5 is an XPS diagram of the catalysts prepared in examples 1 and 2 of the present invention.
FIG. 6 is a H-TPR chart of the catalyst prepared in example 1, example 2 and comparative example 1 of the present invention.
Detailed Description
To facilitate understanding of the present invention, an ultra-dispersed Ag-CeO 2 The catalyst and the preparation method thereof are described as follows 2 The catalyst and its preparation are more fully described, examples of the invention are given, but the scope of the invention is not limited thereby.
The present invention compares Ag-CeO prepared by the method of the present invention with the comparative examples 2 Catalytic effect of the catalyst.
Example 1: according to Ce 0.81 Ag 0.19 Al 4 Target formationAnd (3) weighing the Ce, ag and Al element materials, and uniformly mixing to obtain a smelting raw material, wherein the purity of each element material is more than 99.8%. Smelting raw materials in a vacuum arc smelting furnace, smelting in an argon protective atmosphere, continuously smelting the raw materials for 2 minutes after smelting, stopping heating, cooling the alloy along with a crucible until solidification, overturning the alloy, repeatedly smelting for 5 times, and cooling to obtain a mother alloy ingot with uniform components; crushing the obtained master alloy ingot into small blocks, loading the small blocks of alloy ingot into a quartz tube with the opening diameter of 1-2 mm, placing the quartz tube into an induction coil of a vacuum melt-spinning device for fixation, adjusting the distance between the quartz tube and a copper roller, closing a cavity, and pumping the cavity to a vacuum degree of less than or equal to 9 multiplied by 10 -4 Pa, filling inert gas argon as protective atmosphere, and adjusting the air pressure difference between the inside and the outside of the cavity; and (3) melting the alloy blocks by adopting induction melting, and spraying alloy liquid in a molten state on a copper roller with the linear speed of 2500r/min by utilizing pressure difference to obtain the amorphous alloy thin strip, wherein the melting temperature is about 2000 ℃. The Ce obtained 0.81 Ag 0.19 Al 4 The alloy ribbon is placed in 5mol/L sodium hydroxide solution and placed at 30 ℃ for 20 hours to perform chemical dealloying. Ce is prepared from 0.81 Ag 0.19 Al 4 Taking out the powder product obtained after dealloying the alloy thin strip, repeatedly cleaning and drying to obtain the Ag-CeO with the silver loading of 13% in the nano rod-shaped structure 2 An intermediate; drying Ag-CeO 2 Calcining the intermediate for 3 hours at 300 ℃ in oxygen atmosphere to obtain Ag-CeO 2 -300 catalyst, wherein Ag-CeO 2 300 in the 300 catalyst represents 300℃for the purpose of preparing Ag-CeO with other temperatures 2 The catalysts are distinguished.
Example 2: according to Ce 0.81 Ag 0.19 Al 4 The target components are weighed and mixed evenly to obtain smelting raw materials, and the purity of each element material is more than 99.8%. Smelting raw materials in a vacuum arc smelting furnace, smelting in an argon protective atmosphere, continuously smelting the raw materials for 2 minutes after smelting, stopping heating, cooling the alloy along with a crucible until solidification, overturning the alloy, repeatedly smelting for 5 times, and cooling to obtain a mother alloy ingot with uniform components; crushing the obtained master alloy ingot into small blocks, and grindingThe block alloy ingot is put into a quartz tube with the opening diameter of 1-2 mm and is placed into an induction coil of a vacuum melt-spinning device for fixation, the distance between the quartz tube and a copper roller is adjusted, a cavity is closed, and the vacuum degree of the cavity is less than or equal to 9 multiplied by 10 -4 Pa, filling inert gas argon as protective atmosphere, and adjusting the air pressure difference between the inside and the outside of the cavity; and (3) melting the alloy blocks by adopting induction melting, and spraying alloy liquid in a molten state on a copper roller with the linear speed of 2500r/min by utilizing pressure difference to obtain the amorphous alloy thin strip, wherein the melting temperature is about 2000 ℃. The Ce obtained 0.81 Ag 0.19 Al 4 The alloy ribbon is placed in 5mol/L sodium hydroxide solution and placed at 30 ℃ for 20 hours to perform chemical dealloying. Ce is prepared from 0.81 Ag 0.19 Al 4 Taking out the powder product obtained after dealloying the alloy thin strip, repeatedly cleaning and drying the powder product to obtain the Ag-CeO with the nano rod-shaped structure 2 An intermediate; drying Ag-CeO 2 Calcining the intermediate for 3 hours at 500 ℃ in oxygen atmosphere to obtain Ag-CeO 2 -500 catalyst.
Comparative example 1:
preparation of Ag/CeO by impregnation 2 Catalyst, firstly, ce which is prepared by smelting the alloy thin strip in the preparation method of the invention 10 Al 90 The alloy thin strip is corroded to remove Al in a dealloying mode, and the dried material is soaked in AgNO 3 Impregnating for 5h in the solution, drying the impregnated material, calcining for 1h in a muffle furnace at 500 ℃ to remove NO 3 - Obtaining Ag/CeO 2 A catalyst. Then calcining the prepared catalyst at 300 ℃ in oxygen atmosphere to obtain Ag/CeO 2 -300 catalyst.
The catalysts obtained by different methods are further compared in CO oxidation performance, and the specific operation process is as follows: ag-CeO in example 1 2 Intermediate, ag-CeO prepared in example 1 2 -300 catalyst, ag-CeO prepared in example 2 2 -500 catalyst, ag/CeO in comparative example 1 2 Ag/CeO prepared by catalyst and comparative example 1 2 -300 catalyst for CO oxidation reaction performance test under the conditions of 1% CO and 10% O 2 ，(CO：5mL/min，O 2 50mL/min, ar 50mL/min, 105mL/min total), airspeed 315000 mL/(h.g).
Results and analysis
Table 1 comparative results of CO oxidation performance of catalysts prepared in examples and comparative examples
We obtained Ce by the process of the present invention 0.81 Ag 0.19 Al 4 The alloy ribbon, as shown in FIG. 1, FIG. 1 is Ce 0.81 Ag 0.19 Al 4 XRD pattern of alloy ribbon, ce 0.81 Ag 0.19 Al 4 The alloy ribbon is mainly made of Ag 3 Al 17 Ce 5 、CeAl 4 And Ce, and then obtaining the ultra-dispersed Ag-CeO through the process combining dealloying and low-temperature calcination 2 Catalyst (Ag-CeO) 2 300 catalyst), as described in example 1. In the preparation process of the catalyst, the low-temperature calcination is favorable for loading CeO 2 The ultra-dispersion of the Ag component on the surface can fully exert the catalytic activity of the catalyst, in addition, the calcination temperature is also a key factor influencing the dispersion of the Ag, and when the calcination temperature is higher, the Ostwald ripening phenomenon can occur, so that the aggregation of the Ag is caused, and the catalytic activity of the catalyst is reduced. We further investigated the effect of different calcination temperatures on the activity and dispersibility of the final catalyst by setting different calcination temperatures, we obtained ag—ceo using a calcination temperature of 500 ℃ as described in example 2 2 -500 catalyst. We will prepare Ag-CeO from example 1 2 Intermediate, ag-CeO prepared in example 1 2 -300 catalyst, ag-CeO prepared in example 2 2 -500 catalyst in an X-ray powder diffraction pattern expressed in terms of diffraction angle 2. Theta. As shown in FIG. 2, we found that Ag-CeO 2 Intermediate and Ag-CeO prepared in example 2 2 The 500 catalyst had a diffraction peak characteristic of 38℃Ag, whereas the Ag-CeO prepared in example 1 2 -300 catalyst at 38℃and noCharacteristic diffraction peaks of Ag appear, we consider that the phenomenon of Ag super-dispersion appears at the calcining temperature of 300 ℃, and the super-dispersed Ag is loaded on CeO 2 Applying; while when the calcination temperature is too high (500 ℃), it is believed that Ostwald ripening occurs, resulting in sintering of Ag. To further verify its own hypothesis, ag-CeO prepared in example 1 was used 2 Characterization of the 300 catalyst in a transmission electron microscope to obtain Ag-CeO 2 -TEM and HAADF images of the 300 catalyst, as shown in fig. 3. As can be seen from FIG. 3a, the Ag-CeO was prepared 2 The catalyst sample 300 is a nanorod structure, and can be further observed in FIG. 3b, the stripe spacing and CeO in the photograph 2 No streak conforming to the Ag interplanar spacing was found, and Ag-CeO of FIG. 3 (c-f) 2 Ag-CeO is further disclosed in the elemental energy spectrum profile of the-300 catalyst 2 -300 super-dispersion of Ag in catalyst, which shows super-dispersion of Ag in CeO 2 On a nanorod carrier. Therefore, ag-CeO prepared by the method of the invention 2 The intermediate has the phenomenon of anti-Ostwald ripening during low-temperature roasting, and active component Ag is dispersed into ultra-dispersed Ag clusters below sub-nanometer from nano particles, so that ultra-dispersed Ag is loaded on CeO 2 Is provided.
We have further studied the preparation of Ag/CeO using impregnation 2 Catalyst, ag/CeO to be obtained 2 The catalyst was calcined at the calcination temperature of the present invention as shown in comparative example 1, and it was confirmed whether the calcination temperature of the present invention also caused Ag in the catalyst obtained by other preparation methods to be super-dispersed in CeO 2 And (3) upper part. We compared the Ag/CeO of comparative example 1 before calcination at low temperature (300 ℃ C.) 2 Ag/CeO prepared by catalyst and comparative example 1 2 -300 catalyst in an X-ray powder diffraction pattern expressed in terms of diffraction angle 2. Theta. As shown in FIG. 4, ag/CeO can be found 2 Catalyst and Ag/CeO prepared in comparative example 1 2 The 300 catalyst still has a diffraction peak characteristic of 38 deg. of Ag, it being seen that the ultra-dispersed Ag obtained by the present invention is not only dependent on the calcination temperature. Preparation of Ag/CeO by conventional methods such as impregnation in comparative example 1 2 Ag-O is directly bonded in the catalyst, and electrons are transferred from Ag to O; whereas the preparation of the inventionIn the process, in the atomic percentage range of each alloy element designed by the alloy ribbon, a ternary alloy solid solution material with Ag, ce and Al uniformly mixed can be obtained by a high-temperature smelting method, wherein Ag-Ce is combined by metal bonds, and then Al element in the ternary alloy is removed by a dealloying method, so that Ag-CeO directly bonded with Ag-Ce is obtained 2 An intermediate, electrons are transferred from Ce to Ag; enrichment of negative charges on the surface of Ag can promote exchange and diffusion of surface oxygen and subsurface oxygen of Ag, and can cause super-dispersion phenomenon of Ag particles in the low-temperature calcination process (not more than 350 ℃) to obtain super-dispersion Ag-CeO with more stable nanorod-like structure 2 Catalyst, thereby improving Ag-CeO 2 Catalytic activity of the catalyst. All the conditions are not separated from the conditions of atomic percentage, sodium hydroxide concentration and the like of each alloy element selected by us, and only the appropriate atomic percentage and sodium hydroxide concentration can form Ag-CeO with a nano rod-shaped structure 2 The intermediate is favorable for realizing the ultra-dispersion of Ag particles under low-temperature calcination.
We have further compared the CO oxidation reaction performance of the various catalysts prepared as described above and the results are shown in Table 1. As can be seen from Table 1, the Ag-CeO prepared according to the present invention 2 The 300 catalyst has better catalytic performance than other catalysts, and can catalyze the T of CO oxidation 50 At 80 ℃, ag/CeO obtained by the traditional dipping method 2 Catalyst-catalyzed CO oxidation T 50 160 ℃; the catalyst prepared by the invention catalyzes the T of CO oxidation 100 At 130 ℃, ag/CeO obtained by the traditional method 2 Catalyst-catalyzed CO oxidation T 100 Is 182 ℃. The catalyst prepared by the invention has obviously higher activity. The reason for the high catalytic activity is explored, and the Ag-CeO prepared by the method 2 XPS diagram of 300 catalyst (FIG. 5), one can see Ag-CeO 2 Intermediate, ag-CeO 2 -300、Ag-CeO 2 The difference between the orbital binding energy of-500 Ag 3d5/2 and Ag 3d3/2 is 6eV, which indicates that Ag exists in a metallic state in the material. And Ag-CeO 2 The Ag 3d5/2 binding energy of the intermediate is 367.9eV, which is lower than the standard value 368.2eV of the Ag 3d5/2 binding energy, thus indicating that Ag gets electrons, and side surface evidenceFormation of Ag-Ce bond, in addition, ag-CeO 2 The Ag 3d5/2 orbital binding energy of the 300 catalyst becomes 368.1eV and is closer to the standard value, and the Ag 3d orbital electron binding energy is increased due to the fact that the super-dispersion of Ag promotes the formation of more Ag-O bonds. The invention also carries out H 2 Characterization test of TPR, as shown in FIG. 6, ag-CeO 2 The 300 catalyst has lower reduction temperature and better activity of surface oxygen species, which is also attributed to the fact that the ultra-dispersed Ag better promotes the reduction of the reduction temperature and the Ag-CeO is improved under the combined influence of the factors 2 -300 catalytic activity of the catalyst.
In summary, ag-CeO prepared by the present invention 2 The catalyst has super-dispersed Ag loaded on CeO 2 The nano rod makes the catalyst have lower reduction temperature, more oxygen vacancies and excellent catalytic performance, and has important value in the fields of catalysis, energy sources, optics and the like.
It should be noted that the above-mentioned embodiments are only preferred embodiments of the present invention, and are not intended to limit the present invention, and any modifications, equivalent substitutions, improvements, etc. within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (9)
1. Ultra-dispersed Ag-CeO 2 The catalyst is characterized in that the Ag-CeO 2 The catalyst is super-dispersed metal Ag loaded on CeO 2 The catalyst with the nano rod structure is prepared by dispersing Ag-CeO 2 No Ag characteristic peak exists in the XRD pattern of the catalyst, no Ag particles exist in a TEM pattern with a 5nm multiplying power, and Ag in a dispersed state exists in an energy spectrum distribution diagram; wherein Ag represents silver, ceO 2 Indicating ceria.
2. An ultra-dispersed Ag-CeO according to claim 1 2 The catalyst is characterized in that the loading amount of Ag is not higher than 14%.
3. An ultra-dispersed Ag-CeO according to claim 1 2 A catalyst, characterized in thatThe diameter of the nano rod is 10nm-20nm.
4. An ultra-dispersed Ag-CeO according to claim 1 2 The catalyst is characterized in that the Ag-CeO 2 A catalyst having characteristic XRD diffraction peaks of 28 °, 34 °, 48 °, 57 °, 69 °, 77 °; the Ag-CeO 2 The XPS energy spectrum of the catalyst has characteristic peaks of 368.1eV and 374.1 eV.
5. The ag—ceo according to any one of claims 1 to 4 2 A method of preparing a catalyst, the method comprising:
s1: preparation of Ce x Ag y Al z The alloy thin strip, wherein x, y and z respectively correspond to the atomic percentages of all alloy elements, ce represents cerium and Al represents aluminum, wherein x is more than or equal to 0.80 and less than or equal to 0.95, y is more than or equal to 0.05 and less than or equal to 0.2, z=4, and x+y+z=5;
s2: ce is prepared from x Ag y Al z Placing the alloy ribbon in 5-10 mol/L sodium hydroxide solution for chemical dealloying;
s3: ce is prepared from x Ag y Al z Taking out the powder product formed after dealloying the alloy thin strip, cleaning and drying to obtain Ag-CeO with a nano rod-shaped structure 2 An intermediate;
s4: ag-CeO of the obtained nanorod-like structure 2 Calcining at the temperature of not higher than 350 ℃ in the oxygen atmosphere to obtain the ultra-dispersed Ag-CeO 2 A catalyst.
6. The process according to claim 5, wherein the S1 is prepared Ce x Ag y Al z The process of alloying the ribbon includes the steps of following Ce x Ag y Al z The method comprises the steps of weighing Ce, ag and Al element materials respectively according to target components, uniformly mixing to obtain smelting raw materials, smelting in an argon protective atmosphere, continuously smelting the smelting raw materials after smelting, stopping heating, cooling the alloy along with a crucible until solidification, turning over the alloy, repeatedly smelting, and cooling to obtain a mother alloy ingot with uniform components; breaking mother alloy ingot into small piecesLoading small alloy ingots into a quartz tube, spraying molten alloy on a copper roller in a vacuum melt-spinning device under the argon atmosphere by utilizing the vacuum melt-spinning device to prepare Ce x Ag y Al z Alloy ribbons.
7. The method according to claim 6, wherein the continuous melting time after melting the raw material is 100s-140s, the melting temperature is 1800-2200 ℃, the number of repeated melting is 3-5, and the vacuum degree of the vacuum melt-spinning device is not more than 9 x 10 -4 Pa, the linear speed of the copper roller is 2300r/min-2700r/min.
8. The method according to claim 5, wherein the chemical dealloying conditions in S2 are maintained at a temperature of 25 ℃ to 35 ℃ for 19h to 21h.
9. The method according to claim 5, wherein in S3, the drying condition is vacuum drying, the drying temperature is 65-75 ℃ and the drying time is 23-25 h.
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