CN110791809B - Preparation method of single-layer and double-layer reversibly-regulated cerium oxide single crystal nano film - Google Patents
Preparation method of single-layer and double-layer reversibly-regulated cerium oxide single crystal nano film Download PDFInfo
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- BMMGVYCKOGBVEV-UHFFFAOYSA-N oxo(oxoceriooxy)cerium Chemical compound [Ce]=O.O=[Ce]=O BMMGVYCKOGBVEV-UHFFFAOYSA-N 0.000 title claims abstract description 106
- 229910000420 cerium oxide Inorganic materials 0.000 title claims abstract description 103
- 239000002356 single layer Substances 0.000 title claims abstract description 82
- 239000013078 crystal Substances 0.000 title claims abstract description 73
- 239000010410 layer Substances 0.000 title claims abstract description 48
- 238000002360 preparation method Methods 0.000 title claims abstract description 22
- 230000001105 regulatory effect Effects 0.000 title abstract description 11
- 239000002120 nanofilm Substances 0.000 title description 6
- 238000000137 annealing Methods 0.000 claims abstract description 66
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims abstract description 35
- 239000001301 oxygen Substances 0.000 claims abstract description 35
- 229910052760 oxygen Inorganic materials 0.000 claims abstract description 35
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 claims abstract description 32
- 229910002091 carbon monoxide Inorganic materials 0.000 claims abstract description 32
- 239000000758 substrate Substances 0.000 claims abstract description 28
- 229910000422 cerium(IV) oxide Inorganic materials 0.000 claims abstract description 25
- 230000008020 evaporation Effects 0.000 claims abstract description 17
- 238000001704 evaporation Methods 0.000 claims abstract description 17
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims description 96
- 239000011943 nanocatalyst Substances 0.000 claims description 30
- GMPSWULASZPKFN-UHFFFAOYSA-N [O-2].[Ce+3].[Pt+2] Chemical compound [O-2].[Ce+3].[Pt+2] GMPSWULASZPKFN-UHFFFAOYSA-N 0.000 claims description 20
- 238000000034 method Methods 0.000 claims description 14
- 238000000151 deposition Methods 0.000 claims description 13
- 238000004544 sputter deposition Methods 0.000 claims description 9
- XKRFYHLGVUSROY-UHFFFAOYSA-N argon Substances [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 7
- 229910052786 argon Inorganic materials 0.000 claims description 7
- -1 argon ion Chemical class 0.000 claims description 7
- 239000012535 impurity Substances 0.000 claims description 7
- 229910052697 platinum Inorganic materials 0.000 claims description 7
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 claims description 6
- 229910052721 tungsten Inorganic materials 0.000 claims description 6
- 239000010937 tungsten Substances 0.000 claims description 6
- 238000010438 heat treatment Methods 0.000 claims description 5
- 229910052751 metal Inorganic materials 0.000 claims description 5
- 239000002184 metal Substances 0.000 claims description 5
- 238000005566 electron beam evaporation Methods 0.000 claims description 4
- 239000011888 foil Substances 0.000 claims description 4
- 238000007872 degassing Methods 0.000 claims description 2
- 238000004519 manufacturing process Methods 0.000 claims 3
- 239000002086 nanomaterial Substances 0.000 abstract description 14
- CETPSERCERDGAM-UHFFFAOYSA-N ceric oxide Chemical compound O=[Ce]=O CETPSERCERDGAM-UHFFFAOYSA-N 0.000 abstract description 11
- 238000007254 oxidation reaction Methods 0.000 abstract description 6
- 230000003647 oxidation Effects 0.000 abstract description 5
- 230000002441 reversible effect Effects 0.000 abstract description 4
- 230000010718 Oxidation Activity Effects 0.000 abstract description 3
- 229910052684 Cerium Inorganic materials 0.000 abstract 2
- GWXLDORMOJMVQZ-UHFFFAOYSA-N cerium Chemical compound [Ce] GWXLDORMOJMVQZ-UHFFFAOYSA-N 0.000 abstract 2
- 239000000463 material Substances 0.000 abstract 1
- 230000009466 transformation Effects 0.000 abstract 1
- 239000010408 film Substances 0.000 description 26
- 230000005641 tunneling Effects 0.000 description 12
- 238000001000 micrograph Methods 0.000 description 7
- 238000012916 structural analysis Methods 0.000 description 7
- 238000010586 diagram Methods 0.000 description 6
- 239000010409 thin film Substances 0.000 description 6
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 5
- 238000004833 X-ray photoelectron spectroscopy Methods 0.000 description 5
- 229910001882 dioxygen Inorganic materials 0.000 description 5
- 238000010304 firing Methods 0.000 description 5
- 239000003054 catalyst Substances 0.000 description 4
- 230000003197 catalytic effect Effects 0.000 description 4
- 230000008021 deposition Effects 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 230000003993 interaction Effects 0.000 description 4
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 3
- 239000000956 alloy Substances 0.000 description 3
- 229910045601 alloy Inorganic materials 0.000 description 3
- 238000012360 testing method Methods 0.000 description 3
- 238000006555 catalytic reaction Methods 0.000 description 2
- DRVWBEJJZZTIGJ-UHFFFAOYSA-N cerium(3+);oxygen(2-) Chemical group [O-2].[O-2].[O-2].[Ce+3].[Ce+3] DRVWBEJJZZTIGJ-UHFFFAOYSA-N 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 230000000052 comparative effect Effects 0.000 description 2
- 230000001276 controlling effect Effects 0.000 description 2
- 230000001590 oxidative effect Effects 0.000 description 2
- 239000010970 precious metal Substances 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 125000004430 oxygen atom Chemical group O* 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 238000000629 steam reforming Methods 0.000 description 1
- 238000005556 structure-activity relationship Methods 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
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Abstract
本发明涉及一种单层和双层可逆调控的氧化铈单晶纳米结构的制备方法，包括：1)提供一个单晶Pt(111)衬底；2)提供铈(Ce)蒸发源，并在干净的Pt(111)衬底上生长0.3～1单层当量的氧化铈；3)在一氧化碳气氛中将任意0.3～1单层当量氧化铈退火到300～700℃，以获得还原的单层氧化铈；4)在氧气气氛中对还原的单层氧化铈退火到200～500℃，退火时间控制在15分钟以内，以获得氧化的单层氧化铈；5)在氧气气氛中对(3)或(4)中制备的单层氧化铈退火到500～600℃,退火时间控制在15分钟及以上，以获得双层氧化铈。该制备方法可以在同一个CeO2材料表面选择性制备出单层(～0.31nm)或者双层(～0.62nm)氧化铈，并可以实现单层和双层的可逆转变，且制备的氧化的单层氧化铈具有优异的室温CO氧化活性。The invention relates to a preparation method of a single-layer and double-layer reversibly regulated cerium oxide single-crystal nanostructure, comprising: 1) providing a single-crystal Pt(111) substrate; 2) providing a cerium (Ce) evaporation source, and 0.3-1 monolayer equivalent of ceria was grown on a clean Pt(111) substrate; 3) any 0.3-1 monolayer equivalent of ceria was annealed to 300-700 °C in a carbon monoxide atmosphere to obtain reduced monolayer oxidation cerium; 4) annealing the reduced monolayer cerium oxide to 200-500°C in an oxygen atmosphere, and the annealing time is controlled within 15 minutes to obtain an oxidized monolayer cerium oxide; 5) annealing (3) or The single-layer cerium oxide prepared in (4) is annealed to 500-600° C., and the annealing time is controlled at 15 minutes or more to obtain double-layer cerium oxide. The preparation method can selectively prepare single-layer (~0.31nm) or double-layer (~0.62nm) cerium oxide on the surface of the same CeO 2 material, and can realize the reversible transformation of single-layer and double-layer, and the prepared oxidized Monolayer ceria has excellent room temperature CO oxidation activity.
Description
Technical Field
The invention relates to a preparation method of a single-layer and double-layer reversibly regulated cerium oxide single crystal nanostructure, belonging to the technical field of nano materials.
Background
Platinum-cerium oxide exhibits excellent catalytic properties in many industrial catalytic reactions, such as: steam shift reaction, selective oxidation of carbon monoxide, steam reforming of methanol, etc. The excellent catalytic performance is due to the presence of a metal-oxide interface in the catalyst structure. While the performance of the catalyst is also affected by the surface composition and surface electron/geometry. In the platinum-cerium oxide catalyst, the precious metal platinum can transfer electrons to cerium oxide, so that the electronic structure of the cerium oxide can be regulated, and meanwhile, because strong interaction exists between the cerium oxide and the precious metal platinum, some metastable structures can stably exist, so that the geometric structure of the cerium oxide can also be regulated. Therefore, it is important for us to understand the structure-activity relationship in catalysis to build cerium oxide of different thicknesses on Pt (111) single crystal.
At present, the preparation method of cerium oxide nano single crystal on Pt (111) mainly comprises two methods: one is to deposit metal Ce to form alloy with Pt, and then oxidize the alloy to obtain cerium oxide; the other is "active deposition", that is, depositing cerium oxide on a heated substrate under an oxygen atmosphere to obtain cerium oxide. The ceria nano-islands obtained by oxidizing the alloy are usually a plurality of ceria layers (2 nm), while the ceria obtained by active deposition is usually highly non-uniform in surface height, so that it still has great challenges to realize atomic-level controllability of the thickness of the ceria, and even to reversibly regulate the thickness.
Disclosure of Invention
Based on the limitation of the prior art, the invention successfully realizes single-layer (one O-Ce-O layer, about 0.31nm) and double-layer (two O-Ce-O layers, about 0.62nm) CeO on the surface of the same sample by regulating and controlling the annealing atmosphere and time2The selective preparation of the nano single crystal film can reversibly regulate and control the thickness, and the method is simple and easy to implement. With the usual Pt/CeO2The catalyst needs to be higher than 100 ℃ to show obvious CO oxidation activity, but the oxidized single-layer cerium oxide prepared by the method can obviously react with CO at 25 ℃, and the structure has high catalytic activity.
A platinum-cerium oxide nano catalyst, wherein platinum is Pt (111) single crystal, cerium oxide is deposited on the surface of the Pt (111) single crystal, and the cerium oxide is single-layer or double-layer. The single-layer and double-layer can be reversibly regulated.
The monolayer in the invention refers to a single-layer thickness cerium oxide structure (an O-Ce-O layer with the thickness of about 0.31 nm).
The bilayer of the present invention refers to a cerium oxide structure of twice the monolayer thickness (two O-Ce-O layers, about 0.62nm thick).
A method for preparing a single-layer and double-layer reversibly-regulated cerium oxide single-crystal nanostructure comprises the steps of selectively obtaining a single-layer (one O-Ce-O layer) and a double-layer (two O-Ce-O layers) cerium oxide film on the surface of the same Pt (111) single-crystal nanomaterial, and realizing reversible thickness conversion:
the preparation method of the platinum-cerium oxide nano catalyst with the reduced single-layer cerium oxide comprises the following steps:
(1) providing an atomically clean flat single crystal Pt (111) substrate to obtain an atomically clean flat surface;
(2) maintaining the Pt (111) substrate treated in the step (1) at-200-400 ℃, and depositing Ce on the surface of the Pt (111) single crystal through a (Ce) evaporation source in an oxygen atmosphere to obtain 0.3-1 single-layer equivalent of cerium oxide (CeO)2) A nanostructure;
(3) in a carbon monoxide atmosphere, for any 0.3-1 monolayer equivalent of CeO2Annealing at the temperature of 300-700 ℃ to obtain a nano catalyst sample with a reduced single-layer cerium oxide film deposited on Pt;
the reduced single-layer cerium oxide film refers to a single-layer cerium oxide film (an O-Ce-O layer with the thickness of about 0.31nm) after carbon monoxide reduction.
The preparation method of the platinum-cerium oxide nano catalyst with oxidized single-layer cerium oxide comprises the following steps:
(1) providing an atomically clean and flat single crystal Pt (111) substrate to obtain an atomically clean and flat surface;
(2) maintaining the Pt (111) substrate treated in the step (1) at-200-400 ℃, and depositing Ce on the surface of the Pt (111) single crystal through a (Ce) evaporation source in an oxygen atmosphere to obtain 0.3-1 single-layer equivalent of cerium oxide (CeO)2) A nanostructure;
(3) in a carbon monoxide atmosphere, for any 0.3-1 monolayer equivalent of CeO2Annealing at an annealing temperature of300-700 ℃ to obtain a nano catalyst sample with a reduced single-layer cerium oxide film deposited on Pt;
(4) and (3) annealing the nano catalyst sample prepared in the step (3) to 200-500 ℃ in an oxygen atmosphere, wherein the annealing time is controlled within 15 minutes, so as to obtain an oxidized single-layer cerium oxide film sample.
The preparation method of the platinum-cerium oxide nano catalyst with oxidized double-layer cerium oxide comprises the following steps:
(1) providing an atomically clean flat single crystal Pt (111) substrate to obtain an atomically clean flat surface;
(2) maintaining the Pt (111) substrate treated in the step (1) at-200-400 ℃, and depositing Ce on the surface of the Pt (111) single crystal through a (Ce) evaporation source in an oxygen atmosphere to obtain 0.3-1 single-layer equivalent of cerium oxide (CeO)2) A nanostructure;
(3) in a carbon monoxide atmosphere, for any 0.3-1 monolayer equivalent of CeO2Annealing at the temperature of 300-700 ℃ to obtain a nano catalyst sample with a reduced single-layer cerium oxide film deposited on Pt;
(4) and (3) annealing the nano catalyst sample prepared in the step (3) to 200-500 ℃ in an oxygen atmosphere, wherein the annealing time is controlled within 15 minutes, so as to obtain an oxidized single-layer cerium oxide film sample.
(5) Annealing the nano catalyst sample prepared in the step (3) or the step (4) to 500-600 ℃ in an oxygen atmosphere, and controlling the annealing time to be 15 minutes or more to obtain the double-layer CeO2A film.
The method for converting the double-layer cerium oxide into the single-layer cerium oxide comprises the following steps:
(a) annealing the platinum-cerium oxide nano catalyst with oxidized double-layer cerium oxide in a carbon monoxide atmosphere, wherein the annealing temperature is 300-700 ℃;
(b) annealing the nano-catalyst treated in the step (a) to 200-500 ℃ in an oxygen atmosphere, wherein the annealing time is controlled within 15 minutes, and obtaining the platinum-cerium oxide nano-catalyst with oxidized single-layer cerium oxide.
The method provides a Pt (111) single crystal substrateThe method for preparing the Ce evaporation source also comprises the following steps: removing the surface oxide layer of a high-purity Ce foil (the purity is more than 99.95 percent), putting the high-purity Ce foil into a metal tungsten crucible, and putting the metal tungsten crucible into an electron beam evaporation source; putting an electron beam evaporation source into a preparation cavity of an ultrahigh vacuum system, and vacuumizing and baking to obtain 5 x 10-9～5×10-11An ultra-high vacuum environment of millibar (mbar); heating up the evaporation source, degassing the Ce source in the tungsten crucible until the working temperature of the Ce source is 5 x 10-9～5×10-11Background vacuum of mbar;
the single crystal Pt (111) substrate with clean and flat atomic level is characterized in that the single crystal Pt (111) substrate is pretreated to remove impurities on the surface of the single crystal Pt (111), and the pretreatment comprises the following steps: carrying out argon ion sputtering on single crystal Pt (111) in an ultrahigh vacuum preparation cavity, wherein the sputtering energy is 1-3 KeV and is 1 multiplied by 10-8～1×10-5And (3) carrying out oxygen burning at 500-700 ℃ in an oxygen mbar atmosphere, and then heating the Pt single crystal to 700-1000 ℃ for annealing.
When annealing is performed in a carbon monoxide atmosphere in the step (3), the carbon monoxide pressure is 1X 10-7～1×10-5mbar, preferably 1X 10-6mbar; the annealing time is 10 minutes or more; the oxygen pressure in step (3) and step (4) is 1X 10-8～1×10-5mbar。
The invention also provides application of the platinum-cerium oxide nano catalyst in selective oxidation of carbon monoxide.
In the selective oxidation of carbon monoxide, the minimum temperature of carbon monoxide oxidation is 25 ℃.
Oxygen pressure at the time of the Ce deposition was 5X 10-8～5×10-7mbar, which can be 1 × 10-7mbar。
At the time of the Ce deposition, the substrate Pt (111) single crystal temperature may preferably be 300 ℃.
When annealing in the carbon monoxide atmosphere, the carbon monoxide pressure is 1 × 10-7～1×10-5mbar, which may preferably be 1X 10-6mbar。
When annealing in the oxygen atmosphere, the oxygen may preferably be 5 × 10-7mbar
The invention has the advantages that:
compared with the prior art, by simple regulation and control of annealing atmosphere and time, the single-layer (one O-Ce-O layer) and double-layer (two O-Ce-O layers) cerium oxide nano single crystal which cannot be obtained in the prior art is selectively and controllably prepared on the surface of the same sample, the thickness can be reversibly regulated and controlled, and the prepared oxidized single-layer cerium oxide has excellent room-temperature CO oxidation activity.
Drawings
FIG. 1 is a structural analysis diagram of a reduced single-layer cerium oxide nano-single crystal thin film obtained in example 1 of the present invention.
FIG. 2 is a structural analysis diagram of a reduced single-layer cerium oxide nano-single crystal thin film obtained in example 2 of the present invention.
FIG. 3 is a structural analysis diagram of a reduced single-layer cerium oxide nano-single crystal thin film obtained in example 3 of the present invention.
FIG. 4 is a structural analysis diagram of a reduced single-layer cerium oxide nano-single crystal thin film obtained in example 4 of the present invention.
FIGS. 5 to 6 are structural analysis graphs of the cerium oxide thin films obtained before and after the treatment in example 5 of the present invention.
Fig. 7 is a structural analysis diagram of the cerium oxide nano-island obtained in comparative example 1 of the present invention.
FIG. 8 is a structural analysis diagram of a double-layered cerium oxide nano-single crystal thin film obtained in test example 1 of the present invention.
Detailed Description
The present invention is further illustrated by the following examples, and the advantages and effects of the present invention can be easily understood by those skilled in the art from the disclosure of the specification. The following examples are intended only for the purpose of more detailed description and should not be construed as limiting the invention in any way.
EXAMPLE 1 reduced Single layer cerium oxide film
1) Treating Pt (111) single crystal
Repeated argon ion sputtering of Pt single crystal in vacuum chamber (1.5kV, 1)×10-5mbar Ar,10min), oxygen gas firing (600 ℃, 1.0X 10)-7mbar O210min), and then the Pt (111) single crystal is heated and annealed at a high temperature of 700 ℃ for 3 minutes until no impurities are observed by X-ray photoelectron spectroscopy and a scanning tunneling microscope.
2) Growing cerium oxide on Pt (111) surface
Maintaining the temperature of a clean Pt (111) substrate at 300 ℃, and introducing 1.0X 10-7mbar O2Ce was deposited at 70nA of evaporation beam for about 30 minutes, yielding 0.8 monolayer equivalent of cerium oxide nanostructures.
3) Annealing treatment in carbon monoxide atmosphere
At 1.0X 10-6For 0.8 monolayer equivalent of prepared CeO in mbar carbon monoxide atmosphere2Annealing was carried out at 400 ℃ for 15 minutes. FIG. 1a is a scanning tunneling microscope image of a sample of the reduced single-layer cerium oxide film obtained by the process, from which it can be seen that the film has a flat surface and a uniform height. FIG. 1b shows a height profile of the thin nano-film of FIG. 1a at the white line, which is seen to be about 0.31nm, which is comparable to CeO2(111) The individual O-Ce-O layers of (a) are highly similar, indicating a single layer of cerium oxide. This is because the interaction between cerium oxide is stronger than the interaction between cerium oxide and substrate Pt, so cerium oxide does not grow as a wet layer on Pt (111), but grows in multiple layers. And the high-temperature treatment of the carbon monoxide can reduce the cerium oxide, so that the interaction between the cerium oxide and the Pt is stronger than that between the cerium oxide, and a uniform single-layer cerium oxide film can be obtained. It can further be seen from the magnified scanning tunneling microscope image that the surface had many pits, indicating that the surface was missing more oxygen atoms, i.e., the surface was a reduced cerium oxide surface (FIG. 1 c).
EXAMPLE 2 oxidized Single layer cerium oxide film
1) Treating Pt (111) single crystal
Repeated argon ion sputtering (1.5kV, 1X 10) of Pt single crystal in a vacuum chamber-5mbar Ar,10min), oxygen gas firing (600 ℃, 1.0X 10)-7mbar O2,10min), and then heating and maintaining the Pt (111) single crystal at a high temperature of 700 ℃ for 3 minutes until no impurities are observed by X-ray photoelectron spectroscopy and a scanning tunneling microscope.
2) Growing cerium oxide on Pt (111) surface
Maintaining the temperature of a clean Pt (111) substrate at 300 ℃, and introducing 1.0X 10-7mbar O2Ce was deposited at 70nA of evaporation beam for about 30 minutes, yielding 0.8 monolayer equivalent of cerium oxide nanostructures.
3) Annealing treatment in carbon monoxide atmosphere
At 1.0X 10-6For 0.8 monolayer equivalent of prepared CeO in mbar carbon monoxide atmosphere2Annealing was carried out at 550 ℃ for 10 minutes.
4) Annealing treatment in an oxygen atmosphere
At 5.0X 10-7In oxygen atmosphere of mbar to CeO2Annealing to 400 ℃ for 10 minutes. FIG. 2a is a scanning tunneling microscope image of the annealed sample showing a uniform and flat film, while FIG. 2b shows a nano-film having a height of about 0.32nm, which is comparable to CeO2(111) The individual O-Ce-O layers are highly uniform, so that a selectively exposed surface of the oxidized single layer cerium oxide film on Pt (111) is obtained.
EXAMPLE 3 oxidized Single layer cerium oxide film
1) Treating Pt (111) single crystal
Repeated argon ion sputtering (1.5kV, 1X 10) of Pt single crystal in a vacuum chamber-5mbar Ar,10min), oxygen gas firing (600 ℃, 1.0X 10)-7mbar O210min), and then the Pt (111) single crystal is heated and annealed at a high temperature of 700 ℃ for 3 minutes until no impurities are observed by X-ray photoelectron spectroscopy and a scanning tunneling microscope.
2) Growing cerium oxide on Pt (111) surface
Maintaining the temperature of a clean Pt (111) substrate at 300 ℃, and introducing 1.0X 10-7mbar O2Ce was deposited at 70nA of evaporation beam for about 30 minutes, yielding 0.8 monolayer equivalent of cerium oxide nanostructures.
3) Annealing treatment in carbon monoxide atmosphere
At 1.0X 10-6For 0.8 monolayer equivalent of prepared CeO in mbar carbon monoxide atmosphere2Annealing was carried out at 550 ℃ for 10 minutes.
4) Annealing treatment in an oxygen atmosphere
At 5.0X 10-7In oxygen atmosphere of mbar to CeO2Annealing to 500 ℃ for 10 minutes. As shown in fig. 3a, a film sample with a flat surface was obtained after annealing, while the height of the nano-film was about 0.32nm (fig. 3b), so that a selectively exposed surface of the oxidized single-layer cerium oxide film on Pt (111) was obtained.
EXAMPLE 4 oxidized bilayer cerium oxide film
1) Treating Pt (111) single crystal
Repeated argon ion sputtering (1.5kV, 1X 10) of Pt single crystal in a vacuum chamber-5mbar Ar,10min), oxygen gas firing (600 ℃, 1.0X 10)-7mbar O210min), and then the Pt (111) single crystal is heated and annealed at a high temperature of 700 ℃ for 3 minutes until no impurities are observed by X-ray photoelectron spectroscopy and a scanning tunneling microscope.
2) Growing cerium oxide on Pt (111) surface
Maintaining the temperature of a clean Pt (111) substrate at 300 ℃, and introducing 1.0X 10-7mbar O2Ce was deposited at 70nA of evaporation beam for about 30 minutes, yielding 0.8 monolayer equivalent of cerium oxide nanostructures.
3) Annealing treatment in carbon monoxide atmosphere
At 1.0X 10-6For 0.8 monolayer equivalent of prepared CeO in mbar carbon monoxide atmosphere2Annealing was carried out at 550 ℃ for 10 minutes.
4) Annealing treatment in an oxygen atmosphere
At 5.0X 10-7In oxygen atmosphere of mbar to CeO2Annealing to 500 ℃ for 20 minutes. FIG. 4a is a scanning tunneling microscope image of a sample obtained after annealing, wherein a large hole is formed in the middle of the film and the surface is coveredReduced to half of the sample of fig. 2, while the height of the nano-film is about 0.64nm (fig. 4b), i.e. two CeO2(111) The height of the O-Ce-O layer, so that it is obtained that the surface of the double-layer cerium oxide is completely exposed.
Example 5 reversible experiment
1) Annealing treatment in carbon monoxide atmosphere
Fig. 5a is a scanning tunneling microscope image of the surface of the double-layered cerium oxide of 0.8 monolayer equivalent, and it can be seen from fig. 5b that the height of the cerium oxide is 0.64nm, i.e., the height of the double-layered cerium oxide. At 1.0X 10-6The surface was annealed in an atmosphere of mbar carbon monoxide at 550 ℃ for 10 minutes.
2) Annealing treatment in an oxygen atmosphere
At 5.0X 10-7In oxygen atmosphere of mbar to CeO2Annealing to 500 ℃ for 10 minutes. FIG. 6a is a scanning tunneling microscope image of the sample obtained after annealing, the surface of the film being flat, and it can be seen from FIG. 6b that the height of the film is about 0.32nm (FIG. 4b), i.e. the single CeO2(111) The height of the O-Ce-O layer, so that a single layer cerium oxide surface is obtained.
Comparative example 1
1) Treating Pt (111) single crystal
Repeated argon ion sputtering (1.5kV, 1X 10) of Pt single crystal in a vacuum chamber-5mbar Ar,10min), oxygen gas firing (600 ℃, 1.0X 10)-7mbar O210min), and then the Pt (111) single crystal is heated and annealed at a high temperature of 700 ℃ for 3 minutes until no impurities are observed by X-ray photoelectron spectroscopy and a scanning tunneling microscope.
2) Growing cerium oxide on Pt (111) surface
Maintaining the temperature of a clean Pt (111) substrate at 300 ℃, and introducing 1.0X 10-7mbar O2Ce was deposited at 70nA of evaporation beam for about 30 minutes, yielding 0.8 monolayer equivalent of cerium oxide nanostructures. The surface cerium oxide obtained by the active deposition method exists mainly in the form of islands, while the surface is not flat as can be seen from fig. 7a, and single-layer and double-layer cerium oxide nano-islands are co-existed on the surface as can be seen from fig. 7bAnd (4) storing.
Test example 1
We performed activity tests using the surface of the oxidized cerium oxide film obtained in example 3, and we exposed the surface of this sample to 2.0X 10 at 25 deg.C-6mbar CO for 10 minutes of exposure time, FIG. 8a is a scanning tunneling microscope image of the surface after CO exposure, which shows many bright lines with a height of about 0.12nm (FIG. 8b) compared to the sample surface of example 3, indicating that CO adsorbs and reacts at 25 deg.C on the surface of the single layer of cerium oxide and forms a bright line structure on the surface of the single layer of cerium oxide, as compared to the conventional Pt/CeO2The structure has more excellent catalytic activity because the structure needs to show obvious activity at the temperature of more than 100 ℃.
In conclusion, the invention has the advantages that: the method of this example yielded single-layer (one O-Ce-O layer) and double-layer (two O-Ce-O layers) CeO that could not be achieved by the prior art, by simple control of the annealing atmosphere and time2The selectivity of the nano single crystal can be controlled, and the reversible regulation and control of the thickness which is not reported in the prior art can be further realized. The method is simple, feasible and feasible, and provides a method for preparing and oxidizing the single-layer and double-layer reversibly-regulated cerium oxide single crystal nano structure. Meanwhile, the single-layer cerium oxide film can react with CO at 25 ℃, and shows excellent room-temperature CO oxidation reaction activity.
The above examples are provided only for the purpose of describing the present invention, and are not intended to limit the scope of the present invention. The scope of the invention is defined by the appended claims. Various equivalent substitutions and modifications can be made without departing from the spirit and principles of the invention.
Claims (8)
1. A preparation method of a platinum-cerium oxide nano catalyst is characterized in that platinum is a Pt (111) single crystal, cerium oxide is deposited on the surface of the Pt (111) single crystal, and the cerium oxide single crystal is a single layer or a double layer, and is characterized in that: the preparation method of the platinum-cerium oxide nano catalyst with the reduced single-layer cerium oxide comprises the following steps:
(1) providing an atomically clean and flat single crystal Pt (111) substrate;
(2) maintaining the Pt (111) substrate treated in the step (1) at-200-400 ℃, and depositing Ce on the surface of a Pt (111) single crystal through a Ce evaporation source in an oxygen atmosphere;
(3) in a carbon monoxide atmosphere, for any 0.3-1 monolayer equivalent of CeO2Annealing is carried out, wherein the annealing temperature is 300-700 ℃.
2. A preparation method of a platinum-cerium oxide nano catalyst is characterized in that platinum is a Pt (111) single crystal, cerium oxide is deposited on the surface of the Pt (111) single crystal, and the cerium oxide single crystal is a single layer or a double layer, and is characterized in that: the preparation method of the platinum-cerium oxide nano catalyst with oxidized single-layer cerium oxide comprises the following steps:
(1) providing an atomically clean and flat single crystal Pt (111) substrate;
(2) maintaining the Pt (111) substrate treated in the step (1) at-200-400 ℃, and depositing Ce on the surface of a Pt (111) single crystal through a Ce evaporation source in an oxygen atmosphere;
(3) in a carbon monoxide atmosphere, for any 0.3-1 monolayer equivalent of CeO2Annealing at the temperature of 300-700 ℃;
(4) and (3) annealing the nano-catalyst sample prepared in the step (3) to 200-500 ℃ in an oxygen atmosphere, wherein the annealing time is controlled within 15 minutes.
3. A preparation method of a platinum-cerium oxide nano catalyst is characterized in that platinum is a Pt (111) single crystal, cerium oxide is deposited on the surface of the Pt (111) single crystal, and the cerium oxide single crystal is a single layer or a double layer, and is characterized in that: the preparation method of the platinum-cerium oxide nano catalyst with oxidized double-layer cerium oxide comprises the following steps:
(1) providing an atomically clean and flat single crystal Pt (111) substrate;
(2) maintaining the Pt (111) substrate treated in the step (1) at-200-400 ℃, and depositing Ce on the surface of a Pt (111) single crystal through a Ce evaporation source in an oxygen atmosphere;
(3) in a carbon monoxide atmosphere, for any 0.3-1 monolayer equivalent of CeO2Annealing at the temperature of 300-700 ℃;
(4) annealing the nano-catalyst sample prepared in the step (3) to 200-500 ℃ in an oxygen atmosphere, wherein the annealing time is controlled within 15 minutes;
(5) and (3) annealing the nano-catalyst sample prepared in the step (4) to 500-600 ℃ in an oxygen atmosphere, wherein the annealing time is controlled to be 15 minutes or more.
4. A preparation method of a platinum-cerium oxide nano catalyst is characterized in that platinum is a Pt (111) single crystal, cerium oxide is deposited on the surface of the Pt (111) single crystal, and the cerium oxide single crystal is a single layer or a double layer, and is characterized in that: the preparation method of the platinum-cerium oxide nano catalyst with oxidized double-layer cerium oxide comprises the following steps:
(1) providing an atomically clean and flat single crystal Pt (111) substrate;
(2) maintaining the Pt (111) substrate treated in the step (1) at-200-400 ℃, and depositing Ce on the surface of a Pt (111) single crystal through a Ce evaporation source in an oxygen atmosphere;
(3) in a carbon monoxide atmosphere, for any 0.3-1 monolayer equivalent of CeO2Annealing at the temperature of 300-700 ℃;
(4) and (3) annealing the nano-catalyst sample prepared in the step (3) to 500-600 ℃ in an oxygen atmosphere, wherein the annealing time is controlled to be 15 minutes or more.
5. The method of preparing the platinum-cerium oxide nanocatalyst according to claim 3 or 4, wherein the method of converting the double-layer cerium oxide into the single-layer cerium oxide comprises the following steps:
(a) annealing the platinum-cerium oxide nano catalyst with oxidized double-layer cerium oxide in a carbon monoxide atmosphere, wherein the annealing temperature is 300-700 ℃;
(b) annealing the nano-catalyst treated in the step (a) to 200-500 ℃ in an oxygen atmosphere, wherein the annealing time is controlled within 15 minutes, and obtaining the platinum-cerium oxide nano-catalyst with oxidized single-layer cerium oxide.
6. The production method according to claim 1 or 2 or 3 or 4, characterized in that:
the method for preparing the Ce evaporation source comprises the following steps: removing the surface oxide layer of the high-purity Ce foil, putting the high-purity Ce foil into a metal tungsten crucible, and putting the metal tungsten crucible into an electron beam evaporation source; putting an electron beam evaporation source into a preparation cavity of an ultrahigh vacuum system, and vacuumizing and baking to obtain 5 x 10-9～5×10-11An ultra-high vacuum environment of millibar (mbar); heating up the evaporation source, degassing the Ce source in the tungsten crucible until the working temperature of the Ce source is 5 x 10-9～5×10-11Background vacuum of mbar;
the single crystal Pt (111) substrate with clean and flat atomic level is characterized in that the single crystal Pt (111) substrate is pretreated to remove impurities on the surface of the single crystal Pt (111), and the pretreatment comprises the following steps: carrying out argon ion sputtering on single crystal Pt (111) in an ultrahigh vacuum preparation cavity, wherein the sputtering energy is 1-3 KeV and is 1 multiplied by 10-8～1×10-5And (3) carrying out oxygen burning at 500-700 ℃ in an oxygen mbar atmosphere, and then heating the Pt single crystal to 700-1000 ℃ for annealing.
7. The production method according to claim 1 or 2 or 3 or 4, characterized in that: when annealing is performed in a carbon monoxide atmosphere in the step (3), the carbon monoxide pressure is 1X 10-7～1×10-5mbar, annealing time of 10 minutes and more.
8. The production method according to claim 2 or 3, characterized in that: in the step (4), the oxygen pressure is 1X 10-8～1×10-5mbar。
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| US8859455B2 (en) * | 2011-04-08 | 2014-10-14 | The Regents Of The University Of California | Nanocrystal assembly for tandem catalysis |
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