A metal oxide catalyst, a method for preparing the same, and an application thereof

Abstract

The present application belongs to the technical field of catalysts, and particularly relates to a metal oxide catalyst, a preparation method and application thereof. The oxide carrier is placed in a carbon dioxide-containing atmosphere for heat preservation treatment to obtain a primary activated carrier; the primary activated carrier is calcined to obtain an activated carrier; the calcination temperature is 500-800 DEG C; metal nanoparticles are deposited on the surface of the activated carrier to obtain the metal oxide catalyst; the deposition is atomic layer deposition. The oxide is heat preserved in the carbon dioxide atmosphere to form carbonate on the surface of the oxide, and then the carbonate is removed by high-temperature calcination to generate isolated hydroxyl groups on the surface of the oxide carrier, which are used as nucleation sites of metal nanoparticles, so that the density of the metal nanoparticles can be improved. The metal nanoparticles are deposited on the surface of the activated oxide carrier by atomic layer deposition, which is beneficial to controlling the size of the metal nanoparticles and the uniformity of dispersion.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and in particular relates to a metal oxide catalyst and a preparation method and application thereof. Background Art

[0002] Metal oxide catalysts are widely used in the fields of biology, medicine, petroleum, and chemical engineering. Metal oxides consist of an oxide carrier and a metal supported on the surface of the oxide carrier. Loading a high density of small metal particles on the surface of the oxide carrier can improve the catalytic performance and metal utilization of the metal oxide catalyst.

[0003] Atomic layer deposition (ALD) technology is an advanced particle / thin film preparation technology that alternately introduces two different gas-phase precursor molecules to cause a self-limiting chemical reaction on the support surface, and the deposit grows layer by layer at the atomic level. By controlling the number of deposition cycles, metal nanoparticles with uniform and controllable size can be deposited on the surface of the oxide support. However, it is difficult to control the density of metal particles on the oxide surface by atomic layer deposition, because this is not only related to the atomic layer deposition process, but also to the nucleation sites on the support surface. The more nucleation sites there are, the higher the activity, and a higher density of metal particles can be obtained under the same deposition conditions.

[0004] To increase the number of nucleation sites on the support surface, the support can be treated with strong acids (such as sulfuric acid and nitric acid) or strong oxidizing gases (such as ozone and oxygen plasma) to generate oxygen-containing functional group nucleation sites on its surface. However, this treatment can damage the support surface composition and even its physical structure. Alternatively, a polymer layer can be attached to the support surface as a seed layer, using the oxygen-containing functional groups in the polymer as nucleation sites for deposition. However, this method introduces a polymer layer, which changes the surface properties of the support and may be detrimental to subsequent catalytic reactions. Furthermore, the polymer layer easily falls off the support surface, reducing catalyst stability.

[0005] Based on this, there is an urgent need to explore a new method that can prepare ultrafine and ultra-high density metal nanoparticles on its surface without changing the physical and chemical properties of the oxide support itself. Summary of the Invention

[0006] In view of this, the present invention provides a metal oxide catalyst and its preparation method and application. The metal nanoparticles loaded in the metal oxide catalyst provided by the present invention have a small particle size and a large density and are uniformly dispersed on the surface of the oxide carrier, and have good catalytic performance.

[0007] In order to solve the above technical problems, the present invention provides a method for preparing a metal oxide catalyst, comprising the following steps:

[0008] placing the oxide support in an atmosphere containing carbon dioxide and performing heat preservation treatment to obtain a primary activated support;

[0009] calcining the primary activated carrier to obtain an activated carrier; the calcination temperature is 500-800°C;

[0010] Metal nanoparticles are deposited on the surface of the activated carrier to obtain a metal oxide catalyst; the deposition is atomic layer deposition.

[0011] Preferably, the volume percentage of carbon dioxide in the carbon dioxide-containing atmosphere is greater than 80%.

[0012] Preferably, the temperature of the heat preservation treatment is 100-200° C., and the time of the heat preservation treatment is 10-20 hours.

[0013] Preferably, the calcination time is 1.5 to 3 hours.

[0014] Preferably, the oxide support is an aluminum oxide support, a titanium oxide support or a zinc oxide support.

[0015] Preferably, the metal nanoparticles include platinum nanoparticles or palladium nanoparticles.

[0016] Preferably, the number of cycles of the atomic layer deposition is 1 to 50 times.

[0017] The present invention also provides a metal oxide catalyst prepared according to the preparation method of the metal oxide catalyst described in the above technical solution, comprising an oxide carrier and metal nanoparticles loaded on the surface of the oxide carrier, wherein the average particle size of the metal nanoparticles is 1 to 3 nm, and the loading density of the metal nanoparticles on the surface of the metal oxide catalyst is 100 nm. 2 The metal oxide catalyst contains 6 to 10 metal nanoparticles.

[0018] The present invention also provides the use of the metal oxide catalyst described in the above technical solution in organic hydrogenation reactions or automobile exhaust treatment.

[0019] The present invention provides a method for preparing a metal oxide catalyst, comprising the following steps: heat-treating an oxide support in a carbon dioxide atmosphere to obtain a primary activated support; calcining the primary activated support to obtain an activated support; the calcination temperature is 500-800°C; and depositing metal nanoparticles on the surface of the activated support to obtain a metal oxide catalyst; the deposition is performed by atomic layer deposition. In the present invention, the oxide support is heat-treated in a carbon dioxide atmosphere to form carbonates on the oxide surface, and then calcined at high temperature to remove the carbonates. Isolated hydroxyl groups are generated on the surface of the oxide support, serving as nucleation sites for metal nanoparticles, thereby increasing the density of the metal nanoparticles. The use of atomic layer deposition to deposit metal nanoparticles on the surface of the activated oxide support facilitates control of the size and uniformity of the metal nanoparticles. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 TEM images of the metal oxide catalysts prepared in Example 1 and Comparative Example 1;

[0021] Figure 2 This is the infrared spectrum of the activated carrier in Example 1. DETAILED DESCRIPTION

[0022] The present invention provides a method for preparing a metal oxide catalyst, comprising the following steps:

[0023] placing the oxide support in an atmosphere containing carbon dioxide and performing heat preservation treatment to obtain a primary activated support;

[0024] calcining the primary activated carrier to obtain an activated carrier; the calcination temperature is 500-800°C;

[0025] Metal nanoparticles are deposited on the surface of the activated carrier to obtain a metal oxide catalyst; the deposition is atomic layer deposition.

[0026] The present invention places an oxide support in an atmosphere containing carbon dioxide and performs a heat treatment to obtain a primary activated support. In the present invention, the oxide support is preferably an alumina support, a titania support, or a zinc oxide support, more preferably an alumina support or a titania support. In the present invention, the volume percentage of carbon dioxide in the carbon dioxide-containing atmosphere is preferably 80% or more, more preferably 80-100%. In the present invention, the carbon dioxide-containing atmosphere is preferably a mixture of carbon dioxide and oxygen, or carbon dioxide.

[0027] In the present invention, the temperature of the heat preservation treatment is preferably 100-200° C., more preferably 100-150° C.; the time of the heat preservation treatment is preferably 10-20 h, more preferably 10-15 h.

[0028] In the present invention, the heat preservation treatment is preferably performed in a tube furnace.

[0029] In the present invention, after the heat preservation treatment, the process preferably further comprises: cooling the heat-insulated product to room temperature. In the present invention, the room temperature is preferably 20-35° C., more preferably 25-30° C. In the present invention, the cooling is preferably furnace cooling.

[0030] After obtaining the primary activated support, the present invention calcines the primary activated support to obtain the activated support. In the present invention, the calcination temperature is 500-800°C, preferably 500-600°C; the calcination time is preferably 1.5-3 hours, more preferably 2-3 hours.

[0031] In the present invention, the calcination is preferably carried out in an air atmosphere. In the present invention, the calcination is preferably carried out in a muffle furnace.

[0032] In the present invention, after the calcination, the process preferably further comprises: cooling the calcined product to room temperature. In the present invention, the room temperature is preferably 20-35° C., more preferably 25-30° C. In the present invention, the cooling is preferably furnace cooling.

[0033] The present invention limits the calcination temperature to the above range, ensuring the removal of carbonates on the support surface while avoiding damage to the support. The present invention activates the oxide support through heat preservation and calcination. The activation process provided by the present invention does not destroy the physical structure of the oxide support (such as specific surface area, pore structure, and crystal form), nor does it cause surface corrosion or surface-attached additives, thereby not changing the original properties of the oxide support. The physical and chemical properties of the activated oxide support remain essentially unchanged, and will not affect the subsequent use of the catalyst.

[0034] After obtaining the activated support, the present invention deposits metal nanoparticles on the surface of the activated support to obtain a metal oxide catalyst. In the present invention, the metal nanoparticles preferably include platinum nanoparticles or palladium nanoparticles, more preferably platinum nanoparticles.

[0035] In the present invention, the deposition is atomic layer deposition. In the present invention, the atomic layer deposition preferably includes the following steps:

[0036] (1) placing the activated carrier in an atomic layer deposition reaction chamber, introducing a metal precursor by pulse, and then sequentially performing a first gas holding and a first inert gas purge;

[0037] (2) pulse-introducing an oxide gas into the reaction chamber, followed by a second gas holding and a second inert gas purge;

[0038] Repeat steps (1) and (2) 1 to 50 times.

[0039] The present invention places an activated carrier in an atomic layer deposition reaction chamber, pulses a metal precursor, and then sequentially performs a first gas hold and a first inert gas purge. In the present invention, the temperature of the reaction chamber is preferably 100-200°C, more preferably 150°C. In the present invention, the process preferably further includes evacuating the reaction chamber before pulses of the metal precursor are introduced.

[0040] The present invention has no special requirements for the metal precursor; conventional materials in the art can be used. In the present invention, taking platinum metal nanoparticles as an example, the platinum metal precursor is gaseous (trimethyl)methylcyclopentadienylplatinum. In the present invention, the pulse time of the pulsed metal precursor is preferably 0.01 to 100 seconds, more preferably 1 to 10 seconds.

[0041] In the present invention, the introduction of the metal precursor is preferably stopped before the first gas holding period. In the present invention, the first gas holding period is preferably 1 to 100 seconds, more preferably 15 to 30 seconds. During the first gas holding period, the gas-phase metal precursor molecules chemically react with the hydroxyl groups on the surface of the activated support.

[0042] In the present invention, the first inert gas purge is preferably high-purity nitrogen or argon, more preferably high-purity nitrogen. The first inert gas purge duration is preferably 1 to 100 seconds, more preferably 25 to 30 seconds. In the present invention, the purity of the high-purity nitrogen is preferably greater than or equal to 99.99%. The first inert gas purge can purge unadsorbed metal precursor molecules out of the reaction chamber.

[0043] After the first inert gas purge, the present invention introduces a pulsed oxidizing gas into the reaction chamber, followed by a second gas hold and a second inert gas purge. In the present invention, the oxidizing gas preferably comprises oxygen or ozone, more preferably ozone. In the present invention, the pulse duration of the oxidizing gas is preferably 0.01 to 100 seconds, more preferably 1 to 10 seconds.

[0044] In the present invention, the introduction of the oxide gas is preferably stopped before the second gas holding. In the present invention, the second gas holding time is preferably 1 to 100 seconds, more preferably 12 to 30 seconds. In the present invention, the oxide gas and the adsorbed metal precursor molecules undergo a chemical reaction during the second gas holding process.

[0045] In the present invention, the second inert gas purge is preferably high-purity nitrogen or argon, more preferably high-purity nitrogen. The second inert gas purge duration is preferably 1 to 100 seconds, more preferably 20 to 30 seconds. In the present invention, the purity of the high-purity nitrogen is preferably greater than or equal to 99.99%. The second inert gas purge can purge excess oxidizing gas and byproducts (carbon dioxide and methane) generated during the second gas holding step out of the reaction chamber.

[0046] In the present invention, the number of cycles of the atomic layer deposition is preferably 1 to 50 times, more preferably 30 to 40 times.

[0047] The metal nanoparticles deposited by the atomic layer deposition method of the present invention have ultrafine particle size and high dispersibility.

[0048] The present invention also provides a metal oxide catalyst prepared according to the preparation method of the metal oxide catalyst described in the above technical solution, comprising an oxide support and metal nanoparticles supported on the surface of the oxide support, wherein the average particle size of the metal nanoparticles is 1 to 3 nm, preferably 2.3 to 2.4 nm. The loading density of the metal nanoparticles on the surface of the metal oxide catalyst is 100 nm. 2 The metal oxide catalyst contains 6 to 10 metal nanoparticles, preferably 100 nm 2 The metal oxide catalyst contains 7 to 8 metal nanoparticles.

[0049] The present invention also provides the use of the metal oxide catalyst described in the above technical solution in organic hydrogenation reactions or automobile exhaust treatment.

[0050] In order to further illustrate the present invention, the technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0051] Example 1

[0052] 1. Carrier activation

[0053] (1) 100 mg of alumina was placed in a porcelain boat, which was then placed in a tube furnace. A CO2 / O2 mixture was introduced into the tube furnace, wherein the volume percentage of CO2 in the mixture was 80%. The tube furnace was heated to 100°C, kept at this temperature for 10 hours, and then naturally cooled to 25°C to obtain a primary activated carrier.

[0054] (2) placing the primary activated carrier in a muffle furnace, calcining it at 500°C for 1.5 h in an air atmosphere, and then naturally cooling it to 25°C to obtain an activated carrier;

[0055] 2. Deposition of Pt nanoparticles on the surface of activated support using ALD technology

[0056] Put the activated carrier into the atomic layer deposition reaction cavity, the reaction cavity temperature is 150℃, vacuumize; after stabilization, the following steps are carried out:

[0057] (1) introduce Pt precursor: pulse introduction of gas phase platinum precursor (trimethyl) methyl cyclopentadienyl platinum, pulse time 1s;

[0058] (2) hold up: stop introducing gas, keep for 15s;

[0059] (3) inert gas purge: introduce high-purity nitrogen (purity 99.99%) to purge the oxide surface, purge time 25s;

[0060] (4) introduce oxide gas: pulse introduction of oxide gas ozone into the reaction cavity, pulse time 1s;

[0061] (5) hold up: stop introducing gas, keep for 12s;

[0062] (6) inert gas purge: introduce high-purity nitrogen (purity 99.99%) to purge the oxide surface, purge time 20s;

[0063] Repeat steps (1) to (6) 30 times to obtain a platinum alumina catalyst.

[0064] Example 2

[0065] Put 100mg of alumina into a porcelain boat, and put the porcelain boat into a tube furnace; introduce pure CO2 gas into the tube furnace; increase the temperature of the tube furnace to 200℃, and after heat preservation treatment for 10h, naturally cool to 25℃ to obtain a primary activated carrier;

[0066] Put the primary activated carrier into a muffle furnace, and after calcination at 600℃ for 3h in an air atmosphere, naturally cool to 25℃ to obtain an activated carrier;

[0067] Deposit Pt nanoparticles on the surface of the activated carrier according to the method of Example 1 to obtain a platinum alumina catalyst.

[0068] Example 3

[0069] Put 100mg of titanium oxide into a porcelain boat, and put the porcelain boat into a tube furnace; introduce pure CO2 gas into the tube furnace; increase the temperature of the tube furnace to 200℃, and after heat preservation treatment for 10h, naturally cool to 25℃ to obtain a primary activated carrier;

[0070] Put the primary activated carrier into a muffle furnace, and after calcination at 500℃ for 1.5h in an air atmosphere, naturally cool to 25℃ to obtain an activated carrier;

[0071] Pt nanoparticles were deposited on the surface of the activated support according to the method of Example 1 to obtain a platinum titanium oxide catalyst.

[0072] Example 4

[0073] 1. Carrier activation

[0074] (1) 100 mg of titanium oxide was placed in a porcelain boat, and the porcelain boat was placed in a tube furnace; pure CO gas was introduced into the tube furnace; the temperature of the tube furnace was raised to 150°C, kept at this temperature for 20 hours, and then naturally cooled to 25°C to obtain a primary activated carrier;

[0075] (2) placing the primary activated carrier in a muffle furnace, calcining it at 600°C for 2 h in an air atmosphere, and then naturally cooling it to 25°C to obtain an activated carrier;

[0076] 2. Deposition of Pt nanoparticles on the surface of activated support using ALD technology

[0077] Place the activated carrier in the atomic layer deposition reaction chamber at 150°C and evacuate the chamber. After stabilization, proceed with the following steps:

[0078] (1) Introduction of Pt precursor: Pulse introduction of gaseous platinum precursor (trimethyl)methylcyclopentadienylplatinum with a pulse time of 0.5 s;

[0079] (2) Breath holding: stop the gas flow and hold for 30 seconds;

[0080] (3) Inert gas purge: high-purity nitrogen (purity of 99.99%) is introduced to purge the oxide surface for 40 seconds;

[0081] (4) Introducing oxide gas: Pulse the oxide gas ozone into the reaction chamber with a pulse time of 0.5 s;

[0082] (5) Breath holding: stop the gas flow and hold for 30 seconds;

[0083] (6) Inert gas purge: high-purity nitrogen (purity of 99.99%) is introduced to purge the oxide surface for 40 seconds;

[0084] Repeat steps (1) to (6) 30 times to obtain a platinum titanium oxide catalyst.

[0085] Comparative Example 1

[0086] The alumina support was not activated and Pt was directly deposited;

[0087] Place the aluminum oxide in an atomic layer deposition reaction chamber at 150°C and evacuate the chamber. Once the chamber is stable, proceed with the following steps:

[0088] (1) Introduction of Pt precursor: Pulse introduction of gaseous platinum precursor (trimethyl)methylcyclopentadienylplatinum with a pulse time of 1 s;

[0089] (2) Breath holding: stop the gas flow and hold for 15 seconds;

[0090] (3) Inert gas purge: high-purity nitrogen (purity of 99.99%) is introduced to purge the oxide surface for 25 seconds;

[0091] (4) Introducing oxide gas: Pulse the oxide gas ozone into the reaction chamber with a pulse time of 1 s;

[0092] (5) Breath holding: stop the gas flow and hold for 12 seconds;

[0093] (6) Inert gas purge: high-purity nitrogen (purity of 99.99%) is introduced to purge the oxide surface for 20 seconds;

[0094] Repeat steps (1) to (6) 30 times to obtain a platinum alumina catalyst.

[0095] Comparative Example 2

[0096] 1. Carrier activation (calcination in direct air without heat preservation in an atmosphere containing carbon dioxide)

[0097] 100 mg of alumina was placed in a muffle furnace, calcined at 500 °C for 1.5 h in air atmosphere, and then naturally cooled to 25 °C to obtain an activated carrier;

[0098] 2. Deposition of Pt nanoparticles on the surface of activated support using ALD technology

[0099] Place the activated carrier in the atomic layer deposition reaction chamber at 150°C and evacuate the chamber. After stabilization, proceed with the following steps:

[0100] (1) Introduction of Pt precursor: Pulse introduction of gaseous platinum precursor (trimethyl)methylcyclopentadienylplatinum with a pulse time of 1 s;

[0101] (2) Breath holding: stop the gas flow and hold for 15 seconds;

[0102] (3) Inert gas purge: high-purity nitrogen (purity of 99.99%) is introduced to purge the oxide surface for 25 seconds;

[0103] (4) Introducing oxide gas: Pulse the oxide gas ozone into the reaction chamber with a pulse time of 1 s;

[0104] (5) Breath holding: stop the gas flow and hold for 12 seconds;

[0105] (6) Inert gas purge: high-purity nitrogen (purity of 99.99%) is introduced to purge the oxide surface for 20 seconds;

[0106] Repeat steps (1) to (6) 30 times to obtain a platinum alumina catalyst.

[0107] The metal oxide catalysts prepared in Example 1 and Comparative Example 1 were examined by transmission electron microscopy to obtain TEM images, as shown in FIG. Figure 1 shown. Figure 1 The black dots in the middle are Pt nanoparticles. As can be seen from the figure, the Pt nanoparticles supported on the surface of alumina in the platinum alumina catalyst prepared in Example 1 have a high density and are evenly dispersed.

[0108] For the metal oxide catalysts prepared in Examples 1 to 3 and Comparative Examples 1 to 2, the mass percentage of platinum in the samples was measured by inductively coupled plasma optical emission spectroscopy (ICP-OES), and the loading density and average particle size of platinum in the samples were statistically analyzed by transmission electron microscopy (TEM). The results are listed in Table 1.

[0109] Table 1 Mass percentage of platinum in the catalysts of Examples 1 to 3 and Comparative Examples 1 to 2

[0110]

[0111] Combined with Table 1 and Figure 2 It can be seen that the metal oxide catalyst prepared according to the preparation method provided by the present invention has a higher metal content and a higher density and is evenly dispersed.

[0112] The surface of the activated carrier in Example 1 was detected by infrared spectroscopy to obtain an infrared spectrum, as shown in FIG. Figure 2 shown. Figure 2 Middle at 3745cm -1 An obvious infrared peak appears at the 400 nm tantalum phosphate buffered saline solution, which is the infrared characteristic peak of isolated hydroxyl groups, indicating that isolated hydroxyl groups are generated on the surface of alumina after calcination.

[0113] Although the above embodiment provides a detailed description of the present invention, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a metal oxide catalyst, comprising the following steps: Placing an oxide support in an atmosphere containing carbon dioxide and performing a heat preservation treatment to obtain a primary activated support; the oxide support is an aluminum oxide support, a titanium oxide support, or a zinc oxide support; the volume percentage of carbon dioxide in the carbon dioxide-containing atmosphere is greater than 80%; the heat preservation treatment temperature is 100-200° C., and the heat preservation treatment time is 10-20 hours; calcining the primary activated carrier to obtain an activated carrier; the calcination temperature is 500 to 800° C., and the calcination time is 1.5 to 3 hours; Metal nanoparticles are deposited on the surface of the activated carrier to obtain a metal oxide catalyst; the deposition is atomic layer deposition.

2. The method for preparing the metal oxide catalyst according to claim 1, wherein: The metal nanoparticles include platinum nanoparticles or palladium nanoparticles.

3. The method for preparing the metal oxide catalyst according to claim 1 or 2, characterized in that: The number of cycles of the atomic layer deposition is 1 to 50.

4. The metal oxide catalyst prepared by the method for preparing a metal oxide catalyst according to any one of claims 1 to 3, comprising an oxide support and metal nanoparticles supported on the surface of the oxide support, characterized in that: The average particle size of the metal nanoparticles is 1 to 3 nm, and the loading density of the metal nanoparticles on the surface of the metal oxide catalyst is 100 nm. 2 The metal oxide catalyst contains 6 to 10 metal nanoparticles.

5. Use of the metal oxide catalyst according to claim 4 in organic hydrogenation reactions or automobile exhaust treatment.

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