CN115382572B - Palladium catalyst with stable double sites and preparation method and application thereof - Google Patents

Palladium catalyst with stable double sites and preparation method and application thereof Download PDF

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CN115382572B
CN115382572B CN202211080049.3A CN202211080049A CN115382572B CN 115382572 B CN115382572 B CN 115382572B CN 202211080049 A CN202211080049 A CN 202211080049A CN 115382572 B CN115382572 B CN 115382572B
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palladium
palladium catalyst
carrier
time
pulse
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CN115382572A (en
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张斌
王哲
杨新春
孟繁春
覃勇
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Shanxi Institute of Coal Chemistry of CAS
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Shanxi Institute of Coal Chemistry of CAS
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    • 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
    • B01J31/00—Catalysts comprising hydrides, coordination complexes or organic compounds
    • B01J31/02—Catalysts comprising hydrides, coordination complexes or organic compounds containing organic compounds or metal hydrides
    • B01J31/0201—Oxygen-containing compounds
    • B01J31/0205—Oxygen-containing compounds comprising carbonyl groups or oxygen-containing derivatives, e.g. acetals, ketals, cyclic peroxides
    • B01J31/0208—Ketones or ketals
    • 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
    • B01J23/002—Mixed oxides other than spinels, e.g. perovskite
    • 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
    • B01J23/40—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals of the platinum group metals
    • B01J23/44—Palladium
    • 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
    • B01J23/56—Platinum group metals
    • B01J23/63—Platinum group metals with rare earths or actinides
    • 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
    • B01J29/00—Catalysts comprising molecular sieves
    • B01J29/03—Catalysts comprising molecular sieves not having base-exchange properties
    • B01J29/0308—Mesoporous materials not having base exchange properties, e.g. Si-MCM-41
    • B01J29/0316—Mesoporous materials not having base exchange properties, e.g. Si-MCM-41 containing iron group metals, noble metals or copper
    • B01J29/0325—Noble metals
    • 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
    • B01J29/00—Catalysts comprising molecular sieves
    • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
    • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
    • B01J29/40—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11, as exemplified by patent documents US3702886, GB1334243 and US3709979, respectively
    • B01J29/42—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11, as exemplified by patent documents US3702886, GB1334243 and US3709979, respectively containing iron group metals, noble metals or copper
    • B01J29/44—Noble metals
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C45/00—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds
    • C07C45/27—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation
    • C07C45/32—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation with molecular oxygen
    • C07C45/37—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation with molecular oxygen of >C—O—functional groups to >C=O groups
    • C07C45/38—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation with molecular oxygen of >C—O—functional groups to >C=O groups being a primary hydroxyl group
    • 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
    • B01J2229/00—Aspects of molecular sieve catalysts not covered by B01J29/00
    • B01J2229/10—After treatment, characterised by the effect to be obtained
    • B01J2229/18—After treatment, characterised by the effect to be obtained to introduce other elements into or onto the molecular sieve itself
    • B01J2229/186—After treatment, characterised by the effect to be obtained to introduce other elements into or onto the molecular sieve itself not in framework positions
    • 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
    • B01J2231/00—Catalytic reactions performed with catalysts classified in B01J31/00
    • B01J2231/70—Oxidation reactions, e.g. epoxidation, (di)hydroxylation, dehydrogenation and analogues
    • B01J2231/76—Dehydrogenation
    • B01J2231/763—Dehydrogenation of -CH-XH (X= O, NH/N, S) to -C=X or -CX triple bond species

Abstract

The invention provides a palladium catalyst with stable double sites, and a preparation method and application thereof, and belongs to the technical field of catalytic chemistry. The invention provides a palladium catalyst with stable double sites, which comprises a carrier and palladium species dispersed on the surface of the carrier, wherein the palladium species comprises Pd 0 And Pd (Pd) 2+ The Pd is 2+ Occupy Pd 0 And Pd (Pd) 2+ 60 to 75 percent of the total amount, pd after the palladium catalyst is used 2+ Occupy Pd 0 And Pd (Pd) 2+ 70-85% of the total amount. The palladium catalyst provided by the invention has stable double sites, and has high catalytic efficiency and selectivity when being used for catalyzing alcohol to oxidize to prepare aldehyde; and the palladium catalyst provided by the invention is not easy to deactivate after being stored in an air atmosphere for a long time.

Description

Palladium catalyst with stable double sites and preparation method and application thereof
Technical Field
The invention relates to the technical field of catalytic chemistry, in particular to a palladium catalyst with stable double sites, and a preparation method and application thereof.
Background
Aldehydes are precursors or intermediates for the fine chemical synthesis of pharmaceuticals, fragrances, pesticides, and dyes, and are one of the most basic and useful chemical products, and are generally produced industrially by oxidation of alcohols. Conventional benzyl alcohol oxidation processes typically use inorganic oxidants such as chromates and permanganates, but these are highly corrosive, have high toxicity as by-products after oxidation of the alcohol, and have a high number of by-products and low aldehyde selectivity. Compared with the traditional method, the method for preparing the aldehyde by using the alcohol solvent-free liquid phase catalytic oxidation method uses the supported metal catalyst, uses oxygen molecules as an oxidant, uses byproducts as water, and has the advantages of mild conditions, environmental protection and high economic value.
The supported metal catalyst used in the above process is typically a palladium-based catalyst, and it is generally believed that the active site of the palladium-catalyzed alcohol liquid phase oxidation is Pd 0 . By comparison of a single valence catalyst, pdHAP-0 (Pd) 0 ) And PdHAP-1 (Pd) 2+ ) Catalyst Performance, catalyst active center was found to be Pd at the corners of 3.8nm nanoparticles 0 Generated in situ (j.am. Chem. Soc.,2004,126,10657-10666). Grunwaldt also indicates that metallic palladium species are more active (J.Phys.chem.B, 2006,110,25586-25589).
But with Pd only 0 The palladium-based catalyst serving as an active site catalyzes alcohol to oxidize to prepare aldehyde, palladium species are unstable in the reaction process, in-situ conversion is needed, and oxidation reduction occurs at a single siteCatalytic efficiency and selectivity remain to be improved. The palladium-based catalyst is easy to deactivate after being stored in an air atmosphere for a long time, and needs to be subjected to reduction treatment before being used.
Disclosure of Invention
The invention aims to provide a palladium catalyst with stable double sites, a preparation method and application thereof, and the palladium catalyst provided by the invention has stable double sites, is used for preparing aldehyde by catalyzing alcohol oxidation, and has good stability, high catalytic efficiency and high selectivity in the reaction process; and the palladium catalyst provided by the invention is not easy to deactivate after being stored in an air atmosphere for a long time.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides a palladium catalyst with stable double sites, which comprises a carrier and palladium species dispersed on the surface of the carrier, wherein the palladium species comprises Pd 0 And Pd (Pd) 2+ The Pd is 2+ Occupy Pd 0 And Pd (Pd) 2+ 60 to 75 percent of the total amount, pd after the palladium catalyst is used 2+ Occupy Pd 0 And Pd (Pd) 2+ 70-85% of the total amount.
Preferably, the palladium in the palladium catalyst is present in the form of clusters.
Preferably, the palladium element content in the palladium catalyst is 0.1 to 2wt%.
Preferably, the support comprises an oxide support or a molecular sieve support.
Preferably, the oxide support comprises titania, ceria or alumina and the molecular sieve support comprises an SBA-15 molecular sieve or ZSM-5 molecular sieve.
The invention provides a preparation method of the palladium catalyst, which comprises the following steps:
(1) Based on an atomic layer deposition method, sequentially pulsing gaseous palladium hexafluoroacetylacetonate and gaseous reducing agent to perform deposition treatment on the surface of a carrier to obtain a palladium catalyst; wherein, in the process of the deposition treatment, the pulse time of the palladium hexafluoroacetylacetonate is not longer than the pulse time of the reducing agent;
or (2) carrying out deposition treatment on the surface of the carrier loaded with palladium by using pulse gaseous hexafluoroacetylacetone based on an atomic layer deposition method to obtain the palladium catalyst.
Preferably, the reducing agent comprises hydrogen or formaldehyde solution.
Preferably, the number of deposition treatments in (1) and (2) is independently 1 to 100.
The invention provides an application of the palladium catalyst prepared by the technical scheme or the preparation method of the technical scheme in preparing aldehyde by catalyzing alcohol to undergo oxidation reaction.
Preferably, the alcohol comprises benzyl alcohol, 4-methylbenzyl alcohol, 2-phenylethanol or 1-octanol.
The invention provides a palladium catalyst with stable double sites, which comprises a carrier and palladium species dispersed on the surface of the carrier, wherein the palladium species comprises Pd 0 And Pd (Pd) 2+ The Pd is 2+ Occupy Pd 0 And Pd (Pd) 2+ 60 to 75 percent of the total amount, pd after the palladium catalyst is used 2+ Occupy Pd 0 And Pd (Pd) 2+ 70-85% of the total amount. The palladium catalyst provided by the invention has higher Pd 2+ /(Pd 0 +Pd 2+ ) The proportion of the double-site palladium catalyst is good in stability of the position and valence of Pd species, and the palladium catalyst is used for catalyzing alcohol to oxidize to prepare aldehyde, so that stable Pd can be maintained in the reaction process 2+ /(Pd 0 +Pd 2+ ) Proportion of Pd 0 And Pd (Pd) 2+ Can respectively play the dehydrogenation function and the oxygen activation function of alcohol, and has high catalytic efficiency and high selectivity. Meanwhile, the palladium catalyst provided by the invention is not easy to deactivate after being stored in an air atmosphere for a long time.
The invention provides a preparation method of the palladium catalyst, which comprises the following steps: (1) Based on an atomic layer deposition method, sequentially pulsing gaseous palladium hexafluoroacetylacetonate and gaseous reducing agent to perform deposition treatment on the surface of a carrier to obtain a palladium catalyst; wherein, in the process of the deposition treatment, the pulse time of the palladium hexafluoroacetylacetonate is not longer than the pulse time of the reducing agent; alternatively, (2) in the presence of pulsed gaseous hexafluoroacetylacetone based on atomic layer depositionAnd carrying out deposition treatment on the surface of the carrier loaded with palladium to obtain the palladium catalyst. The invention can prepare and obtain the high Pd with stable double sites based on atomic layer deposition 2+ /(Pd 0 +Pd 2+ ) The proportion of palladium catalyst, in particular Pd, due to oxidation state 2+ Species are typically present at the metal-oxide interface or are generated by in situ oxidation, so for larger sized palladium nanoparticles, pd 2+ The content is low. The invention prepares the palladium catalyst based on atomic layer deposition, can accurately control and stabilize the size, the position and the valence state of the catalytic center, has stable double sites compared with the palladium supported catalyst prepared by the traditional wet chemical method, and can keep higher and stable Pd in the alcohol oxidation reaction process 2+ /(Pd 0 +Pd 2+ ) The ratio can promote the efficient coupling of alcohol dehydrogenation and oxidation reaction, and has the catalytic activity far higher than that of palladium supported catalyst prepared by the traditional wet chemical method. In addition, the palladium catalyst prepared by the atomic layer deposition method is probably due to the fact that the position and valence of Pd species can be stabilized in the deposition treatment process by pulse proper amount of palladium hexafluoroacetylacetonate or hexafluoroacetylacetonate, so that the palladium catalyst can be stored for a long time in an air atmosphere without inactivation, and can also maintain good stability in the alcohol oxidation reaction process; however, the palladium catalyst prepared by the method is easy to be deactivated in the storage process due to unstable palladium valence state, and is easy to be deactivated under the combined action of a heat source, oxygen and alcohol reactants when the palladium catalyst is applied to the alcohol oxidation reaction process.
Further, the invention can control the pulse quantity of palladium hexafluoroacetylacetonate or hexafluoroacetylacetone by controlling the times of deposition treatment in an atomic layer deposition method, thereby controlling Pd in a gradient way 0 And Pd (Pd) 2+ And regulating the catalytic performance of the target catalyst.
Drawings
FIG. 1 is a 20Pd/CeO prepared in example 1 2 HRTEM images of (a);
FIG. 2 is 20Pd +.CeO 2 AC-HAADF-STEM diagram of FIG. 2, a is 20Pd/CeO 2 The AC-HAADF-STEM pattern of (2), b, c and d are 20Pd/CeO 2 EDS diagram of medium elements Ce, O and Pd;
FIG. 3 is a 20Pd/CeO prepared in example 1 2 Is a Pd K-edge XANES diagram.
Detailed Description
The invention provides a palladium catalyst with stable double sites, which comprises a carrier and palladium species dispersed on the surface of the carrier, wherein the palladium species comprises Pd 0 And Pd (Pd) 2+ The Pd is 2+ Occupy Pd 0 And Pd (Pd) 2+ 60 to 75 percent of the total amount, pd after the palladium catalyst is used 2+ Occupy Pd 0 And Pd (Pd) 2+ 70-85% of the total amount.
The palladium catalyst provided by the invention comprises a carrier. In the present invention, the support preferably comprises an oxide support or a molecular sieve support; the oxide support preferably comprises titanium dioxide (TiO 2 ) Cerium oxide (CeO) 2 ) Or alumina (Al) 2 O 3 ) The molecular sieve support preferably comprises an SBA-15 molecular sieve or a ZSM-5 molecular sieve. In the present invention, the carrier is in the form of powder, and the particle size of the carrier is not particularly limited, and carriers having a particle size well known to those skilled in the art may be used. In the present invention, the carrier is preferably dispersed on the surface of a substrate, the substrate is preferably a quartz plate, and the size of the substrate is preferably 80mm×80mm×2mm; the support is preferably supported on the surface of the substrate at a loading of 15 to 25mg, more preferably 20mg, based on the substrate having dimensions 80mm by 2 mm.
The palladium catalyst provided by the invention comprises a palladium species dispersed on the surface of the carrier, wherein the palladium species comprises Pd 0 And Pd (Pd) 2+ The Pd is 2+ Occupy Pd 0 And Pd (Pd) 2+ 60 to 75% of the total amount, specifically 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74% or 75%; pd after the palladium catalyst is used 2+ Occupy Pd 0 And Pd (Pd) 2+ 70 to 85% of the total amount, specifically 70%, 71%, 72%, 73%, and,74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84% or 85%. In the present invention, palladium in the palladium catalyst is particularly present in the form of clusters; in the present invention, the palladium active center in the palladium catalyst is specifically a PdO cluster (a small amount of Pd is packed 0 ) Rather than Pd clusters. In the present invention, the content of palladium element in the palladium catalyst is preferably 0.1 to 2wt%, more preferably 0.2 to 1.8wt%, further preferably 0.4 to 0.8wt%, and still further preferably 0.5 to 0.7wt%.
The invention provides a preparation method of the palladium catalyst, which comprises the following steps:
(1) Based on an atomic layer deposition method, sequentially pulsing gaseous palladium hexafluoroacetylacetonate and gaseous reducing agent to perform deposition treatment on the surface of a carrier to obtain a palladium catalyst; wherein, in the process of the deposition treatment, the pulse time of the palladium hexafluoroacetylacetonate is not longer than the pulse time of the reducing agent;
or (2) carrying out deposition treatment on the surface of the carrier loaded with palladium by using pulse gaseous hexafluoroacetylacetone based on an atomic layer deposition method to obtain the palladium catalyst.
In the present invention, the raw materials for preparation are commercially available products well known to those skilled in the art unless otherwise specified. Two methods for preparing the palladium catalyst are described in detail below, respectively.
The invention is based on an atomic layer deposition method, and the palladium catalyst is obtained by sequentially pulsing gaseous palladium hexafluoroacetylacetonate and gaseous reducing agent to perform deposition treatment on the surface of a carrier; and in the deposition treatment process, the pulse time of the palladium hexafluoroacetylacetonate is not longer than that of the reducing agent, and the breath holding time of the palladium hexafluoroacetylacetonate is not shorter than that of the reducing agent.
In the present invention, the reducing agent preferably includes hydrogen or formaldehyde solution; the concentration of the formaldehyde solution is preferably 37wt%; the solvent of the formaldehyde solution is preferably water. In an embodiment of the invention, the deposition process is preferably performed in a vacuum reaction chamber of an atomic layer deposition apparatus. In the invention, the carrier is preferably dispersed on the surface of the substrate, and then the substrate with the carrier dispersed on the surface is placed in a vacuum reaction chamber of an atomic layer deposition device for deposition treatment. In the present invention, the method of dispersing the carrier on the surface of the substrate preferably includes: and mixing the carrier with ethanol, coating the obtained carrier feed liquid on the surface of a substrate, and drying to form a carrier layer on the surface of the substrate. The concentration of the carrier feed liquid is not particularly limited, and the carrier can be dispersed so as to facilitate subsequent coating. The specific conditions for the coating and drying are not particularly limited in the present invention, and conditions well known to those skilled in the art may be employed.
After placing the substrate with the carrier dispersed on the surface in the vacuum reaction cavity, the invention preferably sets deposition parameters, wherein the deposition parameters preferably comprise: the temperature of the vacuum reaction cavity is preferably 140-180 ℃, more preferably 150-160 ℃; the pressure is preferably 10 to 70MPa, more preferably 20 to 50MPa; the temperature of the palladium hexafluoroacetylacetonate is preferably 55-70 ℃, more preferably 60-65 ℃; the temperature of the reducing agent is preferably 20 to 30 ℃, more preferably 25 ℃; the volume ratio of the flow rate of the carrier gas to the vacuum reaction chamber is preferably 1: (12 to 20), more preferably 1: (15-20); the carrier gas is preferably nitrogen, argon or helium.
After setting the deposition parameters, the invention preferably carries out a deposition treatment on the surface of the carrier, wherein the deposition treatment preferably comprises sequentially pulsing gaseous palladium hexafluoroacetylacetonate and a gaseous reducing agent; wherein, in the deposition treatment process, the pulse time of the palladium hexafluoroacetylacetonate is not longer than the pulse time of the reducing agent. In the present invention, the pulse time of the palladium hexafluoroacetylacetonate is preferably 0.01 to 2s, more preferably 0.5 to 1s; the holding time is preferably 2 to 30 seconds, more preferably 2.2 to 8 seconds; the evacuation time is preferably 3 to 70 seconds, more preferably 20 to 35 seconds. In the present invention, the pulse time of the reducing agent is preferably 0.01 to 2s, more preferably 0.6 to 1s; the breath hold time is preferably 2 to 30 seconds, more preferably 8 to 28 seconds; the evacuation time is preferably 3 to 70 seconds, more preferably 5 to 25 seconds. In the present invention, the palladium hexafluoroacetylacetonate in the primary gas state and the reducing agent in the primary gas state are referred to as a single phaseThe number of deposition cycles during the deposition treatment is preferably 1 to 100, more preferably 5 to 60, still more preferably 10 to 50, still more preferably 15 to 40, still more preferably 20 to 30. In the present invention, during the deposition treatment, palladium hexafluoroacetylacetonate reacts with a reducing agent to change the valence state of palladium in palladium hexafluoroacetylacetonate and form palladium clusters (specifically, the palladium clusters are formed with Pd 0 And PdO double sites, and PdO clusters based on PdO species), to obtain a specific and stable Pd 2+ /(Pd 0 +Pd 2+ ) A palladium catalyst in a proportion. The invention preferably adjusts the pulse quantity of the palladium hexafluoroacetylacetonate and the reducing agent by controlling the deposition parameter and the circulation times, thereby being capable of controlling Pd in a gradient way 0 And Pd (Pd) 2+ Is a ratio of (2).
Or, the invention is based on an atomic layer deposition method, and the palladium catalyst is obtained by carrying out deposition treatment on the surface of a carrier loaded with palladium through pulse gaseous hexafluoroacetylacetone.
In the present invention, the palladium-supported carrier is preferably prepared by wet chemical method, that is, palladium is supported on the surface of the carrier by wet chemical method. In the present invention, the wet chemical method preferably includes an immersion method, a sol-gel method, or a precipitation deposition method. Taking an impregnation method as an example, the preparation method of the palladium-loaded carrier according to the present invention preferably includes the following steps: the vector was subjected to PdCl 2 And (3) carrying out dipping treatment in the solution, and then drying to obtain the palladium-loaded carrier. The invention preferably comprises dispersing the carrier in water and then mixing the aqueous carrier dispersion obtained with said PdCl 2 Mixing the solutions; the concentration of the carrier in the carrier aqueous dispersion is preferably 250-400 mg/mL, more preferably 300-350 g/mL; the PdCl 2 The concentration of the solution is preferably 7 to 8mg/mL, more preferably 7.4mg/mL; the vector and PdCl 2 The dosage ratio of the solution is preferably 1000mg: (500-1200) mL, more preferably 1000mg: (600-1000) mL. In the present invention, the impregnation treatment is preferably performed at room temperature, and the time of the impregnation treatment is preferably 20 to 30 hours, more preferably 24 hours; the impregnation treatment is preferably carried out under stirring. At the bookIn the invention, the drying temperature is preferably 65-75 ℃, more preferably 70 ℃; the time is preferably 10 to 15 hours, more preferably 12 hours. In the present invention, the content of palladium element in the palladium-supporting carrier is preferably 0.1 to 2wt%, and specifically may be 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 1wt%, 1.2wt%, 1.5wt%, 1.8wt% or 2wt%.
After the palladium-loaded carrier is obtained, the palladium-loaded carrier is preferably dispersed on the surface of a substrate, and then the substrate with the carrier dispersed on the surface is placed in a vacuum reaction chamber of an atomic layer deposition device for deposition treatment; in the present invention, the method for dispersing the palladium-loaded carrier on the surface of the substrate is preferably consistent with the method for dispersing the carrier on the surface of the substrate in the above technical solution, and will not be described herein.
After placing the substrate with the carrier dispersed on the surface in the vacuum reaction cavity, the invention preferably sets deposition parameters, wherein the deposition parameters preferably comprise: the temperature of hexafluoroacetylacetone is preferably 20 to 55 ℃, more preferably 45 to 50 ℃; the optional ranges of other deposition parameters are preferably consistent with those of the above technical solutions, and will not be described herein.
After setting the deposition parameters, the invention preferably carries out a deposition treatment on the surface of the support, said deposition treatment preferably comprising pulsed gaseous hexafluoroacetylacetone. In the present invention, the pulse time of hexafluoroacetylacetone is preferably 0.01 to 2s, more preferably 0.5 to 1s; the breath hold time is preferably 2 to 60 seconds, more preferably 3 to 10 seconds; the evacuation time is preferably 3 to 70 seconds, more preferably 4 to 10 seconds. In the present invention, the number of deposition cycles in the deposition treatment is preferably 1 to 100, more preferably 5 to 60, still more preferably 10 to 50, still more preferably 15 to 40, in which one pulse of gaseous hexafluoroacetylacetone is referred to as one deposition cycle. In the present invention, hexafluoroacetylacetone is capable of redispersing palladium in a palladium-supporting carrier to form small clusters during the deposition treatment, and redispersing to form palladium clusters by controlling the number of cycles of hexafluoroacetylacetone to control the size and valence ratio thereof (specifically, theThe palladium clusters are Pd-bearing 0 And PdO double sites, and PdO clusters based on PdO species), to obtain a specific and stable Pd 2+ /(Pd 0 +Pd 2+ ) A palladium catalyst in a proportion. The invention preferably adjusts the pulse quantity of hexafluoroacetylacetone by controlling the deposition parameters and the cycle times, thereby being capable of controlling Pd in a gradient way 0 And Pd (Pd) 2+ Is a ratio of (2).
The invention provides an application of the palladium catalyst prepared by the technical scheme or the preparation method of the technical scheme in preparing aldehyde by catalyzing alcohol to undergo oxidation reaction. In the present invention, the alcohol preferably includes benzyl alcohol, 4-methylbenzyl alcohol, 2-phenylethanol or 1-octanol. In the present invention, the conditions of the oxidation reaction preferably include: the temperature is preferably 100 to 160 ℃, more preferably 120 ℃; the oxygen pressure is preferably 0.2 to 0.4MPa, more preferably 0.3MPa; the ratio of palladium catalyst to alcohol is preferably 20mg: (8-12) mL, more preferably 20mg:10mL; the oxidation reaction is preferably carried out in the absence of a solvent; the oxidation reaction is preferably carried out under stirring, and the stirring speed is preferably 800 to 1200rpm, more preferably 1000rpm.
The technical solutions of the present invention will be clearly and completely described in the following in connection with the embodiments of the present invention. It will be apparent that the described embodiments are only some, but not all, embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Example 1
Taking 20mg CeO 2 Mixing with ethanol as carrier, mixing the obtained CeO 2 Coating the feed liquid on the surface of a quartz plate with the size of 80mm multiplied by 2mm, and forming CeO on the surface of the quartz plate after airing 2 The layer is placed in a vacuum reaction cavity of an atomic layer deposition device and is deposited on CeO by an atomic layer deposition method 2 The surface of the layer is subjected to deposition treatment, wherein the precursor is palladium hexafluoroacetylacetonate, the reducing agent is formaldehyde solution (the concentration is 37wt percent), and the solvent is water;
the deposition parameters are set as follows: the temperature of the vacuum reaction cavity is 150 ℃ and the pressure is 50MPa; the temperature of the hexafluoroacetylacetone palladium is 65 ℃, the temperature of the formaldehyde solution is 25 ℃, and the volume ratio of the carrier gas (argon) flow to the vacuum reaction cavity is 1:20, a step of;
the deposition treatment specifically comprises the following steps: firstly, pulse hexafluoroacetylacetone palladium vapor into the vacuum reaction cavity, wherein the pulse time is 0.5s, the breath holding time is 8s, and the air extracting time is 20s; then, the steam of formaldehyde solution is pulsed into the vacuum reaction cavity, the pulse time is 0.6s, the breath holding time is 8s, and the air extracting time is 25s; the deposition cycle was completed once, and the operation was repeated 20 times in total to obtain a hexafluoroacetylacetone-modified palladium catalyst, which was designated as 20Pd/CeO 2 The mass percentage of Pd element is 0.42%.
FIG. 1 is a 20Pd/CeO prepared in example 1 2 HRTEM images of (a); FIG. 2 is a 20Pd/CeO prepared in example 1 2 AC-HAADF-STEM diagram of FIG. 2, a is 20Pd/CeO 2 The AC-HAADF-STEM pattern of (2), b, c and d are 20Pd/CeO 2 EDS diagram of medium elements Ce, O and Pd; FIG. 3 is a 20Pd/CeO prepared in example 1 2 PdK-edge XANES graph of (c). The carrier CeO can be seen from a in FIGS. 1 and 2 2 But on the carrier CeO 2 No palladium particles were observed above; meanwhile, as can be seen from a-d in FIG. 2, palladium element is uniformly distributed in CeO 2 Applying; as can be seen from FIG. 3, 20Pd/CeO 2 The palladium is present in the form of PdO clusters.
Example 2
1000mg CeO 2 Evenly dispersed in 3mL of water, 600mL of PdCl with the concentration of 7.4mg/mL is added 2 The solution was stirred at 500rpm for 24 hours at room temperature and then dried in an oven at 70 ℃ for 12 hours to give a palladium-supported support (Pd mass fraction 0.43 wt%);
mixing 20mg of the carrier loaded with palladium with ethanol, coating the obtained feed liquid on the surface of a quartz plate with the size of 80mm multiplied by 2mm, airing to obtain a carrier layer formed by the carrier loaded with palladium on the surface of the quartz plate, placing the carrier layer in a vacuum reaction chamber of an atomic layer deposition device, and performing deposition treatment on the surface of the carrier layer by utilizing an atomic layer deposition method, wherein a precursor is hexafluoroacetylacetone;
the deposition parameters are set as follows: the temperature of the vacuum reaction cavity is 160 ℃, and the pressure is 50MPa; the temperature of the hexafluoroacetylacetone is 50 ℃; the volume ratio of the carrier gas (argon) flow to the vacuum reaction cavity is 1:12;
the deposition treatment specifically comprises the following steps: the hexafluoroacetylacetone vapor is pulsed into the vacuum reaction cavity, the pulse time is 0.5s, the breath holding time is 10s, the air extracting time is 10s, so far, one deposition cycle is completed, the repeated operation is carried out for 20 times, and the palladium catalyst modified by hexafluoroacetylacetone is obtained and is recorded as 20hacacPd/CeO 2 。
Examples 3 to 4
The palladium catalysts of examples 3 to 4 were prepared in substantially the same manner as in example 1, except that:
the deposition parameters were adjusted as follows: the temperature of the vacuum reaction cavity is 150 ℃ and the pressure is 70MPa;
the deposition process is adjusted as follows: firstly, pulse hexafluoroacetylacetone palladium vapor into a vacuum reaction cavity, wherein the pulse time is 0.5s, the breath holding time is 8s, and the air extracting time is 20s; then, the steam of formaldehyde solution is pulsed in the vacuum reaction cavity, the pulse time is 0.6s, the breath holding time is 8s, and the air extracting time is 25s; and the cycle times of the deposition treatment in examples 3 to 4 were 10 times and 15 times, respectively;
the final palladium catalysts obtained in examples 3 to 4 were each designated 10Pd/CeO 2 And 15Pd/CeO 2 Wherein the mass percentage of Pd element is 0.22% and 0.28%, respectively.
Examples 5 to 6
The palladium catalysts of examples 5 to 6 were prepared in substantially the same manner as in example 1, except that:
CeO is added with 2 Replaced by TiO 2 ；
The deposition parameters were adjusted as follows: the temperature of the vacuum reaction cavity is 180 ℃ and the pressure is 20MPa;
the deposition process is adjusted as follows: firstly, pulse hexafluoroacetylacetone palladium vapor into a vacuum reaction cavity, wherein the pulse time is 2s, the breath holding time is 30s, and the air extracting time is 70s; then, the steam of formaldehyde solution is pulsed into the vacuum reaction cavity, the pulse time is 2s, the breath holding time is 28s, and the air extracting time is 70s; and the cycle times in the deposition treatment process are 30 times and 50 times respectively;
the final palladium catalysts obtained in examples 5 to 6 were designated 30Pd/TiO, respectively 2 And 50Pd/TiO 2 Wherein the mass percentage of Pd element is 1.1% and 1.8%, respectively.
Example 7
The palladium catalyst in example 7 was prepared in substantially the same manner as in example 1 except that:
CeO is added with 2 Replaced by Al 2 O 3 ；
The deposition parameters were adjusted as follows: the temperature of the vacuum reaction cavity is 140 ℃ and the pressure is 10MPa;
the deposition process is adjusted as follows: firstly, pulse hexafluoroacetylacetone palladium vapor into a vacuum reaction cavity, wherein the pulse time is 0.01s, the breath holding time is 2.2s, and the air extracting time is 3s; then, the steam of formaldehyde solution is pulsed into the vacuum reaction cavity, the pulse time is 0.01s, the breath holding time is 2s, and the air extracting time is 5s; and the cycle times in the deposition treatment process are 100 times;
the mass percentage of Pd element in the finally obtained palladium catalyst is 0.1 percent.
Examples 8 to 9
The palladium catalysts of examples 8 to 9 were prepared in substantially the same manner as in example 1, except that:
CeO is added with 2 The molecular sieve is replaced by SBA-15 molecular sieve;
the deposition process is adjusted as follows: firstly, pulse hexafluoroacetylacetone palladium vapor into a vacuum reaction cavity, wherein the pulse time is 0.6s, the breath holding time is 10s, and the air extracting time is 35s; then, the steam of formaldehyde solution is pulsed into the vacuum reaction cavity, the pulse time is 1s, the breath holding time is 7s, and the air extracting time is 35s; and the number of cycles during the deposition treatment in examples 8 to 9 was 10 and 40, respectively;
the mass percentage of Pd element in the finally obtained palladium catalyst is 0.21% and 0.75%, respectively.
Example 10
The palladium catalyst in example 10 was prepared in substantially the same manner as in example 1 except that:
CeO is added with 2 Replacing with ZSM-5 molecular sieve;
the deposition process is adjusted as follows: firstly, pulse hexafluoroacetylacetone palladium vapor into a vacuum reaction cavity, wherein the pulse time is 0.6s, the breath holding time is 10s, and the air extracting time is 35s; then, the steam of formaldehyde solution is pulsed into the vacuum reaction cavity, the pulse time is 1s, the breath holding time is 7s, and the air extracting time is 35s; and the cycle times in the deposition treatment process are 20 times;
the mass percentage of Pd element in the finally obtained palladium catalyst is 0.4 percent.
Example 11
The palladium catalyst in example 11 was prepared in substantially the same manner as in example 2 except that:
the deposition parameters were adjusted as follows: the temperature of hexafluoroacetylacetone is 55 ℃;
the deposition process is adjusted as follows: the cycle number in the deposition treatment process is 40 times;
the final palladium catalyst was designated as 40hacacPd/CeO 2 。
Example 12
The palladium catalyst in example 12 was prepared in substantially the same manner as in example 2 except that:
CeO is added with 2 Replaced by TiO 2 ；
The deposition parameters were adjusted as follows: the temperature of the vacuum reaction cavity is 140 ℃ and the pressure is 50MPa; the temperature of hexafluoroacetylacetone is 55 ℃; the volume ratio of the carrier gas (argon) flow to the vacuum reaction cavity is 1:15;
the deposition process is adjusted as follows: the cycle number in the deposition treatment process is 40 times;
the final palladium catalyst was designated as 40hacacPd/TiO 2 。
Example 13
The palladium catalyst in example 14 was prepared in substantially the same manner as in example 2 except that:
PdCl 2 the volume of the solution is 1000mL, and the mass fraction of Pd in the finally obtained palladium-loaded carrier is 0.73wt%;
the deposition parameters were adjusted as follows: the temperature of hexafluoroacetylacetone is 55 ℃;
the deposition process is adjusted as follows: the cycle number in the deposition process is 100 times;
the final palladium catalyst was designated as 100hacacPd/CeO 2 。
Comparative example 1
1000mg CeO 2 Evenly dispersed in 3mL of water, 600mL of PdCl with the concentration of 7.4mg/mL is added 2 The solution was stirred at 500rpm for 24 hours at room temperature and then dried in an oven at 70℃for 12 hours to give a palladium-supported carrier (Pd mass fraction: 0.43 wt%).
Comparative example 2
1000mg CeO 2 Evenly dispersed in 3mL of water, 600mL of PdCl with the concentration of 7.4mg/mL is added 2 The solution was stirred at 500rpm for 24 hours at room temperature and then dried in an oven at 70 ℃ for 12 hours to give a palladium-supported support (Pd mass fraction 0.43 wt%);
placing 20mg of palladium-loaded carrier into a porcelain boat, and placing into a tube furnace in H 2 Ar Mixed atmosphere (H) 2 Volume fraction of 5%) is heated to 250 ℃ at a heating rate of 5 ℃/min, the temperature is kept for reduction treatment for 3 hours, and the obtained catalyst is named as H-Pd/CeO 2 。
Test example 1
The palladium catalyst prepared by the embodiment of the invention catalyzes benzyl alcohol solvent-free liquid phase oxidation reaction, and the specific method comprises the following steps: 20mg of the palladium catalyst prepared in the example of the present invention and 10mL of benzyl alcohol were placed in a three-necked flask, and oxidation reaction was carried out at 120℃and 1000rpm under an oxygen pressure of 0.3MPa for 15 minutes; comparison was made based on a similar method using a catalyst in the literature to catalyze the solvent-free liquid phase oxidation of benzyl alcohol. The specific results are shown in Table 1. As can be seen from Table 1, 20Pd/CeO prepared in example 1 2 The activity (TOF value) and selectivity of catalyzing the benzyl alcohol solvent-free liquid phase oxidation reaction are best, and the conversion rate is higher. In addition, in the case of the optical fiber,20Pd/CeO in the process of catalyzing benzyl alcohol solvent-free liquid phase oxidation reaction 2 Having a stable Pd 2+ /(Pd 0 +Pd 2+ ) Proportion, and Pd during the reaction 2+ /(Pd 0 +Pd 2+ ) The content is kept at 75-85%.
Table 1 results of comparison of catalytic performances of catalysts in examples and literature
The references referred to in table 1 are specifically as follows:
[1]J.Yang,K.Cao,M.Gong,B.Shan,R.Chen,Atomically decorating of MnO x on palladium nanoparticles towards selective oxidation of benzyl alcohol withhigh yield,J Catal,386(2020)60-69.
[2]P.Zhang,Y.Gong,H.Li,Z.Chen,Y.Wang,Solvent-free aerobic oxidation of hydrocarbons and alcohols with Pd@N-doped carbon from glucose,Nat.Commun.,4(2013)1593.
[3]Q.He,P.J.Miedziak,L.Kesavan,N.Dimitratos,M.Sankar,J.A.Lopez-Sanchez,M.M.Forde,J.K.Edwards,D.W.Knight,S.H.Taylor,C.J.Kiely,G.J.Hutchings,Switching-off toluene formation in the solvent-free oxidation of benzyl alcohol using supported trimetallic Au-Pd-Pt nanoparticles,Faraday Discuss.,162(2013)365-378.
[4]J.Pritchard,M.Piccinini,R.Tiruvalam,Q.He,N.Dimitratos,J.A.Lopez-Sanchez,D.J.Morgan,A.F.Carley,J.K.Edwards,C.J.Kiely,G.J.Hutchings,Effect of heat treatment on Au–Pd catalysts synthesized by sol immobilisation for the direct synthesis of hydrogen peroxide and benzyl alcoholoxidation,Catal.Sci.Technol.,3(2013)308-317.
[5]J.Wang,S.A.Kondrat,Y.Wang,G.L.Brett,C.Giles,J.K.Bartley,L.Lu,Q.Liu,C.J.Kiely,G.J.Hutchings,Au-Pd nanoparticles dispersed on composite titania/graphene oxide-supports as a highly active oxidation catalyst,ACS Catal.,5(2015)3575-3587.
[6]Y.-M.Lu,H.-Z.Zhu,J.-W.Liu,S.-H.Yu,Palladium nanoparticles supported on titanate nanobelts for solvent-free aerobic oxidation of alcohols,ChemCatChem,7(2015)4131-4136.
[7]H.Wang,X.-K.Gu,X.Zheng,H.Pan,J.Zhu,S.Chen,L.Cao,W.-X.Li,J.Lu,Disentangling the size-dependent geometric and electronic effects of palladium nanocatalysts beyond selectivity,Sci.Adv.,5(2019)6413.
test example 2
The catalysts prepared in examples 1 to 2 and comparative examples 1 to 2 (fresh catalyst and left in an air atmosphere for 1 month or 3 months) were subjected to a catalytic performance test by: 20mg of the catalyst and 10mL of benzyl alcohol were placed in a three-necked flask, and oxidation reaction was carried out at 120℃and 1000rpm under an oxygen pressure of 0.3MPa for 1 hour, and the results of the performance test are shown in Table 2. It can be seen from Table 2 that the catalysts prepared in examples 1 and 2 were not only high in catalytic activity, but also the catalysts could be stored for a long period of time and were not easily deactivated.
TABLE 2 results of Performance test of the catalysts prepared in examples 1 to 2 and comparative examples 1 to 2
Test example 3
The catalysts of the examples and comparative examples were subjected to catalytic performance testing according to the method of test example 2, and Pd was measured for each catalyst 2+ /(Pd 0 +Pd 2+ ) The specific results of the ratios are shown in Table 3. As can be seen from Table 3, the palladium catalyst provided in the embodiment of the invention has stable Pd during the catalytic benzyl alcohol solvent-free liquid phase oxidation reaction 2+ /(Pd 0 +Pd 2+ ) Proportion, and Pd during the reaction 2+ /(Pd 0 +Pd 2+ ) All greater than 71%.
TABLE 3 results of Performance test of catalysts prepared in examples and comparative examples
As can be seen from the above examples and comparative examples, the palladium catalyst with stable double sites provided by the invention has a catalytic activity far higher than that of the conventional palladium catalyst in the alcohol oxidation reaction, the selectivity of the generated aldehyde is higher (more than 93%), the palladium-based catalyst after the reaction is easy to separate and can be reused, regeneration treatment and the like are not needed, and the palladium catalyst has a high practical value.
The foregoing is merely a preferred embodiment of the present invention and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the present invention, which are intended to be comprehended within the scope of the present invention.

Claims (7)

1. A palladium catalyst with stable double sites comprises a carrier and palladium species dispersed on the surface of the carrier, wherein the palladium species comprises Pd 0 And Pd (Pd) 2+ The Pd is 2+ Occupy Pd 0 And Pd (Pd) 2+ 60-75% of the total amount of Pd after the palladium catalyst is used 2+ Occupy Pd 0 And Pd (Pd) 2+ 70-85% of the total amount; the palladium in the palladium catalyst exists in a cluster form;
the carrier is an oxide carrier or a molecular sieve carrier; the oxide carrier is titanium dioxide, cerium dioxide or aluminum oxide, and the molecular sieve carrier is SBA-15 molecular sieve or ZSM-5 molecular sieve;
the use is to use the palladium catalyst for catalyzing alcohol to prepare aldehyde through oxidation reaction, wherein the oxidation reaction conditions comprise: the temperature is 100-160 ℃, and the oxygen pressure is 0.2-0.4 MPa;
the preparation method of the palladium catalyst comprises the following steps:
(1) Based on an atomic layer deposition method, sequentially pulsing gaseous palladium hexafluoroacetylacetonate and gaseous reducing agent to perform deposition treatment on the surface of a carrier to obtain a palladium catalyst; wherein, in the process of the deposition treatment, the pulse time of the palladium hexafluoroacetylacetonate is not longer than the pulse time of the reducing agent; the pulse time of the palladium hexafluoroacetylacetonate is 0.01-2 s, the breath holding time is 2-30 s, and the air extracting time is 3-70 s; the pulse time of the reducing agent is 0.01-2 s, the breath holding time is 2-30 s, and the air extracting time is 3-70 s;
or (2) carrying out deposition treatment on the surface of the carrier loaded with palladium by using pulse gaseous hexafluoroacetylacetone based on an atomic layer deposition method to obtain a palladium catalyst; the pulse time of hexafluoroacetylacetone is 0.01-2 s, the breath holding time is 2-60 s, and the air extracting time is 3-70 s.
2. The palladium catalyst according to claim 1, wherein the content of palladium element in the palladium catalyst is 0.1 to 2wt%.
3. The method for preparing the palladium catalyst according to any one of claims 1 to 2, comprising the steps of:
(1) Based on an atomic layer deposition method, sequentially pulsing gaseous palladium hexafluoroacetylacetonate and gaseous reducing agent to perform deposition treatment on the surface of a carrier to obtain a palladium catalyst; wherein, in the process of the deposition treatment, the pulse time of the palladium hexafluoroacetylacetonate is not longer than the pulse time of the reducing agent; the pulse time of the palladium hexafluoroacetylacetonate is 0.01-2 s, the breath holding time is 2-30 s, and the air extracting time is 3-70 s; the pulse time of the reducing agent is 0.01-2 s, the breath holding time is 2-30 s, and the air extracting time is 3-70 s;
or (2) carrying out deposition treatment on the surface of the carrier loaded with palladium by using pulse gaseous hexafluoroacetylacetone based on an atomic layer deposition method to obtain a palladium catalyst; the pulse time of hexafluoroacetylacetone is 0.01-2 s, the breath holding time is 2-60 s, and the air extracting time is 3-70 s.
4. A method of preparation according to claim 3, wherein the reducing agent comprises hydrogen or formaldehyde solution.
5. The method according to claim 3, wherein the number of deposition treatments in (1) and (2) is independently 1 to 100.
6. Use of a palladium catalyst according to any one of claims 1 to 2 or a palladium catalyst prepared by a preparation method according to any one of claims 3 to 5 in the preparation of aldehydes by catalytic oxidation of alcohols.
7. The use according to claim 6, wherein the alcohol comprises benzyl alcohol, 4-methylbenzyl alcohol, 2-phenylethanol or 1-octanol.
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