A pd-based catalyst, its preparation method and use

Abstract

The application provides a Pd-based catalyst and a preparation method and application thereof, and relates to the technical field of catalytic chemistry.The Pd-based catalyst comprises a carrier, Pd and a non-noble metal active component supported on the surface of the carrier; and the non-noble metal of the Pd and the non-noble metal active component is in an atomic-scale spatial separation structure.The Pd-based catalyst has a stable atomic-scale spatial separation structure, and when applied to alcohol catalytic oxidation reaction, alcohol is adsorbed and dehydrogenated on a Pd active site, the removed hydrogen atoms migrate to a non-noble metal active site in an atomic-scale range, and combine with active oxygen adsorbed on the non-noble metal active site to form H2O and are removed, alcohol adsorption and oxygen adsorption are separated on the Pd and the non-noble metal active site, and the catalytic efficiency is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalytic chemistry, and in particular relates to a Pd-based catalyst and a preparation method and application thereof. Background Art

[0002] Aldehydes are the most basic and useful industrial products, serving as precursors or intermediates for the synthesis of fine chemicals such as pharmaceuticals, fragrances, pesticides, and dyes. The dehydrogenation of alcohols to produce aldehydes is of great significance and value. Traditional benzyl alcohol oxidation methods use inorganic oxidants (chromates and permanganates) for the oxidation reaction, but these reagents are highly corrosive, and the products after alcohol oxidation are highly toxic. The oxidation process also produces numerous byproducts, and the selectivity for aldehydes is low. Compared with traditional methods, solvent-free liquid-phase catalytic oxidation of alcohols uses supported metal catalysts, with oxygen molecules as the oxidant and water as the byproduct. These methods are mild, environmentally friendly, and have high economic value. Pd-based catalysts are the most promising catalysts for alcohol oxidation, but they suffer from problems such as low atom utilization, large loadings, and high costs.

[0003] In the prior art, bimetallic catalysts, typically prepared by doping Pd with non-precious metals such as Ni, Fe, and Co, not only reduce the cost of precious metal Pd catalysts but also increase the atomic utilization of the catalyst, thereby improving catalytic activity. Bimetallic Pd-based catalysts in the prior art (such as Pd-Ni catalysts) typically have alloy structures, core-shell structures, or modified bimetallic structures. However, these bimetallic structures have overlapping sites and limited active sites. During the alcohol catalytic oxidation reaction, benzyl alcohol and oxygen compete for adsorption, resulting in low catalytic efficiency. Summary of the Invention

[0004] The purpose of the present invention is to provide a Pd-based catalyst, a preparation method and application thereof. The Pd-based catalyst provided by the present invention has a stable bimetallic active component with an atomic-scale spatial separation structure. When applied to the catalytic oxidation reaction of alcohol, it can reduce the competitive adsorption of alcohol and oxygen, thereby having a higher catalytic efficiency.

[0005] In order to achieve the purpose of the present invention, the present invention provides the following technical solutions:

[0006] A Pd-based catalyst comprises a carrier and Pd and a non-noble metal active component loaded on the carrier surface; the Pd and the non-noble metal active component present an atomic scale spatial separation structure.

[0007] Preferably, the non-noble metal in the non-noble metal active component includes nickel, iron or cobalt.

[0008] Preferably, the total mass fraction of the Pd and non-noble metal active components is 0.2-15 wt%.

[0009] Preferably, the mass ratio of Pd to non-precious metal is 1:0.2-10.

[0010] Preferably, the support comprises a carbon material support and / or an oxide support.

[0011] The present invention provides a method for preparing the Pd-based catalyst described in the above technical solution, comprising the following steps:

[0012] The non-noble metal precursor is subjected to a pulse treatment on the surface of a carrier, and then subjected to a reduction treatment to load the non-noble metal active component on the surface of the carrier to obtain a catalyst precursor;

[0013] The Pd precursor and the reducing agent are sequentially pulse-treated on the surface of the catalyst precursor, so that Pd is loaded on the surface of the catalyst precursor in the form of single atoms, thereby obtaining the Pd-based catalyst.

[0014] Preferably, the non-noble metal precursor includes nickelocene, ferrocene or cobaltocene; and the Pd precursor includes palladium hexafluoroacetylacetonate.

[0015] Preferably, the method of subjecting the carrier surface to pulse treatment with the non-noble metal precursor includes chemical vapor deposition or atomic layer deposition; the method of subjecting the catalyst precursor surface to pulse treatment with the Pd precursor and the reducing agent includes atomic layer deposition.

[0016] Preferably, the reduction treatment is carried out in a reducing atmosphere; the temperature of the reduction treatment is 200-400° C., and the time is 0.5-5 h.

[0017] The present invention also provides the use of the Pd-based catalyst described in the above technical solution or the Pd-based catalyst prepared by the preparation method described in the above technical solution in the catalytic oxidation reaction of alcohols.

[0018] The present invention provides a Pd-based catalyst comprising a carrier and Pd and a non-precious metal active component supported on the carrier surface; the non-precious metal in the Pd and non-precious metal active components exhibits an atomic-scale spatially separated structure. The Pd-based catalyst of the present invention has a stable atomic-scale spatially separated structure. When used in an alcohol catalytic oxidation reaction, alcohol is adsorbed and dehydrogenated on the Pd active sites. The removed hydrogen atoms migrate to the atomic-scale non-precious metal active sites and combine with the active oxygen adsorbed on the non-precious metal active sites to form H2O, which is then removed. This achieves separation of alcohol adsorption and oxygen adsorption on the Pd and non-precious metal active sites, thereby improving catalytic efficiency.

[0019] Further, the non-noble metal active component of the present application includes nickelocene, ferrocene or cobaltocene, on the one hand, due to the steric hindrance of the non-noble metal active component adsorbed on the carrier, not only hinders the deposition of Pd on the non-noble metal precursor, but also hinders the aggregation of the non-noble metal active component and Pd on the surface of the carrier, thereby forming a stable atomic-scale spatially-separated structure Pd-non-noble metal b-site catalyst; on the other hand, due to the organic functional group (alkenyl) with alcoholophilic and hydrophobic properties contained in the non-noble metal precursor, which is loaded on the surface of the carrier, will change the adsorption and desorption properties of the reactant alcohol and product water on the surface of the catalyst, further improve the catalytic efficiency of the Pd-based catalyst, and the Pd-based catalyst of the present application has a long storage time and is not easy to deactivate.

[0020] The present application also provides a preparation method of the Pd-based catalyst, and the present application utilizes chemical vapor deposition and / or atomic layer deposition specific anchoring technology, which is beneficial to form a Pd-based catalyst with a stable spatially-separated structure, and can accurately control the loading amount, size, distribution density and spatial distance of the non-noble metal precursor and Pd on the surface of the carrier, thereby realizing the separation of alcohol adsorption and oxygen adsorption on the Pd and non-noble metal active sites. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced below, and obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0022] Figure 1 Performance comparison chart of benzyl alcohol solvent-free liquid phase oxidation reaction of 10Pd / rGO, 30Ni / rGO and 10Pd30Ni / rGO;

[0023] Figure 2 AC-HAADF-STEM and EDS charts of 10Pd / rGO, 30Ni / rGO and 10Pd30Ni / rGO;

[0024] Figure 3 Contact angle shape chart of rGO, 10Pd / rGO, 30Ni / rGO and 10Pd30Ni / rGO;

[0025] Figure 4 Performance comparison chart of benzyl alcohol solvent-free liquid phase oxidation reaction of 10Pd / rGO, 30Ni / rGO, 10Pd30Ni / rGO, 10Pd / rGO+30Ni / rGO and IM-PdNi / rGO. DETAILED DESCRIPTION

[0026] The present invention provides a Pd-based catalyst comprising a carrier and Pd and a non-noble metal active component loaded on the surface of the carrier; the non-noble metal in the Pd and non-noble metal active components presents an atomic scale spatial separation structure.

[0027] In the present invention, the non-noble metal in the non-noble metal active component preferably includes nickel, iron or cobalt.

[0028] In the present invention, the total mass fraction of the Pd and non-noble metal active components is preferably 0.2 to 15 wt%, more preferably 2 wt%.

[0029] In the present invention, the mass ratio of Pd to non-noble metal is preferably 1:0.2-10, more preferably 1:3.

[0030] In the present invention, the support preferably comprises a carbon material support and / or an oxide support. In the present invention, the carbon material support is preferably carbon nanotubes, carbon helical fibers, or graphene, more preferably graphene; the graphene is preferably reduced graphene oxide (rGO). In the present invention, the oxide support is preferably aluminum oxide or titanium oxide.

[0031] The present invention also provides a method for preparing the Pd-based catalyst described in the above technical solution, comprising the following steps:

[0032] A non-noble metal precursor is subjected to a pulse treatment on a carrier surface, followed by a reduction treatment, to load a non-noble metal active component on the carrier surface to obtain a catalyst precursor;

[0033] A Pd precursor and a reducing agent are sequentially pulse-treated on the surface of the catalyst precursor, so that Pd is loaded on the surface of the catalyst precursor in a single-atom form, thereby obtaining the Pd-based catalyst.

[0034] In the present invention, unless otherwise specified, all preparation raw materials are preferably commercially available products.

[0035] The present invention pulse-treats a non-precious metal precursor on a support surface, followed by a reduction treatment, to load a non-precious metal active component onto the support surface to obtain a catalyst precursor. In the present invention, the non-precious metal precursor preferably comprises nickelocene, ferrocene, or cobaltocene.

[0036] In the present invention, the method of pulse-treating the non-precious metal precursor on the support surface preferably includes chemical vapor deposition or atomic layer deposition. In the present invention, the operating parameters of the chemical vapor deposition include: the pressure is preferably atmospheric pressure; the temperature is preferably 130-180°C, more preferably 150-160°C; the carrier gas is preferably N2, He, or Ar; and the pulse time of the non-precious metal precursor is preferably 0.5-5 hours, more preferably 1-3 hours.

[0037] In the present invention, the operating parameters of the atomic layer deposition include: the temperature of the atomic layer deposition reaction chamber is preferably 130-180°C, more preferably 150°C; the chamber pressure is preferably 30-70 MPa, more preferably 50 MPa; the temperature of the non-precious metal precursor is preferably 60-65°C; the pulse time is preferably 1-10s, more preferably 5-8s; the holding time is preferably 2-30s, more preferably 14-20s; the pumping time is preferably 3-50s, more preferably 30-40s.

[0038] In the present invention, the reduction treatment is performed in a reducing atmosphere. The reducing atmosphere is preferably one or more of H2, Ar, and He, more preferably a mixture of H2 and Ar. The H2 content of the H2 and Ar mixture is preferably 5% by weight. The reduction treatment temperature is preferably 200-400°C, more preferably 300°C, and the duration is preferably 0.5-5 hours, more preferably 1-3 hours.

[0039] The present invention denotes the pulsed non-precious metal precursor and reduction treatment as one deposition process. After the first deposition process, the present invention repeats the deposition process to load the non-precious metal on the support surface in the form of single atoms, thereby obtaining a catalyst precursor. In the present invention, the total number of deposition processes is preferably 1 to 100, more preferably 10 to 50, and even more preferably 30.

[0040] After obtaining a catalyst precursor, the present invention sequentially pulse-treats a Pd precursor and a reducing agent on the surface of the catalyst precursor, thereby loading Pd on the surface of the catalyst precursor in the form of single atoms to obtain the Pd-based catalyst. In the present invention, the Pd precursor preferably comprises palladium hexafluoroacetylacetonate. In the present invention, the catalyst is preferably H2 and / or formaldehyde solution.

[0041] In the present invention, the method of pulse-treating the Pd precursor and the reducing agent on the surface of the catalyst precursor preferably includes atomic layer deposition. In the present invention, the operating conditions of the atomic layer deposition include: the atomic layer deposition reaction chamber temperature is preferably 130-180°C, more preferably 150°C; the chamber pressure is preferably 30-70 MPa, more preferably 50 MPa.

[0042] In the present invention, the pulse processing parameters of the Pd precursor preferably include: the temperature of the Pd precursor is preferably 55-70°C, more preferably 60°C; the pulse time is preferably 0.1-3s, more preferably 0.5s; the holding time is preferably 3-20s, more preferably 3-12s; the pumping time is preferably 5-50s, more preferably 10-25s.

[0043] In the present invention, the pulse treatment parameters of the reducing agent preferably include: the temperature of the reducing agent is preferably room temperature; the pulse time is 0.1 to 3 seconds, more preferably 0.5 seconds; the breath holding time is preferably 3 to 20 seconds, more preferably 3 to 12 seconds; the air pumping time is preferably 5 to 50 seconds, more preferably 10 to 25 seconds.

[0044] In the present invention, the pulsed Pd precursor and pulsed reducing agent are referred to as one deposition process. After the first deposition process, the deposition process is repeated to load Pd in ​​the form of single atoms on the surface of the catalyst precursor to obtain the Pd-based catalyst. In the present invention, the total number of deposition processes is preferably 1 to 100, more preferably 10 to 50, and even more preferably 30.

[0045] The present invention also provides the use of the Pd-based catalyst described in the above technical solution or the Pd-based catalyst prepared by the preparation method described in the above technical solution in the catalytic oxidation reaction of alcohols.

[0046] In the present invention, the alcohol preferably includes one of benzyl alcohol, methanol and ethanol, and more preferably benzyl alcohol.

[0047] In the present invention, the solid-to-liquid ratio of the Pd-based catalyst to the alcohol is preferably 1-3:1 mg / mL, more preferably 1-2:1 mg / mL. In the present invention, the temperature of the alcohol catalytic oxidation reaction is preferably 100-150°C, more preferably 120°C; the pressure is preferably 0.1-0.5 MPa, more preferably 0.3 MPa; and the reaction time is preferably 1-5 hours, more preferably 3 hours.

[0048] In order to further illustrate the present invention, the Pd-based catalyst provided by the present invention is described in detail below with reference to the accompanying drawings and examples, but they should not be construed as limiting the scope of protection of the present invention.

[0049] Example 1

[0050] 10 mg of reduced graphene oxide (rGO) was mixed with ethanol as a carrier. The resulting rGO solution was coated on the surface of a quartz wafer measuring 80 mm × 80 mm × 2 mm. After drying, an rGO layer was formed on the surface of the quartz wafer, which was then placed in a vacuum reaction chamber of an atomic layer deposition device.

[0051] Atomic layer deposition was used to perform pulse treatment on the surface of the rGO layer, wherein the non-precious metal precursor was nickelocene; the deposition parameters of nickelocene were set as follows: the temperature of the vacuum reaction chamber was 150°C, the pressure was 50 MPa; the temperature of the nickelocene was 65°C; the pulse time was 1 s, the breath holding time was 2 s, and the exhaust time was 3 s. After the pulse was completed, the pulsed carrier was reduced in a H2 / Ar mixed atmosphere (H2 content was 5%) at 400°C for 0.5 h, thus completing one deposition treatment. The operation was repeated for a total of 30 cycles to obtain a catalyst precursor, which was recorded as 30Ni / rGO.

[0052] Based on the atomic layer deposition method, hexafluoroacetylacetonate palladium was pulsed onto 30Ni / rGO. The deposition parameters of hexafluoroacetylacetonate palladium were set as follows: the hexafluoroacetylacetonate palladium temperature was 60°C, the pulse time was 0.5s, the hold time was 12s, and the pumping time was 25s. Then, a gaseous formaldehyde solution was pulsed. The deposition parameters of the formaldehyde solution were set as follows: the formaldehyde solution temperature was room temperature, the pulse time was 0.5s, the hold time was 12s, and the pumping time was 25s. This completed one deposition process. The operation was repeated for a total of 10 cycles to obtain a Pd-based catalyst, recorded as 10Pd30Ni / rGO. The mass percentage of Ni element in the 10Pd30Ni / rGO catalyst was 1.5%, and the mass percentage of Pd element was 0.5%.

[0053] Example 2

[0054] 10 mg of reduced graphene oxide (rGO) was mixed with ethanol as a carrier. The resulting rGO solution was coated on the surface of a quartz wafer measuring 80 mm × 80 mm × 2 mm. After drying, an rGO layer was formed on the surface of the quartz wafer, which was then placed in a vacuum reaction chamber of an atomic layer deposition device.

[0055] Atomic layer deposition was used to perform pulse treatment on the surface of the rGO layer, wherein the non-precious metal precursor was nickelocene; the deposition parameters of nickelocene were set as follows: the temperature of the vacuum reaction chamber was 180°C, the pressure was 70 MPa; the temperature of the nickelocene was 60°C; the pulse time was 1 s, the breath holding time was 2 s, and the exhaust time was 3 s. After the pulse was completed, the pulsed carrier was reduced in a 5% H2 / Ar mixed atmosphere (H2 content was 5%) at 400°C for 0.5 h, thus completing one deposition treatment; the deposition treatment was repeated for a total of 50 cycles to obtain a catalyst precursor, recorded as 50Ni / rGO;

[0056] Based on the atomic layer deposition method, gaseous hexafluoroacetylacetonate palladium was pulsed on 50Ni / rGO, and the deposition parameters of hexafluoroacetylacetonate palladium were set as follows: the temperature of hexafluoroacetylacetonate palladium was 55°C; the pulse time was 3s, the holding time was 20s, and the pumping time was 50s; then the gaseous formaldehyde solution was pulsed, and the deposition parameters of the formaldehyde solution were set as follows: the temperature of the formaldehyde solution was room temperature; the pulse time was 0.5s, the holding time was 12s, and the pumping time was 25s; thus completing one deposition process, the operation was repeated for a total of 5 cycles to obtain a Pd-based catalyst, recorded as 5Pd50Ni / rGO.

[0057] Example 3

[0058] The Pd-based catalyst was prepared by referring to the preparation method described in Example 2, except that the nickelocene deposition treatment was repeated for 30 cycles; and the hexafluoroacetylacetonate palladium deposition treatment was repeated for 30 cycles.

[0059] Example 4

[0060] The Pd-based catalyst was prepared by referring to the preparation method described in Example 2, except that the nickelocene deposition treatment was repeated for 50 cycles; and the hexafluoroacetylacetonate palladium deposition treatment was repeated for 50 cycles.

[0061] Example 5

[0062] The Pd-based catalyst was prepared by referring to the preparation method described in Example 2, except that the nickelocene deposition treatment was repeated for a total of 10 cycles; and the hexafluoroacetylacetonate palladium deposition treatment was repeated for a total of 50 cycles.

[0063] Example 6

[0064] The Pd-based catalyst was prepared by referring to the preparation method described in Example 2, except that the nickelocene deposition treatment was repeated for 50 cycles; and the hexafluoroacetylacetonate palladium deposition treatment was repeated for 30 cycles.

[0065] Example 7

[0066] The Pd-based catalyst was prepared by referring to the preparation method described in Example 2, except that the nickelocene deposition treatment was repeated for 50 cycles; and the hexafluoroacetylacetonate palladium deposition treatment was repeated for 10 cycles.

[0067] Example 8

[0068] 10 mg of reduced graphene oxide (rGO) was mixed with ethanol as a carrier. The resulting rGO solution was coated on the surface of a quartz wafer measuring 80 mm × 80 mm × 2 mm. After drying, an rGO layer was formed on the surface of the quartz wafer, which was then placed in a vacuum reaction chamber of an atomic layer deposition device.

[0069] The surface of the rGO layer was pulsed using atomic layer deposition, wherein the non-precious metal precursor was cobaltocene. The deposition parameters of the cobaltocene were set as follows: the temperature of the vacuum reaction chamber was 130°C, the pressure was 30 MPa, the temperature of the cobaltocene was 65°C, the pulse time was 10 s, the breath holding time was 30 s, and the exhaust time was 50 s. After the pulse was completed, the support was reduced in a 5% H2 / Ar mixed atmosphere (H2 content was 5%) at 200°C for 5 h, thus completing one deposition process. The operation was repeated for a total of 100 cycles to obtain a catalyst precursor, which was recorded as 100Co / rGO.

[0070] Based on the atomic layer deposition method, gaseous hexafluoroacetylacetonate palladium was pulsed on 100Co / rGO, and the deposition parameters of hexafluoroacetylacetonate palladium were set as follows: the temperature of hexafluoroacetylacetonate palladium was 70°C; the pulse time was 0.1s, the holding time was 3s, and the pumping time was 5s; then the gaseous formaldehyde solution was pulsed, and the deposition parameters of the formaldehyde solution were set as follows: the temperature of the formaldehyde solution was room temperature; the pulse time was 0.1s, the holding time was 3s, and the pumping time was 5s; thus completing one deposition process, the operation was repeated for a total of 10 cycles to obtain a Pd-based catalyst, recorded as 100Co10Ni / rGO.

[0071] Example 9

[0072] A Pd-based catalyst was prepared according to the preparation method described in Example 8, except that the support was carbon nanotubes, the cobaltocene deposition treatment was repeated for 10 cycles, and the palladium hexafluoroacetylacetonate deposition treatment was repeated for 100 cycles.

[0073] Example 10

[0074] 10 mg of carbon helical fiber was mixed with ethanol as a carrier. The resulting carbon helical liquid was coated on the surface of a quartz plate with dimensions of 80 mm × 80 mm × 2 mm. After drying, a carbon helical layer was formed on the surface of the quartz plate, which was then placed in a chemical vapor deposition apparatus.

[0075] Chemical vapor deposition technology was used to pulse the surface of the carbon spiral layer, wherein the non-precious metal precursor was ferrocene; the deposition parameters of ferrocene were set as follows: pressure was atmospheric pressure, temperature was 180°C, carrier gas was N2 gas, and pulse time was 0.5h; after the pulse was completed, the carrier was reduced in a 5% H2 / Ar mixed atmosphere (H2 content was 5%) at 400°C for 0.5h, thus completing one deposition process. The operation was repeated for a total of 30 cycles to obtain a catalyst precursor, which was recorded as 30Fe / carbon spiral;

[0076] Based on the atomic layer deposition method, gaseous hexafluoroacetylacetonate palladium was pulsed on the 30Fe / carbon spiral, and the deposition parameters of the hexafluoroacetylacetonate palladium were set as follows: the temperature of the hexafluoroacetylacetonate palladium was 60°C; the pulse time was 0.5s, the holding time was 12s, and the pumping time was 25s; then the gaseous formaldehyde solution was pulsed, and the deposition parameters of the formaldehyde solution were set as follows: the temperature of the formaldehyde solution was room temperature; the pulse time was 0.5s, the holding time was 12s, and the pumping time was 25s; thus completing one deposition process, the operation was repeated for a total of 10 cycles to obtain a Pd-based catalyst.

[0077] Example 11

[0078] The Pd-based catalyst was prepared by referring to the preparation method described in Example 10, except that:

[0079] The deposition parameters of ferrocene were set as follows: pressure at atmospheric pressure, temperature at 130°C, carrier gas at He, and pulse time at 5 h.

[0080] The deposition parameters of hexafluoroacetylacetonate palladium were set as follows: the temperature of hexafluoroacetylacetonate palladium was 70°C; the pulse time was 0.1s, the holding time was 3s, and the pumping time was 5s;

[0081] The deposition parameters of the formaldehyde solution were set as follows: the temperature of the formaldehyde solution was room temperature; the pulse time was 0.1 s, the breath holding time was 12 s, and the pumping time was 25 s.

[0082] Example 12

[0083] The Pd-based catalyst was prepared by referring to the preparation method described in Example 10, except that:

[0084] The deposition parameters of ferrocene were set as follows: pressure at normal pressure, temperature at 160°C, carrier gas at Ar, and pulse time at 1 h.

[0085] Comparative Example 1

[0086] 10 mg of reduced graphene oxide (rGO) was mixed with ethanol as a carrier. The resulting rGO solution was coated on the surface of a quartz wafer measuring 80 mm × 80 mm × 2 mm. After drying, an rGO layer was formed on the surface of the quartz wafer, which was then placed in a vacuum reaction chamber of an atomic layer deposition device.

[0087] Atomic layer deposition was used to perform pulse treatment on the surface of the rGO layer, wherein the non-precious metal precursor was nickelocene. The deposition parameters were set as follows: the temperature of the vacuum reaction chamber was 150°C, the pressure was 50 MPa, the temperature of the nickelocene was 65°C, the pulse time was 1 s, the breath holding time was 2 s, and the exhaust time was 3 s. This completed one deposition treatment, and the operation was repeated for a total of 30 cycles to obtain a Ni-based catalyst, recorded as 30Ni / rGO.

[0088] Comparative Example 2

[0089] 10 mg of reduced graphene oxide (rGO) was mixed with ethanol as a carrier. The resulting rGO solution was coated on the surface of a quartz wafer measuring 80 mm × 80 mm × 2 mm. After drying, an rGO layer was formed on the surface of the quartz wafer, which was then placed in a vacuum reaction chamber of an atomic layer deposition device.

[0090] Atomic layer deposition was used to perform pulse treatment on the surface of the rGO layer, wherein the Pd precursor was palladium hexafluoroacetylacetonate. The deposition parameters were set as follows: the temperature of the vacuum reaction chamber was 150°C, the pressure was 50 MPa, the temperature of the palladium hexafluoroacetylacetonate was 60°C, the pulse time was 0.5 s, the breath holding time was 12 s, and the exhaust time was 25 s. This completed one deposition treatment, and the operation was repeated for a total of 10 cycles to obtain a Pd-based catalyst, recorded as 10Pd / rGO.

[0091] Comparative Example 3

[0092] 10 mg of the 30Ni / rGO described in Comparative Example 1 and the 10Pd / rGO described in Comparative Example 2 were weighed respectively, and mechanically mixed to obtain a 10Pd / rGO+30Ni / rGO catalyst.

[0093] Comparative Example 4

[0094] The IM-PdNi / rGO catalyst was prepared by an impregnation method. The specific steps are as follows: at room temperature, deionized water, Ni(NO3)2·6H2O, PdCl2 and rGO (the mass ratio of Ni:Pd:rGO is 3:1:200) were added to a beaker in sequence, and the mixture was stirred for 24 hours to obtain a mixed system; the obtained mixed system was placed in an 80°C oven for drying for 12 hours, and then treated in an air atmosphere at 350°C for 3 hours; finally, the obtained product was placed in a 5% H2 / Ar atmosphere and maintained at 350°C for 3 hours to obtain a Pd-based catalyst, recorded as IM-PdNi / rGO, in which the mass percentage of Ni element in the IM-PdNi / rGO catalyst is 1.5%, and the mass percentage of Pd element is 0.5%.

[0095] Comparative Example 5

[0096] The Pd-based catalyst was prepared by referring to the preparation method described in Example 1, except that the non-noble metal precursor nickelocene was not subjected to reduction treatment after being deposited on the surface of the rGO layer.

[0097] Test Example 1

[0098] 10 mg of the Pd-based catalysts described in Example 1 (10Pd30Ni / rGO), Comparative Example 1 (30Ni / rGO), and Comparative Example 2 (10Pd / rGO) were placed in a three-necked flask with 10 mL of benzyl alcohol. The oxidation reaction was carried out at 120°C, 1000 rpm, and 0.3 MPa for 1 h, and the catalytic performance was compared. The results are shown in the figure below.

[0099] Figure 1 The performance comparison of 10Pd / rGO, 30Ni / rGO and 10Pd30Ni / rGO for solvent-free liquid phase oxidation of benzyl alcohol is shown in Figure 2. Figure 1 The results show that the catalytic activity of 30Ni / rGO is extremely low (conversion rate <1%). The catalytic performance of the 10Pd30Ni / rGO catalyst (conversion rate 38.15%) modified with Ni atoms is significantly improved compared to the 10Pd / rGO catalyst (conversion rate 5.57%), with the catalytic activity increased by 7 times and the selectivity also slightly improved, demonstrating that the Pd-based catalyst provided by the present invention has excellent catalytic performance.

[0100] Figure 2 AC-HAADF-STEM and EDS images of 10Pd / rGO, 30Ni / rGO and 10Pd30Ni / rGO (Note: Figure 2 a~c are dark-field spherical aberration electron microscopy images of 0Pd / rGO, 30Ni / rGO and 10Pd30Ni / rGO, respectively; d~f are element distribution maps of 10Pd / rGO, 30Ni / rGO and 10Pd30Ni / rGO, respectively; g~i are complete EDS spectra of 10Pd / rGO, 30Ni / rGO and 10Pd30Ni / rGO, respectively).

[0101] Depend on Figure 2 The results show that no Pd and Ni particles or clusters were observed on the carrier rGO. After the reaction, Pd and Ni in the catalyst existed in the form of single atoms and no aggregation occurred after the reaction. Since the elastic scattering of the electron beam is proportional to the atomic number of the sample element, the larger the atomic number of the element to be measured under the same conditions, the stronger the brightness of the light spot. Compared with the Ni element, the atomic number of the Pd element is nearly twice as high (the atomic numbers of Ni and Pd are 28 and 46, respectively). Therefore, the brightness of the light spot corresponding to the Pd element is stronger. The Pd and Ni species in the 10Pd30Ni / rGO catalyst are mainly evenly distributed on the rGO in the form of single atoms. The distance between the two single atoms of Pd and Ni is small, and some Pd and Ni exist in an adjacent form. In summary, we have successfully prepared a Pd-based catalyst with atomic-scale spatial separation structure of Pd and non-precious metals.

[0102] The contact angles of pure rGO, 10Pd / rGO, 30Ni / rGO and 10Pd30Ni / rGO were tested at room temperature with benzyl alcohol and water as liquid phases, respectively. The test results are shown in Figure 2. Figure 3 shown.

[0103] Figure 3 Contact angle shapes of rGO, 10Pd / rGO, 30Ni / rGO and 10Pd30Ni / rGO (Note: a~d are the benzyl alcohol contact angles of rGO, 10Pd / rGO, 10Pd30Ni / rGO and 30Ni / rGO respectively; e~h are the water contact angles of rGO, 10Pd / rGO, 10Pd30Ni / rGO and 30Ni / rGO respectively).

[0104] Depend on Figure 3 As shown in Figures a to d, rGO, 10Pd / rGO, 10Pd30Ni / rGO and 30Ni / rGO all exhibit good adsorption properties for benzyl alcohol. Among them, the contact angle of the carrier rGO is 15° ( Figure 3 -a), the contact angle of 10Pd / rGO decreased to 25° ( Figure 3 -b), indicating that the deposition of Pd species weakens the adsorption of benzyl alcohol on the catalyst surface. However, the modification of rGO with NiCp accelerates the adsorption of benzyl alcohol on the catalyst surface. The adsorption rates of benzyl alcohol on both 10Pd30Ni / rGO and 30Ni / rGO surfaces exceed the detection limit of the contact angle meter. Figure 3 As shown in Figures e to g, there are significant differences in the hydrophilicity and hydrophobicity of rGO, 10Pd / rGO, 10Pd30Ni / rGO, and 30Ni / rGO. The contact angles of rGO and 10Pd / rGO are 53.4° and 58°, respectively, indicating that they are hydrophilic materials. This may be due to the presence of a large number of hydrophilic functional groups (alkenyl groups) on the support surface. The deposition of Pd slightly reduces the number of oxygen-containing / hydrophilic functional groups on the material surface. However, after the reduced graphene oxide support is modified with Ni species, the contact angles of 10Pd30Ni / rGO and 30Ni / rGO increase to 123° and 106°, respectively, indicating that Ni species modification can increase the contact angle of water on the catalyst surface. The reason is that since Ni species are insoluble in water, Ni species may be deposited on the hydrophilic functional groups on the rGO surface, causing the hydrophilic functional groups on the material surface to decrease sharply. Therefore, the modification of the support by Ni species makes benzyl alcohol more easily adsorbed on 10Pd30Ni / rGO and 30Ni / rGO, while the product water is more easily desorbed, thereby promoting the oxidation reaction of benzyl alcohol.

[0105] Test Example 2

[0106] The catalytic performance of 20 mg of the catalysts described in Example 1 (10Pd30Ni / rGO), Comparative Example 1 (30Ni / rGO), Comparative Example 2 (10Pd / rGO), Comparative Example 3 (10Pd / rGO+30Ni / rGO), Comparative Example 4 (IM-PdNi / rGO) and Comparative Example 5 was compared by carrying out an oxidation reaction of benzyl alcohol in 10 mL of benzyl alcohol in a three-necked flask at 120°C, 1000 rpm and 0.3 MPa for 1 h, and the results are shown in Table 1. Figure 4

[0107] Figure 4 The performance comparison chart of the benzyl alcohol solvent-free liquid phase oxidation reaction of 10Pd / rGO, 30Ni / rGO, 10Pd30Ni / rGO, 10Pd / rGO+30Ni / rGO and IM-PdNi / rGO (Note: Since the catalytic activity (conversion rate) of the catalyst described in Comparative Example 5 is almost zero, Figure 4 Figure 4 It can be seen from the results that the catalytic activity of 10Pd / rGO+30Ni / rGO (conversion rate 4.93%) is basically the same as that of 10Pd / rGO (conversion rate 5.57%), both of which are much lower than that of 10Pd30Ni / rGO (conversion rate 38.15%), which shows that only the 10Pd / rGO component in 10Pd / rGO+30Ni / rGO plays a catalytic role. This may be because the single-atom Pd species and the Ni species must be kept at a relatively close distance within the atomic scale range to have a synergistic effect. Compared with 10Pd30Ni / rGO, the catalytic performance of IM-0.5Pd1.5Ni / rGO (conversion rate 2.51%, selectivity 69.74%) is also poor, which shows that the particle size and mixing state of the Pd and Ni species in the catalyst are key factors affecting the catalytic performance.

[0108] Although the above examples have made a detailed description of the present application, it is only a part of the embodiments of the present application, not all the embodiments, and other embodiments can be obtained according to the present embodiments without creativity, which are within the protection scope of the present application.​​

Claims

1. A Pd-based catalyst comprising a carrier and Pd and a non-precious metal active component supported on the carrier surface; the Pd and the non-precious metal in the non-precious metal active component are in an atomic-scale spatially separated structure; the non-precious metal in the non-precious metal active component comprises nickel, iron, or cobalt; The preparation method of the Pd-based catalyst comprises the following steps: A non-noble metal precursor is subjected to a pulse treatment on a carrier surface, followed by a reduction treatment, to load a non-noble metal active component on the carrier surface to obtain a catalyst precursor; sequentially subjecting the surface of the catalyst precursor to a pulse treatment with a Pd precursor and a reducing agent, so that Pd is loaded on the surface of the catalyst precursor in a single-atom form, thereby obtaining the Pd-based catalyst; The method of subjecting the non-noble metal precursor to pulse treatment on the carrier surface includes chemical vapor deposition or atomic layer deposition; the method of subjecting the Pd precursor and the reducing agent to pulse treatment on the catalyst precursor surface includes atomic layer deposition.

2. The Pd-based catalyst according to claim 1, characterized in that The total mass fraction of the Pd and non-noble metal active components is 0.2-15 wt %.

3. The Pd-based catalyst according to claim 1, characterized in that The mass ratio of Pd to non-precious metal is 1:0.2-10.

4. The Pd-based catalyst according to claim 1, characterized in that The support includes a carbon material support and / or an oxide support.

5. The method for preparing the Pd-based catalyst according to any one of claims 1 to 4, comprising the steps of: A non-precious metal precursor is subjected to a pulse treatment on a carrier surface, followed by a reduction treatment, to load a non-precious metal active component on the carrier surface to obtain a catalyst precursor; the non-precious metal precursor includes nickelocene, ferrocene or cobaltocene; sequentially subjecting the surface of the catalyst precursor to pulse treatment with a Pd precursor and a reducing agent, so that Pd is loaded on the surface of the catalyst precursor in the form of single atoms, thereby obtaining the Pd-based catalyst; the Pd precursor comprises palladium hexafluoroacetylacetonate; The method of subjecting the non-noble metal precursor to pulse treatment on the carrier surface includes chemical vapor deposition or atomic layer deposition; the method of subjecting the Pd precursor and the reducing agent to pulse treatment on the catalyst precursor surface includes atomic layer deposition.

6. The preparation method according to claim 5, characterized in that The reduction treatment is carried out in a reducing atmosphere; the temperature of the reduction treatment is 200-400° C., and the time is 0.5-5 hours.

7. Use of the Pd-based catalyst according to any one of claims 1 to 4 or the Pd-based catalyst prepared by the preparation method according to claim 5 or 6 in the catalytic oxidation reaction of alcohols.

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