A pd / scm-1 molecular sieve catalyst, a preparation method and application thereof

Abstract

The application discloses a Pd / SCM-1 molecular sieve catalyst, a preparation method and application thereof. The Pd / SCM-1 molecular sieve catalyst comprises SCM-1 molecular sieve and metal component Pd, and on the surface of the catalyst, Pd metal particles with a particle size of 2-4 nm account for more than 85% of all Pd metal particles. The preparation method of the catalyst comprises the following steps: a palladium source vapor is contacted with SCM-1 molecular sieve to perform a reaction; inert gas is used to perform a first blowing; a reducing agent is contacted with the product after blowing to perform a reaction; and inert gas is used to perform a second blowing. The catalyst is used in a benzene hydrogenation alkylation reaction, and has good cyclohexylbenzene selectivity and yield.

Description

Technical Field

[0001] This invention relates to the field of catalyst synthesis technology, specifically to a Pd / SCM-1 molecular sieve catalyst, its preparation method, and its catalytic applications. Background Technology

[0002] Phenol and cyclohexanone are important industrial raw materials, currently mainly prepared by the oxidation of cumene and cyclohexane, which suffers from drawbacks such as high energy and material consumption and significant environmental pollution. A new green method for synthesizing cyclohexylbenzene through the hydrogenation of benzene, followed by further oxidation and decomposition to simultaneously produce phenol and cyclohexanone, two high-value-added products, has attracted considerable attention. Cyclohexylbenzene can also be used as an additive in lithium-ion battery electrolytes to improve the battery's overcharge protection performance. With the large-scale development of cyclohexylbenzene oxidation to phenol technology and the rise of the electric vehicle revolution, the preparation and production of cyclohexylbenzene has significant theoretical research value and industrial application prospects. Bifunctional supported metal / molecular sieve catalysts, formed by combining zeolite molecular sieves with excellent acidity with metals, are among the most valuable catalysts for this reaction.

[0003] Patents US3839477 and US4177165 disclose catalysts loaded with noble metals on X- or Y-type molecular sieves, respectively, and apply them to the hydrogenation alkylation reaction of benzene. However, the conversion rate of benzene and the selectivity of cyclohexylbenzene are relatively low. Patents US5054571, US5146024, US6037513, CN101687728A, CN101754940A, CN101796000A, CN101925561A, CN101754940A, and CN103261126A report methods for preparing hydrogenation alkylation catalysts by loading at least one metal (Pt, Pd, Ru, Ir) on molecular sieves. These methods mainly use impregnation and ion exchange methods, which suffer from uneven metal particle size distribution. The cyclohexylbenzene selectivity of the obtained catalysts needs further improvement.

[0004] CN114130421A discloses a bifunctional catalyst for the hydrogenation alkylation reaction of benzene. The catalyst is prepared by reacting a metal component with specific inorganic / organic ligands to form a complex, adjusting the acidity / alkalinity of the solution, mixing it with the reactants for synthesizing molecular sieves, and then crystallizing the mixture to obtain a metal / molecular sieve catalyst. While this method produces the catalyst in a one-pot process, the metal complex introduced during molecular sieve synthesis has unknown effects on the formation of the molecular sieve framework, and the mechanism of metal nucleation is difficult to understand, lacking controllability. Furthermore, because the noble metal precursor is introduced during the molecular sieve crystallization process, rather than being loaded onto the sieve after crystallization, the metal particle size is heavily dependent on the properties of the molecular sieve itself and cannot be controlled solely by regulating the metal synthesis process.

[0005] In summary, the key to further developing metal loading methods for molecular sieves with high metal dispersibility, small and uniform particle size, and improved selectivity of cyclohexylbenzene is to improve the metal loading method. Summary of the Invention

[0006] The technical problem this invention aims to solve is that existing molecular sieve catalysts exhibit poor metal dispersion uniformity, large metal particle size, and poor selectivity for cyclohexylbenzene in the hydrogenation alkylation of benzene. This invention provides a Pd / SCM-1 molecular sieve catalyst, its preparation method, and its applications. The catalyst of this invention features high metal dispersion, small and uniform particle size. The Pd / SCM-1 molecular sieve catalyst of this invention, when used in the hydrogenation alkylation of benzene to cyclohexylbenzene, demonstrates good selectivity and yield for cyclohexylbenzene.

[0007] The first aspect of the present invention provides a Pd / SCM-1 molecular sieve catalyst, the catalyst comprising an SCM-1 molecular sieve and a metal component Pd, wherein on the surface of the catalyst, Pd metal particles with a particle size of 2-4 nm account for more than 85% of all Pd metal particles.

[0008] Furthermore, in the SCM-1 molecular sieve, the crystals have a nanosheet morphology, and the average thickness of the crystals is not higher than 15 nm, preferably 2 to 12 nm, and more preferably 8 to 10 nm.

[0009] Furthermore, the external specific surface area of ​​the SCM-1 molecular sieve is not less than 150 m². 2 / g, preferably 150-250m 2 / g.

[0010] Furthermore, in the catalyst, based on the weight of the catalyst, the content of the metal component Pd, calculated as an element, is 0.01% to 5.0%, preferably 0.1% to 2.0%, and the remainder is SCM-1 molecular sieve.

[0011] Furthermore, on the surface of the catalyst, Pd metal particles with a particle size of 2.5–3.5 nm account for more than 90% of all Pd metal particles.

[0012] A second aspect of this invention provides a method for preparing the above-mentioned Pd / SCM-1 molecular sieve catalyst, comprising the following steps:

[0013] (1) Palladium source vapor reacts with SCM-1 molecular sieve;

[0014] (2) The product obtained in step (1) is purged for the first time with an inert gas;

[0015] (3) React the product after purging in step (2) with a reducing agent;

[0016] (4) The product obtained in step (3) is purged a second time with an inert gas to obtain the Pd / SCM-1 molecular sieve catalyst.

[0017] Furthermore, the preparation method of the Pd / SCM-1 molecular sieve catalyst is carried out in a closed chamber atomic layer deposition reactor (ALD).

[0018] Furthermore, the number of deposition cycles for Pd ALD is one cycle, that is, steps (1) to (4) constitute one deposition cycle.

[0019] Further, the palladium source vapor in step (1) is obtained by heating a palladium source to 55–80°C, preferably 60–70°C. The palladium source vapor is introduced into the reactor using a carrier gas. Further, the carrier gas is preferably high-purity nitrogen, with a purity preferably above 99.999 vol%. In step (1), the flow rate of the carrier gas relative to 1–3 g of SCM-1 molecular sieve is 5–50 mL / min, preferably 10–30 mL / min.

[0020] Furthermore, in step (1), the reaction temperature is 80–300°C, preferably 120–250°C.

[0021] Furthermore, in step (1), the reaction time is no more than 2000 seconds, preferably 800 to 1800 seconds, and more preferably 800 to 1200 seconds.

[0022] Further, in step (1), the palladium source is at least one of di(hexafluoroacetylacetone)palladium (Pd(hfac)2), (2,2,6,6-tetramethyl-3,5-heptadecanoic acid)palladium, and palladium acetylacetone.

[0023] Furthermore, in step (2) or step (4), the inert gas is preferably high-purity nitrogen, with a purity preferably above 99.999v%.

[0024] Furthermore, in step (2), the first purging time is 500-800 seconds.

[0025] Furthermore, in step (3), the reducing agent is at least one of formaldehyde and hydrogen.

[0026] Furthermore, in step (3), the reaction time is no more than 2000 seconds, preferably 800 to 1800 seconds, and even more preferably 800 to 1200 seconds.

[0027] Furthermore, in step (4), the second purging time is 500-800 seconds.

[0028] Furthermore, the preparation method of the SCM-1 molecular sieve includes the following steps:

[0029] The SCM-1 molecular sieve is prepared by mixing silicon source, aluminum source, alkali source, organic structure directing agent I, organic structure directing agent II and water, crystallizing and calcining.

[0030] Furthermore, organic structure directing agent I is hexamethyleneimine (HMI), and organic structure directing agent II is dicyclohexylamine (DCHA).

[0031] Furthermore, the aluminum source is selected from at least one of sodium aluminate and aluminum isopropoxide, preferably sodium aluminate; the silicon source is selected from at least one of silica sol and tetraethyl silicate, preferably silica sol; and the alkali source is selected from at least one of sodium hydroxide and potassium hydroxide, preferably sodium hydroxide.

[0032] Further, the silicon source is SiO2, and the aluminum source is Al2O3. The molar ratio of each material is: SiO2:Al2O3:NaOH:Organic structure directing agent I:Organic structure directing agent II:H2O = 1:0.020~0.060:0.08~0.15:0.15~0.35:0.2~0.6:10~40, preferably SiO2:Al2O3:NaOH:Organic structure directing agent I:Organic structure directing agent II:H2O = 10~40. Structure directing agent II: H2O = 1: 0.025-0.040: 0.09-0.13: 0.20-0.30: 0.3-0.5: 18-33; more preferably SiO2: Al2O3: NaOH: organic structure directing agent I: organic structure directing agent II: H2O = 1: 0.025-0.040: 0.09-0.13: 0.20-0.30: 0.30-0.50: 22-33.

[0033] Furthermore, the crystallization temperature of SCM-1 molecular sieve is 140–170℃, preferably 145–155℃; the crystallization time is 1–5 days, preferably 3–4 days.

[0034] Furthermore, the calcination temperature is 450–650℃, preferably 500–600℃, the calcination time is 4–8h, preferably 5–6h, and the calcination atmosphere is air.

[0035] Furthermore, the SCM-1 molecular sieve described in step (1) is a hydrogen-form molecular sieve. Generally, the SCM-1 molecular sieve can be prepared by directly obtaining a hydrogen-form molecular sieve, or by converting a sodium-form or potassium-form molecular sieve into a hydrogen-form SCM-1 molecular sieve through conventional ammonium exchange.

[0036] The third aspect of the present invention also provides the application of the Pd / SCM-1 molecular sieve catalyst prepared according to any of the methods described in the first aspect or according to any of the methods described in the second aspect in the catalytic reaction of benzene hydrogenation alkylation.

[0037] Furthermore, the reaction conditions are as follows: reaction temperature 100–250℃, hydrogen pressure 1.0–4.0 MPa, hydrogen / benzene molar ratio 0.5–2.0, and benzene / catalyst mass ratio 40–60.

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0039] (1) In the Pd / SCM-1 molecular sieve catalyst of the present invention, the SCM-1 molecular sieve crystal has a nanosheet morphology and the thickness of the crystal is no more than 15nm. The two-dimensional morphology, high specific surface area and narrow thickness distribution of the molecular sieve material are conducive to the uniform distribution of the metal precursor, and then the metal Pd nanoparticles with small particle size and narrow distribution are loaded through atomic layer deposition (ALD).

[0040] (2) Small-sized metals are prone to aggregation during synthesis, so obtaining a narrower particle size distribution is not difficult with smaller particle sizes. This invention utilizes atomic layer deposition (ALD) technology, a gas-phase method, to load Pd metal nanoparticles onto SCM-1 molecular sieves with a specific two-dimensional structure under suitable reaction conditions. The Pd particles synthesized by this method have uniform particle size and high dispersibility, with Pd metal particles of 2–4 nm accounting for more than 85% of all Pd metal particles, preferably more than 90% with a particle size of 2.5–3.5 nm. Furthermore, this method can be performed on pre-formed molecular sieves, exhibiting high versatility.

[0041] (3) The Pd / SCM-1 molecular sieve catalyst prepared in this invention showed high selectivity in the hydrogenation alkylation of benzene. Under suitable reaction conditions, the selectivity of cyclohexylbenzene was not less than 45%, and the selectivity of cyclohexane was not more than 55%. Attached Figure Description

[0042] Figure 1 The X-ray diffraction pattern of the SCM-1 molecular sieve obtained in Example 1;

[0043] Figure 2 This is a transmission electron microscope image of the Pd / SCM-1 molecular sieve catalyst obtained in Example 1;

[0044] Figure 3 The image shows a transmission electron microscope image of the catalyst obtained in Comparative Example 2.

[0045] Figure 4 The image shows a transmission electron microscope image of the catalyst obtained in Comparative Example 3.

[0046] Figure 5 The image shows the X-ray diffraction pattern of the molecular sieve sample obtained in Comparative Example 1. Detailed Implementation

[0047] In the context of this specification, including in the following examples and comparative examples, the X-ray powder diffractometer used for the molecular sieves is a Panalytical X-PERPRO type X-ray powder diffractometer, used to analyze the phase composition of the samples, and a CuKα ray source. Nickel filter, 2θ scanning range 2~50°, operating voltage 40KV, current 40mA, scanning rate 10° / min.

[0048] In the context of this specification, including in the following examples and comparative examples, the method for measuring the crystal thickness of the molecular sieve is as follows: the molecular sieve is observed using a transmission electron microscope (FEI G2F30 transmission electron microscope, operating voltage 300kV) at a magnification of 100,000x, a field of view is randomly selected, and the thickness of all crystals in that field of view is measured. This operation is repeated 5 times, and the average value of the 5 measurements is taken as the average thickness of the crystal.

[0049] In the context of this specification, including in the following examples and comparative examples, the method for measuring the particle size of Pd metal particles is as follows: the catalyst is observed using a transmission electron microscope (FEI G2F30 transmission electron microscope, operating voltage 300kV) at a magnification of 100,000x, a field of view is randomly selected, the size of all Pd particles in the field of view is measured, the number of samples is greater than 100, and then the average particle size value is obtained.

[0050] In the context of this specification, the loading of Pd metal on the catalyst was characterized by inductively coupled plasma optical emission spectroscopy (ICP-OES). The valence state of Pd metal was characterized by X-ray photoelectron spectroscopy (XPS).

[0051] In the context of this specification, the reaction products benzene, cyclohexane, cyclohexylbenzene, dicyclohexylbenzene, etc., were analyzed by gas chromatography (GC). The gas chromatograph was an Agilent 7890B, the detector was a flame ionization detector (FID), and the column was an SE-54 capillary column (30m, 0.53mm).

[0052] In the context of this specification, when calculating product selectivity and cyclohexylbenzene yield, all amounts of substances are expressed by mass.

[0053] To facilitate understanding of the present invention, the following embodiments are provided. However, these embodiments are only for the purpose of helping to understand the present invention and should not be regarded as specific limitations of the present invention.

[0054]

Example 1

[0055] Take a reaction vessel, add 21.08 g of water, and while stirring, add 0.21 g of sodium hydroxide solution containing 10 wt%. Then add 1.09 g of hexamethyleneimine, 3.17 g of dicyclohexylamine, 0.367 g of sodium aluminate, and 6.07 g of silica sol. Continue stirring at room temperature for 3 hours to obtain a mixture. The final material ratio (molar ratio) is:

[0056] SiO2 / Al2O3 = 30;

[0057] NaOH / SiO2 = 0.09;

[0058] Hexamethyleneimine / SiO2 = 0.25;

[0059] Dicyclohexylamine / SiO2 = 0.40;

[0060] H2O / SiO2 = 32.

[0061] After the reactants were thoroughly mixed, they were transferred to a stainless steel reactor and crystallized at 150°C for 72 hours under stirring. After crystallization, the mixture was washed repeatedly with deionized water until the pH of the washing solution was neutral. It was then dried at 80°C for 24 hours and transferred to a muffle furnace for calcination at 550°C in air for 6 hours to obtain sodium-form SCM-1 molecular sieve. The sodium-form SCM-1 molecular sieve was then subjected to ammonium ion exchange with 0.5 mol / L NH4Cl solution at 45°C for 2 hours, followed by centrifugation and washing. This ammonium ion exchange was repeated three times. The resulting sample was dried overnight at 80°C and calcined in air at 550°C for 6 hours to obtain hydrogen-form SCM-1 molecular sieve sample A. Its X-ray diffraction pattern is shown below. Figure 1 .

[0062] A closed-chamber atomic layer deposition (ALD) reactor was used, with di(hexafluoroacetylacetone)palladium (Pd(hfac)₂) and formaldehyde solution as precursors, and PdALD was carried out at 150 °C. High-purity N₂ (99.999%) was used as the carrier gas at a flow rate of 30 mL / min. During the experiment, the Pd precursor source bottle was heated to 65 °C to achieve sufficient vapor pressure, the inlet pipe was maintained at 115 °C, and the chamber was heated to 150 °C to allow for precursor condensation. In the catalyst preparation process, specifically, 2g of SCM-1 molecular sieve powder A is placed into the reaction chamber. (1) High-purity N2 gas is used to introduce Pd(hfac)2 vapor into the reaction chamber to react with the SCM-1 molecular sieve powder for 900 seconds; (2) After the Pd(hfac)2 source is turned off, high-purity N2 gas is used to purge and remove unreacted Pd(hfac)2 precursor and precursor molecular fragments after reaction for 600 seconds; (3) The formaldehyde solution source bottle is opened and introduced into the reaction chamber for 900 seconds; (4) After the formaldehyde source is turned off, high-purity N2 gas is used to purge for 600 seconds. The above steps (1)-(4) are called one atomic layer deposition cycle. After one atomic layer deposition cycle is completed, the sample is taken out from the reaction chamber to obtain catalyst A.

[0063] The results of high-angle annular dark-field scanning transmission electron microscopy of catalyst A ( Figure 2 It can be seen that the Pd nanoparticles are highly dispersed on the molecular sieve, with Pd metal particles of 2.5–3.5 nm in diameter accounting for 95% of all Pd metal particles. The metal loading of Pd measured by ICP-OES is 0.2 wt.%.

[0064]

Example 2

[0065] Take a reaction vessel, add 18.33g of water, and while stirring, add 0.26g of a 10wt% sodium hydroxide solution, then add 1.66g of hexamethyleneimine, 3.93g of dicyclohexylamine, 0.405g of sodium aluminate, and 8.16g of silica sol. Continue stirring at room temperature for 3 hours to obtain a mixture. The final material ratio (molar ratio) is:

[0066] SiO2 / Al2O3 = 30;

[0067] NaOH / SiO2 = 0.09;

[0068] Hexamethyleneimine / SiO2 = 0.25;

[0069] Dicyclohexylamine / SiO2 = 0.40;

[0070] H2O / SiO2 = 24.

[0071] After the reactants were thoroughly mixed, they were transferred to a stainless steel reactor and crystallized at 150°C for 72 hours under stirring. After crystallization, the mixture was washed multiple times with deionized water until the pH of the washing solution was neutral. It was then dried at 80°C for 24 hours and transferred to a muffle furnace for calcination at 550°C in air for 6 hours to obtain sodium-form SCM-1 molecular sieve. The sodium-form SCM-1 molecular sieve was then subjected to ammonium ion exchange with 0.5 mol / L NH4Cl solution at 45°C for 2 hours, followed by centrifugation and washing. This ammonium ion exchange was repeated three times. The resulting sample was dried overnight at 80°C and calcined in air at 550°C for 6 hours to obtain hydrogen-form SCM-1 molecular sieve sample B, whose X-ray diffraction pattern was similar to... Figure 1 .

[0072] SCM-1 molecular sieve powder B was used to obtain catalyst B by ALD deposition of metal, as described in Example 1.

[0073] In the obtained catalyst B, Pd nanoparticles were highly dispersed on the molecular sieve, with Pd metal particles of 2.5–3.5 nm in diameter accounting for 91% of all Pd metal particles. The Pd metal loading was measured to be 0.2 wt.% by ICP-OES.

[0074]

Example 3

[0075] Take a reaction vessel, add 20.5g of water, and while stirring, add 0.22g of a 10wt% sodium hydroxide solution, then add 1.15g of hexamethyleneimine, 3.33g of dicyclohexylamine, 0.386g of sodium aluminate, and 6.91g of silica sol. Continue stirring at room temperature for 3 hours to obtain a mixture. The final material ratio (molar ratio) is:

[0076] SiO2 / Al2O3 = 30;

[0077] NaOH / SiO2 = 0.09;

[0078] Hexamethyleneimine / SiO2 = 0.25;

[0079] Dicyclohexylamine / SiO2 = 0.40;

[0080] H2O / SiO2 = 30.

[0081] After the reactants were thoroughly mixed, they were transferred to a stainless steel reactor and crystallized at 150°C for 72 hours under stirring. After crystallization, the mixture was washed repeatedly with deionized water until the pH of the washing solution reached neutral. It was then dried at 80°C for 24 hours and transferred to a muffle furnace for calcination at 550°C in air for 6 hours to obtain sodium-form SCM-1 molecular sieve. The sodium-form SCM-1 molecular sieve was then subjected to ammonium ion exchange with 0.5 mol / L NH4Cl solution at 45°C for 2 hours, followed by centrifugation and washing. This ammonium ion exchange was repeated three times. The resulting sample was dried overnight at 80°C and calcined in air at 550°C for 6 hours to obtain hydrogen-form SCM-1 molecular sieve sample C, whose X-ray diffraction pattern is similar to... Figure 1 .

[0082] SCM-1 molecular sieve powder C was used to obtain catalyst C by the same method as in Example 1, which involved metal deposition via ALD.

[0083] In the obtained catalyst C, Pd nanoparticles are highly dispersed on the molecular sieve, with Pd metal particles of 2.5–3.5 nm in diameter accounting for 93% of all Pd metal particles. The Pd metal loading was measured to be 0.2 wt.% by ICP-OES.

[0084]

Example 4

[0085] Take a reaction vessel, add 15.21g of water, and while stirring, add 0.32g of a 10wt% sodium hydroxide solution. Then add 1.66g of hexamethyleneimine, 4.80g of dicyclohexylamine, 0.556g of sodium aluminate, and 9.95g of silica sol. Continue stirring at room temperature for 3 hours to obtain a mixture. The final material ratio (molar ratio) is:

[0086] SiO2 / Al2O3 = 30;

[0087] NaOH / SiO2 = 0.09;

[0088] Hexamethyleneimine / SiO2 = 0.25;

[0089] Dicyclohexylamine / SiO2 = 0.40;

[0090] H2O / SiO2 = 18.

[0091] After the reactants were thoroughly mixed, they were transferred to a stainless steel reactor and crystallized at 150°C for 72 hours under stirring. After crystallization, the mixture was washed repeatedly with deionized water until the pH of the washing solution was neutral. It was then dried at 80°C for 24 hours and transferred to a muffle furnace for calcination at 550°C in air for 6 hours to obtain sodium-form SCM-1 molecular sieve. The sodium-form SCM-1 molecular sieve was then subjected to ammonium ion exchange with a 0.5 mol / L NH4Cl solution at 45°C for 2 hours. After centrifugation and washing, the ammonium ion exchange was repeated three times. The resulting sample was dried overnight at 80°C and calcined in air at 550°C for 6 hours to obtain hydrogen-form SCM-1 molecular sieve sample D.

[0092] SCM-1 molecular sieve powder D was used to obtain catalyst D by the same method as in Example 1, which involved metal deposition via ALD.

[0093] In the obtained catalyst D, Pd metal particles with a particle size of 2.5–3.5 nm accounted for 85% of all Pd metal particles. The Pd metal loading was measured to be 0.2 wt.% by ICP-OES.

[0094]

Example 5

[0095] Take a reaction vessel, add 21.08 g of water, and while stirring, add 0.20 g of sodium hydroxide solution containing 10 wt%. Then add 1.07 g of hexamethyleneimine, 3.10 g of dicyclohexylamine, 0.358 g of sodium aluminate, and 6.41 g of silica sol. Continue stirring at room temperature for 3 hours to obtain a mixture. The final material ratio (molar ratio) is:

[0096] SiO2 / Al2O3 = 30;

[0097] NaOH / SiO2 = 0.09;

[0098] Hexamethyleneimine / SiO2 = 0.25;

[0099] Dicyclohexylamine / SiO2 = 0.4;

[0100] H2O / SiO2 = 33.

[0101] After the reactants were thoroughly mixed, they were transferred to a stainless steel reactor and crystallized at 150°C for 72 hours under stirring. After crystallization, the mixture was washed repeatedly with deionized water until the pH of the washing solution reached neutral. It was then dried at 80°C for 24 hours and transferred to a muffle furnace for calcination at 550°C in air for 6 hours to obtain sodium-form SCM-1 molecular sieve. The sodium-form SCM-1 molecular sieve was then subjected to ammonium ion exchange with 0.5 mol / L NH4Cl solution at 45°C for 2 hours, followed by centrifugation and washing. This ammonium ion exchange was repeated three times. The resulting sample was dried overnight at 80°C and calcined in air at 550°C for 6 hours to obtain hydrogen-form SCM-1 molecular sieve sample E, whose X-ray diffraction pattern is similar to... Figure 1 .

[0102] SCM-1 molecular sieve powder E was used to obtain catalyst E by the same method as in Example 1, which involved metal deposition via ALD.

[0103] In the obtained catalyst E, Pd nanoparticles were highly dispersed on the molecular sieve, with Pd metal particles of 2.5–3.5 nm in diameter accounting for 94% of all Pd metal particles. The Pd metal loading was measured to be 0.2 wt.% by ICP-OES.

[0104]

Example 6

[0105] The preparation of hydrogen-form SCM-1 molecular sieve is the same as in Example 1.

[0106] A closed-chamber atomic layer deposition (ALD) reactor was used, with bis(hexafluoroacetylacetone)palladium (Pd(hfac)₂) and formaldehyde solution as precursors, and PdALD was carried out at 150 °C. High-purity N₂ (99.999%) was used as the carrier gas at a flow rate of 30 mL / min. During the experiment, the Pd precursor source bottle was heated to 65 °C to achieve sufficient vapor pressure, the inlet pipe was maintained at 115 °C, and the chamber was heated to 150 °C to allow for precursor condensation. In the catalyst preparation process, specifically, 2g of SCM-1 molecular sieve powder is placed into the reaction chamber. (1) High-purity N2 gas is used to introduce Pd(hfac)2 vapor into the reaction chamber to react with the SCM-1 molecular sieve powder for 1400 seconds; (2) After the Pd(hfac)2 source is turned off, high-purity N2 gas is used to purge and remove unreacted Pd(hfac)2 precursor and precursor molecular fragments after reaction for 600 seconds; (3) The formaldehyde solution source bottle is opened and introduced into the reaction chamber for 1400 seconds; (4) After the formaldehyde source is turned off, high-purity N2 gas is used to purge for 600 seconds. The above steps (1)-(4) are called one atomic layer deposition cycle. After one atomic layer deposition cycle is completed, the sample is taken out from the reaction chamber to obtain catalyst F.

[0107] In the obtained catalyst F, Pd nanoparticles were highly dispersed on the molecular sieve, with Pd metal particles of 2.5–3.5 nm in diameter accounting for 91% of all Pd metal particles. The Pd metal loading was measured to be 0.3 wt.% by ICP-OES.

[0108]

Example 7

[0109] The preparation of hydrogen-form SCM-1 molecular sieve is the same as in Example 1.

[0110] A closed-chamber atomic layer deposition (ALD) reactor was used, with bis(hexafluoroacetylacetone)palladium (Pd(hfac)₂) and formaldehyde solution as precursors, and PdALD was carried out at 150 °C. High-purity N₂ (99.999%) was used as the carrier gas at a flow rate of 30 mL / min. During the experiment, the Pd precursor source bottle was heated to 65 °C to achieve sufficient vapor pressure, the inlet pipe was maintained at 115 °C, and the chamber was heated to 150 °C to allow for precursor condensation. In the catalyst preparation process, specifically, 2g of SCM-1 molecular sieve powder is placed into the reaction chamber. (1) High-purity N2 gas is used to introduce Pd(hfac)2 vapor into the reaction chamber to react with the SCM-1 molecular sieve powder for 1300 seconds. (2) After the Pd(hfac)2 source is turned off, high-purity N2 gas is used to purge and remove unreacted Pd(hfac)2 precursor and precursor molecular fragments after the reaction for 600 seconds. (3) The formaldehyde solution source bottle is opened and introduced into the reaction chamber for 1800 seconds. (4) After the formaldehyde source is turned off, high-purity N2 gas is used to purge for 600 seconds. The above steps (1)-(4) are called one atomic layer deposition cycle. After one atomic layer deposition cycle is completed, the sample is taken out from the reaction chamber to obtain catalyst G.

[0111] In the obtained catalyst G, Pd nanoparticles were highly dispersed on the molecular sieve, with Pd metal particles of 2.5–3.5 nm in diameter accounting for 92% of all Pd metal particles. The Pd metal loading was measured to be 0.2 wt.% by ICP-OES.

[0112]

Examples 8-14

[0113] The Pd / SCM-1 molecular sieve catalysts synthesized in Examples 1-7 were used to carry out benzene hydrogenation alkylation reactions in closed reactors. 0.3 g of the Pd / SCM-1 molecular sieve catalysts from Examples 1-7 and benzene were added to a high-pressure reactor equipped with a magnetic stirrer. Hydrogen gas was introduced to purge the reactor three times, and then the reactor was purged with hydrogen to a certain pressure and sealed. The reaction conditions were: reaction temperature 150℃, hydrogen pressure 2.0 MPa, hydrogen / benzene molar ratio 1.5, benzene / catalyst mass ratio 50, and reaction time 4 hours. Gas chromatography was used to quantitatively analyze the products in the reaction solution. The selectivity of the catalytic products is shown in Table 1.

[0114] Comparative Example 1

[0115] Compared with the preparation of hydrogen-form SCM-1 molecular sieve in Example 1, the reaction conditions and material ratios are the same as in Example 1, except that dicyclohexylamine is not added, and the final material ratio (molar ratio) is:

[0116] SiO2 / Al2O3 = 30;

[0117] NaOH / SiO2 = 0.09;

[0118] Hexamethyleneimine / SiO2 = 0.25;

[0119] H2O / SiO2 = 32.

[0120] After the reactants were thoroughly mixed, they were transferred to a stainless steel reactor and crystallized at 150°C for 72 hours under stirring. After crystallization, the mixture was washed repeatedly with deionized water until the pH of the washing solution reached neutral. It was then dried at 80°C for 24 hours and transferred to a muffle furnace for calcination at 550°C in air for 6 hours to obtain sodium-type SCM-1 molecular sieve. The sodium-type SCM-1 molecular sieve was then subjected to ammonium ion exchange with 0.5 mol / L NH4Cl solution at 45°C for 2 hours, followed by centrifugation and washing. This ammonium ion exchange was repeated three times. The resulting sample was dried overnight at 80°C and calcined in air at 550°C for 6 hours to obtain hydrogen-type molecular sieve sample DA. Its X-ray diffraction pattern is shown below. Figure 5 It is significantly different from the hydrogen-type SCM-1 molecular sieve obtained in Example 1.

[0121] The molecular sieve powder DA was used to obtain catalyst H by depositing metal using the same ALD method as in Example 1.

[0122] In the obtained catalyst H, Pd metal particles with a particle size of 2.5–3.5 nm accounted for 65% of all Pd metal particles. The Pd metal loading was measured to be 0.3 wt.% by ICP-OES.

[0123] Comparative Example 2

[0124] The preparation method of hydrogen-form SCM-1 molecular sieve is the same as in Example 1.

[0125] Pd metal was loaded onto SCM-1 using a wet chemical method. 2 g of hydrogen-form SCM-1 molecular sieve was dispersed in 60 mL of deionized water, followed by the addition of a 1.7 × 10⁻⁶ ppm solution. -3 6 mL of a mol / L palladium chloride solution (with palladium chloride solid dissolved in 1 M HCl beforehand) was added and stirred at room temperature for 6 hours. In a separate reaction vessel, 25 mL of deionized water was added, followed by 70 mg of sodium borohydride. After stirring to dissolve, an aqueous solution of sodium borohydride was obtained, denoted as solution B. Solution B was added dropwise to solution A, and the reaction was carried out with stirring at room temperature for 8 hours. The mixture was then centrifuged and washed three times with deionized water. After drying overnight at 80 °C, catalyst I was obtained. Its transmission electron microscope image is shown below. Figure 3 .

[0126] The TEM results for catalyst I obtained show that ( Figure 3 The Pd metal particles were extremely unevenly dispersed, with no Pd metal particles in the 2–4 nm range. ICP-OES analysis showed that the Pd metal loading was 0.3 wt.%.

[0127] Comparative Example 3

[0128] The preparation method of hydrogen-form SCM-1 molecular sieve is the same as in Example 1.

[0129] Pd metal was loaded onto SCM-1 using a wet chemical method. 2 g of hydrogen-form SCM-1 molecular sieve was dispersed in 60 mL of deionized water, followed by the addition of a 1.7 × 10⁻⁶ ppm solution. -3 6 mL of a mol / L palladium chloride solution (palladium chloride solid was previously dissolved in 1 mol / L HCl) was added and stirred at room temperature for 6 hours. The reaction temperature was then increased to 70 °C, and stirring continued until the liquid was completely evaporated. The resulting powder solid was placed in a 10% H₂ / Ar mixture, and the temperature was programmed to 300 °C for 2 hours to obtain catalyst J. Its transmission electron microscope image is shown below. Figure 4 .

[0130] The TEM results for the obtained catalyst J show that ( Figure 4 The Pd metal particles were extremely unevenly dispersed, with no Pd metal particles in the 2–4 nm range. ICP-OES analysis showed that the Pd metal loading was 0.3 wt.%.

[0131] Comparative Example 4

[0132] The preparation method of hydrogen-form SCM-1 molecular sieve is the same as in Example 1.

[0133] The deposition method of Pd metal on hydrogen-type SCM-1 molecular sieve is the same as in Example 1, except that the introduction time of Pd(hfac)2 precursor and formaldehyde is extended to 2700 seconds and 2700 seconds respectively to obtain catalyst K.

[0134] In the obtained catalyst K, Pd metal particles with a particle size of 2.5–3.5 nm accounted for 63% of all Pd metal particles. The Pd metal loading was measured to be 0.6 wt.% by ICP-OES.

[0135] Comparative Example 5

[0136] The preparation method of hydrogen-form SCM-1 molecular sieve is the same as in Example 1.

[0137] The deposition method of Pd metal on the hydrogen-form SCM-1 molecular sieve is the same as in Example 1, except that the introduction time of Pd(hfac)2 precursor and formaldehyde is shortened to 500 seconds and 500 seconds respectively, resulting in catalyst L. In this catalyst, effective metal deposition cannot be achieved, Pd metal particles with a diameter between 2.5 and 3.5 nm cannot be observed, and due to the extremely low metal content, it has virtually no activity.

[0138] Comparative Examples 6-10

[0139] Similar to Examples 8-14, the catalyst materials synthesized in Comparative Examples 1-5 were subjected to catalytic reactions of benzene hydrogenation alkylation. The selectivity of the catalytic products is shown in Table 1.

[0140] Table 1. Catalyst performance results for Examples 8-14 and Comparative Examples 6-10

[0141]

[0142]

[0143] Table 2 shows the properties of the SCM-1 molecular sieves obtained in each example.

[0144] Molecular sieve number Average thickness / nm <![CDATA[External specific surface area / (m 2 / g)]]> Example 1 A 9.0 120 Example 2 B 10.0 100 Example 3 C 9.5 115 Example 4 D 12 95 Example 5 E 8.5 125 Comparative Example 1 DA 22 50

[0145] The specific embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A Pd / SCM-1 molecular sieve catalyst, characterized in that, The catalyst comprises SCM-1 molecular sieve and metal component Pd. On the surface of the catalyst, Pd metal particles with a particle size of 2-4 nm account for more than 85% of all Pd metal particles. In the SCM-1 molecular sieve, the crystals have a nanosheet morphology and the thickness of the crystals is not higher than 15 nm. Based on the weight of the catalyst, the content of metal component Pd, calculated as an element, is 0.01% to 5.0%, and the remainder is SCM-1 molecular sieve.

2. The catalyst according to claim 1, characterized in that, In the SCM-1 molecular sieve, the thickness of the crystal is 2~12nm.

3. The catalyst according to claim 2, characterized in that, In the SCM-1 molecular sieve, the thickness of the crystal is 8~10 nm.

4. The catalyst according to claim 1, characterized in that, Based on the weight of the catalyst, the content of the metal component Pd, calculated as an element, is 0.1% to 2.0%.

5. The catalyst according to claim 1, characterized in that, On the surface of the catalyst, Pd metal particles with a particle size of 2.5~3.5nm account for more than 90% of all Pd metal particles.

6. A method for preparing the Pd / SCM-1 molecular sieve catalyst according to any one of claims 1-5, comprising the following steps: (1) Palladium source vapor reacts with SCM-1 molecular sieve; (2) The product obtained in step (1) is purged for the first time with an inert gas; (3) React the product after purging in step (2) with a reducing agent; (4) The product obtained in step (3) is purged a second time with an inert gas to obtain the Pd / SCM-1 molecular sieve catalyst.

7. The preparation method according to claim 6, characterized in that, The palladium source is at least one of di(hexafluoroacetylacetone)palladium (Pd(hfac)2), (2,2,6,6-tetramethyl-3,5-heptadecanoic acid)palladium, and palladium acetylacetone; the reducing agent is at least one of formaldehyde and hydrogen.

8. The preparation method according to claim 6, characterized in that, In step (1), the reaction temperature is 80~300℃; the reaction time is no more than 2000 seconds; And / or, in step (3), the reaction time is no more than 2000 seconds.

9. The preparation method according to claim 8, characterized in that, In step (1), the reaction temperature is 120~250℃; the reaction time is 800~1800 seconds; And / or, in step (3), the reaction time is 800~1800 seconds.

10. The preparation method according to claim 6, characterized in that, In step (2), the first purging time is 500~800 seconds; And / or, in step (4), the second purging time is 500~800 seconds.

11. The application of the Pd / SCM-1 molecular sieve catalyst according to any one of claims 1-5 in the catalytic reaction of benzene hydrogenation alkylation.

12. The application according to claim 11, characterized in that, The reaction conditions are as follows: reaction temperature 150~250℃, hydrogen pressure 1.0~4.0MPa, hydrogen / benzene molar ratio 0.5~2.0, and benzene / catalyst mass ratio 40~60.

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