CN110170326B - High-dispersion supported noble metal catalytic material and preparation method thereof - Google Patents

High-dispersion supported noble metal catalytic material and preparation method thereof Download PDF

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CN110170326B
CN110170326B CN201910382273.XA CN201910382273A CN110170326B CN 110170326 B CN110170326 B CN 110170326B CN 201910382273 A CN201910382273 A CN 201910382273A CN 110170326 B CN110170326 B CN 110170326B
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noble metal
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李殿卿
李海萍
贺宇飞
冯俊婷
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Beijing University of Chemical Technology
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    • 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
    • B01J23/66—Silver or gold
    • B01J23/68—Silver or gold with arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
    • B01J23/688—Silver or gold with arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium with manganese, technetium or rhenium
    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • 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
    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/89—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals
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    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/89—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals
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    • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
    • B01J35/391—Physical properties of the active metal ingredient
    • B01J35/394—Metal dispersion value, e.g. percentage or fraction
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    • 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

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Abstract

The invention discloses a high-dispersion supported noble metal catalytic material and a preparation method thereof. Because the variable valence metal is directly introduced into the LDHs laminate in the process of preparing the LDHs, the highly dispersed LDHs carrier with the reducing sites is prepared; the highly dispersed reducing sites can spontaneously induce reduction of the oxidation state noble metal, so that the highly dispersed active component particles of the supported noble metal catalyst are realized, and reduction is carried out without using a reducing agent or high-temperature roasting. The control of the particle size, distribution and stable load of the active components can be realized by changing the preparation temperature of the catalyst and the condition of adding the surfactant. The high-dispersion supported catalyst shows good application effect in the selective oxidation reaction of benzyl alcohol and the hydrogenation reaction of anthraquinone.

Description

High-dispersion supported noble metal catalytic material and preparation method thereof
Technical Field
The invention belongs to the field of catalyst preparation, and particularly relates to a high-dispersion supported noble metal catalytic material and a preparation method thereof.
Background
The catalytic technology is a common key technology of petrochemical industry, fine chemical industry, coal chemical industry, environmental chemical industry and the like, plays a great role in promoting economic development and social progress, and the supported noble metal catalyst is an important catalytic material in the catalytic technology, plays an important role in the petrochemical industry, the fine chemical industry, the coal chemical industry and the environmental chemical industry, and especially plays an important role in the fields of selective hydrogenation and selective oxidation. The supported noble metal catalyst plays a catalytic role by depending on the activation of the simple substance state active noble metal nano particles on the surface of the carrier on reactant molecules. However, the reserves of precious metals in China are rare and expensive, and under the condition that the demand of petrochemical industry, fine chemical industry, coal chemical industry and environmental chemical industry for precious metals is increasing, in order to effectively improve the utilization rate of the precious metals, the development of a novel and strong-universality supported precious metal catalyst and a precious metal high-dispersion method are always a research hotspot.
In the preparation process of the supported noble metal catalyst, active components are required to be adsorbed on the surface or in a pore channel of a carrier, and noble metal precursor salt is reduced through high-temperature roasting or under the action of a reducing agent. Because the electrons at the outermost layer of atoms in the d orbit of the noble metal simple substance easily form covalent bonds with hydrogen or oxygen atoms, and the noble metal has stable properties at normal temperature, the noble metal has good catalytic performance for various reduction reactions and oxidation reactions. In recent years, methods for improving the dispersion degree of noble metals, such as liquid-phase solution immersion, plasma plating, ion beam implantation, and sol fixation, have been reported in succession. The literature Xu Jie, Shang Jiekun, Chen Ye, Wang Yue, Li Yongxin, Applied Catalysis A: General,2017,542:380-4The Pd/CN catalyst with good dispersion on the CN carrier is prepared by an impregnation method as a reducing agent, and the mesoporous CN material has rich basic groups, namely nitrogen-containing groups, so that noble metal Pd nano-particles can be well dispersed and fixed, and the average particle size of the high-dispersion Pd nano-particles is 3.6nm, thereby effectively improving the activity of the catalyst. However, the problem of particle agglomeration still exists due to the influence of solvation and clustering effect in the preparation process of the supported noble metal catalyst by the impregnation method, and a reducing agent needs to be added in the preparation process. In documents Qi Hetong, YuPing, Wang yuexing, Han Guangchao, Liu Huibiao, Yi yuanaping, Li Yuliang, MaoLanqun, JACS, 2015, 137, 5260, a graphite oxide alkyne catalyst is prepared by using a graphite oxide alkyne material as a carrier and directly reducing a noble metal active precursor by utilizing the characteristics of the carrier, and a step of adding a reducing agent is omitted. Thus, go toThe development of a green and efficient preparation method of the supported high-dispersion noble metal catalyst to save noble metal resources and improve the economy of noble metal atoms is still of great significance.
Layered metal hydroxides (LDHs) are commonly called hydrotalcite, are two-dimensional layered inorganic functional materials with a brucite-like structure, and have a chemical general formula [ MII 1-xMIII x(OH)2]x+(An-)x/n·yH2O, wherein MIIAnd MIIIRespectively divalent and trivalent metal cations on the laminate, An-Represents an interlayer anion, x is MIII/(MII+MIII) M represents the amount of interlayer crystal water.
Based on the structural characteristics that LDHs metal cations are highly dispersed in a laminate and the species and proportion can be flexibly regulated within a certain range, the inventor finds that variable valence metals are introduced into an LDH material, and the variable valence metals and oxidized noble metal ions generate oxidation-reduction reaction to generate metal ions with higher valence and noble metals with zero valence, so the discovery is utilized to prepare the high-dispersion supported noble metal catalyst.
Disclosure of Invention
The invention aims to provide a high-dispersion supported noble metal catalyst, and also aims to provide a carrier spontaneous reduction method capable of regulating and controlling the dispersion degree of an active component of the supported catalyst. The catalyst has good application effect in the selective oxidation reaction of benzyl alcohol and the hydrogenation reaction of anthraquinone.
The high-dispersion supported noble metal catalyst provided by the invention is expressed as M/ZT-S, wherein M represents a noble metal active component, and M is one or two of Pd, Au and Pt; ZT represents a carrier, and ZT is one of CoAl-LDH, MnAl-LDH, FeAl-LDH, CoMgAl-LDH and CoZnAl-LDH hydrotalcite; s represents a surfactant, and is one of Cetyl Trimethyl Ammonium Chloride (CTAC), Cetyl Trimethyl Ammonium Bromide (CTAB) and Sodium Dodecyl Sulfate (SDS).
The preparation method of the high-dispersion supported noble metal catalyst provided by the invention comprises the following specific steps:
A. dissolving soluble divalent metal salt containing variable valence metal ions and soluble trivalent metal salt in deionized water to prepare mixed salt solution; with Na2CO3Dissolving NaOH and the mixed alkali solution in deionized water to prepare a mixed alkali solution; and simultaneously dropping the two solutions into a reactor at a constant speed, stirring at a constant temperature of 60-90 ℃ for reaction for 2-16h, filtering, centrifugally washing a filter cake to be neutral by using deionized water, and drying for 8-15 h to obtain the reducing hydrotalcite carrier ZT containing the variable valence metal ions.
The variable valence metal ions refer to low oxidation state divalent transition metal ions and are Co2+、Fe2+、Mn2+One of (1);
the soluble divalent metal salt is Co (NO)3)2·6H2O、FeSO4·7H2O、Mn(NO3)2·4H2O、Mg(NO3)2·6H2O or Zn (NO)3)2·6H2One or two of O, wherein at least one variable valence transition metal salt is contained; the soluble trivalent metal salt is Al (NO)3)3·9H2O or Fe (NO)3)3·9H2One of O; wherein the concentration of the divalent metal salt is 0.1-1 mol/L; the concentration of the trivalent metal salt is 0.025-0.5mol/L, and the molar ratio of the divalent metal salt to the trivalent metal salt is 2-4: 1;
na in the mixed alkali solution2CO3The concentration of the sodium hydroxide is 0.3-10mol/L, and the concentration of NaOH is 0.1-3 mol/L;
the dropping amount of the mixed salt solution and the mixed alkali solution is according to OH-The molar ratio of the total cations to the total cations is 1-2: 1;
B. preparing an aqueous solution of surfactant S with the concentration of 5-15mmol/L, dispersing the ZT powder prepared in the step A in the surfactant S solution, preparing a suspension with the solid content of 100-200mL/g, stirring at room temperature for 5-10min to uniformly disperse, and continuously stirring at constant temperature of 0-50 ℃ for 5 min.
The surfactant S is one of cetyltrimethylammonium chloride (CTAC), cetyltrimethylammonium bromide (CTAB) and Sodium Dodecyl Sulfate (SDS);
C. continuously stirring the suspension liquid in the step B for 10-20min at a constant temperature of 0-50 ℃, dropwise adding a noble metal M salt solution, and determining the addition amount of M salt according to the mass ratio of M to ZT in the prepared catalyst M/ZT-S of 0.2-1%; and continuously stirring at constant temperature for 3-6h, gradually deepening the color of the suspension, finishing the reaction, filtering, centrifugally washing a filter cake to be neutral by using deionized water, and carrying out vacuum freeze drying at the temperature of-50 to-20 ℃ for 7-8 h to obtain the catalyst M/ZT-S, wherein the average size range is 1.00-1.50 nm.
The noble metal M salt is Na2PdCl4、K2PdCl4、HAuCl4、NaAuCl4、H2PtCl6、Na2PtCl6One or two of them, the concentration of M salt is 20-50 mmol/L.
In the step, variable valence metal ions in the carrier and Pd in the precursor salt of the noble metal2+、Au3+、Pt4+Oxidation-reduction reaction is carried out to reduce the Pd0、Au0、Pt0And is uniformly dispersed on the surface of the carrier.
Vacuum freeze-drying is used in order to prevent the reduced noble metal particles from agglomerating or being oxidized during ordinary heat-drying.
The resulting catalyst was characterized as follows:
FIG. 1 is an X-ray diffraction analysis (XRD) pattern of the support prepared in step A and the catalyst prepared in step C of example 1. As can be seen from fig. 1, both have characteristic diffraction peaks for LDH, demonstrating that step a successfully prepared LDH supports while step C prepared catalysts retained the hydrotalcite structure after loading with active components.
FIG. 2 is a Scanning Electron Microscope (SEM) photograph of the support prepared in step A of example 1. From fig. 2, it is shown that the carrier presents a hexagonal sheet structure with uniform size, which is a typical hydrotalcite morphology.
FIG. 3 is a comparison of the Fourier Infrared Spectroscopy (IR) of the support prepared in step A, CTAC, pure surfactant, and the catalyst prepared in step C of example 1. Fig. 3 shows that characteristic peaks of both the carrier and CTAC are present in the catalyst prepared in step C, indicating that both species are present in the catalyst structure.
FIG. 4 is a High Resolution Transmission Electron Microscopy (HRTEM) photograph of the catalyst prepared in step C of example 1 and a statistical plot of the Pd particles size thereof. From FIG. 4, it is shown that the Pd species as the active component in the catalyst is uniformly and highly dispersed on the surface of the LDHs laminate, and the average particle size of the Pd particles is 1.05 nm.
FIG. 5 is a High Resolution Transmission Electron Microscopy (HRTEM) photograph of the catalyst prepared in step C of example 1 after 3 reuses. From fig. 5, it is shown that the active component particles still maintain a highly dispersed state after the catalyst is repeatedly used for 3 times, which indicates that the highly dispersed supported noble metal catalyst prepared by the method can effectively resist the agglomeration of the active component particles.
FIG. 6 is a High Resolution Transmission Electron Microscopy (HRTEM) photograph of the catalyst prepared in step C of example 2 and a statistical plot of the Au particle size thereof. FIG. 6 shows that the active component Au particles in the catalyst are uniformly dispersed on the surface of the carrier, and the average particle diameter is 1.28 nm.
FIG. 7 is a High Resolution Transmission Electron Microscope (HRTEM) photograph of the catalyst prepared in step C of example 3 and a statistical plot of the Pd particle size thereof. Fig. 7 shows that the active component Pd particles in the catalyst were uniformly dispersed on the surface of the carrier, and the average particle diameter was 1.41 nm.
The invention has the beneficial effects that:
the invention directly introduces variable valence metals into the LDHs laminate to prepare the highly dispersed LDHs carrier with reducing sites; based on the electron donating effect of the reducing carrier, the highly dispersed reducing sites spontaneously induce reduction of the oxidation state noble metal, and the high dispersion of the active component particles of the supported noble metal catalyst can be realized. In the noble metal salt loading process, a reducing agent is not required to be added or high-temperature roasting is not required, the carrier supports and disperses the active component, and meanwhile, the precursor of the active component of the noble metal is directly reduced by utilizing the self-reducibility, so that the supported noble metal catalyst with catalytic activity is obtained in one step.
By changing the reaction temperature and adding the surfactant in the preparation process of the catalyst, the reduction rate of the active component can be improved, aggregation can be prevented, and the control of the particle size, distribution and stable load of the active component can be realized.
The prepared catalyst shows better conversion rate and selectivity in the selective oxidation of benzyl alcohol and the hydrogenation reaction of anthraquinone, and the reaction process has mild conditions and is convenient to recover.
Description of the drawings:
fig. 1 is an XRD spectrum of the carrier prepared in example 1 after loading noble metal Pd.
FIG. 2 is a SEM of the support prepared in example 1.
FIG. 3 is an IR spectrum of CTAC of the carrier, catalyst and surfactant prepared in example 1.
FIG. 4 is a HRTEM photograph and a Pd particle size histogram of the catalyst prepared in example 1.
Fig. 5 is a HRTEM photograph of the catalyst prepared in example 1 after 3 times of repeated use.
FIG. 6 is a HRTEM photograph and Au particle size statistical chart of the catalyst prepared in example 2.
FIG. 7 is a HRTEM photograph and a Pd particle size histogram of the catalyst prepared in example 3.
FIG. 8 is a HRTEM photograph and a Pt particle size statistical chart of the catalyst prepared in example 4.
The specific implementation mode is as follows:
the invention is described in further detail below with reference to the following examples:
example 1
A. FeSO (ferric oxide) is added4·7H2O 1.3901g，Al2(SO4)3·18H2Dissolving O1.6650 g in 150mL of deionized water to prepare a mixed salt solution; NaOH 0.6400g and Na2CO31.0600g of the mixed alkali solution is dissolved in 150mL of deionized water to prepare the mixed alkali solution. Dropping the two into a flask at a constant speed, and controlling the volume ratio of the two to be 10: and 13, adjusting the pH value to 8.5-9.5, keeping the flask closed, and stirring at the constant temperature of 60 ℃ for reaction for 4 hours. And naturally cooling to room temperature, filtering, washing the precipitate to be neutral, and drying at 60 ℃ for 8h to obtain the reducing hydrotalcite carrier FeAl-LDH.
B. Weighing 0.5000g of FeAl-LDH powder obtained in the step A, dispersing the FeAl-LDH powder in 100mL of surfactant CTAC solution with the concentration of 6.25mmol/L, and stirring at room temperature for 10-20min to form uniformly dispersed suspension;
C. continuously stirring the suspension obtained in the step B at a constant temperature of 0 ℃, and simultaneously dropwise adding 470 microliters of K with the concentration of 50mmol/L2PdCl4Stirring the solution at constant temperature for 6h, washing the suspension after the reaction to be neutral, and freeze-drying the suspension in a vacuum constant-temperature freeze drying oven at-50 ℃ for 8h to obtain Pd/FeAl-LDH-CTAC. The percentage content of Pd therein was found to be 0.41%, and the average particle diameter of the Pd particles was found to be 1.05 nm.
Example 2
A. Adding Mn (NO)3)2·4H2O 1.6065g，Al(NO3)3·9H2Dissolving O1.2006 g in 150mL of deionized water to prepare a salt solution; mixing NaOH 0.6144g and Na2CO30.6783g of the mixed alkali solution is dissolved in 150mL of deionized water to prepare the mixed alkali solution. The two are simultaneously dripped into the flask at a constant speed by a double-dripping method, and the volume ratio of the two is controlled to be 5: and 7, adjusting the pH value to 8-9, stirring at the constant temperature of 80 ℃ for reaction for 10 hours, naturally cooling to room temperature, filtering, washing the precipitate to be neutral, and drying at the temperature of 60 ℃ for 8 hours to obtain the reducing hydrotalcite carrier MnAl-LDH.
B. Weighing 0.5000g of MnAl-LDH powder in the step A, dispersing in 100mL of surfactant CTAB solution with the concentration of 10.85mmol/L, and stirring at room temperature for 15min to form uniformly dispersed suspension;
C. continuously stirring the suspension obtained in the step B at a constant temperature of 25 ℃, and simultaneously dropwise adding 785 microliters of HAuCl with the concentration of 30mmol/L4Stirring the solution at constant temperature for 4h, centrifugally washing the suspension after the reaction to be neutral by using deionized water, transferring the collected product to a vacuum constant-temperature freeze drying box, and freeze-drying for 8h at-50 ℃ to obtain Au/MnAl-LDH-CTAB. The Au content was found to be 0.26%, and the average particle size of the Au particles was found to be 1.28 nm.
Example 3
A. Mixing Co (NO)3)2·6H2O 2.9105g，Al(NO3)3·9H2Dissolving O1.8757 g in 150mL of deionized water to prepare a mixed salt solution; 0.9600g of NaOH and Na2CO31.0600g of the compound is dissolved in 150mL of deionized water to prepareMixing the alkali solution. The two are dripped into the flask simultaneously at a constant speed by a double-dripping method, and the volume ratio of the two is controlled to be 1: stirring and reacting at constant temperature of 1 and 90 ℃ for 2 hours. Naturally cooling to room temperature, filtering, washing the precipitate to be neutral, and drying for 10h at 60 ℃ to obtain the reducing hydrotalcite carrier CoAl-LDH.
B. Weighing 0.5000g of CoAl-LDH powder obtained in the step A, dispersing in 100mL of CTAC solution with the concentration of 6.25mmol/L, and stirring at room temperature for 15min to obtain a uniformly dispersed suspension;
C. continuously stirring the suspension obtained in the step B at a constant temperature of 50 ℃, and dropwise adding 470 microliters of Na with the concentration of 50mmol/L2PdCl4And (3) stirring the solution at a constant temperature for 6h, centrifugally washing the suspension after the reaction to be neutral by using deionized water, and freeze-drying the suspension for 8h at the temperature of-50 ℃ in a vacuum constant-temperature freeze drying oven to obtain the catalyst Pd/CoAl-LDH-CTAC. The percentage content of Pd therein was found to be 0.96%, and the average particle diameter of the Pd particles was found to be 1.41 nm.
Example 4
A. Mixing Co (NO)3)2·6H2O 1.3969g，Mg(NO3)2·6H2O 0.4103g，Al(NO3)3·9H2Dissolving O1.2000 g in 150mL of deionized water to prepare a mixed salt solution; mixing NaOH 0.6144g and Na2CO30.6783g of the mixed alkali solution is dissolved in 150mL of deionized water to prepare the mixed alkali solution. The two are dripped into the flask simultaneously at a constant speed by a double-dripping method, and the volume ratio of the two is controlled to be 1: stirring and reacting at constant temperature of 1 and 90 ℃ for 4h, naturally cooling to room temperature, filtering, washing the precipitate to be neutral, and drying at 60 ℃ for 10h to obtain the reducing hydrotalcite carrier CoMgAl-LDH.
B. Weighing 0.5000g of CoMgAl-LDH powder obtained in the step A, dispersing in 100mL of surfactant SDS solution with the concentration of 11.35mmol/L, and stirring at room temperature for 10-15min to form uniformly dispersed suspension;
C. continuously stirring the suspension obtained in the step B at a constant temperature of 0 ℃, and simultaneously dropwise adding 470 microliters of H with the concentration of 50mmol/L2PtCl6Stirring the solution at constant temperature for 5h, centrifugally washing the suspension after the reaction to be neutral by using deionized water, transferring the collected product to vacuum constant-temperature freeze dryingAnd freeze-drying for 8 hours at the temperature of 50 ℃ below zero in a drying box to obtain Pt/CoMgAl-LDH-SDS. The percentage of Pt was found to be 0.38% and the average particle size of the Pd particles was found to be 1.12 nm.
Application example 1:
evaluation of the performance of the catalysts of examples 1 to 4 for the selective oxidation reaction of benzyl alcohol
The evaluation device is a parallel reactor and the operation steps are as follows:
firstly, according to the molar ratio of benzyl alcohol to noble metal of 10000: 1, 5mL of toluene as a reaction solvent and 3mL of benzyl alcohol as a reactant and a catalyst were added to a 50mL quartz reaction flask. The reactor temperature was first raised to 100 ℃ before the reaction started. Oxygen-filled high-purity O2Degassing for 1min, and immediately sealing the quartz reaction bottle. The reaction temperature is controlled at 100 ℃, and the stirring speed is 900 r/min. High-purity O with reaction system pressure of 0.1MPa2The reaction time is 5 h. After the reaction is finished, cooling to room temperature by using an ice water bath, centrifuging, filtering, and detecting the reaction liquid by Shimadzu high performance liquid chromatography. And an internal standard method is adopted for data processing. The catalyst conversion of benzyl alcohol and selectivity results for benzaldehyde at 100 ℃ are shown in table 1:
TABLE 1
Catalyst sample Example 1 Example 2 Example 3 Example 4
Conversion ratio of benzyl alcohol (%) 96 95 92 95
Benzaldehyde Selectivity (%) 98 96 95 97
Application example 2:
the catalysts of examples 1 to 4 and the comparative samples were applied to the hydrogenation reaction of anthraquinones for performance evaluation, and the specific steps were as follows:
the evaluation device is a polytetrafluoroethylene inner container reaction kettle with a magnetic stirring and heating device, 50mg of catalyst and 60mL of anthraquinone working solution (the anthraquinone working solution with the concentration of 100g/L consists of 100g of 2-ethyl anthraquinone, 1,3, 5-trimethylbenzene and 400mL of trioctyl phosphate) are added into the reaction kettle and sealed, hydrogen is introduced to replace the air in the reaction kettle, and the process is repeated for 5 times. Heating the reaction kettle to 50 ℃, introducing hydrogen to ensure that the pressure reaches 0.3MPa, and starting timing after the stirring speed is adjusted to 1200 r/min. After reacting for 1.5H, collecting reaction samples from a reaction gas outlet valve for activity and selectivity evaluation and calculating H2O2Yield. H of catalyst2O2The yields and space-time yields are shown in Table 2.
TABLE 2
Catalyst sample Example 1 Example 2 Example 3 Example 4
H2O2Yield (g/mL) 13.70 12.36 11.38 12.78
Space-time yield (gH)2O2/(gPd·h)) 2563 2528 2367 2532

Claims (2)

1. A preparation method of a high-dispersion supported noble metal catalytic material comprises the following specific steps:
A. dissolving soluble divalent metal salt containing variable valence metal ions and soluble trivalent metal salt in deionized water to prepare mixed salt solution; with Na2CO3Dissolving NaOH and the mixed alkali solution in deionized water to prepare a mixed alkali solution; simultaneously dropping the two solutions into a reactor at a constant speed, stirring at a constant temperature of 60-90 ℃ for reaction for 2-16h, filtering, centrifugally washing a filter cake to be neutral by using deionized water, and drying for 8-15 h to obtain a reducing hydrotalcite carrier ZT containing variable valence metal ions;
the variable valence metal ions refer to low oxidation state divalent transition metal ions and are Co2+、Fe2+、Mn2+One of (1);
the soluble divalent metal salt is Co (NO)3)2·6H2O、FeSO4·7H2O、Mn(NO3)2·4H2O、Mg(NO3)2·6H2O or Zn (NO)3)2·6H2One or two of O, wherein at least one variable valence transition metal salt is contained; the soluble trivalent metal salt is Al (NO)3)3·9H2O or Fe (NO)3)3·9H2One of O; wherein the concentration of the divalent metal salt is 0.1-1 mol/L; the concentration of the trivalent metal salt is 0.025-0.5mol/L, and the molar ratio of the divalent metal salt to the trivalent metal salt is 2-4: 1;
na in the mixed alkali solution2CO3The concentration of the sodium hydroxide is 0.3-10mol/L, and the concentration of NaOH is 0.1-3 mol/L;
the dropping amount of the mixed salt solution and the mixed alkali solution is according to OH-The molar ratio of the total cations to the total cations is 1-2: 1;
B. preparing an aqueous solution of surfactant S with the concentration of 5-15mmol/L, dispersing the ZT powder prepared in the step A in the surfactant S solution, preparing a suspension with the solid content of 100-200mL/g, stirring at room temperature for 5-10min to uniformly disperse, and continuously stirring at constant temperature of 0-50 ℃ for 5 min.
The surfactant S is one of hexadecyl trimethyl ammonium chloride, hexadecyl trimethyl ammonium bromide and lauryl sodium sulfate;
C. continuously stirring the suspension liquid in the step B for 10-20min at a constant temperature of 0-50 ℃, dropwise adding a noble metal M salt solution, and determining the addition amount of M salt according to the mass ratio of M to ZT in the prepared catalyst M/ZT-S of 0.2-1%; continuously stirring at constant temperature for 3-6h, gradually deepening the color of the suspension, finishing the reaction, filtering, centrifugally washing a filter cake to be neutral by using deionized water, and carrying out vacuum freeze drying at-50 to-20 ℃ for 7-8 h to obtain a catalyst M/ZT-S with the average size range of 1.00-1.50 nm;
the noble metal M salt is Na2PdCl4、K2PdCl4、HAuCl4、NaAuCl4、H2PtCl6、Na2PtCl6One or two of them, the concentration of M salt is 20-50 mmol/L.
2. A highly dispersed supported noble metal catalyst prepared according to the process of claim 1, which catalyst is denoted as M/ZT-S, wherein M represents a noble metal active component, M is one or two of Pd, Au, Pt; ZT represents a carrier, and ZT is one of CoAl-LDH, MnAl-LDH, FeAl-LDH, CoMgAl-LDH and CoZnAl-LDH hydrotalcite; s represents a surfactant, and is one of cetyl trimethyl ammonium chloride, cetyl trimethyl ammonium bromide and lauryl sodium sulfate.
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