CN113083309B - Catalyst for preparing glyceric acid by efficiently catalyzing glycerol oxidation, preparation method and application thereof - Google Patents
Catalyst for preparing glyceric acid by efficiently catalyzing glycerol oxidation, preparation method and application thereof Download PDFInfo
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Abstract
The invention relates to aCatalyst for preparing glyceric acid by efficiently catalyzing glycerol oxidation, preparation method and application thereof, wherein the catalyst is Pt1+CCo/CaCoTiO3Wherein, the carrier is CaCoTiO3The characteristic diffraction peaks of the perovskite structure appear at 23.39 degrees, 33.32 degrees, 39.29 degrees, 41.11 degrees, 59.54 degrees and 69.97 degrees of 2 theta in an XRD characterization diagram, and are respectively attributed to CaCoTiO3Crystal planes (200), (022), (-113), (-222), (400), (-224), and (440) in (1); CaCoTiO as a support3Is a monoclinic crystal structure JCPDS 34-0394; and Pt and Co exist in the form of nanoparticles, and the average particle size is 2nm +/-0.2 nm. The catalyst of the invention is characterized in that Pt is monatomic (by Pt)1Expressed) and Pt cluster (in Pt)CIndicating that) coexist to form a concerted catalysis effect, in the reaction for preparing glyceric acid by glycerol oxidation, Pt monoatomic sites activate C-H bonds of glycerol and C-H bonds of aldehyde groups, Pt cluster sites activate O-H bonds of glycerol, and OH (hydroxyl new substances) insertion and acid (acid substances existing in a reaction system) removal are realized.
Description
Technical Field
The invention relates to the fields of chemistry and chemical engineering and catalysts, in particular to a catalyst for efficiently catalyzing glycerol to be oxidized to prepare glyceric acid and a preparation method thereof.
Background
Biomass energy is an ideal renewable alternative resource, and in view of the excellent performances of low pollution, renewability and the like of biomass energy, the development and utilization of biomass energy are receiving wide attention. Glycerol is a by-product produced during the transesterification of biodiesel (100 Kg of glycerol is produced per ton of biodiesel produced), however its downstream conversion capacity is insufficient and excess capacity occurs. Therefore, it is of great significance to catalyze the conversion of glycerol to high value-added products.
Glyceric acid is a multifunctional high-value fine chemical, can be applied to the industries of medicine and food, and is also an important intermediate. The existing catalyst for preparing glyceric acid by oxidizing glycerol mainly comprises a homogeneous catalysis method and a multi-phase catalysis method. At present, heterogeneous catalysis is favored by researchers because of easy operation in reaction control, simple process flow and green. In recent years, the goal of heterogeneous catalytic oxidation production of glycerol has become a focus of research. There are many problems in the research report, such as low catalytic activity, poor selectivity, limitation of reaction conditions (addition of base), deactivation of catalyst, etc.
In the prior art, the preparation of glyceric acid from glycerol requires two reaction steps, first the oxidative dehydrogenation of glycerol to aldehyde and then the second step of the insertion of OH species into the glyceraldehyde to produce glyceric acid. The oxidative dehydrogenation process of alcohol mainly uses oxygen as oxidant, glycerol primary hydroxyl, hydrogen fracture of alpha-position C-H and oxygen atom generated by oxygen activation are combined to generate water for removal, and aldehyde oxidation relates to activation of aldehyde group and hydrogen of alpha-position C-H, and OH species insertion is generated by oxygen activation in aqueous solution. Efficient glycerol production requires selective activation of primary hydroxyl groups, inhibition of deep oxidation, and avoidance of C-C bond cleavage. See literature on Science 2010VOL330, P74 for OH (hydroxyl active).
The Pt-based bimetallic catalyst is used for catalyzing selective oxidation of glycerol to prepare glyceric acid under the liquid phase condition, and researchers add non-noble metals Co, Cu and Sn into the Pt-based catalyst to obtain more excellent performance. The highly dispersed PtCo bimetallic nanoparticles prepared by microwave irradiation have the advantages that compared with Pt/RGO and Co/RGO, the oxidation performance of PtCo/RGO to glycerol is obviously improved, and the conversion rate (70.2%) of glycerol and the selectivity (85.9%) of glyceric acid are obviously higher than those of single metals Pt/RGO and Co/RGO (J.catalysis Today,2017,298: 234-240). Under the same reaction conditions, the 2.0% Pt/C-R catalyzed glycerol conversion rate is lower, the 2h conversion rate is only 29.8%, and after Sn is added, 2.0% Pt9Sn1the/C-R increased to 43.1%, and after 6h of reaction, the glycerol conversion reached 91.1%, mainly because the added Sn was able to promote the activation of the oxygen molecules (J.applied Catalysis B Environmental,2016,180: 78-85). Highly dispersed Pt-Cu/C catalysts, Pt-Cu/C ratio Pt/C pair selectionThe activity of the sex oxidized glycerol to the glyceric acid is stronger, when the reaction is carried out for 6 hours under the alkali-free condition and the conversion rate of the glycerol is 86.2 percent, the selectivity of the glyceric acid reaches 70.8 percent (J.catalysis Communications,2011,12(12): 1059-.
However, the above-mentioned existing research reports still have some problems, such as the reaction conditions need to involve alkali, which causes environmental pollution, and the selectivity and activity of the catalyst are still not ideal enough, so it is a technical problem to be solved to provide a highly active and highly selective catalyst capable of performing the oxidation of glycerol to prepare glyceric acid under the alkali-free condition.
Disclosure of Invention
In order to solve the defects, the invention provides a catalyst for preparing glyceric acid by efficiently catalyzing glycerol oxidation, and the catalyst has the synergistic effect of Pt monoatomic atoms and Pt clusters and has more excellent catalytic performance.
The invention provides a catalyst for preparing glyceric acid by efficiently catalyzing glycerol oxidation, which is PtCo/CaCoTiO3Supported CaCoTiO3The characteristic diffraction peaks of the perovskite structure appear at 23.39 degrees, 33.32 degrees, 39.29 degrees, 41.11 degrees, 59.54 degrees and 69.97 degrees of 2 theta in an XRD characterization diagram, and are respectively attributed to CaCoTiO3Crystal planes (200), (022), (-113), (-222), (400), (-224), and (440) in (1); CaCoTiO as a support3Is a monoclinic crystal structure JCPDS 34-0394; and Pt and Co exist in the form of nanoparticles, and the average particle size is 2nm +/-0.2 nm.
The invention further provides a preparation method of the catalyst, which comprises the following steps:
1) preparation of the support
Synthesis of CaCoTiO by sol-gel method3A composite oxide support;
2) reduction of the support
Taking the CaCoTiO3Reducing the composite oxide carrier in hydrogen atmosphere to obtain Co/CaCoTiO3；
3) Replacement of Pt
Mixing the Co/CaCoTiO3Sealing with deionized water, and pouring into containerThen dropwise adding H into the container in an atmosphere of magnetic stirring and inert gas2PtCl6Reacting the aqueous solution at normal temperature under vigorous stirring, repeatedly washing the solid product after the reaction is finished, and drying the solid product under vacuum condition to obtain PtCo/CaCoTiO3A catalyst.
Further, in step 1), Ca (NO) is taken3)2·4H2O and Co (NO)3)2·6H2Preparing O into mixed solution, stirring and mixing uniformly, then adding C6H8O7·H2Continuously stirring O (citric acid monohydrate) to obtain a solution A;
taking tetrabutyl titanate and absolute ethyl alcohol in another container, and uniformly mixing to obtain a solution B;
dropwise adding the solution B into the solution A, adjusting the pH value of the mixed solution to 5-7 after the dropwise addition is finished, and continuously keeping the temperature and stirring to prepare wet gel;
drying the wet gel to obtain dry gel, grinding the dry gel, roasting to remove citric acid, cooling to room temperature, and roasting again to obtain CaCoTiO3A composite oxide.
Further, the Ca (NO)3)2·4H2O and said Co (NO)3)2·6H2The molar ratio of O is 1: (0.1-0.3); preferably, the molar ratio is 1: 0.2.
further, said C6H8O7·H2The adding amount of O (citric acid monohydrate) is 1-5 times of the mole number of metal ions, and the metal ions are Ca ions, Co ions and Ti ions; preferably, the amount added is 1 to 2 times the number of moles of metal ions.
Further, in step 1), C is added6H8O7·H2And after O, continuing stirring for 0.1-1 h.
Further, in the step 1), the volume ratio of the tetrabutyl titanate to the absolute ethyl alcohol is 1: (1-3).
Further, in the step 1), the tetrabutyl titanate and the absolute ethyl alcohol are uniformly mixed, the stirring is continued for 0.1-2h, and a clear and transparent solution B is obtained by stirring.
Further, in step 1), the pH is adjusted to 6 with ammonia.
Further, in the step 1), after the pH value is adjusted, stirring is carried out for 3-6h at the constant temperature of 30-50 ℃.
Further, in the step 1), the wet gel is dried for 24-72h at the temperature of 60-90 ℃ to form dry gel.
Further, in the step 1), the xerogel is ground into powder and then is heated to 350 ℃ from room temperature in a muffle furnace and is kept for 1-5h, wherein the heating rate is 2 ℃/min. The temperature rise rate was 2 ℃/min to remove citric acid. Preferably, the temperature is raised to 300 ℃.
Further, in the step 1), the second roasting is to raise the temperature of the roasted solid reduced to room temperature from room temperature to 550-650 ℃ and keep the temperature for 1.5-3h, wherein the temperature raising rate is 5 ℃/min.
Further, in the step 2), the carrier is reduced by adding the CaCoTiO3Spreading solid powder of composite oxide at the bottom of a porcelain boat, placing the porcelain boat in a central constant-temperature area of a quartz tube of a tube furnace, vacuumizing the porcelain boat by using a vacuum pump in a closed state, slowly introducing reducing gas until the pressure value reaches normal pressure, keeping the gas flow rate at 40ml/min, gradually heating the tube furnace at the heating rate of 10 ℃/min, keeping the temperature for 1.5-3h when the temperature of the central constant-temperature area of the quartz tube reaches 550-650 ℃, and then cooling the quartz tube to room temperature to obtain Co/CaCoTiO3A composite oxide. Preferably, the temperature of the constant temperature zone reaches 600 ℃ and the holding time is 2 h.
Further, in step 3), the Co/CaCoTiO is added3The composite oxide is sealed and poured into a container by deionized water, and H is dripped into the container under the stirring of 600-800 r/min and the protection of nitrogen2PtCl6The aqueous solution is vigorously stirred for 15-72h at normal temperature, and the ion equation of the generated replacement reaction is as follows:
2Co(s)+PtCl6 2-(aq)＝Pt(s)+2Co2+(aq)+6Cl-(aq)
after the displacement reaction is finished, separating a solid product, repeatedly washing the solid product by using deionized water, carrying out centrifugal separation after each washing, washing the solid product by using absolute ethyl alcohol at least once, and then carrying out vacuum drying on the washed solid product for 0.1-48h at 50-70 ℃ to obtain PtCo/CaCoTiO3A catalyst. Preferably, the temperature of vacuum drying is 60 ℃ and the time is 24 h. Preferably, the vigorous stirring is 700 revolutions per minute.
The invention further provides the application of the catalyst, in particular the application of the catalyst in the reaction for preparing glyceric acid by oxidizing glycerol. By using the catalyst, the conversion rate of the glycerol can reach 99.0%, the selectivity of the glycerol can reach 72.0%, and the Nippon flower-like laugh of a glyceric acid product can reach 71.1%.
The invention has the beneficial effects that:
1. according to the catalyst, the catalyst structure with coexisting Pt monoatomic atoms and Pt clusters can be accurately controlled by matching raw materials and preparation conditions in the preparation process;
2. in the catalyst of the present invention, since Pt is monoatomic (with Pt)1Expressed) and Pt cluster (in Pt)CRepresenting) coexisting to form a concerted catalysis effect, in the reaction for preparing glyceric acid by glycerol oxidation, Pt monoatomic sites activate C-H bonds of glycerol and C-H bonds of aldehyde groups, Pt cluster sites activate O-H bonds of glycerol, and OH (hydroxyl new substances) insertion and acid (acid substances existing in a reaction system) removal are realized;
3. by using the catalyst of the invention, the conversion rate of glycerol is 99.0%, the selectivity of glyceric acid is 72.0%, and the yield of glyceric acid product is 71.1% in the reaction for preparing glyceric acid by oxidizing glycerol.
Drawings
FIG. 1 is a schematic diagram of a process for preparing a catalyst according to example 1 and comparative examples 1 and 2;
FIG. 2 is an electron micrograph of HADDF-STEM of the catalysts prepared in example 1 and comparative examples 1 and 2;
FIG. 3 is a supplementary view of the catalysts prepared in example 1 and comparative examples 1 and 2 under an electron microscope;
FIG. 4 is a propanol absorption/desorption test curve of the catalysts prepared in example 1 and comparative examples 1 and 2
FIG. 5 is a simulated graph of propanol adsorption configurations for catalysts prepared in example 1 and comparative examples 1 and 2;
fig. 6 is an XRD characterization chart of the supported composite oxide and the corresponding products of the respective steps of preparation.
Detailed Description
Example 1 sample-Pt1+C Co/CaCoTiO3Catalyst (Pt)1+CCo/rCCT, wherein Co/rCCT is Co particles reduced in perovskite
The second sample is that Pt exists in the catalyst in the form of single atoms and clusters in the Co particles, and the preparation method of the catalyst comprises the following steps:
1) preparation of the support
5.244g Ca (NO) were taken in one vessel3)2·4H2O and 0.6467g Co (NO)3)2·6H2Dissolving O in 30ml deionized water to prepare a mixed solution, stirring and mixing uniformly, and then adding C with the mole number 1.25 times of that of the total metal ions6H8O7·H2Continuously stirring O (11.667 g citric acid monohydrate) to obtain a solution A;
in another container, 6.807g of tetrabutyl titanate with the same volume is taken and mixed with 6.8mL of absolute ethyl alcohol uniformly to obtain a solution B, wherein the solution B is clear and transparent;
dropwise adding the solution B into the solution A, adjusting the pH value of the mixed solution to 6 after the dropwise addition is finished, and continuously keeping the temperature and stirring for 5 hours at the temperature of 40 ℃ to prepare wet gel;
then, the wet gel is placed in an oven at 80 ℃ for drying for 48h to form dry gel, the dry gel is ground, the temperature is raised to 300 ℃ from the room temperature in a muffle furnace at the heating rate of 2 ℃/min and is kept for 2h, then the temperature is lowered to the room temperature, the temperature is raised to 600 ℃ from the room temperature at the heating rate of 5 ℃/min and is kept for 2h, and CaCoTiO is obtained3Composite oxideA carrier;
the carrier CaCoTiO3The characteristic diffraction peaks of the perovskite structure appear at 23.39 degrees, 33.32 degrees, 39.29 degrees, 41.11 degrees, 59.54 degrees and 69.97 degrees of 2 theta in an XRD characterization diagram, and are respectively attributed to CaCoTiO3Crystal planes (200), (022), (-113), (-222), (400), (-224), and (440) in (1); CaCoTiO as a support3Is a monoclinic crystal structure JCPDS 34-0394;
2) reduction of the support
The reduction of the carrier is to reduce the CaCoTiO3Spreading solid powder of a composite oxide carrier at the bottom of a porcelain boat, then placing the porcelain boat into a central constant-temperature area of a quartz tube of a tube furnace, vacuumizing the porcelain boat by using a vacuum pump in a closed state, slowly introducing hydrogen until the pressure value reaches normal pressure, keeping the gas flow rate at 40ml/min, gradually heating the tube furnace at the heating rate of 10 ℃/min, keeping the temperature for 2 hours when the temperature of the central constant-temperature area of the quartz tube reaches 600 ℃, and then cooling the quartz tube to room temperature to obtain Co/CaCoTiO3；
3) Replacement of Pt
0.3g of the Co/CaCoTiO was taken3Directly liquid-sealed with 5ml of deionized water from which oxygen has been removed and then poured into a container, and 15.4mol/L of H was added dropwise to the container under magnetic stirring at 700 rpm and an atmosphere of nitrogen2PtCl610ml of aqueous solution is reacted for 12 hours under normal temperature and vigorous stirring, and the ion equation of the generated replacement reaction is as follows:
2Co(s)+PtCl6 2-(aq)＝Pt(s)+2Co2+(aq)+6Cl-(aq)
after the displacement reaction is finished, separating a solid product, repeatedly washing the solid product with deionized water for three times, carrying out centrifugal separation after each washing, washing the solid product with absolute ethyl alcohol once, and then carrying out vacuum drying on the washed solid product at 60 ℃ for 24 hours to obtain PtCo/CaCoTiO3A catalyst; the PtCo/CaCoTiO is mixed3Spreading the solid powder of the catalyst at the bottom of the porcelain boat, placing the porcelain boat in a quartz tube central constant temperature area of a tube furnace, evacuating the porcelain boat by using a vacuum pump in a closed state, and then performing vacuum filtrationSlowly introducing hydrogen until the pressure value reaches normal pressure, keeping the gas flow rate at 40ml/min, gradually heating the tube furnace at the heating rate of 10 ℃/min, keeping the temperature for 2h when the temperature of a central constant-temperature area of the quartz tube reaches 600 ℃, and then cooling to room temperature; reducing to obtain a sample Pt1+C Co/CaCoTiO3(wherein Pt coexists as monoatomic and cluster on the Co particles, corresponding to Pt1+CCo/rCCT)。
Comparative example 1 comparative sample PtCo/CaCoTiO3Catalyst (Pt)1Co/rCCT, i.e. Pt exists only in monoatomic form)
The sample is that Pt and Co exist in the catalyst in the form of single-atom alloy, and the preparation method of the catalyst comprises the following steps:
1) preparation of the support
5.244g Ca (NO) were taken in one vessel3)2·4H2O and 0.6467g Co (NO)3)2·6H2Dissolving O in 30ml deionized water to prepare a mixed solution, stirring and mixing uniformly, and then adding C with the mole number 1.25 times of that of the total metal ions6H8O7·H2Continuously stirring O (11.667 g citric acid monohydrate) to obtain a solution A;
taking tetrabutyl titanate with the same volume in another container, and uniformly mixing with absolute ethyl alcohol to obtain a solution B, wherein the solution B is clear and transparent;
dropwise adding the solution B into the solution A, adjusting the pH value of the mixed solution to 6 after the dropwise addition is finished, and continuously keeping the temperature and stirring for 5 hours at the temperature of 40 ℃ to prepare wet gel;
then, the wet gel is placed in an oven at 80 ℃ for drying for 48h to form dry gel, the dry gel is ground, the temperature is raised to 300 ℃ from the room temperature in a muffle furnace at the heating rate of 2 ℃/min and is kept for 2h, then the temperature is lowered to the room temperature, the temperature is raised to 600 ℃ from the room temperature at the heating rate of 5 ℃/min and is kept for 2h, and CaCoTiO is obtained3A composite oxide support;
2) reduction of the support
The reduction of the carrier is to reduce the CaCoTiO3Composite oxide carrierSpreading solid powder of the body at the bottom of a porcelain boat, then placing the porcelain boat into a quartz tube central constant-temperature area of a tube furnace, vacuumizing the porcelain boat by using a vacuum pump in a closed state, slowly introducing reducing gas until the pressure value reaches normal pressure, keeping the gas flow rate at 40ml/min, gradually heating the tube furnace at the heating rate of 10 ℃/min, keeping the temperature for 2 hours when the temperature of the quartz tube central constant-temperature area reaches 600 ℃, and then cooling the quartz tube central constant-temperature area to room temperature to obtain Co/CaCoTiO3；
3) Replacement of Pt
Mixing the 0.3g Co/CaCoTiO3Directly liquid-sealed with 5ml of deionized water from which oxygen is removed and then poured into a container, and then 1.5mol/LH is dropwise added into the container under the magnetic stirring and nitrogen atmosphere of 700 revolutions per minute2PtCl610ml of aqueous solution is reacted for 10min under normal temperature and vigorous stirring, and the ion equation of the generated replacement reaction is as follows:
2Co(s)+PtCl6 2-(aq)＝Pt(s)+2Co2+(aq)+6Cl-(aq)
after the displacement reaction is finished, separating a solid product, repeatedly washing the solid product with deionized water for three times, carrying out centrifugal separation after each washing, washing the solid product with absolute ethyl alcohol once, and then carrying out vacuum drying on the washed solid product at 60 ℃ for 24 hours to obtain PtCo/CaCoTiO3Spreading the solid powder at the bottom of a porcelain boat, placing the porcelain boat in a central constant-temperature area of a quartz tube of a tube furnace, vacuumizing the porcelain boat by using a vacuum pump in a closed state, slowly introducing reducing gas until the pressure value reaches normal pressure, keeping the gas flow rate at 40ml/min, gradually heating the tube furnace at the heating rate of 10 ℃/min, keeping the temperature for 2 hours when the temperature of the central constant-temperature area of the quartz tube reaches 600 ℃, and then cooling the quartz tube to room temperature to obtain Pt1Co/CaCoTiO3Wherein Pt is present in monatomic form on Co, corresponding to Pt1Co/rCCT。
Comparative example 2 comparative sample PtcCo/CaCoTiO3Catalyst (Pt)CCo/rCCT, i.e. Pt exists only in clusters)
The second comparative sample is that Pt exists in the catalyst in the form of clusters on Co particles, and the preparation method of the catalyst comprises the following steps:
1) preparation of the support
5.244g Ca (NO) were taken in one vessel3)2·4H2O and 0.6467g Co (NO)3)2·6H2Dissolving O in 30ml deionized water to prepare a mixed solution, stirring and mixing uniformly, and then adding C with the mole number 1.25 times of that of the total metal ions6H8O7·H2Continuously stirring O (11.667 g citric acid monohydrate) to obtain a solution A;
in another container, 6.807g of tetrabutyl titanate with the same volume is taken and mixed with 6.8ml of absolute ethyl alcohol uniformly to obtain a solution B, wherein the solution B is clear and transparent;
dropwise adding the solution B into the solution A, adjusting the pH value of the mixed solution to 6 after the dropwise addition is finished, and continuously keeping the temperature and stirring for 5 hours at the temperature of 40 ℃ to prepare wet gel;
then, the wet gel is placed in an oven at 80 ℃ for drying for 48h to form dry gel, the dry gel is ground, the temperature is raised to 300 ℃ from the room temperature in a muffle furnace at the heating rate of 2 ℃/min and is kept for 2h, then the temperature is lowered to the room temperature, the temperature is raised to 600 ℃ from the room temperature at the heating rate of 5 ℃/min and is kept for 2h, and CaCoTiO is obtained3A composite oxide support;
2) reduction of the support
The reduction of the carrier is to reduce the CaCoTiO3Spreading solid powder of a composite oxide carrier at the bottom of a porcelain boat, then placing the porcelain boat into a central constant-temperature area of a quartz tube of a tube furnace, vacuumizing the porcelain boat by using a vacuum pump in a closed state, slowly introducing hydrogen until the pressure value reaches normal pressure, keeping the gas flow rate at 40ml/min, gradually heating the tube furnace at the heating rate of 10 ℃/min, keeping the temperature for 2 hours when the temperature of the central constant-temperature area of the quartz tube reaches 600 ℃, and then cooling the quartz tube to room temperature to obtain Co/CaCoTiO3；
3) Replacement of Pt
0.3g of the Co/CaCoTiO3Directly liquid-sealed with 5ml of deionized water from which oxygen has been removed and then poured into a containerIn the container, 1.5mol/LH is dripped into the container under the magnetic stirring of 700 r/min and the atmosphere of nitrogen2PtCl610ml of aqueous solution is reacted for 24 hours under normal temperature and vigorous stirring (700 r/min), and the ion equation of the generated replacement reaction is as follows:
2Co(s)+PtCl6 2-(aq)＝Pt(s)+2Co2+(aq)+6Cl-(aq)
after the displacement reaction is finished, separating a solid product, repeatedly washing the solid product with deionized water for three times, carrying out centrifugal separation after each washing, washing the solid product with absolute ethyl alcohol once, and then carrying out vacuum drying on the washed solid product at 60 ℃ for 24 hours to obtain PtCCo/CaCoTiO3The preparation method comprises the steps of flatly paving the solid powder at the bottom of a porcelain boat, then placing the porcelain boat in a central constant-temperature area of a quartz tube of a tube furnace, vacuumizing the porcelain boat by using a vacuum pump in a closed state, slowly introducing reducing gas until the pressure value reaches normal pressure, keeping the gas flow rate at 40ml/min, gradually heating the tube furnace at the heating rate of 10 ℃/min, keeping the temperature for 2 hours when the temperature of the central constant-temperature area of the quartz tube reaches 600 ℃, and then cooling the quartz tube to room temperature to obtain a comparative sample, namely the tri-PtCCo/CaCoTiO3Catalyst, noted PtCCo/rCCT。
Fig. 1 is a schematic diagram of a catalyst preparation process of example 1 (b in fig. 1), comparative example 1 (a in fig. 1) and comparative example 2 (c in fig. 1), and it can be seen from the diagram that the present invention precisely controls the dispersion state of Pt on the surface of Co/rctc by using a potential displacement method. In the catalyst of example 1, Pt is present in the form of coexistence of a single atom and a group; in the catalyst of comparative example 1, Pt is present only in a monoatomic form; in the catalyst of comparative example 2, Pt exists only in the form of clusters.
Fig. 2 is a graph showing the surface structure of PtCo particles and the distribution of Pt on Co nanoparticles in three samples of example 1, comparative example 1 and comparative example 2, which are observed by using the HAADF-STEM electron microscopy technique, and it can be seen that the result of surface atoms of PtCo nanoparticles can be observed in the dark-field high-resolution HAADF-STEM photograph. As can be seen from a of FIG. 2, the catalyst of comparative sample oneWherein Pt is distributed on Co particles in isolated single atoms (red circles); as can be seen from b of fig. 2, in the catalyst of the sample of example 1, both isolated monoatomic atoms (red circles) and Pt cluster structures (yellow circles) exist on the Co particles, the monoatomic Pt surrounds the Pt clusters, and the Pt is found by counting the Pt atomic number ratio1/PtC1/3; as can be seen from c of fig. 2, Pt in the catalyst of comparative sample two exists in the form of clusters on the Co particles. Color-resolved dark-field high-resolution HAADF-STEM photographs may further demonstrate the above structure.
Fig. 3 is a PtCo nanoparticle electron microscope complement chart, which assists in proving the above results. From EDX mapping, it can be seen that PtCo nanoparticles are mainly composed of Pt (yellow) and Co (pink) elements, Pt1Co/rCCT (for comparative example 1), Pt1+CCo/rCCT (representative of example 1) and PtCThe aggregation state of Pt (yellow) in Co/rCCT (representing comparative example 2) gradually increased. In addition, a distribution of a portion of Ti (green) and O (red) was observed on the surface of PtCo nanoparticles, which was initially presumed to be amorphous TiOxSpecies of the species. Further, by using bright field high resolution HAADF-STEM photographs, a coating layer is found on the surface of the PtCo particles, and obvious excited state signals of Ti and O are found on the surface of the particles by EELS point selection measurement on the outside (I) of the particles, the surface (II) of the particles and the carrier (III). Deducing that strong interface interaction between the nano particles and the carrier is formed by 600 ℃ treatment after Pt is replaced, and TiO appears on the surfaces of the nano particlesxSpecies of the species.
As can be seen from the propanol absorption/desorption performance test results of the catalyst of fig. 4, the catalyst of example 1 exhibited excellent performance regardless of the slurry bed reaction and the tank reaction data. Further, in order to explore the adsorption mode of the glycerol on the surface of the PtCo catalyst, the invention researches the adsorption activation mode of the primary hydroxyl by adopting in-situ infrared adsorption and desorption of propanol.
The ir absorption spectra of propanol on comparative example 1, example 1 and comparative example 2 are shown in fig. 4. As can be seen from A in FIG. 4, the main oscillation peaks of propanol on comparative sample 1 are 2969, 2941, 2885, 1471, 1447, 1407, 1340, 1231, 1185, 1067 and 1053cm-1. Therein 2969、2941、2885cm-1Belonging to adsorption of CH in alkoxy3And CH2Stretching vibration, 1471 and 1447, 1407cm-1Respectively CH with undissociated adsorbed propanol2And CH3Deformation vibration, 1231cm-1Deformation vibration of undissociated O-H, 1185cm-1 is deformation vibration of C-C, 1067 and 1053cm-1Undissociated and dissociated C-O stretching vibrations [59-62]. From C in FIG. 4, the catalyst sample of example 1 was found to be 1470cm-1The absorption peak of (A) is obviously enhanced, and 1340cm does not appear-1Absorption peak of (2), estimation of Pt1The CoOx structure has the capacity of adsorbing and activating C-H; however, Pt is considered to be adsorbed at the O-H and C-O strengthsCThe adsorption capacity to hydroxyl groups is stronger, which shows that the adsorption of Pt clusters to hydroxyl groups is advantageous. From Pt1+CPt can be seen from C in FIG. 4 of the adsorption infrared spectrum of the Co/rCCT sample on propanol1And PtnThere is synergy between these two adsorption activation functions. Pt1+CC-O bond and CH on Co/rCCT sample3And CH2The absorption strength is significantly stronger than the catalyst samples of comparative example 1 and comparative example 2, and the presence of multiple hydroxyl group deformation vibration peaks indicates Pt1+CCo/rCCT was the most strongly adsorbed to hydroxyl, of which 1340cm was also observed-1The CH deformation vibration of (a) shows that the adsorption activation of propanol by Pt1 and Ptn is synergistic.
Based on the analysis of the in situ ir propanol adsorption profile, the adsorption configurations of propanol in comparative example 1 (a in fig. 5), example 1 (B in fig. 5) and comparative example 2 (C in fig. 5) were simulated, see fig. 5, due to Pt1-CoOxThe Pt cluster has the capability of adsorbing and activating C-H bonds, and the Pt cluster has stronger adsorption capability on primary hydroxyl. Wherein the brown ball is Co, the yellow ball is Pt, the white ball is H, the gray ball is C and the red ball is O.
As can be seen from fig. 6, in the catalytic preparation process, a Co-doped perovskite structure precursor is first synthesized. As can be seen in the figure, the perovskite structure characteristic diffraction peaks appear at 23.39 °, 33.32 °, 39.29 °, 41.11 °, 47.83 °, 59.54 ° and 69.97 ° respectively attributed to CaTiO3The crystal planes of (200), (022), (-113), (-222), (400), (-224), and (440) in (1) indicate the carrier CaCoTiO3Belonging to a monoclinic crystal structure (JCPDS 34-0394). In the figure, Pt1Co/rCCT stands for comparative example 1, Pt1+ CCo/rCCT stands for example 1, PtCCo/rCCT stands for comparative example 2.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in any way, but any modifications or equivalent variations made according to the technical spirit of the present invention are within the scope of the present invention as claimed.
Claims (14)
1. The preparation method of the catalyst for efficiently catalyzing the oxidation of glycerol to prepare glyceric acid is characterized in that the catalyst is Pt1+CCo/CaCoTiO3Wherein, the carrier is CaCoTiO3The characteristic diffraction peaks of the perovskite structure appear at 23.39 degrees, 33.32 degrees, 39.29 degrees, 41.11 degrees, 59.54 degrees and 69.97 degrees of 2 theta in an XRD characterization diagram, and are respectively attributed to CaCoTiO3Crystal planes (200), (022), (-113), (-222), (400), (-224), and (440) in (1); and Pt and Co exist in the form of nano particles, and the average particle size is 2nm +/-0.2 nm; wherein in the catalyst, Pt is as monatomic Pt on Co particles1And cluster PtCThe forms co-exist;
the preparation method comprises the following steps:
1) preparation of the support
Synthesis of CaCoTiO by sol-gel method3A composite oxide support;
2) reduction of the support
Taking the CaCoTiO3Reducing the composite oxide carrier in hydrogen atmosphere to obtain Co/CaCoTiO3；
3) Replacement of Pt
Mixing the Co/CaCoTiO3Pouring into a container in a liquid seal mode by using deionized water, and then dropwise adding H into the container in an atmosphere of magnetic stirring and inert gas2PtCl6Reacting the aqueous solution at normal temperature under vigorous stirring, repeatedly washing the solid product after the reaction is finished, and drying the solid product under vacuum condition to obtain PtCo/CaCoTiO3A catalyst; for the PtCo/CaCoTiO3The catalyst is subjected to secondary reduction to finally obtain the catalyst Pt1+CCo/CaCoTiO3。
2. The method according to claim 1, wherein in the step 1), Ca (NO) is used3)2•4H2O and Co (NO)3)2•6H2Preparing O into mixed solution, stirring and mixing uniformly, then adding C6H8O7•H2Continuously stirring the solution O to obtain a solution A;
taking tetrabutyl titanate and absolute ethyl alcohol in another container, and uniformly mixing to obtain a solution B;
dropwise adding the solution B into the solution A, adjusting the pH value of the mixed solution to 5-7 after the dropwise addition is finished, and continuously keeping the temperature and stirring to prepare wet gel;
drying the wet gel to obtain dry gel, grinding the dry gel, roasting to remove citric acid, cooling to room temperature, and roasting again to obtain CaCoTiO3A composite oxide.
3. The method according to claim 2, wherein the Ca (NO) is3)2•4H2O and said Co (NO)3)2•6H2The molar ratio of O is 1: (0.1-0.3).
4. The preparation method according to claim 3, wherein the molar ratio is 1: 0.2.
5. the method according to claim 2, wherein C is6H8O7•H2The addition amount of O is 1-5 times of the mole number of the metal ions.
6. The method according to claim 2, wherein in step 1), C is added6H8O7•H2And after O, continuing stirring for 0.1-1 h.
7. The method according to claim 2, wherein in step 1), the volume ratio of the tetrabutyl titanate to the absolute ethyl alcohol is 1: (1-3).
8. The method according to claim 1, wherein the reduction of the carrier in step 2) is carried out by subjecting the CaCoTiO to reduction3Spreading solid powder of composite oxide at the bottom of a porcelain boat, placing the porcelain boat in a central constant-temperature area of a quartz tube of a tube furnace, vacuumizing the porcelain boat by using a vacuum pump in a closed state, slowly introducing reducing gas until the pressure value reaches normal pressure, keeping the gas flow rate at 40ml/min, gradually heating the tube furnace at the heating rate of 10 ℃/min, keeping the temperature for 1.5 to 3 hours when the temperature of the central constant-temperature area of the quartz tube reaches 550-650 ℃, and then cooling the quartz tube to room temperature to obtain Co/CaCoTiO3A composite oxide.
9. The method according to claim 8, wherein the temperature of the constant temperature zone reaches 600 ℃ and the holding time is 2 hours.
10. The method according to claim 2, wherein the Co/CaCoTiO is added to the mixture in step 3)3The composite oxide is sealed and poured into a container by deionized water, and H is dripped into the container under the stirring of 600-800 r/min and the protection of nitrogen2PtCl6The aqueous solution is vigorously stirred for 15-72h at normal temperature, and the ion equation of the generated replacement reaction is as follows:
2Co(s) + PtCl6 2− (aq) =Pt(s) + 2Co2+ (aq) + 6Cl− (aq)
after the displacement reaction is finished, repeatedly washing the solid product by using deionized water, carrying out centrifugal separation after each washing, washing the solid product by using absolute ethyl alcohol at least once, and then carrying out vacuum drying on the washed solid product at 50-70 ℃ for 0.1 to 48 hours to obtain PtCo/CaCoTiO3A catalyst.
11. The method according to claim 10, wherein the temperature of the vacuum drying is 60 ℃ and the time is 24 hours.
12. A catalyst prepared by the process of any one of claims 1 to 11.
13. Use of a catalyst prepared by the process of any one of claims 1 to 11 for catalysing a reaction.
14. Use according to claim 13, characterized in that it is a reaction for the oxidation of glycerol to produce glyceric acid.
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