CN110252308B

CN110252308B - Supported catalyst with active metal dispersed in carrier in atomic level, preparation method and application thereof

Info

Publication number: CN110252308B
Application number: CN201910541097.XA
Authority: CN
Inventors: 张国新; 张颖; 孙晓明; 白爽; 陈建雯
Original assignee: China University of Petroleum East China; Shandong University of Science and Technology
Current assignee: China University of Petroleum East China; Shandong University of Science and Technology
Priority date: 2019-06-21
Filing date: 2019-06-21
Publication date: 2022-02-22
Anticipated expiration: 2039-06-21
Also published as: CN110252308A

Abstract

The invention discloses a load type catalyst with active metal in carrier in atomic level dispersion, which comprises: an active metal species; a support metal oxide; wherein the active metal comprises one or more of Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ru, Rh, Pd, Ag, W, Ir, Pt and Au, and the carrier metal comprises one or more of Ti, Zr, Nb, Ce, Al, Ga, In, Si, Ge and Sn. The invention also discloses a preparation method and application of the catalyst. The invention prepares the supported catalyst with the active metal dispersed in the carrier in atomic scale by the method of in-situ generation of the carrier, wherein aggregation-state particles of the active metal species with the particle size of more than 1nm do not exist. The raw materials have low cost, the reaction operation is simple, the safety is high, the post-treatment step is not needed, and the industrial scale-up production is facilitated. Meanwhile, the method has wide application range, and is beneficial to scientific research and production expansion aiming at different catalytic systems.

Description

Supported catalyst with active metal dispersed in carrier in atomic level, preparation method and application thereof

Technical Field

The invention belongs to the field of novel material preparation, and particularly relates to a supported catalyst with an active metal dispersed in a carrier at an atomic level, and a preparation method and application thereof.

Background

It is generally believed that sub-nanoclusters have better catalytic activity or selectivity than nanoparticles, bulk materials because when the particle dispersion reaches monoatomic size, many new properties are induced, such as drastically increased surface free energy, quantum size effects, unsaturated coordination environments, and metal-support interactions. Theoretically, the ideal supported metal catalyst dispersion is one in which the metal is uniformly distributed on the support in the form of a single atom. Compared with a nano-grade supported catalyst, each metal atom of the atomic-grade catalyst is used as an active site, so that the catalytic efficiency is greatly improved. Particularly for expensive metals, the active catalytic component is atomized, so that the use amount of the catalyst can be greatly reduced, the cost of the catalyst is reduced, and the potential of the catalyst in large-scale application in industrial production is improved.

Currently, supported catalysts at atomic level have shown great advantages in the fields of CO oxidation and selective oxidation, hydrogenation and selective hydrogenation, NO reduction and oxidation, water gas shift, organic synthesis, methanol steam reforming, fuel cells, photoelectrocatalysis, formaldehyde oxidation, and the like. However, single atom or cluster grade catalysts also suffer from significant disadvantages. When the metal particles are reduced to an atomic level, the specific surface area is increased rapidly, so that the free energy of the metal surface is increased rapidly, and agglomeration coupling is easy to occur during preparation and reaction to form larger particles, so that the activity of the catalyst is greatly reduced, and therefore, the preparation of the atomic-level supported catalyst with stable physicochemical properties faces a great challenge.

The preparation method of the existing atomic-scale dispersed supported catalyst mainly comprises the following steps: coprecipitation, impregnation, atomic layer deposition, inverse Ostward aging, solid-phase melting, and the like. Generally, the methods can effectively prepare the supported catalyst with atomic-scale dispersion, but most methods involve harsh synthesis conditions, expensive medicines and raw materials and complex post-treatment processes, so that the application of the supported catalyst with atomic-scale dispersion in production practice is greatly limited.

The invention creatively starts from cost control, uses metal source materials and formamide with economic price, and realizes the universal preparation of the atomic-level dispersion metal supported catalyst with low cost and large-scale macro preparation by designing a simple reaction synthesis path.

Disclosure of Invention

In a first aspect, the present invention provides a supported catalyst in which an active metal is dispersed in a carrier at an atomic level, comprising:

an active metal species;

a support metal oxide;

wherein the active metal comprises one or more of Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ru, Rh, Pd, Ag, W, Ir, Pt and Au, and the carrier metal comprises one or more of Ti, Zr, Nb, Ce, Al, Ga, In, Si, Ge and Sn.

Preferably, the active metal is bonded to oxygen atoms on the surface of the support metal oxide.

Preferably, the active metal species and/or the support metal oxide is at least partially sulphided, nitrided, phosphated or borated and correspondingly at least part of the active metal is bonded to sulphur, nitrogen, phosphorus or boron atoms on the surface of the support metal oxide.

Preferably, wherein aggregated particles of said active metal species having a particle size greater than 1nm are absent.

In a second aspect, the present invention provides a method for preparing a supported catalyst in which an active metal is atomically dispersed in a carrier, comprising the steps of:

1) dissolving at least one first metal salt and at least one second metal salt in formamide, and carrying out complexation reaction on the first metal salt and the formamide to obtain a formamide solution of mixed metal salts; wherein, the metal element in the first metal salt is one of Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ru, Rh, Pd, Ag, W, Ir, Pt and Au; the metal element In the second metal salt is one of Ti, Zr, Nb, Ce, Al, Ga, In, Si, Ge and Sn;

2) reacting the formamide solution of the mixed metal salt obtained in the step 1) at the temperature of 100-300 ℃ for 1 to 99 hours to polymerize formamide, wherein the byproduct water of the formamide polymerization reaction and the second metal salt in the formamide polymerization reaction are subjected to hydrolysis reaction;

3) and (3) carrying out solid-liquid separation on the mixture after the reaction in the step 2), and roasting the obtained solid substance for 1 to 99 hours at the temperature of 300-900 ℃ in the air atmosphere to obtain the supported catalyst.

Preferably, in step 1), the total concentration of the first metal salt in formamide is 0.001-0.1 mol/L, and the total concentration of the second metal salt in formamide is: 0.009-1.0 mol/L.

Preferably, the method further comprises the step 4): at least partially nitriding, sulfiding, phosphatizing or boronizing the supported catalyst obtained in step 3).

Wherein "at least partially nitriding, sulfiding, phosphatizing or boriding" means that by controlling the extent to which the nitriding, sulfiding, phosphatizing or boriding reaction proceeds, the support metal oxide in the supported catalyst obtained in step 3) is at least partially replaced by one of a support metal nitride, a support metal sulfide, a support metal phosphide, a support metal boride, and accordingly at least a portion of the active metal is bonded to sulfur, nitrogen, phosphorus or boron atoms on the surface of the support metal oxide.

Preferably, the nitriding is a reaction of a nitrogen source and the supported catalyst obtained in the step 3), wherein the nitrogen source comprises ammonia gas, ammonia water, sodium amide and sodium azide;

the sulfuration is carried out by reacting a sulfur source with the supported catalyst obtained in the step 3), wherein the sulfur source comprises sulfur powder, sodium sulfide, hydrogen sulfide, thioacetamide and thiourea;

the phosphorization is to use a phosphorus source to react with the supported catalyst obtained in the step 3), wherein the phosphorus source comprises phosphorus powder, phosphoric acid, alkali metal phosphate and triphenylphosphine;

the boronizing is carried out by reacting a boron source with the supported catalyst obtained in the step 3), wherein the boron source comprises boron powder, boric acid and alkali metal borate.

Preferably, the liquid phase means comprises flask heating and hydrothermal reaction kettle heating, and the gas phase means comprises tube furnace heating.

Preferably, the mixing method comprises manual shaking, mechanical shaking, ultrasound and stirring.

Preferably, the reaction vessels of step 1) and step 2) are safe vessels with good heat resistance, and comprise flasks and polytetrafluoroethylene reaction kettles.

Preferably, the solid-liquid separation method comprises centrifugation, filtration and standing sedimentation.

In the step 2), formamide is self-polymerized and carbonized to form a nitrogen-carbon material, wherein nitrogen elements can directionally chelate first metal cations, so that the first metal ions are distributed on the nitrogen-carbon material in an atomic-scale dispersed state to form the active metal nitrogen-carbon material. Water, a by-product of the polymerization and carbonization of formamide, reacts with a second metal ion to form the corresponding support oxide or hydroxide.

The two reactions occur simultaneously to form rich interfaces of the active metal nitrogen-carbon material and the carrier metal oxide or hydroxide. Therefore, the active metal nitrogen-carbon material dispersed at atomic level forms uniform and compact load on the carrier metal oxide or hydroxide substrate material generated in situ, and the load type catalyst precursor is obtained.

In the step 3), the supported catalyst precursor is roasted in the air atmosphere, the metal hydroxide generates metal oxide, the nitrogen-carbon material is removed, the acting force for stabilizing the atomic-level active metal component is transferred to the interface of the carrier oxide, the nitrogen-carbon material has strong anchoring effect on surrounding active metal atoms in the roasting process, the agglomeration of the active metal component is delayed to a great extent, and when the active metal is bonded with oxygen atoms on the surface of the carrier metal oxide, the supported catalyst with the active metal in atomic-level dispersion in the carrier is obtained.

In a third aspect, the present invention provides a use of the supported catalyst in which the active metal of the first aspect is atomically dispersed in a carrier, which comprises: the method is suitable for all non-electric reactions, such as hydrogenation reaction, dehydrogenation reaction, isomerization reaction, desulfurization reaction, catalytic polymerization reaction and the like.

The preparation method of the invention is different from the dipping method as follows:

the invention realizes atomic-level high-dispersion load of a wide range of metal elements on various substrates by a two-step method, and in the first step, firstly, an atomic-level dispersed active metal nitrogen-carbon material forms uniform and compact load on a carrier metal oxide or hydroxide substrate material generated in situ;

and secondly, in the process of removing nitrogen and carbon by roasting, the nitrogen and carbon material plays an anchoring effect on active metal atoms, before the active metal components are stabilized by the carrier oxide, the agglomeration of the active metal components is delayed to a great extent, the atomic-level dispersion state of the active metal is continuously maintained, and finally the active metal is atomically dispersed on the carrier metal oxide.

However, most of the traditional impregnation methods achieve atomic-scale adsorption at low temperature, and the migration of active metals is often serious after temperature rise roasting because no force is applied to delay the aggregation of active metal components in the roasting process, so that the active metals cannot be in an atomic-scale dispersion state on a carrier metal oxide, and finally the active metals are in an aggregated nano-scale, micron-scale or even millimeter-scale particle form.

The invention has the following beneficial effects:

(1) the invention prepares the supported catalyst with the active metal dispersed in the carrier in atomic scale by the method of in-situ generation of the carrier, wherein aggregation-state particles of the active metal species with the particle size of more than 1nm do not exist. The raw materials have low cost, the reaction operation is simple, the safety is high, the post-treatment step is not needed, and the industrial scale-up production is facilitated. Meanwhile, the method has wide application range, and is beneficial to scientific research and production expansion aiming at different catalytic systems.

(2) The catalyst has high mechanical strength, high active component dispersion degree, high catalytic activity and high selectivity, and is easier to reduce compared with similar non-atomic-level dispersed catalysts.

Drawings

FIG. 1 shows Ni/Al prepared in example 1 of the present invention₂O₃Transmission electron micrograph (c).

FIG. 2 shows Ni/CeO prepared in example 2 of the present invention₂Transmission electron micrograph (c).

FIG. 3 shows Ni/Al prepared in example 3 of the present invention₂O₃Transmission electron micrograph (c).

FIG. 4 shows Ni/Al prepared in example 4 of the present invention₂O₃Transmission electron micrograph (c).

FIG. 5 shows Ni/Al prepared in example 5 of the present invention₂O₃Transmission electron micrograph (c).

FIG. 6 shows Co/Al prepared in example 6 of the present invention₂O₃Transmission electron micrograph (c).

FIG. 7 shows Cu/Al prepared in example 7 of the present invention₂O₃Transmission electron microscope photograph of

FIG. 8 shows Au/Al prepared in example 8 of the present invention₂O₃Transmission electron micrograph (c).

FIG. 9 shows Pd/Al prepared in example 9 of the present invention₂O₃Transmission electron micrograph (c).

FIG. 10 shows CuZrO produced in example 10 of the present invention₂Transmission electron micrograph (c).

FIG. 11 shows Ni-W/Al prepared in example 11 of the present invention₂O₃Transmission electron micrograph (c).

FIG. 12 shows Ni-W/Al prepared in example 11 of the present invention₂O₃Element plane scan photo.

FIG. 13 shows Al prepared in examples 1, 3 to 9 and 11 of the present invention₂O₃X-ray diffraction pattern of supported monatomic catalyst.

FIG. 14 shows Ni/Al prepared in example 1 of the present invention₂O₃Wherein De. represents the desorption curve and Ab. represents the adsorption curve.

FIG. 15 shows Ni/Al prepared in example 1 of the present invention₂O₃XPS Ni2p peak separation curve.

FIG. 16 shows Co/MoO prepared in example 12 of the present invention₃X-ray diffraction pattern of (a).

FIG. 17 shows Co/MoS prepared in example 12 of the present invention₂X-ray diffraction pattern of (a).

FIG. 18 shows Ni/Al prepared in example 1 of the present invention₂O₃In CO₂And (4) evaluating the performance of the hydrogenation methane preparation reaction.

FIG. 19 shows Ni/CeO prepared in example 2 of the present invention₂In CO₂And (4) evaluating the performance of the hydrogenation methane preparation reaction.

FIG. 20 shows Ni/CeO prepared in example 2 of the present invention₂Temperature programmed reduction curve of hydrogen.

Detailed Description

The present invention will be further described with reference to the following embodiments.

Example 1

60.0mL of anhydrous NiCl dissolved in 0.009mol/L₂And 0.091mol/L anhydrous AlCl₃The formamide solution was placed in a Teflon reaction vessel having a volume of 100.0mL and reacted at 180 ℃ for 12 hours. After the reaction time is over, naturally cooling, taking out the solid-liquid mixture, and solidifying by using a centrifugal modeSeparating liquid, drying the solid in an oven at 80 ℃, collecting dry powder, and roasting for 3 hours at 450 ℃ by using a muffle furnace to obtain a target product Ni/Al₂O₃The transmission electron micrograph is shown in FIG. 1, the nitrogen desorption curve is shown in FIG. 14, and the XPS Ni2p peak separation curve is shown in FIG. 15.

Example 2

Except that B type salt anhydrous AlCl₃Replacement by Ce (NO)₃)₂·6H₂O, otherwise, the same as example 1 was repeated to obtain the target Ni/CeO₂The transmission electron micrograph is shown in FIG. 2.

Example 3

Except that anhydrous NiCl is removed₂The concentration of the solution is increased to 0.018mol/L, and AlCl is added₃The concentration is increased to 0.182mol/L, and the other steps are the same as the example 1, thus obtaining the target product Ni/Al₂O₃The transmission electron micrograph is shown in FIG. 3.

Example 4

Except that anhydrous NiCl is removed₂The concentration of the solution is increased to 0.027mol/L, and AlCl is added₃The concentration is increased to 0.273mol/L, and the other steps are the same as the example 1, thus obtaining the target product Ni/Al₂O₃The transmission electron micrograph is shown in FIG. 4.

Example 5

The same procedure as in example 1 was repeated except that the temperature and time for the muffle furnace calcination were adjusted to 550 ℃ and 3 hours, respectively, to obtain the target Ni/Al product₂O₃The transmission electron micrograph is shown in FIG. 5.

Example 6

Except that the A metal salt is anhydrous NiCl₂Replacement with anhydrous CoCl₂Otherwise, the target product Co/Al is obtained in the same manner as in example 1₂O₃The same TEM photograph as that shown in FIG. 6.

Example 7

Except that the A metal salt is anhydrous NiCl₂Replacement by anhydrous Cu (NO)₃)₂Otherwise, the same as example 1 was repeated to obtain the target product Cu/Al₂O₃The transmission electron micrograph is shown in FIG. 7.

Example 8

Except that the A metal salt is anhydrous NiCl₂Is replaced byAqueous AuCl₃Otherwise, the same procedure as in example 1 was repeated to obtain the target product Au/Al₂O₃The transmission electron micrograph is shown in FIG. 8.

Example 9

Except that the A metal salt is anhydrous NiCl₂Replacement with anhydrous PdCl₃Otherwise, the same as example 1 was carried out to obtain the target product Pd/Al₂O₃The transmission electron micrograph is shown in FIG. 9.

Example 10

Except that the A metal salt is anhydrous NiCl₂Replacement by anhydrous Cu (NO)₃)₂Anhydrous AlCl, class B salts₃Replacement by Zr (SO)₄)₂Otherwise, the same procedure as in example 1 was repeated to obtain the target product Cu/ZrO₂The transmission electron micrograph is shown in FIG. 10.

Example 11

The metal salt of type A is expanded to a double active metal system except NiCl as the metal salt of type A₂Is replaced by anhydrous WCl of equimolar concentration₃Otherwise, the same as example 1 was repeated to obtain the target Ni-W/Al₂O₃The transmission electron micrograph is shown in FIG. 11, and the elemental surface scanning micrograph is shown in FIG. 12.

The products obtained in examples 1 to 12 were characterized and analyzed:

wherein M is_ARepresents a metal of the first type, wherein M_BRepresenting a second type of metal.

Transmission electron micrographs (FIGS. 1, 3-10, 11) show: formamide and AlCl are used₃M synthesized with different transition metal salts_A/Al₂O₃The shape of the supported catalyst is granular, Al₂O₃The average particle size is within 5-10nm, and no aggregated particles of active metal species with a particle size greater than 1nm are seen under normal high resolution transmission.

The transmission electron micrograph (FIG. 2) shows: using formamide, NiCl₂Ni/M synthesized with precursor metal salts of different supports_BO_xThe morphology of the supported catalyst is granular, M_BO_xThe average particle size is within 5-10nm, and under normal high-resolution transmission, no Ni aggregation state with the particle size larger than 1nm is observedAnd (3) granules.

A transmission mirror element surface scanning photograph (fig. 12) shows: using formamide, NiCl₂、WCl₃And AlCl₃Synthetic Ni-W/Al₂O₃In the supported catalyst particles, the Ni and W active metal components are uniformly distributed and no particles are formed.

The X-ray powder diffraction pattern (fig. 13) shows: in examples 1 to 12 included in the present invention, only the diffraction peak of the support material was detected, and no diffraction peak of the active metal component was observed, demonstrating that the active metal species exist in the form of sub-nanometer or cluster, i.e., in an atomically dispersed state.

The specific surface area test (FIG. 14 nitrogen adsorption and desorption curve) shows that formamide and NiCl are used₂And AlCl₃Synthetic Ni/Al₂O₃The specific surface area of the supported catalyst was 407m²The pore diameter form is mainly wedge-shaped.

XPS Ni2p peak separation curves (FIG. 15) show the use of formamide, NiCl₂And AlCl₃Synthetic Ni/Al₂O₃The Ni component of the supported catalyst is bonded with oxygen atoms on the surface of the carrier metal oxide, and no zero-valent metal aggregation state exists.

Example 12

60.0mL of anhydrous CoCl dissolved with 0.009mol/L₂(M_AMetalloid salt) and 0.091mol/L anhydrous MoCl₃(M_BSalt-like) formamide solution was placed in a polytetrafluoroethylene reaction vessel having a volume of 100.0mL and reacted at 180 ℃ for 12 hours. Naturally cooling after the reaction time is over, taking out a solid-liquid mixture, separating solid from liquid by using a centrifugal mode, drying the solid in an oven at 80 ℃, collecting dry powder, roasting for 3 hours at 450 ℃ by using a muffle furnace to obtain the supported catalyst Co/MoO with active metal and carrier metal both in oxide form₃. After stirring the product in 30mL of an aqueous solution of thiourea for 0.5h, the mixture was placed in a reaction kettle having a volume of 50.0mL and reacted at 220 ℃ for 18 h. Naturally cooling after the reaction time is over, taking out a solid-liquid mixture, separating the solid from the liquid in a centrifugal mode, putting the solid in a 60 ℃ oven for vacuum drying, and collecting dry powder to obtain the target product Co/MoS₂The supported catalyst, i.e. the support metal oxide is entirely replaced by a support metal sulphide, the active metal being bonded to sulphur atoms on the surface of the support metal sulphide. FIG. 16 shows the Co/MoO prepared in this example₃X-ray diffraction pattern of (a). FIG. 17 shows the Co/MoS prepared in this example₂X-ray diffraction pattern of (a).

Example 13

Ni/Al synthesized in examples 1 and 2₂O₃And Ni/CeO₂Supported catalysts for catalyzing CO₂Hydrogenation reaction under the test conditions: grinding and tabletting the obtained catalyst to prepare 20-60-mesh particles, wherein the filling amount of the adsorbent is 0.5g, the pre-reduction temperature is 450 ℃, the pressure is 0.1MPa, the hydrogen flow is 30mL/min, and the reduction time is half an hour. CO 2₂Hydrogenation evaluation conditions: the temperature is 200 ℃ and 350 ℃, the pressure is normal, after the temperature is stable, the reaction is carried out for 1 hour, a product is taken out every 10 minutes, and the product is analyzed by gas chromatography. The reaction gas is CO₂And H₂Mixed gas of (1) and (2) in a mixing ratio of CO₂:H₂＝1:4。

The conclusion is as follows:

at a reaction temperature of 200 deg.C, 230 deg.C, 260 deg.C, 290 deg.C, 320 deg.C, 350 deg.C, Ni/Al₂O₃The catalytic selectivity of (A) was 85.86%, 84.48%, 85%, 90.56%, 100%, respectively, see FIG. 18. At a test temperature of 200 ℃, 230 ℃, 260 ℃ and Ni/CeO₂The catalytic selectivity of (A) is 96.85%, 99.99% and 100%, respectively, see FIG. 19. Thus, both catalysts show good catalytic selectivity.

Example 14

Characterization of Ni/CeO synthesized in example 2 Using a Hydrogen temperature programmed reduction test₂The catalyst was supported and three groups of reduction peaks appeared in the characterization results (fig. 20): they are respectively at 270 ℃, 326 ℃ and 434 ℃, wherein 326 ℃ is the reduction peak of the nickel oxide on the surface of the carrier. Reference to Ni particles loaded on CeO₂Ni/CeO prepared as above₂Five groups of reduction peaks appear in the result of hydrogen temperature programming reduction data of the supported catalyst, and the five groups of reduction peaks respectively have the temperature of 210 ℃, 265 ℃ and 360 DEG C500 ℃ and 582 ℃ (morphological dependence of catalytic properties of Ni/CeO)₂ for CO₂ methanation:A kinetic and mechanism study[J]Catalysis Today,2018, DOI 10.1016/j. cat.2018.04.067.). Wherein 360 ℃ is the reduction peak of the nickel oxide on the surface of the carrier. Comparison with this catalyst shows that the atomically dispersed Ni/CeO synthesized in example 2₂The supported catalyst is more easily activated and reduced.

The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A method for preparing a supported catalyst with an active metal dispersed in a carrier in an atomic scale is characterized by comprising the following steps:

2. The process for preparing a supported catalyst according to claim 1, wherein in step 1), the total concentration of the first metal salt in formamide is 0.001 to 0.1mol/L, and the total concentration of the second metal salt in formamide is: 0.009-1.0 mol/L.

3. The method for preparing a supported catalyst according to claim 1, further comprising step 4): at least partially nitriding, sulfiding, phosphatizing or boronizing the supported catalyst obtained in step 3).

4. The preparation method of claim 3, wherein the nitriding is carried out by reacting the supported catalyst obtained in step 3) with a nitrogen source, wherein the nitrogen source comprises ammonia gas, ammonia water, sodium amide and sodium azide;