CN113398950B - Crystal face regulated and controlled supported nano alloy catalyst and preparation method and application thereof - Google Patents
Crystal face regulated and controlled supported nano alloy catalyst and preparation method and application thereof Download PDFInfo
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- 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
- B01J23/8933—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 also combined with metals, or metal oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
- B01J23/894—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 also combined with metals, or metal oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with rare earths or actinides
-
- B01J35/393—
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/08—Heat treatment
- B01J37/10—Heat treatment in the presence of water, e.g. steam
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/16—Reducing
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
- C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
- C01B3/04—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by decomposition of inorganic compounds, e.g. ammonia
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
Abstract
The invention discloses a crystal face regulated and controlled supported nano alloy catalyst and a preparation method and application thereof. The catalyst comprises a metal alloy active phase and a metal oxide carrier phase, wherein the metal alloy active phase is dispersed and distributed on the surface of the metal oxide carrier phase in a nanoparticle form, and one to two crystal faces of (111), (200) and (220) are selectively exposed out of the metal oxide carrier phase. Synthesizing oxide carriers with different morphologies under different hydrothermal conditions to expose different crystal faces; and then adsorbing two different metal precursor salts on an oxide carrier, and carrying out heat treatment reaction on the obtained product in a reducing atmosphere to obtain the high-dispersion supported nano alloy catalyst. The preparation method has the advantages of easily available raw materials, simple process and easy mass production. The prepared catalyst has high intrinsic catalytic activity and abundant active sites, and can efficiently catalyze hydrazine hydrate to decompose and prepare hydrogen under alkaline conditions.
Description
Technical Field
The invention belongs to the field of irreversible hydrogen storage materials, and particularly relates to a crystal surface-regulated supported nano alloy catalyst, and a preparation method and application thereof.
Background
Energy and the environment are the basis on which human beings live and develop. With the continuous and deep development of the economic globalization, the human demand for energy reaches an unprecedented stage. Therefore, the development of sustainable clean energy has become a major issue concerning the sustainable development of human beings. Hydrogen is a clean and efficient renewable energy source, is easy to realize hydrogen/electricity conversion, and is expected to play an extremely important role in the process of relieving the great pressure of reduction of fossil energy and environmental pollution. However, from the technical aspect, the realization of large-scale industrial application of hydrogen energy requires the construction of a complete hydrogen energy industrial chain including hydrogen production, hydrogen storage, hydrogen utilization and other links, wherein the hydrogen storage link is most challenging because the hydrogen storage link needs to simultaneously meet harsh technical indexes in the aspects of hydrogen storage density, operating conditions, safety, cost and the like, and is known as a bottleneck restricting the application of hydrogen energy. The rise of the chemical hydrogen storage technology provides a chance for breaking through the bottleneck of hydrogen storage until 2000 years ago and later. Among the various chemical hydrides of choice, hydrazine hydrate (N)2H4·H2O) is a hot spot of attention of various researchers due to its comprehensive performance advantages and unique decomposition reaction behaviors. N is a radical of2H4·H2O has the advantages of high mass hydrogen storage density (8.0 wt%), low material cost (2$/L), good chemical stability and the like, particularly, no solid by-product and harmful gas are generated in the decomposition reaction, and the O has the application potential of moving hydrogen sources.
N2H4·H2The O decomposition hydrogen production system is used as a chemical controllable hydrogen production system with extremely high application potential, and a catalyst with low cost, high activity and high stability is developed to selectively promote N2H4·H2Decomposition of O to H2And N2While suppressing side reaction NH3And N2Is generated by N2H4·H2The key of the hydrogen production by O catalytic decomposition. The research finds thatSupported bimetallic alloy catalyst composed of metal (such as Pt and Ir) and non-noble metal (such as Ni, Co and Fe) for catalyzing N2H4·H2The hydrogen production activity and selectivity of O decomposition are excellent. However, the research on the supported catalyst has been focused on the metal oxide nanoparticles. The catalytic performance of the nano material is not only related to the size and shape of the nano particles, but also closely related to the exposed crystal faces, the types of surface atoms and the distribution state of alloy particles. By controlling the shape structure of the metal oxide, the concept of the shape-dependent nano-catalysis not only can fundamentally understand the structure-performance relationship, but also has important significance for designing and preparing the high-efficiency catalyst.
Disclosure of Invention
Aiming at the defects and shortcomings of the prior art, the invention mainly aims to provide a supported nano alloy catalyst suitable for preparing hydrogen by decomposing hydrazine hydrate and application thereof. The catalyst has high intrinsic catalytic activity and rich active sites. Research shows that the catalyst can efficiently catalyze hydrazine hydrate to decompose and produce hydrogen under alkaline conditions.
The invention also aims to provide a preparation method of the supported hydrazine hydrate decomposition hydrogen production catalyst based on crystal face regulation. The method has simple preparation process, is convenient for mass production, and can be applied to the field of other catalytic materials.
The purpose of the invention is realized by the following technical scheme:
a supported nano alloy catalyst with a regulated crystal plane comprises a metal alloy active phase and a metal oxide carrier phase, wherein the metal alloy active phase is dispersed and distributed on the surface of the metal oxide carrier phase in a nanoparticle form, and one or two crystal planes of (111), (200) and (220) are selectively exposed out of the metal oxide carrier phase.
Preferably, the metal oxide matrix phase is one of La-based La and Ce, and the metal alloy active phase is an active phase obtained by alloying one of transition metals Fe, Co, Ni, and Cu with one of noble metals Pt, Ir, Ru, Rh, and Pd. More preferably, the metal alloy active phase refers to Ni-Pt, Ni-Ir, Ni-Ru, Ni-Rh, Ni-Pd, Co-Pt, Co-Ir, Co-Ru, Co-Rh and Co-Pd binary alloy.
Preferably, the particle size of the metal alloy active phase is 1-2 nm.
Preferably, the metal oxide support phase is nanostructured.
The preparation method of the catalyst can be divided into three steps of hydrothermal, co-adsorption and reduction heat treatment, firstly, a metal oxide carrier precursor with a specific morphology is synthesized by a hydrothermal method, the metal oxide carrier precursor is calcined in an air atmosphere to obtain a metal oxide carrier, then, a bimetallic precursor is adsorbed on the surface of the metal oxide by co-adsorption, and finally, the two metals are alloyed by regulating and controlling the reduction heat treatment conditions to prepare the supported nano-alloyed catalyst with the specific morphology.
The preparation method of the supported nano alloy catalyst with the controlled crystal surface comprises the following steps:
(1) dissolving a precursor salt of a metal oxide carrier in deionized water, adding a precipitator to obtain a mixed solution, carrying out stirring reaction for 0-2 h, then carrying out hydrothermal reaction at 100-200 ℃, carrying out centrifugal drying to obtain a metal oxide precursor, and calcining the metal oxide precursor in an air atmosphere at 200-500 ℃ for 1-5 h to obtain the metal oxide carrier;
(2) adjusting the pH value of the salt solution of the bimetallic precursor, adsorbing the bimetallic precursor on the surface of the metal oxide carrier in the step (1) by a co-adsorption method, and performing suction filtration and drying;
(3) and (3) carrying out heat treatment reaction on the product in the step (2) at the temperature of 300-600 ℃ in a reducing atmosphere, and sequentially reducing and alloying the active metals to obtain the supported nano alloy catalyst.
Preferably, the precipitant in step (1) is selected from one of dimethyl oxalate, urea, sodium hydroxide, tetramethylammonium hydroxide and sodium phosphate;
preferably, the concentration of the precipitant in the mixed solution in the step (1) is 50-3000 mM;
preferably, the hydrothermal reaction in step (1) is carried out in a stainless steel autoclave containing a polytetrafluoroethylene lining;
preferably, the hydrothermal reaction time in the step (1) is 8-30 h.
Preferably, the pH value of the bimetallic precursor salt solution in the step (2) is determined according to the isoelectric point of the metal oxide carrier in the step (1), the dosage of the bimetallic precursor salt is determined according to the specific surface area and the mass of the metal oxide carrier, and the conversion coefficient is 1000m2 L-1(ii) a The electrostatic adsorption was at room temperature 25 ℃.
Preferably, the precursor salt of the metal oxide carrier in the step (1) refers to nitrate, sulfate and acetate of one of La and Ce;
preferably, one of the bimetallic precursor salts in step (2) is nitrate, sulfate or acetate of one of transition metals of Fe, Co, Ni and Cu, and the other metal salt is chlorate or nitrate of one of noble metals of Pt, Ir, Pd, Ru and Rh.
Preferably, the concentration of the precursor salt of the metal oxide carrier in the mixed solution in the step (1) is 1-100 mM;
preferably, the temperature of the stirring reaction in the step (1) is 25-100 ℃; stirring and reacting for 0-1 h; further preferably, the temperature of the stirring reaction in the step (1) is 25-80 ℃.
Preferably, the concentration of the bimetallic precursor salt in the step (2) is 0.1-5 mM;
preferably, the reducing atmosphere in step (3) is a hydrogen atmosphere;
preferably, the time of the heat treatment in the step (3) is 1-2 h.
The supported nano alloy catalyst with the regulated crystal face is applied to catalyzing hydrazine hydrate to decompose and prepare hydrogen.
The crystal face regulation and control supported nano alloy catalyst is applied to catalyzing hydrazine hydrate to decompose and prepare hydrogen.
The principle of the invention is as follows: at present, most of high-efficiency hydrazine hydrate decomposition hydrogen production catalysts are supported bimetallic alloy nanoparticles, and the preparation method is a 'one-pot method', so that most of catalytic active sites are coated on a bulk phase, the utilization efficiency of precious metals is greatly reduced, and the types of exposed crystal faces prepared in the way are not single, and the relevance of the catalyst structure and performance cannot be fundamentally analyzed. Therefore, the catalyst with a specific morphology is prepared while reducing the noble metal load on the premise of not influencing the catalytic performance, so that different crystal faces are exposed, the relevance of the catalyst structure and the performance can be effectively analyzed, and the method is an effective way for solving the problem. The invention optimizes the design idea and provides a simple and easy preparation method for realizing. The preparation method of the catalyst can be divided into three steps of hydrothermal-co-adsorption-reduction heat treatment, firstly, deionized water solution containing precursor salt of the metal oxide carrier is used as an initial raw material, the metal oxide carrier precursor with a specific morphology structure is synthesized by a hydrothermal method, and then the metal oxide is obtained by calcining in an air atmosphere, so that material composition and a structural foundation are laid for synthesizing the high-performance catalyst; and then adjusting a proper pH value range by a co-adsorption method, adsorbing a bimetallic precursor on the surface of the metal oxide, and finally alloying the bimetal by regulating and controlling the reduction heat treatment condition to prepare the supported nano alloy catalyst with a specific morphology. The catalyst with specific morphology exposes different crystal faces to have different interactions with the alloy metal phase loaded on the surface, thereby influencing the decomposition behavior of hydrazine molecules adsorbed on the surface. In addition, the surface modification method of co-adsorption is adopted, so that the loaded metal alloy is more uniformly dispersed, the utilization rate of the noble metal is improved, and the intrinsic activity is improved. In conclusion, the catalyst for hydrogen production by hydrazine hydrate decomposition provided by the invention has high intrinsic activity and abundant active sites.
Compared with the prior art, the invention has the following advantages and beneficial effects:
(1) the key point of the method is that the metal oxide carrier with a specific morphology is synthesized, so that different crystal faces are exposed, and the relevance of the catalyst structure and performance is more effectively analyzed. In addition, the method improves the utilization rate of the noble metal and reduces the material cost. On the synthesis of a metal oxide carrier with a specific morphology, a surface modification method (co-adsorption method) is used for carrying out surface fine regulation and condition optimization on loaded bimetal, and the double design of crystal face exposure and surface adsorption of the bimetal enables a metal alloy phase to be highly and uniformly distributed on the surface of the metal oxide carrier in the form of ultra-small nano particles, and the metal alloy phase has strong interaction between metal and the carrier. The in-situ bimetal alloy phase generated in the heat treatment process can not only improve the intrinsic activity of the catalyst, but also increase the number of active sites to the maximum extent.
(2) The preparation method has the advantages of easily available raw materials, simple process and easy mass production.
(3) The invention provides a high-performance supported nano alloy catalyst which can efficiently catalyze hydrazine hydrate decomposition reaction under alkaline conditions, and has high activity and 100% hydrogen production selectivity.
Drawings
FIG. 1 shows a hydrothermal sample CeO obtained in example 1 of the present invention2Rod and target catalyst Ni-Pt/CeO2-X-ray diffraction pattern of Rod.
FIGS. 2a and 2b are Ni-Pt/CeO, respectively, target catalysts obtained in inventive example 12-transmission electron microscopy topography and high resolution electron microscopy of Rod.
FIG. 3 shows Ni-Pt/CeO of the target catalyst sample in example 1 of the present invention2H of Rod2-a TPR data map.
FIG. 4 shows a sample of CeO in example 1 of the present invention2Isoelectric Point assay of Rod.
FIG. 5 shows Ni-Pt/CeO target catalysts obtained under different adsorption time preparation conditions in example 1 of the present invention2p-N of Rod in solution containing 0.5M hydrazine hydrate and 2.0M sodium hydroxide2H4·H2O decomposition kinetics test chart.
FIG. 6 shows a sample CeO in hydrothermal state in example 2 of the present invention2Cube and target catalyst Ni-Pt/CeO2-X-ray diffraction pattern of Cube.
FIGS. 7a and 7b are Ni-Pt/CeO, respectively, target catalysts obtained in inventive example 22Transmission electron micrograph and high resolution electron micrograph of Cube.
FIG. 8 shows the preparation at the optimum adsorption time in example 2 of the present inventionTarget catalyst Ni-Pt/CeO2p-N of Cube in a solution containing 0.5M hydrazine hydrate and 2.0M sodium hydroxide2H4·H2O decomposition kinetics test chart.
FIG. 9 shows a hydrothermal sample of CeO obtained in example 3 of the present invention2-Oct and target catalyst sample Ni-Pt/CeO2-X-ray diffraction pattern of Oct.
FIGS. 10a and 10b are Ni-Pt/CeO, respectively, samples of the target catalyst obtained in inventive example 32-transmission electron micrograph and high resolution electron micrograph of Oct.
FIG. 11 shows Ni-Pt/CeO as the target catalyst in example 3 of the present invention2para-N of Oct in solution containing 0.5M hydrazine hydrate and 2.0M sodium hydroxide2H4·H2O decomposition kinetics test chart.
FIG. 12 shows a hydrothermal sample of CeO obtained in example 4 of the present invention2-Rod and target catalyst sample Ni-Ru/CeO2-X-ray diffraction pattern of Rod.
FIGS. 13a and 13b are Ni-Ru/CeO, respectively, samples of the target catalyst obtained in inventive example 42-transmission electron microscopy topography and high resolution electron microscopy micrograph of Rod.
FIG. 14 shows Ni-Ru/CeO as target catalysts in example 4 of the present invention2p-N of Rod in solution containing 0.5M hydrazine hydrate and 2.0M sodium hydroxide2H4·H2O decomposition kinetics test chart.
FIG. 15 shows Ni-Pt/CeO target catalysts in examples 1, 2 and 3 of the present invention2-Rod、Ni-Pt/CeO2-Cube、Ni-Pt/CeO2para-N of Oct in solution containing 0.5M hydrazine hydrate and 2.0M sodium hydroxide2H4·H2O decomposition kinetics test chart.
Detailed Description
The present invention will be described in further detail with reference to the following examples and drawings, but the embodiments and the scope of the present invention are not limited thereto.
The hydrazine hydrate decomposition hydrogen production system test and related calculation method comprises the following steps:
1. catalyst catalysis performance testing device
The catalyst samples were placed in a 50mL two-necked round bottom flask and tested in a water bath at constant temperature (indicated temperature). The reaction is started by injecting hydrazine hydrate (alkali solution) with a certain concentration into the round-bottom flask, and simultaneously the magnetic stirring is started, so that the influence of mass transfer in heterogeneous catalytic reaction on performance test results is reduced. N is a radical of2H4·H2The gas generated by O decomposition passes through a Meng's washing bottle filled with dilute acid to absorb NH generated by incomplete decomposition reaction3. The water is drained, the water is weighed in real time by an electronic balance (the precision is 0.01g), and the weighing data is recorded by a computer (the data acquisition interval can be selected according to the requirement). Typical test conditions are a reaction solution volume of 2mL, N2H4·H2The concentration of O is 0.5M, the concentration of NaOH is 2M, the reaction temperature is 30-80 ℃, and the dosage of the catalyst and N are2H4·H2The molar ratio of O was 1/20. It should be noted that, during the test, the test is performed after the gas in the system is thermally balanced. In addition, when the water discharge mass is converted into the molar quantity of the generated gas, the influence of the ambient temperature on the gas volume needs to be considered.
2. Index of catalytic performance of catalyst
(1) Catalytic activity is usually measured by the Turnover Frequency (TOF), the number of reactant conversions per unit time at a single active site, which can be determined by equation (1).
Wherein n ismetalIs the molar amount of the active metal of the catalyst,
is N2H4·H2O is added in half the molar amount and t is the time required for the reaction to proceed in half.
(2) And (4) calculating hydrogen production selectivity. The hydrogen production selectivity of the catalyst is a measure of N2H4·H2The important index of the hydrogen storage capacity of the O decomposition hydrogen production system. According to N2H4·H2The general formula of O decomposition reaction:
3N2H4→4(1-X)NH3+(1+2X)N2↑+6XH2↑ (2)
wherein N (N)2+H2) To generate N2And H2Total molar amount of (C), N (N)2H4) Is N2H4·H2The molar amount of O and the ratio of Y to each other. The hydrogen production selectivity X can be calculated from the formula (2-3).
Example 1
Ni-Pt/CeO2The preparation of the-Rod catalyst can be divided into three steps of hydrothermal treatment, co-adsorption treatment and reduction heat treatment, wherein the first step is as follows: 4mmol of CeCl3·6H2O is completely dissolved in 40ml of deionized water solution, and 100mmol of sodium hydroxide (NaOH) is weighed and rapidly added into the solution to be vigorously stirred for 10 min. The reaction solution was then transferred to a 50mL stainless steel autoclave containing a polytetrafluoroethylene liner and thermostated at 130 ℃ for 18 h. Naturally cooling to room temperature, centrifugally washing, vacuum drying, and calcining at 300 deg.C for 2h to obtain metal oxide CeO2-Rod; the second step is that: weighing CeO with certain mass according to the ratio of the specific surface area to the volume of the solution2-Rod(1000m2·L-1) In a vial, then [ Ni (NH) was added at a concentration of 1mmol/L at pH 113)6]Cl2And [ Pt (NH)3)4]Cl2Stirring the solution for 1h, and filtering and drying to obtain an intermediate product; in the third step, the product obtained is in H2The atmosphere is heated to 300 ℃ at 10 ℃ for min-1The temperature rising rate is kept constant for 1 hour, the metal Pt is firstly reduced, then the Ni is reduced under the influence of hydrogen overflow and is alloyed with Pt to obtain the target catalyst Ni-Pt/CeO2-rod. The prepared catalyst samples were stored in a glove box filled with Ar atmosphere to minimize oxidation.
Phase/structure characterization of the catalyst obtained in this example:
(1) hydrothermal sample CeO obtained in this example2Rod and target catalyst Ni-Pt/CeO2X-ray diffraction analysis (XRD) of Rod CeO for the hydrothermal sample shown in FIG. 12At peak position 2 θ of 28.5 °, 33.0 °, 47.5 °, 56.3 ° with compound CeO2(JCPDS #43-1002) was well matched, indicating that the metal oxide support CeO in the catalyst2The crystal structure of the fluorite phase is complete. Hydrothermal sample CeO2Compared with Rod, the target catalyst Ni-Pt/CeO is obtained by introducing Ni and Pt through a co-adsorption method and performing reduction heat treatment2Rod, no diffraction peak of any Ni-or Pt-containing phase is observed in its XRD pattern, which may be attributed to the catalyst prepared by this method forming fine-grained, highly dispersed Ni-Pt alloy nanoclusters during reduction or existing in amorphous form.
(2) The target catalyst Ni-Pt/CeO obtained in this example2High resolution electron micrographs of Rod are shown in FIG. 2a and FIG. 2b, and it can be seen from FIG. 2a that nanorods with narrow diameter distribution of about 5 + -2 nm and uniform length distribution of 100-500 nm are successfully prepared. As shown in FIG. 2b, the lattice spacing of 0.270nm for the lattice fringes can be matched to CeO2The {200} crystal face of the catalyst prepared by the method is shown to selectively expose the {200} crystal face. It is noted that no Ni or Pt-containing phase could be observed from the high resolution photographs, which is consistent with XRD results, probably due to the high dispersion of ultra-small Ni-Pt alloy nanoparticles in the substrate CeO2Of (2) is provided.
(3) The target catalyst Ni-Pt/CeO obtained in this example2Rod and comparative sample Ni/CeO2Rod and Pt/CeO2H of Rod2The TPR curve is shown in FIG. 3. As can be seen from FIG. 3, for Ni/CeO2The Rod sample, the reduction peak appearing around 270 ℃ is Ni2+Species, similarly, for Pt/CeO2The Rod sample, the reduction peak appearing around 180 ℃ is Pt2+Species, and Ni-Pt/CeO for the target catalyst2Rod sample, Ni2+The reduction peak of (2) appears in the vicinity of 190 ℃ due to Ni flooding phenomenon2+Reduction temperature of species, indicating in catalystThe Pt-Ni atoms of (a) are located close, i.e. a Ni-Pt alloy is present in the sample. By H2TPR confirmed the formation of Ni-Pt alloy while confirming the presence of Ni and Pt elements. Combining XRD and HRTEM results, the following conclusions can be drawn: the Ni-Pt alloy prepared by the method is highly dispersed in the metal oxide CeO exposing the {200} crystal face in the form of nano clusters with extremely small sizes or in the form of non-crystal2And (4) the surface of the nano rod.
The target catalyst Ni-Pt/CeO obtained in this example2-testing of catalytic performances of Rod:
(1) the co-adsorption method is one of the most effective methods for preparing uniform alloy nano-catalysts. The pH value and adsorption time of the solution are the main variables for controlling the loading of the adsorbed metal. Firstly, the metal oxide carrier CeO needs to be determined2The isoelectric point of Rod to identify the type of adsorbed ions and the pH of the solution. FIG. 4 shows 1000m2 L-1The pH value change data of the matrix in the solution, the final pH value platform is isoelectric point, CeO2The isoelectric point of-Rod is 6.4. Here, it should be noted that the ammonia complex of Ni is stable under alkaline conditions, and the pH is adjusted to 11 at the maximum by ammonia water. Therefore, the optimum pH condition was selected to be 11. Subsequently, the adsorption time of the prepared Ni-Pt/CeO was investigated2Influence of Rod-catalyzed hydrazine hydrate decomposition performance. From FIG. 5, it can be found that, as the adsorption time is prolonged, the target catalyst pair N prepared corresponding to the adsorption time is2H4·H2The activity and selectivity of O decomposition are gradually improved. For the sample with shorter adsorption time (5min), [ Ni (NH) due to shorter adsorption time3)6]2+And [ Pt (NH)3)4]2+Incomplete adsorption, resulting in N being the target catalyst pair2H4·H2The O decomposition exhibits Ni-rich kinetic behavior; for samples with longer adsorption time (30min and 60min), the Ni/Pt ratio is optimal due to sufficient adsorption, so that the catalytic performance of the samples is maximized. Catalytically decomposing N at 50 deg.c and 2M NaOH solution2H4·H2The O reaction activity is 1439h-1And the selectivity is 100%.
Example 2
(1) Preparation of the catalyst:
in order to further expose the influence of crystal catalytic hydrazine hydrate decomposition hydrogen production performance in other shapes, the change of the metal oxide CeO is tried2In the shape of (1), preparation of Ni-Pt/CeO2Cube catalyst, the preparation of which is still divided into three steps of hydrothermal-co-adsorption-reductive heat treatment. The first step is as follows: 4.5mmol of Ce (NO)3)3·6H2Dissolving O in 40ml deionized water solution (solution A), weighing 400mmol sodium hydroxide (NaOH) and dissolving in 30ml deionized water solution (solution B), adding solution B dropwise into solution A via constant pressure dropping funnel, and stirring for 30 min. The reaction solution was then transferred to a 100mL stainless steel autoclave containing a polytetrafluoroethylene liner and thermostated at 180 ℃ for 24 h. Naturally cooling to room temperature, and then carrying out centrifugal washing, vacuum drying and calcining at 300 ℃ in air atmosphere for 2h to obtain a metal oxide CeO-Cube; the preparation conditions of the second step and the third step are the same as those of the example 1, and the target catalyst sample Ni-Pt/CeO can be obtained2Cube, the prepared catalyst sample was stored in a glove box filled with Ar atmosphere to minimize oxidation.
Phase and structure characterization of the catalyst:
(1) hydrothermal sample CeO obtained in this example2Cube and target catalyst Ni-Pt/CeO2XRD pattern of-Cube is shown in FIG. 6, and similar to the XRD result in example 1, the hydrothermal sample CeO2Cube and target catalyst Ni-Pt/CeO obtained by introducing Ni and Pt through co-adsorption method and performing reduction heat treatment2The Rod samples, all of which are observed in the XRD pattern only with CeO2(JCPDS #43-1002) well-matched fluorite phase crystal structure metal oxide carrier CeO2While no diffraction peak was observed for any Ni-or Pt-containing phase.
(2) The target catalyst Ni-Pt/CeO obtained in this example2High-resolution electron micrographs of Cube are shown in fig. 7a and 7b, and from fig. 7a, it can be seen that nanocubes with the edge length of 20-50 nm are successfully prepared. As shown in FIG. 7b, the lattice fringes of 0.270nm and the lattice spacing of 0.191nm correspond to CeO2{200} and {220} crystal planes, illustrating the optional use ofThe catalyst prepared by the method selectively exposes the crystal faces of {200} and {220 }. It is noted that from the high resolution photographs, no Ni or Pt containing phases could be observed, which is consistent with XRD results, and the following conclusions can be drawn in connection with example 1: the Ni-Pt alloy prepared by the method is highly dispersed in metal oxide CeO exposing {200} and {220} crystal faces in the form of nano clusters with extremely small sizes or in the form of amorphous metal2The surface of the nanocube.
(3) And (3) testing the performance of the catalyst:
FIG. 8 shows the Ni-Pt/CeO target catalysts obtained in this example2-Cube catalyzed N2H4·H2And (3) a performance diagram of hydrogen production by O decomposition. As can be seen from the figure, Ni-Pt/CeO2The reaction speed of the Cube catalyst in 2M alkali liquor at room temperature needs 170 minutes to completely decompose hydrazine hydrate, and is 170h-1The selectivity is only 60%. Compared with Ni-Pt/CeO2the-Rod catalyst sample has obviously reduced catalytic activity and selectivity, and is due to the fact that different crystal faces of metal oxides are exposed, the electronic structure of the Ni-Pt alloy loaded on the surface is influenced, and therefore decomposition behaviors of hydrazine molecules serving as reactants are influenced to a certain degree.
Example 3
(1) Preparation of the catalyst:
preparation of Ni-Pt/CeO2-Oct (nano-octahedron) catalyst, the preparation of which is still divided into three steps of hydrothermal-co-adsorption-reduction heat treatment. The first step is as follows: 1mmol of Ce (NO)3)3·6H2O was completely dissolved in 20ml of deionized water (solution A), and 0.01mmol of sodium phosphate (Na) was further weighed3PO4) Completely dissolved in 20ml of deionized water solution (solution B), and the solution A is added dropwise into the solution B through a constant pressure dropping funnel and uniformly stirred for 60 min. The reaction solution was then transferred to a 50mL stainless steel autoclave lined with Teflon and thermostated at 170 ℃ for 12 hours. Naturally cooling to room temperature, centrifugally washing, vacuum drying, and calcining at 300 deg.C for 2h to obtain metal oxide CeO2-Oct; the preparation conditions of the second step and the third step are the same as those of the example 1, and the target catalyst sample Ni-Pt/CeO can be obtained2-Oct, prepared catalyst sample storageIn a glove box filled with Ar atmosphere to minimize oxidation.
Phase and structure characterization of the catalyst:
(1) hydrothermal sample CeO obtained in this example2-Oct and target catalyst Ni-Pt/CeO2The XRD pattern of-Oct is shown in FIG. 9, and similar to the XRD results of example 1, the hydrothermal sample CeO2-Oct and target catalyst Ni-Pt/CeO obtained by introducing Ni and Pt through co-adsorption method and performing reduction heat treatment2-Oct samples, all of which were observed in XRD pattern only with CeO2(JCPDS #43-1002) well-matched fluorite phase crystal structure metal oxide carrier CeO2While no diffraction peak was observed for any Ni-or Pt-containing phase.
(2) The target catalyst Ni-Pt/CeO obtained in this example2High-resolution electron micrographs of Oct are shown in FIGS. 10a and 10b, and it can be seen from FIG. 10a that a nanooctahedron with a ridge length of 100-150 nm was successfully prepared. As shown in FIG. 10b, the lattice fringes at 0.270nm and the lattice spacing at 0.312nm correspond to CeO2The {200} and {111} crystal planes of the catalyst prepared by the method are used for selectively exposing the {200} and {111} crystal planes of the catalyst. It is noted that from the high resolution photographs, no Ni or Pt containing phases could be observed, which is consistent with XRD results, and the following conclusions can be drawn in connection with example 1: the method is used for preparing the metal oxide CeO with the Ni-Pt alloy in the form of the nanocluster with extremely small size or the metal oxide CeO which is in the form of amorphous and highly dispersed in the crystal faces of the exposed {200} crystal face and the {111} crystal face2The surface of the nanocube.
(3) And (3) testing the performance of the catalyst:
FIG. 11 shows the Ni-Pt/CeO target catalysts obtained in this example2-Oct catalyzed N2H4·H2And (3) a performance diagram of hydrogen production by O decomposition. As can be seen from the figure, Ni-Pt/CeO2The reaction rate of catalyzing the hydrazine hydrate to completely decompose by the Oct catalyst in 2M alkali liquor at room temperature is 765h-1The selectivity was 64%.
FIG. 15 shows Ni-Pt/CeO target catalysts in examples 1, 2 and 3 of the present invention2-Rod、Ni-Pt/CeO2-Cube、Ni-Pt/CeO2-Oct in the presence of 0.5M hydrazine hydrateAnd para-N in 2.0M sodium hydroxide solution2H4·H2O decomposition kinetics test chart. As shown in FIG. 15, Ni-Pt/CeO2Oct compared to Ni-Pt/CeO of example 12The Rod catalyst sample, the catalytic activity of which is reduced by about one time, but which is comparable to the Ni-Pt/CeO of example 22Compared with the sample of the Cube catalyst, the catalytic activity of the sample of the catalyst is improved by 4.5 times.
The above results are combined to show that different crystal faces have great influence on the hydrogen production performance by hydrazine hydrate decomposition, and the sequence of the performance is as follows: Ni-Pt/CeO2-Rod>Ni-Pt/CeO2-Oct>Ni-Pt/CeO2-Cube。
Example 4
In order to further influence other adsorbed metal precursor salts on the hydrogen production performance by catalyzing the decomposition of hydrazine hydrate, the method tries to change the types of different adsorbed precursor salts to prepare Ni-Ru/CeO2The preparation of the-Rod catalyst is still divided into three steps of hydrothermal treatment, co-adsorption and reduction heat treatment. The first step is the same as in example 1, with CeO being obtained first2-Rod metal oxide; the second step is that: weighing CeO with certain mass according to the ratio of the specific surface area to the volume of the solution2-Rod in a vial, then [ Ni (NH) at PH 11, 1mmol/L is added3)6]Cl2And [ Ru (NH) ]3)4]Cl2Stirring the solution for 1h, and filtering and drying to obtain an intermediate product; in the third step, the product obtained is in H2The atmosphere is heated to 300 ℃ at 10 ℃ for min-1The temperature rising rate is kept constant for 1 hour, the metal Pt is firstly reduced, then the Ni is reduced under the influence of hydrogen overflow and is alloyed with Ru to obtain the target catalyst Ni-Ru/CeO2-rod. The prepared catalyst samples were stored in a glove box filled with Ar atmosphere to minimize oxidation.
Phase and structure characterization of the catalyst:
(1) hydrothermal sample CeO obtained in this example2-Rod and target catalyst Ni-Ru/CeO2The XRD pattern of-Rod is shown in FIG. 12, and similar to the XRD results of example 1, the hydrothermal sample CeO2-Rod and target catalyst Ni-Ru/Ru obtained by introducing Ni and Ru through a co-adsorption method and then performing reduction heat treatmentCeO2The Rod samples, all of which are observed in the XRD pattern only with CeO2(JCPDS #43-1002) fluorite phase crystal structure well matched metal oxide carrier CeO2While no diffraction peak was observed for any Ni-or Ru-containing phase.
(2) The target catalyst Ni-Ru/CeO obtained in the example2High resolution electron micrographs of Rod are shown in FIGS. 13a and 13b, and it can be seen from FIG. 13a that nanorods with narrow diameter distribution of about 5 + -2 nm and uniform length distribution of 100-500 nm are successfully prepared. As shown in FIG. 13b, the lattice fringes at 0.270nm and the lattice spacing at 0.312nm correspond to CeO2The {200} and {111} crystal planes of the catalyst prepared by the method are used for selectively exposing the {200} and {111} crystal planes of the catalyst. It is noted that any Ni or Pt-containing phase is not observed from the high-resolution photograph, and this result is consistent with the XRD result, and the following conclusion can be drawn in conjunction with this example 1: the Ni-Ru alloy prepared by the method is highly dispersed in the form of nanoclusters with extremely small size or amorphous metal oxide CeO exposing {200} and {111} crystal faces2And (4) the surface of the nano rod.
(3) And (3) testing the performance of the catalyst:
FIG. 14 shows the target catalysts Ni-Ru/CeO obtained in this example2-Rod catalytic N2H4·H2And (3) a performance diagram of hydrogen production by O decomposition. As can be seen from the figure, Ni-Ru/CeO2The reaction rate of catalyzing the hydrazine hydrate to completely decompose in 2M alkali liquor at room temperature by the aid of-Rod catalyst is 510h-1The selectivity was 15%.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.
Claims (8)
1. A preparation method of a crystal face-regulated supported nano alloy catalyst for catalyzing hydrazine hydrate to decompose and prepare hydrogen is characterized by comprising the following steps:
(1) dissolving a precursor salt of a metal oxide carrier in deionized water, adding a precipitator to obtain a mixed solution, carrying out stirring reaction for 0-2 h, then carrying out hydrothermal reaction at 100-200 ℃, carrying out centrifugal drying to obtain a metal oxide precursor, and calcining the metal oxide precursor at 200-500 ℃ for 1-5 h in an air atmosphere to obtain the metal oxide carrier; the precursor salt of the metal oxide carrier in the step (1) is at least one of nitrate, sulfate and acetate of one metal of La and Ce; one or two crystal faces of (111), (200) and (220) are selectively exposed on the metal oxide carrier;
(2) adjusting the pH value of the solution of the bimetallic precursor salt, adsorbing bimetallic precursor ions on the surface of the metal oxide carrier in the step (1) by a co-adsorption method, and performing suction filtration and drying; determining the pH value of the bimetal precursor salt solution in the step (2) according to the isoelectric point of the metal oxide carrier in the step (1); in the step (2), one metal salt in the bimetallic precursor salt is at least one of nitrate, sulfate and acetate of one transition metal of Fe, Co, Ni and Cu, and the other metal salt is at least one of chlorate and nitrate of one precious metal of Pt, Ir, Pd, Ru and Rh;
(3) and (3) carrying out heat treatment reaction on the product in the step (2) at the temperature of 300-600 ℃ in a reducing atmosphere, and sequentially reducing and alloying the active metals to obtain the supported nano alloy catalyst.
2. The method according to claim 1, wherein the precipitating agent in step (1) is selected from one of dimethyl oxalate, urea, sodium hydroxide, tetramethylammonium hydroxide, and sodium phosphate; the concentration of the precipitator in the mixed solution is 50-3000 mM; the hydrothermal reaction in the step (1) is carried out in a stainless steel autoclave with a polytetrafluoroethylene lining, and the time of the hydrothermal reaction is 8-30 h.
3. The preparation method according to claim 1, wherein the amount of the bimetallic precursor salt solution used in step (2) is determined according to the specific surface area and mass of the metal oxide support,conversion factor of 1000m2 L-1(ii) a The adsorption temperature was 25 ℃ at room temperature.
4. The method according to claim 1, wherein the concentration of the metal oxide support precursor salt in the mixed solution of step (1) is 1 to 100 mM; the temperature of the stirring reaction is 25-100 ℃; stirring and reacting for 0-1 h; the concentration of the bimetal precursor salt in the step (2) is 0.1-5 mM; the reducing atmosphere in the step (3) is hydrogen atmosphere; the time of the heat treatment is 1-2 h.
5. The supported nano alloy catalyst for regulating the crystal face for catalyzing the hydrogen production by decomposing hydrazine hydrate, which is prepared by the preparation method according to any one of claims 1 to 4, is characterized by comprising a metal alloy active phase and a metal oxide carrier phase, wherein the metal alloy active phase is dispersed and distributed on the surface of the metal oxide carrier phase in a nano particle form, and one to two crystal faces of (111), (200) and (220) are selectively exposed out of the metal oxide carrier phase;
the metal oxide carrier phase is one of La and Ce, and the metal alloy active phase is obtained by alloying one of transition metals Fe, Co, Ni and Cu with one of noble metals Pt, Ir, Ru, Rh and Pd.
6. The crystal plane-regulated supported nano alloy catalyst of claim 5, wherein the metal alloy active phase is any one of binary alloys of Ni-Pt, Ni-Ir, Ni-Ru, Ni-Rh, Ni-Pd, Co-Pt, Co-Ir, Co-Ru, Co-Rh and Co-Pd.
7. The crystal face-regulated supported nano alloy catalyst according to claim 5, wherein the particle size of the metal alloy active phase is 1-2 nm.
8. The use of the supported nano-alloy catalyst with a controlled crystal face as defined in claim 5 in the catalysis of hydrazine hydrate decomposition for hydrogen production.
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