Alloy catalyst for catalyzing synthesis gas to directly prepare ethanol and preparation method of alloy catalyst
By preparing Rh-M alloy catalysts and controlling the size and morphology of metal clusters, the activity and selectivity problems of Rh-based catalysts in the direct ethanol production of synthesis gas are solved, and efficient ethanol production and catalyst stability are achieved.
Patent Information
- Application Number
- CN202410031547.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-01-09
- Publication Date
- 2025-07-11
AI Technical Summary
During the process of direct ethanol production of synthesis gas, the catalytic activity and ethanol selectivity of existing Rh-based catalysts need to be improved, and they are prone to carbon accumulation, making it impossible to form an efficient alloy structure, resulting in limited performance improvement.
Rh-M alloy catalyst is prepared by mixing rhodium salt and M metal salt solution through aging, drying and calcining steps, controlling the size and morphology of metal clusters, optimizing the catalyst performance, and forming an efficient alloy cluster structure.
High CO conversion, low methane selectivity, low C2+ hydrocarbon selectivity and high ethanol selectivity are achieved, good catalyst stability, significantly improved ethanol yield and long service life.
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Figure CN120286020A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of catalyst synthesis, and particularly relates to an alloy catalyst for directly synthesizing ethanol from syngas and a preparation method thereof. Background Art
[0002] The direct synthesis of ethanol from syngas (DES) is a reaction that directly prepares ethanol from syngas (CO + H2) converted from coal, biomass, and natural gas in one step, and is also an important way to alleviate the shortage of petroleum resources and meet the rapidly increasing energy demand currently.
[0003] The catalysts for directly synthesizing ethanol from syngas mainly include Rh-based, molybdenum-based (Mo), modified Fischer-Tropsch catalysts (Co), modified methanol catalysts (Cu), and multifunctional catalysts. Among them, compared with the other four catalysts, the rhodium-based (Rh) catalyst has attracted much attention because of its high catalytic activity, high ethanol selectivity, and difficulty in carbon deposition during the reaction process. Since Basin et al. reported the Rh / SiO2 catalyst for hydrogenation of CO to ethanol, the Rh-based catalyst has been widely studied in the DES reaction. The Rh-based catalyst is considered to be one of the most promising catalysts for synthesizing C2 oxygenates (such as ethanol and acetic acid) from syngas. The Rh content, carrier, promoter, and preparation method have a great influence on the structure of the Rh-based catalyst, and it is particularly important to promote the formation of ethanol and inhibit the selectivity of hydrocarbons during the DES reaction.
[0004] In view of this, the present invention is specifically proposed. Summary of the Invention
[0005] The purpose of the present invention is to provide an alloy catalyst for directly synthesizing ethanol from syngas and a preparation method thereof to solve the above problems.
[0006] To achieve the above purpose, the present invention specifically adopts the following technical solutions:
[0007] The present invention provides a preparation method of an alloy catalyst for directly synthesizing ethanol from syngas, comprising the following steps:
[0008] S1: Mix a rhodium salt solution and an M metal salt solution evenly in a solvent to obtain a mixed solution;
[0009] The rhodium salt solution includes a rhodium nitrate solution and / or a rhodium chloride solution; preferably, the mass concentration of the rhodium salt solution is 0.01% - 10%;
[0010] The M metal includes any one or more of Fe, Co, Ni, Mn, and Ce; preferably, the M metal salt is any one or more of cobalt nitrate hexahydrate, cobalt acetate, nickel nitrate, nickel acetate, iron nitrate, iron acetate, manganese nitrate, manganese acetate, cerium nitrate, and cerium acetate; the doping of the M metal directly affects the size of the metal clusters, and thus affects the performance of the alloy catalyst. In the present invention, by optimizing the M metal source and controlling the raw materials, the size of the metal clusters is controlled, and the performance of the alloy catalyst is adjusted, especially the CO conversion rate and ethanol selectivity are optimized;
[0011] The solvent includes any one of absolute ethanol, deionized water, and methanol; the selection of the solvent also has an important impact on the performance of the alloy catalyst;
[0012] Preferably, the mass percentages of rhodium and the M metal in the rhodium salt solution and the M metal salt solution are 0.01%-10%: 0.01%-10%.
[0013] S2: Add a carrier to the mixed solution obtained in S1 and stir evenly to obtain a paste containing the alloy;
[0014] The carrier includes any one of nano-titanium dioxide, lanthanum oxide, cerium dioxide with different crystal phases, rutile, anatase, chromium oxide, zinc oxide, magnesium oxide, silicon dioxide, aluminum oxide with different crystal phases, vanadium pentoxide, and arsenic oxide;
[0015] S3: Subject the paste obtained in S2 to aging, heating and drying, cooling, and calcination in sequence to obtain the alloy catalyst.
[0016] The aging is carried out at room temperature for 0-24 h;
[0017] The temperature for heating and drying is 60-120°C, and the time is 6-24 h; preferably, the heating and drying conditions are any one of drying under vacuum conditions or drying in air; the drying conditions affect the interaction between the metal clusters and the carrier, and vacuum drying is more conducive to improving the comprehensive performance of the alloy catalyst.
[0018] The target temperature for cooling is 20-35°C;
[0019] The temperature for calcination is 350-550°C, and the time is 4-6 h; preferably, the calcination includes: heating at a rate of 1-1.5°C / min in an air atmosphere and calcining at 350-550°C for 4-6 h.
[0020] The method of the present invention fully mixes a rhodium source and an M metal source to obtain a uniformly mixed liquid in a solvent, which is an essential step for preparing an alloy catalyst. An active component-rhodium-based bimetallic paste is obtained by the incipient wetness impregnation method, that is, an Rh-M alloy cluster with a special morphology is synthesized by the impregnation method. Then, this paste is aged to fully load the active centers on the carrier, so that the active components are fully dispersed, and then dried and calcined to turn the metal salt into a metal oxide. By modulating the type of M metal, a rhodium-based bimetallic alloy cluster catalyst with a special morphological structure is obtained, and thus high active sites are obtained.
[0021] Conventional techniques usually adopt the method of first preparing a rhodium-based catalyst and then compounding other metals. Although a bimetallic catalyst can also be prepared, the simple superposition and compounding of two metals cannot form a brand-new alloy structure. In terms of performance, only the technical effect of 1 + 1 = 2 or even less than 2 of the bimetallic is achieved, and the effect of 1 + 1 > 2 brought by the alloy structure of the present invention cannot be realized. In the solution of the present invention, the aging time, solvent selection, drying conditions, and roasting time and temperature will all affect the performance of the alloy catalyst. Under the preferred conditions of the present invention, it is more conducive to the formation of alloy clusters, and the comprehensive performance of the catalyst is better.
[0022] The present invention also provides an alloy catalyst for catalytically synthesizing ethanol directly from syngas prepared by the above-mentioned preparation method. The alloy catalyst includes an active component and a carrier;
[0023] Wherein, the active component is loaded on the carrier in the form of an Rh-M alloy cluster structure.
[0024] Preferably, the diameter of the Rh-M alloy cluster is 0.5 - 1.5 nm.
[0025] Preferably, by mass percentage, the composition of the alloy catalyst includes 0.01% - 10% of rhodium, 0.01% - 10% of M metal, and the balance of the carrier.
[0026] Further preferably, the specific surface area of the alloy catalyst is 52.7 - 60.0 m 2 / g;
[0027] Preferably, the average pore diameter of the alloy catalyst is 15.2 - 16.8 nm;
[0028] Preferably, the pore volume of the alloy catalyst is 0.216 - 0.239 mL / g.
[0029] Further preferably, when the catalyst is applied to the direct synthesis of ethanol from syngas, the reducing atmosphere can be any one of pure H2, a mixture of 5-10% H2 and 90-95% N2, pure CO, a mixture of 5-10% CO and 90-95% N2, syngas with a H2 to CO ratio of 1-3:1, and a mixture of 5-10% syngas and 90-95% N2, and the reduction time is 2-12 h.
[0030] The catalyst provided by the present invention has an alloy cluster structure and is composed of an active component and a carrier. Usually, the particle size is 0.1-5 nm, and the catalyst has an alloy cluster structure with a size of 0.5-1.5 nm. The size of the alloy cluster structure does not have a simple linear relationship with the performance of the catalyst. It is not that the larger the better. Both too small or too large cluster structures are not conducive to the improvement of the comprehensive performance of the catalyst. Through experimental verification, the alloy cluster with a size of 0.5-1.5 nm preferably selected in the present invention makes the comprehensive performance of the catalyst better.
[0031] Advantages of the present invention:
[0032] The preparation method of the alloy catalyst provided by the present invention enables the size of the alloy clusters of the catalyst to be adjustable, which is beneficial to the selective control of direct ethanol synthesis. First, by varying the M metal, the size of the metal clusters is adjusted; secondly, by controlling the calcination temperature and time, the size of the metal clusters is further regulated; finally, the size of the metal clusters is controlled by the ratio of the reducing atmosphere (H2, CO or syngas) and the reduction time.
[0033] By creatively preparing an alloy cluster structure catalyst, the present invention realizes that when the Rh-M alloy catalyst is used for the direct synthesis of ethanol from syngas, the methane selectivity can be as low as 5.9%, the C 2+ hydrocarbon selectivity is as low as 1.5%, the CO conversion rate is as high as 63.7%, the ethanol selectivity is 48.2%, and the ethanol yield is 30.7%. Moreover, the catalyst has good stability and a long service life, and the ethanol yield (11.6%) is 19.1% higher than that of the best catalyst for the synthesis of ethanol from syngas reported in the current literature. Description of the Drawings
[0034] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.
[0035] Figure 1 TEM image of the Rh-Co alloy catalyst prepared in Example 1;
[0036] Figure 2 HADDF-STEM image of the Rh-Co alloy catalyst provided for Example 1;
[0037] Figure 3 STEM-EDS elemental mapping of the Rh-Co alloy catalyst provided for Example 1; Figure 3 Element Rh is at the upper left, Figure 3 Element O is at the upper right, Figure 3 Element Ti is at the lower left, Figure 3 Element Co is at the lower right;
[0038] Figure 4 EDX line analysis spectrum of the Rh-Co alloy catalyst provided for Example 1;
[0039] Figure 5 EDS spectrum of the Rh-Co alloy catalyst provided for Example 1;
[0040] Figure 6 Rh K-edge XANES spectrum of the Rh-Co alloy catalyst prepared in Example 1;
[0041] Figure 7 Rh K-edge EXAFS spectrum in the R space of the Rh-Co alloy catalyst provided for Example 1;
[0042] Figure 8 k of the catalyst provided in Example 1 3 Morlet wavelet transform plot of the weighted EXAFS signal;
[0043] Figure 9 k of the metal Rh standard sample 3 Morlet wavelet transform plot of the weighted EXAFS signal;
[0044] Figure 10 k of the catalyst provided for Comparative Example 1 3 Morlet wavelet transform plot of the weighted EXAFS signal;
[0045] Figure 11 k of the rhodium(III) oxide standard sample 3 Morlet wavelet transform plot of the weighted EXAFS signal. Detailed implementation manners
[0046] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.
[0047] Example 1
[0048] Prepare an alloy catalyst according to the preparation method provided by the present invention. The specific steps are as follows:
[0049] Dissolve 0.211 g of Co(NO3)2·6H2O and 0.518 g of Rh(NO3)3 in 8 mL of absolute ethanol, stir evenly until completely dissolved to obtain a particulate-free mixed solution, then slowly add 5.0 g of nano-titanium dioxide support to the obtained mixed solution, stir at room temperature for 30 min until it becomes viscous, and age at room temperature for 24 hours. Then transfer it to an oven, dry at 120 °C for 12 hours, and then cool to room temperature. Calcinate in an air atmosphere at 350 °C for 4 hours to obtain the Rh-Co alloy catalyst.
[0050] Characterize the Rh-Co alloy catalyst prepared in this example, specifically:
[0051] Figure 1 is the TEM image of the Rh-Co alloy catalyst prepared in this example, showing the morphology of the Rh-Co alloy clusters; Figure 2 is the HADDF-STEM image of the Rh-Co alloy catalyst. It can be seen from Figure 2 that the morphology of the Rh-Co alloy clusters and the state where the active component Rh-Co alloy clusters are highly dispersed on the support; Figure 3 is the STEM-EDS elemental mapping of the Rh-Co alloy catalyst, where Figure 3 the upper left is the element Rh, Figure 3 the upper right is the element O, Figure 3 the lower left is the element Ti, Figure 3 the lower right is the element Co; Figure 4 is the EDX line analysis spectrum of the Rh-Co alloy catalyst, which again proves that the catalyst prepared in this example forms Rh-Co alloy clusters; Figure 5 is the EDS spectrum of the Rh-Co alloy catalyst, which shows the existence of Rh-Co through the EDS spectrum. It can be seen from Figures 1-5 that in this example, an Rh-Co alloy catalyst supported by titanium dioxide is successfully prepared, and it has a special alloy cluster structure.
[0052] Figure 6 The Rh K-edge XANES spectrum of the Rh-Co alloy catalyst prepared in this example shows that Figure 6 the valence state of the Rh species in the Rh-Co alloy cluster is between that of a metal and an oxide; Figure 7 The Rh K-edge EXAFS spectrum of the Rh-Co alloy catalyst in the R space shows that Figure 7 the presence of the Rh-Co bond indicates that the catalyst forms an Rh-Co alloy cluster; Figure 8 This is the Morlet wavelet transform diagram of the k 3 weighted EXAFS signal of the catalyst in this example, Figure 9 This is the Morlet wavelet transform diagram of the k 3 weighted EXAFS signal of the Rh metal standard sample. By Figure 8 comparing with Figure 9 it can be seen that the catalyst in this example forms an alloy cluster structure.
[0053] Combined with the attached figures, it can be seen from the electron microscope images and synchrotron radiation images that the Rh-Co particles form an alloy cluster structure.
[0054] Example 2
[0055] Dissolve 0.159 g of Ni(NO3)2·6H2O and 0.521 g of Rh(NO3)3 in 8 mL of absolute ethanol, stir evenly until completely dissolved to obtain a particulate-free mixed solution, then slowly add 5.0 g of nano-titanium dioxide support to the obtained mixed solution, stir at room temperature for 30 min until it becomes viscous, age at room temperature for 24 hours, then transfer to an oven, dry at 120 °C for 12 hours, and then cool to room temperature. Calcinate in an air atmosphere at 350 °C for 4 hours to obtain the Rh-Ni alloy catalyst.
[0056] Example 3
[0057] The difference from Example 1 is that deionized water is used instead of absolute ethanol as the solvent for the mixed solution.
[0058] Comparative Example 1
[0059] Dissolve 0.513 g of rhodium nitrate in absolute ethanol, stir evenly until the solution is particulate-free, then slowly add 5.0 g of TiO2 support. Stir at room temperature for 30 min until it becomes viscous, age at room temperature for 24 hours, then transfer to an oven, dry at 120 °C for 12 hours. Cool to room temperature and calcinate in air at 350 °C for 4 hours to obtain the Rh-based catalyst.
[0060] Figure 10 This is the k 3Morlet wavelet transform diagram of weighted EXAFS signal Figure 11 is the k of the rhodium sesquioxide standard sample 3 Morlet wavelet transform diagram of weighted EXAFS signal, by Figure 10 and Figure 11 it can be seen that the catalyst of Comparative Example 1 formed Rh clusters and did not form alloy clusters.
[0061] Comparative Example 2
[0062] Dissolve 0.315 g of Rh(NO3)3·2H2O and 0.36 g of Fe(NO3)3·9H2O in 7.5 mL of deionized water. After proper stirring, add 5 g of TiO2 dropwise until initially moistened to prepare a 2 wt% Rh-1 wt% Fe / TiO2 catalyst. The paste was dried overnight in air at 413 K and then calcined in air at 723 K for 4 hours.
[0063] Comparative Example 3
[0064] A mixed aqueous solution of Rh(NO3)3 hydrate and Cu(NO3)2·3H2O was co-impregnated on 5.0 g of TiO2, and a paste was formed after sufficient stirring. The paste was aged at room temperature for 24 h, dried overnight at 80 °C, and calcined in air at 350 °C for 4 h (heating rate 1 °C / min). That is, a 1% Rh-1% Cu / TiO2 catalyst was obtained.
[0065] The textural properties of the catalysts prepared in Examples 1-3 and Comparative Examples 1-3 are shown in Table 1 below:
[0066] Table 1 Textural property parameter table of the catalysts prepared in Examples 1-3
[0067]
[0068] The catalysts prepared in Examples 1-3 and Comparative Examples 1-3 were applied to the direct synthesis of ethanol from syngas and relevant analyses were carried out. The application conditions were: for a fixed-bed reactor for the direct synthesis of ethanol from syngas, and the reduction conditions were: pure hydrogen atmosphere, 300-500 °C, 0.5-5 MPa, and the volume space velocity was 1000-20000 mL·h -1 ·g -1 , and reduced for 2-10 hours. The performance parameters are shown in Table 2 below:
[0069] Table 2 Catalytic performance parameter table of the catalysts in Examples and Comparative Examples for the direct synthesis of ethanol from syngas
[0070]
[0071]
[0072] As can be seen from Table 2, the alloy catalyst prepared by the preparation method provided by the present invention has overall better catalytic performance for the reaction of directly synthesizing ethanol from syngas, and the CO conversion rate, ethanol selectivity and ethanol yield are all significantly higher than those of the comparative example.
[0073] The influence of the solvent on the catalytic performance of the alloy catalyst for the direct synthesis of ethanol from syngas is investigated as described in Table 3 below:
[0074] Table 3 Performance parameter table of the alloy catalyst prepared with different solvents for the direct synthesis of ethanol from syngas
[0075]
[0076] The difference between the preparation processes of Example 1 and Example 3 lies only in the different solvents for dissolving the metal source. As can be seen from Table 3, in the method provided by the present invention, compared with water as the solvent, the alloy catalyst prepared by selecting ethanol as the solvent has better catalytic performance.
[0077] Please note that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification. The above embodiments only represent several implementation manners of the present application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be pointed out that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the appended claims.
Claims
1. A preparation method of an alloy catalyst for directly synthesizing ethanol from syngas, characterized in that, It includes the following steps: S1: Mix a rhodium salt solution and an M metal salt solution evenly in a solvent to obtain a mixed solution; S2: Add a carrier to the mixed solution obtained in S1 and stir evenly to obtain a paste containing an alloy; S3: Subject the paste obtained in S2 to aging, heating and drying, cooling, and calcination in sequence to obtain the alloy catalyst.
2. The preparation method according to claim 1, wherein, Step S1 satisfies one or more of the following conditions: a. The rhodium salt solution includes a rhodium nitrate solution and / or a rhodium chloride solution; b. The M metal includes any one or more of Fe, Co, Ni, Mn, and Ce; c. The solvent includes any one of absolute ethanol, deionized water, and methanol.
3. The preparation method according to claim 1 or 2, characterized in that, Step S1 also satisfies one or more of the following conditions: d. The mass concentration of the rhodium salt solution is 0.01%-10%; e. The M metal salt is any one or more of cobalt nitrate hexahydrate, cobalt acetate, nickel nitrate, nickel acetate, iron nitrate, iron acetate, manganese nitrate, manganese acetate, cerium nitrate, and cerium acetate.
4. The preparation method according to claim 1, characterized in that, The carrier includes any one of nano-titanium dioxide, lanthanum oxide, cerium dioxide with different crystal phases, rutile, anatase, chromium oxide, zinc oxide, magnesium oxide, silicon dioxide, aluminum oxide with different crystal phases, vanadium pentoxide, and arsenic oxide.
5. The preparation method according to claim 1, wherein Step S3 satisfies one or more of the following conditions: f. The aging is carried out at room temperature for 0-24 h; g. The temperature for heating and drying is 60-120 °C, and the time is 6-24 h; h. The target temperature for cooling is 20-35 °C; i. The temperature for calcination is 350-550 °C, and the time is 4-6 h.
6. The preparation method according to claim 5, characterized in that, The condition for heating and drying is either drying under vacuum conditions or drying in air.
7. The preparation method according to claim 1 or 5, characterized in that, The calcination includes: heating at a rate of 1-1.5 °C / min in an air atmosphere and calcining at 350-550 °C for 4-6 h.
8. An alloy catalyst for directly synthesizing ethanol from syngas prepared by the preparation method according to any one of claims 1-7, characterized in that, The alloy catalyst includes an active component and a carrier; wherein, the active component is loaded on the carrier in the form of a Rh-M alloy cluster structure.
9. The alloy catalyst according to claim 8, wherein, By mass percentage, the composition of the alloy catalyst includes 0.01%-10% of rhodium, 0.01%-10% of the M metal, and the balance of the carrier.
10. The alloy catalyst according to claim 8 or 9, characterized in that, The specific surface area of the alloy catalyst is 52.7 - 60.0 m 2 / g; Preferably, the average pore diameter of the alloy catalyst is 15.2-16.8 nm; Preferably, the pore volume of the alloy catalyst is 0.216-0.239 mL / g.