Rh / MnO nanocatalyst, preparation method and application thereof

Abstract

This invention provides a Rh / MnO nanocatalyst, its preparation method, and its application, comprising the following steps: A) adding a manganese source solution dropwise to a ligand solution to obtain a mixed solution; the ligand solution includes a complexing agent and a polyol; B) drying and calcining the mixed solution to obtain manganese oxide; C) mixing the manganese oxide and a rhodium source in water to obtain a mixed slurry; the mass ratio of the manganese oxide to the rhodium source is (75~150):(1~10); D) drying and calcining the mixed slurry to obtain a precursor; E) reducing the precursor in a reducing atmosphere to obtain the Rh / MnO nanocatalyst. The nanocatalyst of this invention exhibits high conversion rate and high selectivity in the direct synthesis of multi-carbon oxygen-containing compounds from syngas. The multi-carbon oxygen-containing compounds produced by the Rh / MnO catalyst provided by this invention contain a high proportion of ethanol and acetaldehyde, achieving the co-production of ethanol and acetaldehyde.

Description

Technical Field

[0001] This invention belongs to the field of chemical catalysis technology, and particularly relates to a Rh / MnO nanocatalyst, its preparation method and application. Background Technology

[0002] Syngas is a mixture of carbon monoxide (CO) and hydrogen (H2) in a certain proportion, and is an important platform chemical in coal chemical and petrochemical industries. Syngas can be converted into various high-value-added products through catalytic processes. Multi-carbon oxygenated compounds are organic compounds containing two or more carbon atoms and at least one oxygen atom, including ethanol, acetaldehyde, acetic acid, propanol, and butanol. They can serve not only as clean fuels but also as important chemical raw materials. Therefore, the direct production of multi-carbon oxygenated compounds (C2O2) from syngas is a promising technology. 2+ The syngas-to-oxygenated gas (S-Oxy) reaction is a promising chemical production route that has attracted widespread attention in recent years. This reaction is a typical exothermic reaction with a variety of byproducts, including methane, methanol, multi-carbon hydrocarbons, and CO2. Rh-based catalysts for the direct production of multi-carbon oxygenated compounds from syngas exhibit relatively high selectivity, but they face challenges such as uneven dispersion of Rh nanoparticles, low atom utilization, and limited selectivity control. Therefore, controlling catalyst selectivity is a key research focus in this field. Summary of the Invention

[0003] The purpose of this invention is to provide a Rh / MnO nanocatalyst, its preparation method and application. The Rh / MnO nanocatalyst of this invention has both high conversion rate and high selectivity as a catalyst for the direct production of multi-carbon oxygen-containing compounds from syngas.

[0004] This invention provides a method for preparing Rh / MnO nanocatalysts, comprising the following steps:

[0005] A) The manganese source solution is added dropwise to the ligand solution to obtain a mixed solution;

[0006] The ligand solution comprises a complexing agent and a polyol;

[0007] B) The mixed solution was dried and calcined to obtain manganese oxide;

[0008] C) Manganese oxide and rhodium source are mixed in water to obtain a mixed slurry;

[0009] The mass ratio of the rhodium source to the manganese oxide is (1~10):(75~150);

[0010] D) The mixed slurry is dried and calcined to obtain the precursor;

[0011] E) The precursor was reduced in a reducing atmosphere to obtain Rh / MnO nanocatalyst;

[0012] The reducing atmosphere comprises a mixture of CO2, H2, and Ar.

[0013] Preferably, the manganese source solution comprises a manganese source and an aqueous solvent;

[0014] The manganese source includes one or more of manganese nitrate, manganese chloride, manganese sulfate, and their hydrates; the aqueous solvent includes water and / or ethanol; the mass ratio of the manganese source to the aqueous solvent is (0.7~1.5):(0.4~20).

[0015] The dropping rate of the manganese source solution is 0.1~2 mL / min;

[0016] The complexing agent includes one or more of citric acid, tartaric acid, and malic acid; the polyol includes one or more of ethylene glycol, 1,2-propanediol, and glycerol.

[0017] The mass ratio of the manganese source, complexing agent, and polyol is (0.3~1.5):(0.5~1.0):(0.03~0.1).

[0018] Preferably, the drying in step B) is divided into two stages: the drying temperature in the first stage is 50~100℃ and the drying time is 8~15 hours; the drying temperature in the second stage is 100~150℃ and the drying time is 2~12 hours.

[0019] Preferably, the calcination temperature in step B) is 300~500℃, the calcination time is 8~15 hours, and the calcination heating rate is 2~10℃ / min.

[0020] Preferably, the rhodium source includes one or more of rhodium chloride, rhodium nitrate, and their hydrates.

[0021] Preferably, in step D), the drying temperature is 50~150℃ and the drying time is 6~24 hours.

[0022] Preferably, in step D), the calcination temperature is 400~600℃, the calcination time is 2~8 hours, and the calcination heating rate is 2~10℃ / min.

[0023] Preferably, in step E), the reduction temperature is 250~600℃, the reduction time is 1~5 hours, and the reduction heating rate is 2~10℃ / min.

[0024] This invention provides a Rh / MnO nanocatalyst, which is prepared according to the preparation method described above;

[0025] The Rh / MnO nanocatalyst includes an MnO oxide support.

[0026] Rh nanoparticles loaded on the surface of the MnO oxide support and partially coated thereon;

[0027] The mass ratio of Rh atoms to MnO support in the Rh / MnO nanocatalyst is (0.5~5): (75~150).

[0028] This invention provides the application of the Rh / MnO nanocatalyst as described above in the catalytic preparation of multi-carbon oxygen-containing compounds from syngas.

[0029] This invention provides a method for preparing Rh / MnO nanocatalysts, comprising the following steps: A) adding a manganese source solution dropwise to a ligand solution to obtain a mixed solution; the ligand solution includes a complexing agent and a polyol; B) drying and calcining the mixed solution to obtain manganese oxide; C) mixing the manganese oxide and a rhodium source in water to obtain a mixed slurry; the mass ratio of the manganese oxide to the rhodium source is (75~150):(1~10); D) drying and calcining the mixed slurry to obtain a precursor; E) reducing the precursor in a reducing atmosphere to obtain the Rh / MnO nanocatalyst. The Rh active sites in the Rh / MnO catalyst obtained by the stepwise synthesis method provided in this application are exposed on the support surface, ensuring maximum atom utilization. In the preparation method provided in this application, Mn2O3 in the synthetic precursor is reduced to MnO during the reduction process, and the Rh source is reduced to Rh metal nanoparticles with a truncated octahedral morphology. This application utilizes the process of Mn2O3 being reduced to MnO to induce the formation of a special strong metal-support interaction in the catalyst, resulting in non-stoichiometric MnO formation on the MnO surface. x The species partially coats the Rh nanoparticles, improving their dispersion and uniformity, and also modifies their surface. The preparation method provided by this invention controls the phase composition of the precursor and the reducing atmosphere to regulate the local structure of the Rh nanoparticles in the Rh / MnO catalyst, thereby enabling the nanocatalyst to exhibit high conversion and selectivity in the direct synthesis of multi-carbon oxygen-containing compounds from syngas. The multi-carbon oxygen-containing compounds produced by the Rh / MnO catalyst provided by this invention contain a high proportion of ethanol and acetaldehyde, achieving the co-production of ethanol and acetaldehyde. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0031] Figure 1The X-ray diffraction pattern of the Rh / MnO nanoparticle catalyst obtained in Example 1 of this invention is shown below.

[0032] Figure 2 This is a transmission electron microscopy image of the Rh / MnO nanoparticle catalyst obtained in Example 1 of the present invention;

[0033] Figure 3 This is a high-resolution transmission electron microscopy image of the Rh / MnO nanoparticle catalyst obtained in Example 1 of this invention;

[0034] Figure 4 The images show high-angle annular dark-field scanning transmission electron microscopy images of the Rh nanoparticle catalyst supported on MnO obtained in Example 1 of this invention, and the electron energy loss spectra at the corresponding positions.

[0035] Figure 5 The conversion rate and selectivity of Rh / MnO nanoparticle catalysts obtained in Examples 1, 2 and 3 of this invention for the direct production of multi-carbon oxygen-containing compounds from syngas;

[0036] Figure 6 The conversion rate and selectivity of Rh / MnO nanoparticle catalysts obtained in Examples 2, 4 and 5 of this invention for the direct production of multi-carbon oxygen-containing compounds from syngas;

[0037] Figure 7 This invention relates to the conversion rate and selectivity of Rh / MnO nanoparticle catalysts obtained in Examples 2 and Comparative Examples 1-4 for the direct production of multi-carbon oxygen-containing compounds from syngas. Detailed Implementation

[0038] This invention provides a method for preparing Rh / MnO nanocatalysts, comprising the following steps:

[0039] A) The manganese source solution is added dropwise to the ligand solution to obtain a mixed solution;

[0040] The ligand solution comprises a complexing agent and a polyol;

[0041] B) The mixed solution was dried and calcined to obtain manganese oxide;

[0042] C) Manganese oxide and rhodium source are mixed in water to obtain a mixed slurry;

[0043] The mass ratio of the manganese oxide to the rhodium source is (75~150):(1~10);

[0044] D) The mixed slurry is dried and calcined to obtain the precursor;

[0045] E) The precursor was reduced in a reducing atmosphere to obtain Rh / MnO nanocatalyst.

[0046] In this invention, it is preferred to first prepare a manganese source solution and a ligand solution, and then add the manganese source solution dropwise to the ligand solution to obtain a mixed solution.

[0047] This invention mixes a manganese source and an aqueous solvent and stirs to obtain a manganese source solution; this invention also mixes a complexing agent, a polyol, and an aqueous solvent and stirs to obtain a ligand solution.

[0048] In this invention, the manganese source is preferably one or more of manganese nitrate, manganese chloride, manganese sulfate and their hydrates, such as manganese nitrate, manganese nitrate hydrate, manganese chloride, manganese chloride hydrate, manganese sulfate and manganese sulfate hydrate; the aqueous solvent preferably includes water and / or ethanol; the mass ratio of the manganese source to the aqueous solvent is preferably (0.7~1.5):(0.4~20), more preferably (0.8~1.2):(0.5~1.0).

[0049] In this invention, the complexing agent is preferably one or more of citric acid, tartaric acid, and malic acid; the polyol includes one or more of ethylene glycol, 1,2-propanediol, and glycerol; the aqueous solvent preferably includes water and / or ethanol; the mass ratio of the complexing agent, polyol, and aqueous solvent is preferably (0.5~1.0):(0.03~0.10):(1~5), more preferably (0.5~1.0):(0.04~0.07):(1.5~3).

[0050] In this invention, the mass ratio of the manganese source, complexing agent, and polyol is (0.3~1.5):(0.5~1.0):(0.03~0.1), more preferably (0.5~1.2):(0.6~0.8):(0.05~0.08); the dropping rate of the manganese source solution is preferably 0.1~2 mL / min, more preferably 0.2~1 mL / min. Continuous stirring is preferably maintained during the dropping process of the manganese source solution. This dropping process ensures that the manganese ions in the solution are rapidly dispersed and the concentration of the manganese ion complex is uniformly distributed.

[0051] After obtaining the mixed solution, the present invention sequentially dries, grinds and calcines the mixed solution to obtain manganese oxide.

[0052] In this invention, the drying of the mixed solution is preferably divided into two stages. The drying temperature of the first stage is preferably 50~100℃, more preferably 60~90℃, such as 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, preferably within the range of any of the above values ​​as the upper or lower limit. The drying time of the first stage is preferably 8~15 hours, more preferably 10~12 hours. The drying temperature of the second stage is preferably 100~150℃, more preferably 110~140℃, such as 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, preferably within the range of any of the above values ​​as the upper or lower limit. The drying time of the second stage is preferably 2~12 hours, more preferably 5~10 hours.

[0053] The present invention grinds the solid obtained by drying above, preferably for 5 to 30 minutes, more preferably for 10 to 20 minutes, to ensure that the ground solid powder is sufficiently fine and uniform, without obvious large uneven particles.

[0054] In this invention, the organic ligands in the ground solid powder are removed by calcination and a manganese oxide solid powder intermediate is formed, wherein the manganese oxide is a mixture of Mn2O3 and Mn3O4.

[0055] In this invention, the calcination atmosphere is preferably dry air; the calcination temperature is preferably 300~500℃, more preferably 350~450℃, such as 300℃, 350℃, 400℃, 450℃, 500℃, preferably a range of values ​​with any of the above values ​​as the upper or lower limit; the calcination time is preferably 8~15 hours, more preferably 10~12 hours; the calcination heating rate is preferably 2~10℃ / min, more preferably 5~8℃ / min.

[0056] After obtaining manganese oxide, the present invention mixes the manganese oxide and rhodium source in water to obtain a mixed slurry.

[0057] In this invention, the rhodium source preferably includes one or more of rhodium chloride, rhodium nitrate and their hydrates, such as one or more of rhodium chloride, rhodium chloride hydrate, rhodium nitrate and rhodium nitrate hydrate; the mass ratio of the rhodium source to manganese oxide is preferably (1~10):(75~150), more preferably (2~8):(80~120).

[0058] In this invention, the mixed slurry is preferably allowed to stand and air dry before further drying. The grinding time is preferably 5-30 minutes, more preferably 10-20 minutes, to ensure that the ground solid powder is sufficiently fine and uniform, without obvious large, uneven particles. The powder is then calcined to obtain the precursor.

[0059] In this invention, the drying temperature is preferably 50~150℃, more preferably 80~120℃, such as 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, preferably a range of values ​​with any of the above values ​​as the upper or lower limit; the drying time is preferably 6~24 hours, more preferably 8~15 hours.

[0060] In this invention, the calcination atmosphere is preferably dry air; the calcination temperature is preferably 400~600℃, more preferably 450~550℃, such as 400℃, 450℃, 500℃, 550℃, 600℃, preferably within the range of any of the above values ​​as the upper or lower limit; the calcination time is preferably 2~8 hours, more preferably 3~5 hours; the calcination heating rate is preferably 2~10℃ / min, more preferably 5~8℃ / min. The calcination causes the manganese oxide to form a stable Mn2O3 phase, improves the dispersion of the supported Rh species, and enhances the bonding with the support.

[0061] The catalyst precursor prepared by the present invention through two-step calcination has a larger specific surface area and higher surface activity. The Rh nanoparticles obtained by the reduction process of the Rh source are smaller in size, more uniformly distributed on the MnO support, and form a strong metal-support interaction with the support, which helps to improve the stability of the Rh nanoparticles and improve the selectivity of the catalyst for ethanol and acetaldehyde.

[0062] After obtaining the precursor, the present invention reduces the precursor in a reducing atmosphere to obtain Rh nanocatalyst supported on MnO support.

[0063] In this invention, the reducing atmosphere preferably comprises a mixture of CO2, H2 and Ar. Further, the volume ratio of CO2, H2 and Ar is preferably (1~30):(1~20):(50~90), more preferably (10~25):(1~10):(60~80). Specifically, in some embodiments of this invention, the reducing atmosphere is 20%CO2+2%H2+78%Ar (volume percentage).

[0064] In this invention, the reduction temperature is preferably 250~600℃, more preferably 250~400℃, such as 250℃, 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, preferably within a range where any of the above values ​​is the upper or lower limit; the reduction time is preferably 1~5 hours, more preferably 2~4 hours; the reduction heating rate is preferably 2~10℃ / min, more preferably 5~8℃ / min. During the reduction process, Mn2O3 in the precursor is reduced to MnO, and the Rh source is reduced to Rh nanoparticles. Simultaneously, non-stoichiometric MnO is induced on the surface of the Rh nanoparticles. x Partial coating layer.

[0065] This invention first prepares manganese oxide, and then loads a rhodium source onto the surface of the manganese oxide support using an impregnation method. After a certain pretreatment process, a Rh / MnO nanocatalyst is obtained. The preparation method of Rh nanoparticles loaded on a manganese oxide support in this invention has simple raw materials, high reproducibility, high Rh atom utilization, and uniform dispersion of Rh particles on the surface of the manganese oxide support. The experimental equipment required for the preparation method is simple, the product is easy to separate, and the yield is high. A strong metal-support interaction is formed in the Rh / MnO nanocatalyst, with MnO acting as both a support and an additive. The support induces non-stoichiometric MnO... x The species partially coats the Rh nanoparticles, which not only contributes to the stability and high dispersion of the Rh nanoparticles on the support surface, but also modulates the chemical properties of the Rh active sites, giving the catalyst high selectivity. The Rh / MnO catalyst provided by this invention produces multi-carbon oxygen-containing compounds containing a high proportion of ethanol and acetaldehyde, achieving the co-production of ethanol and acetaldehyde.

[0066] The present invention also provides a Rh / MnO nanocatalyst, which is prepared according to the preparation method described above;

[0067] The Rh / MnO nanocatalyst includes an MnO oxide support.

[0068] Rh nanoparticles loaded on the surface of the MnO oxide support and partially coated thereon;

[0069] The mass ratio of Rh atoms to MnO support in the Rh / MnO nanocatalyst is (0.5~5): (75~150).

[0070] In this invention, the Rh nanoparticles in the Rh / MnO nanocatalyst are induced by Mn oxide to produce non-stoichiometric MnO. x The species are encapsulated, and the Rh nanoparticles exhibit a truncated octahedral morphology with a uniform size distribution.

[0071] In this invention, the preferred mass ratio of Rh atoms to MnO support in the Rh / MnO is (0.5~5):(75~150). Based on the above mass ratio, the Rh loading can be increased without significantly increasing the size of Rh nanoparticles. Specifically, in some embodiments of this invention, the preferred mass ratio of Rh atoms to MnO support in the Rh / MnO is (2~3.5):(75~150).

[0072] This invention also provides an application of the Rh / MnO nanocatalyst described above in the catalytic preparation of multi-carbon oxygen-containing compounds from syngas.

[0073] In this invention, the synthesis gas is preferably subjected to a catalytic reaction in the presence of the Rh / MnO nanocatalyst described above to prepare multi-carbon oxygen-containing compounds.

[0074] In this invention, the synthesis gas comprises carbon monoxide, hydrogen, and nitrogen. The volume fraction of carbon monoxide is preferably 20-40%, more preferably 25-35%; the volume fraction of hydrogen is preferably 50-70%, more preferably 55-65%; and the volume fraction of nitrogen is preferably 5-20%, more preferably 10-15%. Specifically, in some embodiments of this invention, the synthesis gas contains 30% carbon monoxide, 60% hydrogen, and 10% nitrogen by volume. The temperature of the catalytic reaction is preferably 260-350°C, more preferably 280-320°C, and the space velocity (GHSV) of the catalytic reaction is preferably 400-2500 h⁻¹. -1 More preferably 600~1500h -1 The pressure of the catalytic reaction is preferably 1.5~5.0 MPa, more preferably 2.0~4.0 MPa.

[0075] Using the Rh / MnO nanocatalyst of this invention to catalyze the synthesis of gas, the resulting products contain a high proportion of ethanol and acetaldehyde, with a combined selectivity of 50-65% and a combined proportion of 80-95% in multi-carbon oxygen-containing compounds. The molar ratio of ethanol to acetaldehyde is (0.8-1.2):(0.2-1.5), thus achieving the co-production of ethanol and acetaldehyde.

[0076] This invention provides a method for preparing Rh / MnO nanocatalysts, comprising the following steps: A) adding a manganese source solution dropwise to a ligand solution to obtain a mixed solution; the ligand solution includes a complexing agent and a polyol; B) drying and calcining the mixed solution to obtain manganese oxide; C) mixing the manganese oxide and a rhodium source in water to obtain a mixed slurry; the mass ratio of the manganese oxide to the rhodium source is (75~150):(1~10); D) drying and calcining the mixed slurry to obtain a precursor; E) reducing the precursor in a reducing atmosphere to obtain the Rh / MnO nanocatalyst. The Rh active sites in the Rh / MnO catalyst obtained by the stepwise synthesis method provided in this application are exposed on the support surface, ensuring maximum atom utilization. In the preparation method provided in this application, Mn2O3 in the synthetic precursor is reduced to MnO during the reduction process, and the Rh source is reduced to Rh metal nanoparticles with a truncated octahedral morphology. This application utilizes the process of Mn2O3 being reduced to MnO to induce the formation of a special strong metal-support interaction in the catalyst, resulting in non-stoichiometric MnO formation on the catalyst surface. x The species partially coats the Rh nanoparticles, improving their dispersion and uniformity, and also modifies their surface. The preparation method provided by this invention controls the phase composition of the precursor and the reducing atmosphere to regulate the local structure of the Rh nanoparticles in the Rh / MnO catalyst, thereby enabling the nanocatalyst to exhibit high conversion and selectivity in the direct synthesis of multi-carbon oxygen-containing compounds from syngas. The multi-carbon oxygen-containing compounds produced by the Rh / MnO catalyst provided by this invention contain a high proportion of ethanol and acetaldehyde, achieving the co-production of ethanol and acetaldehyde.

[0077] To further illustrate the present invention, the following detailed description of a Rh / MnO nanocatalyst, its preparation method, and its application, in conjunction with embodiments, is provided by the present invention, but should not be construed as limiting the scope of protection of the present invention.

[0078] Example 1

[0079] At room temperature, 28 g of deionized water was placed in a beaker, followed by 8.4 g of citric acid and 0.56 g of ethylene glycol, and stirred until all components were fully dissolved. 12.0 g of a 50 wt% manganese nitrate aqueous solution was added to 6.0 mL of deionized water, and stirred until the solution was thoroughly mixed. The manganese ion solution was added dropwise to the ligand solution at a rate of 0.8 mL / min, with continuous stirring, to obtain a mixed solution. The beaker containing the above solution was placed in an oven and dried first at 80 °C for 12 h, then heated to 120 °C for another 6 h. The dried solid was ground into a fine powder and calcined in a muffle furnace at 400 °C, a heating rate of 5 °C / min, and a calcination time of 4 h to obtain manganese oxide solid powder.

[0080] At room temperature, 550 mg of the above-mentioned manganese oxide solid powder was prepared and 4.8 mg of rhodium chloride hydrate was placed in 550 μL of deionized water and sonicated to dissolve it completely. The aqueous solution was added dropwise to the manganese oxide powder while stirring with a glass rod until a slurry was formed. The slurry was left to dry overnight and then ground into powder. The powder was then dried in an oven at 60 °C for 12 h. The dried powder was transferred to a muffle furnace for calcination at 550 °C at a heating rate of 5 °C / min for 4 h. The resulting solid powder was then reduced in an atmosphere of 20% CO2 + 2% H2 + 78% Ar (volume percentage) at 320 °C at a heating rate of 2 °C / min for 4 h to obtain Rh nanocatalyst supported on a MnO support.

[0081] The catalytic performance test conditions were as follows: the reaction gas composition was 30% CO + 60% H2 + 10% N2, the reaction temperature was 300℃, the reaction pressure was 3.0 MPa, and the reaction space velocity (GHSV) was 1000 h⁻¹. -1 The remaining reactants in the reaction tail gas and the generated products such as methane, ethane, and ethylene are analyzed online by gas chromatography for qualitative and quantitative analysis, while the generated liquid products are analyzed offline by gas chromatography for qualitative and quantitative analysis.

[0082] Example 2

[0083] At room temperature, 25 g of deionized water was placed in a beaker, followed by 7.5 g of citric acid and 0.50 g of ethylene glycol, and stirred until all components were fully dissolved. 10.7 g of a 50 wt% manganese nitrate aqueous solution was added to 5.0 mL of deionized water, and stirred until the solution was thoroughly mixed. The manganese ion solution was added dropwise to the ligand solution at a rate of 0.8 mL / min, with continuous stirring, to obtain a mixed solution. The beaker containing the above solution was placed in an oven and dried first at 80 °C for 12 h, then heated to 120 °C for another 6 h. The dried solid was ground into a fine powder and calcined in a muffle furnace at 400 °C, a heating rate of 5 °C / min, and a calcination time of 4 h to obtain manganese oxide solid powder.

[0084] At room temperature, 500 mg of the above-mentioned manganese oxide solid powder was prepared and 5.8 mg of rhodium chloride hydrate was placed in 500 μL of deionized water and sonicated to dissolve it completely. The above aqueous solution was added dropwise to the above manganese oxide powder while stirring with a glass rod, eventually forming a slurry. The resulting slurry was left to dry overnight, then ground into powder and dried in an oven at 60°C for 12 h. The dried powder was transferred to a muffle furnace for calcination at 550°C, a heating rate of 5°C / min, and a calcination time of 4 h. The resulting solid powder was then reduced in an atmosphere of 20% CO2 + 2% H2 + 78% Ar (volume percentage) at 320°C, a heating rate of 2°C / min, and a reduction time of 4 h to obtain Rh nanocatalysts supported on the surface of a MnO support.

[0085] The catalytic performance test conditions were as follows: the reaction gas composition was 30% CO + 60% H2 + 10% N2, the reaction temperature was 300℃, the reaction pressure was 3.0 MPa, and the reaction space velocity (GHSV) was 1000 h⁻¹. -1 The remaining reactants in the reaction tail gas and the generated products such as methane, ethane, and ethylene are analyzed online by gas chromatography for qualitative and quantitative analysis, while the generated liquid products are analyzed offline by gas chromatography for qualitative and quantitative analysis.

[0086] Example 3

[0087] At room temperature, 20 g of deionized water was placed in a beaker. 6.0 g of citric acid and 0.40 g of ethylene glycol were then added to the beaker sequentially, and the mixture was stirred until all components were fully dissolved. 8.6 g of a 50 wt% manganese nitrate aqueous solution was added to 6.0 mL of deionized water, and the mixture was stirred until fully combined. The manganese ion solution was added dropwise to the ligand solution at a rate of 0.6 mL / min, with continuous stirring, to obtain a mixed solution. The beaker containing the above solution was placed in an oven and dried first at 80 °C for 12 h, then heated to 120 °C and treated for another 6 h. The dried solid was ground into a fine powder and calcined in a muffle furnace at 400 °C, a heating rate of 5 °C / min, and a calcination time of 4 h to obtain manganese oxide solid powder.

[0088] At room temperature, 480 mg of the above-mentioned manganese oxide solid powder was prepared and 10.1 mg of rhodium chloride hydrate was placed in 500 μL of deionized water and sonicated to dissolve it completely. The above aqueous solution was added dropwise to the above manganese oxide powder while stirring with a glass rod, eventually forming a slurry. The resulting slurry was left to dry overnight, then ground into powder and dried in an oven at 60 °C for 12 h. The dried powder was transferred to a muffle furnace for calcination at 550 °C, a heating rate of 5 °C / min, and a calcination time of 4 h. The resulting solid powder was then reduced in an atmosphere of 20% CO2 + 2% H2 + 78% Ar (volume percentage) at 320 °C, a heating rate of 2 °C / min, and a reduction time of 4 h to obtain Rh nanocatalyst supported on the surface of MnO.

[0089] The catalytic performance test conditions were as follows: the reaction gas composition was 30% CO + 60% H2 + 10% N2, the reaction temperature was 300℃, the reaction pressure was 3.0 MPa, and the reaction space velocity (GHSV) was 1000 h⁻¹. -1 The remaining reactants in the reaction tail gas and the generated products such as methane, ethane, and ethylene are analyzed online by gas chromatography for qualitative and quantitative analysis, while the generated liquid products are analyzed offline by gas chromatography for qualitative and quantitative analysis.

[0090] Example 4

[0091] At room temperature, 30 g of deionized water was placed in a beaker, followed by 9.0 g of citric acid and 0.60 g of ethylene glycol, and stirred until all components were fully dissolved. 12.8 g of a 50 wt% manganese nitrate aqueous solution was added to 6.0 mL of deionized water, and stirred until the solution was thoroughly mixed. The manganese ion solution was added dropwise to the ligand solution at a rate of 1 mL / min, with continuous stirring, to obtain a mixed solution. The beaker containing the above solution was placed in an oven and dried first at 80 °C for 12 h, then heated to 120 °C and treated for another 6 h. The dried solid was ground into a fine powder and calcined in a muffle furnace at 400 °C, a heating rate of 5 °C / min, and a calcination time of 4 h to obtain manganese oxide solid powder.

[0092] At room temperature, 500 mg of the above-mentioned manganese oxide solid powder was prepared and 5.8 mg of rhodium chloride hydrate was placed in 500 μL of deionized water and sonicated to dissolve it completely. The above aqueous solution was added dropwise to the above manganese oxide powder while stirring with a glass rod until a slurry was formed. The slurry was left to dry overnight and then ground into powder. The powder was then dried in an oven at 60 °C for 12 h. The dried powder was transferred to a muffle furnace for calcination at 550 °C, a heating rate of 5 °C / min, and a calcination time of 4 h. The resulting solid powder was then reduced in an atmosphere of 20% CO2 + 2% H2 + 78% Ar (volume percentage) at 270 °C, a heating rate of 2 °C / min, and a reduction time of 4 h to obtain Rh nanocatalyst supported on the surface of MnO.

[0093] The catalytic performance test conditions were as follows: the reaction gas composition was 30% CO + 60% H2 + 10% N2, the reaction temperature was 300℃, the reaction pressure was 3.0 MPa, and the reaction space velocity (GHSV) was 1000 h⁻¹. -1 The remaining reactants in the reaction tail gas and the generated products such as methane, ethane, and ethylene are analyzed online by gas chromatography for qualitative and quantitative analysis, while the generated liquid products are analyzed offline by gas chromatography for qualitative and quantitative analysis.

[0094] Example 5

[0095] At room temperature, 25 g of deionized water was placed in a beaker, followed by 7.5 g of citric acid and 0.50 g of ethylene glycol, and stirred until all components were fully dissolved. 10.7 g of a 50 wt% manganese nitrate aqueous solution was added to 6.0 mL of deionized water, and stirred until the solution was thoroughly mixed. The manganese ion solution was added dropwise to the ligand solution at a rate of 0.8 mL / min, with continuous stirring, to obtain a mixed solution. The beaker containing the above solution was placed in an oven and dried first at 80 °C for 12 h, then heated to 120 °C and treated for another 6 h. The dried solid was ground into a fine powder and calcined in a muffle furnace at 400 °C, a heating rate of 5 °C / min, and a calcination time of 4 h to obtain manganese oxide solid powder.

[0096] At room temperature, 500 mg of the above-mentioned manganese oxide solid powder was prepared and 5.8 mg of rhodium chloride hydrate was placed in 500 μL of deionized water and sonicated to dissolve it completely. The aqueous solution was added dropwise to the manganese oxide powder while stirring with a glass rod until a slurry was formed. The slurry was left to dry overnight and then ground into powder. The powder was then dried in an oven at 60 °C for 12 h. The dried powder was transferred to a muffle furnace for calcination at 550 °C at a heating rate of 5 °C / min for 4 h. The resulting solid powder was then reduced in an atmosphere of 20% CO2 + 2% H2 + 78% Ar (volume percentage) at 370 °C at a heating rate of 2 °C / min for 4 h to obtain Rh nanocatalyst supported on a MnO support.

[0097] The catalytic performance test conditions were as follows: the reaction gas composition was 30% CO + 60% H2 + 10% N2, the reaction temperature was 300℃, the reaction pressure was 3.0 MPa, and the reaction space velocity (GHSV) was 1000 h⁻¹. -1 The remaining reactants in the reaction tail gas and the generated products such as methane, ethane, and ethylene are analyzed online by gas chromatography for qualitative and quantitative analysis, while the generated liquid products are analyzed offline by gas chromatography for qualitative and quantitative analysis.

[0098] Comparative Example 1

[0099] At room temperature, 25 g of deionized water was placed in a beaker, followed by 7.5 g of citric acid and 0.50 g of ethylene glycol, and stirred until all components were fully dissolved. 10.7 g of a 50 wt% manganese nitrate aqueous solution was added to 5.0 mL of deionized water, and stirred until the solution was thoroughly mixed. The manganese ion solution was added dropwise to the ligand solution at a rate of 0.8 mL / min, with continuous stirring, to obtain a mixed solution. The beaker containing the above solution was placed in an oven and dried first at 80 °C for 12 h, then heated to 120 °C for another 6 h. The dried solid was ground into a fine powder and calcined in a muffle furnace at 400 °C, a heating rate of 5 °C / min, and a calcination time of 4 h to obtain manganese oxide solid powder.

[0100] At room temperature, 500 mg of the above-mentioned manganese oxide solid powder was prepared and 5.8 mg of rhodium chloride hydrate was placed in 500 μL of deionized water and sonicated to dissolve it completely. The aqueous solution was added dropwise to the manganese oxide powder while stirring with a glass rod until a slurry was formed. The slurry was left to dry overnight and then ground into powder. The powder was then dried in an oven at 60 °C for 12 h. The dried powder was transferred to a muffle furnace for calcination at 550 °C at a heating rate of 5 °C / min for 4 h. The resulting solid powder was then reduced in an atmosphere of 10% H₂ + 90% Ar (volume percentage) at 320 °C at a heating rate of 2 °C / min for 4 h to obtain Rh nanocatalysts supported on a MnO support.

[0101] The catalytic performance test conditions were as follows: the reaction gas composition was 30% CO + 60% H2 + 10% N2, the reaction temperature was 300℃, the reaction pressure was 3.0 MPa, and the reaction space velocity (GHSV) was 1000 h⁻¹. -1 The remaining reactants in the reaction tail gas and the generated products such as methane, ethane, and ethylene are analyzed online by gas chromatography for qualitative and quantitative analysis, while the generated liquid products are analyzed offline by gas chromatography for qualitative and quantitative analysis.

[0102] Comparative Example 2

[0103] At room temperature, 25 g of deionized water was placed in a beaker, followed by 7.5 g of citric acid and 0.50 g of ethylene glycol, and stirred until all components were fully dissolved. 10.7 g of a 50 wt% manganese nitrate aqueous solution was added to 5.0 mL of deionized water, and stirred until the solution was thoroughly mixed. The manganese ion solution was added dropwise to the ligand solution at a rate of 0.8 mL / min, with continuous stirring, to obtain a mixed solution. The beaker containing the above solution was placed in an oven and dried first at 80 °C for 12 h, then heated to 120 °C for another 6 h. The dried solid was ground into a fine powder and calcined in a muffle furnace at 400 °C, a heating rate of 5 °C / min, and a calcination time of 4 h to obtain manganese oxide solid powder.

[0104] The obtained manganese oxide solid powder was reduced in an atmosphere of 10% H2 + 90% Ar (volume percentage) at a reduction temperature of 700℃, a heating rate of 2℃ / min, and a reduction time of 4h. This step first reduced the obtained manganese oxide to MnO solid powder, and then loaded Rh species.

[0105] At room temperature, 500 mg of the above MnO powder was prepared and 5.8 mg of rhodium chloride hydrate was placed in 500 μL of deionized water and sonicated to dissolve it completely. The aqueous solution was added dropwise to the manganese oxide powder while stirring with a glass rod until a slurry was formed. The slurry was left to dry overnight and then ground into powder. The powder was then dried in an oven at 60 °C for 12 h to obtain a synthesis precursor powder with MnO as the phase. The obtained solid powder was reduced in an atmosphere of 20% CO2 + 2% H2 + 78% Ar (volume percentage) at a reduction temperature of 320 °C, a heating rate of 2 °C / min, and a reduction time of 4 h to obtain Rh nanocatalysts supported on the surface of MnO support.

[0106] The catalytic performance test conditions were as follows: the reaction gas composition was 30% CO + 60% H2 + 10% N2, the reaction temperature was 300℃, the reaction pressure was 3.0 MPa, and the reaction space velocity (GHSV) was 1000 h⁻¹. -1 The remaining reactants in the reaction tail gas and the generated products such as methane, ethane, and ethylene are analyzed online by gas chromatography for qualitative and quantitative analysis, while the generated liquid products are analyzed offline by gas chromatography for qualitative and quantitative analysis.

[0107] Comparative Example 3

[0108] 500 mg of MnO solid powder was prepared at room temperature. 5.8 mg of rhodium chloride hydrate was dissolved in 500 μL of deionized water by sonication. The aqueous solution was added dropwise to the MnO solid powder while stirring with a glass rod until a slurry was formed. The slurry was left to dry overnight, then ground into powder and dried in an oven at 60 °C for 12 h. The dried powder was then transferred to a muffle furnace for calcination at 550 °C at a heating rate of 5 °C / min for 4 h. The resulting solid powder was then reduced in an atmosphere of 20% CO2 + 2% H2 + 78% Ar (volume percentage) at 320 °C at a heating rate of 2 °C / min for 4 h to obtain Rh nanocatalysts supported on the MnO support.

[0109] The catalytic performance test conditions were as follows: the reaction gas composition was 30% CO + 60% H2 + 10% N2, the reaction temperature was 300℃, the reaction pressure was 3.0 MPa, and the reaction space velocity (GHSV) was 1000 h⁻¹. -1 The remaining reactants in the reaction tail gas and the generated products such as methane, ethane, and ethylene are analyzed online by gas chromatography for qualitative and quantitative analysis, while the generated liquid products are analyzed offline by gas chromatography for qualitative and quantitative analysis.

[0110] Comparative Example 4

[0111] At room temperature, 25 g of deionized water was placed in a beaker, and 7.5 g of citric acid and 0.50 g of ethylene glycol were added sequentially to the beaker, stirring until all components were fully dissolved. 5.8 mg of rhodium chloride hydrate was placed in 500 μL of deionized water and sonicated until fully dissolved, then added dropwise to the above solution. 10.7 g of 50 wt% manganese nitrate aqueous solution was added to 5.0 mL of deionized water, stirring until the solution was thoroughly mixed. A manganese ion solution was added dropwise to the above solution at a rate of 0.8 mL / min, with continuous stirring, to obtain a mixed solution of manganese ions, rhodium ions, and a complexing agent. The beaker containing the above solution was placed in an oven and dried first at 80 °C for 12 h, then heated to 120 °C for another 6 h. The dried solid was ground into a fine powder and calcined in a muffle furnace at 400 °C, a heating rate of 5 °C / min, and a calcination time of 4 h to obtain manganese oxide solid powder. The powder was then further calcined at 550℃, with a heating rate of 5℃ / min, for 4 hours. The resulting solid powder was then reduced in an atmosphere of 20%CO2 + 2%H2 + 78%Ar (volume percentage) at 320℃, with a heating rate of 2℃ / min, for 4 hours, to obtain Rh nanocatalysts supported on the surface of MnO.

[0112] Catalyst morphology detection

[0113] The X-ray diffraction pattern of the catalyst in Example 1 is shown below. Figure 1 As shown, Figure 1 This indicates that in the preparation process provided by the present invention, the initially synthesized manganese oxide powder is a mixture of Mn2O3 and Mn3O4, the precursor in the subsequent steps is a pure Mn2O3 phase, and the support in the nanocatalyst obtained after reduction treatment (the curve corresponding to "Example 1") exists in the form of MnO. Figure 1 The absence of diffraction peaks for Rh-related species indicates that the Rh particles are small in size and have not undergone significant sintering.

[0114] Transmission electron microscopy image of the catalyst in Example 1 is shown below. Figure 2 As shown, Figure 2 This indicates that Rh nanoparticles are uniformly dispersed on the surface of the manganese oxide support.

[0115] High-resolution transmission electron microscopy image of the catalyst in Example 1 is shown below. Figure 3 As shown, Figure 3 The crystal structure of Rh nanoparticles and MnO support is clearly shown. According to... Figure 3 The projected structure of Rh nanoparticles in the image shows that the morphology of the Rh nanoparticles is a truncated octahedron.

[0116] Example 1: High-angle annular dark-field scanning transmission electron microscopy image of the catalyst and electron energy loss spectrum at selected locations, as shown below. Figure 4 As shown, Figure 4 This indicates that, because the preparation method provided by the present invention involves the reduction process of Mn2O3 to MnO, a strong metal-support interaction is induced in the catalyst, and the non-stoichiometric MnO generated by the Mn oxide from the Rh nanoparticles... x The species is partially wrapped.

[0117] Catalyst reaction performance evaluation

[0118] The conversion rate and selectivity of the catalytic synthesis gas to multi-carbon oxygen-containing compound reaction in the embodiments of the present invention were detected. The CO conversion rate was calculated as follows:

[0119]

[0120] Where N in (CO) and N in (N2) corresponds to the number of moles of CO and N2 in the feed gas introduced per hour, respectively. out (CO) and N out (N2) corresponds to the number of moles of CO and N2 in the reaction tail gas flowing out per hour, respectively.

[0121] The selectivity of the product is calculated using the following formula:

[0122]

[0123] Where C i For a product containing i carbon atoms, N(C) i ) is the C generated per hour i The number of moles of the product.

[0124] Multicarbon oxygenated compounds (C 2+ The proportion of -Oxy) is calculated using the following formula:

[0125]

[0126] Where C io For a multi-carbon oxygen-containing compound containing i carbon atoms, N(C io ) is the C generated per hour io The molar number of products, N(CH3OH) is the number of moles of methanol (CH3OH) product generated per hour.

[0127] Depend on Figure 5As shown in b, the main components of multi-carbon oxygen-containing compounds are acetaldehyde, ethanol, and acetic acid, with ethanol and acetaldehyde accounting for the highest proportions. The remaining components are n-propanol, isopropanol, n-butanol, isobutanol, n-pentanol, and isopentanol. The Rh / MnO nanocatalyst prepared in this invention enables the one-step co-production of acetaldehyde and ethanol.

[0128] Depend on Figure 6 It can be seen that, within a certain reduction temperature range, the CO conversion rate and product selectivity of the catalyst in the examples remained at a high level, with no significant decrease observed.

[0129] Depend on Figure 7 It is evident that, in the preparation method provided by this invention, using an atmosphere containing CO2 and H2 to reduce precursor G can significantly improve the conversion rate and selectivity of the catalyst in the examples. Figure 7 It is evident that if Mn₂O₃ is pre-reduced to MnO and then loaded with Rh species (Comparative Example 2), the conversion rate and selectivity of the obtained catalyst are significantly reduced. Similarly, if MnO solid powder is directly loaded with Rh species (Comparative Example 3), the catalytic performance is also reduced. This indicates that in the preparation method provided by this invention, the synthetic precursor with reducible Mn₂O₃ as the main phase is crucial for improving the conversion rate and selectivity of the catalyst. Furthermore, if manganese ions, rhodium ions, and a complexing agent are pre-mixed (Comparative Example 4), the catalytic performance of the obtained catalyst is also reduced, demonstrating that the preparation method provided by this invention helps to improve the catalytic performance of Rh-based catalysts supported on manganese oxides.

[0130] In summary, the preparation method provided by this invention can significantly improve the conversion rate and selectivity of the prepared Rh / MnO nanocatalyst by controlling the phase composition of the precursor and the reducing atmosphere.

[0131] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing Rh / MnO nanocatalysts, comprising the following steps: A) The manganese source solution is added dropwise to the ligand solution to obtain a mixed solution; The ligand solution comprises a complexing agent and a polyol; B) The mixed solution was dried and calcined to obtain manganese oxide; C) Manganese oxide and rhodium source are mixed in water to obtain a mixed slurry; The mass ratio of the rhodium source to the manganese oxide is (1~10):(75~150); D) The mixed slurry is dried and calcined to obtain the precursor; E) The precursor was reduced in a reducing atmosphere to obtain Rh / MnO nanocatalyst; The reducing atmosphere comprises a mixture of CO2, H2, and Ar.

2. The method for preparing Rh / MnO nanocatalyst according to claim 1, characterized in that, The manganese source solution includes a manganese source and an aqueous solvent; The manganese source includes one or more of manganese nitrate, manganese chloride, manganese sulfate, and their hydrates; the aqueous solvent includes water and / or ethanol; the mass ratio of the manganese source to the aqueous solvent is (0.7~1.5):(0.4~20). The dropping rate of the manganese source solution is 0.1~2 mL / min; The complexing agent includes one or more of citric acid, tartaric acid, and malic acid; the polyol includes one or more of ethylene glycol, 1,2-propanediol, and glycerol. The mass ratio of the manganese source, complexing agent, and polyol is (0.3~1.5):(0.5~1.0):(0.03~0.1).

3. The method for preparing Rh / MnO nanocatalyst according to claim 1, characterized in that, The drying process in step B) is divided into two stages. The drying temperature in the first stage is 50~100℃ and the drying time is 8~15 hours. The drying temperature in the second stage is 100~150℃ and the drying time is 2~12 hours.

4. The method for preparing Rh / MnO nanocatalyst according to claim 1, characterized in that, In step B), the calcination temperature is 300~500℃, the calcination time is 8~15 hours, and the calcination heating rate is 2~10℃ / min.

5. The method for preparing Rh / MnO nanocatalyst according to claim 1, characterized in that, The rhodium source includes one or more of rhodium chloride, rhodium nitrate, and their hydrates.

6. The method for preparing Rh / MnO nanocatalyst according to claim 1, characterized in that, In step D), the drying temperature is 50~150℃ and the drying time is 6~24 hours.

7. The method for preparing Rh / MnO nanocatalyst according to claim 1, characterized in that, In step D), the calcination temperature is 400~600℃, the calcination time is 2~8 hours, and the calcination heating rate is 2~10℃ / min.

8. The method for preparing Rh / MnO nanocatalyst according to claim 1, characterized in that, In step E), the reduction temperature is 250~600℃, the reduction time is 1~5 hours, and the reduction heating rate is 2~10℃ / min.

9. A Rh / MnO nanocatalyst, prepared according to the preparation method of any one of claims 1 to 8; The Rh / MnO nanocatalyst includes an MnO oxide support. Rh nanoparticles loaded on the surface of the MnO oxide support and partially coated thereon; The mass ratio of Rh atoms to MnO support in the Rh / MnO nanocatalyst is (0.5~5): (75~150).

10. The application of the Rh / MnO nanocatalyst as described in claim 11 in the catalytic preparation of multi-carbon oxygen-containing compounds from syngas.

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