Calcium tungsten double perovskite type nickel-based catalyst for acetic acid autothermal reforming

Abstract

The present application relates to a kind of calcium tungsten double perovskite type nickel-based catalyst for hydrogen production by acetic acid autothermal reforming.The present application provides a new catalyst with high activity,carbon deposition resistance and oxidation resistance to solve the deactivation problem of existing catalyst in the process of acetic acid autothermal reforming.The molar composition of the catalyst of the present application is as follows: a (CaO) b (WO3) c Wherein, a is 0.75-0.86, b is 3.00-3.35, and c is 0.64-0.72.The Ca3WO6 double perovskite type nickel-based catalyst is prepared by Pechini method, and Ni-Ca-W-O active center is formed after reduction, in which Ni is uniformly dispersed in Ca3WO6 framework.The catalyst of the present application effectively improves the stability of the catalyst and the yield of hydrogen, and inhibits the generation of by-products such as methane and acetone.

Description

Technical Field

[0001] This invention relates to a Ca3WO6 perovskite-tungsten double perovskite nickel-based catalyst for hydrogen production from acetic acid via autothermal reforming, belonging to the field of hydrogen production from acetic acid via autothermal reforming. Background Technology

[0002] Faced with the world's ever-increasing energy demand, hydrogen, as a clean energy source, has great potential in replacing traditional energy sources. Currently, hydrogen production mainly uses raw materials such as natural gas, coal, biomass, and water electrolysis. Among these, natural gas and coal are the most common raw materials, while biomass-based hydrogen production is receiving increasing attention.

[0003] Biomass can be rapidly pyrolyzed into biomass oil. The composition of biomass oil varies considerably depending on the source of the biomass, but it can always be divided into an oil phase and an aqueous phase. The aqueous phase of biomass oil contains approximately 33% acetic acid. Therefore, the acetic acid in the aqueous phase of biomass oil can serve as a renewable and inexpensive feedstock for hydrogen production.

[0004] Acetic acid hydrogen production typically involves steam reforming (SR), partial oxidation (CPOX), and autothermal reforming (ATR). Steam reforming is an endothermic reaction (CH3COOH + 2H2O → 2CO2 + 4H2, ΔH = +131.4 kJ / mol), requiring a continuous external heat supply for the reaction to proceed. While partial oxidation does not require an external heat source, the active components are prone to oxidation and sintering in an oxygen atmosphere, resulting in low hydrogen yield. In contrast, the autothermal reforming of acetic acid for hydrogen production (CH3COOH + 0.28O2 + 1.44H2O → 2CO2 + 3.44H2, ΔH = 0) combines steam reforming and partial oxidation processes. It introduces a certain proportion of oxygen or air into the feedstock and achieves self-heating by controlling the ratio of oxygen to acetic acid, thus balancing the heat supply of the reaction system. This process is characterized by rapid start-up and low investment.

[0005] In autothermal reforming, catalyst selection is crucial in addition to process conditions. Nickel-based catalysts have a strong ability to activate C-C and CH bonds, exhibiting good activity in acetic acid steam reforming, and have therefore attracted widespread attention. Acetic acid molecules (CH3COOH) are adsorbed and activated on Ni-based catalysts, undergoing dehydrogenation and dehydroxylation steps to form intermediates such as CH3COO*, CH3CO*, CH3*, and CO*, which further undergo dehydrogenation and deoxygenation to form C* species. However, the polymerization of a large amount of C* leads to deposition on the catalyst surface, forming coke deposits that cover the active sites, thus reducing the catalyst's reactivity. Furthermore, nickel metal is prone to sintering at high temperatures, resulting in a decrease in the active surface area.

[0006] To address these issues with Ni-based catalysts, selecting suitable supports and promoters is crucial for promoting efficient acetic acid conversion. This invention creatively introduces Ca and W, employing the Pechini method to construct a Ni-Ca-WO catalyst with a mesoporous structure, a Ca3WO6 double perovskite structure supporting the active component Ni, exhibiting the following characteristics.

[0007] First, this invention introduces the alkaline earth metal Ca and the transition metal W to form a single monoclinic phase structure of double perovskite Ca3WO6, with space group P. 21 / n, belonging to the B-site ordered double perovskite structure. This invention is based on the A2BB′O6 double perovskite structure, which has an additional B′ position, giving it excellent structural modulation performance and monoclinic crystal structure characteristics. In the double perovskite structure, the A ion is located at the vertices of the crystal lattice, playing a role in providing lattice stability and charge balance; the B and B′ ions are located at the center and face-centered positions of the crystal lattice, respectively, giving the double perovskite structure more lattice sites for ion filling; among them, the B′ ion is usually surrounded by eight oxygen ions, forming a [B′O6] octahedral coordination environment. This octahedral structure is conducive to electronic transitions and oxygen hole formation in the catalytic process. In addition, by substituting the A or B sites, the surface defect degree of the perovskite catalyst can be increased, thereby promoting the conversion behavior of acetic acid in the autothermal reforming process. In the Ca3WO6 structure of this invention, part of the Ca 2+ Located at the A site with 12 coordination, it has low symmetry, and the rest of Ca... 2+ Located in C i The B position and O position are inversely centrally symmetric 2- Hexacoordination, with W at the B′ site in the crystal lattice 6+ It exhibits a rock salt structure, displaying a rock salt-type B-site cation sublattice composed of alternating [CaO6] and [WO6] octahedra. The W at the B′ site combines with oxygen to form a high-bond-energy WO bond, which is conducive to the absence of surface oxygen, promotes the formation of oxygen vacancies and the diffusion of oxygen ions, and facilitates the adsorption, activation and decomposition of CH3COOH, H2O and O2 in the reaction gas. In particular, it enhances the conversion ability of carbon-containing intermediate products (CH3COO*, CH3CO*, CH3*, etc.) and effectively inhibits the formation of by-products such as acetone.

[0008] Secondly, after hydrogen reduction, Ni is uniformly dispersed within the Ca3WO6 double perovskite framework, forming Ni-Ca-WO active centers and increasing the number of active sites on the catalyst. Among these, Ca species, as an alkaline earth metal, enhances the overall basicity of the catalyst, facilitating the adsorption and activation of water molecules to form intermediate species such as *OH and *O. *OH species participate in the reforming reaction, while *O species can convert CH4 into CH4. xThe C* coking precursor produced by the *(x=1-3) conversion is gasified into CO and CO2, effectively inhibiting coking formation; while the W species at the B′ site has multiple valence states, through W 6+ / W 4+ Valence state transitions act as intermediate electron transfer bridges in catalysis. On the one hand, they can promote electron transfer to Ni during hydrogen reduction. 2+ Transfer, which benefits Ni 2+ It can be reduced to elemental Ni; on the other hand, it can maintain Ni in the autothermal reforming of oxygen-containing acetic acid. 0 The oxidation state of the catalyst is adjusted to improve its antioxidant properties, thereby stabilizing the active conversion sites and increasing the hydrogen yield.

[0009] Finally, the Ca3WO6 double perovskite support constructed in this invention can maintain structural stability during high-temperature autothermal reforming reactions, maintain the dispersion of the active component Ni, and enhance the catalyst's resistance to sintering.

[0010] The innovations in catalyst composition and structure in this invention enable the catalyst to exhibit good activity, stability, anti-sintering and anti-coking properties in the autothermal reforming reaction of acetic acid, and improve the conversion rate of acetic acid and the selectivity of hydrogen, thus demonstrating excellent catalytic activity. Summary of the Invention

[0011] The problem to be solved by this invention is that existing catalysts in the process of hydrogen production by autothermal reforming of acetic acid suffer from poor thermal stability, easy oxidation, sintering and coking, which lead to catalyst deactivation. This invention provides a novel catalyst with stable structure, resistance to coking, oxidation and sintering.

[0012] This invention uses Ni as the active component and introduces alkaline earth metal Ca and transition metal W through the Pechini method to form a double perovskite structure, constructing a catalyst in which Ni is uniformly dispersed in the Ca3WO6 double perovskite framework, forming Ni-Ca-WO active centers. When the preferred catalyst of this invention is applied to the reaction process of acetic acid autothermal reforming to produce hydrogen, at a reaction temperature of 700℃, the conversion rate of acetic acid is close to 100%, and the hydrogen yield is stable at about 2.54 mol-H2 / mol-HAc.

[0013] Technical solution of the present invention:

[0014] This invention addresses the characteristics of acetic acid autothermal reforming by preparing a Ca3WO6 double perovskite nickel-based catalyst using the Pechini method. The molar composition of the catalyst in this invention is (NiO). a (CaO) b (WO3) cWherein, a is 0.75-0.86, b is 3.00-3.35, and c is 0.64-0.72; the weight percentage composition based on oxides is: nickel oxide content 13.6%-16.9%, calcium oxide content 42.1%-47.9%, and tungsten trioxide content 37.0%-42.7%, and the sum of the weight percentages of each component is 100%. The preferred molar composition of the catalyst in this invention is (NiO). 0.80 (CaO) 3.21 (WO3) 0.69 The weight percentage composition based on oxides is as follows: nickel oxide 15.0%, calcium oxide 45.0%, and tungsten trioxide 40.0%.

[0015] The specific preparation and reaction steps are as follows:

[0016] 1) Weigh a certain amount of calcium nitrate, ammonium metatungstate, and nickel nitrate, place them in a beaker, and stir at room temperature until completely dissolved to obtain solution #1;

[0017] 2) Weigh out citric acid in a 1:1 ratio with the total number of metal cations, dissolve it in deionized water to obtain solution #2; weigh out ethylene glycol in a 1:1 ratio with the total number of metal cations to obtain solution #3.

[0018] 3) Under stirring, slowly add solution #2 to solution #3, then slowly add solution #3 to solution #1, and stir until gel-like under a 65℃ water bath. Remove and dry in an oven at 100℃ for 12 hours to obtain the catalyst precursor.

[0019] 4) The obtained catalyst precursor was heated to 700℃ in a tube furnace at a heating rate of 10℃ / min and maintained for 4 hours. After reduction in H2 at 700℃ for 1 hour, a nickel-based catalyst Ni / Ca3WO6 was obtained, in which Ni was uniformly dispersed in the Ca3WO6 double perovskite framework. A Ni-Ca-WO active center with double perovskite Ca3WO6 as the main component was also obtained. Its typical structure is shown in the X-ray diffraction pattern (see attached diagram). Figure 1 As shown in the attached figure, the resulting mesoporous structure is as follows. Figure 2 As shown;

[0020] 5) Reduce 0.1-0.3g of catalyst in H2 at 700℃ for 1h, purge with nitrogen, and introduce a mixed gas with a molar ratio of acetic acid / water / oxygen / nitrogen of 1.0 / (1.3-5.0) / (0.21-0.35) / (2.5-4.5) through the catalyst bed for reaction at 600-800℃.

[0021] The beneficial effects of this invention are:

[0022] 1) This invention employs the Pechini method to construct a Ca3WO6 double perovskite nickel-based catalyst. After hydrogen reduction, Ni is dispersed within the Ca3WO6 framework, forming Ni-Ca-WO active centers, exposing more active sites, which facilitates the adsorption and conversion of CH3COOH, H2O, and O2 into products such as H2 and CO2. Furthermore, the formed Ca3WO6 support belongs to an ordered double perovskite structure at the B-site (A2BB′O6), in which some Ca... 2+ Located at the A site with 12 coordination, it has low symmetry, and the rest of Ca... 2+ Located in C i The B position and O position are inversely centrally symmetric 2- Hexacoordination, with W at the B′ site in the crystal lattice 6+ It exhibits a rock salt structure, displaying a rock salt-type B-site cation sublattice composed of alternating [CaO6] and [WO6] octahedra. The W at the B′ site combines with oxygen to form a high-bond-energy WO bond, which is conducive to the absence of surface oxygen, promotes the formation of oxygen vacancies and the diffusion of oxygen ions, and facilitates the adsorption, activation and decomposition of CH3COOH, H2O and O2 in the reaction gas. In particular, it has a strong ability to convert intermediate carbon-containing products (CH3COO*, CH3CO*, CH3*, etc.) and effectively inhibits the formation of by-products such as acetone.

[0023] 2) In the formed Ca3WO6 double perovskite structure, the Ca species, as an alkaline earth metal, can increase the overall basicity of the catalyst, which helps to adsorb and activate water molecules to form intermediate species such as *OH and *O. The *OH species participates in the reforming reaction, while the *O species can convert CH4 into CH4. x The C* coking precursor produced by the *(x=1-3) conversion is gasified into CO and CO2, effectively inhibiting coking formation; while the W species at the B′ site has multiple valence states, through W 6+ / W 4+ Valence state transitions act as intermediate electron transfer bridges in catalysts. On the one hand, they can promote electron transfer to Ni during hydrogen reduction. 2+ Transfer, which benefits Ni 2+ It can be reduced to elemental Ni; on the other hand, it can maintain Ni in the autothermal reforming of oxygen-containing acetic acid. 0 The oxidation state of the catalyst is adjusted to improve its antioxidant properties, thereby stabilizing the active conversion sites and increasing the hydrogen yield.

[0024] 3) The Ca3WO6 double perovskite support constructed in this invention maintains structural stability during high-temperature autothermal reforming reactions, preserves the dispersion of the active component Ni, and enhances the catalyst's resistance to sintering. Furthermore, the catalyst constructed in this invention possesses a mesoporous structure, which facilitates the transfer and diffusion of reactant acetic acid molecules and product gases.

[0025] 4) The catalyst of the present invention was used in the autothermal reforming of acetic acid to produce hydrogen. The results showed that the catalyst of the present invention exhibited advantages such as anti-coking, anti-oxidation, anti-sintering, stable catalytic activity and high hydrogen yield. Attached Figure Description

[0026] Figure 1 X-ray diffraction pattern of the CDUT-NCW-40 catalyst of this invention.

[0027] Figure 2 BJH pore size distribution diagram of the CDUT-NCW-40 catalyst of this invention.

[0028] Figure 3 X-ray diffraction pattern of the CDUT-NC catalyst of this invention

[0029] Figure 4 BJH pore size distribution diagram of the CDUT-NC catalyst of this invention. Detailed Implementation

[0030] Reference example one

[0031] Weigh 2.336 g of Ni(NO3)2·6H2O and 14.318 g of Ca(NO3)2·4H2O into a beaker and stir at room temperature until completely dissolved to obtain solution #1; weigh 14.429 g of citric acid and dissolve it in deionized water to obtain solution #2; weigh 4.262 g of ethylene glycol to obtain solution #3; while stirring, slowly add solution #2 dropwise to solution #3, and then slowly add solution #3 dropwise to solution #1. The mixture was stirred until it reached a gel-like consistency in a 65℃ water bath, then removed and dried in a 100℃ oven for 12 hours to obtain the catalyst precursor. The precursor was then heated to 700℃ in a tube furnace at a rate of 10℃ / min and maintained at this temperature for 4 hours. After reduction in H₂ at 700℃ for 1 hour, the CDUT-NC catalyst was obtained, forming a Ni-based catalyst Ni / CaO supported on CaO. Its typical structure is shown in the X-ray diffraction pattern (attached). Figure 3 As shown in the figure, typical Ni and CaO species appear; the molar composition of this catalyst is (NiO). 0.80 (CaO) 6.06 The weight percentage composition based on oxides is as follows: nickel oxide content is 15.0%, and calcium oxide content is 85.0%.

[0032] The activity evaluation of the acetic acid autothermal reforming reaction was carried out in a continuous flow fixed-bed reactor. The catalyst was ground and compressed into tablets, then sieved into 20-40 mesh particles. 0.1-0.3 g of the tablets were weighed and loaded into the reactor, and reduced in H2 at 700℃ for 1 h. Then, a mixed solution of acetic acid and water was injected into the vaporizer by a constant flow pump. After vaporization, oxygen was mixed in, and nitrogen was used as an internal standard gas to form a reaction feed gas with a molar composition of CH3COOH / H2O / O2 / N2=1.0 / (1.3-5.0) / (0.21-0.35) / (2.5-4.5). This feed gas was introduced into the reaction bed. The reaction conditions were 600-800℃, atmospheric pressure, and space velocity of 10000-35000 mL / (g-catalyst·h). The reaction tail gas was analyzed online by gas chromatography.

[0033] The activity of the CDUT-NC catalyst in the autothermal reforming of acetic acid was investigated. Under the following conditions: atmospheric pressure, space velocity 25000 mL / (g-catalyst·h), reaction temperature 700℃, and feed gas molar composition of acetic acid / water / oxygen / nitrogen 1.0 / 4.0 / 0.28 / 3.9, the CDUT-NC catalyst exhibited low activity, low hydrogen yield (around 2.00 mol-H2 / mol-HAc), CO2 selectivity of approximately 52.5%, CO selectivity of approximately 40.0%, and CH4 selectivity of approximately 7.5%. Low-temperature nitrogen adsorption characterization of the CDUT-NC catalyst was performed, and the results are attached. Figure 4 As shown, a specific surface area of ​​26.6 m² was obtained. 2 / g, pore volume is 0.124cm³ 3 / g, with an average pore size of 7.9nm; XRD characterization results showed that the catalyst had poor stability during the autothermal reforming of acetic acid, and the Ni metal particle size increased from 23.1nm to 28.0nm after 10 hours of reaction.

[0034] Example 1

[0035] Weigh out 2.336g of Ni(NO3)2·6H2O, 7.580g of Ca(NO3)2·4H2O, and 1.700g of (NH4)6H2W. 12 O 40• xH2O was dissolved in a beaker and stirred at room temperature until completely dissolved to obtain solution #1; 8.554g of citric acid was weighed and dissolved in deionized water to obtain solution #2; 2.527g of ethylene glycol was weighed to obtain solution #3; under stirring, solution #2 was slowly added dropwise to solution #3, and then solution #3 was slowly added dropwise to solution #1, and stirred in a 65℃ water bath until gel-like, then placed in a 100℃ oven to dry for 12h to obtain the catalyst precursor; the obtained catalyst precursor was heated to 700℃ in a tube furnace at a heating rate of 10℃ / min and maintained for 4h; after reduction in H2 at 700℃ for 1h, a nickel-based catalyst CDUT-NCW-40 with Ca3WO6 double perovskite structure as the main component was obtained, and its typical structure is shown in the X-ray diffraction pattern (attached). Figure 1 As shown in the figure, a Ni-Ca-WO active center supported by a double perovskite Ca3WO6 was formed, and its BJH mesoporous structure distribution is shown in the attached figure. Figure 2 The catalyst has a molar composition of (NiO). 0.80 (CaO) 3.21 (WO3) 0.69 The weight percentage composition based on oxides is as follows: nickel oxide 15.0%, calcium oxide 45.0%, and tungsten trioxide 40.0%.

[0036] The activity of catalyst CDUT-NCW-40 in the autothermal reforming of acetic acid was investigated. Under the following conditions: atmospheric pressure, space velocity 25000 mL / (g-catalyst·h), reaction temperature 700℃, and feed gas molar composition of acetic acid / water / oxygen / nitrogen 1.0 / 4.0 / 0.28 / 3.9, the catalyst exhibited stable performance, achieving 100% conversion of acetic acid, maintaining a hydrogen yield of 2.54 mol-H2 / mol-HAc, CO2 selectivity of approximately 58.7%, CO selectivity of approximately 40.1%, and CH4 selectivity of 0.87%, with no acetone produced as a byproduct. The catalyst activity remained stable as the reaction proceeded. The reduced CDUT-NCW-40 catalyst was characterized by XRD, as shown in the attached figure. Figure 1 As shown, a Ca3WO6 double perovskite phase was formed, while the diffraction peak of metallic Ni was weak, indicating that Ni was highly dispersed in the Ca3WO6 support, forming a Ni / Ca3WO6 structure. Temperature-programmed reduction (TPR) tests showed a reduction peak of free NiO at around 480℃, indicating a strong interaction between Ni and the Ca3WO6 support. Low-temperature nitrogen adsorption characterization of the CDUT-NCW-40 catalyst was performed, as shown in the attached figure. Figure 2 As shown, the result is: specific surface area is 14.1 m². 2 / g, pore volume is 0.115cm³ 3The catalyst has an average pore size of 9.6 nm and a g / g. Results show that this catalyst effectively suppresses the formation of acetone byproducts and also effectively inhibits methanation. XRD and TPR characterization results indicate that the catalyst structure did not undergo phase transitions or sintering during the reaction. The mesoporous structure promotes the conversion of acetic acid, with no coking or oxidation, exhibiting high catalytic activity and stable hydrogen yield.

Claims

1. The application of a perovskite-type nickel-based catalyst in the autothermal reforming of acetic acid to produce hydrogen, characterized in that: 0.1-0.3 g of catalyst was reduced in H2 at 700°C for 1 h, purged with nitrogen, and then a mixed gas with a molar ratio of acetic acid / water / oxygen / nitrogen of 1.0 / (1.3-5.0) / (0.21-0.35) / (2.5-4.5) was introduced through the catalyst bed for reaction at 600-800°C. The catalyst was prepared by the following method: a certain amount of calcium nitrate, ammonium metatungstate, and nickel nitrate were weighed, placed in a beaker, and stirred at room temperature until completely dissolved to obtain solution #1; then citric acid with a total molar ratio of 1:1 to the metal cations was weighed and dissolved in deionized water to obtain solution #2; and then the metal cations were weighed... Ethylene glycol with a total cation molar ratio of 1:1 yielded solution #3. Solution #2 was slowly added dropwise to solution #3 under stirring, and then solution #3 was slowly added dropwise to solution #1. The mixture was stirred until a gel-like consistency was reached under a 65°C water bath. The gel was then removed and dried in a 100°C oven for 12 hours to obtain the catalyst precursor. The obtained catalyst precursor was then calcined in a tube furnace at a heating rate of 10°C / min to 700°C for 4 hours to obtain product A. After reduction treatment, a nickel-based catalyst was obtained, in which Ni is uniformly dispersed in a Ca3WO6 double perovskite framework, forming Ni-Ca-WO active centers. The molar composition of product A is (NiO). a (CaO) b (WO3) c The composition of the oxides is as follows: nickel oxide content is 13.6%-16.9%, calcium oxide content is 42.1%-47.9%, and tungsten trioxide content is 37.0%-42.7%, with the sum of the weight percentages of each component being 100%.

2. The application of the perovskite-tungsten double perovskite nickel-based catalyst according to claim 1 in the autothermal reforming of acetic acid to produce hydrogen, characterized in that: Product A has the following composition by weight percentage based on oxides: nickel oxide 15.0%, calcium oxide 45.0%, and tungsten trioxide 40.0%.

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