Zircon-type derivative nickel-based catalyst for hydrogen production by autothermal reforming of acetic acid

Abstract

The present application relates to a kind of zircon type derivative nickel-based catalyst for hydrogen production by acetic acid autothermal reforming.The present application provides a new catalyst with anti-carbon deposition, sintering resistance and high activity in view of the deactivation of existing catalysts in the process of acetic acid autothermal reforming.The chemical composition of the catalyst of the present application is (NiO) a (PrO 1.5 ) b (VO 2.5 ) c Wherein a is 0.75-0.86, b is 1.19-1.39, and c is 1.24-1.57.The present application uses sol-gel method to prepare a new catalyst with Ni species supported on zircon type PrVO4 derivative and Ni-Pr-V-O active center formed by introducing Pr and V elements, which effectively improves the reaction activity of hydrogen production by acetic acid autothermal reforming.

Description

Technical Field

[0001] This invention relates to a zircon-type derivative 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] Biomass oil obtained through high-temperature pyrolysis contains acetic acid, which can reach up to 33 wt% in its aqueous phase. Converting acetic acid into hydrogen through autothermal reforming is a promising hydrogen production route.

[0003] Nickel-based catalysts exhibit activity comparable to noble metal catalysts but at a lower cost. They can effectively cleave CH bonds, making them suitable for the autothermal reforming of acetic acid. However, the oxygen introduced into the autothermal reforming system can create an oxidation zone as high as 1100°C at the catalyst bed front. This easily leads to the collapse of the internal catalyst structure, causing the active nickel species to agglomerate and sinter. Simultaneously, because the catalyst bed front is in an oxygen atmosphere, it can also cause the active Ni species to... 0 Oxidation to Ni 2+ The catalyst loses its ability to convert the reactant acetic acid. Furthermore, intermediates such as acetone and *CHx produced during the dissociation of acetic acid molecules undergo further dehydrogenation to generate coking precursors. If these precursors cannot be oxidized to CO and CO2 in time, they will form coke deposits, covering the active sites and leading to a decrease in catalyst activity. Therefore, developing catalysts with structural stability, resistance to sintering, and excellent anti-coking properties is key to improving the acetic acid conversion activity.

[0004] To address the sintering and coking problems of catalysts in the autothermal reforming conversion process of acetic acid, this invention prepares a nickel-based catalyst supported on zircon-type PrVO4 derivatives via a sol-gel method, forming Ni-Pr-VO active centers for use in the autothermal reforming hydrogen production process of acetic acid.

[0005] On the one hand, regarding the directional conversion of acetic acid, water, and oxygen reactants in the autothermal reforming process of acetic acid, the PrVO4 constructed in this invention has a tetragonal zircon-type structure and I41 / amd space group characteristics, wherein the Pr ion occupies D 2dSymmetry and a coordination number of 8, with the VO tetrahedron sharing corners and edges with the twisted PrO8 dodecahedron, this tetragonal zircon-type structure can stabilize metal cations even in oxidizing environments, preventing sintering during the autothermal reforming of acetic acid. Simultaneously, the multiple oxidation states of vanadium in the PrVO4 structure described in this invention, and the special 4f electron configuration and energy level structure of the rare earth element Pr, endow it with special structural stability, low charge transfer resistance, and a large number of oxygen vacancies. The inherent oxygen vacancies in V2O5 lead to the formation of numerous defect planes between the valence and conduction bands, which is beneficial for the separation of electrons and holes. The reaction between O2 and H2O in the electron or hole environment can generate hydroxyl radicals *OH and oxygen radicals *O, effectively vaporizing CH3* to generate CO / CO2, while also inhibiting its combination with H* to form CH4, improving the selectivity for the reaction product H2. Furthermore, the structure will be combined with V... 5+ Pr with a significantly different ionic radius (0.0735nm) 3+ The introduction of (0.113nm) into V2O5 induces lattice expansion, resulting in local mismatches in the structure. This is compensated for by the overall charge imbalance generated within the crystal. This process produces a large number of oxygen vacancies, promoting adsorption and generating numerous surface-active *O2 molecules. This increases the mobility of reactive oxygen species O*, effectively oxidizing the CH3COOH molecules to remove OH* and form the CH3CO* intermediate, generating carbon-containing products such as CO and CO2. This avoids the formation of carbon precursors that cover the active sites Ni. 0 .

[0006] On the other hand, the redox pairs formed during the reaction process Promotes charge cycling at the reaction interface, thereby creating more oxygen vacancies (O). v This process enhances the catalyst's redox capacity and the efficiency of oxygen species (O*) transfer, which is beneficial for the carbon oxidation reaction in the reaction system (CH3*→C*+O*→CO*+O*→CO / CO2), thereby promoting the elimination of carbon deposits on the catalyst surface. Simultaneously, by utilizing the basicity of rare earth element Pr and its interaction with Lewis acid centers, the number and strength of Lewis basicity are adjusted to inhibit the dehydration and polymerization reactions of adsorbed dehydrogenated species during the reaction (which leads to the formation of unsaturated compounds such as ethylene), and to suppress the ketylation reaction of acetate (2CH3COOH→CH3COCH3+H2O+CO2). It also enhances the adsorption and activation of CO2, driving the Boudouard reaction in reverse (CO2+C→2CO), thus further reducing carbon deposition.

[0007] Furthermore, the valence band configuration of Pr₂O₃ itself ([Xe)) 54 4f 3 6s 2As a Lewis base, it can donate electrons and establish abundant Pr-OV interfaces in the system through interfacial covalent bonds, allowing electrons to transfer from V sites to Pr sites. As a result, the d band center of the V site moves downward relative to the Fermi level. The lower the d band center of the metal surface, the less overlap there is between the metal d orbitals and the O2 2p orbitals, and the higher the bonding orbitals, the lower the adsorption energy. This can effectively promote charge transfer efficiency and the adsorption and activation of oxygen-containing intermediates (CH3COO*, CH3CO*, CH2CO*, CO* and O*, etc.) in the system.

[0008] The innovations in catalyst structure and composition of this invention improve the anti-coking ability, thermal stability and anti-sintering ability of Ni-based catalysts in the autothermal reforming reaction of acetic acid. Summary of the Invention

[0009] The technical problem solved by this invention is to provide a novel catalyst that is resistant to coking and sintering, has poor stability, and is resistant to sintering, in the autothermal reforming reaction of acetic acid.

[0010] This invention uses Ni as the active component and introduces Pr and V components to prepare a nickel-based catalyst supported on a zircon-type PrVO4 derivative using the sol-gel method, forming a Ni-Pr-VO active center. When this catalyst is used in the autothermal reforming of acetic acid to produce hydrogen, at a reaction temperature of 700℃, the conversion rate of acetic acid (HAc) is close to 100%, and the hydrogen yield is stable at approximately 2.57 mol-H2 / mol-HAc.

[0011] Technical solution of the present invention:

[0012] This invention addresses the characteristics of acetic acid autothermal reforming by employing a sol-gel method to prepare a nickel-based catalyst supported on a zircon-type PrVO4 derivative. The molar composition of the catalyst in this invention is (NiO). a (PrO 1.5 ) b (VO 2.5 ) c The composition of nickel oxide by weight percentage is as follows: nickel oxide 14.0%-16.0%, praseodymium oxide 49.1%-57.3%, and vanadium pentoxide 28.2%-35.6%, with the sum of the weight percentages of each component being 100%.

[0013] The specific preparation method steps are as follows:

[0014] 1) Based on the molar composition of each component in the catalyst (NiO) a (PrO 1.5 )b (VO 2.5 ) c Where a is 0.75-0.86, b is 1.19-1.39, and c is 1.24-1.57, weigh appropriate amounts of nickel nitrate, praseodymium nitrate, and ammonium metavanadate, add appropriate amount of deionized water and stir continuously until completely dissolved to obtain solution #1;

[0015] 2) Weigh out citric acid with a molar ratio of 1:1 to the total molar ratio of metal cations, dissolve it in deionized water, and stir until homogeneous to obtain solution #2. Weigh out ethylene glycol with a molar ratio of 1:1 to the total molar ratio of metal cations to obtain solution #3.

[0016] 3) Slowly add solution #2 to solution #3, and then slowly add the mixed solution to solution #1 under a 65°C water bath. Stir until a gel is formed, and then dry it in an oven at 105°C for 12 hours to obtain the catalyst precursor.

[0017] 4) The dried precursor sample was placed in a tube furnace and heated to 700-800℃ at a heating rate of 10℃ / min. After calcination at this temperature for 4 hours, a nickel-based catalyst with PrVO4 as the support was obtained, the crystal structure of which is shown in the attached figure. Figure 1 As shown, a zircon-type PrVO4 phase and a NiO phase were formed, and a Ni / PrVO4 interface was created, simultaneously constructing a mesoporous structure. The typical BJH pore size distribution is shown in the attached figure. Figure 2 As shown, the aforementioned catalyst was reduced in an H2 atmosphere at a temperature of 600-800℃ for 1 hour; nitrogen was used as the carrier gas, and a mixed gas with a molar ratio of acetic acid / water / oxygen = 1 / (3.0-5.0) / (0.2-0.5) was introduced through the catalyst bed to carry out the autothermal reforming reaction of acetic acid at a reaction temperature of 600-800℃.

[0018] The beneficial effects of this invention are:

[0019] 1) The catalyst of this invention uses Ni as the active component and introduces Pr and V components. A zircon-type PrVO4 derivative nickel-based catalyst is prepared by sol-gel method. The active component Ni is highly dispersed on the PrVO4 structural derivative, which promotes the formation of Ni-Pr-VO active centers and effectively improves the catalyst activity and anti-coking and anti-sintering ability.

[0020] 2)① The zircon-type PrVO4 structure formed by the catalyst of this invention has significant structural stability and is conducive to the separation of electrons and holes. In this environment, the acetic acid autothermal reforming reactants O2 and H2O generate hydroxyl radicals *OH and oxygen radicals *O, which effectively vaporize the acetic acid-derived CH3* species, improve the catalyst's resistance to coking, and at the same time, inhibit its combination with H* to form CH4. Furthermore, the high *OH mobility is beneficial to the WGS reaction (CO+H2O→CO2+H2), improving the selectivity for H2.

[0021] ② On the Ni-Pr-VO active center formed by this catalyst, the basicity of rare earth element Pr and the interaction of L acid centers are used to adjust the number and strength of L basicity in the system, thereby promoting the adsorption and activation of acidic reactant molecules CH3COOH and driving the Boudouard reaction to proceed in reverse (CO2+C→2CO), reducing catalyst coking.

[0022] ③At the same time, introduce V 5+ Pr with significantly different ionic radii 3+ Inducing lattice expansion generates numerous oxygen vacancies in the PrVO4 structure, which in turn adsorb and generate a large number of surface-active *O2 molecules, thereby increasing the mobility of reactive oxygen species O* and effectively oxidizing carbon-containing intermediates such as *CHx and C*, while preventing carbon precursors from covering the active sites Ni. 0 .

[0023] 3) In this invention, the Pr and V species in the PrVO4 derivative carrier have multiple valence states, forming during the reaction process. as well as Electron transfer promotes charge cycling at the reaction interface, effectively inhibiting dehydration and polymerization reactions during the reaction process. At the same time, more oxygen vacancies are formed in this process, which is beneficial for eliminating carbon deposits on the catalyst surface.

[0024] 4) The catalyst possesses abundant Pr-OV interfaces, promoting electron transfer from V sites to Pr sites. This causes the d-band center of the V site to shift downwards relative to the Fermi level, further enhancing charge transfer efficiency and the adsorption and activation of oxygen-containing intermediates (CH3COO*, CH3CO*, CO*, and O*, etc.). Simultaneously, the active component Ni... 0 The interaction with the Pr-OV interface can inhibit the migration and agglomeration of nickel particles under high temperature conditions, and improve the anti-sintering ability of the catalyst during the autothermal reforming of acetic acid.

[0025] 5) Results of the autothermal reforming reaction of acetic acid show that the catalyst of the present invention can induce the efficient conversion of acetic acid molecules during the conversion of acetic acid, effectively inhibit the generation of byproducts such as methane and acetone, improve hydrogen selectivity, and has the characteristics of anti-coking, stable activity and sintering resistance. Attached Figure Description

[0026] Figure 1 X-ray diffraction pattern of the catalyst of this invention

[0027] Figure 2 BJH pore size distribution diagram of the catalyst of this invention. Detailed Implementation

[0028] Reference example one

[0029] Weigh 1.175g of Ni(NO3)2·6H2O and 12.497g of Al(NO3)3·9H2O, pour them into a beaker, add an appropriate amount of deionized water, and stir thoroughly until dissolved to obtain solution #1; then weigh 7.849g of citric acid, dissolve it in deionized water, and stir evenly to obtain solution #2; weigh 2.318g of ethylene glycol to obtain solution #3; slowly add solution #2 dropwise to solution #3, and then, under a 70℃ water bath, slowly... The solution was slowly added dropwise to solution #1 and stirred until a gel formed. The gel was then dried in an oven at 105°C for 24 hours to obtain the catalyst precursor. This precursor sample was placed in a tube furnace and heated to 750°C at a rate of 5°C / min, and calcined at this temperature for 4 hours to obtain the CDUT-NA catalyst, forming a Ni-based catalyst supported on Al₂O₃. The catalyst's composition by weight percentage of oxides was: nickel oxide (NiO) 15.1%, aluminum oxide (Al₂O₃) 15.1%, and so on. 1.5 The figure was 84.9%.

[0030] 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. 0.1-0.2 g of the compressed catalyst was weighed, mixed with quartz sand, and loaded into the reactor. It was reduced in H2 at 600℃-800℃ for 1 h. Then, the acetic acid-water mixture was injected into the vaporizer by a constant flow pump, vaporized, and then mixed with nitrogen gas. Nitrogen gas was used as an internal standard gas to form a reaction feed gas with a molar ratio of CH3COOH / H2O / O2=1 / (3.0-5.0) / (0.2-0.5). This feed gas was introduced into the reaction bed. The reaction conditions were 600-800℃, atmospheric pressure, and space velocity of 20000-60000 mL / (g-catalyst·h). The reaction tail gas was analyzed online by gas chromatography.

[0031] The activity of the CDUT-NA catalyst was investigated during the autothermal reforming of acetic acid. Under reaction conditions of 25000 mL / (g-catalyst·h), 650℃, and a feed molar ratio of CH3COOH / H2O / O2 = 1 / 4.0 / 0.28, the initial conversion of acetic acid was 99.6%. After 10 hours of reforming, the acetic acid conversion decreased to 64.6%, the H2 yield gradually decreased to 0.65 mol-H2 / mol-HAc, the CO2 selectivity fluctuated around 49.0%, the CO selectivity fluctuated around 38.5%, the methane byproduct selectivity fluctuated around 5.6%, and the selectivity for the byproduct acetone increased to around 35.7%. XRD and other characterization results showed that the catalyst had low activity and produced a large number of byproducts during the autothermal reforming of acetic acid, and exhibited sintering and coking phenomena during the reaction, resulting in poor overall stability.

[0032] Example 1

[0033] Weigh 1.161g of Ni(NO3)2·H2O, 2.893g of Pr(NO3)3·6H2O, and 0.778g of NH4VO3, and add an appropriate amount of deionized water. Stir until homogeneous to obtain solution #1. Then weigh 3.634g of citric acid, dissolve it in deionized water, and stir until homogeneous to obtain solution #2. Weigh 1.074g of ethylene glycol to obtain solution #3. Slowly add solution #2 to solution #3, and under 65℃ water bath conditions, slowly add the mixed solution to solution #1, stirring until a gel is formed. Then dry it in an oven at 105℃ for 12h to obtain the catalyst precursor. Place the sample in a tube furnace, heat it to 800℃ at a heating rate of 10℃ / min, and calcine it at this temperature for 4 hours to obtain the catalyst CDUT-NPV of this invention. Its typical crystal structure is shown in the attached figure. Figure 1 As shown, significant PrVO4 diffraction peaks are formed at 24.4°, 32.8°, and 48.5°, while NiO diffraction peaks appear at 37.2°, 43.3°, and 62.9°, yielding a zircon-type PrVO4 derivative nickel-based catalyst, forming a Ni / PrVO4 structure with Ni-Pr-VO active centers. Low-temperature nitrogen physical adsorption-desorption testing results indicate that the catalyst's pore size is concentrated at 11.1 nm, and its typical mesoporous structure is shown in the attached figure. Figure 2 As shown; the molar composition of this catalyst is (NiO). 0.79 (PrO 1.5 ) 1.33 (VO 2.5 ) 1.33 The weight percentage composition of the oxides is as follows: nickel oxide 14.9%, praseodymium oxide 54.9%, and vanadium pentoxide 30.2%.

[0034] The activity of the CDUT-NPV catalyst was investigated via autothermal reforming of acetic acid. Under reaction conditions of a space velocity of 25000 mL / (g-catalyst·h), a reaction temperature of 700℃, and a feed molar ratio of CH3COOH / H2O / O2 = 1 / 4.0 / 0.28, the catalyst maintained a stable 100% conversion rate for acetic acid, a stable H2 yield of approximately 2.57 mol-H2 / mol-HAc, a CO2 selectivity of approximately 58.6%, and a CO selectivity of approximately 41.3%. No byproducts, methane and acetone, were detected, indicating stable catalyst activity and no deactivation. Low-temperature nitrogen physical adsorption-desorption results showed that the catalyst has a specific surface area of ​​8.0 m² / h. 2 / g, pore volume 0.05cm³ 3 With an average pore size of 11.1 nm and a most probable pore size of 2.3 nm, the catalyst belongs to the mesoporous material category. Characterization results show that the catalyst exhibits no significant coking or sintering, and demonstrates high and stable acetic acid conversion. It also effectively suppresses the generation of byproducts methane and acetone, exhibiting high activity in the autothermal reforming of acetic acid for hydrogen production.

Claims

1. The application of zircon-type derivative nickel-based catalysts in the autothermal reforming process of acetic acid, characterized in that: 0.1-0.2 g of catalyst was reduced in an H2 atmosphere at 600-800℃ for 1 h before the acetic acid autothermal reforming reaction. A mixed gas with a molar ratio of acetic acid / water / oxygen = 1 / (3.0-5.0) / (0.2-0.5) was introduced and passed through the catalyst bed for the acetic acid autothermal reforming reaction at a reaction temperature of 600-800℃. The catalyst was prepared as follows: According to the chemical composition, a certain amount of nickel nitrate, praseodymium nitrate, and ammonium metavanadate were weighed, and an appropriate amount of deionized water was added. The mixture was stirred evenly at room temperature to obtain solution #1. Citric acid with a molar ratio of 1:1 to the total molar ratio of metal cations was weighed, dissolved in deionized water, and stirred evenly to obtain solution #2. Ethylene glycol with a molar ratio of 1:1 to the total molar ratio of metal cations was weighed to obtain solution #3. Solution #2 was slowly added dropwise to solution #3, and the mixture was then slowly added dropwise to solution #1 under a 65°C water bath. The mixture was stirred until a gel was formed, then dried in an oven at 105°C for 12 hours. The resulting solution was then placed in a tube furnace and heated to 700-800°C at a rate of 10°C / min, and calcined at this temperature for 4 hours. This yielded a zircon-type PrVO4 derivative nickel-based catalyst, forming a Ni / PrVO4 structure with Ni-Pr-VO as the active center. Its molar chemical composition is (NiO). a (PrO 1.5 ) b (VO 2.5 ) c The composition of nickel oxide by weight percentage is as follows: nickel oxide 14.0%-16.0%, praseodymium oxide 49.1%-57.3%, and vanadium pentoxide 28.2%-35.6%, with the sum of the weight percentages of each component being 100%.

2. The application of the zircon-type derivative nickel-based catalyst according to claim 1 in the autothermal reforming of acetic acid to produce hydrogen, characterized in that: The catalyst has the following composition by weight percentage based on oxides: nickel oxide 14.9%, praseodymium oxide 54.9%, and vanadium pentoxide 30.2%.

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