A rare earth tungstate-type nickel-based catalyst for hydrogen production by autothermal reforming of acetic acid

Abstract

This invention relates to a rare-earth tungstate-type nickel-based catalyst for hydrogen production through autothermal reforming of acetic acid. Addressing the deactivation problem of existing catalysts during the autothermal reforming of acetic acid, this invention provides a novel catalyst with stable structure and high activity. The molar composition of the catalyst of this invention is (NiO). a (SmO 1.5 ) b (WO3) c Where a is 0.75–0.86, b is 1.07–1.24, and c is 0.55–0.64. This invention employs a co-precipitation method to prepare the catalyst precursor, which is then calcined and reduced to obtain a rare-earth tungstate-type nickel-based catalyst containing Ni and Sm₂WO₆. The catalyst of this invention effectively improves catalyst stability and hydrogen yield, and effectively suppresses the formation of byproducts such as methane and acetone.

Description

Technical Field

[0001] This invention relates to a rare earth tungstate-type nickel-based catalyst for hydrogen production from acetic acid via autothermal reforming and its preparation method, belonging to the field of hydrogen production from acetic acid via autothermal reforming. Background Technology

[0002] Hydrogen is considered an important clean energy source due to its renewable, high energy density, and environmentally friendly characteristics. Traditional hydrogen production methods often use fossil fuels such as natural gas and coal, which frequently lead to environmental pollution. Biomass is widely distributed, renewable, inexpensive, and readily available, making it a better feedstock for hydrogen production. Biomass pyrolysis can yield biomass oil with high energy density, and the main aqueous component of biomass oil is acetic acid, which can be used to produce hydrogen through catalytic reforming of acetic acid.

[0003] Acetic acid catalytic reforming for hydrogen production generally includes steam reforming (SR), partial oxidation reforming (POX), and autothermal reforming (ATR). Steam reforming is a strongly endothermic reaction with high energy consumption; partial oxidation is an exothermic reaction that can achieve self-heating, but in an oxygen atmosphere, localized overheating often occurs in the catalyst bed, and excess oxygen consumes feedstock, reducing hydrogen yield. Autothermal reforming combines steam reforming and partial oxidation processes, balancing the heat supply of the reaction system, and is an effective route for acetic acid hydrogen production.

[0004] The autothermal reforming of acetic acid to produce hydrogen requires a highly efficient and structurally stable reforming catalyst to control the adsorption and activation of reactant molecules, regulate the transformation pathway of intermediate products, suppress the formation of byproducts, and promote hydrogen production. Nickel-based catalysts exhibit high activation capabilities for the C-C and CH bonds in acetic acid molecules, demonstrating good activity in the autothermal reforming of acetic acid. However, during the autothermal reforming process, the carbon precursor CH produced by the decomposition of acetic acid molecules... x Further dehydrogenation of *(x=0-3) forms C* species that coat the surface of the active metal Ni, causing a sharp decrease in reactivity. On the other hand, ethylene and acetone produced via acetic acid dehydration and ketylation reactions can also cause catalyst deactivation by clogging the catalyst's pore structure through polymerization. Furthermore, Ni-based catalysts in the high-temperature oxidizing atmosphere of autothermal reforming exhibit… 0 It is easily oxidized or aggregated and grows, thus losing its activity.

[0005] To address the various problems encountered by Ni-based catalysts in the autothermal reforming of acetic acid, this invention creatively introduces a Ni-based catalyst supported on Sm2WO6 oxide with a rare earth metal tungstate Re2WO6 structure, which has the following characteristics.

[0006] This invention addresses the characteristics of the autothermal reforming conversion of acetic acid by constructing a rare-earth tungstate Sm2WO6-type nickel-based catalyst, Ni / Sm2WO6, with Ni-Sm-WO as the active center, using a co-precipitation method. This Ni / Sm2WO6 catalyst exhibits excellent thermal stability and strong oxygen mobility. Its high specific surface area and concentrated pore size distribution facilitate the diffusion of acetic acid molecules and their contact with the catalyst, thus improving the catalyst's catalytic performance. The active component Ni, supported on Sm2WO6, forms a strong metal-support interaction, preventing Ni grain aggregation and growth, and demonstrating good anti-sintering properties in the autothermal reforming hydrogen production reaction of acetic acid. Furthermore, the constructed Ni / Sm2WO6 catalyst possesses typical mesoporous material characteristics; its mesoporous structure facilitates the transport and diffusion of reactant and product molecules, and promotes the release of active metal Ni after hydrogen reduction. 0 Highly dispersed on a stable reaction interface supported by Sm2WO6, the catalyst's catalytic activity and anti-sintering properties are enhanced. Simultaneously, through the "confined effect" of the catalyst's mesoporous structure, the condensation effect of intermediate species such as CH2CO* and CH3OCH3 in the autothermal reforming of acetic acid to produce hydrogen is effectively suppressed, reducing coke formation and thus improving hydrogen yield and CO2 selectivity.

[0007] In the rare earth tungstate Sm2WO6 structure described in this invention, both Sm and W elements possess multivalent electron transfer capabilities, which is beneficial for suppressing the active component Ni during the autothermal reforming of acetic acid. 0 The oxidation of NiO promotes the activation of NiO to generate highly active Ni. 0 The species, by exposing more active sites, effectively promotes the adsorption and activation transformation of CH3COOH, H2O, and O2 in the reaction gas, thereby improving the reaction activity and the catalyst's antioxidant capacity; it also constructs a special Sm 3+ / Sm 2+ and W 6+ / W 4+ In redox pairs, electrons are transferred through the "Sm-OW" bridge structure, enhancing the mobility of oxygen-containing species, promoting the activation and transfer of O* molecules, and further promoting the formation of the CH4 coking precursor from the autothermal reforming of acetic acid. x The oxidation of *(x=0-3), the gasification reaction of C* (C*+O*→CO and C*+CO*→CO2) and the water-gas shift WGS reaction inhibit the formation of coke deposits and prevent catalyst deactivation, thereby improving the stability of the catalyst and the hydrogen yield.

[0008] The innovations in catalyst composition and structure in this invention enable the catalyst to exhibit good activity and stability in the autothermal reforming reaction of acetic acid, and effectively suppress the production of byproducts methane and acetone, thereby improving the conversion rate of acetic acid and the yield of hydrogen. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a novel catalyst with stable structure, high conversion rate, good selectivity, and resistance to sintering and oxidation, which is a problem in the existing acetic acid autothermal reforming reaction catalysts, where the active components are easily oxidized, sintered and coked, leading to reduced catalyst activity or even deactivation.

[0010] This invention uses Ni as the active component and introduces Sm and W components to prepare a rare earth tungstate-type nickel-based catalyst using a co-precipitation method, forming Ni-Sm-WO active centers. When the catalyst of this invention is used in the autothermal reforming of acetic acid to produce hydrogen, at a reaction temperature of 700℃, the preferred catalyst achieves an acetic acid conversion rate close to 100%, and the hydrogen yield is consistently around 2.44 mol-H2 / mol-HAc.

[0011] Technical solution of the present invention:

[0012] This invention addresses the characteristics of acetic acid autothermal reforming by preparing a rare-earth tungstate-type nickel-based catalyst via a co-precipitation method. The molar composition of the catalyst in this invention is (NiO). a (SmO 1.5 ) b (WO3) c Where a is 0.75-0.86, b is 1.07-1.24, and c is 0.55-0.64; the composition by weight percentage is: nickel oxide 14.0%-16.0%, samarium oxide 46.9%-54.0%, and tungsten trioxide 31.9%-37.4%. The preferred molar composition of the catalyst in this invention is (NiO). 0.81 (SmO 1.5 ) 1.17 (WO3) 0.59 The weight percentage composition is as follows: nickel oxide 15.1%, samarium oxide 51.0%, and tungsten trioxide 33.9%.

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

[0014] 1) Based on the molar composition of each component in the catalyst (NiO) a (SmO 1.5 ) b (WO3) c Where a is 0.75-0.86, b is 1.07-1.24, and c is 0.55-0.64, a certain amount of nickel nitrate, samarium nitrate, and sodium tungstate are weighed, and nickel nitrate and samarium nitrate are placed in a beaker and stirred to dissolve, to obtain solution #1;

[0015] 2) Dissolve the sodium tungstate in another beaker by stirring, and label this solution #2;

[0016] 3) Based on the molar ratio [Ni]2+ +Sm 3+ +W 6+ ]:[OH - ] = 1:8, [CO3 2- ]:[OH - =1:16, prepare a mixed solution containing Na2CO3 and NaOH, and denote it as solution #3;

[0017] 4) At a water bath temperature of 65℃, solutions #1, #2 and #3 were added dropwise to a beaker to carry out a co-precipitation reaction, and the pH of the mixed solution was controlled within the range of 12±0.5. The mixture was then kept at a constant temperature of 65℃ and stirred for 24 hours.

[0018] 5) After aging, the precipitate was collected by filtration and washed three times with deionized water. The precipitate was then dried in an oven at 105°C for 18 hours. The dried sample was placed in a tube furnace and heated from room temperature to 750°C at a rate of 10°C / min. After calcination at this temperature for 4 hours, it was reduced in H2 at 600-800°C for 1 hour to obtain the rare earth tungstate-type nickel-based catalyst Ni / Sm2WO6 of this invention. Its main components are Ni and Sm2WO6, forming Ni-Sm-WO active centers. Its typical structure is shown in the attached figure. Figure 1 As shown, a mesoporous structure is constructed simultaneously, and its typical BJH pore size distribution is shown in the attached figure. Figure 2 As shown.

[0019] 6) Catalytic activity test: A mixed solution of acetic acid and water is injected into the vaporizer by a constant flow pump and vaporized. After vaporization, oxygen is mixed in, and nitrogen is used as an internal standard gas to form a reaction feed gas with a molar composition of CH3COOH / H2O / O2 / N2=1 / (1.3-5.0) / (0.21-0.35) / (2.5-4.5). This feed gas is then introduced into the catalyst bed, and the reaction temperature is 600-800℃.

[0020] The beneficial effects of this invention are:

[0021] 1) This invention uses Ni as the active component and introduces Sm and W components to prepare a Ni / Sm2WO6 rare earth tungstate nickel-based catalyst by co-precipitation. This catalyst exhibits excellent thermal stability and strong oxygen mobility. Sm2WO6 belongs to a body-centered monoclinic crystal system, and the entire structure consists of six twisted [WO6] crystals. 6- The alternating arrangement of octahedral units and 12 separate Sm atoms improves the dispersion of the loaded active component Ni, exposes more active sites, and forms Ni-Sm-WO active centers, which is beneficial to the adsorption and transformation of reactants CH3COOH, H2O, and O2, and prevents the aggregation and growth of Ni grains. It exhibits good anti-sintering properties in the autothermal reforming of acetic acid to produce hydrogen.

[0022] 2) In the rare earth tungstate structure Sm2WO6, both Sm and W elements have the ability to transfer electrons in multiple valence states, which is beneficial for suppressing the active component Ni during the autothermal reforming of acetic acid. 0 The oxidation of NiO promotes its reduction to Ni. 0 This species structure forms more active sites, effectively promoting the adsorption, activation, decomposition, and re-conversion of CH3COOH, H2O, and O2 in the reaction gas, thus improving the reaction activity and the catalyst's antioxidant capacity; a special Sm group is formed in this structure. 3+ / Sm 2+ and W 6+ / W 4+ Redox pair (2Sm) 3+ +W 4+ →2Sm 2+ +W 6+ Electrons are transferred through the "Sm-OW" bridge structure, while O2 can be transferred from Sm... 2+ It gains electrons and produces O. - and Sm 3+ You can also ask W 6+ Transporting electrons, producing O* and W 4+ This enhances the mobility of oxygen-containing species, promotes the activation and transfer of O* molecules, and further promotes the formation of the CH4 coke precursor produced by the autothermal reforming of acetic acid. x The oxidation of *(x=0-3) promotes the gasification reaction of C* (C*+O*→CO and C*+CO*→CO2) and the water-gas shift WGS reaction (CO+H2O→CO2+H2), inhibits the formation of coke, and prevents catalyst deactivation, thereby improving the stability of the catalyst and the hydrogen yield.

[0023] 3) This invention prepares a Ni / Sm2WO6 catalyst with a mesoporous structure via co-precipitation. The mesoporous structure facilitates the transport and diffusion of reactant and product molecules. Furthermore, the catalyst, after hydrogen reduction, promotes the reaction of the active metal Ni. 0 Highly dispersed on a stable reaction interface supported by Sm2WO6, the catalyst's catalytic activity and anti-sintering properties are enhanced. Furthermore, through the "confined effect" of the catalyst's mesoporous structure, the condensation effect of intermediate species such as CH2CO* and CH3OCH3 in the autothermal reforming of acetic acid to produce hydrogen is effectively suppressed, reducing coke formation and thus improving hydrogen yield and CO2 selectivity.

[0024] 4) The results of the autothermal reforming reaction of acetic acid show that the catalyst of the present invention achieves high efficiency in the conversion of acetic acid, high hydrogen yield, and effectively inhibits the generation of by-products, and has the characteristics of anti-oxidation, anti-sintering, and anti-coking. Attached Figure Description

[0025] Figure 1X-ray diffraction pattern of the catalyst of this invention

[0026] Figure 2 BJH pore size distribution diagram of the catalyst of this invention. Detailed Implementation

[0027] Reference example one

[0028] Weigh 2.34g of Ni(NO3)2·6H2O and 8.67g of Sm(NO3)3·6H2O into a beaker, add a certain amount of deionized water to dissolve them, and record this as solution #1; then, according to the molar ratio [Ni 2+ +Sm 3+ ]:[OH - ] = 1:8, [CO3 2- ]:[OH - =1:16, weigh 4.41g of NaOH and 0.73g of Na2CO3 and dissolve them in deionized water, denoted as solution #2; at a water bath temperature of 65℃, solution #1 and solution #2 are added dropwise to a beaker for co-precipitation reaction, and the pH of the mixed solution is controlled within the range of 12±0.5, and the mixture is aged at a constant temperature of 65℃ for 24h with stirring; after aging, the precipitate is collected by filtration and washed three times with deionized water, and then the precipitate is dried in an oven at 105℃ for 18h to obtain the catalyst precursor; the dried sample is placed in a tube furnace and heated from room temperature to 750℃ at a heating rate of 10℃ / min, and calcined at this temperature for 4h, and then reduced in H2 at 700℃ for 1h to obtain the CDUT-NS catalyst, and a Ni / Sm2O3 structure is obtained; the weight percentage composition of the catalyst based on oxides is: nickel oxide (NiO) 15.0%, samarium oxide (SmO) 15.0%, and samarium oxide (SmO) 15.0%. 1.5 The figure was 85.0%.

[0029] 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 tablets were weighed and loaded into the reactor, and reduced in H2 at 600-800℃ 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 / (1.3-5.0) / (0.21-0.35) / (2.5-4.5). This feed gas was introduced into the catalytic 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.

[0030] The activity of catalyst CDUT-NS in the autothermal reforming of acetic acid was investigated. After hydrogen reduction at 700℃, under the following conditions: atmospheric pressure, space velocity 25000 mL / (g-catalyst·h), reaction temperature 700℃, and feed gas CH3COOH / H2O / O2 = 1 / 4.0 / 0.28, catalyst CDUT-NS exhibited low hydrogen yield, acetic acid conversion of approximately 95.7%, hydrogen yield of approximately 2.1 mol-H2 / mol-HAc, CO selectivity of approximately 64.4%, CO selectivity of approximately 20.7%, and CH4 selectivity of approximately 6.5%, with a small amount of acetone as a byproduct. Low-temperature nitrogen physical adsorption characterization of the CDUT-NS catalyst showed a specific surface area of ​​7.2 m². 2 / g, pore volume 0.03cm³ 3 The catalyst has an average pore size of 7.0 nm and a most probable pore size of 3.1 nm. Characterization results show that the catalyst produces many byproducts, has poor stability and low activity in the autothermal reforming of acetic acid to produce hydrogen. The acetone reaction is not effectively inhibited, and the catalyst undergoes sintering, coking and partial oxidation.

[0031] Example 1

[0032] Weigh out 2.35g of Ni(NO3)2·6H2O and 5.20g of Sm(NO3)3·6H2O, dissolve them in deionized water, and label this solution #1; weigh out 1.93g of Na2WO4·2H2O, dissolve it in deionized water, and label this solution #2; according to the molar ratio [Ni 2+ +Sm 3+ +W 6+ ]:[OH - ] = 1:8 and [CO3 2- ]:[OH - =1:16, weigh 4.10g of NaOH and 0.68g of Na2CO3 and dissolve them in deionized water, denoted as solution #3; at a water bath temperature of 65℃, solutions #1, #2 and #3 are added dropwise to a beaker for co-precipitation reaction, and the pH of the mixed solution is controlled within the range of 12±0.5, while maintaining stirring and aging at a constant temperature of 65℃ for 24h; after aging, the precipitate is collected by filtration and washed three times with deionized water, and then the precipitate is dried in an oven at 105℃ for 18h to obtain the catalyst precursor; the dried sample is placed in a tube furnace and heated from room temperature to 750℃ at a heating rate of 10℃ / min, and calcined at this temperature for 4h, and then reduced in H2 at 700℃ for 1h to obtain the rare earth tungstate type nickel-based catalyst CDUT-NSW-21, whose main crystal phase structure is rare earth tungstate structure Sm2WO6 and Ni, forming Ni-Sm-WO active centers, and its typical crystal structure is shown in the attached figure. Figure 1 As shown in the attached figure, a typical mesoporous structure is... Figure 2As shown; the molar composition of this catalyst is (NiO). 0.81 (SmO 1.5 ) 1.17 (WO3) 0.59 The catalyst has the following composition by weight percentage of oxides: nickel oxide 15.1%, samarium oxide 51.0%, and tungsten trioxide 33.9%.

[0033] The activity of catalyst CDUT-NSW-21 in the autothermal reforming of acetic acid was investigated. After hydrogen reduction at 700℃, under the following conditions: atmospheric pressure, space velocity 25000 mL / (g-catalyst·h), reaction temperature 700℃, and feed gas molar composition CH3COOH / H2O / O2=1 / 4.0 / 0.28, the catalyst achieved 100% conversion of acetic acid, a hydrogen yield of approximately 2.4 mol-H2 / mol-HAc, a CO2 selectivity of approximately 61.3%, and a CO selectivity of approximately 33.1%. No byproducts methane or acetone were detected. Low-temperature nitrogen physical adsorption characterization of the CDUT-NSW-21 catalyst was performed, as shown in the following figures. Figure 2 As shown, the specific surface area is 7.5 m². 2 / g, pore volume 0.05cm³ 3 The catalyst exhibits a concentrated pore size distribution, with an average pore size of 10.5 nm and a most probable pore size of 2.9 nm, classifying it as a mesoporous material. Characterization results show that the catalyst did not undergo sintering or carbon deposition, and it effectively suppressed the formation of the byproduct acetone, demonstrating high catalytic activity.

Claims

1. The application of rare earth tungstate-type nickel-based catalysts in the autothermal reforming of acetic acid to produce hydrogen, characterized in that: The catalyst was reduced in an H2 atmosphere at 600-800℃ for 1 hour. Nitrogen was used as an internal standard, and a mixed gas with a molar ratio of CH3COOH / H2O / O2 / N2 = 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℃. The catalyst was prepared by the following method: Based on the catalyst composition, a certain amount of nickel nitrate and samarium nitrate were weighed and dissolved in deionized water, and the solution was stirred thoroughly to obtain solution #1; a certain amount of sodium tungstate was weighed and dissolved in deionized water, and the solution was stirred thoroughly to obtain solution #2; based on the requirement that the total molar ratio of the metal cations nickel, samarium, and tungsten to sodium hydroxide is 1:8, and the molar ratio of sodium carbonate to sodium hydroxide is 1:16, a solution containing carbon was prepared. A mixed solution of sodium tungstate and sodium hydroxide (#3) was prepared. Solutions #1, #2, and #3 were added dropwise to a beaker in a 65°C water bath for co-precipitation, with the pH of the mixed solution controlled within the range of 12±0.

5. The mixture was aged at a constant temperature of 65°C with stirring for 24 hours. After aging, the precipitate was collected by filtration and washed three times with deionized water. The washed precipitate was then dried in an oven at 105°C for 18 hours to obtain the catalyst precursor. The obtained precursor was placed in a tube furnace and heated from room temperature to 750°C at a rate of 10°C / min. It was then calcined at this temperature for 4 hours. After reduction with hydrogen, a Ni-based catalyst supported on Sm2WO6 oxide with a rare-earth tungstate Re2WO6 structure was obtained, forming a Ni-Sm-WO active center. The molar composition of this catalyst, based on oxides, is (NiO). a (SmO 1.5 ) b (WO3) c The composition of the oxides is as follows: nickel oxide 14.0%-16.0%, samarium oxide 46.9%-54.0%, tungsten trioxide 31.9%-37.4%, and the sum of the weight percentages of each component is 100%.

2. The application of the rare earth tungstate-type 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 oxide weight percentage composition: nickel oxide 15.1%, samarium oxide 51.0%, and tungsten trioxide 33.9%.

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