Strontium-chromium-based monazite-type nickel-based catalyst for hydrogen production by autothermal reforming of acetic acid

Abstract

The application relates to a strontium-chromium-based monazite type nickel-based catalyst for hydrogen production by self-thermal reforming of acetic acid. a (SrO) b (CrO 1.5 ) c Wherein a is 0.75-0.86, b is 1.81-2.01, and c is 1.68-2.05. The application adopts a Pechini sol-gel method to prepare a new catalyst in which a Ni species is loaded on a strontium-chromium-based monazite type SrCrO4 carrier and forms a Ni-Sr-Cr-O active center, so that the hydrogen production reaction activity and stability of self-thermal reforming of acetic acid are effectively improved.

Description

Technical Field

[0001] This invention relates to a specific method for preparing a Ni-based catalyst supported on strontium chromium-based monazite oxide (SrCrO4) and its application in the autothermal reforming of acetic acid to produce hydrogen, belonging to the technical field of autothermal reforming of acetic acid to produce hydrogen. Background Technology

[0002] Global economic development and population growth have led to increased energy consumption, with fossil fuels currently being the primary energy source. However, the consumption of non-renewable fossil fuels has caused environmental problems. Hydrogen, as a clean fuel, boasts high energy density and wide availability, making it one of the future alternatives to fossil fuels. Currently, common hydrogen production methods include fossil fuel-based hydrogen production, industrial by-product-based hydrogen production, and water electrolysis. Fossil fuel-based hydrogen production produces numerous by-products and gaseous impurities, and also raises carbon emissions. Electrolysis and other hydrogen production methods have stringent requirements for technology and equipment and are costly. Acetic acid reforming from renewable biomass oil is a promising green hydrogen production method.

[0003] In the reforming of acetic acid to produce hydrogen, depending on the ratio of acetic acid, water, and oxygen involved in the reaction, three pathways can be used: steam reforming (SR), partial oxidation reforming (POX), and autothermal reforming (ATR). Steam reforming is an endothermic reaction, requiring an external heat supply, which increases the cost of hydrogen production. Partial oxidation reforming introduces oxygen, which can easily cause catalyst deactivation and results in low hydrogen yield. Autothermal reforming, by introducing steam and a suitable amount of oxygen, balances the heat of reaction and reduces the cost of hydrogen production.

[0004] In the autothermal reforming of acetic acid to produce hydrogen, the catalyst plays a crucial role in the activation and conversion of acetic acid and the generation of the target product, hydrogen. Currently, catalysts used for catalytic reforming of acetic acid to produce hydrogen are mainly divided into noble metal catalysts and transition metal catalysts; among them, nickel-based catalysts with nickel as the active component have a good ability to activate the C-C and CH bonds in the acetic acid molecule and exhibit high selectivity for hydrogen, therefore, nickel-based catalysts are often the focus of research. However, the Ni on the catalyst... 0 Intermediate species such as CH3COO* and CH3CO* generated at the active sites will further decompose to form CH3* species. The accumulation of its dehydrogenation product C* will form coke and deposit on Ni. 0The surface of the catalyst is covered, causing the active sites to be obscured and leading to catalyst deactivation. On the other hand, the introduction of oxygen creates a violent oxidation reaction at the front end of the catalyst bed, with local temperatures reaching 1000°C or higher. This easily causes catalyst support sintering, pore blockage, and agglomeration and oxidation of active components, ultimately resulting in catalyst deactivation. Therefore, for the autothermal reforming of acetic acid to produce hydrogen, improving the anti-coking, anti-sintering, and anti-oxidation properties of Ni-based catalysts, and the targeted design and synthesis of catalysts with special structures, are key factors in the autothermal reforming of acetic acid to produce hydrogen.

[0005] To address the above problems, this invention creatively introduces a Ni-based catalyst supported on SrCrO4 oxide with an ABO4 monazite structure, which has the following characteristics.

[0006] First, SrCrO4 belongs to the monazite-type structure in ABO4, with space group p21 / n. It consists of 8- or 9-coordinated strontium ion polyhedra with shared edges and smaller CrO4 tetrahedra. Chromium ions are connected to strontium sites through shared edges. The distorted structure of the shared tetrahedra provides more adsorption sites for the activation of reactant molecules CH3COOH, O2, and H2O. The introduction of the active component Ni forms Ni-Sr-Cr-O active centers, which accelerate the decomposition of acetic acid and enhance the modulation effect on intermediate products such as CH3COO* and CH3CO*.

[0007] Secondly, the SrCrO4 monazite structure contains abundant oxygen vacancies. Furthermore, the heat treatment provided during the autothermal reforming of acetic acid promotes the migration of lattice oxygen from the bulk phase to the catalyst surface, forming more oxygen vacancies. This positively impacts the gasification of C*, the coking precursor formed after the dehydrogenation of acetic acid-derived intermediates such as *CH3, activating it into CO / CO2 molecules (C*+O*→CO, CO*+O*→CO2), thus improving the catalyst's resistance to coking. Simultaneously, the highly dispersed active component Ni on the stable SrCrO4 support surface, and the strong interaction between them inhibits the sintering of the active component Ni, ensuring the stability of the hydrogen production process.

[0008] Finally, in the SrCrO4 monazite structure, the Lewis alkaline sites provided by the alkaline earth element Sr adsorb and activate H2O, O2, and CO2 molecules into active oxygen species O*. O* combines with oxygen vacancies on the catalyst surface and further reacts with the coking precursor C*, eliminating coking species on the catalyst surface. At the same time, the adsorption and activation of CO2 can lead to the forward reaction of WGS, promoting the generation of more hydrogen and improving the hydrogen production yield. In addition, the presence of high-melting-point Cr oxide can alleviate carbon deposition, inhibit the coating effect of coking on the active component Ni, and alleviate the sintering caused by Ni aggregation, thereby improving the catalyst's anti-coking and anti-sintering capabilities. Summary of the Invention

[0009] The problem this invention aims to solve is that, in the autothermal reforming of acetic acid, Ni-based catalysts are easily covered by coking at high temperatures, affecting the adsorption and conversion of acetic acid molecules and thus affecting hydrogen production. At the same time, the catalyst is easily oxidized and sintered at high temperatures, affecting its activity. This invention provides a novel catalyst that is resistant to coking, oxidation, and sintering.

[0010] This invention uses Ni as the active component and prepares a nickel-based catalyst supported on a strontium-chromium-based monazite-type SrCrO4 support with a mesoporous structure via the Pechini sol-gel method. When the catalyst of this invention is used in the autothermal reforming of acetic acid to produce hydrogen, at a reaction temperature of 700°C, the preferred catalyst achieves an acetic acid conversion rate close to 100% and a high hydrogen yield.

[0011] Technical solution of the present invention:

[0012] This invention addresses the characteristics of acetic acid autothermal reforming by preparing a strontium-chromium-based monazite-type Ni / SrCrO4 catalyst using the Pechini sol-gel method. The molar composition of the catalyst, based on oxides, is (NiO). a (SrO) b (CrO 1.5 ) c The composition of nickel oxide is as follows: nickel oxide is 14.0%-16.0%, strontium oxide is 47.0%-52.1%, and chromium oxide is 31.9%-39.0%, with the sum of the weight percentages of each component being 100%.

[0013] The specific preparation steps are as follows:

[0014] (1) Based on the molar composition of the catalyst (NiO) a (SrO) b (CrO 1.5 ) cWhere a is 0.75-0.86, b is 1.81-2.01, and c is 1.68-2.05, weigh appropriate amounts of Ni(NO3)2·6H2O, Sr(NO3)2 and Cr(NO3)3·9H2O and dissolve them in deionized water and stir until completely dissolved to obtain solution #1.

[0015] (2) Prepare a mixed solution 2# of citric acid and ethylene glycol according to the total number of metal cations: molar ratio of citric acid: ethylene glycol of 1:1:1. Mix solution 2# with solution 1#, and then keep the water bath temperature at 65℃ and continue stirring until gel is formed.

[0016] (3) The obtained gel was placed in an oven at 105℃ for 24 hours, and then calcined in a tube furnace at a rate of 10℃ / min from room temperature to 750℃ for 4 hours to obtain the Ni / SrCrO4 catalyst, which is a NiO supported on a strontium-chromium-based monazite-type SrCrO4 oxide crystal structure, and forms Ni-Sr-Cr-O 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;

[0017] (4) Catalyst activity test: Before use, the catalyst of the present invention is reduced in H2 at a temperature of 500-800℃ for 1h. Then, a mixed solution of acetic acid and water is injected into the vaporizer by a constant flow pump and vaporized. 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 introduced into the reaction bed and the reaction temperature is 500-800℃.

[0018] The beneficial effects of this invention are:

[0019] (1) In view of the characteristics of the acetic acid reforming process, a nickel-supported strontium-chromium-based monazite Ni / SrCrO4 catalyst was constructed. SrCrO4 belongs to the monazite structure with space group p21 / n. It is composed of 8 or 9-coordinated strontium ion polyhedra with shared edges and smaller CrO4 tetrahedra. Chromium ions are connected to strontium sites through edge sharing. The distorted structure of the edge-shared tetrahedra provides more adsorption sites for the activation of reactant molecules CH3COOH, O2 and H2O in the autothermal reforming process of acetic acid. The introduction of the active component Ni forms a Ni-Sr-Cr-O active center. Through the auxiliary effect of multivalent chromium and the basicity of strontium, the decomposition of acetic acid (CH3COOH*→CH3COO*+H*) is accelerated, and the modulation effect on intermediate products such as CH3COO* and CH3CO* is enhanced (CH3COO*→CH3CO*+O*, CH3CO*→CH3*+CO*).

[0020] (2) The SrCrO4 monazite structure constructed during the autothermal reforming of acetic acid forms abundant oxygen vacancies. At the same time, the heat treatment during the autothermal reforming of acetic acid promotes the migration of lattice oxygen from the bulk phase to the catalyst surface, forming more oxygen vacancies. This promotes the gasification of the coking precursor C* (CH3*→CH2*→CH*→C*) formed after the dehydrogenation of acetic acid-derived intermediate species CH3*, and activates it into CO / CO2 molecules (C*+O*→CO, CO*+O*→CO2), thus improving the catalyst's resistance to coking. Meanwhile, the active component Ni is highly dispersed on the stable SrCrO4 support surface, and the strong interaction between the two inhibits the sintering of the active component Ni, ensuring the stability of the hydrogen production process.

[0021] (3) In the SrCrO4 monazite structure described in this invention, the Lewis alkaline sites provided by the alkaline earth element Sr adsorb and activate H2O, O2, and CO2 molecules into active oxygen species O* (H2O*→O*+OH*, O2*→O*+O*, CO2*→O*+CO*). O* combines with oxygen vacancies on the catalyst surface and further reacts with the coking precursor C*, eliminating coking species on the catalyst surface. At the same time, the adsorption and activation of CO2 can lead to the forward reaction of WGS (CO+H2O→CO2+H2), promoting the generation of more hydrogen. In addition, the high melting point Cr oxide and multivalent state promote oxygen transfer, alleviate carbon deposition, inhibit the coating effect of coking on the active component Ni, and alleviate the sintering caused by Ni aggregation, thereby improving the catalyst's anti-coking and anti-sintering ability.

[0022] (4) The catalyst of the present invention was used in the process of hydrogen production by autothermal reforming of acetic acid. The results showed that the catalyst of the present invention exhibited advantages such as anti-coking, anti-sintering, anti-oxidation, high catalytic activity and stability. Attached Figure Description

[0023] Figure 1 X-ray diffraction pattern of the catalyst of this invention

[0024] Figure 2 BJH pore size distribution diagram of the catalyst of this invention. Detailed Implementation

[0025] Reference example one

[0026] 2.341 g of Ni(NO3)2·6H2O and 17.896 g of Cr(NO3)3·9H2O were weighed and poured into a beaker, and a certain amount of deionized water was added to dissolve them, resulting in solution 1#. Based on a molar ratio of total metal cations:citric acid:ethylene glycol of 1:1:1, 11.090 g of citric acid and 3.276 g of ethylene glycol were weighed, dissolved, and mixed to obtain solution 2#. Solution 2# was mixed with solution 1#, and the mixture was stirred while maintaining a water bath temperature of 65℃ until gel formation. The resulting gel was placed in a 105℃ oven for 24 hours, then removed and calcined in a tube furnace at a rate of 10℃ / min to 750℃ for 4 hours to obtain the CDUT-NC catalyst, forming a Ni-based catalyst supported on Cr2O3. The catalyst's composition by weight percentage of oxides was: nickel oxide (NiO) 15.0%, chromium oxide (CrO) 15.0%, and chromium oxide (CrO) 15.0%. 1.5 The figure was 85.0%.

[0027] 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. 0.2 g of the tablets were weighed and loaded into the reactor, and reduced in H2 at 500-800℃ 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 reaction bed. The reaction conditions were 500-800℃, atmospheric pressure, and space velocity of 10000-35000 mL / (g-catalyst·h). The reaction tail gas was analyzed online by gas chromatography.

[0028] The activity of catalyst CDUT-NC in the autothermal reforming of acetic acid was investigated. Under the reaction conditions of atmospheric pressure, space velocity of 25000 mL / (g-catalyst·h), reaction temperature of 700℃, and feed gas ratio of acetic acid / water / oxygen = 1 / 4.0 / 0.28, the initial conversion rate of acetic acid was 100.0%, and the initial hydrogen yield was 2.4 mol-H2 / mol-HAc. After 10 hours of reaction, the conversion rate of acetic acid decreased to 84.5%, and the hydrogen yield gradually decreased to 1.89 mol-H2 / mol-HAc. The selectivity for CO2 was approximately 37.3%, the selectivity for CO was approximately 55.8%, the selectivity for CH4 was 4.2%, and the selectivity for the byproduct acetone increased to approximately 1.5%. Characterization results by XRD and BET showed that the catalyst had poor stability during the autothermal reforming of acetic acid, produced a large number of byproducts, and the acetone reaction was not effectively inhibited, resulting in sintering, coking, and partial oxidation, indicating low activity.

[0029] Example 1

[0030] 2.339 g of Ni(NO3)2·6H2O, 4.005 g of Sr(NO3)2, and 7.573 g of Cr(NO3)3·9H2O were weighed and poured into a beaker. A certain amount of deionized water was added to dissolve them, resulting in solution 1#. Based on a molar ratio of total metal cations to citric acid to ethylene glycol of 1:1:1, 9.644 g of citric acid and 2.849 g of ethylene glycol were weighed, dissolved, and mixed to obtain solution 2#. Solution 2# was mixed with solution 1#, and the mixture was stirred while maintaining a water bath temperature of 65℃ until gel formation. The resulting gel was placed in an oven at 105℃ for 24 hours, then removed and calcined in a tube furnace at a rate of 10℃ / min to 750℃ for 4 hours. This yielded the Ni / SrCrO4 catalyst, i.e., the CDUT-NSC catalyst, whose typical crystal structure is shown in the attached figure. Figure 1 As shown, a NiO-supported crystal structure of SrCrO4 oxide was formed, and Ni-Sr-Cr-O active centers were established. The catalyst, after low-temperature nitrogen physical adsorption testing, showed a pore size concentrated around 8 nm, and its mesoporous structure is shown in the attached figure. Figure 2 As shown; the molar composition of this catalyst, based on oxides, is (NiO). 0.80 (SrO) 1.89 (CrO 1.5 ) 1.89 The catalyst has the following composition by weight percentage based on oxides: nickel oxide (NiO) 15.0%, strontium oxide (SrO) 49.0%, and chromium oxide (CrO) 15.0%. 1.5 The figure was 36.0%.

[0031] The activity of the CDUT-NSC 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 acetic acid / water / oxygen ratio = 1 / 4.0 / 0.28, the catalyst achieved 100% conversion of acetic acid, a stable hydrogen yield of approximately 2.3-2.5 mol-H2 / mol-HAc, a CO2 selectivity of approximately 48.7%, a CO selectivity of approximately 42.8%, and no acetone as a byproduct. Low-temperature nitrogen physisorption characterization of the CDUT-NSC catalyst showed a specific surface area of ​​6.1 m². 2 / g, pore volume 0.03cm³ 3 The catalyst exhibits a concentrated pore size distribution, with an average pore size of 8.2 nm and a most probable pore size of 3.9 nm, classifying it as a mesoporous material. Furthermore, TPR characterization results show that the reduction peak at 670℃ can be attributed to the strong interaction between nickel and the support SrCrO4, which enhances the stability of the active component nickel and inhibits catalyst sintering. This demonstrates that the catalyst exhibits high and stable activity during the reaction process, without sintering or carbon buildup, and effectively suppresses the formation of the byproduct acetone.

Claims

1. The application of strontium-chromium-based monazite-type nickel-based catalysts in the autothermal reforming of acetic acid to produce hydrogen, characterized in that: A strontium-chromium-based monazite-type nickel-based catalyst was reduced in H2 at 500-800°C for 1 h. Then, a mixed solution of acetic acid and water was injected into a vaporizer using a constant flow pump. After vaporization, oxygen was mixed in, and nitrogen was used as an internal standard gas to form a reactant gas with a molar composition of CH3COOH / H2O / O2 / N2 = 1 / (1.3-5.0) / (0.21-0.35) / (2.5-4.5). This reactant gas was introduced into the reaction bed, and the reaction temperature was 500-800°C. The catalyst was prepared by the following method: weighing an appropriate amount of Ni ( NO3)2·6H2O, Sr(NO3)2, and Cr(NO3)3·9H2O were dissolved in deionized water and stirred until completely dissolved to obtain solution #1. A mixed solution #2 of citric acid and ethylene glycol was prepared according to a molar ratio of total metal cations:citric acid:ethylene glycol of 1:1:

1. Solution #2 was mixed with solution #1, and then stirred while maintaining a water bath temperature of 65℃ until gel formation. The resulting gel was placed in an oven at 105℃ for 24 h, and then calcined in a tube furnace at a rate of 10℃ / min from room temperature to 750℃ for 4 h, forming a crystalline structure of NiO supported on a strontium-chromium-based monazite-type SrCrO4 oxide with Ni-Sr-Cr-O active centers. This crystalline structure has a mesoporous structure, thus yielding the Ni / SrCrO4 catalyst. The molar composition of this catalyst, based on oxides, is (NiO). a (SrO) b (CrO 1.5 ) c The composition of nickel oxide is as follows: nickel oxide is 14.0%-16.0%, strontium oxide is 47.0%-52.1%, and chromium oxide is 31.9%-39.0%, with the sum of the weight percentages of each component being 100%.

2. The application of the strontium-chromium-based monazite-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 composition by weight percentage based on oxides: 15.0% nickel oxide, 49.0% strontium oxide, and 36.0% chromium oxide.

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