Sulfur loading-oxygen storage bifunctional catalyst
By preparing LaNi0.05MxFe1-0.05-xO3 catalyst, the problem of catalyst poisoning caused by H2S impurities accompanying CH4 source was solved, and efficient conversion into synthesis gas and excellent sulfur resistance were achieved, which is suitable for large-scale production and practical application.
Patent Information
- Application Number
- CN202510824063.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-19
- Publication Date
- 2025-09-30
AI Technical Summary
In existing CH4 chemical chaining technology, CH4 sources such as natural gas, biomass and industrial exhaust are accompanied by acidic impurities such as H2S, which causes catalyst poisoning, affects catalyst activity and stability, and makes it difficult to achieve efficient conversion into synthesis gas.
LaNi0.05MxFe1-0.05-xO3 catalyst was designed and prepared, in which Ni is an active element for activating CH4 and CO2, and M is a sacrificial agent that prevents the catalyst from being sulfurized. They are co-doped at the B position of LaFeO3 to achieve regulation of activity and sulfur resistance.
The catalyst has a high CH4 conversion rate and excellent sulfur resistance. It can serve stably for more than 50 times in a 50ppm H2S atmosphere, avoiding the deep desulfurization step of complex gas sources and improving the sulfur resistance and thermal stability of the catalyst.
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Figure CN120714643A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of methane chemical looping technology, and in particular to a sulfur-carrying and oxygen-storing dual-function catalyst used in methane chemical looping technology and a preparation method thereof. Background Art
[0002] As society's demand for energy continues to increase, the combustion of fossil fuels as the primary energy source has led to a continuous rise in atmospheric CO2 concentrations, with annual emissions currently exceeding 40 billion tons. As a major greenhouse gas, excessive CO2 emissions contribute to the global warming effect, leading to a series of environmental problems such as increased pests and diseases, rising sea levels, climate anomalies, and intensified ocean storms. To address this issue, CO2 capture, utilization, and storage have become effective strategies for addressing rising CO2 concentrations. On the one hand, the greenhouse effect of methane (CH4), the main component of natural gas, is 20 to 26 times greater than that of an equivalent amount of CO2. On the other hand, due to its abundant reserves, low price, and relative cleanliness, CH4 is a viable alternative to oil and coal as a fuel and chemical feedstock.
[0003] Traditional CH4 utilization technologies primarily focus on fuel and chemical conversion feedstock. Among these, CH4 combustion is the most traditional method, widely used for heating, power generation, transportation fuel, industrial process fuel, and flaring. However, its inevitable CO2 emissions and fugitive CH4 emissions can still exacerbate the greenhouse effect. On the other hand, technologies such as CH4 partial oxidation, CH4 steam reforming, CH4 dry reforming, and autothermal reforming combine CH4 with CO2 (or H2O, O2, etc.) to produce synthesis gas (syngas). This syngas can be used as a feedstock for synthesizing high-value-added products through methanol production, Fischer-Tropsch synthesis, hydroformylation, and carbonylation. However, the syngas produced by these technologies has a low hydrogen-to-carbon ratio, making it difficult to meet the production needs of downstream users. Furthermore, the coexistence of reactants and products increases the potential for side reactions. To overcome these shortcomings, scientists have proposed CH4 chemical looping technology. In this technology, a catalyst first reacts with CH4 to produce H2 and CO (or CO2 and H2O). The reduced catalyst is then oxidized by CO2 (or H2O, O2), simultaneously producing CO (or H2).
[0004] The key to CH4 chemical looping technology lies in the design of suitable catalysts. Perovskite-structured oxides have attracted the interest of many researchers due to their excellent structural stability and oxygen-carrying capacity during redox processes. As a representative perovskite oxide, LaFeO3 has been widely used in chemical looping technology. Ni has been shown to be one of the most active metal elements in CH4 activation, and studies have successfully implemented chemical looping technology by doping Ni into the B site of perovskites. Notably, CH4 sources such as natural gas, biomass, and industrial exhaust are often accompanied by acidic impurities such as H2S, which can easily poison catalysts. Previous studies have found that sulfur components not only react directly with catalysts but also undergo complex homogeneous and heterogeneous competitive reactions with CO2 and H2O to form different gas-phase sulfur species. Specifically, H2S tends to adsorb on catalysts to form stable sulfides, which can cause poisoning (especially for Ni-based materials). In this context, although the addition of Ni can significantly enhance the activity of LaFeO3, the presence of H2S is likely to be a significant issue for the industrial application of Ni-based catalysts. Therefore, improving the sulfur tolerance of catalysts is crucial for the development of chemical looping technology.
[0005] Therefore, in order to address the problem that CH4 sources such as natural gas, biomass and industrial exhaust gas are accompanied by acidic impurities such as H2S, it is an urgent problem for technical personnel in this field to design and prepare a catalyst with dual functions of sulfur loading and oxygen storage to achieve efficient conversion of methane into synthesis gas under a sulfur-containing atmosphere. Summary of the Invention
[0006] Given this, CH4 sources such as natural gas, biomass, and industrial exhaust are often accompanied by acidic impurities such as H2S. Running undesulfurized CH4 through methane chemical looping technology can easily cause H2S to adsorb on the catalyst, forming stable sulfides, leading to catalyst poisoning. The present invention aims to provide a catalyst that combines high CH4 conversion activity with high tolerance to high sulfur impurities. By analyzing the effects of H2S on catalysts, this invention explores the pathways of catalyst deactivation caused by sulfurization, identifies key factors for avoiding catalyst deactivation, and incorporates them into catalyst design, thereby developing a new design strategy for sulfur-resistant catalysts.
[0007] To achieve the above object, the present invention adopts the following technical solutions:
[0008] A sulfur-carrying and oxygen-storing dual-function catalyst, the general structural formula of the catalyst is LaNi 0.05 M x Fe 1-0.05-x O3;
[0009] Wherein, x is 0-0.95; M is any one of Mo, W, Ca, Cu, and Zn;
[0010] In the catalyst, Ni is an active element for activating CH4 and CO2, and M is a sacrificial agent that prevents the catalyst from being sulfided. Ni and M are co-doped at the B position of LaFeO3 to achieve regulation of activity and sulfur resistance.
[0011] The present invention provides a sulfur-carrying and oxygen-storing bifunctional catalyst for methane chemical chaining technology with simple process, strong repeatability, and suitability for large-scale production. It can realize the large-scale preparation of the catalyst and the promotion of practical engineering applications, providing a reliable solution for the high-quality conversion of low-carbon energy under complex gas sources.
[0012] The present invention also provides a method for preparing the above-mentioned sulfur-carrying-oxygen storage bifunctional catalyst for methane chemical looping technology, comprising the following steps:
[0013] (1) La(NO3)3·6H2O, Fe(NO3)3·9H2O, Ni(NO3)2·6H2O and the corresponding metal salt of M are weighed according to the metal atom molar ratio in the catalyst structure formula of claim 1, and then La(NO3)3·6H2O, Fe(NO3)3·9H2O and Ni(NO3)2·6H2O are added to water and stirred to obtain a precursor solution A;
[0014] (2) dissolving the weighed corresponding metal salt of M in water and stirring evenly to obtain a precursor solution B;
[0015] (3) Precursor solution A and precursor solution B are mixed to obtain precursor solution C, which is heated in a water bath for the first time. Then, citric acid is added and the water bath temperature is increased. The precursor is heated in a water bath again until the precursor becomes a wire-like substance.
[0016] (4) The wire-like precursor is transferred to a drying oven for drying, and then the dried product is taken out and ground into powder, which is then transferred to a muffle furnace for heating treatment to obtain a sulfur-loaded and oxygen-storage bifunctional catalyst for methane chemical chain technology.
[0017] Furthermore, the corresponding metal salt of M in step (1) is (NH4)6Mo7O 24 4H2O, (NH4)6W7O 24 ·6H2O, Ca(NO3)2·4H2O, Cu(NO3)2·3H2O, Zn(NO3)2·6H2O.
[0018] Furthermore, the first water bath heating temperature in step (3) is 20-50° C., and the water bath heating time is 20 min.
[0019] Furthermore, in step (3), the water bath temperature is raised to 50° C. before adding citric acid, and the water bath temperature is raised to 70° C. after adding citric acid.
[0020] Furthermore, the amount of citric acid added is 1.25 times the total molar mass of the metal cations C in the precursor solution.
[0021] Furthermore, in step (4), the drying temperature is 120° C. and the drying time is 12 h.
[0022] Furthermore, in step (4), the muffle furnace was heated from room temperature to 500°C at a heating rate of 5°C / min and kept at this temperature for 3 hours, and then heated to 800°C at a heating rate of 10°C / min and kept at this temperature for another 3 hours.
[0023] Performance evaluation method of sulfur-supported-oxygen storage bifunctional catalyst:
[0024] The reaction temperature in both the reduction and oxidation reactors was 800°C, and H2S concentrations varied in the reduction reactor (0 ppm, 50 ppm, 200 ppm, and 1000 ppm, respectively). In the reduction reactor, CH4 gas containing H2S was partially oxidized by the catalyst to form synthesis gas. In the oxidation reactor, the reduced catalyst was oxidized by CO2 (or H2O, O2) to replenish lattice oxygen. The initial CH4 concentration was 5% by volume, and after mixing with H2S, the concentration was 3.53% by volume. The flow rate was 100 mL / min. The CO2 (or H2O, O2) concentration was 4.5% by volume, and the flow rate was 130 mL / min.
[0025] The beneficial effects of the present invention are: the catalyst designed and prepared by the present invention has excellent reaction activity, and the conversion rate of CH4 exceeds 95%. The product prepared by the present invention has excellent sulfur resistance and thermal stability, and can stably serve for more than 50 redox cycles in a 50ppm H2S atmosphere, and can avoid the deep desulfurization step of complex gas sources. By studying the reaction mechanism between the catalyst and H2S, the present invention found that H2S is adsorbed on the M site of the catalyst during the CH4 conversion stage and generates sulfide, and the sulfide is restored to oxide after the oxidation stage. This mechanism is defined as sulfur transport, that is, sulfur carrying. Based on the above, the present invention successfully designed and prepared a catalyst with sulfur carrying and oxygen storage dual functions. BRIEF DESCRIPTION OF THE DRAWINGS
[0026] Figure 1 CH4 (50ppmH2S) and CO2 with LaNi at 800℃ 0.05 Mo x Fe 1-0.05-x Gas product evolution diagram during the reaction of O3 series catalysts;
[0027] Figure 2 The effect of H2S concentration on LaNi 0.05 Fe 0.95 O3 and LaNi 0.05 Mo 0.07 Fe0.88 Effect diagram of O3 on CH4 conversion, H2 and CO production;
[0028] Figure 3 LaNi at 50ppm H2S 0.05 Mo 0.07 Fe 0.88 O3 CH4 chemical looping dry reforming redox stability test diagram;
[0029] Figure 4 LaNi for CH4 conversion and CO2 cracking 0.05 Mo 0.07 Fe 0.88 Characterization results of O3 (where a is XRD, b is Raman, c is Far-infrared, and d is Mid-infrared). DETAILED DESCRIPTION
[0030] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.
[0031] Example 1 Sulfur-carrying and oxygen-storage dual-function catalyst for methane chemical looping dry reforming
[0032] (1) According to the molar ratio La 3+ :Fe 3+ :Ni 2+ =1:0.95:0.05, adding the required amount of La(NO3)3·6H2O, Fe(NO3)3·9H2O, and Ni(NO3)2·6H2O to deionized water, and stirring thoroughly to obtain a precursor solution A;
[0033] (2) Raise the water bath temperature to 50°C and add citric acid in an amount 1.25 times the amount of the total metal cations;
[0034] (3) heating the water bath to 70°C and stirring continuously until the precursor appears in a stringy state;
[0035] (4) Transfer the precursor to a drying oven at 120 °C and dry for 12 h;
[0036] (5) Take out the powder, grind it into powder, transfer it to a muffle furnace, heat it to 500℃ at a heating rate of 5℃ / min and keep it for 3h, then heat it to 800℃ at a heating rate of 10℃ / min and keep it for 3h, and finally obtain black powder LaNi 0.05 Fe0.95 O3.
[0037] Example 2 Sulfur-carrying and oxygen-storage dual-function catalyst for methane chemical looping dry reforming
[0038] (1) According to the molar ratio La 3+ :Fe 3+ :Ni 2+ =1:0.88:0.05, adding the required amount of La(NO3)3·6H2O, Fe(NO3)3·9H2O, and Ni(NO3)2·6H2O to deionized water, and stirring thoroughly to obtain a precursor solution A;
[0039] (2) According to the molar ratio La 3+ :Mo 6+ =1:0.07 ratio, add the required amount of (NH4)6Mo7O in deionized water 24 4H2O, stir thoroughly to obtain precursor solution B;
[0040] (3) Precursor solutions A and B were mixed to obtain precursor solution C, and the mixture was stirred in a 30°C water bath for 20 min.
[0041] (4) When the water bath temperature rises to 50°C, add citric acid in an amount 1.25 times the amount of the metal cation;
[0042] (5) Heat the water bath to 70°C and continue stirring until the precursor appears in a stringy state;
[0043] (6) Transfer the precursor to a drying oven at 120 °C and dry for 12 h;
[0044] (7) Take out and grind into powder, transfer to a muffle furnace, heat to 500℃ at a heating rate of 5℃ / min and keep warm for 3h, then heat to 800℃ at a heating rate of 10℃ / min and keep warm for 3h to obtain LaNi 0.05 Mo 0.07 Fe 0.88 O3.
[0045] Example 3 Catalyst Activity Evaluation
[0046] Heating stage: LaNi prepared in Example 1 and Example 2 0.05 Fe 0.95 O3 and LaNi 0.05 Mo 0.07 Fe 0.88 O3 were respectively charged into a fixed bed reactor and heated to 800 °C under N2 atmosphere at a heating rate of 10 °C / min.
[0047] Reduction reaction stage: 5% CH4 / N2 gas (100 mL / min) and N2 (30 mL / min) were introduced, the reaction temperature was maintained at 800°C, the reaction time was 20 minutes, and the CH4 concentration in the tail gas and the product concentration were recorded.
[0048] Nitrogen purge stage: Close the CH4 gas line and switch to pure N2 gas (70 mL / min) for 10 minutes to remove residual gas in the pipeline and reactor, avoid cross contamination between different gases, and ensure that each stage can be carried out in the most optimized manner.
[0049] Oxidation reaction stage: close the N2 gas line and switch to 5% CO2 / N2 gas (130mL / min), and regenerate the catalyst at the same temperature for 30 minutes, so that the reduced catalyst is reoxidized to restore its initial state for the next cycle.
[0050] The results of catalyst activity evaluation are as follows Figure 1 As shown. When CH4 enters the reactor, the conversion of CH4 can be observed immediately, and the concentrations of H2 and CO increase sharply. By calculating the CH4 conversion rate, it is found that the doping of Mo in a single redox reaction does not cause the activity of the catalyst to decrease. It is worth noting that in the case of LaNi 0.05 Fe 0.95 After 10 minutes of CH4 mixed gas injection into the O3 reactor, the CO concentration began to decrease. 0.05 Mo 0.07 Fe 0.88 O3 did not show this phenomenon until the reaction lasted for about 13 minutes. This shows that Ni and Mo co-doping can increase the content of reducible lattice oxygen in perovskite oxide, thereby selectively oxidizing CH4. In addition, in LaNi 0.05 Fe 0.95 After adding Mo to the O3 catalyst, the formation of CO2 in the initial stage of the reaction is suppressed. The above phenomenon shows that the doping of Ni and Mo can adjust the activity and selectivity of the perovskite catalyst, enabling the selective oxidation of CH4 to CO and H2;
[0051] Example 4 Evaluation of the sulfur resistance of the catalyst
[0052] The poisoning of H2S to the catalyst is not a cluster, but a continuous decline in the performance of the catalyst during the redox cycle. 0.05 Fe 0.95 O3 and LaNi 0.05 Mo 0.07 Fe 0.88 O3 underwent 10 redox cycles in the presence of different H2S concentrations.
[0053] Redox cycle: Repeat the reduction reaction and oxidation reaction steps in Example 3 for a total of 10 cycles.
[0054] Operation with different H2S concentrations: 0 ppm H2S was used when N2 was introduced during the reduction stage; other concentrations were achieved by replacing N2 in the reduction stage with 50 ppm, 200 ppm and 1000 ppm H2S.
[0055] The test results of the catalyst's sulfur resistance are as follows: Figure 2 As shown, under the condition of no H2S atmosphere, LaNi 0.05 Fe 0.95 O3 and LaNi 0.05 Mo 0.07 Fe 0.88 O3 can operate stably in 10 redox cycles; when 50ppm H2S is introduced into the reactor, LaNi 0.05 Fe 0.95 The CH4 conversion rate of O3 decreased from 92.4% to 74.8% in 10 cycles, while LaNi 0.05 Mo 0.07 Fe 0.88 The change in CH4 conversion rate of O3 is negligible; when the H2S concentration increases to 200 and 1000 ppm, LaNi 0.05 Fe 0.95 O3 and LaNi 0.05 Mo 0.07 Fe 0.88 O3 showed a trend of decreasing conversion rate, but LaNi 0.05 Mo 0.07 Fe 0.88 The rate of O3 decrease is significantly lower than that of LaNi 0.05 Fe 0.95 O3.
[0056] Example 5 Regeneration cycle test
[0057] In 50ppm H2S atmosphere, the LaNi 0.05 Mo 0.07 Fe 0.88 O3 underwent 50 redox cycles. Figure 3 shown.
[0058] LaNi 0.05 Mo 0.07 Fe 0.88 O3 can stably cycle more than 50 times in an atmosphere containing 50 ppm H2S, and has excellent thermal stability and sulfur resistance, indicating that Mo doping is a very effective strategy for improving the sulfur resistance of the catalyst.
[0059] Example 6: Mechanism of action between catalyst and H2S
[0060] The LaNi prepared in Example 2 0.05 Mo 0.07 Fe 0.88 O3 was subjected to 20 redox cycles in 1000ppmH2S atmosphere, and the catalyst was characterized by XRD, Raman, far infrared and mid-infrared. Figure 4 .
[0061] In the reduction stage of the 20th cycle, characteristic peaks of MoS2 were found in XRD, Raman and far infrared diffraction and spectral characterizations; the difference is that no characteristic peaks of MoS2 were found in the CO2 cracking stage, but characteristic peaks of MoO3 were found. 0.05 Fe 0.95 The Raman spectrum of O3 does not show the 0.05 Mo 0.07 Fe 0.88 NiS was found on the O3 sample. Based on the above characterization results, we believe that H2S is reduced by LaNi 0.05 Mo 0.07 Fe 0.88 The Mo site of O3 is adsorbed and converted into MoS2, and the generated MoS2 is restored to MoO3 after the CO2 cracking stage and the sulfur-containing substances are removed. Based on this, the doping of Mo makes LaNi 0.05 Mo 0.07 Fe 0.88 O3 has a sulfur-carrying function similar to that of oxygen storage for H2S.
[0062] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.
Claims
1. A sulfur-supporting-oxygen storage bifunctional catalyst, characterized in that: The general structural formula of the catalyst is LaNi 0.05 M x Fe 1-0.05-x O3; Wherein, x is 0-0.95; M is any one of Mo, W, Ca, Cu, and Zn; In the catalyst, Ni is an active element for activating CH4, M is a sacrificial agent that prevents the catalyst from being sulfided, and Ni and M are co-doped at the B site of LaFeO3.
2. A method for preparing the sulfur-carrying-oxygen storage dual-function catalyst according to claim 1, characterized in that: The following steps are involved: (1) La(NO3)3·6H2O, Fe(NO3)3·9H2O, Ni(NO3)2·6H2O and the corresponding metal salt of M are weighed according to the metal atom molar ratio in the catalyst structure formula of claim 1, and then La(NO3)3·6H2O, Fe(NO3)3·9H2O and Ni(NO3)2·6H2O are added to water and stirred to obtain a precursor solution A; (2) dissolving the weighed corresponding metal salt of M in water and stirring evenly to obtain a precursor solution B; (3) Precursor solution A and precursor solution B are mixed to obtain precursor solution C, which is heated in a water bath for the first time. Then, citric acid is added and the water bath temperature is increased. The precursor is heated in a water bath again until the precursor becomes a wire-like substance. (4) The wire-like precursor is transferred to a drying oven for drying, and then the dried product is taken out and ground into powder, which is then transferred to a muffle furnace for heating treatment to obtain a sulfur-loaded and oxygen-storage bifunctional catalyst for methane chemical chain technology.
3. The method for preparing a sulfur-supporting-oxygen storage dual-function catalyst according to claim 2, characterized in that: The corresponding metal salt of M in step (1) is (NH4)6Mo7O 24 4H2O, (NH4)6W7O 24 ·6H2O, Ca(NO3)2·4H2O, Cu(NO3)2·3H2O, Zn(NO3)2·6H2O.
4. The method for preparing a sulfur-supporting-oxygen storage dual-function catalyst according to claim 2, characterized in that: The first water bath heating temperature in step (3) is 20-50° C., and the water bath heating time is 20 min.
5. The method for preparing a sulfur-supporting-oxygen storage dual-function catalyst according to claim 4, characterized in that: In step (3), the water bath temperature is raised to 50° C. before adding citric acid, and the water bath temperature is raised to 70° C. after adding citric acid.
6. The method for preparing a sulfur-supporting-oxygen storage dual-function catalyst according to claim 5, characterized in that: The amount of citric acid added is 1.25 times the total molar mass of the metal cations C in the precursor solution.
7. The method for preparing a sulfur-supporting-oxygen storage dual-function catalyst according to claim 2, characterized in that: In step (4), the drying temperature is 120° C. and the drying time is 12 h.
8. The method for preparing a sulfur-supporting-oxygen storage dual-function catalyst according to claim 7, characterized in that: In step (4), the muffle furnace was heated from room temperature to 500°C at a heating rate of 5°C / min and kept at this temperature for 3 h, and then heated to 800°C at a heating rate of 10°C / min and kept at this temperature for another 3 h.