Bifunctional catalyst as well as preparation method and application thereof

Abstract

The invention relates to the field of gas adsorption and catalysis, in particular to a bifunctional catalyst and a preparation method and application thereof. The catalyst is of a hollow tubular structure, takes calcium oxide as a basic component, and further comprises a nickel oxide, a cobalt oxide and a nickel-cobalt bimetallic oxide, wherein the molar ratio of the Ca element in the calcium oxide to the nickel oxide to the Ni element in the nickel-cobalt bimetallic oxide to the cobalt oxide to the Co element in the nickel-cobalt bimetallic oxide is (5-25): (2-15): 1; the Ni element comprises two valence states of Ni < 2 + > and Ni < 3 + >; and the Co element comprises three valence states of Co < 2 + >, Co < 3 + > and Co < 4 + >. Due to the specific elements and content of the hollow tubular catalyst, the gasification catalysis capability and adsorption capability of biomass and waste plastics are improved, and carbon deposition of the catalyst is inhibited.

Description

Technical Field

[0001] The invention relates to the technical field of gas adsorption and catalysis, and in particular to a bifunctional catalyst and a preparation method and application thereof. Background Art

[0002] In the steam gasification process of traditional biomass plastic raw materials, the gas produced contains a large amount of CO2 and a low concentration of H2, and subsequent gas purification is required to finally produce pure hydrogen suitable for utilization. In addition, the output of hydrogen produced by biomass plastic gasification is relatively limited, which shows that the technology is still in an immature state. Adsorption enhancement technology is considered to be an attractive improvement technology for steam gasification of biomass plastics, which can produce high-purity hydrogen and reduce CO2 emissions. The adsorption enhancement process introduces adsorbents into the gasification system, captures CO2 by the adsorbents, reduces the concentration of CO2 in the reaction system, thereby breaking the reaction balance and shifting the reaction to the product side. This improved process not only improves the raw material conversion rate based on the original biomass plastic gasification, but also increases the hydrogen production and concentration, while simplifying the subsequent gas separation process.

[0003] Combining the adsorbent and catalyst together can make the contact between the catalytic domain and the adsorption domain more complete, thereby enhancing the heat and mass transfer between the catalytic site and the adsorption site. The chemical adsorption kinetics are improved, and the diffusion limitation is also improved, thereby reducing the complexity of the reaction process and obtaining better catalytic and adsorption performance in the adsorption enhancement reaction of biomass waste plastics. Calcium-based materials are most widely used by researchers in the adsorption field due to their low cost, abundant resource distribution and high carbon dioxide absorption capacity. On the other hand, the rapid kinetics of CaO capturing and releasing CO2 makes it more suitable for adsorption enhanced steam gasification (SESG), thereby combining traditional steam gasification with calcium circulation to achieve efficient biomass conversion, CO2 capture and H2 generation reaction. High-purity hydrogen is produced by promoting the methane steam reforming reaction (SMR) (CH4(g)+H2O(g)=CO(g)+3H2(g)) and the water gas shift reaction (WGS) (CO(g)+H2O(g)=CO2(g)+H2(g)).

[0004] CaO is generally used as a carrier, and the preparation of Ni-Co-CaO bifunctional materials can be achieved by wet mixing, that is, loading catalytic metals nickel and cobalt on the CaO adsorbent. However, this traditional preparation method has a significant defect, that is, it easily leads to uneven distribution of Ni particles on the CaO carrier, which affects the adsorption performance and catalytic efficiency of the bifunctional material. Summary of the invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the defects of existing catalysts in the process of adsorption-enhanced gasification of biomass waste plastics, such as poor catalytic activity, poor adsorption capacity and high carbon deposition, thereby providing a bifunctional catalyst and its preparation method and application.

[0006] The first aspect of the present invention protects a bifunctional catalyst, wherein the catalyst is a hollow tubular structure, with calcium oxide as the basic component, and further comprising nickel oxide, cobalt oxide, and nickel-cobalt bimetallic oxide; wherein the molar ratio of the Ca element in the calcium oxide, the Ni element in the nickel oxide and the nickel-cobalt bimetallic oxide, and the Co element in the cobalt oxide and the nickel-cobalt bimetallic oxide is 5-25:2-15:1;

[0007] Ni elements include Ni 2+ and Ni 3+ Two valence states, based on the two forms of Ni element, Ni 2+ The atomic percentage of Ni is 31-53%, 3+ The atomic percentage is 47-69%;

[0008] Co elements include Co 2+ 、Co 3+ 、Co 4+ Three valence states, based on the three forms of Co element, Co 2+ The atomic percentage of Co is 26-46%. 3+ The atomic percentage is 37-51%, Co 4+ The atomic percentage is 9-24%.

[0009] The present invention adopts a method of precisely controlling raw materials so that the calcium element in calcium oxide, the nickel element in nickel oxide and nickel-cobalt bimetallic oxide, and the cobalt element in cobalt oxide and nickel-cobalt bimetallic oxide meet a specific molar ratio; nickel oxide, cobalt oxide, and nickel-cobalt bimetallic oxide are conventional oxides in the art, and typically, but not limitingly, nickel oxide includes NiO, cobalt oxide includes Co3O4, and nickel-cobalt bimetallic oxide includes NiCo2O4.

[0010] XPS was used to test the different valence states of Ni and Co elements.

[0011] According to the present invention, the molar ratio of the Ca element in the calcium oxide, the Ni element in the nickel oxide and the nickel-cobalt bimetallic oxide, and the Co element in the cobalt oxide and the nickel-cobalt bimetallic oxide is 20-22:3-5:1.

[0012] According to the present invention, the average grain size of the calcium oxide is 25-27 nm.

[0013] In the present invention, the specific average crystal size of calcium oxide can further improve the catalytic effect on biomass waste plastics and reduce the generation of catalyst carbon deposition.

[0014] In the present invention, since the high-temperature removal of the template may cause the tube wall to break, the length of the tube wall is a conventional length in the art, typically but not limitingly, the length is 1-50 μm, and the tube wall thickness is 1-2 μm.

[0015] The second aspect of the present invention protects a method for preparing the aforementioned bifunctional catalyst, wherein the preparation method comprises the following steps:

[0016] A calcium source, a nickel source and a cobalt source are added into water to obtain a mixed solution, a fiber template is immersed in the mixed solution, and then dried and calcined to obtain a bifunctional catalyst;

[0017] Wherein, the molar ratio of the Ca element in the calcium source, the Ni element in the nickel source, and the Co element in the cobalt source is 5-25:2-15:1;

[0018] The calcination temperature is 750-800°C.

[0019] According to the present invention, the molar ratio of the Ca element in the calcium source, the Ni element in the nickel source, and the Co element in the cobalt source is 20-22:3-5:1.

[0020] According to the present invention, the calcium source includes a soluble calcium salt, and optionally includes at least one of calcium nitrate tetrahydrate, calcium nitrate, and calcium acetate. Further optionally, the calcium source is calcium nitrate tetrahydrate and / or calcium nitrate.

[0021] According to the present invention, the nickel source includes a soluble nickel salt, optionally including at least one of nickel nitrate hexahydrate, nickel nitrate, and nickel chloride, and further optionally nickel nitrate hexahydrate and / or nickel nitrate.

[0022] According to the present invention, the cobalt source includes a soluble cobalt salt, and optionally includes at least one of cobalt nitrate hexahydrate, cobalt nitrate, and cobalt chloride, and further optionally includes cobalt nitrate hexahydrate and / or cobalt nitrate.

[0023] According to the present invention, the usage ratio of the nickel source to water is 1:15-30, in units of mmol / mL.

[0024] According to the present invention, the fiber template is absorbent paper.

[0025] In the present invention, the microstructure of the bio-template presents a columnar structure. After the absorbent paper is immersed in the mixed precursor solution, the precursor solution completely penetrates into the fiber. At high temperature, the fiber is calcined, the absorbent paper is removed, and a tubular structure is obtained. During the calcination, the organic matter in the absorbent paper will decompose and release gas to form a porous material.

[0026] According to the present invention, the ratio of water to the fiber template is 200:2000-4000, in mL / cm 2 .

[0027] According to the present invention, the immersion temperature is 10-30°C and the time is 24-28h.

[0028] According to the present invention, the drying temperature is 80-100° C. and the drying time is 6-12 hours.

[0029] According to the present invention, the calcination time is 1-2h.

[0030] The third aspect of the present invention protects the use of the aforementioned bifunctional catalyst or the bifunctional catalyst prepared by the aforementioned preparation method in the field of adsorption and catalysis.

[0031] In the present invention, the application of adsorption enhances the co-gasification of biomass waste plastics to produce hydrogen.

[0032] The technical solution of the present invention has the following advantages:

[0033] 1. The present invention provides a bifunctional catalyst, wherein the catalyst is a hollow tubular structure, with calcium oxide as the basic component, and further comprising nickel oxide, cobalt oxide, and nickel-cobalt bimetallic oxide; wherein the molar ratio of the Ca element in the calcium oxide, the Ni element in the nickel-cobalt bimetallic oxide, and the Co element in the cobalt oxide and the nickel-cobalt bimetallic oxide is 5-25:2-15:1; the Ni element comprises Ni 2+ and Ni 3+ Two forms, based on the two forms of Ni element, Ni 2+ The atomic percentage of Ni is 31-53%, 3+ The atomic percentage is 47-69%; Co elements include Co 2+ 、Co 3+ 、Co 4+ Three forms, based on the three forms of Co element, Co 2+ The atomic percentage of Co is 26-46%. 3+ The atomic percentage is 37-51%, Co 4+The atomic percentage is 9-24%. The hollow tubular structure of the bifunctional catalyst increases the contact area between the catalyst and the gas. The presence of Co promotes the electron transfer between Ni and Co, increases the electron density at the Ni metal, and transfers more electrons to the antibonding orbit of the carbon-hydrogen bond to enhance the cracking ability of the carbon-hydrogen bond, while improving the gasification catalytic ability of biomass and waste plastics. The CaO in the catalyst has more alkaline sites. The increase in alkalinity can increase the affinity of the material for CO2, thereby improving the CO2 capture ability of the calcium-based material, significantly reducing the CO2 concentration in the product gas, and thus breaking the original thermodynamic equilibrium state. This change causes the reaction to shift toward hydrogen generation, which not only improves the conversion efficiency of the raw materials, but also increases the yield and concentration of hydrogen, while inhibiting catalyst carbon deposition.

[0034] 2. The specific average grain size of CaO of the present invention can further improve the catalytic effect on biomass waste plastics and reduce the generation of carbon deposits.

[0035] 3. The present invention provides a method for preparing a bifunctional catalyst, wherein the preparation method comprises the following steps: adding a calcium source, a nickel source, and a cobalt source into water to obtain a mixed solution, immersing a template in the mixed solution, drying, and calcining to obtain a bifunctional catalyst; wherein the molar ratio of the Ca element in the calcium source, the Ni element in the nickel source, and the Co element in the cobalt source is 5-25:2-15:1; the calcination temperature is 750-800°C; the specific elements and dosages of the present invention improve the catalyst's gasification catalytic ability and adsorption ability for biomass and waste plastics and inhibit catalyst carbon deposition; the specific calcination temperature can further completely remove the biological template to obtain a structurally complete hollow structure, thereby increasing the contact area between the catalyst and the gas; when the temperature is too high, a large amount of calcium carbonate will be produced, and the gas adsorption and catalytic effects on the gas will decrease.

[0036] 4. The molar ratio of the Ca element in the calcium source, the Ni element in the nickel source, and the Co element in the cobalt source of the present invention can further improve the catalyst's gasification catalytic ability for biomass and waste plastics. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0038] Figure 1SEM images of some embodiments and comparative examples, including: (a) SEM image of Ni3Co1-WM; (b) external side view of Ni3Co1-T, (c) tube mouth view of Ni3Co1-T, (d) cross-sectional view of Ni3Co1-T, (e) external side view of Ni1Co3-T; (f) tube mouth view of Ni1Co3-T; (h) SEM-EDX mapping image of Ni3Co1-T;

[0039] Figure 2 2p orbital diagrams of Ni in some embodiments and comparative examples;

[0040] Figure 3 2p orbital diagrams of Co in some embodiments and comparative examples;

[0041] Figure 4 XRD patterns of some embodiments and comparative examples;

[0042] Figure 5 CO2-TPD programmed temperature diagrams of some embodiments and comparative examples;

[0043] Figure 6 H2-TPR programmed temperature diagrams of some embodiments and comparative examples;

[0044] Figure 7 Thermodynamic performance graphs of some embodiments and comparative examples, wherein the left side is the TG graph and the right side is the DSC graph;

[0045] Figure 8 Raman spectra of some embodiments and comparative examples. DETAILED DESCRIPTION

[0046] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0047] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0048] Example 1

[0049] This embodiment provides a method for preparing a bifunctional catalyst, which is as follows:

[0050] 0.05 mol of calcium nitrate tetrahydrate, 0.0075 mol of nickel nitrate hexahydrate, and 0.0025 mol of cobalt nitrate hexahydrate were added to 200 mL of deionized water at a molar ratio of 20:3:1, and stirred to obtain a mixed solution; absorbent paper was immersed in the mixed solution at 25°C for 24 hours, and the ratio of water to absorbent paper was 200:4000, and the unit was mL / cm 2 ; Take out the absorbent paper and dry it at 80℃ for 6h, put it into a muffle furnace and calcine it at 750℃ for 2h, remove the absorbent paper to obtain Ni3Co1-T, in which the molar ratio of Ca element in CaO, Ni element in NiO and NiCo2O4, and Co element in Co3O4 and NiCo2O4 is 20:3:1.

[0051] Example 2

[0052] This embodiment provides a method for preparing a bifunctional catalyst, which is as follows:

[0053] 0.0125 mol of calcium nitrate tetrahydrate, 0.0075 mol of nickel nitrate hexahydrate, and 0.0025 mol of cobalt nitrate hexahydrate were added into 200 mL of deionized water at a molar ratio of 5:3:1, and stirred to obtain a mixed solution; absorbent paper was immersed in the mixed solution at 25°C for 24 h, and the amount ratio of water to absorbent paper was 200:4000, and the unit was mL / cm 2 ; Take out the absorbent paper and dry it at 80℃ for 6h, put it into a muffle furnace and calcine it at 750℃ for 2h, remove the absorbent paper to obtain Ni3Co1-T', in which the molar ratio of Ca element in CaO, Ni element in NiO and NiCo2O4, and Co element in Co3O4 and NiCo2O4 is 5:3:1.

[0054] Example 3

[0055] This embodiment provides a method for preparing a bifunctional catalyst, which is as follows:

[0056] Compared with Example 1, the difference is that the calcium source used is "calcium acetate" instead of "calcium nitrate tetrahydrate", and Ni3Co1-T-calcium acetate is finally obtained.

[0057] Example 4

[0058] This embodiment provides a method for preparing a bifunctional catalyst, which is as follows:

[0059] Compared with Example 1, the difference is that it is placed in a muffle furnace and calcined at 850°C for 2 hours to finally obtain Ni3Co1-T-850.

[0060] Comparative Example 1

[0061] This comparative example provides a method for preparing a bifunctional catalyst, which is as follows:

[0062] Compared with Example 1, the difference is that the molar ratio of 0.05 mol of calcium nitrate tetrahydrate, 0.005 mol of nickel nitrate hexahydrate, and 0.005 mol of cobalt nitrate hexahydrate is 20:2:2, and Ni2Co2-T is obtained, wherein the molar ratio of the Ca element in CaO, the Ni element in NiO and NiCo2O4, and the Co element in Co3O4 and NiCo2O4 is 20:2:2.

[0063] Comparative Example 2

[0064] This comparative example provides a method for preparing a bifunctional catalyst, which is as follows:

[0065] Compared with Example 1, the difference is that the molar ratio of 0.05 mol of calcium nitrate tetrahydrate, 0.0025 mol of nickel nitrate hexahydrate, and 0.0075 mol of cobalt nitrate hexahydrate is 20:1:3, and Ni1Co3-T is obtained, wherein the molar ratio of the Ca element in CaO, the Ni element in NiO and NiCo2O4, and the Co element in Co3O4 and NiCo2O4 is 20:1:3.

[0066] Comparative Example 3

[0067] This comparative example provides a method for preparing a bifunctional catalyst, which is as follows:

[0068] 0.05 mol of calcium nitrate tetrahydrate, 0.0075 mol of nickel nitrate hexahydrate and 0.0025 mol of cobalt nitrate hexahydrate were added into 200 mL of deionized water in a molar ratio of 20:3:1, and stirred to obtain a mixed solution. The mixed solution was transferred into an oven, dried at 80°C for 6 h, and then calcined in a muffle furnace at 750°C for 2 h to obtain Ni3Co1-WM, wherein the molar ratio of the Ca element in CaO, the Ni element in NiO and NiCo2O4, and the Co element in Co3O4 and NiCo2O4 is 20:3:1.

[0069] Comparative Example 4

[0070] This comparative example provides a method for preparing a bifunctional catalyst, which is as follows:

[0071] Compared with Example 1, the difference is that the molar ratio of 0.05 mol of calcium nitrate tetrahydrate to 0.01 mol of nickel nitrate hexahydrate is 20:4, and Ni4-T is obtained, wherein the molar ratio of the Ca element in CaO to the Ni element in NiO is 20:4.

[0072] Test Case

[0073] (1) The specific SEM morphologies of some embodiments and comparative examples are as follows Figure 1 As shown, from Figure 1 (a) It can be seen that Ni3Co1-WM is not a hollow tubular structure. Figure 1 (cd) It can be seen that Ni3Co1-T is a hollow tubular structure. Figure 1 (b) It can be seen that there are many pores on the surface of the Ni3Co1-T tube wall, while the catalyst in the comparative example Figure 1 (ef) The tube wall surface of Ni1Co3-T is relatively smooth; Figure 1 From the SEM-EDX image of Ni3Co1-T (h), it can be seen that the Ni, Co and Ca elements are evenly distributed in the catalyst, the hollow tube is composed of CaO, and the Ni and Co metals are evenly dispersed in the hollow tube structure.

[0074] (2) XPS was used to analyze the surface of the bifunctional catalysts prepared in some embodiments and comparative examples. The specific results are shown in Tables 1 and 2. Figure 2 , Figure 3 shown.

[0075] Table 1

[0076]

[0077] Table 1 Figure 2 , Figure 3 The data proves that the specific element types, valence states, and atomic percentages present in the catalyst are conducive to the formation of electron sites rich in Ni elements, inhibiting the oxidation and agglomeration of Ni elements; the binding energy shift is caused by the strong electronic interaction between Ni and Co elements, which causes the electron density of Co elements to decrease, and Ni elements accept electrons from neighboring Co elements, forming an electron-rich environment and increasing the electron density at Ni elements. The increase in electron density can enhance the cracking ability of carbon-hydrogen bonds by transferring more electrons to the antibonding orbit of carbon-hydrogen bonds, thereby improving the catalytic ability to gasify biomass and waste plastics.

[0078] Table 2

[0079]

[0080] Note: Oads is the surface chemically adsorbed oxygen, Olatt is the lattice oxygen, and OH is the oxygen contained in the surface adsorbed water.

[0081] It can be seen from the data in Table 2 that Example 1 has the highest surface adsorbed oxygen concentration, which is related to the surface oxygen vacancies of the catalyst. Example 1 has more oxygen vacancies and better oxygen mobility, which promotes the cracking of molecules in the gasification reaction when used, and effectively adjusts the gas composition in the gasification product gas.

[0082] (3) From Figure 4 It can be seen that the high-intensity diffraction peaks observed at 32.32°, 37.52°, 54.02°, 64.2° and 67.54° of the catalyst Ni1Co3-T correspond to the PDF card of CaO (PDF#77-2010), proving that CaO is the main component in the bifunctional material. The average crystal size and lattice parameters of calcium oxide in the Ni-Co series bifunctional catalysts were calculated based on the XRD results according to the Scherrer formula and the Nelson-Riley function as shown in Table 3.

[0083] Table 3

[0084]

[0085] Average lattice constant of CaO in catalyst and standard CaO lattice parameter The results are consistent with those of Table 3, proving that the Ca element mainly exists in the form of CaO. At the same time, it can be seen from the data in Table 3 that the average grain size of CaO is small, which may help to improve the catalytic effect on biomass waste plastics and reduce carbon deposits.

[0086] Application Examples

[0087] (1) The experimental reaction system for enhanced gasification of biomass plastic adsorption consists of five systems: a carrier gas system, a steam injection system, a two-stage vertical fixed-bed reactor, a product condensation system, and a gas detection system. A quartz basket is suspended in the upper layer of the reaction tube to carry plastic and biomass raw materials. The quartz wool placed in the lower layer of the reaction tube supports the dual-functional materials of catalyst and adsorbent, and the position is fixed by a liner. The liquid product in the process is collected using a condenser bottle immersed in an ice water bath. The liquid in the condenser bottle is dichloromethane. In each experiment, biomass and plastic are mixed completely in a 1:1 ratio as raw materials, placed in a quartz crucible, and 1g of catalyst is placed on top of the quartz wool. N2 is injected into the system at a flow rate of 50mL / min, and the double-layer reactor is heated to the required specific temperature (600℃ for the catalytic bed and 700℃ for the pyrolysis gasification bed) at a heating rate of 10℃ / min. After the temperature stabilizes for 20min, the steam injection pump is turned on to inject water into the reaction system at a flow rate of 5mL / h. The steam feed pipe is wrapped with a 120°C heating tape to prevent steam condensation. After the reaction system is set up, the quartz basket containing biomass and plastic is quickly pushed into the upper reaction zone, and the injection valve of the air bag is opened at the same time. The steam gasification of the mixture of biomass and plastic is carried out in the upper layer, and the intermediate gas produced passes through the catalyst and adsorbent bed and is reformed in the lower layer. Each experiment is timed for 30 minutes, and the product gas sampling time is 30 minutes. After each reaction, the steam injection pump is immediately turned off, and the reaction system is purged with N2 at 650°C for 20 minutes to exhaust the steam in the system. After each adsorption enhanced gasification experiment, high-purity air is introduced, calcined at 850°C for 10 minutes, and the next adsorption enhanced biomass gasification test is carried out. The gas products after the reaction include H2, CO, CO2 and CH4, and the specific content is analyzed by TCD detector. The relative concentrations of H2, CO, CO2 and CH4 in the product gas are calculated by the following formula,

[0088]

[0089] The gas production is determined by adding the volume of gas collected in the sampling bag to its corresponding gas concentration, calculated as follows,

[0090]

[0091] Where: Yi represents gas production (mmol / gbiomass); V represents product gas volume (mL); X i Represents the gas concentration.

[0092] The catalysts prepared in the examples and comparative examples were tested, and the results are shown in Table 4.

[0093] Table 4

[0094]

[0095] Ni3Co1-T, which has the best catalytic performance, increased the hydrogen yield from 5.54mmol / g in blank conditions to 50.27mmol / g, and the H2 concentration from 32.93vol.% to 83.46vol.%. The concentrations of CO and CH4 were also low, indicating that the presence of the catalyst catalyzed the SMR reaction and WGS reaction, and the CO2 content was less than 5%, proving that CaO in the dual-functional material component adsorbed the generated CO2 during the reaction.

[0096] Compared with the comparative example Ni3Co1-WM, the hydrogen production and concentration of the example Ni3Co1-T are lower, which can prove that the hollow structure increases the contact area between the catalyst and the gas.

[0097] Compared with the comparative examples Ni2Co2-T and Ni1Co3-T, the production of H2 and CO2 in Example Ni3Co1-T decreases with the increasing percentage of cobalt atoms. It is speculated that the excessive cobalt content covers the Ni metal surface, reduces the accessibility of the reaction gas to Ni, reduces the nickel active sites, and significantly reduces the catalytic activity and anti-carbon deposition performance.

[0098] Comparison of the examples Ni3Co1-T and Ni4-T shows that the catalyst does not contain the Co element and cannot achieve good adsorption and catalytic performance.

[0099] The best example Ni3Co1-T was used to conduct adsorption enhanced gasification tests with some existing catalysts. The results are shown in Table 5.

[0100] Table 5

[0101]

[0102] Note: There are two temperatures in the reaction conditions, the first one is the catalyst bed temperature and the second one is the pyrolysis gasification bed temperature; if there is only one temperature, it means that the catalyst bed temperature and the pyrolysis gasification bed temperature are the same value.

[0103] (2) CO2-TPD characterization of some embodiments and comparative examples. Specific results are shown in Figure 5, all four materials have two CO2 desorption peaks, located at 300-400℃ and 500-600℃ respectively. The first desorption peak corresponds to the adsorption of CO2 by the alkaline sites on the surface of the material, and the second desorption peak corresponds to the adsorption of CO2 by the strong alkaline sites on the surface of the material. Moving towards the high temperature direction indicates that the alkalinity strength has increased. The alkalinity strength is ranked from large to small: Ni3Co1-T>Ni1Co3-T>Ni3Co1-WM>Ni2Co2-T, and Ni3Co1-T has the highest alkalinity and more alkaline sites. The increase in alkalinity can increase the affinity of the material for acidic CO2, thereby improving the CO2 capture capacity of the calcium-based material. Therefore, Ni3Co1-T has the highest CO2 capture capacity. The use of the bifunctional material Ni3Co1-T to remove CO2 from the gas product in situ significantly reduces the CO2 concentration in the product gas, thereby breaking the original thermodynamic equilibrium state. This change causes the reaction to shift toward hydrogen production, which not only improves the conversion efficiency of the raw materials but also increases the yield and concentration of hydrogen.

[0104] (3) H2-TPR characterization was performed on some examples and comparative examples to further study the redox function of the catalyst. The specific results are shown in Figure 6 There are at least three peaks in the figure. The multi-peak phenomenon may be due to the fact that Co and Ni have multiple different oxidation states. The first peak of Ni1Co3-T is located at 289℃, 306℃, 305℃ and 326℃, which is attributed to Co 4+ Transformed into Co 3+ and Ni 3+ Transformed into Ni 2+ The shoulder peak of Ni3Co1-T at 400℃ is attributed to the reduction of Co3O4 to CoO and Ni 2+ The combined effect of reduction to Ni. The third peak catalyst is located at 538°C, 555°C, 582°C, and 597°C and is classified as the NiO and CoO reduction peaks. The peak temperature of Ni3Co1-T moves toward the low temperature direction relative to the position of the Ni3Co1-WM peak, indicating that the special three-dimensional hollow structure helps to reduce the difficulty of reduction of bifunctional materials and improve the reduction ability of materials, thereby promoting the reduction of Ni and Co active metal sites. In addition, with the increase of Ni content, the area of ​​the reduction peak is larger, which confirms that the strong interaction between Ni and Co forms a Ni-Co alloy, which can enhance the reducibility of the catalyst.

[0105] (4) Carbon deposition

[0106] The catalysts of Example 1 and the comparative example after the biomass plastic adsorption enhanced gasification experiment were subjected to thermogravimetric testing, and the results obtained were as follows: Figure 7 , Figure 7In the TG graph on the left, the mass increase in the 300-400℃ range is due to the metal particles Ni being reduced on the surface after the catalyst reaction. 0 / Co 0 Then it is oxidized to NiO, Co3O4 or CoO. The weight loss at 400-550℃ is attributed to the oxidation of amorphous carbon, while the weight loss at 550-750℃ is mainly related to the thermal decomposition of CaCO3 and the oxidation of carbon deposits. Figure 7 In the DSC graph on the right, Ni3Co1-T has the lowest weight loss, which is 26.31% at the end of the thermogravimetric analysis, and is mainly related to amorphous carbon, indicating that only a small amount of amorphous carbon is attached to the surface of Ni3Co1-T after the reaction. Ni3Co1-WM has a weight loss of 36.6%, proving that the weight loss is greater when it does not contain hollow tubular structures, and the hollow tubular structure can inhibit the formation of carbon deposits. The end of the reaction of Ni1Co3-T Figure 7 The TG graph on the left drops sharply in the range of 400-550℃, indicating that a large amount of carbon deposits with low graphitization degree and less filamentous carbon are formed on the surface during the reaction process. The combination of Ni-Co catalysts shows high catalytic activity and the ability to inhibit carbon deposition during the reaction. However, as the percentage of cobalt atoms increases, the amount of carbon deposition gradually increases (Ni1Co3-T>Ni2Co2-T>Ni3Co1-T). This may be attributed to the fact that a small amount of Co content promotes the activity of the catalyst, but too high a Co content will inhibit the activity of the catalyst, making it lower than the activity of the Ni single metal catalyst. This may be because, on the one hand, excessive cobalt content leads to an increase in alloy size and a decrease in nickel active sites, resulting in a significant decrease in catalytic activity and anti-coking performance; on the other hand, the promotion of Co on the activity of Ni-Co bimetallic catalysts mainly stems from Co's strong affinity for oxygen, thereby inhibiting carbon deposition. In the gasification process of biomass plastics, reducing gases (CH4, H2 and CO) and oxidizing gases (CO2 and steam) coexist, and metals can be oxidized and reduced at the same time. Co 0 The activity of Co in CC pyrolysis and WGS reaction is much higher than that of Co 2+ ,Co 2+ The main function is to promote the formation of CH4. When the generation and oxidation removal of carbon on the surface of the material reach a balance, the oxidation and carbon deposition of the metal can be suppressed to achieve high stability.

[0107] At the same time, Raman spectroscopy analysis was also performed on some embodiments and comparative examples. The results are as follows: Figure 8 As shown. The samples are all at 1350cm -1 and 1600cm -1 The characteristic peaks of carbon appear near the D peak (representing lattice defects and disordered structure of carbon atoms) and the G peak (representing the stretching movement of carbon-carbon atom pairs in carbon rings or long chains). D / I GRepresents the disorder degree of carbon materials. The larger the value, the higher the disorder degree of carbon materials, indicating that the graphitization degree of carbon deposits is reduced and it is easier to be eliminated. The D peak and G peak of Ni3Co1-T and Ni2Co2-T are extremely small, proving that the surface carbon content of Ni3Co1-T and Ni2Co2-T bifunctional materials is small, which is consistent with the TG-DSC results. Amorphous carbon and graphite carbon appeared on the surface of Ni3Co1-WM and Ni1Co3-T. D / I G The values ​​are 1.84 and 0.87 respectively.

[0108] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the scope of protection of the invention.

Claims

1. A bifunctional catalyst, characterized in that: The bifunctional catalyst is a hollow tubular structure, with calcium oxide as the basic component, and also includes nickel oxide, cobalt oxide, and nickel-cobalt bimetallic oxide; The molar ratio of the Ca element in calcium oxide, the Ni element in nickel oxide and nickel-cobalt bimetallic oxide, and the Co element in cobalt oxide and nickel-cobalt bimetallic oxide is 5-25:2-15:1; Ni elements include Ni 2+ and Ni 3+ Two valence states, based on the two forms of Ni element, Ni 2+ The atomic percentage of Ni is 31-53%, 3+ The atomic percentage is 47-69%; Co elements include Co 2+ 、Co 3+ 、Co 4+ Three valence states, based on the three forms of Co element, Co 2+ The atomic percentage of Co is 26-46%. 3+ The atomic percentage is 37-51%, Co 4+ The atomic percentage is 9-24%.

2. The bifunctional catalyst according to claim 1, characterized in that The molar ratio of the Ca element in the calcium oxide, the Ni element in the nickel oxide and the nickel-cobalt bimetallic oxide, and the Co element in the cobalt oxide and the nickel-cobalt bimetallic oxide is 20-22:3-5:

1.

3. The bifunctional catalyst according to claim 1 or 2, characterized in that The average grain size of the calcium oxide is 25-27 nm.

4. A method for preparing a bifunctional catalyst according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: A calcium source, a nickel source and a cobalt source are added into water to obtain a mixed solution, a fiber template is immersed in the mixed solution, and then dried and calcined to obtain a bifunctional catalyst; Wherein, the molar ratio of the Ca element in the calcium source, the Ni element in the nickel source, and the Co element in the cobalt source is 5-25:2-15:1; The calcination temperature is 750-800°C.

5. The preparation method according to claim 4, characterized in that: The molar ratio of the Ca element in the calcium source, the Ni element in the nickel source, and the Co element in the cobalt source is 20-22:3-5:

1.

6. The preparation method according to claim 4 or 5, characterized in that: The calcium source includes a soluble calcium salt, and optionally includes at least one of calcium nitrate tetrahydrate, calcium nitrate, and calcium acetate. Further optionally, the calcium source is calcium nitrate tetrahydrate and / or calcium nitrate; And / or, the nickel source comprises a soluble nickel salt, optionally comprising at least one of nickel nitrate hexahydrate, nickel nitrate, and nickel chloride, further optionally nickel nitrate hexahydrate and / or nickel nitrate; And / or, the cobalt source includes a soluble cobalt salt, optionally including at least one of cobalt nitrate hexahydrate, cobalt nitrate, and cobalt chloride, and further optionally is cobalt nitrate hexahydrate and / or cobalt nitrate.

7. The preparation method according to any one of claims 4 to 6, characterized in that: The nickel source and water usage ratio is 1:15-30, in units of mmol / mL; Optionally, the fiber template is absorbent paper; Optionally, the ratio of water to the fiber template is 200:2000-4000, in mL / cm 2 .

8. The preparation method according to any one of claims 4 to 7, characterized in that: The calcination time is 1-2h.

9. The preparation method according to any one of claims 4 to 8, characterized in that: The immersion temperature is 10-30°C and the time is 24-28h; And / or, the drying temperature is 80-100° C. and the drying time is 6-12 hours.

10. Use of the bifunctional catalyst according to any one of claims 1 to 3 or the bifunctional catalyst prepared by the preparation method according to any one of claims 4 to 9 in the field of adsorption and catalysis.

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