Method for regulating Ni-MOFC catalyst metal-carrier interface interaction through reduction activation and application

Abstract

The invention discloses a method for regulating and controlling Ni-MOFC catalyst metal-carrier interface interaction through reduction activation and application. The invention belongs to the field of reduction activation of nickel-based catalysts. The invention aims to solve the problem that the traditional reduction activation method generally lacks accurate regulation and control of process parameters and is difficult to effectively control the MSI state of the catalyst. The method comprises the following steps: in a mixed reducing atmosphere consisting of H2, water vapor, CO and N2, heating the Ni-MOFC catalyst from room temperature to 500-800 DEG C at a heating rate of 5-10 DEG C / min, and keeping the temperature for 1-2 hours; or after the temperature is kept at 600-900 DEG C for 1-2 h, the temperature is reduced to the room temperature at the cooling rate of 5-10 DEG C / min. By screening the reducing atmosphere, adjusting the flow and optimizing the reaction time, the active sites of the catalyst are fully activated, the MSI state of the catalyst is accurately controlled, and the catalytic activity and long-term stability of the catalyst are remarkably improved.

Description

Technical Field

[0001] The invention belongs to the field of reduction activation of nickel-based catalysts, and specifically relates to a method and application of reducing and activating the Ni-MOFC catalyst metal-carrier interface interaction. Background Art

[0002] Nickel-based catalysts have important application value in many catalytic processes such as hydrogenation reaction, gas desulfurization, and methane conversion due to their excellent catalytic performance. The performance of nickel-based catalysts is mainly determined by their microscopic and macroscopic structures, among which the choice of carrier plays a vital role in the activity and stability of the catalyst. Different carriers give catalysts different characteristics. Although traditional carriers such as alumina and silica are widely used, they have many disadvantages. For example, traditional carriers have limited active sites, and the reactants and active ingredients are not in sufficient contact, which limits the catalytic efficiency. In addition, the preparation process of traditional carriers is demanding and expensive, and the performance between batches is difficult to be stable. Moreover, it is easy to deactivate under harsh conditions such as high temperature and strong acid and alkali, which makes it difficult to meet the long-term use requirements of catalysts. In contrast, Ni-based MOF-derived carbon material carriers show excellent performance. It not only has an ultra-high specific surface area, which can fully expose active sites, greatly increase the contact area between reactants and catalysts, and significantly improve catalytic efficiency; but also its unique porous structure is conducive to material transport, which can quickly transport reactants and products; in addition, the carrier can maintain structural integrity under harsh reaction conditions, ensuring the long-term stable operation of the catalyst. In summary, Ni-based MOF-derived carbon material carriers overcome the shortcomings of traditional carriers with their high specific surface area, unique porous structure and good stability, providing a new path for the efficient and stable application of nickel-based catalysts, and having an important impact on the field of catalysis.

[0003] Nickel-based catalysts usually need to go through multiple stages such as pretreatment, activation, reaction, and deactivation, among which the activation process is particularly critical to the performance of the catalyst. Through reduction activation, the dispersibility of the catalyst metal particles can be optimized, the number of active sites can be increased, and the metal-support interaction (MSI) between the metal and the carrier can be improved. Good MSI can significantly improve the activity and stability of the catalyst and is one of the key factors in catalyst performance. However, traditional reduction activation methods usually lack precise regulation of process parameters and it is difficult to effectively control the MSI state of the catalyst. For example, in the traditional hydrogen reduction activation process, excessively high reduction temperatures can cause excessive migration and agglomeration of nickel atoms, resulting in a sharp decrease in active sites; at the same time, it may destroy the chemical bonding between Ni and the MOF carrier, weakening the carrier's ability to stabilize metal particles and synergistic catalysis. On the contrary, if the reduction temperature is too low and the time is too short, the metal nickel cannot be fully reduced to a highly active state, and it is also difficult to achieve excellent catalytic performance. This MSI imbalance caused by improper reduction activation makes it difficult for the catalyst to exert its due catalytic activity in the actual specific reaction system. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a method and application of reducing and activating the Ni-MOFC catalyst metal-support interface interaction.

[0005] One of the purposes of the present invention is to provide a method for reducing and activating the metal-support interface interaction of a Ni-MOFC catalyst, the method being carried out according to the following steps:

[0006] In H 2 , water vapor, CO and N 2 In a mixed reducing atmosphere composed of the above, the Ni-MOFC catalyst is heated from room temperature to 500-800°C at a heating rate of 5-10°C / min and maintained for 1-2h;

[0007] Or, in H 2 , water vapor, CO and N 2 In a mixed reducing atmosphere composed of the above, the temperature is maintained at 600-900°C for 1-2 hours and then cooled to room temperature at a cooling rate of 5-10°C / min.

[0008] Preferably, the mixed reducing atmosphere contains H 2 , water vapor, CO and N 2 The volume ratio is (10-12):(4-6):1:(2-4).

[0009] Preferably, the preparation process of Ni-MOFC catalyst is:

[0010] S1: Using biomass as substrate, pyrolytic carbon was prepared by two-step carbonization combined with KOH activation;

[0011] S2: Use pyrolytic carbon, nickel salt and imidazole as reaction substrates to carry out solvent thermal reaction. After the reaction is completed, filter and dry, and then carry out pyrolysis to obtain Ni-MOFC catalyst.

[0012] Further preferably, the biomass in S1 is sewage sludge.

[0013] Further preferably, in the process of preparing pyrolytic carbon in S1: the biomass is dried, ground and sieved, and then pre-carbonized, followed by adding KOH solution for stirring and activation, filtered and dried, and then carbonized for the second time, and after carbonization, hydrochloric acid is added, stirred, and then washed with water until neutral, and finally dried.

[0014] More preferably, the drying temperature is 100-110° C., and the mesh size of the ground sieve is 100 mesh.

[0015] More preferably, the pre-carbonization temperature is 300-500° C., the time is 2-4 h, the heating rate is 5-10° C. / min, the protective gas is argon or nitrogen, and the flow rate is 50-100 mL / min.

[0016] More preferably, the concentration of KOH solution is 3-5 mol / L, the mass ratio of pre-carbonized product to KOH is 1:(1-9), the stirring activation temperature is 50-70°C, the time is 1-3h, and the drying temperature is 60-70°C, and the time is 10-14h.

[0017] More preferably, the secondary carbonization temperature is 700-900° C., the time is 1-3 h, the heating rate is 5-10° C. / min, the protective gas is argon or nitrogen, and the flow rate is 50-100 mL / min.

[0018] More preferably, the concentration of hydrochloric acid is 1 to 3 mol / L, the volume is 25 to 100 mL, the stirring time is 10 to 14 h, and after washing to neutrality, the drying temperature is 70 to 80° C. and the time is 10 to 14 h.

[0019] Further preferably, the nickel salt in S2 is one of nickel nitrate, chloride or sulfate.

[0020] Further preferably, the molar ratio of pyrolytic carbon, nickel salt and imidazole in S2 is (0.2-1.8):(0.2-1.8):2.

[0021] More preferably, the organic solvent of the solvothermal reaction in S2 is N,N-dimethylformamide (DMF).

[0022] More preferably, the solvent thermal reaction temperature in S2 is 100-200° C., and the reaction time is 12-72 h.

[0023] More preferably, the drying temperature in S2 is 160-180° C. and the drying time is 10-14 h.

[0024] Further preferably, the protective gas for pyrolysis in S2 is argon, the temperature is 800-900° C., and the reaction time is 2-4 h.

[0025] The second object of the present invention is to provide a Ni-MOFC catalyst reduced and activated according to the above method.

[0026] The third object of the present invention is to provide a use of the Ni-MOFC catalyst reduced and activated according to the above method in high-temperature catalytic cracking of tar.

[0027] It is further defined that the specific steps of high temperature catalytic cracking of tar are as follows: Ni-MOFC catalyst, tar and water vapor are injected into a two-stage catalytic reactor, and catalytic cracking is carried out under argon protection.

[0028] It is further defined that the amount of the catalyst is 0.1 to 1.0 g / mL of tar.

[0029] It is further defined that the mass ratio of water vapor to tar (S / C) is 1-5.

[0030] Further limit, argon gas flow rate is 50 ~ 100mL / min.

[0031] It is further defined that the catalytic cracking temperature is 500-800°C and the time is 30-60 minutes.

[0032] A fourth object of the present invention is to provide an application of the above method in reducing and activating the metal-support interface of Ni-based MOF-derived carbon materials.

[0033] Compared with the prior art, the present invention has the following significant effects:

[0034] (1) Construction of Ni-MOFC catalyst with excellent performance: The present invention adopts a two-step pyrolysis method to prepare the MOF carrier, and then prepares the Ni-MOFC catalyst by an in-situ growth method to obtain a catalyst with excellent performance and superior to the common traditional carrier. This method can effectively control the microstructure and surface properties of the catalyst, providing a high-quality foundation for subsequent catalytic activity. In addition, the biomass used as the carrier raw material further realizes low-cost and environmentally friendly catalyst preparation.

[0035] (2) Accurately control the reduction and activation conditions of the catalyst: The current catalyst reduction and activation technology has insufficient control accuracy for key parameters. It is difficult to accurately control the reduction process when dealing with complex systems, which limits the performance of the catalyst. In response to this, the present invention finely controls the key elements of reduction and activation. Advanced temperature control technology is used to accurately set the temperature and strictly control the heating rate; the reducing atmosphere is selected according to the catalyst characteristics and reaction mechanism, and the flow rate is accurately adjusted; and the reaction time is optimized and set. Under this system, the Ni-MOFC catalyst is efficiently converted, the catalyst active sites are fully activated, and the MSI state of the catalyst is accurately controlled, thereby significantly improving the catalytic activity and long-term stability of the catalyst. Compared with traditional methods, the present invention can more effectively tap the potential activity of the catalyst, significantly improve its performance, and provide strong technical support for the development of this field. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0037] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, methods and instruments used are conventional materials, reagents, methods and instruments in the art unless otherwise specified, and can be obtained through commercial channels by those skilled in the art.

[0038] The terms "comprising," "including," "having," "containing," or any other variations thereof, as used in the following examples, are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article, or apparatus comprising the listed elements is not necessarily limited to only those elements, but may include other elements not expressly listed or inherent to such composition, step, method, article, or apparatus.

[0039] When equivalent, concentration or other value or parameter is represented by the range limited by range, preferred range or a series of upper preferred value and lower preferred value, this should be understood as specifically disclosing all ranges formed by any pairing of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether the scope is disclosed separately. For example, when disclosing range "1 to 5", described range should be interpreted as including range "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5" etc. When numerical range is described in this article, unless otherwise stated, the scope is intended to include its end value and all integers and fractions within the scope. In the present application specification and claims, range limitation can be combined and / or interchanged, if these ranges are not otherwise stated, include all sub-ranges contained therein.

[0040] The indefinite articles "a" and "an" before the elements or components of the present invention have no limitation on the quantity requirements (i.e. the number of occurrences) of the elements or components. Therefore, "a" or "an" should be interpreted as including one or at least one, and the elements or components in the singular form also include the plural form, unless the quantity obviously refers to the singular form only.

[0041] The "one embodiment" or "embodiment" of the present invention refers to a specific feature, structure or characteristic that can be included in at least one implementation of the present invention. The "in one embodiment" that appears in different places in this specification does not refer to the same embodiment, nor is it a separate or selective embodiment that is mutually exclusive with other embodiments.

[0042] The endpoints and any values ​​of the ranges disclosed in the invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in this article.

[0043] Embodiment 1:

[0044] (1) Preparation of Ni-MOFC catalyst:

[0045] First, 250g of sewage sludge was dried at 105℃ for 24h and then ground through a 100-mesh sieve. In a 50mL / min argon atmosphere, the temperature was raised to 500℃ at a heating rate of 5℃ / min, and pre-carbonized at 500℃ for 3h. Then, a 4mol / L KOH solution was used, with a mass ratio of the pre-carbonized product to the KOH solution of 1:6, and the mixture was stirred and activated at 60℃ for 2h. After activation, it was filtered and then dried at 65℃ for 12h. Then, the temperature was raised to 800℃ at a protective argon flow rate of 50mL / min and a heating rate of 5℃ / min, and secondary carbonized at 800℃ for 2h. After carbonization, 50mL of 2mol / L hydrochloric acid solution was added and stirred for acid washing for 12h, and filtered with a 0.22μm water filter membrane, washed with water until the supernatant pH = 7, and finally dried at 75℃ for 12h to obtain pyrolytic carbon AC.

[0046] Then, 0.3 g of the prepared pyrolytic carbon and 7.27 g of nickel nitrate hexahydrate (Ni(NO 3 ) 2 6H 2 O) and 3.4045 g imidazole (C 3 H 4 N 2) was used as a reaction substrate, 80 mL of N,N-dimethylformamide (DMF) was added to dissolve, and a solvent thermal reaction was carried out at 150 ° C in a high temperature and high pressure reactor for 48 h. Subsequently, a 0.22 μm organic membrane was used for vacuum filtration, and then dried at 170 ° C for 12 h to obtain Ni-MOF. Finally, in an argon atmosphere, it was heated to 850 ° C at a heating rate of 5 ° C / min and carbonized at a constant temperature for 3 h to obtain a Ni-MOFC catalyst.

[0047] (2) Reduction activation:

[0048] 0.4 g of Ni-MOFC catalyst sample was evenly loaded into the reaction tube, and the reaction tube was placed in a precisely temperature-controlled heating furnace. The sample tube was first purged with an inert carrier gas for 25 min, and then H 2 / H 2 O / CO / N 2 The temperature was raised from room temperature at a rate of 7°C / min until it reached 650°C and maintained for 1.5h to complete the programmed temperature reduction.

[0049] The active site turnover frequency (TOF) measurement is based on N 2 O reactive frontal chromatography (N 2 The Ni-MOFC catalyst sample was loaded into the reactor to allow N 2 O is mixed with carrier gas (argon) and passed through the catalyst bed for adsorption. 2 The adsorption and reaction amount of O determine the number of Ni sites, and the reaction rate is calculated based on the amount of product generated. The TOF is calculated as reaction rate / number of active sites. The results show that the active site turnover frequency (TOF) before reduction activation is 25h. -1 , after reduction activation, the TOF is 47h -1 , an increase of 88%.

[0050] The determination of metal chemical bond valence and surface defects is to use electron energy loss spectroscopy (EELS) to measure the characteristic signals of active metal nickel atoms and metal oxide valence on the covering layer; in-situ Raman spectroscopy (Raman) is used to characterize metal-oxide-support chemical bonds and surface defects at 633nm; Ni-MOFC catalyst is made into a 30nm thick film sample, and the EELS instrument is evacuated to 10 -6 Pa, adjust the position so that the electron beam irradiates the active metal nickel atom area. The spectrometer selects 633nm laser, power of 2kW, integration time of 50-200ms, scanning times of 3-10 times, and analyzes metal-oxide-support chemical bonds and surface defects with characteristic peaks. The results show that the in-situ Raman spectrum (Raman) shows that the characteristic peak intensity is 1.25 times that before activation.

[0051] The abundance of active metal sites was determined using CO adsorption-diffuse reflectance infrared Fourier transform spectroscopy (CO-DRIFTS). The Ni-MOFC catalyst sample was placed in a diffuse reflectance sample cell, and after argon purging, CO gas was introduced at a flow rate of 40 mL / min. The diffuse reflectance infrared spectrum under CO adsorption was collected. The results showed that the abundance of active metal sites was increased by about 67% compared to that before activation.

[0052] Embodiment 2:

[0053] (1) Preparation of Ni-MOFC catalyst:

[0054] First, 250g of sewage sludge was dried at 105℃ for 24h and then ground through a 100-mesh sieve. In a 50mL / min argon atmosphere, the temperature was raised to 500℃ at a heating rate of 10℃ / min, and pre-carbonized at 500℃ for 3h. Then, a 4mol / L KOH solution was used, with a mass ratio of the pre-carbonized product to the KOH solution of 1:8, and the mixture was stirred and activated at 60℃ for 2h. After activation, it was filtered and then dried at 65℃ for 12h. Then, the temperature was raised to 800℃ at a protective argon flow rate of 50mL / min and a heating rate of 5℃ / min, and secondary carbonized at 800℃ for 2h. After carbonization, 50mL of 2mol / L hydrochloric acid solution was added and stirred for acid washing for 12h, and filtered with a 0.22μm water filter membrane, washed with water until the supernatant pH = 7, and finally dried at 75℃ for 12h to obtain pyrolytic carbon AC.

[0055] Then, 0.45 g of the prepared pyrolytic carbon and 10.905 g of nickel nitrate hexahydrate (Ni(NO 3 ) 2 6H 2 O) and 5.1068 g imidazole (C 3 H 4 N 2 ) was used as a reaction substrate, 80 mL of N,N-dimethylformamide (DMF) was added to dissolve, and a solvent thermal reaction was carried out at 160°C in a high temperature and high pressure reactor for 48 h. Subsequently, a 0.22 μm organic membrane was used for vacuum filtration, and then dried at 170°C for 12 h to obtain Ni-MOF. Finally, under an argon atmosphere, the mixture was heated to 850°C at a heating rate of 5°C / min and carbonized at a constant temperature for 3 h to obtain a Ni-MOFC catalyst.

[0056] (2) Reduction activation:

[0057] 0.4 g of Ni-MOFC catalyst sample was evenly loaded into the reaction tube, and the reaction tube was placed in a precisely temperature-controlled heating furnace. 2 / H 2 O / CO / N 2The reaction tube was purged with a mixed reducing gas composed of 20% NH 2 O (volume ratio of 11:5:1:3) at a flow rate of 80 mL / min. After being kept at 750°C for 2 h, the temperature was lowered to room temperature at a cooling rate of 7°C / min to achieve reverse programmed temperature reduction.

[0058] The active site turnover frequency (TOF) measurement is based on N 2 O reactive frontal chromatography (N 2 The Ni-MOFC catalyst sample was loaded into the reactor to allow N 2 O is mixed with argon and adsorbed through the catalyst bed. 2 The adsorption and reaction amount of O determine the number of Ni sites, and the reaction rate is calculated in combination with the amount of product generated. The TOF is calculated as reaction rate / number of active sites. The results show that the active site turnover frequency (TOF) before reduction activation was determined to be 27h. -1 , after reduction activation, the TOF is 53h -1 , an increase of 96.3%.

[0059] The determination of metal chemical bond valence and surface defects is to use electron energy loss spectroscopy (EELS) to measure the characteristic signals of active metal nickel atoms and metal oxide valence on the covering layer; in-situ Raman spectroscopy (Raman) is used to characterize metal-oxide-support chemical bonds and surface defects at 633nm; the Ni-MOFC catalyst is made into a 30-nanometer-thick film, and the EELS instrument is evacuated to 10 -6 Pa, adjust the position so that the electron beam irradiates the active metal nickel atom area. The spectrometer selects 633nm laser, power of 2kW, integration time of 50-200ms, scanning times of 3-10 times, and analyzes metal-oxide-support chemical bonds and surface defects with characteristic peaks. The results show that the in-situ Raman spectrum (Raman) shows that the characteristic peak intensity is 1.37 times that before activation.

[0060] The abundance of active metal sites was determined using CO adsorption-diffuse reflectance infrared Fourier transform spectroscopy (CO-DRIFTS). The Ni-MOFC catalyst sample was placed in a diffuse reflectance sample cell, and after purging with argon, CO gas was introduced at a flow rate of 40 mL / min. The diffuse reflectance infrared spectrum under CO adsorption was collected. The results showed that the abundance of active metal sites was increased by about 71.2% compared to that before activation.

[0061] The above are only preferred specific embodiments of the present invention, which are all different implementations based on the overall concept of the present invention, and the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for reducing and activating the metal-support interface interaction of a Ni-MOFC catalyst, characterized in that: The method: In a mixed reducing atmosphere consisting of H2, water vapor, CO and N2, the Ni-MOFC catalyst was heated from room temperature to 500-800°C at a heating rate of 5-10°C / min and maintained for 1-2h; Alternatively, in a mixed reducing atmosphere consisting of H2, water vapor, CO and N2, after maintaining at 600-900°C for 1-2 hours, the temperature is lowered to room temperature at a cooling rate of 5-10°C / min.

2. The method according to claim 1, characterized in that The volume ratio of H2, water vapor, CO and N2 in the mixed reducing atmosphere is (10-12):(4-6):1:(2-4).

3. The method according to claim 1, characterized in that Preparation process of Ni-MOFC catalyst: S1: Using biomass as substrate, pyrolytic carbon was prepared by two-step carbonization combined with KOH activation; S2: Use pyrolytic carbon, nickel salt and imidazole as reaction substrates to carry out solvent thermal reaction. After the reaction is completed, filter and dry, and then carry out pyrolysis to obtain Ni-MOFC catalyst.

4. The method according to claim 3, characterized in that The biomass in S1 is sewage sludge, and the process of preparing pyrolytic carbon is as follows: the biomass is dried, ground and sieved, and then pre-carbonized, followed by adding KOH solution for stirring and activation, filtered and dried, and then carbonized for the second time, and after carbonization, hydrochloric acid is added, stirred, and then washed with water until neutral, and finally dried.

5. The method according to claim 4, characterized in that The pre-carbonization temperature is 300-500°C, the time is 2-4h, the heating rate is 5-10°C / min, the concentration of KOH solution is 3-5mol / L, the mass ratio of pre-carbonization product to KOH is 1:(1-9), the stirring activation temperature is 50-70°C, the time is 1-3h, the secondary carbonization temperature is 700-900°C, the time is 1-3h, and the heating rate is 5-10°C / min.

6. The method according to claim 3, characterized in that: The nickel salt in S2 is one of nickel nitrate, chloride or sulfate, the molar ratio of pyrolytic carbon, nickel salt and imidazole is (0.2-1.8):(0.2-1.8):2, the solvent thermal reaction temperature is 100-200°C, the reaction time is 12-72h, the protective gas for pyrolysis is argon, the temperature is 800-900°C, and the reaction time is 2-4h.

7. The Ni-MOFC catalyst reduced and activated by the method according to any one of claims 1 to 6.

8. Use of the Ni-MOFC catalyst reduced and activated by the method according to any one of claims 1 to 6 in high temperature catalytic cracking of tar.

9. The use according to claim 8, characterized in that: Specific steps of high temperature catalytic cracking of tar: Ni-MOFC catalyst, tar and water vapor are injected into a two-stage catalytic reactor for catalytic cracking under argon protection.

10. Use of the method according to any one of claims 1 to 6 in reducing and activating the metal-support interface of Ni-based MOF-derived carbon materials.