A modified biochar-based Ni / MoO2 / C catalyst, its preparation method, and its application.

Abstract

This invention relates to the field of catalysis technology. The purpose of this invention is to provide a method for preparing a modified biochar-based Ni / MoO2 / C catalyst, comprising: calcining pretreated biochar under an oxygen-free atmosphere to obtain biochar; mixing the biochar with a water-soluble metal precursor and treating the mixture in a cell-breaking device; adding a chelating agent; obtaining a Ni-Mo / biochar precursor via a sol-gel method; washing the precursor until the solution is neutral; drying the precursor; calcining the solid Ni-Mo / biochar precursor under an oxygen atmosphere; filtering and drying the solid to obtain NiO-MoO3 / C; and reducing the NiO-MoO2 / C catalyst. This invention solves the problems of high cost, unstable performance, and difficulty in industrial application of existing biogas high-value conversion syngas catalysts. This invention also provides a modified biochar-based Ni / MoO2 / C catalyst and its application.

Description

Technical Field

[0001] This invention relates to the field of catalysis technology, and in particular to a modified biochar-based Ni / MoO2 / C catalyst, its preparation method, and its application. Background Technology

[0002] Syngas refers to a mixture of carbon monoxide and hydrogen. The CO to H2 ratio in syngas varies depending on the raw materials and production methods, with a molar ratio ranging from 1 / 2 to 3 / 1. Syngas is one of the raw materials for organic synthesis and is also a source of hydrogen and carbon monoxide, playing a vital role in the chemical industry. The raw materials for producing syngas are diverse; many carbon-containing resources such as coal, natural gas, petroleum, or residual oil can be used. Syngas can be converted into liquid and gaseous fuels, bulk chemicals, and high-value-added fine organic chemical products. Although the world's energy supply today is mainly based on three non-renewable fossil resources—coal, oil, and natural gas—the rapid pace of globalization in the new century, the dramatic increase in population, and the rapid growth of the economy have led to the excessive exploitation of Earth's resources.

[0003] Nature possesses abundant biogas resources, and biogas is a high-quality, environmentally friendly green resource, releasing far fewer harmful gases than equivalent amounts of coal and oil. In short, biogas has become the third largest energy source after oil, and replacing oil with biogas is an inevitable trend in the future shift of energy and chemical raw material routes. The main components of biogas are methane and carbon dioxide, making it a relatively clean and easily transportable energy source. Biogas can be processed into products closely related to socio-economic development and people's lives; for example, biogas steam can be catalytically converted into syngas. Therefore, using renewable biogas as a raw material to produce syngas, replacing traditional processes based on fossil resources such as coal and oil, can effectively reduce environmental pollution and greenhouse gas emissions. Developing highly efficient catalysts for the high-value conversion of biogas into syngas is of profound significance for my country's current national conditions.

[0004] In the preparation of catalysts for the high-value conversion of biogas into syngas, the selection and design of the catalyst support have a significant impact on catalytic activity and stability. Its surface acidity / basicity and defect structure determine the reactant adsorption rate and the dispersion of active sites, thereby regulating the catalytic process. Carbon materials, due to their low cost, easy availability, and high conductivity, have shown outstanding performance in many catalytic reactions. Studies have shown that carbon materials with defective structures exhibit superior catalytic performance compared to perfectly lattice carbon, not only improving the dispersion of active sites on the support surface but also enhancing metal-support interactions. It is noteworthy that biogas fermentation residues, as difficult-to-treat organic solid waste, are causing severe environmental pressure. Converting biogas residue into defective carbon supports through controlled treatment can achieve both the resource utilization of the biogas ecosystem and significantly alleviate the challenge of green disposal of biogas residue. Currently, noble metal catalysts, such as Pd and Pt, are widely used in the catalytic conversion of biogas into syngas. However, the use of noble metals is costly and difficult.

[0005] Therefore, providing a low-cost, stable, and effective catalyst preparation method to achieve the production of syngas for multiple needs through the high-value conversion of biogas is an urgent problem to be solved. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, the purpose of this invention is to solve the problems of high cost, unstable performance and difficulty in industrial application of existing biogas high-value conversion catalysts.

[0007] To achieve the above objectives, the present invention provides a method for preparing a modified biochar-based Ni / MoO2 / C catalyst, comprising the following steps: S1: The pretreated biogas residue is placed in an oxygen-free atmosphere for calcination to obtain biogas residue-based biochar. S2: After mixing biochar based on sludge with water-soluble metal precursor and processing it in a cell-breaking device, a chelating agent is added, and Ni-Mo / biochar precursor is obtained by sol-gel method. S3: Wash the Ni-Mo / biochar precursor until the solution is neutral, and then dry it to obtain Ni-Mo / biochar precursor solid; S4: After calcining the Ni-Mo / biochar precursor solid in an oxygen atmosphere, filter and dry it to obtain NiO-MoO3 / C; S5: NiO-MoO3 / C is reduced to nickel and MoO3 to MoO. 2， A Ni / MoO2 / C catalyst was obtained.

[0008] Preferably, in step S1, the calcination temperature is 600–700°C and the calcination time is 2–4 hours.

[0009] Preferably, in step S4, the calcination temperature is 500–600°C and the calcination time is 4–6 hours.

[0010] Preferably, the water-soluble metal precursor includes a nickel source and a molybdenum source, the chelating agent includes citric acid, and the molar ratio of the sum of the amounts of nickel and molybdenum in the nickel source to citric acid is 1:1 to 1.5.

[0011] Preferably, the nickel source is an organic acid nickel, and the molybdenum source is an organic acid molybdenum.

[0012] Preferably, the organic acid nickel is nickel acetate, and the organic acid molybdenum is molybdenum acetate.

[0013] Preferably, in step S5, the reduction treatment of NiO-MoO3 / C includes: placing NiO-MoO3 / C in a hydrogen atmosphere for reduction treatment, the reduction temperature being 700-800℃, and the reduction time being 1-3h.

[0014] The present invention also provides a biochar-based Ni / MoO2 / C catalyst supported on biochar, comprising: a biochar-based support and an active component Ni and a co-catalyst MoO2 supported on the biochar-based support, wherein the loading of the active component Ni is 1-5% and the loading of the co-catalyst MoO2 is 5-15%.

[0015] Preferably, the loading of the active component Ni is 2%, and the loading of the co-catalyst MoO2 is 10%.

[0016] The present invention also provides the application of a modified biochar-based Ni / MoO2 / C catalyst in the high-value conversion of biogas to syngas or the preparation of biofuels from said syngas.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: Using biogas residue as raw material, biogas residue-based biochar is obtained through pretreatment and calcination. Then, using Ni as the catalytic active component and MoO2 as the catalytic promoter, the Ni particles are made smaller, more dispersible, and more uniformly dispersed through optimization of loading and calcination conditions. This avoids the problem of nickel-based catalysts being prone to agglomeration and having limited catalytic performance at high temperatures. Through further reduction treatment, the catalyst exhibits high CH4 and CO2 conversion rates and high catalytic stability when catalyzing the conversion of biogas to syngas, making it well-suited for high-value conversion of biogas to syngas. Attached Figure Description

[0018] Figure 1 : This is a catalytic performance diagram of Example 1; Figure 2 : High-resolution TEM image of the Ni / MoO2 / C catalyst supported on modified biochar in Example 1; Figure 3 : This is a TEM image of the reaction in Example 1. Detailed Implementation

[0019] The present invention will now be described in more detail. It should be noted that the following description of the present invention with reference to the accompanying drawings is merely illustrative and not restrictive.

[0020] Where possible, the various embodiments described below can be rearranged to form other embodiments not shown in the following description; the various technical features described below can also be rearranged to form other embodiments not shown in the following description.

[0021] To achieve a simple, low-cost, and efficient method for preparing catalysts for the high-value conversion of biogas into syngas, which effectively utilizes biogas residue and is easy to industrialize, this invention provides a method for preparing a modified biogas residue-based biochar-supported Ni / MoO2 / C catalyst, comprising the following steps: S1: The pretreated biogas residue is placed in an oxygen-free atmosphere for calcination to obtain biogas residue-based biochar. The pretreatment process includes: using biogas residue as raw material, dehydrating and drying it to obtain pretreated biogas residue. This removes free water and some structural water from the biogas residue, reducing energy consumption during subsequent calcination, preventing the collapse of the carbon skeleton structure due to violent moisture evaporation at high temperatures, and improving process economy. Oxygen is isolated during pyrolysis to prevent the carbon material from being oxidized and burned, thus preserving the reducing defect structure in the carbon skeleton.

[0022] In this process, the calcination temperature is 600–700℃, and the calcination time is 2–4 hours. This range allows for the retention of abundant intrinsic defects (edge ​​defects, vacancies / pores, and topological defects, etc.) in the carbon framework, providing ideal anchoring points for subsequent Ni and MoO2 loading, and promoting high dispersion and electronic synergistic effects of the active components. Comparative Example 6, calcined at 600℃, showed a significantly lower final activity (CH4 conversion 68%, CO2 conversion 15%) than Example 1 (700℃, 93 / 43), indicating that a calcination temperature of 700℃ is more conducive to obtaining a high-performance support structure. The limited calcination time ensures that the biogas residue is fully pyrolyzed and carbonized at the target temperature while avoiding over-calcination.

[0023] Specifically, the calcination temperature was 700℃, the time was 3 hours, and the inert atmosphere was nitrogen. The catalyst obtained in Example 1 exhibited the highest CH4 conversion (95%) and CO2 conversion (45%), as well as the best long-term stability over 100 hours. The nitrogen atmosphere is inexpensive and safe to operate.

[0024] In this step, the calcination temperature is increased at a rate of 3–5 °C / min. Controlling the rate of volatile release during pyrolysis prevents the carbon skeleton from cracking or collapsing due to the violent release of volatiles, thus facilitating the acquisition of a biochar support with uniform pore size distribution and good mechanical strength.

[0025] Specifically, the calcination temperature was increased at a rate of 3°C / min. In Example 1, a heating rate of 3°C / min was used. The slower heating rate resulted in a more gradual release of volatiles, leading to better uniformity of the pore structure of the resulting support and more uniform dispersion of the active components. The TEM image showed that the Ni nanoparticles were highly uniformly distributed on the support.

[0026] S2: After mixing biochar based on sludge with water-soluble metal precursor and processing it in a cell-breaking device, a chelating agent is added, and Ni-Mo / biochar precursor is obtained by sol-gel method. In this step, the cell disruption device can be an ultrasonic cell disruptor. This treatment ensures the uniform distribution of the active component precursor on all accessible surfaces of the carrier, and is a key prerequisite for achieving small particle size and high dispersion of the final Ni nanoparticles.

[0027] In this process, the sol-gel method includes: first heating and stirring to form a sol, then converting it into a gel, and finally drying to obtain the Ni-Mo / biochar precursor. The heating can be performed using microwaves or a water bath under specific temperature conditions. Compared to the simple impregnation-drying method, the sol-gel method significantly improves the mixing uniformity and dispersion of the multi-component active phase.

[0028] Specifically, the water-soluble metal precursors include nickel and molybdenum sources, and the chelating agent includes citric acid. The molar ratio of the sum of the amounts of nickel and molybdenum in the nickel source to citric acid is 1:1 to 1.5. A stoichiometric amount of chelating agent is provided to ensure complete chelation. The chelating agent may also include one or more of sodium hydroxide or isopropanol. Citric acid has a high complexation stability constant with metals, effectively inhibiting the hydrolysis of metal ions; upon calcination in an oxygen atmosphere, it can completely decompose into CO2 and H2O, leaving no residual impurities that contaminate the catalyst.

[0029] The amounts of nickel source, molybdenum source, and modified biochar based on sludge can be adjusted according to the Ni / MoO2 loading. The Ni / MoO2 loading has a certain impact on the catalyst performance. If the loading is too low, the sparse distribution of Ni / MoO2 will not achieve a synergistic effect; if the loading is too high, the Ni / MoO2 cells will be too dense, and the nickel elements will easily agglomerate after reduction due to their compact size. By optimizing the loading conditions, the catalytic activity of the modified biochar-supported Ni / MoO2 / C catalyst can be further improved. It should be understood that the loading refers to the amount of the catalytically active component Ni / MoO2 in the entire Ni / MoO2 / C catalyst.

[0030] Specifically, the nickel source is nickel organic acid, and the molybdenum source is molybdenum organic acid. Nickel acetate is the organic nickel source, as it exhibits better compatibility with the citric acid system. In the sol-gel method, acetate ions can participate in the construction of the gel network; its thermal decomposition is relatively gradual, which is beneficial for the uniform nucleation of nickel oxide nanoparticles. Molybdenum acetate is the organic molybdenum source, as it has better compatibility with the citric acid sol-gel system; its thermal decomposition behavior matches that of nickel acetate, which is beneficial for the simultaneous and uniform precipitation of NiO and MoO3.

[0031] S3: Wash the Ni-Mo / biochar precursor until the solution is neutral, and then dry it to obtain Ni-Mo / biochar precursor solid; In this step, the Ni-Mo / biochar precursor is washed 3 to 4 times to remove free metal ions, excess chelating agents or nitrates and other byproducts, thereby eliminating the "contamination sources" that cause subsequent active components to agglomerate and purifying the precursor system.

[0032] S4: After calcining the Ni-Mo / biochar precursor solid in an oxygen atmosphere, filter and dry it to obtain NiO-MoO3 / C; In this step, the calcination temperature is 500–600℃, and the calcination time is 4–6 hours. This range can simultaneously achieve the effects of complete decomposition of the chelating agent and controllable nucleation of oxide particles, creating an ideal precursor for the S5 hydrogen reduction to reconstruct a highly active Ni / MoO2 interface. In Comparative Example 4, the calcination temperature was increased to 650℃, and its final CH4 / CO2 conversion rate (62 / 20%) was much lower than that of Example 1 (550℃, 93 / 43%), demonstrating the necessity of the upper limit: overheating leads to irreversible and poor active phase transformation.

[0033] In this step, the calcination environment is a muffle furnace. After the Ni-Mo / biochar precursor is calcined and cooled, it is filtered in water, washed, and then dried to obtain NiO-MoO3 / C. The "oxidation-water washing" step can remove alkaline / alkaline earth metal impurities from biogas residue, purify the catalytic system, and ensure consistent performance.

[0034] Specifically, the calcination temperature was 550℃, the time was 5 hours, and the oxygen atmosphere was air. Example 1 shows that the combination of 550℃ / 5 hours yielded the best results, with the CH4 conversion rate remaining stable at over 93%, proving the rationality of this temperature and time combination. An air atmosphere is nearly cost-free and safe, and sufficient to complete the oxidation reaction.

[0035] In this step, the calcination temperature is increased at a rate of 3–5 °C / min. The gradual release of decomposition gases and uniform heat transfer ensure production efficiency while effectively protecting the high specific surface area, pore connectivity, and defect structure of the carbon support, providing a stable support environment for the anchoring of the active phase.

[0036] Specifically, the calcination temperature was increased at a rate of 3°C / min. Example 1, using a rate of 3°C / min, yielded the catalyst with the highest final activity, which is inseparable from its perfect protection of the support's pore structure, thus solidifying the foundation for the excellent dispersion of subsequent active sites.

[0037] S5: NiO-MoO3 / C is reduced to nickel and MoO3 to MoO. 2， A Ni / MoO2 / C catalyst was obtained.

[0038] This Ni / MoO2 / C catalyst possesses the advantages of carbon materials, which widely exhibit various structural types, including edge defects, vacancies / pores, and topological defects. These defect structures can alter the charge distribution of surrounding carbon atoms, enhancing electronic activity by regulating the electron density around the carbon framework. This is highly beneficial for gas adsorption and activation, avoiding the problems of nickel-based catalysts' tendency to aggregate and limited catalytic performance at high temperatures. Through reduction treatment, the resulting Ni / MoO2 / C exhibits high conversion rates, effectively catalyzing the high-value conversion of biogas into syngas for downstream applications.

[0039] The reduction treatment of NiO-MoO3 / C in this step includes: placing NiO-MoO3 / C in a hydrogen atmosphere for reduction treatment at a temperature of 700–800℃ for 1–3 hours. NiO / MoO3 itself does not possess catalytic activity, but after being reduced to metallic nickel by hydrogen (resulting in Ni / MoO2 / C), it exhibits catalytic activity. The reduced nickel is more regularly and orderly distributed, with almost constant spacing between them, which better allows the catalytic activity of nickel to be fully utilized. This also improves the catalytic activity without being affected by other factors such as agglomeration and carbon deposition.

[0040] The present invention also provides a modified biochar-based Ni / MoO2 / C catalyst prepared by the above preparation method, comprising: a biochar-based support and an active component Ni and a co-catalyst MoO2 supported on the biochar-based support, wherein the loading of the active component Ni is 1-5% and the loading of the co-catalyst MoO2 is 5-15%.

[0041] Modified biochar based on biogas slag exhibits outstanding performance in various catalytic reactions due to its advantages such as low cost, easy availability, and high conductivity. Studies have shown that carbon materials with defective structures exhibit superior catalytic performance compared to perfectly lattice carbon. This is because they not only improve the dispersion of active sites on the support surface but also enhance metal-support interactions. Furthermore, this invention uses Ni as the catalytically active component and MoO2 as a catalytic promoter. The abundant oxygen vacancies in the redox cycle of Mo activate CO2, continuously generating a large amount of reactive oxygen species. Simultaneously, the introduction of Mo can modify the surface electronic structure of Ni through electron transfer effects. The interfacial synergy between Mo and Ni further enhances the catalytic system's resistance to coking and sintering, enabling the catalyst to possess high catalytic stability and high CH4 and CO2 conversion rates. The resulting modified biogas slag-based biochar-supported Ni / MoO2 / C catalyst exhibits high biogas conversion rates and can effectively catalyze the high-value conversion of biogas into syngas for downstream applications.

[0042] Specifically, the loading of the active component Ni is 2%, and the loading of the co-catalyst MoO2 is 10%.

[0043] The initial activity of Example 1 (Ni 2%, MoO 210%) was 95% CH4 conversion and 45% CO2 conversion, significantly better than other examples and comparative examples. This demonstrates that when the Ni loading is 2% and the MoO 2 loading is 10%, the interfacial synergistic effect between the two is maximized, and the resulting catalyst exhibits optimal catalytic activity and stability in the biogas reforming to syngas reaction.

[0044] This invention also provides the application of a modified biochar-based Ni / MoO2 / C catalyst in the high-value conversion of biogas to syngas or the preparation of biofuels from syngas. This catalyst can catalytically convert biogas into syngas, a mixture mainly composed of CO and H2. The syngas, as a platform chemical feedstock, can be directly used in downstream chemical synthesis or further converted into liquid biofuels through processes such as Fischer-Tropsch synthesis.

[0045] In application, the catalytic reaction is usually carried out under normal pressure and at a temperature of 700–800℃, with 750℃ being the preferred temperature. Specifically, when the biogas flow rate is 80 mL / min, a catalyst dosage of 0.2 g is sufficient to achieve excellent conversion efficiency and stability.

[0046] The methods of this application will be further illustrated below with examples and comparative examples.

[0047] Example 1 A method for preparing a modified biochar-based Ni / MoO2 / C catalyst, comprising the following steps: S1: The pretreated biogas residue was calcined at 700℃ for 3 hours under a nitrogen atmosphere to obtain biogas residue-based biochar. S2: Dissolve 0.254g of nickel acetate and 0.502g of molybdenum acetate in 30mL of deionized water and stir continuously. At the same time, add 2.64g of treated biochar based on sludge residue. Place the solution in an ultrasonic cell disruptor and treat for 30min. Then add citric acid with the same molar amount as acetate and stir under heating conditions for 30min to form a green sol. Continue heating or let stand to convert the sol into a gel. Place the gel in an environment of 110℃ and dry overnight to obtain Ni-Mo / biochar precursor. S3: The Ni-Mo / biochar precursor was washed three times with ethanol until the solution was neutral, and then dried in a drying oven at 35°C for 8 hours to obtain Ni-Mo / biochar precursor solid. S4: The Ni-Mo / biochar precursor solid was calcined in an oxygen atmosphere at a heating rate of 5°C per minute until it reached 550°C. After calcination for 5 hours, the temperature was lowered to room temperature. The resulting solid was added to water and stirred with a magnetic stirrer at 600 r / min for 8 hours. The mixture was then filtered, washed three times with ethanol, and dried in a 35°C oven for 3 hours to obtain NiO / MoO3 / C. S5: Under a hydrogen-nitrogen mixed atmosphere with a hydrogen gas fraction of 5%, NiO-MoO3 / C is reduced at 750℃ for 2 hours to reduce NiO to elemental nickel and MoO3 to MoO. 2， A Ni / MoO2 / C catalyst was obtained. The MoO2 loading in the Ni / MoO2 / C catalyst was 10%, and the Ni loading was 2%.

[0048] See Figures 1-3 It is known that the modified biochar-based catalyst with Ni / MoO2 / C supported on Ni / MoO2 has excellent dispersibility and can resist sintering and carbon deposition during the reaction.

[0049] Example 2 Unlike Example 1, in step S2, 0.254 g of nickel acetate and 0.753 g of molybdenum acetate were dissolved in 30 mL of deionized water with continuous stirring, while 2.49 g of treated biogas residue-based biochar was added. In step S5, the MoO2 loading in the Ni / MoO2 / C catalyst was 15%, and the Ni loading in the Ni / MoO2 / C catalyst was 2%.

[0050] Example 3 Unlike Example 1, in step S2, 0.254 g of nickel acetate and 0.251 g of molybdenum acetate were dissolved in 30 mL of deionized water with continuous stirring, while 2.79 g of treated biogas residue-based biochar was added. In step S5, the MoO2 loading in the Ni / MoO2 / C catalyst was 5%, and the Ni loading in the Ni / MoO2 / C catalyst was 2%.

[0051] Comparative Example 1 Unlike Example 1, in step S2, 0.254 g of nickel acetate was dissolved in 30 mL of deionized water with continuous stirring, while 2.94 g of treated biogas residue-based biochar was added. In step S5, the MoO2 loading in the Ni / MoO2 / C catalyst was 0%, and the Ni loading in the Ni / MoO2 / C catalyst was 2%.

[0052] Comparative Example 2 Unlike Example 1, in step S2, 0.254 g of nickel acetate and 1 g of molybdenum acetate were dissolved in 30 mL of deionized water with continuous stirring, while 2.34 g of treated biogas residue-based biochar was added. In step S5, the MoO2 loading in the Ni / MoO2 / C catalyst was 20%, and the Ni loading in the Ni / MoO2 / C catalyst was 2%.

[0053] Example 4 Unlike Example 1, in step S2, 0.173 g of nickel acetate and 0.502 g of molybdenum acetate were dissolved in 30 mL of deionized water with continuous stirring, while 2.67 g of treated biogas residue-based biochar was added. In step S5, the MoO2 loading in the Ni / MoO2 / C catalyst was 10%, and the Ni loading in the Ni / MoO2 / C catalyst was 1%.

[0054] Example 5 Unlike Example 1, in step S2, 0.382 g of nickel acetate and 0.502 g of molybdenum acetate were dissolved in 30 mL of deionized water with continuous stirring, while 2.61 g of treated biogas residue-based biochar was added. In step S5, the MoO2 loading in the Ni / MoO2 / C catalyst was 10%, and the Ni loading in the Ni / MoO2 / C catalyst was 3%.

[0055] Example 6 Unlike Example 1, in step S2, 0.509 g of nickel acetate and 0.502 g of molybdenum acetate were dissolved in 30 mL of deionized water with continuous stirring, while 2.58 g of treated biogas residue-based biochar was added. In step S5, the MoO2 loading in the Ni / MoO2 / C catalyst was 10%, and the Ni loading in the Ni / MoO2 / C catalyst was 4%.

[0056] Example 7 Unlike Example 1, in step S2, 0.636 g of nickel acetate and 0.502 g of molybdenum acetate were dissolved in 30 mL of deionized water with continuous stirring, while 2.55 g of treated biochar based on sludge was added. In step S5, the MoO2 loading in the Ni / MoO2 / C catalyst was 10%, and the Ni loading in the Ni / MoO2 / C catalyst was 5%.

[0057] Example 8 Unlike Example 1, in step S1, the calcination temperature is raised to 500°C.

[0058] Example 9 Unlike Example 1, in step S1, the calcination temperature is raised to 600°C.

[0059] Comparative Example 3 Unlike Example 1, in step S2, 0.502 g of molybdenum acetate is dissolved in 30 mL of deionized water and stirred continuously.

[0060] Comparative Example 4 Unlike Example 1, in step S3, the calcination temperature is 650°C and the calcination time is 3 hours.

[0061] Comparative Example 5 Unlike Example 1, in step S2, 0.254g of nickel nitrate and 0.502g of ammonium molybdate are dissolved in 30mL of deionized water and stirred continuously.

[0062] Comparative Example 6 Unlike Example 1, in step S3, the calcination temperature is 600°C and the calcination time is 3 hours.

[0063] The catalysts from each embodiment and comparative example were used for high-value conversion of biogas to syngas, and catalytic stability was tested by extending the reaction time. The experimental results are shown in Table 1. (1) Experiment on catalytic conversion of biogas into high-value products Take 0.2g of the catalyst from each example or comparative example into a reaction tube, and continuously introduce CH4, CO2 and nitrogen gas in a volume ratio of 30:20:10 into the reaction tube. At the same time, inject liquid water into the reaction tube at a flow rate of 0.029mL / h using a syringe pump. The reaction is carried out at 750℃ to obtain green syngas. The generated green syngas is then passed through a gas-liquid separator to remove residual water vapor, and then detected by gas chromatography. Gas chromatography revealed that the green syngas contains H2 and CO. Subsequently, gas chromatography was used to continuously track the content of each gas in the syngas.

[0064] (2) Catalytic stability test The stability of the catalysts in each embodiment or comparative example is characterized by comparing their initial activity (CH4 / CO2 conversion, % / %) at 750°C and their final activity (CH4 / CO2 conversion, % / %) after 100 h or 20 h of reaction. The closer the values ​​of the initial activity and the final activity are, the better the stability of the catalyst.

[0065] (3) Biogas conversion rate In this invention, biogas conversion rate refers to CH4 conversion rate and CO2 conversion rate.

[0066]

[0067]

[0068] In the above formula, (CH4 / N2) 进 This refers to the volume ratio of CH4 to N2 introduced into the reactor before the reaction (CH4 / N2). 出 This refers to the volume ratio of CH4 and N2 remaining after the reaction; (CO2 / N2) 进 This refers to the volume ratio of CO2 to N2 introduced into the reactor before the reaction (CO2 / N2). 出 It refers to the volume ratio of CO2 and N2 remaining after the reaction.

[0069] Table 1 Performance test results of each embodiment and comparative example

[0070] Here, CH4 / CO2 conversion rate refers to CH4 conversion rate / CO2 conversion rate; initial activity refers to the conversion rate of CH4 and CO2 at the beginning of the reaction, and final activity refers to the conversion rate of CH4 and CO2 after a period of reaction.

[0071] As shown in Table 1: (1) The modified biochar-based Ni / MoO2 / C catalyst prepared by controlling the loading of MoO2 to 5-15% and the loading of Ni to 1-5% has high CH4 and CO2 conversion rate and high catalytic stability when catalyzing biogas to syngas.

[0072] (2) By comparing Example 1 and Comparative Example 1, it can be seen that when the loading of MoO2 in the Ni / MoO2 / C catalyst is 0, the catalyst does not have a large number of oxygen vacancies generated by the redox cycle of Mo to activate CO2 and continuously generate a large amount of active oxygen. At the same time, it is also impossible to modify the surface electronic structure of Ni through electron transfer effect, thereby reducing the catalytic stability of the catalyst and reducing the CH4 / CO2 conversion rate to 71 / 18%. (3) By comparing Example 1 and Comparative Example 5, it can be seen that when using metal nitrates nickel nitrate and ammonium molybdate, the conversion rates of CH4 and CO2 decrease because the two are not conducive to the synthesis of a uniform and stable Ni / MoO2 / C catalyst after the preparation process, which ultimately affects the catalytic activity and stability.

[0073] Although several specific embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are merely exemplary and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art are within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a modified biochar-based Ni / MoO2 / C catalyst, characterized in that, Includes the following steps, S1: The pretreated biogas residue is placed in an oxygen-free atmosphere for calcination to obtain biogas residue-based biochar. S2: After mixing biochar based on sludge with water-soluble metal precursor and processing it in a cell-breaking device, a chelating agent is added, and Ni-Mo / biochar precursor is obtained by sol-gel method. S3: Wash the Ni-Mo / biochar precursor until the solution is neutral, and then dry it to obtain Ni-Mo / biochar precursor solid; S4: After calcining the Ni-Mo / biochar precursor solid in an oxygen atmosphere, filter and dry it to obtain NiO-MoO3 / C; S5: NiO-MoO3 / C is reduced to nickel and MoO3 to MoO. 2， A Ni / MoO2 / C catalyst was obtained.

2. The preparation method according to claim 1, characterized in that, In step S1, the calcination temperature is 600-700℃, and the heating rate is 3-5℃ / min. The calcination time is 2-4 hours.

3. The preparation method according to claim 1, characterized in that, In step S4, the calcination temperature is 500-600℃, and the heating rate is 3-5℃ / min. The calcination time is 4-6 hours.

4. The preparation method according to claim 1, characterized in that, The water-soluble metal precursor includes a nickel source and a molybdenum source, the chelating agent includes citric acid, and the molar ratio of the sum of the amounts of nickel and molybdenum in the nickel source to citric acid is 1:1 to 1.

5.

5. The preparation method according to claim 4, characterized in that, The nickel source is an organic acid nickel, and the molybdenum source is an organic acid molybdenum.

6. The preparation method according to claim 5, characterized in that, The organic acid nickel is nickel acetate, and the organic acid molybdenum is molybdenum acetate.

7. The preparation method according to claim 1, characterized in that, In step S5, the reduction treatment of NiO-MoO3 / C includes: placing NiO-MoO3 / C in a hydrogen atmosphere for reduction treatment, the reduction temperature is 700-800℃, and the reduction time is 1-3h.

8. A modified biochar-based Ni / MoO2 / C catalyst prepared according to any one of claims 1 to 7, characterized in that, include: The biochar carrier is composed of biogas residue and an active component Ni and a co-catalyst MoO2 supported on the biogas residue. The loading of the active component Ni is 1-5%, and the loading of the co-catalyst MoO2 is 5-15%.

9. The catalyst according to claim 8, characterized in that, The active component Ni is loaded at 2%, and the co-catalyst MoO2 is loaded at 10%.

10. The application of the modified biochar-based Ni / MoO2 / C catalyst as described in claim 8 or 9 in the high-value conversion of biogas to syngas or the preparation of biofuels from said syngas.

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