Preparation method and application of Cr2O3 modified Al2O3 fiber-supported nickel-based catalyst

Abstract

The present invention relates to the field of gas phase catalysis technology, and in particular to a kind of Cr2O3 modified Al2O3 fiber-loaded nickel-based catalyst preparation method and application thereof, preparation method includes step one: nickel salt, Al2O3 precursor, chromium salt and high polymer are respectively weighed and dissolved in solvent, form uniform and transparent electrostatic spinning precursor solution;Step 2: electrostatic spinning precursor solution is sucked into electrostatic spinning push injection device and carries out electrostatic spinning, prepares precursor fiber;Step 3: after precursor fiber is dried 8 24h, is placed in muffle furnace and calcined, is reduced at high temperature and obtains Cr2O3 modified Al2O3 fiber-loaded nickel-based catalyst. Cr2O3 modified Al2O3 fiber-loaded nickel-based catalyst provided by the present invention is simplified the preparation technology of electrostatic spinning precursor solution, while improving the problem that methane partial oxidation reforming conversion rate is not high.

Description

Technical Field

[0001] The present invention relates to the technical field of gas phase catalysis, and in particular to a preparation method of a Cr2O3 modified Al2O3 fiber-supported nickel-based catalyst and its application. Background Art

[0002] Methane is the primary component of natural gas and shale gas. The partial oxidation reforming of methane (POM) to syngas is a mild, exothermic reaction. The resulting syngas, H2 / CO, can be directly used in fuel production reactions such as methanol synthesis and Fischer-Tropsch synthesis. This reaction is an important pathway for utilizing methane. Catalysts used in the POM reaction primarily include precious metal catalysts and non-precious metal catalysts. While precious metal catalysts have high catalytic activity, they are susceptible to deactivation and are prohibitively expensive, making them difficult to commercialize. Non-precious metal catalysts primarily use Ni, Co, Fe, and Cu as active components. Nickel-based catalysts are widely used in industrial production due to their high catalytic activity and relatively low cost. However, nickel-based catalysts are prone to carbon deposition at high temperatures, leading to rapid deactivation and poor stability.

[0003] In recent years, to improve the stability of nickel-based catalysts and slow down their deactivation rate, a large number of researchers have investigated supported nickel-based catalysts. The impregnation precipitation method is a common method for preparing supported nickel-based catalysts. This method involves impregnating an oxide support into a solution containing nickel ions. After drying, calcination, crushing, and screening, a supported catalyst containing nickel as the active component is obtained. While supported nickel-based catalysts prepared using the precipitation impregnation method can improve the dispersion of the active component to a certain extent, the crushed and sieved catalysts are prone to agglomeration and caking, which can easily form large particles. When passing through high-flow gas, they are prone to high pressure drop, leading to reactor blockage and explosion accidents. The carbon deposition resistance of supported nickel-based catalysts is closely related to their macrostructure. When supported nickel-based catalysts exhibit agglomeration and agglomeration, the porosity, pore structure and distribution, specific surface area, and grain size of the catalyst are adversely affected, resulting in low carbon deposition resistance of supported nickel-based catalysts prepared using the precipitation impregnation method. Studies have reported that the use of electrospun nanofiber catalyst supports can effectively increase the surface area of ​​Ni-based catalysts, providing more Ni active sites. The reduced Ni nanoparticles interact strongly with the support, resulting in improved carbon deposition resistance. Prior art supported catalysts using electrospun nanofibers as supports typically require dissolving the active catalyst components, co-catalyst, and polymer in their respective solvents and then mixing and stirring them to form an electrospinning precursor solution. The preparation process for this electrospinning precursor solution is relatively complex and can easily lead to raw material loss during solution transfer. Furthermore, the conversion rate for partial oxidation reforming of methane is low. Summary of the Invention

[0004] In response to the technical problems of relatively complex preparation process of electrospinning precursor solution for supported catalysts using electrospinning nanofibers as supports and low methane partial oxidation reforming conversion rate, the present invention provides a preparation method and application of a Cr2O3-modified Al2O3 fiber-supported nickel-based catalyst. The Cr2O3-modified Al2O3 fiber-supported nickel-based catalyst is prepared by electrospinning technology using Al2O3 fibers as supports and Cr2O3 as a doping element to support catalyst metal nickel nanoparticles. This simplifies the preparation process of the electrospinning precursor solution and improves the problem of low methane partial oxidation reforming conversion rate.

[0005] In a first aspect, the present invention provides a method for preparing a Cr2O3-modified Al2O3 fiber-supported nickel-based catalyst, comprising the following steps:

[0006] Step 1: Weigh nickel salt, Al2O3 precursor, chromium salt and polymer respectively and dissolve them in a solvent. Stir at 30-40°C until completely dissolved. The stirring time is controlled to be more than 6 hours to form a uniform and transparent electrospinning precursor solution, wherein the mass ratio of nickel salt, Al2O3 precursor and polymer is 0.05-0.75:0.5-6.5:0.5-7.5.

[0007] Step 2: The electrospinning precursor solution obtained in step 1 is sucked into an electrospinning push-in device for electrospinning, the spinning voltage is adjusted to -7 to 17 kV, the propulsion rate is 0.02 to 0.05 mL / min, and the receiving distance is 20 to 30 cm to prepare a precursor fiber.

[0008] Step 3: Dry the precursor fiber obtained in step 2 at 70-150°C for 8-24h, place the dried precursor fiber in a muffle furnace and calcine in an air atmosphere, and calcine in a segmented heating mode, first heating to 350-450°C at a rate of 0.5-1.5°C / min and keeping the temperature constant for 1-1.5h, then heating to 750-850°C at a rate of 1.5-2.5°C / min and keeping the temperature constant for 1-1.5h, controlling the total calcination time to be 11-13h, and reducing at high temperature to obtain a catalyst of Al2O3 and Cr2O3 solid solution nanofiber loaded with metal nickel, which is a Cr2O3 modified Al2O3 fiber loaded with nickel-based catalyst. In the Cr2O3 modified Al2O3 fiber loaded with nickel-based catalyst prepared by step 3, the particle size of metal nickel is 5-100nm, the fiber diameter is 50-1000nm, and the fiber specific surface area is 100-400m 2 / g.

[0009] The mass percentage of nickel in the Cr2O3-modified Al2O3 fiber-supported nickel-based catalyst in step three is 0.1%-40%; the mass percentage of chromium in the Cr2O3-modified Al2O3 fiber-supported nickel-based catalyst in step three is 0.1%-10%.

[0010] Furthermore, the nickel salt includes any one of nickel nitrate, nickel chloride, nickel bromide, nickel acetate, nickel nitrate hydrate, nickel chloride hydrate, nickel bromide hydrate, and nickel acetate hydrate, preferably nickel nitrate. The present invention uses a nickel salt with good water solubility to provide the active component nickel for the catalyst, which is conducive to the full dissolution of nickel ions in the solvent, thereby improving the dispersion of nickel in the support.

[0011] Furthermore, the Al2O3 precursor includes any one of ammonium aluminum carbonate, aluminum bicarbonate, aluminum nitrate, and aluminum acetate, or a mixture of two or more thereof, preferably aluminum nitrate. The present invention selects Al2O3 as the catalyst support to increase the mechanical strength of the nickel-loaded fiber. The use of aluminum nitrate, which has good water solubility, facilitates uniform distribution of the Al2O3 within the fiber, providing a larger specific surface area.

[0012] Furthermore, the chromium salt includes chromium nitrate or a hydrate of chromium nitrate. The chromium salt in the precursor fiber, after calcination, generates Cr2O3, which forms a solid solution with the Al2O3 support during the reduction process. This promotes lattice distortion and creates lattice defects, increasing the number of active sites for the catalytic reaction, thereby increasing the conversion rate of the partial oxidation reforming of methane, improving the catalyst's resistance to carbon deposition, and enhancing the stability of the Al2O3 support.

[0013] Furthermore, the high polymer includes any one or a mixture of two or more of polyvinyl alcohol, polyvinyl pyrrolidone, polycaprolactone, and polyacrylic acid, preferably polyvinyl pyrrolidone with an average molecular weight of about 1.3 million. On the one hand, the present invention uses a polymer with good water solubility to prepare an electrospinning precursor solution. The active groups of the hydrophilic polymer, such as carbonyl and / or ether groups, can undergo complexation with metal ions, allowing the polymer to be more evenly mixed with nickel salts, Al2O3 precursors, and chromium salts in a hydrophilic solvent, thereby improving the dispersibility of nickel salts, Al2O3 precursors, and chromium salts in electrospun fibers. On the other hand, the high molecular weight polymer can also play a certain coating role on nickel salts, Al2O3 precursors, and chromium salts, preventing metal particles from agglomerating and reducing the size of the metal particles.

[0014] Furthermore, the solvent is any one of deionized water, ethanol, and N,N-dimethylformamide, or a mixture of two or more thereof.

[0015] Furthermore, the mass of the chromium salt in step 1 is calculated as follows:

[0016] S1: Convert the mass of chromium salt to the mass of Cr2O3, recorded as mCr2O3; convert the mass of Al2O3 precursor to the mass of Al2O3, recorded as mA12O3; calculate the mass of nickel element based on the mass of nickel salt, recorded as mNi;

[0017] S2: Substitute mNi into formula (1) to calculate the mass sum of Cr2O3 and Al2O3, i.e. mCr2O3+mAl2O3:

[0018]

[0019] S3: Substituting the sum of the masses of Cr2O3 and Al2O3 into formula (2), we can obtain the mass range of mCr2O3:

[0020]

[0021] Among them, 0 <X≤10;

[0022] S4: Convert the calculated mass of Cr2O3 into the mass of chromium salt.

[0023] Furthermore, the mass of the solvent in step 1 satisfies formula (3):

[0024]

[0025] Here, mnickle salt represents the mass of nickel salt, mAl2O3 precursor represents the mass of Al2O3 precursor, mchromium salt represents the mass of chromium salt, mpolymer represents the mass of polymer, and msolvent represents the mass of solvent.

[0026] In a second aspect, the present invention also provides a use of a Cr2O3-modified Al2O3 fiber-supported nickel-based catalyst prepared by the above-described preparation method in a catalytic methane partial oxidation reforming reaction. Using the Cr2O3-modified Al2O3 fiber-supported nickel-based catalyst in the catalytic methane partial oxidation reforming reaction can improve the methane conversion rate.

[0027] The beneficial effects of the present invention are:

[0028] The present invention provides a method for preparing a Cr2O3-modified Al2O3 fiber-supported nickel-based catalyst. Cr2O3 is doped into the Al2O3 fiber-supported nickel-based catalyst, and a uniform and transparent electrospinning precursor solution is prepared by a "one-step method". On the one hand, the preparation process of the electrospinning precursor solution is simplified, and the loss of raw materials and solvents is reduced. On the other hand, during the electrospinning process, since nickel ions are difficult to aggregate within a very short fiber formation time, they can be uniformly dispersed in the fibers, thereby improving the dispersibility and stability of metallic nickel in the precursor fibers, reducing the size of metal particles containing nickel, and improving the catalyst's ability to resist carbon deposition.

[0029] After preparing the precursor fiber, the present invention first dries the precursor fiber at 70-150°C for 8-24 hours, then places the dried precursor fiber in a muffle furnace and calcines it in an air atmosphere. Drying the precursor fiber at a relatively low temperature before calcining helps remove residual solvent in the precursor fiber, preventing the precursor fiber from sticking due to the residual solvent, which would result in a decrease in the specific surface area and porosity of the catalyst. The present invention adopts a staged heating mode with a slow heating rate during the calcination process. The temperature is first raised to 350-450°C at a rate of 0.5-1.5°C / min and maintained at this temperature for 1-1.5 hours, so that the polymer in the precursor fiber is solidified and cross-linked into a composite nanofiber with a three-dimensional network structure. The temperature is then raised to 750-850°C at a rate of 1.5-2.5°C / min and maintained at this temperature for 1-1.5 hours, so that the organic components in the polymer are fully burned to prevent the formation of carbon deposits. Inorganic salts are decomposed into metal oxides at this stage. The Al2O3 precursor in the composite nanofiber is converted into Al2O3 fibers, the chromium salt is converted into Cr2O3 and forms a solid solution with the Al2O3 fibers, and the nickel salt is converted into nickel oxide and anchored on the surface of the Al2O3 fibers. The Al2O3 modified Al2O3 fibers loaded with metallic nickel are reduced at high temperature. The Al2O3 support modified by chromium doping has higher stability, which is mainly attributed to the chromium element being dissolved into the aluminum lattice and the two existing in the form of a solid solution. Cr2O3 modified Al2O3 fiber supported nickel-based catalyst has a significant effect in inhibiting the formation of nickel aluminate during the methane partial oxidation reforming reaction, significantly improving the catalytic performance of methane partial oxidation reforming. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0031] Figure 11 is a graph showing the conversion rate-time of the partial oxidation reforming reaction of methane catalyzed by the catalysts prepared in Comparative Example 1 and Examples 1-4 of the present invention.

[0032] Figure 2 This is a local transmission electron micrograph of the Cr2O3-modified Al2O3 fiber-supported nickel-based catalyst prepared in Example 2 of the present invention.

[0033] Figure 3 This is an EDS spectrum analysis diagram of the local O, Al, Ni, and Cr element distributions of the Cr2O3-modified Al2O3 fiber-supported nickel-based catalyst prepared in Example 2 of the present invention.

[0034] Figure 4 This is a Ni element distribution diagram in a local EDS spectrum analysis diagram of the Cr2O3 modified Al2O3 fiber-supported nickel-based catalyst prepared in Example 2 of the present invention.

[0035] Figure 5 This is a Cr element distribution diagram in a local EDS spectrum analysis diagram of the Cr2O3 modified Al2O3 fiber-supported nickel-based catalyst prepared in Example 2 of the present invention.

[0036] Figure 6 This is a scanning electron microscope image of the Cr2O3 modified Al2O3 fiber loaded with nickel-based catalyst prepared in Example 2 of the present invention.

[0037] Figure 7 The XRD patterns of the catalysts prepared in Comparative Example 1 and Examples 1-4 of the present invention after calcination are shown.

[0038] Figure 8 The temperature-programmed desorption CO-TPD curves of the catalysts prepared in Examples 1-4 of the present invention are shown. DETAILED DESCRIPTION

[0039] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0040] Example 1

[0041] A method for preparing a Cr2O3-modified Al2O3 fiber-supported nickel-based catalyst comprises the following steps:

[0042] Step 1: Weigh 0.3105g nickel nitrate, 2.3139g aluminum nitrate, 0.0256g chromium nitrate and 0.6g polyvinylpyrrolidone (PVP) respectively and dissolve them in a mixed solvent containing 2.0g ethanol and 8.0g deionized water. Heat the mixture in a water bath to 30-40℃ and stir for 6h. Then remove the water bath and continue magnetic stirring for 12h to fully dissolve the nitrate to form a uniform and transparent electrospinning precursor solution.

[0043] Step 2: The electrospinning precursor solution obtained in step 1 is sucked into the electrospinning injection device for electrospinning, the positive spinning voltage is adjusted to 17KV, the negative spinning voltage is -7KV, the propulsion rate is 0.03mL / min, and a grid-shaped metal receiver is used with a receiving distance of 25cm to prepare the precursor fiber.

[0044] Step 3: Dry the precursor fiber obtained in step 2 at 120°C for 18 hours, place the dried precursor fiber in a muffle furnace and calcine in an air atmosphere. The calcination adopts a staged heating mode, first heating to 400°C at a rate of 1°C / min and keeping the temperature constant for 1 hour, then heating to 800°C at a rate of 2°C / min and keeping the temperature constant for 1 hour, and controlling the total calcination time to be 12 hours. Reduce at high temperature to obtain a catalyst of Al2O3 and Cr2O3 solid solution nanofibers loaded with metallic nickel, which is a Cr2O3 modified Al2O3 fiber loaded with nickel-based catalyst.

[0045] The Cr2O3 modified Al2O3 fiber supported nickel-based catalyst prepared by the above method was used in the partial catalytic oxidation of methane as follows: 0.1 g of the catalyst obtained in step 3 was placed in a quartz tube, reduced with hydrogen at 750°C, and then reacted with methane, oxygen and argon at a flow rate ratio of 1:1:8 at 750°C. The catalyst evaluation results are shown in FIG. Figure 1 The average conversion rate of CH4 was 15%.

[0046] Example 2

[0047] A method for preparing a Cr2O3-modified Al2O3 fiber-supported nickel-based catalyst comprises the following steps:

[0048] Step 1: Weigh 0.3141g nickel nitrate, 2.2927g aluminum nitrate, 0.0432g chromium nitrate and 0.6g polyvinylpyrrolidone (PVP) respectively and dissolve them in a mixed solvent containing 2.0g ethanol and 8.0g deionized water. Heat the mixture in a water bath to 30-40℃ and stir for 6h. Then remove the water bath and continue magnetic stirring for 12h to fully dissolve the nitrate to form a uniform and transparent electrospinning precursor solution.

[0049] Step 2: The electrospinning precursor solution obtained in step 1 is sucked into the electrospinning injection device for electrospinning, the positive spinning voltage is adjusted to 17KV, the negative spinning voltage is -7KV, the propulsion rate is 0.03mL / min, and a grid-shaped metal receiver is used with a receiving distance of 25cm to prepare the precursor fiber.

[0050] Step 3: Dry the precursor fiber obtained in step 2 at 120°C for 18 hours, place the dried precursor fiber in a muffle furnace and calcine in an air atmosphere. The calcination adopts a staged heating mode, first heating to 400°C at a rate of 1°C / min and keeping the temperature constant for 1 hour, then heating to 800°C at a rate of 2°C / min and keeping the temperature constant for 1 hour, and controlling the total calcination time to be 12 hours. Reduce at high temperature to obtain a catalyst of Al2O3 and Cr2O3 solid solution nanofibers loaded with metallic nickel, which is a Cr2O3 modified Al2O3 fiber loaded with nickel-based catalyst.

[0051] The Cr2O3 modified Al2O3 fiber supported nickel-based catalyst prepared by the above method was used in the partial catalytic oxidation of methane as follows: 0.1 g of the catalyst obtained in step 3 was placed in a quartz tube, reduced with hydrogen at 750°C, and then reacted with methane, oxygen and argon at a flow rate ratio of 1:1:8 at 750°C. The catalyst evaluation results are shown in FIG. Figure 1 The average conversion rate of CH4 was 86%. The transmission electron microscopy (TEM) image of the catalyst obtained in this example after reduction with hydrogen at 750°C for 1 hour is shown in FIG. Figure 2 As shown in Figure 2, the distribution of O, Al, Ni, and Cr elements is as follows: Figure 3 As shown in Figure 2, the distribution of Ni elements is as follows: Figure 4 As shown in Figure 2, the distribution of Cr elements is as follows: Figure 5 As shown in the scanning electron microscope (SEM) Figure 6 shown.

[0052] Figure 2 The black dots in the figure are the reduced active metal Ni. Figure 2 It can be seen that the active metal Ni is distributed more evenly on the surface of the catalyst fiber, which is consistent with Figure 4 The distribution of Ni elements is consistent with that shown in Figure 2. Figure 3 It can be seen that O, Al, Ni, Cr and other elements are dispersed in the catalyst fibers. Figure 5 It can be seen that the Cr element has good dispersion, which indicates that the preparation method described in this embodiment is conducive to the uniform dispersion of the active metal Ni particles.

[0053] Depend on Figure 6It is clearly visible that reduced active metal Ni particles are present on the surface of the Cr2O3-modified Al2O3 fiber support, with a fiber diameter of approximately 200 nm. This type of fibrous nanostructured catalyst exhibits a high specific surface area and a large number of active sites. This provides favorable innate conditions for the catalyst's high catalytic activity. Furthermore, it is clearly visible that the unique fiber structure has a high porosity, which ensures that the catalyst can maintain a very low pressure drop at high gas flow rates, enabling activity and stability testing of methane partial oxidation reforming at high flow rates.

[0054] Example 3

[0055] A method for preparing a Cr2O3-modified Al2O3 fiber-supported nickel-based catalyst comprises the following steps:

[0056] Step 1: Weigh 0.3179 g nickel nitrate, 2.2710 g aluminum nitrate, 0.0612 g chromium nitrate, and 0.6 g polyvinylpyrrolidone (PVP) and dissolve them in a mixed solvent containing 2.0 g ethanol and 8.0 g deionized water. Heat the mixture in a water bath to 30-40 ° C and stir for 6 h. Remove the water bath and continue magnetic stirring for 12 h to fully dissolve the nitrate to form a uniform and transparent electrospinning precursor solution.

[0057] Step 2: The electrospinning precursor solution obtained in step 1 is sucked into the electrospinning injection device for electrospinning, the positive spinning voltage is adjusted to 17KV, the negative spinning voltage is -7KV, the propulsion rate is 0.03mL / min, and a grid-shaped metal receiver is used with a receiving distance of 25cm to prepare the precursor fiber.

[0058] Step 3: Dry the precursor fiber obtained in step 2 at 120°C for 18 hours, place the dried precursor fiber in a muffle furnace and calcine in an air atmosphere. The calcination adopts a staged heating mode, first heating to 400°C at a rate of 1°C / min and keeping the temperature constant for 1 hour, then heating to 800°C at a rate of 2°C / min and keeping the temperature constant for 1 hour, and controlling the total calcination time to be 12 hours. Reduce at high temperature to obtain a catalyst of Al2O3 and Cr2O3 solid solution nanofibers loaded with metallic nickel, which is a Cr2O3 modified Al2O3 fiber loaded with nickel-based catalyst.

[0059] The Cr2O3 modified Al2O3 fiber supported nickel-based catalyst prepared by the above method was used in the partial catalytic oxidation of methane as follows: 0.1 g of the catalyst obtained in step 3 was placed in a quartz tube, reduced with hydrogen at 750°C, and then reacted with methane, oxygen and argon at a flow rate ratio of 1:1:8 at 750°C. The catalyst evaluation results are shown in FIG. Figure 1 The average conversion rate of CH4 is 80%.

[0060] Example 4

[0061] A method for preparing a Cr2O3-modified Al2O3 fiber-supported nickel-based catalyst comprises the following steps:

[0062] Step 1: Weigh 0.3236 g nickel nitrate, 2.2375 g aluminum nitrate, 0.0889 g chromium nitrate, and 0.6 g polyvinylpyrrolidone (PVP) and dissolve them in a mixed solvent containing 2.0 g ethanol and 8.0 g deionized water. Heat the mixture in a water bath to 30-40 ° C and stir for 6 h. Remove the water bath and continue magnetic stirring for 12 h to fully dissolve the nitrate to form a uniform and transparent electrospinning precursor solution.

[0063] Step 2: The electrospinning precursor solution obtained in step 1 is sucked into the electrospinning injection device for electrospinning, the positive spinning voltage is adjusted to 17KV, the negative spinning voltage is -7KV, the propulsion rate is 0.03mL / min, and a grid-shaped metal receiver is used with a receiving distance of 25cm to prepare the precursor fiber.

[0064] Step 3: Dry the precursor fiber obtained in step 2 at 120°C for 18 hours, place the dried precursor fiber in a muffle furnace and calcine in an air atmosphere. The calcination adopts a staged heating mode, first heating to 400°C at a rate of 1°C / min and keeping the temperature constant for 1 hour, then heating to 800°C at a rate of 2°C / min and keeping the temperature constant for 1 hour, and controlling the total calcination time to be 12 hours. Reduce at high temperature to obtain a catalyst of Al2O3 and Cr2O3 solid solution nanofibers loaded with metallic nickel, which is a Cr2O3 modified Al2O3 fiber loaded with nickel-based catalyst.

[0065] The Cr2O3 modified Al2O3 fiber supported nickel-based catalyst prepared by the above method was used in the partial catalytic oxidation of methane as follows: 0.1 g of the catalyst obtained in step 3 was placed in a quartz tube, reduced with hydrogen at 750°C, and then reacted with methane, oxygen and argon at a flow rate ratio of 1:1:8 at 750°C. The catalyst evaluation results are shown in FIG. Figure 1 The average conversion rate of CH4 is 40%.

[0066] Comparative Example 1

[0067] A method for preparing an Al2O3 fiber-supported nickel-based catalyst comprises the following steps:

[0068] Step 1: Weigh 0.3337 g nickel nitrate, 2.1788 g aluminum nitrate, and 0.6 g polyvinylpyrrolidone (PVP) separately and dissolve them in a mixed solvent containing 2.0 g ethanol and 8.0 g deionized water. Heat the mixture in a water bath to 30-40 ° C and stir for 6 h. Then remove the water bath and continue magnetic stirring for 12 h to fully dissolve the nitrate to form a uniform and transparent electrospinning precursor solution.

[0069] Step 2: The electrospinning precursor solution obtained in step 1 is sucked into the electrospinning injection device for electrospinning, the positive spinning voltage is adjusted to 17KV, the negative spinning voltage is -7KV, the propulsion rate is 0.03mL / min, and a grid-shaped metal receiver is used with a receiving distance of 25cm to prepare the precursor fiber.

[0070] Step 3: Dry the precursor fiber obtained in step 2 at 120°C for 18 hours, place the dried precursor fiber in a muffle furnace and calcine in an air atmosphere. The calcination adopts a segmented heating mode, first heating to 400°C at a rate of 1°C / min and keeping the temperature constant for 1 hour, then heating to 800°C at a rate of 2°C / min and keeping the temperature constant for 1 hour. The total calcination time is controlled to be 12 hours, and the Al2O3 nanofiber-loaded metallic nickel catalyst is reduced at high temperature to obtain the Al2O3 nanofiber-loaded nickel-based catalyst, that is, the Al2O3 fiber-loaded nickel-based catalyst.

[0071] The Al2O3 fiber-supported nickel-based catalyst prepared by the above method was used in the partial catalytic oxidation of methane as follows: 0.1 g of the catalyst obtained in step 3 was placed in a quartz tube, reduced with hydrogen at 750°C, and then reacted with methane, oxygen, and argon at a flow rate ratio of 1:1:8 at 750°C. The catalyst evaluation results are shown in FIG. Figure 1 The average conversion rate of CH4 was 10%.

[0072] like Figure 1 As shown, in Comparative Example 1, since Cr2O3-modified Al2O3 fiber-supported nickel-based catalyst was not used, the initial activity of CH4 was low and the average conversion rate of CH4 was only 10%, indicating that the catalyst efficiency was low. Examples 1-4 use the preparation method of Cr2O3-modified Al2O3 fiber-supported nickel-based catalyst disclosed in the present invention, and adopt electrospinning technology to prepare Cr2O3-modified Al2O3 fiber-supported nickel-based catalysts with different mass percentages of chromium, so that Cr2O3 and the Al2O3 support form a solid solution during the reduction process, thereby improving the stability of the support and improving the conversion rate of methane in the partial oxidation reforming reaction of methane. It can be seen that the Cr2O3-modified catalyst has a significant effect on improving the initial catalytic activity of the methane partial oxidation reforming reaction; the Cr2O3-modified Al2O3 fiber-supported nickel-based catalysts prepared in Examples 2-4 have good catalytic stability within 9 hours after the start of the methane partial oxidation reforming reaction, indicating that the preparation method disclosed in the present invention can also improve the stability of its catalyst, so that methane maintains a stable conversion rate for a long time after the start of the reaction, and even the conversion rate is higher than the initial conversion rate as the reaction time is extended.

[0073] The catalysts prepared in Examples 1-4 and Comparative Example 1 were subjected to X-ray diffraction measurements. The results are shown in Figure 7 .Depend on Figure 7It can be seen that the diffraction peaks of the catalyst after calcination are mainly in the form of NiAl2O4, and the XRD patterns of Examples 1-4 do not show the diffraction peaks of chromium oxide, indicating that Cr oxide exists in the Al2O3 support in an amorphous form. 3+ The solid dissolution of ions into the lattice of the Al2O3 support provides favorable conditions.

[0074] The catalysts prepared in Examples 1-4 were purged with a 10% CO / He mixture at a flow rate of 30 ml / min at 200°C for 1 h, and then heated to 550°C with He at a heating rate of 10°C / min for temperature programmed desorption (CO-TPD) to characterize the dispersion of Ni. The results are shown in Table 1. Figure 8 , Figure 8 The vertical axis is the TCD signal characterized by the chemical adsorption instrument. The larger the area, the higher the dispersion of the active metal on the support. Figure 8 It can be seen that CO desorption peaks appeared in Examples 1-4, among which the CO desorption peak area appeared in Examples 1-3 was larger, and the CO desorption peak area appeared in Example 2 was the largest, indicating that different Cr doping amounts have a significant effect on the dispersion of active metal Ni, especially in the temperature range of 250-500°C. The CO-TPD curve shows different desorption areas after different Cr doping amounts, which indirectly proves that Cr is incorporated into the Ni / Al2O3 catalytic system. This supplements the phenomenon that no diffraction peak of Cr is shown in XRD characterization, while CO-TPD has different desorption peaks after Cr doping, further indicating that Cr is doped into the Al lattice and exists in the form of a solid solution with the support. 3+ By acting on the support, it plays a role in improving the catalytic activity of Ni-Al system catalysts.

[0075] Although the present invention has been described in detail with reference to the accompanying drawings and in conjunction with preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, persons of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and such modifications or substitutions shall be within the scope of the present invention. Any changes or substitutions that can be easily conceived by persons skilled in the art within the technical scope disclosed in the present invention shall be within the scope of protection of the present invention.

Claims

1. A method for preparing a Cr2O3-modified Al2O3 fiber-supported nickel-based catalyst, characterized in that: The steps include: Step 1: Weigh nickel salt, Al2O3 precursor, chromium salt and polymer respectively, dissolve them in a solvent, and stir at 30-40°C until completely dissolved to form a uniform and transparent electrospinning precursor solution, wherein the mass ratio of nickel salt, Al2O3 precursor and polymer is 0.05-0.75:0.5-6.5:0.5-7.5; Step 2: The electrospinning precursor solution obtained in step 1 is sucked into an electrospinning push-in device for electrospinning, and the spinning voltage is adjusted to -7-17 kV, the propulsion rate is 0.02-0.05 mL / min, and the receiving distance is 20-30 cm to prepare a precursor fiber; Step 3: drying the precursor fiber obtained in step 2 at 70-150°C for 8-24h, placing the dried precursor fiber in a muffle furnace and calcining it in an air atmosphere, calcining in a staged heating mode, first heating to 350-450°C at a rate of 0.5-1.5°C / min and keeping the temperature constant for 1-1.5h, then heating to 750-850°C at a rate of 1.5-2.5°C / min and keeping the temperature constant for 1-1.5h, controlling the total calcination time to be 11-13h, and reducing at high temperature to obtain an Al2O3 and Cr2O3 solid solution nanofiber-loaded metallic nickel catalyst, which is a Cr2O3-modified Al2O3 fiber-loaded nickel-based catalyst; Wherein, the mass percentage of nickel in the Cr2O3 modified Al2O3 fiber-supported nickel-based catalyst in step three is 0.1%-40%; the mass percentage of chromium in the Cr2O3 modified Al2O3 fiber-supported nickel-based catalyst is 0.1%-10%.

2. The method for preparing a Cr2O3-modified Al2O3 fiber-supported nickel-based catalyst according to claim 1, characterized in that: The nickel salt includes any one of nickel nitrate, nickel chloride, nickel bromide, and nickel acetate.

3. The method for preparing a Cr2O3-modified Al2O3 fiber-supported nickel-based catalyst according to claim 1, characterized in that: The Al2O3 precursor includes any one of ammonium aluminum carbonate, aluminum bicarbonate, aluminum nitrate, and aluminum acetate, or a mixture of two or more thereof.

4. The method for preparing a Cr2O3 modified Al2O3 fiber-supported nickel-based catalyst according to claim 1, characterized in that: Chromium salts include chromium nitrate.

5. The method for preparing a Cr2O3 modified Al2O3 fiber-supported nickel-based catalyst according to claim 1, characterized in that: The high polymer includes any one of polyvinyl alcohol, polyvinyl pyrrolidone, polycaprolactone, and polyacrylic acid, or a mixture of two or more thereof.

6. The method for preparing a Cr2O3 modified Al2O3 fiber-supported nickel-based catalyst according to claim 1, characterized in that: The solvent is any one of deionized water, ethanol, and N,N-dimethylformamide, or a mixture of two or more thereof.

7. The method for preparing a Cr2O3 modified Al2O3 fiber-supported nickel-based catalyst according to claim 1, characterized in that: The mass of the chromium salt in step 1 is calculated as follows: S1: Convert the mass of chromium salt to the mass of Cr2O3, recorded as mCr 2 O 3. Convert the mass of Al2O3 precursor to the mass of Al2O3, recorded as mxD 2 O 3. Calculate the mass of nickel element based on the mass of nickel salt and record it as mxD ; S2: mxD Substituting into formula (1), the sum of the masses of Cr2O3 and Al2O3 is calculated, that is, mCr 2 O 3 +mAl 2 O 3: S3: Substitute the mass sum of Cr2O3 and Al2O3 into formula (2) to obtain mCr 2 O 3 quality ranges: Among them, 0 <X≤10; S4: Convert the calculated mass of Cr2O3 into the mass of chromium salt.

8. The method for preparing a Cr2O3 modified Al2O3 fiber-supported nickel-based catalyst according to claim 1, characterized in that: The mass of the solvent in step 1 satisfies formula (3): Here, mnickle salt represents the mass of nickel salt, mAl2O3 precursor represents the mass of Al2O3 precursor, mchromium salt represents the mass of chromium salt, mpolymer represents the mass of polymer, and msolvent represents the mass of solvent.

9. Use of a Cr2O3 modified Al2O3 fiber-supported nickel-based catalyst prepared by the preparation method according to any one of claims 1 to 8 in catalyzing a methane partial oxidation reforming reaction.

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