Preparation method and application of nickel-based catalyst

Abstract

The invention discloses a nickel-based catalyst and a preparation method and application thereof, the active component of the nickel-based catalyst is Ni, the carrier is a metal oxide, and the loading capacity of the active component Ni is 5-20 wt%. The catalyst has excellent CO selective methanation low-temperature activity, the CO concentration in reformed gas can be reduced to 10 ppm or below in a large reaction temperature range, the CO selectivity is close to 100% in a wide temperature window, and the hydrogen consumption is lower than 10%. In addition, the preparation method of the catalyst is easy to operate, the heat treatment link is optimized compared with a traditional catalyst preparation process, the process complexity is reduced, energy consumption is reduced, and meanwhile the high activity and stability of the catalyst are guaranteed.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy chemical engineering / catalysis, and relates to a nickel-based catalyst, a preparation method thereof and an application thereof. More specifically, it relates to a preparation method of a nickel-based catalyst for low-temperature CO selective methanation in hydrogen-rich gas. Background Art

[0002] Proton exchange membrane fuel cell (PEMFC) is an electrification technology with broad prospects, which mainly uses hydrogen or hydrogen-rich reformed gas as fuel. However, the storage and transportation of hydrogen limit its application in distributed energy systems. Therefore, a fuel processing system has been developed to convert liquid hydrogen-rich carriers such as methanol into hydrogen-rich reformed gas through chemical reactions. Since the Pt positive electrode material of PEMFC is extremely sensitive to CO, trace amounts of CO can cause irreversible poisoning and reduce the battery performance. Therefore, the CO content in hydrogen must be reduced to below 10 ppm before use to avoid electrode poisoning.

[0003] CO selective methanation (CO-SMET) is a method widely used for CO removal in hydrogen-rich gas. Using H 2 and CO in hydrogen-rich gas as reactants, no additional reactants need to be added throughout the process, and methane (CH 4 ) harmless to the battery is directly generated, which is one of the most effective methods for deep CO removal at present. Currently, methanation catalysts mainly include Ru-based and Ni-based catalysts. Among them, Ni-based catalysts are the most widely used methanation catalysts in the chemical industry because of their low price and comparable CO methanation activity to Ru-based catalysts. However, the suitable reduction temperature (greater than 400 °C) and reaction temperature (greater than 300 °C) of conventional Ni-based catalysts are relatively high. The hydrogen-rich reformed gas of organic hydrogen carriers usually contains a high concentration of CO 2 , and the occurrence of competitive methanation of CO 2 and the reverse water-gas shift reaction at high temperature will cause waste of the effective fuel H 2 , as shown in reaction formulas (1) - (3). Therefore, the CO selective methanation process requires very high selectivity and stability for CO methanation throughout the life cycle of the catalyst, and it is necessary to develop a CO methanation catalyst with high activity and high selectivity at low temperature.

[0004]

[0005] The catalyst support mainly plays a role in supporting and dispersing the active metal, and forms a strong metal-support strong interaction (SMSI) with the active metal. SMSI will affect the growth and electronic structure of active metal particles, etc. Metal oxides have been the most widely studied as supports for methanation catalysts. Among them, CeO 2 , ZrO 2 and TiO2 The performance of metal oxides such as 2 in CO methanation catalysts is the most significant. Metal oxide supports suitable for catalysts usually have sufficient specific surface area and pore structure, as well as reliable mechanical strength and stability. To prevent catalyst poisoning and deactivation and improve catalytic performance, surface modification of the catalyst support is usually required. In the traditional preparation process of most supported catalysts, calcination treatment is needed followed by reduction to obtain an active catalyst. However, solid-phase reactions during the high-temperature calcination process may lead to sintering and crystal structure transformation of metal oxides. For example, in Ni / TiO 2 At too high a calcination temperature, NiTiO with poor reducibility will be formed. 3 The heat treatment of the active metal precursor is usually carried out by static air calcination in a muffle furnace. Changes in the calcination atmosphere may also lead to side reactions. For the reduction activation treatment before the catalytic reaction, too low a reduction temperature cannot expose the active Ni well, while too high a reduction temperature will result in strong metal-support interaction, causing sintering and aggregation of metallic Ni and deactivation. The deactivation of the Ni catalyst is caused by the migration and aggregation of free NiO species with weak interaction with the support, which block the pore channels of the support during the reaction. The main factor affecting the catalyst stability is the growth of Ni particles during the reaction, which destroys the morphology of the support. The deactivation caused by changes in the morphology of the active metal and the structure of the support is usually irreversible.

[0006] Therefore, adopting a relatively mild heat treatment process to fully expose the active sites of the catalyst and maintain a stable morphological structure is the basis for ensuring the activity and stability of the catalyst.

[0007] To solve the above problems, the present invention is proposed. Summary of the Invention

[0008] Another object of the present invention is to provide a preparation method of the above-mentioned low-temperature CO selective methanation nickel-based catalyst.

[0009] Another object of the present invention is to provide the application of the above-mentioned low-temperature CO selective methanation nickel-based catalyst.

[0010] To achieve the above objects, the technical solutions adopted by the present invention are as follows:

[0011] In the first aspect of the present invention, a preparation method of a nickel-based catalyst is provided. The active component of the nickel-based catalyst is Ni, and the support is a metal oxide. Based on the mass of the support, the loading amount of the active component Ni is 1 wt% to 30 wt%; that is, the active metal accounts for 1 wt% to 30 wt% of the mass of the support. More preferably, based on the mass of the support, the loading amount of the active component Ni is 5 wt% to 20 wt%. Still more preferably, based on the mass of the support, the loading amount of the active component Ni is 5 wt% to 15 wt%.

[0012] The preparation method of the nickel-based catalyst according to the first aspect of the present invention comprises the following steps:

[0013] (1) Dissolve the precursor salt of Ni in deionized water to obtain a solution;

[0014] (2) Immerse the carrier into the solution prepared in step (1), stir at a constant temperature in a water bath, then dry, perform heat treatment reduction in a reducing atmosphere, and perform annealing treatment after reduction to obtain the catalyst.

[0015] Preferably, in step (1), the precursor salt of the active component Ni is selected from at least one of nickel nitrate, nickel acetate, nickel sulfate, or nickel chloride.

[0016] Preferably, in step (1), the carrier is selected from at least one of titanium dioxide, zirconium dioxide, or cerium dioxide or their mixed oxides.

[0017] Preferably, in step (2), the constant temperature stirring temperature is 30 - 80 °C, and the stirring time is 12 - 24 h.

[0018] Preferably, in step (2), the drying temperature is 70 - 90 °C, and the drying time is 12 - 24 h.

[0019] Preferably, in step (2), the reducing atmosphere is any one, two, or more of N 2 , Ar, He, etc. mixed with H 2 , and the volume ratio of hydrogen in the reducing atmosphere accounts for 20 vol% - 100% of the total amount, and the heat treatment temperature is 300 - 500 °C.

[0020] Preferably, in step (2), the heat treatment time is 1 - 3 h.

[0021] Preferably, in step (2), the catalyst after reduction treatment is annealed under the purge of an annealing atmosphere, and the annealing atmosphere is at least one gas of H 2 , N 2 , Ar, He, etc.

[0022] The second aspect of the present invention provides an application of the nickel-based catalyst according to the first aspect of the present invention. This catalyst is applied to the hydrogen supply system of a proton exchange membrane fuel cell for the selective methanation of low-temperature CO in a hydrogen-rich gas.

[0023] Preferably, the hydrogen-rich gas is usually a mixture of H 2 with a concentration higher than 60 vol% and impurity gases such as CO 2 , CO, etc. Preferably, the hydrogen-rich gas is 69 vol% H 2 , 20 vol% CO 2 、20vol%CO2 、A mixture of 1 vol% CO and 10% N 2 wherein the low temperature refers to a reaction temperature of 150 - 300 °C. For a mixture of 69 vol% H 2 、20 vol% CO 2 、1 vol% CO and 10% N 2 in the mixture, the nickel-based catalyst of the present invention can remove 1 vol% of CO to 10 ppm under the condition of lower than 300 °C.

[0024] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0025] (1) Compared with the traditional Ni catalyst preparation process (impregnation - drying - calcination - reduction), the preparation method of the present invention reduces the calcination step and also reduces the reduction temperature. This makes the active metal Ni in the nickel-based catalyst obtained by the preparation method of the present invention not easy to agglomerate, ensuring the high dispersion of Ni and increasing the active area. The nickel-based catalyst prepared by the present invention has excellent low-temperature activity for CO methanation, and can reduce the CO concentration in the reformed gas to below 10 ppm within a relatively large reaction temperature range. Moreover, the CO selectivity is close to 100% within a relatively wide temperature window, and the hydrogen consumption is less than 10%. For a mixture of 69 vol% H 2 、20 vol% CO 2 、1 vol% CO and 10% N 2 in the mixture, the catalyst obtained in Example 2 of the present invention can reduce the CO concentration in the outlet gas to around 10 ppm within the temperature range of 200 - 270 °C, and the CO selectivity is close to 100%. When the reaction temperature is 200 °C, the CO 2 conversion rate is close to 0, the hydrogen consumption is 4.7%, close to the stoichiometric ratio of hydrogen consumed by CO conversion. When the hydrogen consumption reaction temperature is lower than 270 °C, the hydrogen consumption is less than 13%.

[0026] (2) The catalyst of the present invention uses inexpensive and easily available nickel salts and metal oxides as raw materials, saving costs and having good application prospects.

[0027] (3) The preparation method of the catalyst of the present invention is simple to operate. Compared with the traditional catalyst preparation process (impregnation - drying - calcination - reduction), the preparation method of the present invention reduces the calcination step and also reduces the reduction temperature compared with the traditional Ni catalyst. It directly anneals at a lower reduction temperature to obtain the Ni catalyst, reducing the process complexity and energy consumption while ensuring the high activity and stability of the catalyst.

[0028] (4) The catalyst of the present invention is particularly suitable for the purification of hydrogen-rich gas in the hydrogen supply system of proton exchange membrane fuel cells and has a relatively wide temperature operation window. Description of the Drawings

[0029] Figure 1 The variation curve of the CO conversion rate of the catalyst prepared in Example 1 with the reaction temperature in a hydrogen-rich gas with a CO content of 1 vol%.

[0030] Figure 2 The variation curve of the CO concentration after catalyst treatment with the reaction temperature of the catalyst prepared in Example 1 in a hydrogen-rich gas with a CO content of 1 vol%.

[0031] Among them, the catalyst in Example 1 is Ni / TiO 2 (5 wt%, calcined and reduced at 400 °C), Ni / TiO 2 (5 wt%, calcined and reduced at 500 °C), Ni / TiO 2 (5 wt%, reduced and annealed at 400 °C), Ni / TiO 2 (5 wt%, reduced and annealed at 500 °C), the nickel loading is 5 wt%, and it is synthesized by two heat treatment methods respectively. The heat treatment methods are reduction after air calcination, or annealing in an annealing atmosphere after reduction in a reducing atmosphere.

[0032] Figure 3 The CO conversion rate and CO 2 conversion rate of the catalyst prepared in Example 2 with the reaction temperature in a hydrogen-rich gas with a CO content of 1 vol%.

[0033] Figure 4 The CO concentration and H 2 consumption after catalyst treatment with the reaction temperature of the catalyst prepared in Example 2 in a hydrogen-rich gas with a CO content of 1 vol%.

[0034] Among them, the catalyst in Example 2 is Ni / TiO 2 (5 wt%, reduced and annealed at 300 °C), and the nickel loading is 5 wt%.

[0035] Figure 5 The X-ray diffraction pattern (XRD) of the catalysts prepared in Examples 1 and 2. The higher the reduction temperature, the larger the Ni grain size after annealing, reflecting the difference in active sites.

[0036] Figure 6 The CO conversion rate and CO 2 conversion rate of the catalysts with different Ni loadings prepared in Example 3 at 250 °C in a hydrogen-rich gas with a CO content of 1 vol%.

[0037] Figure 7The CO concentration and H consumption after the reaction of the catalysts with different Ni loadings prepared in Example 3 at 250 °C in a hydrogen-rich gas with a CO content of 1 vol%. 2 Consumption

[0038] Among them, the catalyst in Example 3 is Ni / ZrO 2 (5 wt%, reduced-annealed at 500 °C), Ni / ZrO 2 (10 wt%, reduced-annealed at 500 °C), Ni / ZrO 2 (15 wt%, reduced-annealed at 500 °C), and the Ni loadings are 5 wt%, 10 wt%, and 15 wt% respectively.

[0039] Figure 8 The CO conversion rate and the change curve of CO conversion rate with the reaction temperature of the catalyst prepared in Example 4 in a hydrogen-rich gas with a CO content of 1 vol%. 2 Change curve

[0040] Figure 9 The CO concentration and the change curve of H consumption after the reaction of the catalyst prepared in Example 4 in a hydrogen-rich gas with a CO content of 1 vol% with the reaction temperature. 2 Change curve of consumption

[0041] Among them, the catalyst in Example 4 is Ni / ZrO 2 (5 wt%, reduced-annealed at 500 °C), and the Ni loading is 5 wt%. Detailed implementation method

[0042] The present invention will be further described below through examples, not limited to this example. For the experimental methods without specific conditions in the examples, they are usually carried out according to the conventional conditions and the conditions described in the manual, or the general equipment, materials, reagents, etc. used according to the conditions recommended by the manufacturer. If not otherwise specified, they can all be obtained through commercial channels.

[0043] The specific steps of the method of the present invention are as follows:

[0044] Catalyst performance test in the example: Take 0.5 g of the catalyst prepared in the example and load it into a 316 stainless steel reaction tube with an inner diameter of 8 mm, with a space velocity of 12000 mL·g cat -1 ·h -1 Pass in a gas containing 69 vol% H 2 , 20 vol% CO 2 , 1 vol% CO and 10% N 2The mixed gas is reacted at a reaction temperature in the range of 120 - 300 °C. After drying, the reaction products are detected online by gas chromatography. The performance evaluation index is calculated based on the change in the amount of substance of each component to test the activity and selectivity of the catalyst for the selective methanation of low-content CO in hydrogen-rich gas.

[0045] Example 1

[0046] (1) Preparation of catalyst Ni / TiO 2 : Dissolve 1.24 g of Ni(NO 3 ) 2 ·6H 2 O in an appropriate amount of deionized water. After complete dissolution, add 5.0 g of ZrO 2 and stir at 60 °C for 12 h.

[0047] (2) Dry at 80 °C for 24 h. Grind the dried sample, then press and crush it, and screen out particles with a mesh size of 20 - 40.

[0048] (3) Synthesize catalyst samples using two heat treatment processes:

[0049] One is calcined in air and then reduced at the same calcination temperature. Specifically, calcine in a muffle furnace at 400 °C or 500 °C for 4 h, and then reduce in a reducing atmosphere at the same temperature for 2 h. The catalysts obtained are the 400 °C calcined-reduced catalyst and the 500 °C calcined-reduced catalyst. The obtained catalysts are named Ni / TiO 2 (5 wt%, 400 °C calcined-reduced) and Ni / TiO 2 (5 wt%, 500 °C calcined-reduced).

[0050] The other is reduced in a reducing atmosphere and then annealed in an annealing atmosphere. Specifically, reduce in a mixed gas atmosphere containing 50 vol% H 2 and N 2 at 400 °C or 500 °C for 2 h, and then introduce N 2 for annealing to obtain two catalysts: the 400 °C reduced-annealed catalyst and the 500 °C reduced-annealed catalyst. The obtained catalysts are named Ni / TiO 2 (5 wt%, 400 °C reduced-annealed) and Ni / TiO 2 (5 wt%, 500 °C reduced-annealed). 2 (5 wt%, 500 °C reduced-annealed).

[0051] The Ni loading in the above catalyst samples is all 5 wt%.

[0052] The experimental results of CO methanation show that: Figure 1The curve of the CO conversion rate of the catalyst prepared in Example 1 varying with the reaction temperature in a hydrogen-rich gas with a CO content of 1 vol%. Figure 2 The curve of the CO tail gas concentration varying with the reaction temperature after the catalyst prepared in Example 1 is treated with the catalyst in a hydrogen-rich gas with a CO content of 1 vol%. By Figure 1 and Figure 2 Data comparison shows that: First, by comparing the catalysts calcined-reduced at 400 °C and reduced-annealed at 400 °C, and comparing the catalysts calcined-reduced at 500 °C and reduced-annealed at 500 °C, it can be seen that for the catalysts obtained at the same heat treatment temperature, the CO reaction activity and removal depth of the reduced-annealed catalyst are better than those of the calcined-reduced catalyst. Second, by comparing the catalysts calcined-reduced at 400 °C and the catalysts calcined-reduced at 500 °C, and comparing the catalysts reduced-annealed at 400 °C and the catalysts reduced-annealed at 500 °C, it can be seen that using the same heat treatment process, the CO reaction activity and removal depth of the catalyst prepared at 400 °C are better than those of the catalyst prepared at 500 °C. Therefore, the preparation method of low-temperature reduction annealing can improve the low-temperature activity and removal depth of CO methanation.

[0053] Example 2

[0054] (1) Preparation of the catalyst Ni / TiO 2 : Dissolve 1.24 g of Ni(NO 3 ) 2 ·6H 2 O in an appropriate amount of deionized water. After complete dissolution, add 5.0 g of TiO 2 , and stir at 60 °C for 12 h.

[0055] (2) Dry at 80 °C for 24 h. Grind the dried sample, then press and crush it, and screen out particles with a mesh size of 20 - 40.

[0056] (3) Reduce at 300 °C for 2 h in a mixed gas atmosphere containing 50 vol% of H 2 and N 2 , and then introduce N 2 for annealing to obtain the catalyst. The loading amount of Ni is 5 wt%. The obtained catalyst is named Ni / TiO 2 (5 wt%, reduced-annealed at 300 °C). 2 (5 wt%, reduced-annealed at 300 °C).

[0057] The experimental results of CO methanation show that: Figure 3 The curves of the CO conversion rate and the CO 2 conversion rate varying with the reaction temperature of the catalyst prepared in Example 2 in a hydrogen-rich gas with a CO content of 1 vol%. Figure 4The CO concentration and H 2 The consumption curve changes with the reaction temperature. Figure 3 and Figure 4 It can be seen that the catalyst prepared in this example can reduce the CO concentration in the outlet gas to around 10 ppm in the reaction temperature range of 210-260°C, and the CO selectivity is close to 100%. When the reaction temperature is 200°C, CO 2 The conversion rate is close to 0, and the hydrogen consumption is 4.7%, which is close to the stoichiometric ratio of hydrogen consumption for CO conversion. When the reaction temperature is lower than 270°C, the hydrogen consumption is lower than 13%.

[0058] Figure 5 The X-ray diffraction patterns (XRD) of the catalysts prepared in Examples 1 and 2 are shown in Table 1. Figure 5 It can be seen that the higher the reduction temperature, the larger the Ni grain size after annealing. The present invention reduces the roasting step and reduces the reduction temperature, which can ensure high dispersion of Ni and increase active sites.

[0059] Example 3

[0060] (1) Catalyst Ni / ZrO 2 Preparation: 1.24g, 2.48g and 3.72g of three Ni(NO 3 ) 2 6H 2 O, respectively dissolved in appropriate amount of deionized water, and after fully dissolved, 5.0 g ZrO 2 , stirred at 60°C for 12h.

[0061] (2) Dry at 80°C for 24 hours. Grind the dried sample, crush it into tablets, and sieve out particles of 20-40 mesh.

[0062] (3) In the presence of H 2 50 vol% H 2 and N 2 After reduction at 500 °C for 2 h in a mixed gas atmosphere, N 2 The catalyst was obtained by annealing. The Ni loading was 5wt%, 10wt% and 15wt% respectively. The obtained catalyst was named Ni / ZrO 2 (5wt%, 500℃ reduction-annealing), Ni / ZrO 2 (10wt%, 500℃ reduction-annealing), Ni / ZrO 2 (15wt%, 500°C reduction-annealing).

[0063] The results of CO methanation experiments show that: Figure 6The CO conversion rate and CO 2 conversion rate of the catalysts with different Ni loadings prepared in Example 3 during the reaction at 250 °C in a hydrogen-rich gas with a CO content of 1 vol%. Figure 7 The CO concentration in the gas after being treated by the catalysts with different Ni loadings prepared in Example 3 during the reaction at 250 °C in a hydrogen-rich gas with a CO content of 1 vol% and the H 2 consumption. It can be seen from Figure 6 and Figure 7 that for the Ni / ZrO 2 catalysts with different Ni loadings prepared in this example during the reaction at 250 °C, the CO conversion rate is close to 100%, the CO concentration in the outlet gas can be reduced to below 10 ppm, the CO 2 conversion rate is lower than 2%, the CO selectivity is greater than 98%, and the hydrogen consumption is lower than 10%.

[0064] Example 4

[0065] The catalyst used in Example 4 is the same as the Ni / ZrO 2 (5 wt%, reduced-annealed at 500 °C) used in Example 3. The results of the CO methanation experiment show that: Figure 8 The curves of the CO conversion rate and CO 2 conversion rate of the catalyst prepared in Example 4 during the reaction in a hydrogen-rich gas with a CO content of 1 vol% varying with the reaction temperature. Figure 9 The curves of the CO concentration in the gas after being treated by the catalyst prepared in Example 4 during the reaction in a hydrogen-rich gas with a CO content of 1 vol% and the H 2 consumption varying with the reaction temperature. It can be seen from Figure 8 and Figure 9 that for the catalyst prepared in this example within the reaction temperature range of 240 - 300 °C, the CO conversion rate is close to 100%, the CO concentration in the outlet gas can be reduced to around 10 ppm, the CO 2 conversion rate is lower than 4.3%, the CO selectivity is greater than 96%, and the hydrogen consumption is lower than 10%.

[0066] The above provides an exemplary description of the present invention. It should be noted that without departing from the core of the present invention, any simple deformation, modification, or equivalent substitution that can be made by those skilled in the art without creative labor falls within the protection scope of the present invention.

Claims

1. A method for preparing a nickel-based catalyst, characterized in that: The active component of the nickel-based catalyst is Ni, the carrier is a metal oxide, and the loading amount of the active component Ni is 1wt% to 30wt% based on the mass of the carrier; The method for preparing the nickel-based catalyst comprises the following steps: (1) dissolving a Ni precursor salt in deionized water to prepare a solution; (2) The support is immersed in the solution prepared in step (1), stirred in a water bath at a constant temperature, dried, heat treated in a reducing atmosphere, and annealed to obtain the catalyst.

2. The preparation method according to claim 1, characterized in that: In step (1), the precursor salt of the active component Ni is selected from at least one of nickel nitrate, nickel acetate, nickel sulfate or nickel chloride.

3. The preparation method according to claim 1, characterized in that: In step (1), the carrier is selected from at least one of titanium dioxide, zirconium dioxide or cerium dioxide, or a mixed oxide thereof.

4. The preparation method according to claim 1, characterized in that: In step (2), the constant temperature stirring temperature is 30 to 80° C., and the stirring time is 12 to 24 hours.

5. The preparation method according to claim 1, characterized in that: In step (2), the drying temperature is 70 to 90° C. and the drying time is 12 to 24 hours.

6. The preparation method according to claim 1, characterized in that: In step (2), the reducing atmosphere is a mixed gas of any one, one or more of N2, Ar, He and H2, wherein the volume proportion of hydrogen in the reducing atmosphere is 20 vol% to 100 vol% of the total amount, and the heat treatment temperature is 300 to 500°C.

7. The preparation method according to claim 1, characterized in that: In step (2), the heat treatment time is 1 to 3 hours.

8. The preparation method according to claim 1, characterized in that: In step (2), the catalyst that has undergone reduction treatment is annealed under the purge of an annealing atmosphere, wherein the annealing atmosphere is at least one gas selected from the group consisting of H2, N2, Ar, and He.

9. An application of the nickel-based catalyst obtained by the preparation method according to any one of claims 1 to 8, characterized in that: The catalyst is used in the hydrogen supply system of proton exchange membrane fuel cells for the selective methanation of CO at low temperatures in hydrogen-rich gases.

10. The use according to claim 9, characterized in that: The hydrogen-rich gas is a mixture of H2 with a H2 concentration higher than 60 vol% and impurity gases, wherein the impurity gases include CO2 and CO; the low temperature refers to a reaction temperature of 150 to 300°C.

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