A sulfur-tolerant shift catalyst and a method for preparing the same

Abstract

The application relates to a sulfur-tolerant shift catalyst and a preparation method thereof, and belongs to the technical field of sulfur-tolerant shift catalysts. In the prior art, the adhesion of cobalt-molybdenum active components to carriers in the obtained sulfur-tolerant shift catalyst is poor, or the dispersion is uneven, or the loading capacity is low, and all of them cannot well have high catalyst activity under low water-gas ratio conditions, and cannot maintain long catalytic life. The application comprises a carrier and active centers loaded thereon, the active centers comprising cobalt and molybdenum, and the carrier is tetragonal zirconium oxide. The t-ZrO2 surface is rich in organic groups, the adsorption capacity of the catalyst to water vapor is enhanced, H2O molecules can be locked on the catalyst surface, the water-gas ratio in the catalyst is enhanced, and the catalytic activity and stability of the catalyst under low water-gas ratio conditions are improved.

Description

Technical Field

[0001] A sulfur-resistant shift catalyst and its preparation method are disclosed, belonging to the technical field of sulfur-resistant shift catalysts. Background Technology

[0002] Water-gas shift (WGS) reaction is a crucial method for industrial hydrogen production. The catalyst is the core of the WGS reaction process. Compared to other types of catalysts, cobalt-molybdenum-based catalysts offer advantages such as sulfur resistance, a wide reaction temperature range, low cost, and simple preparation processes, making them the most widely used in domestic and international plants. However, current sulfur-resistant shift catalysts exhibit significantly reduced catalytic activity at low water-to-gas ratios. Therefore, developing a novel sulfur-resistant shift catalyst that maintains high catalytic activity under low water-to-gas ratio conditions is of great significance.

[0003] Patent CN106552637B, a cobalt-molybdenum-based low-temperature sulfur-resistant shift catalyst and its preparation method, and patent WO2022089072A1, a catalyst and a method for sulfur-resistant shift catalytic reaction, both disclose a cobalt-molybdenum-based sulfur-resistant shift catalyst. Both disclose the use of a support to load the cobalt-molybdenum active components, and both mention the presence of zirconium oxide in the support. However, in the above or other prior art, the adhesion between the cobalt-molybdenum active components and the support in the sulfur-resistant shift catalyst is poor, or the dispersion is uneven, or the loading is low. Consequently, they cannot maintain high catalyst activity under low water-to-gas ratio conditions, nor can they maintain a long catalytic lifespan. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a sulfur-resistant shift catalyst with better cobalt and molybdenum bonding and distribution with the support, and with better catalytic activity and stability under low water-to-gas ratio conditions, as well as its preparation method.

[0005] The technical solution adopted by the present invention to solve its technical problem is: a sulfur-resistant conversion catalyst, comprising a support and active centers supported thereon, wherein the active centers include cobalt and molybdenum, characterized in that: the support is tetragonal zirconia.

[0006] ZrO2 has both acidic and basic sites on its surface. Compared with traditional catalyst supports, ZrO2 exhibits higher chemical stability, better mechanical strength, thermal stability, resistance to acid and alkali corrosion, and ion migration ability, making it an excellent catalyst support. When using nanoscale ZrO2 as a catalyst support, its abundant surface defects and unique mesoporous structure provide a large number of surface active sites for the homogenization and highly dispersed loading of the catalyst active components. However, the inventors discovered that in existing technologies, the zirconia used as a support is primarily monoclinic (m-ZrO2) or a mixed crystal form after preparation. This results in poor binding ability between the zirconia and the active components loaded onto the surface, uneven dispersion of active sites on the zirconia surface, and low loading.

[0007] This invention employs tetragonal zirconium oxide (t-ZrO2) as the active center, resulting in a more uniform and ordered pore structure. This allows for full utilization of the unique physicochemical properties of t-ZrO2, effectively dispersing and combining cobalt and molybdenum active centers. The cobalt and molybdenum active centers interact more strongly with zirconium oxide, forming a sulfur-resistant shift catalyst with higher catalytic activity. Simultaneously, the abundant organic groups on the surface of t-ZrO2 enhance the catalyst's adsorption capacity for water vapor, locking H2O molecules onto the catalyst surface. This increases the water-to-gas ratio within the catalyst, thereby improving its catalytic activity and stability under low water-to-gas ratio conditions.

[0008] Preferably, the cobalt is loaded onto the carrier in the form of cobalt tetroxide.

[0009] More preferably, the cobalt tetroxide accounts for 1 to 10% of the weight of the sulfur-resistant conversion catalyst.

[0010] Preferably, the molybdenum is loaded onto the carrier in the form of molybdenum oxide.

[0011] Preferably, the molybdenum oxide accounts for 5-15% of the weight of the sulfur-resistant shift catalyst.

[0012] Preferably, the method for preparing tetragonal zirconia includes the following steps:

[0013] 1) The zirconium precursor solution and a 20-30% (w / w) ammonia solution were co-precipitated in a co-current manner. During the process, the pH of the co-precipitation was controlled to be 9-10 by the flow rate of either solution, and the system temperature was 60-80℃.

[0014] 2) After sedimentation, maintain the temperature for aging for 48~100 hours;

[0015] 3) The precipitate obtained by washing with water should be within 5°C above or below the temperature of the precipitate itself;

[0016] 4) After drying the precipitate, calcination at 500~600℃ for 6~8h yields tetragonal zirconia;

[0017] The zirconium precursor described in step 1) includes at least zirconium oxychloride.

[0018] The zirconium precursor may also include zirconium nitrate, zirconium oxynitrate, and zirconium acetate.

[0019] The above preparation process ensures the formation of tetragonal zirconia with good crystal structure. Under the combined conditions of temperature, pH, and aging time, the formation of monoclinic zirconia can be effectively avoided, ensuring crystal purity. If the temperature of the co-precipitation process is too high, precipitation may be too rapid, resulting in disordered crystal structure; if the temperature is too low, the precipitation rate will be too slow, and the content of tetragonal zirconia will be low. The pH condition is used to maintain the electrical balance of the system during the co-precipitation process. The inventors found that the use of zirconium oxychloride in the zirconium precursor can better maintain the stability and continuity of the entire co-precipitation process, possibly because a specific electrical balance is formed between chloride ions and ammonium ions, thus avoiding the formation of monoclinic crystal structure. An aging time of more than 50 hours is required to ensure the crystal stability of the obtained tetragonal precipitate, while the relatively mild water washing conditions avoid damaging the crystal structure of the precipitate.

[0020] The ammonia concentration allows for a good electrical balance with the zirconium precursor, and also facilitates control of the pH of the co-precipitation process by adjusting the flow rate of the ammonia solution, thus avoiding disruption of the electrical balance.

[0021] A method for preparing the sulfur-resistant shift catalyst described above, characterized by comprising the following steps:

[0022] 1) Tetragonal zirconia is excessively impregnated with an aqueous solution or an ethanol solution of a cobalt precursor, dried, and then calcined at 300-450°C in an atmosphere of air, nitrogen, or hydrogen.

[0023] 2) The material obtained in step 1) is over-impregnated with an aqueous solution or an ethanol solution of the molybdenum precursor, dried, and then calcined at 300~450℃ in an atmosphere of air, nitrogen, or hydrogen. After calcination, a sulfur-resistant conversion catalyst is obtained.

[0024] For the prepared tetragonal zirconia, a loading method of first loading cobalt and then molybdenum is adopted. Cobalt itself has a strong binding ability with zirconia, which is equivalent to forming a cobalt active layer on the zirconia surface, and then loading a molybdenum active layer on the surface of the cobalt active layer. Molybdenum mainly acts as an active agent. If a simultaneous loading method is used, on the one hand, the loading amount of cobalt and molybdenum is relatively small, and on the other hand, the distance between cobalt and molybdenum will be relatively large. Using the above loading method, the cobalt and molybdenum are more uniformly dispersed, and the distance between cobalt and molybdenum is smaller, resulting in better interaction and coordination, which is beneficial to improving the catalytic activity of the catalyst.

[0025] Cobalt nitrate is preferred as the cobalt precursor, and ammonium molybdate is preferred as the molybdenum precursor. This avoids the introduction of other impurity ions such as sulfide ions.

[0026] Preferably, the method for preparing tetragonal zirconia includes the following steps:

[0027] 1) The zirconium precursor solution and a 20-30% (w / w) ammonia solution were co-precipitated in a co-current manner. During the process, the pH of the co-precipitation was controlled to be 9-10 by the flow rate of either solution, and the system temperature was 60-80℃.

[0028] 2) After sedimentation, maintain the temperature for aging for 48~100 hours;

[0029] 3) The precipitate obtained by washing with water should be within 5°C above or below the temperature of the precipitate itself;

[0030] 4) After drying the precipitate, calcination at 500~600℃ for 6~8h yields tetragonal zirconia;

[0031] The zirconium precursor described in step 1) includes at least zirconium oxychloride.

[0032] Compared with the prior art, the beneficial effects of this invention are as follows: The active centers are supported by tetragonal zirconium oxide (t-ZrO2), resulting in a more uniform and ordered pore structure. This allows for full utilization of the unique physicochemical properties of t-ZrO2, effectively dispersing and combining cobalt and molybdenum active centers. The cobalt and molybdenum active centers interact more strongly with zirconium oxide, forming a sulfur-resistant shift catalyst with higher catalytic activity. Simultaneously, the abundant organic groups on the surface of t-ZrO2 enhance the catalyst's adsorption capacity for water vapor, locking H2O molecules onto the catalyst surface, thereby increasing the water-to-gas ratio within the catalyst and improving its catalytic activity and stability under low water-to-gas ratio conditions. Attached Figure Description

[0033] Figure 1 The XRD patterns of ZrO2 obtained in step 1) of Example 1 and Comparative Example 1 are shown, with the upper line representing Comparative Example 1 and the lower line representing Example 1.

[0034] Figure 2 The XRD patterns of the sulfur-resistant shift catalysts prepared in Example 1 and Comparative Example 1 are shown, with the upper line representing Comparative Example 1 and the lower line representing Example 1.

[0035] Figure 3 The XPS O1S spectra of the sulfur-resistant shift catalysts obtained in Example 1 and Comparative Example 1 are shown, with the upper line representing Comparative Example 1 and the lower line representing Example 1.

[0036] Figure 4The Raman spectra of the sulfur-resistant shift catalysts obtained in Example 1 and Comparative Example 1 are shown, with the Co3O4 stretching peaks displayed. The upper line represents Comparative Example 1, and the lower line represents Example 1.

[0037] Figure 5 The graph shows the change in catalytic activity over time of the sulfur-resistant shift catalysts obtained in Example 1, Comparative Example 1, and Comparative Example 6 under a low water-to-gas ratio (water-to-gas ratio = 0.8). The lines from top to bottom represent Example 1, Comparative Example 1, and Comparative Example 6. Detailed Implementation

[0038] The present invention will be further described below with reference to the embodiments, wherein Embodiment 1 is the preferred embodiment of the present invention.

[0039] Example 1

[0040] A sulfur-resistant shift catalyst, wherein cobalt and molybdenum active centers are loaded in the form of cobalt tetroxide and molybdenum oxide, respectively, on a tetragonal zirconia support.

[0041] The preparation method is as follows:

[0042] 1) Dissolve 100g ZrOCl2·8H2O (0.31mol) in 800g deionized water to prepare a solution. Take a 25% (w / w) ammonia solution and titrate the two solutions in a co-precipitation manner. Under the conditions of 80℃ water bath, control the pH to 9~10 by controlling the flow rate of the ammonia solution to obtain a precipitate. After precipitation, keep it at the temperature for 50h.

[0043] 2) The precipitate (70℃±5℃) was washed three times with distilled water at 70℃ to remove chloride ions, dried at 80℃, and calcined at 500~600℃ for 7 hours to obtain tetragonal zirconia t-ZrO2. See the performance testing section for crystal form testing methods.

[0044] 3) Dissolve 2.12g Co(NO3)2·6H2O in 20g ethanol to prepare a cobalt nitrate ethanol solution, and impregnate 8g tetragonal zirconia t-ZrO2 in excess for 12h. Dry at 80~120℃ and then calcine at 300~450℃ in a hydrogen atmosphere for 5h to obtain Co-t-ZrO2.

[0045] 4) Dissolve 1.73g of ammonium molybdate in 20g of ethanol to obtain an ammonium molybdate ethanol solution. Impregnate the Co-t-ZrO2 obtained in step 3) in excess for 12 hours. Dry at 80~120℃ and then calcine at 300~450℃ in a hydrogen atmosphere for 6 hours to obtain Mo / Co-t-ZrO2.

[0046] The final sulfur-resistant shift catalyst prepared contained 7 wt% MoO3, 3 wt% Co3O4, and the remainder was ZrO2.

[0047] Example 2

[0048] A sulfur-resistant shift catalyst and its preparation method, based on Example 1:

[0049] Step 3) The amount of Co(NO3)2·6H2O is set to 3.62g, and the soaking time is set to 48h;

[0050] Step 4) The amount of ammonium molybdate is set to 2.47g;

[0051] The final sulfur-resistant shift catalyst prepared contained 10 wt% MoO3, 5 wt% Co3O4, and the remainder was ZrO2.

[0052] Other conditions are the same as in Example 1.

[0053] Example 3

[0054] A sulfur-resistant shift catalyst and its preparation method, based on Example 2:

[0055] Step 1) Replace 100g of ZrOCl2·8H2O with a mixture of 50g of ZrO(NO3)2·2H2O and 50g of ZrOCl2·8H2O.

[0056] Other conditions are the same as in Example 2.

[0057] Example 4

[0058] A sulfur-resistant shift catalyst and its preparation method, based on Example 2:

[0059] Step 1) Replace 100g ZrOCl2·8H2O with 83g ZrO(NO3)2·2H2O, and keep other conditions the same as in Example 2.

[0060] Example 5

[0061] A sulfur-resistant shift catalyst and its preparation method, based on Example 2:

[0062] Step 1) Set the concentration of the ammonia solution to 20%, and other conditions are the same as in Example 2.

[0063] Example 6

[0064] A sulfur-resistant shift catalyst and its preparation method, based on Example 2:

[0065] Step 1) Set the concentration of the ammonia solution to 30%, and other conditions are the same as in Example 2.

[0066] Example 7

[0067] A sulfur-resistant shift catalyst and its preparation method are based on Example 2: steps 3) and 4) are combined into one step, namely, Co(NO3)2·6H2O and ammonium molybdate are dissolved in ethanol, and 8g of tetragonal zirconia t-ZrO2 is impregnated in excess for 24h. After drying at 80~120℃, it is then calcined in a hydrogen environment at 300~450℃ for 7h to obtain Mo / Co-t-ZrO2.

[0068] Example 8

[0069] A sulfur-resistant conversion catalyst and its preparation method are based on Example 2: Step 2) The temperature of the washing water is set to 30°C, and the conditions are the same as in Example 2.

[0070] Comparative Example 1

[0071] A sulfur-resistant shift catalyst and its preparation method are disclosed, based on Example 2: Step 1) The concentration of the ammonia solution is set to 35%, the pH is set to 7-8, and the water bath temperature for co-precipitation is set to 60°C; other conditions are the same as in Example 2. The zirconia support obtained in Step 1) is monoclinic. See the performance testing section for the crystal form testing method.

[0072] Comparative Example 2

[0073] A sulfur-resistant shift catalyst and its preparation method are disclosed, based on Example 2: Step 1) The concentration of the ammonia solution is set to 15%, and other conditions are the same as in Example 2. The zirconia support obtained in Step 1) is a mixture of monoclinic and tetragonal crystal forms.

[0074] Comparative Example 3

[0075] A sulfur-resistant shift catalyst and its preparation method are disclosed, based on Example 2: In step 1), the pH of the co-precipitation process is controlled at 8, and other conditions are the same as in Example 2. The zirconia support obtained in step 1) is a mixture of monoclinic and tetragonal crystal forms.

[0076] Comparative Example 4

[0077] A sulfur-resistant shift catalyst and its preparation method are disclosed, based on Example 2: In step 1), the pH of the co-precipitation process is controlled at 11, and other conditions are the same as in Example 2. The zirconia support obtained in step 1) is a mixture of monoclinic and tetragonal crystal forms.

[0078] Comparative Example 5

[0079] A sulfur-resistant shift catalyst and its preparation method are disclosed, based on Example 2: Step 1) The aging time is set to 40 h, and other conditions are the same as in Example 2. The zirconia support obtained in Step 1) is a mixture of monoclinic and tetragonal crystal forms.

[0080] Comparative Example 6

[0081] A sulfur-resistant shift catalyst and its preparation method: 8g of a commercially available common zirconia support with mixed t-ZrO2 and m-ZrO2 crystal forms was used to prepare a sulfur-resistant shift catalyst with supported cobalt-molybdenum active centers, as described in steps 3) and 4) of Example 2.

[0082] Performance testing

[0083] The pressurized activity evaluation device in the known technology is used to simulate industrial conditions and compare the conversion activity and stability of catalysts. The reaction tube is a stainless steel tube with a diameter of 45 × 5 mm and a thermocouple tube with a diameter of 8 × 2 mm in the center. A certain amount of water is added according to different water-to-gas ratio requirements, and after being vaporized at high temperature, it enters the reaction tube together with the raw gas to carry out the water-to-gas conversion reaction. The tail gas after the reaction is analyzed by chromatography.

[0084] The final evaluation results of the conversion rate of CO by the sulfur-resistant shift catalysts obtained in each embodiment and comparative example are shown in Table 1 below.

[0085] Table 1 Performance Test Results

[0086] .

[0087] The internal physical structure of the sulfur-resistant shift catalysts obtained in Example 1 and Comparative Example 1 was tested, and the resulting spectra are shown in the appendix. Figures 1-4 ;in, Figure 1 , 2 The comparison shows that the preparation method of the example can produce relatively pure t-ZrO2, while the method of Comparative Example 1 can produce pure m-ZrO2. Moreover, the crystal form of ZrO2 does not change significantly after the addition of Co.

[0088] according to Figure 3 XPS results showed that the catalyst prepared using this invention had more adsorbed oxygen on its surface, indicating that more H2O was adsorbed on the catalyst surface, thus significantly increasing the surface water-to-gas ratio and consequently significantly increasing the catalyst's activity under low water-to-gas ratio conditions.

[0089] according to Figure 4 The displayed spectrum shows the stretching peak of Co3O4. The peak of Example 1 is shifted to a higher wavelength range compared to Comparative Example 1, indicating that the interaction between Co in the catalyst and the support is stronger in Example 1.

[0090] The sulfur-resistant shift catalysts obtained in Examples 1, 1, and 6, under low water-to-gas ratio conditions (water-to-gas ratio = 0.8), showed changes in catalyst activity over reaction time as indicated in the appendix. Figure 5 As shown.

[0091] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A sulfur-resistant shift catalyst, comprising a support and active centers supported thereon, the active centers comprising cobalt and molybdenum, characterized in that: The carrier is tetragonal zirconia; A method for preparing a sulfur-resistant shift catalyst includes the following steps: 1) Tetragonal zirconia is excessively impregnated with an aqueous solution or an ethanol solution of a cobalt precursor, dried, and then calcined at 300-450°C in an atmosphere of air, nitrogen, or hydrogen. 2) The material obtained in step 1) is over-impregnated with an aqueous solution or an ethanol solution of the molybdenum precursor, dried, and then calcined at 300~450℃ in an atmosphere of air, nitrogen, or hydrogen. After calcination, a sulfur-resistant conversion catalyst is obtained.

2. The sulfur-resistant shift catalyst according to claim 1, characterized in that: The cobalt is loaded onto a carrier in the form of cobalt tetroxide.

3. The sulfur-resistant shift catalyst according to claim 2, characterized in that: The cobalt tetroxide accounts for 1-10% of the weight of the sulfur-resistant shift catalyst.

4. The sulfur-resistant shift catalyst according to claim 2, characterized in that: The molybdenum is loaded onto a carrier in the form of molybdenum oxide.

5. The sulfur-resistant shift catalyst according to claim 4, characterized in that: The molybdenum oxide accounts for 5-15% of the weight of the sulfur-resistant shift catalyst.

6. The sulfur-resistant shift catalyst according to claim 1, characterized in that: The method for preparing tetragonal zirconia includes the following steps: 1) The zirconium precursor solution and a 20-30% (w / w) ammonia solution were co-precipitated in a co-current manner. During the process, the pH of the co-precipitation was controlled to be 9-10 by the flow rate of either solution, and the system temperature was 60-80℃. 2) After sedimentation, maintain the temperature for aging for 48~100 hours; 3) The precipitate obtained by washing with water should be within 5°C above or below the temperature of the precipitate itself; 4) After drying the precipitate, calcination at 500~600℃ for 6~8h yields tetragonal zirconia; The zirconium precursor described in step 1) includes at least zirconium oxychloride.

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