Nickel-gallium (magnesium, aluminum) oxide catalyst with stability improved through hydrotalcite modification and preparation method and application of nickel-gallium (magnesium, aluminum) oxide catalyst
The Ni-Ga/(Mg,Al)Ox catalyst was prepared by modifying hydrotalcite, which solved the deactivation problem of nickel-based catalysts caused by carbon deposition and sintering in the methane dry reforming reaction, and achieved high catalytic stability and activity, especially when the Ga/Ni ratio was 0.3.
Patent Information
- Application Number
- CN202510639971.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-19
- Publication Date
- 2025-09-09
AI Technical Summary
Nickel-based catalysts are easily deactivated due to carbon deposition and sintering in methane dry reforming reactions, resulting in decreased activity.
The Ni-Ga/(Mg,Al)Ox catalyst was prepared by modifying hydrotalcite. The Ni-Ga-Mg-Al hydrotalcite precursor was synthesized by coprecipitation and pyrolyzed at 550°C to obtain a catalyst with a mesoporous structure. The molar ratio of Ga/Ni was preferably 0.3.
The stability and activity of the catalyst were improved, with the conversion rates of CH4 and CO2 reaching 66% and 74% respectively, and the H2/CO ratio being 0.92. It maintained good stability during 20 hours of continuous operation and reduced the formation of carbon deposits.
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Abstract
Description
Technical Field
[0001] The present invention relates to the field of dry methane reforming catalysts, and in particular to a Ni-Ga / (Mg, Al)Ox catalyst based on hydrotalcite, which improves the stability of the catalyst by adjusting the gallium (Ga) content, as well as a preparation method and application of the catalyst. Background Art
[0002] Global emissions of the greenhouse gas methane (CH4) have increased by nearly 10% over the past two decades, with atmospheric concentrations reaching a new record of 1.875 ppm. Because CH4 has an 80-fold greater warming potential than CO2, it is the second-most potent greenhouse gas produced by human activities. Therefore, how to deal with these greenhouse gases has become a pressing issue. Converting these two major greenhouse gases, CO2 and CH4, into value-added synthesis gas (H2 and CO), a process known as methane dry reforming, is considered one of the most promising pathways to sustainable development.
[0003] Catalysts used in methane reforming reactions are categorized as either precious metal or non-precious metal catalysts. Precious metal catalysts (such as Rh, Ru, Pt, Pd, and Ir) possess high activity, excellent stability, and can inhibit the nucleation and growth of carbon deposits at high temperatures, exhibiting excellent resistance to carbon deposition. However, the high cost of precious metals prohibits their large-scale use. Nickel-based catalysts, on the other hand, are the preferred choice for large-scale industrial production due to their high activity and correspondingly low cost. Nickel-based catalysts exhibit excellent activity and selectivity in methane dry reforming reactions, but they suffer from two stability issues: first, the sintering and growth of metallic nickel nanoparticles at high temperatures leads to decreased activity; second, the strong affinity between carbon atoms and nickel atoms, particularly at low-coordinate sites (such as step sites), can lead to carbon deposition on the nickel-based catalyst surface, resulting in decreased activity. Based on this, an improved catalyst is proposed that enhances both stability and activity by adding gallium (Ga). Summary of the Invention
[0004] The present invention aims to provide a nickel gallium (magnesium, aluminum) oxide catalyst with improved stability through hydrotalcite modification, a preparation method and application thereof, so as to solve the problem that nickel-based catalysts are easily deactivated due to carbon deposition and sintering.
[0005] In order to achieve the above object, the present invention provides the following technical solutions:
[0006] A nickel gallium (magnesium, aluminum) oxide catalyst with improved stability through hydrotalcite modification has a chemical formula of Ni-Ga / (Mg,Al)Ox. The modified catalyst with a mesoporous structure is obtained by thermal decomposition of a Ni-Ga-Mg-Al hydrotalcite precursor.
[0007] Furthermore, the molar ratio of Ga / Ni in the Ni-Ga / (Mg,Al)Ox is preferably 0.3.
[0008] A second aspect of the present invention provides a method for preparing a nickel-gallium (magnesium, aluminum) oxide catalyst with improved stability by hydrotalcite modification, comprising the Ni-Ga / (Mg, Al)Ox according to claim 1, characterized in that it comprises the following steps:
[0009] S1. Synthesis of Ni-Ga-Mg-Al hydrotalcite precursor by coprecipitation method;
[0010] S2. Pyrolyze the precursor to obtain Ni-Ga / (Mg,Al)Ox catalyst.
[0011] Furthermore, in step S1, the following steps are included:
[0012] S101, Ni(NO3)2·6H2O, Ga(NO3)3·xH2O, Al(NO3)3·9H2O and Mg(NO3)2·6H2O were mixed in deionized water;
[0013] S102, stirring Na2CO3 and NaOH solutions on a magnetic stirrer for 15 minutes and then mixing to prepare an anion precursor solution;
[0014] S103. Add the nitrate solution obtained in S1 dropwise to the anion precursor solution under vigorous stirring, and maintain the solution medium at 65° C. and the pH at 9.5–10.5.
[0015] S104, aging the mixture obtained in S3 at room temperature for about 18 hours with continuous stirring to obtain a hydrotalcite suspension;
[0016] S105. Centrifuge the obtained suspension, wash the solid mixture with distilled water for multiple times, and dry it at 110° C. to obtain a Ni—Ga—Mg—Al hydrotalcite precursor.
[0017] Furthermore, in step S2, the pyrolysis temperature is 550°C and the duration is 5 hours.
[0018] A third aspect of the present invention provides a use of a nickel gallium (magnesium, aluminum) oxide catalyst whose stability is improved by modification with hydrotalcite in dry methane reforming.
[0019] Furthermore, in the dry reforming of methane, a Ni-Ga / (Mg,Al)Ox catalyst was added to react at 700°C, 1 atm, and a GHSV of 42000 mL / h / g.
[0020] The principles and beneficial effects of this technical solution include at least:
[0021] The present invention provides a Ni-Ga / (Mg,Al)Ox catalyst prepared by a coprecipitation method with different Ga / Ni molar ratios (0, 0.1, 0.3, 0.5, and 1). In particular, the Ni-Ga / (Mg,Al)Ox catalyst with a Ga / Ni ratio of 0.3 exhibits the best catalytic performance and stability. Under the conditions of 700°C, 1 atm, and a GHSV of 42,000 mL / h / g, the catalyst achieves CH4 and CO2 conversions of 66% and 74%, respectively, with an H2 / CO ratio of 0.92. Furthermore, the catalyst exhibits good stability during 20 hours of continuous operation. BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Figure 1 Schematic diagram of the catalytic activity test results of CH4 conversion (A) and CO2 conversion (B) at 700°C, 1 atmosphere, and GHSV of 42000 mL / h / g;
[0023] Figure 2 Schematic diagram of CH4 and CO2 conversion rate of Ni-Ga / (Mg,Al)Ox (Ga / Ni=0.3) catalyst during long-term flow process;
[0024] Figure 3 Schematic diagram showing the effect of reaction temperature on the catalytic performance of Ni-Ga / (Mg,Al)Ox (Ga / Ni=0.3) catalyst at 700°C, 1 atm, and GHSV of 42000 mL / h / g (CH4 / CO2 / N2 molar ratio is 1);
[0025] Figure 4 Schematic diagram of (A) thermogravimetric analysis (TGA) and (B) differential thermal analysis (DTA) of the used catalyst;
[0026] Figure 5 is the TPO curve of the used catalyst;
[0027] Figure 6 This is the Raman spectrum of the used catalyst.
[0028] Figure 1 、 4 , 5 and 6: (a) is Ni / (Mg,Al)Ox; (b) is Ni-Ga / (Mg,Al)Ox (Ga / Ni=0.1); (c) is Ni-Ga / (Mg,Al)Ox (Ga / Ni=0.3); (d) is Ni-Ga / (Mg,Al)Ox (Ga / Ni=0.5); (e) is Ni-Ga / (Mg,Al)Ox (Ga / Ni=1.0). DETAILED DESCRIPTION
[0029] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments:
[0030] A nickel gallium (magnesium, aluminum) oxide catalyst with improved stability through hydrotalcite modification, the chemical formula of which is Ni-Ga / (Mg,Al)Ox,
[0031] A method for preparing a nickel gallium (magnesium, aluminum) oxide catalyst with improved stability through hydrotalcite modification comprises the following steps:
[0032] S1. Synthesize Ni-Ga-Mg-Al hydrotalcite precursor by coprecipitation method.
[0033] S101. According to the weight of metal nitrates required by calculation according to the stoichiometric ratio shown in Table 1, Ni(NO3)2·6H2O, Ga(NO3)3·xH2O, Al(NO3)3·9H2O and Mg(NO3)2·6H2O were mixed in 100 mL of deionized water to prepare a nitrate solution containing divalent and trivalent cations.
[0034] Table 1. List of prepared catalysts and their nominal compositions
[0035]
[0036] S102. Prepare an anion precursor solution by mixing Na2CO3 and NaOH, wherein Na2CO3 is in excess, twice the calculated stoichiometric ratio, to ensure that the charge-compensating anion is carbonate CO3 2- Instead of nitrate NO 3- The two solutions were finally mixed after stirring on a magnetic stirrer for 15 minutes.
[0037] S103: Add the nitrate solution containing divalent and trivalent cations from step S101 dropwise to the anion precursor solution through a separatory funnel under vigorous stirring. During the addition process, maintain the solution at 65°C and a pH between 9.5 and 10.5. If necessary, add 0.2M NaOH solution.
[0038] S104. The final mixture is then aged at room temperature for about 18 hours with continuous stirring to obtain a hydrotalcite suspension.
[0039] S105. The resulting suspension is then centrifuged, and the solid mixture is washed multiple times with distilled water to ensure complete removal of nitrate and sodium ions. The sample is then dried at 110° C. to obtain a Ni-Ga-Mg-Al hydrotalcite precursor.
[0040] S2. Pyrolyze the precursor to obtain Ni-Ga / (Mg,Al)Ox catalyst.
[0041] The pyrolysis temperature was 550° C. and the duration was 5 hours, and the Ni-Ga-Mg-Al hydrotalcite precursor was pyrolyzed to obtain the Ni-Ga / (Mg,Al)Ox catalyst.
[0042] The unmodified catalyst samples are denoted as Ni / (Mg,Al)Ox and the gallium-modified catalysts are denoted as Ni-Ga / (Mg,Al)Ox (Ga / Ni=y), where y refers to the above-mentioned Ga / Ni molar ratio (Ga / Ni ratio=0.1, 0.3, 0.5 and 1).
[0043] Catalyst activity test
[0044] The catalytic performance of Ni-Ga / (Mg,Al)Ox (Ga / Ni=0.3) catalyst was tested under the conditions of 700°C, 1 atmosphere and GHSV of 42000 mL / h / g.
[0045] The activities of Ni / (Mg,Al)Ox and Ni-Ga / (Mg,Al)Ox (Ga / Ni = 0.1, 0.3, 0.5 and 1.0) catalysts are expressed in terms of CH4 conversion and CO2 conversion, as shown in Figure 2. Figure 1 As shown in Figure 3 . For all catalysts studied, CH4 conversion was consistently lower than CO2 conversion due to the reverse water-gas shift (RWGS) (CO2 + H2 → CO + H2O) reaction accompanying the DRM reaction. The unmodified catalyst Ni / (Mg,Al)Ox showed initial CH4 and CO2 conversions of approximately 66% and 74%, respectively, but these conversions gradually declined over time.
[0046] For the Ga-modified catalysts, Ni-Ga / (Mg,Al)Ox (Ga / Ni=0.1, 0.3, 0.5, and 1), the initial conversion was comparable to that of the unmodified catalyst. However, after 5 hours of reaction, significant differences appeared in the catalytic stability. Among all the catalysts tested, the Ni-Ga / (Mg,Al)Ox (Ga / Ni=0.3) catalyst performed best in terms of catalytic stability, with no obvious deactivation. The improvement in catalytic stability after Ga incorporation may be attributed to the enhancement of the CO2 activation process. As pointed out in many studies, Ga-doped hydrotalcite-derived mixed oxides have good CO2 adsorption (capture) properties at high temperatures. This in turn will promote the gasification reaction through The proposed mechanism for enhanced stability involves the interaction of carbon produced by methane decomposition with the Ni3Ga alloy to form Ni3GaC0.25. This carbide is subsequently oxidized to CO2 by CO, preventing the accumulation and polymerization of carbon through a cyclic process.
[0047] The catalytic performance of the Ni-Ga / (Mg,Al)Ox (Ga / Ni=0.3) catalyst was further tested at 700°C and a GHSV of 42000 mL / h / g for 20 hours on-time (TOS). Figure 2 The results presented show that CH4 and CO2 conversions remained stable throughout the reaction period. Figure 3 The effect of reaction temperature on the catalytic performance of Ni-Ga / (Mg,Al)Ox (Ga / Ni=0.3) catalyst is shown.
[0048] from Figure 3 As can be seen in the figure, as the reaction temperature increases from 600°C to 850°C, the CH4 conversion increases from 35% to 94%, while the CO2 conversion increases from 46% to 96%. This is due to the endothermic nature of the DRM reaction. Comparison of the CH4 and CO2 conversions shows that within the temperature range studied, the CH4 conversion is always lower than the CO2 conversion, indicating the coexistence of the reverse water gas shift (RWGS) reaction under these reaction conditions. In addition, the H2 / CO ratio increases with increasing reaction temperature from 0.77 at 600°C to 1.00 at 850°C.
[0049] Table 2 provides a comparison of the catalytic activity of the Ni-Ga / (Mg,Al)Ox (Ga / Ni = 0.3) catalyst with other Ga-modified catalysts reported in previous studies. The table shows that the Ni-Ga / (Mg,Al)Ox (Ga / Ni = 0.3) catalyst outperforms its counterparts in the literature, likely due to the promoting effect and improved structural properties of the Ga-modified catalyst.
[0050] Table 2. Comparison of the activity of Ni-Ga / (Mg,Al)Ox (Ga / Ni = 0.3) catalyst with other gallium-containing modified catalysts reported in DRM (dry methane reforming) studies.
[0051]
[0052]
[0053]
[0054] Note: GHSV represents gas hourly space velocity, TOS represents operating time, XCH4 and XCO2 represent the conversion of methane and carbon dioxide respectively, and H2 / CO represents the molar ratio of hydrogen to carbon monoxide.
[0055] Post-use catalyst characterization
[0056] Nickel-based catalysts are often subject to severe carbon deposition during dry methane reforming (DRM) reactions. This is due to the accumulation of carbonaceous species on the catalyst surface, which deactivates the catalytically active sites. Therefore, the catalytic activity and stability of a particular catalyst are closely related to the amount of carbon species formed on the surface during the DRM reaction. Thermogravimetric analysis (TGA) can provide useful information on the amount of carbon deposited on spent catalysts.
[0057] Thermogravimetric analysis (TGA) was performed on spent catalyst samples using a Shimadzu TGA-51. 10–15 mg of spent catalyst sample was placed in an aluminum crucible and heated from room temperature to 1000°C (temperature ramp rate of 20°C / min) in a flowing air atmosphere. The amount of deposited coke was calculated based on the change in mass of the spent catalyst sample during the experiment.
[0058] Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) of the catalyst were performed as Figure 4 As shown in A and B.
[0059] like Figure 4 As shown in Figure 1, the addition of gallium (Ga) improves catalytic stability compared to the unmodified catalyst. The unmodified catalyst exhibits a relatively high weight loss of approximately 24 wt.%, indicating poor resistance to carbon deposition. The incorporation of Ga leads to improved resistance to carbon deposition, as evidenced by a reduction in the amount of deposited carbon. The Ni-Ga / (Mg,Al)Ox catalyst, with a Ga / Ni ratio of 0.3, exhibits the best catalytic stability, with a weight loss of only approximately 13 wt.%.
[0060] like Figure 4 As shown in Figure B, all catalyst samples exhibit a peak at approximately 300°C with comparable intensity, which is associated with the combustion of less ordered (amorphous) carbon. The high-temperature peak is associated with higher-order carbon (graphitic carbon) above 650°C, which requires higher temperatures to decompose.
[0061] TPO analysis can provide additional information about the type and amount of carbon deposited on the used catalyst. Figure 5 The TPO curves of all catalysts show two significant weight loss regions, a low temperature region between 100-400 °C corresponding to the combustion of amorphous carbon or metal carbide species, and a high temperature region above 500 °C associated with the combustion of graphitic carbon.
[0062] As can be seen from the TPO curve, the addition of gallium significantly changes the type and amount of each carbon species. For the unmodified catalyst Ni / (Mg,Al)Ox, the main coke species deposited on its surface is graphitic. At the same time, the Ni-Ga / (Mg,Al)Ox catalyst, with a Ga / Ni ratio of 0.3, has both the least graphitic carbon type and the highest amount of amorphous carbon. This result is consistent with the TGA analysis, indicating that after Ga incorporation, catalyst deactivation is significantly reduced due to the formation of reactive carbon instead of graphitic carbon, which in turn ensures the in situ gasification of the deposited carbon, resulting in better catalytic stability.
[0063] Raman spectroscopy is a useful tool for understanding the structural disorder and defects of carbon-based materials. Figure 6 As shown. The peak at a Raman shift of about 1380 (D band) is due to disordered carbon species (e.g., amorphous or defective filamentous carbon), while the peak at a Raman shift of about 1589 (G band) comes from the first-order scattering E2g mode of ordered graphite. In general, the relative intensity between the D band and the G band is an indicator of the degree of graphitization of the deposited carbon; the lower the value, the more graphitized the structure. Figure 6 As shown in the Raman spectra in Figure 2, the unmodified catalyst shows a more ordered graphite structure with a higher graphitization property, with the lowest ID / IG ratio of 0.93. After Ga modification, this ratio increases to a value greater than 1. Ni-Ga / (Mg,Al)Ox (Ga / Ni = 0.3) has the highest ID / IG ratio of 1.80 among all the catalysts studied. This indicates that for this particular catalyst, the crystallinity of the deposited carbon during the DRM reaction is the lowest. This result is also consistent with the trends discussed previously in the DTA and TPO analyses, as shown in Figure 2. Figure 4 and Figure 5 shown.
[0064] The above is only an embodiment of the present invention, and the common knowledge such as the specific technical solutions and / or characteristics in the solution are not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the description can be used to interpret the content of the claims.
Claims
1. A nickel gallium (magnesium, aluminum) oxide catalyst with improved stability by hydrotalcite modification, characterized in that: Its chemical expression is Ni-Ga / (Mg,Al)Ox, and a modified catalyst with a mesoporous structure is obtained by thermally decomposing a Ni-Ga-Mg-Al hydrotalcite precursor.
2. The nickel gallium (magnesium, aluminum) oxide catalyst with improved stability through hydrotalcite modification according to claim 1, characterized in that: The molar ratio of Ga / Ni in the Ni-Ga / (Mg,Al)Ox is preferably 0.
3.
3. A method for preparing a nickel-gallium (magnesium, aluminum) oxide catalyst with improved stability by hydrotalcite modification, comprising the Ni-Ga / (Mg,Al)Ox according to claim 1, characterized in that: The steps include: S1. Synthesis of Ni-Ga-Mg-Al hydrotalcite precursor by coprecipitation method; S2. Pyrolyze the precursor to obtain Ni-Ga / (Mg,Al)Ox catalyst.
4. The method for preparing a nickel gallium (magnesium, aluminum) oxide catalyst with improved stability through hydrotalcite modification according to claim 3, characterized in that: In step S1, the following steps are included: S101, Ni(NO3)2·6H2O, Ga(NO3)3·xH2O, Al(NO3)3·9H2O and Mg(NO3)2·6H2O were mixed in deionized water; S102, stirring Na2CO3 and NaOH solutions on a magnetic stirrer for 15 minutes and then mixing to prepare an anion precursor solution; S103, adding the nitrate solution obtained in S1 dropwise to the anion precursor solution under vigorous stirring, and maintaining the solution medium at 65° C. and the pH at 9.5–10.5; S104, aging the mixture obtained in S3 at room temperature for about 18 hours with continuous stirring to obtain a hydrotalcite suspension; S105. Centrifuge the obtained suspension, wash the solid mixture with distilled water for multiple times, and dry it at 110° C. to obtain a Ni—Ga—Mg—Al hydrotalcite precursor.
5. The method for preparing a nickel gallium (magnesium, aluminum) oxide catalyst with improved stability through hydrotalcite modification according to claim 3, characterized in that: In step S2, the pyrolysis temperature is 550°C and the duration is 5 hours.
6. Use of the nickel gallium (magnesium, aluminum) oxide catalyst of claim 1 with improved stability through hydrotalcite modification in dry methane reforming.
7. The use according to claim 6, characterized in that In the dry reforming of methane, a Ni-Ga / (Mg,Al)Ox catalyst was added to react at 700°C, 1 atm, and a GHSV of 42000 mL / h / g.