Application of a carbon-modified noble metal catalyst in the low-temperature combustion of propane or mixed alkanes
By modifying noble metal catalysts with carbon, the problem of easy deactivation of noble metal catalysts in high-temperature and oxygen-rich environments was solved, and efficient catalytic combustion of alkane molecules at low temperatures was achieved, thereby improving the activity and stability of the catalyst.
Patent Information
- Application Number
- CN202610315932.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-03-16
- Publication Date
- 2026-05-26
AI Technical Summary
Existing precious metal catalysts are prone to deactivation in high-temperature oxygen-rich environments, single transition metal oxide catalysts have poor performance in activating alkane molecules at low temperatures, and composite metal oxide catalysts have reduced specific surface area during high-temperature preparation, making it difficult to achieve efficient catalytic combustion at low temperatures.
By modifying noble metal catalysts with carbon species, the metal-support interface is modified with carbon species, which significantly improves the activity of lattice oxygen and the valence state of noble metals, thus achieving efficient catalytic combustion under low-temperature conditions.
It significantly reduced the activation temperature of the catalyst and improved its low-temperature catalytic combustion performance, especially showing a significant promoting effect on Pt, Pd, and Ru metal systems, thereby enhancing the activity and stability of the catalyst.
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Figure CN122076430A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of environmental catalytic materials technology, specifically relating to the application of a carbon-modified noble metal catalyst in the low-temperature combustion of propane or mixed alkanes. Background Technology
[0002] Emission reduction and treatment of volatile organic compounds (VOCs) and low-carbon alkanes (such as methane and propane) has become a research hotspot in the field of environmental catalysis. Alkane molecules possess a highly symmetrical structure and extremely high CH bond energy, resulting in extremely stable chemical properties and making them difficult to oxidize and decompose at low temperatures. In alkane emission reduction methods, traditional direct combustion methods typically require extremely high temperatures, consuming enormous amounts of energy and easily producing nitrogen oxides (NOx). x Secondary pollutants such as methane and ethane are difficult to adsorb using adsorption concentration methods, as they have very weak polarity and extremely low boiling points. Low-temperature plasma methods cannot completely oxidize alkanes to CO2, often generating large amounts of toxic intermediates. Catalytic combustion, however, significantly reduces the activation energy of the reaction under the action of noble metal or transition metal oxide catalysts, enabling flameless combustion of low-concentration alkanes at lower temperatures (200℃-500℃). This is currently recognized as the most promising and core technological route.
[0003] Currently used catalysts are classified into three categories. Noble metal catalysts, in oxygen-rich combustion environments, are easily oxidized to high-valence oxides by zero- or low-valence active metals, leading to catalyst deactivation. Single transition metal oxide catalysts, such as Co3O4, MnO2, and CuO, while inexpensive, lack electronic regulation and structural defects, making them difficult to activate alkane molecules at low temperatures. Composite metal oxide catalysts, such as perovskite and spinel, suffer from reduced specific surface area and fewer active sites during high-temperature preparation; moreover, their activation performance for short-chain alkanes is not ideal.
[0004] Although noble metals are currently the most intrinsically active catalytic materials due to their excellent CH bond activation ability, as mentioned earlier, they are prone to thermal sintering in high-temperature, oxygen-rich reaction environments, and their low-valence active centers are easily deeply oxidized, leading to rapid and irreversible deactivation of the catalyst. On the other hand, cerium dioxide (CeO2) is widely used as a catalytic material or basic support due to its excellent oxygen storage and release capabilities. However, at low temperatures (<300℃), the bulk lattice oxygen in pure CeO2 has poor mobility, making it difficult to quickly migrate to the surface to participate in the reaction. This slow oxygen supply severely limits its low-temperature ignition performance.
[0005] To overcome these shortcomings, researchers have explored various modification strategies, such as doping with dissimilar metals (Zr, La, Ti, etc.) or constructing specific morphologies. While these methods can improve thermal stability to some extent, their ability to control the surface microelectronic environment is limited, making it difficult to achieve universal enhancement for Pt, Pd, and Ru metal systems. Furthermore, carbon material modification is also an important approach, but existing carbon modification methods mostly employ "carbon coating" or "core-shell structure" strategies. Although this thick physical carbon layer can suppress metal aggregation, it often results in a "shielding effect," preventing gas molecules from effectively contacting the internal active sites, thus sacrificing the intrinsic activity of the catalyst. Summary of the Invention
[0006] To address the problems existing in the prior art, this invention provides a new application for carbon-modified noble metal catalysts, namely their application in the low-temperature combustion of propane or mixed alkanes. This invention utilizes carbon species to modify the metal-support interface, significantly improving the activity of lattice oxygen and optimizing the valence state of noble metals, thereby achieving efficient catalytic combustion of different alkane molecules under low-temperature conditions.
[0007] The carbon-modified noble metal catalyst is prepared by adding sodium hydroxide solution dropwise to a cerium salt solution, mixing, reacting at 80-120℃ for 10-15 hours, cooling to room temperature, separating the solid and liquid, and drying and calcining the solid to obtain a cerium dioxide support; the cerium dioxide support is then impregnated in an equal volume of a noble metal salt solution, dried and calcined, and the calcined product and glucose are added to deionized water, mixed, and then hydrothermally reacted at 180-200℃ for 8-12 hours, dried, and calcined under an argon atmosphere to obtain the catalyst.
[0008] The mass ratio of sodium hydroxide to cerium salt is 2-5:1; the noble metal salt is Pd salt, Ru salt, or Pt salt, and the amount of noble metal salt added is 0.6-2.5% of the mass of cerium dioxide carrier; the calcination temperature is 400-500℃; and the mass ratio of calcination product to glucose is 0.8-1.2:1.
[0009] This invention utilizes doped carbon species to induce lattice distortion in cerium dioxide, increasing a large number of surface oxygen vacancies. These vacancies act as "oxygen pumps," significantly enhancing the surface concentration and mobility of lattice oxygen, and accelerating the replenishment of gaseous oxygen and the release of lattice oxygen in the Mars-van Krevelen redox cycle. Simultaneously, the existing carbon species reconstruct the electronic environment of the metal-support interface through strong interactions: on the one hand, they act as electron buffers, inhibiting excessive Ru oxidation and stabilizing it in an intermediate valence state conducive to oxygen activation (Ru...). δ+ On the other hand, it provides electronic feedback to Pt / Pd to maintain its high proportion of metallic Pt. 0 / Pd 0This significantly lowers the dissociation energy barrier of the CH bond in alkane molecules; this dual-function synergistic mechanism of "vacancy-captured oxygen-metal-activated hydrocarbon" enables highly efficient catalytic combustion at low temperatures.
[0010] The present invention has the following beneficial effects: (1) The carbon doping strategy showed a significant promoting effect on the three metal systems of Pt, Pd and Ru. The activity results showed that the activation temperature of the modified catalyst for propane and mixed alkanes was significantly reduced. (2) O 1s XPS characterization demonstrated that carbon doping effectively broke the stability of the Ce-O bond, resulting in a higher concentration of lattice oxygen (O2) on the catalyst surface. V This accelerates the oxygen cycle in the reaction; (3) The presence of carbon species optimizes the electronic environment of the metal. For Ru-based catalysts, it inhibits excessive oxidation and maintains high Ru activity. δ+ State; for Pt / Pd-based catalysts, it promotes Pt 0 / Pd 0 The formation of this state facilitates the dissociation of CH bonds. Attached Figure Description
[0011] Figure 1 XRD patterns of the catalysts in Examples 1-2 and Comparative Examples 1-2; Figure 2 XRD patterns of the catalysts in Examples 3-4 and Comparative Examples 3-4; Figure 3 XRD patterns of the catalysts in Examples 5-6 and Comparative Examples 5-6; Figure 4 O1s XPS plots of the catalysts in Examples 1-2 and Comparative Examples 1-2; Figure 5 O1s XPS plots of the catalysts in Examples 3-4 and Comparative Examples 3-4; Figure 6 O1s XPS plots of the catalysts in Examples 5-6 and Comparative Examples 5-6; Figure 7 XPS plots of noble metals in the catalysts of Examples 1-2 and Comparative Examples 1-2; Figure 8 XPS plots of noble metals in the catalysts of Examples 3-4 and Comparative Examples 3-4; Figure 9 XPS plots of noble metals in the catalysts of Examples 5-6 and Comparative Examples 5-6; Figure 10 The propane catalytic combustion conversion curves of the catalysts in Examples 1-2 and Comparative Examples 1-2 are shown. Figure 11The propane catalytic combustion conversion curves of the catalysts in Examples 3-4 and Comparative Examples 3-4 are shown. Figure 12 The propane catalytic combustion conversion curves of the catalysts in Examples 5-6 and Comparative Examples 5-6 are shown. Figure 13 The catalytic combustion conversion curves of the catalyst mixtures of Example 2 and Comparative Example 2 are shown. Figure 14 The catalytic combustion conversion curves of the catalyst mixtures of Example 4 and Comparative Example 4 are shown. Figure 15 The conversion curves of the mixed gas catalytic combustion of the catalysts in Example 6 and Comparative Example 6 are shown. Detailed Implementation
[0012] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.
[0013] Example 1: Preparation of carbon-modified noble metal catalyst Pd / CeO2-C-1 (1) Dissolve 3g of cerium nitrate hexahydrate in 30mL of deionized water and 6.4g of sodium hydroxide in 50mL of deionized water; slowly add the sodium hydroxide solution to the cerium nitrate solution and stir until homogeneous to obtain a mixed solution; (2) The mixed solution was transferred to the Teflon reactor liner and reacted at 100°C for 14 hours. After the reaction was completed, it was cooled to room temperature, the reactor liner was removed, the precipitate was collected by centrifugation, the precipitate was dried at 60°C for 12 hours, the dried powder was placed in a crucible and transferred to a muffle furnace, and heated to 400°C at a heating rate of 5°C / min for 4 hours to obtain rod-shaped cerium dioxide powder. (3) Weigh palladium nitrate dihydrate and dissolve it in water at a ratio of 0.62% of the mass of cerium dioxide. Then add 1g of rod-shaped cerium dioxide powder, stir and mix well, dry at 60℃ for 12h, and then transfer it to a muffle furnace and calcine at 400℃ for 4h at a heating rate of 5℃ / min to obtain Pd / CeO2. (4) Add Pd / CeO2 to 50 mL of deionized water, then add 1 g of glucose, stir well, transfer the mixed solution to a Teflon reactor liner, react at 180 °C for 10 h, after the reaction is completed, cool to room temperature, remove the reactor liner, centrifuge to collect the precipitate, dry the precipitate at 120 °C for 8 h, place the dried powder in a crucible, transfer it to a tube furnace, introduce Ar gas, and calcine at 400 °C for 2 h at a heating rate of 5 °C / min to obtain catalyst Pd / CeO2-C-1, the XRD pattern of which is shown in the figure. Figure 1The figure shows characteristic diffraction peaks typical of the fluorite-phase CeO2 support, with no diffraction peaks related to noble metals or carbon species detected throughout. This indicates that the supported noble metal Pd is highly dispersed on the CeO2 support surface without significant aggregation, providing abundant surface active sites for the catalytic reaction. On the other hand, the introduced carbon species exist on the catalyst in a highly dispersed or amorphous state, without forming encapsulated bulk crystalline carbon, thus effectively avoiding the physical shielding effect on the active centers, confirming the successful construction of the catalyst structure. Example
[0014] The method in this embodiment is the same as in embodiment 1, except that the amount of palladium nitrate dihydrate added is 2.2% of the mass of cerium dioxide; thus, the catalyst Pd / CeO2-C-2 is prepared. Example
[0015] The method in this embodiment is the same as in Example 1, except that palladium nitrate dihydrate is replaced with ruthenium trichloride trihydrate to prepare the catalyst Ru / CeO2-C-1. Example
[0016] The method in this embodiment is the same as in embodiment 3, except that the amount of ruthenium trichloride trihydrate added is 2.2% of the mass of cerium dioxide, and the catalyst Ru / CeO2-C-2 is obtained. Example
[0017] The method in this embodiment is the same as in Example 1, except that palladium nitrate dihydrate is replaced with chloroplatinic acid hexahydrate to prepare the catalyst Pt / CeO2-C-1. Example
[0018] The method in this embodiment is the same as in embodiment 5, except that the amount of chloroplatinic acid hexahydrate added is 2.2% of the mass of cerium dioxide, and the catalyst Pt / CeO2-C-2 is obtained.
[0019] Comparative Example 1: Pd / CeO2-1 is the catalyst Pd / CeO2 prepared in step (3) of Example 1.
[0020] Comparative Example 2: Pd / CeO2-2 is the catalyst Pd / CeO2 obtained in step (3) of Example 2.
[0021] Comparative Example 3: The catalyst Ru / CeO2 prepared in step (3) of Example 3.
[0022] Comparative Example 4: The catalyst Ru / CeO2 prepared in step (3) of Example 4.
[0023] Comparative Example 5: The catalyst Pt / CeO2 prepared in step (3) of Example 5.
[0024] Comparative Example 6: The catalyst Pt / CeO2 prepared in step (3) of Example 6.
[0025] The crystal structure and microstructure of the catalysts in the above embodiments and comparative examples are shown in the figure. Figure 1-3 The results showed that the catalysts of Examples 1-6 and Comparative Examples 1-6 all exhibited a typical cubic fluorite phase CeO2 structure. Compared with Comparative Examples 1-6, the characteristic diffraction peak intensities of the catalysts of Examples 1-6 after the introduction of carbon were significantly weakened, and the full width at half maximum (FWHM) was broadened. This phenomenon indicates that the introduction of carbon species does not change the main crystalline phase of the support, but rather infiltrates or anchors in the interstitial lattice, causing significant lattice distortion. This low crystallinity characteristic usually means that the catalyst has more abundant grain boundaries and high-energy surface sites.
[0026] Surface defects and electronic property analysis are shown in Figure 4-6 , Figure 7-9 XPS characterization visually revealed the role of carbon doping in reconstructing the chemical environment of the catalyst surface. Firstly, as... Figure 4-6 As shown in the O1s XPS spectra, peak fitting revealed a significant change in the surface oxygen species distribution in Examples 1-6. Compared to Comparative Examples 1-6, the characteristic peak area ratio representing defect oxygen / oxygen vacancies in these examples was significantly increased. This result fully demonstrates that the introduction of carbon effectively disrupted the stoichiometric equilibrium of the Ce-O bonds, inducing a high concentration of oxygen vacancies in situ on the support surface. These abundant oxygen vacancies greatly promoted the migration and activation of bulk lattice oxygen to the surface, providing a sufficient source of active oxygen for the oxidation reaction.
[0027] Secondly Figure 7-9 XPS spectra of the metal elements revealed a precise regulatory mechanism by which carbon species control the electronic environment of the active centers: in the Ru system, the introduction of carbon effectively inhibited the excessive oxidation of Ru, allowing active species with valences below +4 (Ru...) to... δ+ The proportion of zero-valent metallic states (Pd) increases significantly; while in the Pd and Pt systems, carbon species stabilize a higher proportion of zero-valent metallic states (Pd) through strong interfacial electronic interactions. 0 and Pt 0 This enrichment of specific low-valence or metallic states significantly enhances the adsorption and activation ability of active metal sites for CH bonds in alkane molecules, thereby effectively reducing the reaction energy barrier of catalytic combustion.
[0028] Example 7: Application of the catalysts in the above examples in the low-temperature combustion of propane or mixed alkanes 1. Propane combustion Catalyst evaluation experiments were conducted in a fixed-bed reactor. During the activity test, 0.1 g of catalyst was placed in the middle of the quartz tube reactor. The particle size of the catalyst sample was strictly controlled within 40-60 mesh to ensure uniform packing and gas flow. The reactor temperature was adjusted to the specified temperature (100℃), and a feed gas with a volume fraction of 0.2% C3H8 + 10% O2 + 89.8% N2 was introduced at a flow rate of 50 mL / min. The temperature was then gradually increased, and the conversion rate of the feed gas was recorded.
[0029] See results Figure 10-12 As can be seen from the figure, the introduction of carbon modification significantly enhances the low-temperature catalytic combustion activity of the catalyst for propane. Specifically, the T90 values for Examples 1-6 are 309℃, 273℃, 351℃, 239℃, 305℃, and 250℃, respectively, while the T90 values for Comparative Examples 1-6 are over 400℃, 390℃, over 400℃, 321℃, 374℃, and 380℃, respectively. The carbon-modified catalyst exhibits a significant decrease in T90 of nearly 100℃. It is precisely this synergistic effect at the structural and electronic levels that endows the catalysts of these examples with superior low-temperature catalytic combustion performance.
[0030] 2. Combustion of mixed alkanes The test method is the same as propane combustion, except that the feed gas is changed to 0.2% C3H8 + 0.2% C2H6 + 1% CH4 + 20% O2 + 78.6% N2.
[0031] See results Figure 13-15 The figure shows the catalytic performance of the catalyst in a mixed gas (containing CH4, C2H6, and C3H8) simulating actual operating conditions. The results indicate that Examples 2, 4, and 6 not only maintain high activity for single components but also exhibit significant promoting effects under multi-component competitive adsorption conditions. Example 2 demonstrates the best activity in the catalytic combustion conversion of the mixed gas. The T90 values of Example 2 in the CH4, C2H6, and C3H8 mixed gas are 312℃, 294℃, and 275℃, respectively, demonstrating its great potential for industrial applications.
Claims
1. The application of a carbon-modified noble metal catalyst in the low-temperature combustion of propane or mixed alkanes, characterized in that: The carbon-modified noble metal catalyst is prepared by adding sodium hydroxide solution dropwise to a cerium salt solution, mixing, reacting at 80-120℃ for 10-15 hours, cooling to room temperature, separating the solid and liquid, and drying and calcining the solid to obtain a cerium dioxide support. The cerium dioxide support is then impregnated in an equal volume of a noble metal salt solution, dried and calcined, and the calcined product and glucose are added to deionized water, mixed, and then hydrothermally reacted at 180-200℃ for 8-12 hours. After drying, it is calcined under an argon atmosphere to obtain the final product.
2. The application according to claim 1, characterized in that: The mass ratio of sodium hydroxide to cerium salt is 2-5:
1.
3. The application according to claim 1, characterized in that: The precious metal salts are Pd, Ru, and Pt salts, and the amount of precious metal salts added is 0.6-2.5% of the mass of the cerium dioxide carrier.
4. The application according to claim 1, characterized in that: The roasting temperature is 400-500℃.
5. The application according to claim 1, characterized in that: The mass ratio of the roasted product to glucose is 0.8-1.2:1.