Dehydrogenation catalyst, and preparation method therefor and use thereof
By using a magnesium-aluminum mixed oxide support modified with Pt metal clusters and ammonium sulfate in a cycloalkane dehydrogenation catalyst, the problems of high precious metal content and coking are solved, achieving high efficiency and stable catalytic performance suitable for industrial applications.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- CNOOC GAS & POWER GRP
- Filing Date
- 2024-12-20
- Publication Date
- 2026-06-25
AI Technical Summary
Existing cycloalkane dehydrogenation catalysts have high platinum content, resulting in high cost, insufficient catalyst activity and stability, and are prone to carbon deposition under high temperature and high pressure conditions, affecting their ability to work continuously for a long time.
A dehydrogenation catalyst with good dispersibility and high stability was prepared by using Pt metal clusters as active centers, combined with a slightly alkaline magnesium-aluminum mixed oxide support, and by surface modification with ammonium sulfate precursor. The metal-support interaction was optimized to improve catalytic performance.
It reduces the amount of precious metals used, improves the activity and selectivity of the catalyst, reduces coking, and enhances the stability of the catalyst, making it suitable for industrial production.
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Figure CN2024141084_25062026_PF_FP_ABST
Abstract
Description
A dehydrogenation catalyst, its preparation method and application Technical Field
[0001] This invention relates to the field of catalyst technology, and in particular to a dehydrogenation catalyst, its preparation method, and its application. Background Technology
[0002] Hydrogen is an ideal clean energy fuel that can replace traditional hydrocarbon feedstocks. It boasts a high gravimetric energy density of 141.6 MJ / kg, three times that of gasoline, while producing water as its only byproduct. The challenges in these applications are related to the difficulty of efficient hydrogen storage. Currently, most hydrogen storage relies on compression and liquefaction technologies, which introduce safety concerns, low storage density, transportation losses, evaporation losses, and other high-cost issues.
[0003] Dehydrogenation is a chemical reaction that can be used for hydrogen production, hydrogen storage, and the generation of value-added unsaturated hydrides. Due to the bond-breaking process, dehydrogenation reactions are typically endothermic, requiring high energy input to achieve sufficient reactivity. Therefore, catalysts enhance activity and reaction rates by lowering the activation energy barrier, and control product selectivity by manipulating reaction pathways on the catalyst surface.
[0004] Liquid organic hydrogen carriers (LOHCs) are an attractive alternative for storing hydrogen in chemically bonded form, addressing many limitations of existing technologies. Reversible LOHC systems always consist of a pair of hydrogen-deficient and hydrogen-rich organic compounds that store hydrogen through hydrogenation and dehydrogenation, showing great potential for hydrogen storage and transportation applications. Cycloalkanes and aromatics with one or more six-membered rings are promising reversible LOHC systems. These stable alkanes exhibit remarkably high storage capacities (between 6-7 wt.% H₂) and can be dehydrogenated / rehydrogenated under relatively low reaction conditions.
[0005] Supported metal catalysts are crucial for many processes in the chemical industry. The overall performance of these catalysts largely depends on the interactions of adsorbates at the atomic level, which can be manipulated and regulated through different components of the active material (i.e., the support and the active metal). In heterogeneous (thermal) catalysis, catalyst activity is described by regulating the relationship between the active component and the support through metal-support interaction (MSI). The catalytic performance can be modulated by controlling the active particle size—atoms, clusters, and nanoparticles supported on metal oxides—to influence the metal-support interaction in catalysis.
[0006] Metal-supported catalysts are the most important catalyst models. Reasonable construction of MSI can effectively enhance catalytic performance. The strategies for regulating metal-support interaction are divided into three directions: (1) Construction of support defects: support composition, support morphology, support doping, and surface modification; (2) Properties of supported active metals: size effect and active composition; (3) Preparation and treatment methods: heat treatment, reducing agent, redox cycle, coating deposition, and adsorbent treatment.
[0007] Constructing defect structures is an important design strategy for catalysts. Based on the physicochemical properties of catalysts, reaction evaluation, and mechanistic kinetics, the core of this study is the construction of defects and their preparation methods for different catalysts. Based on the causes of defect formation, crystal defects are classified into: thermal defects, impurity defects, non-stoichiometric defects, charge defects, and irradiation defects: (1) Thermal defects, also known as inherent defects, are vacancies and / or interstitial protons generated by thermal fluctuations. The concentration of thermal defects is proportional to temperature. (2) Impurity defects, considered as compositional defects, are defects caused by the introduction of external impurities. Therefore, the introduced trace impurities will greatly change the physical properties of the crystal matrix. (3) Non-stoichiometric defects are caused by deviations from the chemical constant ratio law, which is triggered by the exchange between the crystal matrix and certain components in the medium. (4) Charge defects involve defects in which the periodicity of particle arrangement remains unchanged, but the periodic potential field will be distorted due to the generation of electrons or holes. (5) The structural incompleteness of catalysts produced under irradiation is called irradiation defects.
[0008] Supported platinum nanoparticle catalysts are industrially mature and high-quality heterogeneous catalysts used in hydrocarbon refineries. Chiyoda Corporation has developed a liquid organic hydrogen storage system for methylcyclohexane (MCH) dehydrogenation / toluene rehydrogenation based on a sulfidated alumina-supported platinum catalyst (S-Pt / Al₂O₃), demonstrating its feasibility and advantages in hydrogen storage and transportation. However, the high cost and low natural abundance of platinum limit its widespread application. Therefore, how to achieve efficient utilization while reducing the content of the precious metal platinum is a path that needs to be explored technologically.
[0009] The catalytic technology for the dehydrogenation of methylcyclohexane faces several problems and drawbacks in current industrial applications. These mainly include cost issues due to the high platinum content, the inability of weak metal-support interactions to stably anchor platinum nanoparticles leading to active site aggregation and deactivation, carbon buildup on the catalyst surface during the reaction, and catalyst deactivation during long reaction periods. For example, the high platinum content in patent application CN 117899863A (18.02%) and patent application CN 116851023A (5%) (particle size 2 nm) are significant issues. While patent application CN 118162160A employs a strategy of modifying the γ-Al₂O₃ support with ammonium sulfate to reduce platinum content, resulting in a catalyst with a platinum content of less than 1%, it still exhibits significant hydrogen co-feeding in long-term tests (1 hour, 24 hours, and 600 hours) and a relatively slow space-time velocity (0.5 ml / min, 50 times the 0.01 ml / min flow rate of methylcyclohexane). Patent application CN 113070061 A proposes a lanthanide rare earth metal-modified Al2O3 support, with rhodium and ruthenium partially replacing platinum. The attempt to load noble metals in the 1% to 5% range raises concerns about costs in industrialization, and the reaction time in its dehydrogenation test is too short at only 40 minutes. Doping with base metals is also a common strategy in catalysis. Patent application CN 109331823 A proposes a lanthanide cerium metal-modified magnesium-aluminum layered double hydroxide support for platinum loading, but does not specify the mass fraction of platinum or the corresponding reaction time. Patent application CN 114011431 A proposes a strategy of doping nickel metal onto a platinum catalyst supported on γ-Al2O3. Although this method shows good conversion and selectivity in its described laboratory tests, the reactors and steel pipes used in pilot-scale and intermediate-scale industrialization contain nickel. In actual reactions, excess nickel occurs at the catalyst-reactor contact point, leading to excessive cracking of methylcyclohexane and resulting in carbon buildup and blockage of the reactor pipes. Patent CN 107376907 B discloses a strategy of loading platinum onto a tin-modified magnesium aluminum hydrotalcite carrier. The platinum content in the patent is 0.5-5%, the reaction time is 10 hours, and the best example has a methylcyclohexane dehydrogenation conversion rate of 98.5%. However, there are problems such as the cost caused by the high platinum content and the lack of long-term stability testing.
[0010] In view of this, the present invention is proposed. Summary of the Invention
[0011] The high platinum content in cycloalkane dehydrogenation catalysis leads to cost and reduced catalyst activity. Lowering the platinum content on traditional alumina supports results in decreased catalytic activity and difficulty in maintaining stability. Specifically, regarding the decline in catalyst activity and selectivity, the weak interaction between the Pt metal and the alumina support in cycloalkane dehydrogenation causes Pt particles to aggregate during prolonged reactions, leading to decreased catalyst activity. Furthermore, coking under high temperature and pressure conditions is another significant factor affecting stability, reducing its ability to operate continuously for extended periods. This lack of stability limits the catalyst's application in industrial production. Therefore, catalyst preparation strategies should consider maintaining platinum site activity, controlling nanoparticle size, and minimizing coking.
[0012] To address the issues of catalyst activity, stability, and coking in cycloalkane dehydrogenation, the main objective of this invention is to design a catalyst with good Pt dispersion, high stability, and resistance to coking. Using Pt metal clusters as active centers, and combining them with a slightly alkaline magnesium-aluminum mixed oxide as a catalyst support, and adding ammonium sulfate precursors for surface modification, the Pt micro / nano clusters are anchored, resulting in a cycloalkane dehydrogenation catalyst with good dispersion and high stability. By shrinking Pt from nanoparticles to nanoclusters and utilizing its step-like sites, and anchoring these sites through the Pt-S-support, a sulfur-modified magnesium-aluminum mixed oxide support with a synergistic structure (layered hydrotalcite structure, spinel structure, and a transitional mixed state of both) can the catalytic efficiency and stability of Pt atoms be maximized, while simultaneously reducing the amount of precious metal used, thus achieving an effective method for cost reduction.
[0013] Based on this, the present invention provides a dehydrogenation catalyst, its preparation method and application, specifically including the following technical solutions:
[0014] In a first aspect, the present invention provides a dehydrogenation catalyst, characterized in that the dehydrogenation catalyst uses a sulfur-modified magnesium-aluminum mixed oxide as a support and a Pt metal cluster as an active center; wherein the support is a mixed metal oxide having a layered hydrotalcite structure, a spinel structure and a near-crystalline synergistic structure.
[0015] In this invention, the near-crystalline structure refers to a transitional state that is not fully crystalline.
[0016] In this invention, Pt metal clusters refer to a dimension between Pt single atoms and Pt nanoparticles, possessing active sites with higher exponent crystal planes than platinum nanoparticles. They are easier to prepare than single-atom platinum catalysts, thus being more suitable for industrial production and exhibiting higher stability. Clusters are multinuclear aggregates between atoms / molecules and macroscopic matter, possessing definite atomic composition and chemical structure. They represent the initial state of condensed matter and are ideal models relating macroscopic properties and microscopic structures, holding significant importance for a profound understanding of the laws governing material transformation. Clusters and the catalyst support play crucial roles in the interaction between metal catalysts, significantly influencing the performance of catalytic reactions. Specifically, the cluster-metal-support interaction is a unique interaction occurring at the interface between metal nanoparticle clusters and the metal oxide support in solid-phase heterogeneous catalysts. It alters the electronic properties of the catalyst surface, thereby changing the catalytic process. Controlling cluster-metal-support interactions in heterogeneous catalyst design provides numerous opportunities for developing advanced catalysts with better catalytic performance.
[0017] This invention reveals that the interaction between platinum clusters (Pt clusters) and non-metallic sulfur-modified magnesium-aluminum mixed oxide catalysts has a significant impact on catalytic performance in cycloalkane dehydrogenation reactions.
[0018] 1. The role of platinum clusters
[0019] Highly active sites: Platinum clusters typically exhibit high catalytic activity due to their high surface energy and unique electronic structure. In the dehydrogenation of cycloalkanes, platinum clusters can effectively activate hydrogen-hydrogen bonds and carbon-hydrogen bonds, thereby promoting the reaction.
[0020] Size effect: The size of platinum clusters has a significant impact on their catalytic performance. Smaller platinum clusters generally exhibit higher activity, but may also lead to catalyst stability issues. Optimizing the preparation method to achieve controllable cluster size and strong interaction with the support can balance catalytic activity and stability.
[0021] 2. The role of sulfur-modified magnesium-aluminum mixed oxides
[0022] Adjustment of acid-base properties: Sulfur modification of alkaline magnesium-aluminum mixed oxides can alter the acid-base properties of the catalyst support surface. The introduction of sulfides can locally adjust the surface properties of the support, thereby affecting the dispersion and stability of metal clusters.
[0023] Enhanced metal dispersion: Sulfur-modified magnesium-aluminum mixed oxides, used as a support, help improve the dispersion of platinum clusters, reduce cluster aggregation, and thus improve the activity and selectivity of the catalyst.
[0024] 3. The influence of metal-carrier interaction
[0025] Electronic effects: The introduction of sulfur compounds affects the electronic properties of the magnesium-aluminum mixed oxide support surface, thereby altering the microelectronic environment of platinum clusters. This change can adjust the electron density of platinum, enhancing its catalytic activity. The mechanism of action of sulfides may involve their interaction with the electrons of platinum, influencing the catalytic behavior of platinum on the support surface.
[0026] Interfacial effects: The interfacial effects between platinum clusters and sulfur-modified magnesium-aluminum mixed oxide supports are crucial for catalytic performance. Sulfide modification can alter the catalyst's surface structure, active sites, and interactions, affecting reaction rates and selectivity. For example, sulfides can interact with platinum's active sites, modulating its adsorption capacity for reactants.
[0027] Stability of reaction intermediates: The acid-base properties and electronic effects of surface-sulfurized magnesium-aluminum mixed oxides may affect the stability of reaction intermediates, thereby affecting the selectivity and product distribution of cycloalkane dehydrogenation reactions.
[0028] 4. Improved catalytic performance
[0029] Activity and selectivity: Sulfur-modified magnesium-aluminum mixed oxides can improve the dispersibility and stability of platinum clusters, while also modulating their electronic properties, which helps to improve the catalytic activity and selectivity of cycloalkane dehydrogenation reactions.
[0030] Stability: By modifying with sulfur, the stability of platinum clusters in catalysts may be enhanced, reducing catalyst accumulation and deactivation during long-term operation.
[0031] Preferably, the Pt metal clusters have a particle size of 0.2–0.5 nm.
[0032] Preferably, the dehydrogenation catalyst is sulfur-modified Mg x Al y O δ The carrier is x > y, and δ represents any value from 4 to 6; more preferably, x:y = (2 to 3):1; even more preferably, x:y = 3:1.
[0033] Preferably, the surface area of the carrier is 100m². 2 / g or more, pore volume 0.50 cm³ 3 / g or more, with a pore size of 5nm or more.
[0034] Preferably, the content of the platinum metal clusters is 0.1 wt% to 0.8 wt%, based on the mass of the dehydrogenation catalyst.
[0035] Secondly, the present invention provides a method for preparing the aforementioned dehydrogenation catalyst, comprising:
[0036] S1: Mix magnesium salt solution, aluminum salt solution and complexing agent to obtain sol solution;
[0037] S2: The sol solution is heated under low pressure in a rotary evaporator to obtain a gel, and then the gel is dried to obtain a solid precursor of the dry gel. The precursor powder is obtained by grinding.
[0038] S3: The precursor powder is first calcined in a muffle furnace at 300-400°C, and then calcined a second time in a tube furnace at 450-600°C to obtain the carrier.
[0039] S4: The carrier is loaded with sulfur source and Pt clusters sequentially by impregnation.
[0040] In this invention, by controlling two calcinations, it is helpful to obtain a carrier with a layered hydrotalcite structure, a spinel structure, and a synergistic structure in a crystalline state. The layered hydrotalcite structure is a layered magnesium-aluminum oxide with a single layer of magnesium and aluminum ions. Due to the excess magnesium, cubic MgO is aggregated on the surface. Furthermore, due to the second calcination of the carrier, magnesium-aluminum spinel and its near-crystalline transitional crystal morphology also exist in the carrier, ultimately enabling the acquisition of the aforementioned special synergistic structure.
[0041] Preferably, the magnesium salt includes one or more of magnesium acetate, magnesium nitrate, and magnesium chloride;
[0042] And / or, the aluminum salt solution includes one or more of aluminum acetate, aluminum chloride, and aluminum nitrate;
[0043] And / or, the complexing agent includes one or more of EDTA, citric acid, sodium citrate, ammonium citrate, maleic acid, glycine, ethanolamine, diethanolamine and triethanolamine;
[0044] More preferably, the molar ratio of magnesium to aluminum in the magnesium salt solution and the aluminum salt solution is (2-3):1;
[0045] And / or, the molar ratio of the complexing agent to the total magnesium and aluminum metal ions is (4-9):1.
[0046] In this invention, the solvent used to dissolve magnesium salts, aluminum salts, sulfur salts, and platinum salts may include one or more of ethanol, methanol, isopropanol, acetone, and water. Deionized water is preferred.
[0047] The method for preparing the dehydrogenation catalyst is characterized in that,
[0048] S1: Mix magnesium salt solution, aluminum salt solution and complexing agent to obtain sol solution;
[0049] S2: The sol solution is evaporated at 40-90°C to obtain a gel, and then the gel is dried at 80-100°C to obtain a solid precursor of the dry gel. The precursor powder is obtained by grinding.
[0050] S3: The precursor powder is first calcined in a muffle furnace at 300-400°C, and then calcined a second time in a tube furnace at 450-600°C to obtain a carrier.
[0051] S4: The carrier is immersed in a sulfur salt solution, dried at 40-90°C and 0.007-0.07 MPa, and then calcined at 300-400°C to obtain a sulfur-modified carrier.
[0052] S5: The sulfur-modified carrier is impregnated in a platinum salt solution at 0.007-0.07 MPa, dried at 40-90°C, and then calcined at 300-400°C.
[0053] Preferably, the sulfite includes one or more of ammonium sulfate, ammonium sulfite, ammonium bisulfate, ammonium thiosulfate, and ammonium sulfite. More preferably, it is ammonium sulfate.
[0054] Preferably, the platinum salt comprises one or more of chloroplatinic acid, ammonium chloroplatinate, platinum nitrate, platinum tetrachloride, platinum alkoxide, platinum oxide, platinum acetylacetone, and platinum carbonyl compounds. More preferably, it is chloroplatinic acid.
[0055] Preferably, in step S2, the sol solution is rotary evaporated at 40–90°C at a rotation speed of 30–120 rpm, preferably 60 rpm. The water bath temperature is 40–90°C, preferably 60°C. The gas pressure inside the rotary evaporation flask is 0.007–0.07 MPa, preferably 0.02 MPa.
[0056] Thirdly, the present invention provides the application of a dehydrogenation catalyst in the dehydrogenation of cycloalkanes; preferably, the cycloalkanes are methylcyclohexane.
[0057] Preferably, the dehydrogenation catalyst is pretreated before application. The pretreatment includes reducing the dehydrogenation catalyst in a hydrogen atmosphere at 150–250°C, and then cooling it to 25–30°C. Preferably, the hydrogen flow rate is 2–8 mL / min / gcat.
[0058] In this invention, the freshly prepared dehydrogenation catalyst is in a stable oxidized state before application and needs to be reduced before use.
[0059] The dehydrogenation catalyst, its preparation method, and its application provided by this invention can prepare magnesium-aluminum mixed oxides by introducing an alkali metal magnesium precursor into an alumina precursor. By controlling the calcination temperature, a layered structure similar to hydrotalcite, a spinel-like structure, or a mixed magnesium-aluminum oxide in a near-crystalline transition state can be formed. Combined with surface modification of the support, this helps to improve the ability to regulate the interaction between the metal support, thereby helping to maintain the cluster active centers and effectively control the acidity and alkalinity of the magnesium-aluminum mixed oxide support surface, thereby reducing coking and improving the stability of the catalyst. Attached Figure Description
[0060] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.
[0061] Figure 1 shows the Pt-S / Mg3AlO dehydrogenation catalyst provided in Example 1 of the present invention. 4.5 The preparation flow chart of the carrier.
[0062] Figure 2 shows the dehydrogenation catalyst Pt-S / Mg3AlO provided in Example 1 of this invention. 4.5 The preparation process flow chart.
[0063] Figure 3 shows the Pt-S / Mg3AlO dehydrogenation catalyst provided in Example 1 of this invention. 4.5 Transmission electron microscopy (TEM) images before and after the reaction, where image A represents before the reaction and image B represents after the reaction.
[0064] Figure 4 shows the Pt / Mg3AlO dehydrogenation catalyst provided in Comparative Example 1 of this invention. 4.5 Transmission electron microscopy (TEM) images before and after the reaction, where image A represents before the reaction and image B represents after the reaction.
[0065] Figure 5 shows the Pt-S / Mg3AlO dehydrogenation catalyst provided in Example 1 of this invention. 4.5 X-ray diffraction patterns before and after the reaction.
[0066] Figure 6 shows the Pt / Mg3AlO dehydrogenation catalyst provided in Comparative Example 1 of this invention. 4.5 X-ray diffraction patterns before and after the reaction.
[0067] Figure 7 shows the Pt-S / Mg3AlO dehydrogenation catalyst provided in Example 1 of this invention. 4.5 The dehydrogenation catalyst Pt / Mg3AlO provided in Comparative Example 1 4.5 The oxygen 1s orbital energy level diagram of the X-ray photoelectron spectroscopy (XPS) after the dehydrogenation reaction.
[0068] Figure 8 shows the Pt-S / Mg3AlO dehydrogenation catalyst provided in Example 1 of this invention. 4.5 The dehydrogenation catalyst Pt / Mg3AlO provided in Comparative Example 1 4.5 Comparison of hydrogen programmed temperature reduction.
[0069] Figure 9 shows the Pt-S / Mg3AlO dehydrogenation catalyst provided in Example 1 of this invention. 4.5 The dehydrogenation catalyst Pt / Mg3AlO provided in Comparative Example 1 4.5 The nitrogen isothermal adsorption-desorption curve (left) and pore size distribution diagram (right).
[0070] Figure 10 shows the Pt-S / Mg3AlO dehydrogenation catalyst provided in Example 1 of the present invention. 4.5 The dehydrogenation catalyst Pt / Mg3AlO provided in Comparative Example 1 4.5 Thermogravimetric analysis diagram.
[0071] Figure 11 shows the Pt-S / Mg3AlO dehydrogenation catalyst prepared in Example 1 of this invention. 4.5 A schematic diagram of the temperature pretreatment procedure before the 300-hour long-cycle reaction test.
[0072] Figure 12 shows the Pt-S / Mg3AlO dehydrogenation catalyst prepared in Example 1 of this invention. 4.5 A schematic diagram of the programmed temperature rise reaction for a 300-hour long-cycle reaction test.
[0073] Figure 13 shows the dehydrogenation catalyst Pt-S / Mg3AlO prepared in Example 1. 4.5 The conversion rate was tested over a 300-hour long-cycle reaction period. Detailed Implementation
[0074] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.
[0075] Unless otherwise specified, all raw materials used in the examples and comparative examples are commercially available conventional raw materials, and the technical means used are conventional means well known to those skilled in the art.
[0076] Example 1
[0077] This embodiment provides a dehydrogenation catalyst Pt-S / Mg3AlO 4.5 Its preparation method includes the following steps:
[0078] 1. Preparation of carriers by sol-gel method
[0079] Aluminum nitrate and magnesium nitrate, with a magnesium to aluminum molar ratio of 3:1, were sequentially dissolved in deionized water, stirred, and mixed thoroughly to obtain a mixed nitrate solution. Citric acid, a complexing agent, was added to the mixed solution, with the amount added controlled at a total magnesium and aluminum metal ion to complexing agent molar ratio of 1:4 to prevent metal ion hydrolysis and promote uniform dispersion.
[0080] 2. Sol transforms into gel
[0081] Transfer the sol solution to the evaporation flask of a rotary evaporator. Rotate the flask at 60 rpm, maintain a water bath temperature of 60°C, and keep the pressure inside the flask at 0.02 MPa. The solvent will evaporate gradually, forming uniform bubbles, until a uniform viscous gel is formed. Observe the color change of the solution to stop the rotary evaporation step.
[0082] 3. Drying and precursor preparation
[0083] The gel was transferred to a drying oven and dried at 80°C for 18 hours to remove most of the moisture. The resulting solid precursor of the dry gel was then ground into powder.
[0084] 4. Calcination carrier (two-step calcination):
[0085] 100g of precursor powder was placed in a crucible and then placed in a muffle furnace. Air was continuously pumped into the muffle furnace at a rate of 1L / min. The temperature was increased to 350℃ at a rate of 5℃ / min and held for 4 hours. After natural cooling to room temperature, magnesium-aluminum composite oxide was obtained and taken out for use. It was then placed in a tube furnace and calcined at 500℃ for 8 hours. After taking it out, the carrier was obtained (the preparation process is shown in Figure 1).
[0086] 5. Ammonium sulfate for carrier surface modification
[0087] A certain amount of carrier was placed in the evaporation flask of a rotary evaporator; 0.06 g / mL of ammonium sulfate aqueous solution was added dropwise onto the carrier using a burette according to a sulfur element content of 0.5% wt; after adding deionized water, the carrier was placed in the evaporation flask of the rotary evaporator to completely evaporate the solvent; the above powder was calcined in a tube furnace with an air flow rate of 1 L / min at 350 °C for 2 hours; after natural cooling, ammonium sulfate modified carrier was obtained.
[0088] 6. Platinum active component impregnation:
[0089] The sulfur-modified support was placed in an evaporation flask of a rotary evaporator. A 0.01 g / mL aqueous solution of chloroplatinic acid was added dropwise through a burette to achieve a platinum mass fraction of 0.3% wt. The solution was then evaporated to dryness at 60 °C and 0.02 MPa. The platinum-impregnated support was then transferred to a tube furnace and calcined at 350 °C for 4 h to obtain Pt-S / Mg3AlO4. 4.5 Catalyst (preparation process is shown in Figure 2).
[0090] In this invention, when the molar ratio of magnesium to aluminum in the support is 2:1, 2.5:1, and δ is any value other than 4.5 from 4 to 6, the effect of the prepared dehydrogenation catalyst is comparable to that of Example 1. Furthermore, when the temperatures during the first and second calcinations are within the ranges defined in this invention, the effect is comparable to that of Example 1. This is because, within the aforementioned ranges, a support with a synergistic structure possessing a layered hydrotalcite structure, a spinel structure, and a transitional mixed-state structure in a near-crystalline state can be obtained. Due to space limitations, further details are omitted.
[0091] Comparative Example 1
[0092] This comparative example provides a dehydrogenation catalyst Pt / Mg3AlO 4.5 The only difference between its preparation method and that of Example 1 is that it does not contain step 5, that is, it does not involve impregnation with a sulfur source.
[0093] Comparative Example 2
[0094] This comparative example provides a dehydrogenation catalyst Pt-S / Mg3AlO 4.5 The preparation method differs from that in Example 1 only in that the catalyst support is commercially available hydrotalcite, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. (CAS No.: 11097-59-9; Molecular Formula: Mg6Al2(CO3)(OH)16·4H2O; Molecular Weight: 603.98; MDL No.: MFCD01746913; PubChem No.: 159347; PubChem SID: 488188287), wherein the molar ratio of magnesium to aluminum is 3:1.
[0095] Comparative Example 3
[0096] This comparative example provides a dehydrogenation catalyst S-Pt / Mg3AlO 4.5 The only difference between its preparation method and that of Example 1 is that platinum salt is impregnated first, followed by sulfur salt impregnation.
[0097] Comparative Example 4
[0098] This comparative example provides a dehydrogenation catalyst Pt-S / Mg3AlO 4.5The preparation method differs from that in Example 1 only in that the support is prepared by co-precipitation, and the specific preparation method includes the following steps:
[0099] 1. Prepare chloroplatinic acid solution:
[0100] 1) Dissolve chloroplatinic acid in a beaker by adding a small amount of deionized water;
[0101] 2) Use a dropper to transfer the solution from the beaker into a 100 ml brown volumetric flask;
[0102] 3) Continue adding deionized water to bring the volume to 100 ml to prepare a chloroplatinic acid aqueous solution;
[0103] 4) Place in the refrigerator and keep away from light for later use.
[0104] 2. Preparation of ammonium sulfate solution:
[0105] 1) Place ammonium sulfate in a beaker and add a small amount of deionized water to dissolve it;
[0106] 2) Use a dropper to transfer the solution from the beaker into a 100 ml brown volumetric flask;
[0107] 3) Continue adding deionized water to bring the volume to 100 ml, and prepare an ammonium sulfate aqueous solution;
[0108] 4) Place in the refrigerator and keep chilled for later use.
[0109] 3. Preparation of carriers by coprecipitation method:
[0110] 1)Mg 2+ / A1 3+ The molar ratio is 3:1. Weigh 3.84g of Mg(NO)2·6H2O, 1.88g of Al(NO)3·9H2O, and 1.53mL of chloroplatinic acid acetone solution (concentration 0.01g / mL) and add them to 40mL of deionized water to obtain salt solution A.
[0111] 2) Weigh 2.4g NaOH and 0.4g Na2CO3 and dissolve them in 50mL of water to obtain alkaline solution B.
[0112] 3) Add solutions A and B dropwise into a three-necked flask while stirring, and control the pH of the suspension to around 9.8.
[0113] 4) After the addition of solution A is complete, continue stirring the reaction at a pH of approximately 9.8 for 2 hours. Place the resulting suspension in a hydrothermal reactor and age it at 95°C for 10 hours.
[0114] 5) After aging, cool to room temperature and perform vacuum filtration. During the filtration process, wash with water and alcohol three times each. Dry the filter cake obtained by vacuum filtration at 60°C to obtain magnesium aluminum hydrotalcite.
[0115] 6) Calcined magnesium aluminum hydrotalcite:
[0116] (1) Take the synthetic hydrotalcite powder into a crucible and place it in a muffle furnace;
[0117] (2) Calcination in a muffle furnace for 4 hours, with the temperature increased to 350°C at 5°C / min;
[0118] (3) After being transferred to a tube furnace, the temperature is increased to 500°C at 5°C / min and calcined for 8 hours.
[0119] (4) After natural cooling to room temperature, magnesium-aluminum composite oxide is obtained.
[0120] 4. Impregnation of carrier surface active components
[0121] 1) Add the above carrier to the eggplant-shaped flask;
[0122] 2) Take ammonium sulfate solution, mix it thoroughly with deionized water, and draw it into a burette;
[0123] 3) Continuously shake the flask while slowly dripping the liquid from the burette into the flask to mix with the carrier, and continue adding deionized water;
[0124] 4) Place the solution in a flask in a rotary evaporator and run for 30 minutes until all the solution has evaporated, then place it in a vacuum drying oven to dry for 2 hours;
[0125] 5) The catalyst was transferred to a muffle furnace and calcined at 350°C for 2 hours at a programmed heating rate of 5°C / min to obtain a modified catalyst with a surface sulfur mass fraction of 0.5%wt.
[0126] 6) Impregnate with chloroplatinic acid aqueous solution in the same manner as above;
[0127] 7) Transfer the catalyst to a muffle furnace in the same manner as above and calcine it at a programmed temperature of 5℃ / min to 350℃ for 4 hours to obtain a platinum-sulfur surface-modified magnesium-aluminum mixed oxide catalyst impregnated with platinum.
[0128] Comparative Example 5
[0129] This comparative example provides a dehydrogenation catalyst Pt / Mg3AlO 4.5The preparation method differs from that in Example 1 in that: the catalyst support is commercially available hydrotalcite as a reference, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. (CAS No.: 11097-59-9; Molecular Formula: Mg6Al2(CO3)(OH)16·4H2O; Molecular Weight: 603.98; MDL No.: MFCD01746913; PubChem No.: 159347; PubChem SID: 488188287), wherein the molar ratio of magnesium to aluminum is 3:1; and step 5 is not included, i.e., the impregnation of the sulfur source is not performed.
[0130] Comparative Example 6
[0131] This comparative example provides a dehydrogenation catalyst Pt / Mg3AlO 4.5 The difference between its preparation method and that of Example 1 is that the carrier is prepared by coprecipitation (the same method as Comparative Example 4), and it does not contain step 5, that is, it does not impregnate with a sulfur source.
[0132] Test case
[0133] 1. Characterization and testing of catalysts:
[0134] The calcined catalyst can be characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and other methods to determine its structure and the dispersion of platinum particles.
[0135] Figure 3 shows the Pt-S / Mg3AlO dehydrogenation catalyst prepared in Example 1 of this invention. 4.5 The images are scanning transmission electron microscopy (STEM) images, where image A represents the 2 nm image before the reaction, and image B represents the 2 nm image after the reaction. The STEM images show that the Pt nanoparticles are in a clustered state both before and after the reaction.
[0136] Figure 4 shows the dehydrogenation catalyst Pt / Mg3AlO prepared in Comparative Example 1. 4.5 The images are scanning transmission electron microscopy (STEM) images, where image A represents the 2 nm image before the reaction, and image B represents the 2 nm image after the reaction. The STEM images show that the Pt nanoparticles are in a clustered state both before and after the reaction.
[0137] Figure 4 shows that after the reaction, the Pt clusters significantly decreased in size and migrated into the support, while the Pt clusters loaded on the S-modified support surface in Figure 3 maintained their size and relative position to the support surface. The modification of the support surface with trace amounts of sulfur enhanced the interaction between the active metal clusters and the modified support, anchoring Pt to the surface.
[0138] The results show that S-modified catalysts anchored active Pt clusters on the support surface, while the active Pt in the unmodified catalyst exhibited migration of Pt particles into the support crystal during the reaction. This behavior can be attributed to weak metal-support interactions, where Pt cluster atoms gradually migrate into the inner layers of the support in an atmosphere of continuously generated hydrogen gas.
[0139] Figure 5 shows the Pt-S / Mg3AlO dehydrogenation catalyst prepared in Example 1 of this invention. 4.5 The X-ray diffraction (XRD) pattern shows a decrease in the characteristic peaks of MgO and the characteristic signals of magnesium-aluminum mixed oxides (hydrotalcite, spinel), indicating that Mg3AlO 4.5 The sulfur (S) substance impregnated on the surface of the support significantly altered the surface structure of the freshly prepared catalyst.
[0140] Figure 6 shows the Pt / Mg3AlO dehydrogenation catalyst prepared in Comparative Example 1 of this invention. 4.5 The XRD crystallographic pattern of the catalyst clearly shows the crystal signal of MgO, indicating a higher enrichment of magnesium oxide on its surface. Combined with the chemical reaction conversion rates of Example 1 and Comparative Example 1, this confirms the positive effect of sulfur addition on anchoring and stabilizing Pt clusters on the surface of the magnesium-aluminum mixed oxide, and demonstrates that the migration of Pt clusters into the support during dehydrogenation reduces the dehydrogenation efficiency of methylcyclohexane. Therefore, modifying the support surface with sulfur-containing additives helps anchor Pt clusters to maintain a suitable micro-nano state, and indicates that the Pt clusters on the magnesium-aluminum mixed oxide support are 0.2-0.5 nm in size.
[0141] Figure 7 shows the oxygen 1s orbital energy level diagram (O1s orbital) of Pt / Mg3AlO after dehydrogenation reaction under the same conditions. 4.5 (Above) and Pt-S / Mg3AlO modified support with sulfur (S) 4.5 Comparing the two images below, the XPS O1s energy curve of the catalyst without S surface modification shifts to a lower binding energy, indicating the generation of more lattice oxygen. This suggests that the formation of lattice oxygen on the support surface causes atoms of the active Pt noble metal clusters to gradually migrate into the lattice, thereby covering the active sites of Pt. This results in excessively strong metal-support interactions, limiting the performance of the Pt active sites in the surface-catalyzed dehydrogenation of methylcyclohexane. In summary, the doping of S on the support surface alters the crystal structure of the MgO and magnesium-aluminum mixed oxides on the surface, while anchoring the Pt clusters through appropriate metal-support interactions, maintaining excellent stability and catalytic activity.
[0142] Figure 8 shows the results of the hydrogen temperature-programmed reduction (H2-TPR) experiment using the catalysts of Example 1 and Comparative Example 1. This experiment reflects the degree of interaction between the catalyst surface metal and the support, and the reduction properties during the heating process. As can be seen from Figure 8, the first reduction peak of the S-modified mixed oxide on the support surface clearly tends towards the region below 300°C, and it occupies the largest peak area in the overall reduction temperature range. This indicates that the interaction between the S-doped catalyst and the Pt clusters on the support surface maintains the active centers and significantly migrates to lower temperature ranges, providing strong evidence for the beneficial activity and stability of the methylcyclohexane dehydrogenation reaction. In contrast, the main reduction peak of the undoped S magnesium-aluminum mixed oxide catalyst is located in the temperature range above 400°C, indicating weak activity of its Pt active metal clusters. Combined with the example in Figure 7 (XPS) of the sulfur-free S catalyst having more surface lattice oxygen, this shows that the reduced lattice oxygen after S doping promotes the catalytic activity and stability of the Pt clusters.
[0143] Figure 9 shows the nitrogen isothermal adsorption-desorption curve (left) and pore size distribution curve (right) of the catalyst described in Example 1 of this invention. The principle of gas adsorption for determining specific surface area is based on the adsorption characteristics of gases on solid surfaces. Under a certain pressure, the surface of the sample particles (adsorbent) exhibits reversible physical adsorption of gas molecules (adsorbate) at ultra-low temperatures, and a definite equilibrium adsorption amount exists corresponding to a certain pressure. By measuring this equilibrium adsorption amount, the specific surface area of the sample is equivalently calculated using a theoretical model. In the left figure, the nitrogen adsorption and desorption curves basically overlap. The curve is concave because the interaction between adsorbate molecules is stronger than that between the adsorbate and the adsorbent. The heat of adsorption in the first layer is smaller than the heat of liquefaction of the adsorbate, making it difficult for the adsorbate to adsorb in the initial stage. However, as the adsorption process proceeds, a self-accelerating phenomenon occurs, and the number of adsorption layers is not limited. This phenomenon lies between the adsorption-desorption curves of layered hydrotalcite and spinel. Combined with the examples in the references (https: / / doi.org / 10.1016 / j.ceja.2022.100437. and https: / / doi.org / 10.1016 / j.jiec.2022.08.006), it can be seen that the microstructure of Example 1 is in a state of coexistence of two mixed metal oxides, and is mainly in a mesoporous state.
[0144] Figure 10 shows the thermogravimetric analysis (TGA) diagrams of the catalysts prepared by the sol-gel / impregnation method in Example 1 and Comparative Example 1 of this invention. By combining the TGA curves (TG) with the difference thermogravimetry (DTG) curves of the two catalysts in Figure 10, it can be found that the addition of sulfur generally increases the gravimetric decomposition temperature of the catalyst, effectively enhancing its high-temperature resistance.
[0145] 2. The dehydrogenation reaction of the dehydrogenation catalysts in the examples and comparative examples was tested, specifically including the following steps:
[0146] First, the dehydrogenation catalysts in the examples and comparative examples were subjected to reduction pretreatment:
[0147] The catalyst was loaded into a fixed-bed reactor and hydrogen was introduced at a flow rate of 5 mL / min / gcat. The temperature was raised from room temperature to 150°C at a rate of 5°C / min and held for 2 hours. Then the temperature was raised to the reaction temperature of 250°C at a rate of 5°C / min and held for 2 hours.
[0148] The pretreated catalyst is then subjected to a dehydrogenation reaction, which includes the following steps:
[0149] When loading the catalyst, in order to prevent the catalyst from being carried into the pipeline by the gas during the reaction, an appropriate amount of quartz wool needs to be added to the bottom of the fixed bed reactor. Tighten the nut at one end, add the prepared catalyst to the tubular reactor in sequence using a funnel, and add a small amount of quartz wool on the top layer of the catalyst. Tighten the nut at the end with the thermocouple, and then install the reactor on the device.
[0150] Add the catalyst to the reaction tube, seal it, and check for airtightness. Open the hydrogen cylinder and valve to adjust the hydrogen flow rate. Use soapy water to check for leaks. After confirming that there are no leaks, adjust the valve to allow hydrogen to escape at a rate of one to two bubbles per second. After stabilization, as shown in Figure 11, set the heating program to heat the catalyst to 200°C at a heating rate of 5°C / min. Hold the temperature at 200°C for 120 minutes, and then raise it to 375°C at a rate of 5°C / min. Hold this temperature for 120 minutes. With hydrogen gas introduced, allow the temperature to cool naturally to room temperature to obtain the catalyst after hydrogen pretreatment.
[0151] Close the hydrogen cylinder and gas pipeline, purge the remaining hydrogen from the pipeline, and purge with nitrogen as a protective gas. Once all the hydrogen has been purged, stop the nitrogen flow. As shown in Figure 12, set the heating program to heat the catalyst to 350°C at a rate of 5°C / min. Turn on the heating switches for the preheater and vaporization chamber, and set the temperature to 150°C. Then, turn on the micro-flow pump (time set to infinite) at a rate of 0.1 mL / min (space velocity: 0.445 h⁻¹). -1 Methylcyclohexane is fed into the unit at a feed rate of [missing information], where a heterogeneous gas-solid catalytic reaction occurs on a solid catalyst. Hydrogen produced by the catalyst is used to pressurize the catalyst to 0.25 MPa before sampling begins.
[0152] Finally, the collected products were analyzed using an Agilent 7890A gas chromatograph, and the quantification method was the internal standard method (decane was used as the internal standard). The following formula is used to calculate the conversion rate of methylcyclohexane (MCH), the selectivity of toluene, and the hydrogen release rate of the reaction.
[0153] In the formula:
[0154] u is the feed rate of MCH, mL / min;
[0155] ρ is the density of MCH, in g / mL;
[0156] C represents the conversion rate of MCH, in %.
[0157] m represents the amount of catalyst used, in grams;
[0158] M is the molar mass of MCH, in g / mol;
[0159] ω represents the content of the active component Pt, in percentages.
[0160] The conversion results of the dehydrogenation catalysts prepared in the examples and comparative examples after a 300-hour long-cycle reaction test are shown in Table 1.
[0161] Table 1
[0162] Figure 13 shows the conversion rate of the dehydrogenation catalyst prepared in Example 1 over a 300-hour long-cycle reaction test. Figure 13 shows the reaction process over a 300-hour long-cycle process at a conversion temperature of 350°C after heating to reach the steady-state temperature of the reaction (average conversion rate of 95.7%).
[0163] A comparison of Example 1 with Comparative Examples 1-6 demonstrates that the sol-gel method for preparing magnesium-aluminum mixed oxide supports, followed by sulfur doping and platinum impregnation, is beneficial for achieving high MCH dehydrogenation conversion rates. This is because sulfur modification of the magnesium-aluminum mixed oxide support surface enhances the metal-support interaction anchored to Pt clusters, and the alkaline support surface enhances resistance to carbon deposition. In summary, the addition of sulfur enhances the interaction between platinum and the support, inhibiting the migration of trace Pt clusters into the support lattice. Furthermore, for catalysts without sulfur impregnation, the method of preparing the support via sol-gel method followed by impregnation is significantly superior to catalysts using commercially available hydrotalcite and co-precipitation methods under the same formulation.
[0164] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention. Industrial applicability
[0165] This invention provides a dehydrogenation catalyst precursor, a dehydrogenation catalyst, its preparation method, and its application. The dehydrogenation catalyst precursor uses a sulfur-modified magnesium-aluminum mixed oxide as a support and Pt metal clusters as active centers; wherein the support is a mixed metal oxide with a layered hydrotalcite structure, a spinel structure, and a near-crystalline synergistic structure. This invention can prepare magnesium-aluminum mixed oxides by introducing an alkali metal magnesium precursor into an alumina precursor. By controlling the calcination temperature, a layered structure or a spinel structure similar to hydrotalcite can be formed. Combined with surface modification of the support, this helps to improve the ability to regulate the interaction between the metal and the support, thereby helping to maintain the active centers of the Pt clusters and effectively modulating the acidity and basicity of the support surface, thus reducing coking and improving the activity and stability of the catalyst, exhibiting good economic value and application prospects.
Claims
1. A dehydrogenation catalyst, characterized in that, The dehydrogenation catalyst uses sulfur-modified magnesium-aluminum mixed oxide as a support and Pt metal clusters as active centers; wherein, the support is a mixed metal oxide with a layered hydrotalcite structure, a spinel structure and a near-crystalline synergistic structure.
2. The dehydrogenation catalyst according to claim 1, characterized in that, The Pt metal clusters have a particle size of 0.2–0.5 nm.
3. The dehydrogenation catalyst according to claim 1 or 2, characterized in that, The dehydrogenation catalyst is made of sulfur-modified Mg. x Al y O δ The carrier is x>y, where δ represents any value from 4 to 6; preferably, x:y = (2 to 3):
1.
4. The dehydrogenation catalyst according to any one of claims 1 to 3, characterized in that, The surface area of the carrier is 100m² 2 / g or more, pore volume of 0.50cm 3 / g or more, with a pore size of 5nm or more.
5. The dehydrogenation catalyst according to any one of claims 1 to 4, characterized in that, Based on the mass of the dehydrogenation catalyst, the content of the platinum metal clusters is 0.1 wt% to 0.8 wt%.
6. The method for preparing the dehydrogenation catalyst according to any one of claims 1 to 5, characterized in that, include: S1: Mix magnesium salt solution, aluminum salt solution and complexing agent to obtain sol solution; the molar ratio of magnesium to aluminum is (2-3):1; S2: The sol solution is heated under reduced pressure in a rotary evaporator to obtain a gel, and then the gel is dried to obtain a solid precursor of the dry gel. The precursor powder is obtained by grinding. S3: The precursor powder is first calcined in a muffle furnace at 300-400°C, and then calcined a second time in a tube furnace at 450-600°C to obtain the carrier. S4: The carrier is loaded with sulfur source and Pt clusters sequentially by impregnation.
7. The method for preparing the dehydrogenation catalyst according to claim 5, characterized in that, The magnesium salt includes one or more of magnesium acetate, magnesium nitrate and magnesium chloride; And / or, the aluminum salt solution includes one or more of aluminum acetate, aluminum chloride, and aluminum nitrate; And / or, the complexing agent includes one or more of EDTA, citric acid, sodium citrate, ammonium citrate, maleic acid, glycine, ethanolamine, diethanolamine and triethanolamine; Preferably, the molar ratio of magnesium and aluminum ions to the complexing agent is 1:(4-9).
8. The method for preparing the dehydrogenation catalyst according to claim 6, characterized in that, S1: Mix magnesium salt solution, aluminum salt solution and complexing agent to obtain sol solution; the molar ratio of magnesium to aluminum is (2-3):1; S2: The sol solution is rotary evaporated at 40-90°C to obtain a gel, and then the gel is dried at 80-100°C to obtain a solid precursor of the dry gel. The precursor powder is obtained by grinding. S3: The precursor powder is first calcined in a muffle furnace at 300-400°C, and then calcined a second time in a tube furnace at 450-600°C to obtain a carrier. S4: The carrier is impregnated in a sulfur salt solution and gently impregnated in a rotary evaporator at 0.007-0.07 MPa and 40-90°C by reducing the pressure inside the flask to control the boiling degree. Then, it is calcined at 300-400°C to obtain a sulfur-modified carrier. S5: The sulfur-modified carrier is impregnated in a platinum salt solution and gently impregnated in a rotary evaporator at 0.007-0.07 MPa and 40-90°C by reducing the pressure inside the flask to control the boiling degree, and then calcined at 300-400°C. Preferably, the sulfite includes one or more of ammonium sulfate, ammonium sulfite, ammonium bisulfate, ammonium thiosulfate, and ammonium sulfite; Preferably, the platinum salt includes one or more of chloroplatinic acid, ammonium chloroplatinate, platinum nitrate, platinum tetrachloride, platinum alkoxide, platinum oxide, platinum acetylacetone, and platinum carbonyl compounds.
9. The application of the dehydrogenation catalyst according to any one of claims 1 to 4 or the dehydrogenation catalyst prepared by the preparation method according to any one of claims 5 to 8 in the dehydrogenation of cycloalkanes; preferably, the cycloalkanes are methylcyclohexane.
10. The application of the dehydrogenation catalyst according to claim 9 in the dehydrogenation of cycloalkanes, characterized in that, The dehydrogenation catalyst is pretreated before application. The pretreatment includes reducing the dehydrogenation catalyst in a hydrogen atmosphere at 150-250°C, and then cooling it to 25-30°C. Preferably, the hydrogen flow rate is 2–8 mL / min / gcat.