Monolithic joule heat catalysts, methods of making and using the same
An improved in-situ crystallization method was used to prepare a monolithic Joule thermal catalyst in which silicon carbide substrate and active components are tightly bonded, which solved the problem of catalyst exfoliation at high temperature and achieved a monolithic catalyst with high stability and conductivity.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- BEIJING UNIV OF CHEM TECH
- Filing Date
- 2025-12-10
- Publication Date
- 2026-06-12
AI Technical Summary
Existing monolithic catalysts have poor resistance to spalling under high temperature conditions, leading to the spalling and loss of active components, which affects the stability and safety of the catalyst.
An improved in-situ crystallization method was adopted to prepare an integral Joule thermal catalyst in which the silicon carbide substrate and active components are tightly bonded by controlling the molar ratio of organic template agent and silicon source to below 0.5:1, combined with hydrothermal crystallization and calcination treatment.
The catalyst's resistance to spalling and conductivity have been improved, ensuring high stability and electrothermal performance in the dry reforming of methane.
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Figure CN122183684A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of catalyst technology, specifically to a monolithic Joule thermal catalyst, its preparation method, and its application. Background Technology
[0002] Electrothermal reactors directly heat the catalyst bed through Joule heating by applying electricity to it, demonstrating excellent in-situ energy supply in strongly endothermic reactions such as propane dehydrogenation and methane reforming. To achieve this electrification, a monolithic catalyst with a continuous microstructure and suitable electrical conductivity is required. Typically, electrothermal monolithic catalysts consist of a conductive substrate, binder, and active components physically bonded together. Under the high-temperature conditions (above 600°C) of strongly endothermic reactions, the difference in thermal expansion and contraction between the components leads to the shedding and loss of active components. This results in reduced catalyst activity and, more importantly, the shed powder can clog reactor pipes, causing pressure increases and potential explosion hazards. Therefore, preparing monolithic catalysts with strong resistance to shedding at high temperatures is crucial for the operational efficiency and safety of electrothermal reactors.
[0003] The preparation methods of monolithic catalysts are as follows: (1) Rolling coating method: The rolling coating method uses active components and binders to form a slurry. First, the catalyst substrate is added into a rotating disc container at one time. Then, the coating raw material powder and additives are added periodically at a certain rate. Under the action of the additives and the rotation force of the disc container, the coating is gradually formed on the surface of the substrate. It is often used for the preparation of spherical coated catalysts. (2) Spin coating method: The spin coating method is an improvement of the coating method. The active components and binders are mixed to form a uniform and stable liquid slurry. A suitable substrate is selected and placed on the suction plate of the spin coater. The spin coater is started to make the substrate rotate at a certain speed. As the rotation speed increases, the slurry is uniformly coated on the substrate under the action of centrifugal force, which can improve the surface uniformity. (3) Direct molding method: The direct molding method mixes the active components and binders and then granulates them to obtain spherical compound particle samples of the precursor mixture. Then, high-temperature calcination is carried out to obtain the required catalyst particles. The active components and binders are directly pressed into monolithic catalysts, which are not affected by the adhesion of the substrate. (4) In-situ crystallization method: The original crystallization method loads the required seed crystals on the substrate to form an integral substrate, places it in molecular sieve crystallization slurry, and uses the surface of the substrate as the crystal nucleus for molecular sieve growth. The integral catalyst with the active component and the catalyst substrate is obtained by hydrothermal synthesis.
[0004] However, in the roll coating method, the liquid drips during the coating and drying process, resulting in uneven distribution of the active component on the catalyst. Furthermore, limited by the slurry composition and the grain size of the active component, the coating method cannot support active components with larger grains or poor substrate compatibility. While spin coating can improve surface uniformity compared to roll coating, for porous substrates (such as foamed silicon carbide), the sprayed slurry cannot diffuse into the interior, leading to significant differences in coating amount between the inner and outer layers of the catalyst. Direct molding, which involves directly extruding the catalyst active component and binder, lacks a monolithic substrate, resulting in inconsistent catalyst mechanical strength. At high temperatures, it is prone to thermal expansion and contraction, cracking, loss of conductivity, and catalyst loss. Conventional in-situ crystallization methods require strongly alkaline crystallization conditions to cause the silicon carbide substrate to dissolve and lose conductivity. Summary of the Invention
[0005] The purpose of this invention is to overcome the problems of poor stability and weak anti-stripping properties of monolithic catalysts in the prior art, and to provide a monolithic Joule thermal catalyst, its preparation method and application. This monolithic Joule thermal catalyst has the characteristics of good anti-stripping performance, good reaction activity and stability.
[0006] To achieve the above objectives, a first aspect of the present invention provides an integral Joule thermal catalyst, the catalyst comprising a silicon carbide substrate and an active component supported on the silicon carbide substrate; the active component comprising a molecular sieve and a metal component; the metal component being at least one of transition metals; and the molecular sieve being at least one of MFI type molecular sieves, CHA type molecular sieves, MOR type molecular sieves, MEL type molecular sieves, and BEA type molecular sieves. The ultrasonic exfoliation rate of the catalyst is not higher than 10 wt%.
[0007] Preferably, the resistivity of the catalyst is not higher than 1 Ω·m.
[0008] A second aspect of the present invention provides a method for preparing a monolithic Joule thermal catalyst, the method comprising: (1) Prepare a crystallization solution containing a silicon source, a transition metal source, an organic template agent and water; The molar ratio of the organic template agent to the silicon source (calculated as SiO2) is no higher than 0.5:1. (2) The crystallization solution is mixed with the silicon carbide substrate and subjected to hydrothermal crystallization at less than 200°C for 1-324 hours to obtain the intermediate product catalyst; (3) The intermediate catalyst is calcined in an oxygen-containing atmosphere.
[0009] The third aspect of the present invention provides a monolithic Joule thermal catalyst prepared by the method described in the second aspect above.
[0010] The third aspect of the present invention provides the application of the above-described monolithic Joule thermal catalyst in the dry reforming reaction of methane, preferably in the application of the electrothermal dry reforming reaction of methane.
[0011] The monolithic Joule thermal catalyst provided by this invention has strong resistance to exfoliation. The active components are uniformly composited on a silicon carbide substrate, exhibiting excellent electrical conductivity and electrothermal properties, and demonstrating high stability in the dry reforming reaction of methane.
[0012] This invention improves the in-situ crystallization method to prepare monolithic catalysts with high resistance to spalling, thus solving the problem of active component spalling due to thermal expansion and contraction at high temperatures in monolithic catalysts. Simultaneously, it optimizes the in-situ crystallization conditions to avoid silicon dissolution of silicon carbide during molecular sieve crystallization, preserving the conductivity and electrothermal properties of the monolithic catalyst. Attached Figure Description
[0013] Figure 1 This is a photograph of the monolithic catalyst prepared in Example 1; Figure 2 This is a SEM image of the monolithic catalyst prepared in Example 1; Figure 3 These are the XRD patterns of the monolithic catalysts prepared in Examples 1, 2, and 3; Figure 4 This is the XRD pattern of the monolithic catalyst prepared in Example 6.
[0014] Figure 5 This is a comparison chart of the methane conversion rates of the catalysts in Examples 1-3 and Comparative Examples 1-3 during the electrothermal dry reforming reaction test; Figure 6 This is a comparison chart of the carbon dioxide conversion rates of the catalysts in Examples 1-3 and Comparative Examples 1-3 during the electrothermal dry reforming reaction test of methane; Figure 7 The results show the stability of the monolithic catalyst prepared in Example 1 during the dry reforming of methane under high space velocity conditions. Detailed Implementation
[0015] The endpoints and any values of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of the various ranges, the endpoint values of the various ranges and individual point values, and individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.
[0016] The first aspect of the present invention provides an integral Joule thermal catalyst, the catalyst comprising a silicon carbide substrate and an active component supported on the silicon carbide substrate; the active component comprises a molecular sieve and a metal component; the metal component is at least one of transition metals; the molecular sieve is at least one of MFI type molecular sieve, CHA type molecular sieve, MOR type molecular sieve, MEL type molecular sieve and BEA type molecular sieve. The ultrasonic exfoliation rate of the catalyst is not higher than 10 wt%.
[0017] In this invention, "ultrasonic ablation rate" refers to the proportion of catalyst mass lost after ultrasonic treatment, reflecting the strength of the bonding force between the silicon carbide substrate and the active component. If the bonding force between the silicon carbide substrate and the active component is weak, the active component will peel off from the silicon carbide substrate and be lost after ultrasonic treatment. A higher ultrasonic ablation rate indicates a weaker bonding force between the silicon carbide substrate and the active component, while a lower ultrasonic ablation rate indicates a stronger bonding force.
[0018] The "ultrasonic peeling rate" is measured and calculated according to the following method: The mass of the catalyst before peeling is recorded as m1. The catalyst is placed in a beaker and ethanol is added to cover it (the volume ratio of catalyst to ethanol is 1:50). The catalyst is ultrasonically vibrated for 15 minutes in an ultrasonic cleaner at a frequency of 40kHz. Then the catalyst is removed and dried in an oven at 100℃ for 12 hours. The mass of the catalyst after peeling is then measured as m2.
[0019] Ultrasonic peeling rate (%) = (m1-m2) / m1*100%.
[0020] The monolithic Joule thermal catalyst provided by this invention has strong resistance to exfoliation, and the ultrasonic exfoliation rate of the catalyst is no higher than 10 wt%. The active components are uniformly composited on a silicon carbide substrate, exhibiting excellent electrical and electrothermal properties, and demonstrating high stability in the dry reforming reaction of methane.
[0021] Preferably, the ultrasonic exfoliation rate of the catalyst is not higher than 5 wt%, more preferably 0.1-3 wt%, and more preferably 0.1-1 wt%.
[0022] According to the present invention, preferably, the catalyst has both suitable conductivity and binding force, preferably, the resistivity of the catalyst is not higher than 1 Ω·m, and more preferably 0.002-0.5 Ω·m.
[0023] In this invention, the method for measuring the resistivity of the catalyst includes: accurately determining the resistance value using the constant current method. First, the catalyst is loaded into the reactor, a stable current of 0.1A is set, and the voltage drop across the catalyst is precisely measured using an electricity meter. Finally, the resistance value is calculated based on Ohm's law.
[0024] The catalyst of this invention comprises a silicon carbide substrate and an active component supported on the silicon carbide substrate; the active component includes a molecular sieve and a metal component. The composition of the catalyst can be confirmed by X-ray diffraction analysis.
[0025] According to some preferred embodiments of the present invention, in the catalyst, the weight ratio of the molecular sieve content (based on SiO2) to the metal component (based on elemental composition) is (5-1000):1, preferably (20-200):1. For example, it can be a weight ratio of 20:1, 30:1, 40:1, 50:1, 80:1, 90:1, 100:1, 120:1, 150:1, 200:1, or any range between the two. In the above preferred embodiments, it is beneficial to create an ordered and uniform pore structure and ensure that the transition metal is efficiently embedded in the framework.
[0026] Preferably, in the catalyst, the weight ratio of the active component to the silicon carbide substrate is (0.01-0.35):1, more preferably (0.045-0.25):1.
[0027] In this invention, the range of metal components is relatively wide. In order to further improve the conversion rate of the catalyst in the dry reforming reaction of methane, preferably, the metal component is selected from at least one of Ni, Ru, Pd, Rh, Pt, Ir, Au, Ag, Fe and Co, and more preferably Ni.
[0028] According to the present invention, the molecular sieve is selected from at least one of MFI-type molecular sieves, CHA-type molecular sieves, MOR-type molecular sieves, MEL-type molecular sieves, and BEA-type molecular sieves; preferably, the molecular sieve is an MFI-type molecular sieve. The structure of the molecular sieve in the catalyst can be determined by X-ray diffraction analysis.
[0029] According to the present invention, preferably, the silicon carbide substrate is foamed silicon carbide.
[0030] A second aspect of the present invention provides a method for preparing a monolithic Joule thermal catalyst, the method comprising: (1) Prepare a crystallization solution containing a silicon source, a transition metal source, an organic template agent and water; The molar ratio of the organic template agent to the silicon source (calculated as SiO2) is no higher than 0.5:1. (2) The crystallization solution is mixed with the silicon carbide substrate and subjected to hydrothermal crystallization at less than 200°C for 1-324 hours to obtain the intermediate product catalyst; (3) The intermediate catalyst is calcined in an oxygen-containing atmosphere.
[0031] Existing in-situ crystallization methods typically require strongly alkaline crystallization conditions. Silicon carbide substrates are prone to silica dissolution, leading to poor conductivity and electrothermal properties of the catalyst, which is detrimental to the catalytic activity and stability of the electrothermal methane dry reforming reaction. This invention improves the in-situ crystallization method by optimizing the crystallization conditions and controlling the molar ratio of organic template agent to silicon source (based on SiO2) to no more than 0.5:1. Through the synergistic effect of the organic template agent and the crystallization conditions, silica dissolution of silicon carbide during molecular sieve crystallization can be effectively avoided, resulting in a monolithic catalyst with excellent conductivity and electrothermal properties. Simultaneously, it solves the problem of active component detachment due to thermal expansion and contraction at high temperatures in monolithic catalysts.
[0032] According to some preferred embodiments of the present invention, in the crystallization mixture of step (1), the molar ratio of the transition metal source (calculated as metal element) to the silicon source (calculated as SiO2) is 1:(5-1000), preferably 1:(20-200), for example, it can be any molar ratio or a range between the two such as 1:20, 1:30, 1:40, 1:50, 1:80, 1:90, 1:100, 1:120, 1:150, 1:200, etc.
[0033] Preferably, in the crystallization solution of step (1), the molar ratio of organic template agent to silicon source (calculated as SiO2) is (0.01-0.5):1, and more preferably (0.1-0.45):1.
[0034] The present invention does not have any particular limitation on the type of silicon source mentioned in step (1). Silicon sources commonly used in the field for molecular sieve synthesis can be used, such as organosilicone esters or silica sols. Preferably, the silicon source is an organosilicone ester, preferably tetraethyl orthosilicate.
[0035] In this invention, the range of selection for the transition metal source is relatively wide. In order to further improve the conversion rate of the catalyst in the dry reforming reaction of methane, preferably, the metal in the transition metal source is at least one of Ni, Ru, Pd, Rh, Pt, Ir, Au, Ag, Fe and Co, and more preferably Ni.
[0036] In this invention, the transition metal source can be selected from any soluble compound capable of providing a transition metal; there is no particular limitation in this regard. Preferably, the transition metal source is a nitrate. The transition metal source may also contain water of crystallization, and those skilled in the art can select it according to actual needs.
[0037] In this invention, preferably, the organic template agent is at least one of tetrapropylammonium hydroxide, tetramethylammonium hydroxide, tetrabutylammonium hydroxide, tetraethylammonium hydroxide, and N,N,N-trimethyladamantaneammonium, and more preferably tetrapropylammonium hydroxide.
[0038] In this invention, a silicon source, a transition metal source, an organic template agent, and water are mixed to obtain the crystallized mixture. Preferably, the preparation method of the crystallized mixture includes: first, under stirring conditions, a first mixing of the silicon source, the organic template agent, and water to obtain a hydrated gel; then, a second mixing of the transition metal source is added to obtain the crystallized mixture. This mixing method facilitates the creation of an ordered and uniform pore structure and ensures efficient embedding of the transition metal into the framework.
[0039] Preferably, the first mixing time is 1-24 hours.
[0040] The transition metal source can be provided in the form of an aqueous solution of the transition metal source.
[0041] Preferably, in the crystallization mixture, the molar ratio of water to silicon source (based on SiO2) is (0.1-100):1, more preferably (1-50):1.
[0042] In this invention, the hydrothermal crystallization temperature is less than 200°C, and the time is 1-324 hours. Preferably, the hydrothermal crystallization temperature is 150-180°C, for example, 150°C, 160°C, 170°C, 175°C, 178°C, 180°C, etc., and the time is 24-96 hours. Using the above-mentioned preferred hydrothermal crystallization conditions is beneficial for creating an ordered and uniform pore structure and ensuring efficient embedding of the transition metal into the framework.
[0043] According to the present invention, preferably, the amount of silicon carbide substrate is such that, based on the weight of the prepared monolithic catalyst, the content of foamed silicon carbide substrate is 65-99 wt%, preferably 75-98 wt%.
[0044] Preferably, the silicon carbide substrate is foamed silicon carbide. The silicon carbide substrate can be commercially available or prepared using any method known in the art, and the present invention does not have any particular limitation in this regard.
[0045] The preparation method further includes: performing solid-liquid separation on the mixture obtained by hydrothermal crystallization to obtain the intermediate product catalyst. The present invention does not have any particular limitation on the method of solid-liquid separation, and conventional methods can be used.
[0046] According to some preferred embodiments of the present invention, in step (3), calcination is carried out in an oxygen-containing atmosphere, which is preferably provided by air. More preferably, the flow rate of the oxygen-containing atmosphere is 1-200 mL / (g·h), more preferably 100-150 mL / (g·h).
[0047] Preferably, the roasting temperature is 500-600℃, more preferably 550-580℃; the roasting time is 1-5h, more preferably 1.5-3h.
[0048] Preferably, the heating rate of the calcination is 5-15℃ / min.
[0049] The third aspect of the present invention provides a monolithic Joule thermal catalyst prepared by the above-described method for preparing the monolithic Joule thermal catalyst.
[0050] The fourth aspect of the present invention provides the application of the above-described monolithic Joule thermal catalyst in the dry reforming reaction of methane, preferably in the application in the electrothermal dry reforming reaction of methane.
[0051] In this invention, the electrothermal methane dry reforming reaction refers to a reaction method in which the reaction temperature is controlled by applying voltage to the catalyst.
[0052] Preferably, the reaction conditions for the electrothermal dry reforming of methane include: a reaction temperature of 600-900℃, preferably 700-850℃, a molar ratio of methane to carbon dioxide of 3:1-1:3, and a volume hourly space velocity of 1000-21000 L / (g). 金属 ·h).
[0053] The present invention will be described in detail below through embodiments.
[0054] Example 1 (1) A 40% by weight aqueous solution of tetrapropylammonium hydroxide and tetraethyl orthosilicate were placed together in a container and stirred continuously at a stirring rate of 600 rpm for 16 h to obtain a hydrated gel. Then, an aqueous solution of nickel nitrate was added to the hydrated gel and mixed thoroughly. The resulting raw material system was placed in a stainless steel high-pressure reactor lined with polytetrafluoroethylene. A foamed silicon carbide substrate was added to the reactor, the reactor was sealed, and the reaction was carried out in a homogeneous reactor at 175 °C for 96 h. After the reaction was completed, the solid and liquid were separated by filtration, the silicon carbide substrate was taken out and dried in air at 100 °C to obtain the intermediate product catalyst. The molar ratio of element Ni to tetraethyl orthosilicate (calculated as SiO2) in the solution is 1:90; the molar ratio of tetrapropylammonium hydroxide to tetraethyl orthosilicate (calculated as SiO2) is 0.2:1.
[0055] (2) The above intermediate catalyst was placed in a tube furnace under an air atmosphere and heated to 550°C at a heating rate of 10°C / min. It was then calcined in flowing air at a flow rate of 50 mL / (g·h) for 2 h to obtain a monolithic catalyst (denoted as C-1).
[0056] A physical image of the monolithic catalyst is shown below. Figure 1 As shown, the SEM image is as follows: Figure 2As shown, the monolithic catalyst structure is complete and without obvious cracks. The silicon carbide support is uniformly covered by the active component, presenting a porous and uniform white layer. The SEM cross-sectional image shows that the active component and the silicon carbide support are tightly bonded without delamination, indicating that the active component has excellent mechanical stability. X-ray diffraction pattern as follows Figure 3 As shown, combined with inductively coupled plasma atomic emission spectrometry, catalyst C-1 includes silicon carbide, MFI molecular sieve, and Ni components. In the monolithic catalyst C-1, the weight ratio of molecular sieve (based on SiO2) to elemental Ni is 100.8:1.113; in the monolithic catalyst C-1, the weight ratio of active component to silicon carbide is 110.2:989.5.
[0057] Example 2 (1) A 40% by weight aqueous solution of tetrapropylammonium hydroxide and tetraethyl orthosilicate were placed together in a container and stirred continuously at a stirring rate of 600 rpm for 16 h to obtain a hydrated gel. Then, an aqueous solution of nickel nitrate was added to the hydrated gel and mixed thoroughly. The resulting raw material system was placed in a stainless steel high-pressure reactor lined with polytetrafluoroethylene. A foamed silicon carbide substrate was added to the reactor, the reactor was sealed, and the reaction was carried out in a homogeneous reactor at 175 °C for 336 h. After the reaction was completed, the solid and liquid were separated by filtration, the silicon carbide substrate was taken out and dried in air at 100 °C to obtain the intermediate product catalyst. The molar ratio of element Ni to tetraethyl orthosilicate (calculated as SiO2) in the solution is 1:110; the molar ratio of tetrapropylammonium hydroxide to tetraethyl orthosilicate (calculated as SiO2) is 0.2:1.
[0058] (2) The above intermediate catalyst was placed in a tube furnace under an air atmosphere and heated to 550°C at a heating rate of 10°C / min. It was then calcined in flowing air at a flow rate of 50 mL / (g·h) for 2 h to obtain a monolithic catalyst (denoted as C-2).
[0059] X-ray diffraction pattern as follows Figure 3 As shown, combined with inductively coupled plasma atomic emission spectrometry, it can be seen that catalyst C-2 includes silicon carbide, MFI molecular sieve, and Ni component. In the monolithic catalyst C-2, the weight ratio of molecular sieve (based on SiO2) to elemental Ni is 105.6:1.005. In the monolithic catalyst C-2, the weight ratio of the active component to silicon carbide is 108.2:989.5.
[0060] Example 3 (1) A 40% by weight aqueous solution of tetrapropylammonium hydroxide and tetraethyl orthosilicate were placed together in a container and stirred continuously at a stirring rate of 600 rpm for 16 h to obtain a hydrated gel. Then, an aqueous solution of nickel nitrate was added to the hydrated gel and mixed thoroughly. The resulting raw material system was placed in a stainless steel high-pressure reactor lined with polytetrafluoroethylene. A foamed silicon carbide substrate was added to the reactor, the reactor was sealed, and the reaction was carried out in a homogeneous reactor at 175 °C for 144 h. After the reaction was completed, the solid and liquid were separated by filtration, the silicon carbide substrate was taken out and dried in air at 100 °C to obtain the intermediate product catalyst. The molar ratio of element Ni to tetraethyl orthosilicate (calculated as SiO2) in the solution is 1:110; the molar ratio of tetrapropylammonium hydroxide to tetraethyl orthosilicate (calculated as SiO2) is 0.2:1.
[0061] (2) The above intermediate catalyst was placed in a tube furnace under an air atmosphere and heated to 550°C at a heating rate of 10°C / min. It was then calcined in flowing air at a flow rate of 50 mL / (g·h) for 2 h to obtain a monolithic catalyst (denoted as C-3).
[0062] X-ray diffraction pattern as follows Figure 3 As shown, combined with inductively coupled plasma atomic emission spectrometry, catalyst C-1 includes silicon carbide, MFI molecular sieve, and Ni component. In the monolithic catalyst C-3, the weight ratio of molecular sieve (based on SiO2) to elemental Ni is 107.4:0.9996. In the monolithic catalyst C-3, the weight ratio of the active component to silicon carbide is 99.2:899.5.
[0063] Example 4 The method of Example 1 was followed, except that the molar ratio of tetrapropylammonium hydroxide to tetraethyl orthosilicate (based on SiO2) was 0.4:1. A monolithic catalyst (denoted as C-4) was obtained. Catalyst C-4 comprises silicon carbide, MFI molecular sieve, and a Ni component.
[0064] Example 5 The method is the same as in Example 1, except that the hydrothermal crystallization temperature is 180°C and the time is 36 hours.
[0065] A monolithic catalyst (denoted as C-5) was obtained. Catalyst C-5 includes silicon carbide, MFI molecular sieve, and Ni component.
[0066] Example 6 An aqueous solution of N,N,N-trimethyladamantane (25% by weight) and tetraethyl orthosilicate were placed together in a container and stirred continuously at 600 rpm for 16 h to obtain a hydrated gel. Then, an aqueous solution of nickel nitrate was added to the hydrated gel and mixed thoroughly. The resulting raw material system was placed in a stainless steel high-pressure reactor lined with polytetrafluoroethylene. A foamed silicon carbide substrate was added to the reactor, the reactor was sealed, and the reaction was carried out in a homogeneous reactor at 160 °C for 144 h. After the reaction, the solid and liquid were separated by filtration, and the silicon carbide substrate was removed and dried in air at 100 °C to obtain the intermediate product catalyst. The molar ratio of Ni to tetraethyl orthosilicate (calculated as SiO2) in the solution is 1:90; the molar ratio of N,N,N-trimethyladamantane ammonium to tetraethyl orthosilicate (calculated as SiO2) is 0.4:1.
[0067] (2) The above intermediate catalyst was placed in a tube furnace under an air atmosphere and heated to 550°C at a heating rate of 10°C / min. It was then calcined in flowing air at a flow rate of 50 mL / (g·h) for 2 h to obtain a monolithic catalyst (denoted as C-6).
[0068] X-ray diffraction analysis, such as Figure 4 As shown, combined with inductively coupled plasma atomic emission spectrometry, catalyst C-6 includes silicon carbide, CHA molecular sieve, and Ni components. In the monolithic catalyst C-6, the weight ratio of molecular sieve (based on SiO2) to elemental Ni is 101.8:1.105. In the monolithic catalyst C-6, the weight ratio of active component to silicon carbide is 101.9:980.6.
[0069] Comparative Example 1 (Application) (1) A 40% by weight aqueous solution of tetrapropylammonium hydroxide and tetraethyl orthosilicate were placed together in a container and stirred continuously at a stirring rate of 600 rpm for 16 h to obtain a hydrated gel. Then, an aqueous solution of nickel nitrate was added to the hydrated gel and mixed thoroughly. The resulting raw material system was placed in a stainless steel high-pressure reactor lined with polytetrafluoroethylene and reacted at 175 °C for 336 h in a homogeneous reactor. After the reaction was completed, the solid and liquid were separated by filtration and dried in air at 100 °C to obtain the catalyst active component. The molar ratio of element Ni to tetraethyl orthosilicate (calculated as SiO2) in the solution is 1:95; the molar ratio of tetrapropylammonium hydroxide to tetraethyl orthosilicate (calculated as SiO2) is 0.2:1.
[0070] (2) Mix the active component of the catalyst with silica sol (40% aqueous solution of silica) at a mass ratio of 15:85, place it in a glass container and ultrasonically vibrate it for 10 minutes in an ultrasonic cleaner.
[0071] (3) Immerse the foamed silicon carbide substrate in the above mixture and ultrasonically vibrate it for 30 minutes in an ultrasonic cleaner. Remove the foamed silicon carbide and dry it in air at 100°C for 2 hours.
[0072] (4) The above intermediate catalyst was placed in a tube furnace under an air atmosphere and heated to 550°C at a heating rate of 10°C / min. It was then calcined for 2 h in flowing air at a flow rate of 50 mL / (g·h) to obtain a coated catalyst, denoted as DC-1. X-ray diffraction analysis showed that catalyst DC-1 contained silicon carbide, MFI molecular sieve, and Ni components.
[0073] Comparative Example 2 (multiple applications) (1) A 40% by weight aqueous solution of tetrapropylammonium hydroxide and tetraethyl orthosilicate were placed together in a container and stirred continuously at a stirring rate of 600 rpm for 16 h to obtain a hydrated gel. Then, an aqueous solution of nickel nitrate was added to the hydrated gel and mixed thoroughly. The resulting raw material system was placed in a stainless steel high-pressure reactor lined with polytetrafluoroethylene and reacted at 175 °C for 336 h in a homogeneous reactor. After the reaction was completed, the solid and liquid were separated by filtration and dried in air at 100 °C to obtain the catalyst active component. The molar ratio of element Ni to tetraethyl orthosilicate (calculated as SiO2) in the solution is 1:90; the molar ratio of tetrapropylammonium hydroxide to tetraethyl orthosilicate (calculated as SiO2) is 0.2:1.
[0074] (2) Mix the active component of the catalyst with silica sol (aqueous solution of 40% silica) at a mass ratio of 15:85, place it in a glass container and ultrasonically vibrate it for 10 minutes in an ultrasonic cleaner; (3) Immerse the foamed silicon carbide substrate in the above mixture and ultrasonically vibrate it for 30 minutes in an ultrasonic cleaner. Remove the foamed silicon carbide and dry it in air at 100°C for 2 hours; Repeat step (3) 5 times; (4) The above intermediate catalyst was placed in a tube furnace under an air atmosphere and heated to 550°C at a heating rate of 10°C / min. It was then calcined for 2 h in flowing air at a flow rate of 50 mL / (g·h) to obtain a coated catalyst, denoted as DC-2. X-ray diffraction analysis and inductively coupled plasma atomic emission spectrometry showed that catalyst DC-2 included silicon carbide, MFI molecular sieve, and Ni components.
[0075] Comparative Example 3 (1) A 40% by weight aqueous solution of tetrapropylammonium hydroxide and tetraethyl orthosilicate were placed together in a container and stirred continuously at a stirring rate of 600 rpm for 16 h to obtain a hydrated gel. Then, an aqueous solution of nickel nitrate was added to the hydrated gel and mixed thoroughly. The resulting raw material system was placed in a stainless steel high-pressure reactor lined with polytetrafluoroethylene. A foamed silicon carbide substrate was added to the reactor, the reactor was sealed, and the reaction was carried out in a homogeneous reactor at 200 °C for 72 h. After the reaction was completed, the solid and liquid were separated by filtration, the silicon carbide substrate was taken out and dried in air at 100 °C to obtain the intermediate product catalyst. The molar ratio of Ni to tetraethyl orthosilicate (calculated as SiO2) in the solution is 1:92; the molar ratio of tetrapropylammonium hydroxide to tetraethyl orthosilicate (calculated as SiO2) is 0.2:1.
[0076] (2) The above intermediate catalyst was placed in a tube furnace under an air atmosphere and heated to 550°C at a heating rate of 10°C / min. It was then calcined in flowing air at a flow rate of 50 mL / (g·h) for 2 h to obtain a monolithic catalyst (denoted as DC-3).
[0077] In the monolithic catalyst DC-3, the weight ratio of SiO2 to elemental Ni is 102.3:1.103; In the monolithic catalyst DC-3, the weight ratio of catalyst to silicon carbide is 98.2:1000.6.
[0078] X-ray diffraction analysis and inductively coupled plasma atomic emission spectrometry show that catalyst DC-3 includes silicon carbide, MFI molecular sieve, and Ni component.
[0079] Test Example 1 (1) Ultrasonic stripping rate: The mass of the catalyst before stripping is recorded as m1. The catalyst is placed in a beaker and ethanol is added to cover the catalyst (the volume ratio of catalyst to ethanol is 1:50). The catalyst is ultrasonically vibrated for 15 minutes in an ultrasonic cleaner at a frequency of 40kHz. Then the catalyst is taken out and dried in an oven at 100℃ for 12 h. The mass of the catalyst after stripping is measured as m2.
[0080] Catalyst stripping rate = (m1-m2) / m1*100%.
[0081] (2) Resistivity: The resistance value was accurately determined by constant current method. First, the catalyst was loaded into the reactor, a stable current of 0.1A was set, and the voltage drop across the catalyst was precisely measured by an electric energy meter. Finally, the resistance value was calculated according to Ohm's law ρ=(R*S) / L.
[0082] The results are shown in Table 1.
[0083] Table 1
[0084] Test Example 2 (Electrothermal Methane Dry Reforming Reaction Test) The monolithic catalysts prepared in the above examples and comparative examples were placed in a fixed-bed reactor with an inner diameter of 10 mm. A reaction gas of methane and carbon dioxide in a molar ratio of 1:1 was introduced, a voltage was applied to both ends of the catalyst, and the catalyst temperature was measured by a thermocouple to reach 800 °C. The composition of the reaction products was detected by online gas chromatography equipped with a TCD detector.
[0085] The feed gas space velocity is 9500 L / (g) Ni (·h), maintaining the gas flow rate and catalyst temperature for 10 hours, recording the product composition and calculating the conversion rates of methane and carbon dioxide every 0.5 hours. The comparison results of methane and carbon dioxide conversion rates of the catalyst in the dry reforming reaction test of methane in the examples and comparative examples are as follows: Figure 5 and Figure 6 As shown, the results of each embodiment and comparative example are shown in Table 2.
[0086] The feed gas space velocity is 10555 L / (g) Ni The stability of the monolithic catalyst prepared in Example 1 in the dry reforming reaction of methane was tested (·h), and the results are as follows: Figure 7 As shown.
[0087] Wherein, methane conversion rate = (1 - (molar amount of methane in the product) / molar amount of methane in the reactants) * 100%; Carbon dioxide conversion rate = (1 - (molar amount of carbon dioxide in the product) / molar amount of carbon dioxide in the reactants) * 100%.
[0088] Table 2
[0089] From Table 2 and Figure 5 and Figure 6 The results show that the catalyst prepared by the method of this invention exhibits high stability in the dry reforming reaction of methane, maintaining a high conversion rate even after continuous reaction for more than 10 hours. Comparative Example 1 and Comparative Example 2 catalysts, due to their poor anti-stripping performance, showed significant catalyst loss as the reaction proceeded, exhibiting a marked decrease in catalytic activity. Comparative Example 3, due to the hydrothermal crystallization conditions causing the silicon carbide substrate to dissolve and lose conductivity, could not be heated to 800℃, resulting in no conversion of methane and carbon dioxide. Furthermore, through... Figure 7 The results show that the catalyst provided by this invention can maintain high stability even at high space velocities.
[0090] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.
Claims
1. A monolithic Joule thermal catalyst, characterized in that, The catalyst comprises a silicon carbide substrate and an active component supported on the silicon carbide substrate; the active component comprises a molecular sieve and a metal component; the metal component is at least one of transition metals; the molecular sieve is at least one of MFI type molecular sieve, CHA type molecular sieve, MOR type molecular sieve, MEL type molecular sieve and BEA type molecular sieve. The ultrasonic exfoliation rate of the catalyst is not higher than 10 wt%.
2. The catalyst according to claim 1, wherein, The ultrasonic exfoliation rate of the catalyst is not higher than 5 wt%, preferably 0.1-3 wt%.
3. The catalyst according to claim 1, wherein, The resistivity of the catalyst is not higher than 1 Ω·m, preferably 0.002-0.5 Ω·m.
4. The catalyst according to any one of claims 1-3, wherein, In the catalyst, the weight ratio of the molecular sieve content (calculated as SiO2) to the metal component (calculated as an element) is (5-1000):1, preferably (20-200):1; Preferably, in the catalyst, the weight ratio of the active component to the silicon carbide substrate is (0.01-0.35):1, more preferably (0.045-0.25):
1.
5. The catalyst according to any one of claims 1-4, wherein, The metal component is selected from at least one of Ni, Ru, Pd, Rh, Pt, Ir, Au, Ag, Fe and Co, and more preferably Ni; Preferably, the molecular sieve is an MFI type molecular sieve and / or a CHA type molecular sieve, more preferably an MFI type molecular sieve; Preferably, the silicon carbide substrate is foamed silicon carbide.
6. A method for preparing a monolithic Joule thermal catalyst, the method comprising: (1) Prepare a crystallization mixture containing a silicon source, a transition metal source, an organic template agent and water; The molar ratio of the organic template agent to the silicon source (calculated as SiO2) is no higher than 0.5:
1. (2) The crystallization mixture is mixed with a silicon carbide substrate and subjected to hydrothermal crystallization at less than 200°C for 1-324 hours to obtain the intermediate product catalyst; (3) The intermediate catalyst is calcined in an oxygen-containing atmosphere.
7. The preparation method according to claim 6, wherein, In step (1), the molar ratio of the transition metal source (calculated as metal element) to the silicon source (calculated as SiO2) in the crystallization mixture is 1:(5-1000), preferably 1:(20-200). Preferably, in the crystallization mixture of step (1), the molar ratio of the organic template agent to the silicon source (based on SiO2) is (0.01-0.5):1, and more preferably (0.1-0.45):
1.
8. The preparation method according to claim 6 or 7, wherein, The silicon source is an organosilicone ester, preferably tetraethyl orthosilicate; Preferably, the metal in the transition metal source is at least one selected from Ni, Ru, Pd, Rh, Pt, Ir, Au, Ag, Fe, and Co, and more preferably Ni; More preferably, the transition metal source is nickel nitrate; Preferably, the organic template agent is at least one selected from tetrapropylammonium hydroxide, tetramethylammonium hydroxide, tetrabutylammonium hydroxide, tetraethylammonium hydroxide, and N,N,N-trimethyladamantaneammonium; Preferably, the hydrothermal crystallization temperature is 150-180℃ and the time is 24-96h.
9. The preparation method according to any one of claims 6-8, wherein, The amount of silicon carbide substrate used is such that, based on the weight of the prepared catalyst, the content of foamed silicon carbide substrate is 65-99 wt%, preferably 75-98 wt%; Preferably, the silicon carbide substrate is foamed silicon carbide.
10. The preparation method according to any one of claims 6-9, wherein, In step (3), the roasting temperature is 500-600℃, preferably 550-580℃; the roasting time is 1-5h, preferably 1-3h; Preferably, the heating rate of the calcination is 5-15℃ / min.
11. The monolithic Joule thermal catalyst prepared by the method of any one of claims 6-10.
12. The use of the monolithic Joule thermal catalyst according to any one of claims 1-5 and 11 in the dry reforming of methane, preferably in the use in the electrothermal dry reforming of methane.