CN112264043B - Ni-Rh-based diesel reforming catalyst and preparation method and application thereof - Google Patents
Ni-Rh-based diesel reforming catalyst and preparation method and application thereof Download PDFInfo
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- CN112264043B CN112264043B CN202011301002.6A CN202011301002A CN112264043B CN 112264043 B CN112264043 B CN 112264043B CN 202011301002 A CN202011301002 A CN 202011301002A CN 112264043 B CN112264043 B CN 112264043B
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- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
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- B01J23/89—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals
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- B01J23/894—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals also combined with metals, or metal oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with rare earths or actinides
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- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/02—Impregnation, coating or precipitation
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- B01J37/031—Precipitation
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- C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
- C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
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- C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
- C01B2203/02—Processes for making hydrogen or synthesis gas
- C01B2203/0205—Processes for making hydrogen or synthesis gas containing a reforming step
- C01B2203/0227—Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step
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- C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
- C01B2203/10—Catalysts for performing the hydrogen forming reactions
- C01B2203/1041—Composition of the catalyst
- C01B2203/1047—Group VIII metal catalysts
- C01B2203/1052—Nickel or cobalt catalysts
- C01B2203/1058—Nickel catalysts
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- C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
- C01B2203/10—Catalysts for performing the hydrogen forming reactions
- C01B2203/1041—Composition of the catalyst
- C01B2203/1082—Composition of support materials
Abstract
The invention provides a Ni-Rh-based diesel reforming catalyst, a preparation method and application thereof, belonging to the technical field of diesel reforming catalysts. The invention adopts the membrane-dispersed microreactor to carry out coprecipitation reaction to prepare the Ni-Rh-based catalyst, in the membrane-dispersed microreactor, the cross-flow shearing of the microfiltration membrane on the dispersed phase is used for realizing the rapid and uniform mixing of hydroxyl and metal ions in the dispersed phase and the continuous phase, thereby improving the micromixing efficiency, being beneficial to strengthening the mass transfer of the hydroxyl and the metal ions in the nucleation stage in the coprecipitation reaction process, and controlling the pH value of the reaction more accurately, thereby effectively improving the mass transfer efficiency, remarkably improving the dispersion degree of active metal (Ni-Rh alloy), and simultaneously leading Zr to be more uniformly doped in CeO2The Ni-Rh alloy is more uniformly loaded on the cerium-zirconium solid solution carrier, the reaction time is shortened, the production efficiency is high, the production continuity can be realized, and the method has important market value and popularization value.
Description
Technical Field
The invention relates to the technical field of diesel reforming catalysts, in particular to a Ni-Rh-based diesel reforming catalyst and a preparation method and application thereof.
Background
Hydrogen energy is a secondary energy carrier having characteristics of high calorific value, high quality energy density, zero pollution, and the like, and has recently received wide attention from various countries. Existing methods for producing hydrogen include thermochemical methods, electrochemical methods, and the like. Fuel cells (such as solid oxide fuel cells, proton exchange membrane fuel cells) increasingly occupy more hydrogen consumption. At present, the storage and transportation of hydrogen is still a bottleneck to be broken through urgently. Achieving on-demand hydrogen production may be an effective solution to this problem. The diesel oil is a liquid fuel with high volume energy density, is easy to store and transport, and the hydrogen-rich synthetic gas generated by reforming the diesel oil is supplied to a fuel cell for power generation and can be used as auxiliary power for output.
Although diesel oil has the advantage of easy storage and transportation, the low H/C content and the unsaturated aromatic hydrocarbon content increase the difficulty of reforming the diesel oil. When the Ni-based single metal is used for catalyzing the reforming of high-carbon hydrocarbons, the problems of low activity, low selectivity, easy inactivation and the like often exist, the high dispersion of Ni is ensured, the strong interaction between Ni and a carrier is formed, the occurrence of non-ideal phenomena (catalyst carbon deposition) can be inhibited to a certain extent by adopting the carrier with stronger oxygen moving capacity, but the problems of low activity and easy coking are essentially solved, and noble metal and Ni are introduced to form an alloy. At present, the Ni-Pt-based, Ni-Ru-based and Ni-Rh-based catalysts have relatively excellent effects when applied to a diesel reforming system. However, the Ni-Rh based catalyst synthesized by the existing method (sol-gel, adsorption hydrolysis precipitation and stirring method) still has the problems of low active metal dispersity, unsuitability for macro preparation and the like.
Disclosure of Invention
The invention aims to provide a Ni-Rh-based diesel reforming catalyst and a preparation method and application thereof.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides a preparation method of a Ni-Rh-based diesel reforming catalyst, which comprises the following steps:
in a membrane dispersion microreactor, taking a mixed salt solution of nickel salt, rhodium salt, cerium salt and zirconium salt as a continuous phase to enter a main channel of the membrane dispersion microreactor, taking an ammonia water solution as a dispersed phase to enter a microfiltration membrane of the membrane dispersion microreactor, shearing the microfiltration membrane, mixing the microfiltration membrane with the continuous phase, and carrying out coprecipitation reaction to obtain slurry;
sequentially aging and separating the slurry to obtain a catalyst precursor;
drying, calcining and reducing the catalyst precursor in sequence to obtain the Ni-Rh base diesel reforming catalyst;
in the nickel salt, the rhodium salt, the cerium salt and the zirconium salt, the molar ratio of Ce to Zr is (1-9): 1, the molar ratio of Ce to Ni is (1-10): 1, and the molar ratio of Ni to Rh is (5-20): 1.
Preferably, the total metal ion concentration of the mixed salt solution of the nickel salt, the cerium salt and the zirconium salt is 0.1-2 mol/L; the concentration of the ammonia water solution is 0.1-2 mol/L.
Preferably, the length of the main channel is 40mm, and the width and the height of the main channel are 0.5-1 mm independently; the aperture of the microfiltration membrane is 2-5 mu m, the aperture ratio is less than or equal to 60%, and the length and the width of the microfiltration membrane are respectively 3mm and 1 mm.
Preferably, the flow rate of the continuous phase is 1-20 mL/min, the flow rate of the dispersed phase is 5-160 mL/min, and the flow rate ratio of the dispersed phase to the continuous phase is 3-5.
Preferably, the membrane dispersion microreactor is placed in a water bath at 40-80 ℃ to perform the coprecipitation reaction.
Preferably, the aging temperature is 20 ℃ and the aging time is 6-10 h.
Preferably, the calcination is carried out in an oxygen-nitrogen atmosphere, the calcination temperature is 600-800 ℃, and the calcination time is 2-4 hours; the reduction temperature is 600-800 ℃, and the time is 1-2 h.
The invention provides a Ni-Rh-based diesel reforming catalyst prepared by the preparation method in the technical scheme, which comprises a carrier and an active ingredient loaded on the carrier, wherein the active ingredient is Ni-Rh alloy, the carrier is cerium-zirconium solid solution, and the cerium-zirconium solid solution is CexZr1-xO2Wherein x is 0.5-0.9; in the Ni-Rh-based diesel reforming catalyst, the mass percent of Ni is 3-25%, and the mass percent of Rh is 0.1-2%.
Preferably, x is 0.6 to 0.8, the mass percent of Ni is 5 to 20%, and the mass percent of Rh is 0.5 to 1.5%.
The invention provides the application of the Ni-Rh base diesel reforming catalyst in the technical scheme in the preparation of hydrogen by diesel reforming.
The invention provides a preparation method of a Ni-based diesel reforming catalyst, which comprises the following steps: in a membrane dispersion microreactor, taking a mixed salt solution of nickel salt, rhodium salt, cerium salt and zirconium salt as a continuous phase to enter a main channel of the membrane dispersion microreactor, taking an ammonia water solution as a dispersed phase to enter a microfiltration membrane of the membrane dispersion microreactor, shearing the microfiltration membrane, mixing the microfiltration membrane with the continuous phase, and carrying out coprecipitation reaction to obtain slurry; sequentially aging and separating the slurry to obtain a catalyst precursor; drying, calcining and reducing the catalyst precursor in sequence to obtain the Ni-based diesel reforming catalyst; in the nickel salt, the rhodium salt, the cerium salt and the zirconium salt, the molar ratio of Ce to Zr is (1-9): 1, the molar ratio of Ce to Ni is (1-10): 1, and the molar ratio of Ni to Rh is (5-20): 1.
The invention adopts the membrane-dispersed microreactor to carry out coprecipitation reaction to prepare the Ni-Rh-based catalyst, in the membrane-dispersed microreactor, the cross-flow shearing of the microfiltration membrane on the dispersed phase is used for realizing the rapid and uniform mixing of hydroxyl and metal ions in the dispersed phase and the continuous phase, thereby improving the micromixing efficiency, being beneficial to strengthening the mass transfer of the hydroxyl and the metal ions in the nucleation stage in the coprecipitation reaction process, and controlling the pH value of the reaction more accurately, thereby effectively improving the mass transfer efficiency, remarkably improving the dispersion degree of active metal (Ni-Rh alloy), and simultaneously leading Zr to be more uniformly doped in CeO2The cerium-zirconium solid solution is formed, the Ni-Rh alloy is more uniformly loaded on the cerium-zirconium solid solution carrier, the reaction time is shortened (the flow of a dispersed phase is 80mL/min, and when a continuous phase is 20mL/min, only 10min is needed for synthesizing 1L of slurry), the production efficiency is high, the production continuity can be realized, and the method has important market value and popularization value.
The invention controls the proportion of metal, can ensure that Ce and Zr form oxide and play a role of a carrier, and simultaneously ensures that Ni-Rh alloy plays a role of catalytic activity and ensures better catalytic effect.
The method of the invention overcomes the problems of low dispersion degree of Ni and Rh, small number of oxygen vacancies, low catalytic activity and low mixing and mass transfer efficiency of Ni-Rh aggregated on a carrier, low dispersion degree and long synthesis time (1L slurry needs to be synthesized for 1h) in the existing Ni-Rh based catalyst prepared by a stirring method. The results of the examples show that the Ni-Rh-based diesel reforming catalyst prepared by the method shows stronger activity and tolerance to carbon deposition when catalyzing diesel reforming, and the hydrogen yield is greatly improved.
Drawings
FIG. 1 is a flow diagram of a co-precipitation reaction using a membrane-dispersed microreactor in accordance with the present invention;
FIG. 2 is a TEM image of a Ni-Rh-based diesel reforming catalyst prepared in example 1;
fig. 3 is a TEM image of the Ni-Rh-based diesel reforming catalyst prepared in comparative example 1.
Detailed Description
The invention provides a preparation method of a Ni-Rh-based diesel reforming catalyst, which comprises the following steps:
in a membrane dispersion microreactor, taking a mixed salt solution of nickel salt, rhodium salt, cerium salt and zirconium salt as a continuous phase to enter a main channel of the membrane dispersion microreactor, taking an ammonia water solution as a dispersed phase to enter a microfiltration membrane of the membrane dispersion microreactor, shearing the microfiltration membrane, mixing the microfiltration membrane with the continuous phase, and carrying out coprecipitation reaction to obtain slurry;
sequentially aging and separating the slurry to obtain a catalyst precursor;
drying, calcining and reducing the catalyst precursor in sequence to obtain the Ni-based diesel reforming catalyst;
in the nickel salt, the rhodium salt, the cerium salt and the zirconium salt, the molar ratio of Ce to Zr is (1-9): 1, the molar ratio of Ce to Ni is (1-10): 1, and the molar ratio of Ni to Rh is (5-20): 1.
In the present invention, unless otherwise specified, all the starting materials required for the preparation are commercially available products well known to those skilled in the art.
In the membrane dispersion microreactor, mixed salt solution of nickel salt, rhodium salt, cerium salt and zirconium salt is used as a continuous phase to enter a main channel of the membrane dispersion microreactor, and ammonia water solution is used as a dispersed phase to enter a microfiltration membrane of the membrane dispersion microreactor to be sheared and then mixed with the continuous phase to carry out coprecipitation reaction, so that slurry is obtained. The present invention is not particularly limited with respect to the source and configuration of the membrane-dispersion microreactor, and commercially available membrane-dispersion microreactors configured as well known in the art may be used, and the present invention is limited only with respect to the size of the membrane-dispersion microreactor. In the present invention, the length of the main channel of the membrane dispersion microreactor is preferably 40mm, and the width and height thereof are independently preferably 0.5 to 1mm, and more preferably 0.6 to 0.8 mm. By controlling the membrane dispersion microreactor within the size range, the invention can increase the concentration gradient, strengthen the mass transfer effect, facilitate the preparation of highly dispersed catalyst, prevent the blockage of a channel from influencing the mass transfer and ensure the occurrence of precipitation reaction.
In the invention, the aperture of the microfiltration membrane is preferably 2-5 μm, and more preferably 3-4 μm; the aperture ratio is preferably less than or equal to 60%, the length of the microfiltration membrane is preferably 3mm, and the width of the microfiltration membrane is preferably 1 mm. The invention can control the dispersed phase liquid drop by controlling the size of the micro-filtration membrane, and ensures better mass transfer effect, thereby being convenient for forming high-dispersion Ni-Rh catalyst and avoiding the problems of membrane blockage, overhigh pressure drop and the like.
In the present invention, the nickel salt is preferably nickel nitrate or nickel chloride; the rhodium salt is preferably rhodium nitrate or rhodium chloride; the cerium salt is preferably cerium nitrate or cerium chloride; the zirconium salt is preferably zirconium nitrate or zirconium chloride; the total metal ion concentration of the mixed salt solution of the nickel salt, the cerium salt and the zirconium salt is preferably 0.1-2 mol/L. More preferably 0.5 to 1.8mol/L, and still more preferably 1.0 to 1.5 mol/L. In the invention, the preparation method of the mixed salt solution of nickel salt, rhodium salt, cerium salt and zirconium salt is preferably to dissolve zirconium salt and cerium salt in water, stir and mix for more than 6 hours at normal temperature, then add nickel salt and rhodium salt in turn, and continue stirring for 6 hours at normal temperature to obtain the mixed salt solution. The stirring rate is not particularly limited in the present invention, and the raw materials can be uniformly mixed according to a process well known in the art.
In the present invention, the concentration of the aqueous ammonia solution is preferably 0.1 to 2mol/L, more preferably 0.5 to 1.8mol/L, and still more preferably 1.0 to 1.5 mol/L.
In the nickel salt, the rhodium salt, the cerium salt and the zirconium salt, the molar ratio of Ce to Zr is (1-9) to 1, preferably (3-8) to 1, and more preferably (5-6) to 1; the molar ratio of Ce to Ni is (1-10): 1, preferably (2-8): 1, more preferably (5-6): 1; the molar ratio of Ni to Rh is (5-20): 1, preferably (10-20): 1, and more preferably (6-17): 1. The invention controls the proportion of the metal within the range, can ensure that Ce and Zr form oxides and play a role of a carrier, and simultaneously ensures that the Ni-Rh alloy plays a role of catalytic activity and ensures better catalytic effect.
The present invention preferably employs a advection pump to cause the continuous phase to enter the main channel of the membrane dispersion microreactor and to cause the dispersed phase to enter the microfiltration membrane of the membrane dispersion microreactor (as shown in fig. 1). In the invention, the flow rate of the continuous phase is preferably 1-20 mL/min, more preferably 5-15 mL/min, and further preferably 8-12 mL/min; the flow rate of the dispersed phase is preferably 5-160 mL/min, more preferably 10-80 mL/min, and further preferably 30-60 mL/min; the flow ratio of the dispersed phase to the continuous phase is preferably 3 to 5, and more preferably 4.
In the invention, the membrane dispersion microreactor is preferably placed in a water bath at 40-80 ℃ to perform the coprecipitation reaction. In the invention, the time of the coprecipitation reaction is the residence time of the mobile phase and the continuous phase in the microchannel of the membrane dispersion microreactor, the residence time is determined by the size of the microchannel, the mass transfer control of the microchannel is eliminated, and the precipitation time of the coprecipitation reaction controlled by intrinsic dynamics is in a sub-millisecond level and is not particularly limited.
In the coprecipitation reaction process, metal ions in nickel salt, rhodium salt, cerium salt and zirconium salt are coprecipitated to form metal hydroxide.
After the coprecipitation reaction is completed, the obtained product is preferably coiled by a coil pipe (the inner diameter is 2-4 mm) of 3-6 m, and then slurry is collected to be subjected to the subsequent process (as shown in figure 1). The source of the coils is not particularly limited in the present invention and may be any known in the art that can be used in membrane-dispersed microreactors. The invention utilizes the membrane dispersion microreactor to carry out a nucleation process, and then leads the particle growth process to be more orderly through the coil. The collection process is not particularly limited in the present invention, and may be performed according to a process well known in the art. In the invention, the time for collecting the slurry is preferably 10-40 min, and more preferably 10-20 min. In the invention, the pH range of the slurry is preferably 9.0-10.0, and more preferably 9.5; according to the invention, the pH value of the slurry is adjusted by controlling the addition amount of ammonia water, so that the coprecipitation of Ce, Rh, Zr and Ni is realized.
After obtaining the slurry, the invention sequentially ages and separates the slurry to obtain the catalyst precursor. In the invention, the aging is carried out in a water bath, the temperature of the aging is preferably 20 ℃, the time is preferably 6-10 h, and more preferably 7-8 h. The invention leads the small crystal grains generated by the coprecipitation reaction to be continuously fused and grown into more stable large crystal grains through aging.
In the present invention, the separation is preferably performed by centrifugation, and the conditions of the centrifugation are not particularly limited in the present invention, and the precipitate can be separated from the liquid phase according to a procedure well known in the art.
After the separation is completed, the precipitate obtained by the separation is preferably washed with water until the washing solution has a pH of 7 and the adsorbed metal ions of Ni, Rh, Ce, and Zr are not detected, and then washed with ethanol three or more times to obtain a solid, i.e., a catalyst precursor (metal hydroxide of nickel salt, rhodium salt, cerium salt, and zirconium salt).
After the catalyst precursor is obtained, the catalyst precursor is dried, calcined and reduced in sequence to obtain the Ni-Rh-based diesel reforming catalyst. In the invention, the drying is preferably carried out in a vacuum oven, the drying temperature is preferably 60-80 ℃, more preferably 65-75 ℃, and the drying time is preferably 10-12 h.
In the present invention, the calcination is preferably performed in an oxygen-nitrogen atmosphere in which the volume fraction of oxygen is preferably 20%; the calcination temperature is preferably 600-800 ℃, more preferably 650-750 ℃, and the time is preferably 2-4 hours, more preferably 2.5-3.5 hours. The invention converts metal hydroxide in the catalyst precursor into metal oxide by calcination, and simultaneously forms metal bond interaction between Ni-Rh alloy and carrier (cerium-zirconium solid solution).
In the invention, the reduction is preferably carried out in a hydrogen-argon atmosphere, and the volume fraction of hydrogen in the hydrogen-argon atmosphere is preferably 2-10%; the reduction temperature is preferably 600-800 ℃, and more preferably 650-750 ℃; the time is preferably 1 to 2 hours, and more preferably 1.5 hours. The invention reduces nickel-rhodium oxide in metal oxide into nickel-rhodium alloy by controlling reduction temperature, while cerium zirconium oxide exists in oxide form as carrier.
The inventionThe Ni-Rh-based diesel reforming catalyst prepared by the preparation method comprises a carrier and an active ingredient loaded on the carrier, wherein the active ingredient is Ni-Rh alloy, the carrier is cerium-zirconium solid solution, and the cerium-zirconium solid solution comprises CexZr1-xO2Wherein x is 0.5-0.9; in the Ni-Rh-based diesel reforming catalyst, the mass percent of Ni is 3-25%, and the mass percent of Rh is 0.1-2%.
In the present invention, the active ingredient forms a strong metal carrier interaction (SMSI) with the carrier, and the active metal is highly dispersed in the carrier.
In the present invention, x is preferably 0.6 to 0.8, the mass percentage of Ni is preferably 5 to 20%, more preferably 10 to 15%, and the mass percentage of Rh is preferably 0.5 to 1.5%, more preferably 1.0%.
The invention provides the application of the Ni-Rh base diesel reforming catalyst in the technical scheme in the preparation of hydrogen by diesel reforming. In the invention, the application method is preferably that the Ni-Rh-based diesel reforming catalyst is filled in a micro-filling column with the inner diameter of 3-8 mm, diesel steam and water steam are used as reactants to carry out steam reforming reaction, and the obtained reaction product enters a gas chromatography for on-line analysis.
In the present invention, the temperature of the steam reforming reaction is preferably 650 ℃; the water-carbon ratio is preferably 4; the preferred diesel reforming hourly space velocity is 4.5-18 h-1。
The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
Dissolving zirconium nitrate and cerium nitrate in water, stirring and mixing for 6h at normal temperature, sequentially adding nickel nitrate and rhodium nitrate, continuously stirring for 6h at normal temperature to obtain a mixed salt solution (the total ion concentration is 0.2mol/L, the molar ratio of Ce: Zr: Ni: Rh is 42:14:15:1) and an ammonia water solution (0.2mol/L), respectively filling the mixed salt solution and the ammonia water solution into two conical flasks, placing a membrane dispersion microreactor in a water bath at 40 ℃, taking the mixed salt solution as a continuous phase to enter a main channel (the length is 40mm, the width is 1mm), taking the ammonia water solution as a dispersed phase to pass through a microfiltration membrane (the aperture is 5 mu m, the aperture ratio is less than or equal to 60 percent, and the size is 3mm (the length) multiplied by 1mm (width)) of the membrane dispersion microreactor, shearing, then mixing with the continuous phase in the main channel, and carrying out coprecipitation reaction; wherein the continuous phase flow is within 10mL/min, the dispersed phase flow is within 40mL/min, the phase ratio of the dispersed phase to the continuous phase is 4, and the obtained product is collected within 20min after passing through a coil pipe (the inner diameter is 3mm) of 6m to obtain slurry (the pH value is 9.5);
aging the slurry in a water bath at 20 ℃ for 6h, performing centrifugal separation on the obtained material, washing the separated precipitate with water until the pH of the washing liquid is 7 and the adsorbed metal ions of Ni, Rh, Ce and Zr cannot be detected, and washing with ethanol for three times to obtain a catalyst precursor;
drying the catalyst precursor in a vacuum oven at 80 ℃ for 12h, then placing the catalyst precursor in an oxygen-nitrogen atmosphere (the volume fraction of oxygen is 20%), calcining the catalyst precursor at 600 ℃ for 4h, and then reducing the catalyst precursor in a hydrogen-argon atmosphere (the volume fraction of hydrogen is 10%) at 600 ℃ for 2h to obtain the Ni-Rh-based diesel reforming catalyst (the active component is Ni-Rh alloy, and the composition of the carrier cerium-zirconium solid solution is Ce)xZr1-xO2(ii) a x is 0.75, the mass percent of Ni is 9 percent, and the mass percent of Rh is 1 percent).
Example 2
Dissolving zirconium nitrate and cerium nitrate in water, stirring and mixing for 6h at normal temperature, sequentially adding nickel nitrate and rhodium nitrate, continuously stirring for 6h at normal temperature to obtain a mixed salt solution (the total ion concentration is 0.4mol/L, the molar ratio of Ce: Zr: Ni: Rh is 42:14:15:1) and an ammonia water solution (0.4mol/L), respectively filling the mixed salt solution and the ammonia water solution into two conical flasks, placing a membrane dispersion microreactor in a water bath at 40 ℃, taking the mixed salt solution as a continuous phase to enter a main channel (the length is 40mm, the width is 1mm), taking the ammonia water solution as a dispersed phase to pass through a microfiltration membrane (the aperture is 5 mu m, the aperture ratio is less than or equal to 60 percent, and the size is 3mm (the length) multiplied by 1mm (width)) of the membrane dispersion microreactor, shearing the mixed salt solution, mixing the ammonia water solution with the continuous phase in the main channel, and carrying out coprecipitation reaction for 20 min; wherein the flow rate of the continuous phase is 10mL/min, the flow rate of the disperse phase is 40mL/min, the phase ratio of the disperse phase to the continuous phase is 4, and the obtained product is collected in 20min after passing through a coil pipe (the inner diameter is 3mm) of 6m to obtain slurry (the pH value is 9.5);
aging the slurry in a water bath at 20 ℃ for 6h, performing centrifugal separation on the obtained material, washing the separated precipitate with water until the pH of the washing liquid is 7 and the adsorbed metal ions of Ni, Rh, Ce and Zr cannot be detected, and washing with ethanol for three times to obtain a catalyst precursor;
drying the catalyst precursor in a vacuum oven at 80 ℃ for 12h, then placing the catalyst precursor in an oxygen-nitrogen atmosphere (the volume fraction of oxygen is 20%), calcining the catalyst precursor at 600 ℃ for 4h, and then reducing the catalyst precursor in a hydrogen-argon atmosphere (the volume fraction of hydrogen is 10%) at 600 ℃ for 2h to obtain the Ni-Rh-based diesel reforming catalyst (the active component is Ni-Rh alloy, and the composition of the carrier cerium-zirconium solid solution is Ce)xZr1-xO2(ii) a x is 0.75, the mass percent of Ni is 9 percent, and the mass percent of Rh is 1 percent).
Example 3
Dissolving zirconium nitrate and cerium nitrate in water, stirring and mixing for 6h at normal temperature, sequentially adding nickel nitrate and rhodium nitrate, continuously stirring for 6h at normal temperature to obtain a mixed salt solution (the total ion concentration is 0.2mol/L, the molar ratio of Ce: Zr: Ni: Rh is 42:14:15:1) and an ammonia water solution (0.2mol/L), respectively filling the mixed salt solution and the ammonia water solution into two conical flasks, placing a membrane dispersion microreactor in a water bath at 40 ℃, taking the mixed salt solution as a continuous phase to enter a main channel (the length is 40mm, the width is 1mm), taking the ammonia water solution as a dispersed phase to pass through a microfiltration membrane (the aperture is 5 mu m, the aperture ratio is less than or equal to 60 percent, and the size is 3mm (the length) multiplied by 1mm (width)) of the membrane dispersion microreactor, shearing, then mixing with the continuous phase in the main channel, and carrying out coprecipitation reaction for 10 min; wherein the flow rate of the continuous phase is 20mL/min, the flow rate of the disperse phase is 80mL/min, the phase ratio of the disperse phase to the continuous phase is 4, and the obtained product is collected in 10min after passing through a coil pipe (the inner diameter is 3mm) of 6m to obtain slurry (the pH value is 9.5);
aging the slurry in a water bath at 20 ℃ for 6h, performing centrifugal separation on the obtained material, washing the separated precipitate with water until the pH of the washing liquid is 7 and the adsorbed metal ions of Ni, Rh, Ce and Zr cannot be detected, and washing with ethanol for three times to obtain a catalyst precursor;
drying the catalyst precursor in a vacuum oven at 80 ℃ for 12h, then placing the catalyst precursor in an oxygen-nitrogen atmosphere (the volume fraction of oxygen is 20%), calcining the catalyst precursor at 600 ℃ for 4h, and then reducing the catalyst precursor in a hydrogen-argon atmosphere (the volume fraction of hydrogen is 10%) at 600 ℃ for 2h to obtain the Ni-Rh-based diesel reforming catalyst (the active component is Ni-Rh alloy, and the composition of the carrier cerium-zirconium solid solution is Ce)xZr1-xO2(ii) a x is 0.75, the mass percent of Ni is 9 percent, and the mass percent of Rh is 1 percent).
Example 4
Dissolving zirconium nitrate and cerium nitrate in water, stirring and mixing for 6h at normal temperature, sequentially adding nickel nitrate and rhodium nitrate, continuously stirring for 6h at normal temperature to obtain a mixed salt solution (the total ion concentration is 0.2mol/L, the molar ratio of Ce: Zr: Ni: Rh is 42:14:13:2) and an ammonia water solution (0.2mol/L), respectively filling the mixed salt solution and the ammonia water solution into two conical flasks, placing a membrane dispersion microreactor in a water bath at 40 ℃, feeding the mixed salt solution into a main channel (the length is 40mm, the width and the height are 1mm) as a continuous phase, shearing the ammonia water solution as a dispersed phase through a microfiltration membrane (the aperture is 5 mu m, the aperture ratio is less than or equal to 60 percent and the size is 3mm multiplied by 1mm) of the membrane dispersion microreactor, mixing the sheared solution with the continuous phase in the main channel, and carrying out coprecipitation reaction for 10 min; wherein the flow rate of the continuous phase is 20mL/min, the flow rate of the disperse phase is 80mL/min, the phase ratio of the disperse phase to the continuous phase is 4, and the obtained product is collected in 10min after passing through a coil pipe (the inner diameter is 3mm) of 6m to obtain slurry (the pH value is 9.5);
aging the slurry in a water bath at 20 ℃ for 6h, performing centrifugal separation on the obtained material, washing the separated precipitate with water until the pH of the washing liquid is 7 and the adsorbed metal ions of Ni, Rh, Ce and Zr cannot be detected, and washing with ethanol for three times to obtain a catalyst precursor;
drying the catalyst precursor in a vacuum oven at 80 ℃ for 12h, then placing the dried catalyst precursor in an oxygen-nitrogen atmosphere (the volume fraction of oxygen is 20 percent), and calcining the catalyst precursor at 600 ℃ for 4hThen reducing the mixture for 2 hours at 600 ℃ in a hydrogen-argon atmosphere (the volume fraction of the hydrogen is 10 percent) to obtain the Ni-Rh-based diesel reforming catalyst (the active component is Ni-Rh alloy, and the composition of the carrier cerium-zirconium solid solution is Ce)xZr1-xO2(ii) a x is 0.75, the mass percent of Ni is 8 percent, and the mass percent of Rh is 2 percent).
Comparative example 1
Adding a mixed salt solution of nickel nitrate, rhodium nitrate, cerium nitrate and zirconium nitrate (Ce: Zr: Ni: Rh molar ratio is 42:14:15:1) into a stirring kettle at 25 ℃, dropwise adding ammonia water under the condition of stirring (stirring speed is 400rpm) to realize the blending of alkali liquor and the salt solution, stopping dropwise adding and stirring until the pH value of the obtained suspension reaches 9.5, carrying out coprecipitation reaction for 80min, aging the obtained catalyst precursor for 6h, sequentially centrifuging the obtained product, drying the product at 100 ℃ for 12h, calcining the product at 450 ℃ for 4h in an air atmosphere, and reducing the product at 450 ℃ for 2h in a hydrogen-nitrogen atmosphere (the volume fraction of hydrogen is 10%) to obtain the catalyst.
Characterization of
TEM tests were performed on the catalysts prepared in example 1 and comparative example 1, and the results were shown in fig. 2 and fig. 3, wherein fig. 2 is a TEM image of the Ni-Rh-based catalyst prepared in example 1, and fig. 3 is a TEM image of the Ni-Rh-based catalyst prepared in comparative example 1; as shown in the comparison of FIGS. 2 to 3, compared with the conventional stirring method, the Ni-Rh alloy and the cerium-zirconium solid solution are dispersed more uniformly in the Ni-Rh based catalyst prepared by the membrane dispersion microreactor.
Application example
The catalysts prepared in the example 1 and the comparative example 1 are filled in a micro-filled column with the inner diameter of 3-8 mm, reactants are diesel steam and water steam, the steam reforming reaction is carried out under the conditions of 650 ℃ reaction temperature and 4 water-carbon ratio according to the conditions of the table 1, reaction products enter a gas chromatograph for on-line analysis, and the hydrogen yield is calculated, and the results are shown in the table 1.
Table 1 hydrogen yield data for catalysts prepared in example 1 and comparative example 1 under different conditions
As can be seen from table 1, compared with the existing stirring method for preparing Ni — Rh-based catalyst, the co-precipitation reaction performed in the membrane-dispersed microreactor of the present invention can significantly improve the catalytic performance of the catalyst, and further improve the hydrogen yield.
Performance testing
The catalysts prepared in example 1 and comparative example 1 were subjected to performance test by a CO pulse adsorption method to verify the degree of dispersion of active metals, the method comprising:
the catalysts prepared in example 1 and comparative example 1 were packed in a quartz tube reactor having an inner diameter of 4mm at 10% H2Heating to 450 ℃ from room temperature at a heating rate of 10 ℃/min in a mixed gas/He atmosphere (the gas flow is 30mL/min), and keeping the temperature at 450 ℃ for 1 h; switching gas to He (flow rate is 50mL/min) atmosphere at 450 ℃, and purging for 30min for degassing; cooling to room temperature under He atmosphere, injecting 10% CO/He into He atmosphere with flow rate of 50mL/min, performing CO chemisorption, detecting the amount of outlet CO by chromatography TCD, and calculating the catalyst chemisorption amount, the results are shown in Table 2.
Table 2 chemisorption amounts of catalysts prepared in example 1 and comparative example 1
| Catalyst and process for preparing same | Amount of chemisorption (. mu. mol/g) |
| Example 1 | 123.9 |
| Comparative example 1 | 67.0 |
As can be seen from Table 2, the catalyst prepared by the present invention has a significantly higher chemisorption amount of CO than that of comparative example 1, indicating that the catalyst prepared by the present invention has a high degree of dispersion of the active metal (Ni-Rh alloy) and a small particle size.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (10)
1. A preparation method of a Ni-Rh based diesel reforming catalyst is characterized by comprising the following steps:
in a membrane dispersion microreactor, taking a mixed salt solution of nickel salt, rhodium salt, cerium salt and zirconium salt as a continuous phase to enter a main channel of the membrane dispersion microreactor, taking an ammonia water solution as a dispersed phase to enter a microfiltration membrane of the membrane dispersion microreactor, shearing the microfiltration membrane, mixing the microfiltration membrane with the continuous phase, and carrying out coprecipitation reaction to obtain slurry;
sequentially aging and separating the slurry to obtain a catalyst precursor;
drying, calcining and reducing the catalyst precursor in sequence to obtain the Ni-Rh base diesel reforming catalyst;
in the nickel salt, the rhodium salt, the cerium salt and the zirconium salt, the molar ratio of Ce to Zr is (1-9): 1, the molar ratio of Ce to Ni is (1-10): 1, and the molar ratio of Ni to Rh is (5-20): 1.
2. The method according to claim 1, wherein the mixed salt solution of nickel salt, cerium salt and zirconium salt has a total metal ion concentration of 0.1 to 2 mol/L; the concentration of the ammonia water solution is 0.1-2 mol/L.
3. The method of claim 1, wherein the main channel has a length of 40mm, a width and a height of 0.5 to 1mm, independently; the aperture of the microfiltration membrane is 2-5 mu m, the aperture ratio is less than or equal to 60%, and the length and the width of the microfiltration membrane are respectively 3mm and 1 mm.
4. The method according to claim 1, wherein the flow rate of the continuous phase is 1 to 20mL/min, the flow rate of the dispersed phase is 5 to 160mL/min, and the flow rate ratio of the dispersed phase to the continuous phase is 3 to 5.
5. The preparation method according to claim 1, wherein the membrane dispersion microreactor is placed in a water bath at 40-80 ℃ to perform the coprecipitation reaction.
6. The preparation method according to claim 1, wherein the aging temperature is 20 ℃ and the aging time is 6-10 h.
7. The preparation method according to claim 1, wherein the calcination is carried out in an oxygen-nitrogen atmosphere, the calcination temperature is 600-800 ℃, and the calcination time is 2-4 h; the reduction temperature is 600-800 ℃, and the time is 1-2 h.
8. The Ni-Rh-based diesel reforming catalyst prepared by the preparation method of any one of claims 1 to 7, comprising a carrier and an active ingredient loaded on the carrier, wherein the active ingredient is Ni-Rh alloy, the carrier is cerium-zirconium solid solution, and the composition of the cerium-zirconium solid solution is CexZr1-xO2Wherein x is 0.5-0.9; in the Ni-Rh-based diesel reforming catalyst, the mass percent of Ni is 3-25%, and the mass percent of Rh is 0.1-2%.
9. The Ni — Rh-based diesel reforming catalyst according to claim 8, wherein x is 0.6 to 0.8, the mass percentage of Ni is 5 to 20%, and the mass percentage of Rh is 0.5 to 1.5%.
10. Use of the Ni-Rh-based diesel reforming catalyst according to claim 8 or 9 in the production of hydrogen by diesel reforming.
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