CN113398965B - Heat-conducting reversed-loading catalyst, and preparation method and application thereof - Google Patents

Heat-conducting reversed-loading catalyst, and preparation method and application thereof Download PDF

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CN113398965B
CN113398965B CN202110593003.0A CN202110593003A CN113398965B CN 113398965 B CN113398965 B CN 113398965B CN 202110593003 A CN202110593003 A CN 202110593003A CN 113398965 B CN113398965 B CN 113398965B
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foam
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silicon carbide
water
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CN113398965A (en
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刘昆
孙永宾
张亭亭
侯超
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Shandong First Medical University and Shandong Academy of Medical Sciences
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    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
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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
    • C01B3/06—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of inorganic compounds containing electro-positively bound hydrogen, e.g. water, acids, bases, ammonia, with inorganic reducing agents
    • C01B3/12—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of inorganic compounds containing electro-positively bound hydrogen, e.g. water, acids, bases, ammonia, with inorganic reducing agents by reaction of water vapour with carbon monoxide
    • C01B3/16—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of inorganic compounds containing electro-positively bound hydrogen, e.g. water, acids, bases, ammonia, with inorganic reducing agents by reaction of water vapour with carbon monoxide using catalysts
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Abstract

The invention provides a thermal-conductivity reversed-loading catalyst, a preparation method and application thereof. The preparation method of the catalyst comprises the following steps: pretreatment of the support, loading of the metal species and pre-activation of the catalyst. According to the invention, silicon carbide foam with good heat conduction, acid and alkali resistance, good stability and good mass transfer effect is used as a carrier, chloroauric acid and cobalt nitrate are used as catalyst precursors, and the inverted integral Au-CoO/SiC-foam is prepared as a model catalyst to catalyze the water-vapor transformation reaction, so that the purposes of eliminating carbon monoxide and producing hydrogen are achieved; the catalyst provided by the invention is used for water-vapor shift reaction, the conversion rate of carbon monoxide is high, the service life is long, and the catalytic activity can be maintained for 500 hours and is far higher than that of the prior art.

Description

Heat-conducting reversed-loading catalyst, and preparation method and application thereof
Technical Field
The invention belongs to the technical field of water-vapor shift reaction, and particularly relates to a heat-conducting reversed-loading catalyst, and a preparation method and application thereof.
Background
The water-gas shift reaction (WGS) is one of the oldest catalytic reactions in the chemical industry, and has been widely used in the fields of ammonia synthesis, carbon monoxide elimination, hydrogen production, etc. for 90 years. The water gas itself is a low calorific value gas, produced by the reaction of high temperature steam with anthracite or coke. The use of a water-gas shift reaction can convert toxic carbon monoxide to carbon dioxide and produce high calorific hydrogen.
The reaction audience is influenced by a plurality of factors, such as temperature, pressure, water vapor ratio, space velocity, catalyst and the like. This reaction is exothermic and lower temperatures favor the forward reaction, but the reaction rate is reduced. The number of gas molecules before and after the reaction does not change, so the pressure has no influence on the equilibrium constant of the reaction, but higher pressure can improve the reaction rate. Since the water-vapor shift reaction is a reversible reaction, the increase of the water vapor content reduces the pressure quotient, thereby facilitating the forward reaction. The increase in space velocity results in a reduction in the contact time of the catalyst and the reactants, possibly resulting in incomplete reaction.
For this reaction, catalyst development is the key to improving the efficiency of this reaction. Therefore, in order to improve the conversion rate of carbon monoxide, lower the reaction temperature, and prolong the life of the catalyst, great efforts have been made to develop catalysts.
The catalysts for this reaction, which have been used industrially, include iron chromium-based catalysts, cobalt molybdenum-based catalysts and copper-based catalysts. For the iron-chromium catalyst, the reaction temperature is higher than 350 ℃, the particle size of the catalyst is easy to increase at high temperature, the catalyst is easy to deposit carbon to cause rapid inactivation of the catalyst and increase of danger coefficient, and in addition, chromium is heavy metal, so the catalyst has high toxicity and is easy to cause environmental pollution. For cobalt molybdenum series catalysts, the use of a pre-catalyst requires sulfidation to convert metal species into sulfides to maintain activity, but in practical applications, the exhaust gas does not necessarily contain sulfur, so the use of this series of catalysts is limited. Copper-based catalysts are widely used because they can activate water and carbon monoxide, but they also have many problems. Such as: chinese patent CN101518737A discloses a method for preparing a steam shift catalyst under hydrogen-rich conditions, which takes copper iron or copper zinc as an active component and adopts a precipitation method to prepare the catalyst. When the content of carbon monoxide in the feed gas is 5.4%, the conversion rate of carbon monoxide is 98%. Chinese patent CN107583650A discloses a preparation method of high temperature water-vapor transformation catalyst under low water-vapor ratio condition, which uses copper, zinc and aluminum as main components and adopts coprecipitation method to prepare catalyst. When the content of carbon monoxide in the raw material gas is 15%, the conversion rate of carbon monoxide is 93%. However, the two catalysts are not heat conductive and easily cause the growth of nano particles, thereby causing the deactivation of the catalysts.
In recent years, transition metal oxide such as cobalt-based oxide catalysts have been widely used for this reaction. Platinum-cobalt alloys such as those in platinum-cobalt/carbon nanotube catalysts perform very well (g.m. mitchell, et al.j. cat.2020, 391, 25). The dispersion of cobalt after zirconium-modified cobalt/ceria increased, thus favoring this reaction, but the catalyst lifetime was only 50 hours (j.kim, int.j.hydrogen Energy,2021, 10.1016/j.ijhydene.2021.01.147). However, the cobalt oxide reaction still has the characteristics of high reaction temperature, short service life of the catalyst, easy inactivation of the catalyst and the like. The inverted structure catalyst has been reported by us and is widely applied to alcohol oxidation reaction, but the relevant reports of inverted catalyst, catalytic activation and the like for water-vapor shift reaction have not been found. The inverted catalyst has unique characteristics in the reaction due to the special appearance and electronic effect.
Disclosure of Invention
Aiming at the defects of insufficient thermal conductivity and low catalytic efficiency in the prior art, the invention provides a thermal conductivity reversed-loading catalyst, a preparation method thereof and application thereof in a water-vapor shift reaction. The invention is realized by the following technical scheme:
the invention provides a heat-conducting reversed-loading catalyst, which takes silicon carbide foam as a carrier, loads gold nanoparticles and cobalt oxide nanoparticles, is in a reversed-loading structure and is represented by a general formula aAu-bCoO/SiC-foam, wherein a represents the content of Au and ranges from 1 to 5 percent, b represents the content of Co and ranges from 1 to 5 percent, and the balance is the carrier.
Preferably, in the general formula of the catalyst, a = b =3%, and the particle size of the gold nanoparticles is 50nm; the particle size of the cobalt oxide nano-particles is 8nm.
Preferably, in the general formula of the catalyst, a = b =1%, and the particle size of the gold nanoparticles is 35nm; the particle size of the cobalt oxide nano-particles is 6nm.
Preferably, in the general formula of the catalyst, a = b =5%, and the particle size of the gold nanoparticles is 60nm; the particle size of the cobalt oxide nano-particles is 10nm.
Because the water vapor transformation reaction is an exothermic reaction, the heat conducting carrier can remove reaction heat, and the catalyst is prevented from being deactivated due to the fact that the active sites are covered by carbon deposition. The catalyst is commonly known as a supported catalyst, or as a noble metal-oxide, wherein the noble metal has a small particle size and the oxide has a large particle size. Although the noble metal-oxide complex has high activity for water-vapor conversion, the small-particle-size noble metal nanoparticles are easy to sinter under severe reaction conditions, so that the catalyst is quickly deactivated. The invention provides an inverted catalyst, and on the contrary, the particle size of noble metal is large, the particle size of oxide is small, and the gold nanoparticles are effectively prevented from being aggregated; and can effectively prevent the sintering problem under high temperature conditions.
As another aspect of the present invention, there is provided a method for preparing the supported catalyst, comprising the steps of:
step 1, pretreatment of a carrier: sequentially comprises four steps of removing surface oxides by acid washing, removing organic matters by ethanol washing, removing inorganic ions by distilled water washing and drying;
step 2, loading of metal species: firstly, loading cobalt nitrate and chloroauric acid on silicon carbide foam by adopting a co-impregnation method; then, drying for 12-24 hours; finally, roasting the catalyst to obtain a fresh catalyst aAu-bCo 3 O 4 SiC-foam (a, b represent the contents of Au and Co, respectively, wt%);
step 3, pre-activating a catalyst: putting the fresh catalyst aAu-bCO3O4/SiC-foam obtained in the step 2 into a quartz tube, and specifically, adding a magnetic ring into the quartz tube, then placing quartz wool above the magnetic ring, and putting the aAu-bCO 3 O 4 Putting the/SiC-foam catalyst above quartz cotton, and placing the aAu-bCo catalyst 3 O 4 the/SiC-foam catalyst is positioned in a constant temperature area of the tubular furnace and finally in the aAu-bCo 3 O 4 Quartz wool is placed above the/SiC-foam catalyst; at the reaction temperature of 300-600 ℃, the water/carbon monoxide ratio of 0.5-2 and the space velocity of 100000-300000h -1 Pre-activating for 0.5-2h under the condition of (1) to obtain the pre-activated catalyst.
Preferably, step 1 comprises the following steps: placing the foam silicon carbide in a hydrochloric acid solution of 0.1mol/L for standing overnight, wherein the mass volume ratio of the foam silicon carbide to the hydrochloric acid solution is 10g/100ml; then filtering, and collecting a filter cake part which is foam silicon carbide; adding absolute ethyl alcohol, standing overnight, filtering, and collecting a filter cake part which is foam silicon carbide, wherein the mass volume ratio of the foam silicon carbide to the absolute ethyl alcohol is 10g/100ml; adding distilled water, standing overnight until the mass volume ratio of the foam silicon carbide to the distilled water is 10g/100ml, then filtering, and collecting a filter cake part to obtain foam silicon carbide; and finally, putting the filter cake into an oven, and drying at the temperature of 100 ℃ overnight to finish the pretreatment of the carrier foam silicon carbide.
Preferably, step 2 comprises the following steps: adding cobalt nitrate hexahydrate and chloroauric acid into the foam silicon carbide pretreated in the step 1, wherein the nitric acid hexahydrateThe cobalt content is 1-5wt% calculated by cobalt, the chloroauric acid content is 1-5wt% calculated by simple substance gold, deionized water is added, the adding amount of the deionized water is 5ml/g calculated by foam silicon carbide, and then the mixture is transferred into an oven to be dried at the temperature of 100 ℃ overnight; finally, the dried product is placed in a muffle furnace, the temperature is raised to 300-500 ℃ at the speed of 1 ℃/minute in the air atmosphere, and the roasting is kept for 4-8 hours, so that the fresh catalyst aAu-bCo of the product is obtained 3 O 4 /SiC-foam。
Preferably, in the step 3, the fresh catalyst prepared in the step 2 is placed into a quartz tube, a magnetic ring is added into the quartz tube, then quartz wool is placed above the magnetic ring, 0.1-0.3 g of catalyst is placed above the quartz wool, the catalyst is noticed to be positioned in a constant temperature area of a tube furnace, and finally a proper amount of quartz wool is placed above the quartz wool.
In the embodiment of the invention, the influence of temperature, space velocity and material ratio on the catalytic performance is considered, and the catalytic performance is reflected by the conversion rate of carbon monoxide. The data comparison shows that the optimal reaction conditions of the pre-activation reaction are that the reaction temperature is 400 ℃, the water/carbon monoxide ratio is 1.5, and the weight space velocity is 200000h -1 。
Preparing the catalyst aAu-bCoO/SiC-foam, and preparing the aAu/SiC-foam and the bCo 3 O 4 The comparison shows that Au-CoO complex shows higher catalytic activity than Au or CoO nanoparticles by using/SiC-foam as a control.
In the examples of the present invention, it was also determined that the active site of the reaction was Au-CoO.
As a third aspect of the present invention, there is provided an application of the supported catalyst in catalyzing a water-gas shift reaction, which not only increases the conversion rate of carbon monoxide, but also effectively prevents the catalyst from sintering under high temperature conditions.
Compared with the prior art, the invention has the beneficial effects that:
1. the invention provides a heat-conducting inverted-loading catalyst for water-vapor transformation reaction, which takes silicon carbide foam with good heat conduction, acid and alkali resistance, good stability and good mass transfer effect as a carrier, takes chloroauric acid and cobalt nitrate as catalyst precursors, prepares inverted-loading integral Au-CoO/SiC-foam as a model catalyst, catalyzes the water-vapor transformation reaction, and achieves the purposes of eliminating carbon monoxide and producing hydrogen;
2. the catalyst provided by the invention is used for water vapor shift reaction, the conversion rate of carbon monoxide is high, the service life is long, and the catalytic activity can be maintained for 500 hours and is substantially unchanged, which is far higher than that of the prior art;
3. the preparation method of the catalyst provided by the invention has the advantages of simple steps, low cost and convenience for industrial production;
4. the product obtained by the preparation method of the inverted catalyst provided by the invention is the gold nanoparticles with large particle size, the specific surface area is small, the Gibbs free energy is small, and the gold nanoparticles can be effectively prevented from being aggregated; and can effectively prevent the sintering problem under high temperature conditions.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the invention and not to limit the invention.
FIG. 1 is a diagram of a water-gas shift reaction apparatus used in the present invention;
wherein, 1-nitrogen bottle, 2-carbon monoxide bottle, 3-peristaltic pump, 4-reaction tube, 5-condenser, 6-gas chromatography;
FIG. 2 is a diagram of fresh aAu-bCo provided by the present invention 3 O 4 X-ray diffraction pattern of SiC-foam (a = b = 3%);
FIG. 3 is an X-ray diffraction pattern of preactivated aAu-bCoO/SiC-foam (a = b = 3%) provided by the present invention;
FIG. 4 is a diagram of fresh aAu-bCo provided by the present invention 3 O 4 X-ray photoelectron spectroscopy of SiC-foam (a = b = 3%);
FIG. 5 is an X-ray photoelectron spectrum of preactivated aAu-bCoO/SiC-foam (a = b = 3%) provided by the present invention;
FIG. 6 is a diagram of fresh aAu-bCo provided by the present invention 3 O 4 Scanning electron micrograph of/SiC-foam (a = b = 3%);
FIG. 7 is a scanning electron micrograph of preactivated aAu-bCoO/SiC-foam (a = b = 3%) provided by the present invention;
FIG. 8 is a transmission electron micrograph of preactivated aAu-bCoO/SiC-foam (a = b = 3%) provided by the present invention;
FIG. 9 is a graph of the catalytic activity of a catalyst provided by the present invention as a function of time;
FIG. 10 shows Au-Co after reduction at different temperatures 3 O 4 X-ray diffraction pattern of/SiC-foam (a = b = 3%) (reduction at 100 ℃,200 ℃,300 ℃ from bottom to top, respectively).
Detailed Description
It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
In the invention, standing overnight, drying overnight and the like are routine laboratory operations and generally mean more than 12 hours.
Example 1: heat-conducting reversed-loading type catalyst
The silicon carbide foam is taken as a carrier and is expressed as aAu-bCoO/SiC-foam, wherein a represents the content of Au, the content range is 1-5%, and b represents the content of Co, the content range is 1-5%.
When a = b =3%, the gold nanoparticle size range is 50nm for the optimal catalyst; the particle size range of the cobalt oxide nano particles is 8nm.
When a = b =1%, the gold nanoparticles have a particle size range of 35nm; the particle size range of the cobalt oxide nano-particles is 6nm.
When a = b =5%, the gold nanoparticles have a particle size range of 60nm; the particle size range of the cobalt oxide nano-particles is 10nm.
Example 2: preparation method of heat-conducting inverted catalyst
Step 1, catalyst preparation, including carrier pretreatment, metal species loading and catalyst pre-activation:
the carrier pretreatment comprises the following specific steps: 10g of foamed silicon carbide was placed in a beaker, and 100ml of a 0.1mol/L diluted hydrochloric acid solution was added thereto and left to stand overnight. The filter cake was then removed and the filter cake fraction collected. Then, 100ml of absolute ethyl alcohol was added thereto, and the mixture was allowed to stand overnight, and then taken out for filtration, and a cake portion was collected. 100ml of distilled water was added and left to stand overnight, and then taken out for filtration, and a cake portion was collected. Finally, the filter cake was placed in an oven to dry overnight at 100 ℃ and the treatment of the carrier foam silicon carbide was complete.
The loading of the metal species includes: firstly, cobalt nitrate and chloroauric acid are loaded on silicon carbide foam by adopting a co-impregnation method, secondly, the catalyst is dried for a period of time, and finally, the catalyst is roasted at a certain temperature to obtain a fresh catalyst aAu-bCo 3 O 4 A/SiC-foam (Co-impregnation, a, b representing the content of Au and Co, wt.%), in addition, a Au/SiC-foam and bCo were prepared 3 O 4 The control was SiC-foam.
The method comprises the following specific steps: 1 g of the treated foam silicon carbide is added into a beaker, then a certain amount of cobalt nitrate hexahydrate and chloroauric acid (the content is 1-5wt% respectively calculated by cobalt and simple substance gold) are added, 5ml of deionized water is added, and then the mixture is dried in an oven at 100 ℃ overnight. And finally, roasting the dried product. Placing the dried product in a muffle furnace, raising the temperature to 300-500 ℃ at the rate of 1 ℃/min in the air atmosphere, and roasting for 4-8 hours to obtain a product aAu-bCo 3 O 4 /SiC-foam。
As a preparation example, the material was 18mg of chloroauric acid, 51mg of cobalt nitrate hexahydrate, and the product was prepared as aAu-bCo with a = b =1% 3 O 4 A SiC-foam catalyst;
as another preparation example, 36mg of chloroauric acid and 102mg of cobalt nitrate hexahydrate were used as materials to obtain a product of a = b =2%aAu-bCo 3 O 4 a/SiC-foam catalyst;
as another preparation example, 54mg of chloroauric acid and 153mg of cobalt nitrate hexahydrate were fed to produce a product of aAu-bCo with a = b =3% 3 O 4 a/SiC-foam catalyst;
as another preparation example, 72mg of chloroauric acid and 204mg of cobalt nitrate hexahydrate were fed to produce a product of aAu-bCo with a = b =4% 3 O 4 A SiC-foam catalyst;
as another preparation example, 90mg of chloroauric acid, 255mg of cobalt nitrate hexahydrate was charged to produce a product of aAu-bCo with a = b =5% 3 O 4 a/SiC-foam catalyst.
The preparation steps of the aAu/SiC-foam are as follows: 1 g of the treated foam silicon carbide is added into a beaker, then a certain amount of chloroauric acid (the content is 1-5wt% calculated by simple substance gold) is added, 5ml of deionized water is added, and the mixture is placed in an oven and dried at 100 ℃ overnight. And finally, roasting the dried product. And (3) placing the dried product in a muffle furnace, and roasting for 4-8 hours at the temperature of 300-500 ℃ at the speed of 1 ℃/minute in the air atmosphere to obtain the product aAu/SiC-foam.
bCo 3 O 4 The preparation steps of the/SiC-foam are as follows: 1 g of the treated silicon carbide foam was added to a beaker, then a certain amount of cobalt nitrate hexahydrate (1-5% by weight calculated as cobalt) was added, 5ml of deionized water was added, and the mixture was dried overnight in an oven at 100 ℃. And finally, roasting the dried product. Placing the dried product in a muffle furnace, raising the temperature to 300-500 ℃ at the rate of 1 ℃/min in the air atmosphere, and roasting for 4-8 hours to obtain a product bCo 3 O 4 /SiC-foam。
The pre-activation step of the catalyst is as follows: fresh catalyst (aAu-bCo) 3 O 4 /SiC-foam、aAu/SiC-foam、bCo 3 O 4 /SiC-foam) is put into a quartz tube, a magnetic ring is added into the quartz tube, then quartz wool is placed above the magnetic ring, and 0.1-0.3 g of aAu-bCo is added 3 O 4 the/SiC-foam catalyst is placed above the quartz wool, and the aAu-bCo catalyst is added 3 O 4 the/SiC-foam catalyst is positioned in a constant temperature area of the tubular furnace, and finally a proper amount of quartz wool is placed above the catalyst. At the reaction temperature of 300-600 ℃, the water/carbon monoxide ratio of 0.5-2 and the space velocity of 100000-300000h -1 Pre-activating for 0.5-2h under the condition of (1) to obtain the pre-activated catalyst (aAu-bCoO/SiC-foam, aAu/SiC-foam and bCoO/SiC-foam respectively).
As a typical example, at a reaction temperature of 400 ℃, a water/carbon monoxide ratio of 1.5 and a space velocity of 200000h -1 Pre-activating for 1 hour under the condition of (2) to prepare a pre-activated catalyst, and allowing the pre-activated catalyst to enter a subsequent catalytic water vapor shift reaction.
Example 3: catalysis of water-vapor shift reaction by catalyst
The water-vapor shift reaction adopts the device shown in figure 1, which comprises a nitrogen gas bottle 1, a carbon monoxide bottle 2, a peristaltic pump 3, a reaction tube 4 and a condenser 5 connected with the reaction tube, wherein nitrogen gas, carbon monoxide and water controlled by a mass flow meter enter the reaction tube 4 of the fixed bed reactor together, the quartz wool above the catalyst can gasify the water, and the product is detected by a gas chromatography 6.
For preactivation reaction and water-vapor shift reaction, the number of gas molecules before and after reaction is not changed, so that the influence of temperature, airspeed and material ratio on catalytic performance is only considered. Adding a magnetic ring into a quartz tube, placing quartz cotton above the magnetic ring, and adding 0.1-0.3 g of aAu-bCo 3 O 4 the/SiC-foam (a = b = 3%) catalyst was placed above the quartz wool, taking care that the catalyst was located in the thermostatic zone of the tube furnace, and finally a suitable amount of quartz wool was placed above the catalyst.
At the reaction temperature of 300-500 ℃, the water/carbon monoxide ratio of 1-5 and the weight space velocity of 10-1000h -1 The influence of the reaction conditions on the catalytic performance was examined in detail (FIG. 1). The carbon monoxide conversion rate is calculated by gas chromatography by adjusting the catalyst dosage, the water/carbon monoxide ratio, the weight hourly space velocity and sampling after being stabilized at a certain temperature for 1 hour. The product is detected by gas chromatography SP-7820, the chromatographic column is TDX-01, the temperature of a gasification chamber is 120 ℃, the temperature of a detector is 150 ℃, the bridge flow is 130mA, the argon flow rate is 100 ml/min, and the correction factors of various gasesAnd the son is used for calculating the conversion rate of the carbon monoxide after verification.
The conversion rate of carbon monoxide is calculated by the following formula:
Conv.＝F CO2 *A CO2 /(F CO2 *A CO2 +F CO *A CO )
conv. carbon monoxide conversion, F CO2 Correction factor for carbon dioxide, A CO2 For CO in chromatography 2 Peak area of (1), F CO Is a correction factor for carbon monoxide, A CO Is the peak area of CO in the chromatogram.
Calculation formula of correction factor:
injecting 1 ml of mixed gas with the volume ratio of carbon dioxide to methane being 1/1 into a gas chromatography SP-7820 by using a sample injection needle, wherein a chromatographic column is TDX-01, the temperature of a gasification chamber is 120 ℃, the temperature of a detector is 150 ℃, a bridge flow is 130mA, the flow rate of argon is 100 ml/min, peak areas of peaks appearing in 2.2 min and 4.8 min are the areas of methane and carbon dioxide respectively, and then, a correction factor F of the carbon dioxide CO2 ＝A CH4 /A CO2 . Wherein A is CH4 Is the peak area of methane, A CO2 Is the peak area of carbon dioxide.
Injecting 1 ml of mixed gas with the volume ratio of carbon monoxide to methane of 1/1 into a gas chromatograph SP-7820 by using a sampling needle, wherein a chromatographic column is TDX-01, the temperature of a gasification chamber is 120 ℃, the temperature of a detector is 150 ℃, a bridge flow is 130mA, the flow rate of argon is 100 ml/min, peak areas of peaks appearing in 2.2 min and 2.8 min are the areas of methane and carbon monoxide respectively, and then, the correction factor F of the carbon monoxide is CO ＝A CH4 /A CO . Wherein A is CH4 Is the peak area of methane, A CO The peak area of carbon monoxide.
Examples 2-1 to 2-5 the effects of catalyzing the water-gas shift reaction are tabulated below:
Figure BDA0003089899380000081
Figure BDA0003089899380000091
it can be seen that aAu-bCoO/SiC (a = b = 3%) catalyst was able to efficiently promote this reaction, while aAu/SiC (a = 3%) and bCoO/SiC (b = 3%) catalyzed this reaction under the same conditions with lower carbon monoxide conversion. Therefore, au-CoO is the active site of this reaction.
Example 4: activity site determination
To aAu-bCo 3 O 4 the/SiC-foam (a = b = 3%), aAu-bCoO/SiC-foam (a = b = 3%) catalysts were characterized by X-ray diffraction (fig. 2, 3), X-ray photoelectron spectroscopy (fig. 4, 5), scanning electron microscopy (fig. 6, 7) and transmission electron microscopy (fig. 8) for the fresh catalyst, preactivated catalyst to determine the active sites of the reaction. In fig. 2, the left panel demonstrates the presence of Au only, and no AuCo alloy formation, for the fresh catalyst; co confirmation by diffraction peaks shaded in the right 3 O 4 Present in fresh catalyst; the particle size of the cobaltosic oxide is about 8nm; the left panel in fig. 3 confirms that the fresh catalyst has Au only and no AuCo alloy formed; diffraction peaks at the shading of the right panel confirm the presence of CoO in the preactivated catalyst; the particle size of the cobalt oxide is about 8nm; co confirmation by the absence of satellite peak at 787eV in FIG. 4 3 O 4 Present in fresh catalyst; the satellite peak at 787eV in fig. 5 confirms the presence of CoO in the preactivated catalyst; as can be seen from FIG. 6, the Au particle size is about 40-50nm; as can be seen from FIG. 7, the Au particle size is about 40-50nm. At this time, note that: a series of characterizations of both fresh and pre-activated catalyst are required to study the active sites. For the fresh catalyst, the surface structure and the bulk structure of the catalyst are Au-Co after the catalyst is characterized 3 O 4 In contrast, the carbon monoxide conversion rate in the water vapor shift reaction was 10% at 300 ℃ (fig. 9). For the preactivated catalyst, we characterized it and found that the bulk structure of the catalyst is Au — CoO, and accordingly, the carbon monoxide conversion rate in the water-gas shift reaction is 90% at 300 ℃ (fig. 9), and the catalytic activity can be maintained substantially unchanged for 500h, and the stability is far higher than that reported in the literature (j.kim, int.j.hydrogen Energy,2021, 10.1016/j.ijhydene.2021.01.147).
Furthermore, we are directed to Au-Co 3 O 4 After reduction (hydrogen reduction at 100-300 ℃ for 10 min), different phases are found to correspond to different reduction temperatures. The catalyst after reduction at 100 ℃ is Au-Co 3 O 4 The catalyst after reduction at 200 ℃ is Au-Co 3 O 4 And Au-CoO, wherein the catalyst after reduction at 300 ℃ is Au-CoO. 100. The catalysts after reduction at 200 and 300 ℃ had carbon monoxide conversions of 10%,52%,90%. Thus, au-CoO was confirmed as an active site (FIG. 10).
Inverted structural analysis:
the results of X-ray diffraction, scanning electron microscope and transmission electron microscope show that the series of catalysts have an inverted structure. The particle size of the gold nanoparticles and cobalt oxide nanoparticles is about 40-50 and 10 nanometers. Because the gold nanoparticles have larger particle size, the structure can effectively prevent sintering, thereby improving the stability of the gold nanoparticles in the water-vapor shift reaction (fig. 6 and 7 show that the particle size of the gold nanoparticles in the fresh catalyst is about 40-50nm, and the particle size of the catalyst after pre-activation is not increased). The small-particle-size gold nanoparticles have high specific surface area and large Gibbs free energy, and are easy to sinter. And the specific surface area of the gold nanoparticles with large particle size is small, and the Gibbs free energy is small, so that the gold nanoparticles can be effectively prevented from being aggregated. Meanwhile, the gold nanoparticles or the cobalt oxide nanoparticles have almost no catalytic activity, so the reversed gold-cobalt oxide nanoparticles can effectively prevent sintering under high-temperature conditions.
Example 5: comparison of Pre-activation and Water vapor Shift reaction conditions
In the example, the influence of temperature, airspeed and material ratio on the catalytic performance is considered, and the catalytic performance is reflected by the conversion rate of carbon monoxide.
When the water/carbon monoxide ratio is 2, the weight space velocity is 200000h -1 Then, as the temperature was increased from 300 ℃ to 400 ℃, the carbon monoxide conversion rate was increased from 50% to 95%, and the temperature was further increased to 600 ℃, the carbon monoxide conversion rate was almost unchanged, indicating that 400 ℃ was the optimum reaction temperature.
When the water/carbon monoxide ratio is 2 and the temperature is 400 ℃, the space velocity is increased from 100000h -1 Rises to 200000h -1 The conversion rate of carbon monoxide is increased from 30 percent to 95 percent, and the temperature is continuously increased to 300000h -1 The conversion of carbon monoxide drops to 83%, which indicates 200000h -1 For optimal space velocity of the reaction.
When the temperature is 400 ℃, the weight space velocity is 200000h -1 Then, as the water/carbon monoxide ratio was increased from 0.5 to 1.5, the carbon monoxide conversion rate was increased from 20% to 95%, and continuing to increase the water/carbon monoxide ratio to 2, the carbon monoxide conversion rate was hardly changed, indicating that 2 is the optimum water/carbon monoxide ratio.
Therefore, the optimal reaction conditions are that the reaction temperature is 400 ℃, the water/carbon monoxide ratio is 1.5, and the weight space velocity is 200000h -1 。

Claims (4)

1. The application of the heat-conducting reversed-loading catalyst in catalyzing water-vapor conversion reaction is characterized in that the heat-conducting reversed-loading catalyst takes silicon carbide foam as a carrier, loads gold nanoparticles and cobalt oxide nanoparticles, is in a reversed-loading structure and is represented by a general formulaaAu-bThe method comprises the following steps of (1) CoO/SiC-foam, wherein a represents the content of Au, and ranges from 1 to 5%, b represents the content of Co in CoO, and the balance is a carrier;
a = b =3%, and the particle size of the gold nanoparticles is 50nm; the particle size of the cobalt oxide nano particles is 8nm;
a = b =1%, and the particle size of the gold nanoparticles is 35nm; the particle size of the cobalt oxide nano-particles is 6 nm;
a = b =5%, and the particle size of the gold nanoparticles is 60nm; the particle size of the cobalt oxide nano-particles is 10 nm;
the preparation method of the heat-conducting inverted catalyst comprises the following steps:
step 1, pretreatment of a carrier: sequentially comprises four steps of removing surface oxides by acid washing, removing organic matters by ethanol washing, removing inorganic ions by distilled water washing and drying;
step 2, loading of metal species: firstly, loading cobalt nitrate and chloroauric acid on silicon carbide foam by adopting a co-impregnation method; then, drying for 12-24 hours; finally roasting the catalyst to obtain a fresh catalyst aAu-bCo 3 O 4 a/SiC-foam, wherein a and b representContent of Au and Co, wt%;
step 3, pre-activating the catalyst: fresh catalyst aAu-bCo obtained in the step 2 3 O 4 The method comprises the steps of putting the SiC-foam into a quartz tube, adding a magnetic ring into the quartz tube, then putting quartz wool above the magnetic ring, and putting the aAu-bCo 3 O 4 Putting the/SiC-foam catalyst above quartz cotton, and placing the aAu-bCo catalyst 3 O 4 the/SiC-foam catalyst is positioned in a constant temperature area of the tube furnace and finally inaAu-bCo 3 O 4 Quartz wool is placed above the/SiC-foam catalyst; at the reaction temperature of 300-600 ℃, the water/carbon monoxide ratio of 0.5-2 and the weight hourly space velocity of 100000-300000h -1 Pre-activating for 0.5-2h under the condition of (1) to obtain the pre-activated catalyst aAu-bCoO/SiC-foam.
2. The use of a thermally conductive reverse-loaded catalyst in catalyzing a water-gas shift reaction as claimed in claim 1, wherein step 1 comprises the steps of: placing the foam silicon carbide in a 0.1mol/L hydrochloric acid solution for standing overnight, wherein the mass volume ratio of the foam silicon carbide to the hydrochloric acid solution is 10g/100ml; then filtering, and collecting a filter cake part which is foam silicon carbide; adding absolute ethyl alcohol, standing overnight, wherein the mass-volume ratio of the foam silicon carbide to the absolute ethyl alcohol is 10g/100ml, then filtering, and collecting a filter cake part, namely the foam silicon carbide; adding distilled water, standing overnight until the mass volume ratio of the foam silicon carbide to the distilled water is 10g/100ml, then filtering, and collecting a filter cake part to obtain foam silicon carbide; finally, the filter cake is put into an oven and dried overnight at the temperature of 100 ℃, and the pretreatment of the carrier, namely the foam silicon carbide, is finished.
3. The use of a thermally conductive reversed catalyst according to claim 1 for catalyzing a water-gas shift reaction, wherein step 2 comprises the steps of: adding cobalt nitrate hexahydrate and chloroauric acid into the foamed silicon carbide pretreated in the step 1, wherein the content of the cobalt nitrate hexahydrate is 1-5wt% calculated by cobalt, the content of gold is 1-5wt% calculated by simple substance gold, adding deionized water, and the adding amount of the deionized water is 5ml/g calculated by the foamed silicon carbide, and then turning toTransferring to an oven and drying at 100 ℃ overnight; finally, placing the dried product in a muffle furnace, heating to 300-500 ℃ at the speed of 1 ℃/minute in the air atmosphere, and roasting for 4-8 hours to obtain a fresh catalystaAu-bCo 3 O 4 /SiC-foam。
4. The use of a thermally conductive reversed catalyst in catalyzing water-gas shift reaction according to claim 1, wherein the pre-activation reaction conditions of the catalyst in step 3 are as follows: reaction temperature 400 deg.C o C, the water/carbon monoxide ratio is 1.5, and the space velocity is 200000h -1 。
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