CN114939420A - Palladium-based catalyst containing cobalt oxide carrier and preparation method and application thereof - Google Patents
Palladium-based catalyst containing cobalt oxide carrier and preparation method and application thereof Download PDFInfo
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- CN114939420A CN114939420A CN202210734356.2A CN202210734356A CN114939420A CN 114939420 A CN114939420 A CN 114939420A CN 202210734356 A CN202210734356 A CN 202210734356A CN 114939420 A CN114939420 A CN 114939420A
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- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
- 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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- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/02—Impregnation, coating or precipitation
- B01J37/0201—Impregnation
- B01J37/0203—Impregnation the impregnation liquid containing organic compounds
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- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/02—Impregnation, coating or precipitation
- B01J37/0201—Impregnation
- B01J37/0213—Preparation of the impregnating solution
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- F23G7/00—Incinerators or other apparatus for consuming industrial waste, e.g. chemicals
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Abstract
The invention provides a palladium-based catalyst containing a cobalt oxide carrier, and a preparation method and application thereof 3 O 4 The carrier is loaded with low-concentration noble metal Pd by an impregnation method, and the metals Pd and Co are fully utilized 3 O 4 The synergistic effect among the carriers improves the catalytic activity and the stability; the catalytic performance is maximally improved by regulating the ratio of the second solvent to the first solvent and the dosage of the surfactant; and the preparation process is simple, convenient to operate, green and efficient.
Description
Technical Field
The invention belongs to the technical field of catalyst preparation, and particularly relates to a palladium-based catalyst containing a cobalt oxide carrier, and a preparation method and application thereof.
Background
Methane has a strong greenhouse as a major component of natural gas and coal mine gasEffect of CO as its potency 2 21 times of the total weight of the powder. Natural gas automobile exhaust, natural gas industry, mine exhaust, etc. produce large quantities of low concentration (below 5%) methane every day. 5% is lower than the minimum concentration limit of methane combustion, and the low-concentration methane is difficult to completely oxidize by using the conventional flame combustion technology, and the low-concentration methane is directly discharged into the atmosphere, so that the atmospheric greenhouse effect is aggravated, and the living environment is threatened. The total activation energy required for homogeneous combustion of methane is very high, and in conventional flame combustion, methane is in>The oxidative cracking can occur at a high temperature of 1300 ℃, and a large amount of toxic byproducts (NO, CO and the like) are generated. Methane can be converted by combustion over a noble metal, transition metal catalyst at lower temperatures and substantially NO is produced. Therefore, low concentration methane can be eliminated by catalytic combustion at a relatively low temperature.
The methane combustion catalysts developed to date have primarily supported noble and non-noble metal oxides. In recent years, domestic and foreign research on low-concentration methane catalytic combustion catalysts mainly focuses on improving the activity, thermal stability and toxicity resistance of the high-efficiency supported noble metal nano-catalyst for low-concentration methane catalytic combustion at low temperature of the catalyst and reducing the cost of the catalyst. The noble metal oxide has lower ignition temperature, better stability and better resistance to poisoning, thereby becoming a research hotspot of the low-concentration methane catalytic combustion catalyst.
CN106492824A discloses a methane combustion catalyst, which has a core-shell structure of [ Pd] 0.010 [Co 3 O 4 ] 0.300 @[SiO 2 ] 0.690 The core part comprises cobaltosic oxide and noble metal, the shell part comprises silicon dioxide, the noble metal is coated in the shell by a layer of high-temperature-resistant shell, the shell is provided with a pore passage, so that reaction molecules can freely enter the core part to react with the active center of the noble metal, and then generated product molecules are diffused out of the shell, the size of the active center in the whole process is larger than that of the shell reaction pore passage, so that the overflow of active components is avoided, the high-temperature resistance and catalytic combustion performance of the methane combustion catalyst are improved, and the problem that the methane combustion catalyst is easy to sinter at high temperature in the prior art is solved.
However, the catalytic efficiency in the above process still remains to be improved. Therefore, there is a need to provide a new catalyst that maintains good catalytic performance at high space velocity and under steam conditions. In order to realize low-temperature activation and stable conversion of methane, the development of a palladium-based catalyst with low load, high activity and stability has great industrial application significance.
Disclosure of Invention
The invention aims to provide a palladium-based catalyst containing a cobalt oxide carrier, and a preparation method and application thereof, and Co is prepared by a solvothermal method 3 O 4 The carrier is loaded with low-concentration noble metal Pd by an impregnation method, and the metals Pd and Co are fully utilized 3 O 4 The synergistic effect among the carriers improves the catalytic activity and the stability; the catalytic performance is maximally improved by regulating the ratio of the second solvent to the first solvent and the dosage of the surfactant; and the preparation process is simple, convenient to operate, green and efficient.
In order to achieve the purpose, the invention adopts the following technical scheme:
one of the objects of the present invention is to provide a method for preparing a palladium-based catalyst containing a cobalt oxide carrier, which comprises the following steps:
(1) mixing a surfactant and a first solvent, and adding a cobalt source to obtain an initial solution;
wherein the surfactant comprises CTAB and/or PVP;
(2) mixing the initial solution obtained in the step (1) with a second solvent, carrying out a solvothermal reaction, and sequentially carrying out first solid-liquid separation and first roasting to obtain Co 3 O 4 A carrier;
(3) mixing the Co of the step (2) 3 O 4 And (3) soaking the carrier in a palladium source solution, and sequentially carrying out second solid-liquid separation and second roasting to obtain the palladium-based catalyst containing the cobalt oxide carrier.
In the invention, Co is prepared by a solvothermal method 3 O 4 The carrier is loaded with low-concentration noble metal Pd by an impregnation method, and the metals Pd and Co are fully utilized 3 O 4 The synergistic effect among the carriers improves the catalytic activity and the stability; the catalytic performance is maximally improved by regulating the ratio of the second solvent to the first solvent and the dosage of the surfactant; the preparation process is simple, convenient to operate, green and efficient;
it is worth to say that the cobalt source and the surfactant are dissolved in the first solvent, and the second solvent is coated on the outer layer to form a carbon layer protective layer, so that the cobalt precursor is slowly released from the carbon layer in the roasting process, the agglomeration caused in the roasting process is reduced, and the roasted Co is obtained 3 O 4 Has more oxygen vacancies, is beneficial to the conversion between PdO-Pd, and improves the catalytic performance.
As a preferred technical scheme of the invention, the surfactant in the step (1) is CTAB.
Preferably, the first solvent of step (1) comprises ethanol.
Preferably, the cobalt source of step (1) comprises cobalt acetate.
In a preferred embodiment of the present invention, the molar ratio of the cobalt ion in the cobalt source in the step (1) to the surfactant is (10-30):1, for example, 10:1, 12:1, 15:1, 18:1, 20:1, 23:1, 25:1, 27:1, 30:1, etc., more preferably (17-25):1, for example, 17:1, 18:1, 19:1, 20:1, 21:1, 22:1, 23:1, 24:1, 25:1, etc., but the present invention is not limited to the above-mentioned numerical values, and other numerical values not listed in the above-mentioned numerical value range are also applicable.
It is worth mentioning that the molar ratio of the cobalt ions in the cobalt source in the step (1) to the surfactant is (10-30):1, if the surfactant is too little, the cobalt source is not favorably dispersed, and the catalytic performance is reduced; if the surfactant is too much, formation of a protective layer on the surface of the cobalt source is not facilitated, and the catalytic performance is lowered.
Preferably, the mass ratio of the cobalt source to the first solvent in step (1) is 1 (10-15), and may be, for example, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, etc., but is not limited to the enumerated values, and other unrecited values within the above-mentioned range of values are also applicable.
As a preferred embodiment of the present invention, the second solvent in step (2) comprises any one of ethylene glycol, isopropanol, 1, 3-propanediol or glycerol or a combination of at least two thereof, and typical but non-limiting examples of the combination include a combination of ethylene glycol and isopropanol, a combination of ethylene glycol and 1, 3-propanediol, a combination of ethylene glycol and glycerol, a combination of isopropanol and 1, 3-propanediol, a combination of isopropanol and glycerol, and a combination of 1, 3-propanediol and glycerol; further preferred is isopropanol.
Preferably, the volume ratio of the second solvent in the step (2) to the first solvent in the step (1) is 1 (2-16), and may be, for example, 1:2, 1:3, 1:5, 1:7, 1:8, 1:10, 1:11, 1:12, 1:13, 1:15, 1:16, etc., but is not limited to the enumerated values, and other values within the above-mentioned range of values are also applicable.
It is worth mentioning that the volume ratio of the second solvent in the step (2) to the first solvent in the step (1) is 1 (2-16), if the second solvent is too much, the cobalt source is not completely dissolved, and the catalytic performance is reduced; if the second solvent is too small, formation of a protective layer is not facilitated, resulting in a decrease in catalytic performance.
Preferably, the temperature of the solvothermal reaction in step (2) is 120-180 ℃, and may be, for example, 120 ℃, 125 ℃, 130 ℃, 135 ℃, 140 ℃, 145 ℃, 150 ℃, 155 ℃, 160 ℃, 165 ℃, 170 ℃, 175 ℃, 180 ℃, etc., but is not limited to the recited values, and other values not recited in the above-mentioned range of values are also applicable.
Preferably, the solvothermal reaction time in the step (2) is 4 to 36 hours, for example, 4 hours, 5 hours, 8 hours, 10 hours, 12 hours, 15 hours, 18 hours, 20 hours, 22 hours, 24 hours, 26 hours, 28 hours, 30 hours, 32 hours, 34 hours, 36 hours, etc., but is not limited to the enumerated values, and other unrecited values in the above numerical range are also applicable.
In a preferred embodiment of the present invention, the first solid-liquid separation in step (2) is centrifugation.
Preferably, the temperature of the first calcination in step (2) is 600-800 ℃, such as 600 ℃, 620 ℃, 640 ℃, 660 ℃, 680 ℃, 700 ℃, 720 ℃, 740 ℃, 760 ℃, 780 ℃, 800 ℃ and the like, but not limited to the recited values, and other unrecited values in the above-mentioned range are also applicable.
Preferably, the first baking temperature rise rate in the step (2) is 2-5 ℃/min, and may be, for example, 2 ℃/min, 2.5 ℃/min, 3 ℃/min, 3.5 ℃/min, 4 ℃/min, 4.5 ℃/min, 5 ℃/min, etc., but is not limited to the values listed, and other values not listed within the above-mentioned range of values are also applicable.
Preferably, the first calcination time in step (2) is 1-12h, such as 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, etc., but not limited to the recited values, and other values not recited in the above range of values are also applicable.
As a preferred embodiment of the present invention, the content of the palladium source in the palladium source solution of step (3) is 0.02 to 0.03 wt%, and may be, for example, 0.02 wt%, 0.021 wt%, 0.022 wt%, 0.023 wt%, 0.024 wt%, 0.025 wt%, 0.026 wt%, 0.027 wt%, 0.028 wt%, 0.029 wt%, 0.03 wt%, etc., but it is not limited to the exemplified values, and other values not exemplified in the above-mentioned range of values are also applicable.
Preferably, with 1gCo 3 O 4 The amount of the palladium source solution used in step (3) is 90-120mL based on the carrier, and may be, for example, 90mL, 95mL, 100mL, 105mL, 110mL, 115mL, 120mL, etc., but is not limited to the values listed, and other values not listed in the above range are also applicable.
Preferably, the impregnation temperature in step (3) is 10-30 ℃, for example, 10 ℃, 12 ℃, 14 ℃, 16 ℃, 18 ℃, 20 ℃, 22 ℃, 24 ℃, 26 ℃, 28 ℃, 30 ℃ and the like, but not limited to the recited values, and other values not recited in the above range of values are also applicable.
Preferably, the impregnation time in step (3) is 1 to 2 hours, and may be, for example, 1 hour, 1.1 hour, 1.2 hours, 1.3 hours, 1.4 hours, 1.5 hours, 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours, 2 hours, etc., but is not limited to the recited values, and other values not recited in the above-mentioned range of values are also applicable.
In a preferred embodiment of the present invention, the second solid-liquid separation in step (3) is rotary evaporation.
Preferably, the temperature of the second calcination in step (3) is 550-650 ℃, and may be, for example, 550 ℃, 560 ℃, 570 ℃, 580 ℃, 590 ℃, 600 ℃, 610 ℃, 620 ℃, 630 ℃, 640 ℃, 650 ℃, etc., but is not limited to the values listed, and other values not listed in the above range are also applicable.
Preferably, the temperature increase rate of the second baking in the step (3) is 2 to 5 ℃/min, and may be, for example, 2 ℃/min, 2.5 ℃/min, 3 ℃/min, 3.5 ℃/min, 4 ℃/min, 4.5 ℃/min, 5 ℃/min, etc., but is not limited to the values listed, and other values not listed in the above range of values are also applicable.
Preferably, the second calcination time in step (3) is 4-6h, such as 4h, 4.2h, 4.4h, 4.6h, 4.8h, 5h, 5.2h, 5.4h, 5.6h, 5.8h, 6h, etc., but not limited to the recited values, and other values in the above range are also applicable.
As a preferred technical scheme of the invention, the preparation method comprises the following steps:
(1) mixing a surfactant with ethanol, and adding cobalt acetate to obtain an initial solution;
wherein the surfactant comprises CTAB and/or PVP; the molar ratio of cobalt ions in the cobalt acetate to the surfactant is (10-30) to 1; the mass ratio of the cobalt acetate to the ethanol is 1 (10-15);
(2) mixing the initial solution and the second solvent in the step (1), performing solvothermal reaction at the temperature of 120-180 ℃ for 4-36h, centrifuging, heating to the temperature of 600-800 ℃ at the speed of 2-5 ℃/min, and performing first roasting for 1-12h to obtain Co 3 O 4 A carrier;
wherein the second solvent comprises any one of or a combination of at least two of ethylene glycol, isopropanol, 1, 3-propanediol or glycerol; the volume ratio of the second solvent to the ethanol in the step (1) is 1 (2-16);
(3) mixing the Co of the step (2) 3 O 4 The carrier is dipped in 0.02-0.03 wt% palladium nitrate solution for 1-2h, with 1gCo 3 O 4 The carrier is taken as a reference, and the dosage of the palladium nitrate solution is 90-120 mL; after rotary evaporation, the temperature is raised to 550 ℃ and 650 ℃ at the speed of 2-5 ℃/min for second roasting for 4-6h, and the palladium-based catalyst containing the cobalt oxide carrier is obtained.
The second purpose of the invention is to provide a palladium-based catalyst containing a cobalt oxide carrier, which is obtained by the preparation method of the first purpose, wherein the palladium-based catalyst comprises Co 3 O 4 Carrier and carrier supported on said Co 3 O 4 An active component Pd on the carrier; the content of the active component Pd is 0.8 to 1.2 wt%, and may be, for example, 0.8 wt%, 0.82 wt%, 0.86 wt%, 0.9 wt%, 0.94 wt%, 0.97 wt%, 1.0 wt%, 1.13 wt%, 1.18 wt%, 1.2 wt%, etc., but is not limited to the enumerated values, and other unrecited values within the above-mentioned range of values are also applicable.
The third purpose of the invention is to provide an application of the palladium-based catalyst containing the cobalt oxide carrier in the second purpose, and the palladium-based catalyst containing the cobalt oxide carrier is used for methane combustion reaction.
It is worth to say that, when the palladium-based catalyst containing the cobalt oxide carrier of the invention catalyzes the methane combustion reaction, the raw material gas comprises methane, oxygen, carbon dioxide, water vapor and nitrogen, the concentration of the methane is 800-1200ppm, the concentration of the oxygen is 3-5%, the concentration of the carbon dioxide is 5-10%, the content of the water vapor is 5-10%, and the balance is nitrogen.
The recitation of numerical ranges herein includes not only the above-recited numerical values, but also any numerical values between non-recited numerical ranges, and is not intended to be exhaustive or to limit the invention to the precise numerical values encompassed within the range for brevity and clarity.
Compared with the prior art, the invention has the following beneficial effects:
(1) the palladium-based catalyst containing the cobalt oxide carrier uses reductive Co 3 O 4 As a carrier, the low-concentration noble metal Pd is loaded, and the metal Pd and Co are fully utilized 3 O 4 The synergistic effect between the carriers improves the catalytic activity and the stability, and the catalyst can be recycled, thereby reducing the costThen, the process is carried out;
(2) in the preparation method of the palladium-based catalyst containing the cobalt oxide carrier, the catalytic performance is maximally improved by regulating and controlling the proportion of the second solvent to the first solvent and the dosage of the surfactant; and the process is simple, the operation is convenient, and the method is green and efficient.
Drawings
FIG. 1 is a graph showing methane conversion curves of catalysts obtained in examples 1 to 3 and comparative example 1 for catalyzing methane combustion at different temperatures;
FIG. 2 is a graph showing methane conversion curves of the catalysts obtained in examples 1, 4 to 6 and comparative example 2 for catalyzing methane combustion at different temperatures;
FIG. 3 is a stability curve of the catalyst obtained in example 1.
Detailed Description
The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
Example 1
This example provides a palladium-based catalyst containing a cobalt oxide carrier and a method for preparing the same 3 O 4 Carrier and carrier supported on said Co 3 O 4 An active component Pd on the carrier; the content of the active component Pd is 1 wt%;
the preparation method comprises the following steps:
(1) mixing CTAB with ethanol, and adding cobalt acetate to obtain an initial solution;
wherein the molar ratio of cobalt ions in the cobalt acetate to CTAB is 20: 1; the mass ratio of the cobalt acetate to the ethanol is 1: 12.5;
(2) mixing the initial solution obtained in the step (1) with isopropanol, carrying out solvothermal reaction at 160 ℃ for 12h, centrifuging, heating to 700 ℃ at the speed of 2 ℃/min, and carrying out first roasting for 5h to obtain Co 3 O 4 A carrier;
wherein the volume ratio of the isopropanol to the ethanol in the step (1) is 1: 4;
(3) subjecting the product of step (2)The above-mentioned Co 3 O 4 The support was immersed in a 0.025 wt% palladium nitrate solution for 1h with 1g Co 3 O 4 The carrier is taken as a reference, and the dosage of the palladium nitrate solution is 90 mL; after rotary evaporation, the temperature is raised to 600 ℃ at the speed of 2 ℃/min for second roasting for 5h, and the palladium-based catalyst containing the cobalt oxide carrier is obtained.
Example 2
This example provides a palladium-based catalyst containing a cobalt oxide carrier and a method for preparing the same 3 O 4 Carrier and carrier supported on said Co 3 O 4 An active component Pd on the carrier; the content of the active component Pd is 1 wt%;
the preparation is as described in example 1, with the only difference that: the molar ratio of cobalt ions in the cobalt acetate to CTAB in step (1) was 10: 1.
Example 3
This example provides a palladium-based catalyst containing a cobalt oxide carrier and a method for preparing the same 3 O 4 Carrier and carrier supported on said Co 3 O 4 An active component Pd on the carrier; the content of the active component Pd is 1 wt%;
the preparation is as described in example 1, with the only difference that: the molar ratio of cobalt ions in the cobalt acetate to CTAB in step (1) was 30: 1.
Example 4
This example provides a palladium-based catalyst containing a cobalt oxide carrier and a method for preparing the same 3 O 4 Carrier and carrier supported on said Co 3 O 4 An active component Pd on a carrier; the content of the active component Pd is 1 wt%;
the preparation is as described in example 1, with the only difference that: the volume ratio of the isopropanol in the step (2) to the ethanol in the step (1) is 1: 2.
Example 5
This example provides a palladium-based catalyst containing a cobalt oxide carrier and a method for preparing the same 3 O 4 Carrier and carrier supported on said Co 3 O 4 An active component Pd on the carrier; the content of the active component Pd is 1 wt%;
the preparation is as described in example 1, with the only difference that: the volume ratio of the isopropanol in the step (2) to the ethanol in the step (1) is 1: 8.
Example 6
This example provides a palladium-based catalyst containing a cobalt oxide carrier and a method for preparing the same 3 O 4 Carrier and carrier supported on said Co 3 O 4 An active component Pd on a carrier; the content of the active component Pd is 1 wt%;
the preparation is as described in example 1, with the only difference that: the volume ratio of the isopropanol in the step (2) to the ethanol in the step (1) is 1: 16.
Example 7
This example provides a palladium-based catalyst containing a cobalt oxide carrier and a method for preparing the same 3 O 4 Carrier and carrier supported on said Co 3 O 4 An active component Pd on the carrier; the content of the active component Pd is 1.2 wt%;
the preparation method comprises the following steps:
(1) mixing CTAB with ethanol, and adding cobalt acetate to obtain an initial solution;
wherein the molar ratio of cobalt ions in the cobalt acetate to CTAB is 20: 1; the mass ratio of the cobalt acetate to the ethanol is 1: 10;
(2) mixing the initial solution obtained in the step (1) with ethylene glycol, carrying out solvothermal reaction at 120 ℃ for 24h, centrifuging, heating to 600 ℃ at the speed of 3 ℃/min, and carrying out first roasting for 12h to obtain Co 3 O 4 A carrier;
wherein the volume ratio of the ethylene glycol to the ethanol in the step (1) is 1: 4;
(3) mixing the Co of the step (2) 3 O 4 The carrier was impregnated with 1g of Co in a 0.03 wt% palladium nitrate solution for 2 hours 3 O 4 The dosage of the palladium nitrate solution is 120mL by taking the carrier as a reference;after rotary evaporation, the temperature is raised to 550 ℃ at the speed of 3 ℃/min for second roasting for 6h, and the palladium-based catalyst containing the cobalt oxide carrier is obtained.
Example 8
This example provides a palladium-based catalyst containing a cobalt oxide carrier and a method for preparing the same 3 O 4 Carrier and carrier supported on said Co 3 O 4 An active component Pd on the carrier; the content of the active component Pd is 0.8 wt%;
the preparation method comprises the following steps:
(1) mixing CTAB with ethanol, and adding cobalt acetate to obtain an initial solution;
wherein the molar ratio of cobalt ions in the cobalt acetate to CTAB is 20: 1; the mass ratio of the cobalt acetate to the ethanol is 1: 15;
(2) mixing the initial solution obtained in the step (1) with isopropanol, carrying out solvothermal reaction at 180 ℃ for 4h, centrifuging, heating to 800 ℃ at the speed of 5 ℃/min, and roasting for 1h to obtain Co 3 O 4 A carrier;
wherein the volume ratio of the isopropanol to the ethanol in the step (1) is 1: 4;
(3) mixing the Co of the step (2) 3 O 4 The carrier was immersed in a 0.02 wt% palladium nitrate solution for 1.5 hours to obtain 1g of Co 3 O 4 The carrier is taken as a reference, and the dosage of the palladium nitrate solution is 100 mL; after rotary evaporation, the temperature is raised to 650 ℃ at the speed of 5 ℃/min for second roasting for 4h, and the palladium-based catalyst containing the cobalt oxide carrier is obtained.
Comparative example 1
This comparative example provides a palladium-based catalyst with a cobalt oxide support comprising Co and a method for preparing the same 3 O 4 Carrier and carrier supported on said Co 3 O 4 An active component Pd on a carrier; the content of the active component Pd is 1 wt%;
the preparation is as described in example 1, with the only difference that: CTAB was not added in step (1).
Comparative example 2
The comparative example provides a carrier containing cobalt oxideBulk palladium-based catalyst comprising Co and method of making same 3 O 4 Carrier and carrier supported on said Co 3 O 4 An active component Pd on the carrier; the content of the active component Pd is 1 wt%;
the preparation is as described in example 1, with the only difference that: isopropanol was not added in step (2).
Firstly, the catalytic performance of the palladium-based catalyst containing the cobalt oxide carrier obtained in the above examples and comparative examples is tested by the following method:
0.24g of palladium-based catalyst is loaded on a continuous flow micro fixed bed, and mixed gas is introduced at a mass space velocity of GHSV (300,000 mL/h.g), wherein the composition of the mixed gas is as follows: 1000ppm of CH 4 3.5 vol.% O 2 6 vol.% CO 2 10% of H 2 O，N 2 Balancing; measuring the change of the concentration of methane in the tail gas along with the temperature by an infrared flue gas analyzer;
the temperatures T50 and T90 at which the above examples and comparative examples catalyze the combustion of methane to achieve conversions of 50% and 90%, respectively, and the methane conversion at 500 ℃ are shown in Table 1.
The curves of methane conversion at different temperatures when the catalysts obtained in examples 1-3 and comparative example 1 catalyze methane combustion are shown in FIG. 1, and it can be seen from FIG. 1 that when Co is used 2+ The catalyst has the best catalytic performance when the molar ratio of CTAB to CTAB is 20: 1.
The curves of methane conversion at different temperatures when the catalysts obtained in examples 1, 4-6 and comparative example 2 catalyze methane combustion are shown in fig. 2, and it can be seen from fig. 2 that the catalyst performance is best when the volume ratio of isopropanol to ethanol is 4: 1.
Secondly, the stability of the palladium-based catalyst containing the cobalt oxide carrier obtained in example 1 is tested by the following method:
loading 0.24g of palladium-based catalyst on a continuous flow micro fixed bed, controlling the temperature at 475 ℃, keeping the temperature for 12h, and introducing mixed gas at a mass space velocity of 300,000 mL/h.g, wherein the composition of the mixed gas is as follows: 1000ppm of CH 4 3.5 vol.% O 2 6 vol.% CO 2 10% of H 2 O，N 2 Balancing; measuring the change of the concentration of methane in the tail gas within 12h by gas chromatography;
the results of the stability test of example 1 are shown in fig. 3, and it can be seen from fig. 3 that the catalytic performance of the catalyst is kept stable and the concentration of methane in the exhaust gas hardly changes within 12 h.
TABLE 1
The following points can be derived from table 1:
(1) as can be seen from examples 1 and 7 to 8, the present invention utilizes the metals Pd and Co sufficiently 3 O 4 Synergistic effect between carriers, improved catalytic activity and stability, and reduced Co 3 O 4 The catalyst is a carrier, is beneficial to the conversion between PdO-Pd and improves the catalytic performance;
(2) from the comparison between examples 1-3 and comparative example 1, it can be seen that the molar ratio of cobalt ions to CTAB in example 1 is 20:1, the low-temperature catalytic performance is excellent, T50 is 400 ℃, T90 is 460 ℃, and the methane conversion rate at 500 ℃ reaches 95%, and the CTAB can improve the surface appearance and crystal face exposure of the carrier, so that the catalytic performance is excellent; compared with the example 1, the mole ratio of the cobalt ions to CTAB of the example 2 is 10:1, the catalytic performance is reduced, both T50 and T90 are higher than the example 1, and the methane conversion at 500 ℃ is lower than the example 1; compared with the example 1, the molar ratio of cobalt ions to CTAB of the example 3 is 30:1, the catalytic performance is reduced, both T50 and T90 are higher than the example 1, and the methane conversion at 500 ℃ is lower than the example 1; comparative example 1 does not add CTAB compared to example 1, resulting in a decrease in catalytic performance thereof;
(3) from the comparison of examples 1, 4 to 6 and comparative example 2, it can be seen that the volume ratio of isopropanol in step (2) to ethanol in step (1) in example 1 was 1:4, and the low temperature thereof was lowExcellent catalytic performance, and can reduce Co by adding isopropanol 3 O 4 Agglomeration of the precursor in the roasting process; compared with the embodiment 1, the volume ratio of the isopropanol in the step (2) to the ethanol in the step (1) in the embodiment 4 is 1:2, the catalytic performance is reduced, both T50 and T90 are higher than the embodiment 1, and the methane conversion rate at 500 ℃ is lower than the embodiment 1; compared with the example 1, the volume ratio of the isopropanol in the step (2) to the ethanol in the step (1) in the example 5 is 1:8, the catalytic performance is reduced, both T50 and T90 are higher than the example 1, and the methane conversion at 500 ℃ is lower than the example 1; compared with the example 1, the volume ratio of the isopropanol in the step (2) to the ethanol in the step (1) in the example 6 is 1:16, the catalytic performance is reduced, both T50 and T90 are higher than the example 1, and the methane conversion at 500 ℃ is lower than the example 1; comparative example 2, in comparison with example 1, did not add isopropanol, resulting in a substantial decrease in its catalytic performance.
The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention disclosed herein fall within the scope and disclosure of the present invention.
Claims (10)
1. A preparation method of a palladium-based catalyst containing a cobalt oxide carrier is characterized by comprising the following steps:
(1) mixing a surfactant with a first solvent, and adding a cobalt source to obtain an initial solution;
wherein the surfactant comprises CTAB and/or PVP;
(2) mixing the initial solution obtained in the step (1) with a second solvent, carrying out a solvothermal reaction, and sequentially carrying out first solid-liquid separation and first roasting to obtain Co 3 O 4 A carrier;
(3) mixing the Co of the step (2) 3 O 4 And (3) soaking the carrier in a palladium source solution, and sequentially carrying out second solid-liquid separation and second roasting to obtain the palladium-based catalyst containing the cobalt oxide carrier.
2. The method according to claim 1, wherein the surfactant in the step (1) is CTAB;
preferably, the first solvent of step (1) comprises ethanol;
preferably, the cobalt source of step (1) comprises cobalt acetate.
3. The method according to claim 1 or 2, wherein the molar ratio of cobalt ions in the cobalt source to the surfactant in step (1) is (10-30):1, more preferably (17-25): 1;
preferably, the mass ratio of the cobalt source to the first solvent in the step (1) is 1 (10-15).
4. The method according to any one of claims 1 to 3, wherein the second solvent of step (2) comprises any one of ethylene glycol, isopropyl alcohol, 1, 3-propanediol, or glycerin, or a combination of at least two thereof;
preferably, the volume ratio of the second solvent in the step (2) to the first solvent in the step (1) is 1 (2-16);
preferably, the temperature of the solvothermal reaction in the step (2) is 120-180 ℃;
preferably, the solvothermal reaction time of the step (2) is 4-36 h.
5. The production method according to any one of claims 1 to 4, wherein the first solid-liquid separation in step (2) is centrifugation;
preferably, the temperature of the first roasting in the step (2) is 600-;
preferably, the temperature rise rate of the first roasting in the step (2) is 2-5 ℃/min;
preferably, the time of the first roasting in the step (2) is 1-12 h.
6. The production method according to any one of claims 1 to 5, wherein the palladium source solution of step (3) has a palladium source content of 0.02 to 0.03 wt%;
preferably, with 1gCo 3 O 4 The carrier is taken as a reference, and the dosage of the palladium source solution in the step (3) is 90-120 mL;
preferably, the temperature of the impregnation in the step (3) is 10-30 ℃;
preferably, the impregnation time of step (3) is 1-2 h.
7. The production method according to any one of claims 1 to 6, wherein the second solid-liquid separation in step (3) is rotary evaporation;
preferably, the temperature of the second roasting in the step (3) is 550-650 ℃;
preferably, the temperature rise rate of the second roasting in the step (3) is 2-5 ℃/min;
preferably, the time of the second roasting in the step (3) is 4-6 h.
8. The production method according to any one of claims 1 to 7, characterized by comprising the steps of:
(1) mixing a surfactant with ethanol, and adding cobalt acetate to obtain an initial solution;
wherein the surfactant comprises CTAB and/or PVP; the molar ratio of cobalt ions in the cobalt acetate to the surfactant is (10-30) to 1; the mass ratio of the cobalt acetate to the ethanol is 1 (10-15);
(2) mixing the initial solution and the second solvent in the step (1), performing solvothermal reaction at the temperature of 120-180 ℃ for 4-36h, centrifuging, heating to the temperature of 600-800 ℃ at the speed of 2-5 ℃/min, and performing first roasting for 1-12h to obtain Co 3 O 4 A carrier;
wherein the second solvent comprises any one of or a combination of at least two of ethylene glycol, isopropanol, 1, 3-propanediol or glycerol; the volume ratio of the second solvent to the ethanol in the step (1) is 1 (2-16);
(3) mixing the Co of the step (2) 3 O 4 The carrier is soaked in 0.02-0.03 wt% palladium source solution for 1-2h to obtain 1g of Co 3 O 4 The dosage of the palladium source solution is 90-12 on the basis of the carrier0 mL; after rotary evaporation, the temperature is raised to 550 ℃ and 650 ℃ at the speed of 2-5 ℃/min for second roasting for 4-6h, and the palladium-based catalyst containing the cobalt oxide carrier is obtained.
9. A palladium-based catalyst containing a cobalt oxide carrier obtained by the preparation method of any one of claims 1 to 8, wherein the palladium-based catalyst comprises Co 3 O 4 Carrier and carrier supported on said Co 3 O 4 An active component Pd on the carrier; the content of the active component Pd is 0.8-1.2 wt%.
10. Use of a palladium-based catalyst comprising a cobalt oxide support according to claim 9, wherein the palladium-based catalyst comprising a cobalt oxide support is used in a methane combustion reaction.
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