CN115739143B - Pt/alpha-MoC-CeO2Catalyst, preparation method thereof and application of catalyst in hydrogen production by methanol water vapor - Google Patents

Abstract

The present invention belongs to the technical field of catalysts and their preparation, and specifically relates to a Pt/α-MoC- _CeO2 low-temperature methanol steam hydrogen production catalyst, a preparation method thereof, and an application thereof in methanol steam hydrogen production. The catalyst comprises a carrier and an active component, the carrier is α-MoC- _CeO2 , the active component is Pt, and the loading amount of the active component in the catalyst is 0.1-20wt.%. The preparation method of the present invention is simple and low in cost, the size of the obtained catalyst is controllable, and industrial large-scale production can be realized, and the introduction of _CeO2 can slow down the oxidative deactivation of α-phase MoC, thereby enabling the catalyst to achieve a longer life.

Description

A Pt/α-MoC-CeO2 catalyst and its preparation method and application in hydrogen production from methanol and water vapor

Technical Field

The present invention belongs to the technical field of catalysts and their preparation, and specifically relates to a Pt/α-MoC-CeO2 low-temperature methanol-water vapor hydrogen production catalyst, a preparation method thereof, and an application thereof in methanol-water vapor hydrogen production.

Background technique

At present, the main energy supply in my country is still fossil energy such as coal, oil, and natural gas. With the progress of human development, the disadvantages of fossil energy are becoming more and more apparent. People hope to use clean, efficient, and renewable energy to replace fossil energy with limited reserves and environmental pollution. At present, the demand for rapid transformation from fossil energy economy to renewable energy economy is growing. In this context, proton exchange membrane fuel cells that use hydrogen to generate electricity for various mobile devices have received widespread attention due to their high efficiency, cleanliness, and sustainability. However, due to the physical and chemical properties of hydrogen as a combustible gas, the storage and transportation of hydrogen has become a major obstacle to the development of proton exchange membrane fuel cells. One way to solve this problem is to use liquid fuel to reform hydrogen on site. Methanol steam reforming reaction (MSR) is regarded as one of the most promising on-site reforming hydrogen production reactions due to its mild reaction conditions and efficient hydrogen production capacity, as well as the advantages of methanol as a liquid fuel that is easy to store and transport, and has been widely studied.

At present, the commercial catalysts commonly used for hydrogen production by reforming the MSR reaction (CH ₃ OH+H ₂ O→CO ₂ +3H ₂ ) are Cu/ZnO and Cu/Zn/Al ₂ O ₃ represented by Cu-based catalysts, and their operating temperature is often between 250℃-350℃. When the temperature is lower than 250℃, the activity of the commercial Cu-based catalyst will drop significantly. The operating temperature of the Cu-based commercial catalyst is higher than the temperature used by the high-temperature proton exchange membrane fuel cell, which makes it difficult to further improve the power density of the high-temperature proton exchange membrane fuel cell system. Therefore, the development of MSR reaction catalysts with excellent performance under normal pressure and low temperature conditions is of great significance to the improvement of the performance of the high-temperature polymer electrolyte membrane fuel cell system.

Summary of the invention

The purpose of the present invention is to provide a Pt/α-MoC-CeO ₂ catalyst and a preparation method thereof and an application thereof in methanol steam hydrogen production. The catalyst can carry out methanol steam reforming hydrogen production reaction under normal pressure and low temperature conditions, solving the problem that the use temperature of commercial catalysts for methanol steam reforming hydrogen production reaction is too high.

To achieve the above object, the present invention adopts the following technical solutions:

A Pt/α-MoC- _CeO2 catalyst for low-temperature methanol steam reforming to produce hydrogen is provided, wherein the MoC structure is a flaky structure, and the introduction of Ce is utilized to delay the oxidation deactivation of α-MoC, so that the catalyst can achieve high activity for a longer period of time at a lower temperature.

In one aspect, the present invention provides a Pt/α-MoC-CeO ₂ catalyst, comprising a carrier and an active component, wherein the carrier is α-MoC-CeO ₂ , the active component is Pt, and the loading amount of the active component in the catalyst is 0.1-20 wt.%.

In the above technical solution, further, in the carrier, the molar fraction of CeO ₂ is 0.01-30%.

In the above technical solution, further, in the catalyst, the particle size of the active component Pt is 10-50 nm, and the particle size of the carrier is 0.1-5 μm.

Another aspect of the present invention provides a method for preparing the above catalyst, the method comprising the following steps:

(1) dissolving MoO ₃ in water to obtain solution A, and dissolving cerium nitrate in water to obtain solution B;

(2) mixing solution A and solution B obtained in step (1) under stirring, then adding chloroplatinic acid solution dropwise, stirring and dispersing uniformly;

(3) evaporating the liquid in the mixture obtained in step (2) to dryness, drying the obtained solid, and then placing it in a muffle furnace for calcination to obtain a Pt/MoO ₃ -CeO ₂ precursor;

(4) placing the Pt/MoO ₃ -CeO ₂ precursor obtained in step (3) into a vertical muffle furnace, performing programmed temperature carburization in a CH ₄ /H ₂ mixed atmosphere, and then cooling the temperature to room temperature in the original atmosphere;

(5) The gas is switched from CH ₄ /H ₂ to an oxygen-argon mixed gas with an oxygen volume fraction of 1-10% for passivation to obtain a Pt/α-MoC-CeO ₂ catalyst.

In the above technical solution, further, in the step (1), MoO ₃ is prepared by the following method:

Grind ammonium heptamolybdate into powder and put it into a muffle furnace, raise the temperature to 300-600°C, and maintain it for 1-12 hours to obtain MoO ₃ .

In the above technical solution, further, in the step (2), the concentration of MoO ₃ in solution A is 0.05-1 mol/L, and the concentration of cerium nitrate in solution B is 0.01-0.5 mol/L.

In the above technical scheme, further, in the step (3), the evaporation is carried out using a rotary vacuum evaporator; the drying temperature is 60-150°C, and the drying time is 1-12h; the calcination temperature is 300-600°C, maintained for 1-12h, and the programmed heating rate is 1-10°C.

In the above technical solution, further, in the step (4), the carburizing end point temperature is 600°C-800°C, and is maintained at this temperature for 1-6 hours, and the programmed heating rate is 1-10°C/min.

In the above technical solution, further, in the step (5), the passivation time is 1-12h.

In another aspect, the present invention provides an application of the above catalyst in hydrogen production from methanol steam. Under the action of the catalyst, methanol and water react to produce hydrogen. The reaction conditions include: at normal pressure, temperature of 120-300°C, molar ratio of water to methanol of 1-5:1, and mass space velocity of methanol of WHSV=0.5-5h ^-1 .

The catalyst of the present invention has a porous structure, the MoC structure is a sheet structure, and the introduction of Ce is used to delay the oxidation deactivation of α-MoC, so that the catalyst can achieve high activity for a longer period of time at a lower temperature.

The beneficial effects of the present invention are as follows:

(1) The preparation method of the present invention is simple and low in cost, the size of the prepared catalyst is controllable, and industrial large-scale production can be achieved.

(2) The introduction of _CeO2 can slow down the oxidative deactivation of α-phase MoC, thereby enabling the catalyst to achieve a longer life.

(3) Under low temperature and normal pressure conditions, the catalytic activity of Pt/α-MoC- _CeO2 is significantly higher than that of the commercial _CuZnAlOx methanol steam reforming catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is an X-ray diffraction pattern (XRD) of Pt/α-MoC- _CeO2 prepared in Examples 1-3 and Pt/α-MoC catalyst prepared in Comparative Example 1;

FIG2 is a scanning electron microscope image (SEM) of the Pt/α-MoC-CeO ₂ catalyst prepared in Example 1;

FIG3 is a comparison of the catalytic methanol conversion rates of the Pt/α-MoC-CeO ₂ catalyst prepared in Example 1 and the commercial CuZnAlO _x catalyst of Comparative Example 2 under the same conditions;

FIG4 is a comparison chart of the catalytic activity life of the Pt/α-MoC-CeO ₂ catalyst prepared in Example 1 and that of Comparative Example 1 under the same test conditions.

Detailed ways

Example 1

(1) 5 g of ammonium heptamolybdate (NH ₄ ) ₆ Mo ₇ O ₂₄ was ground into powder and placed in a muffle furnace. The temperature was raised to 500°C at a rate of 5 K/min and maintained for 4 h to obtain MoO ₃ ;

(2) Dissolve 1.2105 g of _MoO3 prepared in step (1) in 50 ml of deionized water, and place in an ultrasonic cleaner for ultrasonic treatment for 2 h; Dissolve 0.1827 g of cerium nitrate in 50 ml of deionized water, and place in an ultrasonic cleaner for ultrasonic treatment for 2 h;

(3) under stirring, the MoO ₃ solution was added dropwise to the cerium nitrate solution, and ultrasonic treatment was performed for 2 h. Subsequently, a chloroplatinic acid solution containing 20 mg of Pt was added dropwise under stirring, and ultrasonic treatment was performed for 2 h. After the ultrasonic treatment, stirring was immediately performed for 12 h.

(4) using a rotary vacuum evaporator to evaporate the liquid in the mixture obtained in step (3), placing it in a vacuum drying oven at 110° C. for 6 h, placing the obtained solid in a muffle furnace and heating it to 500° C. at a rate of 10° C./min, and maintaining it for 4 h, to obtain a Pt/MoO ₃ -CeO ₂ precursor;

(5) placing the Pt/MoO ₃ -CeO ₂ precursor obtained in step (4) into a vertical muffle furnace and performing programmed temperature carburization in a CH ₄ /H ₂ (20%/80% v/v) mixed atmosphere, wherein the temperature program is set to directly increase the temperature to 700°C at a rate of 5°C/min, and maintain at this temperature for 2h, and then cool down to room temperature in the original atmosphere;

(6) After cooling to room temperature, the gas was switched from CH ₄ /H ₂ to a mixed gas of O ₂ and Ar with an oxygen volume fraction of 1% for passivation for 2 h.

Example 2

(1) 5 g of ammonium heptamolybdate (NH ₄ ) ₆ Mo ₇ O ₂₄ was ground into powder and placed in a muffle furnace. The temperature was raised to 500°C at a rate of 5 K/min and maintained for 4 h to obtain MoO ₃ ;

(2) Dissolve 1.1370 g of _MoO3 prepared in step (1) in 50 ml of deionized water, and place in an ultrasonic cleaner for ultrasonic treatment for 2 h; Dissolve 0.3402 g of cerium nitrate in 50 ml of deionized water, and place in an ultrasonic cleaner for ultrasonic treatment for 2 h;

(3) under stirring, the MoO ₃ solution was added dropwise to the cerium nitrate solution, and ultrasonic treatment was performed for 2 h. Subsequently, a chloroplatinic acid solution containing 20 mg Pt was added dropwise under stirring, and ultrasonic treatment was performed for 2 h. After the ultrasonic treatment, stirring was immediately performed for 12 h.

(4) using a rotary vacuum evaporator to evaporate the liquid in the mixture obtained in step (3), placing it in a vacuum drying oven at 110° C. for 6 h, placing the obtained solid in a muffle furnace and heating it to 500° C. at a rate of 10° C./min, and maintaining it for 4 h, to obtain a Pt/MoO ₃ -CeO ₂ precursor;

(5) placing the Pt/MoO ₃ -CeO ₂ precursor obtained in step (4) into a vertical muffle furnace and performing programmed temperature carburization in a CH ₄ /H ₂ (20%/80% v/v) mixed atmosphere, wherein the temperature program is set to directly increase the temperature to 700°C at a rate of 5°C/min, and maintain at this temperature for 2h, and then cool down to room temperature in the original atmosphere;

(6) After cooling to room temperature, the gas was switched from CH ₄ /H ₂ to a mixed gas of O ₂ and Ar with an oxygen volume fraction of 1% for passivation for 2 h.

Example 3

(1) 5 g of ammonium heptamolybdate (NH ₄ ) ₆ Mo ₇ O ₂₄ was ground into powder and placed in a muffle furnace. The temperature was raised to 500°C at a rate of 5 K/min and maintained for 4 h to obtain MoO ₃ ;

(2) dissolving 0.9909 g of MoO ₃ prepared in step (1) in 50 ml of deionized water, placing in an ultrasonic cleaning machine for ultrasonic treatment for 2 h, dissolving 0.598 g of cerium nitrate in 50 ml of deionized water, placing in an ultrasonic cleaning machine for ultrasonic treatment for 2 h;

(3) under stirring, the MoO ₃ solution was added dropwise to the cerium nitrate solution, and ultrasonic treatment was performed for 2 h. Subsequently, a chloroplatinic acid solution containing 20 mg Pt was added dropwise under stirring, and ultrasonic treatment was performed for 2 h. After the ultrasonic treatment, stirring was immediately performed for 12 h.

(4) Then, the liquid in the mixture obtained in step (3) was evaporated to dryness using a rotary vacuum evaporator, and the mixture was placed in a vacuum drying oven at 110° C. for 6 h. The obtained solid was placed in a muffle furnace and heated to 500° C. at a rate of 10° C./min and maintained for 4 h to obtain a Pt/MoO ₃ -CeO ₂ precursor;

(5) placing the Pt/MoO ₃ -CeO ₂ precursor obtained in step (4) into a vertical muffle furnace and performing programmed temperature carburization in a CH ₄ /H ₂ (20%/80% v/v) mixed atmosphere, wherein the temperature program is set to directly increase the temperature to 700°C at a rate of 5°C/min, and maintain the temperature for 2 h, and then cool the temperature to room temperature in the original atmosphere;

(6) After cooling to room temperature, the gas was switched from CH ₄ /H ₂ to a mixed gas of O ₂ and Ar with an oxygen volume fraction of 1% for passivation for 2 h.

Comparative Example 1

Comparative Example 1 does not add Ce, and the specific preparation method is as follows:

(1) 5 g of ammonium heptamolybdate (NH ₄ ) ₆ Mo ₇ O ₂₄ was ground into powder and placed in a muffle furnace. The temperature was raised to 500°C at a rate of 5 K/min and maintained for 4 h to obtain MoO ₃ ;

(2) Take 1.3084 g of MoO ₃ prepared in step (1), dissolve it in 50 ml of deionized water, and place it in an ultrasonic cleaner for ultrasonic treatment for 2 h;

(3) adding chloroplatinic acid solution containing 20 mg Pt dropwise under stirring, ultrasonically treating for 2 h, and stirring for 12 h immediately after the ultrasonic treatment;

(4) using a rotary vacuum evaporator to evaporate the liquid in the mixture obtained in step (3), placing it in a vacuum drying oven at 110° C. for 6 h, placing the obtained solid in a muffle furnace and heating it to 500° C. at a rate of 10° C./min, and maintaining it for 4 h, to obtain a Pt/MoO ₃ -CeO ₂ precursor;

(5) placing the Pt/MoO ₃ -CeO ₂ precursor obtained in step (4) into a vertical muffle furnace and performing programmed temperature carburization in a CH ₄ /H ₂ (20%/80% v/v) mixed atmosphere, wherein the temperature program is set to directly increase the temperature to 700°C at a rate of 5°C/min, and maintain the temperature for 2 h, and then cool the temperature to room temperature in the original atmosphere;

(6) After cooling to room temperature, the gas was switched from CH ₄ /H ₂ to a mixed gas of O ₂ and Ar with an oxygen volume fraction of 1% for passivation for 2 h.

Comparative Example 2

Comparative Example 2 is a commercial CuZnAlO _x catalyst.

Figure 1 is the X-ray diffraction pattern (XRD) of the Pt/α-MoC- _CeO2 catalyst prepared in Examples 1-3 and the comparative example 1 Pt/α-MoC without the introduction of Ce. It can be seen from the figure that the addition of Ce does not change the phase state of MoC, and MoC is still in the α phase. In addition, with the increase of the Ce doping amount, the characteristic peak of Pt gradually weakens, which indicates that the addition of Ce can well promote the dispersion of Pt, thereby avoiding the aggregation of Pt particles. And with the increase of the Ce doping amount, the characteristic peak intensity of MoC gradually decreases, and the half-peak width gradually increases. This shows that with the increase of the Ce doping amount, the particle size of MoC is gradually decreasing, thereby forming a larger specific surface area, so that the active sites have more exposure opportunities, thereby improving the catalytic activity.

Figure 2 is a scanning electron microscope (SEM) image of the Pt/α-MoC-CeO ₂ catalyst prepared in Example 1. It can be seen from the figure that the molybdenum carbide carrier has a smooth flaky structure and no obvious cracks are observed. No obvious Pt particles are observed on the surface of the molybdenum carbide in the figure, which indicates that the introduction of Ce makes Pt more evenly dispersed on the surface of the molybdenum carbide.

Example 4

In a fixed bed reactor, the reaction conditions are: normal pressure, reaction temperature 200°C, residence time 0-500kg·s·mol ^-1 , water-to-methanol ratio 1.5, reaction time 1h, and the methanol conversion rate of the Pt/α-MoC-CeO ₂ catalyst prepared in Example 1 and the CuZnAlO _x catalyst prepared in Comparative Example 2 was tested.

FIG3 is a comparison chart of the methanol conversion rate of the Pt/α-MoC- _CeO2 catalyst prepared in Example 1 and the commercial _CuZnAlOx catalyst of Comparative Example 2 under the same conditions. It can be seen from the figure that under the condition of 200°C, the methanol conversion rate of the Pt/α-MoC- _CeO2 catalyst prepared in Example 1 is close to 100% when the residence time is 100kg·s·mol ^-1 , while the conversion rate of the commercial _CuZnAlOx catalyst of Comparative Example 2 under the same test conditions is only 26% at this time. Under low temperature conditions, the catalytic activity of the catalyst of the present invention is significantly higher than that of the commercial _CuZnAlOx catalyst, which shows that the present invention is a low-temperature methanol steam reforming hydrogen production catalyst with great application prospects.

Example 5 In a fixed bed reactor, the reaction conditions are: normal pressure, reaction temperature 350°C, residence time 200kg·s·mol ^-1 , water-to-alcohol ratio 1.5, reaction time 1-5h, and the catalytic activity life of the Pt/α-MoC-CeO ₂ catalyst prepared in Example 1 and the Pt/MoO ₃ -CeO ₂ catalyst prepared in Comparative Example 1 are tested.

Figure 4 is a comparison chart of the catalytic activity life test of the Pt/α-MoC- _CeO2 catalyst prepared in Example 1 and Comparative Example 1 under the same test conditions. It can be seen from the figure that as the reaction time progresses, the catalytic activity of both Comparative Example 1 and Example 1 decreases, but the rate of decrease of Example 1 is lower than that of Comparative Example 1. This shows that the present invention delays the deactivation of the catalyst and prolongs its life.

Claims (9)

1. An application of a Pt/α-MoC-CeO ₂ catalyst in hydrogen production from methanol and water vapor, characterized in that, under the action of the catalyst, methanol and water undergo a hydrogen production reaction to obtain hydrogen; The reaction conditions include: under normal pressure, temperature of 120-300° C., a molar ratio of water to methanol of 1-5:1, and a mass space velocity of methanol of WHSV=0.5-5h ^-1 ; The catalyst comprises a carrier and an active component, wherein the carrier is α-MoC-CeO ₂ , and the active component is Pt. In the catalyst, the loading amount of the active component is 0.01-20 wt.%. 2. The use according to claim 1, characterized in that the molar fraction of _CeO2 in the carrier is 0.01-30%. 3. The use according to claim 1, characterized in that in the catalyst, the particle size of the active component Pt is 10-50 nm, and the particle size of the carrier is 0.01-5 μm. 4. The use according to claim 1, characterized in that the preparation method of the catalyst comprises the following steps: (1) dissolving MoO ₃ in water to obtain solution A, and dissolving cerium nitrate in water to obtain solution B; (2) mixing solution A and solution B obtained in step (1) under stirring, then adding chloroplatinic acid solution dropwise, stirring and dispersing uniformly; (3) evaporating the liquid in the mixture obtained in step (2) to dryness, drying the obtained solid, and then placing it in a muffle furnace for calcination to obtain a Pt/MoO ₃ -CeO ₂ precursor; (4) placing the Pt/MoO ₃ -CeO ₂ precursor obtained in step (3) into a vertical muffle furnace, performing programmed temperature carburization in a CH ₄ /H ₂ mixed atmosphere, and then cooling the temperature to room temperature in the original atmosphere; (5) The gas is switched from CH ₄ /H ₂ to an oxygen-argon mixed gas with an oxygen volume fraction of 1-10% for passivation to obtain a Pt/α-MoC-CeO ₂ catalyst. 5. The use according to claim 4, characterized in that in the step (1), MoO ₃ is prepared by the following method: Grind ammonium heptamolybdate into powder and put it into a muffle furnace, raise the temperature to 300-600°C, and maintain it for 1-12 hours to obtain MoO ₃ . 6. The use according to claim 4, characterized in that in the step (2), the concentration of MoO ₃ in solution A is 0.05-1 mol/L, and the concentration of cerium nitrate in solution B is 0.01-0.5 mol/L. 7. The use according to claim 4, characterized in that in the step (3), the evaporation is carried out using a rotary vacuum evaporator; the drying temperature is 60-150°C, and the drying time is 1-12h; the calcination temperature is 300-600°C, maintained for 1-12h, and the programmed heating rate is 1-10°C. 8. The use according to claim 4, characterized in that in the step (4), the carburizing end point temperature is 600°C-800°C, and is maintained at this temperature for 1-6 hours, and the programmed heating rate is 1-10°C/min. 9. The use according to claim 4, characterized in that in the step (5), the passivation time is 1-12 hours.