CN115770563A - A bimetallic catalyst for hydrogen production by steam reforming of methanol at high temperature and its preparation method and application - Google Patents

Abstract

The invention discloses a bimetallic catalyst and a preparation method thereof. The methanol reforming catalyst comprises ZnZrO _x solid solution and zinc oxide nanoparticles dispersed on the surface of the ZnZrO _x solid solution. The catalyst uses solid solution structure and highly dispersed ZnO nanoparticles on the surface as the active center, and is prepared by impregnation method. After the zinc salt is impregnated on the carrier, the catalyst is formed after standing, drying, roasting and molding. The catalyst of the invention achieves optimal performance at a reaction temperature of 400 DEG C, and the activity can reach 99.9%. The invention has the advantages of high catalyst activity, low CO selectivity and good stability at high temperature.

Description

A bimetallic catalyst for hydrogen production by steam reforming of methanol at high temperature and its preparation Methods and Applications

technical field

The invention belongs to the field of chemical industry and energy, and in particular relates to a bimetallic catalyst for hydrogen production by steam reforming of methanol at high temperature, a preparation method and application thereof.

Background technique

Energy and environmental issues are the most important issues facing the sustainable development of human beings in the future. With the development and use of a large amount of fossil energy, the problems of global environmental degradation and resource shortage have become increasingly prominent. Therefore, the transformation from fossil fuels to sustainable and non-polluting non-fossil energy is an inevitable trend of future energy structure changes. As an ideal chemical fuel, energy carrier and energy storage tool, hydrogen energy has been paid more and more attention by people. Since the storage and transportation of hydrogen are very difficult, which greatly limits its development, people are urgently looking for easy-to-handle and renewable liquid hydrogen carriers. Methanol is an ideal source of hydrogen for the following reasons: First, methanol has a high hydrogen-to-carbon ratio and has no C-C bond connection. Compared with other hydrocarbon hydrogen production temperatures (600-800°C), methanol hydrogen production The temperature is low (150-400°C); second, methanol is a liquid at normal temperature and pressure, which is safe and convenient to store and transport, and is also biodegradable; third, methanol has a wide range of sources, and methanol reserves at home and abroad are abundant, which can be Through coal conversion, carbon dioxide hydrogenation, shale gas, and in the future, it can also be obtained through combustible ice. The shale gas revolution in North America led to the emergence of unconventional natural gas that can be used for more than 200 years, which has accelerated the transformation of the world's energy structure. The conversion of natural gas to methanol has greatly reduced the cost of international shipping and provided considerable raw material guarantee for its steam reforming. Therefore, the reforming of methanol to hydrogen has attracted extensive attention due to its advantages of low cost, mild reaction conditions, less reformed gas products and easy separation.

Currently, there are three main types of catalysts used in methanol reforming reactions: copper-based catalysts, catalysts containing noble metals, and oxide-based catalysts (excluding noble metals and Cu). Copper-based catalysts are the most widely used catalysts because of their low price, high low-temperature activity, and low CO selectivity. However, there are problems of poor stability and prone to sintering and deactivation. The second type of catalysts containing noble metals also has high activity, low CO selectivity, and good stability, but they are expensive and unfavorable for large-scale industrial production. The third category is metal oxide catalysts (without precious metals and Cu). Currently, there are relatively few reports on the use of metal oxides in the steam reforming reaction of methanol in the literature. Different from the former two, metal oxide catalysts have high activity, selectivity and good thermal stability at high temperature, which is beneficial to long-term operation.

High-purity hydrogen can be obtained through methanol steam reforming and supplied to proton exchange membrane fuel cells. However, direct methanol decomposition and reverse water vapor shift reaction may occur during the reaction, producing CO as a by-product. Too high CO concentration will poison the Pt electrode of the fuel cell, so the CO concentration is required to be lower than 10ppm. After years of basic research and application exploration by scientific workers, there is still no efficient, long-term, and economical catalyst for large-scale industrial use of hydrogen energy. At present, the methanol steam reforming reaction still cannot completely convert methanol, and the CO in the reformed gas High concentration, poor stability and other problems.

Contents of the invention

In view of the above-mentioned deficiencies in the prior art, the present invention provides a bimetallic catalyst and a preparation method thereof, aiming at overcoming the disadvantages of incomplete conversion of methanol, poor reaction selectivity, and poor stability in existing high-temperature methanol steam reforming hydrogen production catalysts .

The invention provides a bimetallic catalyst for hydrogen production by steam reforming of methanol at high temperature. The catalyst includes ZnZrO _x solid solution and zinc oxide nanoparticles; the zinc oxide nano particles are dispersed on the surface of the ZnZrO _x solid solution. In the catalyst, the molar amount of zinc element accounts for 4-50% of the total molar weight of zinc element and zirconium element; the specific surface area of the catalyst is 30-50m ² /g.

According to another aspect of the present application, a kind of preparation method of above-mentioned catalyst is provided, comprises the steps:

Step (1): dissolving the zirconium source in water, mixing with the aqueous solution of the precipitating agent at 60-75°C to obtain a precipitate, and drying to obtain a zirconium precursor;

Step (2): dissolving the zinc source in water to obtain a zinc source solution, dropping the zinc source solution onto the zirconium precursor, grinding and stirring, impregnating at room temperature, drying, and calcining to obtain the catalyst.

Wherein, in step (1):

The zirconium source is selected from at least one of zirconium oxynitrate, zirconium nitrate pentahydrate and zirconium oxychloride; the concentration of zirconium in the aqueous solution obtained after the zirconium source is dissolved in water is 0.1-0.2mol/L; the drying The drying temperature is 80-120°C.

The precipitating agent is selected from at least one of ammonium carbonate, sodium carbonate, and ammonia water; when the precipitating agent is ammonium carbonate or sodium carbonate, the concentration of the precipitating agent aqueous solution is 0.1 to 0.2mol/L; when the precipitating agent is ammonia water, the precipitating agent The concentration of the aqueous solution is 10-20%.

Wherein, in step (2):

The zinc source is selected from at least one of zinc acetate and zinc nitrate; the amount of zinc source used per 1 g of zirconium precursor is 0.09-6.5 mmol. The time for grinding and stirring is 5-10 minutes; the time for soaking at room temperature is 6-12 hours; the drying temperature is 80-120° C.; the calcination temperature is 450-550° C.; the time is 3-6 hours.

According to another aspect of the present application, a method for producing hydrogen by steam reforming of methanol at high temperature is provided, using the above-mentioned catalyst or the catalyst prepared by the above-mentioned preparation method.

The method comprises the following steps: under the condition of heating, the raw material containing methanol and water is contacted with a catalyst to react; the reaction is carried out under normal pressure, and the reaction temperature is 350-400°C; the molar ratio of water to methanol is 1.0- 1.6; the reaction mass space velocity is 1.2-4.5h ^-1 .

The catalyst needs to be reduced before reacting; the reduction method is at 400° C. for 2 to 6 hours in a hydrogen atmosphere.

The above-mentioned catalysts have the best catalytic performance at 400°C, methanol can be converted almost completely, CO selectivity is low, and they can maintain good stability at 380°C at high space velocity (9.0h ^-1 ).

Beneficial effects: the invention discloses a high-temperature methanol steam reforming hydrogen production catalyst and its preparation method. The methanol reforming hydrogen production catalyst is composed of ZnZrO _x solid solution and oxidizing nanoparticles, and the solid solution and ZnO particles are both active groups point. The catalyst overcomes the shortcomings of traditional Cu-based catalysts at high temperature, high selectivity of CO reforming reaction and instability at high temperature, the optimum reaction temperature is 400°C, and it can run at high temperature for a long time. In the present invention, the ZnZrO _x solid solution rich in oxygen vacancies on the surface interacts with ZnO nanoparticles to synergize, thereby increasing methanol conversion rate and _H2 production rate, and reducing CO selectivity. The catalyst has the advantages of high activity, good selectivity, etc., and is a catalyst for hydrogen production by steam reforming of methanol with excellent performance.

Description of drawings

Fig. 1 is the XRD spectrogram of all embodiment and comparative example catalyst.

Fig. 2 is the elemental scanning electron micrograph of the bimetallic catalyst prepared in Example 6, wherein a is the HAADF-STEM figure of the catalyst, c and d are the elemental scanning figures of Zn and Zr respectively, and b is the elemental scanning overlap of c and d picture.

Fig. 3 is a graph showing the change of methanol conversion rate with reaction time in Example 4.

Detailed ways

The present application is described in detail below in conjunction with the examples, but the present application is not limited to these examples.

Unless otherwise specified, the raw materials and catalysts in the examples of the present application were purchased through commercial channels.

Analytic method is as follows in the embodiment of the application:

The effluent gas was analyzed online by Agilent gas chromatography equipped with TCD and FID dual detectors, the packed column was TDX-01, and the capillary column was TG BOND Q.

Conversion rate, selectivity are calculated as follows in the embodiment of the application:

In the examples of the present application, the methanol conversion rate and product selectivity are calculated based on the number of carbon moles.

C₁和C₂分别代表进入和流出甲醇的摩尔量。Methanol conversion:

_C1 and _C2 represent the molar amounts of incoming and outgoing methanol, respectively.

其中xi代表i产物的摩尔百分含量；ni代表i产物中含有的碳原子数。Product selectivity:

Among them, xi represents the mole percentage of product i; ni represents the number of carbon atoms contained in product i.

Example 1

Weigh 35.0g Zr(NO ₃ ) ₄ ·5H ₂ O and dissolve in 500mL deionized water, heat and stir at 70°C to dissolve. Another 21.0 mL of ammonia water was diluted to 200 mL of deionized water, and the ammonia solution was quickly added to the Zr solution at a stirring speed of 500 r/min, and the obtained precipitate was continuously stirred at 70°C for 10 min. The resulting precipitate was left to cool at room temperature, filtered with suction, and washed three times with deionized water until the filtrate was neutral. The resulting filter cake was dried overnight at 100 °C to obtain the Zr(OH) ₄ precursor.

Example 2

Weigh 0.19mmol of zinc nitrate and dissolve it in 1ml of deionized water to obtain a Zn solution, weigh 2g of the Zr(OH) ₄ precursor obtained in Example 1 in an evaporating dish, and drop the Zn solution onto the Zr(OH) ₄ precursor , grind and stir for 5min. After impregnated at room temperature for 7 hours, dried at 100°C, and finally calcined in a muffle furnace at 500°C for 4 hours, the obtained catalyst was recorded as 3% ZnO/ZrO ₂ .

Tablets, crushed, and screened with 40-80 meshes for catalyst evaluation. Weigh 0.3 g of the screened catalyst and put it into a reaction tube with an inner diameter of 6 mm, and reduce it at 400° C. for 2 to 5 hours under H ₂ or H ₂ /N ₂ mixed atmosphere. The reaction is carried out under normal pressure, the raw material is a mixed solution of methanol and water, wherein n(MeOH):n(H ₂ O)=1.0, nitrogen is the diluent gas, the flow rate is 30ml/min, the reaction temperature is 400°C, WHSV=4.5 h ^-1 , the catalyst evaluation results are shown in Table 1.

Example 3

Weigh 0.25mmol of zinc nitrate and dissolve it in 1ml of deionized water, weigh 2g of the Zr(OH) ₄ precursor obtained in Example 1 in an evaporating dish, drop the zinc solution onto the Zr(OH) ₄ precursor, grind and stir 5min. After impregnated at room temperature for 7 hours, dried at 100°C, and finally calcined in a muffle furnace at 500°C for 4 hours, the obtained catalyst was recorded as 4% ZnO/ZrO ₂ . Tablets, crushed, and screened with 40-80 meshes for catalyst evaluation. Other evaluation steps are the same as in Example 2, and the catalyst evaluation results are shown in Table 1.

Example 4

Catalyst preparation metal salt used is 1.23mmol zinc nitrate and the Zr(OH) precursor that obtains in 2g embodiment 1, _precursor is placed in evaporating dish, zinc nitrate is dissolved in 1ml deionized water to obtain zinc solution, zinc solution Drop onto the Zr(OH) ₄ precursor, grind and stir for 5 min. After impregnated at room temperature for 7 hours, dried at 100°C, and finally calcined in a muffle furnace at 500°C for 4 hours, the obtained catalyst was recorded as 9% ZnO/ZrO ₂ . Catalyst evaluation at 400°C, n(H ₂ O):n(MeOH)=1.0, pump flow rate 0.040mL/min; 350°C, n(H ₂ O):n(MeOH)=1.0～1.5, pump flow rate 0.012mL/min, other evaluation steps are the same as in Example 1, and the catalyst evaluation results are shown in Table 1. The high temperature resistance test of the catalyst is evaluated under normal pressure, 380°C, n(H ₂ O):n(MeOH)=1.1, WHSV=4.4h ^-1 , pump flow rate 0.040mL/min, in the first 40h of evaluation , the catalyst activity decreased by 6% to 7%, and within the next 200h, the catalyst maintained good stability. The results are shown in Figure 3.

Example 5

Catalyst preparation metal salt used is 1.54mmol zinc nitrate and the Zr(OH) precursor that obtains in 2g embodiment 1, _precursor is placed in evaporating dish, zinc nitrate is dissolved in 1ml deionized water to obtain zinc solution, zinc solution Drop onto the Zr(OH) ₄ precursor, grind and stir for 5 min. After impregnated at room temperature for 7 hours, dried at 100°C, and finally calcined in a muffle furnace at 500°C for 4 hours, the obtained catalyst was recorded as 11% ZnO/ZrO ₂ . Other evaluation steps are the same as in Example 2, and the catalyst evaluation results are shown in Table 1.

Example 6

Catalyst preparation metal salt used is 1.84mmol zinc nitrate and the Zr(OH) precursor that obtains in 2g embodiment 1, _precursor is placed in evaporating dish, zinc nitrate is dissolved in 1ml deionized water to obtain zinc solution, zinc solution Drop onto the Zr(OH) ₄ precursor, grind and stir for 5 min. After impregnated at room temperature for 7 hours, it was dried at 100°C, and finally calcined in a muffle furnace at 500°C for 4 hours. The obtained catalyst was recorded as 13% ZnO/ZrO ₂ . Other evaluation steps are the same as in Example 2, and the catalyst evaluation results are shown in Table 1. The electron microscope image of the prepared catalyst is shown in Figure 2, where a is the HAADF-STEM image of the catalyst, c and d are the element scanning images of Zn and Zr, respectively, and b is the overlapping image of the elements of c and d. The shapes of c and d are basically the same. It can be seen that Zn will appear wherever Zr exists, indicating that Zn is highly dispersed in ZrO ₂ , proving that a ZnZrOx solid solution is indeed formed. It can be seen from b that after superimposing the scanning images of the two elements, there are some Zn bright spots that exist alone and do not overlap with Zr, which indicates that there are also some individual ZnO nanoparticles in the catalyst.

Example 7

Catalyst preparation metal salt used is 3.14mmol zinc nitrate and the Zr(OH) _precursor that obtains in 2g embodiment 1, precursor is placed in evaporating dish, zinc nitrate is dissolved in 1ml deionized water to obtain zinc solution, zinc solution Drop onto the Zr(OH) ₄ precursor, grind and stir for 5 min. After impregnated at room temperature for 7 hours, dried at 100°C, and finally calcined in a muffle furnace at 500°C for 4 hours, the obtained catalyst was recorded as 20% ZnO/ZrO ₂ . Other evaluation steps are the same as in Example 2, and the catalyst evaluation results are shown in Table 1.

Example 8

Catalyst preparation metal salt used is 6.28mmol zinc nitrate and the Zr(OH) precursor that obtains in 2g embodiment 1, _precursor is placed in evaporating dish, zinc nitrate is dissolved in 1ml deionized water to obtain zinc solution, zinc solution Drop onto the Zr(OH) ₄ precursor, grind and stir for 5 min. After impregnated at room temperature for 7 hours, dried at 100°C, and finally calcined in a muffle furnace at 500°C for 4 hours, the obtained catalyst was recorded as 33% ZnO/ZrO ₂ . Other evaluation steps are the same as in Example 2, and the catalyst evaluation results are shown in Table 1.

Example 9

Catalyst preparation metal salt used is 12.56mmol zinc nitrate and the Zr(OH) precursor that obtains in 2g embodiment 2, _precursor is placed in evaporating dish, zinc nitrate is dissolved in 1ml deionized water to obtain zinc solution, zinc solution Drop onto the Zr(OH) ₄ precursor, grind and stir for 5 min. After impregnating at room temperature for 7 hours, drying at 100°C, and finally calcining in a muffle furnace at 500°C for 4 hours, the obtained catalyst is recorded as 50% ZnO/ZrO ₂ . Other evaluation steps are the same as in Example 2, and the catalyst evaluation results are shown in Table 1.

Example 10

Catalyst preparation metal salt used is the Zr(OH) ₄ precursor that obtains in 1.23mmol zinc acetate and 2g embodiment 2, precursor is placed in evaporating dish, zinc acetate is dissolved in 1ml deionized water to obtain zinc solution, zinc solution Drop onto the Zr(OH) ₄ precursor, grind and stir for 5 min. After soaking at room temperature for 7 hours, dry it at 100°C, and finally calcinate it in a muffle furnace at 500°C for 4 hours. The obtained catalyst is recorded as 9% ZnO/ZrO ₂ -2. The other evaluation steps are the same as in Example 2. The evaluation results of the catalyst are shown in Table 1. .

Comparative example 1

The metal salt used for catalyst preparation was 5mmol Zn(NO ₃ ) ₂ ·6H ₂ O dissolved in 100mL water, and 0.1mol urea and 0.005mmol F127 were added, stirring continuously, and the pH value was adjusted to 5.0 with acetic acid. After aging at room temperature for 2 hours, it was transferred to a crystallization kettle, crystallized at 90°C for 24 hours, cooled to room temperature, filtered with suction, washed with deionized water three times, and dried overnight at 100°C. The obtained solid was calcined at 400°C for 2h in a muffle furnace, and the obtained catalyst was designated as ZnO. Other evaluation steps are the same as in Example 2, and the catalyst evaluation results are shown in Table 1.

Comparative example 2

Catalytic performance test of the carrier: Weigh 0.042mol ZrO(NO ₃ ) ₂ ·H ₂ O and 0.105mol urea in a beaker, add 70mL deionized water, stir and dissolve, transfer the mixed solution to a 100mL crystallization kettle, 150 ℃ overnight crystallization. After cooling, washing, filtering and drying, the monoclinic ZrO ₂ precursor is obtained. Finally, it was calcined at 400°C for 4 hours in a muffle furnace, and the obtained catalyst was recorded as monoclinic ZrO ₂ . Other evaluation steps are the same as in Example 2, and the catalyst evaluation results are shown in Table 1.

Comparative example 3

Take by weighing 1.62mmol zinc nitrate and dissolve it in a small amount of deionized water, take by weighing 2g monoclinic- _ZrO2 carrier obtained in Example 11 in an evaporating dish, dissolve zinc nitrate in 1ml deionized water to obtain a zinc solution, and drop the zinc solution to Carrier, grind and stir for 5min. After soaking at room temperature for 7 hours, it was dried at 100°C, and finally calcined in a muffle furnace at 500°C for 4 hours. The obtained catalyst was recorded as 9% ZnO/monoclinic ZrO ₂ . Tablets, crushed, and screened with 40-80 meshes for catalyst evaluation. Other evaluation steps are the same as in Example 2, and the catalyst evaluation results are shown in Table 1.

Comparative example 4

Weigh 500 mg of 13% ZnO/ZrO ₂ in Example 6 into a small flask, add 3 mL of 1 mol/L HNO ₃ aqueous solution, and heat and stir at 70° C. for 1 h. After the solution was cooled, it was filtered, washed with deionized water until the filtrate was neutral, and finally dried at 100 ° C. The obtained catalyst was recorded as 13% ZnO/ZrO ₂ pickling. Tablets, crushed, and screened with 40-80 meshes for catalyst evaluation. Other evaluation steps are the same as in Example 2, and the catalyst evaluation results are shown in Table 1.

Table 1 embodiment and comparative example catalyst evaluation result

It can be seen from the table that it is extremely challenging to increase methanol conversion and carbon dioxide selectivity while reducing carbon monoxide selectivity at high temperature in methanol steam reforming hydrogen production reaction. It can be seen from Comparative Example 1 that zinc oxide alone has certain catalytic activity, but its conversion rate is low, and the actual catalytic efficiency is not high.

It can also be seen from the table that after washing the ZnO nanoparticles on the surface of the catalyst in Example 6 with nitric acid solution, that is, Comparative Example 4, the activity is greatly reduced, indicating that the highly dispersed ZnO nanoparticles on the surface can also improve the activity of the catalyst.

It can be seen from Example 4 and Comparative Example 3 that the catalyst containing a solid solution structure has obvious advantages in increasing methanol conversion and reducing CO selectivity compared with a catalyst not containing a solid solution. Overall, the performance of the catalyst is better when the molar percentage of Zn in the catalyst is 4%-50%.

Fig. 1 is the XRD spectrogram of all embodiment and comparative example catalyst. It can be seen from the figure that with the increase of Zn content, the position of the 30.2° peak moves to a higher angle, indicating that Zn enters the _ZrO2 lattice and forms a ZnZrOx solid solution. When Zn/(Zn+Zr) increases to 20%, the ZnO diffraction peak can be clearly seen from XRD.

The above are only a few embodiments of the application, and do not limit the application in any form. Although the application is disclosed as above with preferred embodiments, it is not intended to limit the application. Any skilled person familiar with this field, Without departing from the scope of the technical solution of the present application, any changes or modifications made using the technical content disclosed above are equivalent to equivalent implementation cases, and all belong to the scope of the technical solution.

Claims (10)

1. A bimetallic catalyst for high-temperature methanol steam reforming hydrogen production is characterized in that,

the catalyst comprises ZnZrO _x Solid solutions and zinc oxide nanoparticles;

the zinc oxide nano-particles are dispersed in ZnZrO _x The surface of a solid solution.

2. The bimetallic catalyst of claim 1, wherein the molar amount of zinc is 4-50% of the total molar amount of zinc and zirconium;

the specific surface area of the catalyst is 30-50 m ² /g。

3. A method for preparing the catalyst of claim 1, comprising the steps of:

step (1): dissolving a zirconium source in water, mixing the zirconium source with a precipitant aqueous solution at the temperature of between 60 and 75 ℃ to obtain a precipitate, and drying the precipitate to obtain a zirconium precursor;

step (2): dissolving a zinc source in water to obtain a zinc source solution, dripping the zinc source solution on the zirconium precursor, grinding and stirring, dipping at room temperature, drying, and calcining to obtain the catalyst.

4. The production method according to claim 3, wherein in step (1):

the zirconium source is selected from at least one of zirconyl nitrate, pentahydrate zirconium nitrate and zirconium oxychloride;

the zirconium concentration in the water solution obtained after the zirconium source is dissolved in water is 0.1-0.2 mol/L;

the drying temperature is 80-120 ℃.

5. The production method according to claim 3, wherein in step (1):

the precipitant is selected from at least one of ammonium carbonate, sodium carbonate and ammonia water;

when the precipitant is ammonium carbonate or sodium carbonate, the concentration of the precipitant aqueous solution is 0.1-0.2 mol/L;

when the precipitant is ammonia water, the concentration of the precipitant aqueous solution is 10-20%.

6. The method according to claim 3, wherein in the step (2):

the zinc source is at least one selected from zinc acetate and zinc nitrate;

the amount of the zinc source used per 1g of the zirconium precursor is 0.09 to 6.5mmol.

7. The method according to claim 3, wherein in the step (2):

the grinding and stirring time is 5-10 min;

the room temperature dipping time is 6-12 h;

the drying temperature is 80-120 ℃;

the calcination temperature is 450-550 ℃; the time is 3 to 6 hours.

8. A method for producing hydrogen by steam reforming of methanol at high temperature, characterized in that the catalyst according to claim 1 or 2 or the catalyst produced by the production method according to any one of claims 3 to 7 is used.

9. The method of claim 8, comprising the steps of: under the condition of heating, raw materials containing methanol and water contact with a catalyst to react;

the reaction is carried out under normal pressure, and the reaction temperature is 350-400 ℃;

the molar ratio of the water to the methanol is 1.0-1.6;

the reaction mass space velocity is 1.2-4.5 h ^-1 。

10. The method of claim 8, wherein: the catalyst is reduced before reaction;

the reduction mode is to reduce for 2 to 6 hours at 400 ℃ in a hydrogen atmosphere.

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