CN115770563B

CN115770563B - Bimetallic catalyst for high-temperature methanol steam reforming hydrogen production and preparation method and application thereof

Info

Publication number: CN115770563B
Application number: CN202111040091.8A
Authority: CN
Inventors: 李�灿; 杨启华; 陈雪莲; 韩哲; 汤驰洲; 王集杰; 李成斌
Original assignee: Dalian Institute of Chemical Physics of CAS
Current assignee: Dalian Institute of Chemical Physics of CAS
Priority date: 2021-09-06
Filing date: 2021-09-06
Publication date: 2024-02-02
Anticipated expiration: 2041-09-06
Also published as: CN115770563A

Abstract

The invention discloses a bimetallic catalyst and a preparation method thereof, wherein the methanol reforming catalyst comprises ZnZrO _x Solid solutions and dispersions in ZnZrO _x Zinc oxide nanoparticles on the surface of solid solutions. The catalyst takes ZnO nano particles with solid solution structures and high surface dispersion as active centers, is prepared by adopting an impregnation method, and is formed by standing, drying, roasting and forming after zinc salts are impregnated on a carrier. The catalyst of the invention achieves the optimal performance at the reaction temperature of 400 ℃ and the activity can reach 99.9 percent. The invention has the advantages that: the catalyst has high activity, low CO selectivity and good stability at high temperature.

Description

Bimetallic catalyst for high-temperature methanol steam reforming hydrogen production and preparation method and application thereof

Technical Field

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

Background

Energy and environmental problems are the most significant problems facing human sustainable development in the future. With the development and use of large amounts of fossil energy, the global environmental deterioration and resource shortage problems are increasingly highlighted, so the transition from fossil fuels to sustainable, pollution-free, non-fossil energy is a necessary trend for the change of future energy structures. Hydrogen energy is becoming increasingly important as an ideal chemical fuel, energy carrier and energy storage tool. Because of the difficulty in storing and transporting hydrogen gas, the development of which is greatly limited, there is an urgent need for a readily handled and renewable liquid hydrogen carrier. Methanol is an ideal hydrogen source for the following reasons: firstly, the methanol has high hydrogen-carbon ratio, no connection of C-C bond and lower reaction temperature (150-400 ℃) of hydrogen production of the methanol compared with the hydrogen production temperature of other hydrocarbon compounds (600-800 ℃); secondly, methanol is liquid at normal temperature and normal pressure, and the storage and transportation are safe and convenient, and the methanol has biodegradability; thirdly, the source of the methanol is wide, the reserve of the methanol at home and abroad is quite abundant, and the methanol can be obtained through coal conversion, carbon dioxide hydrogenation, shale gas, combustible ice and other modes in the future. The North America shale gas revolution has the advantages that unconventional natural gas which can be used for more than 200 years appears, the transformation of the world energy structure is accelerated, the natural gas is converted into methanol, the international maritime cost is greatly reduced, and considerable raw material guarantee is provided for steam reforming of the shale gas. Therefore, the methanol reforming hydrogen production has received a great deal of attention because of the advantages of low cost, mild reaction conditions, less reformate, easy separation, and the like.

Currently, there are three main types of catalysts for methanol reforming reactions: copper-based catalysts, noble metal-containing catalysts, and oxide-based catalysts (free of noble metals and Cu). Copper-based catalysts are the most widely used catalysts because of their low cost, high low temperature activity, low CO selectivity, and the like. However, the stability is poor, and the problem of deactivation by sintering is likely to occur. The second class of noble metal-containing catalysts also have high activity and low CO selectivity, and good stability, but are expensive and unfavorable for industrial mass production. The third type is a metal oxide-based catalyst (containing no noble metals and Cu), and few reports are made in the literature on the use of metal oxides for methanol steam reforming reactions. Unlike the former two, the metal oxide catalyst has high activity, selectivity and good thermal stability at high temperature, and is favorable for long-time operation.

High purity hydrogen can be obtained through a methanol steam reforming reaction and supplied to a proton exchange membrane fuel cell for use, but direct methanol decomposition and reverse steam shift reaction may occur while the reaction is carried out, resulting in CO as a byproduct. Too high a concentration of CO can poison the Pt electrode of the fuel cell, thus requiring a CO concentration below 10ppm. Through basic research and application exploration of scientists for many years, the problems that the methanol cannot be completely converted, the concentration of CO in reformed gas is high, the stability is poor and the like in the prior methanol steam reforming reaction are still solved, and the catalyst is used for large-scale industrial use of hydrogen energy in a high-efficiency, long-term and economic mode.

Disclosure of Invention

In view of the shortcomings of the prior art, the invention provides a bimetallic catalyst and a preparation method thereof, and aims to overcome the defects of incomplete conversion of methanol, poor reaction selectivity and poor stability of the existing high-temperature methanol steam reforming hydrogen production catalyst.

The invention provides a bimetallic catalyst for preparing hydrogen by reforming high-temperature methanol and steam, which comprises ZnZrO _x Solid solutions and zinc oxide nanoparticles; the zinc oxide nano particles are dispersed in ZnZrO _x Solid solution surface. In the catalyst, the molar quantity of zinc element accounts for 4-50% of the total molar quantity of zinc element and zirconium element; the specific surface area of the catalyst is 30-50 m ² /g。

According to another aspect of the present application, there is provided a method for preparing the above catalyst, including the steps of:

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

step (2): and (3) dissolving a zinc source in water to obtain a zinc source solution, dripping the zinc source solution on a zirconium precursor, grinding and stirring, dipping at room temperature, drying and calcining to obtain the catalyst.

Wherein, in the step (1):

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

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

Wherein, in the step (2):

the zinc source is at least one selected from zinc acetate and zinc nitrate; the amount of the substance corresponding to the zinc source used is 0.09 to 6.5mmol per 1g of zirconium precursor. The grinding and stirring time is 5-10 min; the time of the room temperature dipping is 6-12 h; the drying temperature is 80-120 ℃; the calcination temperature is 450-550 ℃; the time is 3-6 h.

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

The method comprises the following steps: under the heating condition, the raw material containing methanol and water is contacted with a catalyst for reaction; 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 space velocity of the reaction mass is 1.2 to 4.5 hours ^-1 。

The catalyst is reduced before reaction; the reduction mode is to reduce for 2-6 h at 400 ℃ in hydrogen atmosphere.

The catalyst has the best catalytic performance at 400 ℃, can convert methanol basically and completely, has low CO selectivity, and has high space velocity at 380 ℃ (9.0 h ^-1 ) The running can keep good stability.

The beneficial effects are that: the invention discloses a catalyst for preparing hydrogen by reforming high-temperature methanol and steam and a preparation method thereof, wherein the catalyst for preparing hydrogen by reforming methanol comprises ZnZrO _x Solid solutionsAnd oxidative nanoparticles, solid solutions and ZnO particles being the same active component. The catalyst overcomes the defects of high CO selectivity and instability at high temperature of the reforming reaction of the traditional Cu-based catalyst at high temperature, has an optimal reaction temperature of 400 ℃, and can operate at high temperature for a long time. The invention uses ZnZrO with oxygen vacancy enriched surface _x The solid solution and ZnO nano particles have synergistic interaction, and the methanol conversion rate and H are improved ₂ The yield reduces the CO selectivity. The catalyst has the advantages of high activity, good selectivity and the like, and is a catalyst for preparing hydrogen by reforming methanol steam with excellent performance.

Drawings

Figure 1 is an XRD spectrum of all example and comparative catalysts.

FIG. 2 is an elemental scanning electron microscope image of the bimetallic catalyst prepared in example 6, wherein a is the HAADF-STEM image of the catalyst, c and d are elemental scans of Zn and Zr, respectively, and b is the elemental scan overlap image of c and d.

FIG. 3 is a graph showing the methanol conversion as a function of reaction time in example 4.

Detailed Description

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

Unless otherwise indicated, both the starting materials and the catalysts in the examples of the present application were purchased commercially.

The analytical method in the examples of the present application is as follows:

the effluent gas was analyzed on-line using an Agilent gas chromatograph equipped with a TCD and FID dual detector, wherein the packed column was TDX-01 and the capillary column was TG BOND Q.

In the embodiment of the application, conversion rate and selectivity are calculated as follows:

in the examples herein, methanol conversion and product selectivity were calculated based on moles of carbon.

Methanol conversion:C ₁ and C ₂ Respectively are provided withRepresenting the molar amount of methanol entering and exiting.

Product selectivity:wherein xi represents the mole percent of the i product; ni represents the number of carbon atoms contained in the i product.

Example 1

35.0g of Zr (NO) was weighed out ₃ ) ₄ ·5H ₂ O was dissolved in 500mL deionized water, and the solution was heated at 70deg.C with stirring. And diluting 21.0mL of ammonia water into 200mL of deionized water, rapidly adding the ammonia water solution into the Zr solution, and stirring at a speed of 500r/min, wherein the obtained precipitate is continuously stirred at 70 ℃ for 10min. The obtained precipitate is stood at room temperature for cooling, suction filtration is carried out, deionized water is used for washing for three times, and the filtrate is neutral. The obtained filter cake was dried overnight at 100℃to give Zr (OH) ₄ A precursor.

Example 2

0.19mmol of zinc nitrate was dissolved in 1ml of deionized water to obtain a Zn solution, and 2g of Zr (OH) obtained in example 1 was weighed out ₄ The precursor was placed in an evaporation dish and the Zn solution was dropped onto Zr (OH) ₄ On the precursor, grinding and stirring for 5min. After 7h of immersion at room temperature, drying at 100℃and finally calcining for 4h in a muffle furnace at 500℃the catalyst obtained is designated 3% ZnO/ZrO ₂ 。

Tabletting, crushing and screening the mixture to 40-80 meshes for catalyst evaluation. Weighing 0.3g of the screened catalyst, loading into a reaction tube with an inner diameter of 6mm, and placing in H ₂ Or H ₂ /N ₂ Reducing for 2-5 h at 400 ℃ under the mixed atmosphere. The reaction is carried out under normal pressure, and the raw materials are mixed solution of methanol and water, wherein n (MeOH) is n (H) ₂ O) =1.0, nitrogen as diluent gas at a flow rate of 30ml/min, reaction temperature of 400 ℃, whsv=4.5 h ^-1 The results of the catalyst evaluation are shown in Table 1.

Example 3

0.25mmol of zinc nitrate was dissolved in 1ml of deionized water, and 2g of Zr (OH) obtained in example 1 was weighed out ₄ The precursor was placed in an evaporation dish and the zinc solution was dropped onto Zr (OH) ₄ On the precursor, grinding and stirring for 5min. After 7h of immersion at room temperature, at 100deg.COven drying, calcining in muffle furnace at 500deg.C for 4 hr, and recording the obtained catalyst as 4% ZnO/ZrO ₂ . Tabletting, crushing and screening the mixture to 40-80 meshes for catalyst evaluation. The other evaluation procedures were the same as in example 2, and the catalyst evaluation results are shown in Table 1.

Example 4

The metal salt used for the preparation of the catalyst was 1.23mmol of zinc nitrate and 2g of Zr (OH) obtained in example 1 ₄ A precursor, placing the precursor in an evaporation dish, dissolving zinc nitrate in 1ml deionized water to obtain zinc solution, and dripping the zinc solution into Zr (OH) ₄ On the precursor, grinding and stirring for 5min. After 7h of immersion at room temperature, drying at 100℃and finally calcining for 4h in a muffle furnace at 500℃the catalyst obtained is designated as 9% ZnO/ZrO ₂ . Catalyst evaluation at 400℃n (H) ₂ O): n (MeOH) =1.0, pump flow rate 0.040mL/min;350 ℃, n (H) ₂ O) n (MeOH) =1.0 to 1.5, pump flow rate 0.012mL/min, and other evaluation procedures were the same as in example 1, and the catalyst evaluation results are shown in table 1. High temperature resistance test of catalyst under normal pressure, 380 ℃, n (H ₂ O):n(MeOH)＝1.1，WHSV＝4.4h ^-1 The catalyst activity is reduced by 6 to 7 percent in the first 40 hours of evaluation under the condition that the pump flow rate is 0.040mL/min, and the catalyst keeps good stability within the following 200 hours. The results are shown in FIG. 3.

Example 5

The metal salt used for the preparation of the catalyst was 1.54mmol of zinc nitrate and 2g of Zr (OH) obtained in example 1 ₄ A precursor, placing the precursor in an evaporation dish, dissolving zinc nitrate in 1ml deionized water to obtain zinc solution, and dripping the zinc solution into Zr (OH) ₄ On the precursor, grinding and stirring for 5min. After 7h of immersion at room temperature, drying at 100℃and finally calcining for 4h in a muffle furnace at 500℃the catalyst obtained is designated 11% ZnO/ZrO ₂ . The other evaluation procedures were the same as in example 2, and the catalyst evaluation results are shown in Table 1.

Example 6

The metal salt used for the preparation of the catalyst was 1.84mmol of zinc nitrate and 2g of Zr (OH) obtained in example 1 ₄ A precursor, placing the precursor in an evaporation dish, dissolving zinc nitrate in 1ml deionized water to obtain zinc solution, and dripping the zinc solution into Zr (OH) ₄ On the precursor, grinding and stirring for 5min. After 7h of immersion at room temperature, drying at 100℃and finally calcining for 4h in a muffle furnace at 500℃the catalyst obtained is designated as 13% ZnO/ZrO ₂ . The other evaluation procedures were the same as in example 2, and the catalyst evaluation results are shown in Table 1. The electron microscopy image of the catalyst prepared is shown in fig. 2, wherein a is an HAADF-STEM image of the catalyst, c and d are element scanning images of Zn and Zr respectively, and b is an element scanning overlap image of c and d. The shapes of c and d are substantially the same, and it can be seen that Zn is present in the presence of Zr, indicating that Zn is present in ZrO ₂ The medium was highly dispersed, confirming that ZnZrOx solid solution did form. It can be seen from b that after overlapping the scans of the two elements, there are some individual spots of aggregated Zn that do not coincide with Zr, indicating that there are also some individual ZnO nanoparticles present in the catalyst.

Example 7

The metal salt used for the preparation of the catalyst was 3.14mmol of zinc nitrate and 2g of Zr (OH) obtained in example 1 ₄ A precursor, placing the precursor in an evaporation dish, dissolving zinc nitrate in 1ml deionized water to obtain zinc solution, and dripping the zinc solution into Zr (OH) ₄ On the precursor, grinding and stirring for 5min. After 7h of immersion at room temperature, drying at 100℃and finally calcining for 4h in a muffle furnace at 500℃the catalyst obtained is designated as 20% ZnO/ZrO ₂ . The other evaluation procedures were the same as in example 2, and the catalyst evaluation results are shown in Table 1.

Example 8

The metal salt used for the preparation of the catalyst was 6.28mmol of zinc nitrate and 2g of Zr (OH) obtained in example 1 ₄ A precursor, placing the precursor in an evaporation dish, dissolving zinc nitrate in 1ml deionized water to obtain zinc solution, and dripping the zinc solution into Zr (OH) ₄ On the precursor, grinding and stirring for 5min. After 7h of immersion at room temperature, drying at 100℃and finally calcining for 4h in a muffle furnace at 500℃the catalyst obtained is designated 33% ZnO/ZrO ₂ . The other evaluation procedures were the same as in example 2, and the catalyst evaluation results are shown in Table 1.

Example 9

The metal salt used for the preparation of the catalyst was 12.56mmol of zinc nitrate and 2g of Zr (OH) obtained in example 2 ₄ A precursor, the precursor is placed in evaporationIn a dish, zinc nitrate was dissolved in 1ml deionized water to obtain a zinc solution, and the zinc solution was dropped to Zr (OH) ₄ On the precursor, grinding and stirring for 5min. After 7h of immersion at room temperature, drying at 100℃and finally calcining for 4h in a muffle furnace at 500℃the catalyst obtained is designated as 50% ZnO/ZrO ₂ . The other evaluation procedures were the same as in example 2, and the catalyst evaluation results are shown in Table 1.

Example 10

The metal salt used for the preparation of the catalyst was 1.23mmol of zinc acetate and 2g of Zr (OH) obtained in example 2 ₄ A precursor, placing the precursor in an evaporation dish, dissolving zinc acetate in 1ml deionized water to obtain a zinc solution, and dripping the zinc solution into Zr (OH) ₄ On the precursor, grinding and stirring for 5min. After 7h of immersion at room temperature, drying at 100℃and finally calcining for 4h in a muffle furnace at 500℃the catalyst obtained is designated as 9% ZnO/ZrO ₂ -2 other evaluation steps the same as in example 2, the catalyst evaluation results are shown in table 1.

Comparative example 1

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

Comparative example 2

Catalytic performance test of the support: 0.042mol ZrO (NO) ₃ ) ₂ ·H ₂ O and 0.105mol of urea are placed in a beaker, 70mL of deionized water is added, after stirring and dissolution, the mixed solution is transferred to a 100mL crystallization kettle for overnight crystallization at 150 ℃. Then cooling, washing, filtering and drying to obtain monoclinic ZrO ₂ A precursor. Finally, roasting for 4 hours at 400 ℃ in a muffle furnace, wherein the obtained catalyst is named as monoclinic ZrO ₂ . The other evaluation procedures were the same as in example 2, and the catalyst evaluation results are shown in Table 1.

Comparative example 3

1.62mmol of zinc nitrate was dissolved in a small amount of deionized water, and 2g of monoclinic-ZrO obtained in example 11 was weighed ₂ The carrier is placed in an evaporation dish, zinc nitrate is dissolved in 1ml of deionized water to obtain zinc solution, and the zinc solution is dripped onto the carrier and ground and stirred for 5min. After 7h of immersion at room temperature, drying at 100℃and finally calcining for 4h in a muffle furnace at 500℃the catalyst obtained is designated as 9% ZnO/monoclinic ZrO ₂ . Tabletting, crushing and screening the mixture to 40-80 meshes for catalyst evaluation. The other evaluation procedures were the same as in example 2, and the catalyst evaluation results are shown in Table 1.

Comparative example 4

Weighing 13% ZnO/ZrO in example 6 ₂ 500mg in a small flask, 1mol/L HNO is additionally added ₃ 3mL of aqueous solution, and stirred at 70℃for 1h. Cooling the solution, filtering, washing with deionized water until the filtrate is neutral, and oven drying at 100deg.C to obtain catalyst 13% ZnO/ZrO ₂ And (5) acid washing. Tabletting, crushing and screening the mixture to 40-80 meshes for catalyst evaluation. The other evaluation procedures were the same as in example 2, and the catalyst evaluation results are shown in Table 1.

Table 1 results of catalyst evaluation for examples and comparative examples

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

It can also be seen from the table that the activity of comparative example 4, which is a catalyst prepared by washing the ZnO nanoparticles on the surface of example 6 with nitric acid solution, is greatly reduced, indicating that the ZnO nanoparticles with high surface dispersion can also increase the activity of the catalyst.

From example 4 and comparative example 3, it is apparent that the catalyst containing a solid solution structure has a very significant advantage in terms of improving the methanol conversion and reducing the CO selectivity over the catalyst containing no solid solution. Taken together, the catalyst has better performance when the mole percentage of Zn is 4-50%.

Figure 1 is an XRD spectrum of all example and comparative catalysts. As can be seen from the graph, as the Zn content increases, the 30.2℃peak position moves to a high angle, indicating that Zn enters ZrO ₂ Lattice, form ZnZrOx solid solution. When Zn/(Zn+Zr) was increased to 20%, the appearance of a ZnO diffraction peak was clearly seen from XRD.

The foregoing description is only a few examples of the present application and is not intended to limit the present application in any way, and although the present application is disclosed in the preferred examples, it is not intended to limit the present application, and any person skilled in the art may make some changes or modifications to the disclosed technology without departing from the scope of the technical solution of the present application, and the technical solution is equivalent to the equivalent embodiments.

Claims

1. A bimetallic catalyst for preparing hydrogen by high-temperature methanol steam reforming 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 Solid solution surface.

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

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:

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

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

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

the drying temperature is 80-120 ℃.

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

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

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

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

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

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

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

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

the grinding and stirring time is 5-10 min;

the time of the room temperature dipping is 6-12 h;

the drying temperature is 80-120 ℃;

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

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

9. The method according to claim 8, comprising the steps of: under the heating condition, the raw material containing methanol and water is contacted with a catalyst for reaction;

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 space velocity of the reaction mass is 1.2 to 4.5 hours ^-1 。

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

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