WO2019134423A1 - Preparation method for catalyst for use in methane steam reforming in fuel cell - Google Patents

Abstract

The present invention relates to the technical field of catalysts and specifically relates to a preparation method for a catalyst for use in methane steam reforming in a fuel cell and particularly for use in a molten carbonate fuel cell, with the steps of ball mill mixing, powder molding, pretreatment, carrier calcination, and immersed decomposition. The present invention employs an immersion method preparation process, a catalyst carrier is prepared first, then an active component is loaded on the carrier, the catalyst so prepared has a large average aperture and a stable structure, thus further increasing the resistance of the catalyst against alkali metal poisoning, and increasing the activity, stability, and service life of the catalyst.

Description

Method for preparing catalyst for steam reforming of methane in fuel cell Technical field

The invention belongs to the technical field of catalysts, and in particular relates to a preparation method of a catalyst for use in a fuel cell, in particular for steam reforming of methane in a molten carbonate fuel cell.

Background technique

A molten carbonate fuel cell ("MCFC") is a high temperature fuel cell that generates electricity through an electrochemical reaction between a cathode, an anode, and an electrolyte master between the cathode and the anode. In such a battery, a molten eutectic (for example, a molten eutectic composed of lithium carbonate and potassium carbonate) of an alkali metal carbonate mixed melt impregnated with a carrier material (for example, a membrane carrier composed of LiAlO 2 /Al 2 O 3 ) is used as Electrolyte. The hydrogen required for fuel cell operation can be produced directly in the cell by a methane steam reforming reaction. The steam reforming reaction of methane is shown in the following example: CH4+H2O→CO+3H2(1)CO+H2O→CO2+H2(2) The first reaction has strong endothermicity and can be directly consumed by electrochemical reaction. The heat. The reaction is a catalytic reaction requiring the use of a reforming catalyst, and natural gas (also optionally methane, petroleum gas, naphtha, heavy oil or crude oil) can be used as a starting material for fuel cell operation.

At present, the hydrogen required for fuel cell operation comes from two parts, one part is partially reformed by the pre-reformer outside the fuel cell, and part of the generated hydrogen can be used immediately after entering the battery, and another part of methane steam is reformed in the fuel cell. This is called direct internal reforming (DIR). During operation of the molten carbonate fuel cell at 580 ° C to 675 ° C, some of the electrolyte was observed to evaporate as an alkali metal compound such as KOH, NaOH or LiOH. These alkali metal ions can be deposited on the reforming catalyst, and the catalyst is deactivated by poor poisoning. Catalyst poisoning is one of the key factors affecting the life of the battery pack. Therefore, even if the initial activity of the conventional catalyst is good, there is a technical problem that the activity is degraded rapidly after poisoning, and the stability of the activity is poor, not to mention the fact that some catalysts are not active.

A homogeneous catalyst having a single phase perovskite oxide, wherein at least one doping element of the ABO3 perovskite type oxide site A and/or site B is substituted, is disclosed in US Pat. The wettability with the liquid molten carbonate electrolyte may be lowered. The catalyst may have higher catalytic activity, inhibit catalyst poisoning caused by leakage and evaporation of the liquid molten carbonate electrolyte, maintain high reactivity for a long period of time, achieve high methane conversion rate, and produce a synthesis gas having a high hydrogen ratio.

The catalyst of the patent is prepared by a solid state mixing method. The catalyst prepared by the preparation method is unstable in structure, and the strength and the specific surface decrease rapidly after the reduction. As the catalyst strength and the specific surface decrease, the activity of the catalyst rapidly decreases, thereby leading to activity stability. Poor.

A catalyst composition for methane steam reforming in a fuel cell, particularly for direct internal reforming of methane in a molten carbonate fuel cell, and a catalyst material made therefrom are disclosed in US 2013/0116118 Al. And a method of producing the catalyst compound. Low activity and high stability to alkali metal ions.

The catalyst of the patent is prepared by a precipitation method, and the catalyst prepared by the preparation method is unstable in structure, and the strength and the specific surface decrease rapidly after the reduction. As the strength of the catalyst and the specific surface decrease, the activity of the catalyst decreases rapidly, resulting in activity stability. difference.

Summary of the invention

In order to solve the above technical problems, the present invention provides a preparation method of a catalyst for steam reforming of methane in a molten carbonate fuel cell, which is prepared by a dipping method, and a stable skeleton structure can be obtained, and the strength before and after reduction The pore structure and the specific surface change are small, thereby ensuring the activity stability of the catalyst to prolong the service life of the catalyst, and introducing a pretreatment process based on the conventional impregnation method, which can form a new stable crystal phase structure between different oxides. , new pores are formed, larger and more pores are obtained than the conventional method, and the large pore diameter is not easily blocked by the alkali metal of the electrolyte, so that the active channel of the reforming reaction can be continuously provided, and the activity stability of the catalyst is improved.

A method for preparing a catalyst for steam reforming of methane in a molten carbonate fuel cell according to the present invention, which is characterized in that it comprises the following steps:

(1) Ball-milling mixture: crushing and mixing three kinds of oxide powders of aluminum, zirconium and hafnium; mixing different materials uniformly and further breaking, which is beneficial to form stable crystal phase during pretreatment and calcination .

(2) Powder molding: The powder in step 1 is made into small particles, which are then pressed into pellets of a predetermined shape to meet the filling size requirements of the fuel cell device. The prescribed shape is determined by the fuel cell device, and the size of the fuel cell device must be filled. The oversized or undersized size cannot be incorporated into the fuel cell device.

(3) Pretreatment: The particles of the prescribed shape prepared in the step (2) are subjected to a new stable pore structure and a crystal phase structure during the pretreatment.

(4) carrier calcination: the particles pretreated in step (3) are calcined at a high temperature to form a carrier;

(5) Impregnation decomposition: The step (4) carrier is immersed in a nickel nitrate solution, and the active component is attached to the carrier, followed by drying and pyrolysis.

In the step (1), the mixing time is from 1 to 12 h, preferably from 1 to 8 h, particularly preferably from 6 to 8 h. If the mixing time is too short, it is not conducive to the mixing of multi-component materials. The prepared product is not uniform, the activity is unstable, and the mixing time is too long, the material will be knotted, which is not conducive to the molding of the next process.

In the step (2), the small particle size is 10-500 mesh, preferably 60-400 mesh, particularly preferably 120-320 mesh; the particle size mainly affects the uniformity of the product after molding, and the 120-320 mesh particle is more favorable. Enter the press mold. Products that are too large or too small to enter the mold are not uniform.

In the step (3), the temperature is 50 to 700 ° C, preferably 100 to 600 ° C, and particularly preferably 200 to 500 ° C. The pretreatment is carried out at a pressure of from 0.01 to 2.0 MPa, preferably from 0.1 to 1.5 MPa, particularly preferably from 1 to 1.5 MPa, a residence time of from 1 to 24 h, preferably from 5 to 12 h, particularly preferably from 6 to 8 h, such that aluminum, zirconium and The three oxides of yttrium interact to form a new crystalline phase structure, while at the same time forming a new stable pore structure during the pretreatment process.

At a certain temperature and pressure, a new stable crystal phase structure is formed between different oxides, and new pores are formed at the same time, thereby obtaining larger and more pores, and the large pore diameter is not easily blocked by the alkali metal of the electrolyte, enriching The pores continue to provide an active channel for the reforming reaction and increase the activity stability of the catalyst.

In the step (4), the calcination temperature is >675 ° C, preferably the calcination temperature is ≥700 ° C, particularly preferably the calcination temperature is 750 ° C, and the calcination temperature is 1400 ° C, preferably the calcination temperature is ≤1350 ° C, particularly preferably the calcination temperature ≤ 1300 ° C, calcination time ≥ 30 min, preferably calcination time ≥ 40 min, particularly preferably calcination time ≥ 50 min, and calcination time ≤ 10 h, preferably calcination time ≤ 8 h, particularly preferably calcination time ≤ 6 h.

The calcination temperature mainly affects the strength and specific surface of the carrier. When the temperature is less than 700 °C, the specific surface is high, but the strength is too low. It is easy to be pulverized during use, affecting the service life. The calcination temperature is higher than 1400 ° C, the strength is high, but the surface is high. Too low, the use of activity is too low. The calcination time has an effect on the formation of the pore structure.

In the step (4), the carrier has a specific surface area of >70 m ² /g. The specific surface is guaranteed to provide sufficient active surface.

In the step (5), the immersion temperature is 60-90 ° C, preferably the immersion temperature is 70-90 ° C, particularly preferably the immersion temperature is 80-90 ° C, the immersion time ≥ 5 minutes, preferably the immersion time ≥ 10 minutes, particularly preferably The immersion time is ≥ 15 minutes, and the immersion time is ≤ 2 hours, preferably the immersion time ≤ 1.6 hours, particularly preferably the immersion time ≤ 1.5 hours.

A suitable impregnation temperature and time allows the impregnation solution to fully enter the pores of the support while ensuring uniformity of solution distribution.

In the step (5), the concentration of the nickel nitrate solution is 0.1-l mol/L.

The lower the concentration of the solution, the less active ingredient is loaded on the carrier each time, and the concentration of the solution is selected according to the amount of active component required to be loaded.

After the impregnation in the step (5), the carrier is taken out, and the elevated temperature is dried, wherein the drying temperature is ≥90 ° C, preferably the drying temperature is ≥100 ° C, particularly preferably the drying temperature is ≥110 ° C, and the drying time is 10 min -10 h. Preferably, the drying time is from 20 min to 8 h, and particularly preferably the drying time is from 30 min to 4 h.

The drying temperature and time are to ensure that the free water and the crystal water of the nickel nitrate solution adsorbed on the carrier are completely removed, and are prepared for the next decomposition.

The decomposition temperature in the step (5) is >150 ° C, preferably the decomposition temperature is ≥200 ° C, particularly preferably the decomposition temperature is ≥250 ° C, and the decomposition temperature is ≤700 ° C, preferably the decomposition temperature ≤650 ° C, particularly preferably the decomposition temperature ≤600 ° C, Decomposition time ≥ 30 min, preferably decomposition time ≥ 40 min, particularly preferably decomposition time ≥ 50 min, and decomposition time ≤ 10 h, preferably decomposition time ≤ 8 h, particularly preferably decomposition time ≤ 6 h.

A suitable decomposition temperature and time allows nickel nitrate to be completely decomposed into nickel oxide.

In the present invention, the nickel oxide is detected by chemical analysis, and if the content of the nickel oxide in the step (5) is less than or equal to 40%, the step (5) is repeated. If the content of nickel oxide is less than 40%, the active center participating in the catalytic reaction is reduced during use, the activity is decreased rapidly, and the service life is shortened.

The prepared catalyst may include the following mass percentage components:

Nickel oxide 35-60%, alumina 30-50%, zirconia 1-15%, lanthanum oxide 1-15%, total mass content 100%; or catalyst comprising the following mass percentage components: nickel oxide 35-55 %, alumina 35-50%, zirconia 6-10%, cerium oxide 4-5%, total mass content is 100%.

Or nickel oxide 37-42%, alumina 42-48%, zirconia 6-12%, lanthanum oxide 3.5-5%, total mass content is 100%; or may also include the following mass percentage components: nickel oxide 40 -42%, alumina 43-47%, zirconia 7-11%, cerium oxide 4-5%, total mass content 100%; or components including the following mass percentages: nickel oxide 40%, alumina 46% 9% of zirconia and 4.5% of yttrium oxide, the remainder being impurities.

The cerium may be replaced by other rare earth elements, and any other rare earth element is any one of cerium, lanthanum, cerium, lanthanum, cerium, lanthanum, cerium, lanthanum, cerium, lanthanum, cerium, lanthanum, cerium, lanthanum or cerium.

The preparation method of the catalyst for steam reforming of methane in a fuel cell adopts the preparation process of the impregnation method, first prepares the catalyst carrier, and then carries the active component on the carrier, so that the prepared catalyst has a large average pore diameter and a stable structure. High thermal stability and resistance to toxicity. Average pore diameter of the catalyst

The pore volume is 0.200-0.400 ml/g, the specific surface area is more than 45 m 2 /g, and the loss on ignition at 900 ° C is less than 5%.

DRAWINGS

The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

1 and 2 are comparative diagrams of different catalyst pore sizes in the present invention.

Figure 3 is a comparison diagram of methane conversion rate in the present invention

Figure 4 is a comparison chart before and after poisoning in the present invention

Figure 5 is a comparison chart before and after self-made poisoning in the present invention

Detailed ways

The present invention will be further described below in conjunction with the drawings and specific embodiments of the specification:

In the following examples, the catalyst is a structured particulate support made of an oxide of aluminum, zirconium and hafnium, then loaded with an oxide of nickel, and finally a regular granular catalyst formed from oxides of nickel, aluminum, zirconium and hafnium. The raw materials used for the catalyst are alumina powder, zirconia powder, cerium oxide powder and nickel nitrate solution, and the mass ratio of the alumina powder, the zirconia powder and the cerium oxide powder is 7-11:43-47:4-5. The concentration of the nickel nitrate solution is 0.1-lmol/L. The prepared particulate catalyst may be a cylindrical particulate catalyst having a diameter of from 1 to 3 mm and a height of from 0.5 to 5 mm.

Example 1

The preparation method of the catalyst for steam reforming of methane in a molten carbonate fuel cell comprises the following steps:

(1) Ball-milling compound: The three oxide powders of aluminum, zirconium and hafnium are added to the ball mill according to the ratio of the final demand of the catalyst, and the three oxide powders are further crushed and thoroughly mixed by ball milling, and the mixing time is 1 hour.

(2) Powder molding: the powder prepared in the step (1) is passed through a granulator to form a uniform granular fine particle material having a particle size of 10 mesh, and then the fine particle material is added to a rotary tableting machine or a hydroforming tableting machine. Medium is pressed into pellets of a prescribed shape.

(3) pretreatment: the particles of the specified shape prepared in the step (2), at a temperature of 50 ° C, a pressure of 0.01 Mpa, a residence time of 1 hour;

(4) Carrier calcination: The pellet of the predetermined shape pretreated in the step (4) is calcined at a high temperature, the calcination temperature is higher than the use temperature of 680 ° C, and the calcination time is 30 minutes. The specific surface area and pore size of the calcined support were controlled by adjusting the calcination time and the calcination temperature, and the specific surface area was more than 72 m ² /g.

(5) Impregnation decomposition: The carrier prepared in the step (4) is immersed in a nickel nitrate solution, the immersion temperature is 60 ° C, the immersion time is 5 minutes, and the nickel nitrate solution concentration is 0.1 mol/L. After the impregnation, the carrier was taken out, and the temperature was elevated at a raised temperature of 90 ° C for 10 minutes. Further, the carrier after the completion of the drying is further raised in temperature, and the nitrate is decomposed by high temperature to remove the nitrate to leave an oxide of nickel. The decomposition temperature was 155 ° C for 30 minutes. The nickel oxide is detected by chemical analysis, and if the nickel oxide content is less than 40% (mass percentage), the step (5) is repeated.

The catalyst prepared by the method of the invention has large pore size and stable pore structure, and the large pore diameter is not easily blocked by the alkali metal of the electrolyte, and can continuously provide an active channel for the reforming reaction; aluminum, lanthanum and zirconium act together to displace the carrier crystal grains. The increase in the number of active centers increases the overall activity of the catalyst.

Example 2

The preparation method of the catalyst for steam reforming of methane in a molten carbonate fuel cell comprises the following steps:

(1) Ball-milling compound: The three oxides of aluminum, zirconium and hafnium were added to a ball mill according to the ratio of the final demand of the catalyst, and the three oxides were further crushed and thoroughly mixed by ball milling for a mixing time of 12 hours.

(2) Powder molding: the powder prepared in the step (1) is passed through a granulator to form a uniform granular fine particle material having a particle size of 500 mesh, and then the fine particle material is added to a rotary tableting machine or a hydroforming tableting machine. Medium is pressed into pellets of a prescribed shape.

(3) pretreatment: the particles of the specified shape prepared in step (2), at a temperature of 700 ° C, a pressure of 2.0 Mpa, a residence time of 24 h;

(4) Carrier calcination: the pellet of the predetermined shape pretreated by the step (3) is calcined at a high temperature, and the calcination temperature is 700 ° C.

The calcination time was 40 minutes. The specific surface area and pore size of the calcined support are controlled by adjusting the calcination time and the calcination temperature, and the specific surface area is usually required to be more than 75 m ² /g.

(5) Impregnation decomposition: The carrier prepared in the step (4) was immersed in a nickel nitrate solution, the immersion temperature was 70 ° C, the immersion time was 10 minutes, and the nickel nitrate solution concentration was 0.6 mol/L. After the impregnation, the carrier was taken out, and the temperature was elevated at an elevated temperature, wherein the temperature was 100 ° C and the time was 20 minutes. The carrier after drying is further elevated in temperature, and the nitrate is decomposed by high temperature to remove nitrate, leaving an oxide of nickel. The decomposition temperature was 200 ° C and the time was 40 minutes. The nickel oxide is detected by chemical analysis, and if the nickel oxide content is less than 40% (mass percentage), the step (5) is repeated.

Example 3

The preparation method of the catalyst for steam reforming of methane in a molten carbonate fuel cell comprises the following steps:

(1) Ball milling mixture: The three oxides of aluminum, zirconium and hafnium are added to a ball mill according to the ratio of the final demand of the catalyst, and the three oxides are further crushed and thoroughly mixed by ball milling for a mixing time of 6 hours.

(2) Powder molding: the powder prepared in step 1 is passed through a granulator to form a fine particle material having a uniform particle size of 60 mesh, and then the fine particle material is added to a rotary tablet press or a hydroforming tablet press. It is pressed into pellets of a prescribed shape.

(3) pretreatment: the predetermined shape of the particles prepared in step (2), at a temperature of 100 ° C, a pressure of 0.1 Mpa, a residence time of 5 h;

(4) Carrier calcination: The pellet of the predetermined shape pretreated in step 3 was calcined at a high temperature, calcined at a temperature of 750 ° C, and calcined for 10 hours. The specific surface area and pore size of the calcined support are controlled by adjusting the calcination time and the calcination temperature, and the specific surface area is usually required to be more than 80 m ² /g.

(5) Impregnation decomposition: The carrier prepared in the step (4) was immersed in a nickel nitrate solution, the immersion temperature was 80 ° C, the immersion time was 1.6 hours, and the nickel nitrate solution concentration was 1 mol/L. After the impregnation, the carrier was taken out, and the temperature was elevated at an elevated temperature, wherein the temperature was 110 ° C for 2 hours. The carrier after drying is further elevated in temperature, and the nitrate is decomposed by high temperature to remove nitrate, leaving an oxide of nickel. The decomposition temperature was 250 ° C and the time was 50 minutes.

The nickel oxide is detected by chemical analysis, and if the nickel oxide content is less than 40% (mass percentage), the step (5) is repeated.

The catalyst prepared by the method of the invention has large pore size and stable pore structure, and the large pore diameter is not easily blocked by the alkali metal of the electrolyte, and can continuously provide an active channel for the reforming reaction; aluminum, lanthanum and zirconium act together to displace the carrier crystal grains. The increase in the number of active centers increases the overall activity of the catalyst.

Example 4

The preparation method of the catalyst for steam reforming of methane in a molten carbonate fuel cell comprises the following steps:

(1) Ball-milling compound: The three oxides of aluminum, zirconium and hafnium were added to a ball mill according to the ratio of the final demand of the catalyst, and the three oxides were further crushed and thoroughly mixed by ball milling for a mixing time of 8 hours.

(2) Powder molding: the powder prepared in step 1 is passed through a granulator to form a uniform granular fine particle material having a particle size of 400 mesh, and then the fine particle material is added to a rotary tablet press or a hydroforming tablet press. , pressed into pellets of a prescribed shape.

(3) pretreatment: the specified shape of the particles prepared in step (2), at a temperature of 600 ° C, a pressure of 1.5 Mpa, a residence time of 12 h;

(4) Carrier calcination: The pellet of the predetermined shape pretreated in step 3 is calcined at a high temperature, calcined at a temperature of 1400 ° C, and calcined for 1 hour. The specific surface area and pore size of the calcined support are controlled by adjusting the calcination time and the calcination temperature, and a specific surface area of 76 m ² /g is usually required.

(5) Impregnation decomposition: The carrier prepared in the step 3 was placed in a nickel nitrate solution, and the immersion temperature was 90 ° C, the immersion time was 1 hour, and the nickel nitrate solution concentration was 0.5 mol/L. After the impregnation, the carrier was taken out and dried at a raised temperature, wherein the temperature was 130 ° C and the time was 4 hours. The carrier after drying is further elevated in temperature, and the nitrate is decomposed by high temperature to remove nitrate, leaving an oxide of nickel. The decomposition temperature was 700 ° C and the time was 6 hours.

The nickel oxide is detected by chemical analysis, and if the nickel oxide content is less than 40% (mass percentage), the step (5) is repeated.

Example 5

The preparation method of the catalyst for steam reforming of methane in a molten carbonate fuel cell comprises the following steps:

(1) Ball-milling compound: The three oxides of aluminum, zirconium and hafnium were added to a ball mill according to the ratio of the final demand of the catalyst, and the three oxides were further crushed and thoroughly mixed by ball milling for 7 hours.

(2) Powder molding: the powder prepared in step 1 is passed through a granulator to make a fine particle material with a uniform particle size of 120 mesh, and then the fine particle material is added to a rotary tablet press or a hydroforming tablet press. , pressed into pellets of a prescribed shape.

(3) pretreatment: the specified shape of the particles prepared in step (2), at a temperature of 200 ° C, a pressure of 1 Mpa, a residence time of 6 h;

(4) Carrier calcination: The pellet of the predetermined shape pretreated in step 3 was calcined at a high temperature, the calcination temperature was 900 ° C, and the calcination time was 4 hours. The specific surface area and pore size of the calcined support are controlled by adjusting the calcination time and the calcination temperature, and the specific surface area is usually required to be more than 85 m ² /g.

(5) Impregnation decomposition: The carrier prepared in the step 4 was placed in a nickel nitrate solution, and the immersion temperature was 85 ° C, the immersion time was 1 hour, and the nickel nitrate solution concentration was 0.6 mol/L. After the impregnation, the carrier was taken out and dried at a raised temperature, wherein the temperature was 120 ° C and the time was 3 hours. The carrier after drying is further elevated in temperature, and the nitrate is decomposed by high temperature to remove nitrate, leaving an oxide of nickel. The decomposition temperature was 500 ° C for 3 hours.

The nickel oxide is detected by chemical analysis, and if the nickel oxide content is less than 40% (mass percentage), the step (5) is repeated.

The catalyst prepared by the method of the invention has large pore size and stable pore structure, and the large pore diameter is not easily blocked by the alkali metal of the electrolyte, and can continuously provide an active channel for the reforming reaction; aluminum, lanthanum and zirconium act together to displace the carrier crystal grains. The increase in the number of active centers increases the overall activity of the catalyst.

Example 6

The preparation method of the catalyst for steam reforming of methane in a molten carbonate fuel cell comprises the following steps:

(1) Ball-milling compound: The three oxides of aluminum, zirconium and hafnium were added to a ball mill according to the ratio of the final composition of the catalyst, and the three oxides were further crushed and thoroughly mixed by ball milling for a mixing time of 4 hours.

(2) Powder molding: the powder prepared in step 1 is passed through a granulator to make a fine particle material with a uniform particle size of 320 mesh, and then the fine particle material is added to a rotary tablet press or a hydroforming tablet press. , pressed into pellets of a prescribed shape.

(3) pretreatment: the particles of the specified shape prepared in step (2), at a temperature of 500 ° C, a pressure of 1.5 Mpa, a residence time of 8 h;

(4) Carrier calcination: The pellet of the predetermined shape prepared in the step 3 was calcined at a high temperature, the calcination temperature was 1100 ° C, and the calcination time was 2 hours. The specific surface area and pore size of the carrier after calcination were controlled by adjusting the calcination time and the calcination temperature, and the specific surface area was 83 m ² /g.

(5) Impregnation decomposition: The carrier prepared in the step 4 was placed in a nickel nitrate solution, and the immersion temperature was 75 ° C, the immersion time was 1.5 hours, and the nickel nitrate solution concentration was 0.4 mol/L. After the impregnation, the carrier was taken out and dried at an elevated temperature, wherein the temperature was 95 ° C and the time was 8 hours. The carrier after drying is further elevated in temperature, and the nitrate is decomposed by high temperature to remove nitrate, leaving an oxide of nickel. The decomposition temperature was 400 ° C and the time was 2 hours.

The nickel oxide is detected by chemical analysis, and if the nickel oxide content is less than 40% (mass percentage), the step (5) is repeated.

Example 7

The preparation method of the catalyst for steam reforming of methane in a molten carbonate fuel cell comprises the following steps:

(1) Ball-milling compound: The three oxides of aluminum, zirconium and hafnium are added to a ball mill according to the ratio of the final demand of the catalyst, and the three oxides are further crushed and thoroughly mixed by ball milling for a mixing time of 10 hours.

(2) Powder molding: the powder prepared in step 1 is passed through a granulator to form a uniform granular fine particle material having a particle size of 200 mesh, and then the fine particle material is added to a rotary tableting machine or a hydroforming tableting machine. , pressed into pellets of a prescribed shape.

(3) Pretreatment: The pellet of the predetermined shape prepared in the step (2) was at a temperature of 300 °C. The pressure is 1.2Mpa and the residence time is 7h;

(4) Carrier calcination: The pellet of the predetermined shape pretreated in the step 3 was calcined at a high temperature, the calcination temperature was 800 ° C, and the calcination time was 6 hours. The specific surface area and pore size of the carrier after calcination were controlled by adjusting the calcination time and the calcination temperature, and the specific surface area was 71 m ² /g.

(5) Impregnation decomposition: The carrier prepared in the step 3 was placed in a nickel nitrate solution, and the immersion temperature was 65 ° C, the immersion time was 50 minutes, and the nickel nitrate solution concentration was 0.2 mol/L. After the impregnation, the carrier was taken out, and the temperature was elevated at a raised temperature of 105 ° C for 10 hours. The carrier after drying is further elevated in temperature, and the nitrate is decomposed by high temperature to remove nitrate, leaving an oxide of nickel. The decomposition temperature was 300 ° C for 10 hours.

The nickel oxide is detected by chemical analysis, and if the nickel oxide content is less than 40% (mass percentage), the step (5) is repeated.

Example 8

The preparation method of the catalyst for steam reforming of methane in a molten carbonate fuel cell comprises the following steps:

(1) Ball-milling compound: The three oxides of aluminum, zirconium and hafnium were added to a ball mill according to the ratio of the final demand of the catalyst, and the three oxides were further crushed and thoroughly mixed by ball milling for 7 hours.

(2) Powder molding: the powder prepared in step 1 is passed through a granulator to make a fine particle material with uniform particle size of 260 mesh, and then the fine particle material is added to a rotary tablet press or a hydroforming tablet press. , pressed into pellets of a prescribed shape.

(3) Pretreatment: The pellet of the predetermined shape prepared in the step (2) was at a temperature of 400 °C. The pressure is at 1.3Mpa and the residence time is 8h;

(4) Carrier calcination: The pellet of the predetermined shape pretreated in the step 3 was calcined at a high temperature, the calcination temperature was 1300 ° C, and the calcination time was 1.5 hours. The specific surface area and pore size of the calcined support were controlled by adjusting the calcination time and the calcination temperature, and the specific surface area was 84 m ² /g.

(5) Impregnation decomposition: The carrier prepared in the step 3 was placed in a nickel nitrate solution, and the immersion temperature was 85 ° C, the immersion time was 30 minutes, and the nickel nitrate solution concentration was 0.7 mol/L. After the impregnation, the carrier was taken out and dried at a raised temperature, wherein the temperature was 140 ° C and the time was 30 minutes. The carrier after drying is further elevated in temperature, and the nitrate is decomposed by high temperature to remove nitrate, leaving an oxide of nickel. The decomposition temperature was 200 ° C and the time was 8 hours.

The nickel oxide is detected by chemical analysis, and if the nickel oxide content is less than 40% (mass percentage), the step (5) is repeated.

Test one

Experimental examples (pretreated samples) and control groups (not pretreated samples) were set. The experimental examples are the catalysts prepared by the method of Example 1 in the present invention, and the control group is otherwise described in the contents of Example 1, but without steps ( 3), but no pre-processing steps.

The pore size distribution of the comparative sample and the catalyst of the present invention (self-made catalyst sample, the same below) was measured by the mercury intrusion method according to ASTM UOP 578-02, using a contact angle of 140 ° and a pressure ranging from 0.6 to 60,000 psig, as shown in FIG.

As can be seen from Figure 1, the pretreated product has a higher pore size and pore distribution than the unpretreated product.

Test 2

The pore size distribution of the catalyst produced by the comparative method and the preparation method of the present invention (self-made catalyst sample, the same below) was measured by the mercury intrusion method using a mercury intrusion method, using a contact angle of 140 ° and a pressure ranging from 0.6 to 60,000 psig, such as figure 2.

The control was a catalyst prepared according to the preparation method of US Pat. No. 2013/0116118 Al: 420 g of a homogeneous mixture comprising nickel, aluminum and zirconium oxide (BET surface area = 160 m ^{2 /} g; NiO = 72 wt.%, Al) ₂ O ₃ = 19 wt.%, ZrO ₂ = 9 wt.%, d ₅₀ = 137 μm) was used as the active reforming phase (ingredient a). 180 g of an alumina powder containing γ-Al ₂ O ₃ , _δ-A/2 O ₃ and θ-Al ₂ O ₃ (BET = 126 m ² /g, d ₅₀ = 116 μm;) was added. The powder mixture was then mixed with 3 wt.% graphite and thoroughly mixed by a tumbler mixer. The obtained mixture was compacted on a compactor and subsequently treated on a hydraulic eccentric press to obtain solid pellets (diameter = 2.5 mm; height = 2.5 mm) (total composition of the oxide-based catalyst: 50.4 wt.% of NiO) , 43.65 wt.% of A1 ₂ O ₃ and 5.95 wt.% of ZrO ₂ ).

As can be seen from the examination of Fig. 2, the present invention has a larger pore diameter than the comparative sample, and provides an active channel for the reforming reaction. The alkali metal of the electrolyte is less likely to cause clogging of the pore diameter and lower the activity of the catalyst.

Test 2 Catalyst poisoning test

The comparative sample and the catalyst prepared by the method of the present invention were taken for poisoning test, wherein the comparative sample was the comparative sample in the test 1, and the test was as follows:

Reaction tube: Φ25×3 mm; catalyst size: Φ2×4 mm Test particle size: original particle size; catalyst loading volume: 3 ml; catalyst loading height: about 1 cm; electrolyte weight: 31 g; electrolyte particle size: <5 mm; reduction pressure: atmospheric pressure; reduction Temperature: inlet 550 ° C, middle 550 ° C, outlet 550 ° C; reducing gas flow: N2: 1.25 NL / min, 75 NL / h; H ₂ : 0.505 NL / min, 30.3 NL / h; reduction time: 4 h;

Test pressure: atmospheric pressure; test temperature: inlet 1cm 650 ° C, inlet 650 ° C, outlet 650 ° C (according to the actual temperature); test gas flow: H ₂ : 1.01 NL / min, 60.6 NL / h; H ₂ O : 8 ml/min, 480 ml/h; CO ₂ : 0.25 NL/min, 15 NL/h; CH ₄ : 2.5 NL/min, 150 NL/h; N 2 : 0.3 NL/min, 18 NL/h;

Test inlet gas composition:

composition	N2 (%)	CH4 (%)	CO2 (%)	H2 (%)	H2O (%)
Dry basis	7.39	61.57	6.16	24.88	——
Wet basis	2.14	17.84	1.78	7.21	71.03

Test water to carbon ratio: 3.98; test water to hydrogen ratio: 9.86; test carbon space velocity: 10000h ^-1 ;

Test process: under normal pressure, the catalyst bed is heated by N2. When the bed temperature rises to 550 °C, H2 is introduced for reduction; after the reduction is completed, water is pumped through the advection pump to drive into the water catalyst bed. After the layer was stabilized at 550 ° C, CO _{2 was introduced} , and the temperature of the catalyst bed layer continued to rise to 650 ° C. After stabilization, N 2 was turned off, and CH 4 was passed to conduct initial activity measurement of the catalyst. In order to carry out the poisoning study, the reactor was cooled to room temperature, and the test gas was re-introduced through the electrolyte layer under an inert gas (N ₂ ), and the time was started after the temperature of the electrolyte layer was raised to 650 ° C, and analyzed once every 4 hours during the poisoning test. The composition of the inlet and outlet was measured periodically during the entire test period (about 800 hours), and the results are shown in Figure 3.

As can be seen from Figure 3, the catalyst of the present invention has a relatively stable methane conversion activity throughout the test period. The initial methane conversion of the comparative catalyst is slightly higher than the initial methane conversion of the catalyst of the present invention, but after initial poisoning by alkali metal hydroxide or alkali metal carbonate vapor, the initial methane conversion decreases, after about 100 hours, The initial methane conversion is lower than the methane conversion of the catalyst of the present invention.

Trial three

The comparative sample and the catalyst prepared by the method of the invention were tested and analyzed for pore size and pore volume before, after and after poisoning, and the pore size distribution was measured by mercury intrusion method according to ASTM UOP 578-02 method, using a contact angle of 140° and The pressure ranged from 0.6 to 60,000 psig, and the comparative sample results are shown in Figure 4. The catalyst results in the invention are shown in Figure 5.

The comparative sample is the comparison sample in Test 1.

As can be seen from Fig. 5, the structure of the catalyst of the present invention is stable, and the pore diameter changes little before, after, and after poisoning, and particularly after reduction and after poisoning, the pore size and pore distribution are substantially unchanged. As can be seen from Fig. 4, the comparative samples changed significantly before, after, and after the toxic pore size and pore distribution, indicating that the catalyst structure was unstable and was greatly affected by temperature and alkali metal. The stable structure of the catalyst of the invention can provide stable pore size and pore distribution for a long time, is more favorable for stability of activity, and improves the service life of the catalyst.

The catalyst prepared by the preparation method of the invention has large pore diameter and stable pore structure, and the large pore diameter is not easily blocked by the alkali metal of the electrolyte, and can continuously provide an active channel for the reforming reaction; aluminum, lanthanum and zirconium act together to make the carrier The crystal grains are misaligned and the active center is increased, which improves the overall activity of the catalyst.

The present invention has been shown and described with respect to the embodiments of the present invention and the embodiments of the invention. Various changes and modifications are possible which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and their equivalents.

Claims (10)

1. A method for preparing a catalyst for steam reforming of methane in a molten carbonate fuel cell, comprising the steps of:

   (1) Ball-milling mixture: crushing and mixing three kinds of oxides of aluminum, zirconium and hafnium;

   (2) Powder molding: the powder in step 1 is granulated and then pressed into granules of a prescribed shape;

   (3) Pretreatment: the particles of the prescribed shape prepared in the step (2) are formed into a new stable pore structure through the pretreatment process;

   (4) carrier calcination: the particles of the predetermined shape pretreated in step 3 are calcined at a high temperature to form a carrier;

   (5) Impregnation decomposition: The carrier is placed in a nickel nitrate solution for immersion, drying and pyrolysis.
2. The method for preparing a catalyst for steam reforming of methane in a molten carbonate fuel cell according to claim 1, wherein in the step (1), the mixing time is 1-12 h, preferably 1 -8h, particularly preferably 6-8h.
3. A method for preparing a catalyst for steam reforming of methane in a molten carbonate fuel cell according to claim 1, wherein in the step (2), the particle size is from 10 to 500 mesh, preferably 60-400 mesh, particularly preferably 120-320 mesh;
4. A method for preparing a catalyst for steam reforming of methane in a molten carbonate fuel cell according to claim 1, wherein in the step (3), at a temperature of 50 to 700 ° C, preferably 100 -600 ° C, particularly preferably 200-500 ° C; pressure in the range of 0.01-2.0 MPa, preferably 0.1-1.5 MPa, particularly preferably 1-1.5 MPa, residence time 1-24 h, preferably 5-12 h, particularly preferably 6-8h;
5. The method for preparing a catalyst for steam reforming of methane in a molten carbonate fuel cell according to claim 1 or 4, wherein in the step (3), the calcination temperature is > 675 ° C, preferably Calcination temperature ≥ 700 ° C, particularly preferably calcination temperature ≥ 750 ° C, and calcination temperature ≤ 1400 ° C, preferably calcination temperature ≤ 1350 ° C, particularly preferably calcination temperature ≤ 1300 ° C, calcination time ≥ 30 min, preferably calcination time ≥ 40 min, particularly preferred The calcination time is ≥ 50 min, and the calcination time is ≤ 10 h, preferably the calcination time is ≤ 8 h, and particularly preferably the calcination time is ≤ 6 h.
6. A method for preparing a catalyst for steam reforming of methane in a molten carbonate fuel cell according to claim 1 or 3, wherein in the step (4), the specific surface area of the carrier is > 70 m ² / g; in the step (5), the concentration of the nickel nitrate solution is 0.11 mol / L.
7. The method for preparing a catalyst for steam reforming of methane in a molten carbonate fuel cell according to claim 1, wherein in the step (5), the immersion temperature is 60-90 ° C, preferably impregnation The temperature is 70-90 ° C, particularly preferably the immersion temperature is 80-90 ° C, the immersion time ≥ 5 minutes, preferably the immersion time ≥ 10 minutes, particularly preferably the immersion time ≥ 15 minutes, and the immersion time ≤ 2 hours, preferably the immersion time ≤ 1.6 In the hour, it is particularly preferred that the immersion time is ≤ 1.5 hours.
8. The method for preparing a catalyst for steam reforming of methane in a molten carbonate fuel cell according to claim 1, wherein the carrier is taken out after the impregnation in the step (5), and the elevated temperature is obtained. The drying treatment is carried out, wherein the drying temperature is ≥ 90 ° C, preferably the drying temperature is ≥ 100 ° C, particularly preferably the drying temperature is ≥ 110 ° C, the drying time is 10 min - 10 h, preferably the drying time is 20 min - 8 h, and particularly preferably the drying time is 30 min - 4 h.
9. The method for preparing a catalyst for steam reforming of methane in a molten carbonate fuel cell according to claim 1, wherein the decomposition temperature in the step (5) is >150 ° C, preferably the decomposition temperature is ≥ 200 °C, particularly preferably decomposition temperature ≥ 250 ° C, and decomposition temperature ≤ 700 ° C, preferably decomposition temperature ≤ 650 ° C, particularly preferably decomposition temperature ≤ 600 ° C, decomposition time ≥ 30 min, preferably decomposition time ≥ 40 min, particularly preferably decomposition time ≥ 50 min, And the decomposition time is ≤10 h, preferably the decomposition time is ≤8 h, and particularly preferably the decomposition time is ≤6 h.
10. A method for preparing a catalyst for steam reforming of methane in a molten carbonate fuel cell according to claim 1, wherein: nickel oxide is detected by chemical analysis, and nickel oxide is supported in said step (5) If the content of the mass percentage is <40%, repeat the step (5).

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