Methanol steam reforming hydrogen production catalyst and preparation method thereof

Abstract

The invention belongs to the technical field of catalyst preparation, and particularly relates to a methanol steam reforming hydrogen production catalyst and a preparation method thereof.The preparation method comprises the following steps that Cu / Zn basic carbonate binary parent slurry with the pH value being 8-10 is prepared through a reverse addition coprecipitation method; the preparation method comprises the following steps: preparing a pseudo-boehmite sol carrier with the pH value of 4.5-6.5 by adopting a positive addition precipitation method; the binary parent slurry and the sol-like carrier slurry are fully stirred, mixed and pulped, a precious metal nitrate solution is dropwise added while heating and cooking are conducted, and the pH value is adjusted to be neutral through alkali liquor; washing, filtering, drying, calcining and forming the neutral material to obtain the methanol steam reforming hydrogen production catalyst. The catalyst prepared by the method provided by the invention has high catalytic activity in a temperature zone of 210-380 DEG C, and has the advantages of good thermal stability, strong anti-sintering ability, long service life and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst preparation, and particularly relates to a hydrogen production catalyst by methanol steam reforming and a preparation method thereof. Background Art

[0002] As a "clean" energy, hydrogen is considered to be the new key to cracking the energy crisis in the future and building a clean, low-carbon, safe and efficient modern energy system. However, the difficulty in hydrogen storage and transportation is the problem faced by the current hydrogen utilization. Methanol (CH3OH) is the simplest saturated monohydric alcohol, which is a colorless liquid at normal temperature and pressure, easy to store and transport, and has high hydrogen production yield and efficiency. It is an ideal chemical hydrogen storage carrier. Taking the methanol industry as a hub can promote the optimization of the hydrogen energy industry and solve the problems of difficult transportation and storage of hydrogen.

[0003] The methanol hydrogen production reaction system includes direct cracking, steam reforming and partial oxidation. From the perspective of "atom economy", methanol steam reforming for hydrogen production is the hydrogen production method with the highest theoretical hydrogen production. This reaction has mild conditions, easy separation and few by-products, and has received the attention of many researchers. As an irreplaceable auxiliary in the production process of methanol steam reforming for hydrogen production, the performance of the catalyst is crucial. At present, the research and development of methanol steam reforming for hydrogen production catalysts mainly focuses on copper-based catalysts and noble metal catalysts. Compared with noble metal catalysts, copper-based catalysts have better low-temperature reforming activity, can selectively produce hydrogen and carbon dioxide under mild conditions, and have low cost. They are the main catalysts considered for industrial production of methanol steam reforming for hydrogen production. However, the Tammann temperature and Hüttig temperature of the active metal Cu in copper-based catalysts are very low. It is easy to migrate and agglomerate at high temperature, especially under hydrothermal conditions. The active particles sinter and grow, and the specific surface area decreases severely, resulting in a decrease in the reaction activity of the catalyst. Preventing and slowing down the migration of Cu active centers has become the key to improving the anti-sintering ability of the catalyst and the core of improving the stability of the catalyst and extending the service life of the catalyst.

[0004] Compared with copper-based catalysts, noble metal catalysts have better stability and can ensure that they will not lose activity at higher temperatures, but they are expensive and have insufficient low-temperature reaction activity. The optimal reaction temperature is usually higher than 250 °C, and they need to be used in combination with other catalysts to improve the low-temperature performance. The test cost is high, which is not convenient for large-scale industrial application. Summary of the Invention

[0005] In view of the deficiencies of the prior art, the present invention provides a methanol steam reforming hydrogen production catalyst and a preparation method thereof. The method adopts a structural confinement and precious metal composite strategy to modify a copper-based methanol steam reforming catalyst, prepares a (Cu, Zn)2CO3(OH)2 matrix slurry by controlling the process, and introduces an auxiliary agent to obtain a pseudo-boehmite carrier, thereby enhancing the combination of the matrix and the carrier, improving the Cu dispersion and specific surface area, reducing Cu agglomeration, and enhancing the sintering resistance. At the same time, the precious metal Pt or Pd is deposited and precipitated on the catalyst surface to achieve interface composite, broaden the use temperature range, and extend the service life.

[0006] The technical solution provided by the present invention is as follows:

[0007] The present invention provides a method for preparing a catalyst for hydrogen production by methanol steam reforming, comprising the following steps: Cu soluble salt and Zn soluble salt are prepared into a mixed salt solution, and the mixed salt solution is dropped into a precipitant under stirring conditions for precipitation, and the end point pH is controlled at 8.0-10.0. After the precipitate color changes from light blue to emerald green, it is aged and washed to obtain a (Cu, Zn)2CO3(OH)2 single phase binary matrix slurry; The precipitant is dropped into an aluminum nitrate solution containing an auxiliary agent under stirring conditions to precipitate, and the end point pH is controlled at 4.5-6.5. After the precipitation is completed, the precipitant is aged to obtain a pseudo-boehmite sol carrier slurry; The (Cu, Zn)2CO3(OH)2 single phase binary matrix slurry and the pseudo-boehmite sol carrier slurry are fully stirred, mixed and slurried, boiled, and a noble metal nitrate solution is dropped into it. After being fully mixed, an alkali solution is added to adjust the pH value to neutral, aged, and finally washed, filtered, dried, calcined and formed to obtain a methanol steam reforming hydrogen production catalyst.

[0008] Furthermore, the total concentration of metal ions in the mixed salt solution is 60-150 g / L, and the atomic ratio of Cu to Zn is (2.0-2.5):1; wherein the Cu soluble salt is at least one of copper nitrate and copper acetate, and / or the Zn soluble salt is at least one of zinc nitrate and zinc acetate.

[0009] Furthermore, in the preparation process of (Cu, Zn)2CO3(OH)2 single phase binary matrix slurry, the speed of dripping the mixed salt solution into the precipitant is not less than 500 mL / min, the entire dripping process does not exceed 8 minutes, and the precipitation temperature is 60~70°C.

[0010] Furthermore, the concentration of the aluminum nitrate solution is 0.1-0.5 mol / L.

[0011] Further, the auxiliary agent is a metal nitrate capable of changing the structure of the boehmite sol, and the auxiliary agent is at least one of zinc nitrate, cerium nitrate, and gallium nitrate. The number of metal atoms in the auxiliary agent is 10% - 30% of the number of aluminum atoms in the aluminum nitrate solution.

[0012] Further, during the preparation of the boehmite-like sol support, the precipitation temperature is 30 - 50°C.

[0013] Further, the (Cu,Zn)2CO3(OH)2 single-phase binary mother slurry is washed by the centrifugation-sedimentation method, and the washing end point is that no blue color appears when 10 drops of 10% diphenylamine sulfate solution are dropped into the supernatant.

[0014] Further, the precipitant is at least one of sodium bicarbonate, sodium carbonate, potassium carbonate, and potassium bicarbonate, with a concentration of 0.5 mol / L - 2 mol / L; the alkali solution for adjusting the pH value is sodium hydroxide or potassium hydroxide solution, with a concentration of 0.5 mol / L - 2 mol / L.

[0015] Further, the noble metal nitrate is at least one of platinum nitrate and palladium nitrate, with a concentration of 0.001 mol / L - 0.005 mol / L.

[0016] Further, during the preparation of the (Cu,Zn)2CO3(OH)2 single-phase binary mother slurry, the preparation of the boehmite-like sol support slurry, and the preparation of the methanol steam reforming hydrogen production catalyst, the aging time is 30 - 60 min.

[0017] Further, during the preparation of the methanol steam reforming hydrogen production catalyst, the steaming temperature is 70 - 80°C.

[0018] The present invention also provides a methanol steam reforming hydrogen production catalyst prepared by the above method. The catalyst includes CuO, ZnO, Al2O3, noble metal oxide, and auxiliary agent metal oxide. The weight percentage contents of each component are as follows: CuO is 40 - 60%, ZnO is 20 - 30%, Al2O3 is 5 - 15%, noble metal oxide is 0.2 - 1%, and auxiliary agent metal oxide is 1 - 5%. Beneficial effects

[0019] The present invention prepares a binary parent slurry of Cu / Zn basic carbonate with a pH value of 8 - 10 by the reverse addition co - precipitation method, prepares a pseudoboehmite - like sol support with a pH value of 4.5 - 6.5 by the forward addition precipitation method, then fully stirs and mixes the binary parent slurry and the sol - like support slurry to make a pulp, heats and cooks while dripping a noble metal nitrate solution, adjusts the pH value to neutral with an alkali solution, and the neutral material is washed, filtered, dried, calcined, and formed to obtain a catalyst for methanol steam reforming to produce hydrogen. The catalyst prepared by this method has high catalytic activity in the temperature range of 210 - 380 °C, and has advantages such as good thermal stability, strong anti - sintering ability, and long service life.

[0020] Based on the catalyst modification strategy of structure confinement and noble metal composite synergy, the present invention modifies a copper - based methanol steam reforming catalyst, controls the preparation process to obtain a (Cu,Zn)2CO3(OH)2 single - phase binary parent slurry, introduces an additive during the support preparation process to obtain a pseudoboehmite - like sol support, enhances the combination of the parent phase and the support through the additive, makes the support particles and the active center particles evenly intertwined, improves the dispersion of Cu and the specific surface area of the catalyst, evenly separates the Cu active centers by the support, reduces the probability of Cu particle agglomeration and growth, and enhances the anti - sintering ability of Cu in the catalyst; at the same time, deposits and precipitates noble metals Pt or Pd evenly on the catalyst surface by the deposition - precipitation method to achieve the synergistic effect of noble metal catalysts and copper - based catalysts, broaden the catalyst use temperature range, and extend the catalyst service life. Compared with the catalysts prepared by traditional methods, the catalysts prepared by the method of the present invention have advantages such as good activity, large specific surface area, strong anti - sintering ability, good thermal stability, wide applicable temperature range, and long service life. Brief Description of the Drawings

[0021] Figure 1 It is a preparation flow chart of the catalyst for methanol steam reforming to produce hydrogen of the present invention. Detailed Embodiments

[0022] Example 1

[0023] First step: Prepare a mixed salt solution with copper nitrate, zinc acetate and deionized water (the total metal ion concentration is 60 g / L, and the Cu / Zn atomic ratio is 2.5). Under the conditions of 62 °C and stirring, the mixed salt solution is dripped into a 1 mol / L NaHCO3 solution at a flow rate of 700 mL / min, and the whole dripping process does not exceed 8 min. Control the end - point pH value to 9.0. After the precipitate color changes from light blue to emerald green, age for 40 min, and centrifuge - sediment and wash until 10 drops of 10% diphenylamine sulfate solution dropped into the upper clear liquid do not turn blue, to obtain a (Cu,Zn)2CO3(OH)2 single - phase binary parent slurry;

[0024] Step 2: Under stirring conditions at 40 °C, a 1 mol / L NaHCO3 solution was added dropwise to a nitrate aluminum salt solution containing 0.5 mol / L zinc nitrate (where the number of Zn atoms in zinc nitrate accounted for 30% of the number of aluminum atoms). The final pH value was controlled at 5.0, and the aging time was 30 min to obtain a pseudo-boehmite-based sol carrier slurry;

[0025] Step 3: The binary matrix slurry and the sol-like carrier slurry were fully stirred and mixed to make a pulp, which was steamed to 80 °C. A 0.001 mol / L palladium nitrate solution was added dropwise, and the pH value was adjusted to neutral with a 1 mol / L NaOH alkali solution. After aging for 45 min, the final material was washed, filtered, dried, calcined, and formed to obtain a methanol steam reforming hydrogen production catalyst cat1.

[0026] The catalyst of this example included CuO, ZnO, Al2O3, noble metal oxide, and promoter metal oxide. The weight percentage content of each component was as follows: CuO was 59.8%, ZnO was 24.3%, Al2O3 was 10.1%, PdO was 1.0%, and the promoter metal oxide was 4.8%.

[0027] Example 2

[0028] Step 1: A mixed salt solution (total metal ion concentration was 80 g / L, Cu / Zn atomic ratio was 2.3) was prepared with copper acetate, zinc nitrate, and deionized water. Under stirring conditions at 65 °C, the mixed salt solution was added dropwise to a 0.8 mol / L Na2CO3 solution at a flow rate of 600 mL / min. The whole dropping process did not exceed 8 min, and the final pH value was controlled at 10. After the precipitate color changed from light blue to emerald green, it was aged for 60 min, and then centrifuged and washed until 10 drops of 10% diphenylamine sulfate solution dropped into the supernatant did not turn blue, obtaining a (Cu,Zn)2CO3(OH)2 single-phase binary matrix slurry;

[0029] Step 2: Under stirring conditions at 45 °C, a 0.5 mol / L KHCO3 solution was added dropwise to a nitrate aluminum salt solution containing 0.3 mol / L cerium nitrate (where the number of Ce atoms in cerium nitrate accounted for 15% of the number of aluminum atoms). The final pH value was controlled at 4.8, and the aging time was 50 min to obtain a pseudo-boehmite-based sol carrier slurry;

[0030] Step 3: The binary matrix slurry and the sol-like carrier slurry were fully stirred and mixed to make a pulp, which was steamed to 70 °C. A 0.003 mol / L platinum nitrate solution was added dropwise, and the pH value was adjusted to neutral with a 1 mol / L NaOH alkali solution. After aging for 60 min, the final material was washed, filtered, dried, calcined, and formed to obtain a methanol steam reforming hydrogen production catalyst cat2.

[0031] The catalyst of this example includes CuO, ZnO, Al2O3, noble metal oxide and promoter metal oxide, and the weight percentage content of each component is as follows: CuO is 58.5%, ZnO is 25.9%, Al2O3 is 9.8%, PtO2 is 0.8%, and the promoter metal oxide is 5%.

[0032] Example 3

[0033] Step 1: Prepare a mixed salt solution with copper nitrate, zinc nitrate and deionized water (the total metal ion concentration is 150 g / L, and the Cu / Zn atomic ratio is 2.0). Under the conditions of 60 °C and stirring, the mixed salt solution is dropped into 1 mol / L KHCO3 solution at a flow rate of 500 mL / min. The whole dropping process does not exceed 8 min. Control the end point pH value to 8.0. After the precipitate color changes from light blue to emerald green, age for 40 min, and centrifuge-settle and wash until 10 drops of 10% diphenylamine sulfate solution dropped into the upper clear liquid do not turn blue, to obtain a (Cu,Zn)2CO3(OH)2 single-phase binary mother slurry;

[0034] Step 2: At 30 °C, under stirring conditions, drop 0.8 mol / L K2CO3 solution into a nitrate aluminum salt solution containing indium nitrate with a concentration of 0.1 mol / L (where the indium atoms in indium nitrate account for 10% of the aluminum atoms), control the end point pH value to 5.5, and the aging time is 30 min to obtain a pseudo-boehmite type sol carrier slurry;

[0035] Step 3: Stir and mix the binary mother slurry and the sol-like carrier slurry thoroughly, cook to 75 °C, drop 0.005 mol / L platinum nitrate solution, adjust the pH value to neutral with 1 mol / L KOH alkali solution, age for 50 min, and finally the material is washed, filtered, dried, calcined and formed to obtain a methanol steam reforming hydrogen production catalyst cat3.

[0036] The catalyst of this example includes CuO, ZnO, Al2O3, noble metal oxide and promoter metal oxide, and the weight percentage content of each component is as follows: CuO is 58.2%, ZnO is 29.6%, Al2O3 is 9.3%, PtO2 is 0.4%, and the promoter metal oxide is 4.8%.

[0037] Example 4

[0038] Step 1: Prepare a mixed salt solution with copper nitrate, zinc acetate and deionized water (total metal ion concentration is 100 g / L, Cu / Zn atomic ratio is 2.2). Under the conditions of 65 °C and stirring, the mixed salt solution is dropped into 1 mol / L K2CO3 solution at a flow rate of 600 mL / min. The whole dropping process does not exceed 8 min. Control the end point pH value to 8.5. After the precipitate color changes from light blue to emerald green, age for 50 min. Centrifuge - sediment and wash until 10 drops of 10% diphenylamine sulfate solution dropped into the supernatant do not turn blue, obtaining a binary matrix slurry of single-phase (Cu,Zn)2CO3(OH)2;

[0039] Step 2: At 45 °C, under stirring conditions, drop 1 mol / L KHCO3 solution into a nitrate aluminum salt solution containing 0.3 mol / L zinc nitrate (where the number of zinc atoms in zinc nitrate accounts for 10% of the number of aluminum atoms). Control the end point pH value to 5.0 and the aging time to 40 min, obtaining a pseudo-boehmite sol carrier slurry;

[0040] Step 3: Stir and mix the binary matrix slurry and the sol-like carrier slurry thoroughly to make a pulp, cook to 75 °C, drop 0.003 mol / L palladium nitrate solution, adjust the pH value to neutral with 1 mol / L NaOH alkali solution, age for 30 min. Finally, the material is washed, filtered, dried, calcined and formed to obtain a methanol steam reforming hydrogen production catalyst cat4.

[0041] The catalyst of this example includes CuO, ZnO, Al2O3, noble metal oxide and promoter metal oxide. The weight percentage content of each component is as follows: CuO is 59.5%, ZnO is 27.7%, Al2O3 is 10.4%, PbO is 0.8%, and the promoter metal oxide is 1.6%.

[0042] Comparative Example 1

[0043] The preparation steps are the same as those in Example 2, except that in the first step of preparing the binary matrix slurry, control the end point pH value to 7.2; in the second step of preparing the carrier slurry, do not add a promoter and the end point pH value is 7.2; in the third step, directly mix and make a pulp of the matrix slurry and the carrier slurry, and cook to obtain a methanol steam reforming hydrogen production catalyst cat5.

[0044] Evaluate the performance of the catalysts obtained in the above examples.

[0045] Use a fixed-bed continuous flow reactor. The catalyst loading is 4 g. The reduction of the catalyst is carried out in a low-hydrogen (H2:N2 = 5:95) atmosphere. Program the temperature to rise to 210 °C (20 °C / h) and reduce for 12 hours. Switch the reducing gas to the raw material gas (produced by vaporizing the methanol aqueous solution, and the temperature of the vaporizer is controlled at 210 °C) for activity testing. The activity testing conditions are reaction pressure 2.0 MP, space velocity 1.0 h-1 , at a temperature of 210 °C and an H2O / CH3OH ratio of 1.2 (molar ratio), after the reaction was stable for 2 h, the liquid in the vent liquid collector (the collector was cooled with circulating water at 5 °C to achieve gas-liquid separation) was collected and timing was started. The product gas (H2, CO, CO2, CH4) entered the chromatograph for on-line analysis; after 2.5 h, the liquid in the collector was collected and weighed. Three heat-resistant programs (thermal shock means) were added. In the first program, the gas source was switched to N2. After the catalyst was heat-treated at 450 °C for 5 h, the activity after the first heat resistance was measured at 270 °C; in the second program, the gas source was switched to N2. After the catalyst was heat-treated at 450 °C for 5 h, the activity after the second heat resistance was measured at 330 °C; in the third program, the gas source was switched to N2. After the catalyst was heat-treated at 450 °C for 5 h, the activity after the third heat resistance was measured at 400 °C.

[0046] Chromatographic analysis conditions for liquid-phase products: hydrogen flame ionization detector (FID), HP-INNOWax chromatographic column (column length 60 m, inner diameter 0.32 mm, wall thickness 0.5 μm), programmed temperature rise, nitrogen as the carrier gas, injection port temperature 250 °C, constant pressure 10 psi, split mode 10:1, detection chamber temperature 300 °C, hydrogen flow rate 30 mL / min, air flow rate 400 mL / min, tail gas blow flow rate 25 mL / min. Chromatographic analysis conditions for gas-phase products: thermal island detector (TCD), ShinCarbon ST packed column (column length 2 m, outer diameter 1 / 8 foot, inner diameter 1.0 mm), nitrogen as the carrier gas, injection port temperature 150 °C, column oven temperature 120 °C, detection chamber temperature 200 °C.

[0047] Table 1 Performance evaluation results

[0048]

[0049] The performance evaluation results of each catalyst are shown in Table 1. It can be seen from Table 1 that the high-performance methanol steam reforming hydrogen production catalyst prepared by the method of the present invention has a higher methanol conversion rate and H2 content in the product at the same temperature before and after heat resistance than the catalyst samples prepared by the traditional process. Affected by the heat treatment conditions, the methanol conversion rate of the catalyst prepared by the traditional process first increases and then decreases with the increase of temperature, reaching a peak of 100% at 330 °C. The catalyst prepared by the method of the present invention is not affected by the heat treatment conditions, and the methanol conversion rate continuously increases with the increase of temperature until 400 °C, indicating that the catalyst sample prepared by the method of the present invention has stronger anti-sintering ability, higher activity, better stability and longer service life.

[0050] It should be noted that the above are only the preferred embodiments of the present invention. For those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and deformations can still be made, and these improvements and deformations should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of a hydrogen production catalyst by methanol steam reforming, characterized in that, It includes the following steps: Prepare a mixed salt solution of soluble Cu salt and soluble Zn salt, and drop the mixed salt solution into a precipitant under stirring conditions for precipitation. Control the final pH value to be 8.0 - 10.

0. After the precipitate color changes from light blue to emerald green, age it, wash it to obtain a (Cu,Zn)2CO3(OH)2 single-phase binary mother slurry; Drop the precipitant into an aluminum nitrate solution containing an additive under stirring conditions for precipitation. Control the final pH value to be 4.5 - 6.

5. After the precipitation is completed, age it to obtain a pseudo-boehmite sol carrier slurry; Fully stir and mix the (Cu,Zn)2CO3(OH)2 single-phase binary mother slurry and the pseudo-boehmite sol carrier slurry for beating, cook it, drop a noble metal nitrate solution. After full mixing, drop an alkali solution to adjust the pH value to neutral, age it, and finally obtain a methanol steam reforming hydrogen production catalyst through washing, filtering, drying, calcining, and forming.

2. The preparation method of the hydrogen production catalyst by methanol steam reforming according to claim 1, characterized in that, The total concentration of metal ions in the mixed salt solution is 60 - 150 g / L, and the atomic ratio of Cu to Zn is (2.0 - 2.5):1; among them, the soluble Cu salt is at least one of copper nitrate and copper acetate, and / or the soluble Zn salt is at least one of zinc nitrate and zinc acetate.

3. The preparation method of the hydrogen production catalyst by methanol steam reforming according to claim 1, characterized in that, During the preparation of the (Cu,Zn)2CO3(OH)2 single-phase binary mother slurry, the dropping speed of the mixed salt solution into the precipitant is not less than 500 mL / min, the whole dropping process does not exceed 8 min, and the precipitation temperature is 60 - 70 °C.

4. The preparation method of the hydrogen production catalyst by methanol steam reforming according to claim 1, characterized in that, The concentration of the aluminum nitrate solution is 0.1 - 0.5 mol / L.

5. The preparation method of the hydrogen production catalyst by methanol steam reforming according to claim 1, characterized in that, The additive is a metal nitrate that can change the structure of the pseudo-boehmite sol. The additive is at least one of zinc nitrate, cerium nitrate, and gallium nitrate. The number of metal atoms in the additive is 10% - 30% of the number of aluminum atoms in the aluminum nitrate solution.

6. The preparation method of the hydrogen production catalyst by methanol steam reforming according to claim 1, characterized in that, During the preparation of the pseudo-boehmite sol carrier, the precipitation temperature is 30 - 50 °C.

7. The preparation method of the hydrogen production catalyst by methanol steam reforming according to claim 1, characterized in that, The (Cu,Zn)2CO3(OH)2 single-phase binary mother slurry is washed by centrifugation-sedimentation method, and the washing end point is that no blue color appears when 10 drops of 10% diphenylamine sulfate solution are dropped into the supernatant.

8. The preparation method of the hydrogen production catalyst by methanol steam reforming according to claim 1, characterized in that, The precipitant is at least one of sodium bicarbonate, sodium carbonate, potassium carbonate, and potassium bicarbonate, with a concentration of 0.5 mol / L - 2 mol / L; the alkali solution for adjusting the pH value is sodium hydroxide or potassium hydroxide solution, with a concentration of 0.5 mol / L - 2 mol / L.

9. The preparation method of the hydrogen production catalyst by methanol steam reforming according to claim 1, characterized in that, The noble metal nitrate is at least one of platinum nitrate and palladium nitrate, with a concentration of 0.001 mol / L - 0.005 mol / L.

10. A hydrogen production catalyst by methanol steam reforming, characterized in that, Prepared by the method according to any one of claims 1 - 9, the catalyst includes CuO, ZnO, Al2O3, noble metal oxide, and additive metal oxide. The weight percentage content of each component is as follows: CuO is 40 - 60%, ZnO is 20 - 30%, Al2O3 is 5 - 15%, noble metal oxide is 0.2 - 1%, and additive metal oxide is 1 - 5%.

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