CATALYST FOR HYDROGEN COMBUSTION, PROCESS FOR PRODUCING SAME, AND METHOD FOR HYDROGEN COMBUSTION

Abstract

The hydrogen combustion catalyst includes a catalyst metal supported on a carrier made of an inorganic oxide, wherein: a functional group having at least one alkyl group with three or less carbon atoms is bonded to a terminal of a hydroxyl group on the carrier surface by substitution; platinum and palladium are supported as the catalyst metal; and a chlorine content is 300 ppm to 2,000 ppm per 1 mass % of the total supported amount of a supported amount of platinum and a supported amount of palladium. The total supported amount of platinum and palladium is preferably 0.1 to 5.0 mass % based on mass of a whole catalyst. In the hydrogen combustion catalyst according to the present invention, when treating a gas that contains iodine and hydrogen, catalyst poisoning by iodine is suppressed.

Claims

1. A hydrogen combustion catalyst comprising a catalyst metal supported on a carrier composed of an inorganic oxide, wherein: a functional group having at least one alkyl group with three or less carbon atoms is bonded to a terminal of a hydroxyl group on the carrier surface by substitution; platinum and palladium are supported as the catalyst metal; and a chlorine content is 300 ppm to 2,000 ppm per 1 mass % of a total supported amount of a supported amount of platinum and a supported amount of palladium.

2. The hydrogen combustion catalyst according to claim 1, wherein the functional group bonded to a hydroxyl group on the carrier surface is an organic silane.

3. The hydrogen combustion catalyst according to claim 1, wherein the inorganic oxide constituting the carrier is any of alumina, silica, silica-alumina, zeolite, zirconia and titania.

4. The hydrogen combustion catalyst according to claim 1, wherein the total supported amount of a supported amount of platinum and a supported amount of palladium is 0.1 to 5.0 mass % based on mass of a whole catalyst.

5. A manufacturing method of the hydrogen combustion catalyst, the hydrogen combustion catalyst being defined in claim 1, comprising: a hydrophobization step of immersing an inorganic oxide to be a carrier in a solution of a compound containing a functional group having an alkyl group with three or less carbon atoms at a terminal, to thewreby bond the functional group to a hydroxyl group on the carrier surface by substitution; a supporting step of bringing a platinum compound solution and a palladium compound solution into contact with the carrier after the hydrophobization step to thereby support a platinum ion and a palladium ion; and a heat treatment step of heat-treating the carrier after the supporting step to thereby reduce the platinum ion and the palladium ion, wherein: in the supporting step, chloride of platinum is used for the platinum compound solution and chloride of palladium is used for the palladium compound solution; and the heat treatment step is to heat the carrier in a reducing atmosphere at 150 to 280 C. in temperature.

6. The manufacturing method of the hydrogen combustion catalyst according to claim 5, wherein the compound containing a functional group is a silane inorganic surface modifier.

7. The manufacturing method of the hydrogen combustion catalyst according to claim 6, wherein the silane inorganic surface modifier is any of trimethylmethoxysilane, trimethylethoxysilane, trimethylchlorosilane, dimethyldimethoxysilane, dimethyldiethoxysilane, dimethyldichlorosilane, methyltrimethoxysilane, methyltriethoxysilane, methyltrichlorosilane, triethylmethoxysilane, triethylethoxysilane, triethylchlorosilane, diethyldimethoxysilane, diethyldiethoxysilane, diethyldichlorosilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltrichlorosilane, tripropylmethoxysilane, tripropylethoxysilane, tripropylchlorosilane, dipropyldimethoxysilane, dipropyldiethoxysilane, dipropyldichlorosilane, propyltrimethoxysilane, propyltriethoxysilane and propyltrichlorosilane.

8. The manufacturing method of the hydrogen combustion catalyst according to claim 5, wherein the reducing atmosphere in the heat treatment step is a mixed gas in which hydrogen concentration is 1 to 10 volume % and a residual part. is an inert gas.

9. A hydrogen combustion method of causing a hydrogen-containing gas to pass through the hydrogen combustion catalyst according to claim 1 and combusting hydrogen in the hydrogen-containing gas, wherein: the hydrogen-containing gas contains moisture of not more than an amount of saturated vapor at reaction temperature and 0.01 ppm or more of iodine; and hydrogen is combusted while the reaction temperature is set to 10 to 500 C.

10. The hydrogen combustion catalyst according to claim 2, wherein the inorganic oxide constituting the carrier is any of alumina, silica, silica-alumina, zeolite, zirconia and titania.

11. The hydrogen combustion catalyst according to claim 2, wherein the total supported amount of a supported amount of platinum and a supported amount of palladium is 0.1 to 5.0 mass % based on mass of a whole catalyst.

12. The hydrogen combustion catalyst according to claim 3, wherein the total supported amount of a supported amount of platinum and a supported amount of palladium is 0.1 to 5.0 mass % based on mass of a whole catalyst.

13. A manufacturing method of the hydrogen combustion catalyst, the hydrogen combustion catalyst being defined in claim 2, comprising: a hydrophobization step of immersing an inorganic oxide to be a carrier in a solution of a compound containing a functional group having an alkyl group with three or less carbon atoms at a terminal, to thewreby bond the functional group to a hydroxyl group on the carrier surface by substitution; a supporting step of bringing a platinum compound solution and a palladium compound solution into contact with the carrier after the hydrophobization step to thereby support a platinum ion and a palladium ion; and a heat treatment step of heat-treating the carrier after the supporting step to thereby reduce the platinum ion and the palladium ion, wherein: in the supporting step, chloride of platinum is used for the platinum compound solution and chloride of palladium is used for the palladium compound solution; and the heat treatment step is to heat the carrier in a reducing atmosphere at 150 to 280 C. in temperature.

14. A manufacturing method of the hydrogen combustion catalyst, the hydrogen combustion catalyst being defined in claim 3, comprising: a hydrophobization step of immersing an inorganic oxide to be a carrier in a solution of a compound containing a functional group having an alkyl group with three or less carbon atoms at a terminal, to thewreby bond the functional group to a hydroxyl group on the carrier surface by substitution; a supporting step of bringing a platinum compound solution and a palladium compound solution into contact with the carrier after the hydrophobization step to thereby support a platinum ion and a palladium ion; and a heat treatment step of heat-treating the carrier after the supporting step to thereby reduce the platinum ion and the palladium ion, wherein: in the supporting step, chloride of platinum is used for the platinum compound solution and chloride of palladium is used for the palladium compound solution; and the heat treatment step is to heat the carrier in a reducing atmosphere at 150 to 280 C. in temperature.

15. A manufacturing method of the hydrogen combustion catalyst, the hydrogen combustion catalyst being defined in claim 4, comprising: a hydrophobization step of immersing an inorganic oxide to be a carrier in a solution of a compound containing a functional group having an alkyl group with three or less carbon atoms at a terminal, to thewreby bond the functional group to a hydroxyl group on the carrier surface by substitution; a supporting step of bringing a platinum compound solution and a palladium compound solution into contact with the carrier after the hydrophobization step to thereby support a platinum ion and a palladium ion; and a heat treatment step of heat-treating the carrier after the supporting step to thereby reduce the platinum ion and the palladium ion, wherein: in the supporting step, chloride of platinum is used for the platinum compound solution and chloride of palladium is used for the palladium compound solution; and the heat treatment step is to heat the carrier in a reducing atmosphere at 150 to 280 C. in temperature.

16. The manufacturing method of the hydrogen combustion catalyst according to claim 6, wherein the reducing atmosphere in the heat treatment step is a mixed gas in which hydrogen concentration is 1 to 10 volume % and a residual part. is an inert gas.

17. The manufacturing method of the hydrogen combustion catalyst according to claim 7, wherein the reducing atmosphere in the heat treatment step is a mixed gas in which hydrogen concentration is 1 to 10 volume % and a residual part. is an inert gas.

18. A hydrogen combustion method of causing a hydrogen-containing gas to pass through the hydrogen combustion catalyst according to claim 2 and combusting hydrogen in the hydrogen-containing gas, wherein: the hydrogen-containing gas contains moisture of not more than an amount of saturated vapor at reaction temperature and 0.01 ppm or more of iodine; and hydrogen is combusted while the reaction temperature is set to 10 to 500 C.

19. A hydrogen combustion method of causing a hydrogen-containing gas to pass through the hydrogen combustion catalyst according to claim 3 and combusting hydrogen in the hydrogen-containing gas, wherein: the hydrogen-containing gas contains moisture of not more than an amount of saturated vapor at reaction temperature and 0.01 ppm or more of iodine; and hydrogen is combusted while the reaction temperature is set to 10 to 500 C.

20. A hydrogen combustion method of causing a hydrogen-containing gas to pass through the hydrogen combustion catalyst according to claim 4 and combusting hydrogen in the hydrogen-containing gas, wherein: the hydrogen-containing gas contains moisture of not more than an amount of saturated vapor at reaction temperature and 0.01 ppm or more of iodine; and hydrogen is combusted while the reaction temperature is set to 10 to 500 C.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0032] FIGS. 1A and 1B show results of hydrogen combustion tests of hydrogen catalysts according to Examples 1 to 5.

[0033] FIGS. 2A and 2B show results of hydrogen combustion tests of hydrogen catalysts according to Comparative Examples 1 to 5.

DESCRIPTION OF EMBODIMENTS

[0034] Hereinafter, the best embodiment in the present invention will be explained. In the present embodiment, silica having been subjected to hydrophobization treatment was set as a carrier, and a hydrogen combustion catalyst was manufactured by supporting platinum and palladium on the silica.

EXAMPLE 1

[0035] First, 100 g of a silica carrier (specific surface area: 230 m.sup.2/g) was prepared as a carrier, and was subjected to a hydrophobization treatment. The hydrophobization treatment was performed by adding a mixed liquid of 40 g of methyltrimethoxysilane, 50 g of pure water and 50 g of ethanol to the silica carrier and by shaking and stirring the same. After a lapse of one day, the resultant substance was taken out and washed with pure water, and then, was dried at 200 C. Prior to a treatment, the carrier was washed with pure water, and was immersed in an ethanol solution of each of silane inorganic surface modifiers (concentration: 15 wt %) for 24 hours. Then, the carrier was taken out, washed with pure water, and then dried at 200 C. Note that increase in weight by the silane treatment in this case was about 12%.

[0036] Next, 50 g of a chloroplatinic acid ethanol solution (Pt concentration: 1.46 mass %, which corresponds to 0.73 g of platinum) and 50 g of a palladium chloride solution (Pd concentration: 0.80 mass %, which corresponds to 0.40 g of palladium) were added, as a mixed liquid, to the silica carrier having been subjected to the hydrophobization treatment and were impregnated (supporting ratio between platinum and palladium was 1:1 in mole ratio). After that, ethanol was vaporized with a rotary evaporator, and the carrier was then set in a column, and 3 volume % hydrogen gas (N.sub.2 balance) was flown at 230 C. for 2 hours to thereby perform reduction, and a hydrogen combustion catalyst was manufactured.

[0037] Furthermore, a chlorine content was measured as to the hydrogen combustion catalyst manufactured as described above. The measurement of the chlorine content was performed by sufficiently crushing the catalyst into a powder with an agate mortar, and by measuring a chlorine content in the powder through the use of a coulometric chlorine analyzer. From the analysis, the measurement value of the chlorine content of the hydrogen combustion catalyst according to the Example was 1000 ppm. In addition, since the total supported amount of the catalyst metal (platinum, palladium) in the hydrogen combustion catalyst manufactured in the Example is 1.0 mass %, the chlorine content per 1 wt % of the total supported amount of platinum and palladium in the catalyst is 1000 ppm.

EXAMPLE 2

[0038] In Example 1, a catalyst was manufactured by setting the hydrogen concentration in a reduction atmosphere to be 10 volume % as a heat treatment condition after impregnating a compound solution of platinum and palladium. Other manufacturing conditions are the same as those in Example 1. The chlorine content of the catalyst manufactured in this Example 2 was 400 ppm per 1 wt % of the total supported amount of platinum and palladium.

EXAMPLE 3

[0039] In Example 1, a heat treatment temperature was set as low as 180 C. while setting the hydrogen concentration to be 3 volume % in the same way as in Example 1 as a heat treatment condition after impregnating the compound solution of platinum and palladium. Other manufacturing conditions are the same as those in Example 1. The chlorine ion concentration of the catalyst manufactured in this Example 3 was 1500 ppm per 1 wt % of the total supported amount of platinum and palladium.

EXAMPLE 4

[0040] In this Example 4, a ratio (mole ratio) of supported amounts between platinum and palladium being catalyst metals is changed relative to Example 1 (Pt:Pd=1:1). In the Example 4, when impregnating a chloroplatinic acid ethanol solution and a palladium chloride solution, Pt concentration in a chloroplatinic acid solution was set to 0.35 mass % and Pd concentration in a palladium chloride solution was set to 1.91 mass %. The use amount of each solution was set to 50 g (corresponding to 0.175 g of platinum and corresponding to 0.955 g of palladium) in the same way as in Example 1. A ratio of supported amounts between platinum and palladium is Pt:Pd=1:10 in terms of mole ratio. Other manufacturing conditions including the heat treatment condition were set to the same as those in Example 1. The total supported amount of the catalyst metal (platinum, palladium) in the catalyst manufactured here is 1 mass %. In addition, the chlorine content of the catalyst was 1000 ppm per 1 wt % of the total supported amount of platinum and palladium.

EXAMPLE 5

[0041] In contrast to Example 4, a ratio of supported amounts between platinum and palladium is set to Pt:Pd=10:1 in terms of mole ratio. In the present Example, when impregnating a chloroplatinic acid ethanol solution and a palladium chloride solution, a Pt concentration in a chloroplatinic acid solution was set to 2.142 mass % and a Pd concentration in a palladium chloride solution was set to 0.116 mass %. The use amount of each solution was set to 50 g (corresponding to 1.071 g of platinum and corresponding to 0.058 g of palladium) in the same way as in Example 1. Other manufacturing conditions including the heat treatment condition were set to the same as those in Example 1. The total amount of the supported catalyst metal (platinum, palladium) in the catalyst manufactured here is 1 mass %. In addition, the chlorine content of the catalyst was 600 ppm per 1 wt % of the total supported amount of platinum and palladium.

COMPARATIVE EXAMPLE 1

[0042] In Comparative Example for the above Example, acetylacetonate complexes (bis(acetylacetonate)platinum (II), bis(acetylacetonate)palladium (II)) not containing chlorine were used as a platinum compound and a palladium compound to be raw materials of catalyst metal. As a platinum compound solution, 50 g of an ethanol solution of bis(acetylacetonate)platinum (Pt concentration: 1.46 mass %, corresponding to 0.73 g of platinum), and 50 g of an ethanol solution of bis(acetylacetonate)palladium (Pd concentration: 0.80 mass %, corresponding to palladium 0.40 g) were impregnated into the same hydrophobized silica carrier as in Example 1, which was used as a catalyst in the same process as in Example 1. Heat treatment conditions were set to 230 C. and 2 hours. The chlorine content of the catalyst manufactured in this Comparative Example was 10 ppm per 1 wt % of the total supported amount of platinum and palladium.

COMPARATIVE EXAMPLE 2

[0043] In the Comparative Example, as compared with the above Example 1, a catalyst was manufactured by setting a hydrogen concentration as high concentration as 30 volume % as to a heat treatment condition after impregnating the compound solution of platinum and palladium. Other manufacturing conditions are the same as those in Example 1. The chlorine content of the catalyst manufactured in the Comparative Example was 50 ppm per 1 wt % of the total supported amount of platinum and palladium.

COMPARATIVE EXAMPLE 3

[0044] In the Comparative Example, a heat treatment condition after the impregnation of the compound solution is set to high temperature. Heat treatment conditions were set so as to be a heat treatment temperature of 300 C. while setting a hydrogen concentration to 3 volume % that is the same as in Example 1. Other manufacturing conditions are the same as those in Example 1. Chlorine ion concentration of the catalyst manufactured in the Comparative Example was 200 ppm per 1 wt % of the total supported amount of platinum and palladium.

COMPARATIVE EXAMPLES 4 AND 5

[0045] In order to confirm the significance of supporting platinum and palladium at the same time as the configuration of catalyst metal, catalysts supporting platinum alone (Comparative Example 4) and palladium alone (Comparative Example 5) were manufactured. Basic manufacturing processes were similar to those in Example 1, but either a platinum compound solution alone or a palladium compound solution alone was impregnated into a hydrophobized silica carrier. After that, a heat treatment was performed under the same condition as that in Example 1. Chlorine ion concentrations of catalysts manufactured in these Comparative Examples were 500 ppm (per 1 wt % of the supported amount of platinum: Comparative Example 4) and 1100 ppm (per 1 wt % of the supported amount of palladium: Comparative Example 5).

[0046] Combustion performance of hydrogen mixture was evaluated for each of catalysts manufactured in Examples 1 to 5 and Comparative Examples 1 to 5. In a hydrogen combustion test, hydrogen (H.sub.2) mixed gas that contains hygroscopic moisture was introduced, as a reaction gas, into a catalyst layer filled with 20 mL of each catalyst immediately after the manufacture, hydrogen concentrations in mixed gases before and after passing through the catalyst layer were measured with gas chromatograph, and hydrogen combustion ratios at the respective reaction temperatures were calculated. Calculation was performed as: hydrogen combustion ratio=(hydrogen concentration before reactionhydrogen concentration after reaction)/hydrogen concentration before reaction100. A reaction gas to be introduced for use includes two types, that is, a gas made into a moist condition (water vapor concentration: 22000 ppm) by bubbling a mixed gas of 1000 ppm of a hydrogen concentration (air balance) to pure water, and a gas made into a moist condition (water vapor concentration: 22000 ppm, iodine gas concentration: 4 ppm) by bubbling a similar mixed gas to iodine-saturated water (iodine concentration: 0.33 g/L). Test conditions were set as follows. [0047] Mixed gas flow rate: 1.6 NL/min [0048] SV: 4800 h.sup.1 [0049] Reaction temperature: 100 C. to 160 C. [0050] Test method: Temperature rising rate was set to 2 C./min, kept for 2 hours after reaching a prescribed reaction temperature, and the reaction gas was analyzed.

[0051] FIGS. 1 and 2 show results of hydrogen combustion test for the respective catalysts of Examples 1 to 5 and Comparative Examples 1 to 5. From FIG. 1, catalysts according to Examples 1 to 5 exhibit a slight decrease in activity in the presence of moist iodine as compared with a case of not containing iodine, but the activity rises along with the reaction temperature and the decrease in activity of hydrogen combustion is suppressed as compared with the respective Comparative Examples. The chlorine content is appropriately adjusted in catalysts in these Examples.

[0052] Furthermore, the ratio (mole ratio) between supported platinum and supported palladium at the time of catalyst manufacturing was set in a range of 1:10 to 10:1 (1:1 in Examples 1 to 3), and results were excellent also in the case of these catalysts. Note that, although chlorine contents are different when making a comparison between Examples 4 and 5 having the same heat treatment condition, it is assumed that this is because adsorption capability for chlorine is different depending on metal species (platinum, palladium), and it is considered that this is because an chlorine adsorption amount by palladium is larger than that by platinum.

[0053] In contrast, when results of the respective Comparative Examples in FIG. 2 are referred to, first, in Comparative Example 1 (chlorine content: 10 ppm) in which chloride as a raw material of a catalyst is not used, the activity tends to decrease along with temperature rise in the presence of iodine. This is because iodine poisoning gradually progresses from the start of a reaction to thereby lead to deactivation.

[0054] Furthermore, even when a chloride is used as a raw material of a catalyst, in a case where chlorine disappears in a manufacturing process, suppression of iodine poisoning can not be observed. In Comparative Example 2, a hydrogen concentration at the time of the heat treatment was set as high as 30% and the catalyst had a low chlorine content of 50 ppm, and the activity of the catalyst also decreased with a lapse of reaction time. In addition, Comparative Example 5 gives a catalyst having a low chlorine content (chlorine content: 200 ppm) by setting a heat treatment temperature to rather high temperature (300 C.), and the same also applies to the catalyst.

[0055] However, even if a catalyst appropriately contains chlorine, influence by iodine poisoning cannot be avoided in the case where the catalyst does not support both platinum and palladium concurrently as catalyst metal. Comparative Examples 4 and 5 gave catalysts in which platinum alone (Comparative Example 4, chlorine content: 500 ppm) and palladium alone (Comparative Example 5, chlorine content: 1100 ppm) were respectively applied as catalyst metals, and decrease in activity caused by iodine poisoning was observed in these catalysts.

[0056] The maintenance of catalytic activity in an iodine-existing state is an essential effect in the present invention, and, for the purpose, it is necessary to set appropriately both the configuration of catalyst metal and chlorine content in a catalyst. It was confirmed that the respective Comparative Examples not provided with these were not suitable ones.

INDUSTRIAL APPLICABILITY

[0057] As described, the hydrogen combustion catalyst according to the present invention is a catalyst obtained by suppressing catalyst poisoning by iodine in combustion of hydrogen gas. In the catalyst according to the present invention, influence caused by moisture is also eliminated. Accordingly, the present invention is useful as a catalyst for a hydrogen combustion device in nuclear power facilities.