Catalyst for producing hydrogen and preparing method thereof

Abstract

The present invention provides a catalyst for producing hydrogen and a preparing method thereof. The method includes the steps of adding a first metal source, a second metal source, a third metal source and a cerium source into a first organic solvent containing a surfactant to form a colloidal mixture, wherein a metal of the first metal source is a Group IIIB metal; a metal of the second metal source is selected from the group consisting of alkali metals, alkaline earth metals and Group IIIB metals, and a metal of the third metal source is a transition metal; calcining the colloidal mixture to form a metal solid solution; and allowing the metal solid solution to be carried on a carrier to obtain the catalyst. When the catalyst of the present invention is used for an ethanol oxidation reformation, the reaction temperature of the ethanol oxidation reformation can be significantly decreased. After the catalyst is used for long periods of time, the ethanol oxidation reformation still has high ethanol conversion ratio and hydrogen selection ratio.

Claims

1. A catalyst for producing hydrogen, comprising: a carrier; and a metal solid solution represented by formula (I) and being formed on the carrier,
(A.sub.2-xA.sub.x)(Ce.sub.yB.sub.2-y)O.sub.7-(I) wherein A is selected from one of Group IIIB metals; A is selected from the group consisting of alkali metals, alkaline earth metals and Group IIIB metals, and A is different from A; B is a transition metal and is exclusive from a Group IIIB metal or lanthanides; x is 0.1 to 1.0; y is 1.8 to 1.9; and is greater than 0 to 0.5.

2. The catalyst of claim 1, wherein the carrier is selected from the group consisting of aluminum oxide, magnesium oxide, lanthanum oxide and silicon dioxide.

3. The catalyst of claim 1, wherein A is selected from the group consisting of scandium, yttrium, and lanthanum; and A is selected from the group consisting of alkali metals, alkaline earth metals, scandium, yttrium, and lanthanum.

4. The catalyst of claim 1, wherein A is lanthanum, A is lithium, and B is ruthenium.

5. The catalyst of claim 1, wherein A is lanthanum, A is magnesium or calcium, and B is ruthenium.

6. The catalyst of claim 1, wherein A is yttrium, A is scandium, and B is ruthenium.

7. The catalyst of claim 1, wherein B is selected from the group consisting of ruthenium, osmium, rhodium, iridium and rhenium.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows X-ray diffraction pattern of Y.sub.2-xSc.sub.xCe.sub.yRu.sub.2-yO.sub.7- as catalyst according to the present invention.

(2) FIG. 2 shows an analysis curve diagram of carbon-to-oxygen ratio of each product by the use of Y.sub.1.0Sc.sub.1.0Ce.sub.1.9Ru.sub.0.1O.sub.7- as catalyst in an ethanol reformer according to the present invention;

(3) FIG. 3 shows X-ray diffraction pattern of La.sub.2-xMg.sub.xCe.sub.yRu.sub.2-yO.sub.7- as catalyst according to the present invention;

(4) FIG. 4 shows an analysis curve diagram of time-on-steam of each product by the use of La.sub.1.7Mg.sub.0.3Ce.sub.1.8Ru.sub.0.2O.sub.7- as catalyst in an ethanol reformer according to the present invention;

(5) FIG. 5 shows X-ray diffraction pattern of La.sub.2-xCa.sub.xCe.sub.yRu.sub.2-yO.sub.7- as catalyst according to the present invention;

(6) FIG. 6 shows an analysis curve diagram of time-on-steam of each product by the use of La.sub.1.8Ca.sub.0.2Ce.sub.1.8Ru.sub.0.2O.sub.7- as catalyst in an ethanol reformer according to the present invention;

(7) FIG. 7 shows X-ray diffraction pattern of La.sub.2-xLi.sub.xCe.sub.yRu.sub.2-yO.sub.7- as catalyst according to the present invention;

(8) FIG. 8 shows an analysis curve diagram of the product by the use of La.sub.1.4Li.sub.0.6Ce.sub.1.8Ru.sub.0.2O.sub.7- as catalyst in an ethanol reformer according to the present invention and

(9) FIG. 9 shows reaction temperature for different catalysts used in an ethanol reformer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(10) The following specific examples are used for illustrating the present invention. A person skilled in the art can easily conceive the other advantages and effects of the present invention.

(11) For ease of presentation, the third metal source specifically indicated herein is not a Group IIIB metal or lanthanides in Group IIIB

(12) The present invention develops the pyrochlore structure A.sub.2B.sub.2O.sub.7 as host materials of the catalyst. Such structure can reduce the content of the noble metals by doping alkali metals and alkali earth metals in the position of A. Furthermore, the use of the catalyst in the ethanol oxidative reformation can promote the reaction temperature to be significantly reduced. After reacting for long periods of time, the high selection ratio of hydrogen can be maintained and it conforms to the need of the industry.

(13) In the preparing method of a catalyst for producing hydrogen of the present invention, a metal solid solution is prepared according to a sol-gel method. First of all, a first metal source, a second metal source, a third metal source and cerium source are added into a first organic solvent containing a surfactant. Subsequently, stirring the first organic solvent to form a colloidal mixture, wherein a metal of the first metal source is a Group IIIB metal; a metal of the second metal source is selected from the group consisting of alkali metals, alkaline earth metals and Group IIIB metals, the first metal source is different from the second metal source, and a metal of the third metal source is a transition metal and is exclusive from a Group IIIB metal or lanthanides.

(14) In the above method, the amount of the surfactant is not specifically limited. In one embodiment, relative to 5 grams (g) of the first organic solvent, the amount of the surfactant is from 0.25 to 1.0 g, preferably 0.5 g. The example of the surfactant includes, but is not limited to, P123, F68, F108 and F127. Among these, the chemical formula of P123 is HO(CH.sub.2CH.sub.2O).sub.20(CH.sub.2CH(CH.sub.3)O).sub.70(CH.sub.2CH.sub.2O).sub.20H. The first organic solvent is alcohols which can be selected from the group consisting of methanol, ethanol, butanol and isopropanol.

(15) According to the above method, the first metal source, the second metal source, the third metal source and the cerium source are added into the first organic solvent based on the weighed metal nitrates or metal chlorides at different stoichiometry ratio, and the total concentration of the metal ions contained in the formed mixture is about 5 mmol After stirring, a colloidal mixture is formed. In one embodiment, after stirring for at least 1 hour, the mixture is gelled at 40 C. for three days to form the colloidal mixture.

(16) Furthermore, in one embodiment, the metal of the first metal source is selected from scandium, yttrium or lanthanum. The metal of the second metal source is selected from the group consisting of alkali metals, alkaline earth metals, and Group IIIB metal. More specifically, the metal of the second metal source is selected from alkali metals, alkaline earth metals, scandium, yttrium or lanthanum. The metal of the third metal source is a transition metal and is not a Group IIIB metal or lanthanides. For example, the metal of the third metal source is selected from the group consisting of ruthenium, osmium, rhodium, iridium and rhenium.

(17) In another embodiment of the present invention, the metal of the second metal source is selected from alkali metals, alkaline earth metals, scandium, yttrium or lanthanum. The metal of the first metal source is a Group IIIB metal. Similarly, the metal of the third metal source is a transition metal and is not a Group IIIB metal or lanthanides. For example, the metal of the third metal source is selected from the group consisting of ruthenium, osmium, rhodium, iridium and rhenium.

(18) After that, a calcination step is operated according to the conventional method. In a non-limited embodiment, the colloidal mixture is calcined for 1 to 7 hours, preferably 5 hours, to form a metal solid solution, wherein the calcination temperature is from 600 C. to 900 C.

(19) Subsequently, the prepared metal solid solution is dispersed in a second organic solvent. For example, in a non-limited embodiment, relative to the volume of the second organic solvent being not more than 10 mL, the amount of the metal solid solution is 0.1 to 1.0 g, preferably 0.1 g. The second organic solvent is performed an ultrasonic agitation, and then a carrier is immersed in the second organic solvent. The ratio of the carrier and the metal solid solution is 10:1. Finally, the catalyst is obtained by removing the second organic solvent at 80 C. to 100 C.

(20) According to the above method, the second organic solvent is alcohols and it can be selected from the group consisting of methanol, ethanol, butanol and isopropanol.

(21) In addition, the carrier is selected from the non-reactive materials. For example, the carrier is selected from the group consisting of aluminum oxide, magnesium oxide, lanthanum oxide and silicon dioxide. Further, the aluminum oxide can be -aluminum oxide.

(22) On the other hand, the catalyst for producing hydrogen prepared by the method of the present invention comprises a carrier and a metal solid solution which is formed on the carrier surface. The metal solid solution is represented by formula (I),
(A.sub.2-xA.sub.x)(Ce.sub.yB.sub.2-y)O.sub.7-(I)

(23) wherein A is selected from one of Group IIIB metals; A is selected from the group consisting of alkali metals, alkaline earth metals and Group IIIB metals, and A is different from A; B is a transition metal, and is exclusive from a Group IIIB metal or lanthanides; x is 0.1 to 1.0; y is 1.8 to 1.9; and is greater than 0 to 0.5.

(24) In addition, the value is changed with the valence number of the transition metals. Therefore, the catalyst has the value greater than 0 to 0.5 and the 6 value is not fixed.

(25) According to the catalyst for producing hydrogen, the carrier is selected from the group consisting of aluminum oxide, magnesium oxide, lanthanum oxide and silicon dioxide. Further, the aluminum oxide can be -aluminum oxide.

(26) In addition, in one embodiment of A is selected from scandium, yttrium or lanthanum, and A is selected from alkali metals, alkaline earth metals, scandium, yttrium or lanthanum. B is selected from the group consisting of ruthenium, osmium, rhodium, iridium and rhenium.

(27) Furthermore, the alkali metal is lithium, or the alkaline earth metal is selected from magnesium or calcium.

(28) In one embodiment, A is lanthanum, A is lithium, and B is ruthenium. Further, in one embodiment, A is lanthanum, A is magnesium or calcium, and B is ruthenium. In another embodiment, when A is magnesium or calcium, x is 0.1 to 0.5.

(29) In one embodiment, A is yttrium, A is scandium, and B is ruthenium.

EXAMPLES

(30) The following specific examples are used for illustrating the present invention. A person skilled in the art can easily conceive the other advantages and effects of the present invention.

Synthetic Example 1

Preparation for Y2-xScxCeyRu2-yO7- as Catalyst

(31) According to the preparing method of a catalyst for producing hydrogen of the present invention, P123 (0.5 g) was dissolved in ethanol (5 g), and then yttrium nitrate hexahydrate (Y(NO.sub.3).sub.3.6H.sub.2O, 0.25 mole), scandium nitrate hydrate (Sc(NO.sub.3).sub.3H.sub.2O, 0.25 mole), cerium nitrate hexahydrate (Ce(NO.sub.3).sub.3.6H.sub.2O, 0.475 mole) and ruthenium chloride with multi-crystalline water ((RuCl.sub.3.XH.sub.2O, 0.025 mole) were added into ethanol. After ultrasonic agitation and stirring for at least 1 hour, the mixture was gelled at 40 C. for three days to form a colloidal mixture. Subsequently, the colloidal mixture was calcined at 600 C. to 900 C. for 5 hours, and the surfactant was removed to obtain a metal solid solution.

(32) The metal solid solution (0.05 g) was dispersed in ethanol (3 mL to 10 mL) and added -aluminum oxide (Corundum; 18 mesh, 1 g, S.sub.BET>300 m.sup.2/g, 0.5 g) followed by ultrasonic agitation. Finally, the second organic solvent was removed at 90 C. and the above processes were repeated at least 5 times to allow the metal solid solution to completely disperse on -aluminum oxide. Thus, Y.sub.1.0Sc.sub.1.0Ce.sub.1.9Ru.sub.0.1O.sub.7- as catalyst with x being 1.0 and y being 1.9 was obtained.

(33) Besides, the catalysts with x being 0.8, 0.5 and 0.3 and y being 1.9 were prepared respectively based on the weighed stoichiometric amount. Afterwards, an ethanol conversion ratio and hydrogen selection ratio were tested.

Synthetic Example 2

Preparation for La2-xMgxCeyRu2-yO7- as Catalyst

(34) The catalyst was prepared in the same manner as stated in Synthetic example 1, expect that lanthanum nitrate (0.375 mole), magnesium nitrate hexahydrate (Mg(NO.sub.3).sub.2.6H.sub.2O, 0.125 mole), cerium nitrate hexahydrate (0.45 mole) and ruthenium chloride (0.05 mole) were used as the metal sources. Thus, La.sub.1.5Mg.sub.0.5Ce.sub.1.8Ru.sub.0.2O.sub.7- as catalyst with x being 0.5 and y being 1.8 was obtained.

(35) Besides, the catalysts with x being 0.4, 0.3, 0.2 and 0.1 and y being 1.8 were prepared respectively based on the weighed stoichiometric amount. Afterwards, an ethanol conversion ratio and hydrogen selection ratio were tested.

Synthetic Example 3

Preparation for La2-xCaxCeyRu2-yO7- as Catalyst

(36) The catalyst was prepared in the same manner as stated in Synthetic example 1, expect that lanthanum nitrate (0.375 mole), calcium nitrate tetrahydrate (Ca(NO.sub.3).sub.2.4H.sub.2O, 0.125 mole), cerium nitrate hexahydrate (0.45 mole) and ruthenium chloride (0.05 mole) were used as the metal sources. Thus, La.sub.1.5Ca.sub.0.5Ce.sub.1.8RU.sub.0.2O.sub.7- as catalyst with x being 0.5 and y being 1.8 was obtained.

(37) Besides, the catalysts with x being 0.4, 0.3, 0.2 and 0.1 and y being 1.8 were prepared respectively based on the weighed stoichiometric amount. Afterwards, an ethanol conversion ratio and hydrogen selection ratio were tested.

Synthetic Example 4

Preparation for La2-xLixCeyRu2-yO7- as Catalyst

(38) The catalyst was prepared in the same manner as stated in Synthetic example 1, expect that lanthanum nitrate (0.35 mole), lithium nitrate (LiNO.sub.3, 0.15 mole), cerium nitrate hexahydrate (0.45 mole) and ruthenium chloride (0.05 mole) were used as the metal sources. Thus, La.sub.1.4Li.sub.0.6Ce.sub.1.8Ru.sub.0.2O.sub.7- as catalyst with x being 0.6 and y being 1.8 was obtained. Afterwards, an ethanol conversion ratio and hydrogen selection ratio were tested.

(39) Besides, the catalysts with x being 0.8, 0.7, 0.5, 0.4, 0.3, 0.2 and 0.1 and y being 1.8 were prepared respectively based on the weighed stoichiometric amount. Afterwards, an ethanol conversion ratio and hydrogen selection ratio were tested.

Test Example 1

(40) Y.sub.2-xSc.sub.xCe.sub.yRu.sub.2-yO.sub.7- as catalyst prepared in Synthetic example 1 in which x is 1.0, 0.8, 0.5, 0.3 and y is 1.9 were analyzed by X-ray diffraction patterns. As shown in FIG. 1, all components are pure phase, that is, the preparing method of Synthetic example 1 can obtain Y.sub.2-xSc.sub.xCe.sub.yRu.sub.2-yO.sub.7- as catalyst with high purity.

(41) Moreover, for Y.sub.1.0Sc.sub.1.0Ce.sub.1.9Ru.sub.0.1O.sub.7- as catalyst prepared in Synthetic example 1, a product analysis of the ethanol reformer was performed. The product analysis of the ethanol reformer was performed at a gas hourly space velocity (GHSV) of 160,000 h.sup.1, a ethanol/water ratio of 1:3 and a reaction temperature of 270 C. As shown in FIG. 2, when a carbon-to-oxygen ratio is changed, after reacting for 12 hours, it is still maintained at high ethanol conversion ratio. When the carbon-to-oxygen ratio is 0.6, the hydrogen selection ratio is as high as 70%.

Test Example 2

(42) La.sub.2-xMg.sub.xCe.sub.yRu.sub.2-yO.sub.7- as catalyst prepared in Synthetic example 2 in which x is 0.5, 0.4, 0.3, 0.2, 0.1 and y is 1.8 were analyzed by X-ray diffraction patterns. As shown in FIG. 3, all components are pure phase, that is, the method of Synthetic example 2 can obtain La.sub.2-XMg.sub.xCe.sub.yRu.sub.2-yO.sub.7- as catalyst with high purity.

(43) Moreover, for La.sub.1.7Mg.sub.0.3Ce.sub.1.8Ru.sub.0.2O.sub.7- as catalyst prepared in Synthetic example 2, a product analysis of the ethanol reformer was performed. The product analysis of the ethanol reformer was performed at the carbon-to-oxygen ratio (C/O ratio) of 0.6, the GHSV of 160,000 h.sup.1, ethanol/water ratio of 1:3 and a reaction temperature of 380 C. As shown in FIG. 4, after reacting for a long period of 350 hours, it is still maintained at 100% of ethanol conversion ratio. With regard to the hydrogen selection ratio, the reaction was quenched after reacting for 240 hours. Then, the reaction was restarted after a period of time. After reacting for 50 hours, the catalyst was beginning to stabilize and the hydrogen selection ratio was still around 80%. The result shows that a lifetime of the catalyst is not dramatically reduced after reacting for long periods of times. That is to say, the catalyst does not be affected by the high temperature and does not increase the fracture between carbon and carbon, so as to prevent byproducts deposited on the catalyst surface.

Test Example 3

(44) La.sub.2-xCa.sub.xCe.sub.yRu.sub.2-yO.sub.7- as catalyst prepared in Synthetic example 3 in which x is 0.5, 0.4, 0.3, 0.2, 0.1 and y is 1.8 were analyzed by X-ray diffraction patterns. As shown in FIG. 5, all components are pure phase, that is, the method of Synthetic example 3 can obtain La.sub.2-xCa.sub.xCe.sub.yRu.sub.2-yO.sub.7- as catalyst with high purity.

(45) Moreover, for La.sub.1.8Ca.sub.0.2Ce.sub.1.8Ru.sub.0.2O.sub.7- as catalyst prepared in Synthetic example 3, a product analysis of the ethanol reformer was performed. The product analysis of the ethanol reformer was performed at the C/O ratio of 0.6, ethanol/water ratio of 1:3, the GHSV of 160,000 h.sup.1. The reaction was started at 240 C. and was performed at 280 C. As shown in FIG. 6, after reacting for 40 hours, it is still maintained at 90% of ethanol conversion ratio and hydrogen selection ratio.

Test Example 4

(46) La.sub.2-xLi.sub.xCe.sub.yRu.sub.2-yO.sub.7- as catalyst prepared in Synthetic example 4 in which x is 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1 and y is 1.8 were analyzed by X-ray diffraction patterns. As shown in FIG. 7, all components are pure phase, that is, the method of Synthetic example 4 can obtain La.sub.2-xLi.sub.XCe.sub.yRu.sub.2-yO.sub.7- as catalyst with high purity.

(47) Moreover, for La.sub.1.4Li.sub.0.6Ce.sub.1.8Ru.sub.0.2O.sub.7- as catalyst prepared in Synthetic example 4, a product analysis of the ethanol reformer was performed. The product analysis of the ethanol reformer was performed at the GHSV of 160,000 h.sup.1, ethanol/water ratio of 1:3. The reaction was started at 260 C. and was performed at 350 C. As shown in FIG. 8, when the C/O ratio is 0.6, after reacting for 120 hours, the ethanol conversion ratio is approximately 100% and the hydrogen selection ratio is approximately 105%.

(48) Furthermore, the reaction temperatures for Y.sub.1.0Sc.sub.1.0Ce.sub.1.9Ru.sub.0.1O.sub.7- of Synthetic example 1, La.sub.1.7Mg.sub.0.3Ce.sub.1.8Ru.sub.0.2O.sub.7- of Synthetic example 2, La.sub.1.8Ca.sub.0.2Ce.sub.1.8Ru.sub.0.2O.sub.7- of Synthetic example 3, and La.sub.1.4Li.sub.0.6Ce.sub.1.8Ru.sub.0.2O.sub.7- of Synthetic example 4 are integrated. As shown in FIG. 9, when the above catalysts are used in the ethanol reformer, all of the reaction temperatures are not over 400 C., so as to avoid generating byproducts deposited on the catalyst surface due to high temperatures as well as avoid the catalysts losing their activities.

(49) In summary, the preparing method of a catalyst for producing hydrogen and the prepared catalyst of the present invention, in the case of avoiding the use of noble metals (such as rhodium and platinum) as well as a relatively low amount of transition metals, can reduce production costs and still maintain a relatively high hydrogen selection ratio. Moreover, when the reaction temperatures of the catalysts are significantly reduced, the byproducts (such as CO.sub.2, C.sub.2H.sub.4 and CH.sub.3CHO) generated from the fracture between carbon and carbon in the reaction can be reduced as well as the carbon deposited on the catalyst surface can be avoided, and then high catalytic activities of the catalysts is still maintained after using the catalysts for long periods of time.