Provided are: a uniformly, highly dispersed metal catalyst including a catalyst carrier and a catalyst metal being loaded thereon dispersed throughout the carrier, the uniformly, highly dispersed metal catalyst having excellent performances with respect to catalytic activity, selectivity, life, etc.; and a method of producing the same. The uniformly, highly dispersed metal catalyst includes a catalyst carrier made of a metal oxide and a catalyst metal having catalytic activity, the catalyst metal being loaded on the catalyst carrier, in which the catalyst carrier is a sulfur-containing catalyst carrier having sulfur or a sulfur compound almost evenly distributed throughout the carrier and the catalyst metal is loaded on the sulfur-containing catalyst carrier in a substantially evenly dispersed manner over the entire carrier substantially according to the distribution of the sulfur or the sulfur compound.
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1. An uniformly, highly dispersed metal catalyst, comprising:
a catalyst carrier made of a metal oxide; and
a catalyst metal having catalytic activity,
the catalyst metal being loaded on the catalyst carrier, wherein:
the catalyst carrier is a sulfur-containing catalyst carrier which comprises an aluminum a porous γ-alumina carrier having a surface area of 150 m2/g or larger, a fine pore volume of 0.4 cm3/g or larger, an average fine pore diameter of 40 to 300 Å, and the proportion of fine pores having an a diameter within ±30 Å of the average fine pore diameter of 30 Å is 60% or higher with respect to a total pore volume and sulfur or a sulfur compound which is dispersed throughout a cross section of the aluminum porous γ-alumina carrier and whose content is 0.15 to 3.0% by weight in terms of a sulfur element; and
in the sulfur-containing catalyst porous γ-alumina carrier, platinum or rhodium is dispersed in a dispersion ratio of greater than 60% but not greater than 80% as measured by a CO pulse adsorption method and loaded as the catalyst metal over an entire cross section of the catalyst carrier substantially in agreement with distribution of the sulfur or the sulfur compound.
8. A method of producing an uniformly, highly dispersed metal catalyst, comprising:
carrying out a pH swing process of a slurry of aluminum hydroxide generated by neutralizing aluminum salt to grow crystals of alumina hydrogel in which a pH of alumina hydrogel is alternately fluctuated between a pH range of the dissolution of alumina hydrogel and a pH range of the precipitation of boehmite gel and simultaneously an alumina hydrogel forming substance is added when the pH is fluctuated from at least either one of the pH ranges to the other one of the pH ranges;
kneading sulfur powder in an aluminum gel the obtained alumina hydrogel serving as a precursor of an alumina;
forming the resulting gel hydrogel into a predetermined shape, followed by drying and calcining to prepare a sulfur-containing catalyst porous γ-alumina carrier in which sulfur or a sulfur compound is dispersed throughout a cross section thereof;
impregnating the obtained sulfur-containing catalyst porous γ-alumina carrier with an aqueous solution of catalyst metal compound of platinum and/or rhodium;
drying the resulting catalyst porous γ-alumina carrier to obtain a dried matter loading the catalyst metal compound;
reducing the dried matter loading the catalyst metal compound as it is in a hydrogen atmosphere; or calcining the obtained dried matter loading the catalyst metal compound to obtain a calcined matter loading catalyst metal; and
reducing the obtained calcined matter loading the catalyst metal with hydrogen to produce a uniformly, highly dispersed metal catalyst in which platinum and/or rhodium is dispersed in a dispersion ratio of greater than 60% but not greater than 80% as measured by a CO pulse adsorption method and loaded as the catalyst metal over an entire cross section of the catalyst carrier substantially in agreement with distribution of the sulfur or the sulfur compound.
2. An uniformly, highly dispersed metal catalyst according to
3. An uniformly, highly dispersed metal catalyst according to
4. An uniformly, highly dispersed metal catalyst according to
0. 5. An uniformly, highly dispersed metal catalyst according to
6. A method of dehydrogenating a hydrogenated aromatic, comprising dehydrogenating hydrogenated aromatic using the uniformly, highly dispersed metal catalyst according to any one of claim claims 1, 2, 3, or 4, or 5.
7. A method of dehydrogenating a hydrogenated aromatic according to
9. A method of producing the uniformly, highly dispersed metal catalyst according to
0. 10. A method of producing the uniformly, highly dispersed metal catalyst according to
11. A method of producing the uniformly, highly dispersed metal catalyst according to claim 10 9, wherein the sulfur-containing porous γ-alumina carrier has a surface area of 150 m2/g or more, a fine pore volume of 0.40 cm3/g, an average fine pore diameter of 40 to 300
12. A method of producing the uniformly, highly dispersed metal catalyst according to claim 10 9, wherein the sulfur-containing catalyst porous γ-alumina is prepared at a calcination temperature of 350 to 800° C. for a calcination time of 1.0 to 24 hours.
0. 13. The method of claim 1, wherein the content of the sulfur or the sulfur compound is 0.15 to 0.5% by weight in terms of a sulfur element.
0. 14. The method of claim 8, wherein the content of the sulfur or the sulfur compound is 0.15 to 0.5% by weight in terms of a sulfur element.
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The present invention relates to a metal loaded catalyst for use in manufacturing chemical products, producing hydrogen, cleaning the environment, such as cleaning exhaust gas, etc. More especially, the present invention relates to a uniformly, highly dispersed metal loaded catalyst in which sulfur or a sulfur compound are substantially uniformly dispersed throughout the cross section of a catalyst carrier and catalyst metal is loaded on the carrier in a state where the catalyst metals are substantially uniformly dispersed throughout the cross section of the carrier almost substantially in agreement with the distribution of the sulfur or sulfur compound, a method of using the same, and a sulfur-containing porous metal oxide for use in producing the same.
A metal loaded catalyst in which various catalytic metal species are loaded on a catalyst carrier made of a metal oxide is used in an extremely wide range of fields, for example, not only dehydrogenation reaction in which hydrogenated aromatics such as methylcyclohexane, cyclohexane, and decalin are dehydrogenated into the corresponding aromatics and hydrogen but also manufacturing of chemical products and fuels by dehydrogenation reaction of various compounds, hydrogenation reaction which is a reverse reaction of the dehydrogenation reaction and reforming reaction; and environmental clean-up such as cleaning automobile exhaust gas, and the like.
Generally, such metal loaded catalysts are manufactured as follows: a porous catalyst carrier made of a metal oxide such as alumina or silica etc., is prepared; when platinum is loaded on the obtained porous catalyst carrier, the obtained porous catalyst carrier is impregnated with a solution of a catalyst metal compound, such as a chloroplatinic acid aqueous solution, a platinum ammonium chloride aqueous solution, and a solution of an organoplatinum compound such as platinum acetylacetonate; the resultant is dried to form a dried matter loading the catalyst metal compound; the dried matter is calcined, e.g., at 350 to 800° C. for 0.5 to 24 hours to form a calcined matter loading the catalyst metal compound; and, as required, the obtained calcined matter loading the catalyst metal compound is subjected to hydrogen reduction, e.g., at 250 to 800° C. for 0.5 to 24 hours.
However, the metal loaded catalyst manufactured by such a procedure has the following problems. For example, when a platinum-loaded alumina catalyst in which platinum, being one of typical active metal species as catalyst metal, is loaded on an alumina carrier, being used most widely as a catalyst carrier, is taken as an example, it is known that since the adsorbability of a platinum compound to the alumina carrier is high, the platinum compound is adsorbed and fixed as it is to the outer shell part of the alumina carrier before the platinum compound is dispersed inside the alumina carrier, which forms a so-called egg shell-type metal loaded catalyst, as viewed in the cross section, the catalyst metal being loaded only on the outer shell part and no catalytic metal species being loaded inside the carrier (see 14th “Catalysis School Text” (2003), pages 35 to 44 and 15th “Catalysis School Text” (2004), pages 35 to 44, organized by Kanto Branch Commission, Catalysis Society of Japan).
In the case of the reaction in which the dispersion resistance is high inside a catalyst, the reaction occurs preferentially in the outer shell of the catalyst. Thus, the egg shell-type catalyst is advantageous in such a reaction. However, when a certain amount of active metal is to be loaded only on the outer shell of the catalyst particles, the density of the active metal particles increase, which presumably leads to possibilities that the active metal particles can not be sufficiently dispersed, catalyst deactivation due to sintering or coking is likely to occur, etc. Therefore, in a reaction which is not influenced by the dispersion resistance, it is presumably advantageous to design a catalyst in such a manner as to reduce the influences by fully utilizing the surface area of a carrier.
However, it is not easy that the active metal such as platinum is uniformly dispersed as far as the inside of catalyst carrier particles, and a method using a competitive adsorption agent having high adsorbability to a carrier has been used heretofore (Catalyst Design, volume 5, pages 134 to 141, Catalyst Lecture edited by Catalysis Society of Japan). However, also in the method, it is relatively difficult to prepare a catalyst in which the active metal is uniformly dispersed thoroughly, and there is a possibility that the concentration gradient of loaded metal appears toward the center of the catalyst particles.
- Non-patent Document 1: 14th “Catalysis School Text” (2003), pages 35 to 44, organized by Kanto Branch Commission, Catalysis Society of Japan
- Non-patent Document 2: 15th “Catalysis School Text” (2004), pages 35 to 44, organized by Kanto Branch Commission, Catalysis Society of Japan
- Non-patent Document 3: Catalyst Design, volume 5, pages 134 to 141, Catalyst Lecture edited by Catalysis Society of Japan
The inventors of the present invention carried out extensive research on loading catalyst metal such as platinum on a catalyst carrier such as alumina or silica in a state where the catalyst metal is uniformly dispersed as far as the inside of the catalyst carrier by an impregnation method. As a result, it is unexpectedly found that, by substantially uniformly dispersing sulfur or a sulfur compound throughout the cross section of the catalyst carrier beforehand, catalyst metal is loaded substantially in agreement with the distribution of the sulfur or sulfur compound, thereby easily obtaining a uniformly, highly dispersed metal loaded catalyst in which the catalytic metal is substantially uniformly dispersed and loaded over the entire cross section of the catalyst carrier, and thus the present invention has been accomplished.
Accordingly, the present invention aims to provide a uniformly, highly dispersed metal catalyst in which the catalytic metal is loaded on the catalyst carrier in a state where the catalytic metal is substantially uniformly dispersed throughout the cross section of the catalyst carrier and which has excellent performances in terms of catalytic activity, selectivity, life, etc.
The present invention also aims to provide a method of producing such a uniformly, highly dispersed metal catalyst which has excellent performances in terms of catalytic activity, selectivity, life, etc., a method of using the same, and a sulfur-containing porous metal oxide for use in the method of producing the same.
The present invention provides a uniformly, highly dispersed metal catalyst including: a catalyst carrier made of a metal oxide; and a catalyst metal having catalytic activity, the catalyst metal being loaded on the catalyst carrier, in which: the catalyst carrier is a sulfur-containing catalyst carrier containing sulfur or a sulfur compound which is dispersed throughout across section of the carrier; and in the sulfur-containing catalyst carrier, the catalyst metal is dispersed and loaded over an entire cross section of the catalyst carrier substantially in agreement with distribution of the sulfur or the sulfur compound.
In addition, the present invention provides a method of producing a uniformly, highly dispersed metal catalyst including: preparing a sulfur-containing catalyst carrier in which sulfur or a sulfur compound is dispersed throughout a cross section thereof; impregnating the obtained sulfur-containing catalyst carrier with an aqueous solution of catalyst metal compound and drying the resulting catalyst carrier to obtain a dried matter loading the catalyst metal compound; reducing the dried matter loading the catalyst metal compound as it is in a hydrogen atmosphere or calcining the dried matter loading the catalyst metal compound to obtain a calcined matter loading catalyst metal; and reducing the obtained calcined matter loading the catalyst metal with hydrogen.
In this specification, the wording “uniform-type” used in the uniformly dispersed metal catalyst of the present invention refers to a state where catalyst metal particles are substantially uniformly loaded over the entire cross section of the catalyst carrier, and the wording “highly dispersed” refers to a state where the particle diameter of the loaded metal is sufficiently small and the particle is dispersed to a high degree. More specifically, the uniformly, highly dispersed metal catalyst of the present invention refers to a uniformly, highly dispersed metal catalyst in which: the numerical value of a metal dispersion degree, which will be mentioned later, is high; and the metal particles are substantially uniformly loaded over the entire cross section of the catalyst carrier while a high dispersion state, in which the particle diameter of the loaded metal is sufficiently small, is maintained.
Examples of the metal oxides used for a catalyst carrier in the present invention include metal oxides containing one or two or more metals selected from aluminum (Al), silicon (Si), zirconium (Zi), magnesium (Mg), calcium (Ca), titanium (Ti), vanadium (Va), chromium (Cr), manganese (Mn), iron, (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), gallium (Ga), yttrium (Y), niobium (Nb), molybdenum (Mo), tungsten (W), lanthanum (La), and cerium (Ce). Alumina, silica, titania, zirconia, ceria, and the like are preferred.
When the above-mentioned catalyst carrier is alumina, a porous γ-alumina carrier is preferable as disclosed in JP 06-72005 B, for example. The porous γ-alumina carrier is obtained by washing by filtration a slurry of aluminum hydroxide generated by neutralizing aluminum salt, dehydrating and drying the obtained alumina hydrogel, and then calcining the resultant at 400 to 800° C. for about 1 to 6 hours. More preferable is a porous γ-alumina carrier obtained through a pH swing process in which the pH of alumina hydrogel is alternately fluctuated between a pH range of the dissolution of alumina hydrogel and a pH range of the precipitation of boehmite gel and simultaneously an alumina hydrogel forming substance is added for growing crystals of the alumina hydrogel when the pH is fluctuated from at least either one of the pH ranges to the other one of the pH ranges. The porous γ-alumina carrier obtained through the pH swing process is excellent in the uniformity of pore distribution, and excellent in that the physical properties of each pellet are stable because there is less variation in the physical properties also in the alumina carrier pellet after the formation of the carrier.
There is no limitation on the sulfur or sulfur compound to be dispersed in such a catalyst carrier beforehand for incorporation thereof insofar as the sulfur or sulfur compound has a sulfur element and can be uniformly dispersed in the catalyst carrier during the preparation of the catalyst carrier or after the preparation of the catalyst carrier. For example, sulfur crystal powders, and sulfur-containing compounds such as sulfuric acid, sulfate including ammonium sulfate can be mentioned. From the viewpoint that sulfur is likely to disperse on a carrier, sulfur compounds having solubility in water or an organic solvent are preferable, and sulfuric acid, ammonium sulfate, etc., can be mentioned as such sulfur compounds.
The amount of sulfur to be contained in a carrier is preferably 0.15% by weight or more and 5% by weight or less, and more preferably 0.15% by weight or more and 3% by weight or less. When the sulfur content is less than 0.15% by weight, the degree that metal is uniformly loaded as far as the center of the catalyst is low, while when the sulfur content exceeds 5% by weight, a problem is likely to occur that sulfur is likely to locally agglomerate and metal is not dispersed and loaded on such a portion. In view of the above, the most suitable sulfur content range is preferably 0.15 to 3.0% by weight considering the effect that metal is uniformly dispersed and loaded.
In the present invention, with respect to a method of preparing a sulfur-containing catalyst carrier containing the above-mentioned sulfur or sulfur compound, usable is a method capable of incorporating the sulfur or sulfur compound in a state where the sulfur or sulfur compound is uniformly dispersed throughout the cross section of the carrier. For example, the following methods are mentioned: method A involving kneading sulfur powder in a metal hydroxide gel serving as a precursor of a metal oxide obtained when preparing a catalyst carrier, forming the resultant into a predetermined shape, and drying and calcining the resultant; method B involving preparing a metal hydroxide gel serving as a precursor of a metal oxide containing sulfur using metal sulfate and/or sulfuric acid when preparing a catalyst carrier, forming the resultant into a predetermined shape, and drying and calcining the resultant; method C involving forming a metal hydroxide gel serving as a precursor of a metal oxide into a predetermined shape when preparing a catalyst carrier, drying the resultant to form a dry metal hydroxide gel, impregnating the dry metal oxide with a sulfur compound solution, and calcining the same; method D involving forming a metal hydroxide gel serving as a precursor of a metal oxide into a predetermined shape when preparing a catalyst carrier, drying the resultant to form a dry metal hydroxide, impregnating the dry metal hydroxide with a sulfur compound solution, and calcining the same; and method E involving forming a metal hydroxide gel serving as a precursor of a metal oxide into a predetermined shape, drying the resultant to form a dry metal hydroxide gel, calcining the dry metal hydroxide gel to form a calcined metal oxide, impregnating the calcined metal oxide with a sulfur compound solution such as an sulfuric acid aqueous solution and an ammonium sulfate solution, and further calcining the resultant.
With respect to calcining conditions when preparing the sulfur-containing catalyst carrier, the calcining temperature is usually 100° C. or higher and 1,000° C. or lower, and preferably 350° C. or higher and 800° C. or lower, and the calcining time is 0.5 hour or more and 48 hours or less, and preferably 1 hour or more and 24 hours or less. When the calcining temperature is lower than 350° C., conversion to an oxide from a hydroxide may not be fully performed, while when the calcining temperature is higher than 800° C., the surface area after calcining may be dramatically reduced.
In the present invention, there is no limitation on the catalyst metal to be loaded on the sulfur-containing catalyst carrier, and preferable is one or two or more metals selected from platinum (Pt), palladium (Pd), iridium (Ir), rhodium (Rh), ruthenium (Ru), nickel (Ni), copper (Cu), and zinc (Zn), and more preferably is platinum. When the catalyst carrier is, for example, the above-mentioned porous γ-alumina carrier and the catalyst metal is platinum, the loading amount of catalyst metal is 0.05% by weight or more and 5.0% or less, and preferably 0.1% by weight or more and 3.0% by weight or less. When the loading amount of platinum is less than 0.05% by weight, there is a problem that the activity is low, while when the loading amount of platinum exceeds 5.0% by weight, there are problems that the particle diameter of platinum increases, the selectivity is reduced, sintering is likely to occur, resulting in that deactivation is likely to occur.
The catalyst prepared as mentioned above may be formed into a general pellet in the forming process, or can also be fixed on a support in various forms such as a honeycomb and plate. In other words, the catalyst may be fixed on a support in the preparation processes of the sulfur-containing catalyst carrier described above or catalyst powder after loading catalyst metal may be fixed thereon. The sulfur-containing catalyst carrier or the catalyst to such a support can be fixed by a binder, calcining, or sintering, which are generally used for fixing an oxide catalyst to a honeycomb, a plate, etc.
In the present invention, it can be confirmed as to whether the catalyst metal s uniform, and in other words, the catalyst metal is substantially uniformly dispersed throughout the cross section of the carrier by observing quantitatively the concentration distribution of catalyst metal elements on the catalyst cross section by EPMA (Electron probe micro analyzer). According to the EPMA, fluorescence X rays, which are peculiar to elements and generated by irradiating a sample with electron beams, are detected, and the concentration of a specific element of the electron-beam-irradiation part is quantified from the detected intensity. Usually, the following analyses are possible: the surface analysis in which electron beams are emitted while shifting target irradiation portions, and the distribution states of specific elements throughout the sample cross section are indicated in different colors according to the detected intensity, whereby the distribution state thereof throughout the cross section is shown; and the line analysis which shows, in a graph, the detected intensity at the measurement position linearly traversing the sample cross section as a relative value.
In the cross section of the egg shell-type catalyst, catalyst metal is detected only in the outer shell of the cross section. The detected intensity in the measurement position inside the outer shell is notably small, and the catalyst metal concentration of the center is about ½ or less compared with that of the outer shell part. In contrast, in the uniformly, highly dispersed metal catalyst of the present invention, metal is loaded with high concentration as far as the center of the carrier cross section as well as the outer shell part of the carrier cross section. The metal concentration of the center with respect to the outer shell part, the catalyst metal can be uniformly dispersed from the outer shell part to the center of the cross section of the carrier within the range of preferably ±50%, more preferably ±30%, and still more preferably ±15% in terms of the detected intensity.
Moreover, it can be quantitatively captured as to whether the catalyst metal is highly dispersed, and in other words, the metal particle diameter is sufficiently small and the metal particles are highly dispersed, by the dispersion ratio (%) of the metal particles determined by a CO pulse adsorption method mentioned below. Here, the metal dispersion ratio is defined by the ratio of the number of metal atoms which are present on the outer face of the loaded metal particles with respect to a total number of the loaded metal atoms. For example, when metal particles containing 100 atoms are loaded, and 40 metal atoms out of the 100 atoms are present on the outer surface, the metal dispersion ratio is 40%. The metal dispersion ratio is usually measured by the CO pulse adsorption method, and the measurement is carried out by a method of determining the number of CO molecules adsorbing metal atoms which are present on the outer surface. When the forms of the metal particles are assumed to have a form of a cube or a regular octahedron, the metal particle diameter based on the assumption can be estimated from the result.
That is, the dispersion ratio of the catalyst metal of the present invention is 40% or higher, and preferably 60% or higher and 80% or lower. The average metal particle size equivalent to the dispersion ratio of 60% or higher is 10 Å or smaller, and the average metal particle size equivalent to the dispersion ratio of 70% is about 7 Å. The significances of increasing the metal dispersion ratio for reducing the size of the loaded metal particles as described above mainly reside in the following two respects. It is primarily mentioned that as the dispersion ratio of metal increases, the proportion of atoms which are present on the outer surface of metal particles increases, whereby the surface area of active metal increases, and the activity is improved. Second, in a cluster of small noble metal particles, since the number of platinum atoms forming a flat portion is small, flat adsorption of components such as a reaction raw material on metal is presumably difficult to achieve. For example, when hydrogenated aromatics are dehydrogenated using a platinum-loaded alumina catalyst in which platinum is highly dispersed as high as 10 Å or smaller, the flat portions of the noble metal surface to which aromatic molecules are adsorbed flat are presumably extremely small in view of the molecule size. Therefore, it is presumed that decomposition reactions can be inhibited because it is extremely rare that two or more carbon atoms of aromatics adsorb on the noble metal surface.
When platinum is taken as an example, the particle size of a commonly commercially-available platinum-loaded alumina catalyst is about 20 to 30 Å and the metal dispersion ratio is about 20 to 40% in many cases. It is said that it is relatively difficult to load platinum in a dispersion ratio as high as 20 Å or smaller. A highly dispersed catalyst with a dispersion ratio of 10 Å or smaller has been demanded not only from the viewpoint of increasing catalyst activity but also from the viewpoint of effectively using platinum resources. However, a catalyst having such a high dispersion ratio has not yet been prepared.
In the present invention, a porous metal oxide in which sulfur or a sulfur compound is contained preferably has the pore size controlled as uniformly as possible so that the pore distribution becomes sharp. Specifically, preferable is a porous metal oxide in which a sulfur-containing porous metal oxide has a surface area of 150 m2/g or larger, a pore volume of 0.4 cm3/g or larger, an average pore diameter of 40 to 300 Å, and the proportion of pores having
Here, when the metal content of the sample is defined as C (%) and the atomic weight of the loaded metal is defined as M, the number of moles R of the loaded metal per g of the sample is calculated according to the following equation (2).
R=(C/100)×(1/M) (mol/g·cat) (2)
The number of moles K of the adsorption gas amount per g of the sample is calculated according to the following equation (3).
K=V/(22.4×10−3×106) (mol/g·cat) (3)
Based on the above, the dispersion ratio B (proportion of effective surface metal in the loaded metal) is calculated according to the following equation (4).
B=(K/R)×100(%) (4)
When the lattice constant of the loaded metal catalyst is defined as a (()), and it is assumed that one adsorption gas molecule is adsorbed to a lattice constant area a2, the specific surface area S of metal is calculated according to the following equation.
S=the number of gas molecules adsorbed to 1 g of sample×a2=K×6.02×1023×(a×10−10)2 (5)
When a loaded metal particle is assumed to be a cube D (m) on each side, five surfaces out of six surfaces of the particle are effective. Based on the fact, the following equations are established.
Effective area S of one particle=5D2 (m2) (6)
Volume of one particle ν=D3 (m3) ( 7)
When the number of particles of the loaded metal per g of sample is defined as n, the following equations are established.
Specific surface area S of loaded metal=ns=n5D2 (m2) (8)
Volume Vc of loaded metal=nν=Nd3 (m3) (9)
From equations (10 to 11) and equations (10 to 12),
S/Vc=5/D∴D=5Vc/S(m) (10)
When the content of loaded metal is defined as C (%) and the specific gravity is defined as d(g/cm3), the volume Vc of the loaded metal per g of sample is calculated according to the following equations.
The measurement results of the dispersion ratio of platinum measured by the CO pulse adsorption method in the catalysts No. 1 to No. 7 prepared in Comparative Example and Examples 1 to 3 above are shown in the following Table 1 (dispersion ratio and particle diameter measured by the CO pulse adsorption method).
TABLE 1
Sulfur
Platinum-
Dispersion
Particle
Catalyst
Support
content
loading
ratio
diameter
No.
(%)
(wt %)
amount (wt %)
(%)
(Å)
1
A
0
0.6
69
7.1
2
B
0.5
0.6
46
11
3
C
0.5
0.6
68
7.2
4
D
0.5
0.6
74
6.7
5
E
0.1
0.6
67
7.4
6
F
0.5
0.6
76
6.5
7
G
1.2
0.6
71
6.9
A carrier A containing no sulfur and a carrier D containing sulfur were impregnated with an aqueous ammonium rhodium hexachloride solution for 50 hours, and then the solvents were removed with an evaporator. The resultants were dried (at 120° C. for 3 hours), thereby and calcined (at 400° C. for 3 hours), thereby yielding a 0.6 wt % rhodium-loaded alumina catalysts. The concentrations of sulfur element and platinum element on each of the catalyst cross sections were quantified by surface analysis and line analysis using EPMA. The results are shown in
As is clear from the results shown in
Among the 0.6% by weight platinum-loaded alumina catalysts obtained in each Example above, the dehydrogenation reaction test of methylcyclohexane (MCH) was carried out for the catalyst No. 3 (Example 1), catalyst No. 4 (Example 2), catalyst No. 6 (Example 3), catalyst No. 7 (Example 3), and catalyst No. 1 (Comparative Example). 10 cc of each catalyst above was placed in a stainless steel reaction tube whose inside diameter is 12.6 mmφ×300 mm and which is equipped with a protective tube for a thermocouple whose outer dimension was ⅛ inch in the center of the cross section of the reaction tube in such a manner that the center of a catalyst bed was positioned in the longitudinal center of the reaction tube, and 10 cc of α-alumina beads with a diameter of 1 mmφ was placed on the upper side of the catalyst as a preheating layer. The temperature of the catalyst bed was increased in a hydrogen stream (LHSV=5.0; 50 cc/hr) so that the central temperature of the catalyst bed reached 320° C. Subsequently, methylcyclohexane (MCH) in an amount equivalent to LHSV=2.0 (20 cc/hr) was supplied to a reactor with a liquid-supply pump for high speed liquid chromatography (HPLC) (HPLC pump). Immediately, a hydrogen flow rate was adjusted so that the hydrogen gas amount was adjusted to 5 mol % with respect to the total amount of MCH and hydrogen gas. The reaction test was performed while adjusting the output of an electric furnace so that the central temperature of a catalyst bed was 320° C. during the reaction.
A vapor-liquid separator was placed at the outlet of the reaction tube, and the resultant was separated into a liquid reaction product such as toluene and gas such as hydrogen gas, which were generated by the dehydrogenation reaction. The collected liquid product and gas were separately analyzed by gas chromatography.
The MCH conversion rate (%), toluene selectivity (%), toluene yield (%), and hydrogen generation amount (cc/h/cc-cat) 2 hours after and 300 hours after the initiation of the reaction were calculated. The results are shown in Table 2.
The dehydrogenation reaction test of methylcyclohexane was carried out for the catalyst No. 3 (Example 1), catalyst No. 4 (Example 2), catalyst No. 6 (Example 3), catalyst No. 7 (Example 3), and catalyst No. 1 (Comparative Example) prepared in Comparative Example and Examples 1 to 3 above. The results are shown in Table 2.
TABLE 2
Catalyst No.
1
3
4
6
7
Support
A
C
D
F
G
Sulfur content (wt %)
0
0.5
0.5
0.5
1.2
Platinum-loading amount
0.6
0.6
0.6
0.6
0.6
(wt %)
24 hours after the initiation of reaction
MCH conversion (%)
98.2
98.0
98.0
98.2
97.9
Toluene selectivity (%)
99.88
99.97
99.94
99.92
99.95
Toluene yield (%)
98.1
98.0
97.9
98.1
97.9
Concentration of generated
180
70
55
50
45
methane (ppm)
300 hours after the initiation of reaction
MCH conversion (%)
94.5
97.83
97.68
97.7
97.4
Toluene selectivity (%)
99.9
99.97
99.93
99.93
99.97
Toluene yield (%)
94.4
97.8
97.6
97.6
97.4
Concentration of generated
115
55
40
35
30
methane (ppm)
As is clear from the results shown in Table 2, it is revealed that the dehydrogenated catalyst of the present invention shows notably high selectivity and markedly low concentration of methane, which is generated by a side reaction, compared with a catalyst prepared from an alumina carrier containing no-sulfur, even if the acid site is not masked using alkali metal such as potassium. Moreover, considering that stable performances are maintained over 300 hours and deactivation in catalyst performances is not observed, hydrogen can be stably generated with favorable selectivity over a long period of time.
In the uniformly, highly dispersed metal catalyst of the present invention, catalyst metal is loaded on a catalyst carrier in a state where the catalyst metal is uniformly dispersed throughout the catalyst carrier. Therefore, the loading amount of the catalyst metal increases and excellent performances are exhibited in terms of catalytic activity, selectivity, life, etc. Thus, the uniformly, highly dispersed metal catalyst of the present invention is suitably used as a dehydrogenation catalyst for a hydrogen storage for use in a chemical hydride hydrogen supply system and the like, and suitably used for manufacturing chemical products, producing hydrogen, cleaning the environment, such as cleaning of exhaust gas. Moreover, according to the production method for the uniformly, highly dispersed metal catalyst of the present invention, such a uniformly, highly dispersed metal catalyst can be readily manufactured industrially.
Okada, Yoshimi, Makabe, Toshiji, Saito, Masashi, Nishijima, Hiroaki
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