JP2013132612A - Fuel reforming catalyst, fuel reforming system and fuel reforming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel reforming catalyst capable of sufficiently accelerating fuel reforming reaction even with a low carried quantity under a low-temperature condition, to provide a fuel reforming system using the fuel reforming catalyst, and further a fuel reforming method.SOLUTION: A lanthanum aluminate (LaAlO) is formed on a surface of an aluminum oxide particle to coat the surface thereof, and rhodium is carried as a catalyst component on a surface of the lanthanum aluminate. Preferably, LaOand CeOare dispersed on the surface of lanthanum aluminate, and the rhodium is carried on the surface thereof to obtain the fuel reforming catalyst.

Description

The present invention relates to a fuel reforming technique for generating a hydrogen-containing reformed gas from an exhaust gas containing water and carbon dioxide and a fuel, and reforms the fuel at a lower temperature condition with high efficiency to produce hydrogen (H ₂ ). The present invention relates to a fuel reforming catalyst capable of generating a reformed gas having a high concentration, and a fuel reforming system and method using the same.

In recent years, due to consideration for the global environment, reduction of carbon dioxide (CO ₂ ) emissions has been screamed, and development of technologies for reducing CO ₂ emissions from various combustors, internal combustion engines, etc. has been vigorously conducted. .
The internal combustion engine for automobiles has also been improved in fuel efficiency by steadily improving efficiency by improving combustion and reducing friction. In addition, as energy problems become more prominent, further CO ₂ reduction has been demanded, and it has become necessary to develop more effective technologies.

Heat is released from the internal combustion engine together with the exhaust gas. At present, energy is wasted, but if the exhaust gas and exhaust heat energy can be recovered effectively, CO ₂ can be recovered. Can be directly reduced, and a greater fuel efficiency improvement effect should be obtained.

It is known that chemical energy recovery is possible by performing an endothermic fuel reforming reaction using moisture and CO ₂ in exhaust gas.
In this case, not only the reformed gas containing H _{2 having} a larger amount of heat than the fuel supplied with exhaust heat is obtained, but also the obtained H ₂ has an effect of promoting combustion of the internal combustion engine. Since the exhaust heat recovery effect is also taken into account, a large CO ₂ reduction is possible.

Therefore, many proposals have already been made on H ₂ generation by a fuel reforming reaction using exhaust gas and exhaust heat on an automobile and its supply method to an internal combustion engine with the aim of greatly improving fuel consumption. The following patent document 1 is given as a typical proposal.

Japanese Patent Publication No. 61-35375

In this proposal, a part of the exhaust gas is taken out, a part of the fuel is added to this, and the fuel is sent to the reforming catalyst device installed in the system where the exhaust gas circulation (EGR) device is installed. Use of steam reforming reaction and CO ₂ reforming reaction is considered.

However, in order to effectively promote the endothermic reforming reaction, relatively high performance catalysts such as current nickel (Ni), ruthenium (Ru), and rhodium (Rh) catalysts are used. However, it is not sufficient in terms of temperature.
That is, since the exhaust gas temperature from the internal combustion engine frequently becomes 700 ° C. or less even at the manifold or at a position immediately below the manifold, improvement in the low-temperature activity of the reforming catalyst is required.

On the other hand, with noble metal catalysts, the activity can be improved to some extent by increasing the amount of catalyst used. However, a significant increase in cost is unavoidable due to the higher loading of the catalyst.
Moreover, high loading of the catalyst is to induce side reactions, it may cause an increase in CH ₄ and CO, which is because in some cases interfere with the combustion improvement of the internal combustion engine by H _2, the selection of H ₂ produced It is also important to improve sex.

  The present invention has been made in view of the above problems in the conventional fuel reforming technology, and the object thereof is to sufficiently promote the fuel reforming reaction even under low loading and low temperature conditions. It is an object to provide a fuel reforming catalyst, a fuel reforming system using the same, and a reforming method.

  As a result of intensive investigations to achieve the above object, the present inventors have made rhodium a catalyst component, and a catalyst supporting rhodium as a catalyst component on the surface of lanthanum aluminate formed on the surface of aluminum oxide particles. The present inventors have found that the above problems can be achieved and have completed the present invention.

That is, the present invention is based on the above knowledge, and the fuel reforming catalyst of the present invention is used in a fuel reforming system that generates reformed gas containing hydrogen, and rhodium (Rh) is used as a catalyst component. Lanthanum aluminate (LaAlO ₃ ) is formed on the surface of aluminum oxide (Al ₂ O ₃ ) particles, and the rhodium is supported on the surface of the lanthanum aluminate.
The catalyst production method of the present invention is characterized in that, when producing the fuel reforming catalyst, aluminum oxide powder having a primary particle diameter of 0.2 to 1 μm is used as a starting material for aluminum oxide.

  A fuel reforming system of the present invention is a system that generates a reformed gas containing hydrogen using exhaust gas and heat from an on-board internal combustion engine, and is a fuel reformer equipped with the fuel reforming catalyst of the present invention. The quality reaction device, the fuel injection device, and the air supply device are installed in the exhaust circulation system.

  In the fuel reforming method of the present invention, the oxygen concentration contained in the exhaust gas discharged from the internal combustion engine is 1.2 vol% or less, or the air / fuel mass ratio (A / F) is rich. The fuel reforming reactor is operated under stoichiometric operating conditions.

According to the present invention, LaAlO ₃ is formed on the surface of Al ₂ O ₃ particles, and Rh is supported on this LaAlO ₃ surface as a catalyst component. Therefore, the reforming reaction is efficiently promoted even under low temperature conditions. And the amount of Rh supported can be significantly reduced.
In addition, by incorporating such a catalyst in the EGR system of the in-vehicle internal combustion engine, exhaust heat and substance supply to the fuel reforming reaction device can be facilitated, and the generated H ₂ can be directly used for the internal combustion engine. For this reason, the effect of improving the fuel efficiency becomes large. Furthermore, the amount of H ₂ generated can be increased and stably supplied by an air supply device that introduces secondary air into the system.

It is a schematic diagram which shows the particle structure of the fuel reforming catalyst of this invention. It is an X-ray diffraction pattern of the fuel reforming catalyst obtained by Example 2 of the present invention. It is explanatory drawing which shows an example of the vehicle-mounted fuel reforming system to which the fuel reforming catalyst of this invention is applied. It is a figure which shows the structure of the fuel reforming reaction apparatus used for the performance evaluation of the fuel reforming catalyst in the Example. Is a graph showing the effect of LaAlO ₃ formed on the _Al 2 _{O 3} particles surface on the hydrogen producing ability. It is a graph showing the effect of additional addition of _La 2 _{O 3} and CeO ₂ on the hydrogen producing ability. It is a graph showing the effect of the catalyst by on the hydrogen concentration in the reformed gas O _{2 /} C mole ratio of the present invention. The effect of the catalyst by on the hydrogen concentration in the reformed gas H _{2 O} / C molar ratio of the present invention is a graph showing.

  Hereinafter, the fuel reforming catalyst, the fuel reforming method, and the fuel reforming system used therefor will be described in more detail. In the present specification, “%” for concentration, content, blending amount and the like represents mass percentage unless otherwise specified.

The fuel reforming catalyst of the present invention is used in a fuel reforming system that generates reformed gas containing hydrogen. As described above, LaAlO ₃ is formed on the surface of Al ₂ O ₃ particles, and The surface of this LaAlO ₃ carries Rh as a catalyst component. By using such a fuel reforming catalyst, the reforming reaction can be efficiently promoted under low temperature conditions even with a small amount of Rh supported, and a reformed gas having a high H ₂ concentration is generated. be able to.

In the fuel reforming catalyst of the present invention, oxides of lanthanum (La) and cerium (Ce) are dispersed and supported on the surface of the catalyst in which the LaAlO ₃ phase is formed on the surface of Al ₂ O ₃ particles. Thus, by supporting Rh thereon, the low temperature activity can be further enhanced.
At this time, the _Al 2 _{O 3} particles made by forming a LaAlO ₃ phase on its surface, it is preferable secondary particle diameter thereof is 0.8～3.8Myuemu.

FIG. 1 is a schematic diagram showing the form of the fuel reforming catalyst of the present invention, which is considered to have a structure in which LaAlO ₃ is formed in the outer shell with Al ₂ O ₃ particles as nuclei.
FIG. 2 is an X-ray diffraction pattern of the fuel reforming catalyst according to Example 2 of the present invention, which will be described later. In this diffraction pattern, no La ₂ O ₃ peak is detected, and the LaAlO ₃ relatively A broad peak is detected, and it is considered that aluminate is formed on the outer surface of the Al ₂ O ₃ particles.

In this case, it is desirable to coat the surface of the Al ₂ O ₃ particles with LaAlO ₃ , and when the Al ₂ O ₃ surface remains on the surface, it acts as an active site that causes a side reaction due to the acid point, thereby decomposing the fuel. There is a tendency that the production of coke is promoted and catalyst deterioration is promoted.

Further, by supporting La oxide and further Ce oxide, not only the influence of Al ₂ O ₃ can be suppressed, but also the effects of La and Ce can be added, so that further effects can be obtained. It will be.
Moreover, the Al ₂ O ₃ particles preferably have a relatively large particle diameter and few micropores. When there are many pores, the catalyst component Rh is also supported inside, resulting in a decrease in the effective utilization rate of Rh and a longer residence time of the fuel component that has entered the pores, resulting in side reactions. It becomes easy to occur together. From such a viewpoint, in the present invention, it is effective that the secondary particle diameter of the Al ₂ O ₃ particles is 0.8 to 3.8 μm as described above.

As described above, the amount of La added to coat the outer shell with the LaAlO ₃ phase with the Al ₂ O ₃ particles as the core is the surface area of the Al ₂ O ₃ particles as the starting material and the LaAlO ₃ covering the surface. It is largely determined by the thickness of the phase. When the Al ₂ O ₃ particle size is small, the total surface area becomes large, so it is necessary to increase the La addition amount. On the contrary, when the Al ₂ O ₃ particle diameter is large, the total surface area becomes small, so that the Al ₂ O ₃ particles can be covered with a smaller La addition amount.

On the other hand, when La is excessively added to the particle surface, the loaded state of Rh is adversely affected.
The effective La addition amount is 5 to 15% as lanthanum oxide (La ₂ O ₃ ) with respect to Al ₂ O ₃ . As a result, the Al ₂ O ₃ particle surface can be effectively coated with LaAlO ₃ , and even if excess La is generated, it is dispersed on the catalyst surface as lanthanum oxide (La ₂ O ₃ ) having a relatively small particle size. The state is thought to be preserved.

Further, it is considered that the addition of Ce can effectively supplement the action of La (particularly, the action as La ₂ O ₃ ). The effective amount of Ce added is 0.1 to 30% as cerium oxide (CeO ₂ ) with respect to Al ₂ O ₃ .

In producing the LaAlO ₃ phase / Al ₂ O ₃ oxide support particles as described above, it is preferable to use an aluminum oxide powder having a primary particle diameter of 0.2 to 1 μm as a starting material of Al ₂ O _3. .
In the present invention, by using particles having a relatively large diameter as a starting material of Al ₂ O ₃ , La components added later can be effectively arranged on the particle surface without forming excessive pores. By forming the LaAlO ₃ phase, a surface effective for activation of H ₂ O and CO ₂ can be exposed.

As aluminum oxide, various alumina raw materials such as boehmite alumina, γ-alumina, θ-alumina, and δ-alumina can be used. However, the surface condition of the alumina raw material varies depending on the type. That is, since the reactivity between the La component and the alumina surface changes, it is necessary to adjust the La raw material addition conditions, the firing temperature conditions, and the like in forming the LaAlO ₃ phase.
For example, when boehmite alumina is used, since the surface contains many OH groups and many pores, it is also effective to crush the pores to some extent by preliminary firing. In this case, since the surface reactivity is relatively high, the LaAlO ₃ formation temperature can be made relatively low. On the other hand, when θ-alumina is used as a starting material, since there are few pores and the particle surface has a relatively low reactivity, the alumina surface is activated using a La aqueous solution having a relatively low pH, and the firing temperature is further increased. It is necessary to promote the production of LaAlO ₃ .

Such Al ₂ O ₃ particles are immersed in an aqueous solution of La nitrate, carbonate, acetate or the like, dried, and then fired at about 700 to 800 ° C., whereby La ₂ dispersed on the surface of the Al ₂ O ₃ particles. The component is reacted with Al on the particle surface to form a LaAlO ₃ phase. At this time, the dissolved state of the Al ₂ O ₃ particle surface changes depending on the pH condition of the La salt aqueous solution to be used, which also affects the formation of the LaAlO ₃ phase.

Further, when additionally supporting La and Ce oxides, similarly, LaAlO ₃ phase / Al ₂ O ₃ oxide support particles are immersed in a mixed aqueous solution of La and Ce nitrates, carbonates, acetates and the like. Then, La oxide and Ce oxide are dispersed and supported on the particle surface through a drying and firing process.
In this case, after immersing the LaAlO ₃ phase / Al ₂ O ₃ oxide support particles, a coprecipitation method in which a basic precipitation agent such as ammonia, urea, ammonium hydrogen carbonate or the like is added to form a precipitate, or a uniform precipitation method, May also be a sol-gel method starting from a metal alkoxide.

A fuel reforming system incorporating such a fuel reforming catalyst can efficiently generate reformed gas containing H ₂ by utilizing combustion exhaust gas from an internal combustion engine and its heat on the vehicle.
Specifically, as shown in FIG. 3, a fuel reforming reaction apparatus incorporating a fuel reforming catalyst is installed in a system in which an EGR device is placed, and further in this system, together with a fuel injection device, By the system equipped with an air (secondary air) supply device, the action of the catalyst can be maximized.

In this case, in particular, the fuel reforming reaction apparatus can be operated more effectively by adding oxygen (O ₂ ) to the exhaust gas and setting its concentration to 1.2 vol% or less. By controlling the oxygen amount as the O ₂ / C molar ratio based on the C1 equivalent amount of the fuel, the oxygen addition effect can be surely exhibited.
The effective O ₂ / C molar ratio is 0.01 to 0.27, and the range of the O ₂ / C molar ratio that is more effective is 0.15 to 0.20. By controlling the exhaust gas, fuel, and air supply amounts to the fuel reforming reactor, the O ₂ / C molar ratio can be controlled within the optimum range.

When the technology of the present invention is applied to an automobile equipped with an internal combustion engine, when the operating condition of the internal combustion engine is from the rich to the stoichiometric (14.6) condition at the air / fuel mass ratio (A / F), the fuel modification is performed. The quality reactor can be operated effectively.
The reaction in the fuel reforming of the present invention is basically a steam reforming reaction, and CO ₂ reforming can occur under a high temperature condition of 550 ° C. or higher, but once under a lean condition where a large amount of oxygen exists, H 2 _{Even if 2} is generated, it is immediately oxidized by oxygen, so that it is effective to apply stoichiometric or rich.

On the other hand, the addition of slightly oxygen as described above, it is possible to promote and H ₂ generated by controlling the A / F slightly lean side within the range not adversely affect the performance of the exhaust gas purifying catalyst, It is also possible to increase the amount of oxygen.
At this time, the required amount of oxygen can be optimized by controlling the amount of secondary air with respect to the amount of fuel supplied by detecting the amount of oxygen in the exhaust with an oxygen sensor installed in the EGR system. it can.

On the other hand, the amount of H ₂ O is governed by the required EGR amount in the mode. The amount of H ₂ required is determined from the EGR amount, and the reformed fuel supply amount is determined relative thereto. The amount of H ₂ O that can be secured at this time is determined from the operating conditions.
If the operating condition of the internal combustion engine is stoichiometric, it is considered that the amount of H ₂ O necessary for promoting the steam reforming reaction is almost ensured. By controlling the exhaust gas and fuel to the fuel reforming reactor, the H ₂ O / C molar ratio is controlled to be more than 1.5 and 4.3 or less with reference to C1 of the fuel. H ₂ can promote the formation.

By securing more H ₂ O than the equivalent amount, it is possible to reliably obtain the effect of improving fuel consumption. Furthermore, by making it possible to introduce secondary air and controlling the amount thereof with high response, it becomes possible to respond to exhaust conditions that change rapidly with high response.
Of course, in order to improve the responsiveness to exhaust conditions with such large fluctuations, it is necessary to always expose the catalyst to appropriate conditions, and the amount of fuel supplied to the catalytic reactor depends on the amount of exhaust, moisture, and oxygen. Control can provide a significant fuel efficiency improvement effect.

The amount of Rh supported in the fuel reforming catalyst is preferably a low amount supported in terms of cost. The amount of Rh supported in the catalyst of the present invention is desirably 0.1% or more and less than 2%.
When the amount of Rh supported is increased, the reforming performance is improved according to the amount of Rh supported, and in particular, although the durability performance is improved, the performance improvement allowance corresponding to the increased amount of the supported amount cannot be obtained. When the amount of Rh supported exceeds 2%, a side reaction is induced and coking becomes remarkable, which may cause a decrease in performance. As initial performance, sufficient performance is obtained even at 0.1%, but 0.4 to 1.2% is a preferable range in consideration of durability.

As a form of the fuel reforming catalyst of the present invention, a catalyst powder having a structure of Rh / CeO ₂ —La ₂ O ₃ / LaAlO ₃ —Al ₂ O ₃ is used as a honeycomb or foam monolith made of ceramic or metal. Those coated on a carrier are preferred.
In addition, an “offset honeycomb” in which offset fins are provided inside the cells of the honeycomb-shaped carrier is extremely effective in increasing the effective utilization rate of the reforming catalyst. The number of cells or the number of pores of such a monolith carrier is preferably about 400 to 900 cells per square inch.

The amount of the reforming catalyst applied to the monolith carrier is preferably about 50 to 200 g / L, although it depends on the material of the monolith.
In the case of a metal carrier having no pores, the catalyst particles can be effectively used even with a relatively small amount of catalyst applied, but the adhesion of the catalyst particles to the surface of the monolith carrier becomes a problem.

  On the other hand, in the case of a ceramic carrier such as cordierite having pores, a relatively large amount of catalyst is required for the catalyst particles to enter and bury the pores on the surface of the monolith carrier, but the catalyst particles are attached to the surface of the monolith carrier. The wearing power is relatively strong. However, if the amount of catalyst applied is too large, fuel molecules will hardly reach the inner particles, resulting in waste. If the coating amount exceeds 200 g / L in particular, the ratio of the catalyst layer in which the reactive fuel molecules cannot reach the catalyst layer coated on the inside cannot be ignored, and the pressure loss increases, which is not preferable.

The fuel reforming catalyst of the present invention is combined with a device that generates heat and exhaust gas such as an internal combustion engine, a combustor, or a fuel cell mounted on an automobile, and uses the heat of the exhaust gas on the automobile to generate H. ₂ can be used in a fuel reforming system that generates reformed gas containing ₂ and its performance can be utilized to the maximum in such usage.
In this case, it is effective to use a catalytic reactor equipped with a monolithic fuel reforming catalyst in a system of an EGR device and further equipped with an air supply device for supplying secondary air into the system. is there.

  Particularly effective when the device for generating heat and exhaust gas mounted on the automobile is an internal combustion engine, and the ratio of air / fuel mass (A / F) in the operating condition of the internal combustion engine is rich to stoichiometric. Used for.

Since slight oxygen addition promotes H ₂ production, the amount of oxygen is controlled before the reforming catalyst in the EGR system. One specific method is a method of operating the EGR device and the intake air variable device based on predictive control (see Japanese Patent No. 3918402).

  EXAMPLES Hereinafter, although this invention is clarified more concretely based on an Example and a comparative example, this invention is not limited to these Examples.

[Manufacture of fuel reforming catalyst]
<Examples 1-5>
Into an aqueous solution of lanthanum nitrate (La (NO ₃ ) ₃ ) having five kinds of concentrations, γ-alumina having an average primary particle size of 0.6 μm was added, stirred while heating, and water was gradually removed. . The obtained powder was further dried at 120 ° C. all day and night to remove excess water, and the lump was pulverized into a powder. Subsequently, the powder was baked at 800 ° C. for 2 hours in the air using an electric furnace to obtain LaAlO ₃ / Al ₂ O ₃ powder in which LaAlO ₃ was formed on the surface of alumina particles.

The obtained powder was pulverized by a kneader and powders (1) to (5) having average secondary particle diameters of 1.2, 1.5, 1.8, 2.4 and 2.8 μm, respectively. Obtained. The addition amount of La as _La 2 _{O 3,} were, respectively 4,9,13,16 and 21%.
Next, five kinds of LaAlO ₃ / Al ₂ O ₃ powder particles having different secondary particle diameters and LaAlO ₃ addition amounts are added to diluted aqueous solution of rhodium nitrate (Rh (NO ₃ ) ₃ ) and stirred while heating. Thus, moisture was gradually removed to obtain a dry powder. These powders were overnight drying at each 120 ° C., it was further remove water and calcined 2 hours at 500 ° C., Rh support amount in 1%, LaAlO ₃ content five different Rh / LaAlO ₃ / Al ₂ O ₃ catalyst powder (Examples 1 to 5) was obtained.

<Examples 6 to 8>
A 9% LaAlO ₃ / Al ₂ O ₃ powder (2) obtained by the above process with a secondary particle size of 1.5 μm and an La addition amount of La ₂ O ₃ of ₃ % lanthanum acetate (La The mixture was poured into a mixed aqueous solution of (CH ₃ COO) ₃ ) and cerium acetate (Ce (CH ₃ COO) ₃ ), stirred while heating, and water was gradually removed. The obtained powder was further dried at 120 ° C. for a whole day and night to remove excess water to form a powder.

Next, it was calcined in the atmosphere at 600 ° C. for 2 hours using an electric furnace, and similarly pulverized with a kneader, so that three kinds of average secondary particle diameters of 1.6, 2.1 and 3.2 μm were obtained. la ₂ was obtained _{O 3 -CeO 2 / LaAlO 3 /} Al 2 O 3 powder.
Regarding the amount of La ₂ O ₃ —CeO ₂ supported, 0.1% CeO ₂ −1% La ₂ O ₃ , 9% CeO ₂ −1% La ₂ O ₃ , and 30% CeO ₂ −1% La, respectively. ₂ O ₃ .

Then, by repeating the same operation as in Example 1-5, the three types of _{La 2 O 3 -CeO 2 / LaAlO} 3 / Al 2 O 3 powder 1% of Rh is carried on the Rh / _La 2 O _{3 -CeO 2 / LaAlO 3 / Al} 2 O 3 catalyst powder (example 6-8) was obtained.

<Comparative example 1>
Rh / γ-Al ₂ O ₃ catalyst powder in which 1% of Rh is supported on the surface of alumina particles by directly supporting Rh without forming LaAlO ₃ on the γ-alumina particles used in the above examples ( Comparative Example 1) was obtained.

[Catalyst performance test]
Using the fuel reforming reaction apparatus shown in FIG. 4, the catalytic performance of the fuel reforming catalysts obtained by the above examples and comparative examples was evaluated.
Here, a steam reforming reaction was performed using 2-, 2-, 4-trimethylpentane (commonly known as isooctane) as a gasoline simulated fuel.

In the reaction characteristic test, the test catalyst was sized to a size of 355 to 500 μm, and 100 mg was weighed and packed in a quartz reaction tube (outer diameter 6 mm, inner diameter 4 mm) as shown in FIG. At this time, a thermocouple is inserted into the catalyst layer so that the catalyst temperature can be measured.
In the performance evaluation, nitrogen (N ₂ ) was used as a carrier gas at a flow rate of 70 ml / min, carbon dioxide (CO ₂ ) at 40 ml / min, and isooctane at a flow rate of 0.035 ml / min. Water and O ₂ were supplied depending on the O ₂ / C molar ratio and the H ₂ O / C molar ratio.

[Catalyst performance test results]
FIG. 5 shows the catalyst of Comparative Example 1 in which Rh is directly supported on Al ₂ O ₃ without forming LaAlO ₃ in terms of hydrogen generation ability at each temperature of the fuel reforming catalysts obtained in Examples 1 to 5. It is shown in comparison with.
As is clear from this figure, the fuel reforming catalyst according to the embodiment of the present invention in which LaAlO ₃ is formed on the surface of Al ₂ O ₃ particles has high low-temperature activity and performs steam reforming reaction even at 450 ° C. since it promoted, it can be seen that can generate high concentration of H ₂ reformed gas. In particular, it was confirmed that the H ₂ concentration in the reformed gas was high when the amount of La added as La ₂ O ₃ was 5 to 15%.

Further, as a result of analyzing components other than H ₂ in the reformed gas, the catalyst according to the example produced less CH ₄ than the comparative example catalyst, and the amount of carbon deposited after the reaction was also reduced. This is because the formation of CH ₄ is suppressed by coating the surface of the Al ₂ O ₃ particles with the LaAlO ₃ phase, and the influence of coking is small because the acid sites are crushed by introducing La. It is done.
Since the material of the present invention is based on alumina, it has high heat resistance and can exhibit performance stably over a long period of time. In fact, after the continuous reaction at 620 ° C. where coking is likely to occur for about 50 hours, the amount of carbon produced in the catalyst was quantified, and it was confirmed that the amount of C decreased as the amount of La introduced into Al ₂ O ₃ increased. doing.

FIG. 6 shows the effect of additional loading of La ₂ O ₃ (1%) and CeO ₂ (0.1%, 9%, 30%), where the addition of these oxides is responsible for the formation of H ₂ . It is effective for promotion. This is considered because the activation of H ₂ O is strengthened. As is apparent from the figure, the H ₂ generation ability is enhanced when the amount of CeO ₂ added is increased, but the effect is saturated when it exceeds 30%.

FIG. 7 shows the effect when oxygen is added to the gas using the fuel reforming catalyst according to Example 2, and shows the H ₂ concentration in the reformed gas with respect to the O ₂ / C molar ratio. It is a thing.
It was confirmed that the low-temperature activity was increased by adding a small amount of O ₂ and the H ₂ concentration could be increased. The addition of O ₂ to exhibit the effect of increasing the concentration of _{H 2} in trace _{amounts, O} 2 / C molar ratio decreases sharply concentration of _{H 2} exceeds 0.27. This is because the generated H ₂ is combusted and consumed by excess O ₂ . After all, it can be said that the range of the effective O ₂ / C molar ratio is 0.01 to 0.27.

FIG. 8 shows the reformed gas H ₂ concentration with respect to the H ₂ O / C molar ratio when the fuel reforming catalyst according to Example 2 is used.
According to the figure, it can be seen that the reforming performance is drastically reduced when the H ₂ O / C molar ratio is less than 1.5. H 2 _{O /} C as the molar ratio ratio is high but reforming performance is improved, H ₂ concentration exceeds a H 2 _{O /} C molar ratio is 4.0 is not a rise commensurate therewith. This is because the space velocity increases and the residence time of the reaction components on the catalyst surface decreases.

The actual fuel reforming system, H 2 _O exploits of H _{2 O} containing exhaust gas. Since the exhaust also contains N ₂ , CO _{2 and the} like, it is necessary to significantly increase the exhaust gas circulation rate in order to increase the H ₂ O / C molar ratio. As a result, the space velocity condition of the catalyst becomes severe and the catalyst performance is deteriorated. Considering the space velocity condition, 3.0 to 4.0 is a preferable range as a more preferable H ₂ O / C molar ratio.

As described above, the fuel reforming catalyst of the present invention uses Rh as a catalyst component, and a LaAlO ₃ phase is formed on the surface of Al ₂ O ₃ particles having a relatively large particle diameter. Rh is supported.
By using such a fuel reforming catalyst, the acid sites on the surface of Al ₂ O ₃ can be crushed, decomposition of fuel components, CH ₄ generation and coking can be suppressed, and H ₂ O can be activated effectively. Thereby, even with a small amount of Rh supported, the reforming reaction can be efficiently promoted even under low temperature conditions, and a reformed gas having a high H ₂ concentration can be generated. Furthermore, La ₂ O ₃ and CeO ₂ are additionally supported and dispersed on the surface, whereby the activation of H ₂ O is enhanced and the low temperature activity is enhanced.

In the fuel reforming system and the reforming method, the fuel reforming reaction apparatus is incorporated into the EGR piping system, thereby facilitating exhaust heat and substance supply to the fuel catalyst catalyst and generating H ₂ generated by the reaction in the internal combustion engine. Because it can be directly supplied to the intake air, a great fuel efficiency improvement effect can be obtained. Furthermore, it is equipped with an air supply device that can introduce secondary air and control the amount thereof with high response, detects the catalyst temperature, and depending on the temperature, an O ₂ / C molar ratio or H ₂ O / C By controlling the molar ratio, exhaust conditions that fluctuate rapidly can be dealt with with a high response, so that H ₂ can be generated effectively and a great fuel efficiency improvement effect can be obtained.
Furthermore, by controlling the O ₂ / C molar ratio and the H ₂ O / C molar ratio finely according to the catalyst temperature, an excessive load on the catalyst is suppressed, so that the life of the catalyst can be extended. It can also contribute to savings.

Claims (11)

A fuel reforming catalyst used in a fuel reforming system that generates reformed gas containing hydrogen,
A fuel reforming catalyst comprising rhodium as a catalyst component, lanthanum aluminate formed on the surface of aluminum oxide particles, and the rhodium supported on the surface of the lanthanum aluminate.   The fuel reforming catalyst according to claim 1, wherein oxides of lanthanum and cerium are dispersed on the surface of the lanthanum aluminate, and rhodium is supported on the surface.   The fuel reforming catalyst according to claim 1 or 2, wherein the secondary particle diameter of the aluminum oxide particles having lanthanum aluminate formed on the surface is 0.8 to 3.8 µm.   The fuel reforming catalyst according to any one of claims 1 to 3, wherein lanthanum is contained in an amount of 5 to 15% by mass with respect to aluminum oxide as lanthanum oxide.   The fuel reforming catalyst according to any one of claims 2 to 4, wherein 0.1 to 30% by mass of cerium is contained as cerium oxide with respect to aluminum oxide.   In producing the fuel reforming catalyst according to any one of claims 1 to 5, an aluminum oxide powder having a primary particle diameter of 0.2 to 1 µm is used as a starting material for aluminum oxide. A method for producing a fuel reforming catalyst. In a fuel reforming system that generates reformed gas containing hydrogen using exhaust gas and heat from an onboard internal combustion engine,
A fuel reforming reaction apparatus including the fuel reforming catalyst according to any one of claims 1 to 5, a fuel injection device, and an air supply device are installed in a system of an exhaust gas circulation device. A featured fuel reforming system. A fuel reforming method using the fuel reforming system according to claim 7,
A fuel reforming method, wherein the fuel reforming reaction device is operated under a condition that an oxygen concentration contained in exhaust gas discharged from the internal combustion engine is 1.2% by volume or less. The exhaust gas, fuel, and air supply amounts to the fuel reforming reactor are controlled so that the molar ratio of oxygen to carbon in the fuel (O ₂ / C) is 0.01 to 0.27. The fuel reforming method according to claim 8.   The fuel reforming method according to claim 8 or 9, wherein the fuel reforming reaction device is operated under a condition where the operation state of the internal combustion engine is rich to stoichiometric. Control the amount of exhaust gas, fuel and air supplied to the fuel reforming reactor so that the molar ratio of water to carbon in fuel (H ₂ O / C) exceeds 1.5 and is 4.3 or less. The fuel reforming method according to any one of claims 8 to 10, wherein:

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