JPS6279847A - Catalyst system for combustion of lower hydrocarbon fuel and combustion method using said system - Google Patents

Abstract

PURPOSE:To obtain a fuel combustion system having excellent efficiency by incorporating palladium, platinum and nickel oxide into the front stage from an inlet side, palladium and nickel oxide into the middle stage and platinum or platinum and palladium into the rear stage. CONSTITUTION:The front-stage catalyst layer contg. the active component consisting of the palladium, platinum and nickel oxide is provided to the gas inlet side of the system for pollution-free combustion of lower hydrocarbon fuel of 1-4C such as methane or ethane and the rear-stage catalyst layer contg. the active component consisting of the platinum or platinum and palladium is provided to the outlet side. The middle-stage catalyst layer packed with the palladium and nickel oxide is provided therebetween. This catalyst makes the contact combustion of the lower hydrocarbon fuel, more particularly, natural gas essentially consisting of hardly flammable methane to form the combustion gas contg. no harmful components. The quantity of the heat thereof is used as an energy source.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a combustion catalyst system for lower hydrocarbon fuel and a combustion method using the same. To be more specific, carbon atoms such as methane, ethane, propane, butane, etc.
~4 lower hydrocarbon fuels, especially flame-retardant methane or natural gas containing methane as a main component, are catalytically burned to produce nitrogen oxides (hereinafter referred to as NOx), -carbon oxides (
A catalyst system that obtains combustion gas that does not substantially contain harmful components such as CO (hereinafter referred to as CO), unburned hydrocarbon hydrocarbon (hereinafter referred to as UHC), etc., and uses its calorific value as various energy sources. This article is about the combustion method using 15 methods.

<Conventional technology> A catalytic combustion system in which a thin mixture of fuel and air at a low temperature below the combustible range is introduced into a catalyst layer and catalytically combusted with catalyst F to obtain high-temperature combustion gas. is publicly known.

Furthermore, using such a catalytic combustion system, e.g.
When obtaining combustion gas between 00°C and 1500°C, for example, even if air is used as a source, little or no NOx will be generated, and it will not contain substantially any CO. It is also well known that

Is this clean? Various systems have been proposed to generate heat or power using S-temperature combustion gas, and have been put into practical use in general industrial exhaust gas treatment and thermal power recovery systems.

In addition, in recent years, due to increasing NOx and compliance with regulations,
Research is being conducted to utilize this high-temperature combustion gas as a primary power source for power generation gas turbines and the like.

When used for these purposes, the combustion gas is normally heated to a high temperature of 1000 to 1300'C under 6 to 15 atmospheres, and even higher temperatures and pressures are required to improve the efficiency of gas turbines. There is a tendency to

Under such conditions, if a catalyst is used, what is a normal catalyst? :1
The temperature causes rapid deterioration, and in the worst case scenario, the catalyst carrier may melt down and fly off, potentially damaging turbine blades and other parts.

As a combustion method that avoids the deterioration and loss of the catalyst as described above and achieves the same purpose, the fuel is combusted with J5 in the catalyst layer.
The gas temperature is raised to a temperature that induces secondary combustion, and then the remaining unburned fuel is subjected to secondary combustion behind the catalyst layer, or if necessary, secondary fuel is introduced to fuel the remaining unburned fuel. A combustion method has been discovered in which the newly added secondary free material is secondarily combusted to produce clean combustion gas at or above the target temperature.

In this case, the purpose of combustion in the catalyst layer is to tear the gas temperature up to a temperature that induces secondary combustion, and it is not necessarily necessary to avoid complete combustion in the catalyst layer. ! If the gas temperature reaches above 6, it is necessary to raise the temperature in the catalyst layer to avoid deterioration of the catalyst and I0 damage, and also to maintain stable secondary combustion. In fact, it is preferable to have a large amount of remaining unburned fuel.

For the fuel, all the R that can change the target temperature may be introduced into the catalyst layer, a part of it is burned to warm the stomach, and the remaining unburned fuel is then secondaryly combusted. This may be introduced from the catalyst layer 1 as a secondary fuel and combined with the remaining unburned fuel for secondary combustion. In this case, it is possible to avoid making the catalyst layer temperature higher than necessary, and deterioration of,
It is more preferable because it can prevent damage.

The temperature required to induce secondary combustion here is determined by the type of fuel, residual fuel concentration (theoretical adiabatic combustion gas temperature), linear velocity, etc., and varies widely depending on the type of fuel.

In other words, in the case of easily flammable fuels such as propane and monomer oil, a temperature of about 700'C is sufficient under normal usage conditions, but for flammable methane or natural gas whose main component is methane, When using it as fuel, a high temperature of 750 to 1000°C is required, although it varies depending on the conditions of use.

<Object of the Invention> Accordingly, an object of the present invention is to provide a novel catalyst system for combustion of lower hydrocarbon fuels.

Another object of the present invention is to catalytically burn a lower hydrogen fuel, particularly flame-retardant methane or natural gas containing methane as a main component, to obtain a combustion gas that does not substantially contain harmful components, and to eliminate various The object of the present invention is to provide a catalyst system for use as an energy source and a combustion method using the same.

A further object of the present invention is to ignite methane, which is said to be relatively flame-retardant among hydrocarbons, or a natural gas fuel containing methane as a main component at low temperature using a catalyst at a high linear velocity and from normal pressure to high pressure. , heat the stomach to a temperature sufficient to induce secondary combustion, then introduce secondary fuel as necessary to burn the remaining unburned fuel and secondary fuel to reach the target temperature or lower. 11. Catalyst systems suitable for use in combustion systems that reach high temperatures above and combustion methods using the same. It is about providing.

Another object of the present invention is to ignite flame-retardant fuel, mainly methane, at a high linear velocity and under pressure at as low a temperature as possible, and to heat the combustion gas to a temperature of 750 to 1000°C; Another object of the present invention is to provide a catalyst system having low pressure loss and durability, and a combustion method using the same.

<Means of the Invention> These various methods contain an active component consisting of palladium, platinum and nickel oxide on the gas inlet side for a flow of a flammable mixed gas containing lower hydrocarbons and molecular oxygen. A front catalyst layer is filled with a catalyst consisting of a catalyst, and a catalyst containing one type of catalyst selected from the group consisting of an active component consisting of platinum and an active component consisting of platinum and palladium is filled on the outlet side. and a middle catalyst layer filled with a catalyst containing an active component of palladium and nickel oxide between the first stage d5 and the second stage catalyst layer. the catalytic system, further supplying the combustible gas mixture to the catalyst system, and causing at least a portion of the lower hydrocarbons in the gas mixture to catalytically burn in the catalyst system to induce secondary combustion; This is achieved by providing a method of combustion of lower hydrocarbon fuels which comprises drying the combustion gas to a temperature at which

The catalyst system according to the present invention has a catalyst essentially divided into three layers: a catalyst that can be ignited at a relatively low temperature and is used in the front and middle layers, and a catalyst that can be used in the rear layer to raise the combustion gas temperature to 750 to 100°C. The catalyst used in the first layer consists of palladium, platinum, and nickel oxide as active components, and the active component of the catalyst used in the middle layer The catalyst used in the latter layer is a catalyst system consisting of platinum or platinum and palladium as active components, and the combustion method is such that the combustion temperature in the catalyst layer is 1.
It is constructed in such a way that the temperature does not exceed 000°C.

Catalysts containing palladium as the main active component are known to have particularly excellent low-temperature ignitability of methane and excellent heat resistance at high temperatures of about 1000°C.

However, when a conventional catalyst containing palladium as an active ingredient is used for the purpose of the present invention, the palladium is oxidized and loses its methane ignition performance because it is exposed to high concentrations of oxygen at temperatures below 500°C near the entrance of the catalyst layer. On the other hand, in the high-temperature region near the outlet of the catalyst layer, the combustion reaction by the catalyst is suppressed, presumably due to a change in the oxidation state of palladium, and the combustion gas temperature is substantially lower than 75%.
It has the disadvantage that it cannot rise to a high temperature above 0'C.

In contrast, according to the present invention, by avoiding the coexistence of raw platinum in the front stage catalyst near the catalyst system entrance 1, the low I; Furthermore, since the middle-stage catalyst can be used effectively, the combustion gas temperature can be stabilized at high linear speeds and under pressure, reaching r600-750.
It was also found that the presence of platinum in the downstream catalyst near the outlet of the catalyst layer further promoted combustion, allowing the combustion gas to reach a temperature of 750 to 1000°C. It was issued.

As a result, it has become possible to ignite methane or a natural gas fuel containing methane as a main component at high linear velocity, under pressure, and at low temperatures to raise the combustion gas to a temperature of 750 to 1000 degrees Celsius while the catalyst layer is inactive. Moreover, it has become possible to maintain this performance for a long time.

In the present invention, it is preferable to coexist nickel oxide in the catalyst of the front stage catalyst layer. In this case, the presence of nickel particularly improves the low-temperature ignition performance of methane, which is a flame-retardant fuel, and the nickel acts as an oxide. Because oxygen is stably supplied to palladium, the combustion gas temperature can be kept at 650~650℃ even under high linear velocity r fill pressure.
It can be heated up to 900℃.

It is also preferable that palladium be present as an active component in the catalyst of the latter catalyst layer. In this case, combustion is further promoted by the presence of palladium, and 100'
In the case of 1 damage to C, platinum is oxidized and becomes PtO21.
It has been discovered that this can prevent sublimation.

In the present invention, a three-stage system is provided in which a middle catalyst layer made of a catalyst containing palladium and nickel oxide as active components is provided between the above-mentioned front catalyst layer and rear catalyst layer. It has been found that this provides a combustion catalyst system with excellent activity. In particular, the first half of the catalyst system has a two-stage structure, and the first half is made of palladium.
By using a catalyst layer containing platinum-nickel oxide as the active component and a catalyst layer containing palladium-nickel oxide as the active component in the second half, the first half catalyst system can be used even under high linear velocity and high pressure conditions. Improvement in combustion activity was observed as
This made it possible to smoothly perform the combustion function of the downstream catalyst containing platinum or platinum-palladium as the active ingredient.

In this case, if J3 is in the first half of the first half catalyst system, 500
The temperature rises to a temperature in the range of ~800'C, and the temperature in the second half (middle catalyst layer) of the first half catalyst system is 650-900'C.
℃ range, and in the downstream catalyst layer 750-1
By respectively raising the temperature to a range of 0.000°C, the combustion activity is maintained at a high level.

This catalyst system is characterized by a three-stage structure that takes advantage of the characteristics of each negative metal or combines them. In other words, with this catalyst system, 4J 300-40
It ignites at a low temperature of 0℃, has a combustion activity to achieve a combustion gas temperature of 750 to 1000"C, and has a combustion activity of 1000"C.
It is necessary to ensure heat resistance above ℃.

However, as described above, palladium alone does not lose its ignition performance as the combustion progresses, and due to its characteristics, the combustion gas temperature does not substantially rise to a high temperature of 750° C. or higher. Even a palladium-nickel oxide catalyst loses its ignition performance in the same way as palladium alone. In addition, if the combustion is methane or NG with platinum alone, the combustion rate is 300 to 400.
Although it is impossible to ignite at temperatures above 500°C and requires an ignition temperature of 500°C or above, it has excellent combustion activity, especially under high linear velocity and pressurized combustion conditions. . In addition, although palladium-platinum-nickel oxide or palladium-platinum catalysts have sufficient ignition performance, it is necessary to raise the combustion gas temperature above the temperature at which secondary combustion is induced under high linear velocity and pressurized combustion conditions. It is not possible.

As described above, each of the one-stage configurations has drawbacks and cannot be used as a practical catalyst, especially under pressurized combustion conditions, and is not preferred.

In the present invention, one of the catalysts for the front stage decoy, the middle stage, and the rear stage may be prepared separately, and both catalysts may be directly connected or installed with a space between them, or the inlet portion of the integrated catalyst may be prepared separately. In addition, a completed catalyst may be obtained by supporting the first stage catalyst, the middle stage catalyst in the middle part, and the latter stage catalyst in the outlet part.

Although a pellet type catalyst can be used, a monolith type catalyst is preferable for the purpose of reducing pressure loss. Any monolith support commonly used in the field can be used, in particular cordierite, mullite, alpha-alumina, zirconia, titania, titanium phosphate, aluminum titanate, petalite, spodumene, aluminosilicate, silica. Heat-resistant ceramic materials such as magnesium acid, zirconia-spinel, zircon-mullite, silicon carbide, and silicon nitride, and metal materials such as kanthal and feclaroy are used.

The cell size of the monolithic carrier is preferably large as long as the combustion efficiency is not reduced; each catalyst layer may have the same cell size, or a combination of different cell sizes may be used. ~400t? Those from 1999 are used.

The total catalyst bed length varies depending on the inlet linear velocity used, but
A length of 50 to 500 m is usually adopted due to the need to reduce pressure loss, and the lengths of the front layer, middle layer, and rear layer are also optimally selected depending on usage conditions such as inlet linear velocity and inlet temperature.
Normally, each layer has a length of 20 to 250 m.

The catalyst used in the first layer is usually a monolithic carrier coated with an active refractory metal oxide such as alumina, silica-alumina, magnesia, titania, zirconia, or silica-magnesia, preferably alumina, titania, or zirconia. do. The coating amount of the oxide is 5 per finished catalyst.
-50% by weight, preferably 10-30% by weight. Alumina is particularly preferred, and alkaline earth metal oxides such as barium and strontium, lanthanum, cerium,
It is more preferable to add a rare earth metal oxide such as neodymium or praseodymium or silicon, preferably a rare earth metal oxide, for stabilization. The amount added is 2 to 20% by weight, preferably 5 to 15% by weight, based on the oxidized breast. The active components of palladium, platinum and nickel are then catalyzed by impregnation in the form of water-soluble or alcohol-soluble compounds. It can be catalyzed by coating it on a monolithic support.

Platinum, which is an active ingredient, can be supported together with an active refractory metal oxide as platinum black having an average particle size of 0.01 to 5 microns.

Examples of water-soluble salts include nitrates, sulfates, phosphates, halides, and dinitrodiamino salts. - Examples include palladium nitrate, palladium chloride, dinitrodiaminoplatinum, chloroplatinic acid, nickel nitrate, nickel chloride, etc., by impregnating a carrier with an aqueous solution of these and
1 at a temperature of ~1000°C, preferably 600-900°C
It can be obtained by baking for 24 hours, preferably 2 to 6 hours.

The carrier of the active component of the catalyst used in the first layer contains 0.5 to 15 weight % of palladium, preferably 2 to 10 weight % of palladium, and 0.1 to 10 weight % of platinum, preferably 0. .2 to 5% by weight, and nickel is preferably in the range of 0.1 to 20% by weight as Ni○, preferably 1 to 10% by weight, and platinum is in the range of ff1 to palladium.
The ratio to f2 is in the range of 0.01 to 1, preferably 0.1 to 0.6.

The catalyst forming the middle layer is also prepared in the same manner as above. And the first layer and the middle layer contain paranium nickel oxide as an active ingredient! l! l! Ffli
The ratio of palladium to nickel in 1 J is used in combination in the range of 0.001 to 20, preferably 0.1 to 5 in terms of Pd/NiO ratio.

Similarly, the catalyst used in the latter layer can be catalyzed by supporting platinum or platinum and palladium.

The amount of active component supported is 0.1 to 1 platinum per finished catalyst.
5% by weight, preferably 0.2-10% by weight, and if palladium is added, 0.1% by weight as palladium.
A range of from 15 to 15% by weight, preferably from 0.2 to 1071% by weight, is suitable, and in the case of catalysts containing palladium and platinum as active components, platinum is 0.01 to 20% by weight relative to palladium. ．． It is preferably in the range of 0.2 to 10.

When only platinum is used as the active ingredient, the catalyst becomes highly talkative and the temperature in the catalyst layer rises to a temperature exceeding 1000°C, causing deactivation phenomena such as Wt i+i of platinum1.
It has a tendency to oxidize. To avoid this, the catalyst layer temperature should be kept at 1000°C.
In order to maintain the following, it is particularly preferable to use coarse platinum particles such as platinum black, other methods to reduce the supported platinum, and to heat the finished catalyst at a high temperature exceeding 1000"C before use. Examples include a method of calcination, a method of optimally selecting the cellulose of the catalyst and the length of the catalyst.Furthermore, it is possible to prevent IF of platinum by coexisting palladium with platinum. At the same time, it is possible to control the combustion activity of platinum.

These are the conditions of use, i.e. fuel type, temperature (
It can be optimally selected depending on the theoretical adiabatic combustion gas temperature), linear velocity, pressurization conditions, etc. As for pressurization conditions, it is possible to use from normal pressure to 25 atmospheres, but preferably L;L
The pressure is 6 to 15 atmospheres. Regarding the fuel concentration, when the lower hydrocarbon fuel is methane, it depends on the temperature of the mixed gas introduced into the catalyst system, but it is 1.51 to 4.75%, preferably 2.37 to 4.31% by volume ω%. It is the primary fuel for -
If secondary fuel is further supplied to the combustion gas that has been heated to a temperature that induces secondary combustion by the secondary fuel, O~3
．． 24 volume ω%, preferably 0.44 to 2.38 volume ω%. Further, the linear velocity is 7 to 40 m/sec, preferably 10 to 30 m/sec. If the speed is less than 7 m/sec, a flashback phenomenon may occur, while if it exceeds 40 m/sec, excessive fuel blowout will occur, resulting in insufficient combustion.

The fuel used in the combustion system using the catalyst of the present invention is methane or a fuel containing methane as a main component. A typical example is natural gas. Natural gas contains over 80% methane, although the composition ratio varies slightly depending on the region of production.

Furthermore, fermented methane from activated silt treatment and low-calorie methane gas from coal gasification are also fuels that can be used in the present invention. Further, more easily flammable T-tane, propane, and butane can also be used, and light oil and the like can also be conveniently used.

The catalyst of the present invention or the combustion system using the catalyst is optimally incorporated into a gas turbine system for power generation as described above, but it is also suitable for use in power generation boilers, heat recovery boilers, and gas from gas engines. It is used to efficiently recover heat and power in post-processing and Koriyama gas heating applications.

The present invention will be explained in more detail below with reference to Examples, but the present invention is not limited to these Examples.

Example 1 25 mm diameter with 200 tons/in2 aperture.
A cordierite honeycomb carrier with a diameter of 4 mm and a thickness of 50 m is coated with alumina containing 5% lanthanum oxide.
After coating and drying a mixed slurry of nickel powder and nickel chloride, the finished catalyst is fired at 700°C in air.
19% by weight of lanthanum oxide-containing alumina and 6% by weight of nickel oxide were coated and supported.

Next, this was immersed in an aqueous solution containing palladium nitrate and dinitrodiaminoplatinum, dried, and heated to 900°C in air.
Calcinate at ℃ for 5 hours to obtain 4 palladium per finished catalyst.
．． A completed catalyst was obtained by supporting 0.81 m% of platinum with a width of ♀%.

Example 2 A finished catalyst was obtained in the same manner as in Example 1, by loading 6% by weight of nickel oxide, 1.2% by weight of palladium, and 0.3% by weight of platinum.

Example 3 A slurry of alumina powder containing 7% lanthanum oxide and 3% by weight neodymium chloride was placed on the same carrier as in Example 1. lli! The catalyst was covered and calcined at 800° C. in air to provide a coating of 30 ma% of alumina containing lanthanum oxide A3 and neodymium oxide per finished catalyst.

This carrier was then refined into an aqueous solution containing palladium nitrate and nickel nitrate, dried and then heated in air for 7 hours.
By calcining at 00°C for 5 hours, a finished catalyst was obtained in which 4.7 En m% of palladium and 13.3 small % of nickel oxide were supported per finished catalyst.

Example 4 25.4 diameter with 100 cells/inch square aperture
A 50InIn mullite honeycomb carrier was coated with a mixed slurry of alumina powder and nickel oxide containing 2% lanthanum oxide and 5% cerium oxide, and fired at 900°C in air. Alumina containing lanthanum oxide and cerium oxide was supported in an amount of 15% by weight, and nickel oxide was supported in an amount of 3.7% by weight and 61% per completed catalyst. Next, is this water containing palladium nitrate? A finished catalyst was obtained by immersing the catalyst in 8 liquid, drying, and calcining it in the air at 800°C for 4 cycles, so that 2.5% of palladium was supported on the finished catalyst.

Example 5 As in Example 3, 2.7% as palladium and 13% as nickel oxide per finished catalyst.
A completed catalyst was obtained by loading 3% by weight of u.

Example 6 In the same manner as in Example 1 except that nickel oxide was not included, 21,000% of lanthanum oxide-containing alumina was coated and supported.

Next, this was immersed in an aqueous solution containing chloroplatinic acid and treated in the same manner as in Example 1 to give 2.0% platinum per finished catalyst.
% by weight to prepare the finished catalyst.

Example 7 Diameter 25,4 with 200 cells/inch square aperture
m aluminum titanate honeycomb carrier with 8 weight percent
A slurry of alumina powder containing lanthanum oxide of By calcining and overlaying the finished catalyst as lanthanum oxide J3 and silicon dioxide-containing alumina powder as 18x and platinum as 2.2 iu
A finished catalyst was obtained by reducing the amount of supported U.

Example 8 A finished catalyst was obtained as in Run IPI 6, except that the platinum black support was 0.6% by weight.

Example 9 The same procedure as in Example 3 was carried out except that nickel oxidized was not included, and the finished catalyst was immersed in an aqueous solution containing palladium nitrate and chloroplatinic acid to give a catalyst containing 3.6% by weight of palladium and 1.8% of platinum. % for 1u! At least I got the finished catalyst.

Comparative Example 1 A finished catalyst was obtained in the same manner as in Example 3 except that it did not contain nickel.

Example 10 Using a sufficiently heat-insulated cylindrical combustor, from the upstream side, the catalyst obtained in Example 1 was placed in the front layer, the catalyst obtained in Example 3 was placed in the middle layer, and the catalyst obtained in Example 6 was placed in the rear layer. Fill the catalyst with
A methane-air mixture gas containing 3% by volume of methane was introduced into J5 at an inlet temperature of 350°C at 167 Nm per hour under a pressure of 10 atm to evaluate the combustion efficiency and catalyst bed outlet Wlff.
was measured.

In this case, the catalyst inlet linear velocity was about 30 m/sec.

As a result, the combustion efficiency was about 74%, and the catalyst layer outlet temperature was about 850°C.

Next, when methane at 88 degrees Celsius was adjusted to 4.1% by volume, the combustion efficiency became 100%, and a clean combustion gas containing substantially no UHC, CO, or NOX was obtained. in this case,
Touch II! I! Temperature at a point 100 mm behind the layer +1 approx. 13
The temperature at the outlet of the catalyst layer was approximately 900°C.
Met.

Subsequently, the same combustion experiment was conducted by introducing methane equivalent to 3 volume d% from upstream of the catalyst layer and the remaining methane equivalent to 1.1 volume % from the catalyst h1 outlet from the 30 mm ff2 side. .

As a result, the catalyst bed outlet temperature was about 895°C, and clean combustion gas of about 1300'C was obtained.

Moreover, this performance was maintained continuously for 1000 hours.

Example 11 In the same manner as in Example 10, using the catalyst shown in Table 1,
Methane equivalent to 38% was taken from upstream of the catalyst layer, and the remaining 1.1%
The methane corresponding to the volume ω% is removed from the catalyst layer outlet J: 30 mm.
Table 1 shows the results of combustion experiments carried out by introducing the catalyst from the te side, which show that if the catalyst system according to the present invention is used, the catalyst layer temperature can be maintained at 1000°C or less without causing a decrease in activity. Despite this, clean combustion gas of about 1300'C was obtained, whereas the catalyst system using the catalyst of Comparative Example 1 in the front stage rapidly became unable to ignite. In addition, in the catalyst system using the catalysts of Example 6 in the front stage, Example 3 in the middle stage, and Example 9 in the rear stage, ignition did not occur in the front stage catalyst, and some ignition occurred in the middle stage catalyst and the rear stage catalyst, but the outlet temperature was 670. ℃, and furthermore, in the catalyst system using the catalyst of Comparative Example 1 in the later stage, combustion did not occur in the later stage and the outlet temperature was 680°C, and secondary combustion was not induced behind the catalyst layer. .

Example 12 In the same manner as in Example 10, the first stage was filled with the catalyst obtained in Example 2, the middle stage was filled with the catalyst obtained in Example 5, and the second stage was filled with the catalyst obtained in Example 8, and the inlet temperature was 300°C. a3 and 1.
3% worth of propane from upstream of the catalyst layer, remaining 0.5%
A combustion experiment was conducted by introducing a corresponding amount of propane from 30M behind the catalyst bed outlet.

As a result, the catalyst layer outlet temperature was 960°C, and UHC,
A clean combustion gas of approximately 1300° C. containing substantially no CO,j> and NOx was obtained.

Moreover, this performance was maintained continuously for 1000 hours.

Claims (3)

[Claims] (1) A catalyst containing an active component made of palladium, platinum, and nickel oxide on the gas inlet side for a flow of a flammable mixed gas containing a lower hydrocarbon having 1 to 4 carbon atoms and molecular oxygen. A second stage catalyst layer is formed by filling the outlet side with a catalyst containing one selected from the group consisting of an active ingredient made of platinum and an active ingredient made of platinum and palladium. catalyst layer,
A catalyst for combustion of lower hydrocarbon fuel, characterized in that a middle catalyst layer filled with a catalyst containing an active component of palladium and nickel oxide is provided between the front and rear catalyst layers. system. (2) Each active ingredient is dispersed and supported on a monolithic carrier coated with at least one refractory oxide selected from the group consisting of alumina, silica-alumina, magnesia, titania, zirconia, and silica-magnesia. A catalyst system according to claim (1), characterized in that: (3) A catalyst containing an active component made of palladium, platinum, and nickel oxide on the gas inlet side for a flow of a flammable mixed gas containing a lower hydrocarbon having 1 to 4 carbon atoms and molecular oxygen. A second stage catalyst layer is formed by filling the outlet side with a catalyst containing one selected from the group consisting of an active ingredient made of platinum and an active ingredient made of platinum and palladium. catalyst layer,
and supplying the combustible mixed gas to a combustion catalyst system comprising a middle catalyst layer filled with a catalyst containing an active ingredient of palladium and nickel oxide between the front and rear catalyst layers. , a method of combustion of lower hydrocarbon fuel, characterized in that at least a part of the lower hydrocarbons in the mixed gas is catalytically combusted in the catalyst system to raise the temperature of the combustion gas to a temperature at which secondary combustion is induced. .