JPS6388041A - Oxidizing catalyst - Google Patents

Abstract

PURPOSE:To prevent the lowering in catalytic activity at an early stage, by laminating an intermetallic compound layer of a PdM or PdMO type wherein M is a rare earth metal and a catalytically active layer composed of Pd and PdO to a carrier composed of ceramics. CONSTITUTION:An activated Al2O3 layer 2 is formed to a monolithic structure 1 and a Pd-rare earth metal intermetallic compound layer 4 is provided on said layer 2 and a catalytically active component 2 composed of Pd, PdO or Pd/PdO is applied to the layer 4 to obtain an oxidizing catalyst. The amounts of the rare earth metal and O to Pd of the intermetallic compound layer 4 are pref. 0.1-10% and 0-5% by wt. of total Pd. The oxidizing catalyst obtained does not change from the state before use even when said catalyst is used in the catalytic combustion of methane at 1,100 deg.C for 100hr and the deterioration of the catalytic activity thereof is hardly noted. Further, the consumption of Pd or PdO being the active component is also hardly confirmed.

Description

[Detailed Description of the Invention] (Industrial Application Field) According to the catalytic combustion method, which uses the oxidizing action of a catalyst to burn fuel, the generation of nitrogen oxides (NOx), which are air pollutants, can be significantly suppressed. , and the resulting clean combustion gas can be used in a wide range of fields as a working thermal fluid for power generation and other purposes.

The present invention relates to an oxidation catalyst, particularly a catalyst for catalytic combustion of various fuels used at temperatures of 600 to 1500C.

(Prior art and its problems) In general, oxidation catalysts that completely oxidize hydrocarbons etc. into carbon dioxide gas and water in the presence of air or oxygen usually use structures such as alumina or ceramic structures such as mullite. The carrier is coated with alumina or the like, and these carriers are coated with platinum group metals such as Pt, oxides of these metals, mixtures of these metals and metal oxides, or alloys of these metals as the main component. is used.

Among these platinum group metals, oxidation catalysts containing Pd, PdO, or a mixture of Pd and PdO as an active ingredient, which have excellent low-temperature activity and stable combustibility, are suitable as catalysts for catalytic combustion of hydrocarbons, etc. . However, when this catalyst is used at a temperature of 600 to 1500°C, aggregation and growth of Pd and PdO occur, resulting in a significant decrease in catalytic activity.

In addition, Pd and PdO have a weak bond with the carrier in a high-temperature oxidizing atmosphere and easily fall off, so they are rapidly consumed.

However, the active ingredient according to the prior art is Pd or Pd
Oxidation catalysts using O or a mixture of Pd and PdO have problems in terms of decreased activity and short life.

(Object of the invention) The present invention has been made to improve the above-mentioned problems, and is to improve the oxidation of Pd, Pdo or P.
This was done to take advantage of the low-temperature activity of d/PdO and to overcome the early decline in catalytic activity to extend the life of the oxidation catalyst.

(Structure of the Invention) The present invention provides an oxidation catalyst in which a carrier such as alumina or a ceramic structure such as mullite coated with alumina or the like is coated with Pd, PdO or Pd/PdO as an active ingredient. During PdM
The present invention is characterized in that it is provided with an intermetallic compound layer of type or PdMO type, and M is a rare earth metal.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 3 schematically shows a cross section of an oxidation catalyst in an initial state in which active A 1 z O32 is coated on a monolithic structure 1 using a conventional supporting method, and Pd3 is further coated thereon. It shows. Active A 1 z Os
The pore size of No. 2 can be controlled to be very small, usually several hundred to several 1.
000 people. Such activity A1zo: P on +2
When supporting d3, the particle size of Pd3 is several tens to
It is possible to control several hundred people.

Figure 4 shows the temperature of 1100℃ in methane catalytic combustion.
This figure schematically shows a cross section of an oxidation catalyst manufactured by a conventional method that was used for 100 hours. As described above, the particle size of Pd3 aggregates and grows to a size of 0.1 to several tens of micrometers, and the catalyst activity after 100 hours of use is lower than that at the initial stage, and more Pd3 is consumed due to falling off.

As a result of the detailed study of the aggregation and growth of Pd3 or Pd03, the present inventors found that Pd3 or Pd03
Because the bond with the underlying AI, 0,2 is weak, when exposed to a high temperature atmosphere, Pd3 or Pd03 easily becomes active A j! It was concluded that particles of Pd3 or Pd03 move on top of zO32 and aggregate and grow together.

Furthermore, active A also has an effect on the consumption of Pd3 or Pd03.
Since the binding force with l t O32 is weak, it easily falls off (as a result, the catalyst life is shortened).

Therefore, the present inventors investigated Pd, PdO, or Pd
We thought that increasing the bonding strength between PdO and active A Il t O3 would prevent the agglomeration and growth of Pd or PdO and provide a long-life oxidation catalyst.As a result of various studies, we found that Pd
Alternatively, if a Pd-rare earth metal intermetallic compound layer is provided between PdO or Pd/PdO and AlzO3, Pd and Aβ! 0. We have reached the conclusion that the bonding strength of the two can be dramatically improved.

FIG. 1 schematically shows a cross section of an oxidation catalyst according to the present invention. Active Al 203 in monolithic structure 1
2 is coated, and Pd-
A state in which a rare earth metal intermetallic compound layer 4 is present is shown.

Figure 2 schematically shows the cross section of the oxidation catalyst of the present invention shown in Figure 3 after being used for 100 hours at a temperature of 1100°C in methane catalytic combustion, and the cross section of the oxidation catalyst of the present invention shown in Figure 1 before use. The situation was almost unchanged. 100 again
The catalyst activity remained high with almost no change before and after use. Furthermore, almost no depletion of the active ingredient Pd5PdO was observed.

In this way, by providing a Pd-rare earth metal intermetallic compound layer between Pd, PdO, or Pd5PdO and activated AlzOx, consumption of Pd can be reduced while maintaining the low-temperature activity and stable combustibility against hydrocarbons, which are the advantages of Pd. It is possible to prevent this and extend the life of the oxidation catalyst.

The amount of rare earth metal and O relative to Pd in the intermetallic compound layer in the present invention is 0.1-1% to 10% relative to the total Pd.
wt% and 0 to 5 wt% are appropriate; if the rare earth metal is less than 0.1 wt%, it has no effect on strengthening the Pd AJzO+ bonding force, and if the rare earth metal and O exceeds 10 wt% and 5 wt%, the catalytic activity of Pd is This reduces the

Furthermore, the Pd-rare earth metal intermetallic compound layer of the present invention is Pd
Either the dM type or the PdMO type (M is an alkaline earth metal) is effective.

To produce the oxidation catalyst of the present invention, a mixed aqueous solution of a water-soluble salt of Pd and a water-soluble salt of an alkaline earth metal is applied to a carrier having a monolithic structure coated with active Al2O3 by a method such as dipping. , After drying, temperature 300-1000℃
It can be obtained by firing. In this case, if fired in a reducing atmosphere, PdM type is produced, and if fired in an oxidizing atmosphere, PdM type is produced.
O type is obtained respectively. Here, M is a rare earth metal. It is also possible to use methods such as physical coating and chemical coating, and any method that results in the formation of a Pd-rare earth metal intermetallic compound layer between Pd and active A42zCh may be used.

In order to clarify the effects of the present invention, conventional examples and embodiments will be described below.

(Conventional example) Diameter 50 mm with cell pitch 5,5 am, length 2
γ-Al2O3 in a 511m mullite honeycomb structure
The carrier coated with 100 g/β of PdC1z was immersed in a hydrochloric acid solution of PdC1z, dried, and then calcined at 500°C in an H2 atmosphere to obtain an oxidation catalyst consisting of a Pd/TA12os/mullite carrier. At this time, the amount of Pd supported was 20g/
It was l.

(Example 1) A carrier coated with γ-A1t03 in the same process as the conventional example was prepared by adding lanthanum nitrate to a palladium nitrate aqueous solution.
The honeycomb carrier was immersed in this solution and fired in the atmosphere at 800°C, and then subjected to a reduction treatment in a hydrogen atmosphere at 500°C.
dLaO2/TAj! An oxidation catalyst consisting of 203/mullite carrier was obtained. The total amount of Pd supported at this time was 20g/l
Met.

(Example 2) In the same process as in the conventional example, a support coated with T AlzOa was added to a hydrochloric acid solution of PdCJz and cerium chloride was added to C for Pd.
The honeycomb carrier was immersed in this solution, dried, fired in the atmosphere at 800°C, and further partially reduced with a hydrogen burner flame to form Pd-
An oxidation catalyst consisting of Pd0/PdCe0z/A2□03/mullite was obtained.

The total amount of Pd supported at this time was 20 g/l.

Next, natural gas containing 90% methane was catalytically burned using the catalysts of the conventional example, Example 1, and Example 2 under normal pressure in an air amount of 30 n? N/h, catalyst inlet gas flow rate 10 m/sec,
The combustion temperature was 1200℃, and the combustion start temperature was 1
When measuring time and combustion efficiency after 1000 hours, as well as catalyst component reduction rate and specific surface reduction rate after 1000 hours, the results shown in the table below were obtained.

As is clear from the above table, the combustion start temperature of Example 1.2 is almost the same as that of the conventional example, and the activity is high, and the combustion efficiency, catalyst component reduction, and specific surface area reduction rate after 1000 hours, which indicates the life, are higher than that of the conventional example. It was significantly improved compared to .

As described above, it can be seen that the catalyst of Example 1.2 according to the present invention has a long life with very little decrease in activity even when used at high temperatures for a long time without impairing the advantages of Pd's low-temperature activity and stable combustibility. .

(Effects of the Invention) As is clear from the above explanation, the oxidation catalyst of the present invention is provided with an intermetallic compound layer of PdM type or PdMO type, in which M is a rare earth metal, between the active component and the support. Therefore, the binding force between the active ingredient and the carrier is large, and the decrease in activity due to migration and aggregation of the active ingredient at high temperatures and consumption is extremely small, making it durable for long-term use. Moreover, it is applicable not only to hydrocarbons but also to fuels such as hydrogen, carbon oxide, methanol, etc., and has high industrial value as an oxidation catalyst and can be used for a long period of time.

[Brief explanation of the drawing]

Figure 1 is a schematic cross-sectional diagram of the oxidation catalyst of the present invention before use, Figure 2 is a schematic diagram of the cross-sectional area of the oxidation catalyst of Figure 1 after it has been used at 1100°C for 100 hours, and Figure 3 is the conventional An initial cross-sectional diagram of the oxidation catalyst, FIG. 4 shows the oxidation catalyst of FIG.
It is a cross-sectional schematic diagram after being used for 100 hours at °C. Applicant Tanaka Kikinzoku Kogyo Co., Ltd. Figure 1 Figure 2 Figure 3 Figure 4

Claims (2)

[Claims] (1) As an intermediate material layer between the active ingredient and the carrier, the active ingredient is Pd, PdO, or a mixture of Pd and PdO, and the carrier is a ceramic whose main component is Al_2O_3, and M is a rare earth metal.
An oxidation catalyst characterized by having a dMO type intermetallic compound layer. (2) The content of alkaline earth metal and O in the intermetallic compound layer is 0.1 to 10 wt% and 0 to 5 wt%, respectively, based on the total Pd. Oxidation catalyst.