JPH01210033A - Base metal catalyst for automatic exhaust gas treatment - Google Patents

Abstract

PURPOSE: To improve activity persistence or the like by dispersing and depositing a copper oxide and a metal oxide selected from titania, zirconia, tin oxide, niobium oxide, tantalum oxide or the like on an alumina support. CONSTITUTION: The catalyst for an internal-combustion engine exhaust gas treatment is formed by dispersing and depositing the copper oxide and one kind of metal oxide selected from a group consisting of the titania, the zirconia, the tin oxide, the niobium oxide, the tantalum oxide and hafnium oxide on the alumina support. The alumina support adequately consists of solid ceramics or honeycomb-shaped monolithic of metals. the alumina support consisting of 15 to 100 wt.% monolithic support is more adequate. The shape of the alumina support is adequately pellet, spherical or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to a catalytic composite for treating exhaust gas from an internal combustion engine, a method of farming the composite, and a method of using the composite.

BACKGROUND OF THE INVENTION Gaseous consumption products from internal combustion engines are a major source of pollution. Among the pollutants are carbon monoxide, hydrocarbons and oxygen nitrides. It is well known that these pollutants can be converted into harmless products through the use of catalysts. These catalysts usually consist of inorganic oxides having dispersed therein one or more noble metals such as platinum, palladium, rhodium, etc. Promoters and stabilizers may be added to increase the activity and durability of the catalyst.

Although these catalysts work very well, the availability and price of precious metals is becoming increasingly problematic. Therefore, there is a need for non-noble metal (base metal) catalysts that can perform the same functions as noble metal catalysts. Base metal catalysts received considerable attention when controls to limit the amount of pollutants from automobiles were first introduced. In fact, several patents have been issued and base metal catalysts for automobile exhaust gas treatment have been disclosed and claimed.

For example, U.S. Pat. No. 3,447,895 shows that copper oxide on transitional alumina (a combination of ether alumina and alpha alumina monohydrate) was tested over time in a single cylinder engine with good results. It teaches that. The space velocity of the gas on the catalyst bed is the same as the actual car exhaust gas (approximately 12,000v when the throttle is opened, 60
,000hr). The '895 patent also states that results with copper oxide on other supports, including another alumina support, were poor.

Another patent disclosing copper oxide on alumina is US Pat. No. 2, Reissue No. 926. This patent discloses that the copper oxide preferably has low crystallinity.

This catalyst was tested without any form of sulfur compounds in the gas stream. Additionally, the exhaust gas streams of both patents were highly oxidizing, ie, there was a significant excess of oxygen.

After all, U.S. Patent No. 4,034,060 claims at least one
A catalyst composition is disclosed comprising a heavy metal oxide, an alkali metal-alkaline earth metal, and optionally at least one noble metal or aluminum oxide. Heavy metals constitute at least 50% of the catalyst. No. 4,03
No. 4,060 patent is copper.

It lists a long list of heavy metals, including chromium and titanium. Although the patentee has shown good results with this type of catalyst, the burn test gas did not contain any sulfur compounds and the test gas was highly oxidizing.

Although the catalysts of the above-mentioned patents are required to have good activity, no base metal catalysts have been used commercially due to poor performance and durability. Therefore, there remains a need for effective and durable base metal catalysts. Applicant's invention meets this urgent need.

In particular contrast to the prior art, applicants provide base metal catalysts that require an alumina support having a copper oxide and a metal oxide, such as titania or tin oxide, dispersed therein. Applicants have surprisingly discovered that the addition of titania or tin oxide to an alumina support containing copper oxide substantially improves the catalytic activity and durability of the catalyst composite. Also - Applicant's catalyst has good activity when tested in highly stoichiometric and oxidizing conditions. The prior art is silent about base metal catalysts being used at stoichiometric exhaust gas conditions. The Applicant shall be able to function effectively under actual industrial/engine exhaust gas conditions,
Catalysts have been discovered that are durable when exposed to such exhaust gases for extended periods of time (50 hours or more).

In summary, Applicants have provided base metal catalysts that effectively convert carbon monoxide, hydrocarbons, and nitrogen oxides under practical engine exhaust gas conditions. This invention meets the increasing need to remove precious metals from emission control catalysts. Prior art catalysts have not been able to meet this need, as demonstrated by the fact that no base metal catalysts are currently in commercial use.

(Means for solving the problem) The catalyst composite of Kono's invention is made of copper oxide, titania,
It consists of an alumina support having a metal oxide selected from the group consisting of zirconia, tin oxide, niobium oxide, tantalum oxide and hafnium oxide dispersed therein.

Accordingly, a particular embodiment of the invention is an alumina support deposited on a solid ceramic or metal nornicum monolithic support, the alumina support having titania and copper oxides dispersed therein. A catalytic composite consisting of

Another particular embodiment of this invention is a catalyst composite comprising a spherical or pelleted alumina support with titania and copper oxides dispersed therein.

Another object of the invention is a method for producing a catalytic composite for the treatment of exhaust gas from internal combustion engines, which comprises: a) coating a solid honeycomb support of metal or ceramic with an alumina support; b) Treating the alumina-coated honeycomb carrier with a solution containing a precursor of a metal oxide, and converting the precursor to a metal oxide by calcining; c) Treating the coated honeycomb carrier of b) with a solution containing a precursor of a metal oxide; treated with solution and calcined to obtain a catalyst composite with copper oxide as active phase;

In addition, another object of the present invention is to combine copper oxide, titania,
Zirconia, tin oxide, niobium oxide.

Provided is a method for treating exhaust gas from an internal combustion engine, comprising contacting gas with a catalyst composite comprising an alumina support having dispersed therein one metal oxide selected from the group consisting of tantalum oxide and hafnium oxide. That's true.

Other objects and embodiments will become apparent from a more detailed description of the invention.

As stated above, the present invention relates to a catalytic composite and a method of manufacturing the composite for use in the treatment of exhaust gas from internal combustion engines. The composite consists of copper oxide and a metal oxide alumina modifier (mo
(difier) f dispersed in an alumina support. The catalytic composites have several advantages over prior art catalytic composites, including that the composites of the present invention are more durable, less likely to lose activity, and more effective in treating real-world automotive engine exhaust gases. make a target

So, if we first consider the alumina support,
Desirably, the alumina has a specific surface area in the range of 75 to 200 m"/f, preferably in the range of about 100 to about 180 m"/f.
Preferably, the porous bulk volume ranges from 1 to 1.0 cd/f.

The second essential feature of the catalyst composite is the metal oxides that are uniformly distributed throughout the alumina support.

The metal oxide is selected from the group consisting of titania, zirconia, tin oxide, niobium oxide, tantalum oxide and hafnium oxide. The preferred metal oxidation is by known technical means such as impregnating an alumina support with a solution containing a metal oxide precursor and then t-calcining the impregnated alumina support thereby converting the precursor to the metal oxide. The material is dispersed on an alumina support. The only criteria imposed on the precursor is that it be a decomposable metal compound and soluble in the chosen solvent. A compound that can be decomposed means a compound whose corresponding metal oxide can be obtained by heating in the atmosphere. Other methods used to disperse metal oxides in alumina supports include co-precipitation or co-gelation of metal and aluminum compounds involving a calcination step to produce metal oxides dispersed in alumina. It is.

The sixth feature of the catalyst composite is copper oxide. Copper oxide is dispersed in the alumina support by known technical means such as impregnation with a solution containing a decomposable copper compound and firing, thereby converting the copper compound to copper oxide. Although not necessarily with equivalent results, the copper compound can be impregnated into the alumina support prior to, after, or at the same time as being impregnated with the desired metal compound. Details regarding the preparation of the catalyst composite are provided below.

The catalytic composite of the present invention is conveniently employed in particulate form, or alternatively the catalytic composite is deposited on a solid monolithic support. When particulate shapes are desired, the catalyst composite is formed into shapes such as tablets, pellets, granules, rings, spheres, and the like.

Particle shapes are particularly preferred when large quantities of catalyst composite are required and for use in environments where periodic replacement of the catalyst composite is desired. Where small amounts are desired, or as a result of movement or agitation of refractory inorganic oxide particles.

consumed and dusted, resulting in loss of placement metal;
Alternatively, monolithic morphology is preferred in environments where the pressure drop across the grain increases inappropriately.

When monolithic forms are employed, it is usually most convenient to employ the catalyst composite as a thin film or coating deposited on an inert carrier material that provides structural support for the catalyst composite. The inert carrier material can be any refractory material such as a ceramic or metallic material. Preferably, the support material is non-reactive with the catalyst composite and is not degraded by the gases to which it is exposed. An example of a suitable ceramic material is sillimanite (
sillLmanite), petalite (peta
lite).

cordierite, mullite, zircon, zircon mullite, apodum
Contains ene3゜alumina-titanate, etc. therefore.

Metallic materials within the scope of this invention include metals and alloys such as those disclosed in US Pat. No. 3,920,583 that are oxidation resistant and capable of withstanding high temperatures.

The carrier material is best utilized in a solid, unitary form providing a large number of holes or grooves extending in the direction of gas flow. The shape is preferably a honeycomb structure. Advantageously, the honeycomb structure is used as a single feature or as an array of multiple modules. Honeycomb structures are typically arranged so that gas flow is generally in the same direction as the cells or channels of the honeycomb structure.

For a more detailed discussion of quasi-E structures, see U.S. Pat.
, 785,998 and U.S. Pat. No. 3,767.45.
See No. 3.

Another embodiment of this invention is a method of making a catalyst composite. The first step in this preparation process is to coat a solid honeycomb support of metal or ceramic with an alumina support. This step can be accomplished by preparing a slurry of alumina support and then coating the honeycomb support with the slurry. Nitric acid with appropriate amount of alumina support,
hydrochloric acid.

The slurry is prepared by well known means of combining with an aqueous solution of an acid such as sulfuric acid. The resulting slurry is ball milled for about 2 to 6 hours to form a convenient slurry for use. Other types of mills such as impact mills are used to reduce milling time to about 5 to 60 minutes. This slurry is now used to deposit thin films or coatings on monolithic supports by well-known means. One such method involves dipping a single stone support into the slurry, blotting off excess slurry, drying, and heating at about 500 to 700°C.
This consists of burning for about 1 to 4 hours at a temperature of (■ burning means heating in the atmosphere).

This process is repeated until the desired amount of alumina support is obtained on the monolithic support. Preferably, the alumina support is present on the single stone support in an amount ranging from about 15 to about 100 weight percent of the honeycomb support, preferably from about 25 to about 50 weight percent of the honeycomb support.

Next, one or more metal oxides selected from the group consisting of titania, zirconia, tin oxide, niobium oxide, tantalum oxide, and tin oxide are dispersed in the alumina support. The metal oxide may be dispersed in the alumina in any suitable manner.

For example, a honeycomb carrier coated with an alumina support is impregnated with a solution containing a metal oxide precursor, and this precursor is a metal compound.

Impregnation is carried out by immersing the honeycomb carrier in a solution containing a decomposable metal compound of the desired metal oxide. Alternatively, the honeycomb carrier may be sprayed with a solution. Solutions may be aqueous or prepared from organic solvents or mixtures thereof. Examples of organic solvents used are ethanol, acetone, pentane and toluene.

The precursor may be any compound that is soluble in the desired solvent. Examples of these compounds are titanium hydroxyl lactate, titanium tetrachloride, titanium dichloride, titanium impropoxide.

Titanium ethoxide, titanium oxide sulfate, zirconium tetrachloride, zirconium ethoxide, zirconium oxide dichloride, zirconylam nitrate, tin tetrachloride, tin (n) chloride, tin (IV) acetate, tin (■) ethoxide, hafnium ( IV) Chloride, hafnium oxide dichloride, niobium (V
) chloride, niobium oxide dichloride, niobium (V
) ethoxide, tantalum ethoxide and tantalum chloride.

The honeycomb support impregnated with the desired metal compound is about 40
The alumina support is baked at a temperature of 0°C to about 700°C for about 30 minutes to about 2 hours until the metal oxide is dispersed in the alumina support. Preferably, the metal oxide is present in the alumina support in an amount of about 5 to about 50 weight percent, preferably about 10 to about 30 weight percent of the alumina support.

Of the metal oxides contemplated within the scope of this invention, some may be better than others in improving the individual properties of the catalyst. For example, it has been discovered that tin oxide significantly improves the nitrogen oxide conversion performance of catalysts over other metal oxides such as titania. On the other hand, titania substantially improves hydrocarbon oxidation performance over tin oxide.

Therefore, some metal oxides are more preferred for certain applications than others.

The next step in this manufacturing process is to deposit on a honeycomb carrier,
Copper oxide is dispersed in an alumina support having metal oxide dispersed therein. The copper oxide is dispersed in the alumina support by impregnating the alumina coated honeycomb support with a decomposable copper compound and firing to obtain the copper oxide.

The only other criterion for selecting a copper compound is that the compound is soluble in the chosen solvent. Impregnation is carried out by immersing the alumina-coated honeycomb carrier in a solution containing a decomposable copper compound. Solutions may be aqueous, prepared using organic solvents, or mixtures thereof. Examples of organic solvents that can be used at this stage of the process are ethanol,
Acetone, pentane and toluene. Examples of copper compounds used are copper nitrate, chlorinated steel, sulfated steel, copper ethoxide and copper acetate.

Once the copper compound is impregnated into the alumina-coated honeycomb carrier, the honeycomb carrier is quenched at a temperature of about 400°C to about 700°C for about 60 minutes to about 2 hours. Preferably, the copper oxide is present in an amount of about 2 to about 40 weight percent of the alumina support.

Another embodiment of the invention consists of impregnating an alumina support with the desired metal compound (metal oxide precursor) and annealing followed by impregnation with a copper compound and annealing. A slurry of the catalyst composite is then prepared and the catalyst composite is deposited on the honeycomb support by dipping the honeycomb support in the prepared slurry as described above for the alumina slurry. It should be noted that the two methods of preparation may not yield equivalent catalyst composites.

If a particulate catalyst composite is desired, the alumina support may be spherical, pelleted, or the like. For example, alumina spheres are produced continuously in the well-known oil drop process described in US Pat. No. 2,620,314 and incorporated herein by reference. These alumina spheres are then impregnated with the desired metal compound and fired as described above.
Obtain alumina spheres in which metal oxides are dispersed. The copper oxide is then dispersed as described above to obtain a special shaped catalyst.

In an alternative method, the metal oxides are dispersed onto the alumina support by adding the desired metal oxides to the alumina precursor during the oil drop manufacturing process. ■
The desired metal oxide can be obtained by calcination. After this step, copper oxide is dispersed thereon as described above.

Another alternative method consists of preparing a powder mixture of alumina and the desired metal oxide. This mixture is used to prepare a slurry which is subsequently used to coat the honeycomb carrier. Alternatively, the powder mixture is extruded to obtain extrudates of various shapes and sizes. Regardless of which of the above options is chosen, the alumina containing the metal oxide is impregnated with a copper compound and ■ to disperse the copper oxide into the alumina containing the modifier.
Burned. It should be pointed out that the copper oxide is dispersed into the alumina and metal oxide mixture before the slurry is prepared or the mixture is extruded, although not necessarily with equivalent results.

All of the above-mentioned preparation methods involve the step of depositing copper oxide on a metal oxide-containing alumina support.

It involves the precipitation of metal oxides onto alumina.

The metal oxide and copper oxide do not necessarily have to be dispersed in the above order. That is - the copper oxide is dispersed in the alumina and then the metal oxide is dispersed thereon. Alternatively, a solution containing both metal oxide and copper compound is used to simultaneously impregnate the alumina support with the desired metal oxide and copper compound. ■ By calcination, the corresponding oxide is obtained. Although the copper oxide may be dispersed into the alumina before, after, or simultaneously with the metal oxide, the resulting catalyst composites are not necessarily equivalent.

Another embodiment of the invention is a method for treating exhaust gas from an internal combustion engine. This method uses an alumina support having a dispersed metal oxide and one metal oxide selected from the group consisting of titania, zirconia, tin oxide, niobium oxide, tantalum oxide, and hafnium oxide. contact with a catalytic composite consisting of

To more fully demonstrate the effectiveness of this invention.

Examples will be described below. It is to be understood that the examples are merely illustrative and are not intended to unduly limit the broad scope of the invention as set forth in the claims.

Example ■ This example provides the preparation of copper oxide on an alumina catalyst composite. Alumina spheres prepared by the method of US Pat. No. 2,620,314 were used as the alumina support. These spheres had an apparent bulk density (ABD) of 0.489/rat. 31. in a beaker.
1f alumina ball is 15. Of Cu (NOs)*
” 2 /2 Ha O and 4 7.1 m
1 of an aqueous solution. All solution was absorbed by the spheres. The spheres containing copper nitrate were dried in a steam bath and baked in a gas oven at 540°C for 2 hours. The amount of copper oxide present in this catalyst composite is 12.5% by weight.
! It was M. This catalyst composite was named Sample A.

Example ■ This example provides the preparation of a catalyst composite consisting of alumina titania and copper oxide.

Alumina spheres were prepared according to the examples. These spheres were made of Ti by the process described in U.S. Pat. No. 4,459,372.
α, processed. The amount of titania on the sphere was 9% of the weight of the alumina. There are 30 balls in the beaker and 12 of balls.
．． It was mixed with 42.5 rnl of an aqueous solution containing 569 Cu(No,)t·2′/2H,O.

All the solution was absorbed into the spheres. The impregnated spheres were dried in a steam bath and baked in a gas oven at 540° C. for 2 hours. The amount of copper oxide present in this catalyst composite was 12.5% by weight. This catalyst composite was named Sample B.

Example ■ This example provides the laboratory test conditions used to evaluate Samples A and Bt.

The catalyst sample (2 t) was introduced into a test device consisting of a mixing section generating the test gas mixture, a reaction tube placed in a tube furnace and containing the catalyst sample, and an analytical section. Two gas mixtures are used in the test: a lean gas mixture and a rich gas mixture. The characteristics of these gas mixtures are shown in Table 1.

Table 1 Characteristic components of test gas Lean gas (pPm) Concentrated gas CPPM
)”0, 6500 2790C
o 3550 8000H
,11832667 C,H,355800 C,Imu 500 50ONO
18351835 C0,118,800118,800 80!20 20 H,O (10th section) (10%)N,
Residual Residual At a dry pace the test is carried out by cycling alternating plugs of lean and rich gas mixtures over the catalyst sample at a frequency of 0.5 Hz. The temporal gas hourly space velocity of the gas mixture at standard state (STP) gas volume was approximately 300.000 hr.

The test procedure is = 1] heating the catalyst from 200 to 900 °C while flowing the gas mixture over the catalyst; 2) holding the catalyst at 900 °C for 1 hour while flowing the gas mixture described above; 6) heating the catalyst to 200 °C; 4) heating the catalyst to 400°C.

All heating and cooling were performed at a rate of 15°C/min. The purpose of the second stage mentioned above was to determine the durability of the catalyst. Thus, the first temperature increase represents new activity, while the second temperature increase represents activity after durability testing. The results of the new test are shown in Table 2.

Table 2 New Laboratory Test Results Sample Name Percent Co Conversion Temperature Required to Achieve Conversion ('C) CuO on catalyst
/T i OH/M t Os showing improvement of the catalyst.

Similar results were observed in hydrocarbon conversion. The results after laboratory durability testing are shown in Table 6.

Table 3 Aging laboratory test results Sample name CO conversion percentage Tt5Tho
T.

A 385 465 540B
305 367 452 The temperature required to achieve the described conversion ('C) These results demonstrate that durability is substantially improved when titania is added to copper oxide on an alumina catalyst composite. clearly shown.

Example ■ A single stone catalyst of the present invention was prepared as follows. 6.
7000f of gamma alumina was added to a container containing 5 liters of water and 435 mlf of concentrated nitric acid (HNO,). This mixture was ball milled for 12 hours. , short axis 3.2 inches, long axis 5. A finch, semi-E of oval cordierite having a length of 6 inches and 400 square channels per square inch of surface area, was immersed in the slurry described above. After soaking, excess slurry was blown away with an air gun. The semi-E coated slurry was baked at about 540° C. for 1 hour. The above-described soaking, blowing, and firing steps were repeated until Quasi-E contained 21% by weight alumina.

The above-described semi-E was then immersed in an aqueous solution containing 447.22 v of tin chloride (SnCl,.5H,O) per liter of solution. After placing the quasi-E into the solution, the container was placed under a vacuum of at least 25"Hg for 4 minutes. After soaking, the impregnated single stone was dried and calcined at 540 °C for about 1 hour. The tin oxide (
The amount of tin analyzed as 5nOt) is 13.6% in alumina.
Weight percent.

The semi-E containing alumina and tin oxide was then impregnated with a copper nitrate solution. Standard E: 458t per liter of solution
of copper nitrate (Cu(NOs)t"3HtO). The container containing the quasi-E and the solution was placed under a vacuum of at least 25"Hg for 4 minutes, dried, and
It was baked at 0°C for about 1 hour. The amount of copper oxide (Cub) analyzed was 11.6 weight percent of the alumina. The catalyst was named Sample C.

Example V The process of Example 1 was repeated except for the tin chloride solution. 50% titanium hydroxyl lactate (Ti(OH)*(CH,CHOH) in H,O(9,9%Ti)
A solution containing 9101 COO)t) was diluted to 11 with concentrated ammonium hydroxide and used to disperse titania in alumina. The amount of titania is 25.
It was analyzed to be 3% by weight. The amount of copper oxide present on the catalyst was analyzed to be 13.94 by weight of alumina.

The catalyst was named Sample Ri.

Example ■ The following test was conducted to demonstrate that the catalyst of this invention has good durability.

Samples C and D were individually placed in converters, each placed in the exhaust gas from a bank of V-8 gasoline fueled engines. The engine was operated according to the following cycles.

The engine used in this endurance cycle was equipped with a choke-cycler that simulates closed-loop air-to-fuel (A/F) ratio control.
It was a Chevy 5.7LV-8 engine equipped with Endurance cycle is 143 A/F ratio and 0.
The operation consisted of a stable cruise at a modulation frequency of 0.4 A/F at 1 Hz. In this way, the catalyst was exposed to alternating pulses of lean and rich exhaust gas. The converter inlet temperature was maintained at 621°C. The catalyst was exposed to these conditions for 50 hours.

Catalyst C, D, El! As mentioned above, durability and aging (a
After testing, the catalyst was evaluated using an engine dynamometer run test. The test was carried out at 7 different A/F points (14, 71, 14,
66, 14, 61, 14, 56, 14, 51.

14.46, 14.41). At each A/F point, the air/fuel oscillated plus and minus 0.4 A/F at a 1 Hertz frequency. The degree of conversion of hydrocarbons, carbon oxides and nitrogen oxides is calculated at each A/F.
The overall effective conversion was then obtained by averaging all conversions. The catalyst was also evaluated at an A/F of 14.2 to determine nitrogen oxide conversion under rich conditions. The space velocity for this test is approximately 30,000 hr
Met.

The results of these evaluations are shown in Table 4.

Table 4 Engine behavior of catalyst HCCONOx NO Catalyst C at A/F=14.2 CuO/5nO1/M, 0. 61 81 6!
+8 catalyst D CuO/1rlOt/Aj? tOs 74 88 3
24 The data presented in Table 4 shows that the catalyst of this invention
It shows that it has good activity under actual exhaust gas conditions after a 0 hour durability test. especially.

This was not previously observed when tin oxide was added.

A considerable amount of nitrogen oxides are converted. Furthermore, titania improves activity towards hydrocarbons over tin oxide.

Although the invention has been described with particular reference to particular embodiments,
Without being limited thereto, modifications may be made within the fully intended scope of the invention as defined by the claims.

Claims (1)

[Claims] 1. Copper oxide and one metal oxide selected from the group consisting of titania, zirconia, tin oxide, niobium oxide, tantalum oxide and hafnium oxide are dispersed. A catalytic composite for the treatment of internal combustion engine exhaust gas consisting of an alumina support. 2. The composite of claim 1, wherein the alumina support is deposited on a solid ceramic or metal honeycomb monolithic support. 3. The composite of claim 2, wherein the alumina support is present on the single stone support in an amount from about 15 percent to about 100 percent by weight of the single stone support. 4. The composite according to claim 1, wherein the alumina support is pellet-shaped or spherical. 5. The composite of claim 1, wherein the copper oxide is present in an amount ranging from about 2 weight percent to about 40 weight percent of the alumina support. 6. The composite of claim 1, wherein the metal oxide is present in an amount ranging from about 5 weight percent to 50 weight percent of the alumina support. 7. Contains an alumina support having dispersed copper oxide and one metal oxide selected from the group consisting of titania, zirconia, tin oxide, niobium oxide, tantalum oxide and hafnium oxide A method of treating exhaust gas from an internal combustion engine, which comprises contacting the exhaust gas with a catalytic composite.