WO2004002247A2

WO2004002247A2 - Cigarette comprising a catalyst for smoke treatment

Info

Publication number: WO2004002247A2
Application number: PCT/FR2003/001962
Authority: WO
Inventors: Franck Fajardie
Original assignee: Rhodia Acetow Gmbh
Priority date: 2002-06-26
Filing date: 2003-06-25
Publication date: 2004-01-08
Also published as: WO2004002247A3; AU2003260626A8; FR2841438A1; AU2003260626A1

Abstract

The invention concerns a cigarette comprising a catalyst for smoke treatment. The inventive cigarette is characterized in that it comprises either in the tobacco, or in the paper wrapping the tobacco, or in the filter, as catalyst for smoke treatment, at least a compound selected among: compounds based on at least one rare earth, zirconium or manganese oxide or hydroxide, zinc aluminate, a compound based on at least one metal selected among the elements included in the IIIA to IIIB groups of the periodic table on a support based on silica and titanium oxide.

Description

CIGARETTE COMPRISING A CATALYST FOR TREATMENT

FUMES

The present invention relates to a cigarette comprising a catalyst for the treatment of smoke.

It is known that cigarette smoke contains many compounds which can be harmful to health. Mention may in particular be made of carbon monoxide, nitrogen oxides NOx, organic compounds of the nitrosamine, aldehyde, hydrocarbon or aromatic amine type and the organic compounds having carboxylate, sulphate, sulphonate or PO _{2 functions} . These fumes can also contain metals of the cadmium, nickel or zinc type. These fumes are also made up of fine particles. In order to reduce the harmfulness of cigarettes, we are therefore looking for ways to treat this smoke.

The object of the invention is the development of a catalyst capable of eliminating or making less harmful the dangerous compounds of these fumes.

For this purpose, the cigarette according to the invention is characterized in that it comprises either in tobacco, or in the paper surrounding the tobacco, or in the filter, as catalyst for the treatment of fumes, at least one compound chosen from:

- compounds based on at least one oxide or hydroxide of a rare earth, zirconium or manganese; - zinc aluminate;

- a compound based on at least one metal chosen from the elements included in groups IIIA to IIB of the periodic table on a support based on silica and titanium oxide.

The catalyst of the invention allows the oxidation of CO to CO ₂ . It also promotes the combustion of particles contained in the fumes. It also allows the reduction of nitrogen oxides in the fumes, it can also act as complexing organic compounds and metals mentioned above. Finally, it can act as an oxidant for hydrocarbon compounds.

Other characteristics, details and advantages of the invention will appear even more completely on reading the description which follows.

The periodic classification of the elements to which reference is made is that published in the Supplement to the Bulletin of the Société Chimique de France No. 1 (January 1966). By rare earth is meant the elements of the group constituted by ryttrium and the elements of the periodic classification with atomic number included inclusively between 57 and 71.

By specific surface is meant the specific surface B.E.T. determined by nitrogen adsorption in accordance with standard ASTM D 3663-78 established from the BRUNAUER - EMMETT-TELLER method described in the periodical "The Journal of the American Chemical Society, 60, 309 (1938)".

The catalyst of the invention may be present in the cigarette either in tobacco, or in the filter or even in the paper surrounding the tobacco. As indicated above and according to a first embodiment of the invention, the catalyst of the invention is a compound based on at least one oxide or hydroxide of a rare earth, zirconium or manganese. This compound can also comprise a metal which can be iron or gold or a combination of the two. The metal contents of the compounds of the invention are not critical, they correspond to the contents generally used in catalysts to obtain a catalytic activity. By way of example, the aforementioned metal content is between 0.01% and 5%, more particularly between 0.01 and 2%. These contents are expressed in percentage by mass relative to the oxide (or to the oxides) or to the hydroxide (or to the hydroxides) of the rare earth, of zirconium or of manganese.

In the particular case of gold, this element can be deposited on the abovementioned oxide or hydroxide using a method using as a gold precursor a chloride type product which is brought into contact with a suspension of the oxide or hydroxide under basic pH conditions, for example a pH between 7 and 10. One such method is that described by Haruta et al. in Studies in Surface Science and Catalysis - Preparation of Catalysts VI, 1995, 227.

The rare earth may more particularly be cerium or praseodymium. Catalysts based on rare earth oxide or hydroxide are particularly useful as complexing agents for organic compounds (nitrosamines, aldehydes, hydrocarbons or aromatic amines, compounds with carboxylate, sulphate, sulphonate or PO _{2 functions} ) and metals (cadmium, nickel, zinc) mentioned above. It is more particularly possible to use cerium oxides with a high specific surface. By this is meant cerium oxides which have a high specific surface even after being exposed to high temperatures. In this case, the catalysts are particularly useful for their oxidative function (oxidation of CO, hydrocarbon compounds and soot).

We can thus mention the cerium oxides described in patent applications EP-A-153227, EP-A-153228, EP-A-239478, EP-A-275733. These oxides can have surfaces of at least 85m ² / g, in particular at least 100m ² / g, after calcination at a temperature between 350 and 450 ° C over a period of 6 hours for example.

It is also possible to use the cerium oxide described in EP-A-300 852 which has a specific surface of at least 15 m ² / g after calcination at a temperature between 800 ° C and 900 ° C for at least 2 hours or alternatively the cerium oxide described in EP-A-388567 which has an area of at least 190m ² / g after calcination at a temperature between 350 ° C and 450 ° C for at least 2 hours with also a specific surface at least 15m ² / g after calcination at a temperature between 800 ° C and 900 ° C over the same period.

As an interesting catalyst and also with a high specific surface, it is also possible to use compositions based on a cerium oxide and a zirconium oxide. The respective proportions of cerium and zirconium in these compositions can vary over a wide range, for example in a mass ratio of cerium oxide / zirconium oxide of between 1/99 and 99/1. However, it is possible to use more particularly the compositions for which there is a cerium / zirconium atomic proportion of at least 1.

Mention may thus be made of the cerium oxide described in EP-A-207 857 which has a specific surface greater than 10 m ² / g up to a temperature of 900 ° C. This oxide may in particular have a zirconium oxide content of between 1 and 20% relative to the weight of the ceric oxide. Mention may also be made of the composition based on cerium oxide and zirconium oxide which is the subject of EP-A-605274 and in which the zirconium is in solid solution in cerium oxide. This composition can have a specific surface of at least 30 m ² / g after calcination at 800 ° C for 6 hours.

It is also possible to use compositions with a high specific surface of the type based on a cerium oxide and a zirconium oxide and on at least one oxide chosen from scandium oxide and rare earth oxides other than cerium.

Such compositions are in particular described in EP-A-906244. In the latter document, the compositions have a cerium / zirconium atomic proportion of at least 1 and a specific surface of at least minus 35m ² / g after 6 hours calcination at 900 ° C. This surface can more particularly be at least 40 m 2 / g. It can be even more particularly at least 45 m 2 / g.

These compositions may correspond to the formula Ce _x ZryM _z θ2 in which M represents at least one element chosen from the group comprising scandium and rare earths with the exception of cerium and z preferably has a value of at most 0, 3 and which can be more particularly between 0.02 and 0.2, the x / y ratio can be between 1 and 19, more particularly between 1 and 9 and even more particularly between 1, 5 and 4, the values of bounds other than 0 being included and x, y and z being linked by the relation x + y + z = 1.

Other catalysts that can be used more particularly for their NOx reduction or trap properties will be described below in addition to their oxidizing properties (oxidation of CO, hydrocarbon compounds and soot).

A composition based on a cerium oxide and at least one other oxide chosen from iron, manganese and praseodymium oxides can also be used in the context of the present invention, as described in particular in EP-A- 802,824. Compositions based on cerium, iron and praseodymium oxides in combination can be used very particularly. The amount of manganese, iron and / or praseodyme in this type of composition can vary within wide limits. Generally, this proportion can go up to a mass ratio expressed as the oxide of this or these elements with respect to the cerium oxide of 50%. It is usually at least 0.5%. This proportion can thus be between 1 and 40%, in particular between 1 and 20%, more particularly between 1 and 10%. According to a variant, the composition can also comprise zirconium. Finally, the compositions of this type have, after calcination for 6 hours at 400 ° C., a specific surface of at least 10 m 2 / g, preferably of at least δOm ^ / g and more particularly of at least 80 m 2 / g.

It is also possible to use according to the invention a composition comprising manganese oxide, cerium oxide or a mixture of cerium oxide and zirconium oxide and in addition at least one other element chosen from terbium, gadolinium, europium, samarium, neodymium and praseodymium. These are compositions of the type described in EP-A-1034026 and which can function in particular as a NOx trap.

In compositions of this type, cerium oxide or the mixture of cerium oxide and zirconium oxide can form a support, the other elements forming a supported phase. This means that the cerium oxide or the mixture of cerium oxide and zirconium oxide can constitute the main element or elements of the composition on which or on which the other elements are deposited. The composition may comprise a supported phase which is based on manganese in combination with terbium, gadolinium, samarium, neodymium or praseodyme or else a mixture of manganese and at least two of these elements. According to a variant, the composition can also comprise an alkali which can be more particularly sodium or potassium. This alkaline element can belong to the supported phase. The amounts of elements in the composition can vary within wide proportions. Thus, the manganese proportions can vary between 2 and 50%, more particularly between 5 and 30%. Those in terbium, gadolinium, samarium, neodymium, praseodymium and / or alkaline can vary between 1 and 50%, more particularly between 5 and 30%. These proportions are expressed in atomic% relative to all the elements of the composition.

It is also possible to use in cigarettes in accordance with the invention a composition comprising manganese and at least one other element Ai chosen from alkali metals and alkaline earth metals, manganese and element Ai being chemically linked.

The compositions of this type, which can also act as a Nox trap, are described in particular in EP-A-1171236. More particularly, these compositions comprise a support and an active phase. The active phase is based on manganese and at least one other element Ai as described above and which can be more particularly sodium and potassium. As alkaline earth element, there may be mentioned in particular barium. Furthermore, the elements manganese and Ai are in a chemically linked form. By this is meant that there are chemical bonds between the manganese and the element Ai resulting from a reaction between them, these two elements not being simply juxtaposed as in a simple mixture. Thus, the elements manganese and Ai can be present in the form of a compound or of a phase of mixed oxide type. This compound or this phase can in particular be represented by the formula (1) (Aι) χMnyθ2 ± _δ in which 0.5 <y / x <6. As phase or compound of formula (1) there may be mentioned by way of example those of the vernadite, hollandite, romanechite or psilomelane, birnessite, todorokite, buserite or lithiophorite type. The compound can optionally be hydrated. The compound can moreover have a lamellar structure of the Cdl2 type. As a support, any porous support that can be used in the field of catalysis can be used. It is preferable that this support has a chemical inertness with respect to the elements manganese and Ai sufficient to avoid a substantial reaction of one or of these elements with the support which would be likely to hinder the creation of a chemical bond between the manganese and the element Ai. However, in the case of a reaction between the support and these elements, it is possible to use larger quantities of manganese and of element Ai in order to obtain the desired chemical bond between these elements. More particularly, the support is based on an oxide chosen from cerium oxide, optionally with silica, zirconium oxide or their mixtures.

The total content of manganese, alkaline, and alkaline earth can vary within wide limits. This content can be in particular between 2% and 50%, more particularly between 5% and 30%, this content being expressed in atomic% relative to the sum of the moles of oxide (s) of the support and of the elements concerned of the active phase.

The cigarettes of the invention can also comprise, as catalyst, a composition based on manganese and on at least one other element A ₂ chosen from alkaline-earths and rare earths, this composition having a specific surface of at least 10m / g, more particularly at least 20 m / g, after calcination for 8 hours at 800 ° C.

Compositions of this type are described in EP-A-1181094. These compositions include a support and an active phase. The active phase of the composition is based on manganese and at least one element A ₂ as described above. As alkaline earth, there may be mentioned more particularly barium. The rare earth can be more particularly chosen from cerium, terbium, gadolinium, samarium, neodymium and praseodyme. The total manganese, alkaline earth or rare earth contents can vary between 1% and 50%, more particularly between 5% and 30%. These proportions are expressed in atomic% relative to the sum of the moles of oxide (s) of the support and of the elements concerned of the supported phase. The respective manganese, alkaline-earth or rare earth contents can also vary within wide proportions, the manganese content can be in particular equal or close to that of element A ₂ .

As indicated above, a characteristic of these compositions is

2 that they have a specific surface of at least 10 m / g after calcination for 8 hours at 800 ° C. This specific surface can be in particular at least 20m / g after calcination at the same temperature and for the same duration. More particularly, this specific surface is at least 80 m / g and even more particularly at least 100 m / g after calcination for 8 hours at 800 ° C. This surface characteristic is obtained by the choice of a suitable support, in particular having a sufficiently high specific surface.

This support can be based on alumina. Any type of alumina capable of having a specific surface sufficient for a catalysis application can be used here. Mention may be made of aluminas resulting from the rapid dehydration of at least one aluminum hydroxide, such as bayerite, hydrargillite or gibbsite, nordstrandite, and / or from at least one aluminum oxyhydroxide such as boehmite , pseudoboehmite and diaspore. A stabilized alumina can be used more particularly as a support. As stabilizing element, there may be mentioned rare earths, barium, silicon and zirconium. As rare earth there may be mentioned very particularly cerium, lanthanum or the lanthanum-neodymium mixture.

The stabilizer content expressed by weight of stabilizer oxide relative to the stabilized alumina is generally between 1.5% and 15%, more particularly between 2.5% and 11%.

The support can also be based on silica.

It can also be based on silica and titanium oxide in an atomic proportion Ti / Ti + Si of between 0.1 and 15%. This proportion can be more particularly between 0.1 and 10%. Such a support is described in particular in patent application WO 99/01216 to which reference may be made.

As other suitable support, those based on cerium oxide and zirconium oxide can be used, these oxides possibly being in the form of a mixed oxide or of a solid solution of zirconium oxide in cerium oxide or vice versa.

The cigarettes according to the invention may also comprise a composition based on manganese in the form of a mixed oxide of formula

(2): A _x Mnι _-y By0 _{2 ±} δ in which:

A represents one or more elements chosen from groups IA, II A, III A of the periodic table; B is a metal chosen from tin and the elements of groups IV A to III B of the periodic table; x and y having the following values: 0.16 <x <1 and 0 ≤ y <0.5, the oxide having a lamellar or tunnel crystallographic structure.

The catalyst corresponding to the above formula is described in WO 01/56685 It is more specifically a mass catalyst. By this is meant a catalyst in which the oxide of formula (2) is present throughout the volume of the catalyst in a homogeneous manner and not according to a distribution or concentration gradient, for example at the surface of the volume of the catalyst. In other words, the catalyst used here is an unsupported catalyst, the active phase, ie the oxide of formula (2), is not deposited on a porous support of the cerium oxide type, oxide of zirconium or silica for example.

With regard to the constituent elements of the oxide of formula (2), A can represent one or more elements chosen from the aforementioned groups of the periodic table.

A can first of all be chosen from lithium, sodium, potassium, rubidium and cesium. A can be more particularly potassium or sodium or a combination of these two elements in variable respective proportions.

A can also be chosen from magnesium, calcium, strontium or barium. A can also be an element chosen from scandium, ryttrium and rare earths.

As indicated above, x can be between 0.16 and 1, the terminal values being included. More particularly, x can verify the relation 0.25 ≤ x ≤ 0.7. In the oxide of formula (2), the manganese can be substituted by an element B.

Element B can first of all be chosen from transition metals, that is to say from elements of groups IV A, VA, VI A, VII A, VIII, IB and II B. As element of group IV A we can mention titanium.

Mention may more particularly be made, as element of group VIII, of iron, platinum, palladium or rhodium. Silver can be chosen more particularly as an element of group I B.

As an element of group II B, zinc can be mentioned. Finally, element B can be tin in the oxidation state IV. The proportion of element B in the oxide is given by the value of y mentioned above. More particularly, y can verify the relationship 0.001 <y <0.01.

It will be noted that the value of δ will depend on the nature of the elements A and B and on the oxidation state of the manganese which can vary between +3 and +7. The oxide of formula (2) also has a specific crystallographic structure. This structure is either lamellar or of the tunnel type. The lamellar structure corresponds to a structure in which the elements Mn and O together form a first layer separated from a second layer of these same elements by a third layer of elements A, this stack of layers being repeated. In the tunnel structure, the layers formed by all of the elements Mn and O form a tunnel inside which the elements A are located.

Such structures may be mentioned those of vernadite type hollandite, romanéchite or psilomélane, birnessite, todorokite, buserite, lithiophorite, RUB-7, Rb _0, ₂₇ MnO _2, Na _0, _4, MnO _2, Li _0, 4 ₄ MnO _2, Ba ₆ Mn ₂ 4θ ₄ 8, alpha-NaMnO ₂ , alpha-LiMn0 ₂ , beta -NaMnθ2, beta-LiMn0 ₂ .

Finally, it should be noted that the oxide of formula (2) can optionally be hydrated by intercalation of H ₂ O molecules and / or H ⁺ protons between the lamellae or in the tunnels. As indicated above and according to a second embodiment of the invention, the cigarette can also comprise, as catalyst, a zinc aluminate

As aluminate of this type, the one described in EP-A-1098701 can be used. This aluminate has a spinel-type structure ZnA ^ O II can be present in one or more lacunar or excess zinc phases compared to ZnAl2θ4, these phases meeting the formulas Zn-j. χAl2θ4_δ and Znι _{+ x} Al2θ4 + δ, with 0 <x <0.95. The values of x can more particularly correspond to the following relationships: 0 <x <0.85, 0 <x <0.8 and more particularly 0 <x <0.5. Finally, x can verify the relationship 0.4 <x <0.85. The aluminate can also comprise one or more additives. These additives are chosen from the elements of groups IA, MA, VIIA to IB of the periodic table and from tin, gallium and rare earths. Mention may more particularly be made, as group VII A element, of manganese; as element of group VIII, there may be mentioned in particular iron; as elements of group IB, mention may be made more particularly of copper and silver. These additives can in particular be present in the aluminate in partial substitution for zinc or aluminum.

A characteristic of this same aluminate is its specific surface. Even after calcination at high temperature, this aluminate still has a significant surface level. Thus, after calcination at 800 ° C, 8 hours this specific surface is at least 85m2 / g. It can be at least 90m2 / g and more particularly at least 100m2 / g, always after calcination at 800 ° C, 8 hours. Values of at least 120rrι2 / g can be reached.

This surface is maintained at significant values at even higher temperatures since the aluminate can have, after calcination at 900 ° C, 2 hours, a specific surface of at least 70m2 / g, more particularly at least 80m2 / g. In addition, at 1000 ° C. after a 6 hour calcination, specific surfaces of at least 50 m 2 / g, more particularly at least 70 m 2 / g can be observed. This means that the aluminate surface is stable over a wide temperature range. The values which have just been given above are understood for calcinations in air.

This same aluminate can also have a pore volume of at least 0.6 ml / g, this porosity is determined by porosimetry by mercury intrusion. The measurements were made on a Micromeretics Auto Pore 9220 device on powders put to degas overnight in an oven heated to 200 ° C. The operating parameters are as follows: Constant penetrometer: 21, 63, capillary volume: 1, 1, contact angle: 140 °. The porosity can more particularly be at least 2 ml / g and for example be between 2.5 and 3.5 ml / g. Finally, according to a third embodiment of the invention, the cigarette may contain a catalyst which is a compound based on at least one metal chosen from the elements included in groups IIIA to IIB of the periodic table on a support to based on silica and titanium oxide.

Such a compound is described in EP-A-994749. This compound comprises a support based on silica and titanium oxide in an atomic proportion Ti / Ti + Si of between 0.1% and 15%. This proportion can be more particularly between 1% and 10%. It is advantageous in the case of this compound to use supports having a high specific surface area and thermally stable. One can thus advantageously use supports having a specific surface of at least 350m ² / g and more particularly of at least 600m ² / g after calcination 6 hours at 750 ° C. The support based on silica and titanium oxide can be prepared by any process capable of leading to a support of sufficient specific surface.

One can thus mention a process by micellar texturing using surfactants and, as a source of silica, alkyl-silicates such as tetraethyl orthosilicate. These alkyl silicates are generally used in the form of solutions in alcohols, in particular in aliphatic alcohols. Likewise, alkyl or alkoxy titanates can be used as source of titanium which are also used in the form of alcoholic solutions. The alkyl silicates and the alkyl or alkoxy titanates are mixed and then heated. The surfactant is then added to the mixture thus heated. The precipitate obtained is separated from the reaction medium. This precipitate is then calcined, generally in air, to obtain the support which can then be shaped. Calcination can be done in two parts. In the first part, calcination is carried out at a temperature sufficient to remove the surfactant. This temperature can be around 650 ° C. In the second part, calcination is carried out at a temperature at least equal to that at which the catalyst will be used. This temperature can be around 750 ° C.

The support can be in various forms such as granules, balls, cylinders or honeycomb of variable dimensions. The support can comprise, as additives, one or more rare earth oxides. Mention may be made, as rare earth, of lanthanum more particularly. The additive content expressed in atomic% additive / Ti + Si + additive can be at most 20%, more particularly at most 10%.

The catalytic phase on the support can be based on at least one metal chosen from the elements included in groups IIIA to MB of the periodic table.

More particularly, the catalytic phase is based on at least one metal chosen from the metals of group VIII of the periodic table. By way of example of metals which can be used in the catalytic phase, mention may be made of platinum, palladium, rhodium, ruthenium, iridium. Mention may also be made of iron, copper, chromium as well as vanadium, niobium, tantalum, molybdenum and tungsten. The metal content of the catalytic phase and, in particular of platinum, of the composition can vary within wide proportions. Usually, this proportion, expressed by weight of metal relative to the support weight is between 500 and 40,000 ppm, preferably between 2,500 and 20,000 ppm and even more particularly between 5,000 and 15,000 ppm.

Examples will now be given.

EXAMPLE 1

A salt of chlorauric acid (III) trihydrate (HAuCI, 3H ₂ 0) was deposited by the deposition-precipitation method (described by Haruta et al. In Studies in Surface Science and Catalysis - Preparation of Catalysts VI, 1995, 227 ) on a cerium oxide developing a specific surface of 180 m ² / g so as to obtain a catalyst containing 1% by weight of gold relative to the mass of cerium oxide. In this method, the aqueous gold solution is added to an aqueous suspension of the oxide and the pH is fixed at 9. After stirring for 2 h at room temperature, the medium is filtered. The solid obtained is then dried at 120 ° C. overnight to yield the Au / CeO ₂ compound. The catalyst obtained is returned to the air before testing.

EXAMPLE 2

A cerium oxide developing a specific surface of 180 m ² / g was dry impregnated with a salt of iron nitrate (lll) nonahydrate (Fe (NO ₃ ) ₃ , 9H ₂ θ) so as to obtain a catalyst containing 1% by weight of iron relative to the mass of cerium oxide. The Fe / Ce0 ₂ compound obtained was then dried at 120 ° C overnight and then calcined at 500 ° C in air for 2 h.

The catalyst obtained was then activated by reduction under hydrogen diluted to 3% by volume in argon for 4 h at 400 ° C. then returned to the air before testing.

The catalysts are then subjected to an evaluation test.

Test

In this test, the catalyst is subjected, at ambient temperature, to a synthetic mixture, the composition of which is as follows: 10% vol CO 10% vol CO ₂

10% vol O ₂ 1, 8% vol H ₂ 0 qs N ₂ The gaseous mixture circulates continuously at a flow rate of 30 L / h through a tubular quartz reactor in which is placed 50 mg of catalyst previously mixed with 150 mg of carborundum SiC which plays no catalytic role here. In this test, the space velocity of the gases is equal to 600,000

Cm / h / g _ca talyseur-

The catalyst is deposited in the form of powder on the frit of the reactor which plays here only the role of physical support of the catalyst for the course of the test. We can therefore consider that this test simulates the composition and the flow rate of the gas phase to which the catalyst could be subjected in a cigarette.

Initially, the catalyst is at room temperature. During the test, it is subjected to a temperature ramp from 10 ° C / min up to 300 ° C. The gases having passed through the catalyst are analyzed by infrared spectrometry at intervals of approximately 10 s.

This device therefore makes it possible to follow the composition of the gas flow as a function of the temperature to which the catalyst is subjected. In particular, the temperature at which the CO conversion is 50% can be determined. The results obtained are given below.

Claims

1- Cigarette, characterized in that it comprises either in tobacco, or in the paper surrounding the tobacco, or in the filter, as a catalyst for the treatment of fumes, at least one compound chosen from:

- compounds based on at least one oxide or hydroxide of a rare earth, zirconium or manganese;

- zinc aluminate; - a compound based on at least one metal chosen from the elements included in groups NIA to MB of the periodic table on a support based on silica and titanium oxide.

2- Cigarette according to claim 1, characterized in that it comprises a compound based on at least one oxide or hydroxide of a rare earth and of a metal chosen from iron or gold.

3- Cigarette according to claim 1 or 2, characterized in that the rare earth is cerium or praseodymium.

4- Cigarette according to one of the preceding claims, characterized in that it comprises a composition based on a cerium oxide and a zirconium oxide, more particularly in a cerium / zirconium atomic proportion of at least 1 .

5- Cigarette according to claim 4, characterized in that it comprises a composition based on a cerium oxide and a zirconium oxide and at least one oxide chosen from scandium oxide and the oxides of rare earths other than cerium.

6- Cigarette according to one of claims 1 to 3, characterized in that it comprises a composition based on a cerium oxide and on at least one other oxide chosen from oxides of iron, manganese and praseodyme .

7- Cigarette according to one of claims 1 to 3, characterized in that it comprises a composition comprising manganese oxide, cerium oxide or a mixture of cerium oxide and zirconium oxide and in in addition to at least one other element chosen from terbium, gadolinium, europium, samarium, neodymium and praseodyme.

8- Cigarette according to one of claims 1 to 3, characterized in that it comprises a composition comprising manganese and at least one other element Ai chosen from alkalis and alkaline-earths, manganese and element Ai being chemically linked.

9- Cigarette according to one of claims 1 to 3, characterized in that it comprises a composition based on manganese and at least one other element A ₂ chosen from alkaline earths and rare earths and which has

2 a specific surface of at least 10 m / g, more particularly at least 20 m / g, after calcination for 8 hours at 800 ° C.

10- Cigarette according to one of claims 1 to 3, characterized in that it comprises a composition based on an oxide of formula:

A _x Mnι _-y B _y O _{2 ± δ} in which:

A represents one or more elements chosen from groups I A, II A, III A of the periodic table;

B is a metal chosen from tin and the elements of groups IV A to III B of the periodic table; x and y with the following values:

0.16 <x <1 and 0 ≤ y <0.5, the oxide having a lamellar or tunnel crystallographic structure.