The invention relates to an at least partly stratified combustion chamber comprising at least two successive distinct burning zones, and a gas outlet, for burning a combustible material in presence of air or oxygen enriched air, whereby said chamber comprises a first burning zone provided with at least one inlet for the combustible to be burnt and at least one inlet for the admission of air and/or oxygen enriched air, as well as possibly an inlet for the admission of water vapour, whereby said first burning zone is extended with a channel for collecting all gases and some solid particles issued from the first burning zone, whereby said channel is provided with a series of guiding catalytic channels extending each between a first end directed towards the first burning zone and a second end directed towards the gas outlet of the combustion chamber, said guiding catalytic channels being provided each with a means for forming at least one restricted passage adjacent to the second end, said restricted passage of a guiding catalytic _. channel having an open surface which is comprised between 25% and 90% of the open surface of the guiding catalytic channel considered adjacent to the first open end,

whereby at least the one or more channels of the catalytic system is provided with a cerium oxide - carbon containing coating, said coating of the catalytic system further comprising at least comprising oxides of the followings elements Pr, Nd, La and at least Y and/or Zr, whereby said cerium oxide - carbon containing coating with the oxides of the followings elements Pr, Nd, La and at least Y and/or Zr, is adapted for controlling the formation of H+ species on the wall of the chamber, while controlling the hydrogen branching reactions by catalysing the use of oxygen atoms from Ce, Pr, Nd, La and at least Y and/or Zr oxides for reacting with hydrogen ¾ for the formation of ¾0 on the wall of the chamber, whereby the weight metal content of the metal element selected from Y, Zr and mix thereof expressed as oxide in the total metal weight content of metal elements selected from Ce, Pr, Nd, La, Y and Zr expressed as oxide is at least 10%, advantageously at least 15%, preferably from 16 to 40%, most preferably from 20 to 30%.

The combustion chamber is of the open type, meaning that the burning is not operated in a closed chamber with moving piston(s). The combustion chamber is for example a combustor. The combustion chamber has thus an opening through which exhaust gases can flow out of the combustion zone, and is associated (like a burner) to ensure a continuous or substantially continuous flame combustion. Advantageously, the cerium - carbon coating of the guiding catalytic channels is adapted for capturing photons emitted by the flame with wavelength from 6500 to 7500A, advantageously for capturing 5 to 25% of the photons with wavelength from 6500 to 7500A emitted by the flame having a temperature higher than 800°C.

Preferably, the cerium - carbon coating of the guiding catalytic channels is adapted for ensuring a photon amplified spectrum emission radiation at least at a temperature comprised between 500 and 800°C, said spectrum covering advantageously substantially the whole range from about 4000A up to 7500A.

According to details of specific embodiments, said embodiments have one or more of the following characteristics :

- the guiding catalytic channels have each a miriimal passage with a open cross section of at least 2.5cm ² , advantageously at least 5cm ² , preferably from 5cm ² to 20cm ² .

- the guiding catalytic channels are made at least partly in a temperature ceramic like material, advantageously comprising aluminium, the wall of which being provided with a catalytic coating with a thickness from 50μ ^η ι up to 1mm, preferably from ΙΟΟμηι to 5000μπι. The combustion chamber which comprises at least 20 distinct and parallel guiding catalytic channels (located in the second burning zone..

The combustion chamber is associated with a system adapted for the admission of air or oxygen enriched air within the first burning zone and/or in the second burning zone.

The combustion chamber is associated to at least one injector for the admission of water vapour within the first burning zone. the cerium - carbon contaiiiing coating comprises at least Y and Zr, advantageously the weight ratio Y/Zr expressed as oxides present in the catalyst coating is comprised between 1 : 10 and 10: 1 , preferably between 2: 10 and 10:2. the cerium - carbon containing coating comprises some aluminium, preferably in its oxide or hydroxide form and/or in the form of aluminosilicate, whereby the aluminium metal content of the catalyst coating with respect to the total metal weight content of the catalyst coating of metal selected from Al, Ce, Pr, Nd, La and at least Y and/or Zr is comprised between 1 and 10%. the relative weight of the metals selected from Ce, Pr, La, Nd, Y and Zr, expressed respectively as the following oxides Ce0 ₂ , Pr ₆ On, La ₂ 0 ₃ , Nd ₂ 0 ₃ , Y ₂ 0 ₃ . and Zr0 ₂ of the cerium - carbon containing coating of said guiding catalytic channels with respect to total weight of the said metals expressed as oxides are :

Ce (as Ce0 ₂ ) : 25 to 50%, preferably from 35 to 45%,

Pr (as Pr ₆ Oi : 2 to 10%, preferably from 2.5 to 6%

La (as La ₂ 0 ₃ ) : 15 to 37%, preferably from 20 to 32% Nd (as Nd ₂ 0 ₃ ) : 4 to 15%, preferably from 5 to 13%

Y (as Y ₂ 0 ₃ ) : 5 to 15%, preferably from 8 to 12%

Zr (as Zr0 ₂ ) : 5 to 25%, preferably from 10 to 17% The invention relates also to a burning installation comprising at least a combustion chamber according to the invention, as well as an exhaust system provided with means for treating the flue gases corning from the combustion chamber (such a filter, an absorption treatment step, a cleaning step, a heat recovery step, etc.).

The invention relates also to a process of burning coal in presence of air within an installation of the invention, and/or to a process for burning a biomass

combustible in presence of air within an installation of the invention. Fuel burning of waste materials or coal or biomass combustible material is nowadays more problematic, due to pollution regulation (NO, NOx, S02, etc.), particles, and health problems generated by said pollution.

The invention is using a heterogeneous catalytic system comprising rare earth metals. Problems associated to heterogeneous catalytic system are among other limited catalytic life time, variable working efficiency in function of reaction conditions, etc.

The experience and further searches carried out by the inventor have shown that catalyst could be still be improved, for burning efficiency purposes for a long period of time, as well as for variable working conditions. The new catalyst of the invention enables also an easier control of the burning, while being submitted to variation of load or amount of combustible to be burnt. The system of the invention is thus a dynamic bi functional or hybrid system combining rare earth metal oxides and non rare earth metal oxides, together with carbon particles. The system of the invention uses a catalytic coating having a good thermal resistance, a good catalytic longevity, a good mechanical and chemical resistance, pressure variations. It seems that some metal elements of the catalyst coating are sintered with the metal surface of the combustion chamber (for example of the aluminium alloy of the combustion chamber). It was observed that catalytic efficiency or working was achieved from low temperature (such as temperature of less than 300°C) up to high temperature (such as temperature higher that 700°C, or even higher than 900°C). It was observed that catalyst coatings of the invention were suitable to catalyse redox reactions on and in the porous catalytic coating. It was also observed that due to the catalyst coating of the invention, some flame quenching could be prevented, such as side wall quenching and/or tube quenching (channel quenching). It was also observed that ionisation current was better conserved adjacent to the catalyst coating. Without being bound to any theory, it is expected that the catalyst coating ensures within the free volume of the combustion chamber a thicker intermediate layer between the flame plasma and the catalyst coating of the invention, with respect to a combustion chamber not provided with the catalyst coating. Without being bound to any theory, it is expected that the catalyst coating of the invention ensures a more controlled ionisation level, with reduced chemi ionisation peak and thermal ionisation peak, even in presence of large excess of air, such as with lambda value of more than 1.4, or even 1.5.

The control of chemical catalysis is disclosed in US7998538 (California Institute of Technology). As stated in said documents, many catalytic reactions have a temperature threshold. Prior art methods utilise macroscopic heat source to provide heat for such reactions and typically entail gross convection, gross conduction, or gross radiation. Inherent with the use of such conventional methods of heating, is the difficulty of having control of the temperature of a catalyst, the vicinity of the catalyst and/or the heat applied, both temporally and spatially. Carbon containing coating in the present invention means a coating comprising graphite carbon, most preferably like as 2dimensional-graphene structures (such as structures with a larger Raman intensity peak between 2600 - 2700 Raman shift (1/cm) than the Raman peak intensity between 1500 - 1700 Raman shift (1/cm). The carbon containing coating of the invention is preferably a coating for which at least 30% by weight of the carbon is in a form of 2dimensional-graphene structure, advantageously mixed with graphite having the structure of nanotubes (such as single wall carbon nano tubes, double wall carbon nano tubes or multi wall carbon nano tubes) and/or fullerene and/or combinations thereof.

According to an advantageous embodiment, the cerium - carbon coating of said inner wall and/or of the catalytic element is adapted for ensuring a photon amplified spectrum emission radiation at least at a temperature comprised between 500 and 800°C, said spectrum covering advantageously substantially the whole range from about 4000A up to 7500A (i.e. ensuring thus emission of rays in the violet range (wave length from 4000A up to about 4500A), in the blue range ( wave length from 4500 A up to 5200 A), in the green range (from about 5200 A up to about 5700A), in the yellow range (from about 5700A up to about 5900A), in the orange range (from about 5900 A up to 6250 A) and in the red range (from about 6250A up to about 7500A). The emission is advantageously controlled so that emission from the coating occurs substantially continuously from about 300°C up to about 900°C.

According to a further embodiment, the cerium oxide - carbon coating of said inner wall and/or of the catalytic element comprising oxides of the followings elements Pr, Nd, La and at least Y and/or Zr, is adapted for uptake of hydrogen atoms (especially in the form of hydrogen species H ^' ) at least at temperature comprised between 300 and 700°C. It is expected that some cracking of the combustible material (gazeous or small particles) is operated in the second burning zone at temperature below 500°C and at pressure lower than 5 10 ⁵ Pa. According to an embodiment, the presence of Pr, Nd, La and at least Y and/or Zr, oxides in the cerium oxide - carbon containing coating of said guiding channels acts advantageously as catalyst for the reaction of oxygen stored in the coating with hydrogen H ₂ and/or hydrogen species for the formation of water at least at temperature above 500°C and pressure lower than 5 10 ⁵ Pa, such as lower than 2 10 ⁵ Pa. _.

Advantageous embodiments of the invention comprise one or more of the following characteristics, advantageously a plurality of the following

characteristics :

- the cerium oxide - carbon containing coating comprises enough oxides of Pr, La, Nd and at least Y and/or Zr, so as to reduce at least by 75 mole % that hydrogen H ₂ molecules contacting the cerium - carbon containing coating is converted into free H species and free OH species, at temperature below 900°C and pressure below 5 10 ⁵ Pa.

- the cerium - carbon containing coating is adapted, after capturing photon emitted by the flame generated by the combustion of the carbon containing fuel, for generating at least adjacent to the cerium - carbon containing coating, spectra covering substantially continuously the whole range of spectra from about 4000 A up to about 7500 A.

- the cerium - carbon containing coating is adapted for capturing photon emitted by the flame generated by the combustion of the carbon containing fuel, and/or, advantageously and, for generating at least adjacent to the cerium - carbon containing coating, spectra covering substantially continuously the whole range of spectra from about 4000 A up to about 7500 A.

- the cerium - carbon containing coating is adapted for controlling the number of photons in the combustion chamber during at least the combustion of the carbon containing fuel, said photons being advantageously a mix of photons covering the whole range spectra from about 4000 A up to about 7500 A. - the cerium - carbon containing coating comprises at least Y and Zr,

advantageously the weight ratio Y/Zr present in the catalyst coating is comprised between 1 : 10 and 10: 1 , preferably between 2: 10 and 10:2.

- the cerium - carbon containing coating comprises some aluminium, preferably in its oxide or hydroxide form and/or in the form of alumino-silicate, whereby the aluminium metal content with respect to the total metal weight content of the catalyst coating of metal selected from Al, Ce, Pr, Nd, La and at least Y and/or Zr is comprised between 1 and 10%.

- the relative weight of the metals selected from Ce, Pr, La, Nd, Y and Zr (metal elements which can be present in the coating as oxides and/or hydroxides), expressed as the following respective oxides Ce0 ₂ , Pr ₆ On, La ₂ 0 ₃ , Nd ₂ 0 ₃ , Y ₂ 0 ₃ . and Zr0 ₂ of the cerium - carbon containing coating with respect to total weight of the said metals expressed as oxides are :

Ce (as Ce0 ₂ ) : 25 to 50%, preferably from 35 to 45%,

Pr (as Pr ₆ Oi i) : 2 to 10%, preferably from 2.5 to 6%

La (as La ₂ 0 ₃ ) : 15 to 37%, preferably from 20 to 32%

Nd (as Nd ₂ 0 ₃ ) : 4 to 15%, preferably from 5 to 13%

Y (as Y ₂ 0 ₃ ) : 5 to 15%, preferably from 8 to 12%

Zr (as Zr0 ₂ ) : 5 to 25%, preferably from 10 to 17%

- the catalyst coating further comprises aluminium oxide and/or aluminosilicate.

- The catalyst coating of said inner wall and/or of the catalytic element has a thickness of less than 500nm, advantageously less than 300nm.

- the catalyst coating has the structure of largest particles with a size greater than lOOnm, with particles with a size of less than 70nm (preferably less than 30nm) extending within the void created between the largest particles.

- the cerium oxide - carbon containing catalyst is a catalyst controlling at least the branching reaction of H ^' species with 0 ₂ on the said catalyst, as well as for controlling the branching reaction of '0 ^' species with H ₂ on the said catalyst.

- the catalyst coating is substantially free or free of Pd, Pt, Rh, Cu and combinations thereof. -at least 50% of the carbon present in the cerium oxide - carbon containing coating is the form of graphene units, possibly with some overlapping portions. - the cerium oxide - carbon containing catalyst is adapted for controlling the formation of carbon particles in the form of porous graphite, especially in the form of graphene particles, within the combustion chamber, especially on the catalyst coating, and/or for reducing the exhaust of soot particles from the combustion chamber.

- the cerium oxide - carbon containing catalyst is adapted for emitting in function of the temperature rays with wave lengths in the violet range, rays in the blue range, rays in the green range, rays in the yellow range, as well as rays within the red range.

- the cerium oxide - carbon containing catalyst is adapted for controlling the formation of carbon particles in the form of porous graphite, especially in the form of graphene particles, within the combustion chamber, especially on the cerium oxide - carbon containing coating, and/or for reducing the exhaust of soot particles from the combustion chamber.

- the cerium oxide - carbon containing catalyst is adapted for emitting in function of the temperature rays with wave lengths in the violet range, rays with wavelengths in the blue range, rays with wave lengths in the green range, rays with wave lengths in the yellow range, as well as rays with wave lengths in the red range.

- combinations thereof.

Brief Description of the drawing

Figure 1 is a schematic view of a burning installation of the invention, and Figure 2 is another schematic view of a burning installation of the invention. Description of preferred embodiments

Figure 1 shows an incineration plant comprising an at least partly stratified combustion chamber C in the form of a fluidised bed, a flue gas collecting system D for collecting the flue gases exhausted by the combustion of the combustible material in the combustion chamber C, a heat exchanger E, and a flue gases exhaust treatment system F comprising a system Fl for treating flue gases with a dry absorbent (such calcium hydroxide) and a filter system F2 for recovering solid particles still present in the flue gases.

The combustion chamber C comprising at least two successive distinct burning zones C 1 ,C2, a flue gas outlet C3, and an ash outlet system C4. The combustion chamber C is adapted for burning a combustible material in presence of air or oxygen enriched air, whereby said chamber comprises a first burning zone C I ( a fluid bed burning zone) provided with at least one inlet 1 1 for the combustible material to be burnt (admitted above the fluid bed support 10) and at least one inlet 12 for the admission of air and/or oxygen enriched air below the fluid bed support 10 for keeping the material to be burnt in suspension above the fluid bed support 10. The first burning zone is also provided with an inlet 13 for the admission of water vapour above the fluidised bed, preferably just before flue gases enters the second burning zone C2.

Said first burning zone C 1 is extended with a channel system forming the second burning zone C2, said channel system collecting all gases and some solid particles issued from the first burning zone CI , whereby said channel system is provided with a series of guiding catalytic channels 15 extending each between a first end 15A directed towards the first burning zone CI and a second end 15B directed towards the gas outlet D of the combustion chamber C, said guiding catalytic channels 15 being provided each with a means 15C (located adjacent to the end 15B of the guiding catalytic channel 15), 15D (located in between the ends 15 A and 15B, post particularly between the end 15A and the means 15C) for forming at least one restricted passage adjacent to the second end 15B, as well as within (such as at half way) the guiding channels, said restricted passage of a guiding catalytic channel having an open surface which is comprised between 25% and 90% of the open surface of the guiding catalytic channel considered adjacent to the first open end 15 A. The restricted passage of a guiding channel formed by the means 15C is for example from 40 to 50% of the open passage of said guiding channel at its end 15 A, while the restricted passage of a guiding channel at the level of the means 15D is for example from 51 to 65%> of the open passage of said guiding channel at its end 15 A.

The channels 15 can be formed by placing elements 15E adjacent the one to the other, so as to define there between channels 15. The elements 15E are advantageously mounted mobile on a support, so as to enable a easy replacement of one element 15E, when required. The elements 15E can be provided with a precursor coating or a catalytic coating at the production plant.

The channels of the catalytic channel system C2 (forming the second burning zone) is provided with a cerium oxide - carbon containing coating, said coating of the channels further comprising at least comprising oxides of the followings elements Pr, Nd, La and at least Y and/or Zr, whereby said cerium oxide - carbon containing coating with the oxides of the followings elements Pr, Nd, La and at least Y and/or Zr, is adapted for controlling the formation of H+ species on the wall of the chamber, while controlling the hydrogen branching reactions by catalysing the use of oxygen atoms from Ce, Pr, Nd, La and at least Y and/or Zr oxides for reacting with hydrogen H ₂ for the formation of H ₂ 0 on the wall of the chamber, whereby the weight metal content of the metal element selected from Y, Zr and mix thereof expressed as oxide in the total metal weight content of metal elements selected from Ce, Pr, Nd, La, Y and Zr expressed as oxide is at least 10%, advantageously at least 15%, preferably from 16 to 40%, most preferably from 20 to 30%. The cerium - carbon coating of the guiding catalytic channels 15 forming the second burning zone is adapted for capturing photons emitted by the flame with wavelength from 6500 to 7500A, advantageously for capturing 5 to 25% of the photons with wavelength from 6500 to 7500A emitted by the flame having a temperature higher than 800°C.

Advantageously, the cerium - carbon coating of the guiding catalytic channels is adapted for ensuring a photon amplified spectrum emission radiation at least at a temperature comprised between 500 and 800°C, said spectrum covering advantageously substantially the whole range from about 4000A up to 7500A.

The guiding catalytic channels have each a minimal passage with a open cross section of at least 2.5cm ² , advantageously at least 5cm ² , preferably from 5cm ² to 20cm ² .

The guiding catalytic channels are made at least partly in a temperature ceramic like material, advantageously comprising aluminium, the wall of which being provided with a catalytic coating with a thickness from 50μπι up to 1mm, preferably from Ι ΟΟμιη to 5000μη .

The second burning zone C2 comprises at least 20 (such as 50 to 200) distinct and parallel guiding catalytic channels 15.

The second burning zone can also be provided with an air admission system 16, as well as a water vapour admission system 17.

The cerium - carbon containing coating comprises at least Y and Zr,

advantageously the weight ratio Y/Zr expressed as oxides present in the catalyst coating is comprised between 1 : 10 and 10: 1 , preferably between 2: 10 and 10:2. It has been observed that the presence of zirconium was beneficial for ensuring a catalytic efficiency on a long period of time, as well as beneficial for ensuring a more constant and less variable catalytic activity.

The cerium - carbon containing coating comprises some aluminium, preferably in its oxide or hydroxide form and/or in the form of aluminosilicate, whereby the aluminium metal content of the catalyst coating with respect to the total metal weight content of the catalyst coating of metal selected from Al, Ce, Pr, Nd, La and at least Y and/or Zr is comprised between 1 and 10%.

The relative weight of the metals selected from Ce, Pr, La, Nd, Y and Zr, expressed respectively as the following oxides Ce0 ₂ , Pr ₆ Oi i, La ₂ 0 ₃ , Nd ₂ 0 ₃ ,

Y ₂ 0 ₃ . and Zr0 ₂ of the cerium - carbon containing coating of said guiding catalytic channels with respect to total weight of the said metals expressed as oxides are :

Ce (as Ce0 ₂ ) : 25 to 50%, preferably from 35 to 45%,

Pr (as Pr ₆ O _u ) : 2 to 10%, preferably from 2.5 to 6%

La (as La ₂ 0 ₃ ) : 15 to 37%, preferably from 20 to 32%

Nd (as Nd ₂ 0 ₃ ) : 4 to 15%, preferably from 5 to 13%

Y (as Y ₂ 0 ₃ ) : 5 to 15%, preferably from 8 to 12%

Zr (as Zr0 ₂ ) : 5 to 25%, preferably from 10 to 17%

It was observed that substantially all the hydrogen species were reacted with oxygen into water/water vapour in the catalytic guiding channels 15. When leaving the guiding catalytic channels 15, the pressure of the flue gases was a little reduced with respect to the pressure inside of the channels 15. The pressure thereafter increased due to a phase expansion of the steam (dry superheated steam) in the collecting system D, whereby enabling a first heat/energy recovery). Then the steam containing flue gas passes within the condenser / heat exchange E for a second heat/energy recovery, meaning a drop of pressure. The (wet) flue gases enter then into the heat exchanger E for recovering heat from the flue gases. The heat recovery was quite effective, as large amount of water could be. condensed, said water being acid. The temperature of the flue gases was below 100°C, such as from 70 to 90°C. The so collected condensed water was then further treated for neutralising acid components and for removing solid particles (dust, fly ash, etc.), before being naturally treated in lagoons. The flue gases exhausted from the heat exchanger E are then treated with an absorbent, such as a dry absorbent like calcium hydroxide or calcium hydroxide based absorbent, if required..

After said latest treatment substantially all noxious compounds of the flue gases were removed.

It was observed that some catalyst of the second burning zone C2 formed a deposit on the surface of the flue gases collecting system D as well within the outlet of the chamber, whereby ensuring a further catalytic treatment of the flue gases into the collecting system.

It was also observed that the flue gases exhausted from the catalytic guiding channels 15 were equivalent to a superheated - dry - steam, said superheated steam being submitted to some expansion (zone 25) in the gases collecting system adjacent to the outlet 15B of the second burning zone (i.e. with the gas outlet of the chamber). Said superheated dry steam expansion and the condenser E ensuring a high velocity outflow of the hot flue gases, whereby enabling to reduce the velocity of the air necessary for ensuring a fluidisation of the combustible material.

If necessary some extra liquid or gaseous fuel can be admitted within the first burning zone CI through an injector 21.

For ensuring some rejuvenation of the catalyst of the second burning zone, methane (or possibly some fuel) and water can be injected within the first burning zone, advantageously without the presence of some waste material or other combustible material.

Figure 2 is an installation similar to that of figure 1, except the installation is provided with an injector 22 for injecting particle combustible material and/or liquid fuel and/or gaseous fuel within the first burning zone CI (said injection being operated substantially without the presence of oxygen/ air), and a system 30 for injecting air in the combustion chamber C. Said system is for example a fan 31 conducting air within a tube 32 extending within the combustion chamber, whereby the injector 22 is located within the said tube 32. The inner wall of the tube is provided with a catalytic coating. The channel system C2 is similar to that of figure 1. The installation of Figure 2 can also be provided with a water vapour injector. The catalytic coating of the tube is advantageously of the same type as the catalytic coating within the second burning zone, as well as on the wall of the flue gases collecting system D.

The combustion chamber, especially the second burning zone is provided with a catalyst or a catalyst precursor.

The catalytic guiding channels or the tube 32 are for example a support (alumino silicate, alumina silico phosphate, ceramic, etc.) provided with a catalyst coating or a precursor coating suitable for generating a catalyst coating.

The precursor used was a mix of nano scale particles possibly dispersed in a wax or liquid, the composition of said mix being:

1. nano carbon primary particles with a size of less than 10 nm (possibly agglomerated into a structure with a size of less than 500nm. Said nano carbon primary particles are present in the precursor mix at a rate of 10 to 50% by weight, advantageously from 15 to 30% by weight, preferably about 20% by weight.

Instead of using carbon nano particles as such, a wax possibly with carbon nano particles can be used.

The carbon particles are preferably comprising some particles forming a two dimensional graphene structure, most particularly a mono layered two

dimensional graphene structure.

2. a mix of metal oxide particles, especially of nanoparticles (particles with a size of less than 200nm, preferably at least partly less than 50nm. Said mix of metal particles comprises advantageously with respect to the total mix of said metal oxide particles (as weight %) :

Ce (as Ce0 ₂ ) : 25 to 50%, preferably from 35 to 45%,

Pr (as Pr ₆ O _u ) : 2 to 10%, preferably from 2.5 to 6%

La (as La ₂ 0 ₃ ) : 15 to 37%, preferably from 20 to 32%

Nd (as Nd ₂ 0 ₃ ) : 4 to 15%, preferably from 5 to 13%

Y (as Y ₂ 0 ₃ ) : 5 to 15%, preferably from 8 to 12%

Zr (as Zr0 ₂ ) : 5 to 25%, preferably from 10 to 17%

Al (as A1 ₂ 0 ₃ ) : 0 to 10%, preferably from 1 % to 5%

Si (as Si02) : 0 to 10%, preferably from 0.5 to 5% (Said silicon can be in the form of liquid or soluble tetra ethoxy silane, in a solvent system, such as methanol, ethanol, etc.)

The mix of nano oxide particles is advantageously a mix of nano oxide particles with a weight average size of more than 100 nm and of nano oxide particles with a weight average size of less than 70 nm, the weight ratio nano oxide particle with a weight average size greater than lOOnm / nano particles with a weight average size lower than 70nm being comprised between 5: 1 and 1 :5, advantageously between 4: 1 and 2: 1. 3. possibly a wax or liquid system, for enabling some adhesion of the particles on the surface to be coated, said wax or liquid being preferably molecules comprising carbon and hydrogen, as well as preferably oxygen atoms, the weight ratio wax / mix of metal oxide particles is advantageously greater than 2, such as comprised from 2.5 up to 6.

The precursor was used for coating (for example by bmshing, blowing, spraying, etc.) wall of the combustion chamber. The combustion chamber is then burning fuel with air for 30 minutes. After said burning step, the excess of catalyst was removed.

The catalyst coating had a thickness of less than about 70nm, with metal particles homogeneously dispersed.

The combustion chamber will moreover have the following advantages:

- high thermal stability of the catalyst

- high ionic conductivity of the coating

- possibility to burn at least partly the carbon and the hydrogen from the fuel separately, namely a large portion of the fuel carbon in the volume of the chamber (comprising the plasma zone adjacent to the catalyst coating(s), i.e. in a N2 enriched environment with respect to ai ), and a large portion of the fuel hydrogen on or in the catalyst coating(s) (i.e. namely in a 0 ₂ rich environment or in a reduced N2 environment with respect to air)

- High oxygen storage capacity, with high uptake and release oxygen rate

- High hydrogen storage capacity

- Possible down sizing of the filter or gas cleaning unit, due to less small particle emissions, as well as excellent working of the condenser/cooler.

- Possibility to use a filter with large pore size

- Possibility to reduce pressure drop in the exhaust, at the level of the filter, - quicker activation of the three way catalyst

- stable working of the catalyst during time, whereby less catalyst rejuvenation is needed

- possible working of the engine with lambda value higher than 1.3, such as higher than 1.4, such as from 1.4 to 1.3, such as from 1.5 to 2.1.

- improved post treatment

- less NOx

- low HC content in the exhaust gases

less carbon particles exhaust (especially substantially no small sized carbon particles exhaust, such as substantially no carbon particle with a size of less ΐ!ΐΛη 5 μΓη)

- no soot formation in the combustion chamber

no soot deposit in the exhaust pipe

- high water vapour exhaust.

- Higher global amount of free electrons in the combustion chamber.