ES2392989B2 - CATALYTIC TRAP OF HYDROCARBONS CONTAINED IN THE EMISSIONS OF AN INTERNAL COMBUSTION ENGINE. - Google Patents

Abstract

The present invention refers to a catalytic trap of hydrocarbons contained in exhaust gases produced by an internal combustion engine, characterized in that it is free of noble metals and comprises at least one layer of a molecular sieve of formula XH-ZSM-5, where X represents one or more transition metals and H-ZSM-5 represents a zeolite with a Si / Al ratio between 10 and 20, which presents in its internal structure an ionic exchange of protons for metal cations in a percentage comprised between 20 % and 60% of the total protons present in the zeolite in its original state. The invention also contemplates the method of obtaining said trap, its use in a catalytic converter of a combustion engine and in the engine itself, as well as the method of removing hydrocarbons by means of said trap.

Description

CATALYTIC TRAP OF HYDROCARBONS CONTAINED IN THE EMISSIONS FROM AN INTERNAL COMBUSTION ENGINE TECHNICAL SECTOR

This invention falls within the area of chemical technology and more specifically it is a catalyst not based on noble metals (free of any noble metal) for the reduction of hydrocarbon emissions, mainly during cold start

of

motors  of combustion internal even if act during everything

the

cycle of functioning of the same, since  the start

until

the stop.

STATE

OF THE TECHNIQUE

In

the motors of combustion internal the fuels

fed liquids are burned with the necessary amount of air producing their complete combustion to carbon dioxide and water, along with other by-products of incomplete combustion, such as carbon monoxide and unburned hydrocarbons, and other polluting gases, such as oxides nitrogen. The liquid fuels that are fed are generally gasoline and diesel, although different alcohols can also be fed, such as ethanol or methanol and some of their mixtures. In accordance with the above, the exhaust gases from engines contain polluting gases that have to be cleaned before being released into the atmosphere in order to comply with the environmental regulations set by different government policies.

The treatment of exhaust gases from internal combustion engines to convert toxic compounds such as hydrocarbons (HC), carbon monoxide (CO), oxides of nitrogen (NOx) and even particles (for example soot in the case of diesel engines) in harmless compounds such as water, C02 and nitrogen it is a well established technology. This process is carried out by contacting the exhaust gas stream with a device

or control and reduction system for said pollutants, known in the field as a catalytic converter, and which usually comprises, in the current state of the art, a three-way catalyst in gasoline engines. These catalysts, located in the exhaust before the gases exit into the atmosphere, are capable of oxidizing HC and CO and reducing NOx; some examples of three-way catalysts are those described in U. S. Pat. No. 4, 52 8, 2 7 9. However, the three-way catalysts are not active during the entire conduction cycle, but unfortunately do not start operating until the catalyst reaches temperatures of the order of 2O O ° C. Thus, hydrocarbon emissions in gasoline vehicles occur mainly during the cold start of their combustion engines.

In the case of diesel engines, the device for reducing / removing pollutants from the engine exhaust gas stream usually comprises a two-way oxidation catalyst to reduce emissions of HC and CO, a particulate filter for soot removal, as well as various devices for NOx control. Again, two-way oxidation catalysts are not active throughout the entire driving cycle, and most HC emissions occur during cold start. As can be seen, it is a much more complex device than that of gasoline engines, since it works in excess of oxygen, conditions that do not allow the reduction of NOx to be carried out simultaneously in a single system for its elimination , as if it happens in the case of three-way catalysts.

In general, this device for the control and reduction of gases and particles is going to be called in this document "catalytic converter", which includes or encompasses different control systems depending on the type

of fuel used in the engine. Thus, this system includes the catalyst that performs the oxidation function of HC and CO, which can be two-way in diesel engines or three-way in gasoline engines (since it also reduces NOx). Said catalytic converter would include, in addition to the aforementioned oxidation catalyst, other necessary elements such as a casing, detection sensors and gas measurement,

valves,

filters of particles and devices of control

of

NOx in the case  of motors diesel, traps  of HC or

traps

catalytic how the definite in the Present

request.

The

appearance of normative every time plus restrictive

Regarding emissions for vehicles, it has led both automobile manufacturers and catalytic converters / catalysts to try to reduce hydrocarbon emissions during cold start. This is because, as already mentioned, the catalyst used in cars takes between 60 and 120 seconds to reach a temperature of around 200 to 300 ° C. During this period, the catalyst has no activity and the amount of hydrocarbons (HC) released has been estimated at 50-80% of the total. For the resolution of this environmental problem, different alternatives have been proposed. Among them, it is worth highlighting the incorporation of inorganic solids as adsorbents before the double-way or three-way catalyst (CTV), which is known as hydrocarbon traps. In this system, ideally, HCs are retained at low temperatures and are not released until the dual-way or three-way catalyst has reached ignition temperature.

The materials that have been studied for its application as HC traps are numerous, highlighting different types of molecular sieves and in particular zeolites. Thus, materials such as ZSM-5, Mordenite,

BETA, Y, SAPO-S and SAP0-41 among many others. Some references recently found in the bibliography are: M.H. Zahedi-Niaki, M. Eic, S. Kaliaguine, Microporous Mesoporous Mater. 102 (2007) 171-177. J. M. 5 López, M. V. Navarro, T. García, R. Murillo, A. M. Mastral,

F. J. Varela-Gandía, D. Lozano-Castelló, A. Bueno-López, D. Cazorla-Amorós. Microporous Mesoporous Mater. 130 (2010) 239-247. S.P. Elangovan, M. Ogura, S. Ernst, M. Hartmann,

S. Tontisirin, M.E. Davis, T. Okubo, Micropor. Mesopor. 1O Mater. 9 6 (2 O O 6) 21 O.

Numerous references can be found in the state of the art describing the preparation and use of hydrocarbon traps to minimize their emissions during cold start. For example, one of these references

Recent 15 is U.S. Pat. No. 2008/0159936. In this patent, the reduction of hydrocarbon emissions during the cold start of an engine is claimed through the joint effect of a hydrocarbon trap and a current three-way catalyst. The trap of

Hydrocarbons consists of a mixture of several molecular sieves with different pore sizes, simulating the presence of one or more molecular sieves with pores no larger than those present in solids with 8-membered rings; with one to several molecular sieves with sizes

25 pores larger than those present in solids with rings of at least 10 members. In this patent references are given on other methods of preparation and uses of HC traps, in which different configurations are used in the arrangement of the hydrocarbon trap, either prior to

30 catalyst that performs the oxidation function (double-track or three-way) or after it, which entails the incorporation of complicated valve systems for the treatment of the concentrated HC stream, once its desorption occurs from the HC trap at high

35 temperatures. In all of them the materials only act as HC adsorbents that are subsequently treated in another bed by means of an oxidation catalyst

(two or three way). As an alternative to these two-bed systems, and previously shown by other inventors, in U.S. Patent No. Pat. No. 2008/0159936 it is also indicated that the incorporation of noble metals that act as HC oxidation catalysts, such as Pt, Pd, Rh and Ru or their mixtures, impregnated on the previous molecular sieves leads to the development of HC catalytic traps based on noble metals, where the HC are adsorbed at low temperatures and oxidized to C02 and H20 before desorption occurs. The incorporation of adsorbent and catalyst in a single bed is of great interest, since it not only reduces the complexity of the system but can also lead to a reduction in the weight of the catalytic converter.

The use of systems incorporating the hydrocarbon trap and an element that acts as an oxidation catalyst for the HCs (being called said catalytic trap system) as two different materials in the same substrate contained in the catalytic converter is also shown in U.S. Pat. No. 5,772,972. This system consists of a hybrid system formed by a hydrocarbon trap and one or more noble metals that act as oxidation catalysts deposited on the same cordierite monolith. Where the hydrocarbon trap consists of an H-ZSM-5 zeolite exchanged with Cu or Pt. In this invention, the Si / Al ratio is postulated as a very important parameter. Setting ratios between 30 and 150 as necessary values to reduce the effect

negative

of the presence of big percentages of Water.

Further,

I know make necessary the incorporation of metals

noble

for than the material I know behavior how trap

catalytic.

In U.S. Pat. No. 6,074,973 gives a method for developing a mixed hydrocarbon trap / oxidation catalyst or noble metal based catalyst trap, from a physical mixture of solids. In this case, palladium and silver are dispersed on particles of a refractory inorganic oxide and particles of one or more among the following zeolites ZSM-5, BETA, Y, MCM-22 or EU-1 with a Si: Al ratio of at least 10.

U.S. Pat. No. 2007/0129236 shows a HC catalyst trap based on noble metals that act as oxidation catalysts composed of silver exchanged zeolites as the HC trap and noble metals as an oxidation catalyst. Adsorbent and catalyst are placed on the same substrate, either in a single layer or as two independent layers on top of each other.

An adsorbent-catalyst or trap is shown in the summary of Japanese patent application JP 6-153650

catalytic

based in metals noble than they act how

catalysts

of oxidation of HC, the which consists in

particles

in the than I know combine a cap of a

catalyst

of P.S on alumina stabilized with ceria and

another layer with the adsorbent acting as an HC trap. The HC trap is made up of zeolites with a Si: Al ratio of 40 or greater, which includes ZSM-5 and BETA. Different ions can be incorporated into these zeolites, either by immersion or ion exchange methods. The presence of metal ions increases the adsorption capacity of HC. These ions include those of Ag, Pd, Pt, Au, Ni, Cu, Zn, Co, Fe, Mn, V, Ti and Al. Among all of them, it is highlighted that the presence of at least one of the cations Cu, Ag or Au leads to a great adsorption of HC even in the presence of H20. It is indicated that the content of the metal ion must be greater than 20% and

preferably greater than 40%, with respect to the Al atoms in the zeolite.

An improved catalytic trap system in which HC oxidation is increased, although also based on noble metals, is shown in WO 02/07859 A2. The composition of this invention comprises a multi-layered substrate. A first layer with zeolite, which acts as an adsorbent for HC. Another layer of an active metal in close contact with the zeolite and one or more layers of a HC oxidation catalyst. The main difference from previous inventions is that the active metal only favors the total oxidation of the HC, but does not affect the adsorption capacity of the material. The active metal can be made up of one or more alkali or alkaline earth metals, mainly Cs, while the HC traps can be synthetic or natural zeolites, as well as acidic, basic or neutral zeolites. Synthetic zeolites include ZSM-5, BETA, Y, ultrastable-Y, ferrierite, mordenite, and MCM-22, preferring ZSM-5 and BETA. The Si: Al ratio can be between 1 and 500, with preferred values between 15 and 150.

As it has been tried to highlight in this section, the problem for controlling the emissions of the polluting gases contained in the exhaust stream of an internal combustion engine, in particular of hydrocarbons, is more pronounced during the cold start of engines, a period during which the engine is below the standard operating temperature giving rise to a greater number of emissions and during which the catalysts in the state of the art used to

turn into

these emissions in products innocuous I know

find

with great probability by below of its

temperature

of operation. During the first 30 to 12 O

seconds, CO levels are in the range of 1 to 2% by volume, while hydrocarbons range from 500 to 1000 ppmv. This invention

provides a catalytic trap and a method for reducing hydrocarbon emissions during and after the cold start of an internal combustion engine, and which, additionally and very advantageously, also acts as an oxidation catalyst during hot engine operation , without using noble metals.

DESCRIPTION OF THE INVENTION Brief description of the invention The invention relates firstly to a catalytic trap based on an adsorbent material to reduce hydrocarbon (HC) emissions in the exhaust gases of an internal combustion engine and, in particular, to minimize emissions of these compounds during the cold start operation of an engine. Said catalytic trap is characterized in its most essential form in that it is free of noble metals and comprises one or more layers of a molecular sieve of the formula

XH-ZSM-5, where X represents one or more transition metals and H-ZSM-5 represents a zeolite with a Si / Al ratio between 10 and 20, including both limits, and which has an ion exchange in its internal structure of protons by metal cations of X in a percentage between 20% and 60%, including both limits, of the total protons present in the zeolite in its original state.

Unlike the catalytic traps hitherto known in the field, this adsorbent material can capture the hydrocarbons during the cold start of the engine and oxidize the gases during the hot operation of the engine without using noble metals, which are used in the state of the technique as oxidation catalysts. The advantages are structural (simplification

of pollutant control and reduction systems in

internal combustion engines) as economical (the price

of commonly used noble metals can be of

up to 100 times greater than other non-noble metals)

5

Basically the catalytic trap bed free of

noble metal is composed of a H-ZSM-5 zeolite with

a Si / Al ratio between 10 and 20, said zeolite

being partially exchanged with cations of one or

various non-noble metals (for example, copper), where the

1 O

exchange percentage must be between

20% and 60% of the total protons present in the

original material, giving rise to a material called XH-

ZSM-5. For optimal trap behavior

catalytic, the metal or metals must be exchanged in

fifteen

inside the zeolite structure and never on the

external surface of it. The zeolites covered

this invention as hydrocarbon catalytic traps are

limited to H-ZSM-5 acidic zeolites with Si / Al ratio

under 20 and always over 10, so that

2 O

provide enough sites and in positions

suitable to carry out the partial exchange with

metal cations. The percentage of metal cations

exchanged is always equal to or greater than 20% and less or

equal to 60% of the total protons in the material

25

reference zeolitic, and all this metal (or metals)

must be present as cations exchanged in the

Zeolite internal structure.

This material is capable of reducing emissions of

hydrocarbons both in internal combustion engines

30

working with quasi stoichiometric mixtures as with

fuel-poor blends.

In this way, the outflow of gases from

escape is passed through a bed of the object catalytic trap

of this invention that adsorbs HC at low temperatures

35

such as those that predominate during engine start

combustion. Additionally, it has the advantage that

high temperatures is able to carry out both the

total oxidation of the HC retained by the trap

catalytic like that of those present in the stream

5

exhaust gases, giving rise to an exhaust current of

gases are harmless in HC and can be released into the atmosphere.

The main difference between this invention and others

materials previously described in the state of the art are

based on the fact that this material is a catalytic trap that

1 O

allows to dispense with any additional element or layer

consisting of an oxidation catalyst based on one or

various noble metals, so that in a single bed and without

the need to incorporate high-cost materials is

can totally eliminate HC emissions without requiring

fifteen

further treatment of the current. This allows

the catalytic trap can be placed anywhere

position with respect to the different control systems

already described in the state of the art for the reduction of

emissions of other pollutants present in the stream

2 O

of gases, since the total elimination of HC occurs

about the catalytic trap. Preferably the trap

catalytic is situated in a position posterior to the others

control systems, facilitating the elimination of

HC emissions not only during cold start but

25

also during the driving cycle, without the need for

complex valve systems or other devices and

significantly reduces the thermal stress at which

submits to an oil trap located before the

other converter emission control systems

30

catalytic. In addition, in a novel way, the use of

of a ZSM-5 zeolite with a Si / Al ratio lower than

used by other authors in exchanged zeolites,

despite his supposedly proven loss of benefits

as a hydrocarbon trap in the presence of water (10%

35

v / v), since you need to have a solid that contains

a high number of protons for their subsequent partial exchange with the metal or metals. This characteristic is key in the development of the present invention, since it allows obtaining a solid in which the coexistence of the metal occurs.

or metals and protons in an optimal relationship inside the channels, which gives rise to a catalytic trap where, in a novel way, the role of the HC trap and the oxidation catalyst is combined in a single bed throughout the start-up cycle cold.

Another advantage of the present catalytic trap is that it can achieve the effective reduction of hydrocarbon emissions during the cold start of vehicles with internal combustion engines during at least 500 cold starts, that is, it is not deteriorated by its use.

The present invention also encompasses a bed or substrate of the catalytic trap described herein.

Also, another object of the present invention is a catalytic converter comprising the catalytic trap described here that is not based on noble metals. Usually, but not necessarily, such a catalytic converter further comprises, like others

systems

of control of emissions, a catalyst of

oxidation

of HC, than is of three tracks in the case of

vehicles

than operate with motors of gasoline and a

catalyst

of two tracks together to a filter of particles and

a NOx emission control system in vehicles with diesel engines. Likewise, another objective of the present invention is the combustion engine that comprises the catalytic trap for the elimination of hydrocarbons, or the catalytic converter in which it is integrated.

Detailed description of the invention

X is preferably selected from the group consisting of Cu, Fe, Zn, Co, Ni and any combination thereof, and still more preferably X is copper.

Also preferably, the zeolite has in its internal structure an ionic exchange of protons for metal cations of X in a percentage comprised between 30% and 50% including both limits, said exchange being still more preferably 40%.

In a preferred embodiment, the noble metal free catalytic trap consists specifically of one or more layers of the molecular sieve described in the previous section, in any of its variants.

In another more preferred embodiment, the noble metal free catalytic trap consists of one or more layers of a molecular sieve of the formula

CuH-ZSM-5, where Cu is copper and H-ZSM-5 represents a zeolite with a Si / Al ratio of between 10 and 20, including both limits, and which presents in its internal structure an ionic exchange of protons for Cu cations in a percentage between 20% and 60%, including

both limits,

of the total of protons present in the

zeolite

in its state original.

The

trap catalytic usually introduce oneself, even if not

always necessarily, in the form of a bed or substrate through which the stream of gases to be treated is passed.

Also preferably, the catalytic trap can be supported on a matrix, as is usually the case with this type of material, and more preferably the matrix is a cordierite monolith.

As already indicated with regard to the system or device for the control and reduction of polluting gases and particles contained in an exhaust stream of an internal combustion engine, which is called a catalytic converter and which comprises the catalytic trap described here, this represents the current state of the art in reducing polluting emissions in exhaust gases such as CO and NOx, among others. Said converter

Catalytic may preferably comprise an HC oxidation catalyst, which in the case of gasoline powered vehicles is a three-way catalyst that can be connected to the catalytic trap at its rear (after gases pass through the trap) or earlier (before the trap), although the latter position is more preferred (that is, the trap is located in a position after the three-way catalyst, depending on the direction of passage of the gas stream to be treated). In the case of vehicles with diesel engines, the oxidation catalyst is preferably a two-way catalyst. Additionally, and more preferably, the catalytic converter in diesel engines further comprises a particulate filter and a NOx removal system. As derived from these comments, the nature of this converter will depend on both the type of fuel used (gasoline or diesel) and the stoichiometry of

mix

fed in the case of motors of gasoline. Of

way

preferred, the converter catalytic not employs (I know

find

free of) elements and devices of

recirculation

of the gases of escape, already than not are

necessary

Thank you to the trap catalytic used.

With "connected here"; or quot; locatedquot; the present memory refers to the possibility that one element connects to another or is located in a certain position, in the manner of "it can be connected here", or "it can be located".

In the present invention, the method for removing hydrocarbons contained in a gas exhaust stream from the internal combustion engine comprises passing said stream through a bed of the catalytic trap described here. Therefore, the use of the catalytic trap object of the present invention for the removal of hydrocarbons in internal combustion engines is also described. This catalytic trap is preferably applied in catalytic converters (or control systems and

reduction of polluting gases and particles contained in

an exhaust stream from an internal combustion engine)

that do not use (free of) gas recirculation

escape.

5

In a preferred embodiment, the flow or current of

gases is passed through a HC oxidation catalyst,

more preferably three-way in a vehicle operated with

a gasoline engine and a two-way in a diesel engine,

which is located in the catalytic converter that

1O

represent the current state of the art in reducing

pollutant emissions in exhaust gases, such as

previously discussed. That is, in this embodiment

concrete it is proposed to pass the mixture of exhaust gases from the

HC oxidation catalyst, preferably three

fifteen

two-way on gasoline engines and two-way on engines

diesel, through the described catalytic trap,

preferably being a CuH-ZSM-5 zeolite partially

exchanged with copper that has the characteristics

described here and acting as a catalytic trap for

twenty

hydrocarbons. Thus, it is not necessary to incorporate a

catalyst that treats the stream later as

mentioned in other inventions. However, other

catalyst-catalytic trap assembly arrangements

are also possible to achieve the reduction of

25

hydrocarbon emissions during cold start,

like those described in the state of the art.

Another object of the present invention is a method of

obtaining a catalytic trap free of noble metals

comprising one or more layers of a molecular sieve of

30

formula

XH-ZSM-5,

where X represents one or more transition metals and H-

ZSM-5 represents a zeolite with a Si / Al ratio

between 10 and 20, including both limits, and that

35

presents in its internal structure an ionic exchange of

protons by metal cations in a percentage between 20% and 60%, including both limits, of the total protons present in the zeolite in its original state.

Said method comprises: synthesizing the H-ZSM-5 zeolite in its acid form, by calcination (in its ammonium form); and exchanging metal ions of the metal or metals with ions of the internal structure of the zeolite, by means of immersion with stirring of said zeolite in a precursor solution of the metal or metals, and subsequent drying and calcination.

X is preferably selected from the group consisting of Cu, Fe, Zn, Co, Ni and any combination thereof, and even more preferably X is copper, such that the molecular sieve has the formula CuH-ZSM-5.

The H-ZSM-5 zeolites of the present invention are preferably synthesized by the following process: The zeolite is started in its ammonium form, NH4 + -ZSM-5, in a preferred case with a silicon / aluminum atomic ratio of 15 (supplied by Zeolyst International) and is calcined in air in a temperature range between 450 ° C and 600 ° C, including both

limits.

Of way plus preferred still, I know calcine in

air

to 450 ° C during 6 hours, employing a ramp of

warming up

5 ° C per minute.

In another preferred embodiment, the exchange with metal cations, preferably copper, is carried out using the following procedure:

-

contacting zeolite H-ZSM5 in acidic form with a precursor solution of the metal or metals,

Stir the mixture in a thermostatted bath at a temperature between 40 ° C and 80 ° C for a -drive the solid at a temperature between 100 ° C and 150 ° C, including both limits; and

weather

understood between 10 and 25 hours, included

both of them

limits;

-filter the

liquid;

-wash the

solid obtained with Water distilled;

calcine the solid at a temperature between 450 ° C and 600 ° C, including both limits, for 4 hours using a heating ramp of 1 ° C per minute. Basically, the ZSM-5 zeolite is contacted in

its acid form, H-ZSM-5, prepared as described in the previous paragraph, with a certain volume and concentration of precursor solution of the metal or metals, being for example in a preferred (although not exclusive) case Cu (N03) 2 3H20, more preferably concentration 3. 4 5 * 10-3 M. The mixture remains stirred in a thermostated bath at an optimal temperature and time (preferred conditions: 77 ° C for 18 hours). After this time, the solid is filtered and washed with distilled water. The sample is then dried at temperatures between 100 ° C and 150 ° C in air including both limits, more preferably at 110 ° C and, finally, it is calcined at temperatures between 450 ° C and 600 ° C including both limits, more preferably at 600 ° C, for a time interval between 2 and 6 hours, more preferably for 4 hours, using a heating ramp of 1 ° C per minute.

As said, the catalytic trap described in this invention can be deposited on a cordierite monolith by means of the different methods known in the state of the art. Basically, you first have to anchor the zeolite to the monolith; to, secondly, proceed to drying and calcining the material to

acidify the zeolite, before proceeding to the cation exchange with the metal or metals. Thus, in a preferred embodiment, the method of obtaining the catalytic trap supported on a matrix comprises at least the following steps:

-

depositing the zeolite in its NH4 + -zsM5 ammonium form on the matrix by: preparing a suspension of said zeolite

with

to the less a binder and to the less a agent

surfactant,

later

immersion of the matrix in bliss

suspension,

and

·

drying and calcination;

acidify

the zeolite impregnated in the matrix

by calcining the material formed in the previous stage at a temperature between 450 ° C and 600 ° C, both limits included; and - proceed to the exchange of metal ions of X with ions of the internal structure of the zeolite, by means of immersion with agitation of said zeolite impregnated in the matrix in its acidic form in a precursor solution of the metal or metals X, and - subsequent drying calcination. The method preferably used to deposit the

Zeolite ZSM-5 on cell structure cordierite monolith is the immersion method, also known as "dip-coating". For this, an aqueous suspension is prepared which, in addition to the commercial zeolite in its ammonium form, contains at least one binder (eg colloidal silica) to ensure the anchoring of the zeolite to the monolith and at least one surfactant to disperse the solid. ; As the surfactant, for example, but not exclusively, any of the compounds registered under the name Teepol can be used, such as Teepol 610 and Teepol 410 (secondary alkyl sulfates); Teepol 514 (mixture of

secondary alkyl sulfate and alkyl benzene sulphonate); Teepol 515 (alkyl benzene sulfonate); or Teepol CH53f (mixture of alkyl benzene sulphonates with condensed alkyl phenol / ethylene oxides), among others. Subsequently, the cordierite monolith is immersed in said suspension for between 1 and 10 minutes, preferably 3, and then the excess suspension can be removed using, for example, a compressed air gun. Drying is then carried out, preferably at room temperature for a period of time between 12 and 24 hours, including both limits, and more preferably for 12 hours, using for example a rotary device, so that the zeolite is uniformly distributed throughout of the monolith channels. After this time, the monoliths can be dried preferably using a temperature between 150 ° C and 250 ° C including both limits, and more preferably at 200 ° C, between 2 and 10 hours, more preferably for 4 hours, using a very warm ramp. slow (preferably 1 ° C per minute), since a higher drying speed can cause the abrupt water adsorbed on the zeolite to leave, leading to cracks in the zeolite film, which could affect the mechanical stability of said zeolite zeolite layer.

Then

I know calcine the monoliths to a temperature

preferably

understood between 350 ° C and 450 ° C, plus

preferably

to 400 ° C, between 2 and 10 hours, plus

preferably

4 hours. So much the drying how the

calcination can be carried out in a flask. In order for the zeolite coating to be stable, the monoliths are optionally treated with an ultrasound bath, so that the mechanically unstable zeolite is detached from the monolith.

In this way, a deposit of ZSM-5 zeolite in its ammonium form is obtained, and then the monoliths are calcined in air at a temperature preferably between 450 ° C and 600 ° C including both limits, more preferably at 450 ° C , between 2 and 10 hours, more preferably 6 hours, to obtain the acid form, H-ZSM-5, from which it starts to perform the exchange with metal cations. In order to carry out this exchange, the zeolite supported on the monolith is contacted with a precursor solution of the metal or metals of determined concentration, in this case illustrative and not limiting in that X is Cu a solution of Cu (N03) 2.3 H20. The mixture remains stirred in a thermostated bath at an optimal temperature for a certain time, after which time the monolith is filtered and washed with distilled water. It is then preferably dried at 11 ° C in air and, finally, it is calcined at a temperature between 450 ° C and 600 ° C including both limits, more preferably at 600 ° C, between 2 and 10 hours, more preferably 4, using a very slow heating ramp (preferably 1 ° C per minute).

The importance of carrying out the partial exchange of protons for metal cations of non-noble metals is shown in Figure l. This figure represents the behavior of an H-ZSM-5 hydrocarbon trap with a Si / Al ratio greater than 10 and less than 20 during a simulated cold start cycle. The experimental conditions used to carry out the cold start cycle were as follows:

•

100 ppmv propene, 87 ppmv toluene, l. 0% 02, 10% H2 0 and balance Ar.

•

Space speed: 10000 hours-1

•

Heating ramp: 50 ° C / min

•

Catalytic trap in powder form

You can see in Figure 1 the evolution of the concentration of propene (solid black line) and toluene (dashed black line) at the exit of the H-ZSM zeolite-

5. In this solid, it is observed that both propene and toluene are released from the trap, so it is not suitable as a catalytic trap in a post-three-way catalyst arrangement, as proposed in the present invention. Furthermore, the fact that the hydrocarbons are released at temperatures below 200 ° C, makes this solid also not suitable for application as a hydrocarbon trap in any of the existing state of the art provisions.

The need to optimize the percentage of protons exchanged with metal cations is reflected in Figure 2, which shows the behavior of a CuH-ZSM-5 hydrocarbon catalytic trap partially exchanged with copper cations with a Si / Al ratio greater than 10 and less than 20 during a simulated cold start cycle and a percentage of copper exchanged less than 20%. The experimental conditions used to carry out the cold start cycle were as follows:

•

100 ppmv propene, 87 ppmv toluene, l. 0% 0 2, 10% H2 0 and balance Ar.

•

Space speed: 10000 hours-1

•

Heating ramp: 50 ° C / min

•

Catalytic trap in powder form You can see in Figure 2 the evolution of the

concentration of propene (solid black line) and toluene (dashed black line) at the exit of the CuH-ZSM-5 zeolite. In an analogous way to the zeolite not exchanged with copper, in this solid it is also observed that both propene and toluene are released from the trap, so it is not suitable as a catalytic trap in a post-catalyst three-way arrangement, as proposed in the present invention. Furthermore, the fact that hydrocarbons are released at temperatures below 200

° C, makes this solid also not suitable for application as a hydrocarbon trap in any of the provisions existing in the state of the art.

The importance of the location of the copper cations inside the zeolite channels is shown in the results presented in Figure 3. These results correspond to a solid CuH-ZSM-5 with Si / Al ratio greater than 10 and less than 20 and that has a total copper content of 1.4% by weight, of which only a part is exchanged inside the structure of the zeolite, and the rest of the copper is forming copper oxide nanoparticles on the surface of the zeolite (observed using TEM images (Figure

4) •

The experimental conditions used to carry out the cold start cycle were as follows:

•

100 ppmv propene, 87 ppmv toluene, l. 0% 0 2, 10% H2 0 and balance Ar.

•

Space speed: 10000 hours-1

•

Heating ramp: 50 ° C / min

•

Catalytic trap in powder form You can see in Figure 3 the evolution of the

concentration of propene (solid black line) and toluene (dashed black line) at the exit of the CuH-ZSM-5 zeolite partially exchanged with copper in which not all the copper is inside the zeolite channels. In this sample it is observed that while the toluene is released from the trap, the propene is retained until temperatures high enough for its catalytic combustion to take place. Therefore, this material is also not suitable as a catalytic trap in a post-three-way catalyst arrangement, as proposed in the present invention. However, in this case, the fact that only hydrocarbons are released to

temperatures above 250 ° C, this solid does

which is suitable for application as a hydrocarbon trap in any of the existing state of the art provisions, in which the catalyst is arranged before the three-way catalyst.

The importance of having a solid with the appropriate content and location of copper ions is shown in the results shown in Figure 5. These results correspond to a CuH-ZSM-5 solid with Si / Al ratio greater than 10 and less to 20, which was prepared using a sufficient amount of copper so that the ion exchange was in a range between 20-60% and choosing optimal exchange conditions so that all the copper was exchanged inside the zeolite channels and never forming copper oxide nanoparticles on the surface of the zeolite (confirmed by TEM images (Figure 6). It should be noted that, due to the exchange conditions used (optimal conditions necessary for the preparation of the materials object of the present invention), the resulting solid has a higher ion exchange percentage than the solid presented in Figure 3 (confirmed by a Spectroscopic study Diffuse Reflectance Infrared (DRIFT); results not included in the present patent).

The experimental conditions used to carry out the cold start cycle were as follows:

•

100 ppmv propene, 87 ppmv toluene, l. 0% 0 2, 10% H2 0 and balance Ar.

•

Space speed: 10000 hours-1

•

Heating ramp: 50 ° C / min

•

Catalytic trap in powder form

You can see in Figure 5 the evolution of the concentration of propene (solid black line) and toluene

(dashed black line) at the exit of the CuH-ZSM-5 zeolite partially exchanged with copper (within the optimal range between 20-60%) in which all the copper is inside the zeolite channels. In this sample, it is observed that both toluene and propene are retained at temperatures high enough for their catalytic combustion to take place. Therefore, this material becomes a suitable material as a catalytic trap in a post-three-way catalyst arrangement, as proposed in the present invention. Furthermore, the fact that no hydrocarbons are released throughout the temperature range, makes this solid also suitable for application as a hydrocarbon trap in any of the existing state-of-the-art arrangements.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 shows the behavior of an H-ZSM-5 zeolite (obtained by calcining the commercial ZSM-5 zeolite at 600 ° C for 6 hours) during simulated cold starting of an internal combustion engine. The composition of the gas stream is: 100 ppmv propene, 87 ppmv toluene, 1.0% 02, 10% H20 and balance Ar. The solid line shows the evolution of the toluene concentration and the dashed line the evolution of the propene concentration over time. The temperature ramp is shown in gray.

Figure 2 shows the behavior of a CuH-ZSM-5 zeolite partially exchanged with copper cations (theoretical exchange percentage less than 20%) with a copper content of 0.5% by weight during the simulated cold start of an internal combustion engine . The composition of the gas stream is: 100 ppmv propene, 87 ppmv toluene, 1.0% 02, 10% H20 and balance Ar. The solid line shows the evolution of the toluene concentration and the dashed line the evolution of the

Propene concentration over time. The temperature ramp is shown in gray.

Figure 3 shows the behavior of a CuH-ZSM-5 zeolite partially exchanged with copper cations with a total copper content of l. 4% by weight, of which only a part is exchanged as copper cations, during the simulated cold start of an internal combustion engine. The composition of the gas stream is: 1 O O ppmv propene, 87 ppmv toluene, l. 0% 02, 10% H20 and balance Ar. The solid line shows the evolution of the toluene concentration and the dashed line the evolution of the propene concentration over time. The temperature ramp is shown in gray.

Figure 4 shows images obtained by transmission electron microscopy of the CuH-ZSM-5 sample partially exchanged with copper cations with a total copper content of 1.4%.

Figure 5 shows the behavior of a CuH-ZSM-5 zeolite partially exchanged with copper cations with a total copper content of 0.7% by weight, of which practically everything is exchanged as copper cations, during the simulated cold start of a internal combustion. The composition of the gas stream is: lOO ppmv propene, 87 ppmv toluene, l. 0% 02, 10% H20 and balance Ar. The solid line shows the evolution of the toluene concentration and the dashed line the evolution of the propene concentration over time. The temperature ramp is shown in gray.

Figure 6 shows images obtained by transmission electron microscopy of the CuH-ZSM-5 sample partially exchanged with copper cations with a copper content of 0.7%.

Figure 7 compares the behavior of two CuH-ZSM-5 zeolites partially exchanged with copper cations in the fourth cycle of a simulated cold start of an engine

internal combustion. These two zeolites have different degrees of ion exchange: a first CuH-ZSM-5 zeolite with a total copper content of 1.4% by weight, of which only a part is exchanged inside the zeolite structure and the rest of the copper is forming copper oxide nanoparticles on the surface of the zeolite; a second CuH-ZSM-5 zeolite with a copper content of O. 7% by weight, of which practically everything is exchanged as copper cations. The selection of appropriate ion exchange conditions in the case of this second zeolite has resulted in a higher ion exchange percentage in this solid compared to that obtained for the first zeolite, despite its lower total copper content. The composition of the gas stream for all cycles is approximately: lOO ppmv propene, 87 ppmv toluene, 1.0% 02, 10% H20 and balanceAr. The solid black and gray lines show the evolution of the toluene concentration for the CuH-ZSM-5 zeolites with 1.4% by weight and 0.7% by weight, respectively, and the dashed lines in black and gray show the evolution of the propene concentration over time for the CuH-ZSM-5 zeolites at 1.4% by weight and 0.7% by weight, respectively. The temperature ramp is shown in a dotted black line.

Figure 8 shows the behavior of a CuH-ZSM-5 zeolite partially exchanged with copper cations with a copper content of O. 7% by weight supported on a cordierite monolith during the simulated cold start of an internal combustion engine. The composition of the gas stream is: lOO ppmv propene, 87 ppmv toluene,

l. 0% 02, 10% H2 0 and balance Ar. The solid line shows the evolution of the toluene concentration and the dashed line the evolution of the propene concentration over time. The temperature ramp is shown in gray.

EXAMPLES OF CARRYING OUT THE INVENTION Example l. Preparation of H-ZSM-5 sample with 0.7% Cu

The following describes the experimental procedure used in the preparation of an H-ZSM-5 sample partially exchanged with copper, with a copper content of O. 7% by weight, of which practically everything is exchanged as copper cations (percentage of exchange 30%) It starts from the zeolite in its ammonium form, NH4 + -zsM-5, with Si / Atomic ratio equal to 15

(supplied by the company ZEOLYST INTERNATIONAL) and calcined in air at 450 o C for 6 hours, using a heating ramp of 5 ° C per minute. The exchange with copper cations is then carried out under suitable conditions that allow all the copper to be exchanged inside the zeolite channels. Said sample was prepared by contacting the zeolite in its acid form with a copper precursor solution, Cu (N03) 2.3H20 3.45 millimolar (zeolite / solution ratio of 315 O g 1-1) • Said mixture is kept stirring in a thermostated bath at 77 ° C for 18 hours. The suspension is then filtered and washed with distilled water. The zeolite is then dried at 110 ° C for 15 hours and, finally, it is calcined in air at 550 ° C for 4 hours, using a heating ramp of 1 degree centigrade per minute.

Example 2. Simulation of cold start cycles

To determine the behavior of the catalytic trap described above under conditions close to actual operating conditions, simulated cold start cycles have been carried out. For this, the catalytic trap bed, whose mass is 200 mg, is located in the center of a stainless steel tube with an internal diameter of 0.64 cm and a length of 36 cm. At the start of each of the cold ignition cycles, a simulated exhaust gas flow is passed to establish

space velocity conditions of 10,000 hours-1,

simultaneously increasing the temperature from 30 ° C to

600 ° C at a speed of 50 ° C per minute maintaining the

zeolite at this temperature for a period of 1 hour.

5

This gas mixture is composed of 100 ppmv of

propene, 87 ppmv toluene, 1 vol.% oxygen, 10% vol.

of water and argon balance. During this experiment, the

exhaust gases from the system are analyzed using a

mass spectrometer that detects the concentration of each

10

one of the gases leaving the adsorbent bed. The

results obtained for the H-ZSM-5 zeolite partially

exchanged with copper as shown in Example 1

(exchange percentage 30%) are presented in Figure

5. You can see how this catalytic trap presents

fifteen

100% efficiency in reducing emissions

propene and toluene during the cold start cycle

simulated. Therefore, this material is a material

optimal as a catalytic trap in a subsequent arrangement

to the three-way catalyst, as proposed herein

2 O

invention. Also, the fact that they are not released

hydrocarbons in the entire temperature range, makes

this solid is also suitable for application as

hydrocarbon trap in any of the provisions

existing in the state of the art.

25

Example 3. Evaluation of the stability of the zeolite CuH-

ZSM-5.

Example 2 was repeated four times. So after

that the sample was kept at 600 ° C for 1 hour was

let cool until bed temperature reached

30

30 ° C. Subsequently, the

experiment in the same conditions as those described

previously. The results are shown in Figure 7

obtained in the fourth cycle, in which the

high stability of the catalytic trap despite the high

35

moisture content and high temperature reached.

Higher temperatures cannot be expected in the catalytic trap during its operation, due to its subsequent disposition to the three-way catalyst, within the exhaust gas circuit. The same figure also includes the results obtained in the fourth cycle corresponding to the zeolite CuH-ZSM-5 partially exchanged with copper cations and which has a total copper content of 1.4% by weight, of which only part is exchanged inside the zeolite structure, and the rest of the copper is forming copper oxide nanoparticles on the surface of the zeolite (observed by TEM images (Figure 4). Due to the exchange conditions used (outside the optimum necessary for the preparation of the materials object of the present invention), the resulting solid has a lower ion exchange percentage than the solid prepared in Example 1, and whose results are also presented in the present figure. of both solids in Figure 7 shows that the sample with the lowest content of copper cations exchanged inside the zeolite structure (sample c With a higher total copper content, l. 4% by weight), in addition to not being suitable as a hydrocarbon catalytic trap, it undergoes deactivation with the number of cycles, as can be seen comparing with the results shown in Figure 3.

Example 4. Preparation of a monolith of cordierite supported with zeolite CuH-ZSM-5

Initially, the ZSM-5 zeolite, in its ammonium form, is supported on the cordierite monolith, 2 cm long and 1 cm in diameter, using the method

of

immersion. TO continuation I know makes a treatment

thermal

to 450 ° C during 6 hours, employing a ramp of

heating

of 5 ° C by minute for obtain the shape

acidic, H-ZSM-5. The zeolite is then contacted

supported with a solution of Cu (N03) 2.3H20 3.45 millimolar and perform the same experimental steps described in Example 1 for the zeolite powder. To determine the behavior of the catalytic trap in its monolith form in conditions close to the real ones of operation, simulated cold start cycles have been carried out. For this, the previously described monolith is placed in the center of a stainless steel tube with an internal diameter of 2.05 cm and a length of 36 cm. In each of the cold ignition cycles, a simulated exhaust gas mixture is passed through the monolith from the start of the experiment under space velocity conditions equivalent to those used in the powder zeolite experiments (Example 2 ), but adjusting them to the supported zeolite mass, simultaneously increasing the temperature from 30 ° C to 600 ° C at a speed of 50 ° C per minute keeping the zeolite at this temperature for a period of 1 hour. Said gas mixture is composed of 100 ppmv of propene, 87 ppmv of toluene, 1% vol. oxygen, 10% vol. of water and argon balance. During this experiment, the exhaust gas from the system is analyzed using a mass spectrometer that detects the concentration of each of the gases leaving the adsorbent bed. The results obtained for this cordierite monolith with the zeolite CuH-ZSM-5 partially exchanged with copper cations (exchange percentage 30%) are shown in Figure 8. It can be seen how this catalytic trap has 100% efficiency in the reduction of propene and toluene emissions during the simulated cold start cycle. In this way, it is verified how the catalytic trap behaves efficiently both in powder form and supported on a cordierite monolith.

Claims (22)

l. Catalytic trap of hydrocarbons contained in exhaust gases produced by an internal combustion engine, characterized in that it is free of noble metals and 5 comprises at least one layer of a molecular sieve of the formula XH-ZSM-5, where X represents one or more transition metals and H-ZSM-5 represents a zeolite with a Si / Al ratio 10 comprised between 10 and 20, including both limits, and which presents in its internal structure an ion exchange of protons for metal cations in a percentage comprised between 20% and 60%, including both limits, of the total protons present in the zeolite in its state 15 original. 2. Catalytic trap according to claim 1, where X is selected from the group consisting of Cu, Fe, Zn, Co, Ni and any combination thereof.

3.

Catalytic trap according to any one of claims 1 or 2, where X is copper.

Four.

Catalytic trap according to any one of the

2 5 claims 1 to 3, where the zeolite has in its internal structure an ionic exchange of protons for metal cations of X in a percentage between 30% and 50%, including both limits. Catalytic trap according to any one of Claims 1 to 4, characterized in that it is supported on a matrix. 6. Catalytic trap according to claim 5, wherein the matrix is a monolith of cordierite.

7.

A bed of the catalytic trap described according to any one of the preceding claims.

8.

A catalytic converter for the control and reduction of polluting gases and particles contained in an exhaust stream of an internal combustion engine, which comprises the catalytic trap described in any one of claims 1 to 6 and which is free of recirculation elements of exhaust gases.

9.

Catalytic converter according to the preceding claim, further comprising a hydrocarbon oxidation catalyst positioned before the catalytic trap according to the direction of passage of the gas stream.

10.

Catalytic converter according to claim 9, wherein the catalyst is a three-way catalyst in the case of a gasoline engine, or a two-way catalyst in a diesel engine.

eleven.

Internal combustion engine comprising the catalytic trap described in any one of claims 1 to 6.

12.

Use of the described catalytic trap according to any one of claims 1 to 6 in an internal combustion engine.

13.

Method for removing hydrocarbons from an exhaust gas stream produced in an internal combustion engine, characterized in that it comprises directing and passing said stream through a bed of the catalytic trap described according to any one of claims 1 to

6.

14.

Method according to the preceding claim, where the gas stream is directed and passes through a hydrocarbon oxidation catalyst before passing said stream through the catalytic trap.

fifteen.

Method for obtaining the catalytic trap described according to any one of claims 1 to 4, characterized in that it comprises at least:

synthesize zeolite H-ZSM-5 in its acid form, by calcination; and - proceed to the exchange of metal ions of X with ions of the internal structure of the zeolite, by means of immersion with stirring of said zeolite in a precursor solution of the metal or metals, and - subsequent drying and calcination.

16.

Method according to the preceding claim, where the synthesis of the H-ZSM5 zeolite in acidic form is carried out by calcining in air an NH4 + -zsM5 ammonium form of said zeolite with a silicon / aluminum atomic ratio equal to 15, at a temperature comprised between 450 ° C and 600 ° C, including both limits.

17.

Method according to any one of claims 15 or 16, where the cation exchange is carried out by the following steps:

-

contacting zeolite H-ZSM5 in acidic form with a precursor solution of the metal or metals,

Shake the mixture in a thermostated bath at a temperature between 40 ° C and 80 ° C, for a time between 1 O and 2 5 hours, including both limits; -filtrate the liquid; -wash the solid obtained with distilled water; - drying the solid at a temperature between 100 ° C and 150 ° C, including both limits; and calcine the solid at a temperature between 450 ° C and 600 ° C, including both limits, for 4 hours using a heating ramp of 1 ° C per minute. 18. Method for obtaining the catalytic trap described according to any one of claims 5 or 6, characterized in that it comprises at least the following steps:

-

deposit the zeolite in its ammonium form NH4 + -ZSM5 on the matrix by: · preparing a suspension of said zeolite

with

to the less a binder and to the less a agent

surfactant,

later

immersion of the matrix in bliss

suspension,

and

·

drying and calcination;

acidify

the zeolite impregnated in the matrix

by calcining the material formed in the previous stage; and - proceed to the exchange of metal ions of X with ions of the internal structure of the zeolite, by means of immersion with agitation of said zeolite impregnated in the matrix in its acidic form in a precursor solution of the metal or metals X, and - subsequent drying calcination.

19.

Method according to the preceding claim, where the matrix is immersed in the suspension for a time comprised between 1 and 10 minutes; drying before acidification is carried out first at room temperature for 12 hours and then at a temperature between 150 ° C and 250 ° C for a time between 2 and 10 hours, with a temperature ramp of l ° C per minute .

twenty.

Method according to any one of claims 18 or 19, where the calcination for the acidification of the zeolite is carried out at a temperature comprised between 450 ° C and 600 ° C, including both limits.

21. Method according to any one of claims 18 to 2 O, wherein drying after ion exchange is carried out in air at 110 ° C and calcination between 450 ° C and 600 ° C for 2 to 10 hours. 22. Method according to any one of claims 18 to 21, wherein after depositing the zeolite in the matrix and before acidification, the material is subjected to an ultrasound bath.