FR2765120A1 - Reduction of nitrogen gas emission using a ruthenium and tin based catalyst - Google Patents

Abstract

The reduction of nitrogen gas emission using a ruthenium or a ruthenium and tin based catalyst is claimed. It consists of using a catalytic composition comprising of ruthenium on a rutile support or a support containing an alkaline or an alkaline-earth or a rare earth, the ruthenium being deposited onto the support in the salt or in a sol or in a complex form.

Description

GAS TREATMENT PROCESS FOR REDUCING EMISSIONS OF

  NITROGEN OXIDES. USING A BASED CATALYST

  RUTHENIUM OR RUTHENIUM AND TIN

RHONE-POULENC CHEMISTRY

  The present invention relates to a gas treatment process for the reduction of emissions of nitrogen oxides, using a ruthenium or catalyst based

ruthenium and tin.

  It is known that the reduction of emissions of nitrogen oxides (NOx) from the exhaust gases of automobile engines in particular is carried out using three-way catalysts which use the reducing gases present in the mixture stoichiometrically. Any excess oxygen results in a sudden deterioration of

catalyst performance.

  However, certain engines such as diesel engines or gasoline engines operating in lean burn are fuel efficient but emit exhaust gases which permanently contain a large excess of oxygen of at least 5% for example. A standard three-way catalyst therefore has no effect on the NOx emissions of these engines. In addition, the limitation of NOx emissions is made imperative by the tightening of standards in automotive post combustion which

  now extend to this type of engine.

  Furthermore, the catalytic systems which have been shown to be active for the removal of NOx in the presence of oxygen exhibit a field of activity which greatly decreases above 300 C. In addition, when these systems operate in the presence of a

  hydrocarbon, they can give rise to the production of a certain amount of N20.

  The object of the invention is to provide a catalytic system which can be used for the treatment of gases containing NOx and in particular those with a high oxygen content. Another object of the invention is to have a system capable of being effective at temperatures above 300 "C and, possibly, which results in only a limited production of N 2 O when it is used in the treatment. gas in

presence of hydrocarbon.

  For this purpose, according to a first embodiment of the invention, the gas treatment process for the reduction of emissions of nitrogen oxides is characterized in that a catalytic composition comprising ruthenium is used on a support which

  is either a support with a rutile structure, or a support containing an alkali, an alkaline-

  earthy or a rare earth, the ruthenium having been deposited on the support in the form of a

salt, soil or complex.

  According to a second embodiment of the invention, the gas treatment process for the reduction of emissions of nitrogen oxides is characterized in that a catalytic composition is used, the catalytic phase of which comprises ruthenium and

tin.

  Other characteristics, details and advantages of the invention will also appear

  more fully on reading the description which follows, as well as the various

  concrete but non-limiting examples intended to illustrate it.

  The method according to the first embodiment of the invention uses a composition, a characteristic of which is the combination of ruthenium with a support

specific.

  This support can first of all be a support with a rutile structure. As support for

  this type, one can quote titanium oxide or tin oxide SnO2.

  The support can also be a support which contains an alkaline, an alkaline-earth or a rare earth. By rare earth is meant the elements of the group constituted by yttrium and the elements of the periodic classification with atomic number included

inclusive between 57 and 71.

  As support of this type, mention may be made of spinels containing an alkaline-earth type MgAI204. Mention may also be made, as other supports, of aluminas, silicas, titanium oxide of anatase structure, supports based on titanium oxide of anatase structure and tungsten oxide (TiO2-WO3) or based on titanium oxide of anatase structure and vanadium oxide (TiO2-V205), these supports in alumina, silica or based on titanium oxide being doped with at least one element chosen from alkaline earths and rare earths. As alkaline earth, there may be mentioned barium or strontium more particularly. As rare earth, one can quote the

lanthanum in particular.

  As other usable supports, there may be mentioned cerium oxide as well as cerium oxide-zirconium oxide mixtures in which cerium oxide

  may be in the majority or not. Rare earth oxide mixtures can also be used.

  zirconium oxide, the rare earth possibly being in particular lanthanum.

  The supports containing an alkali or an alkaline earth can also be chosen from zeolites. As another support containing rare earths, mention may be made of rare earth phosphates. Finally, we can mention magnesium oxide. It is of course possible to use as support a mixture of the support compounds which come

to be described.

  The amount of ruthenium is generally between 0.1% and 10% by mass of ruthenium metal relative to the support. This quantity may be more

  particularly between 0.5 and 5%.

  The composition of the invention can also comprise, in its catalytic phase, tin, manganese, bismuth, copper or else an element chosen from group VIII of the periodic classification, such as iron, cobalt, rhodium, platinum and

palladium.

  The catalytic composition of the first embodiment is obtained by a process in which the ruthenium is deposited on the support in the form of a salt, a sol or a ruthenium complex. The salt can be, for example, a chloride, a nitrate, an acetate or a ruthenium formate. As ruthenium complexes, there may be mentioned

  acetylacetonate, carbonyl or EDTA complexes.

  The deposition of ruthenium in the form of a perovskite-type oxide is excluded from the

present invention.

  The deposit on the support can be done by exchange or by dry impregnation.

  Dry impregnation consists in adding a volume of a solution to the product to be impregnated

  aqueous of the element to be deposited which is equal to the pore volume of the solid to be impregnated.

  According to the second embodiment of the invention, a composition is used whose essential characteristic is the nature of its catalytic phase. As stated more

  top, this composition comprises a catalytic phase based on ruthenium and tin.

  The composition used according to this second embodiment can be presented under

different forms.

  It can first of all be a mass composition. By this is meant that ruthenium and tin are present in a homogeneous manner throughout the volume of the composition and not, for example, on the surface thereof. In this case

  ruthenium content is preferably at least 10 atomic%.

  It can also be a supported composition. In this case, the catalytic phase based on ruthenium and tin can be placed on any type of support usually used in this technical field such as alumina, silica, titanium oxide, zirconium oxide, lanthanide oxides, spinel type oxides, zeolites, silicates, crystalline silicoaluminum phosphates, phosphates

  crystalline aluminum, rare earth phosphates or mixtures of these supports.

  In the case of the supported composition, the ruthenium content can be between 0.1 and 50%, more particularly between 0.5 and 10%, content expressed by mass of

  ruthenium metal with respect to the support.

  The ratio of ruthenium to tin in the composition may vary. More particularly, the Sn / Ru atomic ratio can vary between 0.1 and 10. It is in this range of ratios that the results are the best. This ratio can be even more particularly between 1 and 6. The values given above for the ratio

  Sn / Ru apply to the two embodiments of the invention.

  Ruthenium and tin may be present, at least partially, under the

  form of a ruthenium / tin alloy.

  The catalytic compositions based on ruthenium and tin are prepared in a manner known per se. Reference may be made to EP-A539274, FR-A-2740707 and FR-A-2740708, the teaching of which is incorporated here. In the case of supported compositions, the ruthenium is preferably deposited on the support via a salt, a sol or a ruthenium complex. What was mentioned above on ruthenium sets and complexes also applies here. When it is sought to use compositions in which ruthenium and tin are present in the catalytic phase, at least partially, in the form of a ruthenium / tin alloy, a reduction treatment is carried out, for example with composition hydrogen one

once prepared.

  The compositions as described above apply to the treatment of gases which may comprise nitrogen oxides in combination optionally with carbon oxides and / or hydrocarbons, with a view to reducing the emissions of

nitrogen oxides in particular.

  The gases capable of being treated by the present invention are, for example, those originating from gas turbines, boilers of thermal power stations or even internal combustion engines. In the latter case, it may in particular be motors

  diesel or engines working in lean mixture.

  The invention thus applies to the treatment of gases which have a high oxygen content and which contain nitrogen oxides, with a view to reducing the emissions of these oxides. By gas having a high oxygen content is meant gases having an excess of oxygen relative to the quantity necessary for the stoichiometric combustion of fuels and, more specifically, gases having permanently an excess of oxygen relative to the stoichiometric value A = 1. The value. is correlated to the air / fuel ratio in a manner known per se, in particular in the field of internal combustion engines. In other words, the invention applies to the treatment of gases from systems of the type described in the preceding paragraph and operating continuously under conditions such that A is always strictly greater than 1. In the case of gases having a content high in oxygen, the invention thus applies, on the one hand, to the treatment of engine gases operating in a lean burn mixture and which have an oxygen content (expressed by volume) generally between 2.5 and 5% and, on the other hand, to the treatment of gases which have an even higher oxygen content, for example gases from engines of the diesel type, that is to say at least 5% or more than%, more particularly at least 10%, this content can for example be

between 5 and 20%.

  The gases may contain hydrocarbons and, in such a case, one of the reactions

  that we seek to catalyze is the reaction HC (hydrocarbons) + NOx.

  The hydrocarbons which can be used as a reducing agent for the elimination of NOx are in particular the gases or the liquids of the families of saturated carbides, ethylenic carbides, acetylenic carbides, aromatic carbides and hydrocarbons from petroleum fractions such as for example methane , ethane, propane, butane, pentane, hexane, ethylene, propylene,

  Acetylene, butadiene, benzene, toluene, xylene, kerosene and gas oil.

  The gases can also contain, as reducing agent, organic compounds containing oxygen. These compounds can in particular be alcohols of the type, for example saturated alcohols such as methanol, ethanol or propanol; ethers such as methyl ether or ethyl ether; esters like acetate

methyl and ketones.

  The invention also applies to the treatment of gases not containing

  hydrocarbons or organic compounds as a reducing agent.

  The compositions of the invention can allow the treatment of the aforementioned gases with a limited production of N20. By limited production of N20, we mean a

  production of less than 5% by volume of the conversion of NOx to N20.

  The invention also relates to a catalytic system for the treatment of gases with a view to reducing the emissions of nitrogen oxides, gases which may be of the type mentioned above. This system is characterized in that it comprises a

  catalytic composition as described above.

  In this system, the catalytic composition can be present in various

  shapes such as granules, balls, cylinders or honeycomb of variable dimensions.

  The compositions can also be used in catalytic systems comprising a coating (wash coat) incorporating these compositions, the coating being arranged on a substrate of the type, for example metallic or ceramic monolith. The systems are mounted in a known manner in the exhaust pipes

  vehicles in the case of application to the treatment of exhaust gases.

  The invention also relates finally to the process for manufacturing the above-mentioned catalytic systems using a catalytic composition of the type described above. Non-limiting examples will now be given. In the examples, the term "specific surface" means the specific surface B.E.T. determined by nitrogen adsorption in accordance with standard ASTM D 3663-78 established from the BRUNAUER - EMMETTTELLER method described in the periodical The Journal of the

American Society, 0Q, 309 (1938) Y.

Examples

  I - Synthesis of Catalysts Catalyst 1 We start with a ruthenium solution (RuCI3, nH2O) and add a silica (Degussa Ox50 - 50m2 / g). Leave to ripen for one hour and neutralize with ammonia. The final pH is 11.5. After stirring for 10 minutes, it is centrifuged at 3000 rpm for 30 minutes. The centrifugation base is plumped in

  250ml of demineralized water and left to ripen at 20 C for 20 hours.

  Then a solution of SnCl2 (12.5 g / l at 0.25 ml / h) is introduced. After 24 hours of ripening at room temperature, it is dried on a Rotavapor under a light vacuum at C for 3 hours and then passed through the oven again for 3 hours. The active phase is then reduced under hydrogen at 500 ° C. for 2 hours. X-ray diffraction shows the presence of a Ru3Sn7 phase with an Sn / Ru molar ratio of 2.3 (cubic system). The BET surface is 50m2 / g. The catalyst contains 0.60% by

  ruthenium weight and an overall Sn / Ru atomic ratio of 4.

  Catalyst 2 A mass catalyst is prepared by following the method of preparation of catalyst 1 but without the use of silica. The prepared catalyst reports

  atomic Sn / Ru of 2.33 and a content by weight of ruthenium of 20.2%.

  Catalyst 3 A catalyst is prepared by cation exchange on a silica support of the same type as that used in the preparation of catalyst 1. The silica and the ruthenium and tin solutions are heated at 30 ° C. for 24 hours. Then dried with Rotavapor and then proceed as described in Example 1. The catalyst prepared has a

  Sn / Ru atomic ratio of 4 and a ruthenium content by weight of 0.625%.

  Catalyst 4 A catalyst is prepared by following the method of preparation of catalyst 1 but without the step of reduction with hydrogen. The prepared catalyst reports

  atomic Sn / Ru of 1 and a ruthenium content by weight of 0.625%.

  Catalyst 5 A catalyst is prepared according to the method of preparation of catalyst 1. The catalyst prepared has an atomic ratio Sn / Ru of 6.2 and a content by weight

5% ruthenium.

  II - Catalytic tests 50 mg of powdered catalyst are loaded into a quartz reactor. The powder

  used was previously granulated at 0.125 and 0.250mm.

  The reaction mixture at the inlet of the reactor has the following composition (by volume) for the tests carried out in the presence of a reducing agent (reduction): - NO = 300 vpm - C3H6 = 300 vpm - CO = 350 vpm

- 02 = 10%

- CO2 = 10%

- H2O = 10%

- N2 = qs 100%

The overall flow is 30 NI / h.

  The VVH is between 400,000 and 500,000 h-1.

  Some tests are carried out with a propane / propylene mixture at the rate of

  vpm each in the total reaction mixture.

  For tests carried out in the absence of a reducing agent (decomposition), the CO and C3H6 flow rates are eliminated and replaced by an equivalent nitrogen flow rate.

keep the same WH.

  The signals of HC (C3H6), CO and NOx (NOx = NO + NO2) are recorded in

  permanence as well as the temperature in the reactor.

  The HC signal is given by a BECKMAN detector of the hydrocarbon type

  total, based on the principle of flame ionization detection.

  The NOx signal is given by an ECOPHYSICS NOx analyzer, based on the

principle of chemistry-luminescence.

  The CO and N20 signal is given by a ROSEMOUNT infrared analyzer.

  The catalytic activity is measured from the HC (C3H6), CO and NOx signals as a function of the temperature during a programmed temperature rise from 150 to 700 C at a rate of 1 5 C / min and from the following relationships : - The conversion rate of HC (THC) in% which is given by: T (HC) = 100 (HC -HC) / HC with HOC "signal of HC at the instant t = O which corresponds to the signal of HO obtained with the reaction mixture during the reactor bypass

  catalytic and HC is the signal of HO at time t.

  - The CO conversion rate (TCO) in% which is given by: T (CO) = 100 (CO "-CO) / CO with CO CO signal at time t = 0 which corresponds to the CO signal obtained with the reaction mixture during the reactor bypass

  catalytic and CO is the CO signal at instant t.

  - The NOx conversion rate (TNOx) in% which is given by: T (NOx). 100 (NOx-NOx) / NOx = with NOx NOx signal at time t = 0 which corresponds to the NOx signal obtained with the reaction mixture during the by-pass of the

  catalytic reactor and NOx is the NOx signal at time t.

  Because the catalysts can activate under the conditions of the tests, catalytic activity is given during the second consecutive passage under test under the same conditions.

EXAMPLE 1

  Catalyst 1 is used. The results are given in Table 1 below.

Table 1

  Temperature (C) TCO (%) THC (%) TNOx (%) TN20 (%) 1st dry test. test 1st dry test.test 1st dry test. test 1st test and dry test

O O 0.7 0 0 0 0

250 O 0.1 1.0 0 0 0 0

300 2.4 6.6 2.7 1.7 0.2 0 0

350 45.1 35.8 51.8 41.7 112 2.6 0

  400 91.5 88.6 94.2 96.3 1 36.1 27.0 0

450 100 100 100 100 27.5 17.9 0

500 100 100 100 100 18.0 8.7 0

550 100 100 100 100 12.6 4.9 0

600 l 100 100 8.5 2.6 0

650 100 100 100 100 6.9 1.2 0

700 100 100 I 100 100 6.3 1.0 0

EXAMPLE 2

  Catalyst 2 is used. The results are given in Table 2 below.

Table 2

  Temperature (C) TCO (%) THC (%) TNOX (%) TN20 (%) 1 st dry test. test ler dry test. test 1ler dry test. test 1ler test and I _sec. test 1 l 0.3. 0 0 00 0

250. 8..2 3.0 1.5 0.8 0 0 0

300 143.3 27.4 114 7.2 0 0 0

350 86.5 78.4 65.0 61.6 8.0 5.2 0

400 100 96.8 97.1 96.5 33.3 34.0 0

450 100 100 100 100 24.3 23.8 0

500 100 100 100 100 14.2 13O6 0

550 100 100 100 100 7.2 7.1 0

600 100 100 100 100 4.5 3.4 0

650 1100 100 10_ 0 100 2.6 1.7 0

700 100 100 10 2.6 I 0.9

EXAMPLE 3

  Catalyst 3 is used but with a propane / propene mixture. The results are given in Table 3 below.

Table 3

  Temperature (C) TCO (%) THC (%) TNOX (%) TN20 (%)

  1st dry test. test 1st dry test test 1st dry test test 1st test / sec.

test 2.0 11 0.1 0.1 0 0 0 0/0

250 9.6 1.6 0.4 2.0 0 0 0/0

300 48.1 16.8 7.1 6.3 0 1.0 0/0

  350 1 94.9 77.4 51.0 41.8 23.3 18.9 1 1.7 / 0.9

  400 1,100 95.4 62.1 54.3 25.5 34.0 0.7 / 0.2

450 P 100 100 72.6 13.7 22.4 0.8 / 0

  500 I 100 100 86.8 72.1 7.2 1 13.8 0.3 / 0

  550 i 100 100 96.8 87.9 i 3.6 i 8.9 0

600 [100 100 96.6 14.2 15.9 0

650 100 100 100 100 8.5 1 4.5 0

  700 1 oo100 100 J 100J 100 18.7 5.2 L 7 i 00! 100

EXAMPLE 4

  Catalyst 3 is used but in the absence of a reducing agent (decomposition), it is

  say without CO or C3H6. The results are given in Table 4 below.

  Table 4 Temperature (OC) TNOx (%) TN20 (%)

  1 st dry test. test 1 st test and sec.

test

0.5 0.2 0

250 1.3 1.0 0

300 8.0 3.4 0

350 39.6 27.0 0

400 29.8 33.0 0

450 18.2 20.9 0

500 11.3 11.8 0

550 5.8 6.4 0

600 4.4 4.1 0

650 4.4 .. 5.6 0

700 1 6.7 7.1 0

EXAMPLE 5

  Catalysts 4 and 5 are used. The highest T (NOx) values obtained in

  reduction and decomposition are given in the following tables.

Table 5

  Tests performed in T (NO) Catalyst / Temperature Reduction 1st pass 2nd pass

37% / 390 C 40% / 360 C

Table 6

  Tests carried out on Decomposition Catalyst T (NOJ) / Temperature 1st pass 2nd pass

4 15% / 530 C 12% / 450 C

  All the examples show a maximum activity of the catalyst

  generally located above 350 C as well as the absence of N20 formation.

Claims (14)

  1- A gas treatment process for the reduction of emissions of nitrogen oxides, characterized in that a catalytic composition is used comprising ruthenium on a support which is either a support with a rutile structure, or a support containing an alkali, an alkaline earth or a rare earth, the ruthenium having been deposited on the support under   as a salt, a soil or a complex.   2- A method according to claim 1, characterized in that the mass amount of   ruthenium metal is between 0.1% and 10% relative to the support.   3- A method according to claim 1 or 2, characterized in that the support structure   rutile is titanium oxide or tin oxide.   4- Method according to claim 1 or 2, characterized in that the support is chosen from spinels; cerium oxide; cerium oxide-zirconium oxide mixtures; mixtures of rare earth oxide and zirconium oxide; zeolites; rare earth phosphates; magnesium oxide; aluminas; silicas; titanium oxide of anatase structure; supports based on titanium oxide of anatase structure and tungsten oxide or based on titanium oxide of anatase structure and vanadium oxide, these aluminas, silicas, titanium oxide or supports based on titanium oxide being doped with at least one element chosen from alkaline earths and rare earths;   or the aforementioned mixtures of supports.   5- Method according to one of the preceding claims, characterized in that one uses   a catalytic composition further comprising tin.   6- Gas treatment process for the reduction of nitrogen oxide emissions, characterized in that a composition is used whose catalytic phase comprises ruthenium and tin.   7- A method according to claim 6, characterized in that a composition is used mass catalytic.   8- A method according to claim 6, characterized in that a composition is used catalytic supported.   9- A method according to claim 8, characterized in that a composition is used whose support is chosen from alumina, silica, titanium oxide, zirconium oxide, lanthanide oxides, oxides of spinel type, zeolites, silicates, crystalline silicoaluminum phosphates, crystalline aluminum phosphates, rare earth phosphates or a mixture of these supports.   - Method according to one of claims 5 to 9, characterized in that a   composition in which the atomic ratio Sn / Ru varies between 0.1 and 10.   11- Method according to one of claims 5 to 10, characterized in that one uses a   composition which has undergone a reduction treatment.   12- Method according to one of the preceding claims, characterized in that one treats   an exhaust gas from diesel engines or engines operating in mixture poor.   13- Method according to one of the preceding claims, characterized in that the   oxygen content of the gases is at least 5% by volume.   14- Method according to one of the preceding claims, characterized in that one treats   a gas in the presence of a hydrocarbon or an organic compound containing oxygen. - Catalytic system for implementing the process according to one of the   Claims 1 to 14, characterized in that it comprises a catalytic composition such   as defined in one of claims 1 to 1 l.   16- A method of manufacturing a catalytic system according to claim 15, characterized in that one implements a catalytic composition as defined   in one of claims 1 to 11.