CA2142889A1 - Catalyst and catalytic method for reducing nitrogen oxides - Google Patents
Catalyst and catalytic method for reducing nitrogen oxidesInfo
- Publication number
- CA2142889A1 CA2142889A1 CA002142889A CA2142889A CA2142889A1 CA 2142889 A1 CA2142889 A1 CA 2142889A1 CA 002142889 A CA002142889 A CA 002142889A CA 2142889 A CA2142889 A CA 2142889A CA 2142889 A1 CA2142889 A1 CA 2142889A1
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- catalyst
- temperature
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J29/00—Catalysts comprising molecular sieves
- B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
- B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
- B01J29/40—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11, as exemplified by patent documents US3702886, GB1334243 and US3709979, respectively
- B01J29/42—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11, as exemplified by patent documents US3702886, GB1334243 and US3709979, respectively containing iron group metals, noble metals or copper
- B01J29/44—Noble metals
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
- B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
- B01D53/9404—Removing only nitrogen compounds
- B01D53/9409—Nitrogen oxides
- B01D53/9413—Processes characterised by a specific catalyst
- B01D53/9418—Processes characterised by a specific catalyst for removing nitrogen oxides by selective catalytic reduction [SCR] using a reducing agent in a lean exhaust gas
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
- B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
- B01D53/9445—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC]
- B01D53/945—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC] characterised by a specific catalyst
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2251/00—Reactants
- B01D2251/20—Reductants
- B01D2251/208—Hydrocarbons
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2255/00—Catalysts
- B01D2255/10—Noble metals or compounds thereof
- B01D2255/102—Platinum group metals
- B01D2255/1023—Palladium
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2255/00—Catalysts
- B01D2255/20—Metals or compounds thereof
- B01D2255/207—Transition metals
- B01D2255/20746—Cobalt
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2255/00—Catalysts
- B01D2255/50—Zeolites
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
- Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/10—Internal combustion engine [ICE] based vehicles
- Y02T10/12—Improving ICE efficiencies
Abstract
The invention concerns a catalyst of reduction of the NOX as well as to a catalytic process of reduction of the NOX. The catalyst according to the invention is constituted of a zeolite of the MFI type exchanged with between 0.3% and 2% by weight of palladium with respect to the total weight of catalyst. The catalyst and the process of the invention can be used in any catalytic process of selective reduction of the NOX and more particularly for the treatment of exhaust gases issued from vehicles functioning with natural gas.
Description
The invention concerns a catalyst of reduction of the NOX and more particularly of NO and NO2 as well as a process of reduction of these NOX.
One knows numerous processes of transformation of the NOX in nitrogen.
One of these processes consists in using, as a reducing agent, carbon monoxide or hydrogen and as a catalyst, a catalyst based on precious metals supported on alumina or silica.
But in an oxidizing atmosphere, the oxidation of the hydrogen and carbon monoxide by gaseous oxygen precedes the reduction of NO by hydrogen and this reaction of reduction will therefore only take place when all the oxygen has been consumed.
This means that in the presence of a high excess of oxygen, it is necessary to use processes of selective reduction. The most common process consists in using ammonia as a reducing agent of the NOX in the presence of a catalyst constituted of V2Os and WO3 deposited on TiO2. This catalyst and this process enable the reduction of the NOX into nitrogen even in the presence of sulphur poisons.
But the catalytic materials have a limited lifetime and the installation requests an important investment. Further the storage of ammonia as well as its use are delicate.
IWAMOTO et al., propose in Catal. Today, 10, (1991), 57, to replace ammonia by hydrocarbons. Thus selective reducing hydrocarbons would be the hydrocarbons having more than two carbons and particularly propane and propene. The catalysts used 214~889 are zeolites with a high Si/Al ratio exchanged or not with transition metals.
S. SUBRAMANIAN et al. in Ind Eng. Chem. Res., 31, (1992), 2460, have studied the selective reduction of the NOX by methane in the presence of a catalyst constituted of palladium supported on alumina and conclude that the simultaneous elimination of methane and of NO cannot take place with this type of catalyst.
However, in the European patent application N~ EP 0,499,286 A2, Y. KAWAI discloses catalysts constituted of Co-Ag and of Co-Pd on zeolite which would enable to eliminate simultaneously the carbon monoxide, the NO and the methane even in the presence of 5% of oxygen and at 500~C. In the same conditions a catalyst constituted of palladium supported on a zeolite of the MFI type would not convert NO.
LI and ARMOR in the US patent N~ 5,149,512 use a catalyst constituted of a zeolite, particularly of the MFI type, exchanged with Co for the selective reduction of the NOX.
But cobalt is not usable in industrial processes and in catalytic exhausts of automobile vehicles because it can transform itself in carbonyl cobalt complexes highly toxic and polluting for the environment.
Another disadvantage of the catalysts of the prior art disclosed in particular by LI, BATTAVIO and ARMOR in "Effect of Water Vapor on the Selective Reduction of NO by methane over Cobalt-Exchanged ZSM-5" Journal of catalysis 142,561-571, (1993), is their loss of activity in the presence of water.
3 21~2889 To palliate the above disadvantages and in contrast with this state of the technique, the present invention proposes a catalyst of reduction of the NOX by methane or any mixture containing in majority methane such as for example natural gas, in an oxidizing atmosphere, constituted of a zeolite of the MFI type exchanged w th palladium the weight of which is comprised between 0.3% and 2~ of the total weight of catalyst.
According to a characteristic of the catalyst of the invention, the weight content of palladium is of about 0.5%
According to another characteristic of the invention, the catalyst is obtained from palladium II tetramine hydroxide as a precursor of Pd.
According to yet another characteristic of the invention, the catalyst is activated under oxygen, before utilization by a process comprising the steps of : (a) elevation in temperature from room temperature up to 300~C with a rate of elevation in temperature of 0.5~C/mn, (b) plateau of 300~C during an hour, (c) elevation in temperature from 300~C up to 500~C with a rate of elevation in temperature of 0.5~C/mn, (d) maintaining at 500~C
during an hour, and (e) lowering in temperature from 500~C down to 300~C.
According to still another characteristic of the catalyst of the invention, after the precited step (e) a step (f) of sweeping with an inert gas such as helium is realized.
According to a further characteristic of the catalyst of the invention, the used zeolite of the MFI type has a Si/Al ratio higher than 15.
4 214~89 The catalyst of the invention enables the reduction of the NOX in the presence of up to 10% by volume of H2O in the form of vapor and/or of up to 10% by volume cf ~2 and/or of up to 0.8% by volume of CO.
According to a particularity of the invention, the selective reduction of the NOX is effected at a temperature comprised between about 350~C and 400~C.
The invention has also for object to propose a process of reduction of the NOX, in a oxidizing atmosphere, by methane or any mixture containing in majority methane such as for example natural gas, which comprises a step of reacting a reaction medium comprising among others methane, oxygen and NOX with a catalyst constituted of a zeolite of the MFI type exchanged with between 0.3% and 2% by weight of palladium, with respect to the total weight of catalyst used which enables to obtain the selective reduction of the NOX into N2.
According to a particularity of the process of the invention, the zeolite of the MFI type is exchanged with about 0.5% by weight of palladium with respect to the total weight of catalyst used.
According to another particularity of the process of the invention, the precursor of Pd is the palladium II tetramine hydroxide.
According to yet another particularity of the process of the invention, the catalyst is activated, before utilization, under oxygen, by a process comprising the steps of (a) elevation in temperature from room temperature up to 300~C with a rate of 5 21 l2889 elevation in temperature of 0.5~C/mn, (b) plateau of 300~C during 1 hour, (c) elevation in temperature from 300~C up to 500~C with a rate of elevation in temperature of 0.5~C/mn, (d) maintaining at 500~C during one hour, and (e) lowering in temperature from 500~C to 300~C with oxygen.
Still according to a particularity of the process of the invention, after the above step (e) a step (f) of sweeping with an inert gas such as helium is realized.
According to a characteristic of the process of the invention, the said reaction medium can contain up to 0.8% by volume of CO which is then simultaneously oxidized.
According to another characteristic of the process of the invention, the said reaction medium can contain up to 10% by volume of H2O in vapor form.
According to yet another characteristic of the process of the invention, the said reaction medium can contain up to 10% by volume of ~2 According to a last characteristic of the process of the invention, the said step of reacting is effected at a temperature comprised between about 350~ and about 500~C.
Other details, characteristics and advantages of the invention will appear better in the course of the detailed description that will follow and that is done in reference to the appended figures wherein :
Figure 1 illustrates the influence of the content of Pd exchanged in a zeolite of the MFI type, on the percentage of CH4 and of NO converted to N2 or (N2O + N2).
6 21428~9 Figure 2 illustrates the influence of the content of Pd exchanged in a zeolite of the protonated zeolite type with large pores, on the percentage of CH4 and of NO converted to N2 or (N2O
+ N2) -The zeolite of the MFI type, prepared according to a process known by itself presents a Si/Al ratio very variable that can attain extreme values (1000). This carrier has then served for the preparation of catalysts based on ions of metals of transition by cationic exchange between the ions of zeolite (H+, Na+, Ca2+,...) and those of the metals of transition. This exchange enables one to obtain metallic ions dispersed and stabilized within the zeolitic network.
The zeolites exchanged with precious metals according to the invention were prepared by cationic exchange using adequate precursors. The palladium (II) tetramine hydroxide is a particularly preferred precursor.
The following protocol was followed :
5 g of zeolite are put in a beaker, then the precursor is added after having been diluted in 50 cm3 of distilled water.
Agitation is maintained during an hour at a temperature of 25~C
to obtain the equilibrium of exchange. The solid is then filtered and washed with an abundant quantity of distilled water (about 1 litre). It is then dried in the oven at 120~C overnight.
This preparation process enables one to obtain a catalyst based on palladium exchanged in the MFI zeolite which is interesting in that it has Pd2+ ions, in low quantities indeed, 7 21~28~ 9 but well separated the ones from the others which limits doubly the possibilities of clustering.
The catalytic tests were effected in a reactor with a flow-through bed constituted of a U-tube without sinter wherein one places a little pad in wool of quartz on which is deposited 200 mg of catalyst.
The catalyst is then in situ activated under oxygen by proceeding to a slow temperature elevation (0.5~C/mn) from 25~C
up to 300~C followed by a plateau of 300~C during 1 hour before being brought to a temperature of 500~C with a rate of elevation between 300~C and 500~C of 0.5~C/mn. The temperature is then maintained at 500~C during 1 hour before proceeding at a lowering to 300~C under oxygen. One then sweeps the catalyst during 30 minutes with helium before injecting the reaction mixture comprising gases such as methane, NOX, carbon monoxide, oxygen and water in the form of vapor.
The exhaust gases are analysed with two chromatographs or infrared analysers depending on the nature of the gas to analyse.
The first chromatograph is a chromatograph with a catharometric detection (T.C.D.), INTERSMAT IGC 121 ML. The column of separation is a CTR column of a length of 2 metres, a diameter of 1/4 of an inch of stainless steel containing a molecular sieve 5A
and PORAPAK Q. The vector gas is helium. The oven, the injector and the detector are at a temperature of 40~C. The sensitivity of the detector is 250 mA.
The second chromatograph is a chromatograph with a flame ionization (F.I.D.) INTERSMAT IGC 120 FB. The column has a length 8 214288g of 2 metres and a diameter of 1/8 of an inch and contains PORAPAK
Q-The vector gas is helium. The oven temperature is 130~C. Thetemperature of the injection is 175~C and that of the detector is 170~C.
The Si, Al, Pd contents have been analysed by atomic absorption.
The invention is based~on the surprising discovery and that, contrarily to the teachings of the prior art that a catalyst constituted of a zeolite of the MFI type exchanged with between 0.3% and 2% by weight of palladium with respect to the total weight of catalyst presents numerous proprieties that will be described in relation with the examples that will follow.
In these examples, it ls the reduction of NO rather than that cf NO2 that has been studied because it is admitted by the man skilled in the art that NO is representative of the NOX.
Spacial velocities of 35.000 h-1 were used for the realization of the tests effected in the Examples 1 to 35 and 39 to 43.
Examples 1 to 5.
Different catalysts constituted of MFI zeolite with a Si/Al ratio = 15 exchanged with different contents in Pd were synthesized as previously described and tested at 500~C with a reaction mixture comprising 2% by volume of oxygen, 0.1% by volume of methane and 0.2% by volume of NO.
The convers_ons and selectivities cor espording to the nlt-2 ac iv_-y cf the cata yst are ~egrolped in the following T2b e 1 :
Example Content Conversion Conversion Selec~ivitv Se!ec~ivity N~ of Pd in of CH4 in % of NO in % in N2O in % in ~-2 in %
%
0.3 42 28 0 l 00 2 0.49 78 40 0 l 00 3 0.74 69 28 7 93 4 0.98 73 32 0 lO0 1.94 96 27 8 92 Table 1 These results have also ~een represen ed in the form of curves 1 anc 2 in the appended figure 1.
On the graph of figure 1, one has represented the evolution of the conversions of methane (curve 1) ard of NO ~curve 2) versus the content of Pd (weight %) of tr.e catalyst.
It is then noticed that the conversions of NO and of CH4 are simultaneously high for palladium contents comprised between about 0.4% and about 0.6% by total weight of catalyst, the maximum of activity presenting itself around a palladium content of 0.5% by weight with respect to the total weight of the catalyst.
Further, the selectivity in N2 is excellent with this catalyst. ~hus the formation of N20 , un~esirable, is nearly nil.
- 21~2889 Examples 2 and 6 to 10.
Catalysts constituted of a zeolite of the MFI type with a S-/Al ratio of 15 exchanged with about 0.49~ by weight of palladium for the examples 2 and 6 to 8 and with about 0.97% by weight of palladium for the examples 9 and 10 were tested at 500~C with a reaction mixture containing between 0.2% and 10% by volume of ~2~ 0.1% by volume of CH4 and 0.2~ by volume of NO.
The conversions and selectivities corresponding to the initial activity of the catalyst are regrouped in the following Table 2.
Example Concentration Conversion Conversion Selectivity Selectivity N~ of ~2 in % of CH4 in of NO in % in N2O in % in N2 in %
%
6 0.2 62 37 0 100 7 0.4 72 40 0 100 8 0.8 78 40 0 1 00 9 0.2 39 23 5 95 Table 2 It can be seen from these examples that the excellent capability of converting NO of the catalys s of the invention 11 2l~2889 hardly depends on the content of oxygen when that one varies in the range of 0.2% to 10% by volume.
Examples 2 and 11.
The reagents and conditions of reactions are similar to those of the examples 2 and 6 to 8, but the oxygen concentration is set to 2% in volume and the conversions and selectivities correspond to the initial activity of the catalyst then at the activity of said catalyst after 15 h of sweeping (and therefore of reaction).
The results are regrouped in the following Table 3.
Example Time inConversion Conversion Selectivity Selectivity N~ hoursof CH4 in % of NO in % in N20 in % in N~ in %
Table 3 These results mean that the catalyst of the invention is stable with time.
Examples 11 to 13.
The reagents and conditions of reaction are similar to those of the examples 2 and 11. The stability of the catalyst after 15 hours of reaction having been established in the previous 12 21 ~ 2889 examples, 0.8% by volume of CO was added to the reaction mixture after 15 hours.
The results of these tests are regrouped ln the following Table 4.
Example Time Concen'¢a~ion Conversion Conversion Selectivity Selecavity N~ in in CO of CH4 in of NO in % in N20 in N2 hours in% % in % in%
12 16 0.8 75 40 0 100 13 20 0.8 78 40 0 100 Table 4 As shown by the results regrouped in this Table, the introduction in the reaction mixture of 0.8% of CO modifies neither the conversion of methane nor that of the NO. The carbon monoxide is totally converted to CO2 at temperatures very inferior to those needed for the reduction of NO by methane. This property is important because the gases issued from the combustion of methane may contain CO. The latter may come either from an incomplete oxidation of methane or from WGS (water-gas-shift) :
C~2 + H2 = CO + H20, or also from the reforming of methane :
CH4+H20= CO+3H2 _ 13 21~288 9 In every cases CO appears as a supplementary reducer present in the effluents. CO may then react with NO to provide CO2 and N2. This reaction competes with the reduction of NO by CH4.
Thus one could have thought that the presence of CO in the reaction mixture would have caused a decrease in the methane conversion. In fact, it is not so, the catalyst of the lnvention enabling not to modify the conversions of CH4 even in the presence of 0.8~ of CO. Furthermore the selectivity in N2 is not modified.
Examples 14 to 17.
Tests were effected with catalysts constituted of a zeolite of the MFI type with a Si/Al ratio of l9 exchanged with about 0.97% by weight of Pd and with a reaction mixture comprising l.6%
by volume of oxygen, 0.1% by volume of CH4 and 0.2% by volume of NO and in which water was introduced in the form of vapor, in order to test the activity and the selectivity of this catalyst in the presence of water.
Indeed the gases issued from the combustion of methane contain vapor of water and the latter is known to deteriorate the performances of this type of catalysts.
The results are regrouped in Table 5.
21~2889 Example Time in Concentration Conversion Conversion Selectivity Selectivity N~hours afterin H20 of CH4 in of NO in % in N20 in N2 the beginning in % % in % in %
of the sweeping 0 5.3 91 32 10 90 16 1 7.5 92 31 19 81 Table 5 These results show that up to a content of water of about 10%
in volume, the activity of the catalyst remains excellent. The conversion of methane is constant and that of NO moves from 38 to 27%.
Examples 18 to 21.
The catalyst was then tested with natural gas and that in the presence of oxygen, in order to test the applicability of this catalyst to the treatment of the exhaust gases of motors of vehicles functioning with natural gas or equipped with a bicarburation system (gasoline/natural gas).
The reagents and conditions of reactions are similar to those of the examples 2 and 6 to 8 but the content of palladium is set to 0.97%.
21 ~2889 ~
The volumetric composition of the natural gas ls the following :
CH4 = 91.37%
N2 = 0-70%
C2H6 = 6.70%
C3Hg = 1.10%
isoC4H1o = 0.04%
nC4H1o = 0.04%
neoCsH12 = 0.01%
isoCsH12 = 0.02%
nC5H12 = 0-02%
The conversions and the selectivities corresponding to the initial activity of the catalyst are regrouped in the following Table 6.
Example Concentration Conversion Conversion of Conversion Selectivity Selectivity N~ in 02~f CH4 in hydrocarbons of NO in %in N20 in N2 in % % other than in % in %
CH4in%
18 0.2 91 100 28 6 94 19 0.4 94 100 30 7 93 0.8 95 100 31 6 94 Table 6 16 21 ~2889 These results show that the activity of the catalyst of the invention is just as good, even when using natural gas.
Examples 22 to 24 Finally,-assays were realized with catalysts identical to those of the examples 14 to 17 in the presence of a mixture representative of exhaust gases coming from a combustion of gasoline (stoechiometric mixture) and at different temperatures of reaction.
Indeed in the context of an application to a vehicle equipped with a system with a bicarburation gasoline/natural gas, the catalytic exhaust must be able to treat exhaust gases issued from the combustion of these two fuels.
The reaction mixture then comprises 5025 ppm of CO, 685 ppm of NO, 1060 ppm of C3H6 and 6940 ppm of ~2 The results of these tests are regrouped in the following Table 7.
Example Temperature Conversion Conversion of Conversion Selectivity Selectivity N~ in ~C of CO C3H6 ~f NO in N20 in N2 in % in % in % in ~/O in ~/O
Table 7 21~2889 Therefore, the catalyst shows an excellent activity for exhaust gases issued from the combustion of natural gas and gasoline at temperatures comprised between about 350~C and about 450~C
Moreover, for comparison purposes, different catalysts have been tested :
- catalysts constituted of a zeolite of the mordenite type with large pores exchanged with different contents in Pd, - catalysts constltuted of zeolite of the mordenite type with large pores and MFI type exchanged or impregnated with cokalt at varying concentrations.
Examples 25 to 29.
In these examples, the protonated zeolite with large pores is obtained by firing a commercial ammoniated mordenite of a composition corresponding to a Si/Al ratio of 5.5.
This NH4M zeolite is fired to eliminate NH3 and to obtain the protonated form of the mordenite.
This zeolite is then exchanged with palladium to different contents and tested at a temperature of 500~C with a reaction mixture comprising 2% by volume of oxygen, 0.1% by volume of CH4 and 0.2% by volume of NO.
The conversions and selectivities corresponding to the initial activity of the catalyst are regrouped in the followlng Table 8.
Example Content of Conversion Conversion of Selectivity Selectivi~
N~ Pd in % of CH4 in NO in % in N2O in in N2 % % in%
0.52 67 18 0 100 26 0.7 98 27 0 100 27 0.87 100 24 0 100 28 0.95 91 16 4 96 29 1.26 100 19 0 100 Table 8 Besides, these results have been reported in figure 2 which illustrates the influence of the content of Pd in a zeolite of the mordenite type with large pores on the activity of the catalyst. In this figure, one has plotted on the absciss the percentage by weight with respect to the total weight of catalyst of Pd exchanged in a zeolite of the mordenite type with large pores and on the ordinate the corresponding percentages of converted CH4 (curve 3) and NO (curve 4).
On the whole range of contents of palladium studied, one can note that the activity of this catalyst in converting NO is lower than that of the catalysts of the invention.
Examples 30 to 35.
Assays were also effected on catalysts constituted of zeolite of the MFI type exchanged or impregnated with cobalt.
21~2889 The catalyst constituted of MFI zeolite exchanged with cobalt was prepared by exchanging the protons of the MFI zeolite with cobalt ions.
Other catalysts were prepared by impregnation of cobalt on a carrier of zeolite of the MFI type and on a carrier of zeolite of the protonated mordenite type with large pores according to the following operation mode :
the precursor was cobalt nitrate dissolved in water that had been added to a known weight of zeolite. One left it under agitation during 1 hour then the water was removed by evaporation at 60~C in an evaporator under reduced pressure. After drying overnight at 120~C, the solid was fired under oxygen with a slow elevation in temperature of 0.5~C per minute followed by two successive plateaux of 300~C during 1 hour and cf 500~C during 1 hour.
These catalysts based on cobalt were tested at a temperature of 500~C with a reaction mixture containing 2% by volume of oxygen, 0.1% by volume of methane and 0.2% by volume of NO.
The conversions and selectivities corresponding to an activity of the catalyst after variable times of sweeping (and consequently of reaction) are regrouped in the following Table ~.
Example Catalyst Time in Conversion Conversion Selectivit Selectivit N~ hours after of CH4 of NO y in N2O y in N2 the in % in ~/0 in % in %
beginning of the sweeping 0.4%Co/MFI (e) 0 26 5 0 100 31 0.4%Co/l~:FI (e) 2 26 4 0 100 32 4.65%Co/HMLP* 0 86 33 0 100 (i) 33 4.65%Co/HMLP* 21 88 38 0 100 (i) 34 4.3%Co/MFI (i) 0 80 7 0 100 4.3%Co/MFI (i) 1 81 9 0 100 Table 9 * : mordenite type with large pores (e) : prepared by exchange (i) : prepared by impregnation These results show that only a catalyst constituted of a zeolite of the mordenite type with large pores impregnated with 4.65% by weight of cobalt with respect to the total weight of catalyst presents an activity comparable with that of the catalyst of the invention. However this type of catalyst can lead to the production of toxic complexes of cobalt carbonyl.
21 21~2889 Examples 36 to 38.
The following tests were realized with a reaction mixture comprising 1000 ppm of CH4, 2000 ppm of NO and 2~ Of ~2 on a catalyst of the invention, at a temperature of 500~C, in order to confirm the influence of the spacial velocity on the conversion of CH4 and NO.
Indeed, the higher the spacial velocity, the lower the time of contact of the reaction medium with the catalyst, which leads normally to a decrease in the percentages of converted CH4 and NO.
The conversions of H4 and NO obtained at different spacial velocities are regrouped in the following Table 10.
ExampleSpacial velocit,v Conversion of Conversion of N~ in h-l CH4 in % NO in %
Table 10 The Examples 36 to 38 show that a decrease in the spacial velocity of a factor 4 increases the conversion of NO of about 40% and the conversion of CH4 of about 10%.
Examples 39 to 43.
The influence on the conversion of NO, of the quantity of reducer (methane) used has been studied.
A catalyst constituted of a zeolite of the MFI type with a Si/Al ratio = 18, exchanged with 0.97% of Pd was tested in the presence of 2~ of oxygen, at a temperature of 500~C and a spacial velocity of 35000 h-1. The concentration in NO was maintained constant at 2000 ppm.
The results are regrouped in the followlng Table 11.
ExampleConcentration inCH4 Concentration Conversionof N~ in ppm in NO in ppm NO in %
Table 11 The results regrouped in Table 11 show an increase in the percentage of NO converted when the concentration in methane increases from 1000 ppm to 2000 ppm. After 2000 ppm and up to 5000 ppm of CH4, the percentage of converted NO remains constant.
The catalyst according to the invention presents consequently the advantage of being able to be used in an oxidizing atmosphere, more particularly in an atmosphere containing up to 10% of oxygen, with methane or natural gas or gasoline, in the presence of up to 10% of water, and that in difficult conditions, 23 21~2 889 that is with a low concentration in Pd, high spacial velocities and low concentrations in reducer. Further it does not lead to the production of toxic compounds, such as CO which is totally converted into C02, which would allow in particular a use as a catalyst in the catalytic exhausts of vehicles functioning with natural gas.
Of course, the invention is in no way llmited to the embodiments described and illustrated which were given by way of examples only.
Thus, the catalyst according to the invention could be used in other operation conditions, for example, with different concentrations in NO, CH4, whether in fixed or fluidized bed.
That is to say that the invention comprises all the technical equivalents of the means described as well as their combinations if they are effected according to its spirit.
One knows numerous processes of transformation of the NOX in nitrogen.
One of these processes consists in using, as a reducing agent, carbon monoxide or hydrogen and as a catalyst, a catalyst based on precious metals supported on alumina or silica.
But in an oxidizing atmosphere, the oxidation of the hydrogen and carbon monoxide by gaseous oxygen precedes the reduction of NO by hydrogen and this reaction of reduction will therefore only take place when all the oxygen has been consumed.
This means that in the presence of a high excess of oxygen, it is necessary to use processes of selective reduction. The most common process consists in using ammonia as a reducing agent of the NOX in the presence of a catalyst constituted of V2Os and WO3 deposited on TiO2. This catalyst and this process enable the reduction of the NOX into nitrogen even in the presence of sulphur poisons.
But the catalytic materials have a limited lifetime and the installation requests an important investment. Further the storage of ammonia as well as its use are delicate.
IWAMOTO et al., propose in Catal. Today, 10, (1991), 57, to replace ammonia by hydrocarbons. Thus selective reducing hydrocarbons would be the hydrocarbons having more than two carbons and particularly propane and propene. The catalysts used 214~889 are zeolites with a high Si/Al ratio exchanged or not with transition metals.
S. SUBRAMANIAN et al. in Ind Eng. Chem. Res., 31, (1992), 2460, have studied the selective reduction of the NOX by methane in the presence of a catalyst constituted of palladium supported on alumina and conclude that the simultaneous elimination of methane and of NO cannot take place with this type of catalyst.
However, in the European patent application N~ EP 0,499,286 A2, Y. KAWAI discloses catalysts constituted of Co-Ag and of Co-Pd on zeolite which would enable to eliminate simultaneously the carbon monoxide, the NO and the methane even in the presence of 5% of oxygen and at 500~C. In the same conditions a catalyst constituted of palladium supported on a zeolite of the MFI type would not convert NO.
LI and ARMOR in the US patent N~ 5,149,512 use a catalyst constituted of a zeolite, particularly of the MFI type, exchanged with Co for the selective reduction of the NOX.
But cobalt is not usable in industrial processes and in catalytic exhausts of automobile vehicles because it can transform itself in carbonyl cobalt complexes highly toxic and polluting for the environment.
Another disadvantage of the catalysts of the prior art disclosed in particular by LI, BATTAVIO and ARMOR in "Effect of Water Vapor on the Selective Reduction of NO by methane over Cobalt-Exchanged ZSM-5" Journal of catalysis 142,561-571, (1993), is their loss of activity in the presence of water.
3 21~2889 To palliate the above disadvantages and in contrast with this state of the technique, the present invention proposes a catalyst of reduction of the NOX by methane or any mixture containing in majority methane such as for example natural gas, in an oxidizing atmosphere, constituted of a zeolite of the MFI type exchanged w th palladium the weight of which is comprised between 0.3% and 2~ of the total weight of catalyst.
According to a characteristic of the catalyst of the invention, the weight content of palladium is of about 0.5%
According to another characteristic of the invention, the catalyst is obtained from palladium II tetramine hydroxide as a precursor of Pd.
According to yet another characteristic of the invention, the catalyst is activated under oxygen, before utilization by a process comprising the steps of : (a) elevation in temperature from room temperature up to 300~C with a rate of elevation in temperature of 0.5~C/mn, (b) plateau of 300~C during an hour, (c) elevation in temperature from 300~C up to 500~C with a rate of elevation in temperature of 0.5~C/mn, (d) maintaining at 500~C
during an hour, and (e) lowering in temperature from 500~C down to 300~C.
According to still another characteristic of the catalyst of the invention, after the precited step (e) a step (f) of sweeping with an inert gas such as helium is realized.
According to a further characteristic of the catalyst of the invention, the used zeolite of the MFI type has a Si/Al ratio higher than 15.
4 214~89 The catalyst of the invention enables the reduction of the NOX in the presence of up to 10% by volume of H2O in the form of vapor and/or of up to 10% by volume cf ~2 and/or of up to 0.8% by volume of CO.
According to a particularity of the invention, the selective reduction of the NOX is effected at a temperature comprised between about 350~C and 400~C.
The invention has also for object to propose a process of reduction of the NOX, in a oxidizing atmosphere, by methane or any mixture containing in majority methane such as for example natural gas, which comprises a step of reacting a reaction medium comprising among others methane, oxygen and NOX with a catalyst constituted of a zeolite of the MFI type exchanged with between 0.3% and 2% by weight of palladium, with respect to the total weight of catalyst used which enables to obtain the selective reduction of the NOX into N2.
According to a particularity of the process of the invention, the zeolite of the MFI type is exchanged with about 0.5% by weight of palladium with respect to the total weight of catalyst used.
According to another particularity of the process of the invention, the precursor of Pd is the palladium II tetramine hydroxide.
According to yet another particularity of the process of the invention, the catalyst is activated, before utilization, under oxygen, by a process comprising the steps of (a) elevation in temperature from room temperature up to 300~C with a rate of 5 21 l2889 elevation in temperature of 0.5~C/mn, (b) plateau of 300~C during 1 hour, (c) elevation in temperature from 300~C up to 500~C with a rate of elevation in temperature of 0.5~C/mn, (d) maintaining at 500~C during one hour, and (e) lowering in temperature from 500~C to 300~C with oxygen.
Still according to a particularity of the process of the invention, after the above step (e) a step (f) of sweeping with an inert gas such as helium is realized.
According to a characteristic of the process of the invention, the said reaction medium can contain up to 0.8% by volume of CO which is then simultaneously oxidized.
According to another characteristic of the process of the invention, the said reaction medium can contain up to 10% by volume of H2O in vapor form.
According to yet another characteristic of the process of the invention, the said reaction medium can contain up to 10% by volume of ~2 According to a last characteristic of the process of the invention, the said step of reacting is effected at a temperature comprised between about 350~ and about 500~C.
Other details, characteristics and advantages of the invention will appear better in the course of the detailed description that will follow and that is done in reference to the appended figures wherein :
Figure 1 illustrates the influence of the content of Pd exchanged in a zeolite of the MFI type, on the percentage of CH4 and of NO converted to N2 or (N2O + N2).
6 21428~9 Figure 2 illustrates the influence of the content of Pd exchanged in a zeolite of the protonated zeolite type with large pores, on the percentage of CH4 and of NO converted to N2 or (N2O
+ N2) -The zeolite of the MFI type, prepared according to a process known by itself presents a Si/Al ratio very variable that can attain extreme values (1000). This carrier has then served for the preparation of catalysts based on ions of metals of transition by cationic exchange between the ions of zeolite (H+, Na+, Ca2+,...) and those of the metals of transition. This exchange enables one to obtain metallic ions dispersed and stabilized within the zeolitic network.
The zeolites exchanged with precious metals according to the invention were prepared by cationic exchange using adequate precursors. The palladium (II) tetramine hydroxide is a particularly preferred precursor.
The following protocol was followed :
5 g of zeolite are put in a beaker, then the precursor is added after having been diluted in 50 cm3 of distilled water.
Agitation is maintained during an hour at a temperature of 25~C
to obtain the equilibrium of exchange. The solid is then filtered and washed with an abundant quantity of distilled water (about 1 litre). It is then dried in the oven at 120~C overnight.
This preparation process enables one to obtain a catalyst based on palladium exchanged in the MFI zeolite which is interesting in that it has Pd2+ ions, in low quantities indeed, 7 21~28~ 9 but well separated the ones from the others which limits doubly the possibilities of clustering.
The catalytic tests were effected in a reactor with a flow-through bed constituted of a U-tube without sinter wherein one places a little pad in wool of quartz on which is deposited 200 mg of catalyst.
The catalyst is then in situ activated under oxygen by proceeding to a slow temperature elevation (0.5~C/mn) from 25~C
up to 300~C followed by a plateau of 300~C during 1 hour before being brought to a temperature of 500~C with a rate of elevation between 300~C and 500~C of 0.5~C/mn. The temperature is then maintained at 500~C during 1 hour before proceeding at a lowering to 300~C under oxygen. One then sweeps the catalyst during 30 minutes with helium before injecting the reaction mixture comprising gases such as methane, NOX, carbon monoxide, oxygen and water in the form of vapor.
The exhaust gases are analysed with two chromatographs or infrared analysers depending on the nature of the gas to analyse.
The first chromatograph is a chromatograph with a catharometric detection (T.C.D.), INTERSMAT IGC 121 ML. The column of separation is a CTR column of a length of 2 metres, a diameter of 1/4 of an inch of stainless steel containing a molecular sieve 5A
and PORAPAK Q. The vector gas is helium. The oven, the injector and the detector are at a temperature of 40~C. The sensitivity of the detector is 250 mA.
The second chromatograph is a chromatograph with a flame ionization (F.I.D.) INTERSMAT IGC 120 FB. The column has a length 8 214288g of 2 metres and a diameter of 1/8 of an inch and contains PORAPAK
Q-The vector gas is helium. The oven temperature is 130~C. Thetemperature of the injection is 175~C and that of the detector is 170~C.
The Si, Al, Pd contents have been analysed by atomic absorption.
The invention is based~on the surprising discovery and that, contrarily to the teachings of the prior art that a catalyst constituted of a zeolite of the MFI type exchanged with between 0.3% and 2% by weight of palladium with respect to the total weight of catalyst presents numerous proprieties that will be described in relation with the examples that will follow.
In these examples, it ls the reduction of NO rather than that cf NO2 that has been studied because it is admitted by the man skilled in the art that NO is representative of the NOX.
Spacial velocities of 35.000 h-1 were used for the realization of the tests effected in the Examples 1 to 35 and 39 to 43.
Examples 1 to 5.
Different catalysts constituted of MFI zeolite with a Si/Al ratio = 15 exchanged with different contents in Pd were synthesized as previously described and tested at 500~C with a reaction mixture comprising 2% by volume of oxygen, 0.1% by volume of methane and 0.2% by volume of NO.
The convers_ons and selectivities cor espording to the nlt-2 ac iv_-y cf the cata yst are ~egrolped in the following T2b e 1 :
Example Content Conversion Conversion Selec~ivitv Se!ec~ivity N~ of Pd in of CH4 in % of NO in % in N2O in % in ~-2 in %
%
0.3 42 28 0 l 00 2 0.49 78 40 0 l 00 3 0.74 69 28 7 93 4 0.98 73 32 0 lO0 1.94 96 27 8 92 Table 1 These results have also ~een represen ed in the form of curves 1 anc 2 in the appended figure 1.
On the graph of figure 1, one has represented the evolution of the conversions of methane (curve 1) ard of NO ~curve 2) versus the content of Pd (weight %) of tr.e catalyst.
It is then noticed that the conversions of NO and of CH4 are simultaneously high for palladium contents comprised between about 0.4% and about 0.6% by total weight of catalyst, the maximum of activity presenting itself around a palladium content of 0.5% by weight with respect to the total weight of the catalyst.
Further, the selectivity in N2 is excellent with this catalyst. ~hus the formation of N20 , un~esirable, is nearly nil.
- 21~2889 Examples 2 and 6 to 10.
Catalysts constituted of a zeolite of the MFI type with a S-/Al ratio of 15 exchanged with about 0.49~ by weight of palladium for the examples 2 and 6 to 8 and with about 0.97% by weight of palladium for the examples 9 and 10 were tested at 500~C with a reaction mixture containing between 0.2% and 10% by volume of ~2~ 0.1% by volume of CH4 and 0.2~ by volume of NO.
The conversions and selectivities corresponding to the initial activity of the catalyst are regrouped in the following Table 2.
Example Concentration Conversion Conversion Selectivity Selectivity N~ of ~2 in % of CH4 in of NO in % in N2O in % in N2 in %
%
6 0.2 62 37 0 100 7 0.4 72 40 0 100 8 0.8 78 40 0 1 00 9 0.2 39 23 5 95 Table 2 It can be seen from these examples that the excellent capability of converting NO of the catalys s of the invention 11 2l~2889 hardly depends on the content of oxygen when that one varies in the range of 0.2% to 10% by volume.
Examples 2 and 11.
The reagents and conditions of reactions are similar to those of the examples 2 and 6 to 8, but the oxygen concentration is set to 2% in volume and the conversions and selectivities correspond to the initial activity of the catalyst then at the activity of said catalyst after 15 h of sweeping (and therefore of reaction).
The results are regrouped in the following Table 3.
Example Time inConversion Conversion Selectivity Selectivity N~ hoursof CH4 in % of NO in % in N20 in % in N~ in %
Table 3 These results mean that the catalyst of the invention is stable with time.
Examples 11 to 13.
The reagents and conditions of reaction are similar to those of the examples 2 and 11. The stability of the catalyst after 15 hours of reaction having been established in the previous 12 21 ~ 2889 examples, 0.8% by volume of CO was added to the reaction mixture after 15 hours.
The results of these tests are regrouped ln the following Table 4.
Example Time Concen'¢a~ion Conversion Conversion Selectivity Selecavity N~ in in CO of CH4 in of NO in % in N20 in N2 hours in% % in % in%
12 16 0.8 75 40 0 100 13 20 0.8 78 40 0 100 Table 4 As shown by the results regrouped in this Table, the introduction in the reaction mixture of 0.8% of CO modifies neither the conversion of methane nor that of the NO. The carbon monoxide is totally converted to CO2 at temperatures very inferior to those needed for the reduction of NO by methane. This property is important because the gases issued from the combustion of methane may contain CO. The latter may come either from an incomplete oxidation of methane or from WGS (water-gas-shift) :
C~2 + H2 = CO + H20, or also from the reforming of methane :
CH4+H20= CO+3H2 _ 13 21~288 9 In every cases CO appears as a supplementary reducer present in the effluents. CO may then react with NO to provide CO2 and N2. This reaction competes with the reduction of NO by CH4.
Thus one could have thought that the presence of CO in the reaction mixture would have caused a decrease in the methane conversion. In fact, it is not so, the catalyst of the lnvention enabling not to modify the conversions of CH4 even in the presence of 0.8~ of CO. Furthermore the selectivity in N2 is not modified.
Examples 14 to 17.
Tests were effected with catalysts constituted of a zeolite of the MFI type with a Si/Al ratio of l9 exchanged with about 0.97% by weight of Pd and with a reaction mixture comprising l.6%
by volume of oxygen, 0.1% by volume of CH4 and 0.2% by volume of NO and in which water was introduced in the form of vapor, in order to test the activity and the selectivity of this catalyst in the presence of water.
Indeed the gases issued from the combustion of methane contain vapor of water and the latter is known to deteriorate the performances of this type of catalysts.
The results are regrouped in Table 5.
21~2889 Example Time in Concentration Conversion Conversion Selectivity Selectivity N~hours afterin H20 of CH4 in of NO in % in N20 in N2 the beginning in % % in % in %
of the sweeping 0 5.3 91 32 10 90 16 1 7.5 92 31 19 81 Table 5 These results show that up to a content of water of about 10%
in volume, the activity of the catalyst remains excellent. The conversion of methane is constant and that of NO moves from 38 to 27%.
Examples 18 to 21.
The catalyst was then tested with natural gas and that in the presence of oxygen, in order to test the applicability of this catalyst to the treatment of the exhaust gases of motors of vehicles functioning with natural gas or equipped with a bicarburation system (gasoline/natural gas).
The reagents and conditions of reactions are similar to those of the examples 2 and 6 to 8 but the content of palladium is set to 0.97%.
21 ~2889 ~
The volumetric composition of the natural gas ls the following :
CH4 = 91.37%
N2 = 0-70%
C2H6 = 6.70%
C3Hg = 1.10%
isoC4H1o = 0.04%
nC4H1o = 0.04%
neoCsH12 = 0.01%
isoCsH12 = 0.02%
nC5H12 = 0-02%
The conversions and the selectivities corresponding to the initial activity of the catalyst are regrouped in the following Table 6.
Example Concentration Conversion Conversion of Conversion Selectivity Selectivity N~ in 02~f CH4 in hydrocarbons of NO in %in N20 in N2 in % % other than in % in %
CH4in%
18 0.2 91 100 28 6 94 19 0.4 94 100 30 7 93 0.8 95 100 31 6 94 Table 6 16 21 ~2889 These results show that the activity of the catalyst of the invention is just as good, even when using natural gas.
Examples 22 to 24 Finally,-assays were realized with catalysts identical to those of the examples 14 to 17 in the presence of a mixture representative of exhaust gases coming from a combustion of gasoline (stoechiometric mixture) and at different temperatures of reaction.
Indeed in the context of an application to a vehicle equipped with a system with a bicarburation gasoline/natural gas, the catalytic exhaust must be able to treat exhaust gases issued from the combustion of these two fuels.
The reaction mixture then comprises 5025 ppm of CO, 685 ppm of NO, 1060 ppm of C3H6 and 6940 ppm of ~2 The results of these tests are regrouped in the following Table 7.
Example Temperature Conversion Conversion of Conversion Selectivity Selectivity N~ in ~C of CO C3H6 ~f NO in N20 in N2 in % in % in % in ~/O in ~/O
Table 7 21~2889 Therefore, the catalyst shows an excellent activity for exhaust gases issued from the combustion of natural gas and gasoline at temperatures comprised between about 350~C and about 450~C
Moreover, for comparison purposes, different catalysts have been tested :
- catalysts constituted of a zeolite of the mordenite type with large pores exchanged with different contents in Pd, - catalysts constltuted of zeolite of the mordenite type with large pores and MFI type exchanged or impregnated with cokalt at varying concentrations.
Examples 25 to 29.
In these examples, the protonated zeolite with large pores is obtained by firing a commercial ammoniated mordenite of a composition corresponding to a Si/Al ratio of 5.5.
This NH4M zeolite is fired to eliminate NH3 and to obtain the protonated form of the mordenite.
This zeolite is then exchanged with palladium to different contents and tested at a temperature of 500~C with a reaction mixture comprising 2% by volume of oxygen, 0.1% by volume of CH4 and 0.2% by volume of NO.
The conversions and selectivities corresponding to the initial activity of the catalyst are regrouped in the followlng Table 8.
Example Content of Conversion Conversion of Selectivity Selectivi~
N~ Pd in % of CH4 in NO in % in N2O in in N2 % % in%
0.52 67 18 0 100 26 0.7 98 27 0 100 27 0.87 100 24 0 100 28 0.95 91 16 4 96 29 1.26 100 19 0 100 Table 8 Besides, these results have been reported in figure 2 which illustrates the influence of the content of Pd in a zeolite of the mordenite type with large pores on the activity of the catalyst. In this figure, one has plotted on the absciss the percentage by weight with respect to the total weight of catalyst of Pd exchanged in a zeolite of the mordenite type with large pores and on the ordinate the corresponding percentages of converted CH4 (curve 3) and NO (curve 4).
On the whole range of contents of palladium studied, one can note that the activity of this catalyst in converting NO is lower than that of the catalysts of the invention.
Examples 30 to 35.
Assays were also effected on catalysts constituted of zeolite of the MFI type exchanged or impregnated with cobalt.
21~2889 The catalyst constituted of MFI zeolite exchanged with cobalt was prepared by exchanging the protons of the MFI zeolite with cobalt ions.
Other catalysts were prepared by impregnation of cobalt on a carrier of zeolite of the MFI type and on a carrier of zeolite of the protonated mordenite type with large pores according to the following operation mode :
the precursor was cobalt nitrate dissolved in water that had been added to a known weight of zeolite. One left it under agitation during 1 hour then the water was removed by evaporation at 60~C in an evaporator under reduced pressure. After drying overnight at 120~C, the solid was fired under oxygen with a slow elevation in temperature of 0.5~C per minute followed by two successive plateaux of 300~C during 1 hour and cf 500~C during 1 hour.
These catalysts based on cobalt were tested at a temperature of 500~C with a reaction mixture containing 2% by volume of oxygen, 0.1% by volume of methane and 0.2% by volume of NO.
The conversions and selectivities corresponding to an activity of the catalyst after variable times of sweeping (and consequently of reaction) are regrouped in the following Table ~.
Example Catalyst Time in Conversion Conversion Selectivit Selectivit N~ hours after of CH4 of NO y in N2O y in N2 the in % in ~/0 in % in %
beginning of the sweeping 0.4%Co/MFI (e) 0 26 5 0 100 31 0.4%Co/l~:FI (e) 2 26 4 0 100 32 4.65%Co/HMLP* 0 86 33 0 100 (i) 33 4.65%Co/HMLP* 21 88 38 0 100 (i) 34 4.3%Co/MFI (i) 0 80 7 0 100 4.3%Co/MFI (i) 1 81 9 0 100 Table 9 * : mordenite type with large pores (e) : prepared by exchange (i) : prepared by impregnation These results show that only a catalyst constituted of a zeolite of the mordenite type with large pores impregnated with 4.65% by weight of cobalt with respect to the total weight of catalyst presents an activity comparable with that of the catalyst of the invention. However this type of catalyst can lead to the production of toxic complexes of cobalt carbonyl.
21 21~2889 Examples 36 to 38.
The following tests were realized with a reaction mixture comprising 1000 ppm of CH4, 2000 ppm of NO and 2~ Of ~2 on a catalyst of the invention, at a temperature of 500~C, in order to confirm the influence of the spacial velocity on the conversion of CH4 and NO.
Indeed, the higher the spacial velocity, the lower the time of contact of the reaction medium with the catalyst, which leads normally to a decrease in the percentages of converted CH4 and NO.
The conversions of H4 and NO obtained at different spacial velocities are regrouped in the following Table 10.
ExampleSpacial velocit,v Conversion of Conversion of N~ in h-l CH4 in % NO in %
Table 10 The Examples 36 to 38 show that a decrease in the spacial velocity of a factor 4 increases the conversion of NO of about 40% and the conversion of CH4 of about 10%.
Examples 39 to 43.
The influence on the conversion of NO, of the quantity of reducer (methane) used has been studied.
A catalyst constituted of a zeolite of the MFI type with a Si/Al ratio = 18, exchanged with 0.97% of Pd was tested in the presence of 2~ of oxygen, at a temperature of 500~C and a spacial velocity of 35000 h-1. The concentration in NO was maintained constant at 2000 ppm.
The results are regrouped in the followlng Table 11.
ExampleConcentration inCH4 Concentration Conversionof N~ in ppm in NO in ppm NO in %
Table 11 The results regrouped in Table 11 show an increase in the percentage of NO converted when the concentration in methane increases from 1000 ppm to 2000 ppm. After 2000 ppm and up to 5000 ppm of CH4, the percentage of converted NO remains constant.
The catalyst according to the invention presents consequently the advantage of being able to be used in an oxidizing atmosphere, more particularly in an atmosphere containing up to 10% of oxygen, with methane or natural gas or gasoline, in the presence of up to 10% of water, and that in difficult conditions, 23 21~2 889 that is with a low concentration in Pd, high spacial velocities and low concentrations in reducer. Further it does not lead to the production of toxic compounds, such as CO which is totally converted into C02, which would allow in particular a use as a catalyst in the catalytic exhausts of vehicles functioning with natural gas.
Of course, the invention is in no way llmited to the embodiments described and illustrated which were given by way of examples only.
Thus, the catalyst according to the invention could be used in other operation conditions, for example, with different concentrations in NO, CH4, whether in fixed or fluidized bed.
That is to say that the invention comprises all the technical equivalents of the means described as well as their combinations if they are effected according to its spirit.
Claims (19)
1. A catalyst of reduction of the NOX by methane or any mixture containing essentially methane such as for example natural gas, in an oxidizing atmosphere, characterized in that it is constituted of a zeolite of the MFI type exchanged with between 0.3% and 2% by weight of palladium with respect to the total weight of catalyst.
2. A catalyst according to claim 1, characterized in that the content by weight of palladium is of about 0.5%.
3. A catalyst according to claim 1 or 2, characterized in that it is obtained with palladium II tetramine hydroxide as precursor of Pd.
4. A catalyst according to any one of the preceding claims, characterized in that the catalyst is activated before utilization, under oxygen, by a process comprising the steps of :
(a) elevation in temperature from room temperature up to 300°C with a rate of elevation in temperature of 0.5°C/mn, (b) maintaining at 300°C during 1 hour, (c) elevation from 300°C up to 500°C with a rate of elevation in temperature of 0.5°C/mn, (d) maintaining at 500°C for 1 hour, and (e) lowering in temperature from 500°C down to 300°C.
(a) elevation in temperature from room temperature up to 300°C with a rate of elevation in temperature of 0.5°C/mn, (b) maintaining at 300°C during 1 hour, (c) elevation from 300°C up to 500°C with a rate of elevation in temperature of 0.5°C/mn, (d) maintaining at 500°C for 1 hour, and (e) lowering in temperature from 500°C down to 300°C.
5. A catalyst according to claim 4, characterized in that after the step (e), a step (f) of sweeping with an inert gas, such as helium, is realized at 300°C.
6. A catalyst according to any one of the preceding claims, characterized in that said zeolite of the MFI type has a Si/Al ratio higher than 15.
7. A catalyst according to any one of the preceding claims, characterized in that it enables to simultaneously oxidizes CO
into CO2, CH4 into CO2 and to reduce selectively NOX into N2.
into CO2, CH4 into CO2 and to reduce selectively NOX into N2.
8. A catalyst according to any one of the preceding claims, characterized in that said oxidizing atmosphere can contain up to 10% by volume of water in vapor form and/or up to 10% by volume of O2 and/or up to 0.8% by volume of CO.
9. A catalyst according to any one of the preceding claims, characterized in that said reduction of the NOX is effected at a temperature comprised between about 350°C and about 500°C.
10. Process of reduction of the NOX by methane or any mixture containing in majority-methane such as for example natural gas, characterized in that it comprises a step of contacting a reaction medium comprising among others methane, oxygen and NOX
with a catalyst constituted of a zeolite of the MFI type exchanged with between 0.3% and 2% by weight of palladium with respect to the total weight of catalyst, whereby enabling to reduce selectively NOX and N2.
with a catalyst constituted of a zeolite of the MFI type exchanged with between 0.3% and 2% by weight of palladium with respect to the total weight of catalyst, whereby enabling to reduce selectively NOX and N2.
11. Process according to claim 10, characterized in that the zeolite of the MFI type is exchanged with about 0.5% by weight in palladium with respect to the total weight of catalyst.
12. Process according to claim 10 or 11, characterized in that said catalyst is obtained with palladium II tetramine hydroxide as Pd precursor.
13. Process according to any one of claims 10 to 12, characterized in that the catalyst is activated, before utilization, under oxygen, by a process comprising the steps of :
(a) elevation in temperature from room temperature up to 300°C with a rate of elevation in temperature of 0.5°C/mn, (b) maintaining at 300°C during 1 hour, (c) elevation in temperature from 300°C up to 500°C with a rate of elevation in temperature of 0.5°C/mn, (d) maintaining at 500°C for 1 hour, and (e) lowering in temperature from 500°C down to 300°C.
(a) elevation in temperature from room temperature up to 300°C with a rate of elevation in temperature of 0.5°C/mn, (b) maintaining at 300°C during 1 hour, (c) elevation in temperature from 300°C up to 500°C with a rate of elevation in temperature of 0.5°C/mn, (d) maintaining at 500°C for 1 hour, and (e) lowering in temperature from 500°C down to 300°C.
14. A process according to claim 13, characterized in that after the step (e) a step (f) of sweeping by an inert gas, such as helium, is realized at 300°C.
15. Process according to any one of the claims 10 to 14, characterized in that said zeolite of the MFI type has a Si/Al ratio higher than 15.
16. Process according to any one of claims 10 to 15, characterized in that said reaction medium can contain up to 0.8%
by volume of CO which is then simultaneously oxidized.
by volume of CO which is then simultaneously oxidized.
17. Process according to any one of claims 10 to 16, characterized in that said reaction medium can contain up to 10%
by volume of water in the form of vapor.
by volume of water in the form of vapor.
18. Process according to any one of claims 10 to 17, characterized in that said reaction medium can contain up to 10%
by volume of oxygen.
by volume of oxygen.
19. Process according to any one of claims 10 to 18, characterized in that said reduction is effected at a temperature comprised between about 350°C and about 500°C.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR9308006A FR2707075B1 (en) | 1993-06-30 | 1993-06-30 | NOx reduction catalyst and NOx reduction catalytic process. |
| FR93/08006 | 1993-06-30 | ||
| PCT/FR1994/000792 WO1995001222A1 (en) | 1993-06-30 | 1994-06-29 | Catalyst and catalytic method for reducing nitrogen oxides |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2142889A1 true CA2142889A1 (en) | 1995-01-12 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002142889A Abandoned CA2142889A1 (en) | 1993-06-30 | 1994-06-29 | Catalyst and catalytic method for reducing nitrogen oxides |
Country Status (10)
| Country | Link |
|---|---|
| EP (1) | EP0656810B1 (en) |
| JP (1) | JPH08500772A (en) |
| AT (1) | ATE175591T1 (en) |
| CA (1) | CA2142889A1 (en) |
| DE (1) | DE69415950T2 (en) |
| DK (1) | DK0656810T3 (en) |
| ES (1) | ES2129131T3 (en) |
| FR (1) | FR2707075B1 (en) |
| GR (1) | GR3029936T3 (en) |
| WO (1) | WO1995001222A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2018011552A1 (en) * | 2016-07-12 | 2018-01-18 | Johnson Matthey Public Limited Company | Oxidation catalyst for a stoichiometric natural gas engine |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5874646A (en) * | 1996-08-07 | 1999-02-23 | Solutia Inc. | Preparation of phenol or phenol derivatives |
| GB201504986D0 (en) * | 2015-02-13 | 2015-05-06 | Johnson Matthey Plc | Oxidation catalyst for treating a natural gas emission |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4176050A (en) * | 1978-12-04 | 1979-11-27 | Mobil Oil Corporation | Production of high V.I. lubricating oil stock |
| US4232181A (en) * | 1979-06-28 | 1980-11-04 | Norton Company | Hydroisomerization of pentane utilizing Pd exchanged mordenite |
| FR2619319B1 (en) * | 1987-08-14 | 1990-01-12 | Inst Francais Du Petrole | ALUMINOSILICATE TYPE CATALYST CONTAINING AT LEAST ONE NOBLE METAL AND ITS USE IN ISOMERIZATION OF AN AROMATIC C8 CUT |
| DE3917890A1 (en) * | 1989-06-01 | 1990-12-06 | Steinbach Friedrich | SUPPORTED CATALYSTS FOR THE REMOVAL OF NITROGEN OXIDE, CARBON MONOXIDE AND ORGANIC COMPOUNDS FROM EXHAUST GAS |
| US5171553A (en) * | 1991-11-08 | 1992-12-15 | Air Products And Chemicals, Inc. | Catalytic decomposition of N2 O |
-
1993
- 1993-06-30 FR FR9308006A patent/FR2707075B1/en not_active Expired - Lifetime
-
1994
- 1994-06-29 WO PCT/FR1994/000792 patent/WO1995001222A1/en active IP Right Grant
- 1994-06-29 DE DE69415950T patent/DE69415950T2/en not_active Expired - Fee Related
- 1994-06-29 AT AT94920994T patent/ATE175591T1/en not_active IP Right Cessation
- 1994-06-29 EP EP94920994A patent/EP0656810B1/en not_active Expired - Lifetime
- 1994-06-29 DK DK94920994T patent/DK0656810T3/en active
- 1994-06-29 ES ES94920994T patent/ES2129131T3/en not_active Expired - Lifetime
- 1994-06-29 JP JP7503316A patent/JPH08500772A/en active Pending
- 1994-06-29 CA CA002142889A patent/CA2142889A1/en not_active Abandoned
-
1999
- 1999-04-08 GR GR990401025T patent/GR3029936T3/en unknown
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2018011552A1 (en) * | 2016-07-12 | 2018-01-18 | Johnson Matthey Public Limited Company | Oxidation catalyst for a stoichiometric natural gas engine |
| US10807079B2 (en) | 2016-07-12 | 2020-10-20 | Johnson Matthey Public Limited Company | Oxidation catalyst for a stoichiometric natural gas engine |
Also Published As
| Publication number | Publication date |
|---|---|
| ES2129131T3 (en) | 1999-06-01 |
| WO1995001222A1 (en) | 1995-01-12 |
| FR2707075A1 (en) | 1995-01-06 |
| DE69415950D1 (en) | 1999-02-25 |
| EP0656810B1 (en) | 1999-01-13 |
| ATE175591T1 (en) | 1999-01-15 |
| DK0656810T3 (en) | 1999-09-06 |
| JPH08500772A (en) | 1996-01-30 |
| DE69415950T2 (en) | 1999-08-26 |
| EP0656810A1 (en) | 1995-06-14 |
| FR2707075B1 (en) | 1995-09-22 |
| GR3029936T3 (en) | 1999-07-30 |
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| Date | Code | Title | Description |
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| FZDE | Discontinued | ||
| FZDE | Discontinued |
Effective date: 20010629 |