Selective catalytic reduction catalyst for the treatment of an exhaust gas of a diesel engine

Abstract

The present invention relates to a selective catalytic reduction catalyst for the treatment of an exhaust gas of a diesel engine comprising: a flow-through substrate comprising an inlet end, an outlet end, a substrate axial length extending from the inlet end to the outlet end and a plurality of passages defined by internal walls of the flow through substrate extending therethrough; a coating disposed on the surface of the internal walls of the substrate, wherein the coating comprises a non-zeolitic oxidic material comprising manganese and one or more of the metals of the groups 4 to 11 and 13 of the periodic table, and further comprises one or more of a vanadium oxide and a zeolitic material comprising one or more of copper and iron.

Claims

1. A selective catalytic reduction catalyst for the treatment of an exhaust gas of a diesel engine, comprising: a flow-through substrate comprising an inlet end, an outlet end, a substrate axial length extending from the inlet end to the outlet end, and a plurality of passages defined by internal walls of the flow-through substrate extending therethrough; and a coating disposed on the surface of the internal walls of the substrate, wherein the coating comprises a non-zeolite oxide material comprising manganese and one or more metals of the groups 4 to 11 and 13 of the periodic table, and further comprises one or more of a vanadium oxide and a zeolite material comprising one or more of copper and iron, wherein the coating comprises the non-zeolite oxide material at a loading (l1), and the one or more of a vanadium oxide and a zeolite material comprising one or more of copper and iron at a loading (l2), and wherein the ratio of loading (l1) to loading (l2), (l1):(l2), is in the range of from 0.1:1 to 10:1 wherein from 55 to 90 weight-% of the non-zeolitic oxidic material consist of manganese, present as Mn.sub.2O.sub.3 from 5 to 25 weight-% of the non-zeolitic oxidic material consist of zirconium, calculated as ZrO.sub.2, and from 5 to 25 weight-% of the non-zeolitic oxidic material consist of lanthanum, calculated as La.sub.2O.sub.3.

2. The selective catalytic reduction catalyst of claim 1, wherein the one or more metals of the groups 4 to 11 and 13 of the periodic table are selected from the group consisting of aluminum, gallium, titanium, vanadium, chromium, iron, cobalt, nickel, copper, zirconium, niobium, molybdenum, tantalum, and tungsten.

3. The selective catalytic reduction catalyst of claim 1, wherein the one or more metals of the groups 4 to 11 and 13 of the periodic table are selected from the group consisting of titanium, vanadium, iron, and tungsten, wherein titanium, if present, is in the non-zeolite oxide material as titania, and wherein the non-zeolite oxide material further comprises at least one selected from the group consisting of silicon, antimony, lanthanum, cerium, praseodymium, and neodymium.

4. The selective catalytic reduction catalyst of claim 1, wherein the one or more metals of the groups 4 to 11 and 13 of the periodic table are selected from the group consisting of aluminum, vanadium, iron, and tungsten.

5. The selective catalytic reduction catalyst of claim 1, wherein the one or more metals of the groups 4 to 11 and 13 of the periodic table are selected from the group consisting of vanadium, cobalt, zirconium, and tungsten, wherein the non-zeolite oxide material further comprises one or more selected from the group consisting of silicon, antimony, lanthanum, cerium, praseodymium, and neodymium, and wherein the manganese comprised in the non-zeolite oxide material is present as Mn.sub.2O.sub.3.

6. The selective catalytic reduction catalyst of claim 1, wherein the non-zeolite oxide material comprised in the coating has a loading in the range of from 10 to 100 g/l.

7. The selective catalytic reduction catalyst of claim 1, wherein the coating comprises a zeolite material comprising one or more of copper and iron, and wherein the zeolite material comprised in the coating has at least one framework type selected from the group consisting of ABW, ACO, AEI, AEL, AEN, AET, AFG, AFI, AFN, AFO, AFR, AFS, AFT, AFV, AFX, AFY, AIT, ANA, APC, APD, AST, ASV, ATN, ATO, ATS, ATT, ATV, AVL, AWO, AWW, BCT, BEA, BEC, BIK, BOF, BOG, BOZ, BPH, BRE, BSV, CAN, CAS, CDO, CFI, CGF, CGS, CHA, -CHI, -CLO, CON, CSV, CZP, DAC, DDR, DFO, DFT, DOH, DON, EAB, EDI, EEI, EMT, EON, EPI, ERI, ESV, ETR, EUO, *-EWT, EZT, FAR, FAU, FER, FRA, GIS, GIU, GME, GON, GOO, HEU, IFO, IFR, -IFU, IFW, IFY, IHW, IMF, IRN, IRR, -IRY, ISV, ITE, ITG, ITH, *-ITN, ITR, ITT, -ITV, ITW, IWR, IWS, IWV, IWW, JBW, JNT, JOZ, JRY, JSN, JSR, JST, JSW, KFI, LAU, LEV, LIO, -LIT, LOS, LOV, LTA, LTF, LTJ, LTL, LTN, MAR, MAZ, MEI, MEL, MEP, MER, MFI, MFS, MON, MOR, MOZ, *MRE, MSE, MSO, MTF, MTN, MTT, MTW, MVY, MWF, MWW, NAB, NAT, NES, NON, NPO, NPT, NSI, OBW, OFF, OKO, OSI, OSO, OWE, -PAR, PAU, PCR, PHI, PON, POS, PSI, PUN, RHO, -RON, RRO, RSN, RTE, RTH, RUT, RWR, RWY, SAF, SAO, SAS, SAT, SAV, SBE, SBN, SBS, SBT, SEW, SFE, SFF, SFG, SFH, SFN, SFO, SFS, *SFV, SFW, SGT, SIV, SOD, SOF, SOS, SSF, *SSO, SSY, STF, STI, *STO, STT, STW, -SVR, SW, SZR, TER, THO, TOL, TON, TSC, TUN, UEI, UFI, UOS, UOV, UOZ, USI, UTL, UWY, VET, VFI, VNI, VSV, WEI, -WEN, YUG, ZON, and mixtures thereof.

8. The selective catalytic reduction catalyst of claim 7, wherein the zeolite material comprises copper in an amount, calculated as CuO, in the range of 0.1 to 10 weight-% based on the total weight of the zeolite material, wherein from 95 to 100 weight-% of the framework structure of the zeolite material consists of Si, Al, O, and optionally H, wherein the framework structure of the zeolite material comprises Si and Al, and wherein the framework structure of the zeolite material has a molar ratio of Si to Al, calculated as molar SiO.sub.2:Al.sub.2O.sub.3, in the range of from 2:1 to 50:1.

9. The selective catalytic reduction catalyst of claim 1, wherein the coating comprises the zeolite material at a loading in the range of from 60 to 300 g/l.

10. The selective catalytic reduction catalyst of claim 1, wherein the coating further comprises a metal oxide binder, wherein the metal oxide binder comprises one or more selected from the group consisting of zirconia, alumina, titania, silica, and mixtures thereof, wherein the coating comprises the metal oxide binder at a loading in the range of from 1 to 12 g/l.

11. The selective catalytic reduction catalyst of claim 1, wherein the coating comprises a vanadium oxide, wherein the vanadium oxide is one or more of a vanadium (V) oxide and a vanadium (IV) oxide, wherein the vanadium oxide optionally comprises one or more of tungsten, iron, and antimony, and wherein the vanadium oxide is supported on an oxide material comprising at least one selected from the group consisting of titanium, silicon, zirconium, titania, and tungsten.

12. An exhaust gas treatment system for treating an exhaust gas stream, comprising the selective catalytic reduction catalyst according to claim 1 and at least one selected from the group consisting of a diesel oxidation catalyst, a selective catalytic reduction catalyst, an ammonia oxidation catalyst, and a filter.

13. A process for preparing a selective catalytic reduction catalyst, comprising: (a) providing a flow-through substrate comprising an inlet end, an outlet end, a substrate axial length extending from the inlet end to the outlet end, and a plurality of passages defined by internal walls of the substrate extending therethrough; (b) preparing a slurry comprising a non-zeolite oxide material comprising manganese and one or more metals of the groups 4 to 11 and 13 of the periodic table, and further comprising one or more of a vanadium oxide and a zeolite material comprising one or more of copper and iron, and water; (c) disposing the slurry obtained in (b) on the surface of the internal walls of the flow-through substrate according to (a), obtaining a slurry-treated substrate; (d) optionally drying the slurry-treated substrate obtained in (c), obtaining the substrate having a coating disposed thereon; (e) calcining the slurry-treated substrate obtained in (c), or the substrate having a coating disposed thereon obtained in (d), obtaining the selective catalytic reduction catalyst.

14. A method for selectively catalytically reducing nitrogen oxides in an exhaust gas stream, said method comprising passing the exhaust gas stream through the selective catalytic reduction catalyst of claim 1.

15. A selective catalytic reduction catalyst for the treatment of an exhaust gas of a diesel engine, comprising: a flow-through substrate comprising an inlet end, an outlet end, a substrate axial length extending from the inlet end to the outlet end, and a plurality of passages defined by internal walls of the flow-through substrate extending therethrough; and a coating disposed on the surface of the internal walls of the substrate, wherein the coating comprises a non-zeolite oxide material comprising manganese and one or more metals of the groups 4 to 11 and 13 of the periodic table, and further comprises one or more of a vanadium oxide and a zeolite material comprising one or more of copper and iron, wherein the coating comprises the non-zeolite oxide material at a loading (l1), and the one or more of a vanadium oxide and a zeolite material comprising one or more of copper and iron at a loading (l2), and wherein the ratio of loading (l1) to loading (l2), (l1):(l2), is in the range of from 0.1:1 to 10:1, wherein from 90 to 100 weight-% of the non-zeolitic oxidic material consists of oxygen, manganese and aluminum.

16. A selective catalytic reduction catalyst for the treatment of an exhaust gas of a diesel engine, comprising: a flow-through substrate comprising an inlet end, an outlet end, a substrate axial length extending from the inlet end to the outlet end, and a plurality of passages defined by internal walls of the flow-through substrate extending therethrough; and a coating disposed on the surface of the internal walls of the substrate, wherein the coating comprises a non-zeolite oxide material comprising manganese and one or more metals of the groups 4 to 11 and 13 of the periodic table, and further comprises one or more of a vanadium oxide and a zeolite material comprising one or more of copper and iron, wherein the coating comprises the non-zeolite oxide material at a loading (l1), and the one or more of a vanadium oxide and a zeolite material comprising one or more of copper and iron at a loading (l2), and wherein the ratio of loading (l1) to loading (l2), (l1):(l2), is in the range of from 0.1:1 to 10:1, wherein from 70 to 90 weight of the non-zeolitic oxidic material consist of titania, from 2 to 8 weight of the non-zeolitic oxidic material consist of manganese, calculated as MnO, from 2 to 8 weight-% of the non-zeolitic oxidic material consist of silicon, calculated as SiO.sub.2, and from 0.5 to 4 weight-% of the non-zeolitic oxidic material consist of iron, calculated as FeO.

Description

EXAMPLES

Reference Example 1: Determination of the Dv90 Values

(1) The particle size distributions were determined by a static light scattering method using Sympatec HELOS equipment, wherein the optical concentration of the sample was in the range of from 5 to 10%.

Reference Example 2: Preparation of Cu-CHA

(2) The zeolitic material having the framework type CHA comprising Cu and used in the examples herein (Examples 1, 2 and 5, Comparative Examples 1-4) was prepared according to the teaching of U.S. Pat. No. 8,293,199 B2. Particular reference is made to Inventive Example 2 of U.S. Pat. No. 8,293,199 B2, column 15, lines 26 to 52.

Reference Example 3: Testing of Cu-CHA of Reference Example 2, of a Mixture of Oxides Comprising Titania and Manganese and a Mixture of Oxides Comprising Manganese Oxide—NOx Conversion and N.SUB.2.O Formation

(3) Powder tests have been carried for measuring the performance of pure Cu-CHA, mixture of oxides comprising titania and manganese and a mixture of oxides comprising manganese oxide, respectively, in NOx conversion and N.sub.2O make under standard SCR conditions (Gas Hourly Space Velocity (GHSV): 80000 h.sup.−1, 500 ppm NO, 500 ppm NH.sub.3, 5% H.sub.2O, 10% O.sub.2, balance N.sub.2) and under fast SCR conditions (GHSV: 80000 h.sup.−1, 125 ppm NO.sub.2, 375 ppm NO, 500 ppm NH.sub.3, 5% H.sub.2, 10% O.sub.2, balance N.sub.2). 88 mg of a powder of Cu-CHA of Reference Example 2 (catalyst a), 120 mg of a powder comprising Mn.sub.2O.sub.3 (70 weight-%) impregnated with 15 weight-% of La.sub.2O.sub.3 and 15 weight-% of ZrO.sub.2 (catalyst b) and 120 mg of a powder comprising TiO.sub.2 (87.1 weight-%) with 3.6 weight-% of Si calculated as SiO.sub.2, 1.9 weight-% of Fe, calculated as FeO and 4.1 weight-% of Mn, calculated as MnO (catalyst c), separately, were diluted to approximately 1 ml using corundum. Each sample corresponds to 1 ml of a coated catalyst with 2 g/in.sup.3 washcoat loading. Catalysts a, b and c were aged in air with 10% steam at 650° C. for 50 hours.

(4) The NOx conversions and the N.sub.2O formation during standard SCR reaction are shown in FIGS. 1 and 2. As may be taken from FIGS. 1 and 2, the pure Cu-CHA sample (catalyst a) has 30% NOx conversion at 175° C. and the NOx conversion increases rapidly to almost 100% at 250° C. This conversion rate stays almost constant up to temperatures of 575° C. Catalyst b exhibits 40% NOx conversion at 175° C., but said conversion increases less rapidly with increasing temperature compared to catalyst a. Moreover, the NOx conversion decreases from 70% at the maximum at 250° C. towards highly negative NOx conversion at high temperatures. It is assumed that negative NOx conversion means that NH.sub.3 is more rapidly oxidized to NOx rather than to N.sub.2. Furthermore, there is also a very high N.sub.2O formation with this material. To the contrary, for catalyst c, there is no NOx conversion at low temperatures and the maximum NOx conversion reaches 40% only at 450° C. Furthermore, there is also a higher NOx conversion, from 350 to 575° C., compared to catalyst b that indicates a lower NH.sub.3 oxidation rate at higher temperatures. Only at 550° C. and 575° C., there is significant N.sub.2O formation with catalyst c and there is high N.sub.2O formation with catalyst b at 250 to 550° C.

(5) The NOx conversions and the N.sub.2O formation during fast SCR reaction are shown in FIGS. 3 and 4. As may be taken from FIGS. 3 and 4, the NOx conversion is higher for all catalysts a, b and c. This is especially apparent for catalyst c that had no activity with NO only feed gas (standard SCR) at temperatures of 175 to 250° C. Here, the NOx conversion with catalyst c starts at 40% at 175° C. and increases to 50% at 300° C. There is only very little N.sub.2O formed. With respect to the NOx conversion with catalyst b, it can be recognized that it is more similar to the results with NO only (standard SCR), namely NOx conversion is highest at 175° C. compared to catalyst a and c and reaches 70% at its maximum at 250° C. but is reduced to 50% at 300° C. The N.sub.2O formation with catalyst b is still very high. For catalyst a, the N.sub.2O formation is relative low but higher compared to catalyst c. However, catalyst obtains the highest NOx conversions except for 175° C.

(6) This example illustrated the different issues when using catalyst comprising only Cu-CHA, catalyst comprising only doped manganese and catalyst comprising only titania doped with manganese for standard and fast SCR reactions.

Reference Example 4: General Coating Method

(7) In order to coat a flow-through substrate with a coating, the flow-through substrate was immersed vertically in a portion of a given slurry for a specific length of the substrate which was equal to the targeted length of the coating to be applied. In this manner, the washcoat contacted the walls of the substrate. The sample was left in the slurry for a specific period of time, usually for 1-10 seconds. The substrate was then removed from the slurry, and excess slurry was removed from the substrate by allowing it to drain from the substrate, then by blowing with compressed air (against the direction of slurry penetration).

Example 1: Preparation of a Catalyst According to the Present Invention

(8) a) Preparing a Fresh Catalyst

(9) Manganese oxide powder (Mn.sub.2O.sub.3 (70 weight-%) doped with 15 weight-% of La.sub.2O.sub.3 and 15 weight-% of ZrO.sub.2, having a BET specific surface area of 85 m.sup.2/g, a Dv90 of 10-25 micrometers, a solid content of 94 weight-%), corresponding to a final loading in the catalyst after calcination of 60 g/l, was mixed with deionized water. The resulting slurry having a solid content of 40 weight-% was milled with a ball mill to reach a Dv90 of 6 micrometers.

(10) A zirconyl acetate mixture having a solid content of 15% by weight, such that the final zirconia loading (calculated as ZrO.sub.2) in the catalyst was 8 g/l, was mixed with a Cu-zeolite (Chabazite with a SiO.sub.2 to Al.sub.2O.sub.3 molar ratio (SAR) of 25 comprising 3.3 weight-% of Cu, calculated as CuO), corresponding to a final Cu-CHA loading in the catalyst after calcination of 170 g/l, deionized water. The resulting slurry was milled with a ball mill to reach until the resulting Dv90 determined as described in Reference Example 1 herewith was 5 micrometers.

(11) The metal oxide slurry was added to the zeolite slurry and stirred for 30 min at room temperature, creating the final slurry having a solid content of 40 weight-%. The final slurry was then disposed over the full length of an uncoated honeycomb cordierite monolith substrate using the coating method described in Reference Example 4 (diameter: 10.16 cm (4 inches)×length: 2.54 cm (1 inch) cylindrically shaped with 400/(2.54).sup.2 cells per square centimeter and 0.135 millimeter thickness wall). Afterwards, the coated substrate was dried at a temperature of 120° C. for 2 hours and calcined at 600° C. for 2 hours. The washcoat loading of the coating after calcination was 238 g/l, including 170 g/l of Cu-CHA, 60 g/l of manganese (Ill) oxide with 15 weight % of La, calculated as La.sub.2O.sub.3, and 15 weight-% of Zr, calculated as ZrO.sub.2, and 8 g/l of zirconia.

(12) b) Ageing the Catalyst Obtained in a)

(13) The catalyst obtained in a) was aged in air with 10% steam at 650° C. for 50 hours.

Example 2: Preparation of a Catalyst According to the Present Invention

(14) a) Preparing a Fresh Catalyst

(15) A titania slurry was prepared by mixing a titania powder (TiO.sub.2 (87.1 weight-%) with 3.6 weight-% of Si calculated as SiO.sub.2, 1.9 weight-% of Fe, calculated as FeO and 4.1 weight-% of Mn, calculated as MnO, having a BET specific surface area of 96 m.sup.2/g) with deionized water. The resulting slurry having a solid content of 40 weight-% was milled with a ball mill until the resulting Dv90 determined as described in Reference Example 1 herewith was 5-10 micrometers.

(16) A zirconyl acetate mixture having a solid content of 15% by weight, such that the final zirconia loading (calculated as ZrO.sub.2) in the catalyst after calcination was 8 g/l, was mixed with a Cu-zeolite (Chabazite with a SiO.sub.2 to Al.sub.2O.sub.3 molar ratio (SAR) of 25 comprising 3.3 weight-% of Cu calculated as CuO), corresponding to a final Cu-CHA loading in the catalyst after calcination of 170 g/l, and deionized water. The resulting slurry having a solid content of 40 weight-% was milled with a ball mill until the resulting Dv90 determined as described in Reference Example 1 herewith was 5 micrometers.

(17) The titania slurry was added to the zeolite slurry and stirred for 30 min at room temperature, obtaining a final slurry having a solid content of 40 weight-%. The final slurry was then disposed over the full length of an uncoated honeycomb cordierite monolith substrate using the coating method described in Reference Example 4 (diameter: 10.16 cm (4 inches)×length: 2.54 cm (1 inch) cylindrically shaped with 400/(2.54).sup.2 cells per square centimeter an 0.13 millimeter thickness wall). Afterwards, the coated substrate was dried at a temperature of 120° C. for 2 hours and calcined at 600° C. for 2 hours. The washcoat loading after calcination was 238 g/l, including 170 g/l of Cu-CHA, 60 g/l of titania with 3.6 weight-% of Si calculated as SiO.sub.2, 1.9 weight-% of Fe, calculated as FeO and 4.1 weight-% of Mn, calculated as MnO, and 8 g/l of zirconia.

(18) b) Ageing the Catalyst Obtained in a)

(19) The catalyst obtained in a) was aged in air with 10% steam at 650° C. for 50 hours.

Comparative Example 1: Preparation of a Catalyst not According to the Present Invention without Manganese and One or More Transition Metals

(20) a) Preparing a Fresh Catalyst

(21) A zirconyl acetate mixture having a solid content of 15% by weight, such that the final zirconia loading (calculated as ZrO.sub.2) in the catalyst after calcination was 9 g/l, was mixed with a Cu-zeolite (Chabazite with a SiO.sub.2 to Al.sub.2O.sub.3 molar ratio (SAR) of 25 comprising 3.3 weight-% of Cu calculated as CuO), corresponding to a final Cu-CHA loading in the catalyst after calcination of 174 g/l, and deionized water. The resulting slurry having a solid content of 40 weight-% was milled with a ball mill until the resulting Dv90 determined as described in Reference Example 1 herewith was 5 micrometers. The slurry was then disposed over the full length of an uncoated honeycomb cordierite monolith substrate using the coating method described in Reference Example 4 (diameter: 10.16 cm (4 inches)×length: 2.54 cm (1 inch) cylindrically shaped with 400/(2.56).sup.2 cells per square centimeter and 0.1 millimeter thickness wall). Afterwards, the coated substrate was dried at a temperature of 120° C. for 2 hours and calcined at 600° C. for 2 hours. The washcoat loading after calcination was 183 g/l, including 174 g/l of Cu-CHA and 9 g/l of zirconia.

(22) b) Ageing the Catalyst Obtained in a)

(23) The catalyst obtained in a) was aged in air with 10% steam at 650° C. for 50 hours.

Example 3: Use of the Catalyst of Examples 1 and 2 and Comparative Example 1—NOx Conversion and N.SUB.2.O Formation

(24) The aged catalysts of Examples 1 (b) and 2 (b) and Comparative Example 1 (b) were subjected to a selective catalytic reduction test under standard SCR conditions (GHSV: 80000 h.sup.−1, 500 ppm NO, 500 ppm NH.sub.3, 5% H.sub.2O, 10% O.sub.2, balance N.sub.2) and under fast SCR conditions (GHSV: 80000 h.sup.−1, 125 ppm NO.sub.2, 375 ppm NO, 500 ppm NH.sub.3, 5% H.sub.2O, 10% O.sub.2, balance N.sub.2). The NOx conversion and the N.sub.2O formation were measured at temperatures ranging from 175 to 575° C. for standard SCR and from 175 to 300° C. for fast SCR.

(25) The NOx conversions and the N.sub.2O formation during standard SCR reaction are shown in FIGS. 5 and 6. As may be taken from FIG. 5, from 175 to 200° C. and 300 to 450° C., the NOx conversions of the catalysts of Examples 1 and 2 and of Comparative Example 1 are similar. All samples almost reach 100% NOx conversion at 300° C. From 200 to 300° C., the NOx conversions obtained with the catalysts according to the present invention are slightly higher than with the comparative catalyst (2 to 3%). At higher temperatures, namely 550° C. and 575° C., the catalyst of Example 1 exhibits a lower NOx conversion (5 to 10%) compared the other two samples.

(26) As may be taken from FIG. 6, the N.sub.2O formation obtained with the catalyst of Example 1 is of approximately 3 to 4 ppm at 175 to 300° C., whereas the N.sub.2O formation obtained with the catalyst of Comparative Example 1 is between 4.4 to 10.4 ppm with a peak at 250° C. At said peak, the N.sub.2O formation obtained with the catalysts according to the present invention is more than 50% lower than the N.sub.2O formation obtained with the catalyst of Comparative Example 1. Further the catalyst of Example 2 exhibits lower N.sub.2O formation compared to the catalyst of Comparative Example 1 over the whole temperature range, namely at temperatures from 175 to 575° C. This example demonstrates that, under standard SCR conditions, the catalyst according to the present invention with a non-zeolitic oxidic material comprising mainly manganese permits to reduce the N.sub.2O formation while maintaining or improving NOx conversion at low-medium temperatures, namely at 175 to 350° C., and that the catalyst according to the present invention with a non-zeolitic oxidic material comprising titania and manganese permits to improve the NOx conversion while reducing the N.sub.2O formation in a wide temperature range, namely at from 175 to 575° C.

(27) The NOx conversions and the N.sub.2O formation during fast SCR reaction are shown in FIGS. 7 and 8. As may be taken from FIG. 7, from 175 to 250° C., the catalysts of Examples 1 and 2 exhibit improved NOx conversions compared to the catalyst of Comparative Example 1. At 300° C., the NOx conversions obtained from the three samples are of 100%. As may be taken from FIG. 8, the catalyst of Example 1 exhibits a N.sub.2O formation of from 3.8 to 6.0 ppm, the catalyst of Example 2 exhibits a N.sub.2O formation of from 4.3 to 7.7 ppm, whereas the catalyst of Comparative Example 1 exhibits a higher N.sub.2O formation of from 5.6 to 14.1 ppm. Thus, this example also demonstrates that under fast SCR conditions, the catalysts according to the present invention permit to obtain improved NOx conversion while decreasing the N.sub.2O formation at temperatures between 175° C. to 300° C.

Comparative Example 2: Preparation of a Catalyst not According to the Present Invention, with a Non-Zeolitic Oxidic Material Free of Manganese

(28) A titania slurry was prepared by mixing a titania powder (TiO.sub.2 88 weight-% and 6.5 weight-% of Si calculated as SiO.sub.2, having a BET specific surface area of 200 m.sup.2/g) were mixed with deionized water, corresponding to a final titania material loading in the catalyst after calcination of 60 g/l. The resulting slurry having a solid content of 40 weight-% was milled with a ball mill until the resulting Dv90 determined as described in Reference Example 1 herewith was 6 micrometers.

(29) A zirconyl acetate mixture having a solid content of 15% by weight, such that the final zirconia loading (calculated as ZrO.sub.2) in the catalyst after calcination was 8 g/l, was mixed with a Cu-zeolite (Chabazite with a SiO.sub.2 to Al.sub.2O.sub.3 molar ratio (SAR) of 25 comprising 3.3 weight-% of Cu calculated as CuO), corresponding to a final Cu-CHA loading in the catalyst after calcination of 170 g/l, and deionized water. The resulting slurry having a solid content of 40 weight-% was milled with a ball mill until the resulting Dv90 determined as described in Reference Example 1 herewith was 5 micrometers.

(30) The titania slurry was added to the zeolite slurry and stirred for 30 min at room temperature, forming the final slurry having a solid content of 40 weight-%. The final slurry was then disposed over the full length of an uncoated honeycomb cordierite monolith substrate using the coating method described in Reference Example 4 (diameter: 10.16 cm (4 inches)×length: 2.54 cm (1 inch) cylindrically shaped with 400/(2.56).sup.2 cells per square centimeter and 0.1 millimeter thickness wall). Afterwards, the coated substrate was dried at a temperature of 120° C. for 2 hours and calcined at 600° C. for 2 hours. The washcoat loading of the coating in the catalyst after calcination was 238 g/l, including 170 g/l of Cu-CHA, 60 g/l of Si-containing titania and 8 g/l of zirconia.

Comparative Example 3: Preparation of a Catalyst Comprising Mn—Cu-CHA not According to the Present Invention, without a Non-Zeoltic Oxidic Material Comprising Manganese

(31) A zirconyl acetate mixture having a solid content of 15% by weight, such that the final zirconia loading (calculated as ZrO.sub.2) in the catalyst after calcination was 8 g/l, was mixed with a Cu-zeolite (Chabazite with a SiO.sub.2 to Al.sub.2O.sub.3 molar ratio (SAR) of 25 comprising 3.3 weight-% of Cu calculated as CuO), corresponding to a final Cu-CHA loading in the catalyst after calcination of 170 g/l, and deionized water. The resulting slurry having a solid content of 40 weight-% was milled with a ball mill until the resulting Dv90 determined as described in Reference Example 1 herewith was 5 micrometers. Further, 27 g of a manganese nitrate (Mn(NO.sub.3).sub.3) solution (49 weight-% of Mn calculated as MnO) was added to the resulting slurry and mixed. The obtained slurry was then disposed over the full length of an uncoated honeycomb cordierite monolith substrate using the coating method described in Reference Example 4 (diameter: 10.16 cm (4 inches)×length: 2.54 cm (1 inch) cylindrically shaped with 400/(2.54).sup.2 cells per square centimeter and 0.1 millimeter (4 mil) thickness wall). Afterwards, the coated substrate was dried at a temperature of 120° C. for 2 hours and calcined at 600° C. for 2 hours. The washcoat loading of the coating after calcination was 187 g/l, including 170 g/l of Cu-CHA, 9 g/l of manganese, calculated as MnO, and 8 g/l of zirconia.

Comparative Example 4: Preparation of a Catalyst not According to the Present Invention

(32) A titania slurry was prepared by mixing a titania powder (TiO.sub.2 with 2 weight-% of Fe calculated as FeO and 4 weight-% Si calculated as SiO.sub.2) were mixed with deionized water, corresponding to a final titania material loading in the catalyst after calcination of 60 g/l. The resulting slurry having a solid content of 40 weight-% was milled with a ball mill until the resulting Dv90 determined as described in Reference Example 1 herewith was 5 micrometers.

(33) A zirconyl acetate mixture having a solid content of 15% by weight, such that the final zirconia loading (calculated as ZrO.sub.2) in the catalyst after calcination was 8 g/l, was mixed with a Cu-zeolite (Chabazite with a SiO.sub.2 to Al.sub.2O.sub.3 molar ratio (SAR) of 25 comprising 3.3 weight-% of Cu calculated as CuO), corresponding to a final Cu-CHA loading in the catalyst after calcination of 170 g/l, and deionized water. The resulting slurry having a solid content of 40 weight-% was milled with a ball mill until the resulting Dv90 determined as described in Reference Example 1 herewith was 5 micrometers. The titania slurry was added to the zeolite slurry and stirred for 30 min at room temperature, forming the final slurry having a solid content of 40 weight-%. The final slurry was then disposed over the full length of an uncoated honeycomb cordierite monolith substrate using the coating method described in Reference Example 4 (diameter: 10.16 cm (4 inches)×length: 2.54 cm (1 inch) cylindrically shaped with 400/(2.56).sup.2 cells per square centimeter and 0.1 millimeter thickness wall). Afterwards, the coated substrate was dried at a temperature of 120° C. for 2 hours and calcined at 600° C. for 2 hours. The washcoat loading of the coating in the catalyst after calcination was 238 g/l, including 170 g/l of Cu-CHA, 60 g/l of Si/Fe-containing titania and 8 g/l of zirconia.

Example 4: Use of the Catalysts of Examples 1, 2, Comparative Examples 2, 3 and 4—NOx Conversion and N.SUB.2.O Formation

(34) The catalysts of Examples 1 (a), 2 (a) and Comparative Examples 2, 3 and 4 were aged in air with 10% steam at 800° C. for 16 hours and subjected to a selective catalytic reduction test (GHSV: 80000 h, 250 ppm NO.sub.2, 250 ppm NO, 750 ppm NH.sub.3, 5% H.sub.2O, 10% O.sub.2, balance N.sub.2). The NOx conversion and the N.sub.2O formation were measured at temperatures ranging from 140 to 350° C., the results are depicted in FIGS. 9 and 10.

(35) As may be taken from FIG. 9, the NOx conversions obtained with the catalysts of Example 1 and of Comparative Example 3 are approximately similar. However, the catalyst of Comparative Example 3, which has been prepared by using manganese nitrate solution, exhibits higher N.sub.2O formation. For example, at approximately 240° C., there is more than 16 ppm of N.sub.2O formed with the catalyst of Comparative Example 3 while there is approximately 11 ppm of N.sub.2O formed with the catalyst of Example 1. Furthermore, the NOx conversions obtained with the catalyst of Example 2 are slightly greater than the NOx conversions obtained with the catalyst of Comparative Examples 2 and 4 and greater (from approximately 10-20%) than the NOx conversions obtained with the catalyst of Comparative Example 3. Further, the catalyst of Example 2 also exhibits lower N.sub.2O formation compared to the catalyst of Comparative Examples 2-4. For example, at 350° C., there is approximately 11 ppm of N.sub.2O formed with the catalyst of Example 2 while there is more than 15 ppm of N.sub.2O formed with the catalyst of Comparative Example 2, approximately 17 ppm of N.sub.2O formed with the catalyst of Comparative Example 3 and 15 ppm of N.sub.2O formed with the catalyst of Comparative Example 4. This example demonstrates that the catalyst according to the present invention with a non-zeolitic oxidic material comprising mainly manganese permits to reduce the N.sub.2O formation while maintaining good NOx conversion after a severe ageing and that the catalyst according to the present invention with a non-zeolitic oxidic material comprising titania and manganese permits to improve the NOx conversion while reducing the N.sub.2O formation after a severe ageing. Further, this example shows that using manganese as ions with a Cu-CHA does not permit to obtain a great NOx conversion while reducing the N.sub.2O formation after a severe ageing and that accordingly the presence of a non-zeolitic oxidic material comprising manganese is mandatory.

Example 5: Preparation of a Catalyst According to the Present Invention

(36) a) Preparing a Fresh Catalyst

(37) An oxidic slurry was prepared by mixing an oxidic powder (95.4 weight-% of Al.sub.2O.sub.3 (mixed oxide) and 4.6 weight-% of MnO.sub.2 (mixed oxide), having a BET specific surface area of 140 m.sup.2/g, a total pore volume of 0.82 ml/g and a Dv50 of 54 micrometers) with deionized water.

(38) A zirconyl acetate mixture having a solid content of 15% by weight, such that the final zirconia loading (calculated as ZrO.sub.2) in the catalyst after calcination was 8 g/l, was mixed with a Cu-zeolite (Chabazite with a SiO.sub.2 to Al.sub.2O.sub.3 molar ratio (SAR) of 25 comprising 3.3 weight-% of Cu calculated as CuO), corresponding to a final Cu-CHA loading in the catalyst after calcination of 170 g/l, and deionized water. The resulting slurry having a solid content of 40 weight-% was milled with a ball mill until the resulting Dv90 determined as described in Reference Example 1 herewith was 5 micrometers. The oxidic slurry was added to the zeolite slurry and stirred for 30 min at room temperature. The final slurry was then disposed over the full length of an uncoated honeycomb cordierite monolith substrate using the coating method described in Reference Example 4 (diameter: 10.16 cm (4 inches)×length: 2.54 cm (1 inch) cylindrically shaped with 400/(2.54).sup.2 cells per square centimeter an 0.13 millimeter thickness wall). Afterwards, the coated substrate was dried at a temperature of 120° C. for 2 hours and calcined at 600° C. for 2 hours. The washcoat loading after calcination was 238 g/l, including 170 g/l of Cu-CHA, 60 g/l of aluminum-manganese oxide and 8 g/l of zirconia.

(39) b) Ageing the Catalyst Obtained in a)

(40) The catalyst obtained in a) was aged in air with 10% steam at 650° C. for 50 hours.

Example 6: Use of the Catalyst of Example 5 and Comparative Example 1—NOx Conversion and N.SUB.2.O Formation

(41) The aged catalysts of Example 5 (b) and Comparative Example 1 (b) were subjected to a selective catalytic reduction test under standard SCR conditions (GHSV: 80000 h.sup.−1, 500 ppm NO, 500 ppm NH.sub.3, 5% H.sub.2O, 10% O.sub.2, balance N.sub.2) and under fast SCR conditions (GHSV: 80000 h.sup.−1, 125 ppm NO.sub.2, 375 ppm NO, 500 ppm NH.sub.3, 5% H.sub.2O, 10% O.sub.2, balance N.sub.2). The NOx conversion and the N.sub.2O formation were measured at temperatures ranging from 175 to 575° C. for standard SCR and from 175 to 250° C. for fast SCR. The results are displayed in Tables 1 and 2 below.

(42) TABLE-US-00001 TABLE 1 Results under standard SCR conditions Example 5 Comparative Example 1 NOx N.sub.2O NOx N.sub.2O Temperature conversion formation conversion formation (° C.) (%) (ppm) (%) (ppm) 175 27.4 3.3 27.5 4.4 200 59.5 3.4 59.0 6.7 225 90.2 3.7 87.4 9.6 250 97.9 3.8 96.4 10.4 300 98.9 3.5 98.9 8.9 450 97.9 2.3 98.1 4.0 550 96.6 4.6 95.7 8.1 575 95.4 6.1 94.7 9.4

(43) TABLE-US-00002 TABLE 2 Results under fast SCR conditions Example 5 Comparative Example 1 NOx N.sub.2O NOx N.sub.2O Temperature conversion formation conversion formation (° C.) (%) (ppm) (%) (ppm) 175 52.3 3.7 48.1 5.6 200 79.3 5.5 75.3 9.9 225 96.3 6.7 93.0 13.2 250 99.9 7.2 98.9 14.1

(44) As may be taken from Tables 1 and 2, the NOx conversions obtained with the catalyst of Example 5 are approximately similar or higher than those obtained with the catalyst of Comparative Example 1. However, the catalyst of Comparative Example 1 exhibits higher N.sub.2O formation. For example, under standard conditions, at 250° C., there is 10.4 ppm of N.sub.2O formed with the catalyst of Comparative Example 1 while there is approximately 3.8 ppm of N.sub.2O formed with the catalyst of Example 5 (a N.sub.2O formation more than 2.5 times lower than with the comparative example) and said inventive catalyst exhibits a better NOx conversion. Under fast SCR conditions, the NOx conversions obtained with the catalyst of Example 5 are higher than those obtained with the catalyst of Comparative Example 1 and the catalyst of Comparative Example 1 exhibits higher N.sub.2O formation. In particular, at 225° C., there is 13.2 ppm of N.sub.2O formed with the catalyst of Comparative Example 1, which exhibits a NOx conversion of 93%, while there is approximately 6.7 ppm of N.sub.2O formed with the catalyst of Example 5 which exhibits a higher NOx conversion of 96.3%. Thus, this example demonstrates that under fast and standard SCR conditions, the catalysts according to the present invention permit to obtain improved NOx conversion while decreasing the N.sub.2O formation.

Example 7: Use of the Catalysts of Example 5 and Comparative Example 1—NOx Conversion and N.SUB.2.O Formation

(45) The catalysts of Example 5 (a) and Comparative Example 1 (a) were aged in air with 10% steam at 800° C. for 16 hours and were subjected to a selective catalytic reduction test under standard SCR conditions (GHSV: 80000 h.sup.−1, 500 ppm NO, 500 ppm NH.sub.3, 5% H.sub.2O, 10% O.sub.2, balance N.sub.2). The NOx conversion and the N.sub.2O formation were measured at temperatures ranging from 175 to 575° C. for standard SCR. The results are depicted in Table 3 below.

(46) TABLE-US-00003 TABLE 3 Results under standard SCR conditions Example 5 Comparative Example 1 NOx N.sub.2O NOx N.sub.2O Temperature conversion formation conversion formation (° C.) (%) (ppm) (%) (ppm) 175 25.8 0.5 27.8 1.6 200 55.1 1.1 56.4 4.0 250 96.3 2.1 95.1 7.2 300 98.7 2.6 98.6 7.3 550 91.4 5.0 88.4 12.7 575 89.9 6.2 85.3 13.9

(47) As may be taken from Table 3, the NOx conversions obtained with the catalyst of Example 5 are approximately similar or higher than those obtained with the catalyst of Comparative Example 1. However, the catalyst of Comparative Example 1 exhibits higher N.sub.2O formation. In particular, at 250° C., there is 7.2 ppm of N.sub.2O formed with the catalyst of Comparative Example 1 while there is approximately 2.1 ppm of N.sub.2O formed with the catalyst of Example 5 (a N.sub.2O formation approximately 3.5 times lower than with the comparative example). Thus, this example demonstrates that the catalysts according to the present invention permit to obtain improved NOx conversion while decreasing the N.sub.2O formation even after a severe ageing.

BRIEF DESCRIPTION OF THE FIGURES

(48) FIG. 1 shows the NOx conversions obtained with catalysts a, b and c not according to the present invention after ageing at 650° C. for 50 hours under standard SCR conditions.

(49) FIG. 2 shows the N.sub.2O formation obtained with catalysts a, b and c not according to the present invention after ageing at 650° C. for 50 hours under standard SCR conditions.

(50) FIG. 3 shows the NOx conversions obtained with catalysts a, b and c not according to the present invention after ageing at 650° C. for 50 hours under fast SCR conditions.

(51) FIG. 4 shows the N.sub.2O formation obtained with catalysts a, b and c not according to the present invention after ageing at 650° C. for 50 hours under fast SCR conditions.

(52) FIG. 5 shows the NOx conversions obtained with the catalysts of Examples 1 and 2 and of Comparative Example 1 after ageing at 650° C. for 50 hours under standard SCR conditions.

(53) FIG. 6 shows the N.sub.2O formation obtained with the catalysts of Examples 1 and 2 and of Comparative Example 1 after ageing at 650° C. for 50 hours under standard SCR conditions.

(54) FIG. 7 shows the NOx conversions obtained with the catalysts of Examples 1 and 2 and of Comparative Example 1 after ageing at 650° C. for 50 hours under fast SCR conditions.

(55) FIG. 8 shows the N.sub.2O formation obtained with the catalysts of Examples 1 and 2 and of Comparative Example 1 after ageing at 650° C. for 50 hours under fast SCR conditions.

(56) FIG. 9 shows the NOx conversions obtained with the catalysts of Examples 1, 2 and and of Comparative Examples 2, 3 and 4 after ageing at 800° C. for 16 hours with a gas feed comprising 250 ppm NO.sub.2, 250 ppm NO, 750 ppm NH.sub.3, 5% H.sub.2, 10% O.sub.2, balance N.sub.2).

(57) FIG. 10 shows the N.sub.2O formation obtained with the catalysts of Examples 1, 2 and of Comparative Examples 2, 3 and 4 after ageing at 800° C. for 16 hours with a gas feed comprising 250 ppm NO.sub.2, 250 ppm NO, 750 ppm NH.sub.3, 5% H.sub.2O, 10% O.sub.2, balance N.sub.2).

CITED LITERATURE

(58) Fudong Liua, et al., Selective catalytic reduction of NO with NH.sub.3 over iron titanate catalyst: Catalytic performance and characterization, Applied Catalysis B: Environmental 96 (2010), pages 408-420 Siva Sankar Reddy Putlurua, et al., Mn/TiO.sub.2 and Mn—Fe/TiO.sub.2 catalysts synthesized by depositionprecipitation—promising for selective catalytic reduction of NO with NH.sub.3 at low temperatures, Applied Catalysis B: Environmental 165 (2015), pages 628-635 Douglas W. Crandell, et al., Computational and spectroscopic characterization of key intermediates of the Selective Catalytic Reduction cycle of NO on zeolite-supported Cu catalyst, Inorganica Chimica Acta 430 (2015), pages 132-143 Wei Li, et al., The enhanced Zn resistance of Mn/TiO.sub.2 catalyst for NH.sub.3—SCR reaction by the modification with Nb, Fuel Processing Technology 154 (2016), pages 235-242 U.S. Pat. No. 7,691,769 B2 U.S. Pat. No. 7,601,662 B2 U.S. Pat. No. 8,293,199 B2