Sulfur tolerant metal promoted small pore zeolite catalyst

Abstract

The present invention relates to an SCR catalytic article comprising a substrate and a copper-containing small-pore zeolite, the crystal structure of which is characterized by a reduction of the unit cell volume after sulfation and desulfation of less than 0.0005 A3, as determined by X-ray powder diffraction, wherein the sulfation and desulfation are carried out according to the methods described in the specification, to an exhaust gas treatment system comprising the catalytic article. The present invention further relates to a method of determining whether a metal-promoted small-pore zeolite is resistant to irreversible sulfur poisoning and a method of assessing whether a metal-promoted small-pore zeolite is adequately resistant to irreversible sulfur poisoning.

Description

TECHNICAL FIELD

[0001] The present invention relates to sulfur tolerant, metal-promoted small-pore zeolites, catalytic articles containing the same, and systems and methods for treating exhaust gas from internal combustion engines. BACKGROUND

[0003] Catalytic articles are essential for the treatment of exhaust gas from internal combustion engines in modern times. Exhaust gas from internal combustion engines typically contains particulate matter (PM), nitrogen oxides (NOx) such as NO and / or NO2, unburned hydrocarbons (HC), and carbon monoxide (CO). Due to the environmental negative impact on ecosystems, animal and plant life, the emission control of nitrogen oxides (NOx) has always been one of the most important topics in the automotive field.

[0004] One of the effective techniques for removing NOx from exhaust gas of internal combustion engines, particularly diesel engine exhaust gas, is selective catalytic reduction (SCR) of NOx with NH3. Catalysts useful for the SCR process should be stable under hydrothermal conditions at high temperatures encountered during the regeneration of a diesel particulate filter (a component of an exhaust gas treatment system for removing particulate matter). Small-pore zeolites, particularly metal-promoted small-pore zeolites, have been found promising as SCR catalysts with high NOx reduction activity over a wide temperature range and with the required hydrothermal stability.

[0005] In addition to hydrothermal aging deactivation, another important factor affecting the performance of SCR catalytic articles is chemical poisoning, such as sulfur poisoning. Sulfur poisoning results from the catalyst's cumulative exposure to sulfur species in the fuel and fuel-derived sulfur-containing contaminants. In recent years, the sulfur content in diesel fuel has been significantly reduced, for example, in North America with the introduction of ultra-low sulfur diesel (ULSD), which can be even less than 15 ppm sulfur. However, the cumulative exposure of the catalyst in a heavy-duty diesel engine exhaust treatment system during its lifetime can reach several kilograms of sulfur. The situation can be even worse for some off-road applications or in certain regions where high sulfur diesel (> 350 ppm sulfur) is more prevalent.

[0006] SCR catalytic articles can be regenerated at high temperatures, which is typically achieved during the regeneration of a diesel particulate filter. The NOx reduction activity of an SCR catalytic article degraded by sulfur poisoning is significantly recovered by regeneration. However, a portion of the NOx reduction activity loss cannot be remedied by regeneration, resulting in permanent sulfur poisoning damage to the SCR catalyst activity, which is also referred to as irreversible sulfur poisoning.

[0007] There is a need to provide metal-promoted small-pore zeolites with excellent SCR performance and tolerance to irreversible sulfur poisoning. In addition, there is a need for a method that can be used to simply determine whether a metal-promoted small-pore zeolite is tolerant to irreversible sulfur poisoning. SUMMARY

[0008] In one aspect, the present application provides an SCR catalytic article comprising

[0009] - a substrate, and on it

[0010] - a copper-containing small-pore zeolite, the crystal structure of which is characterized by a reduction of the unit cell volume after sulfation and desulfation of less than 0.0005 A3

[0011] wherein

[0012] sulfation is carried out by passing a gas stream containing 35 ppmv SO2, 350 ppmv NO, 10 vol% O2, 10 vol% H2O, and balance N2 at an inlet temperature of 650°C over a diesel oxidation catalyst (DOC) containing Pt to partially oxidize SO2 to provide a 30:70 SO2 / SO3 ratio, then over the SCR catalytic article at an outlet temperature of 400°C at a space velocity of 10,000 hr -1 of S exposure per liter of the SCR catalytic article, wherein the SCR catalytic article has been hydrothermally aged prior to sulfation; and

[0013] desulfation is carried out by passing a gas stream containing 10 vol% O2, 8 vol% H2O, 7 vol% CO2, and balance N2 at a space velocity of 60,000 hr -1 over the SCR catalytic article that has been subjected to sulfation at 550°C for 30 minutes.

[0014] In another aspect, the present application provides an exhaust gas treatment system comprising

[0015] - an internal combustion engine, such as a gasoline engine or a diesel engine; and

[0016] - an SCR catalytic article as described herein positioned downstream of and in fluid communication with the engine.

[0017] In yet another aspect, the present application provides a method of treating an exhaust gas stream comprising NOx, comprising contacting the exhaust gas stream with an SCR catalytic article or exhaust gas treatment system as described herein.

[0018] In still another aspect, the present application provides the use of a copper-containing small-pore zeolite as described herein as an SCR catalyst.

[0019] In a further aspect, the present application provides a method of determining whether a metal-promoted small-pore zeolite is resistant to irreversible sulfur poisoning, comprising

[0020] - preparing, by applying the metal-promoted small-pore zeolite to a substrate, an SCR catalytic article;

[0021] sulfation, by passing a gas stream containing 35 ppmv S02, 350 ppmv NO, 10 vol% 02, 10 vol% H20, and balance N2at an inlet temperature of 650°C over a Pt-containing diesel oxidation catalyst (DOC) to partially oxidize S02to provide a 30:70 S02 / S03ratio, then over the SCR catalytic article at an outlet temperature of 400°C for a period of time at a space velocity of 10,000 hr -1 based on the volume of the SCR catalytic article, wherein the SCR catalytic article has been hydrothermally aged prior to sulfation;

[0022] desulfation, by passing a gas stream containing 10 vol% 02, 8 vol% H20, 7 vol% C02, and balance N2at a space velocity of 60,000 hr -1 over the sulfated SCR catalytic article for 30 minutes at 550°C; and

[0023] determining the unit cell volume of the metal-promoted small-pore zeolite before sulfation and after desulfation by X-ray powder diffraction,

[0024] wherein the metal-promoted small-pore zeolite is resistant to irreversible sulfur poisoning if the unit cell volume of the metal-promoted small-pore zeolite after desulfation is not less than

[0025] In a further aspect, the present application provides a method of evaluating whether a metal-promoted small-pore zeolite is capable of being resistant to irreversible sulfur poisoning, comprising

[0026] providing a catalytic article comprising a substrate and thereon a reference metal-promoted small-pore zeolite having a minimum qualified NOxconversion recovery ratio after sulfation and desulfation, for example 70% or more:

[0027]

[0028] determining the unit cell volume change of the reference metal-promoted small-pore zeolite before sulfation and after desulfation by X-ray powder diffraction, which is referred to as a predetermined value of unit cell volume change;

[0029] preparing a catalytic article comprising a substrate and thereon a metal-promoted small-pore zeolite to be evaluated;

[0030] ​- determining the change in unit cell volume of the metal-promoted small-pore zeolite before sulfidation and after desulfurization by X-ray powder diffraction under the same conditions as for a catalytic article comprising a reference metal-promoted small-pore zeolite;

[0031] - comparing the change in unit cell volume of the metal-promoted small-pore zeolite to the predetermined value,

[0032] wherein the metal-promoted small-pore zeolite is evaluated as being resistant to irreversible sulfur poisoning if its change in unit cell volume is not greater than the predetermined value. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is a graph showing the S residual content and the respective S / Cu atomic ratio after sulfidation and desulfurization of the copper-containing small-pore zeolites according to Examples 2 and 4.

[0034] Figure 2 is a graph showing the NOx conversion and the NOx conversion recovery ratio before sulfidation and after desulfurization tested for the Cu / SSZ13 containing catalytic articles according to Examples 1 to 4. DETAILED DESCRIPTION

[0036] The present application is described in detail below. It is to be understood that the application can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

[0037] The singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. The terms "comprises," "comprising," and similar terms are used in the open-ended sense and should be interpreted to mean that items include but are not limited to the recited items. That is, the term "comprises" or "comprising" should not be interpreted as being equivalent to the term "consisting" or "consisting of." The term "consisting essentially of" or "consisting essentially of" means including an ingredient plus pro- rata amounts of other ingredients; that is, the amount of the other ingredients present do not affect the essential nature of the composition or method as a whole.

[0038] The term "selective catalytic reduction" (SCR) refers to a catalytic process for the reduction of NOx to N2 using a nitrogen-containing reductant, such as ammonia, urea, and the like.

[0039] According to one aspect of the present application, there is provided an SCR catalytic article comprising:

[0040] - a substrate, and on it

[0041] - a copper-containing small-pore zeolite, the crystal structure of which is characterized by a reduction of the unit cell volume after sulfidation and desulfurization determined by X-ray powder diffraction of less than 0.0005 A3

[0042] wherein

[0043] Sulfurization is performed by passing a gas stream containing 35 ppmv S02, 350 ppmv NO, 10 vol% 02, 10 vol% H20, and balance N2through a Pt-containing diesel oxidation catalyst (DOC) at an inlet temperature of 650 °C to partially oxidize S02to provide a 30:70 S02 / S03ratio, then through the SCR catalytic article at an outlet temperature of 400 °C at a space velocity of 10,000 hr -1 based on the volume of the SCR catalytic article for a time to provide 40 g / L of S exposure based on the volume of the SCR catalytic article, wherein the SCR catalytic article has been hydrothermally aged prior to sulfurization; and

[0044] Desulfurization is performed by passing a gas stream containing 10 vol% 02, 8 vol% H20, 7 vol% C02, and balance N2through the SCR catalytic article that has been subjected to sulfurization at a space velocity of 60,000 hr -1 at 550 °C for 30 minutes.

[0045] As used herein, the term copper-containing small-pore zeolite refers to a small-pore zeolite that includes copper ion-exchanged or impregnated therein and / or thereon. Copper is a typical metal promoter included in the zeolite material to enhance the performance of the zeolite material as an SCR catalyst.

[0046] The copper-containing small-pore zeolite generally has a Cu content of at least 0.1 wt% as CuO and based on the total weight of the copper-containing small-pore zeolite on a volatile-free basis. In some embodiments, the Cu content is in the range of 0.1 wt% to 20 wt%, such as 0.5 wt% to 17 wt%, 2 wt% to 15 wt%, 2 wt% to 10 wt%, or 2 wt% to 7 wt%, in each case as CuO and based on the total weight of the copper-containing small-pore zeolite on a volatile-free basis. In other embodiments, the Cu content can be expressed as a ratio of Cu to framework aluminum within the copper-containing small-pore zeolite. For example, the copper-containing small-pore zeolite has a copper / framework aluminum molar ratio in the range of 0.1 to 0.5, such as 0.25 to 0.5 or 0.30 to 0.50.

[0047] The term "small-pore zeolite" refers to a zeolite having a pore opening of less than about 5 Angstroms .

[0048] In some embodiments, the small pore zeolite can be a small pore 8-ring zeolite. The term "8-ring zeolite" refers to a zeolite having 8-ring pore openings. Some 8-ring zeolites can have a double six-ring (d6r) secondary building unit, within which a cage-like structure is formed from double six-ring building units connected by 4-rings. Exemplary small pore 8-ring zeolites include framework types AEI, AFT, AFX, CHA, EAB, EMT, ERI, FAU, GME, JSR, KFI, LEV, LTL, LTN, MOZ, MSO, MWW, OFF, SAS, SAT, SAV, SBS, SBT, SFW, SSF, SZR, TSC, and WEN.

[0049] In some particular embodiments, the small pore zeolite has a framework type selected from the group consisting of AEI, AFT, AFX, CHA, EAB, ERI, KFI, LEV, SAS, SAT, and SAV. In some further embodiments, the small pore zeolite has a framework type selected from the group consisting of AEI, AFT, AFX, and CHA. In certain embodiments, the small pore zeolite has a CHA framework type.

[0050] More particularly, the small pore zeolite is selected from the group consisting of zeolites having a CHA framework type and can be, for example, an aluminosilicate zeolite, a borosilicate zeolite, a gallosilicate zeolite, a SAPO zeolite, an ALPO zeolite, a MeAPSO zeolite, or a MeAPO zeolite. Suitable zeolites having a CHA framework type can include, but are not limited to, natural chabazite, SSZ-13, SSZ-62, zeolite K-G, Linde D, Linde R, LZ-218, LZ-235, LZ-236, ZK-14, SAPO-34, SAPO-44, SAPO-47, CuSAPO-34, CuSAPO-44, CuSAPO-47, and ZYT-6.

[0051] In some embodiments, the small pore zeolite is selected from the group consisting of aluminosilicate zeolites. Aluminosilicate zeolites can have a variety of silica / alumina ratios over a wide range. In some embodiments, the silica / alumina molar ratio (SAR) can be in the range of 2 to 300, for example, 5 to 250, 5 to 200, 5 to 100, or 5 to 60.

[0052] In some particular embodiments, the small pore zeolite is selected from the group consisting of aluminosilicate zeolites having a CHA framework type. Aluminosilicate zeolites having a CHA framework type can have a silica / alumina ratio in the range of 2 to 200, for example, 5 to 150, 5 to 100, 5 to 100, or 5 to 80. In some further embodiments, the silica / alumina ratio can be in the range of 5 to 60, for example, 10 to 60, 11 to 50, 11 to 40, or 12 to 35.

[0053] The small-pore zeolite can be natural or synthetic, preferably a synthetic zeolite. As one of the commercially available synthetic forms of aluminosilicate zeolites having the CHA framework type, SSZ-13 is specifically mentioned in the present application, which can also be synthesized according to the method described in, for example, US 4,544,538 A, which is incorporated herein by reference.

[0054] Generally, the small-pore zeolite useful in the present application can have an average crystallite size that varies over a wide range, for example, 0.05 to 5 microns, 0.05 to 1 micron, 0.5 to 2 microns, or 0.8 microns to 1.5 microns, as measured by scanning electron microscopy (SEM).

[0055] The copper-containing small-pore zeolite useful in the present application preferably has a crystal structure characterized by a decrease in unit cell volume after sulfation and desulfation of less than or less than or not more than

[0056] The substrate is typically a ceramic or metallic honeycomb structure having fine, parallel gas flow passages extending from one end of the structure to the other.

[0057] Metallic materials useful in constructing the substrate can include heat resistant metals and metal alloys, such as titanium and stainless steel, as well as other alloys having iron as an essential or primary component. Such alloys can contain one or more of nickel, chromium, and / or aluminum, and the total amount of these metals can advantageously constitute at least 15 wt.% of the alloy, for example, 10 to 25 wt.% chromium, 3 to 8% aluminum, and up to 20 wt.% nickel. The alloy can also contain small or trace amounts of one or more metals, such as manganese, copper, vanadium, titanium, and the like. The surface of the metallic substrate can be oxidized at high temperatures, for example, 1000°C and above, to form an oxide layer on the surface of the substrate to improve the corrosion resistance of the alloy and to promote adhesion of the washcoat layer to the metallic surface.

[0058] Ceramic materials useful in constructing the substrate can include any suitable refractory material, such as cordierite, mullite, cordierite-alumina, silicon nitride, zirconium mullite, spodumene, alumina-silica-magnesia, zirconosilicate, silli- cate, magnesium silicate, zircon, petalite, alumina, and aluminosilicate.

[0059] In the present application, a monolithic flow-through substrate is preferred, which has a plurality of fine, parallel gas flow channels extending from the inlet to the outlet of the substrate to open the channels to the fluid stream passing therethrough. The channels, which have a substantially straight path from their fluid inlet to their fluid outlet, are defined by walls on which catalytic material is applied as a washcoat to contact the gases flowing through the channels with the catalytic material. The flow channels of the monolithic substrate are thin-walled channels, which can have any suitable cross-sectional shape and size, such as trapezoidal, rectangular, square, sinusoidal, hexagonal, oval, circular, and the like. Such structures can contain from 60 to 900 or more gas inlets (i.e., cells) per square inch of cross-section. For example, the substrate can have from about 400 to 900, more typically 600 to 750 cells per square inch ("cpsi"). The wall thickness of the flow-through substrate can vary, typically ranging from 2 mils to 0.1 inches.

[0060] The substrate can also be a wall-flow substrate having a plurality of fine, parallel gas flow channels extending from the inlet face to the outlet face of the substrate, with alternate channels plugged at the opposite end. This configuration requires the gas stream to flow through the porous walls of the wall-flow substrate to reach the outlet face. The wall-flow substrate can contain from about 700 cells per square inch (cpsi), for example, from 100 to 700 cpsi, typically 200 to 300 cpsi. The cross-sectional shape of the cells can vary as described above. The wall thickness of the wall-flow substrate can vary, typically ranging from 2 mils to 0.1 inches.

[0061] The copper-containing small-pore zeolite can be deposited on the substrate, typically in the form of a washcoat, either directly or indirectly (i.e., without or with an intermediate deposit).

[0062] In this document, reference to "on a substrate" or similar expressions means not only the surface of the substrate, such as the surface of the channel walls of the substrate, but also, in some cases, the internal pores in the channel walls.

[0063] The term "washcoat" has its ordinary meaning in the art and refers to a thin adherent coating of catalytic material or other material applied to a substrate. Washcoats are typically formed by preparing a slurry containing a particular solids loading (e.g., 15-60 wt%) of particles in a liquid carrier, which is then applied to a substrate, dried and calcined to provide the washcoat.

[0064] Typically, the washcoat can also include a binder, such as one or more selected from the group consisting of alumina, boehmite, silica, titania, and zirconia. When present, the binder is typically included in an amount of 0.5 to 15.0 wt% of the total washcoat loading.

[0065] In some embodiments, the SCR catalytic article according to the present application can comprise a substrate having two or more different washcoat zones loaded thereon. In these embodiments, the copper-containing small-pore zeolite can be present in one or more of the washcoat zones on the substrate.

[0066] The copper-containing small-pore zeolite useful in the present application preferably has an S / Cu atomic ratio after sulfation and desulfation of less than 0.15, for example 0.1 or less, as measured by ICP analysis.

[0067] It has surprisingly been found that the SCR catalytic article according to the present application can have a NOxconversion recovery ratio after sulfation and desulfation at 200°C of at least 70%, for example at least 75%, or at least 80%, or even greater than 80%.

[0068] According to a further aspect of the present application, there is provided an exhaust gas treatment system comprising

[0069] - an internal combustion engine, for example a gasoline engine or a diesel engine; and

[0070] - an SCR catalytic article comprising a substrate and a copper-containing small-pore zeolite thereon as described above positioned downstream of the engine and in fluid communication with the engine.

[0071] In some embodiments, the exhaust gas treatment system can comprise one or more other catalytic articles upstream or downstream of the SCR catalytic article according to the present application. For example, the one or more other catalytic articles can be a catalytic soot filter (CSF), a diesel oxidation catalyst (DOC), and / or another SCR catalytic article.

[0072] According to another aspect of the present application, there is provided a method of treating an exhaust gas stream comprising NOx, comprising contacting the exhaust gas stream with an SCR catalytic article or exhaust gas treatment system as described herein.

[0073] According to a further aspect of the present application, there is provided a method of determining whether a metal-promoted small-pore zeolite is resistant to irreversible sulfur poisoning, comprising

[0074] - preparing, by applying the metal-promoted small-pore zeolite to a substrate, an SCR catalytic article;

[0075] - sulfating by passing a gas stream containing 35 ppmv SO2, 350 ppmv NO, 10 vol% O2, 10 vol% H2O, and balance N2 through a Pt-containing diesel oxidation catalyst at an inlet temperature of 650°C to partially oxidize the SO2 to provide a 30:70 SO2 / SO3 ratio, then through the SCR catalytic article at an outlet temperature of 400°C at a space velocity of 10,000 hr -1 based on the volume of the SCR catalytic article for a time to provide a sulfated SCR catalytic article having 40 g / L of S exposure based on the volume of the SCR catalytic article, wherein the SCR catalytic article has been hydrothermally aged prior to sulfation;

[0076] desulfurization by passing a gas stream containing 10 vol% O2, 8 vol% H2O, 7 vol% CO2, and the balance N2at a space velocity of 60,000 h-1at 550°C through a sulfided SCR catalyst article for 30 minutes; and -1

[0077] determining the unit cell volume of the metal-promoted small-pore zeolite before sulfidation and after desulfurization by X-ray powder diffraction,

[0078] wherein the metal-promoted small-pore zeolite is resistant to irreversible sulfur poisoning if its unit cell volume after desulfurization is not less than

[0079] According to yet another aspect of the present application, there is provided a method of evaluating whether a metal-promoted small-pore zeolite is resistant to irreversible sulfur poisoning, comprising

[0080] providing a catalytic article comprising a substrate and thereon a reference metal-promoted small-pore zeolite having a minimum qualified NOx conversion recovery ratio after sulfidation and desulfurization, for example 70% or more:

[0081]

[0082] determining the unit cell volume change of the reference metal-promoted small-pore zeolite before sulfidation and after desulfurization by X-ray powder diffraction, which is referred to as a predetermined value of unit cell volume change;

[0083] preparing a catalytic article comprising a substrate and thereon a metal-promoted small-pore zeolite to be evaluated;

[0084] determining the unit cell volume change of the metal-promoted small-pore zeolite before sulfidation and after desulfurization by X-ray powder diffraction under the same conditions as the catalytic article comprising the reference metal-promoted small-pore zeolite;

[0085] comparing the unit cell volume change of the metal-promoted small-pore zeolite to the predetermined value,

[0086] wherein the metal-promoted small-pore zeolite is evaluated as resistant to irreversible sulfur poisoning if its unit cell volume change is not greater than the predetermined value.

[0087] ​​In this paper, the term "sulfidation" refers to the process of exposing a catalyst containing metal-promoted microporous zeolite to a gaseous feedstock containing sulfur oxides such as SO2 or a combination of SO2 and SO3 to accumulate sulfur compounds in the catalyst. Therefore, the term "desulfurization" in this paper refers to the process of removing sulfur compounds from a catalyst under thermal conditions. In this paper, the sulfur compounds to be removed from the catalyst can be sulfur (S₂) 2- ), elemental sulfur (S°), sulfite (SO3) 2- ) and sulfate (SO4) 2- The sulfur compounds removed from the catalyst can be in the form of sulfur dioxide (SO2), sulfur trioxide (SO3), or sulfuric acid (H2SO4).

[0088] The method for determining whether metal-promoting microporous zeolites are resistant to irreversible sulfur poisoning and the method for assessing whether metal-promoting microporous zeolites are adequately resistant to irreversible sulfur poisoning can also be referred to as the method for judging tolerance to irreversible sulfur poisoning.

[0089] The method for determining tolerance to irreversible sulfur poisoning is applicable to any metal-promoted microporous zeolite that can be used as an SCR catalyst, such as copper-promoted microporous zeolite.

[0090] Metals are intentionally added to small-pore zeolites to enhance their catalytic activity compared to zeolites without intentionally added metals. Metals (also known as promoters) are typically incorporated into small-pore zeolites using ion exchange or initial wet impregnation methods. Therefore, these ion-exchanged small-pore zeolites are often referred to as "metal-promoted" zeolites.

[0091] As a suitable candidate for a method of determining tolerance to irreversible sulfur poisoning, copper-containing microporous zeolites as described herein with respect to the first aspect of the invention can be mentioned. By reference, any description and preferences of copper-containing microporous zeolites are to be applied to the method of determining tolerance to irreversible sulfur poisoning.

[0092] Based on the practical requirements for the tolerance of metal-promoting small-pore zeolites to irreversible sulfur poisoning, the minimum acceptable NOx conversion recovery ratio after sulfidation and desulfurization can be set to any value, such as 70% or higher, including 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, or even higher. The minimum acceptable NOx conversion recovery ratio can be determined at a predetermined temperature that may be encountered in the exhaust gas, particularly at 200°C.

[0093] Implementation Plan

[0094] Various implementation schemes are listed below. It should be understood that the following implementation schemes can be combined with all aspects and other implementation schemes according to the scope of the invention.

[0095] 1. An SCR catalytic article comprising

[0096] - a substrate, and on it

[0097] - a copper-containing small-pore zeolite having a crystal structure characterized by a decrease in unit cell volume after sulfation and desulfation of less than

[0098] wherein

[0099] sulfation is carried out by passing a gas stream containing 35 ppmv S02, 350 ppmv NO, 10 vol% 02, 10 vol% H20, and balance N2 through a diesel oxidation catalyst (DOC) containing Pt at an inlet temperature of 650 °C to partially oxidize S02 to provide a 30:70 S02 / S03 ratio, then through the SCR catalytic article at an outlet temperature of 400 °C at a space velocity of 10,000 hr -1 -1 based on the volume of the SCR catalytic article for a time to provide 40 g / L of S exposure based on the volume of the SCR catalytic article, wherein the SCR catalytic article has been hydrothermally aged prior to sulfation; and

[0100] desulfation is carried out by passing a gas stream containing 10 vol% 02, 8 vol% H20, 7 vol% C02, and balance N2 through the SCR catalytic article that has been subjected to sulfation at a space velocity of 60,000 hr -1 -1 for 30 minutes at 550 °C.

[0101] 2. The SCR catalytic article according to embodiment 1, wherein the small-pore zeolite has a crystal structure characterized by a decrease in unit cell volume after sulfation and desulfation of less than or less than or not more than

[0102] 3. The SCR catalytic article according to embodiment 1 or 2, wherein the small-pore zeolite is a small-pore 8-ring zeolite, such as having framework type AEI, AFT, AFX, CHA, EAB, EMT, ERI, FAU, GME, JSR, KFI, LEV, LTL, LTN, MOZ, MSO, MWW, OFF, SAS, SAT, SAV, SBS, SBT, SFW, SSF, SZR, TSC, and WEN.

[0103] 4. The SCR catalytic article according to any of the preceding embodiments, wherein the small-pore zeolite has a framework type selected from AEI, AFT, AFX, CHA, EAB, ERI, KFI, LEV, SAS, SAT, and SAV, in particular selected from AEI, AFT, AFX, and CHA, preferably CHA.

[0104] 5. An SCR catalyst according to any of the foregoing embodiments, wherein the microporous zeolite is selected from aluminosilicate zeolites, particularly having a silica / alumina molar ratio in the range of 2 to 300, for example 5 to 250, 5 to 200, 5 to 100, or 5 to 60.

[0105] 6. An SCR catalyst according to any of the foregoing embodiments, wherein the microporous zeolite is selected from aluminosilicate zeolites having a CHA framework type and has a silica / alumina ratio in the range of 5 to 60, for example 10 to 60, 11 to 50, 11 to 40, or 12 to 35.

[0106] 7. An SCR catalyst according to any of the foregoing embodiments, wherein the microporous zeolite has an average crystal size in the range of 0.05 to 5 micrometers, 0.05 to 1 micrometer, 0.5 to 2 micrometers, or 0.8 to 1.5 micrometers as measured by scanning electron microscopy.

[0107] 8. An SCR catalyst product according to any of the foregoing embodiments, wherein the copper-containing microporous zeolite has a Cu content of at least about 0.1 wt% based on CuO and the total weight of the copper-containing microporous zeolite without volatiles, for example, in the range of 0.1 wt% to 20 wt%, 0.5 wt% to 17 wt%, 2 wt% to 15 wt%, 2 wt% to 10 wt%, or 2 wt% to 7 wt%.

[0108] 9. An SCR catalyst according to any of the foregoing embodiments, wherein the copper-containing microporous zeolite has a copper / aluminum molar ratio in the range of 0.1 to 0.5, for example 0.25 to 0.5 or 0.30 to 0.50.

[0109] 10. An SCR catalyst according to any of the foregoing embodiments, wherein the copper-containing microporous zeolite has an S / Cu atomic ratio of less than 0.15, for example 0.1 or less after sulfidation and desulfurization.

[0110] 11. An SCR catalyst product according to any of the foregoing embodiments, wherein the substrate is a wall-flow substrate or a flow-through substrate.

[0111] 12. An SCR catalyst according to any of the foregoing embodiments, wherein the copper-containing microporous zeolite is typically deposited directly or indirectly on a substrate in the form of a wash-out coating.

[0112] 13. An SCR catalyst product according to any of the foregoing embodiments, wherein the SCR catalyst product has a NOx conversion recovery ratio of at least 70%, at least 75%, at least 80%, or even greater than 80% after sulfidation and desulfurization at 200°C.

[0113] 14. An SCR catalytic article comprising

[0114] - a substrate, and on it

[0115] - a copper-containing small pore zeolite having a NOx conversion recovery ratio at 200°C after sulfation and desulfation of at least 70%, at least 75%, at least 80%, or even greater than 80%,

[0116] wherein

[0117] sulfation is carried out by passing a gas stream containing 35 ppmv SO2, 350 ppmv NO, 10 vol% O2, 10 vol% H2O, and balance N2 through a diesel oxidation catalyst (DOC) containing Pt at an inlet temperature of 650°C to partially oxidize SO2 to provide a 30:70 SO2 / SO3 ratio, then through the SCR catalytic article at an outlet temperature of 400°C at a space velocity of 10,000 hr -1 -1 based on the volume of the SCR catalytic article for a period of time to provide an S exposure of 40 g / L based on the volume of the SCR catalytic article, wherein the SCR catalytic article has been hydrothermally aged prior to sulfation; and

[0118] desulfation is carried out by passing a gas stream containing 10 vol% O2, 8 vol% H2O, 7 vol% CO2, and balance N2 through the SCR catalytic article that has been subjected to sulfation at a space velocity of 60,000 hr -1 -1 at 550°C for 30 minutes.

[0119] 15. An exhaust gas treatment system comprising

[0120] - an internal combustion engine, such as a gasoline engine or a diesel engine; and

[0121] - an SCR catalytic article as defined in any of the preceding embodiments positioned downstream of and in fluid communication with the engine.

[0122] 16. A method of treating an exhaust gas stream comprising NOx comprising contacting the exhaust gas stream with an SCR catalytic article as defined in any of the preceding embodiments 1 to 14 or an exhaust gas treatment system as defined in embodiment 15.

[0123] 17. Use of a copper-containing small pore zeolite as defined in any of the preceding embodiments 1 to 14 as an SCR catalyst.

[0124] 18. A method of determining whether a metal-promoted small pore zeolite is resistant to irreversible sulfur poisoning comprising

[0125] - preparing, by applying a metal-promoted small-pore zeolite to a substrate, an SCR catalytic article;

[0126] - sulfation by passing a gas stream containing 35 ppmv SO2, 350 ppmv NO, 10 vol% O2, 10 vol% H2O, and balance N2 through a diesel oxidation catalyst containing Pt at an inlet temperature of 650°C to partially oxidize SO2 to provide a 30:70 SO2 / SO3 ratio, then through the SCR catalytic article at an outlet temperature of 400°C at a space velocity of 10,000 hr -1 -1 of the volume of the SCR catalytic article to provide a sulfated SCR catalytic article having 40 g / L of S exposure based on the volume of the SCR catalytic article, wherein the SCR catalytic article has been hydrothermally aged prior to sulfation;

[0127] - desulfation by passing a gas stream containing 10 vol% O2, 8 vol% H2O, 7 vol% CO2, and balance N2 through the sulfated SCR catalytic article at a space velocity of 60,000 hr -1 -1 at 550°C for 30 minutes; and

[0128] - determining the unit cell volume of the metal-promoted small-pore zeolite before sulfation and after desulfation by X-ray powder diffraction,

[0129] wherein the metal-promoted small-pore zeolite is resistant to irreversible sulfur poisoning if the unit cell volume of the metal-promoted small-pore zeolite after desulfation is less than preferably less than or less than or not more than the unit cell volume of the metal-promoted small-pore zeolite before sulfation.

[0130] 19. A method of evaluating whether a metal-promoted small-pore zeolite is suitably resistant to irreversible sulfur poisoning comprising

[0131] - providing a catalytic article comprising a substrate and thereon a reference metal-promoted small-pore zeolite having a minimum qualified NOx conversion recovery ratio after sulfation and desulfation, for example 70% or more:

[0132]

[0133] - determining the unit cell volume change of the reference metal-promoted small-pore zeolite before sulfation and after desulfation by X-ray powder diffraction, which is referred to as a predetermined value of unit cell volume change;

[0134] - preparing a catalytic article comprising a substrate and thereon a metal-promoted small-pore zeolite to be evaluated;

[0135] -The cell volume change of the metal-promoted microporous zeolite before and after sulfidation was determined by X-ray powder diffraction under the same conditions as the catalyst containing the reference metal-promoted microporous zeolite.

[0136] - Compare the cell volume change of the metal-promoted microporous zeolite with the predetermined value.

[0137] If the change in its cell volume is not greater than a predetermined value, the metal-promoted microporous zeolite is evaluated as adequately resistant to irreversible sulfur poisoning.

[0138] 20. The method according to embodiment 19, wherein the metal-promoting microporous zeolite is selected from iron-promoting microporous zeolite and copper-promoting microporous zeolite, particularly copper-promoting microporous zeolite, such as copper-containing microporous zeolite as defined in any one of embodiments 1 to 9.

[0139] 21. According to the method of implementation scheme 19 or 20, the minimum qualified NOx conversion recovery ratio after sulfidation and desulfurization is 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83% or even higher.

[0140] 22. The method according to any one of embodiments 19 to 21, wherein the minimum acceptable NOx conversion recovery ratio is determined at 200°C.

[0141] 23. According to the methods in implementation schemes 19 to 22, wherein

[0142] - Sulfidation is carried out as follows: a gas stream containing 35 ppmv SO2, 350 ppmv NO, 10 vol% O2, 10 vol% H2O, and the balance N2 is passed through a Pt-containing diesel oxidation catalyst (DOC) at an inlet temperature of 650°C to partially oxidize SO2 to provide an SO2 / SO3 ratio of 30:70, and then at an outlet temperature of 400°C for 10,000 hours based on the volume of the SCR catalyst. -1 The SCR catalyst was passed through at a space velocity for a period of time to provide an S exposure of 40 g / L based on the volume of the SCR catalyst, wherein the catalyst had been hydrothermally aged prior to sulfidation; and

[0143] -Desulfurization is carried out as follows: a gas stream containing 10 vol% O2, 8 vol% H2O, 7 vol% CO2 and the balance N2 is subjected to desulfurization for 60,000 h. -1 The sample was passed through a sulfurized SCR catalyst at 550°C for 30 minutes at a space velocity of 1000 h⁻¹. Example

[0144] Aspects of the application are more fully exemplified by the following examples, which are set forth to exemplify certain aspects of the application and are not to be construed as limiting thereof.

[0145] I. Preparation Examples

[0146] Example 1 Preparation of a catalytic article comprising Cu / SSZ-13 powder (SAR = 30, CuO% = 3.25 wt%)

[0147] Trimethyladamantylammonium hydroxide (TMAdaOH) was used as the template and sodium hydroxide as the additional OH - Source crystalline SSZ-13. The synthesis gel had the following molar composition:

[0148] 36 Si02: 1.2 Al203: 2.6 (TMAdaOH): 3.6 NaOH: 379 H20.

[0149] After hydrothermal crystallization at 170 °C for 40 hours, the suspension was filtered, dried and calcined at 600 °C. A sample of the calcined material was examined by XRD, confirming that the zeolite had a CHA framework. ICP analysis of the resulting Na form of SSZ-13 showed that the material had a Si02 / Al203ratio (SAR) of 30.

[0150] To a stirred tank was added deionized water (78 kg) and heated to 60 °C with stirring, then copper acetate monohydrate (1.56 kg) was added. Once the copper acetate monohydrate was completely dissolved, Na / SSZ-13 (12 kg) was added to the tank and mixing was continued at 60 °C for 2 hours. The suspension was transferred to a plate and frame filter press to remove the supernatant. The solid Cu / SSZ-13 was washed with deionized water until the filtrate conductivity was less than 200 microsiemens, then air dried on the filter press. The copper loading as measured by ICP was 3.25 wt% as CuO, based on the total weight of zeolite on a volatile free basis.

[0151] 95 parts by weight of the resulting Cu / SSZ-13 and 5 parts by weight of zirconium acetate as Zr02were mixed in a 95:5 weight ratio into deionized water to form a slurry. The slurry was then milled to a D 90 particle size of between 7 and 10 pm as measured with a Sympatec particle size analyzer. The milled slurry was coated onto a flow-through cordierite monolith substrate having a cell density of 600 cpsi and a wall thickness of 3 mil, then dried at 130 °C and calcined at 450 °C. The washcoat loading was 2.0 g / in 3 .

[0152] Example 2 Preparation of a catalytic article comprising Cu / SSZ-13 powder (SAR = 19, CuO% = 5.0 wt%)

[0153] SSZ-13 was crystallized using trimethyladamantylammonium hydroxide (TMAdaOH) as a template and the synthesis gel had the following molar composition:

[0154] 20 Si02: 1.0 AI203: 1.42 TMAdaOH: 2.6 NaOH: 220 H20.

[0155] After hydrothermal crystallization at 170 °C for 30 hours, the suspension was filtered, dried and calcined at 540 °C for 6 hours to give Na + SSZ-13 in the form of Na + SSZ-13 was exchanged to NH4 + SSZ-13 having a Na content of < 500 ppm as Na20.

[0156] NH4 + SSZ-13 zeolite (12 kg) in the form of NH4

[0157] 95 parts by weight of the resulting Cu / SSZ-13 and 5 parts by weight of zirconium acetate as Zr02were mixed into deionized water to form a slurry which was milled to a D 90 3

[0158] Example 3 prepared a catalytic article comprising Cu / SSZ-13 powder (SAR = 18, CuO% = 5.6 wt%)

[0159] SSZ-13 was crystallized using trimethyladamantylammonium hydroxide (TMAdaOH) as a template and the synthesis gel had the following molar composition:

[0160] ​​35 Si02: 1.0 Al203: 3.15 TMAdaOH: 28.7 Na: 17.5 OH: 1120 H20.

[0161] After hydrothermal crystallization at 140 °C for 42 hours, the suspension was filtered, dried and calcined at 540 °C for 6 hours to obtain Na + form of SSZ-13. ICP analysis of the resulting Na form of SSZ-13 showed that the material had a Si02 / Al203ratio (SAR) of 18. After calcination, the Na form of SSZ-13 was exchanged to an NH4 + form of SSZ-13 having a Na content of < 500 ppm as Na20, which was then calcined at 450 °C for 6 hours to obtain the hydrogen form of SSZ-13.

[0162] 85.4 parts by weight of the hydrogen form of SSZ-13, 5.1 parts by weight of CuO and 4.8 parts by weight of zirconium acetate as Zr02were mixed into deionized water to form a slurry. The slurry was milled to a D 90 50 of between 4 and 6 μιη as measured with a Sympatec particle size analyzer. The slurry was mixed at room temperature for 24 hours to exchange copper ions into the zeolite framework. Undispersible boehmite alumina was mixed into the slurry in an amount of 4.8 wt% of total slurry solids. The final slurry was coated onto a flow-through cordierite monolith substrate having a cell density of 600 cpsi and a wall thickness of 3 mil, then dried at 130 °C and calcined at 550 °C. The washcoat loading was 2.9 g / in 3 .

[0163] Example 4 prepared a catalytic article comprising Cu / SSZ-13 powder (SAR = 10, CuO% = 6.8%)

[0164] SSZ-13 was crystallized using trimethyladamantylammonium hydroxide (TMAdaOH) as a template and the synthesis gel had the following molar ratio composition:

[0165] 35 Si02: 1.0 Al203: 3.15 TMAdaOH: 28.7 Na: 17.5 OH: 1120 H20.

[0166] After hydrothermal crystallization at 140 °C for 24 hours, the suspension was filtered, dried and calcined at 540 °C for 6 hours to obtain Na + form of SSZ-13. ICP analysis of the resulting Na form of SSZ-13 showed that the material had a Si02 / Al203ratio (SAR) of 18. After calcination, the Na +Form of SSZ-13 exchanged to NH4 + Form of SSZ-13, which was calcined at 450°C for 6 hours to obtain the hydrogen form of SSZ-13.

[0167] A slurry was formed by mixing 84.3 parts by weight of the hydrogen form of SSZ-13, 6.2 parts by weight of CuO, and 4.8 parts by weight of zirconium acetate, as Zr02, into deionized water. The slurry was milled to a D 90 particle size of between 7 and 10 μιη as measured with a Sympatec particle size analyzer. The slurry was mixed at room temperature for 24 hours to exchange copper ions into the zeolite framework. An amount of 2.4 wt% of the total slurry solids of non-dispersible boehmite alumina and an amount of 2.4 wt% of the total slurry solids of dispersible boehmite alumina were mixed into the slurry. The final slurry was coated onto a flow-through cordierite monolith substrate having a cell density of 600 cpsi and a wall thickness of 3 mil, then dried at 130°C and calcined at 550°C. The washcoat loading was 2.9 g / in 3 .

[0168] Example 5 Preparation of a Pt-containing diesel oxidation catalyst (DOC)

[0169] The doped 5% Si02-Al203material was incipient wetness impregnated with a dilute tetraamine platinum (II) hydroxide complex solution and the resulting material was added to deionized (DI) water to form a slurry suspension. The pH of the slurry suspension was adjusted to 4-5 with dilute HNO3. The slurry was milled to a D 90 = 12-15 um and an alumina binder material was added in an amount of 2.5 wt% based on total slurry solids. The slurry was then coated onto a flow-through honeycomb substrate having a cell density of 400 cpsi and a wall thickness of 4 mil at a 30-45% solids content. After drying, the catalyst was calcined in air at 590°C for 1 hour. The washcoat loading was 1.037 g / in 3 and the Pt loading was 10 g / ft 3 .

[0170] II. Measurement and Testing

[0171] II.1 Sulfurization and Desulfurization

[0172] Sulfurization

[0173] A Pt-containing diesel oxidation catalyst (DOC) prepared as in Example 5 was placed upstream of an SCR catalyst. The SCR catalyst had been hydrothermally aged at 650°C for 100 hours under an atmosphere containing 10 vol% H2O, 10 vol% O2, and balance N2 at a flow rate of 20 L / min. A gas stream containing 35 ppmv SO2, 350 ppmv NO, 10 vol% O2, 10 vol% H2O, and balance N2 was passed through the DOC and the SCR catalyst at a space velocity of 10,000 hr -1 -1 based on the volume of the SCR. The inlet temperature of the DOC catalyst was maintained at 650°C and the outlet temperature of the SCR catalyst was maintained at 400°C. After flowing through the DOC, the SO2 contained in the gas stream was oxidized to SO3 such that the SO2 / SO3 ratio was 30:70. The gas stream was continued for a time to produce 40 g / L of S exposure based on the volume of the SCR to provide a sulfided SCR catalyst.

[0174] Desulfation

[0175] A gas stream containing 10 vol% O2, 8 vol% H2O, 7 vol% CO2, and balance N2 was passed through the sulfided SCR catalyst at a space velocity of 60,000 hr -1 -1, 550°C for 30 minutes to provide a desulfated SCR catalyst.

[0176] II.2 Measurement

[0177] Unit Cell Volume (UCV)

[0178] The unit cell volume was measured by X-ray powder diffraction (XRD). The washcoat was removed from the substrate of each SCR catalyst article using a tungsten needle. The powder was then ground using a mortar and pestle. The ground powder was then forward filled onto a Si 0 low background wafer for analysis. Data were collected in Bragg-Brentano geometry using a theta-theta PANalytical X’Pert Pro MPD X-ray diffractometer system. The optical path consists of an X-ray tube, 0.04 rad soller slits, 1 / 8° divergence slits, 15 mm beam mask, 1 / 4° anti-scatter slits, beam knife on sample, 1 / 8° anti-scatter slits, 0.04 rad soller slits, Ni 0 filter, and an X’Celerator linear position sensitive detector with 2.122° effective length. Cu K α radiation was used at a generator setting of 45 kV and 40 mA in this analysis. X-ray diffraction data were collected from 3° to 70° 2-theta using a step size of 0.017° and a count time of 60 s per step. Phase identification was done using Jade software while quantification was done using Topas software.

[0179] Zeolite surface area (ZSA)

[0180] Zeolite surface area (ZSA) is a measure of micropore surface area (pores < 2 nm in diameter) and is expressed in m2 / g. It refers to the zeolite surface area (m2 / g) per gram of catalyst article including washcoat and substrate. ZSA is measured by BET N2 adsorption as described in detail in U.S. Provisional Patent Application 62 / 517,243, which is incorporated herein by reference in its entirety. The catalytic article is measured without removing the washcoat from the substrate and without crushing the catalyst article prior to analysis. 2 2 / g). ZSA is measured by BET N2 adsorption as described in detail in U.S. Provisional Patent Application 62 / 517,243, which is incorporated herein by reference in its entirety. The catalytic article is measured without removing the washcoat from the substrate and without crushing the catalyst article prior to analysis.

[0181] S / Cu atomic ratio

[0182] The S / Cu atomic ratio of the copper-containing small pore zeolite after sulfidation and desulfurization is also a measure of irreversible sulfur poisoning, which is determined by measuring the content of S and Cu on the pulverized catalyst article by ICP analysis and then calculating the atomic ratio thereof.

[0183] The unit cell volume and zeolite surface area measurements before sulfidation (pre) and after desulfurization (post), as well as the S / Cu atomic ratio, are summarized in Table 1 below. The S / Cu atomic ratio determined for the Cu / SSZ-13 zeolites of Example 2 and Example 4 are also shown in Figure 1 .

[0184] Table 1

[0185]

[0186] II. Test for NOx Conversion

[0187] NOx conversion was tested using a flow reactor under pseudo-steady state conditions at a temperature of 200 °C with a gas stream of 1000 ppmv NO, 1050 ppmv NH3, 10 vol% O2, 8 vol% H2O, 7 vol% CO2, and balance N2 at a space velocity of 60,000 h-1. NOx conversion is reported in mole% and measured as NO and NO2. -1

[0188] The NOx conversion recovery ratio after the sulfidation and desulfurization processes was calculated according to the following equation:

[0189]

[0190] NOx conversion and NOx conversion recovery ratio are summarized in Table 2 below.

[0191] Table 2

[0192] ​​

[0193] As shown in Table 2, after sulfation and desulfation, the catalytic articles from Examples 1-3 had significantly higher NOx conversion recovery ratios than the catalytic article from Example 4, indicating much better resistance to irreversible sulfur poisoning. The results are also illustrated in Figure 2 .

[0194] In addition to desulfation at 700 °C, the NOx conversion recovery ratio of the SCR catalyst from Example 4 was further tested after the same sulfation and desulfation as described above. Higher desulfation temperatures can help remove sulfur species more fully from the Cu-CHA zeolite. However, the NOx conversion recovery ratio was found to improve to 72%, which is still lower than the NOx conversion recovery ratios of Examples 1-3 desulfated at 550 °C.

[0195] Without being bound by any particular theory, it is believed that the improved resistance to irreversible sulfur poisoning can be attributed to the lower unit cell volume reduction of the Cu-CHA zeolites of Examples 1-3 after sulfation and desulfation.

[0196] While the application has been described herein with reference to particular embodiments thereof, a latitude of modification, various changes and substitutions are intended in the foregoing disclosures, and it will be appreciated that in some embodiments, teachings of the present application can be applicable to any catalytic article, process, or system, and may, of course, be carried out in other specific ways. Accordingly, it is intended that the application be construed in all its alternative embodiments. For example, the application can be used in conjunction with other catalytic articles, processes, or systems.

Claims

1. A method for determining whether a metal-promoted small-pore zeolite is resistant to irreversible sulfur poisoning, comprising - providing an SCR catalytic article by applying a metal-promoted small-pore zeolite to a substrate; - sulfidation by passing a gas stream containing 35 ppmv S02, 350 ppmv NO, 10 vol% 02, 10 vol% H20, and balance N2 at an inlet temperature of 650 °C over a Pt-containing diesel oxidation catalyst to partially oxidize S02 to provide a 30:70 S02 / S03 ratio, then over the SCR catalytic article at an outlet temperature of 400 °C at a space velocity of 10,000 hr"1 based on the volume of the SCR catalytic article for a period of time to provide a sulfided SCR catalytic article having 40 g / L of S exposure based on the volume of the SCR catalytic article, wherein the SCR catalytic article has been hydrothermally aged prior to sulfidation; -1 - sulfidation by passing a gas stream containing 35 ppmv S02, 350 ppmv NO, 10 vol% 02, 10 vol% H20, and balance N2 at an inlet temperature of 650 °C over a Pt-containing diesel oxidation catalyst to partially oxidize S02 to provide a 30:70 S02 / S03 ratio, then over the SCR catalytic article at an outlet temperature of 400 °C at a space velocity of 10,000 hr"1 based on the volume of the SCR catalytic article for a period of time to provide a sulfided SCR catalytic article having 40 g / L of S exposure based on the volume of the SCR catalytic article, wherein the SCR catalytic article has been hydrothermally aged prior to sulfidation; - desulfurization by passing a gas stream containing 10 vol% O2, 8 vol% H2O, 7 vol% CO2, and balance N2 over a sulfided SCR catalyst article at 60,000 h -1 -1 of space velocity at 550 °C for 30 minutes; and - determining the unit cell volume of the metal-promoted small-pore zeolite before sulfation and after desulfation by X-ray powder diffraction, wherein, If the metal-promoted small-pore zeolite has a unit cell volume after desulfurization that is less than 0.1% greater than its unit cell volume prior to sulfidation then the metal-promoted small-pore zeolite is resistant to irreversible sulfur poisoning.

2. The method according to claim 1, wherein, If the metal-promoted small-pore zeolite has a unit cell volume after desulfurization that is less than 0.1% greater than its unit cell volume prior to sulfidation then the metal-promoted small-pore zeolite is resistant to irreversible sulfur poisoning.

3. The method according to claim 2, wherein, If the metal-promoted small-pore zeolite has a unit cell volume after desulfurization that is less than 0.1% greater than its unit cell volume prior to sulfidation then the metal-promoted small-pore zeolite is resistant to irreversible sulfur poisoning.

4. The method according to claim 3, wherein, The metal-promoted small-pore zeolite is resistant to irreversible sulfur poisoning if the unit cell volume of the metal-promoted small-pore zeolite after desulfurization is not more than 0.1 A3 lower than the unit cell volume of the metal-promoted small-pore zeolite prior to sulfation The metal-promoted small-pore zeolite is resistant to irreversible sulfur poisoning if the unit cell volume of the metal-promoted small-pore zeolite after desulfurization is not more than 0.1 A3 lower than the unit cell 5. A method for evaluating whether a metal-promoted small-pore zeolite is adequately resistant to irreversible sulfur poisoning, comprising - providing a catalytic article comprising a substrate and thereon a reference metal-promoted small-pore zeolite having a minimum adequate NOx conversion recovery ratio after sulfation and desulfation: - determining the unit cell volume change of the reference metal-promoted small-pore zeolite before sulfation and after desulfation by X-ray powder diffraction, which is referred to as a predetermined value of unit cell volume change; - providing a catalytic article comprising a substrate and thereon a metal-promoted small-pore zeolite to be evaluated; - determining the unit cell volume change of the metal-promoted small-pore zeolite before sulfation and after desulfation by X-ray powder diffraction under the same conditions as the catalytic article comprising the reference metal-promoted small-pore zeolite; - comparing the unit cell volume change of the metal-promoted small-pore zeolite with the predetermined value, wherein the metal-promoted small-pore zeolite is evaluated as adequately resistant to irreversible sulfur poisoning if its unit cell volume change is not greater than the predetermined value.

6. The method according to claim 5, wherein the metal-promoted small-pore zeolite is selected from copper-promoted small-pore zeolites.

7. The method according to claim 5 or 6, wherein the minimum adequate NOx conversion recovery ratio after sulfation and desulfation is 70% or more.

8. The method according to claim 7, wherein the minimum adequate NOx conversion recovery ratio after sulfation and desulfation is 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83% or even more.

9. The method according to any one of claims 5, 6 and 8, wherein the minimum adequate NOx conversion recovery ratio is determined at 200 °C.

10. The method according to claim 7, wherein the minimum adequate NOx conversion recovery ratio is determined at 200 °C.

11. The method according to any one of the preceding claims 1-6, 8 and 10, wherein the small-pore zeolite has a framework type selected from the group consisting of AEI, AFT, AFX, CHA, EAB, EMT, ERI, FAU, GME, JSR, KFI, LEV, LTL, LTN, MOZ, MSO, MWW, OFF, SAS, SAT, SAV, SBS, SBT, SFW, SSF, SZR, TSC and WEN.

12. The method according to the preceding claim 11, wherein the small-pore zeolite has a framework type selected from the group consisting of AEI, AFT, AFX and CHA.

13. The method according to the preceding claim 7, wherein the small-pore zeolite has a framework type selected from the group consisting of AEI, AFT, AFX and CHA.

14. The method according to the preceding claim 9, wherein the small-pore zeolite has a framework type selected from the group consisting of AEI, AFT, AFX and CHA.

15. The process according to any one of the preceding claims 12 to 14, wherein the small-pore zeolite has the CHA framework type.

16. The process according to any one of the preceding claims 1 to 6, 8, 10 and 12 to 14, wherein the small-pore zeolite is selected from the group consisting of aluminosilicate zeolites.

17. The process according to the preceding claim 15, wherein the small-pore zeolite is selected from the group consisting of aluminosilicate zeolites.

18. The process according to the preceding claim 16, wherein the aluminosilicate zeolite has a silica / alumina molar ratio in the range of from 5 to 60.

19. The process according to the preceding claim 17, wherein the aluminosilicate zeolite has a silica / alumina molar ratio in the range of from 5 to 60.

20. The process according to the preceding claim 18 or 19, wherein the small-pore zeolite is selected from the group consisting of aluminosilicate zeolites having the CHA framework type and has a silica / alumina ratio in the range of from 12 to 35.

21. The process according to any one of claims 5, 6, 8, 10, 12 to 14 and 17 to 19, wherein - Sulfidation is carried out as follows: a gas stream containing 35 ppmv SO2, 350 ppmv NO, 10 vol% O2, 10 vol% H2O, and the balance N2 is passed through a Pt-containing diesel oxidation catalyst (DOC) at an inlet temperature of 650°C to partially oxidize SO2 to provide an SO2 / SO3 ratio of 30:70, and then at an outlet temperature of 400°C for 10,000 hours based on the volume of the SCR catalyst. -1 The catalyst was passed through at a space velocity for a period of time to provide an S exposure of 40 g / L based on the volume of the SCR catalyst, wherein the catalyst had been hydrothermally aged prior to sulfidation; and - Desulfurization was performed by passing a gas stream containing 10 vol% O2, 8 vol% H2O, 7 vol% CO2, and balance N2at a space velocity of 60,000 h-1over an SCR catalyst article that had been sulfided at 550 °C for 30 min. -1 - Desulfurization was performed by passing a gas stream containing 10 vol% O2, 8 vol% H2O, 7 vol% CO2, and balance N2at a space velocity of 60,000 h-1over an SCR catalyst article that had been sulfided at 550 °C for 30 min.

22. The process according to claim 7, wherein - Sulfidation is carried out as follows: a gas stream containing 35 ppmv SO2, 350 ppmv NO, 10 vol% O2, 10 vol% H2O, and the balance N2 is passed through a Pt-containing diesel oxidation catalyst (DOC) at an inlet temperature of 650°C to partially oxidize SO2 to provide an SO2 / SO3 ratio of 30:70, and then at an outlet temperature of 400°C for 10,000 hours based on the volume of the SCR catalyst. -1 The catalyst was passed through at a space velocity for a period of time to provide an S exposure of 40 g / L based on the volume of the SCR catalyst, wherein the catalyst had been hydrothermally aged prior to sulfidation; and - Desulfurization was performed by passing a gas stream containing 10 vol% O2, 8 vol% H2O, 7 vol% CO2, and balance N2at a space velocity of 60,000 h -1 over an already sulfided SCR catalytic article at 550 °C for 30 minutes.

23. The process according to claim 9, wherein - Sulfidation is carried out as follows: a gas stream containing 35 ppmv SO2, 350 ppmv NO, 10 vol% O2, 10 vol% H2O, and the balance N2 is passed through a Pt-containing diesel oxidation catalyst (DOC) at an inlet temperature of 650°C to partially oxidize SO2 to provide an SO2 / SO3 ratio of 30:70, and then at an outlet temperature of 400°C for 10,000 hours based on the volume of the SCR catalyst. -1 The catalyst was passed through at a space velocity for a period of time to provide an S exposure of 40 g / L based on the volume of the SCR catalyst, wherein the catalyst had been hydrothermally aged prior to sulfidation; and - Desulfurization was performed by passing a gas stream containing 10 vol% O2, 8 vol% H2O, 7 vol% CO2, and balance N2at a space velocity of 60,000 h -1 over an already sulfided SCR catalytic article at 550 °C for 30 minutes.

24. The process according to claim 11, wherein - Sulfidation is carried out as follows: a gas stream containing 35 ppmv SO2, 350 ppmv NO, 10 vol% O2, 10 vol% H2O, and the balance N2 is passed through a Pt-containing diesel oxidation catalyst (DOC) at an inlet temperature of 650°C to partially oxidize SO2 to provide an SO2 / SO3 ratio of 30:70, and then at an outlet temperature of 400°C for 10,000 hours based on the volume of the SCR catalyst. -1 The catalyst was passed through at a space velocity for a period of time to provide an S exposure of 40 g / L based on the volume of the SCR catalyst, wherein the catalyst had been hydrothermally aged prior to sulfidation; and - Desulfurization was performed by passing a gas stream containing 10 vol% O2, 8 vol% H2O, 7 vol% CO2, and balance N2at a space velocity of 60,000 h -1 over an already sulfided SCR catalytic article at 550 °C for 30 minutes.

25. The process according to claim 15, wherein - Sulfidation is carried out as follows: a gas stream containing 35 ppmv SO2, 350 ppmv NO, 10 vol% O2, 10 vol% H2O, and the balance N2 is passed through a Pt-containing diesel oxidation catalyst (DOC) at an inlet temperature of 650°C to partially oxidize SO2 to provide an SO2 / SO3 ratio of 30:70, and then at an outlet temperature of 400°C for 10,000 hours based on the volume of the SCR catalyst. -1 The catalyst was passed through at a space velocity for a period of time to provide an S exposure of 40 g / L based on the volume of the SCR catalyst, wherein the catalyst had been hydrothermally aged prior to sulfidation; and - Desulfurization was performed by passing a gas stream containing 10 vol% O2, 8 vol% H2O, 7 vol% CO2, and balance N2at a space velocity of 60,000 h -1 over an already sulfided SCR catalytic article at 550 °C for 30 minutes.

26. The process according to claim 16, wherein - Sulfidation is carried out as follows: a gas stream containing 35 ppmv SO2, 350 ppmv NO, 10 vol% O2, 10 vol% H2O, and the balance N2 is passed through a Pt-containing diesel oxidation catalyst (DOC) at an inlet temperature of 650°C to partially oxidize SO2 to provide an SO2 / SO3 ratio of 30:70, and then at an outlet temperature of 400°C for 10,000 hours based on the volume of the SCR catalyst. -1 The catalyst was passed through at a space velocity for a period of time to provide an S exposure of 40 g / L based on the volume of the SCR catalyst, wherein the catalyst had been hydrothermally aged prior to sulfidation; and - Desulfurization was performed by passing a gas stream containing 10 vol% O2, 8 vol% H2O, 7 vol% CO2, and balance N2at a space velocity of 60,000 h"1over an SCR catalyst article that had been sulfided at 550 °C for 30 min. -1 at a space velocity of 60,000 h"1over an SCR catalyst article that had been sulfided at 550 °C for 30 min.

27. The process according to claim 20, wherein - Sulfidation is carried out as follows: a gas stream containing 35 ppmv SO2, 350 ppmv NO, 10 vol% O2, 10 vol% H2O, and the balance N2 is passed through a Pt-containing diesel oxidation catalyst (DOC) at an inlet temperature of 650°C to partially oxidize SO2 to provide an SO2 / SO3 ratio of 30:70, and then at an outlet temperature of 400°C for 10,000 hours based on the volume of the SCR catalyst. -1 The catalyst was passed through at a space velocity for a period of time to provide an S exposure of 40 g / L based on the volume of the SCR catalyst, wherein the catalyst had been hydrothermally aged prior to sulfidation; and - Desulfurization was performed by passing a gas stream containing 10 vol% O2, 8 vol% H2O, 7 vol% CO2, and balance N2at a space velocity of 60,000 h"1over an SCR catalyst article that had been sulfided at 550 °C for 30 min. -1 at a space velocity of 60,000 h"1over an SCR catalyst article that had been sulfided at 550 °C for 30 min.

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