Catalyst materials for processing exhaust gases produced by natural gas engines

Abstract

The present invention relates to a catalytic material for treating exhaust gas produced by a natural gas engine, the catalytic material comprising a molecular sieve and a platinum group metal (PGM) supported on the molecular sieve, the molecular sieve having a framework comprising silicon, oxygen, and germanium and having a heteroatom T atom content of about 0.20 mol % or less, the germanium being present in an amount of 15-20 mol %. The present invention further relates to a catalytic article and a compressed natural gas combustion and exhaust system.

Description

Technical Field

[0001] The present invention relates to a catalyst material for treating exhaust gas generated from a natural gas engine, and particularly to a catalyst material having improved methane oxidation activity and hydrothermal durability.

Background Art

[0002] Natural gas has been increasingly attracting attention as an alternative fuel for vehicles and stationary engines that traditionally use gasoline and diesel fuel. Natural gas is mainly composed of methane (typically 70 - 90%), and contains other hydrocarbons such as ethane, propane, and butane (up to 20% in some deposits) and other gases in various proportions. It can be commercially produced from oil fields or natural gas fields and is widely used as a combustion energy source for power generation, industrial co-generation, and domestic heating. It can also be used as a vehicle fuel.

[0003] Natural gas can be used as a transportation fuel in the form of compressed natural gas (CNG) and liquefied natural gas (LNG). CNG is carried in a tank pressurized to 3600 psi (about 248 bar) and has an energy density of about 35% of gasoline per unit volume. LNG has an energy density 2.5 times that of CNG and is mainly used for large vehicles. LNG is cooled to a liquid form at - 162°C, and as a result, its volume is reduced to 1 / 600, which means that LNG is more easily transported than CNG. Bio - LNG can be an alternative to natural (fossil) gas, is produced from biogas, and is obtained by anaerobic digestion of organic substances such as landfill waste or manure.

[0004] Natural gas has many environmental advantages, that is, it is a cleaner combustion fuel that typically contains few impurities, has a higher energy per carbon (Btu) than conventional hydrocarbon fuels, and as a result, has a lower carbon dioxide emission (25% less greenhouse gas emissions), and lower PM and NO compared to diesel and gasoline xEmissions are low. Biogas can further reduce such emissions.

[0005] Further incentives for adopting natural gas include its higher abundance and lower cost compared to other fossil fuels.

[0006] Natural gas engines produce significantly lower PM and NO emissions compared to large and small diesel engines. x These engines emit up to 95% and 70% less emissions, respectively. However, the exhaust gases produced by NG engines often contain a significant amount of methane (the so-called "methane slip"). Regulations limiting emissions from these engines currently include Euro VI and the U.S. Environmental Protection Agency (EPA) Greenhouse Gas Act. These impose limits on emissions of methane, nitrogen oxides (NOx), and particulate matter (PM).

[0007] The two main operating modes used in methane-fueled engines are stoichiometric conditions (λ=1) and lean combustion conditions (λ≧1.3). Palladium-based catalysts are well known as the most active type of catalyst for methane oxidation under both conditions. Regulated emission limits for both stoichiometric and lean combustion compressed natural gas engines can be met by applying either a palladium-rhodium three-way catalyst (TWC) or a platinum-palladium oxidation catalyst, respectively.

[0008] The development of this Pd-based catalyst technology depends on overcoming challenges related to cost and catalyst deactivation due to degradation over time caused by sulfur, water, and heat.

[0009] Methane is the least reactive hydrocarbon, requiring high energy to cleave its primary CH bond. The ignition temperature of alkanes generally decreases as the fuel-air ratio increases and as the hydrocarbon chain length, which correlates with CH bond strength, increases. Pd-based catalysts are known to have a higher wright-off temperature for methane conversion ("wright-off temperature" refers to the temperature at which the conversion rate reaches 50%) than other hydrocarbons.

[0010] When operating under stoichiometric conditions (λ=1), the TWC is used as an effective and cost-effective post-treatment system for burning methane. Due to the very low reactivity of this hydrocarbon and catalyst deactivation by thermal and chemical effects, 200 gft -3 Most binary metal Pd-Rh catalysts with high total platinum group metal (pgm) loads exceeding 100% are required for high levels of methane conversion to meet end-of-life total hydrocarbon (THC) regulations. The use of high pgm loads improves total HC conversion rates in stoichiometric CNG engines. However, high methane conversion rates can be achieved with relatively low pgm loads based on engine calibration, i.e., by controlling the air-fuel ratio to operate near or richer than stoichiometric levels. Pgm loads can also be modified to comply with local legal requirements regarding methane and non-methane conversion.

[0011] NO x The reduction of methane and the oxidation of methane are also more difficult under highly oxidative conditions. For lean-burn CNG applications, a high total pgm load (200 gft) is required for methane combustion at lower temperatures. -3 Pd-Pt is required in the super(super) state. Unlike stoichiometric engines, NO is required in the presence of excess oxygen. x To enable reduction, a reducing agent must also be injected into the exhaust flow. This is usually in the form of ammonia (NH3), and therefore lean combustion applications require a completely different catalytic system than stoichiometric applications, where efficient NO x Reduction can be achieved using CO or HC under slightly rich or stoichiometric conditions.

[0012] Due to the unreactive (or low-reactive) properties of methane at low temperatures, increased methane emissions occur during cold starts and idle periods, primarily in lean combustion where exhaust temperatures are below stoichiometric levels. To improve the reactivity of methane at lower temperatures, one option is to use a higher pgm loading, but this increases costs.

[0013] Natural gas catalysts, particularly Pd-based catalysts, can suffer from poisoning by water (5-12%) and sulfur (SO2 less than 0.5 ppm in lubricating oil), especially under dilute conditions, which leads to a dramatic decrease in catalyst conversion rate over time. Deactivation by water is evident due to the formation of hydroxyls, carbonates, formates, and other intermediates on the catalyst surface. Activity is reversible and can be fully restored once the water is removed. However, this is impractical because methane combustion feedstocks always contain high levels of water due to the high H content in methane.

[0014] H2O can be either an inhibitor or an accelerator, depending on the air-fuel ratio, i.e., λ. Under stoichiometric and reducing conditions, and under conditions where λ is greater than 1, H2O can act as an accelerator for the oxidation of hydrocarbons by steam reforming in both CNG and gasoline engines. However, in lean-burn CNG operating at λ greater than 1, H2O acts as an inhibitor of methane oxidation. Understanding the water inhibitory effect and designing catalysts that are more tolerant of the presence of H2O is crucial. This allows for improvements when attempting to control methane emissions from lean-burn CNG.

[0015] Although sulfur levels in engine exhaust are very low, Pd-based catalysts are significantly deactivated upon sulfur exposure due to the formation of stable sulfates. Regenerating the catalyst to restore activity after sulfur poisoning is difficult and typically requires high temperatures, rich fuel mixtures, or both. This is easily achievable in stoichiometric operation but more difficult in lean combustion. Lean combustion vehicles operate at much higher air-fuel ratios than stoichiometric vehicles and require much higher concentrations of reducing agent injection to switch to rich fuel mixtures. Thermal deactivation resulting from high levels of misfires due to inadequate engine transient control and ignition systems destroys the catalyst, leading to correspondingly high exhaust emissions.

[0016] Palladium-containing catalysts are deactivated under both dilute and analogic conditions, but sulfur poisoning has a more dramatic impact than thermal degradation over time in dilute operation. Sulfur poisoning can be mitigated by adding a small amount of Pt to the Pd catalyst. This is because sulfur inhibition due to palladium sulfate formation can be significantly reduced by the addition of Pt. However, the addition of Pt further increases costs.

[0017] U.S. Patent Application Publication No. 2016 / 0236147 relates to a catalytic material for treating exhaust gases produced by a natural gas engine, the catalytic material comprising a siliceous zeolite having a content of 0.20 mol% or less of heteroatoms (T atoms). The siliceous zeolite may optionally contain germanium in an amount of about 10 mol% or less. The contents of this document are incorporated herein by reference.

[0018] Therefore, there is a need to provide improved systems for natural gas combustion and exhaust gas treatment to reduce methane emissions by addressing catalyst deactivation due to degradation over time caused by sulfur, water, and heat, without increasing catalyst costs. The object of the present invention is to address this problem, address the shortcomings associated with the prior art, or at least provide a commercially useful alternative. [Overview of the project]

[0019] According to the first aspect, A catalytic material for treating exhaust gases produced by a natural gas engine, wherein the catalytic material comprises a molecular sieve and a platinum group metal (PGM) supported on the molecular sieve. The molecular sieve has a skeleton containing silicon, oxygen, and germanium, and contains a heteroatom T atom of about 0.20 mol% or less. A catalytic material is provided in which germanium is present in an amount of 15-20 mol%.

[0020] The inventors have unexpectedly found that this catalyst material with a germanium content of 15-20 mol% has an advantageous oxidation activity towards methane, especially when methane is part of an exhaust gas containing excess oxygen. This catalyst material can achieve a high methane conversion efficiency at a relatively low temperature compared to conventional oxidation catalysts. The catalyst material has good thermal stability and on-stream stability in the presence of a gas mixture and steam.

[0021] The catalyst material of the present invention exhibits surprisingly good oxidation activity towards methane. It can also have a low methane light-off temperature. It may not be necessary to heat the catalyst material to a high temperature to achieve sufficient methane conversion activity.

[0022] Another advantage of the catalyst material of the present invention is that it has good thermal stability, especially under hydrothermal conditions (i.e., in the presence of steam). When the catalyst material is used at a relatively high temperature, the oxidation activity of the catalyst material towards methane does not significantly decrease.

[0023] A further advantage provided by the catalyst material of the present invention is that at a relatively low temperature (e.g., below 500 °C), the on-stream activity in the presence of steam does not decrease as observed in alumina-supported catalysts.

[0024] In the following sections, different aspects / embodiments are defined in more detail. Each aspect / embodiment so defined can be combined with any other aspect / embodiment or aspects / embodiments unless otherwise explicitly indicated. In particular, any feature indicated as being preferred or advantageous can be combined with any other feature or features indicated as being preferred or advantageous.

[0025] The present invention relates to a catalyst material for treating exhaust gas generated by a natural gas engine. That is, the catalyst material is for the catalytic treatment of exhaust gas from a natural gas combustion engine and for converting or transforming the components of the gas before releasing the components into the atmosphere to meet exhaust gas regulations. When natural gas is burned, both carbon dioxide and water are thereby produced, in which case the exhaust gas also contains an amount of additional methane (and other short-chain hydrocarbons) that needs to be catalytically removed before the exhaust gas is released into the atmosphere. The exhaust gas also typically contains significant amounts of water and sulfur that can accumulate and deactivate the catalyst.

[0026] In mobile applications, natural gas combustion can be configured to operate in a lean or stoichiometric configuration. "Mobile applications" means that the system can generally be suitable for use in an automobile or other vehicle (e.g., an off-road vehicle), and in such a system, there can be changes in fuel supply and demand during operation in response to operator requirements such as acceleration. In mobile applications, it is generally possible to temporarily operate the system in a rich mode, which is associated with a significant increase in temperature that helps to burn off sulfur that contaminates the catalyst and remove accumulated water.

[0027] In stationary systems, natural gas combustion can also be configured to operate under lean conditions or stoichiometric conditions. Examples of stationary systems include gas turbines and power generation systems, and in such systems, the combustion conditions and fuel composition are generally kept constant over long operating times. This means that there are fewer opportunities for a regeneration process to remove sulfur and moisture contaminants compared to mobile applications. Therefore, the benefits described herein can be particularly beneficial for stationary applications. That is, it is particularly desirable to provide a catalyst with high sulfur and moisture resistance when the opportunity to regenerate the catalyst is limited.

[0028] The above "dilute" and "stoichiometric" systems are described as "transport" and "stationary," but it should be understood that both system types can be used across a range of different applications.

[0029] The catalyst material comprises a molecular sieve and a platinum group metal (PGM) supported on the molecular sieve. When the PGM includes palladium (Pd), excellent oxidation activity can be obtained. Preferably, the platinum group metal (PGM) is selected from the group consisting of palladium (Pd) and combinations of platinum (Pt) and palladium (Pd). The total amount of palladium may be 0.1 to 20% by weight, preferably 0.2 to 15% by weight, and more preferably 0.5 to 10% by weight.

[0030] When the platinum group metal (PGM) is a combination of platinum (Pt) and palladium (Pd), the combination of Pt and Pd can be selected from the group consisting of separately supported Pt and Pd, a mixture of Pt and Pd, an alloy of Pt and Pd, and both a mixture and an alloy of Pt and Pd. When the PGM is separately supported Pt and Pd, the Pt particles and Pd particles are supported on separate parts of the molecular sieve. The mixture or alloy of Pt and Pd preferably consists of two different metals.

[0031] Preferably, the molecular sieve contains a platinum group metal (i.e., as defined above) as the sole transition metal, and preferably contains only a platinum group metal (i.e., there may be no other platinum group metals other than those explicitly enumerated).

[0032] The catalyst material may preferably consist essentially of (i) a platinum group metal (PGM) and / or an oxide thereof, and (ii) a molecular sieve as defined herein, wherein the platinum group metal (PGM) is selected from the group consisting of platinum (Pt), palladium (Pd), and combinations of platinum (Pt) and palladium (Pd).

[0033] PGMs are supported on molecular sieves. In this context, the term "supported" refers to PGMs associated with the molecular sieve. Typically, PGMs associate with the silanol groups of the molecular sieve (e.g., as ionic associations or covalent associations). While not theoretically bound, it is thought that active PGM sites associate with silanol groups, such as silanol nest sites, and / or terminal Si-OH (or Si-O-) groups that may be present on the outer surface and / or within cavities of the molecular sieve.

[0034] A portion of the PGM may be located inside the pores of the molecular sieve. The catalyst material may have at least 1% by weight, preferably at least 5% by weight, and more preferably at least 10% by weight of the PGM in the catalyst material that is located inside the pores of the molecular sieve. The amount of PGM inside the pores of the molecular sieve can be determined using the prior art or by the method described in SAE 2013-01-0531.

[0035] The catalyst material may have PGM located within the pores of the molecular sieve in an amount of 75% by weight or less, preferably 50% by weight or less (of the amount of PGM in the catalyst material).

[0036] Molecular sieves have a skeleton containing silicon, oxygen, and germanium, and contain approximately 0.20 mol% or less of heteroatoms, specifically T atoms.

[0037] As is known in the art, the term "T atom" is an abbreviation for "tetracoordinate atom" present in the molecular sieve skeleton.

[0038] As used herein in the context of "T atom," the term "heteroatom" refers to an atom that is not silicon, not germanium, and not oxygen (i.e., a non-silicon, non-germanium, non-oxygen heteroatom). A molecular sieve may have a framework containing one or more T atoms which are heteroatoms. The heteroatoms may be selected from the group consisting of, for example, aluminum (Al), boron (B), gallium (Ga), titanium (Ti), zinc (Zn), iron (Fe), vanadium (V), and any two or more combinations thereof. More preferably, the heteroatoms are selected from the group consisting of aluminum (Al), boron (B), gallium (Ga), titanium (Ti), zinc (Zn), iron (Fe), and any two or more combinations thereof.

[0039] Preferably, the molecular sieve has a framework essentially composed of silicon, oxygen, germanium, and a heteroatom T atom. More preferably, the molecular sieve may have a framework essentially composed of silicon, oxygen, and germanium (for example, as constituent atoms of the framework), the amount of germanium as defined herein (for example, the content of the heteroatom T atom is 0.00 mol%).

[0040] The molecular sieve may preferably contain less than about 0.17 mol%, more preferably less than about 0.15 mol%, for example less than about 0.15 mol%, and even more preferably less than about 0.12 mol% (for example less than about 0.12 mol%) of heteroatomic T atoms.

[0041] Optionally, the molecular sieve may contain a heteroatom T atom in an amount of about 0.001 mol% or more, preferably about 0.010 mol% or more, and more preferably about 0.020 mol% or more.

[0042] In some cases, molecular sieves do not need to contain a heteroatom (i.e., molecular sieves do not

[0043] Germanium is present in molecular sieves in an amount of 15-20 mol%, preferably 16-18 mol%.

[0044] Molecular sieves can be microporous or mesoporous. According to the IUPAC definitions of "microporous" and "mesoporous" (see Pure & Appl., 66(8), (1994), 1739-1758), microporous molecular sieves have pores with a diameter of less than 2 nm, and mesoporous molecular sieves have pores with a diameter of 2 nm to 50 nm.

[0045] Molecular sieves can be mesoporous. When molecular sieves are mesoporous molecular sieves, they can typically be selected from the group consisting of MCM-41, MCM-48, MCM-50, FSM-16, AMS, SBA-1, SBA-2, SBA-3, SBA-15, HMS, MSU, SBA-15, and KIT-1.

[0046] Typically, molecular sieves are microporous, especially when the molecular sieve is microporous, and include AEI, AFI, AFX, ANA, AST, ASV, ATS, BCT, BEA, BEC, BOF, BOG, BRE, CAN, CDO, CFI, CGS, CHA, -CHI, CON, DAC, DDR, DOH, DON, EAB, EDI, EEI, EMT, EON, EPI, ERI, ESV, ETR, EUO, FAR, FAU, FER, GON, HEU, IFR, IFW, IFY, IHW, IMF, IRN, IRR, -IRY, ISV, ITE, ITG, ITH, ITN, ITR, ITT, ITV, ITW, IWR, IWS, IWV, IWW, JOZ, KFI, LEV, LOV, LTA, LTF, M AZ, MEI, MEL, MEP, MER, MFI, MFS, MOR, MOZ, MRE, MSE, MSO, MTF, MTN, MTT, MTW, MVY, MWW, NAB, NES, NON, NSI, OBW, OFF, OKO, PAU, PCR, PHI, POS, RHO, -RON, RRO, RSN, RTE, RTH, RUT, RWR, RWY, SE has a skeleton type selected from the group consisting of W, SFE, SFF, SFG, SFH, SFN, SFS, SFV, SFW, SGT, SOD, SOF, SSF, -SSO, SSY, STF, STI, STO, STT, STW, -SVR, SVV, SZR, TON, TUN, UFI, UOS, UOV, UTL, UWY, VET, VNI, and VSV. Each of the three-letter codes mentioned above represents a skeleton type in accordance with the "IUPAC Commission on Zeolite Nomenclature" and / or the "Structure Commission of the International Zeolite Association".

[0047] The molecular sieve is preferably a zeolite. Zeolites can also be called silica-containing zeolites, such as siliceous zeolites. Zeolites may also be germanosilicate zeolites. Therefore, the zeolite may be a siliceous (i.e., high silica-containing) zeolite having low content of aluminum (Al), boron (B), gallium (Ga), and titanium (Ti), and optionally, T atoms which are heteroatoms such as zinc (Zn) and iron (Fe).

[0048] Silica zeolite or pure silica zeolite may be a zeolite selected from the following table.

[0049] As is known in the art, siliceous zeolites have a framework containing SiO4 tetrahedra.

[0050] [Table 1]

[0051] Molecular sieves, especially when the molecular sieve is zeolite, include AEI, ANA, ATS, BEA, CDO, CFI, CHA, CON, DDR, ERI, FAU, FER, GON, IFR, IFW, IFY, IHW, IMF, IRN, -IRY, ISV, ITE, ITG, ITN, ITR, ITW, IWR, IWS, IWV, IWW, JOZ, LTA, LTF, MEL, MEP, MFI, MRE, MS. The molecular sieve or zeolite has a skeleton type selected from the group consisting of E, MTF, MTN, MTT, MTW, MVY, MWW, NON, NSI, RRO, RSN, RTE, RTH, RUT, RWR, SEW, SFE, SFF, SFG, SFH, SFN, SFS, SFV, SGT, SOD, SSF, -SSO, SSY, STF, STO, STT, -SVR, SVV, TON, TUN, UOS, UOV, UTL, UWY, VET, and VNI. More preferably, the molecular sieve or zeolite has a skeleton type selected from the group consisting of BEA, CDO, CON, MEL, MWW, MFI, and FAU, and even more preferably, the skeleton type is selected from the group consisting of BEA and MFI. Most preferably, the zeolite has an MFI skeleton.

[0052] Zeolites can be selected from small-pore zeolites (i.e., zeolites with a maximum ring size of 8 tetrahedral atoms), medium-pore zeolites (i.e., zeolites with a maximum ring size of 10 tetrahedral atoms), and large-pore molecular sieves (i.e., zeolites with a maximum ring size of 12 tetrahedral atoms).

[0053] Various methods for preparing molecular sieves, particularly zeolites, with high silica content (e.g., high SAR), as well as specific skeleton types and pore diameters, are known in the art. Numerous methods for preparing transition metals, such as platinum group metals, supported on zeolites are also known. See, for example, International Publication No. 2012 / 166868.

[0054] Molecular sieves or zeolites may be microporous molecular sieves or zeolites. Microporous molecular sieves or zeolites preferably have a skeleton type selected from the group consisting of AEI, AFX, ANA, CDO, CHA, DDR, EAB, EDI, EPI, ERI, IHW, ITE, ITW, KFI, LEV, MER, NSI, PAU, PHI, RHO, RTH, UFI, and VNI. More preferably, microporous molecular sieves or zeolites have a skeleton type that is CHA, CDO, or DDR.

[0055] The molecular sieve or zeolite may be a medium-pore molecular sieve or zeolite. The medium-pore molecular sieve or zeolite preferably has a skeleton type selected from the group consisting of MFI, MEL, MWW, and EUO. More preferably, the medium-pore molecular sieve has a skeleton type selected from the group consisting of MFI, MEL, and MWW, for example, a skeleton type that is MFI.

[0056] The molecular sieve or zeolite may be a large-pore molecular sieve or zeolite. The large-pore molecular sieve or zeolite preferably has a skeleton type selected from the group consisting of AFI, CON, BEA, FAU, MOR, and EMT. More preferably, the large-pore molecular sieve or zeolite has a skeleton type selected from the group consisting of AFI, BEA, CON, and FAU, for example, a skeleton type that is BEA.

[0057] Preferably, the molecular sieve or zeolite is solid. More preferably, the molecular sieve or zeolite is in the form of fine particles.

[0058] When molecular sieves or zeolites are in particulate form, they typically have a D50 of 0.1–20 microns (e.g., 5–15 microns), or 0.2–15 microns (e.g., 0.2–10 microns, or 7.5–12.5 microns). A D50 of 0.5–10 microns is preferable. To avoid misunderstanding, D50 (i.e., median particle size) measurements can be obtained by laser diffraction particle size analysis, for example, using a Malvern Mastersizer 2000. The measurement is a volume-based technique (i.e., D50 is sometimes called DV50 (or D(v,0.50)) and the particle size distribution is determined by applying a mathematical Mie theory model.

[0059] It has been found that catalyst materials containing molecular sieves or zeolites with a small particle size distribution (i.e., a lower D50) exhibit higher activity and hydrothermal endurance than catalyst materials containing molecular sieves or zeolites with a larger particle size distribution. While not theoretically bound, it is thought that the silanol group sites of molecular sieves or zeolites become more accessible to platinum group metals as the particle size of the molecular sieves or zeolites decreases. However, catalyst materials with a larger particle size distribution may exhibit better endurance.

[0060] Preferably, the molecular sieve has a SAR of 1200 or more. It may be preferable that the SAR is 1300 or more, for example 1500 or more (for example 1700 or more), and more preferably 2000 or more, for example 2200 or more. In particular, when the heteroatom T atom is aluminum, the molecular sieve or zeolite may have a SAR of 1200 or more. It may be preferable that the SAR is 1300 or more, for example 1500 or more (for example 1700 or more), and more preferably 2000 or more, for example 2200 or more.

[0061] The catalyst material of the present invention is particularly advantageous when the zeolite has a large amount of silanol groups. Preferably, the molecular sieve contains at least 0.010 mmol / g of silanol groups. More preferably, the molecular sieve contains at least 0.020 mmol / g of silanol groups (e.g., 0.030 mmol / g of silanol groups). The amount of silanol groups can be measured using a potassium uptake method, such as the potassium uptake method described in the examples. It has been found that advantageous oxidation activity can be obtained when the molecular sieve, especially the zeolite, contains a considerable number of silanol groups. It is preferable that the molecular sieve or zeolite contains silanol groups and that the silanol groups have a decomposition onset temperature of 500°C or higher. The decomposition onset temperature can be measured by differential scanning calorimetry.

[0062] Molecular sieves or zeolites having silanol groups can be obtained by removing an organic template during the synthesis of the molecular sieve or zeolite, or by removing heteroatoms (e.g., Al, B, Ga, Zn, etc.) from the molecular sieve or zeolite by post-synthesis treatment. In some cases, the silanol group may be an intrinsic part of the molecular sieve or zeolite skeleton.

[0063] The presence of silanol groups can be determined using FTIR spectroscopy.

[0064] In a further embodiment, a catalyst article is provided which contains the catalyst material described herein in or on a substrate.

[0065] Catalyst articles are components suitable for use in exhaust gas systems. Typically, such articles are honeycomb monoliths, sometimes referred to as "bricks." They have a high surface area configuration suitable for bringing the gas to be processed into contact with the catalytic material to transform or convert the components of the exhaust gas. Other forms of catalyst articles are also known, including plate configurations and wrapped metal catalyst substrates. While the catalyst articles described herein are suitable for use in all of these known forms, the honeycomb monolith form is particularly preferred because it offers a good balance of cost and ease of manufacture.

[0066] Catalyst articles are for the treatment of exhaust gases from natural gas combustion engines. Specifically, catalyst articles are for the catalytic treatment of exhaust gases from natural gas combustion engines, converting or transforming components to meet exhaust gas regulations before releasing the gas components into the atmosphere. When natural gas is burned, both carbon dioxide and water are produced, but the exhaust gases also contain additional methane (and other short-chain hydrocarbons) in amounts that need to be catalytically removed before the exhaust gases are released into the atmosphere. Exhaust gases also typically contain significant amounts of water and sulfur, which, if accumulated, can deactivate the catalyst.

[0067] Catalyst articles can be prepared by applying a wash coat to the surface of a substrate and / or by extrusion molding. Catalyst articles can be manufactured by preparing a wash coat using methods known in the art and applying the wash coat to a substrate (see, for example, International Publications 99 / 47260, 2011 / 080525, and 2014 / 195685). Methods for producing catalyst articles by extrusion molding are also known (see, for example, our International Publication 2011 / 092519).

[0068] The catalyst material may be disposed on or supported on the substrate (for example, the catalyst material may be applied to the surface of the substrate in the form of a wash coat). The catalyst material may be disposed directly on the substrate (i.e., the catalyst material is in contact with the surface of the substrate). Additionally or alternatively, the catalyst material may be dispersed in the substrate (for example, the catalyst material may be part of the extruded product used to form the substrate). Thus, the substrate is an extruded solid containing the catalyst material.

[0069] When the catalyst material is dispersed in a substrate (for example, when the oxidation catalyst is an extruded product), the resulting oxidation catalyst may perform better than an oxidation catalyst in which the same catalyst material is wash-coated onto a substrate. When the catalyst material is dispersed in a substrate (for example, when the oxidation catalyst is an extruded product), it may be possible to rapidly desulfate the oxidation catalyst, and moreover, it may have superior on-stream stability (e.g., good water and oxygen resistance) compared to an oxidation catalyst produced by wash-coating the catalyst material onto a substrate.

[0070] The extruded solid may contain, or essentially consist of, (i) 5 to 95% by weight of a catalyst material and (ii) 5 to 95% by weight of at least one component selected from the group consisting of binder / matrix components, inorganic fibers, and combinations thereof.

[0071] The binder / matrix components can be selected from the group consisting of cordierite, nitrides, carbides, borides, spinel, refractory metal oxides, lithium aluminosilicate, zircon, and any two or more mixtures thereof.

[0072] The refractory metal oxide may be selected from the group consisting of optionally doped alumina, silica, titania, zirconia, and any two or more mixtures thereof. A suitable source of silica, such as clay, is described in U.S. Patent Application Publication 2014 / 0065042A1.

[0073] Inorganic fibers may be selected from the group consisting of carbon fibers, glass fibers, metal fibers, boron fibers, alumina fibers, silica fibers, silica-alumina fibers, silicon carbide fibers, potassium titanate fibers, aluminum borate fibers, and ceramic fibers.

[0074] When the catalyst material is dispersed in a substrate (for example, when the substrate is an extruded solid containing the catalyst material), the substrate typically has a porosity of 35–75%. The porosity of the substrate can be determined using conventional methods known in the art, such as mercury porosimetry.

[0075] The catalyst article may have a total filling amount of catalyst material of 0.3 to 5.0 g per cubic inch, preferably 0.4 to 3.8 g per cubic inch, more preferably 0.5 to 3.0 g per cubic inch (e.g., 1 to 2.75 g per cubic inch or 0.75 to 1.5 g per cubic inch), and even more preferably 0.6 to 2.5 g per cubic inch (e.g., 0.75 to 2.3 g per cubic inch).

[0076] The substrate may be a flow-through substrate or a filter substrate. If the substrate is a monolith, the equipment may be a flow-through monolith or a filtering monolith. The substrate may also be a honeycomb monolith.

[0077] Flow-through substrates typically include honeycomb substrates (e.g., metal or ceramic honeycomb substrates) having multiple channels that extend through them and open at both ends.

[0078] The filtering substrate generally includes multiple inlet channels and multiple outlet channels, where the inlet channels are open at the upstream end (i.e., the exhaust gas inlet side) and closed or sealed at the downstream end (i.e., the exhaust gas outlet side), and the outlet channels are closed or sealed at the upstream end and open at the downstream end, with each inlet channel separated from the outlet channel by a porous structure.

[0079] If the substrate is a filtering substrate, it is preferable that the filtering substrate is a wall flow filter. In a wall flow filter, each inlet channel is alternately separated from the outlet channel by a porous wall structure, and vice versa. The inlet and outlet channels are preferably arranged in a honeycomb pattern. If a honeycomb pattern is present, it is preferable that channels adjacent to the inlet channel perpendicularly and laterally are closed at their upstream ends, and vice versa (i.e., channels adjacent to the outlet channel perpendicularly and laterally are closed at their downstream ends). When viewed from either end, the alternately closed and open ends of the channels give the appearance of a chessboard.

[0080] In principle, the substrate can be of any shape or size. However, the shape and size of the substrate are usually selected to optimize the exposure of the catalytic material in the catalyst to the exhaust gas.

[0081] The substrate may have, for example, a tubular, fibrous, or fine particle form. Examples of suitable supporting substrates include monolithic honeycomb cordierite type substrates, monolithic honeycomb SiC type substrates, layered fiber or knitted fabric type substrates, foam type substrates, cross-flow type substrates, metal wire mesh type substrates, metal porous type substrates, and ceramic particle type substrates.

[0082] In a further embodiment, a combustion and exhaust system for compressed natural gas, (i) Natural gas combustion engines, and (ii) A system is provided comprising an exhaust treatment system including an intake port for receiving exhaust gases from a combustion engine and a catalytic article described herein, arranged to receive and treat the exhaust gases.

[0083] A natural gas combustion engine is an engine used to burn natural gas. Preferably, a natural gas combustion engine is a stationary engine, preferably a gas turbine or power generation system. In stationary applications, a natural gas combustion engine may also be configured to operate under lean or stoichiometric conditions. In such systems, combustion conditions and fuel composition are generally kept constant over long operating times. This means there are fewer opportunities to have a regeneration step to remove moisture contaminants compared to mobile applications. Therefore, the benefits described herein may be particularly beneficial for stationary applications. Specifically, it is particularly desirable to provide a catalyst with high moisture resistance when opportunities for catalyst regeneration are limited. It should be understood that both lean and stoichiometric system types can be used across a range of different applications.

[0084] An exhaust treatment system is a system suitable for treating exhaust gases from a combustion engine. The exhaust treatment system comprises an intake port for receiving exhaust gases from the combustion engine and a catalytic converter positioned to receive and treat the exhaust gases. [Brief explanation of the drawing]

[0085] The present invention will be further described in relation to the following non-limiting figures. [Figure 1] This demonstrates the improved water heat durability achieved by the present invention. [Examples]

[0086] The present invention will now be further described in relation to the following non-limiting examples in which powder catalyst samples are prepared.

[0087] Example 1 The catalyst of Example 1 has a palladium-containing MFI zeolite containing 0.1 mol% aluminum. The palladium content is 3% by weight.

[0088] The catalyst for Example 1 was prepared by impregnating a powder sample of siliceous MFI zeolite containing 0.1 mol% aluminum with a palladium nitrate solution using a conventional simple wetting technique. After impregnation, the sample was dried at 80°C for 5 hours and then calcined in a static oven at 500°C in air for 2 hours.

[0089] Example 2 The catalyst of Example 2 has a palladium-containing MFI zeolite containing 17 mol% germanium. The palladium content is 3% by weight.

[0090] The catalyst for Example 2 was prepared by impregnating a powder sample of siliceous MFI zeolite containing 17 mol% germanium with a palladium nitrate solution using a conventional simple wetting technique. After impregnation, the sample was dried at 80°C for 5 hours and then calcined in a static oven at 500°C in air for 2 hours.

[0091] Example 3 The catalyst of Example 3 has a palladium-containing MFI zeolite containing 2 mol% titanium. The palladium content is 3% by weight.

[0092] The catalyst for Example 3 was prepared by impregnating a powder sample of siliceous MFI zeolite containing 2 mol% titanium with a palladium nitrate solution using a conventional simple wetting technique. After impregnation, the sample was dried at 80°C for 5 hours and then calcined in a static oven at 500°C in air for 2 hours.

[0093] Example 4 The catalyst of Example 4 has a palladium-containing MFI zeolite containing 5 mol% aluminum. The palladium content is 3% by weight.

[0094] The catalyst for Example 4 was prepared by impregnating a powder sample of siliceous MFI zeolite containing 5 mol% aluminum with a palladium nitrate solution using a conventional simple wetting technique. After impregnation, the sample was dried at 80°C for 5 hours and then calcined in a static oven at 500°C in air for 2 hours.

[0095] Example 5 The catalyst of Example 5 has palladium supported on alumina. The palladium content is 3% by weight.

[0096] The catalyst in Example 5 was prepared by impregnating an alumina powder sample with a palladium nitrate solution using a conventional simple wetting technique. After impregnation, the sample was dried at 80°C for 5 hours and then calcined in a static oven at 500°C in air for 2 hours.

[0097] The methane conversion activity of fresh and degraded powder samples of the catalysts from Examples 1-5 was tested using a synthetic catalyst activity test (SCAT) by flowing a gas mixture containing 1120 ppm CH4, 65 ppm C2H6, 800 ppm CO, 9% O2, 10% H2O, 6% CO2, and the remainder N2 over the catalyst at a space velocity of 100,000 h⁻¹ over a certain temperature range (heating rate of 5°C per minute from 250 to 450°C). Degraded catalysts were obtained by degrading them over time in 10% H2O air at a temperature of 700°C for 40 hours.

[0098] As shown in Figure 1, using germanium in an amount of 17 mol% results in a better fresh methane conversion rate than using alumina or titania, or using an alumina support material, in palladium-containing MFI zeolites. Furthermore, the fresh activity and degraded activity over time of such germanium-containing catalysts are very similar, thereby demonstrating that the presence of germanium in a molecular sieve at an amount of 17 mol% improves the hydrothermal durability of palladium-containing zeolites. Improving the hydrothermal durability of palladium-containing zeolites is particularly advantageous when palladium-containing zeolites are used to treat exhaust gases from natural gas engines, as these exhaust gases contain a high amount of moisture.

[0099] When used herein, the singular forms “a,” “an,” and “the” include multiple referents unless the context clearly indicates otherwise. The use of the term “comprising” is intended to be interpreted as including such features but not excluding other features, and is intended to include a selection of features that are necessarily limited to those described. In other words, the term also includes the limitations of “essentially consisting of” (intended to mean that certain further components may exist on the condition that they do not substantially affect the essential properties of the described feature) and “consisting of” (intended to mean that if the components are expressed as percentages by their proportions, these add up to 100%, while explaining any unavoidable impurities, but not including any other features).

[0100] Terms such as “first,” “second,” etc., may be used herein to describe various elements, layers, and / or parts, but it should be understood that elements, layers, and / or parts should not be limited by these terms. These terms are used only to distinguish one element, layer, or part from another or further elements, layers, or parts. It should be understood that the term “above” is intended to mean “directly above,” such that there is no intervening layer between one material said to be “above” another material. Spatially relative terms such as “under,” “below,” “beneath,” “lower,” “over,” “above,” and “upper” may be used herein to facilitate descriptions of the relationship between one element or feature and another element or feature. It should be understood that spatially relative terms are intended to encompass different orientations of a device in use or operation, in addition to the orientation shown in the drawings. For example, if the device described herein is inverted, elements described as “below” or “downward” other elements or features will be oriented “above” or “upward” other elements or features. Thus, the exemplary term “below” can encompass both upward and downward orientations. The device may be oriented in a different way, and the spatially relative descriptive terms used herein will be interpreted accordingly.

[0101] The detailed description above is provided for illustrative and illustrative purposes only and is not intended to limit the scope of the appended claims. Many modifications of the currently preferred embodiments shown herein will be obvious to those skilled in the art and remain within the scope of the appended claims and their equivalents.

Claims

1. A catalytic material for treating exhaust gases produced by a natural gas engine, wherein the catalytic material comprises a molecular sieve and a platinum group metal (PGM) supported on the molecular sieve. The molecular sieve has a skeleton containing silicon, oxygen, and germanium, and contains 0.001 to 0.20 mol% or less of a heteroatom T atom. The aforementioned germanium is present in an amount of 15 to 20 mol%, A catalyst material in which the heteroatom T atom is selected from the group consisting of aluminum (Al), boron (B), gallium (Ga), titanium (Ti), zinc (Zn), iron (Fe), vanadium (V), and any two or more combinations thereof.

2. The catalyst material according to claim 1, wherein the skeleton consists of silicon, oxygen, germanium, and a T atom which is a heteroatom.

3. The catalyst material according to claim 1, wherein the molecular sieve is a zeolite.

4. The catalyst material according to claim 3, wherein the molecular sieve is an MFI zeolite.

5. The catalyst material according to claim 1, wherein the total amount of the platinum group metal (PGM) is 0.01 to 30% by weight.

6. The catalyst material according to claim 5, wherein the platinum group metal (PGM) is selected from the group consisting of palladium (Pd) and combinations of platinum (Pt) and palladium (Pd).

7. The catalyst material according to claim 6, wherein the total amount of palladium is 0.1 to 20% by weight.

8. The catalyst material according to claim 1, wherein the molecular sieve has a SAR of 1200 or more.

9. The catalyst material according to claim 1, wherein the molecular sieve contains at least 0.010 mmol / g of silanol groups.

10. A catalyst article comprising the catalyst material described in claim 1 on a substrate.

11. The catalyst article according to claim 10, wherein the catalyst material is provided on the substrate as a wash coat.

12. The amount of wash coat carried is 35.3 to 1766 g / m². ３ (1-50 g / ft) ３ The catalyst article according to claim 11, which is the same as the one described in claim 11.

13. A catalyst article comprising the catalyst material according to claim 1 dispersed in a substrate.

14. The catalyst article according to claim 10, wherein the substrate is a flow-through substrate or a filtering substrate.

15. A compressed natural gas combustion and exhaust system, (i) Natural gas combustion engine, and (ii) An exhaust treatment system comprising an intake port for receiving exhaust gas from the combustion engine, and a catalytic article according to claim 10, arranged to receive and treat the exhaust gas, A compressed natural gas combustion and exhaust system equipped with a compressed natural gas combustion and exhaust system.

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