Catalytic material for treating exhaust gases produced by a natural gas engine

Abstract

The 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, wherein the molecular sieve has a framework comprising silicon, oxygen, and germanium, and has a heteroatom T-atom content of < about 0.20 mol%, wherein the germanium is present in an amount of 15 mol% to 20 mol%. The invention also relates to a catalyst article and a compressed natural gas combustion and exhaust system.

Description

[0001] This invention relates to a catalytic material for treating exhaust gas produced by a natural gas engine, and more particularly to a catalytic material having improved methane oxidation activity and hydrothermal durability.

[0002] Natural gas is gaining increasing attention as an alternative fuel to gasoline and diesel fuels traditionally used in vehicles and stationary engines. Natural gas is primarily composed of methane (typically 70%-90%) with varying proportions of other hydrocarbons such as ethane, propane, and butane (up to 20% in some deposits) and other gases. It can be commercially produced from oil or gas fields and is widely used as a combustion energy source for power generation, industrial combined heat and power (CHP), and residential heating. It can also be used as vehicle fuel.

[0003] Natural gas can be used as a transport fuel in the form of compressed natural gas (CNG) and liquefied natural gas (LNG). CNG is stored in tanks at a pressure of 3600 psi (~248 bar) and has an energy density of about 35% of that of gasoline per unit volume. LNG has an energy density 2.5 times that of CNG and is primarily used in heavy-duty vehicles. It is cooled to a liquid state at -162°C, thus reducing its volume by 600 times, meaning that LNG is easier to transport than CNG. Bio-LNG can be an alternative to natural gas (fossil fuel), which is produced from biogas, generated through the anaerobic digestion of organic matter such as landfill waste or manure.

[0004] Natural gas offers numerous environmental benefits: it is a cleaner combustion fuel that typically contains fewer impurities, has a higher energy per carbon (Bti) than conventional hydrocarbon fuels, resulting in lower CO2 emissions (25% reduction in greenhouse gas emissions), and produces lower PM and NO emissions compared to diesel and gasoline. x Emissions. Biogas can further reduce these emissions.

[0005] Further drivers for the adoption of natural gas compared to other fossil fuels include its high abundance and low cost.

[0006] Compared to heavy-duty and light-duty diesel engines, natural gas engines emit less PM and NO. x Very low (as low as 95% and 70%, respectively). However, exhaust from NG engines typically contains significant amounts of methane (so-called "methane leaks"). Regulations currently limiting emissions from these engines include Euro VI and the U.S. Environmental Protection Agency (EPA) greenhouse gas regulations. These set emission limits for 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 conditions (λ ≥ 1.3). Palladium-based catalysts are well known to be the most active type of catalyst for methane oxidation under both conditions. By applying palladium-rhodium three-way catalysts (TWC) or platinum-palladium oxidation catalysts, emission limits for both stoichiometric and lean compressed natural gas engines can be met.

[0008] The development of this palladium-based catalyst technology depends on overcoming the challenges of cost and catalyst deactivation caused by sulfur, water, and thermal aging.

[0009] Methane is the least reactive hydrocarbon and requires high energy to break the primary C–H bond. The ignition temperature of alkanes typically decreases with increasing fuel-air ratio and hydrocarbon chain length, which is related to the C–H bond strength. It is well known that for Pd-based catalysts, the ignition temperature for methane conversion is higher than that for other hydrocarbons (where "ignition temperature" refers to the temperature at which 50% conversion is achieved).

[0010] When operated under stoichiometric conditions (λ = 1), TWC is used as an efficient and cost-effective aftertreatment system for methane combustion. Most bimetallic Pd-Rh catalysts have >200 gft –3 High total platinum group metals (pgm) loadings are required for high levels of methane conversion to meet end-of-life total hydrocarbon (THC) regulations, as these hydrocarbons are highly reactive and catalysts deactivate through thermal and chemical effects. Using high pgm loadings will increase the total HC conversion in stoichiometric CNG engines. However, based on engine calibration, high methane conversion can be achieved with relatively low pgm, i.e., by controlling the air-fuel ratio to operate near or above stoichiometry; pgm loadings can also vary according to regional legislative requirements regarding methane and non-methane conversion.

[0011] NO x The reduction and oxidation of methane are also more difficult under highly oxidizing conditions. For lean CNG applications, methane combustion at lower temperatures requires a high total pgm loading (>200 gft). –3 Pd-Pt. Unlike stoichiometric engines, this requires injecting a reducing agent into the exhaust stream to reduce NO in the presence of excess oxygen. x This is typically in the form of ammonia (NH3), therefore lean-burn applications require catalyst systems entirely different from stoichiometric catalyst systems, where efficient NO can be achieved using CO or HC under slightly enriched or stoichiometric conditions. x reduction.

[0012] Due to the nonreactivity (or poor reactivity) of methane at lower temperatures, methane emissions increase during cold starts and idling, primarily in lean-burn conditions where exhaust temperatures are below stoichiometric levels. One option to improve the reactivity of methane at lower temperatures is to use a high pgm loading, which increases costs.

[0013] Natural gas catalysts (especially Pd-based catalysts) can be poisoned by water (5%-12%) and sulfur (SO2 < 0.5 ppm in lubricating oil), particularly under lean conditions, leading to a sharp decline in catalyst conversion over time. Water-induced deactivation is significant due to the formation of hydroxyl groups, carbonates, formate esters, and other intermediates on the catalyst surface. This activity is reversible and can be fully restored if 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 act as either an inhibitor or a promoter, depending on the air-fuel ratio, λ. Under stoichiometric and reducing conditions, where λ > 1, H₂O can act as a promoter of hydrocarbon oxidation via steam reforming in both CNG and gasoline engines. However, for lean-burn CNG operating at λ > 1, H₂O acts as an inhibitor of methane oxidation. Understanding the inhibitory effect of water and designing catalysts that are more tolerant to the presence of H₂O is crucial. This will allow for improvements when attempting to control methane emissions from lean-burn CNG.

[0015] Although the sulfur content in engine exhaust is very low, Pd-based catalysts are significantly deactivated upon exposure to sulfur due to the formation of stable sulfates. Regenerating the catalyst after sulfur poisoning is challenging and typically requires high temperatures, rich operation, or both. This is easily achieved in stoichiometric operation but is more difficult in lean-burn vehicles. Lean-burn vehicles operate at much higher air-fuel ratios than stoichiometric vehicles and will require much higher concentrations of reducing agent to switch to rich operation. Thermal deactivation resulting from high levels of misfire events due to poor engine transient control and ignition systems damages the catalyst and consequently leads to high levels of exhaust emissions.

[0016] Palladium-containing catalysts deactivate under both lean and stoichiometric conditions, but sulfur poisoning has a more significant impact than thermal aging in lean operation. Sulfur poisoning can be improved by adding a small amount of Pt to the Pd catalyst. This is because the sulfur inhibition caused by the formation of palladium sulfate is significantly reduced upon adding Pt. However, the addition of Pt further increases the cost.

[0017] US2016 / 0236147 relates to a catalytic material for treating exhaust gas from a natural gas engine, the catalytic material comprising a silica zeolite having a heteroatom T-atom content of ≤0.20 mol%. The silica zeolite may optionally contain ≤about 10 mol% germanium. The contents of this document are incorporated herein by reference.

[0018] Therefore, it is desirable to provide an improved system for natural gas combustion and exhaust treatment to reduce methane emissions by suppressing catalyst deactivation (such as through sulfur, water, and thermal aging) without increasing catalyst costs. One object of the present invention is to address this problem, overcome the drawbacks associated with the prior art, or at least provide a commercially useful alternative.

[0019] Based on the first aspect, the following was provided:

[0020] A catalytic material for treating exhaust gas from a natural gas engine, the catalytic material comprising a molecular sieve and platinum group metals (PGMs) supported on the molecular sieve.

[0021] The molecular sieve has a framework comprising silicon, oxygen, and germanium, and has a heteroatom T-atom content of ≤0.20 mol%.

[0022] The germanium is present in an amount of 15 mol% to 20 mol%.

[0023] The inventors unexpectedly discovered that this catalyst, employing a germanium content of 15 mol% to 20 mol%, exhibits favorable oxidation activity for methane, particularly when methane is part of an exhaust gas containing excess oxygen. Compared to conventional oxidation catalysts, this catalyst achieves high methane conversion efficiency at relatively low temperatures. The catalyst also exhibits good thermal and operational stability in the presence of gas mixtures and water vapor.

[0024] The catalytic material of this invention exhibits surprisingly good oxidation activity for methane. It also possesses a low methane ignition temperature. Heating the catalytic material to a high temperature may not be necessary to achieve satisfactory methane conversion activity.

[0025] Another advantage of the catalytic material of the present invention is its good thermal stability, especially under hydrothermal conditions (i.e., in the presence of water vapor). When the catalytic material is used at relatively high temperatures, its oxidation activity for methane does not deteriorate significantly.

[0026] Another advantage provided by the catalytic material of the present invention is that, at relatively low temperatures (e.g., <500°C), the operating activity in the presence of water vapor does not decrease as observed in alumina-supported catalysts.

[0027] The different aspects / implementations are defined in more detail in the following paragraphs. Unless otherwise expressly stated to the contrary, each aspect / implementation so defined may be combined with any other aspect / implementation or multiple aspects / implementations. In particular, any feature indicated as preferred or advantageous may be combined with one or more other features indicated as preferred or advantageous.

[0028] This invention relates to a catalytic material for treating exhaust gas produced by natural gas engines. Specifically, the catalytic material is used to catalytically treat exhaust gas from natural gas combustion engines to convert or transform gaseous components to meet emission regulations before the gas is released into the atmosphere. When natural gas is burned, it produces carbon dioxide and water, but the exhaust gas also contains a certain amount of additional methane (and other short-chain hydrocarbons), which needs to be catalytically removed before being released into the atmosphere. The exhaust gas also typically contains significant amounts of water and sulfur, which can accumulate and deactivate the catalyst.

[0029] In mobile applications, natural gas combustion can be configured to operate in a lean or stoichiometric configuration. "Mobile application" refers to a system typically applicable to automobiles or other vehicles (e.g., off-road vehicles)—in which fuel supply and demand may vary during operation depending on operator requirements (such as acceleration). In mobile applications, the system can often be temporarily operated in a rich mode, which involves a significant increase in temperature, helping to burn off sulfur that poisons the catalyst and remove accumulated water.

[0030] In stationary systems, natural gas combustion can also be configured to operate under lean or stoichiometric conditions. Examples of stationary systems include gas turbines and power generation systems—in which combustion conditions and fuel composition typically remain constant over long operating periods. This means that opportunities for regeneration steps to remove sulfur and moisture contaminants are fewer compared to mobile applications. Therefore, the benefits described herein can be particularly advantageous for stationary applications. That is, when opportunities for catalyst regeneration are limited, a catalyst with high sulfur and moisture resistance is particularly desirable.

[0031] Although the aforementioned “dilute” and “stoichiometric” systems are described as “mobile” and “fixed”, it should be understood that both types of systems can be used in a range of different applications.

[0032] The catalytic material comprises a molecular sieve and a platinum group metal (PGM) supported on the molecular sieve. Excellent oxidation activity is obtained when the PGM contains palladium (Pd). 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 can be from 0.1% to 20% by weight, preferably from 0.2% to 15% by weight, more preferably from 0.5% to 10% by weight.

[0033] When the platinum group metals (PGM) are a combination of platinum (Pt) and palladium (Pd), the combination of Pt and Pd can be selected from the group consisting of: individually loaded Pt and Pd, mixtures of Pt and Pd, alloys of Pt and Pd, and both mixtures and alloys of Pt and Pd. When the PGM is individually loaded with Pt and Pd, the Pt and Pd particles are loaded at individual sites on the molecular sieve. Mixtures or alloys of Pt and Pd are preferably bimetallic.

[0034] Preferably, the molecular sieve contains a platinum group metal (i.e., as defined above) as the only transition metal, and more preferably, only a platinum group metal (i.e., no other platinum group metals exist besides those explicitly listed).

[0035] The catalytic material may preferably consist essentially of: (i) platinum group metals (PGMs) and / or their oxides; and (ii) molecular sieves as defined herein; wherein the platinum group metals (PGMs) are selected from the group consisting of platinum (Pt), palladium (Pd), and combinations of platinum (Pt) and palladium (Pd).

[0036] PGM is loaded onto the molecular sieve. In this context, the term "loaded" refers to PGM associated with the molecular sieve. Typically, the PGM is associated with the silanol groups of the molecular sieve (e.g., as ionic association or as covalent association). Without being bound by theory, it is believed that active PGM sites are associated with silanol groups (such as silanol nesting sites) and / or terminal Si-OH (or Si-O-) groups, which may be present on the outer surface and / or within the cavities of the molecular sieve.

[0037] Some PGM may be located within the pores of the molecular sieve. The catalytic material may have at least 1% by weight (i.e., the amount of PGM in the catalytic material) of PGM located within the pores of the molecular sieve, preferably at least 5% by weight, more preferably at least 10% by weight. The amount of PGM within the pores of the molecular sieve can be determined using conventional techniques or by the method described in SAE 2013-01-0531.

[0038] The catalyst material may have ≤75% by weight (i.e., the amount of PGM in the catalyst material) of PGM located within the pores of the molecular sieve, preferably ≤50% by weight.

[0039] Molecular sieves have a framework containing silicon, oxygen and germanium, and have a heteroatom T-atom content of ≤ about 0.20 mol%.

[0040] As is known in the art, the term "T-atom" is an abbreviation for "tetrahedral coordination atom," which is present in the framework of molecular sieves.

[0041] As used herein in the context of “T-atoms,” 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). Molecular sieves may have a framework comprising one or more heteroatom T-atoms. Heteroatoms may be selected, for example, from the group consisting of aluminum (Al), boron (B), gallium (Ga), titanium (Ti), zinc (Zn), iron (Fe), vanadium (V), and any combination of two or more thereof. More preferably, heteroatoms are selected from the group consisting of aluminum (Al), boron (B), gallium (Ga), titanium (Ti), zinc (Zn), iron (Fe), and any combination of two or more thereof.

[0042] Preferably, the molecular sieve has a framework consisting essentially of silicon, oxygen, germanium, and heteroatom T- atoms. More preferably, the molecular sieve may have a framework consisting essentially of silicon, oxygen, and germanium (e.g., constituent atoms as the framework), wherein the amount of germanium is as defined herein (e.g., the content of heteroatom T- atoms is 0.00 mol%).

[0043] The molecular sieve preferably has a heteroatom T-atom content of < about 0.17 mol%, more preferably ≤ about 0.15 mol%, such as < about 0.15 mol%, or even more preferably ≤ about 0.12 mol% (e.g., < about 0.12 mol%).

[0044] Optionally, the molecular sieve may have a heteroatom T-atom content of ≥ about 0.001 mol%, preferably ≥ about 0.010 mol%, more preferably ≥ about 0.020 mol%.

[0045] In some cases, molecular sieves may not contain a certain amount of heteroatom T- atoms (i.e., molecular sieves do not contain heteroatom T- atoms).

[0046] Germanium is present in the molecular sieve in an amount of 15 mol% to 20 mol%, preferably 16 mol% to 18 mol%.

[0047] Molecular sieves can be microporous or mesoporous. According to the IUPAC definition of “microporous” and “mesoporous” (see Pure & Appl. Chem., 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.

[0048] Molecular sieves can be mesoporous. When the molecular sieve is a mesoporous molecular sieve, it is usually selected from the following groups: MCM-41, MCM-48, MCM-50, FSM-16, AMS, SBA-1, SBA-2, SBA-3, SBA-15, HMS, MSU, SBA-15 and KIT-1.

[0049] Typically, molecular sieves (especially when they are microporous) have framework types selected from the group consisting of: 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, MAZ, 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, RT H, RUT, RWR, RWY, SEW, 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 above represents a skeleton type according to the "IUPAC Zeolite Nomenclature Committee" and / or the "International Zeolite Association Structure Committee".

[0050] Preferably, the molecular sieve is a zeolite. Zeolite can be referred to as a silica-containing zeolite, such as a siliceous zeolite. Zeolite can be a germanium silicate zeolite. Thus, zeolite can be a siliceous (i.e., high silica-containing) zeolite with low content of heteroatomic T-atoms such as aluminum (Al), boron (B), gallium (Ga), and titanium (Ti) and optionally zinc (Zn) and iron (Fe).

[0051] Siliceous zeolite or pure silica zeolite may be selected from the zeolites in the table below.

[0052] As is known in the art, silica zeolites have a framework comprising SiO4 tetrahedra.

[0053]

[0054] Generally, it is preferred that the molecular sieve (especially when the molecular sieve is a zeolite) has a framework type selected from the group consisting of: 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, MSE, MTF, MTN, MTT, MWT, 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, VNI. More preferably, the molecular sieve or zeolite has a framework type selected from the group consisting of: BEA, CDO, CON, MEL, MWW, MFI, and FAU; even more preferably, the framework type is selected from the group consisting of: BEA and MFI. Most preferably, the zeolite has an MFI framework.

[0055] Zeolites can be selected from microporous zeolites (i.e., zeolites with the largest ring size of eight tetrahedral atoms), mesoporous zeolites (i.e., zeolites with the largest ring size of ten tetrahedral atoms), and macroporous zeolites (i.e., zeolites with the largest ring size of twelve tetrahedral atoms).

[0056] Various methods known in the art are used to prepare molecular sieves, particularly zeolites, with high silica content (e.g., high SAR) and specific framework types and pore sizes. Many methods for preparing transition metals (such as platinum group metals) supported on zeolites are also known. See, for example, WO 2012 / 166868.

[0057] The molecular sieve or zeolite can be a small-pore molecular sieve or zeolite. The small-pore molecular sieve or zeolite preferably has a framework 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, the small-pore molecular sieve or zeolite has a framework type of CHA, CDO, or DDR.

[0058] The molecular sieve or zeolite can be a mesoporous molecular sieve or zeolite. The mesoporous molecular sieve or zeolite preferably has a framework type selected from the group consisting of: MFI, MEL, MWW, and EUO. More preferably, the mesoporous molecular sieve or zeolite has a framework type selected from the group consisting of: MFI, MEL, and MWW, such as MFI.

[0059] The molecular sieve or zeolite can be a macroporous molecular sieve or zeolite. The macroporous molecular sieve or zeolite preferably has a framework type selected from the group consisting of: AFI, CON, BEA, FAU, MOR, and EMT. More preferably, the macroporous molecular sieve or zeolite has a framework type selected from the group consisting of: AFI, BEA, CON, and FAU, such as BEA.

[0060] Preferably, the molecular sieve or zeolite is a solid. More preferably, the molecular sieve or zeolite is in granular form.

[0061] When molecular sieves or zeolites are in particulate form, they typically have a D50 of 0.1 μm to 20 μm (e.g., 5 μm to 15 μm), such as 0.2 μm to 15 μm (e.g., 0.2 μm to 10 μm or 7.5 μm to 12.5 μm). Preferably, the D50 is 0.5 μm to 10 μm. To avoid confusion, D50 (i.e., median particle size) measurement can be obtained using laser diffraction particle size analysis, such as that of the Malvern Mastersizer 2000. This measurement is based on volumetric techniques (i.e., D50 can also be referred to as DV50 (or D(v,0.50)) and applies a mathematical Mie theory model to determine the particle size distribution.

[0062] It has been found that catalytic materials with smaller particle size distributions (i.e., lower D50) exhibit higher activity and hydrothermal durability than those containing larger particle size distributions. Unbound by theory, it is believed that as the particle size of the zeolite decreases, the silanol groups of the zeolite become more readily accessible to platinum group metals. However, catalytic materials exhibit better durability when the zeolite has a larger particle size distribution.

[0063] Preferably, the molecular sieve has a SAR of ≥1200. More preferably, the SAR is ≥1300, such as ≥1500 (e.g., ≥1700), more preferably ≥2000, such as ≥2200. In particular, when the heteroatom T-atom is aluminum, the molecular sieve or zeolite may have a SAR of ≥1200. Preferably, the SAR is ≥1300, such as ≥1500 (e.g., ≥1700), more preferably ≥2000, such as ≥2200.

[0064] The catalytic material of the present invention is particularly advantageous when the zeolite has abundant 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 K-absorption spectroscopy, such as the K-absorption spectroscopy described in the examples. It has been found that advantageous oxidation activity can be obtained when the molecular sieve (especially the zeolite) contains a large number of silanol groups. Preferably, the molecular sieve or zeolite contains silanol groups, wherein the silanol groups have an initial decomposition temperature of ≥500°C. The initial decomposition temperature can be measured by differential scanning calorimetry.

[0065] Molecular sieves or zeolites with silanol groups can be obtained by removing the 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 through post-synthetic treatment. In some cases, the silanol groups can be an inherent part of the molecular sieve or zeolite framework.

[0066] The presence of silanol groups can be determined using FTIR spectroscopy.

[0067] According to another aspect, a catalyst article is provided, which comprises, in or on a substrate, the catalytic material described herein.

[0068] Catalyst products are components suitable for use in exhaust systems. Typically, such products are monolithic honeycomb materials, which can also be referred to as "bricks." These have a high surface area structure suitable for contacting the gas to be treated with the catalyst material to achieve the conversion or transformation of exhaust components. Other forms of catalyst products are known and include plate structures as well as encased metal catalyst substrates. The catalyst products described herein are applicable to all these known forms, but are particularly preferred in the form of monolithic honeycomb materials because these catalysts offer a good balance between cost and ease of manufacture.

[0069] This catalyst is used to treat exhaust gas from natural gas combustion engines. In other words, it catalyzes the exhaust gas from natural gas combustion engines to convert or transform gaseous components to meet emission regulations before they are released into the atmosphere. When natural gas burns, it produces carbon dioxide and water, but the exhaust also contains additional methane (and other short-chain hydrocarbons), which needs to be catalytically removed before being released into the atmosphere. The exhaust also typically contains significant amounts of water and sulfur, which can accumulate and deactivate the catalyst.

[0070] Catalyst articles can be prepared by applying a carrier coating to the surface of a substrate and / or by extrusion. Catalyst articles can be manufactured by preparing a carrier coating and applying the carrier coating to a substrate using methods known in the art (see, for example, our WO 99 / 47260, WO 2011 / 080525 and WO 2014 / 195685). Methods for preparing catalyst articles by extrusion are also known (see, for example, our WO 2011 / 092519).

[0071] The catalytic material can be disposed on or loaded onto a substrate (e.g., the catalytic material is applied to the surface of the substrate in the form of a carrier coating). The catalytic material can be disposed directly on the substrate (i.e., the catalytic material is in contact with the surface of the substrate). Additionally or alternatively, the catalytic material can be dispersed in the substrate (e.g., the catalytic material is part of an extrudate used to form the substrate). Thus, the substrate is an extruded solid body containing the catalytic material.

[0072] It is possible that when the catalytic material is dispersed in a substrate (e.g., the oxidation catalyst is an extruded product), the resulting oxidation catalyst may be superior to an oxidation catalyst in which the same catalytic material is washed onto a substrate. When the catalytic material is dispersed in a substrate (e.g., the oxidation catalyst is an extruded product), the oxidation catalyst can rapidly desulfurize and exhibit superior operational stability (e.g., good water and oxygen resistance) compared to oxidation catalysts manufactured by washing the catalytic material onto a substrate.

[0073] The extruded solid bulk may contain or consist substantially of the following components: (i) 5% to 95% by weight of a catalytic 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.

[0074] The binder / matrix components may be selected from the group consisting of cordierite, nitrides, carbides, borides, spinel, refractory metal oxides, lithium aluminosilicate, zircon, and mixtures of any two or more thereof.

[0075] The refractory metal oxide may be selected from the group consisting of: optionally doped alumina, silica, titanium dioxide, zirconium oxide, and mixtures of any two or more thereof. Suitable sources of silica, such as clay, are described in US2014 / 0065042 A1.

[0076] Inorganic fibers can be selected from the following groups: carbon fiber, glass fiber, metal fiber, boron fiber, alumina fiber, silica fiber, silica-alumina fiber, silicon carbide fiber, potassium titanate fiber, aluminum borate fiber, and ceramic fiber.

[0077] When the catalytic material is dispersed in a substrate (e.g., the substrate is an extruded solid bulk containing the catalytic material), the substrate typically has a porosity of 35% to 75%. The porosity of the substrate can be determined using conventional methods known in the art, such as mercury porosimetry.

[0078] The catalyst product may contain 0.3g in -3 Up to 5.0g in -3 0.4g in preferred form -3 Up to 3.8g in -3 Even better, 0.5g in -3 Up to 3.0g in -3 (e.g., 1g in) -3 Up to 2.75g in -3 or 0.75g in -3 Up to 1.5g in -3 ), and even more preferably 0.6g in -3 Up to 2.5g in -3 (e.g., 0.75g in) -3 Up to 2.3g in -3 The total loading of catalytic materials.

[0079] The substrate can be a flow-through substrate or a filter substrate. When the substrate is a monolithic material, it can be either a flow-through monolithic material or a filter monolithic material. The substrate can be a honeycomb structure monolithic material.

[0080] Flow-through substrates typically include a cellular structure substrate (e.g., a metal or ceramic cellular structure substrate) with multiple channels extending through it, the channels being open at both ends.

[0081] A filter substrate typically includes multiple inlet channels and multiple outlet channels, wherein the inlet channels are open at the upstream end (i.e., the exhaust inlet side) and blocked or sealed at the downstream end (i.e., the exhaust outlet side), and the outlet channels are blocked or sealed at the upstream end and open at the downstream end, and each inlet channel is separated from the outlet channel by a porous structure.

[0082] When the substrate is a filter substrate, it is preferred that the filter 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. Preferably, the inlet and outlet channels are arranged in a honeycomb pattern. When a honeycomb arrangement is present, it is preferred that the channels vertically and laterally adjacent to the inlet channel are blocked at the upstream end, and vice versa (i.e., the channels vertically and laterally adjacent to the outlet channel are blocked at the downstream end). When viewed from either end, the alternating blocked and open ends of the channels present a checkerboard appearance.

[0083] In principle, the substrate can have any shape or size. However, the shape and size of the substrate are usually chosen to optimize the exposure of the catalytic material to the exhaust gas.

[0084] The substrate may be, for example, tubular, fibrous, or granular. Examples of suitable load-bearing substrates include monolithic honeycomb cordierite substrates, monolithic honeycomb SiC substrates, layered fiber or knitted fabric substrates, foam substrates, crossflow substrates, wire mesh substrates, porous metal substrates, and ceramic particle substrates.

[0085] According to another aspect, a compressed natural gas combustion and exhaust system is provided, the compressed natural gas combustion and exhaust system comprising:

[0086] (i) Natural gas combustion engine; and

[0087] (ii) An exhaust treatment system comprising an intake for receiving exhaust gas from the combustion engine and a catalyst article as described herein, the catalyst article being arranged to receive and treat the exhaust gas.

[0088] A natural gas combustion engine is an engine used to burn natural gas. Preferably, the natural gas combustion engine is a stationary engine, more preferably a gas turbine or power generation system. In stationary applications, natural gas combustion can be configured to operate continuously under lean or stoichiometric conditions. In such systems, combustion conditions and fuel composition typically remain constant over long operating periods. This means that there are fewer opportunities for regeneration steps to remove moisture contaminants compared to mobile applications. Therefore, the benefits described herein can be particularly advantageous for stationary applications. That is, when opportunities for catalyst regeneration are limited, it is particularly desirable to provide a catalyst with high moisture resistance. It should be understood that both lean and stoichiometric system types can be used in a range of different applications.

[0089] An exhaust treatment system is a system suitable for treating exhaust gas from a combustion engine. An exhaust treatment system includes an intake for receiving exhaust gas from the combustion engine and a catalyst article arranged to receive and treat the exhaust gas. Attached Figure Description

[0090] The invention will now be discussed further with reference to the following non-limiting drawings, in which:

[0091] Figure 1 The improved hydrothermal durability achieved by the present invention is shown. Example

[0092] The invention will now be further described in conjunction with the following non-limiting examples, in which powdered catalyst samples were prepared.

[0093] Example 1

[0094] The catalyst in Example 1 is a palladium-containing MFI zeolite containing 0.1 mol% aluminum. The palladium content is 3% by weight.

[0095] The catalyst of Example 1 was prepared by impregnating a powdered sample of silica MFI zeolite with 0.1 mol% aluminum using a palladium nitrate solution using a conventional initial wet impregnation technique. After impregnation, the sample was dried at 80°C for 5 hours and calcined in air at 500°C for 2 hours in a static oven.

[0096] Example 2

[0097] The catalyst in Example 2 is a palladium-containing MFI zeolite containing 17 mol% germanium. The palladium content is 3% by weight.

[0098] The catalyst of Example 2 was prepared by impregnating a powdered sample of silica-based MFI zeolite containing 17 mol% germanium with palladium nitrate solution using a conventional initial wet impregnation technique. After impregnation, the sample was dried at 80°C for 5 hours and calcined in air at 500°C for 2 hours in a static oven.

[0099] Example 3

[0100] The catalyst in Example 3 is a palladium-containing MFI zeolite containing 2 mol% titanium. The palladium content is 3% by weight.

[0101] The catalyst of Example 3 was prepared by impregnating a powdered sample of silica MFI zeolite containing 2 mol% titanium with palladium nitrate solution using a conventional initial wet impregnation technique. After impregnation, the sample was dried at 80°C for 5 hours and calcined in air at 500°C for 2 hours in a static oven.

[0102] Example 4

[0103] The catalyst in Example 4 is a palladium-containing MFI zeolite containing 5 mol% aluminum. The palladium content is 3% by weight.

[0104] The catalyst of Example 4 was prepared by impregnating a powdered sample of silica MFI zeolite containing 5 mol% aluminum with palladium nitrate solution using a conventional initial wet impregnation technique. After impregnation, the sample was dried at 80°C for 5 hours and calcined in air at 500°C for 2 hours in a static oven.

[0105] Example 5

[0106] The catalyst in Example 5 has palladium supported on alumina. The palladium content is 3% by weight.

[0107] The catalyst of Example 5 was prepared by impregnating alumina powder samples with palladium nitrate solution using a conventional initial wet impregnation technique. After impregnation, the samples were dried at 80°C for 5 hours and then calcined in air at 500°C for 2 hours in a static oven.

[0108] The methane conversion activity of fresh and aged powder samples of the catalysts from Examples 1 to 5 was tested in the Synthetic Catalytic Activity Test (SCAT) by passing a gas mixture containing 1120 ppm CH4, 65 ppm C2H6, 800 ppm CO, 9% O2, 10% H2O, 6% CO2, and the balance N2 through the catalyst at a space velocity of 100,000 h⁻¹ over a temperature range (heating from 250 °C to 450 °C at a heating rate of 5 °C / min). Aged catalysts were obtained by aging in air in 10% H2O at 700 °C for 40 hours.

[0109] like Figure 1 As shown, the use of 17 mol% germanium in palladium-containing MFI zeolite resulted in better fresh methane conversion compared to the use of alumina or titanium dioxide or alumina support materials. Furthermore, the fresh and aged activities of such germanium-containing catalysts were very similar, demonstrating that the presence of germanium at 17 mol% within the molecular sieve improves the hydrothermal durability of palladium-containing zeolite. This improved hydrothermal durability is particularly advantageous when palladium-containing zeolite is used to treat exhaust gas from natural gas engines, given its high moisture content.

[0110] As used herein, unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “the” include plural references. The use of the term “comprising” is intended to be interpreted as including such features but not excluding other features, and also to include feature options that must be limited to those features described. In other words, the term also includes the limitations “consistently made of” (intended to indicate that certain additional components may be present, provided that they do not substantially affect the essential characteristics of the described feature) and “consisting of” (intended to indicate that other features may be excluded such that if these components were expressed as percentages of their proportions, they would total 100%, taking into account any unavoidable impurities), unless the context clearly indicates otherwise.

[0111] It should be understood that although the terms “first,” “second,” etc., may be used herein to describe various elements, layers, and / or portions, the elements, layers, and / or portions should not be limited by these terms. These terms are used only to distinguish one element, layer, or portion from another element, layer, or portion, or additional elements, layers, or portions. It should be understood that the term “on” is intended to mean “directly on”, such that there is no intermediate layer between materials referred to as being “on” another material. Spatial relative terms, such as “under,” “below,” “beneath,” “lower,” “over,” “above,” “upper,” etc., may be used herein to facilitate the description of the relationship between one element or feature and another element or feature. It should be understood that spatial relative terms are intended to cover different orientations of the device in use or operation other than those depicted in the accompanying drawings. For example, if the device as described herein is flipped, an element described as "below" or "under" other elements or features will be oriented "above" or "on top" of other elements or features. Thus, the example term "below" can encompass both above and below orientations. The device may be oriented in other ways, and the spatial relative descriptors used herein are interpreted accordingly.

[0112] The detailed description above has been provided by way of explanation and illustration and is not intended to limit the scope of the appended claims. Many variations of the presently preferred embodiments shown herein will be apparent 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 gas produced by a natural gas engine, said catalytic material comprising a molecular sieve and platinum group metals (PGMs) supported on said molecular sieve. The molecular sieve described herein has a framework comprising silicon, oxygen, and germanium, and has a heteroatom T-atom content of ≤0.20 mol%, wherein the heteroatom refers to atoms that are not silicon, not germanium, and not oxygen. The germanium is present in an amount of 15 mol% to 20 mol%.

2. The catalytic material according to claim 1, wherein 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 combination of two or more thereof.

3. The catalytic material according to claim 1 or claim 2, wherein the framework is substantially composed of silicon, oxygen, germanium and heteroatoms (T-atoms).

4. The catalytic material according to claim 1 or claim 2, wherein the molecular sieve is a zeolite.

5. The catalytic material according to claim 4, wherein the molecular sieve is MFI zeolite.

6. The catalytic material according to claim 1 or claim 2, wherein the total amount of the platinum group metals (PGM) is from 0.01% to 30% by weight.

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

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

9. The catalytic material according to claim 1 or claim 2, wherein the molecular sieve has an SAR of ≥1200.

10. The catalytic material according to claim 1 or claim 2, wherein the molecular sieve comprises at least 0.010 mmol / g of silanol groups.

11. A catalyst article comprising a catalytic material according to any one of claims 1 to 10 on a substrate.

12. The catalyst article of claim 11, wherein the catalytic material is provided as a carrier coating on the substrate.

13. The catalyst product according to claim 12, wherein the carrier coating loading is 1 g / ft. 3 Up to 50g / ft 3 .

14. A catalyst article comprising a catalytic material dispersed in a substrate according to any one of claims 1 to 10.

15. The catalyst article according to any one of claims 11 to 14, wherein the substrate is a flow-through substrate or a filter substrate.

16. A compressed natural gas combustion and exhaust system, the compressed natural gas combustion and exhaust system comprising: (i) Natural gas combustion engine; and (ii) An exhaust treatment system comprising an intake for receiving exhaust gas from the combustion engine and a catalyst article according to any one of claims 11 to 15, the catalyst article being arranged to receive and treat the exhaust gas.

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