Multifunctional catalyst system

Abstract

The present invention relates to a multifunction catalyst system for reducing harmful exhaust emissions in an exhaust stream of a stoichiometric operating engine, the system comprising: a) a coating comprising sulfur oxides and a phosphorus trap (SPT) on a first substrate; b) a three-way catalyst (TWC) on the second substrate; and c) a selective ammoxidation catalyst (SAOC) on the third substrate; wherein the first substrate and the second substrate are different substrates, avoiding any overlap between SPT and TWC; wherein the SPT is located upstream of the TWC and the ammoxidation catalyst is located downstream of the TWC, the multifunction catalyst system adapted to be located downstream of a stoichiometric operating engine, the multifunction catalyst system adapted to be in fluid communication with an exhaust gas stream; wherein the SPT is present in a content of 10-50 vol% of the total volume of TWC; wherein the SAOC is present in a content of 10-50 vol% of the total volume of the TWC.

Description

Technical Field

[0001] The present invention relates to the field of catalyst systems for stoichiometric positive ignition engines fueled with natural gas, biogas, liquefied natural gas or bio-liquefied natural gas, said catalyst system comprising a sulfur oxides (SO x ) and phosphorus (P) trap (SPT), a three-way catalyst (TWC) and a selective ammonia oxidation catalyst (SAOC). The present invention describes the composition of said catalytic system and its applications. Background Art

[0002] As is well known, combustion is incomplete regardless of the fuel used in an internal combustion engine. For hydrocarbon fuels, this incomplete combustion and the high temperature in the cylinder cause nitrogen in the air to be oxidized by oxygen, resulting in exhaust gases being polluted by carbon monoxide (CO), unburned hydrocarbons (HC), nitrogen oxides (NO x ) and particulate matter (PM). These pollutants are harmful to the environment and humans. In order to reduce their emissions and thus improve air quality, national and international authorities have legislated to limit pollutant emissions from stationary and mobile sources. To meet these restrictions, different strategies have been adopted, including improving fuel-air mixing, strictly controlling λ, etc. However, since these restrictions have become increasingly strict over the years, improving the engine alone is usually not sufficient to keep pollutant emissions below the limits. This makes the use of an exhaust gas aftertreatment system including a heterogeneous catalyst inevitable.

[0003] Light passenger cars have always used stoichiometric Otto engines, and under stoichiometric conditions, it is easy to remove CO, HC and NO on the TWC x . Later, lean-burning heavy vehicles (such as buses fueled with natural gas) were introduced. These vehicles initially used diesel engines with a significantly lean air / fuel ratio (excess oxygen). Using natural gas as fuel has several advantages.

[0004] For gasoline or compressed natural gas (CNG) stoichiometric engines, which are characterized by a λ value fluctuating around the stoichiometric point λ = 1, the heterogeneous catalyst is represented by a three-way catalyst (TWC). The TWC can simultaneously treat CO, HC and NO x . The λ fluctuation is inevitably very important for the TWC because, under oxygen-rich conditions (λ < 1, i.e., less oxygen than required for complete oxidation of the fuel), the catalytic NO xReduction is maximized; under lean oxygen conditions (λ > 1, i.e., more oxygen than required for complete oxidation of the fuel), it is easier to catalytically oxidize HC and CO to CO2 and water. Since natural gas contains little sulfur, SO x emissions are very low or non-existent; compared to diesel engines, NO x emissions can be lower under lean burn conditions; while under stoichiometric conditions, due to higher operating temperatures, NO x emissions may be higher. In addition, compared to diesel engines, particulate emissions from engines fueled by natural gas are much lower, producing only trace amounts of black carbon emissions. Additionally, since NG is mainly composed of methane and has a relatively high H / C ratio, CO2 emissions are lower than those of diesel engines.

[0005] TWC technology began to be applied in the late 1970s. Since then, with the development of materials and changes in their costs, the composition of the catalyst has been continuously evolving. However, the main components of TWC remain similar. Therefore, TWC is a multi-component mixture (washcoat) coated on a metal or ceramic substrate. The typical components of this mixture are a carrier, an oxygen storage material, a binder, and platinum group metals (PGM), such as Pt, P), and Rh (the six platinum group metals are ruthenium, rhodium, palladium, osmium, iridium, and platinum). Over time, by introducing dopants and other promoters and stabilizers into the OSC material, this basic composition has become more complex, which has expanded basic properties such as surface area, oxygen mobility, and inhibited sintering. The purpose of expanding and improving these properties is to ensure that the noble metals, as the key active compounds for converting CO, HC, and NO x into less harmful CO2, N2, and water, remain active for as long as possible.

[0006] The biggest challenge faced by natural gas engines is methane leakage. Since methane is the most difficult hydrocarbon to convert, emissions may be high. In stoichiometric applications, TWC can also convert methane. Due to the inertness of methane, high loadings are used in TWC, which makes the catalyst expensive, especially when the price of PGM is high. The catalyst used to convert methane is based on Pd (Pd is the best PGM for converting methane). In addition, a small amount of Rh is also used to improve NO xConversion rate. Due to the high cost of TWC, research is currently underway on how to activate methane conversion catalysts while reducing the use of PGM. Various structures have been tried, such as perovskites, spinels, and other mixed oxides with or without PGM. In addition, a potential way to reduce the cost of PGM is to replace part of Pd and / or Rh with Pt, which is significantly cheaper, but this method requires caution because the threshold of methane oxidation depends to a large extent on the appropriate PGM loading. Although the metal loading can be reduced to a large extent, durability becomes a problem under hydrothermal and poisoning conditions.

[0007] In addition to regulating the main pollutants (CO, HC, and NO x )), starting from EUVI, emission limits also restrict the concentration of ammonia (NH3) in the exhaust gas. In the world harmonized transient test cycle (WHTC), the maximum allowable concentration is 10 ppm. In a natural gas fuel engine operating at stoichiometric ratio, the raw emissions do not contain ammonia. In TWC, NH3 is produced through the reaction of hydrogen present in the raw exhaust gas or hydrogen formed on the catalyst surface through the water-gas shift or steam reforming reaction. The hydrogen content in the exhaust gas also depends on the engine calibration, i.e., how close the λ is to 1 during engine operation, as more hydrogen is formed in the exhaust gas during the rich combustion phase. The amount of ammonia formed in TWC depends to a large extent on the catalyst composition, PGM loading and its ratio, degree of aging, etc. To comply with the emission regulations starting from EUVI, it is necessary to selectively oxidize NH3 to N2. The ammonia generated on TWC and its downstream content can be controlled in the following ways: chemically by formulating TWC to minimize ammonia generation, or using an additional selective ammonia oxidation catalyst for separate control, which can be integrated onto TWC or installed separately after TWC.

[0008] During operation, the performance of TWC gradually degrades due to thermal deactivation and chemical deactivation. Thermal deactivation is usually caused by the temperature rise during stoichiometric combustion or misfire events. High temperatures cause the sintering of noble metal particles, which means that the finely dispersed particles lose their active surface. Through the sintering of the coating layer (collapse of pores), some PGM particles may be buried in the pores and thus no longer function. At higher temperatures, PGM compounds react with the carrier with a higher surface area to form inactive ternary oxides (such as aluminates with γ-alumina), which is an irreversible process and causes permanent deactivation of the catalyst. Fine engine management and the selection of durable catalyst raw materials are the only strategies to cope with the thermal deactivation of TWC.

[0009] Chemical deactivation of the TWC, also known as poisoning, results from the interaction of the catalyst with foreign substances in the fuel or lubricating oil. These materials, known as catalytic poisons, react with the TWC and impair its performance. Poisoning can be selective or non-selective. During selective poisoning, the catalyst poison compound reacts directly with the active sites of the TWC, reducing its activity or selectivity for a specific reaction, leading to permanent deactivation. Non-selective poisoning, also known as fouling or masking, refers to the process in which the toxic material forms a physical deposition layer on the surface of the coating.

[0010] Depending on the composition of the fuel and lubricating oil and the impurities they contain, many TWC catalyst poisons are known, the most common being: Pb, Hg, Cd, S, P, Ca, Zn, and potassium K. Among them, S and P in the form of oxides are the most abundant, and during the service life of the catalyst, their cumulative weight can reach several percent of the total weight of the coating, thus significantly reducing the performance of the catalyst. Summary of the Invention

[0011] In the present work, we propose an integrated system, its preparation method, and application, which combines all components (SPT, TWC, and SAOC).

[0012] As described in the background section above, the present invention solves many problems in the prior art.

[0013] In a first aspect, the present invention relates to a multifunctional catalyst system for reducing harmful exhaust emissions in the exhaust gas stream of an engine operating at stoichiometric ratio, the system comprising:

[0014] a) A coating containing sulfur oxides and a phosphorus trap (SPT) on a first substrate;

[0015] b) A three-way catalyst (TWC) on a second substrate; and

[0016] c) A selective ammonia oxidation catalyst (SAOC) on a third substrate.

[0017] Wherein the SPT is located upstream of the TWC, and the ammonia oxidation catalyst is located downstream of the TWC, and the multifunctional catalyst system is adapted to be located downstream of an engine operating at stoichiometric ratio, and the multifunctional catalyst system is adapted to be in fluid communication with the exhaust gas stream.

[0018] In an embodiment, the first substrate, the second substrate, and the third substrate are different substrates.

[0019] In another embodiment, the second substrate and the third substrate are the same substrate, and the first substrate is a different substrate.

[0020] In another embodiment, the SPT is present in a content of 10 - 50 vol% of the total volume of the TWC. Generally, it is present in a content of 20 - 40 vol% of the total volume of the TWC. Preferably, it is present in a content of 25 - 35 vol% of the total volume of the TWC.

[0021] In yet another embodiment, the SAOC is present in a content of 10 - 50 vol% of the total volume of the TWC. Generally, it is present in a content of 20 - 40 vol% of the total volume of the TWC. Preferably, it is present in a content of 25 - 35 vol% of the total volume of the TWC.

[0022] In another embodiment, the TWC contains at least one of Pt, Pd, and Rh. In an embodiment, the TWC consists of Pt, Pd, and Rh. In another embodiment, the TWC consists of Pt and Pd. In yet another embodiment, the TWC consists of Pd and Rh. In another embodiment, the total coating amount in grams per liter of the coating layer (g / L) is 50 g / L to 400 g / L.

[0023] In yet another embodiment, the Pt / Pd ratio (wt% / wt%) of the TWC is less than 6, preferably 4 or less than 4. In another embodiment, the Pt / Pd ratio (wt% / wt%) of the TWC is 4 or less than 4, and at least 0.05 g Rh per liter of the coating layer.

[0024] In yet another embodiment, the SPT contains at least one of Cu, Mn, and Ce, such as a) Mn, b) Mn and Ce, c) Mn and Cu, or d) Mn, Ce, and Cu. In another embodiment, the total coating amount in grams per liter of the coating layer (g / L) is 50 g / L to 400 g / L.

[0025] In another embodiment, the SP further contains at least one of Pt and Pd. In yet another embodiment, the SPT further contains Pt and Pd.

[0026] In another embodiment, the SPT does not contain any platinum group metals, such as Pt, Pd, and Rh.

[0027] In another embodiment, the SAOC contains at least one of Fe, Cu, Sc, Y, La, Ce, Pr, Nd, Ti, Zr, and Hf. Preferably, the SAOC can selectively convert ammonia to N2, and after being treated by the SAOC, the ammonia remains below 10 ppm. In yet another embodiment, the SAOC contains at least one of Pt and Pd. In another embodiment, the SAOC does not contain any platinum group metals, such as Pt, Pd, and Rh.

[0028] In another embodiment, the first substrate, the second substrate, and / or the third substrate are selected from ceramic or metal honeycomb monoliths, such as flow-through or wall-flow substrates.

[0029] In another embodiment, the stoichiometrically operated engine is a natural gas or biogas engine, such as an engine using CNG, LNG, bio-CNG, and bio-LNG as fuels.

[0030] In a second aspect, the present invention relates to a method for reducing harmful exhaust emissions of a stoichiometrically operated engine, the method comprising using a multifunctional catalyst system according to any one of the above-mentioned first aspect or the embodiments of the first aspect of the present invention.

[0031] In an embodiment, the stoichiometrically operated engine is a natural gas or biogas engine, such as an engine using CNG, LNG, bio-CNG, and bio-LNG as fuels.

[0032] In a third aspect, the present invention relates to the use of the catalyst system according to any one of the above-mentioned first aspect or the embodiments of the first aspect of the present invention for reducing harmful exhaust emissions of a stoichiometrically operated engine, such as a stoichiometrically operated engine using natural gas or biogas as fuel.

[0033] In a fourth aspect, the present invention relates to an exhaust gas treatment system, which system comprises the catalyst system according to any one of the above-mentioned first aspect or the embodiments of the first aspect of the present invention.

[0034] In a fifth aspect, the present invention relates to a multifunctional catalyst system for reducing harmful exhaust emissions in the exhaust gas stream of a stoichiometrically operated engine, the system comprising a three-way catalyst (TWC) on a substrate, the multifunctional catalyst system being adapted to be located downstream of a stoichiometrically operated engine, the multifunctional catalyst system being adapted to be in fluid communication with the exhaust gas stream; wherein the TWC contains Rh, Pt, and Pd, wherein the Pt / Pd ratio (wt% / wt%) is 4 or less than 4, and at least 0.05 g Rh / liter of the coating.

[0035] In an embodiment of the fifth aspect, the total content of Pt, Pd, and Rh in the coating is 0.01 - 5.00 wt%, preferably 0.05 - 3.00 wt%.

[0036] In another embodiment, the coating containing Pt, Pd, and Rh is a 50 - 400 g / L coating, preferably a 200 - 300 g / L coating.

[0037] Other objects and advantages of the present invention will be embodied from the following description and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figures 1-7 Illustrate the test and preferred embodiments of the present invention.

[0039] Figure 1 Illustrate the study of the trapping activity of aged SPC.

[0040] Figure 2 Illustrate the results of an accelerated poisoning test designed to simulate the expected cumulative phosphorus content in aged TWC in actual use.

[0041] Figure 3 Illustrate the emissions of CO, NO x and CH4 and the amount of NH3 generated are below the Euro VI limit, where the TWC function is coated on a ceramic honeycomb.

[0042] Figure 4 Illustrate the emissions of CO, NO x and CH4 and the amount of NH3 generated are below the Euro VI limit, where the TWC function is coated on a ceramic honeycomb.

[0043] Figure 5 Illustrate the emissions of CO, NO x and CH4 and the amount of NH3 generated are below the Euro VI limit, where the TWC function is coated on a ceramic honeycomb.

[0044] Figure 6 Illustrate the emissions of CO, NO x and CH4 and the amount of NH3 generated are below the Euro VI limit, where the TWC function is coated on a ceramic honeycomb.

[0045] Figure 7 Illustrate the emissions of CO, NO x and CH4 and the amount of NH3 generated are below the Euro VI limit, where the TWC function is coated on a ceramic honeycomb.

[0046] Figure 8 Illustrate the relationship between NH3 vs Pt / Pd in the trimetallic TWC samples 2A - 2C (Examples 2A - 2C).

[0047] Figure 9 Illustrate the trend line (linear regression) of NH3 vs Pt / Pd with higher Pt / Pd in the trimetallic TWC samples 2A - 2C.

[0048] Figure 10 Illustrate the trend line of NH3 vs Rh loading with lower Rh loading in the trimetallic TWC 2A - 2C.

[0049] Figure 11Shows NH3 vs Pt / Pd in the partitioned three-metal TWC sample 2D-2F (Example 2D-2F).

[0050] Figure 12 Shows the trend line of NH3 vs Rh loading with lower Rh loading in the partitioned three-metal TWC 2D-2F.

[0051] Figure 13 Shows NH3 vs Pt / Pd in the Pt-Pd TWC. Detailed Description

[0052] Broadly speaking, the present invention has many advantages, and there are even more advantages in terms of the embodiments.

[0053] TWC Function

[0054] In the supporting experiments described herein, the TWC components are applied to a ceramic or metal substrate as one or more coating layers. The total coating amount in grams per liter of coating layer (g / L) is from 50 g / L to 400 g / L, preferably from 200 g / L to 300 g / L. Each of the above coating layers consists of a high-surface-area, heat-resistant alumina-based carrier, a stabilized and / or doped cerium-zirconium mixed oxide (where the dopant is a lanthanide element in the periodic table and the binder is a chemical substance that promotes and / or induces adhesion), and Pt, Pd, and Rh or any of their single-metal / bimetal / trimetal combinations as catalytically active materials.

[0055] In another embodiment, the carrier consists of alumina (Al2O3). In some embodiments, the alumina can be doped with lanthanum oxide (La2O3), and the doping ratio is 1 wt% - 10 wt% of the total coating amount, preferably 1 wt% - 5 wt%.

[0056] In another embodiment, the substrate can consist of a mixed oxide containing Al2O3 and SiO2, where the proportion of SiO2 is 1 wt% - 50 wt% of the total coating amount, preferably 15 wt% - 35 wt%. In some embodiments, the above mixed oxide can contain ZrO2, and its proportion is at most 20 wt% of the total coating amount.

[0057] In yet another embodiment, the oxygen storage material consists of a mixed oxide containing CeO2, ZrO2, and La2O3 and one or more rare earth oxides. Generally, the weight fraction of CeO2 is limited to 20 wt% - 70 wt% of the total coating amount, the weight fraction of ZrO2 is limited to 20 wt% - 70 wt% of the total coating amount, the weight fraction of La2O3 is limited to 1 - 10% of the total coating amount, and the weight fraction of each rare earth oxide is limited to 1 wt% - 10 wt% of the total coating amount.

[0058] In an embodiment, boehmite is used as a binder.

[0059] In another embodiment, the TWC comprises a bimetallic combination of Pd and Rh. The content of Pd and Rh of each metal in the catalyst is 0.01 wt% - 5.00 wt% of the total coating amount, preferably 0.05 wt% - 3.00 wt% of the total coating amount. In yet another embodiment, the distribution of the noble metals Pd and Rh can be such that they are integrated into different coatings respectively. In some embodiments, each catalyst layer can contain both metals. In some embodiments, it is a combination of a single-metal layer and a bimetallic layer. In some embodiments, the total noble metal content can be distributed in different regions. In some embodiments, these regions have different coating combinations.

[0060] In another embodiment, the TWC comprises a trimetallic combination of Pt, Pd and Rh. The content of each metal in the catalyst is 0.01 wt% to 5.00 wt% of the total coating amount, preferably 0.05 wt% to 3.00 wt%. In another embodiment, the distribution of the metals can be such that they are integrated into different coatings respectively. In some embodiments, each catalyst layer can contain two metals. In some embodiments, it is a combination of a single-metal layer and a bimetallic layer. In some embodiments, the total metal loading can be distributed in separate regions. In some embodiments, these regions can have different coating combinations.

[0061] In another embodiment, the TWC component comprises a bimetallic combination of Pt and Pd. The content of each metal in the catalyst is 0.01 wt% to 5.00 wt% of the total coating amount, preferably 0.06 wt% to 3.00 wt%. In another embodiment, the distribution of the metals can be such that they are integrated into different coatings respectively. In some embodiments, each catalyst layer can contain two metals. In some embodiments, it is a combination of a single-metal layer and a bimetallic layer. In some embodiments, the total metal loading can be distributed in separate regions. In some embodiments, these regions can have different coating combinations.

[0062] Sulfur and phosphorus trapping function (SPT)

[0063] In a further embodiment, the SPT function can be applied to a ceramic or metal substrate and one or more coatings. The SPT function can be located in the inlet zone of the TWC, or upstream of the TWC as a separate coating element. The total coating amount is 50 g / L to 400 g / L of the TWC, preferably 200 g / L to 300 g / L. Each coating consists of a high-surface-area, heat-resistant alumina-based carrier, a chemical binder that promotes or induces adhesion, and an active material in the form of a transition metal of Group 4 of the d-block of the periodic table.

[0064] In a further embodiment, the carrier consists of alumina Al2O3. In another embodiment, the alumina can be doped with lanthanum oxide La2O3 in a proportion of 1 wt% - 10 wt%, preferably 1 wt% - 5 wt%.

[0065] In another embodiment, zeolite, cerium dioxide or a mixture thereof can be used as a binder in a proportion of 3.0 - 40 wt% of the total coating amount.

[0066] In a further embodiment, Mn is used as the active ingredient of the SPT, and its loading amount is 10 wt% to 40 wt% of the total coating amount, preferably 15 wt% to 25 wt%. In another embodiment, Ce can be used as the active material, and its loading amount is 1 wt% to 50 wt% of the total coating amount. In another embodiment, a combination of Mn and Ce can be used as the active material, and its total loading amount is 1 wt% to 75 wt% of the total coating amount. In yet another embodiment, the SPT containing Mn, Ce or a combination thereof can include Pt, Pd or their bimetallic combination, and its total loading amount is 0.1 wt% to 1.0 wt% of the total coating amount.

[0067] Selective ammonia oxidation catalyst function (SAOC)

[0068] In a further embodiment, the SAOC coating can be applied to a ceramic or metal substrate and one or more coatings. The catalyst can be a separate element downstream of the TWC or a region located at the TWC outlet section. The total coating amount is 50 - 400 g / L, preferably 100 - 200 g / L. Each coating consists of a carrier made of a mesoporous material, a chemical binder that promotes or induces adhesion, and an active material in the form of PGM.

[0069] In yet another embodiment, the carrier consists of zeolite preferably having a high silica - alumina ratio (SAR > 15) material, which can be doped with copper in a proportion of 1 wt% - 10 wt%, preferably 2 wt% - 4 wt%.

[0070] In another embodiment, the carrier consists of zeolite preferably having a high SAR (> 15) material, which can be doped with iron in a proportion of 1 wt% - 10 wt%, preferably 2 wt% - 4 wt%.

[0071] In yet another embodiment, the carrier consists of zeolite preferably being a high SAR (> 15) material, which can be doped with Fe, Cu, Sc, Y, La, Ce, Pr, Nd, Ti, Zr and Hf. The weight fraction of such oxides is limited to 1 wt% - 10 wt%, preferably 2 wt% - 4 wt%. The purpose of adding the dopant is to extend the heat resistance of the catalyst.

[0072] In another embodiment, an alumina-based sol can be used as a binder in a proportion of 5.0 - 15.0 wt% of the total coating amount. Herein, it refers to the binder content in the zeolyte layer; when the Pt layer is at the bottom, the same binder is used as the Pt carrier.

[0073] In yet another embodiment, PGM is used as the active material in a proportion of 0.04 wt% - 0.125 wt%.

[0074] System functions

[0075] The organizational structure of the entire integrated system is such that, with respect to the exhaust gas flow, the SPT function is upstream of the TWC function, and the SAOC function is downstream of it. Generally, the volume of the SPT function is 10% - 50% of the volume of the TWC function, preferably 20% - 40% of the volume of the TWC function. Generally, the volume of the SAOC function is 10% - 50% of the volume of the TWC function, preferably 20% - 40% of the volume of the TWC function. In one embodiment, each function can be coated on a different substrate (ceramic or metal). In another embodiment, SPT and TWC can be coated as partitions on the same substrate, while the SAOC function is coated on a different substrate. In yet another embodiment, the SPT function can be coated on a different substrate, while the TWC and SAOC functions are coated as partitions on the same substrate.

[0076] All references cited herein, including publications, patent applications, and patents, are incorporated herein by reference to the extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in full herein.

[0077] All headings and subheadings used herein are for convenience only and should not be construed in any way as limiting the subject matter of the present invention.

[0078] Unless otherwise specified herein or clearly contradicted by the context, the present invention encompasses any combination of the above elements in all possible variations thereof.

[0079] The recitation of numerical ranges herein is merely intended as a concise way of individually referring to each discrete value falling within that range, and unless otherwise specified herein, each discrete value is deemed to be incorporated into this specification as if it were individually recited herein. Unless otherwise stated, all exact numerical values provided herein should be considered representative of corresponding approximate values (e.g., all exact example values provided for a particular factor or measurement value can, where appropriate, be considered to also provide the corresponding approximate value modified by "about").

[0080] Unless otherwise specified herein or clearly contradicted by the context, all methods described herein can be performed in any suitable order.

[0081] As used in the description of the present invention, the terms "a", "an", "the" and similar reference pronouns shall be construed to include both the singular and the plural forms, unless otherwise specified herein or the context clearly contradicts. Thus, "a", "an" and "the" mean at least one, or one or more.

[0082] The term "and / or" as used herein is intended to denote two alternative scenarios as well as each alternative individually. For example, the expression "xxx and / or yyy" means "xxx and yyy; xxx; or yyy", and these three alternatives can each be implemented separately.

[0083] Unless otherwise specified, any and all examples or exemplary language provided herein (such as "such as") are only intended to better explain the present invention and do not limit the scope of the present invention. Unless otherwise explicitly stated, no language in the specification should be construed as implying that any element is essential for implementing the present invention.

[0084] The citation and incorporation of patent documents herein are for convenience only and do not reflect any opinion on the validity, patentability and / or enforceability of these patent documents.

[0085] In the present invention, when terms such as "comprising", "having", "including" or "containing" are used to describe aspects or embodiments involving one or more elements, it is intended to support similar aspects or embodiments that "consist of", "consist essentially of" or "substantially include" the specific elements, unless otherwise specified or the context clearly contradicts (for example, a composition described herein as comprising a specific element should be understood to also describe a composition consisting of that element, unless otherwise specified or the context clearly contradicts).

[0086] The present invention includes all modifications and equivalents of the subject matter recited in the aspects or claims described herein to the maximum extent permitted by applicable law.

[0087] The features disclosed in the above description, whether individually or in any combination, can be important materials for implementing the present invention in its different forms.

[0088] Experiment

[0089] Sulfur and phosphorus capture function

[0090] In this embodiment, the SPT consists of two layers. The bottom layer contains a composition of highly dispersed alumina, cerium dioxide, and lanthanum oxide. The top layer contains manganese oxide, alumina, cerium dioxide, and lanthanum oxide. The study of the trapping activity was carried out in a synthetic gas bench (SGB) reactor at a temperature of 450 °C, under conditions close to stoichiometry (λ = 0.99), using a mixed gas simulating the exhaust gas of an NG HD vehicle and adding 95 ppm SO2 (see Figure 1 ). The SO2 concentration was monitored in real time by Fourier transform infrared spectroscopy (FT-IR) to evaluate the SO2 trapping ability of the trap.

[0091] The results show that the SPT can trap 13 wt% of SO2 when the coating layer is newly used, and 5 wt% after high-temperature aging. The analysis of the aged catalyst in actual working conditions shows that the sulfur content accumulated by the TWC during 40,000 - 500,000 km of driving will vary significantly depending on the driving conditions, but generally remains in the range of 0.2 wt% to 1.2 wt% of the coating layer. Therefore, the SPT disclosed in the present invention has a higher capacity, and by effectively protecting the TWC function from SO x poisoning, the durability of the entire integrated catalytic system can be significantly improved.

[0092] Phosphorus poisoning of the TWC is usually accompanied by SO x poisoning because both poisons come from the same source (lubricating oil). Although the recommended limit for the phosphorus concentration in lubricating oil is stricter than that for sulfur concentration (ACEA 2016 European oil sequences), the phosphorus content in the observed poisoned catalysts is usually 2 - 10 times higher than the corresponding sulfur content. Figure 2 The accelerated poisoning test results are shown, which are designed to simulate the expected cumulative phosphorus content of the aged TWC in actual working conditions.

[0093] The cause of this phenomenon is that phosphorus irreversibly binds to the high-surface-area components of the coating layer (especially alumina). Given that the SPT disclosed in the present invention also contains alumina as the substrate, it can be confirmed that it also has anti-phosphorus poisoning activity. Based on the sulfur trapping activity, it is expected that the SPT can trap 25 wt% of phosphorus.

[0094] In all the following partition embodiments, the lengths of the inlet zone and the outlet zone are equal.

[0095] In all the following embodiments, the ratio of Pt / Pd / Rh is expressed in sequence. Therefore, for example, 0:17:1 means 0 Pt, 17 Pd, and 1 Rh.

[0096] TWC function

[0097] Example 1A (Pd / Rh Bimetal)

[0098] In this example, the TWC functional zones were coated on a ceramic honeycomb monolith. The average PGM loading was 4,944 g / L (in this specification, g / lit, g / L, and g / liter are interchangeable). The ratio was 0:17:1. The front zone had a PGM loading of 6,356 g / L with a ratio of 0:13:1. The rear zone had 3,531 g / L of PGM with a ratio of 0:40:1. After the sample was aged in an oven at 950 °C for 24 hours, it was tested on a CNG engine for the WHTC cycle. It was shown that the emissions of CO, NO x and CH4, as well as the NH3 production, were lower than the limits of the Euro VI standard for CNG HD vehicles. See Figure 3 .

[0099] Example 1B (Pd / Rh Bimetal)

[0100] In this example, the TWC functional zones were coated on a ceramic honeycomb monolith with an average loading of 4,238 g / L and a ratio of 0:15:1. The front zone had a PGM loading of 4,216 g / L with a ratio of 0:10:1. The rear zone had a PGM loading of 4,258 g / L with a ratio of 0:28:1. Compared with Example 1A, the loading was reduced, and compared with Example 1, the zones contained more Rh. After the sample was aged in an oven at 950 °C for 24 hours, it was tested on a CNG engine for the WHTC cycle. Compared with Example 1A, although the total loading was reduced, the emissions of CO and NO x and the NH3 production were improved. Only the CH4 emission increased slightly but was still significantly lower than the limit. See Figure 3 .

[0101] Example 1C (Pd / Rh Bimetal)

[0102] In this example, the TWC functional zones were coated on a ceramic honeycomb monolith with an average loading of 5,121 g / L and a ratio of 0:24:1. The front zone had a PGM loading of 5,121 g / L with a ratio of 0:12:1. The rear zone had a PGM loading of 5,121 g / L with a ratio of 0:1:0. In this example, compared with Examples 1A and 1B, the total loading was slightly increased, but it contained less Rh, and the PGM distribution was different from that of Examples 1A and 1B. After the sample was aged in an oven at 950 °C for 24 hours, it was tested on a CNG engine for the WHTC cycle. The results showed that compared with Examples 1A and 1B, all the emissions of CO, CH4, and NO x were significantly improved. Only the NH3 production was higher but was still significantly lower than the limit. See Figure 3 .

[0103] Example 1D (Pd / Rh Bimetal)

[0104] In this example, the TWC function is coated on a ceramic honeycomb monolith and divided into two layers. The average loading is 5,297 g / L, and the ratio is 0:16:1 (non-zoned). The sample is tested on a CNG engine under the WHTC cycle. The results show that the emissions of CO, NO x and CH4 are lower than the limits of the Euro VI standard for CNG HD vehicles. See Figure 4 .

[0105] Example 1E (Pd / Rh Bimetal)

[0106] In this example, the TWC function is coated on a ceramic honeycomb monolith and divided into two layers. The average loading is 5,297 g / L, and the ratio is 0:29:1 (non-zoned). The sample is tested on a CNG engine under the WHTC cycle. The results show that the emissions of CO, NO x and CH4 are lower than the limits of the Euro VI standard for CNG HD vehicles. See Figure 4 . Compared with Example 1D, the PGM with different Pd:Rh ratios after adjustment slightly improves the emissions of CO, NO x and CH4.

[0107] Example 1F (Pd / Rh Bimetal)

[0108] In this example, the TWC function is coated on a ceramic honeycomb monolith in a zoned manner. The average loading is 5,202 g / L, and the ratio is 0:14:1. The front zone PGM has a 5,226 g / L PGM loading, and the ratio is 0:9.4:1. The rear zone has a 5,173 g / L PGM loading, and the ratio is 0:26.2:1. The sample is tested on a CNG engine under the WHTC cycle. The results show that the emissions of CO, NO x and CH4 are lower than the limits of the Euro VI standard for CNG HD vehicles. See Figure 4 . The zoned structure with a higher Rh content significantly improves the performance of NO x . The CH4 level is comparable to that of Examples 1D and 1E, and the CO level is slightly higher but still remains extremely low.

[0109] Example 2A (Pt / Pd / Rh Trimetal)

[0110] In this example, the TWC function is coated on a ceramic honeycomb monolith and divided into two layers. The average loading is 3,531 g / L, and the ratio is 3:6:1 (non-zoned). The sample is tested on a CNG engine under the WHTC cycle. This sample shows that the emissions of CO, NO xThe CO, CH4 emissions and NH3 generation amount are all lower than the limits of the Euro VI standard for CNG HD vehicles, see Figure 5 .

[0111] Example 2B (Pt / Pd / Rh three metals)

[0112] In this example, the TWC function is coated on a ceramic honeycomb monolith and divided into two layers, with an average loading of 2.469 g / L and a ratio of 4:5:1 (non-zoned). The sample is tested on a CNG engine under the WHTC cycle. This sample shows that the CO, NO x The CO, CH4 emissions and NH3 generation amount are all lower than the limits of the Euro VI standard for CNG HD vehicles, see Figure 5 .

[0113] Example 2C (Pt / Pd / Rh three metals)

[0114] In this example, the TWC function is coated on a ceramic honeycomb monolith and divided into two layers, with an average loading of 1,432 g / L and a ratio of 6:3:1 (non-zoned). The sample is tested on a CNG engine under the WHTC cycle. This sample shows that the CO, NO x The CO, CH4 emissions and NH3 generation amount are all lower than the limits of the Euro VI standard for CNG HD vehicles, see Figure 5 .

[0115] Example 2D (Pt / Pd / Rh three metals)

[0116] In this example, the TWC function is coated on a ceramic honeycomb monolith in a zoned manner and divided into two zones, each zone having two layers, with an average loading of 5.561 g / L and a ratio of 5:14:1. The front zone has a PGM loading of 7,062 g / L with a ratio of 6:9:1. The rear zone has a PGM loading of 4,061 g / L with a ratio of 0:35:1. The sample is tested on a CNG engine under the WHTC cycle. The results show that the CO, NO x The CO, CH4 emissions and NH3 generation amount are all lower than the limits of the Euro VI standard for CNG HD vehicles, see Figure 6 .

[0117] Example 2E (Pt / Pd / Rh three metals)

[0118] In this embodiment, the TWC functional partition is coated on a ceramic honeycomb monolith, which is divided into two domain regions, each region having two layers, with an average loading of 5.297 g / L and a ratio of 3:17:1. The front region has a 7,062 g / L PGM loading with a ratio of 4:13:1. The rear region has a 3,531 g / L PGM loading with a ratio of 0:29:1. The sample is subjected to a WHTC cycle test on a CNG engine. The results show that the emissions of CO, NO x and CH4 and the generation amount of NH3 are all lower than the limits of the Euro VI standard for CNG HD vehicles, see Figure 6 .

[0119] Example 2F (Pt / Pd / Rh trimetal)

[0120] In this embodiment, the TWC functional partition is coated on a ceramic honeycomb monolith, which is divided into two regions, each region having two layers, with an average loading of 5.561 g / L and a ratio of 8:24:1. The front region has a 7,062 g / L PGM loading with a ratio of 12:18:1. The rear region has a 4,061 g / L PGM loading with a ratio of 0:35:1. The sample is subjected to a WHTC cycle test on a CNG engine. The results show that the emissions of CO, NO x and CH4 and the generation amount of NH3 are all lower than the limits of the Euro VI standard for CNG HD vehicles, see Figure 6 .

[0121] Example 3A (Pt / Pd bimetal)

[0122] In this embodiment, the TWC function is coated on a ceramic honeycomb monolith and divided into two layers, with an average loading of 5,297 g / L and a ratio of 1:6:0 (not partitioned). After the sample is aged in an oven at 950 °C for 24 hours, it is subjected to a WHTC cycle test on a CNG engine. The results show that the emissions of CO, NO x and CH4 are lower than the limits of the Euro VI standard for CNG HD vehicles, but the NH3 emission exceeds the Euro VI standard limit, see Figure 7 . After SAOC treatment, the NH3 emission level of this Pt / Pd bimetal TWC is reduced below the Euro VI standard limit.

[0123] Example 3B (Pt / Pd bimetal)

[0124] In this embodiment, the TWC function is coated on a ceramic honeycomb monolith and divided into two layers, with an average loading of 5.297 g / L and a ratio of 19:1:0 (not partitioned). After the sample is aged in an oven at 950 °C for 24 hours, it is subjected to a WHTC cycle test on a CNG engine. The results show that the emissions of CO, NO xThe CO and CH4 emissions are both lower than the limits for CNG HD vehicles in the Euro VI standard, but the NH3 emission exceeds the Euro VI standard limit. See Figure 7 . After SAOC treatment, the NH3 emission of this Pt / Pd bimetallic TWC is reduced to below the Euro VI standard limit.

[0125] Example 3C (Pt / Pd bimetallic)

[0126] In this example, the TWC functional zones are coated on a ceramic honeycomb substrate, divided into two regions, with two layers in each region; the average loading is 5.297 g / L, and the ratio is 1:1:0. The front region has a PGM loading of 5,297 g / L with a ratio of 19:1:0. The rear region has a PGM loading of 5,297 g / L with a ratio of 1:6:0. After the sample is aged in an oven at 950 °C for 24 hours, a WHTC cycle test is carried out on a CNG engine. The results show that the CO, NO x and CH4 emissions are both lower than the limits for CNG HD vehicles in the Euro VI standard, but the NH3 emission exceeds the Euro VI standard limit. See Figure 7 . After SAOC treatment, the relatively high NH3 emission of this Pt / Pd bimetallic TWC is reduced to below the Euro VI standard limit.

[0127] SAOC function

[0128] Examples 4A - 4E

[0129] In the first embodiment (4A), the SAOC consists of two layers: a mesoporous material layer at the top (SAR>15, 140 g / L), and a thin oxide layer containing 0.07 g / L of Pt at the bottom (20 g / L). In the second embodiment (4B), the active oxidant is placed in the rear area of the element (20 g / L), and the Pt loading is the same as in Example 4A. In the third embodiment (4C), the SAOC consists of two layers: a mesoporous material different from that of Examples 4A & 4B is coated on the first layer at the top (140 g / L), and a thin oxide layer with a Pt loading of (0.07 g / L) at the bottom (20 g / L). In the fourth embodiment (4D), the SAOC consists of a single-layer structure (140 g / L) of a third mesoporous material (SAR>15) without any Pt layer or stripe. The fifth embodiment (4E) consists of a mesoporous material (SAR>15, 120 g / L) with 3 wt% zirconia at the bottom, the same as in Example 4D, and a thin oxide layer with a Pt loading of (0.07 g / L) at the bottom (20 g / L). The samples were tested on an LD engine bench under the New European Driving Cycle (NEDC), and ammonia generation was measured during the cycle. The ammonia generation of different SAOC samples was compared with that of a sample without any coating (uncoated SAOC) in the SAOC. Downstream of the exhaust pipe, a thermally aged (1000 °C × 10 h) Pd-Rh TWC (Example 1D, Pt:Pd:Rh 0:16.1, 5.297 g / L) was placed to generate ammonia. Fresh SAOC samples and SAOC samples aged at HT-700 °C / 20 h were measured. The results show that the average NH3 level in the test cycle was reduced by 60 - 94% compared with the system without any SAOC coating (Table 1). Hydrothermal aging at 700 °C seems to have only a small effect on the ammonia oxidation ability of the tested SAOC samples. When comparing the efficiency of the samples, it can be seen that the NH3 level of sample 4E is the lowest among the Pt-containing samples. Sample 4D can still reduce the NH3 level even without Pt and after aging. At the same time, the NEDC cycle emissions were measured to evaluate the effect of SAOC on the TWC function (Table 2). Compared with TWC + uncoated SAOC, the relative emissions of CO and THC for TWC + SAOC are very close, indicating that SAOC has little effect on the oxidation of CO and HC. For all tested SAOCs, NO x emissions were improved (relative emissions were lower than TWC + blank SAOC), indicating a higher conversion rate of NO x with the help of SAOC. Fresh and HT-700 °C / 20 h aged SAOC sample 4D achieved the lowest NO x emissions.

[0130] Table 1 Average ammonia (NH3) production of LD vehicles in NEDC cycle tests

[0131]

[0132]

[0133] Table 2 Relative emissions of LD vehicles in NEDC cycle tests compared with TWC + uncoated SAOC

[0134] CO THC <![CDATA[NO x > Aged TWC + Uncoated SAOC 1 1 1 Aged TWC + Sample 4A - As New 1 0.96 0.87 Aged TWC + Sample 4A - Aged 1.1 0.98 0.8 Aged TWC + Sample 4B - As New 1.06 0.96 0.67 Aged TWC + Sample 4B - Aged 1.02 0.96 0.8 Aged TWC + Sample 4C - As New 0.88 0.95 0.67 Aged TWC + Sample 4C - Aged 0.93 1.01 0.96 Aged TWC + Sample 4D - As New 0.95 1 0.63 Aged TWC + Sample 4D - Aged 0.96 0.99 0.70 Aged TWC + Sample 4E - As New 1.02 0.96 0.82 Aged TWC + Sample 4E - Aged 1.04 0.98 0.78

[0135] Table 2 further confirms the selective characteristics of SAOC, which is confirmed by the decrease in the relative value of NO x If the reaction is not selective, due to the conversion of NH3 to NO x , the relative value would be greater than 1.

[0136] Further Conclusions Based on the Above Experiments

[0137] The SPT should be separated from the TWC, that is, the SPT is located on a different first substrate and the TWC is located on a different second substrate, and there is no overlapping area between the two to ensure sulfur and phosphorus capture and the best TWC function. This means that the SPT is specifically used to separately collect sulfur and phosphorus from the TWC to protect the TWC performance from being poisoned. If the capture function is part of the TWC, it will affect the performance of the TWC.

[0138] SAOC selectively converts ammonia to N2 through a specific coating. SAOC not only aims to oxidize NH3 but also selectively converts it to N2. If SAOC is not selective, it will convert ammonia (NH3) to NO x , which is contrary to the expected function.

[0139] Since Rh is the most expensive active PGM and the price of Pd is higher than that of Pt, reducing the amount of Rh in the TWC and replacing part of Pd with Pt can reduce the cost of the TWC; however, ammonia (NH3) production may be a problem.

[0140] When changing the Pd-Rh based TWC to a high Pt content trimetallic or even a Pt-Pd based TWC, the SAOC function is required.

[0141] A special SAOC formulation is required to control the ammonia production below the limit value, so selective ammonia oxidation is needed to avoid oxidation back to NO x . Based on this, when using SAOC, the ammonia production after TWC and SAOC must be less than the ammonia production after a single TWC; at the same time, the selectivity ratio is demonstrated:

[0142]

[0143] In the three-metal TWC, a decrease in the Rh content associated with an increase in the Pt / Pd ratio (i.e., keeping the Pt loading constant while reducing the Pd loading; thus reducing the total loading) significantly reduces the cost of the TWC, but at the same time leads to a higher amount of NH3 production.

[0144] This can be seen in Figure 5 (Examples 2A-2C), which shows the results of the three-metal TWC catalyst. The effect of Rh loading and Pt / Pd ratio on NH3 production can be seen in Figures 8-10 . In the partition samples (Examples 2D-2F and Figure 6 ) where the three-metal TWC is in the front region, the increase in NH3 production is more related to the decrease in Rh content rather than the Pt / Pd ratio (see Figures 11-12 ): when the Rh loading decreases, the NH3 production increases.

[0145] Based on these results, we can determine the maximum Pt / Pd ratio and the minimum Rh value in the three-metal structure: Pt / Pd should be equal to or < 4, and the Rh loading should be equal to or > 0.05 g / L, so that the maximum NH3 production in the WHTC is 10 ppm. For the Pt-Pd TWC structure without Rh, SAOC is crucial.

[0146] This also means that another aspect described herein is a TWC that includes a specific Pt / Pd ratio and a specific Rh-containing coating layer. When using this specific TWC, during the operation of an engine running at stoichiometric ratio, NH3 can be kept at a low level, especially below 10 ppm.

[0147] As Figure 8 shown, when the Pt / Pd ratio in Samples 2A-2C increases, the amount of ammonia (NH3) production increases.

[0148] Figure 9 Shows the trend line (linear regression) of NH3 vs Pt / Pd for higher Pt / Pd in the three-metal TWC Samples 2A-2C.

[0149] Figure 10 Shows the trend line of NH3 vs Rh loading for lower Rh loading in the three-metal TWC 2A-2C.

[0150] In Samples 2A-2C, when the Pt / Pd ratio reaches about 4, the amount of ammonia (NH3) production reaches the limit value of 10 ppm.

[0151] In Samples 2A-2C, the amount of ammonia (NH3) production increases with the decrease in Rh loading.

[0152] Based on the results of Samples 2A - 2C ( Figure 5 ), we can infer (using linear regression to draw a trend line) the amount of NH3 generation when the Rh loading is lower than that of the samples and the similar Pt / Pd ratio is higher than that of the samples. The estimated limit for the maximum NH3 generation of 10 ppm is a Pt / Pd ratio of approximately 4 and a minimum Rh loading of approximately 0.05 g / L.

[0153] Figure 11 NH3 vs. Pt / Pd in the partitioned three - metal TWC Samples 2D - 2F is shown.

[0154] As Figure 12 shown, in Samples 2D - 2F, the amount of ammonia (NH3) generation increases with the decrease of Rh loading.

[0155] For the partitioned Samples 2D - 2F ( Figure 6 ), the Pt / Pd ratio has no significant effect on the NH3 generation level, but the Rh loading has a significant effect on NH3 generation: Making a similar inference for the lower Rh loading in the samples, the minimum Rh loading for generating a maximum of 10 ppm NH3 is approximately 0.05 - 0.1 g / L.

[0156] If Rh is omitted and the TWC is composed of Pt - Pd technology, as shown by the results of Examples 3A - 3C in Figure 7 , it will inevitably lead to a high amount of NH3 generation, so SAOC is obviously required. In the Rh - free TWC, the Pt / Pd ratio has little effect on the amount of NH3 generation: The NH3 generation amounts of all samples in Examples 3A - 3C are at a high level (also as Figure 13 shown).

Claims

1. A multifunctional catalyst system for reducing harmful exhaust emissions in the exhaust gas stream of a stoichiometrically operated engine, the system comprising: a) A coating comprising a sulfur oxide and phosphorus trap (SPT) on a first substrate; b) A three-way catalyst (TWC) on a second substrate; and c) A selective ammonia oxidation catalyst (SAOC) on a third substrate; wherein the first substrate and the second substrate are different substrates, avoiding any overlap between the SPT and the TWC; wherein the SPT is located upstream of the TWC, and the ammonia oxidation catalyst is located downstream of the TWC, the multifunctional catalyst system being adapted to be located downstream of a stoichiometrically operated engine, the multifunctional catalyst system being adapted to be in fluid communication with the exhaust gas stream; wherein the SPT is present in an amount of 10 - 50 vol% of the total volume of the TWC; wherein the SAOC is present in an amount of 10 - 50 vol% of the total volume of the TWC.

2. The catalyst composition according to claim 1, wherein: i) The first substrate, the second substrate and the third substrate are different substrates; or ii) The second substrate and the third substrate are the same substrate, and the first substrate is a different substrate.

3. The catalyst system according to any one of claims 1 - 2, wherein the SPT is present in an amount of 20 - 40 vol% of the total volume of the TWC, most preferably 25 - 35 vol%.

4. The catalyst system according to any one of claims 1 - 3, wherein the SAOC is present in an amount of 20 - 40 vol% of the total volume of the TWC, most preferably 25 - 35 vol%.

5. The catalyst system according to any one of claims 1 - 4, wherein the TWC comprises at least one of Pt, Pd and Rh, and the total amount of the coating in grams per liter of the coating layer (g / L) is from 50 g / L to 400 g / L.

6. The catalyst system according to any one of claims 1 - 4, wherein the Pt / Pd ratio (wt% / wt%) of the TWC is less than 6; preferably 4 or less than 4.

7. The catalyst system according to claim 6, wherein the Pt / Pd ratio (wt% / wt%) of the TWC is 4 or less than 4, and a minimum of 0.05 g Rh / L of the coating layer.

8. The catalyst system according to any one of claims 1 - 7, wherein the SPT comprises at least one of Cu, Mn and Ce, and the total amount of the coating in grams per liter of the coating layer (g / L) is from 50 g / L to 400 g / L.

9. The catalyst system according to claim 8, wherein the SPT further comprises at least one of Pt and Pd.

10. The catalyst system according to any one of claims 1 - 9, wherein the SAOC comprises at least one of Fe, Cu, Sc, Y, La, Ce, Pr, Nd, Ti, Zr and Hf.

11. The catalyst system according to claim 10, wherein the SAOC selectively converts ammonia to N2, and the ammonia is maintained below 10 ppm after being treated by the SAOC.

12. The catalyst system according to claim 11, wherein the SAOC comprises at least one of Pt and Pd.

13. The catalyst system according to any one of claims 1-12, wherein the first substrate, the second substrate, and / or the third substrate is selected from ceramic or metal honeycomb monoliths, such as flow-through or wall-flow substrates.

14. The catalyst system according to any one of claims 1-13, wherein the stoichiometrically operated engine is a natural gas or biogas engine, such as an engine using CNG, LNG, bio-CNG, and bio-LNG as fuels.

15. A method for reducing the harmful exhaust emissions of a stoichiometrically operated engine, comprising using the multifunctional catalyst system according to any one of claims 1-14.

16. The method according to claim 15, wherein the stoichiometrically operated engine is a natural gas or biogas engine, such as an engine using CNG, LNG, bio-CNG, and bio-LNG as fuels.

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