Nitrous oxide removal catalyst, preparation method thereof, emission treatment method and system using the catalyst

Abstract

A catalyst composite for removing nitrous oxide from an exhaust stream includes a ceria-based support, a rhodium component impregnated on a surface of the ceria-based support, and a surface modifier impregnated on the surface of the ceria-based support. The surface modifier includes one or more metal oxides selected from zirconia and oxides of rare earth elements.

Description

NITROUS OXIDE REMOVAL CATALYST, PREPARATION METHOD THEREOF, EMISSION TREATMENT METHOD AND SYSTEM USING THE CATALYST TECHNICAL FIELD

[0001] The present disclosure is directed to the field of exhaust treatment of internal combustion engines. More particularly, the present disclosure pertains to a nitrous oxide (N2O) removal catalyst, a method for preparing the N2O removal catalyst, and an emission system and emission treatment method using the N2O removal catalyst. BACKGROUND

[0002] N2O is considered a powerful greenhouse gas with global warming potential (GWP) of 298 times that of CO2. Automotive exhaust is one common source of N2O emissions, as a byproduct of conventional fuel combustion and as a byproduct formed during catalytic treatments of exhaust gases, e.g., NOx reduction with NH3 assisted by selective catalytic reduction (SCR) catalysts, NH3 oxidation using AMOX catalysts, NOx / HC reduction using Diesel Oxidation Catalyst (DOC) and catalyzed soot filters (CSF), etc. In addition, N2O emission is expected to be a more pressing problem for engines powered by some alternative fuels, such as ammonia or hydrogen. The control of N2O emission is a key component of emission control systems of H2internal combustion engine (H2-ICE) and NH3-ICE. As such, emission regulations in US, EU and China have stringent N2O emission standards.

[0003] One strategy to minimize N2O emissions for internal combustion engines is to optimize catalyst designs for the lowest or acceptable levels of N2O formation. This strategy, however, often limits the catalytic functions for reducing other pollutants, such as NOx, hydrocarbons, or NH3. Another strategy to control N2O emissions is to decompose N2O, after formation, to N2 and O2. Direct N2O abatement is highly desirable for NH3 powered engines, where engine-out N2O is significant. Currently, there is no commercial N2O removal catalyst available for automotive applications. Therefore, it is desired to develop a more active N2O removal catalyst. SUMMARY

[0004] The present disclosure generally provides a catalyst composite for removing nitrous oxide from an exhaust stream, a catalytic article including such catalyst composite, an 1 1622111714.1emission treatment system and method utilizing such catalyst composite, and a method for preparing such catalyst composite.

[0005] One aspect of the present disclosure provides a catalyst composite for removing nitrous oxide from an exhaust stream. The catalyst composite includes a ceria-based support, a rhodium component impregnated on a surface of the ceria-based support, and a surface modifier impregnated on the surface of the ceria-based support, where the surface modifier includes one or more metal oxides selected from zirconia and oxides of rare earth elements.

[0006] In some embodiments, the rhodium component includes either Rh metal nanoparticles or Rh oxide nanoparticles or a combination thereof supported on the surface of the ceria- based support, and the surface modifier is bonded to the surface sites of the ceria-based support.

[0007] In some embodiments, the catalyst composite includes the rhodium component in an amount of about 0.1 wt. % to about 3 wt.% with respect to a weight of the catalyst composite, calculated on a metal basis.

[0008] In some embodiments, the catalyst composite includes the rhodium component in an amount of about 0.5 wt. % with respect to a weight of the catalyst composite, calculated on a metal basis.

[0009] In some embodiments, the surface modifier includes metal oxides selected from oxides of zirconium, yttrium, lanthanum, praseodymium, neodymium, promethium, samarium, europium, and gadolinium.

[0010] In some embodiments, the catalyst composite includes the surface modifier in an amount of about 0.1 wt. % to about 15 wt. % with respect to a weight of the catalyst composite, calculated on a metal oxide basis.

[0011] In some embodiments, the catalyst composite includes the surface modifier in an amount of about 0.5 wt. % to about 5 wt. % with respect to a weight of the catalyst composite, calculated on a metal oxide basis.

[0012] In some embodiments, the ceria-based support is a phase-pure crystalline material having a cubic fluorite structure. 2 1622111714.1

[0013] In some embodiments, the ceria-based support is a phase-pure solid solution comprising at least about 85 wt. % ceria and less than about 15 wt. % one or oxides of Zr, La, Y, Pr, and Nd or combinations thereof.

[0014] In some embodiments, the ceria-based support includes ceria having an average crystallite size about 5 nm to about 20 nm measured by X-ray diffraction (XRD) spectroscopy.

[0015] In some embodiments, the ceria-based support has a BET surface area of about 30 m2 / g to about 200 m2 / g.

[0016] In some embodiments, the ceria-based support has a BET surface area of about 50 m2 / g to about 80 m2 / g.

[0017] Another aspect of the present disclosure provides a catalytic article for nitrous oxide removal from an exhaust stream of an internal combustion engine. The catalytic article includes a substrate and the catalyst composite loaded on the substrate.

[0018] Another aspect of the present disclosure provides an emission treatment system for treatment of an exhaust stream from an internal combustion engine. The emission treatment system includes an exhaust conduit in fluid communication with the internal combustion engine via an exhaust manifold, and the catalyst composite for removing nitrous oxide.

[0019] In some embodiments, the emission treatment system includes one or more components selected from a three-way conversion (TWC) catalyst, a four-way conversion catalyst (FWC), a selective catalytic (NOx) reduction (SCR) catalyst, a lean NOxtrap (LNT), a diesel oxidation catalyst (DOC), catalytic soot filter (CSF), an ammonia oxidation catalyst (AMOX), a H2 oxidation catalyst (OC), and a N2O decomposition catalyst. The catalyst composite is disposed downstream of the one or more components or is disposed on a same carrier of the one or more components.

[0020] Another aspect of the present disclosure provides a method for treating exhaust gases. The method includes providing a catalyst composite and contacting a gaseous stream comprising water, nitrous oxide, and oxygen with the catalyst composite. The catalyst composite includes a ceria-based support, a rhodium component impregnated on a surface of the ceria-based support, and a surface modifier impregnated on the surface of the ceria-based 3 1622111714.1support, where the surface modifier includes one or more metal oxides selected from zirconia and oxides of rare earth elements.

[0021] Another aspect of the present disclosure provides a method for preparing a nitrous oxide removal catalyst composite. The method includes providing a ceria-based support; depositing rhodium component onto a surface of the ceria-based support; and depositing a surface modifier onto the surface of the ceria-based support. The surface modifier includes one or more metal oxides selected from zirconia and oxides of rare earth elements. Depositing the rhodium component and depositing the surface modifier are concurrent or sequential.

[0022] In some embodiments, depositing the rhodium component or depositing the surface modifier is performed by a wetness impregnation method.

[0023] In some embodiments, the wetness impregnation method is an incipient wetness impregnation method.

[0024] In some embodiments, depositing the rhodium component or depositing the surface modifier uses nitrate precursors thereof.

[0025] In some embodiments, the method for preparing the nitrous oxide removal catalyst composite includes pre-calcining the ceria-based support prior to deposition.

[0026] In some embodiments, the method for preparing the nitrous oxide removal catalyst composite includes performing calcination after each deposition.

[0027] In some embodiments, the method for preparing the nitrous oxide removal catalyst composite includes performing calcination after both rhodium component and surface modifier are deposited onto the ceria-based support.

[0028] In some embodiments, the rhodium component includes either Rh metal nanoparticles or Rh oxide nanoparticles or a combination thereof supported on the surface of the ceria- based support, and the surface modifier is bonded to the surface sites of the ceria-based support. 4 1622111714.1

[0029] In some embodiments, a loading of the rhodium component on the catalyst composite is in an amount of about 0.1 wt. % to about 3 wt.% with respect to a weight of the catalyst composite, calculated on a metal basis.

[0030] In some embodiments, the loading of the rhodium component on the catalyst composite is in an amount of about 0.5 wt. % with respect to a weight of the catalyst composite, calculated on a metal basis.

[0031] In some embodiments, the surface modifier includes metal oxides selected from oxides of zirconium, yttrium, lanthanum, praseodymium, neodymium, promethium, samarium, europium, and gadolinium.

[0032] In some embodiments, the ceria-based support is a phase-pure crystalline material having a cubic fluorite structure.

[0033] In some embodiments, the ceria-based support is a phase-pure solid solution comprising at least about 85 wt. % ceria and less than about 15 wt. % one or oxides of Zr, La, Y, Pr, and Nd or combinations thereof.

[0034] In some embodiments, the ceria-based support includes ceria having an average crystallite size about 5 nm to about 20 nm measured by X-ray diffraction (XRD) spectroscopy.

[0035] In some embodiments, the ceria-based support has a BET surface area of about 30 m2 / g to about 200 m2 / g.

[0036] In some embodiments, the ceria-based support has a BET surface area of about 50 m2 / g to about 80 m2 / g.

[0037] In some embodiments, a loading of the surface modifier on the catalyst composite is in an amount of about 0.1 wt. % to about 15 wt. % with respect to a weight of the catalyst composite, calculated on a metal oxide basis.

[0038] In some embodiments, the loading of the surface modifier on the catalyst composite is in an amount of about 0.5 wt. % to about 5 wt. % with respect to a weight of the catalyst composite, calculated on a metal oxide basis. BRIEF DESCRIPTION OF DRAWINGS 5 1622111714.1

[0039] The features of the present disclosure and various advantages thereof will become apparent in consideration of the following detailed description of the embodiments in conjunction with the accompany drawings. Below is a brief description of the accompanying drawings.

[0040] FIG.1 schematically shows a catalyst composite for removing nitrous oxide in accordance with some embodiments of the present disclosure.

[0041] FIG.2A schematically shows a catalytic article for removing nitrous oxide in accordance with some embodiments of the present disclosure.

[0042] FIG.2B schematically shows an enlarged partial cross-sectional view of the catalytic article in FIG.2A.

[0043] FIG.3 schematically shows an enlarged cutaway view of the catalytic article in FIG. 2A.

[0044] FIG.4 schematically shows examples of an emission treatment system in accordance with some embodiments of the present disclosure.

[0045] FIG.5 is a flowchart showing a method for treating exhaust gases in accordance with an embodiment.

[0046] FIG.6 is a flowchart showing a method for preparing a nitrous oxide (N2O) removal catalyst in accordance with some embodiments of the present disclosure.

[0047] FIG.7 is a graphical representation of the N2O conversion of nitrous oxide removal catalysts in accordance with some embodiments of the present disclosure.

[0048] FIG.8 is a graphical representation of the N2O conversion of nitrous oxide removal catalysts in accordance with some embodiments of the present disclosure.

[0049] FIG.9 is a graphical representation of the N2O conversion of nitrous oxide removal catalysts in accordance with some embodiments of the present disclosure.

[0050] FIG.10 is a graphical representation of the N2O conversion of nitrous oxide removal catalysts in accordance with some embodiments of the present disclosure. 6 1622111714.1

[0051] FIG.11 a graphical representation of the N2O conversion of nitrous oxide removal catalysts in accordance with some embodiments of the present disclosure.

[0052] FIG.12 is a graphical representation of the N2O conversion of nitrous oxide removal catalysts in accordance with some embodiments of the present disclosure.

[0053] FIG.13 is a graphical representation of the N2O conversion of nitrous oxide removal catalysts in accordance with some embodiments of the present disclosure.

[0054] FIG.14 is a graphical representation of the N2O conversion of nitrous oxide removal catalysts in accordance with some embodiments of the present disclosure.

[0055] FIG.15 is a bar graph comparing the N2O conversion of nitrous oxide removal catalysts at 400°C in accordance with some embodiments of the present disclosure.

[0056] FIG.16 is a bar graph comparing the N2O conversion of nitrous oxide removal catalysts at 450°C in accordance with some embodiments of the present disclosure.

[0057] FIG.17 is a bar graph comparing the N2O conversion of nitrous oxide removal catalysts with other catalysts at 450°C in accordance with some embodiments of the present disclosure.

[0058] FIG.18 is a graphical representation of the N2O conversion of comparative example catalysts in accordance with some embodiments of the present disclosure. DETAILED DESCRIPTION OF EMBODIMENTS

[0059] The embodiments described below are for illustrative purpose regarding the principles and applications of the present disclosure but are not intended to limit the present disclosure to the details of any particular embodiments. Based on the description of the present disclosure, those skilled in the art should be able to obtain various modifications and variations of the method and apparatus of the present disclosure without departing from the spirit and scope of the present disclosure. Therefore, these modifications and variations are within the scope of the appended claims and their equivalents.

[0060] Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art. Reference throughout this specification to “one embodiment,” “some embodiments,” “one or more embodiments” 7 1622111714.1or “an embodiment” means that one or more particular features, structures, elements, materials, or characteristics described in connection with the referenced embodiment(s) is included in one or more embodiments of the present disclosure. Articles “a,” “an,” and “the” are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article and include plural references unless the context clearly dictates otherwise. As used in this document, the term “comprising” and “including” do not intend to indicate exclusive inclusion. The term “about” used throughout this specification is used to describe and account for small fluctuations. The phrase “at least one” include one or more than one of the objects associated with such phrase. The phrase “A or B” means “A,” “B,” or “A and B.” The phrase “at least one of ... or ...” refers to all possible combinations of the grammatical objects of this phrase. For example, “at least A, B, or C” refers to A alone, B alone, C alone, A and B together, A and C together, B and C together, or A, B, and C all together.

[0061] The term “catalyst” refers to a material that promotes a chemical reaction. A catalyst composite includes active species that have catalytic activity and a “support” that carries or supports such active species. Active species can refer to precious metals, stabilizers, promoters, binders, modifier. The support can receive the active species via a suitable method, e.g., impregnation, precipitation, association, dispersion, deposition, etc. In some embodiments of the present disclosure, ceria-based material is selected as the support to receive active species, e.g., rhodium (Rh) component, surface modifier, etc.

[0062] The rare earth metal elements include scandium, yttrium, and the lanthanum series defined in the Periodic Table of Elements and mixtures thereof. Among the rare earth metal elements, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium are considered light rare earth metal element (LREE). Rare earth metal oxides refer to one or more oxides of rare earth metal elements. In some embodiments of the present disclosure, LREE oxides are selected as the surface modifier to modify the surface of the support, e.g., ceria-based support.

[0063] The term “catalytic article” refers to a component that is used to promote a desired reaction. In some embodiments of the present disclosure, the catalytic article includes a “substrate” having at least one catalytic coating disposed thereon, where the catalytic coating is made by a catalyst composite. 8 1622111714.1

[0064] The term “exhaust stream” refers to flowing engine effluent, including gaseous components and nongaseous components such as liquid droplets, solid particulates and the like. An exhaust stream of a lean burn engine typically further includes combustion products, products of incomplete combustion, oxides of nitrogen, combustible and / or carbonaceous particulate matter (soot) and un-reacted oxygen and / or nitrogen.

[0065] The term “in fluid communication” is used to refer to articles positioned on the same exhaust line, i.e., a common exhaust stream passes through articles that are in fluid communication with each other. Articles in fluid communication may be adjacent to each other in the exhaust line. Alternatively, articles in fluid communication may be separated by one or more articles.

[0066] Term “surface modifier” refers to a component on the surface, instead of in the bulk, of a material and modifies one or more characteristic properties of the material. The surface modifier may be bonded to surface sites of the material. The surface sites may include surface defect sites, for example, surface oxygen vacancies of an oxide material. In some embodiments of the present disclosure, the surface modifier is disposed on a surface of the ceria-based support and boost the catalytic activity of the ceria-based support for N2O removal. The surface modifier may be bonded to the surface sites of the ceria-based support. For example, the surface modifier may occupy the oxygen vacancies of the ceria-based support. As mentioned above, the most active N2O removal catalysts reported, Rh / CeO2 (ceria-based support with Rh oxides impregnated on its surface), do not have sufficient catalytic activity for automotive applications. One possible explanation is, although surface RhOx nanoparticles / ceria support has good redox property and easy oxygen transport, the Rh component may atomically bond with lattice oxygen of ceria, leading to unsatisfactory activity of existing Rh / CeO2catalysts. The RhOx nanoparticles refer to either Rh metal nanoparticles or Rh oxide nanoparticles. In some embodiments of the present disclosure, suitable component (e.g., one or more of zirconia and oxides of rare earth metals) is selected as surface modifier to modify the surface of Rh / CeO2. With introduction of the surface modifier onto the surface of Rh / CeO2, the surface modifier may selectively block the undesired surface sites of CeO2, thereby preventing Rh from atomically bonding with lattice oxygen (i.e., preventing Rh from dissolving into bulk of CeO2). As such, surface modified Rh / CeO2 is more likely to have better catalytic performance over Rh / CeO2with respect to N2O removal. 9 1622111714.1

[0067] As noted above, automotive exhaust is one possible emission source of N2O, a more powerful greenhouse gas than CO2. Currently, N2O decomposition is practiced for treating the off-gases from nitric acid and adipic acid production. The temperatures for these operations are much higher than those of typical automotive exhaust, and the process streams for these operations contain little water (e.g., <1%). The existing N2O decomposition catalysts may be grouped into three categories: (1) supported PGM, (2) metal oxides with spinel structure; and (3) ion exchanged zeolites. Among all the catalysts reported, supported Rh (e.g., Rh / CeO2) seems to be the most active catalyst at lower temperatures under lean, lean / rich, or stoichiometric engine conditions. A precise comparison of reaction rates is difficult because the experiments were conducted at different conditions. However, it is not difficult to conclude that even the Rh / CeO2catalyst does not provide sufficient activity for automotive applications.

[0068] Catalyst composites provided in the present disclosure are determined to significantly surpass Rh / CeO2for N2O decomposition and may possibly be commercialized for catalyzing N2O decomposition in automotive emission controls. In some embodiments, the catalyst composite includes a ceria-based support, a Rh component impregnated on a surface of the ceria-based support, and a surface modifier impregnated on the surface of the ceria-based support, where the surface modifier includes one or more metal oxides selected from zirconia and oxides of rare earth elements. In some embodiments, the surface modifier includes one or more metal oxides selected from zirconia and oxides of light rare earth element (LREE). The Rh component and the surface modifier may be impregnated onto the surface of the ceria-based support in a concurrent manner or in a sequential manner. For example, the Rh component and the surface modifier may be impregnated onto the ceria-based support in a same impregnation step, the impregnation of the Rh component onto the surface of the ceria- based support followed by the impregnation of the surface modifier on to the ceria-based support, or the impregnation of the surface modifier onto the ceria-based support is followed by the impregnation of the Rh component onto the ceria-based support.

[0069] FIG.1 schematically shows a catalyst composite for removing nitrous oxide (N2O) in accordance with some embodiments of the present disclosure. The catalyst composite includes a ceria-based support 110, a Rh component 120 impregnated onto the surface of the ceria-based support 110, and a surface modifier 130 impregnated onto the surface of the ceria-based support 110. In some embodiments, the Rh component 120 is one of a plurality 10 1622111714.1of Rh components 120. In some embodiments, the surface modifier 130 is one of a plurality of surface modifiers 130.

[0070] The ceria-based support 110 may include any structure effective for removing N2O from an exhaust stream. In some embodiments, the ceria-based support 110 includes a crystalline structure, e.g., a cubic fluorite structure. In some embodiments, the ceria-based support 110 includes an amorphous structure. In some embodiments, the ceria-based support 110 is a mixture of crystalline and amorphous structures. For example, in some embodiments, the ceria-based support is a phase-pure crystalline material having a cubic fluorite structure.

[0071] In some embodiments, the ceria-based support 110 is composed by pure ceria. In some embodiments, the ceria-based support 110 is a solid solution including certain weight percentage of ceria. For example, the ceria-based support 110 is a solid solution of about 50 wt. % to about 100 wt. % ceria with respect to the total weight of the solid solution. In some embodiments, the ceria-based support includes ceria doped with other elements. In some embodiments, the ceria-based support is a phase-pure solid solution comprising at least about 85 wt. % ceria and less than about 15 wt. % one or more oxides of Zr, La, Y, Pr, and Nd or combinations thereof.

[0072] In some embodiments, the ceria in ceria-based support has an average crystallite size about 5 nm to about 20 nm measured by X-ray diffraction (XRD) spectroscopy. In some embodiments, the ceria-based support has a BET surface area of about 30 m2 / g to about 200 m2 / g. For example, in some embodiments, the ceria-based support has a BET surface area of about 50 m2 / g to about 80 m2 / g. In some embodiments, the pore volume of the ceria-based support measured by N2 adsorption is about 0.18 to about 0.24 cm3 / g. In some embodiments, the average pore size (in diameter) measured by N2adsorption is about 4 to about 9 nm.

[0073] The Rh component 120 impregnated on the ceria-based support 110 may be measured by weight with respect to the weight of the catalyst composite. The weight of the catalyst composite is the total weight of the catalyst composite including Rh component, surface modifier, ceria-based support. In some embodiments, the loading of Rh component 120 is greater than 0.1 wt. % but up to about 3 wt. %, calculated on a metal basis. For example, the loading of Rh component 120 is about 0.1 wt. % to about 3 wt. %, about 0.2 wt. % to about 2.5 wt. %, about 0.3 wt.% to about 2 wt.%, about 0.4 wt. % to about 1.5 wt. %. In some 11 1622111714.1embodiments, the loading of Rh component 120 is about 0.5 wt. %. The Rh component 120 may be presented as either Rh metal nanoparticles or Rh oxide nanoparticles supported on the surface of the ceria-based support 110.

[0074] Ceria-based support with RhOx nanoparticles on the surface is found to have good redox property and enhanced oxygen transport, where RhOx nanoparticles refer to either Rh metal nanoparticles or Rh oxide nanoparticles. However, the surface Rh can atomically bond with lattice oxygen of the ceria-based support, thereby dissolving into bulk ceria. Such loss of surface Rh into bulk of ceria may be one of the possible mechanisms explaining the insufficient activity of Rh / CeO2 catalysts.

[0075] Surprisingly, adding a suitable surface modifier 130 onto the ceria-based support 110 can significantly increase the activity of Rh / CeO2. In contrast, adding bulk modifier, e.g., adding similar modifier into the bulk to ceria-based support or forming a solid solution of the modifier and ceria, have a negative effect on the catalytic activity of Rh / CeO2 for N2O removal. The suitable surface modifier 130 includes one or more metal oxides selected from zirconia and oxides of rare earth elements. For example, the surface modifier 130 may include zirconia, the surface modifier 130 may include one or more oxides of rare earth elements, or the surface modifier 130 may include zirconia and one or more oxides of rare earth elements. In some embodiments, the rare earth elements are LREE, including e.g., yttrium (Y), lanthanum (La), neodymium (Nd), praseodymium (Pr), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd). In some embodiments, the surface modifier includes one or more oxides of Y, Zr, La, Pr, Nd, Pm, Sm, Eu, and Gd. It is also surprisingly discovered that surface modification of transition metals including Fe, Ni, Cu, Nb, Mo, Sn, Ba, etc., has negative effect on the catalytic activity of Rh / CeO2 for N2O removal.

[0076] In some embodiments, the surface modifier 130 includes Zr component. In some embodiments, Zr component includes ZrO2. The loading of Zr component, i.e., the amount of the Zr component in the catalyst composite may be measured by weight, on the metal oxide basis, with respect to the weight of the catalyst composite. In some embodiments, the loading of Zr component is less than or equal to about 5 wt. %. For example, the loading of Zr component in the catalyst composite is about 0.5 wt. %, or about 1 wt. %, or about 3 wt. %, or about 5 wt. %. 12 1622111714.1

[0077] In some embodiments, the surface modifier 130 includes Pr component. In some embodiments, the Pr component includes Pr6O11. The loading of Pr component, i.e., the amount of the Pr component in the catalyst composite may be measured by weight, on the metal oxide bases, with respect to the weight of the catalyst composite. In some embodiments, the loading of Pr component is less than or equal to about 10 wt. %. For example, the loading of Pr component in the catalyst composite is less than or equal to about 5 wt. %, or about 0.5 wt. % to about 5 wt. %, or about 1 wt. % to about 2.5 wt.%.

[0078] In some embodiments, the surface modifier 130 includes Gd component. In some embodiments, the Gd component includes Gd2O3. The loading of Gd component, i.e., the amount of the Gd component in the catalyst composite may be measured by weight, on the metal oxide basis, with respect to the weight of the catalyst composite. In some embodiments, the loading of Gd component is less than or equal to about 10 wt. %. For example, the loading of Gd component in the catalyst composite is less than or equal to about 7 wt. %, or about 1 wt. % to about 7 wt. %, or about 1 wt. % to about 5 wt. %.

[0079] In some embodiments, the surface modifier 130 includes Y component. In some embodiments, the Y component include Y2O3. The loading of Y component, i.e., the amount of the Y component in the catalyst composite may be measured by weight, on the metal oxide basis, with respect to the weight of the catalyst composite. In some embodiments, the loading of Y component is less than or equal to about 7 wt. %. For example, the loading of Y component in the catalyst composite is less than or equal to about 0.5 wt. % to about 7 wt. %, or about 0.5 wt. % to about 5 wt. %, or about 1 wt. % to about 5 wt. %.

[0080] In some embodiments, the surface modifier 130 includes Nd component. In some embodiments, the Nd component includes Nd2O3. The loading of Nd component, i.e., the amount of the Nd component in the catalyst composite may be measured by weight, one the metal oxide basis, with respect to the weight of the catalyst composite. In some embodiments, the loading of Nd component is less than or equal to about 7 wt. %. For example, the loading of Nd component in the catalyst composite is less than or equal to about 0.5 wt. % to about 7 wt. %, or about 1.1 wt. % to about 5.4 wt. %, or about 1.1 wt. %, or about 1 wt. %.

[0081] In some embodiments, the surface modifier 130 includes Sm component. In some embodiments, the Sm component includes Sm2O3. The loading of Sm component, i.e., the 13 1622111714.1amount of the Sm component in the catalyst composite may be measured by weight, on the metal oxide basis, with respect to the weight of the catalyst composite. In some embodiments, the loading of Sm component is less than or equal to about 7 wt. %. For example, the loading of Sm component in the catalyst composite is less than or equal to about 0.5 wt. % to about 7 wt. %, or about 5 wt. %.

[0082] In some embodiments, the surface modifier 130 includes La component. In some embodiment, the La component includes La2O3. The loading of La component, i.e., the amount of the La component in the catalyst composite may be measured by weight, on the metal oxide basis, with respect to the weight of the catalyst composite. In some embodiments, the loading of La component is less than or equal to about 5 wt. %. For example, in some embodiments, the loading of La component in the catalyst composite is about 0.1 wt. % to about 4 wt. %. In some embodiments, the loading of La component in the catalyst composite is about 0.1 wt. % to about 3.5 wt. %, or about 0.2 wt. % to about 3 wt. %, or about 0.3 wt. % to about 2 wt. %, or about 0.4 to about 1.5 wt.%. For example, in some embodiments, the loading of La component in the catalyst composite is about 0.5 wt. % to about 1 wt. %.

[0083] The present disclosure also provides a catalytic article for N2O removal from an exhaust stream of an internal combustion engine. The catalytic article includes a substrate and the catalyst composite consistent with the embodiments of the present disclosure. FIGs. 2A, 2B, and 3 schematically shows a catalytic article in accordance with some embodiments of the present disclosure.

[0084] FIGs.2A and 2B illustrate a catalytic article 200 including a substrate 210. The substrate 210 has a plurality of porous walls 211 forming a plurality of fine, parallel gas flow passages 220. The substrate 210 has an upstream end face 212 and a corresponding downstream end face 213 identical to upstream end face 212. The substrate is a flow-through substrate has a cylindrical shape and has a cylindrical outer surface 214. The gas flow passages 220 extend through substrate 210 from the upstream end face 212 to the downstream end face 213. The gas flow passages 220 are unobstructed so as to permit the flow of a fluid, e.g., a gas stream, longitudinally through substrate 210 via gas flow passages 220 thereof. As shown in FIG.2B, the plurality of porous walls 211 are so dimensioned and configured that gas flow passages 220 have a substantially regular polygonal shape. As shown, at least one coating layers can be applied to the porous walls 211. In some 14 1622111714.1embodiments, the at least one coating layer includes the catalyst composite consistent with the embodiments of the present disclosure. In some embodiments, the substrate 210 may be coated by two or more coating layers.

[0085] As shown in FIG.3, the catalytic article has a plurality of passages 311 tubularly enclosed by the porous walls 312 of the substrate. The catalytic article has an inlet end 313 and an outlet end 314. Alternate passages are plugged at the inlet end 313 with inlet plugs 315 and at the outlet end 314 with outlet plugs 316 to form opposing checkerboard patterns at the inlet end 313 and the outlet end 314, respectively. A gas stream 321 enters through the unplugged channel inlet 322, is stopped by outlet plug 314 and diffuses through porous walls 312 to the outlet side. The gas cannot pass back to the inlet side of walls because of inlet plugs 315. The porous walls are with one or more catalytic materials 317 including the catalyst composite consistent with the embodiments of the present disclosure. Catalytic materials 317 may be present on the inlet side, the outlet side alone, both the inlet and outlet sides of the catalytic article. In some embodiments, the wall itself may include all, or in part, of the catalytic materials 317.

[0086] The present disclosure also provides an emission treatment system for treatment of an exhaust stream from an internal combustion engine. The emission treatment system includes an exhaust conduit in fluid communication with the internal combustion engine via an exhaust manifold, and the catalyst composite consistent with the embodiments of the present disclosure. FIG.4 schematically shows examples of an emission treatment system in accordance with some embodiments of the present disclosure. As shown in FIG.4, the emission treatment system further includes one or more components selected from a three- way conversion (TWC) catalyst, a four-way conversion catalyst (FWC), a selective catalytic (NOx) reduction (SCR) catalyst, a lean NOxtrap (LNT), a diesel oxidation catalyst (DOC), catalytic soot filter (CSF), an ammonia oxidation catalyst (AMOX), a H2 oxidation catalyst (OC), and a N2O decomposition catalyst, where the catalyst composite may be disposed downstream of the one or more components or may be disposed on the same carrier of the one or more components. In such way, the catalyst composite may be able to aid N2O removal after N2O is formed as a byproduct of the one or more components listed above.

[0087] FIG.5 schematically shows a method for treating exhaust gases in accordance with an embodiment. The method includes providing, at 510, a catalyst composite, the catalyst composite including a ceria-based support, a Rh component impregnated on a surface of the 15 1622111714.1ceria-based support, and a surface modifier impregnated on the surface of the ceria-based support, where the surface modifier including one or more metal oxides selected from zirconia and oxides of rare earth elements.

[0088] The method further includes contacting, at 520, a gaseous stream comprising water, nitrous oxide and oxygen with the catalyst composite. This allows the catalyst composite to remove N2O from the exhaust stream. The exhaust stream may be from any source. In some embodiments, the exhaust stream is from an internal combustion engine.

[0089] In some embodiments, the temperature of the exhaust stream is from ambient temperature to about 700 °C. For example, the exhaust stream has a temperature of about 10 °C to about 650 °C, about 100 °C to about 600 °C, or about 200 °C to 500 °C, or about 300 °C to 400 °C.

[0090] In some embodiments, the water percentage in the exhaust stream is about 10 % to about 25 %.

[0091] FIG.6 schematically shows a method for preparing a N2O removal catalyst in accordance with some embodiments of the present disclosure. The method includes providing, at 310, a ceria-based support, depositing, at 320, Rh component onto a surface of the ceria-based support; and depositing, at 330, a surface modifier onto the surface of the ceria-based support. The surface modifier includes one or more metal oxides selected from zirconia and oxides of rare earth elements. Depositing the Rh component and depositing the surface modifier are concurrent or sequential.

[0092] In some embodiments, the Rh component may be deposited onto the ceria-based support via a wetness impregnation method. In some embodiments, the surface modifier may be deposited onto the surface of the ceria-based support via a wetness impregnation method. For example, the wetness impregnation method may be an incipient wetness impregnation method.

[0093] The Rh component and the surface modifier may be impregnated onto the surface of the ceria-based support in a concurrent manner or in a sequential manner. For example, the Rh component and the surface modifier may be impregnated onto the ceria-based support in a same impregnation step, the impregnation of the Rh component onto the surface of the ceria- based support followed by the impregnation of the surface modifier on to the ceria-based 16 1622111714.1support, or the impregnation of the surface modifier onto the ceria-based support is followed by the impregnation of the Rh component onto the ceria-based support.

[0094] In some embodiments, the deposition of Rh component may be performed by impregnating a Rh nitrate precursor on a cera-based support or a surface modified ceria-based support. The deposition of surface modifier may be performed by impregnating a nitrate precursor of the corresponding surface modifier on a cera-based support or a Rh deposited ceria-based support.

[0095] In some embodiments, prior to the deposition of Rh component and the disposition of the surface modifier, the ceria-based support may be pre-calcined at certain temperature. The pre-calcination step may reduce the initial specific surface area of the ceria-based support and presumably to improve the water-resistance thereof. In some embodiments, the ceria-based support may be pre-calcined at about 500 °C to about 1000 °C, or about 600 °C to about 900 °C. For example, in some embodiments, the ceria-based support may be pre-calcined at about 800 °C. In some embodiments, the ceria-based support may be pre-calcined with programmed elevated temperature. In some embodiments, the ceria-based support may be pre-calcined in ambient air. In some embodiments, the ceria-based support may be pre- calcined by introducing inert gas. In some embodiments, the ceria-based support may be pre- calcined for about 0.5 hour to about 12 hours. For example, the ceria-based support may be pre-calcined for about 2 hours.

[0096] In some embodiments, the material obtained after depositing step. In some embodiments, calcination may be performed after the deposition of Rh, after the deposition of surface modifier, and / or after the deposition of the Rh and surface modifier. For example, when the Rh component and the surface modifier are deposited onto the surface of ceria- based support in a sequential manner, the calcination is performed after each of the deposition is completed. When the Rh component and the surface modifier are deposited onto the ceria- based support concurrently, the calcination is performed after both the Rh component and the surface modifier are deposited on to the surface of the ceria-based support. In some embodiments, the calcination after depositing step may be performed at a temperature from about 300 °C to about 700 °C, or from about 400 °C to 600 °C. For example, the calcination may be performed at 550 °C. In some embodiments, the calcination after depositing step may be performed for about 0.5 hour to about 4 hours, or about 0.5 hr to about 3 hr. In some embodiments, the calcination after depositing step may be performed in air. In some 17 1622111714.1embodiments, the calcination after depositing step may be performed by introducing inert gas. For example, in some embodiments, the calcination may be performed at 400 °C to 600 °C for about 0.5 hr to about 3 hours in air. EXAMPLES

[0097] Example 1: Loading of Pr-based surface modifier

[0098] Testing was performed on the N2O removal properties of Pr component and Rh component impregnated ceria-based support. The ceria-based support was impregnated with 0.5 wt. % Rh component on the surface and impregnated with surface modifier Pr6O11 of various loadings. The Rh component and the Pr6O11 surface modifier were impregnated onto the ceria-based support in a concurrent manner using a mixed solution of rhodium nitrate and praseodymium nitrite via an incipient wetness impregnation method. Prior to the impregnation, the ceria-based support was pre-calcined at 800 °C in air for 2 hours. After the impregnation, the catalyst was calcined again at 550 °C for 2 hours. The calcined catalyst is designated as the “fresh catalyst.” The fresh catalyst was aged for 10 hours at 750 °C with 10% H2O, 10% O2 and balance N2. The aged catalyst was evaluated for N2O decomposition activity in a continuous flow fixed bed tubular microflow reactor with a gaseous flow stream comprising 200 ppm N2O, 5% O2, 5% H2O balanced with % N2at weight hourly space velocity (WHSV) of about 250,000 ml / g-h (or gas hourly space velocity (GHSV) of about 500,000 / h). The testing results are shown in FIG.7. Pr6O11 modified Rh / CeO2 catalysts with Pr6O11loading from about 0.5 wt. % to about 5 wt. % had improved N2O conversion activity compared to the reference catalyst Rh / CeO2-800 without surface modifier. The reference catalyst Rh / CeO2-800 has 0.5 wt. % Rh component on the surface and was calcined and aged in a same way as the catalyst with both Rh component and surface modifier impregnated on the surface. The ceria-based support in the reference catalyst Rh / CeO2-800 was also pre- calcined as described above. Information regarding the testing samples shown in FIG.7 is presented below in TABLE 1. TABLE 118 1622111714.1

[0099] Example 2: Testing sequence of impregnation of Rh component and impregnation of Pr-based surface modifier

[0100] Testing was performed on Pr6O11modified Rh / CeO2catalyst for effect of the sequence of impregnation of Rh component and impregnation of Pr6O11 surface modifier. The ceria-based support was pre-calcined as described in Example 1. The 0.5 wt. % Rh component and the 5 wt. % Pr6O11surface modifier were impregnated onto the ceria-based support in different manners: (a) concurrently in a same impregnation step; (b) the impregnation of the Rh component onto the surface of the ceria-based support followed by the impregnation of the Pr6O11surface modifier on to the ceria-based support, and (c) the impregnation of the Pr6O11surface modifier onto the ceria-based support followed by the impregnation of the Rh component onto the ceria-based support. When the Rh component and the Pr6O11surface modifier were deposited onto the surface of ceria-based support sequentially, i.e., (b) and (c), calcination was performed after each of the deposition was completed. When the Rh component and the Pr6O11 surface modifier were deposited onto the ceria-based support concurrently, i.e., (a), calcination was performed after both the Rh component and the Pr6O11surface modifier were deposited on to the surface of the ceria-based support. The calcination was performed as described in Example 1. After aging treatment as described in Example 1, catalysts prepared with above different impregnation sequences were tested for N2O removal properties as described in Example 1. The results are shown in FIG. 8. Catalysts prepared by different impregnation manners a) - c) displayed similarly activity improvement relative to the reference catalyst Rh / CeO2-800 without surface modifier. Information regarding the testing samples shown in FIG.8 is presented below in TABLE 2. TABLE 219 1622111714.1

[0101] Example 3: Loading of Gd-based surface modifier

[0102] Testing was performed on the N2O removal properties of Gd component and Rh component impregnated ceria-based support. The ceria-based support was impregnated with 0.5 wt. % Rh component on the surface and impregnated with surface modifier Gd2O3 of various loadings. The Rh component and the Gd2O3surface modifier were impregnated in a concurrent manner using a rhodium nitrate solution and gadolinium nitrite solution via an incipient wetness impregnation method. Prior to the impregnation, the ceria-based support was pre-calcined as described in Example 1. After the impregnation, the catalyst was calcined as described in Example 1. After aging treatment described in Example 1, catalysts prepared with different loadings of Gd2O3 were tested for N2O removal properties as described in Example 1. The results are shown in FIG.9. Gd2O3 modified Rh / CeO2 catalysts with Gd2O3loading from about 1 wt. % to about 10 wt. % had improved N2O conversion activity compared to the reference catalyst Rh / CeO2-800 without surface modifier. Gd2O3loadings between about 1 wt. % and 5 wt. % had similar effects and improved N2O conversion by about 100% at 450 °C relative to the reference catalyst Rh / CeO2-800 without surface modifier. Information regarding the testing samples shown in FIG.9 is presented below in TABLE 3 TABLE 320 1622111714.1

[0103] Example 4: Testing sequence of impregnation of Rh component and impregnation of Gd-based surface modifier

[0104] Testing was performed on Gd2O3 modified Rh / CeO2 catalyst for effect of the sequence of impregnation of Rh component and impregnation of Gd2O3surface modifier. The ceria-based support was pre-calcined as described in Example 1. The 0.5 wt. % Rh component and the 5 wt. % Gd2O3 surface modifier were impregnated onto the ceria-based support in different manners: (a) concurrently in a same impregnation step; (b) the impregnation of the Rh component onto the surface of the ceria-based support followed by the impregnation of the Gd2O3 surface modifier on to the ceria-based support, and (c) the impregnation of the Gd2O3surface modifier onto the ceria-based support followed by the impregnation of the Rh component onto the ceria-based support. When the Rh component and the Gd2O3 surface modifier were deposited onto the surface of ceria-based support sequentially (b) and (c), the calcination was performed after each of the deposition is completed. When the Rh component and the Gd2O3surface modifier were deposited onto the ceria-based support concurrently (a), the calcination was performed after both the Rh component and the Gd2O3 surface modifier were deposited on to the surface of the ceria- based support. The calcination was performed as described in Example 1. After aging treatment described in Example 1, catalysts prepared with above different impregnation sequences were tested for N2O removal properties as described in Example 1. The results are shown in FIG.10. Catalysts prepared by different impregnation manners a) - c) displayed similarly activity improvement relative to the reference catalyst Rh / CeO2-800 without surface modifier. Information regarding the testing samples shown in FIG.10 is presented below in TABLE 4. TABLE 421 1622111714.1

[0105] Example 5: Loading of Y-based surface modifier

[0106] Testing was performed on the N2O removal properties of Y component and Rh component impregnated ceria-based support. The ceria-based support was impregnated with 0.5 wt. % Rh component on the surface and impregnated with surface modifier yttrium oxide (Y2O3) of various loadings. The Rh component and the Y2O3 surface modifier were impregnated in a concurrent manner using a rhodium nitrate solution and yttrium nitrite solution via an incipient wetness impregnation method. Prior to the impregnation, the ceria- based support was pre-calcined as described in Example 1. After the impregnation, the catalyst was calcined as described in Example 1. After aging treatment described in Example 1, catalysts prepared with different loadings of Y2O3were tested for N2O removal properties as described in Example 1. The results are shown in FIG.11. Y2O3modified Rh / CeO2catalysts with Y2O3 loading from about 1 wt. % to about 5 wt. % have similar effects and improved N2O conversion by about 100 % at 450 °C relative to the reference catalyst Rh / CeO2-800 without surface modifier. Information regarding the testing samples shown in FIG.11 is presented below in TABLE 5. TABLE 5

[0107] Example 6: Testing pre-calcination of ceria-based support

[0108] Testing was performed on the N2O removal properties of Y2O3 and Rh component impregnated ceria-based support for the effect pre-calcination of the ceria-based support. As shown in FIG.12, for both as-received CeO2and pre-calcined (800 °C for 2h in air) CeO2supports, Y2O3 had a similar degree of promotion relative to the reference catalysts Rh / CeO2 and Rh / CeO2-800, respectively. The difference between Rh / CeO2 and Rh / CeO2-800 is that 22 1622111714.1the ceria-based support in Rh / CeO2is not pre-calcined, while the ceria-based support in Rh / CeO2-800 is pre-calcined as described in Example 1. Pre-calcination step further improves the catalytic activity for N2O removal. The effect of surface modifier promotion and that of support pre-calcination are additive for improving catalytic activity for N2O removal. Information regarding the testing samples shown in FIG.12 is presented below in TABLE 6. TABLE 6

[0109] Example 7: Loading of Nd-based surface modifier

[0110] Testing was performed on the N2O removal properties of Nd component and Rh component impregnated ceria-based support. The ceria-based support was impregnated with 0.5 wt. % Rh component on the surface and impregnated with surface modifier Nd2O3 of various loadings. The Rh component and the Nd2O3 surface modifier were impregnated in a concurrent manner using a rhodium nitrate solution and neodymium nitrite solution via an incipient wetness impregnation method. Prior to the impregnation, the ceria-based support was pre-calcined as described in Example 1. After the impregnation, the catalyst was calcined as described in Example 1. After aging treatment described in Example 1, catalysts prepared with different loadings of Nd2O3 were tested for N2O removal properties as described in Example 1. The results are shown in FIG.13, Nd2O3 modified Rh / CeO2 catalysts with Nd2O3loading around 1 wt. % showed highest improvement, with N2O conversion 2.2 times of the reference catalyst Rh / CeO2-800 without surface modifier at 450 °C. Information regarding the testing samples shown in FIG.13 is presented below in TABLE 7. TABLE 7 23 1622111714.1

[0111] Example 8: Loading of Sm-based surface modifier

[0112] Testing was performed on the N2O removal properties of Sm component and Rh component impregnated ceria-based support. The ceria-based support was impregnated with 0.5 wt. % Rh component on the surface and impregnated with surface modifier Sm2O3 of various loadings. The Rh component and the Sm2O3 surface modifier were impregnated in a concurrent manner using a rhodium nitrate solution and neodymium nitrite solution via an incipient wetness impregnation method. Prior to the impregnation, the ceria-based support was pre-calcined as described in Example 1. After the impregnation, the catalyst was calcined as described in Example 1. After aging treatment described in Example 1, catalysts prepared with different loadings of Sm2O3were tested for N2O removal properties as described in Example 1. The results are shown in FIG.14, Sm2O3 modified Rh / CeO2 catalysts with Sm2O3loading around 5 wt. % showed highest improvement, with N2O conversion 2.3 times of the reference catalyst Rh / CeO2-800 without surface modifier at 450 °C. Information regarding the testing samples shown in FIG.14 is presented below in TABLE 8. TABLE 824 1622111714.1

[0113] Example 9: Testing various types of rare earth element-based surface modifiers and reaction temperature

[0114] Catalysts prepared in Examples 1, 3, 5, 7, and 8 with the highest activities are compared with reference catalyst Rh / CeO2-800 for N2O removal at 400 °C and 450 °C. Comparison results are shown in FIGs.15 and 16. The degree of activity improvement by various rare earth metal oxide surface modifier follows 5 wt. % Sm2O3> 1.1 wt. % Nd2O3> 1 wt. % Y2O3> 3 wt. % Gd2O3> 1 wt. % Pr6O11. Information regarding the testing samples shown in FIGs.15 and 16 is presented below in TABLE 9. TABLE 9

[0115] Example 10: Testing various types of surface modifiers

[0116] The ceria-based support was impregnated with 0.5 wt. % Rh component on the surface and impregnated with different surface modifiers including, Fe2O3, NiO, CuO, ZrO2, Nb2O5, MoO3, SnO2, BaO, La2O3, CeO2, Y2O3, Pr6O11, Nd2O3, Sm2O3, Gd2O3. The Rh component and the surface modifier were impregnated in a concurrent manner using their nitrate solutions via an incipient wetness impregnation method. Prior to the impregnation, the ceria-based support was pre-calcined as described in Example 1. After the impregnation, the catalyst was calcined as described in Example 1. After aging treatment described in Example 1, the catalysts were tested for N2O removal properties as described in Example 1. The results are shown in FIG.17. Fe, Ni, Cu, Nb, Mo, Ba, Sn, and Ce based surface modifier showed negative effect on N2O conversion relative to the Rh / CeO2-800 reference catalyst, while Zr, La, Y, Pr, Nd, Sm, and Gd based surface modifiers improved N2O conversion 25 1622111714.1compared to the reference catalyst Rh / CeO2-800 without surface modifier at 450 °C. Information regarding the testing samples shown in FIG.17 is presented below in TABLE 10. TABLE 10

[0117] Comparative example: Solid solutions comprising ceria and rare earth oxides as Rh support

[0118] Phase-pure solid solutions comprising ceria and a rare earth metal oxide were used as Rh supports. The solid solution supports were pre-calcined at 800oC for 2 hours in air before Rh impregnation. The pre-calcined supports were impregnated with 1 wt. % Rh using the incipient wetness method. After impregnation, the catalysts were calcined at 450oC for 1 hour. The support information, catalyst compositions and preparation methods are listed in Table 11. The calcined catalysts were aged at 750oC for 20 hours in 10% H2O / air stream. The aged catalysts were evaluated for N2O decomposition activity using a high-throughput 26 1622111714.1flow reactor with a gaseous stream comprising 200 ppm N2O, 5% O2, 5% H2O and balance N2 from 250oC to 450oC at 50oC / step. For each test, 0.2 gram powder sample sieved to 250 – 500 ^m fraction was used, which was diluted with corundum to make up 1 cm3volume. The GHSV was 35,000 h-1. FIG.18 compares the N2O conversion of the catalyst samples shown in Table 11 as a function of temperature. The Rh catalysts supported on the solid solution supports had significantly lower N2O activities than that of the reference (1Rh / CeO2- 800). This is in a clear contrast to the effect of surface modification by the same type of elements. TABLE 11

[0119] Various of the above-disclosed and other features and functions, or alternatives thereof, may be combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art, each of which is also intended to be encompassed by the disclosed embodiments. 27 1622111714.1

Claims

CLAIMS: What is claimed is:

1. A catalyst composite for removing nitrous oxide from an exhaust stream, the catalyst composite comprising: a ceria-based support; a rhodium component impregnated on a surface of the ceria-based support; and a surface modifier impregnated on the surface of the ceria-based support, the surface modifier comprising one or more metal oxides selected from zirconia and oxides of rare earth elements.

2. The catalyst composite of claim 1, wherein the rhodium component comprises either Rh metal nanoparticles or Rh oxide nanoparticles or a combination thereof supported on the surface of the ceria-based support, and the surface modifier is bonded to surface sites of the ceria-based support.

3. The catalyst composite of claim 1, wherein the catalyst composite comprises the rhodium component in an amount of about 0.1 wt. % to about 3.0 wt. % with respect to a weight of the catalyst composite, calculated on a metal basis.

4. The catalyst composite of claim 1, wherein the catalyst composite comprises the rhodium component in an amount of about 0.5 wt. % with respect to a weight of the catalyst composite, calculated on a metal basis.

5. The catalyst composite of claim 1, wherein the surface modifier comprises metal oxides selected from oxides of zirconium, yttrium, lanthanum, praseodymium, neodymium, promethium, samarium, europium, and gadolinium.

6. The catalyst composite of claim 1, wherein the catalyst composite comprises the surface modifier in an amount of about 0.1 wt. % to about 15 wt. % with respect to a weight of the catalyst composite, calculated on a metal oxide basis. 28 1622111714.

17. The catalyst composite of claim 1, wherein the catalyst composite comprises the surface modifier in an amount of about 0.5 wt. % to about 5 wt. % with respect to a weight of the catalyst composite, calculated on a metal oxide basis.

8. The catalyst composite of claim 1, wherein the ceria-based support is a phase- pure crystalline material having a cubic fluorite structure.

9. The catalyst composite of claim 1, wherein the ceria-based support is a phase- pure solid solution comprising at least about 85 wt. % CeO2 and less than about 15 wt. % one or more oxides of Zr, La, Y, Pr, and Nd or combinations thereof.

10. The catalyst composite of claim 1, wherein the ceria-based support comprises ceria having an average crystallite size between 5 nm and 20 nm measured by X-ray diffraction (XRD) spectroscopy.

11. The catalyst composite of claim 1, wherein the ceria-based support has a BET surface area of about 30 m2 / g to about 200 m2 / g.

12. The catalyst composite of claim 1, wherein the ceria-based support has a BET surface area of about 50 m2 / g to about 80 m2 / g.

13. A catalytic article for nitrous oxide removal from an exhaust stream of an internal combustion engine, comprising a substrate and the catalyst composite of claim 1 loaded on the substrate.

14. An emission treatment system for treatment of an exhaust stream of an internal combustion engine, the emission treatment system comprising an exhaust conduit in fluid communication with the internal combustion engine via an exhaust manifold, and the catalyst composite of claim 1 disposed in the exhaust conduit and being configured to remove nitrous oxide.

15. The emission treatment system of claim 14 comprising: one or more components selected from a three-way conversion (TWC) catalyst, a four-way conversion catalyst (FWC), a selective catalytic (NOx) reduction (SCR) catalyst, a 29 1622111714.1lean NOxtrap (LNT), a diesel oxidation catalyst (DOC), catalytic soot filter (CSF), an ammonia oxidation catalyst (AMOX), a H2 oxidation catalyst (OC), and a N2O decomposition catalyst; wherein the catalyst composite is disposed downstream of the one or more components or is disposed on a same carrier of the one or more components.

16. A method for treating exhaust gases comprising: providing a catalyst composite, the catalyst composite comprising a ceria-based support, a rhodium component impregnated on a surface of the ceria-based support, and a surface modifier impregnated on the surface of the ceria-based support, wherein the surface modifier comprising one or more metal oxides selected from zirconia and oxides of rare earth elements; and contacting a gaseous stream comprising water, nitrous oxide, and oxygen with the catalyst composite.

17. A method for preparing a nitrous oxide removal catalyst composite, comprising: providing a ceria-based support; depositing rhodium component onto a surface of the ceria-based support; and depositing a surface modifier onto the surface of the ceria-based support, the surface modifier comprising one or more metal oxides selected from zirconia and oxides of rare earth elements; wherein depositing the rhodium component and depositing the surface modifier are concurrent or sequential.

18. The method of claim 17, wherein depositing the rhodium component or depositing the surface modifier is performed by a wetness impregnation method.

19. The method of claim 18, wherein the wetness impregnation method is an incipient wetness impregnation method.

20. The method of claim 17, wherein depositing the rhodium component or depositing the surface modifier uses nitrate precursors thereof. 30 1622111714.

121. The method of claim 17, comprising: pre-calcining the ceria-based support prior to deposition.

22. The method of claim 17, comprising: performing calcination after each deposition.

23. The method of claim 17, comprising: performing calcination after both the rhodium component and the surface modifier are deposited onto the ceria-based support.

24. The method of claim 17, wherein the rhodium component comprises Rh nanoparticles or Rh oxide nanoparticles or combination thereof supported on the surface of the ceria-based support, and the surface modifier is bonded to surface sites of the ceria-based support.

25. The method of claim 17, wherein a loading of the rhodium component on to the ceria-based support is about 0.1 wt. % to about 3 wt.% with respect to a weight of the catalyst composite, calculated on a metal basis.

26. The method of claim 17, wherein a loading of the rhodium component on to the ceria-based support is about 0.5 wt. % with respect to a weight of the catalyst composite, calculated on a metal basis.

27. The method of claim 17, wherein the surface modifier comprises metal oxides selected from oxides of zirconium, yttrium, lanthanum, praseodymium, neodymium, promethium, samarium, europium, and gadolinium.

28. The method of claim 17, wherein the ceria-based support is a phase-pure crystalline material having a cubic fluorite structure.

29. The method of claim 17, wherein the ceria-based support is a phase-pure solid solution comprising at least about 85 wt. % CeO2 and less than about 15 wt. % one or more oxides of Zr, La, Y, Pr, and Nd or combinations thereof. 31 1622111714.

130. The method of claim 17, wherein the ceria-based support comprises ceria having an average crystallite size between 5 nm and 20 nm measured by X-ray diffraction (XRD) spectroscopy.

31. The method of claim 17, wherein the ceria-based support has a BET surface area of about 30 m2 / g to about 200 m2 / g.

32. The method of claim 17, wherein the ceria-based support has a BET surface area of about 50 m2 / g to about 80 m2 / g.

33. The method of claim 17, wherein a loading of the surface modifier onto the ceria-based support is about 0.1 wt. % to about 15 wt. % with respect to a weight of the catalyst composite, calculated on a metal oxide basis.

34. The method of claim 17, wherein a loading of the surface modifier onto the ceria-based support is about 0.5 wt. % to about 5 wt. % with respect to a weight of the catalyst composite, calculated on a metal oxide basis. 32 1622111714.1

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