KR20220152050A - Rhodium-Cerium Oxide Exsolution Catalyst for Steam Reforming with Enhanced Durability at High Temperature by Reduction Treatment, Manufacturing Method Thereof, and Steam Reforming Method Using the Same - Google Patents

Abstract

The present invention relates to a rhodium-cerium oxide exsolution catalyst for a steam reforming reaction with improved durability at high temperatures through reduction heat treatment, a manufacturing method, and a steam reforming reaction method using the same. The present invention provides the method for manufacturing the rhodium-cerium oxide exsolution catalyst for the steam reforming reaction, if used, being capable of acquiring the rhodium-cerium oxide exsolution catalyst for the steam reforming reaction which has enhanced durability at high temperatures through reduction heat-treatment as compared with a conventional Rh/CeO_2 catalyst and high surface area of 55 m^2 or more, and in which Rh nanoparticles separated from a rhodium-doped cerium oxide carrier directly confirmed by in-situ TEM analysis are exsolved. If the catalyst is used, improved hydrogen yield in the steam reforming reaction for a long time at high temperatures, especially in the propane wet reforming reaction can be obtained and a nano-sized catalyst for manufacturing a highly durable exsolution catalyst can be provided since the catalyst according to the present invention has improved resistance to sintering and coke deposition after the steam reforming reaction as compared with the conventional Rh/CeO_2.

Description

Rhodium-cerium oxide elution catalyst for wet reforming reaction with improved durability at high temperature through reduction heat treatment, manufacturing method thereof, and wet reforming reaction method using the same {Rhodium-Cerium Oxide Exsolution Catalyst for Steam Reforming with Enhanced Durability at High Temperature by Reduction Treatment , Manufacturing Method Thereof, and Steam Reforming Method Using the Same}

The present invention was made under the support of Samsung Electronics Co., Ltd. by the task identification number SRFC-MA1502-52, and the research management institution for the above task is the Samsung Electronics Future Technology Development Center, the research project name is "Samsung Future Technology Development Project", the research task The name is “(G01200274) Development of next-generation high-performance catalysts through spontaneous metal/oxide phase change control (year 2020)”, and the contribution rate is 1/1.

The present invention relates to a rhodium-cerium oxide elution catalyst for wet reforming reaction with improved durability at high temperature through reduction heat treatment, a method for preparing the same, and a wet reforming reaction method using the same. More specifically, a method for preparing a catalyst having improved durability and high surface area at high temperature by eluting rhodium nanoparticles through reduction heat treatment, and improved hydrogen yield and improved resistance to sintering and coke deposition in the wet reforming reaction of the present invention It relates to a wet reforming reaction method using a catalyst.

Supported metal catalysts have been used in heterogeneous chemical reactions. When metal nanoparticles are deposited on a support, high performance is provided by considering various aspects such as metal size, shape, and interaction between the metal and the support. However, many supported metal catalysts undergo sintering at high temperatures because of their thermodynamic tendency to minimize surface free energy. Aggregation of metal nanoparticles causes serious problems by losing the desired size or shape for the targeted reaction. In particular, coke deposition can be accelerated in the reforming reaction of the catalyst.

Propane steam reforming (PSR) reaction has been proposed as a promising reforming process for the production of H ₂ in high yield. Propane (C ₃ H ₈ ) is one of the good candidates for effective H ₂ production thanks to its high energy density, well-established distribution infrastructure and easy storage and transportation. However, the PSR reaction generally requires a high temperature of 600° C. or more for high H ₂ yield, and causes problems in that the catalyst is sintered or coke is deposited during the reaction. Because of these limitations, it is difficult to design a PSR reaction such that the catalyst has high durability in long-term reactions without any decomposition.

The exsolution phenomenon has received much attention as a novel method for preparing supported metal catalysts with better thermal stability. This is a fundamental phase transition phenomenon in which the doped metal of perovskite oxide moves in and out of the support during the redox cycle. Since the metal separated from the parent support is not merely deposited on the surface of the support but is anchored into the lattice, the supported metal catalyst synthesized by the elution method can exhibit high durability. . The strong interaction between the metal and the support can be used to solve the stability problem of conventional catalysts, and several literatures have reported that elution catalysts operate at high temperatures for a long time.

Despite these advantages of elution catalysts, their practical application is difficult due to the low surface area associated with the large crystallite size of perovskite oxides. In this regard, some studies have attempted to prepare high surface area perovskites, but only the surface area before reductive treatment for elution was shown. Some studies have reported the possibility of elution with non-perovskite hosts using cerium (Ce)- or zirconium (Zr)-based materials. Among these, cerium(IV) oxide is a promising candidate because it can be easily reduced with heat to form oxygen vacancies known as the driving force for the elution phenomenon. There are few studies that suggest that cerium oxide-doped metals can come from oxides, such as elution phenomena, but there is no direct experimental basis or detailed study.

KR 10-2018-0101427 A

The present inventors have intensively researched to develop a heterogeneous catalyst having a non-perovskite structure having a high surface area and high long-term thermal stability by using the elution phenomenon. As a result, the rhodium-cerium oxide elution catalyst of the present invention elutes rhodium nanoparticles through reduction heat treatment to improve durability at high temperatures, has a high surface area of 55 m ² /g or more, and has a wet reforming reaction, especially at 700 ° C. In the propane wet reforming reaction for a period of time, high hydrogen yield and propane conversion were shown, the catalyst used in the propane wet reforming reaction had sintering and coke resistance, and rhodium nanoparticles separated from the cerium oxide domain through in-situ TEM analysis The present invention was completed by directly and clearly clarifying that it was eluted.

Accordingly, an object of the present invention is to provide a method for preparing a rhodium-cerium oxide eluting catalyst for a steam reforming reaction.

Another object of the present invention is to provide a rhodium-cerium oxide elution catalyst for a wet reforming reaction in which rhodium nanoparticles are eluted on the surface of a cerium oxide carrier doped with rhodium by reduction heat treatment.

Another object of the present invention is to provide a wet reforming reaction method comprising the step of obtaining hydrogen gas by adding the catalyst according to the present invention to hydrocarbon and steam.

According to one aspect of the present invention, the present invention provides a method for preparing a rhodium-cerium oxide eluting catalyst for a steam reforming reaction comprising the following steps:

a) mixing a cerium oxide precursor solution and a rhodium precursor solution;

b) firing the product of step a); and

c) subjecting the product of step b) to reduction heat treatment.

The present inventors prepared a rhodium-cerium oxide elution catalyst for a wet reforming reaction by using a co-precipitation method and reduction heat treatment.

As used herein, the term "co-precipitation method" is the most widely used method for preparing mixed oxide-based solid catalysts, in which trace elements are extracted from minerals during solid formation and recrystallization of minerals. Refers to a controlled chemical equilibrium shift process involving intercalation into a structure. The co-precipitation method of the present invention may include multiple steps such as preparation of a specific solution of a metal compound, mixing of the solution, drying and calcination.

In this specification, the term "calcination" means a treatment of heating at a high temperature in air or oxygen (O ₂ ). In the present invention, heat treatment, that is, firing treatment was performed to oxidize the catalyst through air or oxygen at a high temperature.

In the present specification, the term "rhodium-doped cerium oxide (Rh-doped CeO ₂ , CeRhO)" refers to a carrier prepared through steps a) and b) or prepared by a coprecipitation method according to the manufacturing method of the present invention. , which is in solid solution form.

As used herein, the term "solid solution" refers to a solution in which one or more solutes in a certain solvent are mixed and exist in a solid state.

In the present specification, the term "rhodium-cerium oxide elution catalyst (Exsolved CeRhO)" is a catalyst prepared according to the production method of the present invention, and a reduction heat treatment is performed on a rhodium-doped cerium oxide carrier (Rh-doped CeO ₂ , CeRhO). As a result of eluting rhodium nanoparticles onto the surface of the support, the eluted rhodium nanoparticles refer to a catalyst anchored in a rhodium-doped cerium oxide support lattice. The "rhodium-cerium oxide elution catalyst" of the present invention is a rhodium-deposited cerium oxide (Rh/CeO ₂ ) catalyst synthesized by a conventional wet-impregnation method. It is a novel catalyst distinct from conventional catalysts that are only deposited on the surface of a support and not anchored.

In this specification, the term "wet-impregnation" is widely used to prepare a heterogeneous catalyst comprising a process in which solids are separated using an excess of solvent and the excess solvent is removed by drying. means the way In the present invention, a wet-impregnation method was used to prepare the catalyst of Comparative Example 1 to be described later as a control sample.

In this specification, the term “deposition” refers to a state in which supported metal is superficially placed on the surface of a support. In a catalyst synthesized by a conventional wet-impregnation method, metal particles are deposited on a carrier.

In this specification, the term "reduction heat treatment, reducing treatment, or reducing condition" means a treatment or conditions in which reduction is performed by heating to a high temperature higher than room temperature under hydrogen (H ₂ ). In the present invention, reduction heat treatment was performed to induce elution of metal nanoparticles by reducing the catalyst through hydrogen at high temperature.

In this specification, the term "exsolution or elution phenomenon" refers to a phase transition phenomenon in which doped metal nanoparticles in the lattice structure of the oxide carrier aggregate to the surface of the oxide carrier during a reduction cycle. In the present invention, rhodium nanoparticles are eluted on the non-perovskite oxide surface, that is, on the surface of the rhodium-doped cerium oxide carrier by reduction heat treatment.

This elution phenomenon has conventionally been used as a method for preparing a metal catalyst doped with perovskite oxide, but due to a low surface area of about 10 m ² /g, practical catalytic applications are quite limited. As a method for preparing a metal catalyst doped in non-perovskite oxide, the possibility of an elution phenomenon has been reported in small numbers, but direct experimental grounds are lacking. In the present invention, for the first time, a metal catalyst doped in a non-perovskite oxide has an improved surface area (more than 55 m ² /g) than a conventional perovskite oxide catalyst, and metal nanoparticles are formed on the surface by elution. It was clearly identified that it was eluted.

In this specification, the term 'perovskite oxide' is a metal oxide having an ABO ₃ structural formula, and generally, a lanthanum-based metal cation with a relatively large ionic radius of 12 coordinates is used at the A site, and 6 A 3d transition metal cation having a relatively small ionic radius of coordination is used A catalyst having a perovskite oxide structure has excellent thermal stability, but does not have a wide range of applications as a catalyst support because of its low surface area.

In this specification, the term 'non-perovskite oxide' means a metal oxide that does not have an ABO ₃ structural formula, for example, a pyrochlore (A ₂ B ₂ O ₆ ) type. , oxides having a fluorite-related-type, aragonite-type, spinel (AB ₂ O ₄ )-type structure, etc. may be included, but are not limited thereto. A method for preparing a catalyst having a non-perovskite oxide structure, particularly a cerium oxide structure, having improved durability at high temperatures and a high surface area is provided.

In this specification, the term "anchoring" refers to a state in which supported metal nanoparticles are firmly embedded in the lattice of the support phase, which is enhanced metal-support interaction ( metal-supprt interaction) to give the catalyst excellent stability. The rhodium nanoparticles eluted from the rhodium-cerium oxide elution catalyst of the present invention are anchored in the rhodium-doped cerium oxide carrier lattice.

Hydrocarbon reforming largely includes steam reforming, partial oxidation, and auto-thermal reforming. The wet reforming reaction is commercially used because of its high yield of hydrogen.

In this specification, the term “steam reforming (SR) reaction or steam reforming reaction” refers to an endothermic reaction in which a reformed gas containing hydrogen is produced by a reaction between a hydrocarbon and steam. Syngas such as hydrogen (H ₂ ) and carbon monoxide (CO) may be produced through a wet reforming reaction.

In one embodiment of the present invention, hydrocarbons used in the wet reforming reaction of the present invention include methane, methanol, ethane, ethanol, propane, propanol, ethylene glycol, benzene, etc., but are not limited thereto. Hydrocarbons used in the wet reforming reaction of the present invention include hydrocarbon fuels such as natural gas and diesel, but are not limited thereto.

In this specification, the term “propane steam reforming (PSR) reaction or propane steam reforming reaction” refers to an endothermic reaction in which a reformed gas containing hydrogen is generated by a reaction between propane and steam.

In one embodiment of the present invention, the present invention provides a method for preparing a rhodium-cerium oxide eluting catalyst for propane wet reforming (steam reforming) reaction comprising the following steps:

a) mixing a cerium oxide precursor solution and a rhodium precursor solution;

b) firing the product of step a); and

c) subjecting the product of step b) to reduction heat treatment.

In another embodiment of the present invention, the present invention provides a method for preparing a rhodium-cerium oxide eluting catalyst represented by the following formula (1) for a wet reforming reaction comprising the following steps:

a) mixing a cerium oxide precursor solution and a rhodium precursor solution;

b) firing the product of step a); and

c) subjecting the product of step b) to reduction heat treatment;

[Formula 1]

Ce _{1- x} Rh _x O _2-y

The content ratio of rhodium (Rh) and cerium (Ce) is that rhodium is x and cerium is 1- x , and in Formula 1, x is a rational number in the range of 0.01 ≤ x ≤ 0.08, and y is in the range of 0 < y <2 glass number.

In one embodiment of the present invention, the firing in step b) is performed under air or oxygen at 300 ° C to 500 ° C. In another embodiment of the present invention, the firing in step b) is 300 ° C to 500 ° C, 300 ° C to 450 ° C, 300 ° C to 400 ° C, 300 ° C to 350 ° C, 350 ° C to 500 ° C, 350 ° C to 350 ° C 450 °C, 350 °C to 400 °C, 400 °C to 500 °C, 400 °C to 450 °C, or 450 °C to 500 °C in air or oxygen, but is not limited thereto. In a specific embodiment of the present invention, the firing of the present invention is performed under air at 450°C.

In one embodiment of the present invention, the firing in step b) is performed for 1 hour to 8 hours. In another embodiment of the present invention, the firing in step b) is 1 hour to 8 hours, 1 hour to 7 hours, 1 hour to 6 hours, 1 hour to 5 hours, 1 hour to 4 hours, 1 hour to 1 hour 3 hours, 1 to 2 hours, 2 to 8 hours, 2 to 7 hours, 2 to 6 hours, 2 to 5 hours, 2 to 4 hours, 2 to 3 hours, 3 to 8 hours , from 3 hours to 7 hours, from 3 hours to 6 hours, from 3 hours to 5 hours, from 3 hours to 4 hours, from 4 hours to 8 hours, from 4 hours to 7 hours, from 4 hours to 6 hours, or from 4 hours to 5 hours It may be performed, but is not limited thereto. In a specific embodiment of the present invention, the firing in step b) is performed for 4 hours.

Conventional perovskite oxides require a relatively long (> 4 hours) reduction heat treatment of more than 800 ° C. for elution, but the catalyst having a bar-perovskite oxide structure of the present invention, that is, rhodium-oxidized The cerium elution catalyst can cause elution even under conditions of a temperature of 800° C. or less and a reduction heat treatment of 4 hours or less.

In one embodiment of the present invention, the reduction heat treatment in step c) is performed at a temperature of 400 ° C to 700 ° C for 5 minutes to 4 hours.

In another embodiment of the present invention, the reduction heat treatment in step c) of the present invention is 5 minutes to 4 hours, 5 minutes to 3 hours, 5 minutes to 2 hours, 5 minutes to 1 hour, 5 minutes to 30 minutes, 5 minutes to 10 minutes, 10 minutes to 4 hours, 10 minutes to 3 hours, 10 minutes to 2 hours, 10 minutes to 1 hour, 10 minutes to 30 minutes, 30 minutes to 4 hours, 30 minutes to 3 hours, 30 minutes to 2 hours, 30 minutes to 1 hour, 1 hour to 4 hours, 1 hour to 3 hours, 1 hour to 2 hours, 2 hours to 4 hours, 2 hours to 3 hours, or 3 hours to 4 hours. However, it is not limited thereto. In a specific embodiment of the present invention, the reduction heat treatment in step c) of the present invention is performed for 3 hours.

In another embodiment of the present invention, the reduction heat treatment in step c) of the present invention is 400 ° C to 700 ° C, 400 ° C to 650 ° C, 400 ° C to 600 ° C, 400 ° C to 550 ° C, 400 ° C to 500 ° C, 400°C to 450°C, 450°C to 700°C, 450°C to 650°C, 450°C to 600°C, 450°C to 550°C, 450°C to 500°C, 500°C to 700°C, 500°C to 650°C, 500°C to 600 °C, 500 °C to 550 °C, 550 °C to 700 °C, 550 °C to 650 °C, 550 °C to 600 °C, 600 °C to 700 °C, 600 °C to 650 °C or 650 °C to 700 °C. It may be, but is not limited thereto. In a specific embodiment of the present invention, the reduction heat treatment in step c) of the present invention is performed at 500 °C.

In one embodiment of the present invention, the reduction heat treatment in step c) is performed under hydrogen gas and an inert gas.

In one embodiment of the present invention, the inert gas is at least one selected from the group consisting of nitrogen (N ₂ ), helium (He), and argon (Ar).

In another embodiment of the present invention, the reduction heat treatment in step c) is performed under a hydrogen gas/inert gas gas at a ratio of 5% (v/v) to 30% (v/v). In another embodiment of the present invention, the reduction heat treatment in step c) of the present invention is 5% (v / v) to 30% (v / v) H ₂ /He, 5% (v / v) to 25 % (v/v) H ₂ /He, 5% (v/v) to 20% (v/v) H ₂ /He, 5% (v/v) to 15% (v/v) H ₂ /He , 5% (v/v) to 10% (v/v) H ₂ /He, 10% (v/v) to 30% (v/v) H ₂ /He, 10% (v/v) to 25 % (v/v) H ₂ /He, 10% (v/v) to 20% (v/v) H ₂ /He, 10% (v/v) to 15% (v/v) H ₂ /He , 15% (v/v) to 30% (v/v) H ₂ /He, 15% (v/v) to 25% (v/v) H ₂ /He, 15% (v/v) to 20 % (v/v) H ₂ /He, 20% (v/v) to 30% (v/v) H ₂ /He, 20% (v/v) to 25% (v/v) H ₂ /He , 25% (v/v) to 30% (v/v) H ₂ /He, 5% (v/v) to 30% (v/v) H ₂ /Ar, 5% (v/v) to 25 % (v/v) H ₂ /Ar, 5% (v/v) to 20% (v/v) H ₂ /Ar, 5% (v/v) to 15% (v/v) H ₂ /Ar , 5% (v/v) to 10% (v/v) H ₂ /Ar, 10% (v/v) to 30% (v/v) H ₂ /Ar, 10% (v/v) to 25 % (v/v) H ₂ /Ar, 10% (v/v) to 20% (v/v) H ₂ /Ar, 10% (v/v) to 15% (v/v) H ₂ /Ar , 15% (v/v) to 30% (v/v) H ₂ /Ar, 15% (v/v) to 25% (v/v) H ₂ /Ar, 15% (v/v) to 20 % (v/v) H ₂ /Ar, 20% (v/v) to 30% (v/v) H ₂ /Ar, 20% (v/v) to 25% (v/v) H ₂ /Ar , 25% (v/v) to 30% (v/v) H ₂ /Ar, 5% (v/v) to 30% (v/v) H ₂ /N ₂ , 5% (v/v) to 25% (v/v) H ₂ /N ₂ , 5% ( v/v) to 20% (v/v) H ₂ /N ₂ , 5% (v/v) to 15% (v/v) H ₂ /N ₂ , 5% (v/v) to 10% ( v/v) H ₂ /N ₂ , 10% (v/v) to 30% (v/v) H ₂ /N ₂ , 10% (v/v) to 25% (v/v) H ₂ /N ₂ , 10% (v/v) to 20% (v/v) H ₂ /N ₂ , 10% (v/v) to 15% (v/v) H ₂ /N ₂ , 15% (v/v) ) to 30% (v/v) H ₂ /N ₂ , 15% (v/v) to 25% (v/v) H ₂ /N ₂ , 15% (v/v) to 20% (v/v) ) H ₂ /N ₂ , 20% (v/v) to 30% (v/v) H ₂ /N ₂ , 20% (v/v) to 25% (v/v) H ₂ /N ₂ or 25 % (v/v) to 30% (v/v) H ₂ /N ₂ gas. In a specific embodiment of the present invention, the reduction heat treatment in step c) of the present invention is performed under 10% (v/v) H ₂ /N ₂ gas. In another specific embodiment of the present invention, the reduction heat treatment in step c) of the present invention is performed under 10% (v/v) H ₂ /Ar gas.

In another embodiment of the present invention, the method for preparing a rhodium-cerium oxide eluting catalyst for wet reforming of the present invention further comprises the following steps after step a) and before step b):

i) a pH control step of adding a strong base dropwise until the pH of the product of step a) reaches pH 8.5 to pH 9.5;

ii) a washing step of filtering the product of step i) with ethanol and deionized water; and

iii) A drying step of obtaining a solid by drying the precipitate resulting from step ii).

In another embodiment of the present invention, in step i), the pH of the product of step a) is pH 8.5 to pH 9.5, pH 8.5 to pH 9.4, pH 8.5 to pH 9.3, pH 8.5 to pH 9.2, pH 8.5 to pH 8.5. pH 9.1, pH 8.5 to pH 9.0, pH 8.5 to pH 8.9, pH 8.5 to pH 8.8, pH 8.5 to pH 8.7, pH 8.5 to pH 8.6, pH 8.6 to pH 9.5, pH 8.6 to pH 9.4, pH 8.6 to pH 9.3 , pH 8.6 to pH 9.2, pH 8.6 to pH 9.1, pH 8.6 to pH 9.0, pH 8.6 to pH 8.9, pH 8.6 to pH 8.8, pH 8.6 to pH 8.7, pH 8.7 to pH 9.5, pH 8.7 to pH 9.4, pH 8.7 to pH 9.3, pH 8.7 to pH 9.2, pH 8.7 to pH 9.1, pH 8.7 to pH 9.0, pH 8.7 to pH 8.9, pH 8.7 to pH 8.8, pH 8.8 to pH 9.5, pH 8.8 to pH 9.4, pH 8.8 to pH 9.3, pH 8.8 to pH 9.2, pH 8.8 to pH 9.1, pH 8.8 to pH 9.0. pH 8.8 to pH 8.9, pH 8.9 to pH 9.5, pH 8.9 to pH 9.4, pH 8.9 to pH 9.3, pH 8.9 to pH 9.2, pH 8.9 to pH 9.1, pH 8.9 to pH 9.0, pH 9.0 to pH 9.5, pH 9.0 to pH 9.4, pH 9.0 to pH 9.3, pH 9.0 to pH 9.2, pH 9.0 to pH 9.1, pH 9.1 to pH 9.5, pH 9.1 to pH 9.4, pH 9.1 to pH 9.3, pH 9.1 to pH 9.2, pH 9.2 to pH A strong base may be added dropwise until reaching pH 9.5, pH 9.2 to pH 9.4, pH 9.2 to pH 9.3, pH 9.3 to pH 9.5, pH 9.3 to pH 9.4 or pH 9.4 to pH 9.5, but is not limited thereto. In one specific embodiment of the present invention, in step i), a strong base is added dropwise until the pH of the product of step a) reaches pH 9.0.

In another embodiment of the present invention, the strong base in step i) is lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), rubidium hydroxide (RbOH), cesium hydroxide (CsOH), calcium hydroxide ( Ca(OH) ₂ ), strontium hydroxide (Sr(OH) ₂ ) and barium hydroxide (Ba(OH) ₂ ).

In a more specific embodiment of the present invention, in step i), KOH is added dropwise until the pH of the product of step a) reaches pH 9.0.

In another embodiment of the present invention, the product of step i) is stirred for 2 to 6 hours before step ii). In another embodiment of the present invention, the product of step i) is stirred for 4 hours before step ii).

In another embodiment of the present invention, in step iii), the precipitate resulting from step ii) is dried at 80°C. In another embodiment of the present invention, in step iii), the precipitate resulting from step ii) is dried overnight. In another embodiment of the present invention, the solid obtained as a result of drying in step iii) is ground in a mortar to become a powder.

In another embodiment of the present invention, the method for preparing a rhodium-cerium oxide elution catalyst for wet reforming of the present invention includes steps ii), iii) and before step b) and before step c). b) further carried out by repeating these steps 1 to 3 times in the order of steps. In a more specific embodiment of the present invention, the method for preparing a rhodium-cerium oxide eluting catalyst for a wet reforming reaction of the present invention includes steps ii), iii) and before step b) and before step c). b) further comprising one repetition of these steps in the sequence of steps.

In one embodiment of the present invention, rhodium nanoparticles are eluted by reduction heat treatment in step c).

In one embodiment of the present invention, the weight of rhodium relative to the total weight of the rhodium-cerium oxide elution catalyst is 0.5 wt% to 8.0 wt%.

In another embodiment of the present invention, the weight of rhodium relative to the total weight of the rhodium-cerium oxide elution catalyst is 0.5 wt% to 8.0 wt%, 0.5 wt% to 7.0 wt%, 0.5 wt% to 6.0 wt%, or 0.5 wt%. % to 5.0 wt%, 0.5 wt% to 4.0 wt%, 0.5 wt% to 3.0 wt%, 0.5 wt% to 2.0 wt%, 0.5 wt% to 1.0 wt%, 1.0 wt% to 8.0 wt%, 1.0 wt% to 7.0 wt%, 1.0 wt% to 6.0 wt%, 1.0 wt% to 5.0 wt%, 1.0 wt% to 4.0 wt%, 1.0 wt% to 3.0 wt%, 1.0 wt% to 2.0 wt%, 2.0 wt% to 8.0 wt% %, 2.0 wt% to 7.0 wt%, 2.0 wt% to 6.0 wt%, 2.0 wt% to 5.0 wt%, 2.0 wt% to 4.0 wt%, 2.0 wt% to 3.0 wt%, 3.0 wt% to 8.0 wt%, 3.0 wt% to 7.0 wt%, 3.0 wt% to 6.0 wt%, 3.0 wt% to 5.0 wt%, 3.0 wt% to 4.0 wt%, 4.0 wt% to 8.0 wt%, 4.0 wt% to 7.0 wt%, 4.0 wt% % to 6.0 wt%, 4.0 wt% to 5.0 wt%, 5.0 wt% to 8.0 wt%, 5.0 wt% to 7.0 wt%, 5.0 wt% to 6.0 wt%, 6.0 wt% to 8.0 wt%, 6.0 wt% to 7.0 wt%, or 7.0 wt% to 8.0 wt%, but is not limited thereto. In a specific embodiment of the present invention, the weight of rhodium relative to the total weight of the rhodium-cerium oxide elution catalyst is 1.0 wt%, 2.0 wt%, 4.0 wt%, or 8.0 wt%. In a preferred embodiment of the present invention, the weight of rhodium relative to the total weight of the rhodium-cerium oxide elution catalyst is 4.0 wt%.

In one embodiment of the present invention, the cerium oxide precursor solution of the present invention is cerium (III) nitrate (Ce(NO ₃ ) ₃ ), cerium (III) nitrate hydrate (Ce(NO ₃ ) ₃ xH ₂ O), Cerium(III) sulfate (Ce ₂ (SO ₄ ) ₃ ), cerium(III) sulfate hydrate (Ce ₂ (SO ₄ ) ₃ xH ₂ O), cerium(III) oxalate (Ce ₂ (C ₂ O ₄ ) ₃ ), cerium(III) oxalate hydrate (Ce ₂ (C ₂ O ₄ ) ₃ xH ₂ O), cerium(III) acetate (Ce(CH ₃ CO ₂ ) ₃ ), cerium(III) acetate hydrate (Ce(CH ₃ CO ₂ ) ₃ xH ₂ O), cerium(III) carbonate (Ce ₂ (CO ₃ ) ₃ ), cerium(III) carbonate hydrate (Ce ₂ (CO ₃ ) ₃ xH ₂ O), Cerium(IV) sulfate (Ce(SO ₄ ) ₂ ), cerium(IV) sulfate hydrate (Ce(SO ₄ ) ₂ xH ₂ O), ammonium cerium(IV) nitrate ((NH ₄ ) ₂ Ce(NO ₃ ) ₆ ), ammonium cerium(IV) nitrate hydrate ((NH ₄ ) ₂ Ce(NO ₃ ) ₆ xH ₂ O), ammonium cerium(IV) sulfate (Ce(NH ₄ )4(SO ₄ ) ₄ ), ammonium cerium (IV) at least one selected from the group consisting of sulfate hydrate (Ce(NH ₄ )4(SO ₄ ) ₄ xH ₂ O) and cerium (IV) hydroxide (Ce(OH) ₄ ), but necessarily limited thereto It is not.

The cerium (III) nitrate hydrate (Ce(NO ₃ ) ₃ .xH ₂ O) includes cerium (III) nitrate monohydrate to hexahydrate, but is not limited thereto. More specifically, the cerium (III) nitrate hydrate (Ce(NO ₃ ) ₃ .xH ₂ O) may be cerium (III) nitrate hexahydrate (Ce(NO ₃ ) ₃ .6H ₂ O).

In a specific embodiment of the present invention, the cerium oxide precursor solution of the present invention is cerium (III) nitrate hexahydrate (Ce(NO ₃ ) ₃ 6H ₂ O), cerium (III) chloride heptahydrate (CeCl ₃ 7H ₂ O), cerium(III) acetate (Ce(CH ₃ CO ₂ ) ₃ ), cerium(III) oxalate (Ce ₂ (C ₂ O ₄ ) ₃ ), ammonium cerium(IV) nitrate ((NH ₄ ) ₂ Ce(NO ₃ ) ₆ ), at least one selected from the group consisting of cerium (IV) sulfate (Ce(SO ₄ ) ₂ ) and cerium (IV) hydroxide (Ce(OH) ₄ ), but necessarily limited thereto It is not.

In a more specific embodiment of the present invention, the cerium oxide precursor solution of the present invention is cerium (III) nitrate hexahydrate (Ce(NO ₃ ) ₃ 6H ₂ O), but is not necessarily limited thereto.

In one embodiment of the present invention, the rhodium precursor solution of the present invention is rhodium (III) nitrate hydrate (Rh(NO ₃ ) ₃ xH ₂ O), rhodium (III) sulfate (Rh ₂ (SO ₄ ) ₃ ), Rhodium(III) sulfate hydrate (Rh ₂ (SO ₄ ) ₃ xH ₂ O), rhodium(III) acetate (Rh(OAc) ₃ ), rhodium(III) hydroxide (Rh(OH) ₃ ), rhodium(III ) Chloride (RhCl ₃ ), Rhodium(III) Chloride Hydrate (RhCl ₃ xH ₂ O), Ammonium Hexachlororodate(III) ((NH ₄ ) ₃ RhCl ₆ ), (Trichlorotris(ethylenediamine)rhodium (III) ((H ₂ NCH ₂ CH ₂ NH ₂ ) ₃ RhCl ₃ ) and trichlorotris(ethylenediamine)rhodium(III) trihydrate ((H ₂ NCH ₂ CH ₂ NH ₂ ) ₃ RhCl ₃ 3H ₂ O) at least one selected from the group consisting of, but is not necessarily limited thereto.

The rhodium (III) sulfate hydrate (Rh ₂ (SO ₄ ) ₃ xH ₂ O) includes rhodium (III) sulfate monohydrate to rhodium (III) sulfate hexahydrate and rhodium (III) sulfate aqueous solution (about 8% rhodium in water). (III) including sulfates), but are not limited thereto. More specifically, the rhodium (III) sulfate hydrate (Rh ₂ (SO ₄ ) ₃ .xH ₂ O) may be rhodium (III) sulfate tetrahydrate (Rh ₂ (SO ₄ ) ₃ .4H ₂ O).

The rhodium (III) nitrate hydrate (Rh(NO ₃ ) ₃ xH ₂ O) includes rhodium ( _III ) nitrate monohydrate to hexahydrate and about 36% rhodium. ₃ xH ₂ O), but is not limited thereto.

In a specific embodiment of the present invention, the rhodium precursor solution of the present invention is rhodium (III) nitrate hydrate (Rh(NO ₃ ) ₃ xH ₂ O), rhodium (III) sulfate (Rh ₂ (SO ₄ ) ₃ ) , selected from the group consisting of rhodium(III) sulfate hydrate (Rh ₂ (SO ₄ ) ₃ xH ₂ O), rhodium(III) chloride (RhCl ₃ ) and rhodium(III) acetate (Rh(OAc) ₃ ). One or more, but is not necessarily limited thereto.

In a more specific embodiment of the present invention, the rhodium precursor solution of the present invention is rhodium (III) nitrate hydrate (Rh(NO ₃ ) ₃ xH ₂ O) containing about 36% rhodium, but is not necessarily limited thereto not.

According to another aspect of the present invention, the present invention provides a rhodium-cerium oxide elution catalyst for a wet reforming reaction in which rhodium nanoparticles are eluted on the surface of a cerium oxide carrier doped with rhodium by reduction heat treatment.

As used herein, the term 'catalyst of the present invention' refers to a rhodium for wet reforming reaction in which rhodium nanoparticles are eluted on the surface of the above-described rhodium-doped cerium oxide (Ce _1-x Rh _x O _2-y ) support. A catalyst for eluting cerium oxide or a catalyst prepared by the method for preparing a rhodium-cerium oxide eluting catalyst for a steam reforming reaction described above.

In one embodiment of the present invention, the wet reforming reaction of the present invention is performed on one or more hydrocarbons or fuels selected from the group consisting of methane, methanol, ethane, ethanol, propane, propanol, ethylene glycol, benzene, natural gas and diesel It is performed for, but is not limited thereto.

In a preferred embodiment of the present invention, the present invention is a rhodium-cerium oxide elution for propane steam reforming reaction in which rhodium nanoparticles are eluted on the surface of a cerium oxide carrier doped with rhodium by reduction heat treatment provide a catalyst.

In another embodiment of the present invention, the present invention has the following chemical formula in which rhodium nanoparticles are eluted on the surface of a rhodium-doped cerium oxide (Ce _1-x Rh _x O _2-y ) carrier surface by reduction heat treatment Provided is a rhodium-cerium oxide elution catalyst for a wet reforming reaction denoted by 1:

[Formula 1]

Ce _{1- x} Rh _x O _{2- y}

The content ratio of rhodium (Rh) and cerium (Ce) is that rhodium is x and cerium is 1- x , and in Formula 1, x is a rational number in the range of 0.01 ≤ x ≤ 0.08, and y is in the range of 0 < y <2 glass number.

In one embodiment of the present invention, the weight of rhodium relative to the total weight of the rhodium-cerium oxide eluting catalyst of the present invention is 0.5 wt% to 8.0 wt%.

Although the conventional perovskite oxide requires a relatively long (> 4 hours) reduction heat treatment of more than 800 ° C. for the elution phenomenon, the rhodium-cerium oxide elution of the present invention having a non-perovskite oxide structure The catalyst requires reduction heat treatment for 4 hours or less at a temperature of 800° C. or less for elution.

In one embodiment of the present invention, the reduction heat treatment of the present invention is performed at a temperature of 400 ° C to 700 ° C for 5 minutes to 4 hours.

In one embodiment of the present invention, the reduction heat treatment of the present invention is performed under hydrogen gas and an inert gas.

In one embodiment of the present invention, the inert gas of the present invention is at least one selected from the group consisting of nitrogen (N ₂ ), helium (He), and argon (Ar).

In another embodiment of the present invention, the reduction heat treatment is performed under a hydrogen gas/inert gas gas at a ratio of 5% (v/v) to 30% (v/v).

In one embodiment of the present invention, the eluted rhodium nanoparticles of the present invention are anchored in the lattice of the rhodium-doped cerium oxide carrier.

In one embodiment of the present invention, the catalyst of the present invention has a surface area greater than or equal to 55 m ² /g. In another embodiment of the present invention, the catalyst of the present invention has a surface area of 55 m ² /g to 130 m ² /g.

In another embodiment of the present invention, the catalyst of the present invention has a surface area of 90 m ² /g to 130 m ² /g before reduction heat treatment (ie, as-made, as-made). In another embodiment of the present invention, the catalyst of the present invention has a surface area of 55 m ² /g to 90 m ² /g after reduction heat treatment. In this specification, the surface area of the catalyst means the BET (Brunauer-Emmett-Teller) surface area. The catalyst of the present invention has a higher/improved surface area compared to the conventional deposited Rh/CeO ₂ catalyst both before and after reduction heat treatment, so it is suitable for practical catalytic applications.

In one embodiment of the present invention, the catalyst of the present invention has a metal dispersion of 90.0% to 99.9% with respect to the surface rhodium content before reduction heat treatment. In another embodiment of the present invention, the catalyst of the present invention has a metal dispersion of 90.0% to 99.9%, 90.0% to 97.9%, 90.0% to 95.9%, 90.0% to 93.9%, 90.0% to 91.9%, 92.0% to 99.9%, 92.0% to 97.9%, 92.0% to 95.9%, 92.0% to 93.9%, 94.0% to 99.9%, 94.0% to 97.9%, 94.0% to 95.9%, 96.0% to 99.9%, 96.0% to 97.9%, or 98.0% to 99.9%. In a specific embodiment of the present invention, the catalyst of the present invention has a metal dispersion of 97.4% with respect to surface rhodium content before reduction heat treatment.

In one embodiment of the present invention, the catalyst of the present invention has a metal dispersion with respect to surface rhodium content of 30.0% to 60.0% after reduction heat treatment. In another embodiment of the present invention, the catalyst of the present invention has a metal dispersion with respect to surface rhodium content after reduction heat treatment of 30.0% to 60.0%, 30.0% to 50.0%, 30.0% to 40.0%, 40.0% to 60.0%, or 40.0% to 50.0%. In a specific embodiment of the present invention, the catalyst of the present invention has a metal dispersion of 39.6% with respect to surface rhodium content after reduction heat treatment.

In one embodiment of the present invention, the size of the eluted rhodium nanoparticles of the present invention is 2.0 nm to 3.0 nm. In another embodiment of the present invention, the size of the eluted rhodium nanoparticles of the present invention is 2.0 nm to 3.0 nm, 2.0 nm to 2.9 nm, 2.0 nm to 2.8 nm, 2.0 nm to 2.7 nm, 2.0 nm to 2.6 nm , 2.0 nm to 2.5 nm, 2.5 nm to 3.0 nm, 2.5 nm to 2.9 nm, 2.5 nm to 2.8 nm or 2.5 nm to 2.7 nm. In a specific embodiment of the present invention, the size of the eluted rhodium nanoparticles of the present invention is 2.7 nm.

In one embodiment of the present invention, the size of the eluted rhodium nanoparticles after the wet reforming reaction of the present invention is 2.0 nm to 10.0 nm.

In the rhodium-cerium oxide elution catalyst of the present invention, the size of rhodium nanoparticles is 10.0 nm or less even after wet reforming at 600°C to 800°C. Compared to the increase in rhodium particle size on the surface of the conventional Rh/CeO ₂ catalyst after wet reforming reaction to 25.5 nm, the size of eluted rhodium nanoparticles in the catalyst of the present invention is relatively small at 5.0 nm even after wet reforming reaction, which is This means that the rhodium-cerium oxide elution catalyst of the present invention has improved resistance to sintering compared to the conventional Rh/CeO ₂ catalyst.

In this specification, the term “sintering” refers to a phenomenon in which solid powders are bonded and/or deposited on surfaces in contact with each other and connected to each other when the solid powders are pressed and/or heated. Sintering causes loss of activity of the supported metal catalyst, reducing the surface area of the catalyst and changing the surface structure. In general, supported metal catalysts begin to be affected by sintering at temperatures above 500° C., and once sintered, metal catalysts are difficult to maintain nano-size.

The rhodium-cerium oxide eluting catalyst of the present invention maintains the nano-size of rhodium nanoparticles below 10.0 nm even after wet reforming in propane at 600 °C to 800 °C, so it has improved resistance to sintering compared to the conventional Rh/CeO ₂ catalyst. have

In another embodiment of the present invention, the size of the eluted rhodium nanoparticles after the wet reforming reaction of the present invention is 2.0 nm to 10.0 nm, 2.0 nm to 8.0 nm, 2.0 nm to 6.0 nm, 2.0 nm to 4.0 nm, 4.0 nm to 10.0 nm, 4.0 nm to 8.0 nm, or 4.0 nm to 6.0 nm. In a specific embodiment of the present invention, the size of the eluted rhodium nanoparticles after the wet reforming reaction of the present invention is 5.0 nm. In another specific embodiment of the present invention, the size of the eluted rhodium nanoparticles after the propane wet reforming reaction of the present invention is 5.0 nm.

In one embodiment of the present invention, the D band peak intensity (I _D ) at 1350 cm ^-1 for the G band peak intensity (I _G ) at 1590 cm ^-1 in the Raman spectrum after the wet reforming reaction of the present invention The I _D /I _G ratio is 2.00 to 3.50.

In the present invention, a high-resolution Raman spectrum can be obtained from a laser source having a wavelength of 514 nm using LabRAM HR Evolution Visible NIR (HORIBA). The lower the I _D /I _G value of the Raman spectrum, the higher the graphitization degree of carbon, which generally indicates more severe coke deposition on the catalyst bed. Coke deposition on the catalyst causes problems such as deactivation of the catalyst.

Conventional Rh/CeO ₂ catalysts have an I _D / _IG ratio of less than 2.00 after wet reforming, but the rhodium-cerium oxide eluting catalyst of the present invention has a higher I _D / _IG ratio of 2.00 to 3.50 after wet reforming. Therefore, the rhodium-cerium oxide eluting catalyst of the present invention has improved resistance to coke deposition compared to the conventional Rh/CeO ₂ catalyst.

In another embodiment of the present invention, the D band peak intensity (I _D ) at 1350 cm ^-1 for the G band peak intensity (I _G ) at 1590 cm ^-1 in the Raman spectrum after the wet reforming reaction of the present invention The phosphorus I _D /I _G ratio is from 2.00 to 3.50, from 2.00 to 3.25, from 2.00 to 3.00, from 2.00 to 2.75, from 2.00 to 2.50, from 2.00 to 2.25, from 2.25 to 3.50, from 2.25 to 3.25, from 2.25 to 3.00, from 2.25 to 2.25, from 2.75 2.50, 2.50 to 3.50, 2.50 to 3.25, 2.50 to 3.00, 2.50 to 2.75, 2.75 to 3.50, 2.75 to 3.25, 2.75 to 3.00, 3.00 to 3.50, or 3.00 to 3.25.

In a specific embodiment of the present invention, the D ^band _peak ^intensity (I _D ), the I _D /I _G ratio is 2.92.

Since the rhodium-cerium oxide elution catalyst for wet reforming reaction of the present invention is prepared by the method for preparing a rhodium-cerium oxide elution catalyst for wet reforming reaction, which is another aspect of the present invention described above, in order to avoid excessive complexity described in the present specification Duplicate content is used and its description is omitted.

According to another aspect of the present invention, there is provided a wet reforming reaction method comprising the step of obtaining hydrogen gas by adding the catalyst according to the present invention to hydrocarbon and water vapor.

In one embodiment of the present invention, the hydrocarbon used in the wet reforming reaction method of the present invention includes methane, methanol, ethane, ethanol, propane, propanol, ethylene glycol, benzene, etc., but is not limited thereto. Hydrocarbons used in the wet reforming reaction of the present invention include hydrocarbon fuels such as natural gas and diesel, but are not limited thereto.

In another embodiment of the present invention, there is provided a propane wet reforming reaction method comprising the step of obtaining hydrogen gas by adding the catalyst according to the present invention to propane and water vapor.

In one embodiment of the present invention, the reaction method of the present invention is carried out under feed conditions containing steam and hydrocarbons with a steam to carbon ratio (S/C) of 1 to 4.

In another embodiment of the present invention, the reaction method of the present invention is carried out under feed conditions including steam and hydrocarbons with a water vapor to carbon ratio of S/C of 2.

In one embodiment of the present invention, the reaction method of the present invention is carried out at a total space velocity of 5,000 mL/g _cat /h to 200,000 mL/g _cat /h. In a specific embodiment of the present invention, the reaction method of the present invention is carried out at a total space velocity of 200,000 mL/g _cat /h

In one embodiment of the present invention, the reaction method of the present invention is carried out at 600 ℃ to 800 ℃. In another embodiment of the present invention, the reaction method of the present invention is 600 ℃ to 800 ℃, 600 ℃ to 750 ℃, 600 ℃ to 700 ℃, 600 ℃ to 650 ℃, 650 ℃ to 800 ℃, 650 ℃ to 750 °C, 650 °C to 700 °C, 700 °C to 800 °C, 700 °C to 750 °C or 750 °C to 800 °C. In a specific embodiment of the present invention, the reaction method of the present invention is carried out at 700 ℃.

In one embodiment of the present invention, the reaction method of the present invention is performed showing a hydrogen yield of 70% or more and a hydrocarbon conversion rate of 97% or more for 1 hour to 100 hours. In another embodiment of the present invention, the reaction method of the present invention is 1 hour to 100 hours, 1 hour to 90 hours, 1 hour to 80 hours, 1 hour to 70 hours, 1 hour to 60 hours, 1 hour to 50 hours time, 1 hour to 40 hours, 1 hour to 30 hours, 1 hour to 20 hours, 20 hours to 100 hours, 20 hours to 90 hours, 20 hours to 80 hours, 20 hours to 70 hours, 20 hours to 60 hours, 20 to 50 hours, 20 to 40 hours, 20 to 30 hours, 30 to 100 hours, 30 to 90 hours, 30 to 80 hours, 30 to 70 hours, 30 to 60 hours, 30 hours to 50 hours, 30 hours to 40 hours, 40 hours to 100 hours, 40 hours to 90 hours, 40 hours to 80 hours, 40 hours to 70 hours, 40 hours to 60 hours, 40 hours to 50 hours, 50 hours to 100 time, 50 hours to 90 hours, 50 hours to 80 hours, 50 hours to 70 hours, 50 hours to 60 hours, 60 hours to 100 hours, 60 hours to 90 hours, 60 hours to 80 hours, 60 hours to 70 hours, 70 hours to 100 hours, 70 hours to 90 hours, 70 hours to 80 hours, 80 hours to 100 hours, 80 hours to 90 hours or 90 hours to 100 hours.

In a specific embodiment of the present invention, the propane wet reforming reaction method of the present invention is stably performed with a propane conversion of 100% and a hydrogen yield of 70% or more for 65 hours.

The rhodium-cerium oxide eluting catalyst of the present invention has improved propane conversion and hydrogen yield compared to the conventional Rh/CeO ₂ catalyst in the propane wet reforming reaction for 65 hours.

In another embodiment of the present invention, the reaction method of the present invention has a propane conversion rate of 97.0% to 100.0%. In the present invention, the propane conversion rate was calculated using Equation 1 of Example 5 to be described later.

In another embodiment of the present invention, the reaction method of the present invention has a hydrogen yield of 70.0% to 100.0%. In the present invention, the hydrogen yield was calculated using Equation 2 of Example 5 to be described later.

The rhodium-cerium oxide elution catalyst of the present invention has improved hydrogen yield and propane conversion compared to the conventional Rh/CeO ₂ catalyst, and has improved resistance to sintering and coke deposition.

Since the wet reforming reaction method of the present invention is performed using the rhodium-cerium oxide elution catalyst for the wet reforming reaction, which is another aspect of the present invention described above, redundant contents are used to avoid excessive complexity described in the present specification. omit the description.

The features and advantages of the present invention are summarized as follows:

(a) The present invention provides a method for preparing a rhodium-cerium oxide eluting catalyst for wet reforming.

(b) The present invention provides a rhodium-cerium oxide elution catalyst for a wet reforming reaction in which rhodium nanoparticles are eluted on the surface of a rhodium-doped cerium oxide (Rh-doped CeO ₂ , CeRhO) support by reduction heat treatment do.

(c) It provides a wet reforming reaction method comprising the step of obtaining hydrogen gas by adding the catalyst according to the present invention to hydrocarbon and water vapor.

(d) In the case of using the method for preparing a rhodium-cerium oxide eluting catalyst for a wet reforming reaction of the present invention, durability at high temperature is improved through reduction heat treatment compared to the conventional Rh/CeO ₂ catalyst, and a high value of 55 m ² /g or more It is possible to obtain a rhodium-cerium oxide elution catalyst for a wet reforming reaction in which Rh nanoparticles separated from a cerium oxide domain directly confirmed by in-situ TEM analysis are eluted, and the catalyst is used. Compared to the Rh/CeO ₂ catalyst of the present invention, it is possible to obtain improved hydrogen yield in the wet reforming reaction for a long time and at high temperature, especially in the propane wet reforming reaction, and after the wet reforming reaction, the catalyst of the present invention is sintered and coke compared to the conventional Rh/CeO ₂ catalyst. Since it has improved resistance to deposition, it is possible to provide a nano-sized catalyst for preparing a highly durable elution catalyst.

1a shows that when reduction heat treatment is applied to a rhodium-doped cerium oxide (Rh-doped CeO ₂ , CeRhO) support having a high surface area of the present invention, rhodium nanoparticles are eluted (ex-solution), and the eluted rhodium nanoparticles A schematic diagram of a rhodium-cerium oxide eluting catalyst (exsolved CeRhO), which exhibits strong anchoring with the support, has high durability in propane wet reforming reaction, and can provide very stable production of hydrogen gas.
Figure 1b shows a schematic view of a method for producing a rhodium-doped cerium oxide carrier (Ce _1-x Rh _x O _2-y ) according to an embodiment of the present invention.
2 (a) and (b) show high-resolution TEM images of a 4CeRhO catalyst according to an embodiment of the present invention, and (c) and (d) show high-resolution TEM images of a 4Rh/CeO ₂ catalyst according to a comparative example. .
3 shows the Rh K edge EXAFS results for 1, 2, 4, 8CeRhO and 4Rh/CeO ₂ catalysts. Lines represent experimental data and dots represent fitting results.
4 shows XPS results for 1, 2, 4, 8CeRhO and 4Rh/CeO ₂ catalysts. Dotted lines represent experimental data and solid lines represent fitting results. Rh-O-Ce was observed at 308.7 eV to 309 eV and Rh-O-Rh appeared at 308.1 eV.
5 shows the Rh K edge EXAFS results for reduced 1, 2, 4 and 8CeRhO. Reduction was performed with a 10% H ₂ /N ₂ flow at 500° C. for 3 hours. Lines represent experimental data and dots represent fitting results.
Figure 6 shows the change between reduction according to an embodiment and as-made in one embodiment on 1, 2, 4 and 8CeRhO catalysts. Figure 6 (a) shows a high-resolution XRD pattern and (b) shows the relationship between the amount of doped Rh and the lattice parameter shift (lattice parameter shift). 6(c) shows an XPS spectrum and (d) shows a BET result. The thick line represents the as-made catalyst and the translucent line represents the reduced catalyst.
7 shows high-resolution XRD results for (a) 4CeRhO and (b) 4Rh/CeO ₂ at the PAL 8D beamline. Each fresh sample was reduced with a 30% H ₂ /N ₂ flow at 500° C. for 3 hours and re-oxidized in air at 500° C. for 3 hours.
8 shows in-situ TEM images of the 4CeRhO catalyst under reducing conditions. In (a) of FIG. 8, 4CeRhO samples were exposed to 10% H ₂ /Ar gas at 500° C. and 760 torr for 5 minutes, 10 minutes, and 30 minutes. (b) of FIG. 8 shows the average diameter of Rh nanoparticles within that time. Figure 8(c) is a graph of the number vs. diameter of Rh nanoparticles based on nanoparticles eluted from neighboring regions.
9 shows a high-resolution TEM image of 4CeRhO after reduction (500° C., 3 hours, 10% H ₂ /N ₂ ). 9(a) shows a TEM image of eluted Rh nanoparticles overlapping the surface of cerium oxide. Rh nanoparticles eluted with orange boxes are highlighted, and EDX mapping results are shown on the right. 9(b) shows a TEM image of eluted Rh nanoparticles that do not overlap with cerium oxide. Magnified TEM images of eluted Rh nanoparticles are shown on the left. Orange and green boxes represent eluted Rh nanoparticles and cerium oxide, respectively.
Figure 10 shows the TEM selected-area EDS analysis of the orange box in Figure 9 (a).
11 shows high-resolution TEM images and FFT analysis of 8CeRhO after reduction (700° C., 3 hours, 10% H ₂ /N ₂ ).
12 shows a DRIFT spectrum obtained by CO adsorption on 4CeRhO prepared in one example according to the present invention and a catalyst after reduction (500° C., 3 hours, 10% H ₂ /N ₂ ).
13 shows a DRIFT spectrum obtained by CO adsorption on 4Rh/CeO ₂ prepared in one example according to the present invention and a catalyst after reduction (500° C., 3 hours, 10% H ₂ /N ₂ ).
FIG. 14 shows the results of (a) 4CeRhO and (b) 4Rh/CeO ₂ sinter resistance tests performed after heat treatment at 500° C., 700° C., and 900° C. for 8 hours in an N ₂ atmosphere, respectively. The crystallite size of Rh was calculated by the Scherrer equation from the full width at half maximum (FWHM) of the Rh (Miller index: 111) peak (Powder Diffraction File (PDF) card number: 01-088-2334).
15 shows H ₂ -TPR results of reduced 4CeRhO and 4Rh/CeO ₂ catalysts. Pretreatment was performed with a 5% O ₂ /He flow at 600° C. for 1 hour.
16 shows (a) propane conversion and (b) hydrogen yield in propane steam reforming (PSR) for 4CeRhO and 4Rh/CeO ₂ . The reaction conditions were as follows: Steam to Carbon ratio (S/C) 2, reaction temperature 700 °C, in situ with 10% H ₂ /N ₂ gas at 500 °C for 3 hours before reaction. 60 mg of reduced catalyst (SV = 200,000 mL/g _cat /h).
17 shows the product (CH ₄ , CO, CO ₂ and H ₂ ) selectivities for (a) 4CeRhO and (b) 4Rh/CeO ₂ .
Figure 18 (a) shows the XRD patterns for the 4CeRhO and 4Rh/CeO ₂ catalysts used after reaction for 65 hours, and Figure 18 (b) shows the expanded XRD pattern for the Rh (111) peak.
19 shows (a) 4CeRhO and (b) 4Rh/CeO ₂ phases used. A high-resolution TEM image of the catalyst used after reaction for 65 hours is shown. The deposited coke was further investigated for the catalyst by (c) TPO analysis and (d) Raman spectroscopy.

Hereinafter, the present invention will be described in more detail through examples. These examples are only for explaining the present invention in more detail, and it will be apparent to those skilled in the art that the scope of the present invention is not limited by these examples according to the gist of the present invention. .

Example

Throughout this specification, "%" used to indicate the concentration of a particular substance is (weight/weight) % or wt% for solid/solid, and (weight/volume) for solid/liquid, unless otherwise specified. %, liquid/liquid is (vol/vol) %, and gas/gas is (vol/vol) %, or %(v/v).

Example 1: Catalyst Synthesis

Rhodium-doped cerium oxide was prepared by a co-precipitation method (see FIG. 1B). In a round-shaped flask, 1 g of Ce(NO ₃ ) ₃ 6H ₂ O (99.99%, Kanto chemical) and an appropriate amount of Rh(NO ₃ ) ₃ .xH were added to 35 mL of deionized water (DI water). ₂ O (~36% Rh, Sigma Aldrich) was dissolved. After stirring for 1 hour, 1 M KOH (1 N, SAMCHUN) was added dropwise to the solution until pH 9. The final solution was stirred for 4 hours and filtered with ethanol and deionized water. The precipitate was dried in an oven at 80 °C overnight and the resulting solid was ground in a mortar. The powder was calcined in air at 450° C. for 4 hours. The washing, drying and firing process was then repeated once. The product Ce _{1- x} Rh _x O ₂ support was designated CeRhO. The amount of Rh in the rhodium (Rh)-doped cerium oxide was adjusted to 1 wt%, 2 wt%, 4 wt%, and 8 wt%, and was denoted as 1CeRhO, 2CeRhO, 4CeRhO, and 8CeRhO, respectively.

Comparative Example 1: Rh/CeO ₂ catalyst synthesis

A conventional as-deposited Rh/CeO ₂ catalyst was synthesized by wet-impregnation as a control sample. CeO ₂ powder was prepared in the same manner as described above. 0.3 g of CeO ₂ and an appropriate amount of Rh(NO ₃ ) were dissolved in 10 mL of deionized water in a 3-neck flask. The solution was evaporated while stirring at 80 °C. The resulting solid was dried overnight in an oven at 80° C. and ground in a mortar. The final powder was calcined for 4 hours at 500 °C in air. The product was designated Rh/CeO ₂ . The amount of Rh deposited on the cerium oxide was adjusted to 1 wt%, 2 wt%, 4 wt%, and 8 wt%, respectively, and expressed as 1Rh/CeO ₂ , 2Rh/CeO ₂ , 4Rh/CeO ₂ and 8Rh/CeO ₂ . .

Example 2: Reduction heat treatment method

In order to elute rhodium from the CeRhO support prepared in Example 1, 1CeRhO, 2CeRhO, 4CeRhO, and 8CeRhO were subjected to reducing treatment with 10% H ₂ /N ₂ gas at 500° C. for 3 hours. As control samples, 1Rh/CeO ₂ , 2Rh/CeO ₂ , 4Rh/CeO ₂ and 8Rh/CeO ₂ prepared in Comparative Example 1 were also subjected to the same reducing treatment. In Example 5.8 to be described later, in order to investigate the eluted Rh nanoparticles on 4CeRhO of Example 1 by ex-situ TEM, the above reductive treatment was also performed. Unless otherwise indicated, in Examples to be described later, reduction heat treatment was applied to the catalyst under the above reducing treatment conditions.

In Example 5.7 to be described later, in order to directly confirm the elution of the 4CeRhO phase prepared in Example 1 by in-situ TEM, the catalyst was subjected to 10% H ₂ /Ar- Reductive treatment was performed under gas.

In addition, in order to observe the Rh nanoparticles eluted after reduction, in Example 5.8 to be described later, the 8CeRhO sample of Example 1 was subjected to a reducing treatment at 700° C. for 3 hours under 10% H ₂ /N ₂ gas.

Reduction heat treatment according to Example 2 was applied to the CeRhO support prepared in Example 1 described above to prepare a rhodium-cerium oxide elution catalyst for wet reforming of the present invention. In the following examples, reduction heat treated or 'reduced' 1CeRhO, 2CeRhO, 4CeRhO and 8CeRhO represent rhodium-cerium oxide elution catalysts for the wet reforming reaction of the present invention.

Example 3: Characterization method

3.1: In-situ TEM method

In-situ _gas flow holder (Hummingbird Scientific) and transmission electron microscopy (TEM, Tecnai G2, F30 S- Characterization was performed using a Twin, operating at 300 keV, FEI).

3.2: EDS and HAADF-STEM Analysis Methods

High-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) with spot-energy-dispersive X-ray spectroscopy analysis (EDS) microscopy, Titan cubed G2 60-300, FEI) analysis was performed with an accelerating voltage of 300 kV.

3.3: XPS analysis method

The oxidation state of Rh was investigated by X-ray photoelectron spectroscopy (XPS, K-Alpha, Thermo VG Scientific). The binding energy was calculated using the maximum intensity of the favorable C 1s signal at 284.8 eV as a reference.

3.4: XRD analysis method

X-ray diffaction (XRD) patterns (Rigaku, Cu Kα radiation) were collected in the range of 20° to 90° (2θ) with a step size of 0.01° at a speed of 5°/min. High resolution X-ray diffraction (HR-XRD) was measured using PLS's 8D XRD POSCO beamline.

3.5: ICP-OES Method - Determination of Total Rhodium in Catalyst

The amount of Rh in the catalyst was measured with an inductively coupled plasma optical emission spectrometer (ICP-OES, ThermoFisher Scientific). The total amount of Rh in CeRhO was 0.9 wt%, 2.1 wt%, 3.9 wt% and 7.3 wt% in 1CeRhO, 2CeRhO, 4CeRhO and 8CeRhO, respectively.

3.6: BET Surface Area and Raman Spectrum Measurement Method

BET surface area measurements (Tristar® Micromeritics) were performed. High resolution Raman spectra (High resolution raman sepctrum, LabRAM HR Evolution Visible_NIR, HORIBA) were collected in the range of 1000 cm ^-1 to 2000 cm ^-1 , and the wavelength of the laser source was 514 nm.

3.7: CO chemisorption method - rhodium dispersion

Pulsed CO chemisorption (BELCAT-2, MicrotracBEL) was performed to obtain information on the Rh dispersion of the samples obtained from Takeguchi's method. First, 30 mg of the catalyst was heated in a 5% O ₂ /He flow to 300° C. for 10 min, then cooled to 50° C. for 5 min with He gas for purging. The catalyst was heated in a 5% H ₂ /Ar flow to 200° C. for 15 minutes. After cooling, and before pulse injection, the following sequence was performed. (i) He (5 min); (ii) 5% O ₂ /He (5 min); (iii) C0 ₂ (60 min); (iv) He (20 min); (v) 5% H ₂ /Ar (5 min); and (vi) He (5 minutes). Finally, CO gas was pulsed in the He stream repeatedly every minute until the adsorption of CO onto the catalyst was saturated. In order not to overestimate the Rh dispersion, CO ₂ was injected to form carbonate on the surface of cerium oxide. When measuring the dispersion for the reduced sample, pre-oxidation treatment with a 5% O ₂ /He flow at 600 °C for 1 hour to detect Rh induced by strong metal support interaction (SMSI) The CeO _x layer on the metal was removed. Detailed information is listed in Table 1 below.

Table 1 below shows the CO-chemisorption results of the reduced 4CeRhO sample. Pre-treatment was performed with a 5% O ₂ /He gas flow at 300 °C, 400 °C, 500 °C, 600 °C and 700 °C to remove the CeO _x layer on the Rh nanoparticles.

Note: After reduction, Rh nanoparticles came to the surface by elution. However, the CeO _x thin film was also superimposed onto the Rh metal surface by the SMSI effect. Oxidative pre-treatment at high temperatures is required to remove these thin films, and CO molecules can be adsorbed on the Rh metal surface. By varying the treatment temperature, 600 °C could be selected as the optimized pre-treatment condition.

3.8: Thermal Oxidation (TPO) Method

Temperature-programmed oxidation (TPO BELCAT-2, MicrotracBEL) was performed with the following procedure. First, 30 mg of the sample was loaded and heated in a He flow at 200° C. for 2 hours. After cooling to room temperature, 5% O ₂ /He was introduced and heated to 800° C. at a ramping rate of 10° C./min.

3.9: CO-DRIFT method - Observation of dissolution

CO diffuse reflectance infrared Fourier-transform (CO-DRIFT, Nicolet iS-50, Thermo Scientific) spectroscopy was performed to observe elution from the sample. 5 mg of catalyst was mixed with 95 mg of KBr. The mixed powder was placed in a sample cup and placed into a DRIFT cell. Cells were pretreated with Ar flow at 100 °C for 1 hour. When cooled to room temperature, 2% CO/Ar was introduced for 10 minutes. DRIFT spectra were collected during CO adsorption by Ar flow with evacuation for 30 min at room temperature. Finally, the CO adsorption spectrum onto the sample was measured.

3.10: XAS analysis method

X-ray absorption spectroscopy (XAS) was measured at the 10C Wide XAFS beamline of the Pohang Light Source (PLS). Rh K-edge spectra were obtained in fluorescence mode using a passivated implanted planar silicon (PIPS) detector (Canberra). Each sample was calibrated by simultaneously measuring a reference Rh foil. XAS data were fitted using ARTEMIS and ATHENA software. Coordination number (coordination number) was calculated by fixing the amplitude reduction factor (amplitude reduction factor, S ₀ ² ) of the reference Rh foil. When the number of independent points is limited, the Debye-Waller factor (σ ² ) is fixed at a reasonable value of 3.0×10 ^-3 .

Example 4: Support of Ce-Rh-O

As described in Example 1 above, cerium oxide doped with 1 wt%, 2 wt%, 4 wt%, and 8 wt% Rh was prepared by a co-precipitation method and was denoted as 1CeRhO, 2CeRhO, 4CeRhO, and 8CeRhO, respectively. As described in Comparative Example 1 above, conventional Rh/CeO ₂ was synthesized by a wet-impregnation method as a control sample.

4.1: High-resolution TEM analysis results

TEM images of the 4CeRhO catalyst prepared in Example 1 and the 4Rh/CeO ₂ catalyst of Comparative Example 1 are shown in FIG. 2 . As shown in Figure 2, their domain size was less than 10 nm, indicating nano-domain rhodium-cerium oxide.

4.2: Results of EXAFS analysis

Structures of 1, 2, 4, 8CeRhO and 4Rh/CeO ₂ were compared in Rh K-edge EXAFS (extended X-ray absorption fine structure), and the results are shown in FIG. 3 . As shown in Figure 3, Rh/CeO ₂ has both Rh-O and Rh-O-Rh peaks at 2.0 Å and 3.0 Å, respectively. On the other hand, CeRhO showed the Rh-O peak only at 2.0 Å. Table 2 below shows the EXAFS fitting results.

As shown in Table 2, 1, 2, 4 and 8CeRhO have coordination numbers of 5.8, 5.5, 5.3 and 5.1 for the Rh-O interaction, respectively. Even when the amount of doped Rh was increased to 4 wt%, the coordination number of the Rh-O-Rh interaction was still less than 1. When the amount of Rh was 8 wt%, the coordination number of Rh-O-Rh was 1, indicating the formation of small Rh oxide clusters. In Rh—O—Ce, in which doped Rh atoms occupy Ce sites, lattice distortion occurs due to the formation of oxygen vacancy sites. Comparatively long-range Rh-O-Ce was not observed by EXAFS and overran nearest neighboring Rh atoms. 4Rh/CeO ₂ has a coordination number of 5.2 for the Rh-O interaction and a high coordination number of 4.1 for the Rh-O-Rh interaction, indicating that Rh oxide nanoparticles on the surface are formed.

4.3: Results of XPS analysis

X-ray photoelectron spectroscopy (XPS) analysis showed that the Rh atom (308.7 - 309 eV) in CeRhO was more oxidized than the Rh atom in Rh/CeO ₂ (308.1 eV), as shown in FIG. 4 .

As shown in FIG. 4, the Rh atom substituted in the cerium oxide lattice (Rh-O-Ce) exhibited a higher oxidation state than that of Rh oxide (Rh-O-Rh). These results indicate that Rh was substituted in the cerium oxide lattice of the CeRhO catalyst and Rh oxide was formed on the surface of Rh/CeO ₂ . As the amount of doped Rh increased to 4 wt%, the ratio of Rh-O-Ce was maintained at 100%. On the other hand, when the amount of Rh in CeRhO was increased to 8 wt%, a small proportion (7.7%) of Rh-O-Rh was observed, which is consistent with the EXAFS results for the formation of Rh-O-Rh.

Example 5: Rh elution from carrier

To observe the exsolution of the CeRhO support, the catalyst was subjected to a reducing treatment (Example 2) at 500° C. for 3 hours with 10% H ₂ /N ₂ gas.

5.1: Results of EXAFS analysis of reduced catalyst

The structures of the reduced 1, 2, 4 and 8CeRhO catalysts were investigated by Rh K edge EXAFS, and the results are shown in FIG. 5 .

As shown in Fig. 5, a Rh-Rh peak at 2.6 Å appeared after reduction. EXAFS fitting results are shown in Table 3 below.

As shown in Table 3, reduced 1, 2, 4 and 8CeRhO have coordination numbers for the Rh-Rh interaction of 2.6, 3.3, 5.9 and 5.9, respectively. The coordination number of the Rh-O interaction decreased to 3.1, 2.9, 1.8 and 1.7, respectively. When the amount of doped Rh was increased to 4 wt%, more metallic Rh-Rh bonds were observed, indicating formation of Rh metal nanoparticles by elution. The Rh-Rh bond did not change any more even when the amount of doped Rh increased to 8 wt%. 4 wt% Rh doped may be sufficient to form reduction-eluted Rh nanoparticles.

5.2: Results of high-resolution XRD pattern analysis of reduced catalysts

After reduction, the changed structures of the 1, 2, 4 and 8CeRhO catalysts were investigated, and the results are shown in FIG. 6 . In FIG. 6, the thick line represents the catalyst prepared in Example 1, and the translucent line represents the reduced catalyst subjected to reduction heat treatment according to Example 2. XRD patterns of the 1, 2, 4, 8CeRhO prepared in Example 1 and the catalyst after reduction in Example 2 were investigated, and the results are shown in (a) of FIG. Since the Rh atom has a smaller atomic radius than the Ce atom, the lattice parameter of the CeRhO support decreased. The CeO ₂ (Miller index: 111) peak shifted to a higher degree when Rh atoms were doped into the cerium oxide lattice. When the eluted Rh nanoparticles appeared on the surface after reduction, the lattice constant of cerium oxide broadened and the CeO ₂ (111) peak shifted to a smaller degree. The lattice constant expansion indicated the elution of Rh species from the cerium oxide lattice to the surface.

5.3: Lattice constant shift analysis result of reduced catalyst

The lattice constant shift after reduction was calculated, and the results are shown in (b) of FIG. As shown in (b) of FIG. 6, the lattice constant shifts increased to 0.0019 Å, 0.0111 Å, 0.0186 Å, and 0.0223 Å for 1, 2, 4, and 8CeRhO, respectively. The change in lattice constant increased up to 4CeRhO, but started to saturate when the amount of Rh was 8 wt%. This is consistent with the EXAFS fitting result that the amount of 4 wt% Rh is sufficient for elution.

5.4: Results of high-resolution XRD analysis after re-oxidation of the reduced catalyst

The eluted Rh nanoparticles do not appear to dissolve into the cerium oxide lattice after re-oxidation treatment (500 °C, 3 h, air), which indicates that the CeO ₂ (111) peak is higher after re-oxidation of the reduced 4CeRhO sample. This is because it does not move back to (degree), and these results are shown in FIG.

5.5: Results of XPS analysis of reduced catalyst

XPS results showed the changed surface oxidation state of Rh after reduction, which is shown in FIG. 6(c). The doped-Rh species in CeRhO prepared in Example 1 have higher binding energies from 308.7 eV to 309 eV, indicating the formation of a solid solution. On the other hand, a metallic Rh phase was observed at 307.7 eV after reduction, indicating the formation of eluted Rh metal nanoparticles on the surface.

5.6: Results of BET surface area analysis of catalysts before and after reduction

6(d) and Table 4 below show changes in the BET surface area after reduction.

As shown in FIG. 6(d) and Table 4, CeRhO of nano-domain size still maintained a high surface area (> 55 m ² /g) even after reductive treatment, causing elution. Conventional Rh/CeO ₂ catalysts also obtained surface areas in excess of 40 m ² /g as measured after reduction.

5.7: of the reduced catalyst In-situ TEM analysis results

Elution of the 4CeRhO phase was directly observed by in-situ TEM, and the results are shown in FIG. 8 . 4CeRhO of Example 1 was exposed to 10% H ₂ /Ar- gas at 500° C. for 5 min, 10 min and 30 min. At room temperature, there were no Rh nanoparticles on the surface (see (a) Room T in FIG. 8). After 5 min of reducing treatment, some moire fringe patterns could be observed, which is due to the appearance of eluted Rh nanoparticles superimposed on the cerium oxide surface. The moiré fringe pattern was still confirmed by reduction for 30 minutes. When neighboring Rh nanoparticles were counted in the vicinity of the portion, the average size was about 2 nm to 3 nm. The average size of the eluted Rh nanoparticles did not change after reduction over 30 minutes. These results indicate that short-duration reduction is sufficient for elution of Rh species from nano-domain CeRhO catalysts with high surface area. On the other hand, conventional perovskite materials usually require relatively long (> 4 h) reduction over 800 °C for elution.

5.8: of the reduced catalyst Ex-situ TEM and EDX spectral analysis results

In addition, the eluted Rh nanoparticles on the 4CeRhO catalyst were investigated by ex-situ TEM, and the results are shown in Fig. 9. As shown in (a) of FIG. 9 , after reduction (500° C., 3 hours, 10% H ₂ /N ₂ ), small Rh nanoparticles still appeared in the top TEM image, and Rh identified as a species.

As shown in Fig. 10, the EDX spectrum clearly showed that Rh species were observed only in the orange box, indicating Rh elution from the cerium oxide domains by the reductive treatment. As shown in (b) of FIG. 9 , the bottom TEM image showed that the eluted Rh nanoparticles did not overlap with the cerium oxide. Magnified TEM images of eluted Rh nanoparticles are shown on the left. The orange boxed Rh nanoparticles show the FFT pattern for the Rh crystal. On the other hand, the cerium oxide in the green box had only the FFT pattern for the CeO ₂ crystal. These results clearly showed that small eluted Rh nanoparticles appeared on the surface after reductive treatment. In the 8CeRhO sample with high Rh content, eluted Rh nanoparticles were also observed after reduction at a high temperature of 700 °C, and the results are shown in FIG. 11 . Small Rh nanoparticles were eluted from the cerium oxide domains after reduction.

5.9: Results of CO-DRIFT analysis of 4CeRhO catalyst before and after reduction

The CO-DRIFT results of the catalyst after 4CeRhO and reduction (500°C, 3 hours, 10% H ₂ /N ₂ ) prepared in Example 1 are shown in FIG. 12 . The as-made 4CeRhO in Example 1 exhibited a major CO adsorption peak on oxidative Rh atoms (CO—RhO) at 2106 cm ⁻¹ . The two weak peaks at 2089 cm ^-1 and 2025 cm ^-1 are also attributed to symmetric and asymmetric stretching vibrations of the geminal-dicarbonyl species on the Rh atom (Rh-(CO) ₂ ). each was observed. After reductive treatment, a linear-bound CO adsorption peak and a bridge-bound adsorbed CO peak at 2059 cm ⁻¹ and 1850 cm ⁻¹ respectively were further identified on Rh metal. This indicated that the doped-rhodium atoms separated after reduction to form rhodium nanoparticles on the surface.

5.10: 4Rh/CeO before and after reduction ₂ Results of CO-DRIFT analysis of the catalyst

CO-DRIFT was also performed to observe the structure of Rh/CeO ₂ , and the results are shown in FIG. 13 . As shown in FIG. 13, an additional cross-linked CO peak was obtained at 1960 cm ⁻¹ on the as-made Rh/CeO ₂ phase in Comparative Example 1, indicating the formation of rhodium oxide nanoparticles on the surface.

5.11: 4CeRhO and 4Rh/CeO before and after reduction ₂ Results of CO-chemisorption analysis of the catalyst

The dispersion and estimated size of Rh were measured using CO-chemisorption, and the results are shown in Table 5 below.

As shown in Table 5, in order to investigate the size of Rh nanoparticles eluted from the 4CeRhO catalyst, the amount of surface Rh was measured using a leaching treatment with HNO ₃ at 200 °C. The amount of surface Rh was 1.4 wt% and 2.1 wt% for the 4CeRhO prepared in Example 1 and the catalyst after reduction, respectively. Based on the surface Rh amount, the CO-chemisorption results indicated that the average size of eluted Rh nanoparticles was observed to be 2.7 nm for reduced 4CeRhO, which was similar to the size obtained from in-situ TEM images. As a control sample, the average sizes of the Rh nanoparticles of 4Rh/CeO ₂ and reduced 4Rh/CeO ₂ were 2.3 nm and 3.9 nm, respectively.

5.12: Results of sinter resistance investigation - XRD peak analysis

To evaluate the stability of the eluted Rh nanoparticles, the sintering resistance of the 4CeRhO and 4Rh/CeO ₂ catalysts was investigated through XRD peaks of Rh (111) after heat treatment, and the results are shown in FIG. 14 . As shown in FIG. 14, the 4CeRhO and 4Rh/CeO ₂ catalysts prepared in Example 1 were reduced in 10% H ₂ /N ₂ at 500° C. for 3 hours, and then N ₂ gas was supplied at 500° C. for 8 hours, respectively. , 700 ° C and 900 ° C were introduced. No Rh (111) peak was observed after aging at 500° C. on 4CeRhO and 4Rh/CeO ₂ catalysts, indicating small Rh nanoparticles on the surface. The size was measured to be 3.6 nm and 6.8 nm, respectively, after heat treatment at 700 °C and 900 °C on 4CeRhO. The size of the eluted Rh nanoparticles slightly increased. On the other hand, 4Rh/CeO ₂ showed large Rh nanoparticles of 12.1 nm and 12.5 nm, respectively, after aging at 700°C and 900°C. Rh nanoparticles deposited on CeO ₂ were severely sintered at high temperatures. These results indicated that the eluted Rh nanoparticles were more resistant to the migration of Rh at high temperatures because of the CeRhO support and its strong anchoring.

5.13: Metal-Support Interaction - Temperature Reduction Analysis Result

FIG. 15 shows cryo H ₂ temperature-programmed reduction _{(H 2 -TPR} ) of 4CeRhO and 4Rh/CeO ₂ , which indicates metal-support interaction. The eluted Rh oxide nanoparticles were reduced to Rh metal at 120 °C in 4CeRhO. At high temperatures (~260 °C), the shoulder-like region is believed to be characteristic for the Rh reduction of the CeO ₂ lattice in solid solution form. On the other hand, Rh oxide nanoparticles deposited on CeO ₂ showed a reduction peak at a lower temperature of 75°C. These results indicate that the eluted Rh nanoparticles have a strong metal-support interaction (SMSI) compared to the Rh nanoparticles deposited in Rh/CeO ₂ .

Example 6: Propane wet reforming reaction method

The propane steam reforming (PSR) reaction was observed at atmospheric pressure in a U-shaped quartz glass fixed bed flow reactor. 60 mg of catalyst was carried out under the same feed conditions of 5 sccm C ₃ H ₈ , 155 sccm Ar, 10 sccm N ₂ and 1.34 mL/h water with S/C (Steam to Carbon) of 2. Water was injected with a syringe pump and vaporized along a pre-heating line along with other feed gases. Produced gases (CH ₄ , CO, CO ₂ , and H ₂ ) were analyzed with a gas chromatograph equipped with a thermal conductivity detector (TCD) and a flame ionization detector (FID). Propane conversion, hydrogen yield, and selectivity for the product gas were calculated using Equations 1 to 3 below.

[Equation 1]

Propane conversion rate (%) = (F _{propane, in} - F _{propane, out} )/F _{propane, in} Х 100

[Equation 2]

Hydrogen yield (%) = 2Х ( ₂ moles of H produced)/(total moles of H atoms in the feed) Х 100

[Equation 3]

Selectivity (%) of gas x = F_{gas x, out}/(F_{CH4, out}+F_{CO, out}+ F_{CO2, out}+ F_{H2, out}) Х 100)

Example 7: Propane wet reforming reaction results

Since propane steam reforming (PSR) typically operates at high temperatures (> 600 °C) and causes agglomeration or coke deposition on the active metal sites during reduction, a highly durable catalyst is required for stable hydrogen production. need.

7.1 Propane Conversion and Hydrogen Yield

A long-term PSR reaction was performed for 4CeRhO and 4Rh/CeO ₂ for 65 hours, respectively, and the results are shown in FIG. 16 . Each catalyst was reduced at 500 °C before reaction.

Propane conversion for all catalysts was nearly 100% during the first 20 hours. The conversion rate was maintained for 65 hours with the 4CeRhO catalyst, whereas the conversion rate decreased from 97% to 76% with the 4Rh/CeO ₂ catalyst.

The H ₂ yield remained stable at 70% with 4CeRhO catalyst. On the other hand, it decreased to 51% in 4Rh/CeO ₂ after 65 hours. Selectivity for all catalysts is shown in FIG. 17 . These results indicate that the Rh nanoparticles eluted on the 4CeRhO catalyst can stably produce hydrogen gas without any decomposition.

The activity and durability obtained in the present invention are compared with the literature values and are shown in Table 6 below.

Information on Ref ² to Ref ⁷ referenced in Table 6 is as follows.

Ref ² . Heo, J.N.; Son, N.; Shin, J.; Do, JY; Kang, M. Efficient hydrogen production by low-temperature steam reforming of propane using catalysts with very small amounts of Pt loaded on NiMn2O4 particles. Int. J. Hydrog. Energy 2020 , 45 (41), 20904-20921.

Ref ³ . Im, Y.; Lee, JH; Kwak, B.S.; Do, JY; Kang, M., Effective hydrogen production from propane steam reforming using M/NiO/YSZ catalysts (M = Ru, Rh, Pd, and Ag). Catal. Today 2018 , 303 , 168-176

Ref ⁴ . Hou, T. F.; Yu, B.; Zhang, S.Y.; Zhang, JH; Wang, DZ; Xu, T K; Cui, L.; Cai, WJ, Hydrogen production from propane steam reforming over Ir/Ce0.75Zr0.25O2 catalyst. Appl. Catal. B 2015 , 168 , 524-530.

Ref ⁵ . Lee, HJ; Lim, YS; Park, NC; Kim, YC Catalytic autothermal reforming of propane over the noble metal-doped hydrotalcite-type catalysts. Chem. Eng. J. 2009 , 146 (2), 295-301.

Ref ⁶ . Resini, C.; Arrighi, L.; Delgado, MCH; Vargas, MAL; Alemany, LJ; Riani, P.; Berardinelli, S.; Marazza, R.; Busca, G. Production of hydrogen by steam reforming of C3 organics over Pd-Cu/gamma-Al2O3 catalyst. Int. J. Hydrog. Energy 2006 , 31 (1), 13-19.

Ref ⁷ . Fard, AA; Aruaneh, R.; Alavi, SM; Bazyari, A.; Valaei, A. Propane steam reforming over promoted Ni-Ce/MgAl2O4 catalysts: Effects of Ce promoter on the catalyst performance using developed CCD model. Int. J. Hydrog. Energy 2019 , 44 (39), 21607-21622.

As shown in Table 6 above, the reaction conditions were included in the table list in order to evaluate the stability of the catalyst. The eluted CeRhO catalyst of the present invention has a high H ₂ yield (70%) for 65 hours even under poor conditions of high space velocity (200,000 mL/g _cat /h) and temperature (700 °C) compared to other catalysts. and a low stream to carbon ratio (S/C=2).

7.2: Results of XRD analysis of the catalyst used in the propane wet reforming reaction

XRD patterns for the used 4CeRhO and 4Rh/CeO ₂ were obtained, respectively, and the results are shown in FIG. 18 . A fluorite-type CeO ₂ peak was mainly observed, and a Rh (111) peak also appeared at about 41° for the 4CeRhO and 4Rh/CeO ₂ catalysts, respectively. In particular, a sharp Rh (111) peak was obtained on the used 4Rh/CeO ₂ phase, whereas the used 4CeRhO exhibited a broad peak in the expanded XRD pattern. The size of the Rh nanoparticles was measured, and the results are shown in Table 7 below.

As shown in Table 7, the Rh nanoparticles on 4CeRhO showed a size of 5.0 nm after the PSR reaction, indicating a slight increase in Rh size. On the other hand, 4Rh/CeO ₂ had heavily sintered Rh nanoparticles of 25.5 nm. These results clearly indicated that the eluted Rh nanoparticles had high sintering resistance under harsh conditions compared to conventional 4Rh/CeO ₂ .

7.3: Investigation of coke deposition resistance on catalyst after propane wet reforming reaction

It is known that coke deposition is favored near large metals on the catalyst surface (Kim, JH; Suh, DJ; Park, TJ; Kim, KL Effect of metal particle size on coking during CO2 reforming of CH4 over Ni- alumina airgel catalysts (see Appl. Catal. A 2000 , 197 , 191-200). In order to investigate coke deposition on the 4CeRhO and 4Rh/CeO ₂ catalysts used after the PSR reaction, various characterizations were performed, and the results are shown in FIG. 19 . As shown in (a) and (b) of FIG. 19 , the TEM images showed more severe coke deposition on the 4Rh/CeO ₂ catalyst than on 4CeRhO.

7.3.1: Coke Deposition Resistance - Thermal Oxidation Analysis Results

As shown in (c) of FIG. 19 , temperature programmed oxidation (TPO) showed a CO ₂ signal due to coke deposition, which indicates coke characteristics. The 4CeRhO used showed a CO ₂ production peak at 330 °C, indicating carbon species deposit on the active metal. On the other hand, two peaks were obtained for the 4Rh/CeO ₂ catalyst used. At the high temperature of 600° C., the peak showed a more crystalline or filamentary type of coke on the support associated with catalytic decomposition. The amount of coke deposition at 330° C. was 0.036 mmol _C /g _cat and 0.032 mmol _C /g _cat on 4CeRhO and 4Rh/CeO ₂ , respectively. Moreover, 4Rh/CeO ₂ had more coke deposition at 600° C. in an amount of 0.012 mmol _C /g _cat . These results indicated that 4Rh/CeO ₂ undergoes more coke during the PSR reaction.

7.3.2: Coke deposition resistance - results of Raman spectral analysis

Raman spectra of coke of the used 4CeRhO and 4Rh/CeO ₂ catalysts were investigated. The peak (I _D ) at 1350 cm ^-1 is a result of the D band associated with amorphous or defective carbon, and the peak (I _G ) at 1590 cm ^-1 is more It is a result of the G band associated with carbon with an ordered structure. The I _D /I _G ratio of 4Rh/CeO ₂ (1.56) was smaller than that of 4CeRhO (2.92). A lower value of I _D /I _G indicates a higher graphitization degree of carbon and generally indicates more severe coke deposition on the catalyst. These results clearly indicate that the eluted Rh nanoparticles on the CeRhO catalyst have excellent resistance to coke deposition in the PSR reaction.

conclusion

Nano-domain Rh-doped cerium oxide was prepared by coprecipitation. Elution of the Rh species was induced by reduction at 500° C. for 3 hours with 10% H ₂ /N ₂ flow, and the surface area remained high, above 55 m ² /g. XRD, EXAFS, XPS, and CO-DRIFT results confirmed that Rh nanoparticles eluted from the rhodium-doped cerium oxide carrier were formed on the surface by replacing the cerium oxide lattice. In-situ TEM images clearly revealed that eluted Rh nanoparticles of 2 nm to 3 nm appeared on the surface under reducing conditions. The propane wet reforming reaction of the 4CeRhO catalyst was compared with a control sample, 4Rh/CeO ₂ synthesized by a conventional wet impregnation method. 4CeRhO stably maintained nearly 100% propane conversion and 70% hydrogen yield for 65 hours. On the other hand, the propane conversion rate of 4Rh/CeO ₂ decreased to 76% and the hydrogen yield to 51%. The XRD pattern indicated that the eluted Rh nanoparticles on 4CeRhO had better sintering resistance than 4Rh/CeO ₂ . Moreover, the TPO and Raman spectral results showed lower coke deposition on 4CeRhO after reaction for 65 hours compared to 4Rh/CeO ₂ , indicating the high stability of the rhodium-eluting catalyst. The present invention demonstrates a nano-scale design for highly durable catalysts by elution.

Claims (20)

A method for preparing a rhodium-cerium oxide elution catalyst for steam reforming reaction comprising the following steps:
a) mixing a cerium oxide precursor solution and a rhodium precursor solution;
b) firing the product of step a); and
c) subjecting the product of step b) to reduction heat treatment.
The method of claim 1, wherein the firing in step b) is performed under air or oxygen at 300 °C to 500 °C.
The method of claim 1, wherein the reduction heat treatment in step c) is performed at a temperature of 400° C. to 700° C. for 5 minutes to 4 hours.
The method of claim 3, wherein the reduction heat treatment in step c) is performed under hydrogen gas and an inert gas.
The method of claim 4, wherein the inert gas is at least one selected from the group consisting of nitrogen (N ₂ ), helium (He), and argon (Ar).
The method according to claim 1, wherein rhodium nanoparticles are eluted on the surface of the cerium oxide carrier doped with rhodium by reduction heat treatment in step c).
The method according to claim 1, wherein the rhodium-cerium oxide eluting catalyst has a weight of 0.5 wt% to 8.0 wt% relative to the total weight of the catalyst.
A rhodium-cerium oxide elution catalyst for a wet reforming reaction in which rhodium nanoparticles are eluted on the surface of a cerium oxide carrier doped with rhodium by reduction heat treatment.
The catalyst according to claim 8, wherein the weight of rhodium relative to the total weight of the rhodium-cerium oxide eluting catalyst is 0.5 wt% to 8.0 wt%.
The catalyst according to claim 8, wherein the reduction heat treatment is performed at a temperature of 400 °C to 700 °C for 5 minutes to 4 hours.
The catalyst according to claim 8, wherein the reduction heat treatment is performed under hydrogen gas and an inert gas.
The catalyst according to claim 8, wherein the inert gas is at least one selected from the group consisting of nitrogen (N ₂ ), helium (He), and argon (Ar).
The catalyst according to claim 8, wherein the eluted rhodium nanoparticles are anchored in a lattice of the rhodium-doped cerium oxide carrier.
9. The catalyst according to claim 8, wherein the catalyst has a surface area of 55 m ² /g or greater.
The catalyst according to claim 8, wherein the eluted rhodium nanoparticles have a size of 2.0 nm to 3.0 nm.
The catalyst according to claim 8, wherein the eluted rhodium nanoparticles have a size of 2.0 nm to 10.0 nm after the wet reforming reaction.
The method of claim 8, wherein the D band peak intensity (I _D ) at 1350 cm ^-1 relative to the G band peak intensity (I _G ) at 1590 cm ^-1 in the Raman spectrum after the wet reforming reaction is I _D /I _G The catalyst, wherein the ratio is 2.00 to 3.50.
A wet reforming reaction method comprising the step of obtaining hydrogen gas by adding the catalyst according to any one of claims 8 to 17 to hydrocarbon and steam.
The wet reforming reaction of claim 18, wherein the reaction method is carried out under feed conditions including steam and hydrocarbons with a steam to carbon ratio (S/C) of 1 to 4. Way.
The wet reforming reaction method according to claim 18, wherein the reaction method is carried out at 600 ° C to 800 ° C.

Images