KR102180635B1 - Manganese-doped composite metal oxide catalyst for exhaust gas purification and method for preparing thereof - Google Patents

Abstract

The present invention relates to a complex metal oxide catalyst doped with manganese for purification of exhaust gas and a method for manufacturing the same, wherein the catalyst has improved hydrocarbon oxidation activity and increased stability, thereby being able to be effectively used for exhaust gas purification. Another object of the present invention is to provide the catalyst for purifying exhaust gas containing at least one selected from a group consisting of copper oxide, cobalt oxide, and cerium oxide, and doped with a transition metal.

Description

Manganese-doped composite metal oxide catalyst for exhaust gas purification and method for preparing thereof {Manganese-doped composite metal oxide catalyst for exhaust gas purification and method for preparing thereof}

The present invention relates to a complex metal oxide catalyst doped with manganese for purification of exhaust gas and a method for preparing the same, and more particularly, the hydrocarbon oxidation activity is increased by hydrothermal aging of the CuO-Co ₃ O ₄ -CeO ₂ (CCC) catalyst. The present invention relates to a manganese-doped composite metal oxide catalyst with improved stability and increased stability, and a method for preparing the same.

As environmental regulations on automobile pollutants are strengthened, efforts to reduce fuel consumption and exhaust gas emissions continue. New combustion technologies such as reactivity-controlled compression ignition (RCCI) can improve fuel economy and reduce emissions of NOx and particulate matter. However, as the exhaust gas temperature is lowered, the post-treatment catalyst produces more CO and hydrocarbons. Therefore, there is a great need for better catalysts that can operate at low temperatures.

Platinum-group metals (PGMs) have been widely used as diesel oxidation catalysts (DOC) because they exhibit excellent low-temperature activity against CO oxidation. However, the high activity against CO oxidation is significantly degraded in the presence of hydrocarbons because CO and hydrocarbons are competitively adsorbed on the metal surface. In addition, the post-treatment section often undergoes high temperatures of up to 750° C. which cause severe sintering of metal nanoparticles.

Non-PGM catalysts have received a lot of attention due to their much lower cost and relatively good CO oxidation at low temperatures. In particular, CuO-Co ₃ O ₄ -CeO ₂ (CCC) has great potential for automotive exhaust gas treatment due to its excellent CO oxidation activity and high resistance to hydrocarbon inhibition. This composite oxide showed high activity against CO oxidation without decomposition even in the presence of C ₃ H ₆ because the active sites for CO oxidation and C ₃ H ₆ oxidation were different. The active site for CO oxidation is the interface between CuO and Co ₃ O ₄ or CeO ₂ , whereas the active site for C ₃ H ₆ oxidation is Co ₃ O ₄ .

However, the CCC catalyst exhibits significantly lower hydrocarbon oxidation activity compared to CO oxidation, and the activity of the CCC catalyst for C ₃ H ₆ oxidation, for example, is poor at low temperatures. In addition, the CCC catalyst undergoes severe sintering after hydrothermal aging, resulting in severe deactivation.

The Co ₃ O ₄ phase is known to have high activity against the oxidation of volatile organic compounds (VOC). Its activity can be promoted by introducing other transition metal dopants that produce more surface active oxygen species. In particular, Mn has been reported to improve the activity of Co ₃ O ₄ for oxidation of various VOCs through strong interaction between Mn and Co.

Accordingly, the present inventors synthesized the Mn-doped CCC catalyst represented by CCCM below by a simple co-precipitation method, and as a result, Mn is selectively doped on Co ₃ O ₄ and thus C ₃ H ₆ oxidation activity and It was confirmed that the durability after hot water treatment was improved.

Accordingly, an object of the present invention is at least one selected from the group consisting of a copper (Cu)-containing compound, a cobalt (Co)-containing compound, and a cerium (Ce)-containing compound; And it is to provide a method for producing a catalyst for purification of exhaust gas comprising the step of preparing a precursor solution of a transition metal-containing compound.

Another object of the present invention is to provide a catalyst for purifying exhaust gas comprising at least one selected from the group consisting of copper oxide, cobalt oxide and cerium oxide, and doped with a transition metal.

Another object of the present invention is to provide a system for treating exhaust gas comprising at least one selected from the group consisting of copper oxide, cobalt oxide and cerium oxide, and doped with a transition metal, including a catalyst for purifying exhaust gas. Is to do.

Another object of the present invention relates to a use of a composite metal oxide catalyst doped with manganese to purify exhaust gas.

The present invention relates to a complex metal oxide catalyst doped with manganese for purification of exhaust gas and a method for preparing the same, and a manganese-doped complex metal oxide catalyst having improved hydrocarbon oxidation activity and increased stability by the method according to the present invention Can be manufactured.

In preparing a CuO-Co ₃ O ₄ -CeO ₂ (CCC) catalyst, the present inventors prepared a manganese-doped catalyst by using a manganese-containing compound, which increases C ₃ H ₆ oxidation activity and results in hydrothermal aging. It was confirmed that phase separation was prevented.

Hereinafter, the present invention will be described in more detail.

One aspect of the present invention is a method of preparing a catalyst for purification of exhaust gas including a precursor solution preparation step of mixing a copper (Cu) precursor, a cobalt (Co) precursor and a cerium (Ce) precursor, and a transition metal precursor.

The copper precursor may be a copper nitrate trihydrate (Cu(NO ₃ ) ₂ ·3H ₂ O).

The cobalt precursor may be cobalt chloride hexahydrate (CoCl ₂ ·6H ₂ O).

The cerium precursor may be cerium nitrate hexahydrate (Ce(NO ₃ ) ₂ ·6H ₂ O).

The transition metal may be one or more selected from the group consisting of manganese (Mn), zinc (Zn), titanium (Ti), iron (Fe), and nickel (Ni), for example, manganese. , But is not limited thereto. The manganese precursor may be manganese nitrate hydrate (Mn(NO ₃ ) ₂ ·xH ₂ O, Aldrich).

The precursor solution may contain Cu: Co: Ce: transition metal in a molar ratio of 1 to 5: 8 to 12: 8 to 12: 1 to 5, for example, a molar ratio of 1: 5: 5: 1 It may be contained as, but is not limited thereto.

The method may further include an obtaining step of dropwise adding NaOH solution to the precursor solution to obtain a precipitate.

The method may be to further include a firing step of firing the obtained precipitate for 1 to 8 hours at 200 to 800 ℃.

The firing step is 300 to 800 ℃, 400 to 800 ℃, 500 to 800 ℃, 200 to 700 ℃, 300 to 700 ℃, 400 to 700 ℃, 500 to 700 ℃, 200 to 650 ℃ or 300 to 650 ℃, 400 To 650°C, 500 to 650°C, for example, 550 to 650°C, but is not limited thereto.

The firing step may be performed for 1 to 8 hours, 2 to 8 hours, 3 to 8 hours, 1 to 6 hours, 2 to 6 hours or 3 to 6 hours, for example, 4 to 5 hours, It is not limited thereto.

Another aspect of the present invention is a catalyst for purification of exhaust gas containing copper oxide (CuO), cobalt oxide (Co ₃ O ₄ ) and cerium oxide (CeO ₂ ), and doped with a transition metal.

The transition metal may be one or more selected from the group consisting of manganese, zinc, titanium, iron, and nickel, and may be, for example, manganese, but is not limited thereto.

The transition metal may be selectively doped with cobalt oxide.

Another aspect of the present invention is a system for treating exhaust gas comprising a catalyst for purifying exhaust gas comprising copper oxide, cobalt oxide and cerium oxide and doped with a transition metal.

The transition metal may be one or more selected from the group consisting of manganese, zinc, titanium, iron, and nickel, and may be, for example, manganese, but is not limited thereto.

The transition metal may be selectively doped with cobalt oxide.

The present invention relates to a complex metal oxide catalyst doped with manganese for purification of exhaust gas and a method for producing the same, wherein the catalyst has improved hydrocarbon oxidation activity and increased stability, and thus can be effectively used for exhaust gas purification.

1A is a high angle annular dark field-scanning TEM (HAADF-STEM) image for CuO-Co ₃ O ₄ -CeO ₂ (CCC) and an energy-dispersive X-ray spectroscopy. X-ray spectroscopy (EDS) is a superimposed photo of the elemental Co mapping image.
1B is a superimposed photograph of a HAADF-STEM image and an EDS element Co mapping image for CCC-a (aging CCC).
1C is a superimposed photograph of a HAADF-STEM image and an EDS element Co mapping image for CCCM (Mn-doped CCC).
1D is a superimposed photograph of a HAADF-STEM image and an EDS element Co mapping image for CCCM-a.
2 is a graph showing a powder X-ray diffraction (XRD, Rigaku, Cu Kα radiation) pattern of the CCC, CCCM, CCC-a and CCCM-a catalysts.
3A is a graph showing a Co K-edge Fourier-transformed (FT) X-ray Absorption Fine Structure (EXAFS) spectrum.
3B is a graph showing the Mn K-edge FT-EXAFS spectrum.
Figure 4a is a graph showing the X-ray photoelectron spectroscopy (XPS, K-alpha, ThermoVG Scientific) spectrum of the catalyst Co2p.
4B is a graph showing the Ce3d XPS spectrum of the catalyst.
4c is a graph showing the Mn2p XPS spectrum of the catalyst.
4D is a graph showing the XPS spectrum of O1 of the catalyst.
5A is a graph showing the results of oxidation of CO in simultaneous CO and C ₃ H ₆ oxidation of the catalyst.
5B is a graph showing the result of oxidation of C ₃ H ₆ in simultaneous CO and C ₃ H ₆ oxidation of the catalyst.
5C is a graph showing an Arrhenius plot for CO oxidation of a catalyst.
5D is a graph showing an Arrhenius plot for C ₃ H ₆ oxidation of a catalyst.
6 is a graph showing the NO oxidation result of the catalyst.
7A is a graph showing the result of CO oxidation in the CCCM catalyst according to the amount of Mn.
7B is a graph showing the result of C ₃ H ₆ oxidation in the CCCM catalyst according to the amount of Mn.
7C is a graph showing the result of CO oxidation in the aged CCCM catalyst according to the amount of Mn.
7D is a graph showing the C ₃ H ₆ oxidation result in the aged CCCM catalyst according to the amount of Mn.
8A is a graph showing the CO conversion rate in simultaneous CO and C ₃ H ₆ oxidation of the catalyst.
8B is a graph showing the conversion rate of C ₃ H ₆ in simultaneous CO and C ₃ H ₆ oxidation of the catalyst.
9A is a graph showing an in-situ DRIFT spectrum monitoring result of a CCC catalyst in simultaneous CO and C ₃ H ₆ oxidation.
9B is a graph showing the results of in-situ DRIFT spectrum monitoring of the CCCM catalyst in simultaneous CO and C ₃ H ₆ oxidation.

Hereinafter, the present invention will be described in more detail by the following examples. However, these examples are for illustrative purposes only, and the scope of the present invention is not limited by these examples.

Throughout this specification, "%" used to indicate the concentration of a specific substance is (weight/weight)% for solids/solids, (weight/volume)% for solids/liquids, and Liquid/liquid is (vol/vol)%.

Example 1: Synthesis of CCCM catalyst

The CuO-Co ₃ O ₄ -CeO ₂ (CCC) catalyst was synthesized by co-precipitation.

Copper nitrate trihydrate (Cu(NO ₃ ) ₂ ·3H ₂ O, Aldrich), cobalt chloride hexahydrate (CoCl ₂ ·6H ₂ O, Aldrich) and cerium nitrate hexahydrate (Ce(NO ₃ ) ₂ ·6H ₂ O , Aldrich) in 25 ml of deionized water can be prepared by reacting Cu:Co:Ce = 1:5:5 in a molar ratio. Then, 25 ml of NaOH solution (0.375 M) was added dropwise to the solution with vigorous stirring. After 1 hour, the precipitate was washed with deionized water and ethanol, and dried in a vacuum oven at 50° C. overnight. The obtained cake was crushed into fine powder in a ceramic mortar, and fired at 600° C. in air for 4 hours.

The Mn-doped CuO-Co ₃ O ₄ -CeO ₂ (CCCM) catalyst was synthesized in the same manner as the method for preparing the CCC catalyst, but manganese nitrate hydrate (Mn(NO ₃ ) ₂ ·xH ₂ O, Aldrich) was used as the Mn precursor. Then, it was synthesized by reacting at a molar ratio of Cu:Co:Ce:Mn = 1:5:5:1.

For comparison, a single metal oxide of Co ₃ O ₄ , CeO ₂ and MnO ₂ was also synthesized. The CCC and CCCM catalysts were subjected to hot water treatment at 750° C. for 25 hours while flowing 144.5 ml of air per minute containing 10% H ₂ O to prepare an aged catalyst. Aged CCC and CCCM catalysts were denoted as CCC-a and CCCM-a, respectively.

Example 2: Confirmation of form and elemental distribution of CCCM catalyst

Transmission electron microscopy (TEM) images were obtained using a TEM (Tecnai G2 F30 S-Twin; FEI) with a voltage of 300 kV. Energy-dispersive X-ray spectroscopy (EDS) mapping and high angle annular dark field-scanning TEM (high angle annular dark field-scanning TEM) using a TEM (Talos F200X; FEI) with a voltage of 200 kV. ; HAADF-STEM) image was obtained. These images were obtained to determine the morphology and elemental distribution of the catalyst.

Table 1 shows the actual metal content of the prepared catalyst. ^a The actual metal content of the catalyst was measured by inductively coupled plasma-optical emission spectrometry (ICP-OES 720, Agilent).

catalyst Cu (% by weight) ^a Co (% by weight) ^a Ce (% by weight) ^a Mn (% by weight) ^a CCC 4.6 26.8 59.2 - CCCM 4.6 27.7 57.1 2.4 CCC-a 4.8 26.6 54.0 - CCCM-a 4.4 25.1 53.2 2.6

Elemental distribution shows that all Cu, Co, and Ce are uniformly distributed in the prepared CCC catalyst, but the Co domain is hydrothermal aging (CCC-a, CCCM) by flowing air containing 10% H ₂ O at 750℃ for 25 hours. After -a), the degree of phase separation was confirmed.

As can be seen in FIGS. 1A to 1D, phase separation of Co by aging was clearly observed in the CCC-a catalyst, but much less phase separation was observed in the CCCM-a catalyst. From this, it can be seen that the durability of the catalyst is increased by manganese doping. Even after hot water aging at 750° C. for 25 hours by Mn doping, sintering and phase separation of the catalyst on Co ₃ O ₄ were prevented.

Example 3: Confirmation of the structure characteristics and crystalline structure of the catalyst

The crystal structure was observed by X-ray diffraction (XRD, Rigaku, Cu Kα radiation).

As can be seen in Figure 2, the XRD data of the CCC catalyst shows that CuO or other impurities-free Co ₃ O ₄ spinel (spinel) structure and CeO ₂ face-centered cubic fluorite (face-centered cubic fluorite) structure was observed.

Cu is finely distributed on CeO ₂ and Co ₃ O ₄ . The CCCM catalyst showed almost the same XRD pattern, but a slight change in which the diffraction angle was lowered was observed only in the Co ₃ O ₄ peak, indicating the expansion of the Co ₃ O ₄ lattice cell. CeO ₂ peak did not change. This difference became more evident after hydrothermal aging.

The presence of Mn induces lattice expansion on Co ₃ O ₄ with more surface active oxygen, and Co ₃ O ₄ lattice cell expansion is the result of the larger Ce cations (Ce cations (Mn ³⁺ , r = 0.79 Å)). ⁴⁺ , r = 1.01 Å), but advantageously replaces the smaller Co cations (Co ³⁺ , r = 0.75 Å).

The crystallite size and lattice parameters of Co ₃ O ₄ and CeO _{2 in} the catalyst were evaluated as shown in Table 2 ( ^a Co ₃ O ₄ and CeO ₂ crystallite sizes were Co ₃ O ₄ (311) and CeO ₂ ( 111) from the reflection was estimated using syereo (Scherrer) equation; ^b Co ₃ O ₄ and the lattice parameter of CeO ₂ is Co ₃ O ₄ (311) and a CeO ₂ (111) Bragg's law (Bragg's law) from the reflection, respectively Was estimated using).

catalyst S _BET (m ² /g) d _Co (nm) ^a d _Ce (nm) ^a a _Co (Å) ^b a _Ce (Å) ^b CCC 72 22 7 8.0894 5.4164 CCCM 88 16 5 8.1001 5.4183 CCC-a 12 60 27 8.0873 5.4183 CCCM-a 15 38 28 8.1171 5.4164

Hydrothermal aging showed the CuO phase in CCC, but the CuO phase was less in CCCM. The formation of a Mn-Co solid solution can inhibit the growth of Co ₃ O ₄ nanoparticles. The Co ₃ O ₄ phase was sintered to a smaller amount after hydrothermal aging in the presence of Mn.

Example 4: Confirmation of the location of Mn by confirming the EXAFS spectrum of the catalyst

X-ray absorption fine structure (EXAFS) measurements were performed on an 8C XAFS beamline of a Pohang Light Source (PLS).

FIG. 3A shows the Co K-edge Fourier-transformed (FT) X-ray Absorption Fine Structure (EXAFS) spectrum of the catalyst. The first peak of 1.5 Å corresponds to the interatomic distance of the octahedral Co-O. On the other hand, the peaks of 2.5 Å and 3.0 Å correspond to the atomic distances from an octahedral Co atom to an octahedral or tetrahedral to an adjacent Co atom. The size of the octahedral Co coordination peak of the CCCM catalyst was much weaker than that of the CCC catalyst, and the Co octahedral peak was lowered due to Mn doping.

The Mn K-edge FT-EXAFS spectrum of FIG. 3B shows that the CCCM catalyst has a larger octahedral Mn-O peak at 1.5 Å than that of pure MnO ₂ . A new peak was observed at 2.1 Å while the peak for octahedral Mn-Mn at 2.5 Å did not appear in the CCCM catalyst. The new peak appears to be due to the interaction of octahedral Mn-Co with local distortion.

As a result, EXAFS results suggest that the doped Mn is selectively doped to Co ₃ O ₄ by occupying the octahedral Co site in the Co ₃ O ₄ spinel structure.

Example 5: Checking the chemical state of the catalyst

The surface chemical state of the catalyst was investigated by X-ray photoelectron spectroscopy (XPS, K-alpha, ThermoVG Scientific), and the binding energy was estimated based on the maximum intensity of the C 1s signal at 284.8 eV. The corresponding quantification results are listed in Table 3 ( ^a peak area ratio was obtained from the peak decomposition results of the O 1s spectrum).

catalyst Cu 2p _3/2 (eV) Co 2p _3/2 (eV) Ce 3d _5/2 (eV) Mn 2p _3/2 (eV) O _α /Oβ ^a CCC 933.3 779.1 882.0 - 0.48 CCCM 933.3 779.6 882.1 641.7 0.67 CCC-a 932.6 779.2 882.0 - 0.34 CCCM-a 932.6 779.8 882.1 641.6 0.72

As can be seen in Figures 4a, 4b and Table 3, the Cu and Ce peaks did not move after Mn- doping, but the Co peak was from 779.1 eV of the prepared CCC catalyst in the case of Co2p _3/2 to 779.6 eV of the prepared CCC catalyst. Moved. The same trend was observed even after hydrothermal aging.

This change indicates that the ratio of Co ³⁺ /Co ²⁺ in the CCCM catalyst decreases. In the spinel structure of Co ₃ O ₄ , Co ²⁺ ions and Co ³⁺ ions exist at positions of tetrahedral and octahedron, respectively. Reduction of Co ³⁺ concentrations suggest that the octahedral digit Co ³⁺ is replaced by Mn.

The Mn peak in FIG. 4C indicates that the Mn peak shifted from 642.2 eV of MnO ₂ to 641.7 eV of the CCCM catalyst, and the surface Mn partially decreased and the ratio of Mn ³⁺ /Mn ⁴⁺ increased in the CCCM catalyst. It can be seen that Co ³⁺ in the octahedral site has been replaced by Mn.

As shown in Figure 4d, the O 1s peak was decomposed into O _α and O _β . The O _α peak around 529-530 eV was assigned to defective oxygen or chemically adsorbed oxygen on the surface, and the O _β peak around 531-532 eV was assigned to lattice oxygen. After Mn doping, the peak area ratio of O _α /O _β increased from 0.48 to 0.67, indicating that more defects or chemisorbed oxygen species were produced in the CCCM catalyst.

After hydrothermal aging, the difference became more apparent. The ratio increased from 0.34 of CCC-a to 0.72 of CCCM-a. Defective oxygen can be generated from non-uniform charge and lattice distortion to maintain an electrostatic balance between Mn and Co cations. Obviously, Mn-doped CCCM catalysts have more surface active oxygen species.

Example 6: CO and C ₃ H ₆ Activity and durability of the catalyst in the simultaneous oxidation of

Simultaneous CO and C ₃ H ₆ oxidation was carried out using a quartz fixed-bed reactor with 50 mg of catalyst under atmospheric pressure conditions. The catalyst was pretreated at 100° C. under He flow for 1 hour, then the sample was cooled to room temperature. The reaction was carried out at 240° C. with a gas stream consisting of 0.4% CO, 0.1% C ₃ H ₆ , 10% O ₂ and the balance He. The total flow rate was 100 ml min ^-1 (space velocity (SV) = 120,000 ml g ^-1 h ^-1 ). The samples were held at each temperature to reach a steady state in a continuous feed stream.

The generated gas was filled with a column (bed carboxen 1000, 75035, SUPELCO, 15 ft x 1/8 in.x 2.1 mm / capillary column, GS-GASPRO, Agilent Technologies, 30 mx 0.32 mm) and a thermal conductivity detector detector (TCD)/flame ionization detector (FID) equipped with on-line gas chromatography (GC, Younglin GC 6500).

As can be seen in Figure 5a, the CCC catalyst and the CCCM catalyst showed the same high activity by achieving 100% CO conversion at 155 ℃. It has been reported that CO oxidation on the CCC catalyst mainly occurs by extracting oxygen from weakened metal-oxygen bonds at the interface site between CuO and Co ₃ O ₄ or CeO ₂ . Mn doping did not change the active site for CO oxidation.

The CCCM catalyst showed high resistance to the C ₃ H ₆ inhibitory effect on CO oxidation like the CCC catalyst. After hydrothermal aging, the temperature at which 100% CO conversion was achieved increased significantly to 235°C for the CCC-a catalyst, while the temperature increased to 185°C for the CCCM-a catalyst. It has been reported that the CCC catalyst showed low temperature light-off due to the highly dispersed Cu sites interacting with CeO ₂ , while maintaining high CO conversion due to the Co ₃ O ₄ step.

Co ₃ O ₄ microcrystals of the CCCM-a catalyst had less aggregation after hydrothermal aging, and more interfacial sites were preserved. This lowered the T100 CO, the temperature with 100% CO conversion for the CCCM-a catalyst. In the NO oxidation result of the catalyst, CCC and CCCM catalyst showed almost the same NO conversion rate, whereas CCCM-a showed better activity than CCC-a catalyst.

C ₃ H ₆ oxidation is known to occur on Co ₃ O ₄ in the CCC catalyst.

As can be seen from FIG. 5B, the prepared CCCM catalyst showed more excellent activity than the CCC catalyst having T100 C ₃ H ₆ at 285°C and T100 C ₃ H ₆ at 325°C. After hydrothermal aging, the T100 C ₃ H ₆ of the CCC-a catalyst was much higher at 425° C., while the T100 C ₃ H ₆ of the CCCM-a catalyst was 355° C.

Complete oxidation of C ₃ H ₆ on metal oxides requires initial CH bond cleavage that occurs through reaction with electrophilic oxygen generated by O ₂ adsorption on the surface. It has been reported that the surface lattice oxygen on the metal oxide generally plays a lesser role in the C ₃ H ₆ oxidation.

As can be seen from the XPS O 1s and O ₂ -TPD results, the CCCM catalyst has more surface active oxygen such as chemisorbed O ₂ and O species. The more surface active oxygen of the CCCM catalyst, the higher the oxidation activity of C ₃ H ₆ .

As can be seen in Figures 5c and 5d, Arrhenius graphs and apparent activation energies were obtained for CO and C ₃ H ₆ oxidation. The activation energy of the aged catalyst decreased from 42.8 kJ mol ^-1 to 36.7 kJ mol ^-1 in CO oxidation after Mn doping, and decreased from 49.6 kJ mol ^-1 to 41.6 kJ mol ^-1 in C ₃ H ₆ oxidation.

The long-term durability of the prepared catalyst and the aged catalyst was confirmed by the conversion rate by testing the simultaneous oxidation reaction of CO and C ₃ H ₆ at 240°C.

Example 7: NO conversion and CO conversion

NO oxidation was also carried out using a gas flow consisting of 0.4% CO, 0.1% C ₃ H ₆ , 0.05% NO, 10% O ₂ and the balance Ar. Product gas containing NOx was monitored using an FT-IR spectrometer (Nicolet iS10, Thermo Scientific) at 120,000 ml g ^-1 h ^-1 with a gas cell (internal volume 0.2 L).

As can be seen in FIG. 6, the CCC and CCCM catalysts showed almost the same NO conversion rate, whereas CCCM-a showed superior activity than the CCC-a catalyst.

As can be seen in Figures 7a to 7d, as a result of investigating the effect of the amount of Mn in the CCCM catalyst, the ratio of Cu:Co:Ce:Mn = 1:5:5:X is X = 0, 0.5, 1, 1.5 and When changed to 2, it was confirmed that the CCCM catalyst in the case of X = 1 exhibited the best CO and C ₃ H ₆ oxidation activity.

As can be seen in Figures 8a and 8b, after Mn doping, the CO conversion rate increased from 86.3% to 100.0%, and the CO conversion rate of all catalysts was 100% except for CCC-a. The C ₃ H ₆ conversion rate increased from 17.1% to 50.9%. The Mn-doped CCCM catalyst further markedly improved the activity and durability compared to CCC even after a long-term reaction.

Example 8: Identification of surface species formed during catalytic reaction

In-situ DRIFT analysis for simultaneous CO and C ₃ H ₆ oxidation was performed to investigate the surface species formed during the reaction at elevated temperatures.

CO and C ₃ H ₆ oxidation is monitored in-situ with a diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) using an FT-IR spectroscopy (Nicolet iS-50; Thermo Scientific). I did.

Specifically, 4 mg of the catalyst was pulverized with 196 mg of KBr, and the mixed powder was placed in a DRIFTS cell. The cell was purged with Ar at 100° C. for 1 hour and cooled to room temperature. In order to monitor the formation of intermediate species during the reaction, CO and C ₃ H ₆ oxidation was performed with 0.8% CO, 0.2% C ₃ H ₆ , 10.0% O ₂ and remaining Ar while raising the cell temperature to 50°C. It was carried out with the inlet gas flow that was made.

IR spectra were collected after exposure to the reaction gas for 10 minutes at each temperature. The numbers in black and blue indicate the peak positions derived from CO and C ₃ H ₆ , respectively.

As can be seen in FIG. 9A, in the DRIFT spectrum of the CCC catalyst, the bands indicated in black at low temperature are bicarbonate (1,465 and 1,114 cm ^-1 ), carbon dichloride (1,608 and 1,260 cm ^-1 ) And unidentate carbonate (1,396 cm ^-1 ), a carbonate species derived from the oxidation of CO.

The bands due to C ₃ H ₆ oxidation are formate (1,453, 1,412 and 1,370 cm ^-1 ), acetate (1,582 and 1,490 cm ^-1 ) and acetone (1,678 cm ^-1 ). . These species have been suggested as intermediates of C ₃ H ₆ oxidation on the surface of cobalt oxide.

As can be seen in FIG. 9B, in the DRIFT spectrum of the CCCM catalyst, the tendency of the catalyst to follow the same surface reaction mechanism was almost the same. The aged catalyst exhibited a similar behavior except that the strength was much weaker because of the much smaller surface area.

As a result, it can be seen that a similar reaction intermediate is formed even after manganese doping compared to before manganese doping, so that the same surface reaction mechanism is followed.

Claims (14)

A method for preparing a catalyst for purifying exhaust gas comprising a precursor solution preparation step of mixing a copper (Cu) precursor, a cobalt (Co) precursor and a cerium (Ce) precursor, and a transition metal precursor,
The precursor solution containing copper: cobalt: cerium: transition metal in a molar ratio of 1 to 5: 8 to 12: 8 to 12: 1 to 5. The method of claim 1, wherein the copper precursor is a copper nitrate trihydrate (Cu(NO ₃ ) ₂ ·3H ₂ O). The method of claim 1, wherein the cobalt precursor is cobalt chloride hexahydrate (CoCl ₂ ·6H ₂ O). The method of claim 1, wherein the cerium precursor is cerium nitrate hexahydrate (Ce(NO ₃ ) ₂ ·6H ₂ O). The catalyst according to claim 1, wherein the transition metal is at least one selected from the group consisting of manganese (Mn), zinc (Zn), titanium (Ti), iron (Fe) and nickel (Ni). Method of manufacturing. delete The method of claim 1, wherein the method further comprises an obtaining step of obtaining a precipitate by dropwise adding a NaOH solution to the precursor solution. The method of claim 1, further comprising a firing step of firing the obtained precipitate at 200 to 800° C. for 1 to 8 hours. Copper oxide (CuO), cobalt oxide (Co ₃ O ₄ ) and cerium oxide (CeO ₂ ), and doped with a transition metal, as a catalyst for purification of exhaust gas,
The catalyst contains copper: cobalt: cerium: transition metal in a molar ratio of 1 to 5: 8 to 12: 8 to 12: 1 to 5. The catalyst according to claim 9, wherein the transition metal is at least one selected from the group consisting of manganese (Mn), zinc (Zn), titanium (Ti), iron (Fe) and nickel (Ni). . The catalyst according to claim 9, wherein the transition metal is selectively doped with cobalt oxide. A system for treating exhaust gas comprising a catalyst for purifying exhaust gas containing copper oxide (CuO), cobalt oxide (Co ₃ O ₄ ) and cerium oxide (CeO ₂ ) and doped with a transition metal,
The catalyst contains copper: cobalt: cerium: transition metal in a molar ratio of 1 to 5: 8 to 12: 8 to 12: 1 to 5. The method of claim 12, wherein the transition metal is at least one selected from the group consisting of manganese (Mn), zinc (Zn), titanium (Ti), iron (Fe), and nickel (Ni). system. The system of claim 12, wherein the transition metal is selectively doped with cobalt oxide.

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