Catalyst, process for its preparation and use

Abstract

The application provides a catalyst and a preparation method and application thereof. The catalyst comprises a ceramic carrier and a coating arranged on the outer surface of the ceramic carrier, the coating comprises a platinum layer and a rhodium layer arranged on the outer surface of the ceramic carrier in sequence, and the platinum layer and the rhodium layer each independently contain cerium-zirconium oxide modified by tungsten oxide and gamma-aluminum oxide modified by an alkaline earth metal oxide. In the platinum layer and the rhodium layer, the introduction of the alkaline earth metal element and the tungsten element can effectively improve the uniformity of the active component in the catalyst, the utilization rate of the active component, the catalytic efficiency of the catalyst, the low-temperature activity and the high-temperature stability under the premise of meeting the conventional performance requirements of the catalyst.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalysts, in particular to a catalyst and a preparation method and application thereof. BACKGROUND

[0002] In the prior art, noble metals Pt, Pd and Rh are generally used as active components for catalysts for natural gas vehicle tail gas aftertreatment. For example, a preparation method of a natural gas ternary catalyst is provided in Chinese patent CN 208057201 U. The preparation method of the catalyst in this patent adopts multi-layer coating, and the catalyst has stronger catalytic capacity for gas pollutants. The catalyst coating is divided into three layers. The upper coating layer slurry of the catalyst carrier is loaded with noble metal rhodium, and the coating amount is (60-84) g / L. The middle coating layer slurry is loaded with noble metal platinum, and the coating amount is (20-36) g / L. The catalyst slurry of the lower coating layer is loaded with noble metal palladium, and the coating amount is (100-120) g / L. For another example, a low-temperature catalyst for catalytic oxidation of methanol and a preparation method thereof are provided in Chinese patent CN112007682B. W-Al2O3 with a porous structure and a large specific surface area is used as a substrate coating, which plays a role in uniformly loading noble metals. The addition of tungsten elements can further increase the Lewis acid sites of alumina, thereby effectively improving the performance of the catalyst coating. The prepared catalyst has outstanding low-temperature catalytic oxidation of methanol activity and excellent water resistance.

[0003] However, in the prior art, when noble metals Pt, Pd and Rh are used as active components, there are often problems such as uneven distribution of active components in the catalyst, low utilization rate, poor catalytic efficiency of the catalyst, poor low-temperature activity, poor high-temperature stability, etc. In order to improve the above problems, it is necessary to provide a new catalyst for natural gas vehicle aftertreatment and a preparation method thereof. SUMMARY

[0004] The main purpose of the present application is to provide a catalyst and a preparation method and application thereof, so as to solve the problems of uneven distribution of active components in the catalyst, low utilization rate, poor catalytic efficiency of the catalyst, poor low-temperature activity, poor high-temperature stability, etc. in the prior art when noble metals Pt, Pd and Rh are used as active components.

[0005] In order to achieve the above-mentioned purpose, according to one aspect of the present application, a catalyst is provided, which comprises a ceramic carrier and a coating layer arranged on the outer surface of the ceramic carrier. The coating layer comprises a platinum layer and a rhodium layer arranged on the outer surface of the ceramic carrier in sequence, and the platinum layer and the rhodium layer each independently contain tungsten oxide modified cerium zirconium oxide and alkali earth metal oxide modified γ-alumina.

[0006] Further, in the cerium-zirconium oxide modified by tungsten oxide, the tungsten oxide is physically supported on the outer surface of the cerium-zirconium oxide; in the γ-alumina modified by alkaline earth metal oxide, the alkaline earth metal oxide is physically supported on the outer surface of the γ-alumina; preferably, in the platinum layer and the rhodium layer, the weight ratio of the γ-alumina modified by alkaline earth metal oxide and the cerium-zirconium oxide modified by tungsten oxide is independently 1:1.5-1.5:1; preferably, in the catalyst, the coating amount of the platinum layer and the rhodium layer is independently 100-300 g / L.

[0007] Further, the ceramic carrier is cordierite honeycomb ceramic; preferably, the cordierite honeycomb ceramic has a mesh number of 300-800 mesh and a wall thickness of 0.0508-0.1524 mm.

[0008] Further, in the catalyst, the loading amount of platinum is 10-200 g / ft 3 , and the loading amount of rhodium is 1-20 g / ft 3 ; preferably, the alkaline earth metal oxide is selected from barium oxide and / or strontium oxide; more preferably, the alkaline earth metal oxide is selected from barium oxide.

[0009] According to another aspect of the present application, a preparation method of the aforementioned catalyst is provided, and the preparation method comprises: providing the γ-alumina modified by alkaline earth metal oxide and the cerium-zirconium oxide modified by tungsten oxide; coating a first slurry containing the cerium-zirconium oxide modified by tungsten oxide, the γ-alumina modified by alkaline earth metal oxide, a first competitive adsorbent, the noble metal platinum and a first binder on the outer surface of the ceramic carrier to form a platinum layer after first calcination; coating a second slurry containing the cerium-zirconium oxide modified by tungsten oxide, the γ-alumina modified by alkaline earth metal oxide, a second competitive adsorbent, the noble metal rhodium and a second binder on the outer surface of the platinum layer to obtain the catalyst after second calcination.

[0010] Further, the treatment temperature of the first calcination and the second calcination is independently 500-650 ℃, and the treatment time is independently 2-3 h; preferably, the first coating and / or the second coating is performed by using a negative pressure coating special machine; in the first coating and the second coating, the air pressure of the negative pressure coating special machine is independently -20 to -80 kPa.

[0011] Further, the first and second competitive adsorbents are each independently a polycarboxylic acid; further preferably the polycarboxylic acid is selected from one or more of citric acid, tartaric acid, oxalic acid or malic acid; preferably the first and second binders are each independently selected from one or more of an aluminum sol, a silica sol, a pseudo-boehmite or a nano-alumina; preferably the first and second slurries each further independently contain a thickening agent; further preferably the thickening agent is selected from one or more of hydroxyethyl cellulose, hydroxymethyl cellulose, hydroxypropyl methyl cellulose or polyacrylic acid.

[0012] Further, the alkaline earth metal oxide modified gamma-alumina is prepared by: sequentially subjecting a first mixture of gamma-alumina, an alkaline earth metal salt and a solvent to a first stirring, a first drying and a third calcination to obtain the alkaline earth metal oxide modified gamma-alumina; preferably the first stirring is performed for 1-7h at a stirring rate of 200-500rpm; preferably the first drying is performed at a temperature of 100-140℃ for 10-14h; preferably the third calcination is performed at a temperature of 500-800℃ for 1-3h; preferably the alkaline earth metal salt precursor is selected from barium hydroxide octahydrate and / or strontium nitrate; preferably the pH value of the first mixture is adjusted to 6.0-6.5.

[0013] Further, the tungsten oxide modified cerium-zirconium oxide is prepared by: sequentially subjecting a second mixture containing a tungsten salt, a cerium-zirconium oxide and a solvent to a drying and a fourth calcination to obtain the tungsten oxide modified cerium-zirconium oxide; preferably the drying is performed by rotary evaporation for 3-10h at a temperature of 70-120℃; preferably the fourth calcination is performed at a temperature of 400-800℃ for 2-4h; preferably the tungsten salt is ammonium tungstate.

[0014] According to another aspect of the present application, there is provided use of the aforementioned catalyst in treating exhaust gas from a natural gas vehicle.

[0015] The inventors set a platinum layer and a rhodium layer on the outer surface of the ceramic carrier. Platinum has excellent removal effect on carbon monoxide and hydrocarbons in the tail gas of a gas engine, and rhodium has excellent removal effect on nitrogen oxides in the tail gas of a gas engine. Moreover, platinum and rhodium have very high chemical stability and good corrosion resistance and oxidation resistance, thereby greatly improving the application stability of the catalyst. In addition, compared with other noble metals (such as Pd), platinum and rhodium are also lower in cost. In the above platinum layer and rhodium layer, the introduction of alkaline earth metal elements and tungsten elements can effectively improve the uniformity of the distribution of the active components in the catalyst, the utilization rate of the active components, the catalytic efficiency of the catalyst, the low-temperature activity and the high-temperature stability of the catalyst on the premise of meeting the conventional performance requirements of the catalyst. This is because the alkaline earth metal elements can effectively support the aluminum oxide structure, thereby increasing the high-temperature stability of the aluminum oxide. Compared with other high-temperature metal elements, the tungsten element can improve the dispersion rate of the noble metal active component (such as platinum), so that the noble metal active component is more uniformly distributed in the catalyst, has a higher utilization rate, and the catalytic efficiency of the catalyst is greatly improved. At the same time, the introduction of tungsten elements can also enhance the oxygen storage capacity of cerium-zirconium oxide, widen the temperature window of the catalyst, and further improve the low-temperature catalytic activity of the catalyst. BRIEF DESCRIPTION OF DRAWINGS

[0016] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application and are incorporated in and constitute a part of this application. The embodiments of the present application and its description are used to explain the present application and are not used to limit the present application. In the drawings:

[0017] Figure 1 The morphology characterization diagram of the catalyst in Example 1 of the present application is shown. DETAILED DESCRIPTION

[0018] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0019] As described in the background section of the present application, in the prior art, when noble metals Pt, Pd and Rh are used as active components, there are often problems such as uneven distribution of active components in the catalyst, low utilization rate of active components, poor catalytic efficiency of the catalyst, poor low-temperature activity and poor high-temperature stability. In order to solve this problem, the present application provides a catalyst, which comprises a ceramic carrier and a coating layer arranged on the outer surface of the ceramic carrier, the coating layer comprising a platinum layer and a rhodium layer arranged in sequence on the outer surface of the ceramic carrier, and the platinum layer and the rhodium layer each independently containing tungsten oxide modified cerium-zirconium oxide and alkaline earth metal oxide modified γ-aluminum oxide.

[0020] The inventors provide a platinum layer and a rhodium layer on the outer surface of the ceramic carrier. Platinum is excellent in removing carbon monoxide and hydrocarbons in the tail gas of a gas engine, and rhodium is excellent in removing nitrogen oxides in the tail gas of a gas engine. Moreover, platinum and rhodium have very high chemical stability and good corrosion resistance and oxidation resistance, thereby greatly improving the application stability of the catalyst. In addition, the cost of platinum and rhodium is lower than that of other noble metals (such as Pd).

[0021] In the platinum layer and the rhodium layer described above, the introduction of the alkaline earth metal element and the tungsten element can effectively improve the uniformity of the distribution of the active component in the catalyst, the utilization rate of the active component, the catalytic efficiency of the catalyst, the low-temperature activity, and the high-temperature stability of the catalyst, under the premise of meeting the conventional performance requirements of the catalyst. This is because the alkaline earth metal element can effectively support the aluminum oxide structure, thereby increasing the high-temperature stability of the aluminum oxide. Compared with other high-temperature metal elements, the tungsten element can improve the dispersion rate of the noble metal active component (for example, platinum), thereby making the noble metal active component more uniformly distributed in the catalyst, having a higher utilization rate, and greatly improving the catalytic efficiency of the catalyst. At the same time, the introduction of the tungsten element can also enhance the oxygen storage capacity of cerium-zirconium oxide, widen the temperature window of the catalyst, and further improve the low-temperature catalytic activity of the catalyst.

[0022] Further, the chemical formula of the cerium-zirconium oxide is Ce x Zr 1-x O2, wherein 0 < x < 1. In the tungsten oxide modified cerium-zirconium oxide, the tungsten oxide is physically loaded on the outer surface of the cerium-zirconium oxide. In the alkaline earth metal oxide modified γ-aluminum oxide, the alkaline earth metal oxide is physically loaded on the outer surface of the γ-aluminum oxide.

[0023] In order to further balance the high-temperature stability and the low-temperature catalytic activity of the catalyst, in a preferred embodiment, the weight ratio of the alkaline earth metal oxide modified γ-aluminum oxide and the tungsten oxide modified cerium-zirconium oxide in the platinum layer and the rhodium layer is independently 1:1.5-1.5:1. In order to further balance the application stability of the catalytic active component of the catalyst, in a preferred embodiment, the coating amount of the platinum layer and the rhodium layer in the catalyst is independently 100 g / L-300 g / L.

[0024] In order to further improve the high-temperature stability of the catalyst, in a preferred embodiment, the ceramic carrier is a cordierite honeycomb ceramic. Preferably, the mesh number of the cordierite honeycomb ceramic is 300-800 mesh, and the wall thickness is 0.0508-0.1524 mm.

[0025] In order to further improve the application performance of the catalyst, in a preferred embodiment, the loading amount of platinum in the catalyst is 10-200 g / ft 3 , and the loading amount of rhodium is 1-20 g / ft 3.

[0026] In order to further improve the high-temperature stability of the catalyst, the alkaline earth metal oxide is selected from barium oxide and / or strontium oxide, and more preferably the alkaline earth metal oxide is selected from barium oxide.

[0027] The application also provides a preparation method of the aforementioned catalyst, which comprises: providing alkaline earth metal oxide modified γ-alumina and tungsten oxide modified cerium-zirconium oxide; coating a first slurry containing the tungsten oxide modified cerium-zirconium oxide, the alkaline earth metal oxide modified γ-alumina, a first competitive adsorbent, a noble metal platinum and a first binder on the outer surface of a ceramic carrier to form a platinum layer on the outer surface of the ceramic carrier after first calcination; coating a second slurry containing the tungsten oxide modified cerium-zirconium oxide, the alkaline earth metal oxide modified γ-alumina, a second competitive adsorbent, a noble metal rhodium and a second binder on the outer surface of the platinum layer to obtain the catalyst after second calcination.

[0028] Based on the above reasons, the catalyst obtained by the application has good uniformity of the distribution of the active components in the catalyst, high utilization rate of the active components, high catalytic efficiency, good low-temperature catalytic activity and excellent high-temperature stability. The preparation method is simple and easy to operate, has low energy consumption and has better prospects for industrial application.

[0029] In order to further improve the structural stability of the catalyst, in a preferred embodiment, the treatment temperature of the first calcination and the second calcination is independently 500-650°C, and the treatment time is independently 2-3h.

[0030] In order to further improve the uniformity of the coating and thus the performance uniformity of the catalyst, in a preferred embodiment, the first coating and / or the second coating is performed by using a negative pressure coating machine; and in the first coating and the second coating, the air pressure of the negative pressure coating machine is independently -20 to -80 kPa.

[0031] In a preferred embodiment, before the first coating, the person skilled in the art can first prepare a raw slurry by mixing the alkaline earth metal oxide modified γ-alumina and the tungsten oxide modified cerium-zirconium oxide and a solvent (such as deionized water) in a container and stirring. Then, the first competitive adsorbent, the noble metal platinum, the first binder, the optional auxiliary material and the optional thickening agent are added to the slurry, stirred for 0.5-2h for thickening, and continuously stirred for 2-20h to obtain the first slurry. Preferably, the viscosity of the first slurry at 25°C is 4000-8000 mPa·s.

[0032] In a preferred embodiment, before the second coating, the base metal oxide modified γ-alumina and the tungsten oxide modified cerium-zirconium oxide and a solvent (e.g. deionized water) can be first prepared into a slurry and stirred in a container. Then the second competitive adsorbent, the noble metal rhodium, the second binder, the optional auxiliary material and the optional thickening agent are added into the slurry and stirred for 0.5-2 hours for thickening, and then stirred for 6-20 hours to obtain a second slurry. Preferably, the viscosity of the second slurry is 2000-6000 mPa·s at 25°C.

[0033] In a preferred embodiment, the first competitive adsorbent and the second competitive adsorbent are each independently a polycarboxylic acid; further preferably, the polycarboxylic acid is selected from one or more of citric acid, tartaric acid, oxalic acid or malic acid. The use of a polycarboxylic acid as a competitive adsorbent can bring the following beneficial effects: improving the dispersion rate of the noble metal, and further improving the utilization rate of the noble metal. The type of the binder is not particularly limited in the present application, and a conventional binder in the art can be selected to achieve the binding effect. In order to further improve the catalytic performance and high-temperature stability of the catalyst, the first binder and the second binder are each independently selected from one or more of an aluminum sol, a silicon sol, a pseudo-boehmite or a nano-alumina. In order to further improve the coating efficiency of the slurry, the first slurry and the second slurry each independently contain a thickening agent; further preferably, the thickening agent is selected from one or more of hydroxyethyl cellulose, hydroxymethyl cellulose, hydroxypropyl methyl cellulose or polyacrylic acid.

[0034] In order to further improve the high-temperature stability of the catalyst, in a preferred embodiment, the base metal oxide modified γ-alumina is prepared by the following method: a mixture of γ-alumina, a base metal salt and a solvent (e.g. water) is sequentially subjected to first stirring, first drying and third calcination to obtain the base metal oxide modified γ-alumina; preferably, the stirring time of the first stirring is 1-7 hours, and the stirring rate is 200-500 rpm; preferably, the treatment temperature of the first drying is 100-140°C, and the treatment time is 10-14 hours; preferably, the treatment temperature of the third calcination is 500-800°C, and the treatment time is 1-3 hours; preferably, the base metal salt precursor is selected from barium hydroxide octahydrate and / or strontium nitrate; preferably, the pH value of the mixture is adjusted to 6.0-6.5 using an aqueous acetic acid solution (e.g. an aqueous acetic acid solution with an acetic acid mass concentration of 20-60 wt%) so that the base metal salt can be more fully dissolved.

[0035] In order to further improve the uniformity of the distribution of the active component, the utilization rate, the catalytic efficiency and the low-temperature catalytic activity of the catalyst, in a preferred embodiment, the tungsten oxide modified cerium-zirconium oxide is prepared by the following method: a suspension containing tungsten salt, cerium-zirconium oxide and solvent is sequentially subjected to rotary evaporation and fourth calcination to obtain tungsten oxide modified cerium-zirconium oxide; preferably, the treatment time of rotary evaporation is 3-10 h and the treatment temperature is 70-120°C; preferably, the treatment temperature of fourth calcination is 400-800°C and the treatment time is 2-4 h; preferably, the tungsten salt is ammonium tungstate.

[0036] The application also provides a use of the aforementioned catalyst in natural gas vehicle exhaust treatment. Based on the foregoing reasons, the active component in the catalyst of the application has good uniformity of distribution in the catalyst, high utilization rate, high catalytic efficiency, good low-temperature catalytic activity and excellent high-temperature stability. When the catalyst is applied in natural gas vehicle exhaust treatment, it has good catalytic effect and excellent catalytic stability.

[0037] The application will be further described in detail below in combination with specific examples, which cannot be understood as limiting the scope of the application.

[0038] Example 1

[0039] γ-alumina powder and barium hydroxide octahydrate were weighed, deionized water was added and stirred for 30 min, the slurry pH was adjusted to 6.2 with acetic acid, continuous stirring was performed for 5 h, then it was left to stand for aging for 12 h, then it was dried at 120°C for 12 h, and then it was calcined in a muffle furnace at 550°C for 2 h to obtain barium oxide modified γ-alumina, wherein the barium oxide content was 10wt%;

[0040] Tungsten acid ammonium 13.9 g and Ce 0.5 Zr 0.5 O2 powder were weighed, and a tungsten acid ammonium and Ce 0.5 Zr 0.5 O2 powder suspension was prepared, the prepared suspension was rotary evaporated at 80°C for 4 h, and then calcined at 550°C for 2 h to obtain tungsten oxide modified Ce 0.5 Zr 0.5 O2 powder composite powder, wherein the tungsten oxide content was 10wt%;

[0041] Tungsten oxide modified Ce 0.5 Zr 0.5O2 and 20 g of barium oxide modified γ-alumina were placed in a ball mill jar and ball milled for 30 min, then transferred to a beaker for stirring. Citric acid, platinum nitrate, aluminum sol, and hydroxyethyl cellulose were added to the slurry after ball milling, stirred for 1 h, thickened, and stirred for 2 h. A catalyst coating slurry was obtained, which was coated on a catalyst carrier, dried at 150°C for 3 h, and calcined at 550°C for 2 h to prepare a semi-finished catalyst;

[0042] 20 g of tungsten oxide modified Ce 0.5 Zr 0.5 O2 and 20 g of barium oxide modified γ-alumina were placed in a ball mill jar and ball milled for 30 min, then transferred to a beaker for stirring. Citric acid, rhodium nitrate, aluminum sol, and hydroxyethyl cellulose were added to the slurry after ball milling, stirred for 1 h, thickened, and stirred for 2 h. A catalyst coating slurry was obtained, which was coated on a catalyst carrier, dried at 150°C for 3 h, and calcined at 550°C for 2 h to prepare catalyst 1#;

[0043] In the prepared catalyst, the coating amount of the platinum coating was 100 g / L, and the coating amount of the rhodium coating was 100 g / L. The noble metal loading was: Pt was 56 g / ft 3 , and Rh was 4 g / ft 3 .

[0044] Comparative Example 1

[0045] In the coating material of Example 1, the barium oxide modified γ-alumina was replaced by γ-alumina, and the tungsten oxide modified Ce 0.5 Zr 0.5 O2 was replaced by Ce-Zr composite oxide, and the rest of the coating preparation method was the same as that of Example 1 to prepare catalyst 2#.

[0046] Comparative Example 2

[0047] In the coating material of Example 1, the barium oxide modified γ-alumina was replaced by γ-alumina, and the rest of the coating preparation method was the same as that of Example 1 to prepare catalyst 3#.

[0048] Comparative Example 3

[0049] In the coating material of Example 1, the tungsten oxide modified Ce 0.5 Zr 0.5 O2 was replaced by Ce 0.5 Zr 0.5 O2, and the rest of the coating preparation was the same as that of Example 1 to prepare catalyst 4#.

[0050] Comparative Example 4

[0051] In Example 1, the platinum nitrate was replaced by palladium nitrate to prepare catalyst 5#.

[0052] The prepared catalyst has a coating amount of 100 g / L for the palladium coating and 100 g / L for the rhodium coating. The noble metal loading is 56 g / ft 3 for Pd and 4 g / ft 3 for Rh.

[0053] Comparative Example 5

[0054] Catalyst 6# is prepared by replacing the platinum nitrate in Example 1 with palladium nitrate and platinum nitrate.

[0055] The prepared catalyst has a coating amount of 200 g / L for the platinum palladium coating and 200 g / L for the rhodium coating. The noble metal loading is 28 g / ft 3 for Pt, 28 g / ft 3 for Pd and 4 g / ft 3 for Rh.

[0056] Comparative Example 6

[0057] The iron nitrate and Ce 0.5 Zr 0.5 O2 powder are weighed and water is added to prepare an iron nitrate and Ce 0.5 Zr 0.5 O2 powder suspension. The prepared suspension is rotary evaporated at 80°C for 4 h, and then calcined at 550°C for 2 h to obtain the iron oxide modified Ce 0.5 Zr 0.5 O2 powder composite powder, wherein the Fe content is 10 wt%;

[0058] Catalyst 7# is prepared by replacing the modified W-Ce-Zr composite oxide in the coating material of Example 1 with Fe-Ce-Zr composite oxide, and the rest of the coating is coated and prepared according to Example 1.

[0059] Performance characterization:

[0060] Figure 1 The morphology characterization diagram of the catalyst in Example 1 of the present application is shown.

[0061] Under the same experimental conditions, the fresh catalyst and the aged catalyst are respectively tested for the pollutant light-off temperature (T50), wherein the aged catalyst is obtained by aging at 850°C in a 10% H2O aging furnace for 25 h. The lower the T50, the higher the pollutant conversion capacity of the catalyst.

[0062] The prepared catalyst is subjected to activity evaluation, and the test method is as follows: a mixed gas containing NO, CO2, H2O, CH4, CO, O2 and H2 is introduced into a high-temperature reaction furnace, wherein the content of each component is as follows: NO: 2000 ppm, CO2: 8%, H2O: 10%, CH4: 1000 ppm, O2: 0.6%, CO: 7500 ppm and H2: 0.45%; the temperature is raised at a rate of 5 ℃ / min, and finally raised to 650 ℃.

[0063] The test results of the fresh catalyst are shown in Table 1, and the test results of the aged catalyst are shown in Table 2.

[0064] Table 1

[0065] Catalyst CO (T50) / °C NO (T50) / °C CH4(T50) / °C 1# 157 221 356 2# 178 245 378 3# 179 243 364 4# 195 265 375 5# 126 277 390 6# 134 256 381 7# 156 245 401

[0066] T50: the temperature at which the conversion rate of pollutants reaches 50%.

[0067] Table 2

[0068] Catalyst CO (T50) / °C NO (T50) / °C CH4(T50) / °C 1# 243 338 419 2# 257 361 453 3# 246 358 423 4# 259 363 445 5# 198 387 443 6# 207 376 446 7# 231 431 478

[0069] T50: the temperature at which the conversion rate of pollutants reaches 50%.

[0070] As shown in Table 1, the light-off temperatures T50 of NO and CH4 of the fresh catalyst 1# prepared in Example 1 are 221 ℃ and 356 ℃ respectively, which are relatively low compared with other catalysts, and the catalyst has relatively low catalytic activity of NO and CH4. The Pt-Rh catalyst has relatively high NO selectivity and CH4 catalytic activity.

[0071] As shown in Table 2, the light-off temperatures T50 of NO and CH4 of the aged catalyst 1# prepared in Example 1 are 338 ℃ and 419 ℃ respectively, which are relatively low compared with other catalysts. The Pt-Rh catalyst has relatively strong high-temperature stability.

[0072] In the present application, the Ba doped on the surface of alumina can support the structure of alumina and increase the high-temperature stability of alumina. The tungsten element can improve the dispersion rate of the noble metal Pt, enhance the oxygen storage capacity of Ce-Zr oxide and improve the low-temperature activity of the catalyst. In addition, unlike the traditional natural gas vehicle aftertreatment catalyst which uses Pt-Pd-Rh / Pd-Rh (Pd as the main component) noble metal as the active component, the present application uses the noble metals Pt and Rh as the active component in the three-way catalyst, which greatly reduces the cost of the catalyst while ensuring the catalytic activity.

[0073] The above merely describes the preferred embodiments of the present application, and is not used to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A catalyst comprising a ceramic carrier and a coating disposed on an outer surface of the ceramic carrier, characterized in that, The coating comprises a platinum layer and a rhodium layer arranged successively on the outer surface of the ceramic carrier, and the platinum layer and the rhodium layer each independently contain cerium-zirconium oxide modified by tungsten oxide and γ-alumina modified by alkaline earth metal oxide; In the cerium-zirconium oxide modified by tungsten oxide, tungsten oxide is physically loaded on the outer surface of cerium-zirconium oxide; in the γ-alumina modified by alkaline earth metal oxide, alkaline earth metal oxide is physically loaded on the outer surface of γ-alumina; In the platinum layer and the rhodium layer, the weight ratio of the γ-alumina modified by alkaline earth metal oxide and the cerium-zirconium oxide modified by tungsten oxide is independently 1:1.5~1.5:

1.

2. The catalyst according to claim 1, wherein In the catalyst, the coating amount of the platinum layer and the rhodium layer is independently 100~300g / L.

3. Catalyst according to claim 1 or 2, characterized in that The ceramic carrier is cordierite honeycomb ceramic.

4. The catalyst according to claim 3, wherein The cordierite honeycomb ceramic has a mesh number of 300~800 mesh and a wall thickness of 0.0508~0.1524mm.

5. The catalyst of claim 1, wherein The platinum loading in the catalyst is 10-200 g / ft 3 The rhodium loading in the catalyst is 1-20 g / ft 3 .

6. The catalyst according to claim 5, wherein The alkaline earth metal oxide is selected from barium oxide and / or strontium oxide.

7. The catalyst according to claim 5, wherein The alkaline earth metal oxide is selected from barium oxide.

8. A process for the preparation of the catalyst of claim 1, characterized in that, The preparation method comprises: Providing γ-alumina modified by alkaline earth metal oxide and cerium-zirconium oxide modified by tungsten oxide; First coating a first slurry containing the cerium-zirconium oxide modified by tungsten oxide, the γ-alumina modified by alkaline earth metal oxide, a first competitive adsorbent, noble metal platinum and a first binder on the outer surface of the ceramic carrier, and after first calcination, a platinum layer is arranged on the outer surface of the ceramic carrier; Second coating a second slurry containing the cerium-zirconium oxide modified by tungsten oxide, the γ-alumina modified by alkaline earth metal oxide, a second competitive adsorbent, noble metal rhodium and a second binder on the outer surface of the platinum layer, and after second calcination, the catalyst is obtained.

9. The method of claim 8, wherein the catalyst is prepared by the steps of: The treatment temperature of the first calcination and the second calcination is independently 500~650℃, and the treatment time is independently 2~3h.

10. The preparation method of the catalyst according to claim 9, wherein The first coating and / or the second coating is performed by using a negative pressure coating special machine; in the first coating and the second coating, the air pressure of the negative pressure coating special machine is independently -20~-80kPa.

11. The method of claim 9, wherein the catalyst is prepared by the steps of: The first competitive adsorbent and the second competitive adsorbent are each independently a polycarboxylic acid.

12. The method of claim 11, wherein the catalyst is prepared by the steps of: The polycarboxylic acid is selected from one or more of citric acid, tartaric acid, oxalic acid or malic acid.

13. The preparation method of the catalyst according to claim 11, wherein The first binder and the second binder are each independently selected from one or more of aluminum sol, silicon sol, pseudo-boehmite or nano-alumina; The first slurry and the second slurry each independently further contain a thickening agent.

14. The method of claim 13, wherein the thickening agent is selected from one or more of hydroxyethyl cellulose, hydroxymethyl cellulose, hydroxypropyl methyl cellulose, or polyacrylic acid. The alkaline earth metal oxide modified gamma-alumina is prepared by the following method:

15. The method of claim 9, wherein the catalyst is prepared by the steps of: The first mixture of gamma-alumina, alkaline earth metal salt and solvent is sequentially subjected to first stirring, first drying and third calcination to obtain the alkaline earth metal oxide modified gamma-alumina.

16. The method of claim 15, wherein the first stirring is performed at a stirring speed of 200-500 rpm for 1-7 h. The first drying is performed at a temperature of 100-140 °C for 10-14 h. The third calcination is performed at a temperature of 500-800 °C for 1-3 h. The alkaline earth metal salt precursor is selected from barium hydroxide octahydrate and / or strontium nitrate. The pH value of the first mixture is adjusted to 6.0-6.

5. The tungsten oxide modified ceria-zirconia is prepared by the following method: The second mixture containing tungsten salt, ceria-zirconia and solvent is sequentially subjected to drying and fourth calcination to obtain the tungsten oxide modified ceria-zirconia.

17. The method of claim 11, wherein the catalyst is prepared by the steps of:

18. The method of claim 17, wherein the drying is performed by rotary evaporation at a temperature of 70-120 °C for 3-10 h. The fourth calcination is performed at a temperature of 400-800 °C for 2-4 h. The tungsten salt is ammonium tungstate. The catalyst comprises a ceramic carrier and a coating layer disposed on the outer surface of the ceramic carrier, the coating layer comprising a platinum layer and a rhodium layer disposed on the outer surface of the ceramic carrier in sequence, and the platinum layer and the rhodium layer each independently further comprising tungsten oxide modified ceria-zirconia and alkaline earth metal oxide modified gamma-alumina. ​ ​ 19. Use of the catalyst according to claim 1 for the treatment of exhaust gases from natural gas vehicles, characterized in that, ​

Images