CN107626307B

CN107626307B - Method for regulating and controlling oxidation activity of Pt-based catalyst by doping ZnO

Info

Publication number: CN107626307B
Application number: CN201710910373.6A
Authority: CN
Inventors: 何洪; 刘娅; 宋丽云; 李瑶瑶; 李伶聪; 张宁强
Original assignee: Beijing University of Technology
Current assignee: Beijing University of Technology
Priority date: 2017-09-29
Filing date: 2017-09-29
Publication date: 2021-03-26
Anticipated expiration: 2037-09-29
Also published as: CN107626307A

Abstract

A method for regulating and controlling the oxidation activity of a Pt-based catalyst by doping ZnO belongs to the field of industrial catalysis. Preparing a mixed solution by adopting Pt, Zn precursors, a certain amount of oleamide and oleic acid, heating to prepare Pt-ZnO nanoparticle sol, and adding gamma-Al₂O₃Dipping, placing in a vacuum oven at 60-80 ℃ for 6-8 h, and roasting at 500-800 ℃ to obtain the product. The preparation method has the advantages of simple preparation process, mild reaction conditions, uniform product size, uniform appearance, good dispersion, good catalytic activity and Pt-ZnO/Al₂O₃The catalyst prepared by the catalyst has the characteristic of porous structure and good CO oxidation activity; the amount of Pt is controlled to be unchanged, and Pt// gamma-Al can be adjusted by introducing ZnO₂O₃The oxidation activity of the catalyst.

Description

Method for regulating and controlling oxidation activity of Pt-based catalyst by doping ZnO

Technical Field

The invention belongs to the field of industrial catalysis; in particular to a method for preparing a Pt-based catalyst doped with ZnO, which utilizes the ZnO doping to realize the regulation and control of the oxidation activity of the Pt-based catalyst.

Background

With the development of economy, the problem of atmospheric environmental pollution is more and more serious, China encounters severe haze weather in 2013, the haze occurrence frequency is high, the coverage range is wide, the pollution degree is unprecedented, and one of the main reasons for forming haze pollution is the emission of automobile exhaust. The problem of controlling the automobile emission pollution is mainly solved by a three-way catalytic converter, the active components of the three-way catalyst are precious metals Pt, Rh and Pd, the emission standard is stricter and stricter, the precious metal resources are scarce, and the price of the precious metal which is high and the automobile maintenance quantity which is continuously increased provide new challenges for the three-way catalyst.

The problems faced by three-way catalysts are mainly: improving the catalytic activity, reducing the production cost and controlling the exhaust emission in the cold start stage of the automobile. In recent years, the development of nanocatalysts has brought about eosin to solve the above problems. The invention proceeds from Pt/Al₂O₃Starting from the catalyst, ZnO is introduced to realize the controllable regulation of Pt/Al₂O₃The oxidation activity of the catalyst. The catalyst system can be used for preparing three-way catalysts for CO exhaust emission control and automobile exhaust purification.

The invention takes Pt salt and Zn salt as precursors, oleic acid amide and oleic acid as protective agents and reducing agents, adopts a liquid phase chemical reduction method for preparation, and realizes the particle size regulation of Pt-ZnO nanoparticles by utilizing a controllable preparation technology of bimetallic nanoparticles.

The prepared Pt-ZnO nano particles are loaded on gamma-Al₂O₃Then the mixture is roasted at the temperature of 600 ℃ in the air atmosphere to obtain Pt-ZnO/gamma-Al₂O₃The catalyst is characterized and the CO catalytic oxidation activity is evaluated.

Disclosure of Invention

The invention aims to provide a method for preparing Pt-ZnO nano particles and Pt-ZnO/Al with high thermal stability₂O₃A method of preparing nano catalyst.

According to the invention, oleamide is used as a reducing agent and a stabilizing agent, a co-thermal reduction method is adopted to prepare Pt-ZnO nanoparticles, and the doping amount of ZnO is changed by changing the concentration of a precursor. Pt-ZnO/Al₂O₃The nano particles of Pt and ZnO are respectively and uniformly loaded on Al₂O₃The above.

The Pt-ZnO/Al₂O₃The preparation method of the nano catalyst is characterized by comprising the following steps:

(1) adding a certain proportion of Pt and Zn precursors, a certain amount of oleamide and oleic acid into a reactor, carrying out water bath at 70-90 ℃, preferably 80 ℃, and continuously stirring to completely dissolve the oleamide and completely mix reagents, wherein the mixed solution is yellow;

(2) heating the yellow mixed solution in an argon atmosphere at 220-350 ℃ for 0.5-1.5 h;

(3) stopping heating, cooling, and adding ethanol for purification to obtain Pt-ZnO nanoparticle sol;

(4) then, adding gamma-Al into the Pt-ZnO nano particle sol₂O₃Stirring for 6-13 h, and soaking overnight;

(5) placing the dipped turbid liquid in a vacuum oven at 60-80 ℃ for 6-8 h, roasting at 500-800 ℃ for 2h, grinding, tabletting and sieving the powder to 60-80 meshes to obtain Pt-ZnO/Al₂O₃A catalyst.

The method for regulating the oxidation activity of the Pt-based catalyst by doping ZnO is characterized in that the precursor of Pt can be platinum-containing salts such as platinum acetylacetonate, chloroplatinic acid, platinum nitrate, platinum tetraammine nitrate and the like; the Zn precursor may be zinc-containing salts such as zinc acetylacetonate, zinc sulfate, zinc carbonate, zinc alkoxide, and zinc chloride.

The dosage relation of the oleamide and the oleic acid is that preferably, each 10g of the oleamide corresponds to 2.5mL of the oleic acid;

0.01-0.1gPt precursor for every 10g oleamide.

Finally prepared product Pt-ZnO/Al₂O₃In the method, the doping amounts of Pt and ZnO can be adjusted according to the requirement by adjusting the relation of the use amount of raw materials. The method can keep the amount of Pt unchanged, and change the doping amount of ZnO through the addition amount of the Zn precursor.

The loading amount of Pt is preferably 1wt-4 wt%, and the loading amount of ZnO is preferably 0.2wt-3.5 wt%; further preferably, the supported amount of Pt is 1wt%, and the supported amount of ZnO is preferably 4 wt%.

According to the method for regulating the oxidation activity of the Pt-based catalyst by doping ZnO, ZnO is nano-scale particles and can be uniformly dispersed in Al₂O₃On the carrier, the carrier is coated with a coating,the Pt nano particles can be dragged to be uniformly dispersed. Catalysts Pt and ZnO in Al₂O₃The carrier is uniformly distributed; and the Pt active component has uniform grain diameter, the average grain diameter is 3-4nm, and no agglomeration is generated.

The invention has the beneficial effects that:

Pt-ZnO/Al prepared by the invention₂O₃The catalyst has the characteristics of porous structure and excellent oxidation activity, the loading capacity of Pt is kept unchanged to be 1%, and the doping of ZnO with different concentrations can regulate and control Pt-ZnO/Al₂O₃The catalytic activity of the catalyst for oxidation, for example, Pt-ZnO/γ -Al when the doping amount of ZnO is 1.7%₂O₃The catalyst has the highest catalytic activity for CO oxidation reactions. Meanwhile, the Pt/ZnO (1.7%)/gamma-Al₂O₃The catalyst has high metal dispersion and metal surface area, and simultaneously has smaller Pt particle size.

Drawings

FIG. 1 shows the catalytic activity of 1# in example 1, 2# in example 2, 3# in example 3, and a sample of the catalyst for the CO oxidation reaction of the process of the present invention.

Fig. 2 shows XRD patterns of 2 x nanoparticles in example 2 and 3 x nanoparticles in example 3.

FIG. 3 is a TEM photograph of 2# catalyst sample in example 2 and 3# catalyst sample in example 3 of the process of the present invention.

FIG. 4 is an EDS photograph of 2# catalyst sample in example 2 and 3# catalyst sample in example 3 of the process of the present invention.

Detailed Description

The present invention will be further illustrated with reference to the following examples, but the present invention is not limited to the following examples.

Example 1:

0.04015g of Pt (acac)₂、0.2004g Zn(acac)₂10g of oleamide and 2.5mL of oleic acid were added to a three-necked flask, and the mixture was stirred in a water bath at 80 ℃ for 30 minutes to completely dissolve the oleamide and completely mix the reagents, and the mixture was yellow.

Heating the yellow mixed solution on a heating sleeve under the argon atmosphere, wherein the color of the mixed solution is deepened when the mixed solution is heated to 150 ℃, continuously heating the mixed solution to 250 ℃, and keeping the heated mixed solution for 1 hour.

Stopping heating, cooling, and adding ethanol for purification to obtain the Pt-ZnO nanoparticle sol (sample 1).

2g of gamma-Al is added into the Pt-ZnO nano particle sol₂O₃Stirred for 6h and immersed overnight.

Placing the dipped suspension in a vacuum oven at 80 ℃ for 6h, roasting at 600 ℃ for 2h, grinding, tabletting and sieving the powder to 60-80 meshes to obtain a No. 1 catalyst sample (Pt (1%) -ZnO (3.5%)/Al₂O₃)。

Example 2:

0.04015g of Pt (acac)₂、0.1002g Zn(acac)₂10g of oleamide and 2.5mL of oleic acid were added to a three-necked flask, and the mixture was stirred in a water bath at 80 ℃ for 30 minutes to completely dissolve the oleamide and completely mix the reagents, and the mixture was yellow.

Stopping heating, cooling, and adding ethanol for purification to obtain the Pt-ZnO nanoparticle sol (sample 2).

Placing the dipped suspension in a vacuum oven at 80 ℃ for 6h, roasting at 600 ℃ for 2h, grinding, tabletting and sieving the powder to 60-80 meshes to obtain a No. 2 catalyst sample (Pt (1%) -ZnO (1.7%)/Al)₂O₃)。

Example 3:

0.04015g of Pt (acac)₂、0.01253g Zn(acac)₂10g of oleamide and 2.5mL of oleic acid were added to a three-necked flask, and the mixture was stirred in a water bath at 80 ℃ for 30 minutes to completely dissolve the oleamide and completely mix the reagents, and the mixture was yellow.

Stopping heating, cooling, and adding ethanol for purification to obtain the Pt-ZnO nanoparticle sol (sample 3).

Placing the dipped suspension in a vacuum oven at 80 ℃ for 6h, roasting at 600 ℃ for 2h, grinding, tabletting and sieving the powder to 60-80 meshes to obtain a 3# catalyst sample (Pt (1%) -ZnO (0.2%)/Al₂O₃)。

Test example 1:

the catalyst samples # 1 in example 1, # 2 in example 2 and # 3 in example 3 were tested for their CO oxidation activity, respectively, and the reaction gas compositions were CO, O₂And N₂(CO/O₂/N ₂1/10/89), the total gas flow rate was 30 mL/min. The catalyst dosage is 0.02g, when the activity evaluation is carried out, the catalyst and 0.1g of quartz sand are uniformly mixed and then are arranged in a quartz tube, and a thermocouple is positioned in the middle of a catalyst bed layer. Since the concentration of the solid-gas interface reaction gas is low during the reaction, the gas volumes before and after the reaction are regarded as unchanged during the calculation. The test results (fig. 1) show that: the 2# catalyst sample has higher CO oxidation reaction activity, and CO is completely converted at the temperature of 115 ℃.

Test example 2:

phase structure analysis was performed on 2X nanoparticles samples in example 2 and 3X nanoparticles samples in example 3 by X-ray powder diffraction, respectively, and the test results (fig. 2) showed that: 39.9^o,46.3^o,67.6^oThe peaks at (A) belong to the Pt (111), (200) and (220) crystal planes; 31.5^o，34.1^o，36.0^o，56.4^oAnd 62.6^oThey are classified into ZnO (100), (002), (101), (110) and (103) crystal planes. These diffraction peaks further indicate the formation of ZnO after reduction, with Pt having sharp characteristic peaks, indicating that Pt particles have high crystallinity.

Test example 3:

TEM and ED were performed on 2# in example 2, 3# in example 3, and catalyst samples using transmission electron microscopy, respectivelyS characterization, test results (fig. 3) indicate: the darker spot Pt nano particle is evenly deposited on the larger Al₂O₃On the nanoparticles; at the same time, ZnO particles are in Al₂O₃The nanoparticles are uniformly distributed over the area. Dispersed in Al₂O₃All Pt nanoparticles on the surface of the particles had a spherical morphology. Supported on Al₂O₃The average diameter of the Pt nanoparticles on (a) is about 3-4 nm. Furthermore, it can be noted that the Pt nanoparticles do not agglomerate, a feature that makes them sensitive to gas reactions, more reactive.

Figure 4 shows EDS maps of all elements for catalyst sample # 2 in example 2 and # 3 in example 3. It can be seen that the elements Zn, O and Pt are uniformly distributed over the region. Further, the density of Pt sites is about several percent of the density of Zn and O sites. This is consistent with the expected elemental composition. EDS data confirmed the presence of Pt and indicated that Pt was uniformly dispersed in the mixture of nanoparticles.

Claims

1. Pt-ZnO/Al for CO oxidation₂O₃The preparation method of the nano catalyst is characterized by comprising the following steps:

(1) adding a certain proportion of Pt and Zn precursors, a certain amount of oleamide and oleic acid into a reactor, carrying out water bath at 70-90 ℃ and continuously stirring to completely dissolve the oleamide and completely mix the reagents, wherein the mixed solution is yellow;

(5) placing the dipped turbid liquid in a vacuum oven at the temperature of 60-80 ℃ for 6-8 h, roasting at the temperature of 600-800 ℃ for 2h, grinding, tabletting and sieving the powder to 60-80 meshes to obtain Pt-ZnO/Al₂O₃A catalyst;

the loading of Pt is 1 wt%.

2. The method according to claim 1, wherein the precursor of Pt is a platinum salt and the precursor of Zn is a zinc salt.

3. The preparation method according to claim 1, wherein the precursor of Pt is one or more of platinum acetylacetonate, chloroplatinic acid, platinum nitrate and platinum tetraammine nitrate; the Zn precursor is one or more of zinc acetylacetonate, zinc sulfate, zinc carbonate, zinc alkoxide and zinc chloride.

4. The method according to claim 1, wherein the oleic acid amide and the oleic acid are used in an amount of 2.5mL of oleic acid per 10g of oleic acid amide.

5. The process according to claim 1, wherein the precursor of 0.01 to 0.1gPt is used per 10g of oleamide.

6. The production method according to claim 1,

the loading amount of ZnO is 0.2wt percent to 3.5wt percent.

7. The production method according to claim 1, wherein the loading of ZnO is 1.7% by weight.

8. The method according to claim 1, wherein ZnO is in the form of nano-sized particles uniformly dispersed in Al₂O₃On the carrier, Pt nano particles are uniformly dispersed, and the particle size of the Pt component is uniform.