CN109675558B

CN109675558B - Two-dimensional palladium-tungsten bimetallic nano catalyst, preparation method and application

Info

Publication number: CN109675558B
Application number: CN201910046058.2A
Authority: CN
Inventors: 戴洪兴; 梁仪静; 刘雨溪; 王宇欣; 邓积光
Original assignee: Beijing University of Technology
Current assignee: Beijing University of Technology
Priority date: 2019-01-16
Filing date: 2019-01-16
Publication date: 2021-11-26
Anticipated expiration: 2039-01-16
Also published as: CN109675558A

Abstract

A two-dimensional palladium-tungsten bimetallic nano-catalyst, a preparation method and application belong to the technical field of functional materials. Loading PdW bimetallic nanosheets to TiO₂On a carrier, and then forming PdW/TiO by burning₂A catalyst. The loading of metallic palladium was 0.67 wt%. The preparation method comprises the following steps: adopting a solvothermal synthesis method to simultaneously reduce palladium acetylacetonate and tungsten carbonyl to form ultrathin PdW bimetallic nanosheets, and then adopting an impregnation method to load the bimetallic nanosheets to TiO₂The Pd loading on the support was 0.67 wt%. The supported catalyst is burnt at 350 ℃ to form PdW/TiO₂And (3) a nano catalyst. PdW/TiO prepared by the invention₂The nano catalyst has simple preparation process and good application prospect in the field of catalysis.

Description

Two-dimensional palladium-tungsten bimetallic nano catalyst, preparation method and application

Technical Field

The invention relates to a two-dimensional palladium-tungsten nano catalyst and a preparation method thereof, in particular to a method for preparing an ultrathin two-dimensional PdW nano sheet by adopting solvothermal synthesis and loading the PdW nano sheet on TiO by adopting an impregnation method₂Then firing to form TiO₂A supported PdW bimetallic catalyst. A load type catalyst with higher catalytic activity for benzene oxidation belongs to the technical field of functional materials.

Background

With the development of modern industrial science and technology, the living standard of people is increasingly improved. The emission of the industrial waste gases which follow is one of the important causes of atmospheric pollution. The severe atmospheric pollution situation makes air management urgent. Volatile Organic Compounds (VOCs) are one of the major constituents of industrial waste gases, and most of the VOCs are directly harmful to human health and are also considered as important precursors for formation of fine particulate matter and ozone in the atmosphere. Benzene is a VOCs with strong carcinogenicity. Among the technologies for purifying benzene, catalytic oxidation is one of the most commonly used and most effective abatement technologies at present. And the development of high-efficiency catalysts is the core of the technology.

At present, researchers at home and abroad make a great deal of research on catalytic oxidation catalysts of benzene and obtain some achievements. Liu et Al (J.Liu, et Al, Catal. today,2017,297:211-218) investigated gamma-Al₂O₃The performance of the Pd nanoparticle-supported catalyst for the catalytic oxidation of benzene was found to be at 2.66% Pd nanoparticle-supported TiO₂T of benzene conversion _90％190 ℃ was observed, but the Pd loading was higher. Tabakova et al (T.Tabakova, et al, chem.Eng.J.,2015,260:133-141) investigated the oxidation performance of benzene on Fe-Ce catalysts loaded with Au, Pd. The Fe-Ce catalyst loaded with Au and Pd bimetallic and prepared by an impregnation method realizes the complete oxidation of benzene at 200 ℃. However, the application of noble metal catalysts is limited by the characteristics of high price and easy sintering and deactivation at high temperature. Modification of noble metals with transition metals is an effective way. In addition to the strong interaction between the noble metal and the carrier, it is also widely believed that a strong interaction exists between the bimetallic, and doping with the transition metal generally improves the electronic and geometric structure of the noble metal, further improving the catalytic activity. Hosseini et al (M.Hosseini, et al., Catal. today,2007,122:391-396) studied mesoporous TiO loading₂The series of Pd-Au bimetallic catalysts above found that the catalytic oxidation of either p-toluene or propylene, Pd-Au/TiO₂The catalytic activity of the catalyst is better than that of Pd/TiO₂。

Generally, the structure of a catalyst is closely related to its catalytic properties. The ultrathin two-dimensional nano material has the characteristics of two-dimensional electronic effect, strong covalent bond in a plane and thickness, shows unique physicochemical properties, and has higher specific surface area and abundant active sites. Di and the like (J.Di, et al, mater.today,2018,21:749-770) summarize the application of the ultrathin two-dimensional material in the fields of photoelectrocatalytic hydrogen evolution and electrocatalytic hydrogen evolution.

To our knowledge, no literature and patent reports exist at present about the preparation method of the PdW bimetallic nanocrystal with the ultrathin two-dimensional nanosheet structure and the research on the application of the supported catalyst in catalytic oxidation of benzene.

Disclosure of Invention

The invention aims to provide a method for preparing TiO with ultrathin nanosheet structure and high catalytic activity on benzene by adopting a solvothermal synthesis method₂A method of PdW nano catalyst.

TiO₂The PdW catalyst is characterized in that PdW nanosheets are prepared by a solvothermal synthesis method, and then the PdW nanosheets are loaded on the nano TiO by adopting an impregnation method₂On a support, subsequently calcined to form TiO₂a/PdW catalyst; the above samples were supported at Pd of 0.2 to 1 wt%, preferably 0.67 wt%, and W of 0.5 to 1.5 wt%, preferably 0.93 wt%, and the samples were 0.67 wt% Pd and 0.93 wt% W/TiO, respectively, when the supported amount of Pd was 0.67 wt% and the supported amount of W was 0.93 wt%, respectively₂. The thickness of the Pd nano-sheet is about 1nm, and the surface size is 100-200 nm.

The PdW bimetallic nanosheet is characterized in that the prepared nanosheet has an ultrathin two-dimensional structure, and the preparation method mainly comprises the following steps:

(1) weighing palladium acetylacetonate, adding toluene and oleylamine, placing on a magnetic stirrer, stirring and dissolving for 20min at room temperature, and weighing W (CO)₆Adding the mixed solution to form a mixed precursor solution, continuously stirring at room temperature for 5-10min, then putting the mixed precursor solution into a reaction kettle, and preserving heat in an oven at the temperature of 130-; cooling to room temperature, placing the reaction solution in a centrifuge tube, adding ethanol, performing ultrasonic treatment, centrifuging, and repeatedly washing for 3-4 times to obtain the ultrathin PdW bimetallic nanosheet; finally, uniformly dispersing the prepared PdW nanosheets into cyclohexane for storage;

(2) loading the obtained PdW bimetallic nanosheets onto a carrier by adopting a dipping method, and then obtaining PdW/TiO through a burning process₂A nano-catalyst; the method comprises the following specific steps:

calculating the required amount of solution containing PdW nanosheets according to the load amount, and adding a certain amount of TiO₂Adding the carrier into a weighed cyclohexane solution containing PdW nanosheets; stirring and dipping for 12h, and centrifuging to obtain a supported catalyst; loading the obtained catalyst into a porcelain boat, placing in a muffle furnace, heating from room temperature to 320-380 deg.C, preferably 350 deg.C, at a rate of 5 deg.C/min, and heating at the temperatureKeeping for 1-3h, preferably 2h, and cooling to obtain PdW/TiO₂And (3) a nano catalyst.

Step (1) preferably comprises 1-10ml (preferably 5ml) of toluene and 2-4ml (preferably 3.5ml) of oleylamine per 0.02mmol of palladium acetylacetonate; w (CO)₆The amount of (b) added is based on the W loading.

The catalyst obtained by the invention is used for oxidizing benzene into carbon dioxide and water finally.

Preferably, the catalyst T is prepared under reaction conditions of benzene concentration of 1000ppm, benzene/oxygen molar ratio of 1/400 and space velocity of 40000 mL/(g.h)_50％(reaction temperature required for 50% conversion of benzene) and T_90％(the reaction temperature required for 90% conversion of benzene) was 178 ℃ and 200 ℃ respectively.

The invention has the characteristics of simple preparation process and the like. The invention especially relates to 0.67 wt% Pd0.93wt% W/TiO₂The catalyst has excellent catalytic activity and good application prospect in the field of benzene catalytic oxidation.

The crystal structure, particle morphology and catalytic oxidation activity of the obtained catalyst on benzene were measured by using instruments such as a D8ADVANCE X-ray diffractometer (XRD), a JEOL-2010 Transmission Electron Microscope (TEM), an Shimadzu GC-2014 Gas Chromatography (GC) and the like. The result shows that each sample prepared by the method has better crystallinity, the PdW nanosheet is regular in shape, and the catalytic oxidation activity of the bimetallic supported catalyst on benzene is obviously improved compared with that of a pure palladium supported catalyst.

Drawings

FIG. 1 shows the PdW/TiO thus obtained₂And Pd/TiO₂XRD patterns of the samples, where curves (a) and (b) are Pd/TiO for example 1 and the comparative sample, respectively₂XRD spectrum of (1);

FIG. 2 is TEM photographs of the prepared PdW and Pd samples, wherein (a), (b), (c) and (d) are TEM photographs of Pd particles and example 1 at different proportions, respectively;

FIG. 3 shows PdW/TiO compounds prepared in example 1₂And Pd/TiO₂Activity curve for catalytic oxidation of benzene on sample.

Detailed Description

In order to further understand the present invention, the following examples are given in detail, but the present invention is not limited to the following examples.

Example 1

0.02mmol palladium acetylacetonate was weighed, 5mL toluene and 3.5mL oleylamine were added, the mixture was placed on a magnetic stirrer, and after dissolving for 20min with stirring at room temperature, 0.14mmol W (CO) was weighed₆Adding into the mixed solution to form a mixed precursor solution, continuously stirring at room temperature for 5-10min, placing into a reaction kettle, and keeping the temperature in a 160 ℃ oven for 4 h. And cooling to room temperature, placing the reaction solution in a centrifuge tube, adding ethanol, performing ultrasonic treatment, centrifuging, and repeatedly washing for 3-4 times to obtain the ultrathin PdW bimetallic nanosheet. And finally, uniformly dispersing the prepared PdW nanosheets into 10mL of cyclohexane for storage.

Loading the obtained PdW bimetallic nanosheets onto a carrier by adopting a dipping method, and then obtaining PdW/TiO through a burning process₂And (3) a nano catalyst. The method comprises the following specific steps:

calculating the required amount of the solution containing PdW bimetal according to a certain load amount, and adding a certain amount of TiO₂The carrier is added to the measured cyclohexane solution containing the bimetallic nanocrystals. Stirring, dipping for 12h, and centrifuging to obtain the supported catalyst. Loading the obtained catalyst into a porcelain boat, placing the porcelain boat in a muffle furnace, heating the porcelain boat from room temperature to 350 ℃ at the speed of 5 ℃/min, keeping the porcelain boat at the temperature for 2 hours, and cooling to obtain PdW/TiO₂And (3) a nano catalyst.

Under the reaction conditions of benzene concentration of 1000ppm, benzene/oxygen molar ratio of 1/400 and space velocity of 40000 mL/(g.h), the catalyst T_50％(reaction temperature required for 50% conversion of benzene) and T_90％(the reaction temperature required for 90% conversion of benzene) was 178 ℃ and 200 ℃ respectively. The oxidation products are carbon dioxide and water.

Claims

1.TiO₂The PdW catalyst is characterized in that PdW nanosheets are prepared by a solvothermal synthesis method, and then the PdW nanosheets are loaded on the nano TiO by adopting an impregnation method₂On a support, subsequently calcined to form TiO₂a/PdW catalyst; the preparation method comprises the following steps:

(1) weighing palladium acetylacetonate, adding toluene and oleylamine, placing on a magnetic stirrer, stirring and dissolving for 20min at room temperature, and weighing W (CO)₆Adding the mixed solution to form a mixed precursor solution, continuously stirring at room temperature for 5-10min, then putting the mixed precursor solution into a reaction kettle, and preserving the heat in an oven at the temperature of 130-; cooling to room temperature, placing the reaction solution in a centrifuge tube, adding ethanol, performing ultrasonic treatment, centrifuging, and repeatedly washing for 3-4 times to obtain the ultrathin PdW bimetallic nanosheet; finally, uniformly dispersing the prepared PdW nanosheets into cyclohexane for storage;

calculating the required amount of solution containing PdW nanosheets according to the load amount, and adding a certain amount of TiO₂Adding the carrier into a weighed cyclohexane solution containing PdW nanosheets; stirring and dipping for 12h, and centrifuging to obtain a supported catalyst; loading the obtained catalyst into a porcelain boat, placing the porcelain boat in a muffle furnace, heating the porcelain boat from room temperature to 320-380 ℃ at the speed of 5 ℃/min, keeping the porcelain boat at the temperature for 1-3h, and cooling to obtain PdW/TiO₂A nano-catalyst; the thickness of the PdW nano-sheet is 1nm, and the surface size is 100-200 nm.

2. TiO according to claim 1₂A/PdW catalyst, characterized in that the Pd loading in the sample is 0.2-1 wt.%, preferably 0.67 wt.%, and the W loading is 0.5-1.5 wt.%, preferably 0.93 wt.%.

3. TiO according to claim 1₂The catalyst is characterized in that the load of Pd in the sample is 0.67 wt%, and the load of W is 0.93 wt%.

4. Preparation of the TiO according to any one of claims 1 to 3₂Method for the production of a/PdW catalyst, characterized in that it comprises the following steps:

(1) weighing palladium acetylacetonate, adding toluene and oleylamine, placing on a magnetic stirrer, and stirring at room temperatureAfter stirring and dissolving for 20min, weighing W (CO)₆Adding the mixed solution to form a mixed precursor solution, continuously stirring at room temperature for 5-10min, then putting the mixed precursor solution into a reaction kettle, and preserving the heat in an oven at the temperature of 130-; cooling to room temperature, placing the reaction solution in a centrifuge tube, adding ethanol, performing ultrasonic treatment, centrifuging, and repeatedly washing for 3-4 times to obtain the ultrathin PdW bimetallic nanosheet; finally, uniformly dispersing the prepared PdW nanosheets into cyclohexane for storage;

calculating the required amount of solution containing PdW nanosheets according to the load amount, and adding a certain amount of TiO₂Adding the carrier into a weighed cyclohexane solution containing PdW nanosheets; stirring and dipping for 12h, and centrifuging to obtain a supported catalyst; loading the obtained catalyst into a porcelain boat, placing the porcelain boat in a muffle furnace, heating the porcelain boat from room temperature to 320-380 ℃ at the speed of 5 ℃/min, keeping the porcelain boat at the temperature for 1-3h, and cooling to obtain PdW/TiO₂And (3) a nano catalyst.

5. The method as claimed in claim 4, wherein the temperature in step (2) is raised from room temperature to 350 ℃ at a rate of 5 ℃/min and maintained at that temperature for 2 hours, and the temperature is reduced to obtain PdW/TiO₂And (3) a nano catalyst.

6. The process according to claim 4, wherein in step (1), for every 0.02mmol of palladium acetylacetonate, 1-10ml of toluene and 2-4ml of oleylamine correspond.

7. The method of claim 4, wherein W (CO)₆The amount of (b) added is based on the W loading.

8. The TiO of any one of claims 1 to 3₂Application of a/PdW catalyst for the oxidation of benzene, ultimately to carbon dioxide and water.