CN110639548B - Monoatomic palladium-cobalt bimetallic nano-catalyst for efficiently catalyzing benzene oxidation - Google Patents

Abstract

A single-atom palladium-cobalt bimetallic nano-catalyst for efficiently catalyzing the oxidation of benzene belongs to the technical field of functional materials. The PdCo bimetallic nanoparticles were supported on the γ-Al ₂ O ₃ support and then calcined to form the Pd ₁ Co ₁ /Al ₂ O ₃ catalyst. The loading of metallic palladium was 0.4 wt%. The preparation method is as follows: in the dichlorobenzene system, adopting the method of one-step pyrolysis of the oil phase, simultaneously pyrolyzing and reducing palladium acetylacetonate and dicobalt octacarbonyl to form PdCo bimetallic particles with uniform size, and then adopting the impregnation method to decompose the metal particles. loaded onto an _Al2O3 carrier with a Pd loading _of 0.4 wt%. The supported catalyst was hydrothermally calcined at 800℃ to form Pd ₁ Co ₁ /Al ₂ O ₃ nanocatalysts. The Pd ₁ Co ₁ /Al ₂ O ₃ nano-catalyst prepared by the invention has a simple preparation process, and the bimetal is dispersed in a single atom, and has a good application prospect in the field of catalysis.

Description

An efficient single-atom palladium-cobalt bimetallic nanocatalyst for benzene oxidation

technical field

The invention relates to a Pd ₁ Co ₁ /Al ₂ O ₃ nano-catalyst and a preparation method thereof, in particular to the preparation of PdCo alloy particles with uniform size by an oil phase one-step pyrolysis method, and the impregnation method is used to load them on the surface of Al ₂ O ₃ , followed by hydrothermal calcination to form Pd ₁ Co ₁ /Al ₂ O ₃ . A Pd ₁ Co ₁ /Al ₂ O ₃ nano-catalyst with high catalytic activity for benzene oxidation belongs to the technical field of functional materials.

Background technique

With the rapid progress of urbanization and industrialization, various fine chemicals such as coatings, dyes, and daily necessities are widely used. The large-scale use of these volatile organic compounds-rich items has led to the generation of various types of exhaust gases. These exhaust gases react with each other in the atmosphere to form a large amount of particulate matter (PM _2.5 /PM ₁₀ , etc.), leading to the formation of haze. In addition, these exhaust gases are also oxidized in the atmosphere, generating photochemical smog, ozone holes, etc., causing great air pollution. Moreover, these VOCs themselves, as toxic gases, will pose a serious threat to human health and ecological security. Benzene is one of the more classic pollutants. Therefore, it is very important to find a low-temperature and high-efficiency method for oxidizing benzene (VOCs). Catalytic combustion has been widely studied due to its advantages of low energy consumption and no secondary pollution. The development of new catalysts in catalytic combustion is the key to realizing this process.

At present, domestic and foreign researchers have done a lot of research on the catalytic combustion of benzene, and have achieved more results. The catalysts for the catalytic oxidation of benzene are roughly divided into: (1) supported noble metal (Pt, Rh and Pd) catalysts; (2) transition metal (Ni, Co, Mn, Cu and Fe, etc.) oxides; (3) composite metal oxidation Catalysts, etc. Among them, supported noble metal catalysts are highly valued for their excellent catalytic oxidation activity, low light-off temperature and good anti-poisoning performance. The basic research in this field has a history of several decades, and a lot of meaningful research results have been obtained. At present, the research of supported noble metal catalysts in the catalytic oxidation of benzene (VOCs) is still the focus of research. Among the noble metal elements, Pd has attracted extensive attention due to its advantages such as relatively low price and good catalytic activity. At present, the focus of precious metal catalyst research is to reduce catalyst cost and improve catalyst stability. The more effective way is to reduce the particle size of precious metals to improve the utilization rate of precious metals and to introduce base metals to reduce the amount of precious metals and stabilize the active centers of precious metals.

The preparation of bimetallic alloys has been reported in the literature. For example: Liu Yuxi et al. used oleylamine as solvent, nickel acetylacetonate and gallium acetylacetonate as metal sources, and borane tert-butylamine as reducing agent, and co-reduced metal precursors in oleylamine system to obtain NiGa nanoalloys with narrow size distribution ( Yuxi Liu, Yadong Li, et al. Advanced Materials, 2016, 23(28):4747-4754). Bastian JMEtzold et al. used a liquid phase co-reduction method, using metal acetylacetonate as precursor, benzyl alcohol as solvent, and aniline as reducing agent to prepare bimetallic nanocrystals with narrow size distribution (M. Munozet al.Applied Catalysis B : Environmental, 2016, 192, 1–7). It has been reported in the literature that single-atom noble metal catalysts have been prepared and used for the catalytic oxidation of VOCs with good activity. Pengfei Xie et al. prepared a monoatomic dispersed Pt ₁ @CeO ₂ catalyst with good catalytic activity for the selective conversion of methanol (Pengfei Xie, et al. ACS Catalysis. 2018, 8, 4044-4048). Single-atom catalysts also showed good catalytic activity for benzene. For example, Yang Kuan et al. prepared single-atom dispersed Pt ₁ /Fe ₂ O ₃ and used it for the catalytic oxidation of benzene, showing good catalytic activity Kuan Yang, et al. Applied Catalysis B: Environmental, 2019, 244, 650-659). So far, no literature has reported the preparation method of Pd ₁ Co ₁ /Al ₂ O ₃ catalyst and its research on catalytic oxidation of benzene.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a Pd ₁ Co ₁ /Al ₂ O ₃ nano-catalyst for catalyzing benzene oxidation with high efficiency and a preparation method thereof, in particular to the preparation of PdCo nanocrystals by one-step pyrolysis method of oil phase, and the PdCo nanocrystals are supported by an impregnation method. onto a commercial Al ₂ O ₃ support, followed by firing to form Pd ₁ Co ₁ /Al ₂ O ₃ .

The single-atom palladium-cobalt bimetallic nano-catalyst for efficiently catalyzing benzene oxidation according to the present invention is characterized in that the Al ₂ O ₃ carrier is loaded with single-atom dispersed palladium and cobalt bimetallic catalysts formed by burning PdCo nanocrystals. Metal nanocatalysts are Pd ₁ Co ₁ /Al ₂ O ₃ catalysts.

The molar ratio of palladium and cobalt is 1:(3-7).

Preferably, the loading of palladium is 0.3-0.7%, and the loading of cobalt is 0.1-0.5%.

The above-mentioned PdCo bimetallic nanocrystals are characterized in that the prepared nanocrystals have a uniform size, and their preparation mainly includes the following steps:

(1) be 1:(3-7) feed intake according to the mol ratio of metal palladium and cobalt: take by weighing palladium acetylacetonate and dicobalt octacarbonyl, join in dichlorobenzene, stir 30min at room temperature under argon protection, be denoted as Solution A; weighed didodecylamine and tri-n-octylphosphine were added to dichlorobenzene, dissolved by heating and stirring in an argon atmosphere, and recorded as solution B; solution B was heated to 160 in an argon atmosphere -200°C for 10min, at this time, solution A was quickly injected into solution B; the temperature was raised to 210-230°C for 20min, then lowered to room temperature, and centrifuged to obtain PdCo bimetallic nanocrystals of uniform size; The particles are dispersed in cyclohexane for preservation;

Preferably every 0.05mmol of palladium acetylacetonate corresponds to 1.5-3mmol of double dodecylamine, 0.06-0.090g of tri-n-octylphosphine;

(2) The obtained PdCo bimetallic nanocrystals are supported on the Al ₂ O ₃ carrier by the impregnation method, and then undergo the hydrothermal roasting process to obtain the Pd ₁ Co ₁ /Al ₂ O ₃ nano-catalyst; the specific steps are as follows:

Calculate the required amount of PdCo-containing bimetallic solution according to a certain loading amount, add a certain amount of γ-Al ₂ O ₃ carrier to the measured cyclohexane solution containing bimetallic nanocrystals; stir and impregnate, and centrifuge to obtain a supported catalyst ; Load the obtained catalyst into a porcelain boat and place it in a tubular furnace for calcination, rise from room temperature to 750-850°C at a rate of 3-8°C/min, keep at this temperature for 2-4h, and cool down to obtain Pd ₁ Co ₁ /Al ₂ O ₃ catalyst, air containing 10vol% H ₂ O was passed through the whole calcination process.

During the calcination in step (2), the metal Pd or Co is lost, and the ablation amount can be supplemented according to the relationship between the amount of raw materials.

The catalyst obtained by the invention is applied to the catalytic oxidation of benzene, and carbon dioxide and water are finally obtained.

Under the reaction conditions of a benzene concentration of 1000 ppm, a benzene/oxygen molar ratio of 1/400 and a space velocity of 40000 mL/(g h), the catalyst T _50% (reaction temperature required for benzene conversion to reach 50%) and T _90% (reaction temperature required to reach 90% benzene conversion) were 220°C and 250°C, respectively.

The invention has the characteristics of uniform particle size of nano-particles, controllable size, simple preparation process and the like.

The Pd ₁ Co ₁ /Al ₂ O ₃ catalyst prepared by the invention has the characteristics that the bimetal is dispersed in a single atom and the single atom has good stability, and has a good application prospect in the field of catalysis.

The crystal structure, particle morphology and catalysis of benzene were determined by D8 ADVANCE X-ray diffractometer (XRD), JEOL-2010 transmission electron microscope (TEM) and Shimadzu GC-2014C gas chromatography (GC). oxidative activity. The results show that the samples prepared by the method of the present invention have good crystallinity, Pd single atoms and Co single atoms are highly dispersed on the surface of the carrier, and the catalytic oxidation activity of the bimetallic supported catalysts for benzene is compared. The pure palladium catalyst is significantly improved.

Description of drawings

Fig. 1 is the XRD patterns of the prepared Pd ₁ Co ₁ /Al ₂ O ₃ and Pd/Al ₂ O ₃ samples, in which curves (a) and (b) are the comparative samples Pd/Al ₂ O ₃ and the examples, respectively The XRD pattern of 1;

Figure 2 is a TEM photograph of the prepared PdCo nanocrystals and Pd ₁ Co ₁ /Al ₂ O ₃ samples, wherein (a) and (b) are the TEM photographs of PdCo particles and Example 1, respectively; wherein (b) The circles in the middle mark Pd single atoms;

Fig. 3 is the XAFs spectrum of the prepared Pd ₁ Co ₁ /Al ₂ O ₃ sample, in which (a) is the K3 edge XANES spectrum of Co, (b) is the EXAFS spectrum after Fourier transform, which is the same as that of Co. Comparing foil (metallic state, namely cobalt element) and CoO, the Pd ₁ Co ₁ /Al ₂ O ₃ sample reaches the peak of the existence of CoO bonds, indicating the formation of single atoms.

Figure 4 shows the activity curves of the prepared Pd ₁ Co ₁ /Al ₂ O ₃ and Pd/Al ₂ O ₃ samples for the oxidation of benzene.

Detailed ways

The present invention will be further described below in conjunction with the examples, but the present invention is not limited to the following examples.

Example 1

According to the mol ratio of metal palladium and cobalt, it is 1:10 feeding: take 0.05mmol of palladium acetylacetonate and 0.25mmol of dicobalt octacarbonyl, add in 5ml of dichlorobenzene, stir at room temperature for 30min under argon protection, and denote solution A . 2 mmol of didodecylamine and 0.075 g of tri-n-octylphosphine were weighed and added to 7.5 ml of dichlorobenzene, and dissolved under stirring at 110° C. in an argon atmosphere, which was designated as solution B. The solution B was heated to 180 °C for 10 min in an argon atmosphere, at which time the solution A was rapidly injected into the solution B. The temperature was raised to 200° C. for 20 min, then lowered to room temperature, and centrifuged to obtain PdCo bimetallic nanocrystals of uniform size. The nanoparticles obtained by centrifugation were dispersed in cyclohexane and stored.

The obtained PdCo bimetallic nanocrystals are supported on a carrier by an impregnation method, and then undergo a process of hydrothermal calcination to obtain a Pd ₁ Co ₁ /Al ₂ O ₃ nanocatalyst. Specific steps are as follows:

Calculate the required amount of PdCo-containing bimetallic solution according to a certain loading amount, and add a certain amount of γ-Al ₂ O ₃ carrier to the measured cyclohexane solution containing bimetallic nanocrystals. After stirring and immersing for 12 h, the supported catalyst was obtained by centrifugation. The obtained catalyst was loaded into a porcelain boat and placed in a tube furnace, raised from room temperature to 800°C at a rate of 5°C/min, kept at this temperature for 3 hours, and cooled to obtain a Pd ₁ Co ₁ /Al ₂ O ₃ catalyst , air containing 10vol% H ₂ O was passed through the whole roasting process. After loading, the total loading of bimetal was 0.6 wt%.

Under the reaction conditions of a benzene concentration of 1000 ppm, a benzene/oxygen molar ratio of 1/400 and a space velocity of 40000 mL/(g h), the catalyst T _50% (reaction temperature required for benzene conversion to reach 50%) and T _90% (reaction temperature required to reach 90% benzene conversion) were 220°C and 250°C, respectively.

The XRD patterns of the Pd ₁ Co ₁ /Al ₂ O ₃ samples prepared in the above examples are shown in Figure 1, wherein curves (a) and (b) are the XRD patterns of Pd/Al ₂ O ₃ and Example 1, respectively; The prepared TEM photo of Example 1 is shown in Figure 2, wherein Figure (a) is the PdCo metal particle, and (b) is the TEM photo of Example 1; the XAFs spectrum of the prepared Example 1 sample is shown in Figure 3 , the catalytic activity curves of the prepared Pd ₁ Co ₁ /Al ₂ O ₃ samples and Pd/Al ₂ O ₃ samples for methane oxidation are shown in Figure 4 .

Claims (3)

1. The application of the monatomic palladium-cobalt bimetallic nano-catalyst for efficiently catalyzing benzene oxidation is characterized in that the catalyst is as follows: in Al₂O₃The carrier is loaded with Pd which is a palladium-cobalt bimetallic monoatomic dispersed nano catalyst formed by PdCo nanocrystalline burning₁Co₁/Al₂O₃A catalyst; the catalyst is used for catalytic oxidation of benzene to finally obtain carbon dioxide and water;

the molar ratio of palladium to cobalt is 1: 10.

2. The application of the monatomic palladium-cobalt bimetallic nano-catalyst for efficiently catalyzing benzene oxidation according to claim 1, characterized in that the preparation method of the catalyst mainly comprises the following steps:

(1) feeding materials according to the molar ratio of metal palladium to cobalt of 1: 10: weighing palladium acetylacetonate and cobaltosic carbonyl, adding the palladium acetylacetonate and the cobaltosic carbonyl into dichlorobenzene, stirring the mixture for 30min at room temperature under the protection of argon, and marking the mixture as a solution A; adding the weighed didodecylamine and tri-n-octylphosphine into dichlorobenzene, heating and stirring the mixture to dissolve the didodecylamine and tri-n-octylphosphine in an argon atmosphere, and marking the solution B as a solution; heating the solution B to 160-200 ℃ in an argon atmosphere and keeping the temperature for 10min, and then quickly injecting the solution A into the solution B; heating to 210 ℃ and 230 ℃, preserving the temperature for 20min, cooling to room temperature, and performing centrifugal separation to obtain PdCo bimetallic nanocrystals with uniform size; dispersing the nano particles obtained by centrifugation into cyclohexane for storage;

(2) loading the obtained PdCo bimetal nanocrystalline to Al by adopting a dipping method₂O₃On a carrier, and then subjected to a roasting process to obtain Pd₁Co₁/Al₂O₃A nano-catalyst; the method comprises the following specific steps:

calculating the amount of the required PdCo-containing bimetallic solution according to a certain load amount, and adding a certain amount of gamma-Al₂O₃Adding a carrier into a weighed cyclohexane solution containing bimetallic nanocrystals; stirring, dipping and centrifuging to obtain a supported catalyst; loading the obtained catalyst into a porcelain boat, placing the porcelain boat in a tubular furnace for roasting, raising the temperature from room temperature to 750-850 ℃ at the speed of 3-8 ℃/min, keeping the temperature for 2-4h, and cooling to obtain Pd₁Co₁/Al₂O₃Catalyst is introduced into the furnace in the whole roasting process, and the catalyst contains 10 vol% of H₂O, air.

3. Use according to claim 2, characterized in that 1.5 to 3mmol of didodecylamine, 0.06 to 0.090g of tri-n-octylphosphine per 0.05mmol of palladium acetylacetonate.

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