CN106334587A - Method for preparing supported metal catalyst through cold plasma-alcohol synergetic reduction under atmospheric pressure - Google Patents

Abstract

The invention provides a method for preparing a supported metal catalyst through cold plasma-alcohol synergetic reduction under an atmospheric pressure. The method comprises the steps that an atmospheric pressure cold plasma is adopted, inert gas is used as working gas and carries alcohol steam, and a metal precursor obtained by adopting an impregnation method and supported on a carrier is reduced to prepare the supported metal catalyst. A plasma preparation method belongs to a dry preparation method, and the shortcoming that later-period drying of a wet-method process exists and metal nanoparticles can become large can be effectively avoided. In addition, the method does not need dangerous hydrogen, metal ion reduction is performed by utilizing the synergistic effect of the atmospheric pressure cold plasma and alcohol low in price and easy to obtain, and the method is a novel simple, rapid, safe and environmentally friendly supported metal catalyst preparation process. The preparation process can effectively solve the problem that the metal ion reduction cannot be achieved when inert gas discharge cold plasma electron energy is lower under the atmospheric pressure.

Description

A Supported Metal Catalyst Prepared by Cold Plasma-Alcohol Synergistic Reduction under Atmospheric Pressure agent method

technical field

The invention belongs to the field of preparation of supported metal catalysts, and in particular relates to a method for preparing a supported metal catalyst by atmospheric pressure cooling plasma.

Background technique

Supported metal catalysts have a wide range of applications in chemical engineering and environmental protection. The preparation method mainly includes impregnation-thermal reduction, chemical reduction, photoreduction and other methods. The impregnation-thermal reduction method has a simple operation process, is suitable for large-scale production, and has been widely used in the preparation of supported metal catalysts. However, it usually needs to be reduced in hydrogen for a long time, which tends to cause the metal particle size to become larger and the dispersion to be poor, resulting in its low activity. The chemical reduction method usually requires the use of excessive amounts of toxic and harmful chemical reagents such as sodium borohydride, formaldehyde, and hydrazine. Although metal nanoparticles with small particle size and good dispersion can be obtained, high-performance supported metal catalysts can be obtained. But its environment is not friendly, so it is limited in practical application. Photoreduction is a mild and high-performance method for preparing supported metal catalysts, but it requires high-intensity, long-term light and high energy consumption. In addition, the chemical reduction and photoreduction methods are both carried out in a liquid environment, and subsequent drying and other steps may easily cause the particle size of the metal nanoparticles to increase and the activity to deteriorate.

Plasma, also known as the fourth state of matter, is usually produced by gas discharge. It is composed of electrons (sometimes including electronegative ions) and positive ions with a certain degree of ionization, as well as a neutral ground state and an excited state. Composition of atoms and molecules. Cold plasma is an important plasma with high electron energy and low gas temperature. Cold plasma method is an effective method for preparing supported metal catalysts. Patent application CN200410093820.6 adopts low-temperature plasma, uses inert gas, air or oxygen as working gas, and utilizes electron reduction characteristics to prepare supported metal catalysts. The inventor pointed out that this process can be carried out between 50Pa～0.1MPa, and the reducible metal active components are "H ₂ PtCl ₆ , PdCl ₂ , Ni(NO ₃ ) ₂ , Au(NO ₃ ) ₂ , Cu(NO ₃ ) ₂ , Ag(NO ₃ ) ₂ , Fe(NO ₃ ) ₃ , Co(NO ₃ ) ₂ , Zn(NO ₃ ) ₃ , K ₂ CrO ₃ or one or more of ammonium molybdate”. It is indeed feasible in principle to use atmospheric pressure-cooled plasma, use inert gas as the working gas, and use high-energy electrons to reduce metal ions. However, due to the high density of gas under atmospheric pressure, the increase of collisions, and the low energy of electrons, there have been no reports on the preparation of supported metal catalysts by electron reduction using atmospheric pressure-cooled plasma and inert gas as the working gas. The example of this patent is also the preparation of Pt/TiO ₂ by cold plasma reduction under low pressure. Furthermore, Liu et al. (Changjun Liu, Minyue Li, Jiaqi Wang, Xintong Zhou, Qiuting Guo, Jinmao Yan, Yingzhi Li. Chinese Journal of Catalysis 37(2016) 340-348.) pointed out that electrons can only reduce metals with positive electrode potential ions, and for metal ions with negative electrode potential, such as Ni ²⁺ /Ni(E ^θ =-0.257V), Fe ^{3 +} /Fe(E ^θ =-0.037V), Co ²⁺ /Co(E ^θ = -0.28V), Zn ²⁺ /Zn (E ^θ =-0.7618V), cannot be restored.

In order to solve the problem of low electron energy and the inability to reduce metal ions under atmospheric pressure, researchers have done a lot of related research. Patent application CN200910304664.6 adopts low-temperature plasma, uses hydrogen as the working gas, reduces metal ions under atmospheric pressure, prepares catalyst carrier and metal active components at the same time, and obtains a supported metal catalyst. The embodiment of the invention proves that the method can be reduced to prepare a supported Ni catalyst. In addition, other related reports have also confirmed that supported noble metal catalysts, as well as supported non-noble metal catalysts such as Ni and Co, can be prepared by reduction using cold plasma containing hydrogen. These studies demonstrate that hydrogen-containing cold plasmas are indeed an efficient method for the reduction of metal ions at atmospheric pressure, leading to high-performance supported metal catalysts. However, these processes require the use of hydrogen. Although hydrogen is a clean energy source, it is flammable and explosive, posing safety hazards.

The present invention adopts atmospheric pressure cooling plasma, uses inert gas as the working gas, and uses it to carry alcohol vapor, and under the synergistic effect of atmospheric pressure cooling plasma and alcohol, utilizes various hydrogen-containing active species produced by alcohol in the cold plasma, to The impregnation method obtains the metal precursor loaded on the carrier for reduction to prepare the supported metal catalyst. The method can prepare supported metal catalysts simply, quickly, safely and environmentally friendly.

Contents of the invention

In order to overcome the existing atmospheric pressure cooling plasma, it is unsafe to use hydrogen as the working gas, and use inert gas as the working gas, the electron energy is low, and the shortcomings and deficiencies that cannot restore metal ions, the primary purpose of the present invention is to provide a simple, A fast, safe and environmentally friendly preparation method for supported metal catalysts.

The technical scheme adopted in the present invention is as follows: using atmospheric pressure cooling plasma, using inert gas as the working gas and carrying alcohol vapor, under the synergistic effect of atmospheric pressure cooling plasma and alcohol, a variety of hydrogen-containing active species are produced, and the impregnation method obtains a load The metal precursor on the carrier is reduced to obtain a supported metal catalyst.

The concrete steps of this method are:

(1) Weigh an appropriate amount of metal precursor in a beaker, add a certain amount of deionized water, and prepare a metal precursor salt solution with a certain concentration;

(2) Using the impregnation method, put a certain amount of carrier into the metal precursor salt solution, let it stand, and dry to obtain the metal precursor loaded on the carrier;

(3) Put the metal precursor loaded on the carrier into the plasma reactor, use the inert gas as the working gas, and carry the alcohol vapor into the plasma reactor. A cold plasma is generated under atmospheric pressure, and under the plasma-alcohol synergistic effect, the metal precursor supported on the carrier is reduced to obtain a supported metal catalyst.

Wherein, the metal precursor is a monometallic component, a bimetallic component or a multimetallic component;

The alcohol in the alcohol vapor is one or more of methanol, ethanol, propanol and ethylene glycol;

Described working gas is a kind of or its mixed gas in argon, nitrogen, helium;

The temperature of the cold plasma discharge gas does not exceed 90°C without additional heating.

Further, the carrier is one of titanium dioxide, silicon dioxide, alumina, molecular sieve, metal-organic framework, graphene, activated carbon, activated carbon fiber, iron oxide or cerium oxide.

Further, the atmospheric pressure cold plasma is one of atmospheric pressure dielectric barrier discharge cold plasma, atmospheric pressure radio frequency discharge cold plasma, atmospheric pressure glow discharge cold plasma, and atmospheric pressure direct current discharge cold plasma.

Further, the electron energy of the atmospheric pressure-cooled plasma is not enough to directly reduce the loaded metal ions.

Further, the metal precursor salt is one or more of palladium chloride, palladium nitrate, chloroplatinic acid, chloroauric acid, silver nitrate, copper nitrate, copper chloride, nickel nitrate or cobalt nitrate. Palladium nitrate and copper nitrate are preferred.

Further, the cold plasma discharge voltage is 0.1kV-40kV.

Further, the cold plasma treatment time is 2-30 minutes.

Further, the mass fraction of the metal precursor loaded on the carrier is 0.01%-60%.

Compared with prior art, the advantage of the inventive method is:

The invention provides a simple, rapid, safe and environment-friendly preparation method of a supported metal catalyst. The method effectively overcomes the disadvantages and deficiencies of the existing methods, such as the low electron energy of the cold plasma discharged by the inert gas under atmospheric pressure, and the inability to reduce metal ions. Problems such as the enlargement of metal nanoparticles. Under the synergistic effect of atmospheric pressure cooling plasma-alcohol, the present invention uses various hydrogen-containing active species produced by alcohol in the cold plasma to reduce the metal precursor loaded on the carrier obtained by the impregnation method, without using Hydrogen can be used to prepare supported metal catalysts.

Description of drawings

Fig. 1 is the photo of supported catalyst Pd/ _TiO2 prepared by different methods; wherein (a) is the 2wt% Pd/ _TiO2 sample before treatment; (b) is the use of atmospheric pressure cooling plasma, with argon as the working gas Preparation of 2wt% Pd/TiO ₂ samples by ethanol vapor; (c) using atmospheric pressure cooled plasma, using argon as the working gas, carrying ethanol vapor to prepare 2wt% Pd/TiO ₂ samples; (d) not using cold plasma , directly carried ethanol vapor with argon, and treated at 80 °C for 9 min to obtain photos of 2wt% Pd/TiO ₂ samples.

Fig. 2 is the 2wt%Pd/ _TiO2 sample XRD spectrogram prepared by different methods; Wherein, (a) adopts atmospheric pressure cooling plasma, uses argon as working gas, does not carry ethanol vapor (b) carries ethanol vapor, prepares 2wt respectively The XRD spectrum of the %Pd/TiO ₂ sample, (c) the XRD spectrum of the 2wt% Pd/TiO ₂ sample was obtained by using argon to carry ethanol vapor at 80°C for 9 minutes.

Figure 3 is a photo of supported catalyst Cu/ _TiO2 prepared by different methods; among them, (a) 2wt% Cu/ _TiO2 sample is processed before, and adopts atmospheric pressure cooling plasma, with argon as the working gas, (b) does not carry Photographs of 2wt% Cu/ _TiO2 samples prepared with ethanol vapor or (c) carrying ethanol vapor, respectively.

Fig. 4 is the XRD spectrum of 2wt% Cu/TiO ₂ samples prepared by atmospheric pressure cooling plasma, using argon as the working gas, without ethanol vapor or with ethanol vapor, respectively.

detailed description

The technical solutions of the present invention will be further described below in conjunction with specific examples, but the present invention is not limited by the content of the examples in any form. Unless otherwise specified, the test methods described in the examples are conventional methods; unless otherwise specified, the reagents and biological materials can be obtained from commercial sources.

Example 1

Using palladium nitrate as the precursor, the precursor of 2wt% Pd/TiO ₂ was prepared by impregnation method, left standing, and dried.

Put 0.3 g of the above precursor into a dielectric barrier discharge cold plasma reactor, pass in argon gas (100ml·min ^-1 ), adjust the discharge frequency to 15kHz, the peak-to-peak sinusoidal AC discharge voltage to 10kV, and the discharge gap to 2mm, under the condition of atmospheric pressure, the precursor of 2wt%Pd/TiO ₂ was treated, each treatment time was 3min, and the interval was 8min, and the treatment was 3 times in total to obtain 2wt%Pd/TiO ₂ samples. The cold plasma discharge gas temperature does not exceed 80°C without additional heating.

The photo and X-ray diffraction pattern of the sample of Example 1 are shown in Fig. 1 and Fig. 2 respectively.

The photo of the sample of Example 1 shown in Fig. 1 shows: use argon as the working gas to generate plasma, and under the situation of not carrying alcohol vapor, the precursor of _2wt %Pd/TiO is processed, and the color of the sample does not change, which is preliminary Indicates that Pd ions have not been reduced;

The X-ray diffraction pattern of the sample of Example 1 shown in Figure 2 shows: use argon as the working gas to generate plasma, without carrying alcohol vapor, the precursor of 2wt%Pd/ _TiO2 is processed, there is no Pd metal element produce.

Example 2

Basically the same as in Example 1, argon carries ethanol placed at room temperature in the form of bubbling, and treats the precursor of 2wt% Pd/TiO ₂ . The treatment time is 3 minutes each time, and the middle interval is 8 minutes. , to obtain a 2wt% Pd/ _TiO2 sample. The cold plasma discharge gas temperature does not exceed 80°C without additional heating.

The photos and X-ray diffraction patterns of the sample in Example 2 are shown in Fig. 1 and Fig. 2 respectively.

The photos of the sample of Example 2 shown in Fig. 1 show that: with argon as the working gas to generate plasma, under the condition of carrying ethanol vapor, the precursor of 2wt%Pd/ _TiO2 is processed, and the color of the sample changes obviously, which is preliminary Indicates that Pd ions are reduced;

The X-ray diffraction pattern of the sample of Example 2 shown in Fig. 2 shows: use argon as the working gas to generate plasma, under the situation of carrying ethanol vapor, the precursor of 2wt%Pd/TiO ₂ is processed, there is obvious Pd metal Elemental production. This shows that the atmospheric pressure-cooled plasma-alcohol synergistic effect can effectively overcome the shortcomings of the existing atmospheric pressure-cooled plasma, which uses inert gas as the working gas, has low electron energy, and cannot reduce metal ions.

Example 3

The difference from Example 2 is that no cold plasma is applied, argon gas carries ethanol vapor at room temperature in the form of bubbling, and at 80°C, the precursor of 2wt% Pd/TiO ₂ is treated, co-processing After 9 minutes, a 2wt% Pd/TiO ₂ sample was obtained.

The photo and X-ray diffraction pattern of the sample of Example 3 are shown in Fig. 1 and Fig. 2 respectively.

The photo of the sample of Example 3 shown in Figure 1 shows that: the precursor of 2wt% Pd/TiO ₂ is treated at 80°C with argon carrying ethanol vapor, and the color of the sample does not change, which preliminarily indicates that only alcohol vapor is used Cannot reduce Pd ions;

The X-ray diffraction pattern of the sample of Example 3 shown in FIG. 2 shows that: the precursor of 2wt% Pd/TiO ₂ is treated at 80° C. with argon carrying ethanol vapor, and no metal Pd element is produced.

Example 4

Using copper nitrate as the precursor, the precursor of 2wt% Cu/TiO ₂ was prepared by impregnation method, left to stand, and dried.

Put 0.3 g of the above precursor into a dielectric barrier discharge cold plasma reactor, pass in argon gas (100ml·min ^-1 ), adjust the discharge frequency to 15kHz, the peak-to-peak sinusoidal AC discharge voltage to 10kV, and the discharge gap to 2mm, under the condition of atmospheric pressure, the precursor of 2wt%Pd/TiO ₂ was treated, each treatment time was 3min, and the interval was 8min, and the treatment was 3 times in total to obtain 2wt%Pd/TiO ₂ samples. The cold plasma discharge gas temperature does not exceed 80°C without additional heating.

The photo and X-ray diffraction pattern of the sample of Example 4 are shown in Fig. 3 and Fig. 4 respectively.

The photos of the sample of Example 4 shown in Fig. 4 show that: using argon as the working gas to generate plasma, without carrying alcohol vapor, the precursor of _2wt % Cu/TiO is processed, and the color of the sample does not change, which is preliminary Indicates that Cu ions have not been reduced;

The X-ray diffraction pattern of the sample of Example 4 shown in Figure 4 shows: use argon as the working gas to generate plasma, without alcohol vapor, the precursor of _2wt % Cu/TiO is processed, and there is no Cu metal element produce.

Example 5

Basically the same as in Example 4, argon carries ethanol placed at room temperature in the form of bubbling, and treats the precursor of 2wt% Cu/TiO ₂ , each treatment time is 3 minutes, with an interval of 8 minutes in between, and a total of 3 treatments , to obtain a 2wt% Cu/ _TiO2 sample. The cold plasma discharge gas temperature does not exceed 80°C without additional heating.

The photo and X-ray diffraction pattern of the sample of Example 5 are shown in Fig. 3 and Fig. 4 respectively.

The photos of the sample of Example 5 shown in Fig. 3 show that: using argon as the working gas to generate plasma, carrying ethanol vapor, the precursor of 2wt%Cu/ _TiO2 is processed, and the color of the sample changes significantly, which is preliminary Indicates that Cu ions are reduced;

The X-ray diffraction pattern of the sample of Example 5 shown in Fig. 4 shows: use argon as the working gas to generate plasma, under the situation of carrying ethanol vapor, the precursor of 2wt% Cu/TiO ₂ is processed, there is obvious Cu metal Elemental production. This further shows that the atmospheric pressure-cooled plasma-alcohol synergy can effectively overcome the shortcomings of the existing atmospheric pressure-cooled plasma, which uses inert gas as the working gas, has low electron energy, and cannot reduce metal ions.

Claims (9)

1. under a kind of atmospheric pressure cold plasma -ol collaborative SCM prepare load type metal catalyst method it is characterised in that Using atmosphere cold plasma, with inert gas as working gas and carry alcohol steam, infusion process is obtained and is carried on carrier On metal precursor carry out reduction and prepare load type metal catalyst.

2. under a kind of atmospheric pressure according to claim 1, cold plasma -ol collaborative SCM prepares load type metal catalysis The method of agent is it is characterised in that the method concretely comprises the following steps:

(1) weigh appropriate metal precursor in beaker, add deionized water, be configured to metal precursor salting liquid；

(2) adopt infusion process, carrier is put into metal precursor salting liquid, standing, it is dried, obtain the metal being carried on carrier Presoma；

(3) metal precursor being carried on carrier is put in plasma reactor, with inert gas as working gas, take Band alcohol steam enters plasma reactor, produces cold plasma under atmospheric pressure, under plasma -ol synergy, The metal precursor being carried on carrier is reduced, obtains load type metal catalyst；

Described metal precursor is monometallic component, bimetallic component or many metal components；

In described alcohol steam, alcohol is one or more of methyl alcohol, ethanol, propyl alcohol and ethylene glycol；

Described working gas is one of argon gas, nitrogen, helium or its mixed gas；

Described cold plasma discharge gas temperature is less than 90 DEG C, no extra heating.

3. under a kind of atmospheric pressure according to claim 1, cold plasma -ol collaborative SCM prepares load type metal catalysis The method of agent is it is characterised in that described carrier is titanium dioxide, silica, aluminum oxide, molecular sieve, metallic organic framework material A kind of in material, Graphene, activated carbon, NACF, iron oxide or cerium oxide.

4. under a kind of atmospheric pressure according to claim 1, cold plasma -ol collaborative SCM prepares load type metal catalysis The method of agent is it is characterised in that described atmosphere cold plasma is atmospheric dielectric barrier discharge cold plasma, atmospheric pressure One of radio-frequency glow discharge plasmas, Atomospheric pressure glow discharge cold plasma, atmospheric pressure direct-current discharge cold plasma.

5. under a kind of atmospheric pressure according to claim 1, cold plasma -ol collaborative SCM prepares load type metal catalysis The method of agent it is characterised in that the atmosphere cold plasma electron energy that adopts be not enough to be reduced directly the metal of load from Son.

6. under a kind of atmospheric pressure according to claim 1, cold plasma -ol collaborative SCM prepares load type metal catalysis The method of agent is it is characterised in that described metal precursor is palladium bichloride, palladium nitrate, chloroplatinic acid, gold chloride, silver nitrate, nitric acid One or more of copper, copper chloride, nickel nitrate or cobalt nitrate.

7. under a kind of atmospheric pressure according to claim 1, cold plasma -ol collaborative SCM prepares load type metal catalysis The method of agent is it is characterised in that described cold plasma discharge voltage is 0.1kv～40kv.

8. under a kind of atmospheric pressure according to claim 1, cold plasma -ol collaborative SCM prepares load type metal catalysis The method of agent is it is characterised in that described cold plasma process time is 2-30 minute.

9. under a kind of atmospheric pressure according to claim 1, cold plasma -ol collaborative SCM prepares load type metal catalysis The method of agent is it is characterised in that the mass fraction being carried on the metal precursor on carrier is 0.01%-60%.