CN111111665A

CN111111665A - Supported metal catalyst and preparation method thereof

Info

Publication number: CN111111665A
Application number: CN201911406857.2A
Authority: CN
Inventors: 李兴发; 胡浩栋
Original assignee: Taiyuan University of Technology
Current assignee: Taiyuan University of Technology
Priority date: 2019-12-31
Filing date: 2019-12-31
Publication date: 2020-05-08

Abstract

The invention discloses a supported metal catalyst and a preparation method thereof, and the supported metal catalyst comprises the following steps: mixing a metal ion solution with a pre-prepared buffer solution, adding a carrier, carrying out a soaking reaction for 0.5-24h under a heating condition, dripping alkali liquor into the mixture during the reaction, filtering, washing and drying the mixture after the reaction is finished, and then roasting the mixture under the atmosphere conditions of air, pure oxygen, nitrogen, hydrogen or combined gas to obtain the supported metal catalyst.

Description

Supported metal catalyst and preparation method thereof

Technical Field

The invention relates to the technical field of catalyst materials, in particular to a supported metal catalyst and a preparation method thereof.

Background

The supported metal catalyst has a wide range of applications, ranging from the production of fine chemicals to the treatment of industrial wastewater, and has many advantages over conventional homogeneous and bulk catalysts, in that the supported metal catalyst is formed by immobilizing a metal or metal oxide on a carrier. First, the metal can be highly dispersed on the surface of the support, both to reduce the amount of metal used and to highly disperse the active component formed by the metal. Secondly, the catalyst is easy to separate from the liquid phase reaction system, and is convenient to recover or reuse. Thirdly, some carriers have Lewis acidity or alkalinity which can act in coordination with metal active components on the carriers, thereby improving the reaction efficiency. A large number of researches show that the form and the dispersion state of the metal active component on the carrier have great influence on the activity of the catalyst, and the metal catalytic reaction mainly occurs on active sites taking metal as the center, so that the more uniform the metal active component is, the better the dispersion is, and the stronger the catalytic activity is.

In recent years, much research has been focused on the preparation of catalysts and the search for methods for preparing them, and among the existing methods for preparing supported metal catalysts, the impregnation method is the simplest and most common method, and when the volume of the solution exceeds that of the support, the preparation method is called wet impregnation, by which the active component is relatively uniform, but since the excess solution must be discarded after the impregnation is completed, the metal loading cannot be predetermined. The method of mixed impregnation of an equal volume of solution and a carrier is called dry impregnation or equal volume impregnation, and the metal loading can be predetermined according to the mass of the carrier, but since the amount of the solution is only enough to wet the carrier and fill the pores in the carrier, the metal ions in the solution are difficult to migrate, and therefore the metal ions are deposited and agglomerated after the solvent is rapidly volatilized. In addition, precipitation of metal ions in alkaline solutions is a more common impregnation method, but the rapid reaction between metal ions and hydroxide ions is also prone to nucleation too fast, resulting in agglomeration of the active components. Therefore, there is an urgent need to develop a preparation method, which has an important meaning in precisely controlling the formation of the active ingredient at a predetermined loading amount.

Disclosure of Invention

The present invention aims at providing a preparation method of a supported metal catalyst. The advanced oxidation catalyst prepared by the method has good degradation effect on organic pollutants, high mineralization degree and wide application range, and the preparation method has simple and easy operation process, low process cost and wide application range and can realize industrial production.

In order to achieve the purpose, the invention adopts the technical scheme that:

a preparation method of a supported metal catalyst comprises the following steps: mixing a metal ion solution and a pre-prepared buffer solution to obtain an intermediate 1, adding a carrier into the intermediate 1, wherein the mass percentage of metal ions in the metal ion solution to the carrier is less than 50%, carrying out a soaking reaction for 0.5-24h under an oil bath heating condition with the heating temperature of 25-100 ℃, dripping alkali liquor during the reaction period, the amount of the alkali liquor is determined according to the amount of metal required to be precipitated in the metal ion solution, filtering, washing and drying after the reaction is finished to obtain an intermediate 2, roasting the intermediate 2 under the atmosphere of air, pure oxygen, nitrogen, hydrogen or a combined gas to obtain a supported metal catalyst, wherein the roasting temperature is not higher than 900 ℃, and the roasting time is not more than 6 h.

Further, the pH of the buffer solution must be greater than the pH required for complete precipitation of the metal in the metal ion solution, and the composition of the buffer solution is preferably selected to be completely volatile under the calcination conditions.

Further, the mixing of the metal ion solution and the pre-prepared buffer solution specifically comprises: the metal ion solution is dissolved in the buffer solution, or the metal ion solution and the buffer solution are uniformly mixed.

Further, the dropping of alkali liquor during the reaction period is specifically as follows: and dropwise and slowly adding the alkali liquor into the impregnation reaction system, or adding the alkali liquor into the impregnation reaction system in an excessive manner at one time.

Further, the metal species in the metal ion solution depends on the type of metal required for the catalytic reaction to participate later, for example, iron is commonly used as an active metal in fenton reaction, and cobalt is used as an active metal in persulfate catalytic reaction.

Further, the mass percentage of the metal ions in the metal ion solution to the carrier is 5-10%.

Further, the heating temperature of the oil bath is 70-90 ℃, and the time of the impregnation reaction is 1-3 h.

Further, roasting the intermediate 2 in air for 1-3h to obtain the supported metal catalyst, wherein the roasting temperature is 400-600 ℃.

The invention also provides a supported metal catalyst which is prepared by the preparation method of any one of the technical schemes. For example, in the preparation of the supported metal catalyst, cobalt is used as an active metal, silica is used as a carrier, glycine/sodium hydroxide is used as a buffer solution, the pH of the buffer solution is controlled to be 11.0, and 10mL of sodium hydroxide is added dropwise. The sample was calcined in a muffle furnace at 500 ℃ for 5 h under air conditions.

The invention also provides an application of the supported metal catalyst in degrading organic pollutants in wastewater, and the supported metal catalyst is prepared by the preparation method of the supported metal catalyst according to any technical scheme. For example, organic wastewater is adjusted to a certain pH value, and a catalyst and an oxidant are added for reaction, wherein the concentration of organic pollutant phenol in the wastewater is 10mg/L, the use amount of the catalyst is 0.2 g/L, the concentration of the oxidant peroxymonosulfate is 0.7 g/L, and the degradation time of the wastewater is 1 h.

The invention has the beneficial effects that:

in the invention, the pH is controlled by adopting a buffer solution, the amount of alkali consumed by adding the reaction maintains the pH of the solution not to fluctuate greatly, the alkali required by the precipitation of metal ions is slowly released from the buffer solution during the reaction, and the metal ions and hydroxyl ions (OH)⁻) The dipping and precipitation reaction is slowly and orderly carried out, and the nano particles grow orderly, thereby forming the active component with good dispersibility. Taking the emerging persulfate reaction as an example, Co is the most common active component element, and Co is loaded when a Co component is loaded²⁺With OH in solution⁻Formation of Co (OH)₂Precipitating, then dehydrating, drying and roasting to form the Co catalyst. According to Co²⁺Reaction taking place in solution:

Co²⁺+ 2H₂O ⇌ Co(OH)₂+ 2H⁺（1）

H₂O ⇌ H⁺+ OH⁻（2）

can be obtained by the reactions (1) and (2),

𝐾aP= [Co²⁺(aq)][OH⁻(aq)]²（3）

Co²⁺hydrolysis began at a pH of 7.7 to form a precipitate. If when Co is used²⁺Is less than 1X 10^-6The precipitation was considered complete at mM, when the pH of the solution was due to Co²⁺To 9.8. In fact, if all Co is present²⁺Are precipitated and the pH drops rapidly because about 34.0 mM OH is present during the reaction⁻Will be consumed. Therefore, if Co is to be used²⁺The precipitation is complete and the pH of the buffer solution does not fluctuate greatly during the reaction, the pH of the buffer solution must be higher than 9.8 and OH must be added⁻To slow the impact on the buffer solution.

Because the impregnation method generally hydrolyzes the metal and then forms a precipitate or colloid, and then the metal is calcined under high-temperature aerobic conditions to form the oxide active component. According to the solubility product principle, if the pH value of the metal during hydrolysis can be controlled, the metal precipitation speed can be controlled, so that the precipitation under the condition of controlling the pH value by using a buffer solution is a feasible method. Meanwhile, due to the wide application of advanced oxidation technology, and the advanced oxidation reactions such as ozone catalytic oxidation, fenton oxidation, photocatalytic oxidation and emerging persulfate oxidation all adopt a large amount of supported catalysts to degrade pollutants, the field also urgently needs an efficient supported catalyst preparation method to obtain excellent active components, so that the advanced oxidation technology is firstly applied to the aspect of advanced oxidation after the innovative theory is provided.

Compared with the prior art, the method utilizes the buffer solution to control the pH value of the reaction, so that the metal loading is carried out orderly, the uniformity of the loading is ensured, and the agglomeration of nano particles is prevented; alkali liquor which is consumed by compensating metal precipitation is dripped by the alkali liquor, so that the reaction is complete, and the influence of alkali consumed by the reaction on the buffer solution is avoided; the metal load can reach the preset load capacity, so that the load capacity and the load proportion can be controlled in advance; the preparation method is simple, has wide application range and has good application prospect.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments of the present invention will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.

FIG. 1 is a scanning electron microscope and a transmission electron microscope image of a supported metal catalyst prepared in example 1 and a sample in comparative example 1;

FIG. 2 is a full spectrum and a spectrum of X-ray photoelectron spectroscopy of the supported metal catalyst prepared in example 1;

FIG. 3 is a graph showing the results of phenol degradation by the supported metal catalyst prepared in example 1;

FIG. 4 is a graph of total organic carbon removal for phenol for the supported metal catalyst prepared in example 1 and comparative example 1;

FIG. 5 is a graph of the effect of impregnation temperature on the activity of a supported metal catalyst;

FIG. 6 is a graph of the effect of impregnation time on the activity of a supported metal catalyst;

FIG. 7 is a graph of the effect of buffer solution pH on the activity of a supported metal catalyst;

FIG. 8 is a graph showing the effect of the volume of the alkali solution added to the activity of the supported metal catalyst;

FIG. 9 is a graph showing the degradation result of the supported metal catalyst prepared in example 1 on rhodamine B;

FIG. 10 is a graph showing the results of phenol degradation by the supported metal catalyst prepared in example 2;

FIG. 11 is a graph showing the results of phenol degradation by the supported metal catalyst prepared in example 3.

Detailed Description

The following describes embodiments of the present invention in further detail through a description of examples. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Preparation of the supported metal catalyst:

mixing a metal ion solution containing 0.05g of metal with 50 mL of glycine buffer solution according to data in Table 1, then adding 0.5 g of carrier, heating and stirring in an oil bath kettle after ultrasonic dispersion, simultaneously starting dropwise adding 0.1mol/L of sodium hydroxide solution, standing and aging for 2 h after reaction, then filtering and washing with ultrapure water, drying the obtained solid in an oven at 120 ℃, and then placing in a muffle furnace or a tubular furnace for roasting to obtain the final supported metal catalyst. As a control experiment, corresponding samples were prepared with an aqueous solution of the same pH instead of the buffer solution.

TABLE 1 preparation of Supported Metal catalysts test parameters

Characterization of the supported metal catalyst:

(1) surface morphology of supported metal catalyst

In order to clearly observe the surface morphology of the active ingredient, the surface of the supported metal catalyst was observed using a Scanning Electron Microscope (SEM) and a Transmission Electron Microscope (TEM). As can be seen from fig. 1a and 1c, the supported metal catalyst prepared in example 1 has a uniform and flat surface, while the control sample, comparative example 1, has seen a large mass of agglomerated matter on the sample (fig. 1b and 1 d), indicating that the uniform supported metal catalyst was successfully prepared by the buffer solution route.

(2) Chemical composition of active ingredient

The chemical composition of the loaded active component is identified by X-ray photoelectron spectrometer (XPS), the result is shown in FIG. 2, and it can be seen from FIG. 2a that the XPS full spectrum contains SiO carrier₂Besides the Si and O elements, a distinct Co 2p peak was also detected, confirming the successful loading of metallic Co. Meanwhile, NO N1 s peak is observed in the whole spectrum, which indicates that Co is a precursor of Co (NO)₃)₂And the buffer solution component glycine is completely decomposed after calcination, and thus there is no residue of the cobalt amine complex. The Co 2p spectrum (FIG. 2 b) shows absorption peaks at 781.1 and 796.8 eV, corresponding to Co 2p3/2 and Co 2p1/2, respectively. Furthermore, satellite peak binding energies at approximately 6 eV above the main peak for Co 2p at 787.6 and 803.3 eV, respectively, suggest that Co²⁺And Co³⁺Simultaneously exist. Meanwhile, the difference of the binding energy between Co 2p3/2 and Co 2p1/2 is calculated to be 15.7 eV, and the difference is also calculated to be Co 2p3/2 and Co 2p1/2₃O₄Consistently, these results indicate that the Co species on the catalyst are Co₃O₄Exist in the form of (1).

And (3) testing the performance of the supported metal catalyst:

the catalytic degradation experiments were performed in 150 mL erlenmeyer flasks, and a typical reaction system contained 0.2 g/L catalyst, 10mg/L model contaminant phenol concentration, 100 mL solution volume, pH = 7, PMS 0.7 g/L. The reaction solution was sealed and placed in an incubator and the reaction was carried out at 25 ℃ with shaking at 120 rpm. After a certain time interval, 1 mL of the reaction mixture was taken out and 0.5 mL of methanol was added, and the catalyst was removed by filtration through a 0.22 μm membrane and measured by high performance liquid chromatography at 210 nm. Chromatographic conditions are as follows: 25 ℃, C18 column, methanol: water = 70: 30.

catalytic degradation example 1: confirmation of catalytic Activity

Since many industrial wastewater discharges a large amount of phenol substances, such as coal chemical wastewater, paper-making wastewater, pesticide wastewater, medical wastewater and the like, and phenol is a difficultly biodegradable substance, phenol is the most common model pollutant in advanced oxidation reactions. In addition, the determination of phenol and degradation products have been studied very clearly, so to evaluate the activity of the catalysts prepared in this study, we chose phenol as the model contaminant and carried out the degradation experiment using the catalyst prepared in example 1, taking samples at intervals of 10 min until the time was 1 h. As can be seen from FIG. 3, under the condition of adding Peroxymonosulfate (PMS) as an oxidant, the catalyst has extremely high catalytic removal effect on phenol, which reaches more than 95% within 1 h, while the adsorption under the same condition is only about 2.3%, and meanwhile, under the condition of no catalyst, the degradation caused by the oxidant PMS is 4.3%, which shows that the removal of phenol is completely caused by the degradation of PMS activated by the catalyst.

To confirm that the activity of the catalyst is related to the use of the buffer solution, we prepared sample comparative example 1 by replacing the buffer solution with an aqueous solution during impregnation. As can be seen from fig. 3, the removal rate of phenol in comparative example 1 is significantly lower than that in example 1 under the same conditions. Considering that the composition of the buffer solution contained the organic substance glycine, in order to exclude the interference of glycine, we prepared sample comparative example 2 by replacing the buffer solution with a glycine solution (pH-unadjusted). Figure 3 shows that comparative example 2 only achieves 31.1% phenol removal, indicating that the glycine component alone is not effective in promoting the increase in catalytic activity, again demonstrating the effectiveness of the buffer solution.

Catalytic degradation example 2: demonstration of mineralization Capacity

In advanced oxidation reactions, the mineralization ability is also one of the important factors for evaluating catalytic oxidation performance. Mineralization capacity is generally expressed in terms of Total Organic Carbon (TOC) removal, as a decrease in TOC can indicate a process in which phenol is ring-opened and cleaved to form small molecule acids followed by formation of carbon dioxide and water, inorganic salts, and the like. Due to the TOC test principle, too low an organic concentration, e.g. 10mg/L, is very inaccurate and 100 mg/L phenol is used here in order to test the mineralization ability of the catalyst. As shown in fig. 4, the TOC removal rate for phenol was as high as 68.2% in 2 hours for example 1, while the sample prepared in comparative example 1 reached only 33.6% under the same conditions. This result not only indicates that phenol is mostly mineralized under catalysis, but also confirms the superiority of the buffer solution method.

Catalytic degradation example 3: effect of impregnation parameters on catalyst Activity

In the preparation of the Supported advanced Oxidation catalyst example 1 by the buffer solution method, SiO₂Impregnated in Co²⁺In solution. Because the dipping process is a chemical reaction process, the dipping temperature, the dipping time and the pH value of the buffer solution are all the same to Co (OH)₂Has a crucial role in the formation of and the subsequent formation of Co active components, which ultimately affect the activity of the catalyst. The catalytic removal of phenol by impregnation temperature is shown in fig. 5, and the optimal reaction temperature is 80 ℃ because the temperature is too low, the reaction rate is too slow, the impregnation is incomplete, and the activity is low, however, too high temperature means violent brownian motion, the solubility of the precipitate is increased, and the metal ions are difficult to precipitate.

Reaction time vs. catalyst activity as shown in fig. 6, as the impregnation time was slowly increased from 0.5 h to 12 h, it was found that too short a time, e.g. 0.5 h, and too long a time, e.g. 12 h, were detrimental to the formation of active components, with an optimal impregnation reaction time of 2 h. This phenomenon indicates that the amount of active component formed during the immersion time is small and the catalytic reaction is not efficiently carried out, while the precipitate formed immediately after the immersion time is excessively long and the precipitate is broken under stirring. Therefore, the impregnation reaction time is preferably 2 hours.

Since the pH of the solution during the reaction is controlled by the buffer solution, the pH of the buffer solution has a significant influence on the formation of the active component. The pH of the buffer solution is not exclusive as long as the buffer solution system is kept stable. As shown in fig. 7, the buffer solution system contributed to the preparation of the high activity supported catalyst as the pH of the buffer solution increased from 10.0 to 12.0, resulting in a catalyst with higher catalytic activity than the samples prepared under the same pH aqueous solution conditions. On the other hand, the catalytic removal rate of phenol increases and then decreases with increasing pH, because at lower pH values the precipitation rate is slower and incomplete over time, whereas at higher pH values the nucleation rate is significantly faster and the nanoparticles produced tend to agglomerate, so that the pH of the buffer solution is preferably controlled to around 11.0. The effect of a solution pH above 12.0 was not investigated, as it was reported that too high a pH easily caused dissolution of the carrier silica.

As the amount of alkali required for metal precipitation greatly exceeds that of the buffer solution system, the alkali must be additionally added during the metal precipitation reaction to ensure the stability of the buffer solution system. As can be seen from fig. 8, when the volume of NaOH dropped into the buffer solution was increased from 2.0 mL to 10.0 mL, the amount of the cobalt ions precipitated was also increased, and thus the amount of the cobalt active material was also increased, and finally the catalytic activity continued to be increased. These results suggest that the amount of active ingredient can be precisely controlled by adjusting the impregnation parameters.

Catalytic degradation example 4: degradation of other contaminants by catalysts

The catalyst prepared by the invention can be used for advanced oxidative degradation of organic matters, the types of the organic matters are very wide, and the degradation effects under the action of high-activity free radicals are also greatly different, in order to test the universality of the pollutants applicable to the catalyst prepared by the invention, except phenol, the degradation effect of the catalyst on dye rhodamine B is tested by using the embodiment 1, and the test result (figure 9) shows that the removal of the dye rhodamine B is higher than that of a sample which does not use a buffer solution in the comparative example 1, thereby proving that the catalyst prepared by the invention has good catalytic degradation removal effect on the pollutants which are difficult to degrade biologically.

Catalytic degradation example 5: development of catalyst preparation method

As can be seen from the comparison of example 1 with comparative examples 1 and 2, a precisely controlled buffer solution plays an important role in the uniform formation of the active component. Example 1a glycine/sodium hydroxide buffer was used and to confirm that the other buffers have similar effects, we prepared example 2 using ammonium formate/ammonia as the buffer and performed phenol degradation experiments. As can be seen from fig. 10, this example also has higher catalytic removal for phenol and higher than the sample without buffer solution. This result indicates that the method provided by the present invention is not affected by the type of buffer solution, as long as the buffer solution is within the corresponding buffer range.

The present invention prepares a supported cobalt catalyst with good effects of activating peroxymonosulfate, benefiting from the control of the buffer solution and the compensation of the added base. To demonstrate that the scope of application of the method is not limited to persulfate oxidation, we prepared an iron-based fenton-like catalyst using this method (example 3). The prepared sample also gave satisfactory results when glycine/hydrochloric acid was used as a buffer solution and the pH was controlled at 7.0 (fig. 11). All catalysts prepared by the buffer route had higher phenol removal rates than the corresponding samples without the buffer when the pH of the buffer was increased from 4.2 to 5.0, 6.0, 7.0 and 8.0, respectively. These results mean that the catalyst preparation method provided by the invention can be applied to the preparation of other catalysts, and can even be applied to other fields.

Finally, it should be noted that the above preferred embodiments are only intended to illustrate the technical solution of the present invention and not to limit it, and it should be understood that various changes in form and details can be made by those skilled in the art without inventive efforts. In general, various changes in form and detail may be made by those skilled in the art without departing from the scope of the invention as defined by the appended claims.

Claims

1. A preparation method of a supported metal catalyst is characterized by comprising the following steps: mixing a metal ion solution with a pre-prepared buffer solution to obtain an intermediate 1, adding a carrier into the intermediate 1, wherein the mass percentage of metal ions in the metal ion solution to the carrier is less than 50%, carrying out a soaking reaction for 0.5-24h under an oil bath heating condition with the heating temperature of 25-100 ℃, dripping alkali liquor during the reaction period, wherein the amount of the alkali liquor is determined according to the amount of metal needing to be precipitated in the metal ion solution, filtering, washing and drying after the reaction is finished to obtain an intermediate 2, roasting the intermediate 2 to obtain the supported metal catalyst, wherein the roasting temperature is not higher than 900 ℃, and the roasting time is not more than 6 h.

2. The method of claim 1, wherein the pH of the buffer solution is greater than the pH required for complete precipitation of the metal from the metal ion solution, and the buffer solution is preferably composed of a material that is completely volatile under calcination conditions.

3. The method for preparing a supported metal catalyst according to claim 1, wherein the mixing of the metal ion solution and the pre-prepared buffer solution is specifically: the metal ion solution is dissolved in the buffer solution, or the metal ion solution and the buffer solution are uniformly mixed.

4. The method for preparing a supported metal catalyst according to claim 1, wherein the dropping of the alkali solution during the reaction is specifically: and dropwise and slowly adding the alkali liquor into the impregnation reaction system, or adding the alkali liquor into the impregnation reaction system in an excessive manner at one time.

5. The method of claim 1, wherein the metal species in the metal ion solution is determined according to the type of metal required for the catalytic reaction involving the late stage.

6. The method of preparing a supported metal catalyst according to claim 1, wherein the mass percentage of the metal ions to the support in the metal ion solution is 5 to 10%.

7. The method of claim 1, wherein the oil bath is heated at a temperature of 70-90 ℃ and the immersion reaction is carried out for a period of 1-3 hours.

8. The method for preparing a supported metal catalyst as claimed in claim 1, wherein the intermediate 2 is calcined in air for 1-3h to obtain the supported metal catalyst, and the calcination temperature is 400-600 ℃.

9. A supported metal catalyst prepared by the method for preparing a supported metal catalyst according to any one of claims 1 to 8.

10. Use of a supported metal catalyst for degrading organic pollutants in wastewater, wherein the supported metal catalyst is prepared by the method for preparing the supported metal catalyst according to any one of claims 1 to 8.