CN112958098A - Sulfur-mercury oxidation resistant catalyst, preparation method thereof and flow electrode device - Google Patents

Sulfur-mercury oxidation resistant catalyst, preparation method thereof and flow electrode device Download PDF

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CN112958098A
CN112958098A CN202110172833.6A CN202110172833A CN112958098A CN 112958098 A CN112958098 A CN 112958098A CN 202110172833 A CN202110172833 A CN 202110172833A CN 112958098 A CN112958098 A CN 112958098A
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ceo
sulfur
solution
mercury oxidation
oxidation catalyst
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CN112958098B (en
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王书肖
许力文
吴清茹
李国良
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Tsinghua University
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Tsinghua University
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/70Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/76Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/83Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with rare earths or actinides
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D53/00Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34Chemical or biological purification of waste gases
    • B01D53/74General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/86Catalytic processes
    • B01D53/8665Removing heavy metals or compounds thereof, e.g. mercury
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02Impregnation, coating or precipitation
    • B01J37/03Precipitation; Co-precipitation
    • B01J37/031Precipitation
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/34Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation
    • B01J37/348Electrochemical processes, e.g. electrochemical deposition or anodisation

Abstract

The invention provides a sulfur-resistant mercury oxidation catalyst, a preparation method thereof and a flowing electrode device, wherein the sulfur-resistant mercury oxidation catalyst is CeO with a core-shell structure2@ CuO, of which CeO2Is used as an inner core and CuO is used as a shell layer. The catalyst of the invention is of a core-shell structure and is in SO2Exhibits excellent zero-valent mercury oxidizing ability in the presence of a catalyst. The invention also provides a preparation method of the sulfur-resistant mercury oxidation catalyst, which is prepared by adopting a flowing electrode method to carry out reaction. The method is simple and controllable, and can prepare relatively complete and uniform core compared with the existing solution precipitation methodShell structure, and application scope is wider.

Description

Sulfur-mercury oxidation resistant catalyst, preparation method thereof and flow electrode device
Technical Field
The invention relates to the technical field of environmental protection, and particularly relates to a sulfur-resistant mercury oxidation catalyst, a preparation method thereof and a flow electrode device.
Background
Mercury, commonly known as mercury, is a heavy metal that can exist in gaseous and liquid forms at ambient temperatures. Mercury is extremely toxic, can be migrated and concentrated in a long distance in a biological chain, and has great harm to the environment and human health, wherein the coal burning industry, the colored industry, the waste incineration and the cement industry are main artificial emission sources.
Mercury mainly exists in three forms in industrial flue gas: gaseous elemental mercury (Hg)0) Gaseous active mercury (Hg)2+) And particulate mercury (Hg)p) In which Hg is0Difficult to directly capture and absorb, therefore Hg0The removal of the mercury is an important content for solving the problem of mercury pollution emission of industrial flue gas. Due to Hg0Can be converted into Hg2+Is removed again, for example Hg in the coal industry2+Can be removed cooperatively by the following wet desulphurization equipment, therefore, the key point of the mercury removal of the flue gas is to provide a sulfur-resistant and high-efficiency Hg0Oxidation catalyst at SO2In the presence of Hg0Conversion to Hg2+
The existing mercury oxidation catalysts are usually in a composite structure, such as the catalyst disclosed in CN102698753A, a copper-based composite oxide catalyst and/or a copper-based composite halide catalyst, or a carrier-supported structure, such as the mercury oxidation catalyst disclosed in CN102470345A, with TiO2Loading of the vehicle with V as active component2O5And MoO3However, the sulfur resistance or oxidation efficiency of the above catalyst is desired to be further improved.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a sulfur-resistant mercury oxidation catalyst, a preparation method thereof and a flow electrode device, wherein the catalyst is applied to SO2Exhibits excellent zero-valent mercury oxidizing ability in the presence of a catalyst.
The invention adopts the following technical scheme:
the invention provides a sulfur mercury oxidation resistant catalyst which is CeO with a core-shell structure2@ CuO, of which CeO2Is used as an inner core and CuO is used as a shell layer.
Experiments show that the CeO with a core-shell structure2@ CuO as catalyst and its shell layerCuO can react with SO2The reaction has good effect of resisting sulfur, and after the reaction, the inner core CeO with strong zero-valent mercury oxidation capability2Can contact with zero-valent mercury in the flue gas to remove Hg0Conversion to Hg2+Therefore, the catalyst of the present invention is an excellent sulfur mercury oxidation resistant catalyst.
Preferably, the inner core is spherical particles with the particle size of 50-200 nm.
Preferably, the mass ratio of Cu to Ce in the sulfur-resistant mercury oxidation catalyst is 1 (15-25).
The invention also provides a preparation method of the sulfur-resistant mercury oxidation catalyst. The preparation method provided by the invention adopts a flow electrode method for reaction preparation.
In the prior art, two-step methods are mostly adopted for preparing materials with a core-shell structure, wherein a target core is firstly synthesized by using a traditional hydrothermal method, a sol-gel method, a dipping method, a coprecipitation method and the like in the first step, and then, the shell particles are wrapped into the core particles in the second step. Wherein, reactants of MOCVD are expensive, and the products after reaction need harmless treatment; EPD is difficult to be used for preparing a metal oxide core-shell structure with low conductivity; SILAR is mainly suitable for synthesizing core-shell materials with shell particles having strong adsorption effect on core particles; the commonly adopted solution precipitation method mainly utilizes the particles prepared in the first step as condensation cores, and promotes the shell particles to deposit and grow in the solution by taking the core particles as templates through adjusting the salt adding amount in the solution or adjusting the pH value of the solution.
The flow electrode method is a sewage treatment method which utilizes an electrode and a semipermeable membrane to make ions in liquid directionally move so as to selectively remove the ions in a solution, and is generally used in the field of water treatment. According to the invention, researches show that the material with the core-shell structure can be prepared by adopting a flow electrode method, the method is simple and controllable, and compared with the existing methods such as a solution precipitation method, the core-shell structure with the core-shell structure can be prepared more completely and uniformly, and the application range is wider.
Specifically, the preparation method of the invention uses CeO2The solution is an electrode solution, and a copper salt solution is used as a flowing liquid. Wherein the electrode liquid flows through the cathode chamber and the anode chamber, the flowing liquid flows through the intermediate desalting chamber, and under the action of an electric field, Cu2+Will move towards the outer electrode chamber, the suspended CeO2Capture of the spherical core to finally form CeO2@ CuO structure.
Preferably, the copper salt solution is a copper nitrate solution.
In the prior art, copper acetate is generally used as a precursor for synthesizing the copper shell, and the invention adopts copper nitrate to avoid side reactions such as reaction with an electrode as far as possible.
Preferably, the electrode solution further contains sodium sulfate, and the sodium sulfate and CeO2The mass ratio of (1): (2-4), more preferably 1: 3.
In the invention, sodium sulfate is added into the electrode solution to promote CeO2The solution is conductive and the sodium sulfate is quite stable and substantially retains Na during flow2+And SO4 2-The form (2) does not participate in the electrode reaction, and thus has little influence on the oxidizing ability of the catalyst. Further research of the invention finds that the addition amount of the sodium sulfate is strongly related to the structural integrity and uniformity of the obtained core-shell structure catalyst, and when the addition amount of the sodium sulfate is controlled within the range, the effect is better.
Preferably, in the preparation process, a constant voltage mode is adopted, and the voltage is preferably 4-5V, and more preferably 4.5V.
The invention integrates the reaction rate and energy consumption, and finds that the constant voltage mode is better. And when the voltage is controlled in the range, a core-shell structure which is completely and uniformly wrapped can be obtained.
Preferably, the electrode fluid flows through the cathode chamber and the anode chamber connected in series in sequence.
In the prior art, in order to facilitate rapid desalination, a cathode chamber and an anode chamber are connected in parallel. Hair brushMing due to partial CeO2The nucleus is larger than 100nm and can slowly and naturally deposit in the solution to be unfavorable for the reaction, so that CeO is used2Two outer electrode chambers (cathode chamber and anode chamber) which flow through are connected in series, the length of a flow channel is reduced, and therefore the synthesis efficiency of the catalyst is improved.
After the improvement of the invention, CeO is contained2The electrode solution enters from the cathode chamber and then flows out from the anode chamber, the copper salt solution flows through the middle chamber, and Cu2+Under the action of voltage, the water enters a cathode chamber through a cation exchange membrane and is reduced into Cu under the promotion of electrons0Or indirectly with OH-Formation of Cu (OH)2And also part of Cu2+By CeO2The action of a surface double electric layer is captured, and after subsequent burning treatment, Cu on the surface of the catalyst is obtained0Will be oxidized by air to CuO, and Cu (OH)2Decomposing the CuO into CuO at high temperature, and generating partial CuO in situ in the reaction process, thereby preparing the CeO2The schematic diagram of the catalyst is shown in FIG. 1.
Preferably, after the reaction time reaches 6 hours, the effluent electrode liquid is subjected to solid-liquid separation, and the obtained solid is subjected to burning treatment.
Length of reaction time to CeO2The deposition amount of Cu on the surface has influence, and researches show that the reaction time is more than 6 hours, which is beneficial to obtaining a complete core-shell structure. As described above, the present inventors have found that CeO is reacted by the flow electrode method2The surface not only has CuO, but also has part of Cu0And/or Cu (OH)2Therefore, further calcination is required, which also contributes to the stability of the crystal form. Preferably, the burning temperature is 400-600 ℃. Further, in order to remove the influence of impurity ions in the solution, the solid obtained after solid-liquid separation needs to be cleaned and dried, and then burned.
In a preferred embodiment of the present invention, the parameters in the preparation process by the flow electrode method are as follows: CeO (CeO)2Solution and Cu (NO)3)2The concentration range of the solution is 30-40 g/L; in CeO2Adding Na into the solution2SO4,Na2SO4Concentration in solutionThe range is 10-15 g/L; a constant voltage power-up mode is used in the reaction process, and the voltage range is 4.0-5.0V; CeO (CeO)2The flow rate of the solution is 2-4 ml/min, and the flow rate of Cu (NO) is3)2The flow rate is 1-3 ml/min, and the reaction time is 6 hours.
More preferably, CeO2Solution and Cu (NO)3)2The concentration of the solution was 37.5g/L in CeO2Adding Na into the solution2SO4,Na2SO4The concentration in the solution is 12.5g/L, a constant voltage power-up mode is adopted in the reaction process, the voltage is 4.5V, and CeO is adopted2The solution flow rate was 3ml/min, Cu (NO)3)2The flow rate was 2ml/min and the reaction time was 6 hours.
The invention effectively controls Cu by regulating and controlling the parameters in the preparation process of the flow electrode method2+In CeO2The deposition process and the deposition valence state of the core surface enable the core surface to form a uniform CuO shell.
The invention also provides a flowing electrode device which comprises a left side terminal fixing plate, a left side current collector, an anode chamber, a cation exchange membrane, a desalting chamber, an anion exchange membrane, a cathode chamber, a right side current collector and a right side terminal fixing plate which are sequentially arranged in a close fit manner, wherein the anode chamber is connected with the cathode chamber in series.
A conventional flow electrode apparatus is shown in fig. 2 and includes a left side end plate, a left side current collector (graphite plate), an anode chamber (plastic flow channel), a cation exchange membrane, a desalination chamber (plastic substrate), an anion exchange membrane, a cathode chamber (plastic flow channel), a right side current collector (graphite plate), and a right side end plate. The electrode solution flows through the anode chamber and the cathode chamber respectively, and the solution to be desalted flows through the desalting chamber. According to the invention, researches show that the anode cavity and the cathode cavity are connected in series, so that the length of a flow channel is reduced, and the synthesis efficiency of the catalyst is improved.
Preferably, the left side current collector and the right side current collector are both titanium meshes. The titanium mesh and the lead can be connected by a titanium sheet. The invention changes the current collector from the graphite plate to the titanium mesh, thus effectively avoiding Cu2+A reaction occurs at the electrode to precipitate.
Preferably, the anode chamber and the cathode chamber are both formed by hollowed-out plastic flow channels. The invention hollows out the plastic runner, which is more beneficial to Cu2+In the process of moving to the charged titanium net, CeO in the solution is preferentially mixed2Contact and further grow on its surface.
Preferably, the desalting chamber is formed by a silica gel flow channel between the cation exchange membrane and the anion exchange membrane, and further preferably, the desalting chamber further comprises a nylon grid. The traditional plastic substrate has larger width, the distance between two electrodes is increased, and the width is reduced and the voltage utilization efficiency is improved after the plastic substrate is replaced by a silica gel flow channel. The nylon graticule mesh is additionally added, so that the water distribution is more uniform, and the water path in the cavity is prevented from being broken.
The invention also provides application of the flow electrode method in preparation of core-shell structure materials.
The invention provides a sulfur-resistant mercury oxidation catalyst which is of a core-shell structure and is used in SO2Exhibits excellent zero-valent mercury oxidizing ability in the presence of a catalyst. The invention also provides a preparation method of the sulfur-resistant mercury oxidation catalyst, which is prepared by adopting a flowing electrode method to carry out reaction. Compared with the existing solution precipitation method and other methods, the method has the advantages of simplicity and controllability, capability of preparing a complete and uniform core-shell structure and wide application range.
Drawings
FIG. 1 is a schematic diagram of a flow electrode method for preparing a catalyst according to the present invention;
FIG. 2 is a schematic view of a conventional flow electrode apparatus;
FIG. 3 is a schematic view of a flow electrode assembly provided in example 1 of the present invention;
FIG. 4 shows CeO obtained in example 2 of the present invention2Tem (a) and sem (b) topography of @ CuO;
FIG. 5 shows CeO obtained in example 2 of the present invention2The elemental distribution of @ CuO;
FIG. 6 shows the Cu content and the CeO content in the synthesis process of example 2 of the present invention2Solution, Cu (NO)3)2Distribution pattern among solutions;
FIG. 7 is a graph showing the change of pH with time in the course of the reaction in example 2 of the present invention;
FIG. 8 shows spherical CeO obtained in example 3 of the present invention2And CeO2TEM topography of @ CuO;
FIG. 9 shows a spherical CeO2CeO provided in example 22@ CuO and Cu as provided in comparative example 10.05CeOxA topography of (a);
FIG. 10 shows a spherical CeO2CeO provided in example 22@ CuO and Cu as provided in comparative example 10.05CeOxHg of0And (4) an oxidation performance test result chart.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described below, and it is obvious that the described embodiments are a part of the embodiments of the present invention, but not all of the embodiments. 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.
Example 1
The present embodiment provides a flow electrode device, whose structural diagram is shown as a in fig. 3, and includes a left terminal fixing plate, a left current collector, an anode chamber, a cation exchange membrane, a desalination chamber, an anion exchange membrane, a cathode chamber, a right current collector, and a right terminal fixing plate, which are disposed in close proximity to one another in this order. Wherein, the left terminal fixing plate and the right terminal fixing plate are arranged oppositely in parallel (not shown in the figure); the left current collector and the right current collector are both titanium nets, and the titanium nets are connected with the lead through titanium sheets; the anode chamber and the cathode chamber are both formed by hollow plastic runners (as shown in b in fig. 3), and are connected in series; the desalting chamber is formed by a silica gel flow channel positioned between a cation exchange membrane and an anion exchange membrane, and further comprises a nylon grid.
Further, in this embodiment, the specification of the titanium mesh is 90mm × 90mm × 4mm, 13 flow grooves (44mm × 2mm × 2mm) are engraved on the plastic runner, and each interface is sealed by using an epoxy resin adhesive, and a real diagram of this interface is shown as c in fig. 3.
Example 2
This example provides a sulfur-resistant mercury oxidation catalyst, CeO with core-shell structure2@ CuO, the preparation method is as follows:
the flow electrode device provided in example 1 was used to add Na2SO4CeO (B) of2The solution is electrode solution, enters from the cathode chamber and flows out from the anode chamber, and Cu (NO) is added3)2The solution flows as a flow stream through the intermediate desalination chamber. Wherein, CeO2Solution and Cu (NO)3)2The concentration of the solution is 37.5 g/L; na (Na)2SO4The concentration in the electrode solution is 12.5 g/L; a constant voltage power-up mode is adopted in the reaction process, and the voltage is 4.5V; CeO (CeO)2Solution flow rate was about 3mL/min, Cu (NO)3)2The flow rate was about 2mL/min and the reaction time was 6 hours. After the reaction is finished, the electrode liquid flowing out of the anode chamber is subjected to solid-liquid separation, the obtained solid is washed and dried, and then is burned in the air atmosphere at 500 ℃ to prepare CeO2@CuO。
The element content characterization by ICP-AES shows that CeO2The mass ratio of Cu to Ce element in @ CuO is about 1: 20.
CeO in the present example2Are spherical particles, are commercially available or are synthesized using a template method. The preparation method comprises the following steps:
1.997gCe (NO)3)3·6H2O is dissolved in 56mL of ethylene glycol solution and stirred until Ce (NO)3)3·6H2After the O was completely dissolved, 0.8g of polyvinylpyrrolidone (PVP) was slowly added while keeping stirring to avoid PVP consolidation, 8mL of water was added and stirred for 30 minutes. Adding the prepared suspension into a polytetrafluoroethylene lining of a reaction kettle, then reacting for 24 hours at 160 ℃, cooling the reaction kettle at normal temperature after the reaction is finished, centrifuging and washing for 3 times by deionized water and 3 times by absolute ethyl alcohol in sequence, drying at 80 ℃ overnight after the washing is finished, and roasting for 4 hours at 600 ℃. To obtain the particle sizeSpherical CeO of 50-200 nm and uniform shape2
CeO obtained in this example2TEM and SEM morphology results of @ CuO are shown in FIG. 4, and it can be seen from a in FIG. 4 that CeO2The outer surface of @ CuO is more sparse than the inner layer, and the fluid layer on the surface may be caused by incomplete crystallization of CuO thereon, i.e., CuO and CeO2An interface intersection; as can be seen from b in FIG. 4, CeO2The overall synthesis of @ CuO is quite uniform and the size of the @ CuO is equal to that of CeO2Close to, simultaneously in CeO2The surface had significant "armor" formation of CuO.
CeO obtained in this example2The TEM element distribution of @ CuO is shown in FIG. 5, and it can be seen from a in FIG. 5 that CeO2@ CuO still retains CeO2The spherical structure of (1), in the HAADF imaging mode, the image intensity is positively correlated with the square of the atomic number, a significant intensity-decreasing layer is seen from the core to the interface, whereas the atomic number of Ce is 58 and the atomic number of Cu is 29, so the decrease at the interface also confirms the appearance of the surface CuO layer; it can be seen from the element distribution diagram b-d in FIG. 5 that the distribution of Ce, Cu and O elements is quite uniform, because the invention adopts a two-step method to synthesize the core-shell structure, and CeO2After the crystal form is stabilized by burning at 600 ℃, even if Cu is converted into CeO2Doping of the crystal lattice, also predominantly in CeO2The outer surface of (a); relatively uniform Cu distribution pattern, indicating that CuO is coated on CeO2The outer layer of the core, and the distribution of Cu is quite uniform, there is a strong evidence for CeO2Successful preparation of the catalyst with the structure of @ CuO core shell.
In order to further study the solution change and stability during the flow electrode reaction, the current, pH, Cu ion concentration change during the reaction were measured.
In the reaction process, CeO is respectively added2Solution and Cu (NO)3)2Sampling the solution, and determining Cu element by ICP-AES (inductively coupled plasma-atomic emission Spectrometry), wherein CeO2The solution was centrifuged before testing and the supernatant was taken for testing. The content of copper element in the synthesis process is equal to that of CeO2、Cu(NO3)2The distribution between the solutions is shown in figure 6.From the start of the reaction to 2 hours, CeO2The Cu content in the solution is extremely low, and Cu (NO)3)2The Cu content in the solution continued to decrease, indicating that at the very beginning of the reaction, Cu (NO) was added3)2Solution passing through cation exchange membrane to CeO2Cu through which the solution flows2+May be adsorbed and intercepted by the exchange membrane to separate from the equilibrium state of the solution, and the continuous Cu content difference between the two solutions also shows that the cation exchange membrane has good performance and maintains Cu under certain voltage2+And a passing rate of Cu, and2+the migration of (2) is less affected by the concentration difference. From 1 hour after the start of the reaction to the end of 6 hours, the copper content in the solution continuously decreased, and at the same time, CeO2The Cu element is continuously appeared in the solution, and the proportion is continuously increased. This result indicates that in the negative electrode, Cu was dissolved2+Not all converted to CuO or Cu0、Cu2O deposited on CeO2Surface, also part of Cu2+Is present in the solution.
Since the cation exchange membrane is not a differential pressure membrane, the ion migration on both sides is mainly driven by voltage, and it can be considered that Cu2+Has a constant migration rate and enters CeO2The Cu material in the solution flows to the polar plate and CeO mainly2Surface deposition and continued presence in solution; because the traditional graphite flow channel is replaced by the plastic flow channel in the device, the deposition proportion of the polar plate is effectively controlled, so the rising rate of the concentration of copper in the solution is increased, mainly from CeO2A decrease in the surface deposition rate. According to the copper distribution ratio in three time periods of 0-2 hours, 2-4 hours and 2-6 hours, CeO is distributed every two hours2The copper content proportion in the solution is respectively increased by 1%, 4% and 3%, which indicates that a process of accelerating and slowing down the copper deposition rate possibly exists in the reactor.
To investigate the changes in pH and current during the reaction, to investigate the cause of the change in copper deposition rate and the different types of deposition, CeO was measured every 0.5 hour from the start of the reaction2The pH and current in the solution are shown in fig. 7. The pH was greater than 7 at the very beginning of the reaction, mainly because the pH electrode used a saturated calomel electrode, by conductanceThe difference in rate to measure the pH value, and the ion concentration in ultrapure water is extremely low, so that the measurement is not accurate, in Na2SO4After addition, the pH returned to normal; and the pH value is continuously reduced along with the continuous reaction until the reaction is terminated, and is about 4.3.
During the reaction, the reduction of water existing at the cathode obtains electrons to generate OH-Causing the solution pH to rise, which leads to Cu2+Deposition to Cu (OH)2While in the anode, oxidation of water occurs, electrons are lost, and H is generated+Causing the pH of the solution to drop, which results in Cu (OH)2Decomposed and transformed into Cu2+Theoretically, in equilibrium, the pH should remain at 7 after the solution flows through the anode and cathode cells, however, the pH of the solution is observed to decrease, indicating that the anode produces H+Reaction and cathodic generation of OH-The reaction is not balanced. On the one hand, possibly from the OH groups mentioned above-And Cu2+Binding to form Cu (OH)2On the other hand, may be from Cu2+To Cu0And Cu2And (4) reducing O. In the process of capacitive deionization, the pH is found to be reduced, and Cu can be effectively promoted0To suppress Cu generation on the electrode2+And in Cu2In the formation of O, there is also H+And (4) generating. Thus, as the reaction progresses, Cu (OH) in solution2Will be continuously reduced and balanced to Cu2+The direction of reduction is shifted.
From the change of the current during the reaction, it can also be found that the current is continuously reduced at the beginning of the reaction, and the current is reduced from 7mA to 2mA after 4 hours, and from the node of the turn, the change rate of the Cu content is similar, and the pH is reduced, so that the Cu content is caused to be reduced2+To Cu2O and Cu0The favorable reasoning corresponds. Therefore, it is presumed that the reaction reached Cu in about 4 hours2+To Cu (OH)2And Cu0The turning point of (a); since Cu (OH)2Conductivity is significantly lower than Cu0Therefore, the increase in current indicates that in addition to the concentration of ions in the plate after a long reaction time, there is a part due to the high conductivity of Cu0The result is generated.
From the changes in Cu content and distribution, solution pH, current during the reaction, it is strongly demonstrated that there are two reaction intervals during the synthesis: at the very beginning of the reaction, the flow electrode assembly is in Cu (OH)2Forming a region with Cu2+To Cu (OH)2Mainly generating; after a period of reaction time, the flow electrode assembly was in Cu0Forming a region with Cu2+To Cu0And Cu2O is mainly generated.
Example 3
This example provides a sulfur-resistant mercury oxidation catalyst, CeO with core-shell structure2@ CuO, prepared using a conventional flow electrode apparatus (see FIG. 2), using the same process parameters as in example 2.
As a result, CeO was obtained2The TEM morphology of @ CuO is shown in FIG. 8 as b, where a is spherical CeO prepared by the same preparation method as example 22TEM topography of (a). It can be seen that the catalyst shell prepared using the conventional flow electrode apparatus is less uniform than that of example 2.
Example 4
This example provides a sulfur-resistant mercury oxidation catalyst, CeO with core-shell structure2@ CuO, the preparation method is basically the same as example 2, except that a constant voltage power-on mode is adopted in the reaction process, the voltage is 3.5V, and Na is adopted2SO4The concentration in the electrode solution was 12.5g/L, and the reaction time was 6 hours.
Example 5
This example provides a sulfur-resistant mercury oxidation catalyst, CeO with core-shell structure2@ CuO, the preparation method is basically the same as example 2, except that a constant voltage power-on mode is adopted in the reaction process, the voltage is 4.5V, and Na is adopted2SO4The concentration in the electrode solution was 6.5g/L, and the reaction time was 6 hours.
Results CeO obtained in examples 4 to 52The integrity and uniformity of the shell of the @ CuO catalyst was slightly inferior to that of example 2.
Comparative example 1
The comparative example provides a copper-cerium composite catalyst Cu prepared by adopting a coprecipitation method0.05CeOxThe copper-cerium ratio was the same as that of example 2, specifically, the mass ratio of Cu to Ce was about 1: 20.
Morphology characterization and performance testing
FIG. 9 shows a spherical CeO2CeO provided in example 22@ CuO and Cu as provided in comparative example 10.05CeOxWherein a is the appearance of the three catalysts, and b is CeO2TEM morphology of @ CuO, substantially similar to spherical CeO2In the same way, c is Cu0.05CeOxThe TEM morphology shows uneven distribution, and the particle size is about 10-20 nm.
FIG. 10 shows a spherical CeO2CeO provided in example 22@ CuO and Cu as provided in comparative example 10.05CeOxHg of0And (4) an oxidation performance test result chart. Wherein the test conditions are as follows: hg: 80 μ g/m3,O2:4%,SO2:100ppm,N2As balance gas, space velocity: 200000h-1
The result is that CeO is present in a temperature range of 150-400 DEG C2The @ CuO catalysts all exhibit the best Hg0The oxidation activity can reach 91 percent of Hg at 300 DEG C0The efficiency of oxidation; and Cu0.05CeOxThe activity is low, and the activity of the catalyst is lower than that of spherical CeO when the catalyst is used as a Cu-Ce composite metal oxide catalyst within a temperature range of 150-400 DEG C2This result strongly demonstrates the necessity of structural optimization (modification to a core-shell structure) of the catalyst.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims (10)

1. A kind ofThe sulfur-resistant mercury oxidation catalyst is characterized in that the catalyst is CeO with a core-shell structure2@ CuO, of which CeO2Is used as an inner core and CuO is used as a shell layer.
2. The sulfur-resistant mercury oxidation catalyst according to claim 1, wherein the inner core is a spherical particle having a particle diameter of 50 to 200nm,
and/or the mass ratio of Cu to Ce in the sulfur-resistant mercury oxidation catalyst is 1 (15-25).
3. The method for preparing a sulfur-resistant mercury oxidation catalyst according to claim 1 or 2, wherein the reaction is performed by a flow electrode method.
4. A method for preparing a sulfur-resistant mercury oxidation catalyst as claimed in claim 3, wherein CeO is used2The solution is an electrode solution, and a copper salt solution is used as a flowing liquid;
preferably, the electrode solution further contains sodium sulfate, and the sodium sulfate and CeO2The mass ratio of (1): (2-4).
5. The preparation method of the sulfur-resistant mercury oxidation catalyst according to claim 3 or 4, wherein a constant voltage mode is adopted in the preparation process, and the voltage is preferably 4.0-5.0V;
and/or the electrode solution flows through the cathode chamber and the anode chamber which are connected in series in sequence.
6. The preparation method of the sulfur-resistant mercury oxidation catalyst as claimed in any one of claims 3 to 5, wherein after the reaction time reaches 6 hours, the liquid and solid of the electrode flowing out are separated, and the obtained solid is burned.
7. The utility model provides a flow electrode device which characterized in that, including hugging closely left side terminal fixed plate, left side current collector, positive pole cavity, cation exchange membrane, desalination cavity, anion exchange membrane, cathode chamber, right side current collector and the right side terminal fixed plate that sets up in proper order, positive pole cavity with the cathode chamber is series connection.
8. The flow electrode assembly of claim 7, wherein the left and right current collectors are each a titanium mesh;
and/or the anode cavity and the cathode cavity are both formed by hollow plastic runners.
9. A flow electrode device according to claim 7 or 8, wherein the desalination chamber is formed by a silica gel flow channel between the cation exchange membrane and the anion exchange membrane, preferably wherein the desalination chamber further comprises a nylon mesh.
10. The application of the flow electrode method in preparing the core-shell structure material.
CN202110172833.6A 2021-02-08 Sulfur-mercury oxidation resistant catalyst, preparation method thereof and flow electrode device Active CN112958098B (en)

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