High-purity soluble iridium precipitate as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of preparation of high-purity inorganic matters, and particularly discloses a high-purity soluble iridium precipitate as well as a preparation method and application thereof. The method comprises the following steps: mixing an iridium-containing component, an oxidizing agent and water, and carrying out an oxidation reaction to obtain a reaction solution; then adjusting the temperature and the pH value of the reaction liquid to obtain a crude soluble iridium precipitate; dissolving the crude soluble iridium precipitate to replace the iridium-containing component and water in the previous step, and repeating the operation of the previous step to obtain a high-purity soluble iridium precipitate; a dissolving solvent comprises an acetic acid solution. The iridium precipitate prepared by an oxidation method is extremely easy to dissolve in acetic acid, the purity of the obtained iridium precipitate is very high and reaches 99%, and meanwhile, the yield of iridium can also reach 99%.

Description

Technical Field

[0001] The invention relates to the technical field of high-purity inorganic material preparation, and in particular to a high-purity soluble iridium precipitate and a preparation method and application thereof. Background Art

[0002] Iridium is considered to be the preferred anti-oxidation coating for carbon materials, refractory metal materials, and high melting point carbide ceramics. It is currently the most ideal candidate material for high-temperature anti-oxidation coatings above 1800°C. Iridium oxide can be used as an important metal coating in the military industry, and can be used as an anti-oxidation and high-temperature resistant coating;

[0003] Hydrogen energy plays the dual role of clean secondary energy and energy storage carrier. Through water electrolysis technology, unstable and difficult-to-store electricity such as wind power and photovoltaic power can be converted into storable hydrogen. Hydrogen can be used directly as a chemical raw material, or converted into electricity and heat to meet the needs of transportation, construction, and residents' lives. Water electrolysis technology can be divided into alkaline water electrolysis, proton exchange membrane (PEM) water electrolysis, anion exchange membrane (AEM) water electrolysis, and solid oxide (SOEC) water electrolysis. Among them, PEM water electrolysis technology uses good chemical stability and proton conductivity. Studies have shown that only ruthenium oxide and iridium oxide can have certain stability and activity in PEM electrolysis of water, among which ruthenium oxide is more active than iridium oxide, but iridium oxide is much more stable than ruthenium oxide. In addition, iridium oxide is highly active and durable, and is the current mainstream anode catalyst.

[0004] In the chemical industry, iridium is also an important raw material for other iridium derivatives, such as iridium acetate. Iridium acetate is an important chemical catalyst and can be used as a reaction catalyst for the carbonylation of methanol to produce acetic acid. CN108409554A uses iridium trichloride and silver acetate to produce iridium acetate. The iridium acetate prepared by this method contains unreacted metallic silver and halogen ions, resulting in reduced product purity.

[0005] Iridium oxide plays an important role in military industry, green energy and chemical industry. The purity of iridium precipitate directly affects the purity of iridium oxide, which in turn directly affects the coating quality, the stability of PEM electrodes and the product purity of iridium derivatives, and has a great impact on their application. Therefore, it is extremely important to prepare high-purity soluble iridium precipitate. Summary of the invention

[0006] In view of this, the present invention provides a high-purity soluble iridium precipitate and a preparation method and application thereof, in order to solve the problem that the existing iridium precipitate has low purity, and compounds such as iridium oxide and iridium acetate prepared therefrom also have low purity, which ultimately leads to limited application.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] A method for preparing a high-purity soluble iridium precipitate comprises the following steps:

[0009] 1) mixing an iridium-containing component, an oxidant and water to perform an oxidation reaction to obtain a reaction solution;

[0010] 2) adjusting the temperature and pH value of the reaction solution obtained in step 1) to obtain a crude soluble iridium precipitate;

[0011] 3) Dissolving the crude soluble iridium precipitate in step 2) to replace the iridium-containing component and water in step 1), repeating the operations of step 1) and step 2) to obtain a high-purity soluble iridium precipitate.

[0012] Preferably, the iridium-containing component includes one or more of iridium trichloride, sodium chloroiridate, chloroiridic acid, iridium tetrachloride, ammonium chloroiridate, iridium tribromide, sodium hexachloroiridate, potassium hexachloroiridate and ammonium hexachloroiridate;

[0013] The oxidizing agent includes hydrogen peroxide.

[0014] Preferably, the concentration of iridium in the mixed system in step 1) is 0.5 to 20 wt.%;

[0015] The molar ratio of iridium in the iridium-containing component to the oxidant is 1:0.05-2.

[0016] Preferably, the oxidation reaction time is 20 to 120 minutes.

[0017] Preferably, the temperature of the reaction solution after adjustment in step 2) is -20 to 20°C, and the pH value of the reaction solution after adjustment is 4 to 10.

[0018] Preferably, the step of dissolving the crude soluble iridium precipitate in step 3) is: mixing the crude soluble iridium precipitate with water to form a suspension; and then mixing the suspension with an acetic acid solution to achieve the dissolution of the crude soluble iridium precipitate.

[0019] Preferably, the mass ratio of the crude soluble iridium precipitate to water in step 3) is 1:1 to 100;

[0020] The amount of acetic acid solution added is based on the dissolution of the crude soluble iridium precipitate.

[0021] Preferably, step 3) is repeated once.

[0022] Another object of the present invention is to provide a high-purity soluble iridium precipitate prepared by the above preparation method.

[0023] Another object of the present invention is to provide an application of a high-purity soluble iridium precipitate in the preparation of iridium acetate or iridium oxide.

[0024] It can be seen from the above technical solutions that, compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The iridium precipitate prepared by the oxidation method of the present invention is very soluble in acetic acid. In the presence of an oxidant, the pH is adjusted to a specific value by alkali at a specific temperature, and after a certain reaction time, a crude soluble iridium precipitate that is very soluble in acetic acid is obtained. The iridium precipitate prepared by other methods needs to be partially dissolved in acetic acid under inert gas protection, temperature increase and other specific conditions, and the yield of metallic iridium is low.

[0026] 2. The purity of the iridium precipitate obtained by the present invention is very high. Since the crude soluble iridium precipitate is very soluble in acetic acid, it is reprecipitated to obtain a higher purity refined iridium precipitate. After the acetic acid re-dissolves the crude iridium precipitate, an oxidant is added, and iridium ions are precipitated again using an alkali, thereby obtaining a higher purity refined iridium precipitate, wherein the heterometallic ions contained are not higher than 3ppm (atomic absorption spectroscopy detection), and halogen ions are not detected (or are lower than the ion chromatography detection limit).

[0027] 3. The yield of iridium is as high as 99%. All the liquids produced by the crude soluble iridium precipitate and the refined iridium precipitate are collected and combined. By detecting the iridium content in the waste liquid, it is calculated that the final yield of iridium reaches 99%.

[0028] 4. The iridium oxide prepared by the high-purity soluble iridium precipitate of the present invention has a lower overvoltage than the iridium oxide prepared by other methods (such as CN114920641A). Under the same current density, the lower the overpotential of the IrO2 catalyst for electrolysis of water, the stronger its catalytic ability is, and the lower the required electrolysis energy consumption is.

[0029] 5. The iridium acetate crystals prepared by the high-purity soluble iridium precipitate of the present invention have higher conversion rate and selectivity in the methanol carbonylation test than the iridium acetate obtained by other methods (CN114920641A). BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0031] Figure 1 This is a SEM image of a high-purity soluble iridium precipitate prepared in Example 1 of the present invention, wherein: Figure 1 The a in the figure is a 1000-fold magnification. Figure 1 b in the figure is a 20,000-fold magnification;

[0032] Figure 2 This is a UV spectrum of an acetic acid aqueous solution of iridium acetate prepared in Example 1 of the present invention;

[0033] Figure 3 This is a TEM image of iridium oxide prepared in Example 2 of the present invention;

[0034] Figure 4 It is the LSV curve diagram of hydrogen production by electrolysis of water for the experimental group and the control group of the present invention. DETAILED DESCRIPTION

[0035] The present invention provides a method for preparing a high-purity soluble iridium precipitate, comprising the following steps:

[0036] 1) mixing an iridium-containing component, an oxidant and water to perform an oxidation reaction to obtain a reaction solution;

[0037] 2) adjusting the temperature and pH value of the reaction solution obtained in step 1) to obtain a crude soluble iridium precipitate;

[0038] 3) Dissolving the crude soluble iridium precipitate in step 2) to replace the iridium-containing component and water in step 1), repeating the operations of step 1) and step 2) to obtain a high-purity soluble iridium precipitate.

[0039] In the present invention, the dissolving solvent in step 3) comprises acetic acid solution.

[0040] In the present invention, the iridium-containing component includes one or more of iridium trichloride, sodium chloroiridate, chloroiridic acid, iridium tetrachloride, ammonium chloroiridate, iridium tribromide, sodium hexachloroiridate, potassium hexachloroiridate and ammonium hexachloroiridate.

[0041] In the present invention, the oxidant includes hydrogen peroxide.

[0042] In the present invention, the concentration of iridium in the mixed system in step 1) is 0.5-20wt.%, specifically 0.8wt.%, 1wt.%, 2wt.%, 5wt.%, 8wt.%, 10wt.%, 12wt.%, 15wt.%, 18wt.%.

[0043] In the present invention, the molar ratio of iridium in the iridium-containing component to the oxidant is 1:0.05-2, preferably 1:0.1-1.5, more preferably 1:0.5-1.2, and further preferably 1:1.

[0044] In the present invention, the oxidation reaction time is 20 to 120 min, specifically 30 min, 40 min, 50 min, 60 min, 80 min, or 100 min.

[0045] In the present invention, the temperature of the adjusted reaction liquid in step 2) is -20 to 20°C, specifically -18°C, -15°C, -12°C, -10°C, -8°C, -5°C, -2°C, 0°C, 2°C, 5°C, 8°C, 10°C, 12°C, 15°C, 18°C; the pH value of the adjusted reaction liquid is 4 to 10, specifically 5, 6, 7, 8, or 9.

[0046] In the present invention, the pH value is preferably adjusted by using alkaline solution.

[0047] In the present invention, the alkali solution preferably includes one or more of potassium hydroxide solution, sodium hydroxide solution, potassium carbonate solution, potassium bicarbonate solution, sodium carbonate solution and sodium bicarbonate solution.

[0048] In the present invention, the mass concentration of the alkali solution is preferably 1-40%, specifically 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%.

[0049] In the present invention, the step of dissolving the crude soluble iridium precipitate in step 3) is: mixing the crude soluble iridium precipitate with water to form a suspension; then mixing the suspension with an acetic acid solution to dissolve the crude soluble iridium precipitate. Preferably, the acetic acid solution is added dropwise to the suspension until the suspension becomes clear.

[0050] In the present invention, the concentration of the acetic acid solution is preferably 1 wt.% to 98 wt.%, specifically 1 wt.%, 5 wt.%, 20%, 50 wt.%, 80 wt.%, or 98 wt.%.

[0051] In the present invention, the mass ratio of the soluble iridium precipitate to water is 1:1-100, preferably 1:10-80, more preferably 1:20-60, and further preferably 1:50.

[0052] In the present invention, the amount of acetic acid solution added is based on the dissolution of the soluble iridium precipitate, and the end point of the addition of the acetic acid solution is when the suspension becomes clear.

[0053] In the present invention, the number of repetitions in step 3) is 1.

[0054] The present invention also provides a high-purity soluble iridium precipitate prepared by the preparation method.

[0055] In the present invention, the high-purity soluble iridium precipitate is Ir(OH) x 、IrO x A mixture of Ir(OH) x 、IrO x Iridium is mainly composed of trivalent and tetravalent states, and the valence states of metallic iridium, 3+ and 4+, can be converted spontaneously.

[0056] The invention also provides an application of a high-purity soluble iridium precipitate in the preparation of iridium acetate or iridium oxide.

[0057] In the present invention, the preparation of iridium acetate is as follows:

[0058] Including but not limited to being implemented under an inert gas atmosphere. The high-purity soluble iridium precipitate prepared by the present invention is added to a concentrated acetic acid aqueous solution to form a blue solution after complete dissolution, and a reducing agent is added at a certain temperature to react to obtain a bright green solution, and whether the reaction is completed is determined by ultraviolet spectrum data.

[0059] In the present invention, the concentration of the acetic acid aqueous solution is preferably 80-98wt.%, specifically 82wt.%, 84wt.%, 85wt.%, 86wt.%, 88wt.%, 90wt.%, 92wt.%, 94wt.%, 95wt.%.

[0060] In the present invention, the reaction temperature is 50°C to boiling, specifically 52°C, 55°C, 56°C, 58°C, 60°C; the reaction time is indicated by the ultraviolet spectrum detection result.

[0061] In the present invention, the reducing agent includes one or more of hydrazine hydrate, ethanol, propanol and isopropanol.

[0062] In the present invention, when hydrazine hydrate is selected as the reducing agent, its added amount is 0.1 to 1 eq. of the molar amount of iridium (the molar amount of hydrazine is calculated as N2H4·H2O), and the hydrazine hydrate content in the hydrazine hydrate solution is 1 to 80 wt.%; when alcohols are selected as the reducing agent, the volume ratio of the alcohol used to the acetic acid solvent is 5 to 20:80 to 95.

[0063] In the present invention, the preparation of iridium oxide is as follows:

[0064] The high-purity soluble iridium precipitate is calcined to obtain iridium oxide.

[0065] In the present invention, the calcination temperature is 300-600°C, specifically 350°C, 400°C, 450°C, 500°C, 550°C; the calcination time is 0.5-5h, specifically 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h.

[0066] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0067] Example 1

[0068] Add iridium chloride (iridium content of 3g) to deionized water, then add hydrogen peroxide (iridium concentration in the mixed solution is 4.8wt.%, iridium and H2O2 molar ratio is 1:1), react for 60min, adjust the system temperature to -2℃, then use 2% NaOH aqueous solution to adjust the system pH to 7.4, react for 2h, filter and wash until there is no chloride ion in the filtrate (silver nitrate detection), and obtain a crude soluble iridium precipitate. Mix 6.31g crude soluble iridium precipitate with 93.69g water to form a suspension, then slowly add 50wt.% dilute acetic acid until the crude soluble iridium precipitate is dissolved, then add hydrogen peroxide (the molar ratio of H2O2 to iridium is the same as last time), react for 60min, adjust to -2℃, use 2% NaOH aqueous solution to adjust the pH to 7.4, react for 2h, filter and wash until there is no chloride ion in the filtrate (silver nitrate detection), and the filter cake obtained is a high-purity soluble iridium precipitate.

[0069] After the dried high-purity soluble iridium precipitate was dissolved in acetic acid, ICP was used to detect Na, [Na] = 1.7ppm, and after the iridium solution was treated, ion chromatography was used to detect [Cl] = ND (below the ion chromatography detection limit). The filtrate produced during the preparation process was combined and detected [Ir] = 12.33ppm, with a total weight of 2.67kg. The calculation showed that the yield of iridium reached 99%.

[0070] SEM characterization of high-purity soluble iridium precipitates, such as Figure 1 As shown ( Figure 1 a in the figure is 1000 times magnified. Figure 1 (b in the figure is magnified 20,000 times), it can be seen that the surface is fluffy without obvious lumps.

[0071] Preparation of acetic acid derivatives

[0072] The high-purity soluble iridium precipitate prepared by the above method is added to 80wt.% concentrated acetic acid solution. After complete dissolution, the mass concentration of iridium in the solution is 2.57%. 1g of 20wt.% hydrazine hydrate solution is added, and the system is heated to reflux state. UV detection is continuously used. After reflux for 2.5h, the system is a dark dark green solution. The ultraviolet spectrum data shows that the raw material is completely converted. After standing overnight, no over-reduced metallic iridium is generated at the bottom of the system visible to the naked eye. After removing the solvent and other volatiles, the product dark green iridium acetate crystals are obtained. The total iridium yield is more than 98%. The ultraviolet spectrum of iridium acetate in acetic acid aqueous solution is as follows Figure 2 As shown, through Figure 2 It can be seen that the maximum absorption wavelength of iridium acetate in the ultraviolet-visible spectrum is 669 nm (the iridium acetate content in the solution is 1 wt.%).

[0073] Comparative Example 1

[0074] No oxidant is added in the crude step

[0075] Chloroiridic acid (iridium content is 3g) is added to deionized water, (iridium concentration in the mixed solution is 4.8wt.%), the system temperature is adjusted to -2°C, 2% NaOH aqueous solution is used to adjust pH to 7.4, and the reaction is filtered and washed after 2h of suction until there is no chloride ion in the filtrate (silver nitrate detection), and the filtrate is light blue. As the number of washings increases, the color of the filtrate also changes. 7.04g of crude soluble iridium precipitate is formed into a suspension with 92.96g of water, and acetic acid with a concentration of 50wt.% is slowly added, which cannot be completely dissolved. Even if a large excess of acetic acid is added and the temperature is raised to 70°C, the reaction still cannot be completely dissolved after overnight, and there are more blocky blue-black insolubles at the bottom of the system. The content of Ir in the detection filtrate accounts for 8.2% of the total input. Therefore, the iridium precipitate cannot be purified again and the preparation of acetic acid derivatives cannot be carried out.

[0076] During the washing process of the crude step, a small amount of precipitate is dissolved in the washing water. During the refining process, most of the precipitate is still soluble in acetic acid, and only a small amount of precipitate is insoluble in acetic acid. This insoluble precipitate is still Ir(OH) x or IrO x Due to microscopic reasons such as structure, their solubility in acetic acid varies greatly.

[0077] Comparative Example 2

[0078] No oxidant is added during the refining step

[0079] Add chloroiridic acid (iridium content is 3g) into deionized water, then add hydrogen peroxide (iridium concentration in the mixed solution is 4.8wt.%, and the molar ratio of iridium to H2O2 is 1:1). After reacting for 60min, adjust the system temperature to -2°C, and then use a 2% NaOH aqueous solution to adjust the system pH to 7.4. After reacting for 2h, filter and wash until there is no chloride ion in the filtrate (silver nitrate detection), to obtain a crude soluble iridium precipitate. 5.92 g of crude soluble iridium precipitate was mixed with 94.08 g of water to form a suspension, and an acetic acid aqueous solution with a concentration of 50 wt.% was slowly added until the precipitate was completely dissolved. The reaction was continued for 60 min, adjusted to -2°C, and the pH was adjusted to 7.4 using a 2% NaOH aqueous solution. After reacting for 2 h, the mixture was filtered and washed. During the washing process, the filtrate was light blue in color. As the number of washings increased, the color of the filtrate gradually darkened, and the blue gradually turned into red. The filter cake obtained was significantly less than the crude iridium precipitate, and the utilization rate of iridium was greatly reduced.

[0080] After the dried high-purity soluble iridium precipitate was dissolved in acetic acid, ICP was used to detect Na, [Na] = 1.7ppm, and after the iridium solution was treated, ion chromatography was used to detect [Cl] = ND (below the ion chromatography detection limit). The filtrate produced during the preparation process was combined and detected [Ir] = 873ppm, with a total weight of 2.13kg. The final iridium yield was calculated to be only 38%.

[0081] Comparative Example 3:

[0082] Changing the pH during precipitation

[0083] Chloroiridic acid (iridium content of 3g) was added to deionized water, and then hydrogen peroxide was added (iridium concentration in the mixed solution was 4.8wt.%, and the molar ratio of iridium to H2O2 was 1:1). After reacting for 60min, the system temperature was adjusted to -2°C, and then a 2% NaOH aqueous solution was used to adjust the pH value of the system to 13. No precipitate appeared in the system. After reacting for 2h, the system presented a clear violet solution with a small amount of precipitate at the bottom. The reaction time was extended to 4h, 8h, and 24h. There was no significant increase in the precipitate produced before, and the system was still a clear violet solution with no significant difference in color depth. The iridium yield was very low, and the next steps such as filtration and washing were still impossible.

[0084] Example 2

[0085] Add iridium chloride (iridium content of 3g) to deionized water, then add hydrogen peroxide (iridium concentration in the mixed solution is 2.5wt.%, iridium and H2O2 molar ratio is 1:1.7), react for 60min, adjust the system temperature to -5℃, then use 2% NaOH aqueous solution to adjust the system pH to 7.5, react for 3h, filter and wash until there is no chloride ion in the filtrate (silver nitrate detection), and obtain a crude soluble iridium precipitate. Mix 5.31g crude soluble iridium precipitate with 94.69g water to form a suspension, then slowly add 2% dilute acetic acid until the crude soluble iridium precipitate is dissolved, then add hydrogen peroxide (the molar ratio of H2O2 to iridium is the same as last time), react for 60min, adjust to -5℃, use 2% NaOH aqueous solution to adjust the pH to 7.5, react for 3h, filter and wash until there is no chloride ion in the filtrate (silver nitrate detection), and the filter cake obtained is a high-purity soluble iridium precipitate.

[0086] The dried high-purity soluble iridium precipitate was dissolved in 5wt.% dilute acetic acid, and ICP was used to detect Na, [Na] = 2.4ppm. After the iridium solution was treated, ion chromatography was used to detect [Cl] = ND (or below the ion chromatography detection limit). The filtrate produced during the preparation process was combined and detected to have [Ir] = 6.4ppm, and the total weight of the filtrate was 2.33kg. The calculation showed that the yield of iridium reached 99.5%.

[0087] The high-purity soluble iridium precipitate prepared by the above method was calcined at 350°C for 2 hours, and then cooled to obtain iridium oxide powder, the TEM image of which is shown in FIG. Figure 3 As shown, Figure 3 The magnification is 200,000 times. Figure 3 The scale bar is 100 nm; Figure 3 It can be seen that the diameter of the iridium oxide powder is below 10 nm, and there is no obvious agglomeration phenomenon. The iridium oxide nanoparticles are evenly dispersed and have uniform morphology.

[0088] The high-purity soluble iridium precipitate prepared by the above method is added to 80wt.% concentrated acetic acid solution. After complete dissolution, the mass concentration of iridium in the solution is 3.21%. 1g of 20% hydrazine hydrate solution is added, and the system is heated to reflux state. UV detection is continuously used. After reflux for 2.5h, the system is a dark dark green solution. The UV spectrum data shows that the raw material is completely converted. After standing overnight, no over-reduced metal iridium is generated at the bottom of the system. After removing the solvent and other volatiles, the product dark green iridium acetate crystals are obtained.

[0089] Embodiment 3:

[0090] Add chloroiridic acid (iridium content of 3g) to deionized water, then add hydrogen peroxide (iridium concentration in the mixed solution is 4.8wt.%, iridium and H2O2 molar ratio is 1:1), react for 40min, adjust the system temperature to 3℃, then use 2% KOH aqueous solution to adjust the system pH to 8.6, react for 1.5h, filter and wash until there is no chloride ion in the filtrate (silver nitrate detection), and obtain a crude soluble iridium precipitate. Mix 5.33g crude soluble iridium precipitate with 94.67g water to form a suspension, then slowly add 2% dilute acetic acid until the crude soluble iridium precipitate is dissolved, then add hydrogen peroxide (the molar ratio of H2O2 to iridium is the same as last time), react for 60min, adjust to 3℃, use 2% KOH aqueous solution to adjust the pH to 8.6, react for 1.5h, filter and wash until there is no chloride ion in the filtrate (silver nitrate detection), and the filter cake obtained is a high-purity soluble iridium precipitate.

[0091] After all the filtrates in the preparation process were combined, [Ir] = 2ppm, and the total weight of the filtrate was 3.11kg. The yield of iridium was calculated to be 99.8%. The above-mentioned high-purity soluble iridium precipitate after drying was dissolved in dilute acetic acid, and the concentration of the prepared iridium was 5.3wt.%, and the total amount of liquid was 97.3g. The potassium ion concentration was detected by ICP, and [K] in the solution was 1.9ppm. After the iridium solution was treated, ion chromatography was performed to detect [Cl] = ND (below the detection limit of ion chromatography).

[0092] The refined iridium precipitate is added to the concentrated acetic acid solution. After complete dissolution, the mass concentration of iridium in the solution is 5%. 6 mL of ethanol solution is added, and the system is heated to reflux state. UV detection is continuously used. After reflux for 3.7 hours, the UV spectrum data shows that the raw material is completely converted. The system is a dark green solution. After standing overnight, no over-reduced metallic iridium is generated at the bottom of the system. After removing the solvent and other volatiles, the product dark green iridium acetate crystals are obtained.

[0093] Comparative Example 4

[0094] The iridium precipitate prepared from Chinese patent application CN114920641A is used as comparative example 4. The specific preparation method is as follows:

[0095] Chloroiridic acid (containing 3 g of Ir) was added to deionized water to dilute the concentration of Ir to 2 wt.%, and 11.6 g of sodium hypochlorite aqueous solution (the concentration of sodium hypochlorite was 5 wt.%) was added dropwise under a high-purity nitrogen atmosphere. The temperature was raised to 45°C and reacted for 30 min. The temperature was then raised to 60°C and the pH was adjusted to 7.4 using a 2% NaOH aqueous solution. The reaction was continued for 2 h. The precipitate was filtered off under reduced pressure to obtain a filter cake, which was washed with deionized water until the filtrate was added to silver nitrate without precipitation to obtain an iridium precipitate.

[0096] Experimental Example 1

[0097] The iridium oxide prepared in Example 2 of the present invention was used as the experimental group, and the iridium oxide prepared under the same conditions as in Example 2 of the present invention using the iridium precipitate prepared in Comparative Example 4 was used as the control group to carry out an experiment on hydrogen production by electrolysis of water.

[0098] Electrode preparation: Add 245μL deionized water and 245μL DMF to 4mg IrO2 powder and mix evenly by ultrasonication for 30min. Then, add 20μL Nafion solution and continue ultrasonication for 60min to obtain catalyst ink. Use a pipette to draw 10μL catalyst ink and drop it onto the polished glassy carbon electrode (3mm in diameter), and dry it at room temperature to obtain the working electrode. The working electrodes of the experimental group and the control group were obtained by the above method.

[0099] This electrochemical experiment uses a three-electrode technique, with the glassy carbon electrode prepared above as the working electrode, Hg / HgO as the reference electrode, and a Pt thin film electrode (size 1cm*1cm) as the cathode. 1mol / LKOH aqueous solution is the electrolyte, and the separation membrane is Nafion 117. Before the experiment, the working electrode was subjected to cyclic voltammetry (CV) at -0.1~0.5V vs.Hg / HgO at 10mV / s to obtain a stable working state. Using Hg / HgO as the reference electrode, the working electrode of the experimental group and the working electrode of the control group were used as the anode for water electrolysis to produce hydrogen by electrolysis of water. The LSV curves (scan rate of 5mV / s) of hydrogen production by electrolysis of water for the experimental group and the control group are shown in the figure. Figure 4 As shown (the experimental group of the present invention is recorded as IrO2 (the present invention), and the control group is recorded as IrO2 (CN114920641A)), by Figure 4 It can be seen that the electrode of the experimental group of the present invention is 100mA / cm 2 The overpotential under the control group is only 76.4mV; while the overpotential of the working electrode of the control group is 229mV (overpotential calculation formula: E (过电势) =E (Hg / HgO) +0.0591×14+0.098V–1.23V). Under the same current density, the higher the overpotential, the higher the energy consumption required for electrolysis of water. The IrO2 obtained in Example 2 of the present invention and the IrO2 obtained in Comparative Example 4 were dissolved respectively, and the chlorine content was detected by ion chromatography. No chlorine was detected in the present invention, while [Cl]=322ppm in Comparative Example 4. When used as a catalyst, the Cl contained - Will be better than OH - It loses electrons first, which leads to a delay in the oxygen evolution reaction. Therefore, for IrO2 used in electrodes, its purity is required to be relatively high. The preparation of high-purity iridium oxide has important application significance.

[0100] Methanol carbonylation test:

[0101] The iridium acetate prepared in Example 1 of the present invention was used as the experimental group, and the iridium acetate prepared under the same conditions as in Example 1 of the present invention using the iridium precipitate prepared in Comparative Example 4 was used as the control group to carry out an experiment on hydrogen production by electrolysis of water.

[0102] The conditions are: 48g methanol, 95g 80% acetic acid aqueous solution, 75g methyl acetate as solvent, iridium acetate as catalyst (iridium usage is 0.5wt.%), 12g iodomethane as co-catalyst, the raw materials are added to the autoclave, mixed evenly, oxygen is removed, CO is charged into the reactor, the reaction temperature is increased to 175°C, the reaction pressure is increased to 2.5MPa, and the reaction time is 6h. Gas chromatography is used for detection, and the product yield and selectivity are calculated using the internal standard method.

[0103] Before CO is introduced, the reaction raw materials are mixed evenly, and then samples are taken to detect the sodium ion concentration; [Na] in the reaction solution using the iridium acetate of the present invention is ND. In the same operation mode, when iridium acetate (CN114920641A) is detected as a catalyst, [Na] in the initial reaction solution is 120ppm. In order to examine the influence of sodium ions, when the iridium acetate of the present invention is used as a catalyst, other reaction conditions remain unchanged, and NaI is added to make the Na ion concentration the same as that of the control group, as a comparison group. The catalyst results are shown in Table 1.

[0104] Table 1 Application of iridium acetate in methanol carbonylation

[0105] Catalyst Model Methanol conversion rate Acetic acid yield Selectivity [Na] in the reaction system Experimental Group 99％ 91％ 90％ ND Control group 90％ 82％ 74％ 120ppm Comparison group 88％ 84％ 74％ 132ppm

[0106] It can be seen from Table 1 that when using the iridium acetate prepared by the present invention, the methanol conversion is close to 100%, and the acetic acid selectivity is 90%. After the reaction system is detected, no alkaline earth metal sodium is found. When using iridium acetate (CN114920641A), the methanol conversion decreases, and the acetic acid selectivity also decreases thereupon, and when the initial liquid of the detection reaction is used, the sodium concentration is 120ppm. In order to verify the influence of sodium ion, a comparison group is set, and it can be seen from the comparison group that when the reaction result is as a catalyst, the reaction result is basically consistent, and in the initial liquid of the detection reaction, the sodium ion concentration is 132ppm (ICP detection has a little error, which will not be completely consistent with theory). It is illustrated that the impurity metal ions in the iridium acetate affect the reaction rate and the product selectivity of methanol carbonylation.

[0107] Based on the above analysis, in the preparation process of high-purity soluble iridium precipitate, owing to use the halogen compound of iridium as raw material, alkali usually uses alkaline earth metal sodium and potassium hydroxide as raw material, considering price factor, preferably NaOH is used as precipitation agent. Alkali, in addition to precipitating iridium, also needs to neutralize unnecessary halogen ions, so in the preparation process of crude iridium precipitate, alkali usage is larger, and in the iridium precipitation process, free alkaline earth metal and halogen ions in the solution are wrapped in the precipitate. In the next step of purification process, iridium precursor becomes iridium precipitate rather than halogenated iridium (salt, acid) with high halogen content, etc., and alkaline earth metal hydroxide is mainly used for the precipitation of iridium, rather than neutralizing halogen ions, thereby the alkaline earth metal and halogen content contained in the high-purity soluble iridium precipitate are greatly reduced, greatly improving the purity of the iridium precipitate, and laying a good foundation for the application of its derivatives.

[0108] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0109] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a high-purity soluble iridium precipitate, characterized in that: The steps include: 1) mixing an iridium-containing component, an oxidant and water to perform an oxidation reaction to obtain a reaction solution; 2) adjusting the temperature and pH value of the reaction solution obtained in step 1) to obtain a crude soluble iridium precipitate; 3) dissolving the crude soluble iridium precipitate in step 2) to replace the iridium-containing component and water in step 1), repeating the operations of steps 1) and 2) to obtain a high-purity soluble iridium precipitate; The dissolving solvent in step 3) includes acetic acid solution.

2. The method for preparing a high-purity soluble iridium precipitate according to claim 1, characterized in that: The iridium-containing component includes one or more of iridium trichloride, sodium chloroiridate, chloroiridic acid, iridium tetrachloride, ammonium chloroiridate, iridium tribromide, sodium hexachloroiridate, potassium hexachloroiridate and ammonium hexachloroiridate; The oxidizing agent includes hydrogen peroxide.

3. The method for preparing a high-purity soluble iridium precipitate according to claim 2, characterized in that: The concentration of iridium in the mixed system in step 1) is 0.5 to 20 wt.%; The molar ratio of iridium in the iridium-containing component to the oxidant is 1:0.05-2.

4. A method for preparing a high-purity soluble iridium precipitate according to any one of claims 1 to 3, characterized in that: The oxidation reaction time is 20 to 120 minutes.

5. The method for preparing a high-purity soluble iridium precipitate according to claim 4, characterized in that: The temperature of the reaction solution after adjustment in step 2) is -20 to 20°C, and the pH value of the reaction solution after adjustment is 4 to 10.

6. The method for preparing a high-purity soluble iridium precipitate according to claim 5, characterized in that: The step of dissolving the crude soluble iridium precipitate in step 3) is: mixing the crude soluble iridium precipitate with water to form a suspension; and then mixing the suspension with an acetic acid solution to achieve the dissolution of the crude soluble iridium precipitate.

7. The method for preparing a high-purity soluble iridium precipitate according to claim 6, characterized in that: The mass ratio of the crude soluble iridium precipitate to water in step 3) is 1:1 to 100; The amount of acetic acid solution added is based on the dissolution of the crude soluble iridium precipitate.

8. The method for preparing a high-purity soluble iridium precipitate according to claim 1, characterized in that: The number of repetitions in step 3) is 1.

9. The high-purity soluble iridium precipitate prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the high-purity soluble iridium precipitate according to claim 9 in the preparation of iridium acetate or iridium oxide.

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