CN114308029A - Method for preparing tetravalent uranium by hydrazine reduction of hexavalent uranium with bimetallic catalyst - Google Patents
Method for preparing tetravalent uranium by hydrazine reduction of hexavalent uranium with bimetallic catalyst Download PDFInfo
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Abstract
The invention relates to a method for preparing tetravalent uranium by reducing hexavalent uranium with hydrazine by adopting a bimetallic catalyst. The catalyst adopted by the invention comprises the following components in parts by mass: a) the carrier is cerium oxide accounting for 70-99.89%; b) the active component is any one of metal Pt and Ir, and accounts for 0.1-20%; c) the second metal component is one or more than two of Ru, Pd, Rh and Au, and accounts for 0.01-10%. In an acid system, the catalyst provided by the invention can directly reduce hexavalent uranium into tetravalent uranium by taking hydrazine as a reducing agent, the conversion rate of the hexavalent uranium can reach 99%, and the utilization rate of the hydrazine is higher than 80%. The catalyst has the advantages of easily available raw materials, simple process and good application prospect.
Description
Technical Field
The invention relates to a bimetallic catalyst for preparing tetravalent uranium by reducing hexavalent uranium with hydrazine, and a preparation method and application thereof.
Background
Nuclear fuel reprocessing is the treatment of spent nuclear fuel (spent fuel) in nuclear reactors to recover uranium and plutonium and other valuable elements and to vitrify highly radioactive wastes thereof for deep geological disposal. At present, post-processing plants at home and abroad mainly adopt a process flow of Purex. The Purex process flow mainly utilizes the different extraction capacities of tributyl phosphate (TBP) on uranium and plutonium in different valence states to realize the separation of the uranium, the plutonium and other fission products. First, the fission products are separated from the uranium and plutonium using TBP with less capacity to extract the fission products than uranium and plutonium. Then, the extraction capability of the TBP to the trivalent plutonium is smaller, and the uranium and the plutonium are separated. Therefore, it is necessary to add a reducing agent to reduce tetravalent plutonium to trivalent plutonium. Uranium (u (iv)) is a preferred counterextractant for the reduction of plutonium in the presence of hydrazine as a supporting reductant. Most of the spent fuel post-treatment plants in operation and under construction use hydrazine stabilized U (IV) as a reduction stripping agent, such as UP3 and UP2-800 in France and pilot plant in China.
At present, the preparation methods of U (IV) mainly comprise an electrolysis method, a hydrogenation method and a liquid phase reduction method. The electrolysis method for producing U (IV) can not introduce impurities, and the operation process is simple. In the actual production process, however, the conversion rate of hexavalent uranium (U (VI)) is low, and is only 50% -60%, so that the recovery burden of uranium products in the post-treatment process is increased. The catalytic hydrogenation method adopts high-pressure hydrogen as a reducing agent, and can obtain higher U (VI) conversion rate. However, the use of high pressure hydrogen increases the complexity of the equipment and also creates potential safety hazards. Organic reducing agents such as hydrazine and the like are adopted, and U (VI) can be reduced into U (IV) under the action of a catalyst, as shown in formula 1. The method has the advantages of mild reaction conditions, simple operation process and good application prospect. Other side reactions also exist in a hydrazine reduction U (VI) system, such as a formula 2, which can reduce the reduction capability and the utilization rate of hydrazine. Therefore, there is a need to optimize the catalyst design to make hydrazine more prone to reaction 1, thereby improving the catalyst activity and hydrazine utilization.
N2H5 ++3H++2UO2 2+→2U4++N2+4H2O (1)
3N2H5 ++H+→N2+4NH4 + (2)
Bin et al studied the reaction performance of platinum black catalyst in nitric acid system under different reaction conditions for hydrazine reduction u (vi) to u (iv). At 60 ℃, the uranium concentration is 0.9mol/L, HNO3When the concentration is 0.8mol/L and the hydrazine concentration is 1mol/L, the conversion rate of U (VI) can reach more than 90 percent. (Nuclear and Radioactive chemistry, 2013,35, (1): 24-28). Boltoeva et al studied Pt/SiO2Catalyst in H2SO4、HClO4、HNO3Hydrazine in the system reduces U (VI) to prepare U (IV) Pt particle size effect. It was found that the U (VI) conversion decreased with decreasing Pt particle size (Radiochemistry,2007,49, 603- "606). Anan' ev et al examined the performance of the reaction of hydrazine and formic acid to reduce U (VI) to U (IV) in a nitric acid system (Radiochemistry,2001,43, 39-43). At present, the research on the reaction for preparing U (IV) by reducing U (VI) by hydrazine mainly focuses on the study of process conditions, and the research on the influence of a catalyst carrier on the reaction performance is less.
At present, some relevant patents are applied to the preparation of tetravalent uranium solutions. Several reported patents are listed below for details:
chinese patent CN201110097474 discloses a name: a preparation method of a tetravalent uranium solution. The patent reports the preparation of u (iv) solution by reduction of u (vi) with an organic reducing agent (hydrazine or carboxylic acids and their derivatives) over Pt, Pd, Rh catalysts. The patent does not relate to the support of the catalyst used.
Chinese patent CN201310743451 discloses name: a device for preparing tetravalent uranium by electrolytic reduction. The patent reports an improved device for preparing tetravalent uranium by electrolytic reduction, and mainly solves the problem of low U (VI) conversion rate in a diaphragm-free electrolysis device. In actual production, the effectiveness of the device needs to be further verified.
Although in the above reports, hydrazine reduction U (VI) to U (IV) has been achieved. But the reactivity of the catalyst and the utilization rate of hydrazine are low. Therefore, there is a need to develop a catalyst for preparing U (IV) by hydrazine reduction U (VI) with high activity and high hydrazine utilization rate.
The reducible carrier and the active component can form strong metal-carrier interaction, and the modulation of the structure and the property of the catalyst can be realized, so that the activity and the selectivity of the catalyst are improved. Using CeO2Through the interaction between the reducible carrier and the noble metal and the modulation of the electronic property of the catalyst by the second component, the catalyst for preparing U (IV) by reducing U (VI) with hydrazine with high activity and high hydrazine utilization rate is hopeful to be developed.
Disclosure of Invention
One of the technical problems to be solved by the invention is to solve the problem of preparing U (IV) catalyst by reducing U (VI) hydrazine in an acid system, and provide a novel catalyst for preparing U (IV) by reducing U (VI) hydrazine, wherein the catalyst has high U (VI) conversion rate and hydrazine utilization rate.
The second technical problem to be solved by the present invention is to adopt the method for preparing the catalyst described in the first technical problem. The catalyst has controllable content of each component, and the method has simple preparation process and good reliability.
The third technical problem to be solved by the invention is to adopt the catalyst in one of the above technical problems to realize the catalytic reaction process for preparing U (IV) by reducing U (VI) hydrazine in an acid system.
In order to solve one of the technical problems, the invention adopts the following technical scheme:
the bimetallic catalyst for preparing U (IV) by hydrazine reduction U (VI) in an acid system comprises the following components in parts by mass: a) the carrier is cerium oxide accounting for 70-99.89%; b) the active component is any one of metal Pt and Ir, and accounts for 0.1-20%; c) the second metal component is one or more than two of Ru, Pd, Rh and Au, and accounts for 0.01-10%.
In the scheme, the method is characterized in that: the oxide in the component a) is cerium oxide, and the preferable content is 85-99.89%; the component b) is any one of metal Pt and Ir, and the preferable content is 0.1-10%; the component c) is preferably one or more of Ru, Pd and Rh, and the preferable content is 0.01-5%.
In order to solve the second technical problem, the invention adopts the following technical scheme:
a) preparation of the support
1) Dissolving a certain amount of soluble cerium salt in deionized water to obtain a solution A; wherein the concentration of the metal ions is 0.001-10 mol/L;
2) dissolving a certain amount of urea and/or ammonium carbonate in deionized water to obtain a solution B with the concentration of 0.01-10 mol/L;
3) dropwise adding the solution B into the solution A until the pH value of the mixed solution is 7-10, and stirring and aging the obtained mixture in a water bath at the temperature of 60-95 ℃ for 0.5-24 h;
4) filtering and washing the obtained turbid liquid to be neutral, and drying a filter cake in air at 60-200 ℃ for 12-48 h;
5) and roasting the dried solid for 1-8 h at 300-800 ℃ in an air atmosphere to obtain solid C.
b) Active ingredient loading
1) Taking 1-5g of solid C, dispersing the solid C in 100ml of deionized water, and then taking soluble salt of any one or two of Pt and Ir to dissolve in the deionized water, wherein the concentration of noble metal ions is 0.001-1 mol/L; slowly adding a precursor solution of the noble metal into the dispersion liquid of the solid C, and uniformly stirring;
2) dissolving alkali in deionized water to prepare a precipitator to obtain a solution D with the concentration of 0.001-10 mol/L; adding the solution D into the dispersion liquid of the solid C until the pH value of the mixed solution is between 9 and 10, and stirring the obtained mixture in a water bath at the temperature of between 25 and 90 ℃ for 2 to 12 hours;
3) filtering and washing the obtained turbid liquid to be neutral, and drying a filter cake in air at 60-150 ℃ for 12-48 h; and roasting the dried solid for 1-8 h at 200-600 ℃ in an air atmosphere to obtain a solid E.
c) Second component load
1) Dissolving any one or more soluble salts of Ru, Pd, Rh and Au in deionized water and/or 5-10% hydrochloric acid to prepare a solution F;
2) taking the solid E, and dropwise adding or pouring a required amount of the solution F into the solid E according to the load amount of the second component;
3) soaking the obtained mixture at room temperature for 0.5-48 h, and then drying at 60-120 ℃ for 4-24 h; roasting the dried mixture at 200-500 ℃ for 1-8 h to obtain solid G;
4) and (3) carrying out hydrogen reduction activation on the solid G. Reducing gas to H2(molar purity)>99 percent) and the volume space velocity of the reducing gas is 100--1The heating rate from room temperature to the reduction temperature is 1-10 ℃/min, the reduction temperature is 200-.
In the preparation of the carrier, the soluble cerium salt in the step 1) is one or two of cerium nitrate or ammonium cerium nitrate.
In the preparation of the carrier, the roasting temperature in the step 5) is 300-600 ℃, and the roasting time is 2-6 h;
soluble salts of Pt and Ir in the step 1) in the active component loading are one of nitrates or chlorides of corresponding noble metals;
the alkali in the step 2) in the active component loading is one or more than two of ammonia water, sodium hydroxide, potassium hydroxide, sodium carbonate and potassium carbonate;
in the second component load, the soluble salts of Ru, Pd, Rh and Au in the step 1) are one or more than two of nitrates or chlorides of corresponding noble metals;
in order to solve the third technical problem, the invention adopts the following technical scheme: the acid system is one or more than two of nitric acid, sulfuric acid or perchloric acid systems; the hexavalent uranium is uranyl ions corresponding to acid types in an acid system, and is one or more than two of uranyl nitrate solution, uranyl sulfate solution and uranyl perchlorate solution; the tetravalent uranium is the reduction product of the corresponding hexavalent uranium. The conditions of the catalyst applied to a kettle type reactor or a fixed bed reactor for preparing the uranium quadrivalent solution by hydrazine reduction of hexavalent uranium are as follows: the acid concentration (by hydrogen ion concentration) is 0.5-1.0mol/L, the uranyl ion concentration is 0.5-1.3mol/L, the hydrazine concentration is 0.5-2.0mol/L, the reaction temperature is 25-70 ℃, and the reaction pressure is normal pressure.
The invention has the advantages that:
(1) the catalyst carrier provided by the invention has the advantages of cheap and easily-obtained raw materials, simple preparation method and contribution to realizing mass production.
(2) The catalyst provided by the invention has stable property and is beneficial to prolonging the service life of the catalyst.
(3) The catalyst provided by the invention can reduce U (VI) to U (IV) solution by hydrazine under acidic condition. The interaction between the carrier and the active component and the modulation of the second component improve the conversion rate and the reaction rate of the U (VI). In the tank reactor, the conversion of U (VI) can reach 99 percent within 60 min. And the hydrazine utilization rate is higher than 80%.
Detailed Description
The technical details of the present invention are described in detail by the following examples. The embodiments are described for further illustrating the technical features of the invention, and are not to be construed as limiting the invention.
Catalyst preparation and Performance evaluation
Example 1
21.7g of Ce (NO) was taken3)3·6H2Dissolving O in 100ml deionized water to prepare solution A, wherein the molar concentration of Ce ions is 0.5mol/L. 19.2g of ammonium carbonate is dissolved in 100ml of deionized water to obtain a solution B, and the molar concentration of the ammonium carbonate is 2 mol/L. The solution B was added dropwise to the solution A until the pH of the mixed solution was 10, and the mixture was stirred in a 70 ℃ water bath for 12 hours. Filtering and washing the obtained turbid solution to be neutral, and then drying a filter cake in air at the temperature of 80 ℃ for 12 hours; roasting the dried solid for 4 hours at 400 ℃ in an air atmosphere to obtain CeO2And (3) a carrier.
2.0g of prepared CeO were weighed2Carrier, which is dispersed in 100ml of deionized water. Weighing 0.1642g H2PtCl6·6H2Dissolving the precursor in 2ml deionized water to prepare a mixed solution, wherein the molar concentration of Pt is 0.16mol/L, and adding the Pt precursor solution into CeO2Dispersing in the solution, and stirring uniformly. 4g of NaOH are weighed and dissolved in 100ml of deionized water, the molar concentration of NaOH is 1mol/L, then an alkali liquor is slowly added dropwise to the solution, and the mixture obtained is stirred in a water bath at 60 ℃ for 4 hours. Filtering and washing the obtained turbid solution to be neutral, and placing a filter cake in air at 80 ℃ for drying for 12 hours; roasting the dried solid for 4 hours at 300 ℃ in an air atmosphere to obtain a solid E;
2.0g of the above solid E were weighed, 0.0056g of RuCl was weighed3·3H2Dissolving the mixed solution in 2ml of 10% hydrochloric acid solution to prepare a mixed solution, pouring the mixed solution into the solid E for soaking, wherein the molar concentration of Ru is 0.01mol/L, and uniformly mixing. Dipping at room temperature for 12h, drying at 60 ℃ for 12h, and roasting at 300 ℃ for 4h to obtain the Pt-Ru bimetallic catalyst, wherein the Pt mass content is 3%, the Ru mass content is 0.1%, and the mark is 3Pt-0.1Ru/CeO2。
Catalyst reduction activation conditions: reducing the gas to pure H2Molar purity of>99 percent and the airspeed of 2000h-1The heating rate is 5 ℃/min, the reduction temperature is 300 ℃, the pressure is normal pressure, and the reduction time is 4 h. Reaction conditions in the tank reactor: the concentration of nitric acid (by hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ions is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. The reaction results are shown in Table 1.
Example 2
27.4g of Ce (NH) was taken4)2(NO3)6Dissolving in 100ml deionized water to prepare solution A, wherein the molar concentration of Ce ions is 0.5 mol/L. 19.2g of ammonium carbonate is dissolved in 100ml of deionized water to obtain a solution B, and the molar concentration of the ammonium carbonate is 2 mol/L. The solution B was added dropwise to the solution A until the pH of the mixed solution was 10, and the mixture was stirred in a water bath at 60 ℃ for 24 hours. Filtering and washing the obtained turbid solution to be neutral, and then drying a filter cake in air at 60 ℃ for 48 hours; roasting the dried solid for 6 hours at 300 ℃ in an air atmosphere to obtain CeO2And (3) a carrier.
2.0g of prepared CeO were weighed2Carrier, which is dispersed in 100ml of deionized water. Weighing 0.1642g H2PtCl6·6H2Dissolving the precursor in 2ml deionized water to prepare a mixed solution, wherein the molar concentration of Pt is 0.16mol/L, and adding the Pt precursor solution into CeO2Dispersing in the solution, and stirring uniformly. 5.6g of KOH was weighed and dissolved in 100ml of deionized water with a KOH molar concentration of 1mol/L, then an alkali solution was slowly added dropwise to the above solution until the pH of the mixed solution became 10, and the resulting mixture was stirred in a water bath at 30 ℃ for 12 hours. Filtering and washing the obtained turbid solution to be neutral, and placing a filter cake in air for drying for 48 hours at the temperature of 60 ℃; roasting the dried solid for 8 hours at 200 ℃ in an air atmosphere to obtain a solid E;
2.0g of the solid E obtained are weighed and 0.0034g of PdCl are weighed2The mixture was dissolved in 2ml of a 10% hydrochloric acid solution to prepare a mixed solution with a molar concentration of Pd of 0.01mol/L, and the mixed solution was poured into E and mixed uniformly. Dipping at room temperature for 12h, drying at 60 ℃ for 12h, and roasting at 200 ℃ for 8h to obtain the Pt-Pd bimetallic catalyst, wherein the Pt mass content is 3%, the Pd mass content is 0.1%, and the mark is 3Pt-0.1Pd/CeO2。
Catalyst reduction activation conditions: reducing the gas to pure H2Molar purity of>99 percent and the airspeed of 200h-1The heating rate is 1 ℃/min, the reduction temperature is 200 ℃, the pressure is normal pressure, and the reduction time is 48 h. Reaction conditions in the tank reactor: the concentration of nitric acid (by hydrogen ion concentration) is 0.5mol/L, the concentration of uranyl ion is 0.5mol/L, and the concentration of hydrazine is 0.5mol/L0.5mol/L, 30 ℃ temperature, 800rpm stirring speed and normal pressure. The reaction results are shown in Table 1.
Example 3
27.4g of Ce (NH) was taken4)2(NO3)6Dissolving in 100ml deionized water to prepare solution A, wherein the molar concentration of Ce ions is 0.5 mol/L. 19.2g of ammonium carbonate is dissolved in 100ml of deionized water to obtain a solution B, and the molar concentration of the ammonium carbonate is 2 mol/L. The solution B was added dropwise to the solution A until the pH of the mixed solution was 10, and the mixture was stirred in a water bath at 95 ℃ for 2 hours. Filtering and washing the obtained turbid solution to be neutral, and then drying a filter cake in air at 200 ℃ for 48 hours; roasting the dried solid for 6 hours at 600 ℃ in the air atmosphere to obtain CeO2And (3) a carrier.
2.0g of prepared CeO were weighed2Carrier, which is dispersed in 100ml of deionized water. Weighing 0.1642g H2PtCl6·6H2Dissolving the precursor in 2ml deionized water to prepare a mixed solution, wherein the molar concentration of Pt is 0.16mol/L, and adding the Pt precursor solution into CeO2Dispersing in the solution, and stirring uniformly. 5.6g of KOH was weighed and dissolved in 100ml of deionized water at a KOH molar concentration of 1mol/L, then an alkali solution was slowly added dropwise to the above solution until the pH of the mixed solution became 10, and the resulting mixture was stirred in a water bath at 90 ℃ for 2 hours. Filtering and washing the obtained turbid solution to be neutral, and placing a filter cake in the air for drying for 2 hours at the temperature of 150 ℃; roasting the dried solid for 1h at 600 ℃ in an air atmosphere to obtain a solid E;
2.0g of the solid E obtained are weighed, 0.0053g of RhCl are weighed3·3H2Dissolving the mixed solution in 2ml of 10% hydrochloric acid solution to prepare a mixed solution, pouring the mixed solution into the solution E, and mixing the mixed solution uniformly, wherein the molar concentration of Rh is 0.01 mol/L. Soaking at room temperature for 48h, drying at 120 deg.C for 4h, and calcining at 500 deg.C for 1h to obtain Pt-Rh bimetallic catalyst, wherein the Pt content is 3 wt%, Rh content is 0.1 wt%, and 3Pt-0.1Rh/CeO2。
Catalyst reduction activation conditions: reducing the gas to pure H2Molar purity of>99 percent and the airspeed of 3600h-1Heating rate of 10 deg.C/min, and reducingThe temperature is 600 ℃, the pressure is normal pressure, and the reduction time is 6 h. Reaction conditions in the tank reactor: the concentration of nitric acid (by hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ions is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 70 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. The reaction results are shown in Table 1.
Example 4
2.0g of the form E obtained in example 1 was weighed, and 0.0042g of HAuCl was weighed4·4H2Dissolving the Au in 2ml of deionized water solution to prepare a mixed solution, pouring the mixed solution into the solid E for soaking, and uniformly mixing the solid E and the mixed solution, wherein the molar concentration of Au is 0.005 mol/L. Dipping at room temperature for 12h, drying at 60 ℃ for 12h, and roasting at 300 ℃ for 4h to obtain the Pt-Au bimetallic catalyst, wherein the Pt mass content is 3%, the Au mass content is 0.1%, and the mark is 3Pt-0.1Au/CeO2。
Catalyst reduction activation conditions: reducing the gas to pure H2Molar purity of>99 percent and the airspeed of 2000h-1The heating rate is 5 ℃/min, the reduction temperature is 300 ℃, the pressure is normal pressure, and the reduction time is 4 h. Reaction conditions in the tank reactor: the concentration of nitric acid (by hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ions is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. The reaction results are shown in Table 1.
Example 5
2.0g of CeO prepared in example 1 were weighed2Carrier, which is dispersed in 100ml of deionized water. Weighing 0.0265g H2PtCl6·6H2Dissolving the precursor in 2ml deionized water to prepare a mixed solution, wherein the molar concentration of Pt is 0.026mol/L, and adding the Pt precursor solution into CeO2Dispersing in the solution, and stirring uniformly. 4g of NaOH are weighed and dissolved in 100ml of deionized water, the molar concentration of NaOH is 1mol/L, then an alkali liquor is slowly added dropwise to the solution, and the mixture obtained is stirred in a water bath at 60 ℃ for 4 hours. Filtering and washing the obtained turbid solution to be neutral, and placing a filter cake in air at 80 ℃ for drying for 12 hours; roasting the dried solid for 4 hours at 300 ℃ in an air atmosphere to obtain a solid E;
2.0g of the above solid E were weighed out, 0.2432g R were weighed outhCl3·3H2Dissolving the obtained product in 2ml of 10% hydrochloric acid solution to prepare a mixed solution, wherein the molar concentration of Rh is 0.46mol/L, pouring the mixed solution into the solid E for soaking, and uniformly mixing. Soaking at room temperature for 12h, drying at 60 deg.C for 12h, and calcining at 300 deg.C for 4h to obtain Pt-Rh bimetallic catalyst, wherein the Pt content is 0.5 wt%, Rh content is 5 wt%, and is recorded as 0.5Pt-5Rh/CeO2。
Catalyst reduction activation conditions: reducing the gas to pure H2Molar purity of>99 percent and the airspeed of 2000h-1The heating rate is 5 ℃/min, the reduction temperature is 300 ℃, the pressure is normal pressure, and the reduction time is 4 h. Reaction conditions in the tank reactor: the concentration of nitric acid (by hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ions is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. The reaction results are shown in Table 1.
Example 6
2.0g of CeO prepared in example 1 were weighed2Carrier, which is dispersed in 100ml of deionized water. Weighing 0.4780g H2PtCl6·6H2Dissolving the precursor in 5ml deionized water to prepare a mixed solution, wherein the molar concentration of Pt is 0.18mol/L, and adding the Pt precursor solution into CeO2Dispersing in the solution, and stirring uniformly. 5g of NaOH was weighed and dissolved in 100ml of deionized water at a NaOH molar concentration of 1.25mol/L, then an alkali solution was slowly added dropwise to the above solution, and the resulting mixture was stirred in a water bath at 60 ℃ for 4 hours. Filtering and washing the obtained turbid solution to be neutral, and placing a filter cake in air at 80 ℃ for drying for 12 hours; roasting the dried solid for 4 hours at 300 ℃ in an air atmosphere to obtain a solid E;
5.0g of the above solid E are weighed, 0.0013g of RhCl are weighed3·3H2Dissolving the mixed solution in 2ml of 10% hydrochloric acid solution to prepare a mixed solution, wherein the molar concentration of Rh is 0.0025mol/L, pouring the mixed solution into the solid E for soaking, and uniformly mixing. Soaking at room temperature for 12h, drying at 60 deg.C for 12h, and calcining at 300 deg.C for 4h to obtain Pt-Rh bimetallic catalyst, wherein the Pt content is 10 wt%, Rh content is 0.01 wt%, and 10Pt-0.01Rh/CeO2。
Catalyst reduction activation conditions: reducing the gas to pure H2Molar purity of>99 percent and the airspeed of 2000h-1The heating rate is 5 ℃/min, the reduction temperature is 300 ℃, the pressure is normal pressure, and the reduction time is 4 h. Reaction conditions in the tank reactor: the concentration of nitric acid (by hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ions is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. The reaction results are shown in Table 1.
Example 7
2.0g of CeO prepared in example 1 were weighed2Carrier, which is dispersed in 100ml of deionized water. Weigh 0.1660g H2IrCl6·6H2Dissolving the precursor solution in 2ml of deionized water to prepare a mixed solution, wherein the molar concentration of Ir is 0.16mol/L, and adding the Ir precursor solution into CeO2Dispersing in the solution, and stirring uniformly. 4g of NaOH are weighed and dissolved in 100ml of deionized water, the molar concentration of NaOH is 1mol/L, then an alkali liquor is slowly added dropwise to the solution, and the mixture obtained is stirred in a water bath at 60 ℃ for 4 hours. Filtering and washing the obtained turbid solution to be neutral, and placing a filter cake in air at 80 ℃ for drying for 12 hours; roasting the dried solid for 4 hours at 300 ℃ in an air atmosphere to obtain a solid E;
2.0g of the above solid E were weighed, 0.0056g of RuCl was weighed3·3H2Dissolving the mixed solution in 2ml of 10% hydrochloric acid solution to prepare a mixed solution, wherein the molar concentration of Ru is 0.013mol/L, dropwise adding the mixed solution into the solid E, and uniformly mixing. Dipping for 12h at room temperature, drying for 12h at 60 ℃, and roasting for 4h at 300 ℃ to obtain the Ir-Ru bimetallic catalyst, wherein the Ir mass content is 3%, the Ru mass content is 0.1%, and the mark is 3Ir-0.1Ru/CeO2。
Catalyst reduction activation conditions: reducing the gas to pure H2Molar purity of>99 percent and the airspeed of 2000h-1The heating rate is 5 ℃/min, the reduction temperature is 300 ℃, the pressure is normal pressure, and the reduction time is 4 h. Reaction conditions in the tank reactor: the concentration of nitric acid (by hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ions is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. The reaction results are shown in the table1。
Example 8
2.0g of CeO prepared in example 1 were weighed2Carrier, which is dispersed in 100ml of deionized water. Weigh 0.1660g H2IrCl6·6H2Dissolving the precursor solution in 2ml of deionized water to prepare a mixed solution, wherein the molar concentration of Ir is 0.16mol/L, and adding the Ir precursor solution into CeO2Dispersing in the solution, and stirring uniformly. 4g of NaOH are weighed and dissolved in 100ml of deionized water, the molar concentration of NaOH is 1mol/L, then an alkali liquor is slowly added dropwise to the solution, and the mixture obtained is stirred in a water bath at 60 ℃ for 4 hours. Filtering and washing the obtained turbid solution to be neutral, and placing a filter cake in air at 80 ℃ for drying for 12 hours; roasting the dried solid for 4 hours at 300 ℃ in an air atmosphere to obtain a solid E;
2.0g of the above solid E were weighed, 0.0053g of RhCl was weighed3·3H2Dissolving the obtained product in 2ml of 10% hydrochloric acid solution to prepare a mixed solution, pouring the mixed solution into the solid E, wherein the molar concentration of Rh is 0.01mol/L, and uniformly mixing. Dipping for 12h at room temperature, drying for 12h at 60 ℃, roasting for 4h at 300 ℃ to obtain the Ir-Rh bimetallic catalyst, wherein the Ir mass content is 3 percent, the Rh mass content is 0.1 percent, and the mark is 3Ir-0.1Rh/CeO2。
Catalyst reduction activation conditions: reducing the gas to pure H2Molar purity of>99 percent and the airspeed of 2000h-1The heating rate is 5 ℃/min, the reduction temperature is 300 ℃, the pressure is normal pressure, and the reduction time is 4 h. Reaction conditions in the tank reactor: the concentration of nitric acid (by hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ions is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. The reaction results are shown in Table 1.
Example 9
The 3Pt-0.1Rh/CeO which is subjected to reduction activation in the example 3 is taken2A catalyst. Reaction conditions in the tank reactor: the sulfuric acid concentration is 0.5mol/L (hydrogen ion concentration is 1.0mol/L), the uranyl ion concentration is 0.9mol/L, the hydrazine concentration is 1.0mol/L, the temperature is 60 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. The reaction results are shown in Table 1.
Example 10
The 3Pt-0.1Rh/CeO which is subjected to reduction activation in the example 3 is taken2A catalyst. Reaction conditions in the tank reactor: the perchloric acid concentration (calculated by hydrogen ion concentration) is 1.0mol/L, the uranyl ion concentration is 0.9mol/L, the hydrazine concentration is 1.0mol/L, the temperature is 60 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. The reaction results are shown in Table 1.
Example 11
The 3Pt-0.1Rh/CeO which is subjected to reduction activation in the example 3 is taken2A catalyst. Reaction conditions in a fixed bed: the concentration of nitric acid (calculated by hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ions is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60 ℃, and the liquid space velocity is 0.3h-1The pressure is normal pressure. The reaction results are shown in Table 1.
Comparative example 12
Taking SiO22.0g of support weighed 0.1642g H2PtCl6·6H2Dissolving O in 2ml deionized water to prepare a mixed solution, wherein the molar concentration of Pt is 0.16mol/L, and dissolving SiO in the mixed solution2The carrier is immersed in the mixed solution and mixed uniformly. Dipping for 12h at room temperature, drying for 12h at 60 ℃, and roasting for 4h at 400 ℃ in air atmosphere, wherein the Pt mass content is 3%, and is recorded as 3Pt/SiO2A catalyst.
Catalyst reduction activation conditions: reducing the gas to pure H2Molar purity of>99 percent and the airspeed of 2000h-1The heating rate is 5 ℃/min, the reduction temperature is 300 ℃, the pressure is normal pressure, and the reduction time is 4 h. Reaction conditions in the tank reactor: the concentration of nitric acid (calculated by the concentration of hydrogen ions) is 1.0mol/L, the concentration of uranyl ions is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. The reaction results are shown in Table 1.
Comparative example 13
The CeO prepared in example 1 was taken22.0g of support weighed 0.1642g H2PtCl6·6H2Dissolving O in 2ml deionized water to prepare a mixed solution, wherein the molar concentration of Pt is 0.16mol/L, and adding CeO2The carrier is immersed in the mixed solution and mixed uniformly. At room temperatureSoaking for 12h, drying at 60 deg.C for 12h, and calcining at 400 deg.C in air atmosphere for 4h, wherein the Pt mass content is 3%, and is recorded as 3Pt/CeO2A catalyst.
Catalyst reduction activation conditions: reducing the gas to pure H2Molar purity of>99.9 percent and the airspeed of 2000h-1The heating rate is 5 ℃/min, the reduction temperature is 300 ℃, the pressure is normal pressure, and the reduction time is 4 h. Reaction conditions in the stirred tank: the concentration of nitric acid (calculated by the concentration of hydrogen ions) is 1.0mol/L, the concentration of uranyl ions is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. The reaction results are shown in Table 1.
Comparative example 14
2.0g of the body E obtained in example 1 was weighed, and 1.02g of Ni (NO) was weighed3)2·6H2Dissolving the Ni into 4ml of deionized water to prepare a mixed solution, pouring the mixed solution into the solid E for soaking, wherein the molar concentration of the Ni is 0.88mol/L, and uniformly mixing. Dipping for 12h at room temperature, drying for 12h at 60 ℃, and roasting for 4h at 300 ℃ to obtain the Pt-Ni bimetallic catalyst, wherein the Pt mass content is 3 percent, the Ni mass content is 0.1 percent, and the mark is 3Pt-0.1Ni/CeO2。
Catalyst reduction activation conditions: reducing the gas to pure H2Molar purity of>99 percent and the airspeed of 2000h-1The heating rate is 5 ℃/min, the reduction temperature is 300 ℃, the pressure is normal pressure, and the reduction time is 4 h. Reaction conditions in the tank reactor: the concentration of nitric acid (by hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ions is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. The reaction results are shown in Table 1.
Comparative example 15
2.0g of the body E obtained in example 1 was weighed, and 1.02g of Co (NO) was weighed3)2·6H2Dissolving the mixed solution in 4ml of deionized water to prepare a mixed solution, wherein the molar concentration of Co is 0.88mol/L, pouring the mixed solution into the solid E for soaking, and uniformly mixing. Dipping for 12h at room temperature, drying for 12h at 60 ℃, and roasting for 4h at 300 ℃ to obtain the Pt-Co bimetallic catalyst, wherein the Pt mass content is 3%, the Co mass content is 0.1%, and the mark is 3Pt-0.1Co/CeO2。
Catalyst reduction activation conditions: reducing the gas to pure H2Molar purity of>99 percent and the airspeed of 2000h-1The heating rate is 5 ℃/min, the reduction temperature is 300 ℃, the pressure is normal pressure, and the reduction time is 4 h. Reaction conditions in the tank reactor: the concentration of nitric acid (by hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ions is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. The reaction results are shown in Table 1.
Comparative example 16
2.0g of the body E obtained in example 1 was weighed, and 1.02g of Fe (NO) was weighed3)3·9H2Dissolving the mixture in 4ml of deionized water to prepare a mixed solution, pouring the mixed solution into the solid E for soaking, wherein the molar concentration of Fe is 0.88mol/L, and uniformly mixing. Dipping for 12h at room temperature, drying for 12h at 60 ℃, and roasting for 4h at 300 ℃ to obtain the Pt-Fe bimetallic catalyst, wherein the Pt mass content is 3%, the Fe mass content is 0.1%, and the mark is 3Pt-0.1Fe/CeO2。
Catalyst reduction activation conditions: reducing the gas to pure H2Molar purity of>99 percent and the airspeed of 2000h-1The heating rate is 5 ℃/min, the reduction temperature is 300 ℃, the pressure is normal pressure, and the reduction time is 4 h. Reaction conditions in the tank reactor: the concentration of nitric acid (by hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ions is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 60 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. The reaction results are shown in Table 1.
Comparative example 17
The activated carbon carrier, 2.0g, was weighed and dispersed in 100ml of deionized water. Weighing 0.1642g H2PtCl6·6H2Dissolving the precursor solution in 2ml of deionized water to prepare a mixed solution, wherein the molar concentration of Pt is 0.16mol/L, adding the Pt precursor solution into the active carbon dispersion solution, and uniformly stirring. 5.6g of KOH was weighed and dissolved in 100ml of deionized water at a KOH molar concentration of 1mol/L, then an alkali solution was slowly added dropwise to the above solution until the pH of the mixed solution became 10, and the resulting mixture was stirred in a water bath at 90 ℃ for 2 hours. Subjecting the obtained turbid solution toFiltering and washing to be neutral, and placing a filter cake in air for drying for 2h at 150 ℃; and roasting the dried solid at 600 ℃ for 1h in a nitrogen atmosphere to obtain a solid E.
2.0g of the solid E obtained are weighed, 0.0053g of RhCl are weighed3·3H2Dissolving the mixed solution in 2ml of 10% hydrochloric acid solution to prepare a mixed solution, pouring the mixed solution into the solution E, and mixing the mixed solution uniformly, wherein the molar concentration of Rh is 0.01 mol/L. Dipping for 48h at room temperature, drying for 4h at 120 ℃, and roasting for 1h at 500 ℃ in a nitrogen atmosphere to obtain the Pt-Rh bimetallic catalyst, wherein the mass content of Pt is 3%, the mass content of Rh is 0.1%, and the mark is 3Pt-0.1 Rh/AC.
Catalyst reduction activation conditions: reducing the gas to pure H2Molar purity of>99 percent and the airspeed of 3600h-1The heating rate is 10 ℃/min, the reduction temperature is 300 ℃, the pressure is normal pressure, and the reduction time is 6 h. Reaction conditions in the tank reactor: the concentration of nitric acid (by hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ions is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 70 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. The reaction results are shown in Table 1.
Comparative example 18
Weighing ZrO22.0g of carrier, which was dispersed in 100ml of deionized water. Weighing 0.1642g H2PtCl6·6H2Dissolving the precursor solution in 2ml of deionized water to prepare a mixed solution, wherein the molar concentration of Pt is 0.16mol/L, and adding the Pt precursor solution into ZrO2Dispersing in the solution, and stirring uniformly. 5.6g of KOH was weighed and dissolved in 100ml of deionized water at a KOH molar concentration of 1mol/L, then an alkali solution was slowly added dropwise to the above solution until the pH of the mixed solution became 10, and the resulting mixture was stirred in a water bath at 90 ℃ for 2 hours. Filtering and washing the obtained turbid solution to be neutral, and placing a filter cake in the air for drying for 2 hours at the temperature of 150 ℃; and roasting the dried solid for 1h at 600 ℃ in an air atmosphere to obtain a solid E.
2.0g of the solid E obtained are weighed and 0.0034g of PdCl are weighed2The mixture was dissolved in 2ml of a 10% hydrochloric acid solution to prepare a mixed solution with a molar concentration of Pd of 0.01mol/L, and the mixed solution was poured into E and mixed uniformly. Soaking at room temperature for 12 hr at 60 deg.CDrying for 12h, and roasting at 200 ℃ for 8h to obtain the Pt-Pd bimetallic catalyst, wherein the mass content of Pt is 3%, the mass content of Pd is 0.1%, and the mark is 3Pt-0.1Pd/ZrO2。
Catalyst reduction activation conditions: reducing the gas to pure H2Molar purity of>99 percent and the airspeed of 3600h-1The heating rate is 10 ℃/min, the reduction temperature is 600 ℃, the pressure is normal pressure, and the reduction time is 6 h. Reaction conditions in the tank reactor: the concentration of nitric acid (by hydrogen ion concentration) is 1.0mol/L, the concentration of uranyl ions is 0.9mol/L, the concentration of hydrazine is 1.0mol/L, the temperature is 70 ℃, the stirring speed is 800rpm, and the pressure is normal pressure. The reaction results are shown in Table 1.
Example analysis of results:
from the data analysis in Table 1, it is found that CeO is used2In the reaction of preparing U (IV) and U (VI) by reducing hydrazine under acidic condition, the conversion rate of U (VI) is higher than 90%. 3Pt-0.1Rh/CeO2In the catalyst, the conversion rate of U (VI) reaches 99 percent, and the reaction rate reaches 116.6gU4 g-1min-1And the hydrazine utilization rate reaches 82 percent. The catalyst has better application prospect.
TABLE 1 reactivity of hydrazine reduction of hexavalent uranium (U (VI)) to tetravalent uranium (U (IV)) on different catalysts under acidic conditions
The reaction rates in Table 1 are calculated as the amount of catalyst conversion U (VI) at 40 min.
Claims (8)
1. The method for preparing the tetravalent uranium by reducing the hexavalent uranium with hydrazine by adopting the bimetallic catalyst is characterized by comprising the following steps of: the bimetallic catalyst comprises the following components in parts by weight: a) the carrier is cerium oxide accounting for 70-99.89%; b) the active component is any one of metal Pt and Ir, and accounts for 0.1-20%; c) the second metal component is one or more than two of Ru, Pd, Rh and Au, and accounts for 0.01-10%.
2. The method of claim 1, wherein: the oxide in the component a) is cerium oxide, and the preferable content is 85-99.89%; the component b) is any one of metal Pt and Ir, and the preferable content is 0.1-10%; the component c) is preferably one or more of Ru, Pd and Rh, and the preferable content is 0.01-5%.
3. The method according to any one of claims 1 to 2, wherein: the preparation process of the bimetallic catalyst comprises the following steps:
a) preparation of the support
1) Dissolving a certain amount of soluble cerium salt in deionized water to obtain a solution A; wherein the concentration of the metal ions is 0.001-10 mol/L;
2) dissolving a certain amount of urea and/or ammonium carbonate in deionized water to obtain a solution B with the concentration of 0.01-10 mol/L;
3) dropwise adding the solution B into the solution A until the pH value of the mixed solution is 7-10, and stirring and aging the obtained mixture in a water bath at the temperature of 60-95 ℃ for 0.5-24 h;
4) filtering and washing the obtained turbid liquid to be neutral, and drying a filter cake in air at 60-200 ℃ for 12-48 h;
5) roasting the dried solid for 1-8 h at 300-800 ℃ in an air atmosphere to obtain solid C;
b) active ingredient loading
1) Taking 1-5g of solid C, dispersing the solid C in 100ml of deionized water, and then taking soluble salt of any one of Pt and Ir to dissolve in the deionized water, wherein the concentration of noble metal ions is 0.001-1 mol/L; slowly adding a precursor solution of the noble metal into the dispersion liquid of the solid C, and uniformly stirring;
2) dissolving alkali in deionized water to prepare a precipitator to obtain a solution D with the concentration of 0.001-10 mol/L; adding the solution D into the dispersion liquid of the solid C until the pH value of the mixed solution is between 9 and 10, and stirring the obtained mixture in a water bath at the temperature of between 25 and 90 ℃ for 2 to 12 hours;
3) filtering and washing the obtained turbid liquid to be neutral, and drying a filter cake in air at 60-150 ℃ for 12-48 h; roasting the dried solid in an air atmosphere at the temperature of 200-600 ℃ for 1-8 h to obtain a solid E;
c) second component load
1) Dissolving any one or more soluble salts of Ru, Pd, Rh and Au in deionized water and/or 5-10% hydrochloric acid to prepare a solution F, wherein the concentration of metal ions is 0.001-10 mol/L;
2) taking the solid E, and dropwise adding or pouring a required amount of the solution F into the solid E according to the load amount of the second component;
3) soaking the obtained mixture at room temperature for 0.5-48 h, then drying at 60-120 ℃ for 4-24 h, and roasting the dried mixture at 200-500 ℃ for 1-8 h to obtain solid G;
4) and (3) carrying out hydrogen reduction activation on the solid G. Reducing gas to H2(molar purity)>99 percent) and the volume space velocity of the reducing gas is 100--1The heating rate from room temperature to the reduction temperature is 1-10 ℃/min, the reduction temperature is 200-.
4. The method of claim 3, wherein:
1) in the preparation of the carrier, the soluble cerium salt in the step 1) is one or two of cerium nitrate or ammonium cerium nitrate;
2) in the preparation of the carrier, the roasting temperature in the step 5) is 300-600 ℃, and the roasting time is 2-6 h.
5. The method of claim 3, wherein:
1) soluble salts of Pt and Ir in the step 1) in the active component loading are one of nitrates or chlorides of corresponding noble metals;
2) the alkali in the step 2) in the active component loading is one or more than two of ammonia water, sodium hydroxide, potassium hydroxide, sodium carbonate and potassium carbonate;
3) in the second component load, the soluble salts of Ru, Pd, Rh and Au in the step 1) are one or more than two of nitrates or chlorides of corresponding noble metals.
6. The method according to any one of claims 1 to 5, wherein: the catalyst is used for catalyzing hydrazine to reduce hexavalent uranium in an acid system to prepare a tetravalent uranium solution.
7. The method according to any one of claims 1 to 6, wherein: the acid system is one or more than two of nitric acid, sulfuric acid or perchloric acid systems; the hexavalent uranium is uranyl ions corresponding to acid types in an acid system, and is one or more than two of uranyl nitrate solution, uranyl sulfate solution and uranyl perchlorate solution; the tetravalent uranium is the reduction product of the corresponding hexavalent uranium.
8. The method according to any one of claims 1 to 7, wherein: the conditions of preparing the uranium quadrivalent solution by hydrazine reduction of hexavalent uranium by the catalyst in a kettle type reactor or a fixed bed reactor are as follows: the acid concentration (by hydrogen ion concentration) is 0.5-1.0mol/L, the uranyl ion concentration is 0.5-1.3mol/L, the hydrazine concentration is 0.5-2.0mol/L, the reaction temperature is 25-70 ℃, and the reaction pressure is normal pressure.
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| US5480854A (en) * | 1992-12-18 | 1996-01-02 | Johnson Matthey Public Limited Company | Catalyst |
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| WO2019237892A1 (en) * | 2018-06-11 | 2019-12-19 | 太原氦舶新材料有限责任公司 | Noble metal supported catalyst, preparation method therefor, and application thereof |
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| CN102249331A (en) * | 2011-04-19 | 2011-11-23 | 中国原子能科学研究院 | Preparation method of tetravalent uranium solution |
| US20130142720A1 (en) * | 2011-12-05 | 2013-06-06 | Industrial Technology Research Institute | The method of preparation of cerium oxide supported gold-palladium catalysts and its application in destruction of volatile organic compounds |
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