JP6382701B2 - Palladium colloidal solution and method for producing the same - Google Patents

Description

  The present invention relates to a palladium colloid solution and a method for producing the same. In particular, the present invention provides a palladium colloid solution that hardly causes aggregation and precipitation of palladium particles and a method for producing the same.

  Palladium colloid is widely used as a highly active and highly practical catalyst metal in fields such as organic synthesis and exhaust gas purification. In particular, in the production of chemical products such as agricultural chemicals, pharmaceuticals, fragrances, and dyes, palladium can be used for a wide range of reactions such as hydrogenation of olefins, ketones, aldehydes, etc., and hydrogenolysis of halogen compounds, allyl compounds, etc. Is one of the most widely used transition metal catalysts.

  As such a palladium colloid, a palladium colloid solution in which palladium fine particles of about 1 to 100 nm are dispersed and suspended in a solvent and a liquid is used as a solvent is usually used. As these palladium colloid solutions, those containing a polymer protective agent such as a polymer compound or a surfactant are generally used. As the polymer protective agent, those having a molecular weight of about 40,000 or more are generally known, and examples thereof include polyvinylpyrrolidone and polyethyleneimine. In a palladium colloid solution containing such a protective agent, the protective agent is adsorbed on the surface of the palladium particles, whereby direct contact between the palladium particles is suppressed, and aggregation and precipitation of the colloid can be prevented. Patent Document 1 describes a metal colloid solution using poly (acrylic acid ester) as a protective agent. When poly (acrylic acid ester) is used, in addition to suppressing aggregation of palladium particles, particle size can be controlled.

Japanese Patent Laying-Open No. 2005-2389

  However, in the case of a colloidal palladium solution containing a protective agent, there may be a problem in terms of safety on the human body in chemical products such as agricultural chemicals, pharmaceuticals, fragrances, and dyes. In the catalyst application, the catalyst performance may not be sufficiently exhibited by covering the palladium particle surface with a protective agent. For example, when a metal oxide such as alumina is used as a substrate and a palladium colloid is supported on the substrate, palladium particles can enter the pores (about 30 nm or less) of the metal oxide due to the presence of the polymer protective agent. Therefore, palladium cannot be supported in the pores.

  Moreover, when applying to a functional material, the protective agent used as an impurity may be removed. In this case, it is preferable that not only the above-described polymer protective agent but also a low molecular protective agent having a molecular weight of about 60 to 200 such as an organic amine is not contained, and the organic substance content in the colloidal solution is small.

  As a countermeasure, it may be possible to remove the protective agent by a thermal decomposition step after loading the catalyst on the base material. For example, when polyvinyl pyrrolidone (PVP) is used as the protective agent, it is separated from Pd. Therefore, it is necessary to perform the treatment at a high temperature so that the temperature needs to be 350 ° C. or higher. In this regard, when a combustible material such as paper or plastic is used as a base material, the heat treatment itself is difficult, and a palladium colloid containing no protective agent is required.

  For this reason, although it is required to provide a colloidal palladium solution that does not contain a protective agent depending on the application, compared to a palladium colloid that contains a protective agent, when a protective agent is not included, aggregation and precipitation are likely to occur during production. Even when stored, it was difficult to store for a long time while maintaining dispersibility.

  In addition, when producing a palladium colloid solution, the formation of palladium particles due to reduction of palladium ions tends not to proceed unless a protective agent is used. Even when the formation of palladium particles could proceed, precipitation due to aggregation of the palladium particles was likely to occur, and layer separation and the like were likely to occur.

  Therefore, the present invention relates to a palladium colloid solution containing no protective agent, and provides a palladium colloid solution that is less likely to cause aggregation and precipitation of palladium particles and that has excellent long-term stability. Further, the present invention provides a method for producing a palladium colloid solution containing no protective agent, in which the reduction of palladium ions proceeds stably, the precipitation due to aggregation is prevented, and the occurrence of layer separation or the like can be suppressed.

  In order to solve the above-mentioned problems, the present inventors have intensively studied a palladium colloid solution which does not contain a protective agent and hardly aggregates or precipitates for a long period of time. In this examination, a production method capable of obtaining a highly dispersible palladium colloid solution was found. Such a production method is to add an alkali to a solution of a palladium salt as a raw material to form an insoluble precipitate before the reduction treatment for reducing palladium ions to form palladium particles. Furthermore, as a result of evaluating the palladium colloid solution obtained by the production method for precipitating such insoluble palladium, the palladium particle particle size distribution becomes a highly dispersible palladium colloid solution when the following predetermined conditions are satisfied. A trend was found and the present invention was conceived.

That is, the present invention provides a palladium colloid solution comprising palladium particles and a solvent composed of water or a mixed solution of water and an organic solvent, wherein the palladium particles are a first particle group belonging to a particle diameter range of 1 nm or more and less than 6 nm. And a second particle group belonging to a particle diameter range of 6 nm or more and 60 nm or less, and the particle size distribution of the palladium particles is a first peak having a maximum value within the particle diameter range to which the first particle group belongs. And the number of palladium particles belonging to the first particle group (T ₁ ) having two peaks consisting of a second peak having a maximum value within the range of the particle diameter to which the second particle group belongs. , The ratio (T ₁ / (T ₁ + T ₂ )) of the total number of palladium particles belonging to the first particle group (T ₁ ) and the number of palladium particles belonging to the second particle group (T ₂ ). 20% or more About palladium colloid solution is 90% or less.

  Even if the palladium colloid solution of the present invention does not contain a protective agent, aggregation and precipitation due to insufficient repulsion between palladium particles are unlikely to occur. As described above, the inventors of the present invention have found that the dispersibility of the palladium colloid solution of the present invention is improved because the palladium particles belonging to the second particle group having a large particle diameter (particle diameter of 6 nm to 60 nm) in the colloid solution. This is considered to be due to the presence of palladium particles belonging to the first particle group having a small particle diameter (particle diameter of 1 nm or more and less than 6 nm) around the particle. In the palladium colloidal solution, it is considered that particles with a large particle size exist as Pd metal, and particles with a small particle size exist as Pd hydroxide or oxide. Adsorption of small particles such as Pd hydroxide increases the negative charge on the surface of the palladium particles and increases the repulsive force between the particles, so that the dispersibility is considered to be improved.

In the present invention, the number of palladium particles belonging to the first particle group (T ₁ ) is the number of palladium particles belonging to the first particle group (T ₁ ) and the number of palladium particles belonging to the second particle group. The ratio (T ₁ / (T ₁ + T ₂ )) to the total number (T ₂ ) is 20% or more and 90% or less. Within such a range, the dispersibility of the particles belonging to the second particle group having a large particle diameter is likely to be improved. The ratio T ₁ / (T ₁ + T ₂ ) of the number of particles is preferably 30% or more and 50% or less. If T ₁ / (T ₁ + T ₂ ) is less than 20%, a sufficient dispersion effect cannot be obtained, and if it exceeds 90%, it is difficult to adsorb to the substrate when supported on a substrate such as alumina.

As described above, the dispersion stability in the palladium colloidal solution of the present invention is considered to be realized by surrounding the particles belonging to the second particle group so as to surround the particles belonging to the first particle group. Therefore, with respect to all the particles contained in the colloidal solution, when the ratio of the particles belonging to the first particle group and the second particle group is a predetermined amount or more, the dispersion stability is easily maintained. It will be a thing. From such a viewpoint, the number (T ₁ ) of palladium particles belonging to the first particle group and the palladium belonging to the second particle group with respect to the total number (T _A ) of palladium particles contained in the colloidal solution. The existence ratio of the total (T ₁ + T ₂ ) with the number of particles (T ₂ ) was examined. As a result, it was found that when the ratio ((T ₁ + T ₂ ) / T _A ) was 95% or more, a colloidal solution having a particularly high dispersibility was easily obtained. _{(T 1 + T 2) /} T A is, if it is 97% or more, is more preferable.

  As described above, the palladium colloid solution of the present invention can maintain the dispersion stability due to the high proportion of particles belonging to the first particle group and the second particle group. If the content of is too large, the solution stability may be impaired. Therefore, as an index for considering the existence ratio of palladium particles having a particularly large particle diameter, in the present invention, the average particle diameter of all the other palladium particles is excluded except for the palladium particles belonging to the first particle group having a small particle diameter. A suitable range was also examined. As a result, the average particle diameter of the palladium particles excluding the particles belonging to the first particle group is preferably from 10 nm to 30 nm, particularly preferably from 15 nm to 25 nm. When the average particle diameter is less than 10 nm, it is difficult to adsorb to the substrate, and when it exceeds 30 nm, the dispersibility tends to decrease. Within such a range, it tends to be a highly dispersible colloidal solution.

  As described above, the palladium colloid solution of the present invention exists around the particles belonging to the second particle group so as to surround the particles belonging to the first particle group, and the particle size distribution, the existence ratio of these palladium particles, The stability of the colloidal solution is ensured by setting the average particle diameter and the like within a suitable range. However, in reality, the existence state of the palladium colloid particles in the solvent is complicated, and it can be said that the existence state in which the palladium particles having a large particle diameter surround the particles having a small particle diameter is easily changed by thermal motion. From such a point of view, the present inventors can easily obtain a palladium colloid solution having a particular stability by considering the movement of large and small palladium particles in the solvent in addition to the provisions based on the particle size distribution and the like. I thought. As a result, a unique configuration based on the zeta potential in a predetermined pH range was found. The zeta potential is a physical property that affects the dispersibility and agglomeration properties of dispersed particles in a liquid, but so far, the zeta potential has been rarely studied for metal colloids such as palladium colloids. This is because a conventional colloidal solution generally uses a protective agent, and it is not necessary to consider the behavior of dispersed particles in a solvent and to study dispersion stability.

  The inventors have found that when the colloidal palladium solution has a zeta potential of -30 mV or less at pH 5 or more and pH 8 or less, it tends to have dispersion stability even when stored for a long time. When the zeta potential is larger than −30 mV, palladium particles tend to aggregate and precipitation tends to occur. In addition, although there is no restriction | limiting in particular of a lower limit about zeta potential, when it is less than -80 mV about the palladium colloid solution of this invention, manufacture tends to be difficult.

  The electrical conductivity of the palladium colloid solution is preferably 500 μS / cm or less. When the electric conductivity exceeds 500 μS / cm, aggregation or sedimentation may occur during storage. The palladium concentration in the colloidal solution is preferably 5000 ppm or less. If the palladium concentration exceeds 5000 ppm, aggregation or sedimentation may occur during storage.

  In addition, as the “solvent” in the present invention, water or a mixed solvent of water and an organic solvent can be used. In particular, an aqueous solvent containing no organic solvent is preferable. By excluding organic substances from the solvent together with the above-mentioned protective agent, the content of organic substances in the colloidal solution is reduced, and a palladium colloidal solution that can be applied to applications in which impurities such as functional materials should be avoided. Further, when the aqueous solvent is used, the palladium colloid solution can be applied to a substrate such as paper or plastic by inkjet.

As described above, the palladium colloid solution of the present invention excluding organic substances preferably has a low content of organic substances, and specifically, the chemical oxygen demand (COD) is preferably 1000 ppm or less. In the present invention, the value (COD _Mn ) measured by the acidic high temperature permanganate method is applied as the chemical oxygen demand. The COD _Mn value is particularly preferably 800 ppm or less. When the COD _Mn value exceeds 1000 ppm, the organic matter is adsorbed on the surface of the palladium particles and tends to aggregate. In addition, although there is no restriction | limiting in a lower limit, so that there are few organic substances, there is a limit in the organic substance content which can be reduced, Therefore 50 ppm or more is suitable.

  The palladium colloid solution of the present invention described above can be produced by the following method. That is, a method for producing a palladium colloid solution including a reduction step in which palladium ions in a palladium salt solution are reduced to form palladium particles, and an insolubilization step in which an alkali is added to the palladium salt solution to precipitate insoluble palladium; A reduction step of adding a reducing agent to insoluble palladium to reduce palladium ions in the insoluble palladium, and after the insolubilization step and before the reduction step, the insolubility is insoluble until the electrical conductivity of the cleaning liquid is 100 μS / cm or less. The method further includes a washing step of washing palladium, wherein the insoluble palladium is a method for producing a palladium colloid solution that is palladium hydroxide, palladium oxide, dinitrodiamine palladium, or a complex thereof.

  Thus, according to the production method having the insolubilization step of precipitating insoluble palladium before the reduction and the washing step of washing the precipitate until it becomes a predetermined electric conductivity or less, the protective agent is not included, It is possible to obtain a palladium colloid solution in which aggregation and precipitation of palladium particles are unlikely to occur. Hereinafter, each step in the production method of the present invention will be described in detail.

  In the insolubilization step, alkali is added to the palladium salt solution as a raw material to precipitate insoluble palladium. The starting palladium salt is preferably dinitrodiamine palladium, and the palladium salt solution is preferably a nitric acid solution. With such a raw material, when an alkali described later is added, it is possible to produce a precipitate and obtain a highly dispersible palladium colloid solution after the reduction step. When raw materials other than those described above are used, it may be difficult to generate a precipitate due to alkali addition.

  For such raw material solution, the alkali is preferably an inorganic alkali metal hydroxide or an inorganic alkaline earth metal hydroxide. Particularly preferred are inorganic alkali metal hydroxides such as NaOH and KOH. By adding such an alkali to the raw material solution, palladium hydroxide, palladium oxide, dinitrodiamine palladium, or a complex thereof can be precipitated as insoluble palladium.

  After the insolubilization step, a washing step for washing insoluble palladium is performed. The cleaning process is performed until the electrical conductivity of the cleaning liquid becomes 100 μS / cm or less. By performing such a washing step, it is possible to produce a palladium colloid solution that is highly dispersible and hardly aggregates. As the cleaning liquid in the cleaning process, pure water is preferable. Further, as the cleaning liquid, it is preferable to use a solution whose pH is adjusted in advance by adding an acidic solution such as nitric acid to pure water.

  The insoluble palladium after washing is subjected to a reduction step, and palladium ions are reduced by adding a reducing agent to form palladium particles. As the reducing agent in the reduction step, a secondary alcohol is preferable. Specifically, 2-propanol, 2-butanol, 2-pentanol, 3-pentanol, 3-methyl-2-butanol and the like can be applied as a reducing agent. When the reducing agent is a secondary alcohol, it is easy to form a palladium colloid solution that is highly dispersible and difficult to aggregate.

  After the reduction step, a desalting step of ultrafiltration of the palladium colloid solution is preferably performed. The desalting step is preferably performed until the electric conductivity is 500 μS / cm or less. When the electrical conductivity after the reduction step exceeds 500 μS / cm for the colloidal palladium solution, aggregation or sedimentation may occur when the palladium colloidal solution is stored. In the palladium colloid solution after the desalting step, the palladium concentration is preferably 5000 ppm or less. When the palladium concentration exceeds 5000 ppm, aggregation or sedimentation may occur during storage of the palladium colloid solution.

Further, the palladium colloid solution after the reduction step and before the desalting step is preferably distilled under reduced pressure to remove the reducing agent. When vacuum distillation is performed, it is easy to obtain a palladium colloid solution having a COD _Mn of 1000 ppm or less.

  The palladium colloid solution of the present invention does not contain a protective agent, and is less prone to aggregation and precipitation and has excellent long-term stability. For this reason, it is applicable also to combustible base materials, such as paper and a plastics.

The manufacturing method flow chart of the palladium colloid solution in an embodiment. The TEM photograph of the palladium colloid solution in an embodiment. The particle diameter distribution map of the palladium colloid solution in embodiment.

  Hereinafter, the best embodiment of the present invention will be described.

[First embodiment]
Test No. 1 : Ultrapure water was added to 20 g of a commercially available dinitrodiamine Pd nitric acid solution (5 wt%) as a raw material palladium salt solution to make 1000 g (Pd concentration: 1000 ppm). A 10 wt% NaOH aqueous solution was added dropwise to the palladium salt solution as an alkali to adjust the pH to 7. Then, it was left still and insoluble palladium was precipitated. The insoluble palladium was subjected to the following washing step. First, the supernatant was separated, nitric acid was added to a solution made up to 1000 g by adding ultrapure water, adjusted to pH 5 and allowed to stand. Thereafter, the supernatant and the precipitate of insoluble Pd were separated. The above washing process was repeated until the supernatant became 100 μS / cm or less.

  After adding 400 g of ultrapure water to the precipitate of insoluble Pd washed as described above, 100 g of 2-propanol as a reducing agent was added dropwise and reduced at 65 ° C. for 5 hours. Next, the mixture was distilled under reduced pressure on a rotary evaporator and concentrated to 250 g to remove most of unreacted 2-propanol and the generated acetone. After distillation, the volume was made up to 300 g with ultrapure water, and then ultrafiltered to 100 g with an ultrafiltration membrane having a fractional molecular weight of 10,000 to concentrate. Thereafter, the volume was increased to 300 g with ultrapure water. This ultrafiltration and mess up were repeated until the electric conductivity reached 100 μS / cm, and mess up to 300 g to obtain a Pd colloid solution.

  Test No. obtained above. The result of TEM observation of the palladium colloid solution 1 is shown in FIG. 2, and the measurement result of the particle size distribution of the palladium particles is shown in FIG. The particle size distribution diagram was prepared by the following method based on the TEM observation result of FIG. In FIG. 3, (a) shows the particle size distribution of the whole particles detected as described above, and (b) shows the particle size distribution of particles having a particle size of 5 nm or more.

  Palladium particle diameter: The palladium particle diameter was determined from a TEM observation image. A sample diluted to 15 ppm with ultrapure water was placed on a carbon support membrane and observed with TEM (FEI Tecnai Osiris). It calculated from the obtained TEM image (x55000 times) using image analysis software (A image kun made by Asahi Kasei Engineering Co., Ltd.). The average value was calculated from the minimum length and the maximum length of particles of 1 nm or more that could be visually confirmed as particles, and the particle size was determined. A particle size distribution was created by measuring the particle size of 5,000 or more particles.

  From FIG. In the palladium colloid solution 1, it was found that palladium particles having a particle size of about 20 nm were surrounded by palladium particles having a particle size of about 3 nm.

  From FIG. 1 palladium particles have a first peak with a particle size of 1 nm to 5 nm and a second peak with a particle size of 10 nm to 60 nm in the particle size distribution, and the number of particles in the first peak is the total number of particles. About 37%, the number of particles in the second peak was about 63% of the total number of particles. From (b), the average particle diameter of palladium particles having a particle diameter of 6 nm or more was 22 nm.

Test No. 2-7 : Next, test no. The palladium salt solution, alkali, and reducing agent used in 1 were changed, and the test No. 1 was changed. Two to seven palladium colloid solutions were prepared. Other manufacturing conditions are as follows. Same as 1. About the obtained palladium colloid solution, palladium concentration, electrical conductivity, zeta potential, COD _Mn, and dispersibility were evaluated as follows. The particle size distribution is determined by the above test No. Measurement was performed in the same manner as in 1. The results are shown in the table below.

Palladium concentration : measured by ICP emission spectroscopy. An SPS 5100 manufactured by SII was used as the analyzer.

Electrical conductivity : Measured with a desktop electrical conductivity meter (HORIBA LAQUA act ES-71). The electrical conductivity was measured not only for each of the obtained Pd colloidal solutions but also for the supernatant after the washing step.

Zeta potential : measured by a laser Doppler method (ELS-Z manufactured by Otsuka Electronics Co., Ltd.) which is an electrophoretic light scattering method. A sample prepared by adding 0.5 N nitric acid and 0.5 N NaOH to a colloidal solution diluted to have a palladium concentration of 100 ppm and adjusting the pH to 6 was measured as a sample.

COD _Mn : Measured in accordance with the oxygen demand measurement method (acid high temperature permanganate method) with potassium permanganate at 100 ° C. specified by JIS standard (JIS K 0102 17).

Dispersibility : For each Pd colloid solution obtained above, when it was allowed to stand immediately after synthesis, “○” indicates that it did not agglomerate / precipitate for one month or more. Is “Δ”, and “×” is agglomerated and precipitated in less than one week.

[Second Embodiment]
The palladium colloid solution was obtained by changing the operating conditions of the desalting step and the washing step, and the stability of the colloid solution when the electric conductivity and Pd concentration were different was evaluated.

Test No. 8 : For a Pd solution that had been subjected to vacuum distillation under the same conditions as in Test No. 1, 200 g of pure water after ultrafiltration in the desalting step was used to obtain a palladium colloid solution. For other conditions, test no. Same as 1.

Test No. 9 : After precipitating insoluble palladium, the reduction process was performed without performing the washing process to obtain a palladium colloid solution. For other conditions, test no. Same as 1.

  About the palladium colloid solution obtained above, the measurement result of palladium concentration, electrical conductivity, and organic substance concentration is shown in the following table. Various evaluation methods are described in Test No. Same as 1-7.

  From the above results, No. As shown in FIG. 10, in the method for producing a palladium colloid solution, when insoluble palladium was not washed before the reduction step after the insolubilization step, Pd particles were formed in the subsequent reduction step, and then immediately aggregated and precipitated. . This is considered to be because unnecessary ions were not removed in the cleaning process.

  The palladium colloid solution of the present invention does not contain a protective agent, and is less prone to aggregation and precipitation and has excellent long-term stability. For this reason, it becomes suitable also when carrying | supporting to combustible base materials, such as paper and a plastics.

Claims (10)

In a palladium colloid solution comprising palladium particles and a solvent comprising water or a mixed solution of water and an organic solvent,
The palladium particles have a first particle group belonging to a particle diameter range of 1 nm to 6 nm and a second particle group belonging to a particle diameter range of 6 nm to 60 nm,
In the particle size distribution of the palladium particles, a first peak having a maximum value of the number of particles in a particle size range of 1 nm or more and less than 6 nm to which the first particle group belongs, and a particle size of 6 nm to which the second particle group belongs. Having two peaks, a second peak having a maximum number of particles within a particle diameter range of 60 nm or less ,
The number of palladium particles belonging to the first particle group (T ₁ ) is the number of palladium particles belonging to the first particle group (T ₁ ) and the number of palladium particles belonging to the second particle group (T _2). ) Is a palladium colloid solution having a ratio (T ₁ / (T ₁ + T ₂ )) to the total of 20% or more and 90% or less.   The palladium colloid solution according to claim 1, wherein the average particle diameter of the palladium particles excluding the particles belonging to the first particle group is 10 nm or more and 30 nm or less.   The palladium colloid solution according to claim 1 or 2, wherein a zeta potential of the palladium colloid solution at pH 5 or more and pH 8 or less is -30 mV or less. The palladium colloid solution according to any one of claims 1 to 3, wherein the solvent is water, and the chemical oxygen demand (COD _Mn ) by the acidic high-temperature permanganate method is 1000 ppm or less. A method for producing a palladium colloid solution according to any one of claims 1 to 4, comprising a reduction step of reducing palladium ions in the palladium salt solution to form palladium particles,
An insolubilization step of adding an alkali to the palladium salt solution to precipitate insoluble palladium;
A reducing step of reducing a palladium ion in the insoluble palladium by adding a reducing agent to the insoluble palladium, and
After the insolubilization step and before the reduction step, it further has a washing step of washing insoluble palladium until the electric conductivity of the washing liquid becomes 100 μS / cm or less,
The insoluble palladium is a method for producing a palladium colloid solution in which palladium hydroxide, palladium oxide, dinitrodiamine palladium, or a complex thereof is used.   6. The method for producing a palladium colloid solution according to claim 5, wherein the palladium salt is dinitrodiamine palladium.   The method for producing a palladium colloid solution according to claim 5 or 6, wherein the palladium salt solution is a nitric acid solution.   The method for producing a palladium colloid solution according to any one of claims 5 to 7, wherein the alkali is an inorganic alkali metal hydroxide or an inorganic alkaline earth metal hydroxide.   The method for producing a palladium colloid solution according to any one of claims 5 to 8, wherein the reducing agent is a secondary alcohol. The method for producing a palladium colloid solution according to any one of claims 5 to 9, further comprising a desalting step of ultrafiltration of the palladium colloid solution after the reduction step.