KR20180072100A - Pd octahedron nano catalysts with noble metal doping by galvanic replacement method and method for direct synthesis of hydrogen peroxide using the catalysts - Google Patents

Abstract

In order to increase the production rate of hydrogen peroxide in a direct hydrogen peroxide production reaction, a palladium (Pd) atom is substituted with a noble metal atom such as platinum (Pt) by using a galvanic substitution reaction and a very small amount of palladium The present invention relates to a catalyst for direct preparation of hydrogen peroxide and a method for directly preparing hydrogen peroxide using the same, characterized in that the rate of hydrogen peroxide generation is greatly increased by noble metals such as platinum (Pt) substituted on the surface of palladium (Pd) .

Description

TECHNICAL FIELD [0001] The present invention relates to a palladium nano-octahedral catalyst in which palladium atoms are substituted with noble metal atoms through a galvanic substitution reaction, and a direct preparation method of hydrogen peroxide using the same. BACKGROUND ART [0002]

The present invention relates to a palladium (Pd) nano-octahedral catalyst in which palladium (Pd) existing on the surface of an octahedron is substituted with a noble metal such as platinum (Pt) through a galvanic substitution reaction and a method for producing hydrogen peroxide using the same.

Hydrogen peroxide is an oxidizing agent used in various industrial fields such as bleaching of pulp and paper, treatment of wastewater generated during processing, detergent, bactericide, extraction agent and the like. In particular, since hydrogen peroxide is the environmentally friendly oxidizing agent containing only the largest amount of active oxygen, which is 47 wt.%, Compared with other oxidizing agents such as HNO ₃ , N ₂ O and NaClO, Demand for hydrogen peroxide is expected to increase with regulations.

At present, commercial production of hydrogen peroxide is carried out by the anthraquinone oxidation process (AO process), but the use of toxic anthraquinone compounds and organic solvents in the human body and the risk of explosion during transportation are all important factors in stabilizing agents There is a disadvantage in that the transportation cost is high due to the addition or dilution process.

In order to solve the above problems, direct synthesis of H ₂ O ₂ has been proposed as a process for producing hydrogen peroxide which is nontoxic, environmentally friendly and economical to the human body. Unlike the anthraquinone oxidation process (AO process), direct synthesis does not use toxic organic materials but only water as an byproduct. In addition, since a plant having a small-sized scale is more economical than an anthraquinone oxidation process, it is easy to construct around a plant requiring hydrogen peroxide, thereby greatly reducing the risk of explosion during transportation (Korean Patent Laid-Open Publication No. 2002-0032225 number). However, the direct synthesis of hydrogen peroxide has a disadvantage of low selectivity for hydrogen peroxide. To solve this problem, Pd, a noble metal, is used as a catalyst for directly enhancing the activity of synthesis.

However, since the adverse reactions in which water is generated in the direct hydrogen peroxide reaction also occur spontaneously, studies for obtaining the selectivity and high production rate of hydrogen peroxide are necessary.

Accordingly, the present invention provides a catalyst capable of increasing hydrogen peroxide selectivity and production rate when a palladium (Pd) catalyst is used in a direct production method of hydrogen peroxide. The present invention also provides a method for directly producing hydrogen peroxide using the catalyst.

The present invention provides a palladium (Pd) nano-octahedral catalyst for the production of hydrogen peroxide, wherein the palladium (Pd) nano octahedron is characterized in that a very small amount of palladium (Pd) , And the palladium (Pd) nano octahedral catalyst has a mole ratio of noble metal / palladium of 0.001 to 0.1.

According to an embodiment of the present invention, the noble metal atom may be any one selected from Au, Pt, and Ir.

According to an embodiment of the present invention, the catalyst may be selected from the group consisting of silica (SiO ₂ ), titania (TiO ₂ ), titanium nitride (TiN), magnesium oxide, cerium oxide, carbon or mixtures thereof.

According to one embodiment, the galvanic halogen ions in the displacement reaction ^{(F -, Cl -, Br} -, I -) the use, wherein the galvanic halogen ions (F in the substitution reaction, and ^-, Cl ^-, Br ^-, I ^- ) may be 0.01 to 0.05 M concentration.

The present invention also provides a method for directly producing hydrogen peroxide comprising the step of supplying hydrogen and oxygen to a reactor containing the direct catalyst for preparing hydrogen peroxide and a solvent to react.

According to an embodiment of the present invention, the solvent may be an alcohol solvent selected from methanol, ethanol and mixtures thereof, or may be used for mixing the alcohol solvent and water.

According to one embodiment, the solvent is sulfuric acid (H ₂ SO _4), hydrochloric acid (HCl), phosphoric acid (H ₃ PO ₄₎ and nitric acid (HNO ₃₎ may further include at least one acid selected from have.

According to an embodiment of the present invention, the molar ratio of hydrogen to oxygen may be 1: 5 to 1:15.

According to one embodiment of the present invention, the reaction may be carried out at a pressure of from 1 to 40 atm and at a temperature of from 0 to 30 < 0 > C.

The palladium (Pd) nano-octahedral catalyst in which some palladium (Pd) atoms present on the surface through the galvanic substitution reaction according to the present invention are substituted with noble metal atoms such as platinum (Pt) A high hydrogen peroxide generation rate can be achieved.

1 (a) to 1 (d) each show a Pd nanosecopolymer (a), a Pd nanos octahedron catalyst partially substituted with Pt by galvanic substitution reaction, (c) , And (d) a Pd nanos octahedral catalyst catalyst partly substituted with Pt by a galvanic substitution reaction on a silica carrier.
FIG. 2 is an image in which Pd and Pt are mapped by observing Pd nano octahedral catalyst partially substituted with Pt by galvanic substitution reaction with HAADF.
FIG. 3 is a graph comparing the direct production rate of hydrogen peroxide using a conventional Pd nano octahedral catalyst and a Pd nano octahedral catalyst partially substituted with Pt by a galvanic substitution reaction.

Hereinafter, the present invention will be described in more detail.

One aspect of the present invention is a catalyst for the direct preparation of hydrogen peroxide which is characterized in that a very small amount of palladium (Pd) atom existing on the surface of the palladium (Pd) nano octahedron is substituted with a noble metal such as platinum (Pt) The nano-octahedral catalyst is characterized in that the mole ratio of noble metal / palladium is 0.001 to 0.1. The catalyst according to the present invention exhibits a higher rate of hydrogen peroxide generation than a normal Pd nano-octahedral catalyst in the direct preparation of hydrogen peroxide .

The inventors of the present invention have found that palladium (Pd) nano-octahedral particles surrounded by {111} faces are much better in selectivity and production rate than palladium (Pd) nano-hexahedral particles surrounded by {100} In addition, catalytic particles composed of pure platinum (Pt) increase the rate of hydrogen peroxide decomposition and do not show great activity for the synthesis of hydrogen peroxide. However, when a small amount of platinum (Pt) atom is added to palladium (Pd) And the improvement was confirmed by experiments.

Further, in the present invention, a galvanic substitution reaction is used as a method for replacing a very small amount of palladium (Pd) atoms present on the surface of the palladium (Pd) nanosecuhedral particles with platinum (Pt).

Since the standard reduction potential of Pd ^{2 +} is lower than that of Pt ^{2 +} , a galvanic substitution reaction is possible, and Br ^- ions are adsorbed to etch Pd ^{2 +} to promote galvanic substitution reaction of Pd and Pt. The reaction in which Pd is etched by Br ^- is according to the following formula (1), and the galvanic substitution reaction between Pd and Pt follows the following formula (2).

Pd (s) + 4Br ^- ? PdBr ₄ ^{2 -} + 2e ^-

???????? Pt ^{2 +} + 2e ^- ? Pt (s)

In the present invention, a catalyst production method comprising a galvanic substitution reaction process in which a very small amount of palladium (Pd) atoms existing on the surface of a palladium (Pd) nano octahedron is substituted with a platinum (Pt) atom was used. It was confirmed that the platinum (Pt) atom was substituted on the surface of the octahedron particle, and when the catalyst was applied to the direct preparation of hydrogen peroxide, the hydrogen peroxide generation rate was significantly increased as compared with the ordinary palladium (Pd) nano octahedral catalyst.

The reaction rate constant for the reaction in which hydrogen peroxide is generated increases when a small amount of platinum (Pt) atom is added to the palladium (Pd) catalyst, and the reaction rate constant for the reaction in which water is produced is lowered.

Therefore, when the palladium (Pd) nanoparticle substituted with a very small amount of noble metal platinum (Pt) by galvanic substitution reaction is supported on silica to participate in the hydrogen peroxide direct preparation reaction, the conventional general palladium (Pd) It is possible to obtain a hydrogen peroxide generation rate about twice as high as that of the catalyst supported on the catalyst.

According to another aspect of the present invention, there is provided a method for directly producing hydrogen peroxide comprising the step of supplying hydrogen and oxygen to a reactor including a nanoparticle catalyst and a solvent for direct preparation of hydrogen peroxide according to the present invention and reacting.

The solvent may be an alcohol solvent selected from the group consisting of methanol, ethanol and mixtures thereof, or a mixed solvent of the alcohol solvent and water, preferably a mixed solvent of ethanol and water.

The solvent may further include an acid. The addition of an acid can greatly increase the yield of hydrogen peroxide by inhibiting the decomposition of the produced hydrogen peroxide.

The acid may be one or more selected from sulfuric acid (H ₂ SO ₄ ), hydrochloric acid (HCl), phosphoric acid (H ₃ PO ₄ ) and nitric acid (HNO ₃ ), preferably phosphoric acid, In the solvent may be from 0 to 1 M, preferably from 0 to 0.1 M.

The reactants, hydrogen and oxygen, may be in a gaseous form and may be preferably fed directly to the solvent using a Dip Tube which may be contained in a solvent to improve the solubility in the solvent.

The hydrogen gas may be flowed at a flow rate of 1 to 4 mL / min, and the oxygen gas may be flowed at a flow rate of 10 to 40 mL / min. More preferably, the hydrogen: oxygen molar ratio may be 1: 5 to 1: 15 while the hydrogen gas is maintained at 1.5 to 2.5 mL / min and the oxygen gas is maintained at 15 to 25 mL / min. The ratio of hydrogen to oxygen is 1: 1, but if the concentration of hydrogen is high, there is a danger of explosion. Therefore, if the ratio of oxygen is lower than 1: 5, there is danger of explosion. The range of the hydrogen: oxygen molar ratio is preferable because the concentration of supplied hydrogen is low and thus it is not efficient.

While the hydrogen gas and the oxygen gas are flowed at a constant flow rate, the entire reaction pressure is regulated using a BPR (Back Pressure Regulator), and the reaction pressure can be measured through a pressure gauge connected to the reactor. The reaction pressure is preferably maintained at 1 to 40 atm, preferably at normal pressure, and it may be preferable to conduct the reaction while maintaining the reaction temperature at 0 to 30 占 폚.

Preferably, the reactor is further reacted by supplying nitrogen as a reactant. When using nitrogen, it is possible to deviate from the explosion range even if the ratio of hydrogen to oxygen is set to 1: 1, and there is an advantage that it can be used without additional nitrogen separation when using oxygen in the air in the future.

Hereinafter, the present invention will be described in detail by way of examples. However, these embodiments are provided to explain the present invention more clearly and not to limit the scope of the present invention.

Comparative Example  1. Pd nano octahedral / SiO ₂  Catalyst preparation

Pd nano octahedral particles are synthesized by growing crystals with Pd nanocapsules as seeds. The Pd nanocapsules as seeds follow the following procedure.

Polyvinylpyrrolidone (PVP, MW = 55,000 g / mol, 0.189 mmol) and KBr (Sigma-Aldrich, ≥99%, 5 mmol) Prepare 16 mL of the solution dissolved in DI water. After raising the temperature of this solution to 80 ° C, add 6 mL of 63.8 mM Na ₂ PdCl ₄ (Sigma-Aldrich, ≥98%) solution and stir at 80 ° C for 3 hours. To 5 mL of the synthesized Pd nanocomposite solution, 50 mL of acetone was added, and the Pd nanoclusters were collected by centrifugation. The Pd nanoclusters were collected and washed several times in DI water to remove residual PVP and Br ^- ions in the solution.

The Pd nanocomposite solution after the washing process is dispersed in 22 mL of DI water. 16 mL of a solution of PVP (0.189 mmol) and formaldehyde solution (Sigma-Aldrich, 37 wt.% In H ₂ O, 200 μL) dissolved in DI water and 0.6 mL of a Pd nano hexahedron solution were stirred for 30 minutes, Lt; / RTI > Add 6 mL of 33 mM Na ₂ PdCl ₄ solution and stir at 55 ° C for 4 hours. To 5 mL of the synthesized Pd octahedron solution, 50 mL of acetone was added, and the Pd octahedra was collected by centrifugation. The Pd octahedron was collected and washed several times in DI water to remove remaining PVP in the solution.

The following is the silica supporting process. An appropriate amount of the Pd octahedron solution is dispersed in a silica gel (Sigma-Aldrich, Davisil Grade 633, pore size = 60 Å, 200-425 mesh particle size) solution and stirred for 8 hours to carry on SiO ₂ . To remove the remaining PVP in the solution, acetic acid is added and stirring is continued for 24 hours. This solution is collected by centrifugation, washed several times and dried thoroughly for more than one day in a drying oven at 60 ° C. The catalyst was reduced at 60 DEG C for 2 hours using a mixed gas of hydrogen and nitrogen (hydrogen: nitrogen = 1: 9).

Example  1. Pd nano octahedron substituted with a very small amount of Pt (hereinafter referred to as Pt-Pd nano octahedron (1)) / SiO ₂  Catalyst preparation

The Pd nanosecal body solution prepared by the method up to the silica supporting step of Comparative Example 1 was dispersed in 5 mL of DI water. Increase the temperature of PVD (0.132 g) and KBr (0.06 g) in DI water (11 mL) and Pd octahedron solution (5 mL) to 90 ° C. 6 mL of a solution of K ₂ PtCl ₄ (Sigma-Aldrich, ≥98%, 0.42 mg) in DI water is injected at a rate of 60 mL / hr and stirred at 90 ° C. for 16 hours. To 5 mL of the synthesized Pt-Pd nano-octahedron solution, add 50 mL of acetone, precipitate the Pd octahedra by centrifugation, and wash several times in DI water to remove residual PVP in the solution.

The silica supporting process and the catalyst reduction conditions are the same as in Comparative Example 1.

Example  2. Pd nano octahedron (hereinafter referred to as Pt-Pd nano octahedron (2)) in which a very small amount is substituted with Pt / SiO ₂  Catalyst preparation

Except that 0.02 g of KBr was added instead of 0.06 g, the procedure was the same as that of Example 1 except for the synthesis.

Experimental Example  One. Inductively coupled plasma  Spectrometer (ICP- OES ) To determine the contents of Pd and Pt

The contents of Pd and Pt in the catalysts of Comparative Example 1 and Examples 1 and 2 were measured through ICP-OES analysis, and the results are shown in Table 1 below. In the case of Comparative Example 1 in which Pt was not added, Pd was 7839 ppm, and in Example 2 in which Pt and galvanic substitution proceeded, Pd was 5963 ppm and Pt was 93.58 ppm. The ratio of the number of moles of Pt / Pd calculated by this measurement is 0.0086, or 0.86%.

Pd was 6849 ppm and Pt was 68.76 ppm, and the mole ratio of Pt / Pd was 0.0055 in Example 1 in which KBr was added in a smaller amount.

division catalyst Pd (ppm) Pt (ppm) Pt / Pd (molar ratio) Comparative Example 1 Pd nano octahedral / SiO ₂ 7839 0 0 Example 1 Pt-Pd nano octahedron (1) / SiO- ₂ 6849 68.76 0.0055 Example 2 Pt-Pd nano octahedron (2) / SiO ₂ 5963 93.58 0.0086

Experimental Example  2. Transmission Electron Microscope (Transmission Electron Microscope)

The catalysts of Comparative Example 1 and Examples 1 and 2 were observed with a transmission electron microscope (TEM) and are shown in FIG. The photographs observed with an electron microscope were used as data supplementing the above Experimental Example 1. Comparative Example 1 and Examples 1 and 2 were almost the same size and showed the same octahedral particle shape.

Experimental Example  3. HAADF -STM (High-Angle Annular Dark-Field Imaging-Scanning Transmission Electron Microscope) Observation

The Pt-Pd nano octahedral catalyst particles of Example 2 were observed by HAADF-STEM and are shown in FIG. The photographs observed with HAADF-STEM were used as supplementary data for Experimental Example 1 above.

FIG. 2 shows an image obtained by observing a palladium (Pd) nano-octahedral catalyst in which a palladium (Pd) atom on the octahedron surface is partially substituted with platinum (Pt) by HAADF and mapping palladium (Pd) , It can be confirmed that a substituted platinum (Pt) atom exists on the surface of the octahedron.

Experimental Example  4. Manufacture of hydrogen peroxide

Examples 1 to 2 and Comparative Example 1, the reaction of the catalyst in the at 60 ℃ reduction for 2 hours double jacket reactor solvent (DI water, 120 mL; ethanol (ethanol) 30 mL; and phosphoric acid (H ₃ PO ₄₎ 0.03 M , KBr 0.15 mM) and 0.2 g of the catalyst were added, and the reaction was carried out for 3 hours. The reaction temperature was maintained at 20 ° C and the pressure was maintained at 1 atm. The reaction gas (H ₂ / O ₂ = 1/10) was flowed constantly at 22 mL per minute. The hydrogen peroxide produced after the reaction was collected.

The concentration of the collected hydrogen peroxide was measured by the following equation (1) using the iodometric titration method, and the rate of hydrogen peroxide generation was calculated by the following equation (2). The results of the hydrogen peroxide direct preparation reaction are shown in FIG.

[Equation 1]

&Quot; (2) "

As shown in FIG. 3, the hydrogen peroxide generation rate was measured to be twice as high as that in Comparative Example 1, in which the catalyst of Example 2 was used. In the case of Example 1, although the activity was higher than that of Comparative Example 1, the production rate was lower than that of Example 2.

Claims (10)

A palladium (Pd) nano-octahedral catalyst for the production of hydrogen peroxide, wherein the palladium (Pd) atom on the surface of the octahedron is substituted with a noble metal atom by a galvanic substitution reaction, and the noble metal atom / palladium molar ratio is 0.001 to 0.1 Catalyst for the production of hydrogen peroxide. The method according to claim 1,
Wherein the catalyst is selected from the group consisting of silica (SiO ₂ ), titania (TiO ₂ ), titanium nitride (TiN), magnesium oxide, cerium oxide, carbon or mixtures thereof. The method according to claim 1,
Wherein the noble metal atom is any one selected from Au, Pt, and Ir. The method according to claim 1,
Wherein a halogen ion (F ^- , Cl ^- , Br ^- , I ^- ) is used for the galvanic substitution reaction. 5. The method of claim 4,
Wherein the concentration of the halogen ion (F ^- , Cl ^- , Br ^- , I ^- ) in the galvanic substitution reaction is 0.01 to 0.05M concentration. A process for producing hydrogen peroxide comprising the steps of: supplying hydrogen and oxygen to a reactor comprising a catalyst for the production of hydrogen peroxide according to claim 1 and a solvent; The method according to claim 6,
Wherein the solvent is an alcohol solvent selected from the group consisting of methanol, ethanol and mixtures thereof, or a mixed solvent of the alcohol solvent and water. 8. The method of claim 7,
Wherein the solvent further comprises at least one acid selected from sulfuric acid (H ₂ SO ₄ ), hydrochloric acid (HCl), phosphoric acid (H ₃ PO ₄ ) and nitric acid (HNO ₃ ). The method according to claim 6,
Wherein the molar ratio of hydrogen to oxygen is 1: 5 to 1:15. The method according to claim 6,
Wherein the reaction is carried out at a pressure of from 1 to 40 atm and at a temperature of from 0 to 30 < RTI ID = 0.0 > OC. ≪ / RTI >

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