WO2005092784A1 - Synthesis of platinum and palladium quantum well size nano-particles - Google Patents

Synthesis of platinum and palladium quantum well size nano-particles Download PDF

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Publication number
WO2005092784A1
WO2005092784A1 PCT/IN2004/000072 IN2004000072W WO2005092784A1 WO 2005092784 A1 WO2005092784 A1 WO 2005092784A1 IN 2004000072 W IN2004000072 W IN 2004000072W WO 2005092784 A1 WO2005092784 A1 WO 2005092784A1
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platinum
palladium
nano particles
ethylene glycol
range
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PCT/IN2004/000072
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French (fr)
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Madan Lal Singla
Mewa Singh
Dharam Veer Singh Jain
Ram Kishore
Ram Prakash Bajpai
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Council Of Scientific & Industrial Research
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Priority to PCT/IN2004/000072 priority Critical patent/WO2005092784A1/en
Priority to CNA2004800428894A priority patent/CN1946628A/en
Publication of WO2005092784A1 publication Critical patent/WO2005092784A1/en

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    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/02—Elements
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B01J23/40—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals of the platinum group metals
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B01J23/40—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals of the platinum group metals
    • B01J23/44—Palladium
    • B01J35/23—
    • B01J35/393—
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/16—Reducing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/60—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape characterised by shape
    • C30B29/605—Products containing multiple oriented crystallites, e.g. columnar crystallites
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B7/00—Single-crystal growth from solutions using solvents which are liquid at normal temperature, e.g. aqueous solutions
    • C30B7/02—Single-crystal growth from solutions using solvents which are liquid at normal temperature, e.g. aqueous solutions by evaporation of the solvent
    • C30B7/06—Single-crystal growth from solutions using solvents which are liquid at normal temperature, e.g. aqueous solutions by evaporation of the solvent using non-aqueous solvents
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
    • B01J21/12—Silica and alumina
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/0215—Coating

Definitions

  • TECHNICAL FIELD The present relates to a novel process for synthesis of platinum and palladium quantum well size nano-particles in ethylene gylcol medium in which ethylene glycol acts as a combined dispersing medium, reducing agent and capping agent.
  • BACKGROUND OF THE INVENTION The synthesis and properties of nano particles have commercial importance due to their potential utilization in catalysis, optoelectronic devices, photonics, magnetic and ultra sensitive chemical sensors. Many gas phase catalytic processes exhibit a pronounced, particle size dependence of catalytic activity.
  • the nano particles possess a very large surface to volume ratio; consequently the surface chemistry of nano-particles plays an important role. Control of particle size, the size distribution and particle shape leads to understanding of their specific properties.
  • the nano particles may consist of metals, ceramics and semi-conductors or even composites.
  • a number of methods such as photolytic reduction, radiolytic reduction, sono-chemical reduction method, micro emulsion technique, polyol process, reduction by alcohol and many other methods have been used for the synthesis of Pt & Pd metal nanoparticles.
  • different capping agents have been used alongwith different reducing agents. These capping agents are highly costly and perform under restricted conditions. Moreover, sometimes these add certain impurities also.
  • the Inventors adopt a simple process for the synthesis of Pt, Pd, and Au nano particles using ethylene glycol or glycerol where the same substance acts as dispersing media, self reducing agent and also capping agent.
  • alkane-thiols with various chain lengths (C 3 - C 24 ) and perfluorinated thiols to produce and cap metal nano particles. These involve reduction of metal salts at controlled pH and stabilization in aqueous or organic layer capping with thiol. Number of alkane-thiol have been used as capping agent to provide protecting properties for metal core (Pt, Pd, Au) and allow reasonable solubility in non polar organic solvents.
  • the reported polymers are poly vinylpyriOlidone, poly dithiofulvene, Dendrimers N-isopropylacylamide, chitosan, N-isopropylacrylamide polymer [PNIPA Am-Pfj. N-vinylisobutyramide has been used for encapsulating nanoparticles. These systems produce nano particles with large variation in nano sizes. Colloidal Platinum nano particles in the range of 10-30A were reported in ethanol water mixture in the presence of Poly (N-vinylisobutyramide) (PNVIBA).
  • Thiol functionalised platinum nano particles have been prepared in tetra-hydrofuoran as dispersing medium, lithium-triethyl borohydride as reducing agent and octadecanthiol as stabilizing agent.
  • the size of nano particles is around 3 nm.
  • this method involves the use of a large number of reagents besides this method is quite tedious.
  • Chitosan is a natural polymer which has been used for synthesis Pt, Pd nano particles using hydrazine or borohydride as reducing agent .
  • the diameter of the nano particles is around 3nm, however, synthesis involves the use number of number of reagents.
  • Regular Pt nano particles have been obtained by epitaxial deposition on NaCl surfaces supported by thin film of Ceria subject to hydrogen reduction up to 1073K.
  • a reference may be made to Take Fujimoto, etal ;Scripta Materialial 44,( 2001), P 2183-860.
  • the size of nano particles according to the above reference was found to be 10-15 nm. This process needs high cost equipment and vacuum of the order of 10 ⁇ 6 m bar.
  • Au nano particles have been prepared by sono- chemical reduction in aqueous medium where metal salt, surfactant, reducing agent are being used.
  • a multi wave ultra sound generator with a barium titanate oscillator has been used for sonif ⁇ cation.
  • the particle size is formed 2 to 10 nm.
  • a reference may be made to Chen. D.H. J. Collid interface Science Vol. 219, P 123-129, 155-166, 1999 in this regard.
  • Pt- Ni nano particles were prepared by hydrazine reduction of the metal salts by prolonged reaction at room temperature and microwave assisted reduction.
  • a reference may be made to O.P. Yadav etal, Colloids & Surfaces 221(2003), P 131-134. According to this reference, the average particle size is 2.9 to 5.8 nm.
  • the Pt, Pd nano particles have also been prepared by the reduction of metal ions with hydrazine or Borohydride in oil water micro emulsion and consisting of AOT or other surfactants, cyclohexane and aqueous solution of metal salt varying compositions. These nano particles are stable in micro-emulsion On breaking, the micro-emulsion nano particles start coagulating resulting in increase in size. The technique involves high cost of synthesis as well as a large number of reagents.
  • the main object of the present invention is synthesis of Pt and Pd metal nano particles of quantum well size around 3 nm in ethylene glycol medium, in which ethylene glcycol acts both as reducing and capping agent.
  • Another object of the present invention is that the nano particles do not aggloramate for long storage.
  • Another objective of the present invention is that nano particles do not get oxidized on centrifugation or during synthesis.
  • Another objective of the present invention is that nano particle should be free of impurities.
  • nano particles should work as better catalyst due to large surface area.
  • nano particles may get adsorbed on surface like silica, alumina or porous materials for their use in opto-electonic devices/catalysis.
  • nano particles of varying size can be prepared by varying the composition of the reaction mixture.
  • Yet another objective of the present invention is to synthesize the nano particles at much faster rate than the existing methods.
  • the present invention relates to a process for the synthesis of platinum and palladium quantum well size nano-particles in ethylene gylcol medium in which ethylene glycol acts as a combined dispersing medium, reducing agent and capping agent.
  • the present invention provides a process for preparing quantum well size nano particles of platinum / palladium having particle size in the range of 2 to 10 nm, said process comprising the steps of adding ethylene glycol / glycerol to platinum / palladium , salt solution, wherein ethylene glycol / glycerol acts as a combined dispersing medium, reducing agent and capping agent.
  • ethylene glycol / glycerol acts as a combined dispersing medium, reducing agent and capping agent.
  • a mixture of ethylene glycol / glycerol and platinum / palladium salt solution is heated to a temperature in the range of 105° to 140°C to obtain nano particles of platinum / palladium and a mother liquor.
  • the platinum salt solution used is an aqueous solution of H 2 PtCl 6 .6H 2 O.
  • the palladium salt solution used is an aqueous solution of PdCl 2 .
  • the concentration of platinum / palladium to ethylene glycol / glycerol is in the range of 0.025 to 1%.
  • the mixture of ethylene glycol / glycerol and platinum / palladium salt solution is mixed by stirring for a time period of about 30 about minutes and the pH of the solution is maintained between 4 to 6.
  • the mixture of ethylene glycol / glycerol and platinum / palladium salt solution is a clear transparent solution having an absorption peask for Pt(IV) in ethylene glycol medium at 265nm and at 221 nm for Pd(II).
  • the mixture of ethylene glycol / glycerol and platinum salt solution is heated to a temperature in the range of 130° to 140°C till the mixture initially turns brown and then black.
  • the mixture of ethylene glycol / glycerol and platinum salt solution is heated to a temperature in the range of 130° to 140°C for a time period in the range of 5 to 7 minutes.
  • the mixture of ethylene glycol / glycerol and palladium salt solution is heated to a temperature in the range of 105° to 110°C till the mixture initially turns brown and then black.
  • the mixture of ethylene glycol / glycerol and palladium salt solution is heated to a temperature in, the range of 105° to 110°C for a time period in the range of 5 to 7 minutes.
  • the nano particles of platinum is heated to a temperature in the range of 130° to 140°C for a time period in the range of 5 to 7 minutes.
  • the size of palladium nano particles thus obtained is in the range of 2 to 6nm for solution concentration in the range of 5 to 25 mg of palladium nano particles.
  • the present invention more particularly provides a process for preparing quantum well size nano particles of platinum / palladium having particle size in the range of 2 to 10 nm, said process comprising the steps of adding ethylene glycol / glycerol to platinum / palladium salt solution, wherein ethylene glycol / glycerol acts as a combined dispersing medium, reducing agent and capping agent and heating the same at a temperature in the range of
  • reaction mixture has been stirred for 30 minutes.
  • nano particles are formed at temperature 130°C -140°C for Pt and l05°C - 110°C for Pd by keeping it for 3-7 minutes.
  • the nano particles have been characterized by UV- Visible Spectroscopy, Transmission Electron Microscopy, Electron diffraction analysis, XRD & FTIR.
  • these nano particles have been separated from reacting mixture by centrifugation at a speed of 10,000 revolution per minute.
  • Pt & Pd nano particles have been dispersed in different solvent like ethylene glycol, glycerine & alcohols.
  • Pt & Pd nano particles have been coated on alumina and silica mesh size 230-400.
  • these nano particles has been used for catalytic use.
  • other polyhydric alcohols like glycerol and erythritrol has been used for synthesis of these nano particles.
  • Figure 1(a) represents the TEM micrograph of platinum solution containing 5 mg of platinum. As can be seen, the magnification is 3,90,000 times and the particle size was determined to be equal to about 4 nm.
  • Figure 1(b) represents the Electron diffraction pattern of nanoparticles obtained using platinum solution containing 5 mg of platinum.
  • Figure 2(a) represents the TEM micrograph of platinum solution containing 10 mg of platinum. As can be seen, the magnification is 5,20,000 times and the particle size was determined to be equal to about 3 nm.
  • Figure 2(b) represents the Electron diffraction pattern of nanoparticles obtained using platinum solution containing 10 mg of platinum.
  • Figure 3(a) represents the TEM micrograph of platinum solution containing 15 mg of platinum. As can be seen, the magnification is 5,20,000 times and the particle size was determined to be equal to about 3 nm.
  • Figure 3(b) represents the Electron diffraction pattern of nanoparticles obtained using platinum solution containing 15 mg of platinum.
  • Figure 4(a) represents the TEM micrograph of palladium solution containing 10 mg of palladium. As can be seen, the magnification is 3,90,000 times and the particle size was determined to be in the range of 2 to 6 nm.
  • Figure 4(b) represents the Electron diffraction pattern of nanoparticles obtained using palladium solution containing 10 mg of platinum.
  • reaction mixture was stirred for 30 minutes at room temperature. There is no immediate colour change at room temperature.
  • the reaction mixture was heated to 130°C - 140 °C for Pt and 105°C- 110°C for Pd for 3-7 minutes. On heating the colour of mixture first turn brown and finally black. The complete reduction was confirmed from the absorption spectra. It may be noted that no inert atmosphere has been used during the reaction.
  • the Inventors have also find that the method is quite general for production of nano particles of metals from their ions in higher oxidation state provided the sum of the Gibbs enegy for reduction of metal ions and Gibbs energy for the oxidation of glycol to glyoxal is negative.
  • the Inventors also note that a number of polyhydric alcohols like glycerol and eiythritrol are also suitable for production and capping of metal nano particles. Change in the absorption Spectral with Reduction UV & Visible spectral changes were recorded during the reduction of Pt & Pd ions in ethylene glycol.
  • the spectral of the solution consists of a major peak at 265 nm attributed to Pt Cl 6 "2 ion or 221 nm PdCl 2 .
  • the peak at 265 nm & 221 nm disappear indicating the complete formation of Pt (0) & Pd (0)
  • the colour of the solution also turns black.
  • the Pt - ethyleneglycol or Pd- ethylene glycol nano particles are highly stable and can be dispersed in ethylene glycol, glycerine and alcohols after the removal of excess ethyleneglycol.
  • Typical electron micrographs of ethylene glycol Pt, ethylene glycol Pd colloids are shown in figure.
  • the particle size and size distribution of colloidal Pt & Pd nanoparticles derived from TEM measurement are also shown in f ⁇ gure(Figla-4a).
  • TEM image reveals that well dispersed ethylene glycol — Pt nano particles lie between 3 to 4 nm for 5 to 15 mg of Pt concentration (fig la-3a). The Pd nano particles are found to be higher around 2-6 nm.
  • Platinum system - detail study of diffraction pattern of the corresponding area reveals the formation of single phase cubic platinum nano particles (hid) planes with strong deflection (100) and moderate (200).
  • Pd (220) is a strong crystalline cubic plan with weak
  • Alumina or silica in the ratio 100:1 Al 2 O :Pt or Pd is added in Pt(0), Pd (0) colloidal solution.
  • the dispersion mixture is stirred for half an hour and kept for 24 hours so that metal particles get adsorbed on the surface on the alumina or silica surface.
  • Pt or Pd adsorbed nano particles are separated after centrifugation and calcined at 500°C for one hour. After cooling these materials are stored in vacuum desiccators. XRD pattern showed the coated Pt or Pd nano particles on alumina and silica.
  • Example No. 1 Experiments were carried out to prepare Platinum and palladium nano particles using concentration of 5,10andl5 mg of Pt and 10,15 and20 mg of Pd in ethylene glycol medium. It has been observed that nano particles are formed of uniform size under controlled conditions of temperature. The size of pt nanoparticles lies between 3 to4 nm where as in case of pd it lies between 2 to 6nm.
  • Example No. 2 UV & Visible Spectroscopy was carried out and that there is no absorption peak at 265 nm for Pt (0) and 221 nm Pd (0), which was observed in ethylene glycol for metal chloride before the reduction process, starts.
  • Example No. 3 Transmission and electron diffraction studies were earned out which confirm the formation of nano particles of Quantum size. Electron diffraction studies indicate that the nano particles are monodispersive, single-phase cubic.
  • Example No. 4 The Inventors have separated the Pt & Pd nano particle from ethylene glycol by centifiguration and dispersed the same in different solvents. The Inventors have coated these nano particles on silica & alumina.
  • Example No. 5 The Inventors have tried to use these nano particles as catalyst for conversion of CO into carbon dioxide and other organic reactions and found that their results are far better than those obtained in conventional processes.

Abstract

A process for preparing quantum well size nano particles of platinum / palladium having particle size in the range of 2 to 10 nm, said process comprising the steps of adding ethylene glycol / glycerol to platinum / palladium salt solution, wherein ethylene glycol / glycerol acts as a combined dispersing medium, reducing agent and capping agent and heating the same at a temperature in the range of 100° to 140°C to obtain nano particles of platinum / palladium.

Description

SYNTHESIS OF PLATINUM AND PALLADIUM QUANTUM WELL SIZE NANO-PARTICLES
TECHNICAL FIELD The present relates to a novel process for synthesis of platinum and palladium quantum well size nano-particles in ethylene gylcol medium in which ethylene glycol acts as a combined dispersing medium, reducing agent and capping agent. BACKGROUND OF THE INVENTION The synthesis and properties of nano particles have commercial importance due to their potential utilization in catalysis, optoelectronic devices, photonics, magnetic and ultra sensitive chemical sensors. Many gas phase catalytic processes exhibit a pronounced, particle size dependence of catalytic activity. A reference may be made to J.N. Zoval J. Phys. Chem B. 102 (1998) P 1166-75 and Che. M; Bennelt, CO; Adv. Catal 36 (1989), ,55 for more details in this regard. The nano particles possess a very large surface to volume ratio; consequently the surface chemistry of nano-particles plays an important role. Control of particle size, the size distribution and particle shape leads to understanding of their specific properties. The nano particles may consist of metals, ceramics and semi-conductors or even composites. A number of methods such as photolytic reduction, radiolytic reduction, sono-chemical reduction method, micro emulsion technique, polyol process, reduction by alcohol and many other methods have been used for the synthesis of Pt & Pd metal nanoparticles. However, in each synthesis different capping agents have been used alongwith different reducing agents. These capping agents are highly costly and perform under restricted conditions. Moreover, sometimes these add certain impurities also. In the present application, the Inventors adopt a simple process for the synthesis of Pt, Pd, and Au nano particles using ethylene glycol or glycerol where the same substance acts as dispersing media, self reducing agent and also capping agent.
Some of the earlier reported methods use alkane-thiols with various chain lengths (C3- C24) and perfluorinated thiols to produce and cap metal nano particles. These involve reduction of metal salts at controlled pH and stabilization in aqueous or organic layer capping with thiol. Number of alkane-thiol have been used as capping agent to provide protecting properties for metal core (Pt, Pd, Au) and allow reasonable solubility in non polar organic solvents. A reference may be made to J.F. Rivadulla etal J. Phys. Chem. B 101(1997), P. 8997, Murali Sastry etc. Thin Solid Films 324, (1988) 239-244, H.P. Choo etal J. Mater, Chem 11(2001) P-934, H.P. Choo etal J. Mol.. Achem 165(2001) P-127 and F.P.Zamborini etal, Langmuir 17, 481-488(2001) for more detail in this regard.
Certain Polymers such as those described in the above referred documents and in I Quios; Langmuir 18, 1413-18(2002), M Adlim etal ;J. of Molecular catalysis A chemical . 212e (2004) P 141-149, K V Shastry.etal ;Chem. Common 537-38 (1997), Huri Weichem ,etal; Colloids & Surfaces 169 (2002) P 107-116] and Chanel Yee, etal; Langumuir 15(1999)4 P 14-16 have been used for stabilizing the matrices for nano particles. These polymers must have the properties such as easy process ability and a transparence, permeability or conductivity. The reported polymers are poly vinylpyriOlidone, poly dithiofulvene, Dendrimers N-isopropylacylamide, chitosan, N-isopropylacrylamide polymer [PNIPA Am-Pfj. N-vinylisobutyramide has been used for encapsulating nanoparticles. These systems produce nano particles with large variation in nano sizes. Colloidal Platinum nano particles in the range of 10-30A were reported in ethanol water mixture in the presence of Poly (N-vinylisobutyramide) (PNVIBA).
Thiol functionalised platinum nano particles have been prepared in tetra-hydrofuoran as dispersing medium, lithium-triethyl borohydride as reducing agent and octadecanthiol as stabilizing agent. A reference may be made to S. Penner etal; Surface Science, 532- 535(2003) P-276-80]. The size of nano particles is around 3 nm. However, this method involves the use of a large number of reagents besides this method is quite tedious. Chitosan is a natural polymer which has been used for synthesis Pt, Pd nano particles using hydrazine or borohydride as reducing agent .The diameter of the nano particles is around 3nm, however, synthesis involves the use number of number of reagents.
Regular Pt nano particles have been obtained by epitaxial deposition on NaCl surfaces supported by thin film of Ceria subject to hydrogen reduction up to 1073K. A reference may be made to Take Fujimoto, etal ;Scripta Materialial 44,( 2001), P 2183-860. The size of nano particles according to the above reference was found to be 10-15 nm. This process needs high cost equipment and vacuum of the order of 10~ 6m bar.
Pt & Pd, Au nano particles have been prepared by sono- chemical reduction in aqueous medium where metal salt, surfactant, reducing agent are being used. A multi wave ultra sound generator with a barium titanate oscillator has been used for sonifϊcation. The particle size is formed 2 to 10 nm. A reference may be made to Chen. D.H. J. Collid interface Science Vol. 219, P 123-129, 155-166, 1999 in this regard.
Pt- Ni nano particles were prepared by hydrazine reduction of the metal salts by prolonged reaction at room temperature and microwave assisted reduction. A reference may be made to O.P. Yadav etal, Colloids & Surfaces 221(2003), P 131-134. According to this reference, the average particle size is 2.9 to 5.8 nm. The Pt, Pd nano particles have also been prepared by the reduction of metal ions with hydrazine or Borohydride in oil water micro emulsion and consisting of AOT or other surfactants, cyclohexane and aqueous solution of metal salt varying compositions. These nano particles are stable in micro-emulsion On breaking, the micro-emulsion nano particles start coagulating resulting in increase in size. The technique involves high cost of synthesis as well as a large number of reagents.
Mixture of nano size Pt & Pd particles have been prepared by reduction of salt containing micro emulsion droplet using hydrazine or borohydride as reducing agent. This involves the use of ionic as well as non-ionic surfactant such as AOT, CTAB, poly-oxyethylene 4 laurylether and cyclohexane medium. The reaction takes places after stirring it for 20 hours or more. Structure and catalysis properties of nano sized alumina supported Pt & Pd particles synthesized in micro emulsion has also been reported. TEM showed particles of fairly homogenous in size Pt (20-40 nm) and Pd 2-5 nm. Kinetics of formation of nano sized Pt particles in water in oil micro emulsion was studied using surfactant polyethylene glycol, monododceyl ethers, sodium bis-(2-ethylhexyl) sulphosuccinate (AOT), and mixture of alcohol ethoxylates and AOT in heptanes. The platinum particles are found to be less than 5 nm. However, the nano particles are stable in emulsion only.
Objects of the Present Invention: The main object of the present invention is synthesis of Pt and Pd metal nano particles of quantum well size around 3 nm in ethylene glycol medium, in which ethylene glcycol acts both as reducing and capping agent. Another object of the present invention is that the nano particles do not aggloramate for long storage. Another objective of the present invention is that nano particles do not get oxidized on centrifugation or during synthesis. Another objective of the present invention is that nano particle should be free of impurities. Still another objective of the present invention is that nano particles should work as better catalyst due to large surface area.
Another objective of the present invention is that these nano particles may get adsorbed on surface like silica, alumina or porous materials for their use in opto-electonic devices/catalysis. Another objective of the present invention is that nano particles of varying size can be prepared by varying the composition of the reaction mixture.
• Yet another objective of the present invention is to synthesize the nano particles at much faster rate than the existing methods.
BRIEF SUMMARY OF THE INVENTION: The present invention relates to a process for the synthesis of platinum and palladium quantum well size nano-particles in ethylene gylcol medium in which ethylene glycol acts as a combined dispersing medium, reducing agent and capping agent.
DETAILED DESCRIPTION OF THE PRESENT INVENTION: Accordingly, the present invention provides a process for preparing quantum well size nano particles of platinum / palladium having particle size in the range of 2 to 10 nm, said process comprising the steps of adding ethylene glycol / glycerol to platinum / palladium , salt solution, wherein ethylene glycol / glycerol acts as a combined dispersing medium, reducing agent and capping agent. In an embodiment of the present invention, wherein a mixture of ethylene glycol / glycerol and platinum / palladium salt solution is heated to a temperature in the range of 105° to 140°C to obtain nano particles of platinum / palladium and a mother liquor. In another embodiment of the present invention, wherein the platinum salt solution used is an aqueous solution of H2PtCl6.6H2O. In yet another embodiment of the present invention, wherein the palladium salt solution used is an aqueous solution of PdCl2. In still another embodiment of the present invention, wherein the concentration of platinum / palladium to ethylene glycol / glycerol is in the range of 0.025 to 1%. In a further embodiment of the present invention, wherein the mixture of ethylene glycol / glycerol and platinum / palladium salt solution is mixed by stirring for a time period of about 30 about minutes and the pH of the solution is maintained between 4 to 6. In one more embodiment of the present invention, wherein the mixture of ethylene glycol / glycerol and platinum / palladium salt solution is a clear transparent solution having an absorption peask for Pt(IV) in ethylene glycol medium at 265nm and at 221 nm for Pd(II). In one another embodiment of the present invention, wherein the mixture of ethylene glycol / glycerol and platinum salt solution is heated to a temperature in the range of 130° to 140°C till the mixture initially turns brown and then black. In a further more embodiment of the present invention, wherein the mixture of ethylene glycol / glycerol and platinum salt solution is heated to a temperature in the range of 130° to 140°C for a time period in the range of 5 to 7 minutes. In an embodiment of the present invention, wherein the mixture of ethylene glycol / glycerol and palladium salt solution is heated to a temperature in the range of 105° to 110°C till the mixture initially turns brown and then black. In another embodiment of the present invention, wherein the mixture of ethylene glycol / glycerol and palladium salt solution is heated to a temperature in, the range of 105° to 110°C for a time period in the range of 5 to 7 minutes. In yet another embodiment of the present invention, wherein the nano particles of platinum
/ palladium are separated from the mother liquor by centrifugation at speed in the range of
9,000 to 11,000 revolutions per minutes. In still another embodiment of the present invention, wherein the size of platinum nano particles thus obtained is about 3 nm for solution concentration in the range of 5 to 25 mg of platinum nano particles.
In one more embodiment of the present invention, wherein the size of palladium nano particles thus obtained is in the range of 2 to 6nm for solution concentration in the range of 5 to 25 mg of palladium nano particles.
In one another embodiment of the present invention, wherein the platinum nano particles thus obtained have face centered cubic having hkl planes with strong deflection pack at
(100) and moderate deflection peak at (200).
In a further embodiment of the present invention, wherein the palladium nano particles thus obtained have face centered cubic having pd planes with strong deflection pack at
(220) and weak deflection peaks at (111) and (200).
In a further more embodiment of the present invention, wherein the platinum and palladium nano particles thus obtained is crystalline in nature.
The present invention more particularly provides a process for preparing quantum well size nano particles of platinum / palladium having particle size in the range of 2 to 10 nm, said process comprising the steps of adding ethylene glycol / glycerol to platinum / palladium salt solution, wherein ethylene glycol / glycerol acts as a combined dispersing medium, reducing agent and capping agent and heating the same at a temperature in the range of
100° to 140°C to obtain nano particles of platinum / palladium. In other embodiment of the present invention [ H2PtCl6 ] 6H2O has been prepared by dissolving platinum metal (99.999% pure) and palladium chloride of Arora Matthey
Limited has been used by dissolving in double distilled water and a few drops of concentrated HC1.
In another embodiment of the present invention the reaction mixture has been stirred for 30 minutes. In another embodiment of the present invention nano particles are formed at temperature 130°C -140°C for Pt and l05°C - 110°C for Pd by keeping it for 3-7 minutes.
In another embodiment of the present invention the nano particles have been characterized by UV- Visible Spectroscopy, Transmission Electron Microscopy, Electron diffraction analysis, XRD & FTIR.
In another embodiment of the present invention these nano particles have been separated from reacting mixture by centrifugation at a speed of 10,000 revolution per minute.
Another embodiment of the present invention Pt & Pd nano particles have been dispersed in different solvent like ethylene glycol, glycerine & alcohols.
In yet another embodiment of the present invention Pt & Pd nano particles have been coated on alumina and silica mesh size 230-400.
In other embodiment of the present invention these nano particles has been used for catalytic use. In other embodiment of the present invention other polyhydric alcohols like glycerol and erythritrol has been used for synthesis of these nano particles.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
In the drawings accompanying the specification,
Figure 1(a) represents the TEM micrograph of platinum solution containing 5 mg of platinum. As can be seen, the magnification is 3,90,000 times and the particle size was determined to be equal to about 4 nm.
Figure 1(b) represents the Electron diffraction pattern of nanoparticles obtained using platinum solution containing 5 mg of platinum.
Figure 2(a) represents the TEM micrograph of platinum solution containing 10 mg of platinum. As can be seen, the magnification is 5,20,000 times and the particle size was determined to be equal to about 3 nm.
Figure 2(b) represents the Electron diffraction pattern of nanoparticles obtained using platinum solution containing 10 mg of platinum. Figure 3(a) represents the TEM micrograph of platinum solution containing 15 mg of platinum. As can be seen, the magnification is 5,20,000 times and the particle size was determined to be equal to about 3 nm. Figure 3(b) represents the Electron diffraction pattern of nanoparticles obtained using platinum solution containing 15 mg of platinum.
Figure 4(a) represents the TEM micrograph of palladium solution containing 10 mg of palladium. As can be seen, the magnification is 3,90,000 times and the particle size was determined to be in the range of 2 to 6 nm.
Figure 4(b) represents the Electron diffraction pattern of nanoparticles obtained using palladium solution containing 10 mg of platinum.
MATERIALS & METHODS OF SYNTHESIS
One gm of Pt metal was digested with (3 parts HC1 & 1 part HNO3) on hot plate till Platinum metal is dissolved. The solution was heated to dryness to remove all acid and the residue was dissolved in water to make the final volume equal to 100 ml. Ethylene glycol of Qualigens brand was used. Palladium chloride was dissolved in water and a few drops of cone. HC1 were added to clear the solution.
Preparation of Nano particles Aliquots of 0.33 ml to 1 ml of Chloroplatinic acid [H2PtCl6] 6H2O solution of molar concentration 1.9897 x 10"2 M or 1 and 2 ml of PdCl2 solution concentration of 4.69 x 10"2
M were taken in each 100 ml glass stoppered flasks and added 20ml of ethylene glycol.
Each reaction mixture was stirred for 30 minutes at room temperature. There is no immediate colour change at room temperature. The reaction mixture was heated to 130°C - 140 °C for Pt and 105°C- 110°C for Pd for 3-7 minutes. On heating the colour of mixture first turn brown and finally black. The complete reduction was confirmed from the absorption spectra. It may be noted that no inert atmosphere has been used during the reaction.
The Inventors have also find that the method is quite general for production of nano particles of metals from their ions in higher oxidation state provided the sum of the Gibbs enegy for reduction of metal ions and Gibbs energy for the oxidation of glycol to glyoxal is negative. The Inventors also note that a number of polyhydric alcohols like glycerol and eiythritrol are also suitable for production and capping of metal nano particles. Change in the absorption Spectral with Reduction UV & Visible spectral changes were recorded during the reduction of Pt & Pd ions in ethylene glycol. At the beginning of the refluxing time the spectral of the solution consists of a major peak at 265 nm attributed to Pt Cl6 "2 ion or 221 nm PdCl2. On reduction, the peak at 265 nm & 221 nm disappear indicating the complete formation of Pt (0) & Pd (0) The colour of the solution also turns black. Importantly the Pt - ethyleneglycol or Pd- ethylene glycol nano particles are highly stable and can be dispersed in ethylene glycol, glycerine and alcohols after the removal of excess ethyleneglycol.
TEM Image of Colloidal Nanoparticles
Typical electron micrographs of ethylene glycol Pt, ethylene glycol Pd colloids are shown in figure. The particle size and size distribution of colloidal Pt & Pd nanoparticles derived from TEM measurement are also shown in fϊgure(Figla-4a). TEM image reveals that well dispersed ethylene glycol — Pt nano particles lie between 3 to 4 nm for 5 to 15 mg of Pt concentration (fig la-3a). The Pd nano particles are found to be higher around 2-6 nm.
This reveals that ethylene glycol is acting as protective layer around the particle surface via OH group with Platinum atom, preventing the particle aggregation.
The electron diffraction pattern of platinum and palladium nano particles is shown in figure ( lb to 4b). .
Platinum system : - detail study of diffraction pattern of the corresponding area reveals the formation of single phase cubic platinum nano particles (hid) planes with strong deflection (100) and moderate (200). In case of Pd (220) is a strong crystalline cubic plan with weak
(111) and (200) planes. The results confirm the formation of pure mono disperse Pt & Pd cubic nanoparticles.
Coating of Pt & Pd Nano particle on Alumina & Silica
Alumina or silica in the ratio 100:1 Al2O :Pt or Pd is added in Pt(0), Pd (0) colloidal solution. The dispersion mixture is stirred for half an hour and kept for 24 hours so that metal particles get adsorbed on the surface on the alumina or silica surface.
Pt or Pd adsorbed nano particles are separated after centrifugation and calcined at 500°C for one hour. After cooling these materials are stored in vacuum desiccators. XRD pattern showed the coated Pt or Pd nano particles on alumina and silica. The invention is further described with reference to the following examples which are given by way of illustration and should not be construed to limit the scope of the present invention in any manner.
Example No. 1: Experiments were carried out to prepare Platinum and palladium nano particles using concentration of 5,10andl5 mg of Pt and 10,15 and20 mg of Pd in ethylene glycol medium. It has been observed that nano particles are formed of uniform size under controlled conditions of temperature.The size of pt nanoparticles lies between 3 to4 nm where as in case of pd it lies between 2 to 6nm.
Example No. 2: UV & Visible Spectroscopy was carried out and that there is no absorption peak at 265 nm for Pt (0) and 221 nm Pd (0), which was observed in ethylene glycol for metal chloride before the reduction process, starts.
Example No. 3: Transmission and electron diffraction studies were earned out which confirm the formation of nano particles of Quantum size. Electron diffraction studies indicate that the nano particles are monodispersive, single-phase cubic. Example No. 4: The Inventors have separated the Pt & Pd nano particle from ethylene glycol by centifiguration and dispersed the same in different solvents. The Inventors have coated these nano particles on silica & alumina.
Example No. 5: The Inventors have tried to use these nano particles as catalyst for conversion of CO into carbon dioxide and other organic reactions and found that their results are far better than those obtained in conventional processes.

Claims

CLAIMS:
1. A process for preparing quantum well size nano particles of platinum / palladium having particle size in the range of 2 to .10 nm, said process comprising the steps of adding ethylene glycol / glycerol to platinum / palladium salt solution, wherein ethylene glycol / glycerol acts as a combined dispersing medium, reducing agent and capping agent.
2. The process as claimed in claim 1, wherein a mixture of ethylene glycol / glycerol and platinum / palladium salt solution is heated to a temperature in the range of 105° to 140°C to obtain nano particles of platinum / palladium and a mother liquor.
3. The process as claimed in claim 1, wherein the platinum salt solution used is an aqueous solution of H2PtCl6.6H2O.
4. The process as claimed in claim 1, wherein the palladium salt solution used is an aqueous solution of PdCl2.
5. The process as claimed in claim 1, wherein the concentration of platinum / palladium to ethylene glycol / glycerol is in the range of 0.025 to 1%.
6. The process as claimed in claim 1, wherein the mixture of ethylene glycol / glycerol and platinum / palladium salt solution A mixed by stirring for a time period of about 30 about minutes and the pH of the solution is maintained between 4 to 6.
7. The process as claimed in claim 1, wherein the mixture of ethylene glycol / glycerol and platinum / palladium salt solution is a clear transparent solution having an absorption peask for Pt(IV) in ethylene glycol medium at 265nm and at 221 nm for Pd(II). 8. The process as claimed in claim 2, wherein the mixture of ethylene glycol / glycerol and platinum salt solution is heated to a temperature in the range of 130° to 140°C till the mixture initially turns brown and then black.
. The process as claimed in claim 8, wherein the mixture of ethylene glycol / glycerol and platinum salt solution is heated to a temperature in the range of 130° to 140°C for a time period in the range of 5 to 7 minutes. 10. The process as claimed in claim 2, wherein the mixture of ethylene glycol / glycerol and palladium salt solution is heated to a temperature in the range of 105° to 110°C till the mixture initially turns brown and then black.
11. The process as claimed in claim 10, wherein the mixture of ethylene glycol / glycerol and palladium salt solution is heated to a temperature in the range of 105° to 110°C for a time period in the range of 5 to 7 minutes.
12. The process as claimed in claim 2, wherein the nano particles of platinum / palladium are separated from the mother liquor by centrifugation at speed in the range of 9,000 to 11 ,000 revolutions per minutes.
13. The process as claimed in claim 1, wherein the size of platinum nano particles thus obtained is about 3 nm for solution concentration in the range of 5 to 25 mg of ' platinum nano particles.
14. The process as claimed in claim 1, wherein the size of palladium nano particles thus obtained is in the range of 2 to 6nm for solution concentration in the range of 5 to 25 mg of palladium nano particles.
15. The process as claimed in claim 1, wherein the platinum nano particles thus obtained have face centered cubic having hid planes with strong deflection pack at (100) and moderate deflection peak at (200).
16. The process as claimed in claim 1, wherein the palladium nano particles thus obtained have face centered cubic having pd planes with strong deflection pack at (220) and weak deflection peaks at (111) and (200).
17. The process as claimed in claim 1, wherein the platinum and palladium nano particles thus obtained is crystalline in nature. A process for preparing quantum well size nano particles of platinum / palladium having particle size in the range of 2 to 10 nm, said process comprising the steps of adding ethylene glycol / glycerol to platinum / palladium salt solution, wherein ethylene glycol / glycerol acts as a combined dispersing medium, reducing agent and capping agent and heating the same at a temperature in the range of 100° to 140°C to obtain nano particles of platinum / palladium.
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