Title of Invention	A METHOD FOR SYNTHESIZING RHODIUM METAL FOAM FROM IONIC LIQUIDS
Abstract	A method for synthesizing rhodium metal foam from ionic liquids comprising adding 1- butyl-3-methylimidazolium chloride (bmimCl) ionic liquid in acetonitrile to rhodium chloride solution; subjecting the mixture to the step of stirring removing the solvent from the mixture; separating the crystallized solid from the solution, and subjecting the crystallized solid to the step of fabrication of rhodium foam.

Title of Invention

A METHOD FOR SYNTHESIZING RHODIUM METAL FOAM FROM IONIC LIQUIDS

Abstract

A method for synthesizing rhodium metal foam from ionic liquids comprising adding 1- butyl-3-methylimidazolium chloride (bmimCl) ionic liquid in acetonitrile to rhodium chloride solution; subjecting the mixture to the step of stirring removing the solvent from the mixture; separating the crystallized solid from the solution, and subjecting the crystallized solid to the step of fabrication of rhodium foam.

Full Text	FORM -2 THE PATENTS ACT, 1970 (39 OF 1970) & The Patents Rules, 2003 COMPLETE SPECIFICATION (See section 10 and rule 13) 1. Title of the Invention : A METHOD FOR SYNTHESIZING RHODIUM METAL FOAM FROM IONIC LIQUIDS 2. Applicant(s) Name, Nationality & Address : THE SECRETARY, DEPARTMENT OF ATOMIC ENERGY, O.Y.C. Building, Chartrapathi Shivaji Maharaj Marg, Mumbai 400 001, Maharashtra, India, an India Institute 3. Preamble to the description : COMPLETE : The following specification particularly describes the invention and the manner in which is to be performed. FIELD OF INVENTION: This invention relates to a method for synthesizing rhodium metal foam from ionic liquids. BACKGROUND OF THE INVENTION: Metal foam is a cellular solid material with wide-open structure. It is made up of a single metal or alloy. Metal foam is characterized by high stiffness, high thermal/electrical conductivity and low specific gravity. Rhodium is a noble metal and it is the costliest metal (2375 US$/ troy oz) [Johnson Matthey pic, London, UK] among all the publicly traded metals. The abundance of rhodium in the earth crust is very low (0.001 gram / tonne) [Ache et ah, Technical report series - No. 308, IAEA, Vienna, 1989] and it is being consumed at a rapid rate to cater the huge demand from various industries. Rhodium has been extensively used in the following applications. In catalytic converters in automobile industry to reduce the toxicity of exhaust gases. Each catalytic converter contains ~2 g of rhodium and other noble metals on a ceramic support. The global demand of rhodium from automobile industry itself amounts to more than four-fifths of its annual production. As catalyst for the treatment of gaseous emissions from thermal power plants and industrial waste gases contaminated with harmful organic compounds. For the production of 'syn' gas from methane (natural gas). As catalyst in chemical and pharmaceutical industries. In all these applications, rhodium metal or its alloy with other PGMs are employed as catalyst. While there are several factors that determine the efficacy of catalysis, the most important property that controls the rate, yield and selectivity is the structure of catalyst. The processes could derive immense benefit if the catalysts are fabricated to have large surface to volume ratio. For this purpose, the metal catalysts are usually coated or foamed onto the inert solid support such as alumina to facilitate the surface reaction [Dindi et al, US Patent No.6733692, 2004]. Although these inert supports offer resistance to thermal shock, they have some drawbacks such as the surface of the catalyst attached to the support is not utilized for any catalytic activity and the recovery of catalyst is tedious. These factors in addition to the exorbitant price demands the development of metal foams having -20 - 100 pores per inch (ppi) for such applications. Traditionally, the metal foams are fabricated by one of the several procedures given below. The various synthetic procedures are published by Ashby et al. [Metal Foams: A Design Guide, 2000, p.6]. These include, Bubbling gas through molten Al-SiC or A1-A1203 alloys. [Al, Mg] By stirring a foaming agent (typically TiH2) into a molten alloy (typically an aluminum alloy) and controling the pressure while cooling. [Al] Consolidation of a metal powder (aluminum alloys are the most common) with a particulate foaming agent (TiH2 again) followed by heating into the mushy state when the foaming agent releases hydrogen, expanding the material. [Al, Zn, Fe, Pb, Au] Manufacture of a ceramic mold from a wax or polymer-foam precursor, followed by burning-out of the precursor and pressure infiltration with a molten metal or metal powder slurry which is'then sintered. [Al, Mg Ni-Cr, stainless steel, Cu] Vapor phase deposition or electrodeposition of metal onto a polymer foam precursor, which is subsequently burned out, leaving cell, edges with hollow cores. [Ni, Ti] The trapping of high-pressure inert gas in pores by powder hot isostatic pressing (HIPing), followed by the expansion of the gas at elevated temperature [Ti]. Sintering of hollow spheres, made 6y a modified atomization process, or from metal-oxide or hydride spheres followed by reduction or dehydridation, or by vapor-deposition of metal onto polymer spheres. [Ni, Co, Ni-Cr alloys] Co-pressing of a metal powder with a leacha.ble powder, or pressure infiltration of a bed of leachable particles by a liquid metal, followed by leaching to leave a metal-foam skeleton. [Al, with salt as the leachable powder] Dissolution of gas (typically, hydrogen) in a liquid metal under pressure allowing it to be released in a controlled way during subsequent solidification. [Cu, Ni, Al] Invariably, all these procedures suffer frorn the serious drawbacks such as 1) High temperature processing, 2) Use of inert supports, 3) Tedious procedures, etc. However, the present invention provides a novel, simble and industrially adaptable procedure for the synthesis of rhodium metal foam using room temperature ionic liquid as medium. OBJECTS OF THE INVENTION: An object of this invention is to propose a novel method for synthesizing rhodium metal foam from ionic liquids; Another object of this invention is to propose a simple, industrially adaptable method for the synthesis of rhodium metal foam; Still another object of this invention is to propose a method where rhodium foam was fabricated without the use of any support material at a low temperature using room temperature ionic liquids as medium; Further object of this invention is to propose a method for synthesizing rhodium foam to have -100 pore per inch (ppi). BRIEF DESCRIPTION OF THE INVENTION: According to this invention there is provided a method for synthesizing rhodium metal foam from ionic liquids comprising adding l-butyl-3-methylimidazolium chloride (bmimCl) ionic liquid in acetonitrile to rhodium chloride solution; subjecting the mixture to the step of stirring removing the solvent from the mixture; separating the crystallized solid from the solution, and subjecting the crystallized solid to the step of fabrication of rhodium foam. DETAILED DESCRIPTION OF THIS INVENTION: The present invention provides a novel, simple and industrially adaptable procedure for the synthesis of rhodium metal foam using room temperature ionic liquid as medium. For the first time, rhodium metal foam was fabricated without the use of any support material at relatively much lower temperature (473 K). Studies on room temperature ionic liquids (RTILs) have evolved as a major area of research, in the last few years, owing to their potential and widespread applications in almost all branches of science. Room Temperature Ionic Liquids (RTILs) are organic salts that melt at low temperature ( The invention is a simple and industrially adaptable procedure for the fabrication of rhodium metal foam. This is the first-ever procedure to use ionic liquid to synthesize any metal foam and requires only 473 K for rhodium metal foam formation. The rhodium foam can be formed without any solid support. The surface area of the foam was determined to be 68 m2/g and contains -100 pores per inch. Table 1 shows the comparison in the physical properties of the rhodium foam with the commercial nickel foam. It is observed that the values are comparable indicating the quality of rhodium metal foam is very good. Table 1. Comparison in the physical properties of rhodium metal foam with commercial INCO® nickel foam. Properties (Unit) Rhodium metal foam Commercial nickel foam Bulk density (g/cm3) 0.26 0.2 Pores per inch -100 110 Relative density (%) 2.1 2.2 Porosity (%) 97.8 97.7 Novel simple procedure was developed for the fabrication of rhodium metal foam using room temperature ionic liquids as medium without any support. The method involved the preparation of the formulation composed of rhodium chloride and 1 -alkyl-3-methylimidazolium chloride in a suitable solvent for the formation of ionic liquid - rhodium chloride crystals, which upon heating to 473 K at the rate of 5° K/ min leads to the formation of rhodium foam with -100 ppi openings. The present invention deals with the fabrication of rhodium metal foam using room temperature ionic liquid as medium. The illustration for the fabrication of rhodium metal foam is shown in Figure 1. The details of the procedure are shown in figure 1. Preparation of rhodium chloride - bmimCI solution Rhodium(IM) chloride - bmimCI formulation was prepared by dissolving the required quantity of rhodium chloride in acetonitrile at 343 K in a round bottom flask. 1-butyl-3-methylimidazolium chloride (bmimCI) ionic liquid in acetonitrile was added slowly to rhodium chloride solution. The mixture was stirred for about 3 hours. The solvent in the mixture was partially removed by using rotary evaporator, and the solution was left overnight in a beaker. The solid crystallized from the solution was separated and used for the fabrication of rhodium foam. A similar procedure was used to prepare the crystals with different metal to ionic liquid ratio. Synthesis of rhodium metal foam A known amount of the solid product was weighed and transferred to an alumina crucible. The solid was wetted with a small volume of acetonitrile to make uniform solution. The crucible was placed in a furnace and the temperature was increased from room temperature to a pre-determined value at a constant heating rate of 5°K /min. The furnace temperature was kept at a pre-determined value for about 2 hours. Subsequently, it was cooled to ambient temperature at the rate of 10°C/min and the final product was taken for characterization. EXAMPLES : Synthesis of rhodium foam involved three steps. The synthesis of bmimCl ionic liquid, formulation of rhodium chloride - bmimCl and fabrication of rhodium foam from rhodium chloride - bmimCl formulation. Step 1: Synthesis of l-butyI-3-methylimidazolium chloride (bmimCl) ionic liquid Synthesis of bmimCl involved refluxing of a mixture of 1 -methylimidazole with 1-chlorobutane in the mole ratio of 1:1.2 at 343 K for 72 hours. The resulting product was washed a few times with ethyl acetate and acetonitrile, and evaporated under vacuum at 343 K. A white solid was obtained after cooling with quantitative yield. The carbon, nitrogen and hydrogen content of bmimCI were determined by CHNS analyzer. The measured values are listed along with their theoretical values given in parenthesis, C: 55 (54.9); H: 8.7 (8.6); N: 15.9 (16.0). The melting point of bmimCI was found to be 340 K. 'H-NMR (500 MHz, CDC13, TMS); 6DD(t, 3H, CH3), 1.3 (m, 2H, CH2), 1.8 (m, 2H, CH2), 4.1 (s, 3H, CH3), 4.3 (m, 2H, CH2), 7.6 (m, H, aromatic CH), 7.7 (m, H, aromatic CH), 10.5 (s, H, aromatic CH) Step 2: Preparation of rhodium chloride - bmimCI formulation The rhodium chloride solution and bmimCI solution in acetonitrile were mixed in a RB flask at 343 K at different rhodium: bmimCI mole ratios. The solution was stirred during the course of addition and continued the stirring for about 3 hours. The volume of the solution was then reduced to one third using a rotary evaporator. The final solution was left overnight in a glass beaker. The solid crystallized from the solution was separated and used for the fabrication of rhodium metal foam. Step 3: Effect of temperature studies About 1.5 g of rhodium chloride - bmimCI was taken in a cylindrical alumina crucible and wetted with a few drops of acetonitrile. The crucible was then placed in a furnace and the temperature was increased to 473 K at a heating rate of 5° K/min. The temperature of the furnace was kept at 473 K for two hours and was then cooled at 10° K/min. The crucible was then removed from the furnace and the rhodium foam formed was stored in dessicator. The XRD pattern of the rhodium metal foam characterized is shown in Figure 3. The XRD pattern compares well with the standard pattern (JCPDS 05-0685) of metallic rhodium. The surface area was determined to be 68 m /g. The microscopic image of the rhodium foam is shown in Figure 4. It was observed that the foam contained ~ 100 pores per inch in the final product. In view of these open pores, it was not possible to study the mechanical rigidity of the product. Similarly, the product is a foam (not powder/particle), the particle size was not measured. The XRD pattern shows that bulk of the product is rhodium metal. The formation of rhodium metal could result from the decomposition of ionic liquid. The ionic liquid decomposes to carbon dioxide, water, etc upon heating. The chloride ion present in the ionic liquid is oxidized to Cl2 (gas). In this process Rh(III) is reduced to Rh(0). To confirm the fact that the chloride ion is necessary for reducing Rh(III) to Rh(0), thermal decomposition studies were carried out using the ionic liquids that contain non-chloride anions such as PF6, BF4 (table 2). In those studies the foam formation was not observed. Unlike the XRD pattern shown in figure 1, the pattern obtained was amorphous (from PF6, BF4 ionic liquids). However, when alkyl homologues of bmimCl such as hmimCl (l-hexyl-3-methylimidazolium chloride) and omimCl (l-octyl-3-methylimidazolium chloride) were used, rhodium foam formation was observed. This indicates the important role of CI" ion in rhodium foam formation. Nevertheless, more studies would be required to ascertain the mechanistic aspects of rhodium foam formation. The rhodium foam was characterized by energy dispersive X-ray analysis (EDS) and X-ray photoelectron spectroscopy. The results are shown in Fig. 5. The EDS pattern indicates the presence of rhodium metal in the product. In addition EDS pattern also indicates the presence of small quantities of carbon and oxygen. The XPS data was deconvoluted and the result is shown in Fig. 5 (bottom). The XPS shows a peak at 307.4 eV, which corresponds to the 3ds/i of rhodium metal (Rh(0)). The presence of a peak at 307.4 eV confirms that Rh(Ill) is reduced to Rh(0) by the ionic liquid. In addition, the XPS spectrum also shows the presence of a peak at 309.3 eV, which corresponds to the 3d5/2 of rhodium in trivalent state. This state could arise from the surface oxidation of rhodium metal to rhodium(III) (the sample product was handled in air). Therefore, the product contains small amounts of rhodium (III). The actual amount of rhodium (III) in the product could be less than 5%, otherwise the XRD-pattern of the product (figure 1) could have shown the presence of rhodium (III) compound. In view of the absence of peaks other than rhodium metal in the XRD, it can be concluded that the bulk product is composed of rhodium metal. Effect of various parameters (a) Rhodium chloride: bmimCI ionic liquid ratio The effect of rhodium chloride to bmimCI mole ratio on the rhodium foam formation was studied by varying the rhodium : bmimCI mole ratio from 1:1 to 1:5. Microscopic observation of the product in each case indicated that the foam formation was incomplete and broken when the rhodium: bmimCl ratio was low i.e. 1:1 and However, the foam structure was complete and intact when the rhodium: bmimCl ratio was varied from 1:3 to 1:5. (b) Effect of ionic liquids Formation of rhodium foam was studied by changing nature of ionic liquid. When the bmim cation was retained and anions were changed to BF4, PF6 and NTf2, rhodium foam was not formed. However, when the chloride anion was retained and the cation was changed to [omim]+ and [hmim]+, rhodium foam was observed. Table 2. Effects of various ionic liquids on rhodium foam formation at 473 K. Atmosphere: Air. Ionic liquid Solvent Foam bmimBF4 Acetonitrile No bmimPF6 Acetonitrile No bmimNTf2 Acetonitrile No omimCl Acetonitrile Yes bmimCl Acetonitrile Yes hmimCl Acetonitrile Yes (c) Scaling up Based on the above results, rhodium metal foam was synthesized up to 2 g levels by using rhodium: bmimCl mole ratio 1:3. Rhodium foam was observed in this case with similar properties as indicated above. (d) Effect of temperature The foam obtained at 473 K was heated in air at various temperatures for 2 hours. The product thus obtained was characterized by X-ray diffraction. It was found that the rhodium metal was stable at temperatures below 673 K and the XRD pattern did not change (same as Fig. 1). Above 673 K, the rhodium metal present in foam was oxidized to rhodium (III) oxide. However, the foam structure was intact in all cases (studied up to 1273 K). Rapid oxidation of rhodium to rhodium oxide was observed at higher temperatures (> 873 K). We Claim: 1. A method for synthesizing rhodium metal foam from ionic liquids comprising adding l-butyl-3-methylimidazolium chloride (bmimCl) ionic liquid in acetonitrile to rhodium chloride solution; subjecting the mixture to the step of stirring removing the solvent from the mixture; separating the crystallized solid from the solution, and subjecting the crystallized solid to the step of fabrication of rhodium foam. 2. The method as claimed in claim 1, wherein rhodium (III) chloride bmimcl formulation was prepared by dissolving the required quantity of rhodium chloride in acetonitrile at 343 k. 3. The method as claimed in claim 1, wherein the mixture was stirred for about 3hrs. 4. The method as claimed in claim 1, wherein the solvent is removed by using rotary evaporator. 5. The method as claimed in claim 1, wherein the said rhodium foam was formed comprising: transferring the said solid product into an alumina crucible wetting the solid with acetonitrile to form uniform solution, heating the crucible at a rate of 5°K /min, subjecting the crucible to the step of cooling to ambient temperature. 6. The method as claimed in claim 5, wherein the temperature of the furnace was increased from room temperature to a pre-determined temperature. 7. The method as claimed in claim 5, wherein the furnace temperature was kept at a predetermined value for about 2hrs. 8. The method as claimed in claim 5, wherein the compound was cooled to ambient temperature at the rate of 10°C/min.

Full Text

FORM -2
THE PATENTS ACT, 1970
(39 OF 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. Title of the Invention : A METHOD FOR SYNTHESIZING RHODIUM
METAL FOAM FROM IONIC LIQUIDS
2. Applicant(s)
Name, Nationality & Address :
THE SECRETARY, DEPARTMENT OF ATOMIC ENERGY, O.Y.C. Building, Chartrapathi Shivaji Maharaj Marg, Mumbai 400 001, Maharashtra, India, an India Institute
3. Preamble to the description :
COMPLETE : The following specification particularly describes the invention and the manner in which is to be performed.

FIELD OF INVENTION:
This invention relates to a method for synthesizing rhodium metal foam from ionic liquids.
BACKGROUND OF THE INVENTION:
Metal foam is a cellular solid material with wide-open structure. It is made up of a single metal or alloy. Metal foam is characterized by high stiffness, high thermal/electrical conductivity and low specific gravity.
Rhodium is a noble metal and it is the costliest metal (2375 US$/ troy oz) [Johnson Matthey pic, London, UK] among all the publicly traded metals. The abundance of rhodium in the earth crust is very low (0.001 gram / tonne) [Ache et ah, Technical report series - No. 308, IAEA, Vienna, 1989] and it is being consumed at a rapid rate to cater the huge demand from various industries. Rhodium has been extensively used in the following applications.
In catalytic converters in automobile industry to reduce the toxicity of exhaust gases. Each catalytic converter contains ~2 g of rhodium and other noble metals on a ceramic support. The global demand of rhodium from automobile industry itself amounts to more than four-fifths of its annual production.
As catalyst for the treatment of gaseous emissions from thermal power plants and industrial waste gases contaminated with harmful organic compounds. For the production of 'syn' gas from methane (natural gas). As catalyst in chemical and pharmaceutical industries.

In all these applications, rhodium metal or its alloy with other PGMs are employed as catalyst. While there are several factors that determine the efficacy of catalysis, the most important property that controls the rate, yield and selectivity is the structure of catalyst. The processes could derive immense benefit if the catalysts are fabricated to have large surface to volume ratio. For this purpose, the metal catalysts are usually coated or foamed onto the inert solid support such as alumina to facilitate the surface reaction [Dindi et al, US Patent No.6733692, 2004]. Although these inert supports offer resistance to thermal shock, they have some drawbacks such as the surface of the catalyst attached to the support is not utilized for any catalytic activity and the recovery of catalyst is tedious. These factors in addition to the exorbitant price demands the development of metal foams having -20 - 100 pores per inch (ppi) for such applications.
Traditionally, the metal foams are fabricated by one of the several procedures given
below. The various synthetic procedures are published by Ashby et al. [Metal Foams: A
Design Guide, 2000, p.6]. These include,
Bubbling gas through molten Al-SiC or A1-A1203 alloys. [Al, Mg]
By stirring a foaming agent (typically TiH2) into a molten alloy (typically an aluminum
alloy) and controling the pressure while cooling. [Al]
Consolidation of a metal powder (aluminum alloys are the most common) with a
particulate foaming agent (TiH2 again) followed by heating into the mushy state when the
foaming agent releases hydrogen, expanding the material. [Al, Zn, Fe, Pb, Au]

Manufacture of a ceramic mold from a wax or polymer-foam precursor, followed by burning-out of the precursor and pressure infiltration with a molten metal or metal powder slurry which is'then sintered. [Al, Mg Ni-Cr, stainless steel, Cu] Vapor phase deposition or electrodeposition of metal onto a polymer foam precursor, which is subsequently burned out, leaving cell, edges with hollow cores. [Ni, Ti] The trapping of high-pressure inert gas in pores by powder hot isostatic pressing (HIPing), followed by the expansion of the gas at elevated temperature [Ti]. Sintering of hollow spheres, made 6y a modified atomization process, or from metal-oxide or hydride spheres followed by reduction or dehydridation, or by vapor-deposition of metal onto polymer spheres. [Ni, Co, Ni-Cr alloys]
Co-pressing of a metal powder with a leacha.ble powder, or pressure infiltration of a bed of leachable particles by a liquid metal, followed by leaching to leave a metal-foam skeleton. [Al, with salt as the leachable powder]
Dissolution of gas (typically, hydrogen) in a liquid metal under pressure allowing it to be released in a controlled way during subsequent solidification. [Cu, Ni, Al] Invariably, all these procedures suffer frorn the serious drawbacks such as 1) High temperature processing, 2) Use of inert supports, 3) Tedious procedures, etc. However, the present invention provides a novel, simble and industrially adaptable procedure for the synthesis of rhodium metal foam using room temperature ionic liquid as medium.

OBJECTS OF THE INVENTION:
An object of this invention is to propose a novel method for synthesizing rhodium metal foam from ionic liquids;
Another object of this invention is to propose a simple, industrially adaptable method for the synthesis of rhodium metal foam;
Still another object of this invention is to propose a method where rhodium foam was fabricated without the use of any support material at a low temperature using room temperature ionic liquids as medium;
Further object of this invention is to propose a method for synthesizing rhodium foam to have -100 pore per inch (ppi).
BRIEF DESCRIPTION OF THE INVENTION:
According to this invention there is provided a method for synthesizing rhodium metal
foam from ionic liquids comprising adding l-butyl-3-methylimidazolium chloride
(bmimCl) ionic liquid in acetonitrile to rhodium chloride solution;
subjecting the mixture to the step of stirring
removing the solvent from the mixture;
separating the crystallized solid from the solution, and
subjecting the crystallized solid to the step of fabrication of rhodium foam.

DETAILED DESCRIPTION OF THIS INVENTION:
The present invention provides a novel, simple and industrially adaptable procedure for the synthesis of rhodium metal foam using room temperature ionic liquid as medium. For the first time, rhodium metal foam was fabricated without the use of any support material at relatively much lower temperature (473 K). Studies on room temperature ionic liquids (RTILs) have evolved as a major area of research, in the last few years, owing to their potential and widespread applications in almost all branches of science. Room Temperature Ionic Liquids (RTILs) are organic salts that melt at low temperature ( The invention is a simple and industrially adaptable procedure for the fabrication of rhodium metal foam. This is the first-ever procedure to use ionic liquid to synthesize any metal foam and requires only 473 K for rhodium metal foam formation. The rhodium foam can be formed without any solid support. The surface area of the foam was determined to be 68 m2/g and contains -100 pores per inch. Table 1 shows the comparison in the physical properties of the rhodium foam with the commercial nickel foam. It is observed that the values are comparable indicating the quality of rhodium metal foam is very good.

Table 1. Comparison in the physical properties of rhodium metal foam with commercial INCO® nickel foam.

Properties (Unit) Rhodium metal foam Commercial nickel foam
Bulk density (g/cm3) 0.26 0.2
Pores per inch -100 110
Relative density (%) 2.1 2.2
Porosity (%) 97.8 97.7
Novel simple procedure was developed for the fabrication of rhodium metal foam using room temperature ionic liquids as medium without any support. The method involved the preparation of the formulation composed of rhodium chloride and 1 -alkyl-3-methylimidazolium chloride in a suitable solvent for the formation of ionic liquid - rhodium chloride crystals, which upon heating to 473 K at the rate of 5° K/ min leads to the formation of rhodium foam with -100 ppi openings.
The present invention deals with the fabrication of rhodium metal foam using room temperature ionic liquid as medium. The illustration for the fabrication of rhodium metal foam is shown in Figure 1. The details of the procedure are shown in figure 1.
Preparation of rhodium chloride - bmimCI solution
Rhodium(IM) chloride - bmimCI formulation was prepared by dissolving the required quantity of rhodium chloride in acetonitrile at 343 K in a round bottom flask. 1-butyl-3-methylimidazolium chloride (bmimCI) ionic liquid in acetonitrile was added slowly to rhodium chloride solution. The mixture was stirred for about 3 hours. The solvent in the mixture was partially removed by using rotary evaporator, and the solution was left overnight in a beaker.

The solid crystallized from the solution was separated and used for the fabrication of rhodium foam. A similar procedure was used to prepare the crystals with different metal to ionic liquid ratio.
Synthesis of rhodium metal foam
A known amount of the solid product was weighed and transferred to an
alumina crucible. The solid was wetted with a small volume of acetonitrile to make uniform solution. The crucible was placed in a furnace and the temperature was increased from room temperature to a pre-determined value at a constant heating rate of 5°K /min. The furnace temperature was kept at a pre-determined value for about 2 hours. Subsequently, it was cooled to ambient temperature at the rate of 10°C/min and the final product was taken for characterization.
EXAMPLES :
Synthesis of rhodium foam involved three steps. The synthesis of bmimCl ionic liquid, formulation of rhodium chloride - bmimCl and fabrication of rhodium foam from rhodium chloride - bmimCl formulation.
Step 1: Synthesis of l-butyI-3-methylimidazolium chloride (bmimCl) ionic liquid
Synthesis of bmimCl involved refluxing of a mixture of 1 -methylimidazole with 1-chlorobutane in the mole ratio of 1:1.2 at 343 K for 72 hours. The resulting product was washed a few times with ethyl acetate and acetonitrile, and evaporated under vacuum at 343 K. A white solid was obtained after cooling with quantitative yield.

The carbon, nitrogen and hydrogen content of bmimCI were determined by CHNS analyzer. The measured values are listed along with their theoretical values given in parenthesis, C: 55 (54.9); H: 8.7 (8.6); N: 15.9 (16.0). The melting point of bmimCI was found to be 340 K. 'H-NMR (500 MHz, CDC13, TMS); 6DD(t, 3H, CH3), 1.3 (m, 2H, CH2), 1.8 (m, 2H, CH2), 4.1 (s, 3H, CH3), 4.3 (m, 2H, CH2), 7.6 (m, H, aromatic CH), 7.7 (m, H, aromatic CH), 10.5 (s, H, aromatic CH)
Step 2: Preparation of rhodium chloride - bmimCI formulation
The rhodium chloride solution and bmimCI solution in acetonitrile were mixed in a RB flask at 343 K at different rhodium: bmimCI mole ratios. The solution was stirred during the course of addition and continued the stirring for about 3 hours. The volume of the solution was then reduced to one third using a rotary evaporator. The final solution was left overnight in a glass beaker. The solid crystallized from the solution was separated and used for the fabrication of rhodium metal foam.
Step 3: Effect of temperature studies
About 1.5 g of rhodium chloride - bmimCI was taken in a cylindrical alumina crucible and wetted with a few drops of acetonitrile. The crucible was then placed in a furnace and the temperature was increased to 473 K at a heating rate of 5° K/min. The temperature of the furnace was kept at 473 K for two hours and was then cooled at 10° K/min. The crucible was then removed from the furnace and the rhodium foam formed was stored in dessicator.

The XRD pattern of the rhodium metal foam characterized is shown in Figure 3. The XRD pattern compares well with the standard pattern (JCPDS 05-0685) of metallic rhodium. The surface area was determined to be 68 m /g. The microscopic image of the rhodium foam is shown in Figure 4. It was observed that the foam contained ~ 100 pores per inch in the final product. In view of these open pores, it was not possible to study the mechanical rigidity of the product. Similarly, the product is a foam (not powder/particle), the particle size was not measured.
The XRD pattern shows that bulk of the product is rhodium metal. The formation of rhodium metal could result from the decomposition of ionic liquid. The ionic liquid decomposes to carbon dioxide, water, etc upon heating. The chloride ion present in the ionic liquid is oxidized to Cl2 (gas). In this process Rh(III) is reduced to Rh(0). To confirm the fact that the chloride ion is necessary for reducing Rh(III) to Rh(0), thermal decomposition studies were carried out using the ionic liquids that contain non-chloride anions such as PF6, BF4 (table 2). In those studies the foam formation was not observed. Unlike the XRD pattern shown in figure 1, the pattern obtained was amorphous (from PF6, BF4 ionic liquids). However, when alkyl homologues of bmimCl such as hmimCl (l-hexyl-3-methylimidazolium chloride) and omimCl (l-octyl-3-methylimidazolium chloride) were used, rhodium foam formation was observed. This indicates the important role of CI" ion in rhodium foam formation. Nevertheless, more studies would be required to ascertain the mechanistic aspects of rhodium foam formation.

The rhodium foam was characterized by energy dispersive X-ray analysis (EDS) and X-ray photoelectron spectroscopy. The results are shown in Fig. 5. The EDS pattern indicates the presence of rhodium metal in the product. In addition EDS pattern also indicates the presence of small quantities of carbon and oxygen. The XPS data was deconvoluted and the result is shown in Fig. 5 (bottom). The XPS shows a peak at 307.4 eV, which corresponds to the 3ds/i of rhodium metal (Rh(0)). The presence of a peak at 307.4 eV confirms that Rh(Ill) is reduced to Rh(0) by the ionic liquid. In addition, the XPS spectrum also shows the presence of a peak at 309.3 eV, which corresponds to the 3d5/2 of rhodium in trivalent state. This state could arise from the surface oxidation of rhodium metal to rhodium(III) (the sample product was handled in air). Therefore, the product contains small amounts of rhodium (III). The actual amount of rhodium (III) in the product could be less than 5%, otherwise the XRD-pattern of the product (figure 1) could have shown the presence of rhodium (III) compound. In view of the absence of peaks other than rhodium metal in the XRD, it can be concluded that the bulk product is composed of rhodium metal.
Effect of various parameters
(a) Rhodium chloride: bmimCI ionic liquid ratio
The effect of rhodium chloride to bmimCI mole ratio on the rhodium foam formation was studied by varying the rhodium : bmimCI mole ratio from 1:1 to 1:5.

Microscopic observation of the product in each case indicated that the foam formation was incomplete and broken when the rhodium: bmimCl ratio was low i.e. 1:1 and However, the foam structure was complete and intact when the rhodium: bmimCl ratio was varied from 1:3 to 1:5.
(b) Effect of ionic liquids
Formation of rhodium foam was studied by changing nature of ionic liquid. When the bmim cation was retained and anions were changed to BF4, PF6 and NTf2, rhodium foam was not formed. However, when the chloride anion was retained and the cation was changed to [omim]+ and [hmim]+, rhodium foam was observed.
Table 2. Effects of various ionic liquids on rhodium foam formation at 473 K. Atmosphere: Air.

Ionic liquid Solvent Foam
bmimBF4 Acetonitrile No
bmimPF6 Acetonitrile No
bmimNTf2 Acetonitrile No
omimCl Acetonitrile Yes
bmimCl Acetonitrile Yes
hmimCl Acetonitrile Yes

(c) Scaling up
Based on the above results, rhodium metal foam was synthesized up to 2 g levels by using rhodium: bmimCl mole ratio 1:3. Rhodium foam was observed in this case with similar properties as indicated above.
(d) Effect of temperature
The foam obtained at 473 K was heated in air at various temperatures for 2 hours. The product thus obtained was characterized by X-ray diffraction. It was found that the rhodium metal was stable at temperatures below 673 K and the XRD pattern did not change (same as Fig. 1). Above 673 K, the rhodium metal present in foam was oxidized to rhodium (III) oxide. However, the foam structure was intact in all cases (studied up to 1273 K). Rapid oxidation of rhodium to rhodium oxide was observed at higher temperatures (> 873 K).

We Claim:
1. A method for synthesizing rhodium metal foam from ionic liquids comprising adding
l-butyl-3-methylimidazolium chloride (bmimCl) ionic liquid in acetonitrile to rhodium
chloride solution;
subjecting the mixture to the step of stirring
removing the solvent from the mixture;
separating the crystallized solid from the solution, and
subjecting the crystallized solid to the step of fabrication of rhodium foam.
2. The method as claimed in claim 1, wherein rhodium (III) chloride bmimcl formulation was prepared by dissolving the required quantity of rhodium chloride in acetonitrile at 343 k.
3. The method as claimed in claim 1, wherein the mixture was stirred for about 3hrs.
4. The method as claimed in claim 1, wherein the solvent is removed by using rotary evaporator.

5. The method as claimed in claim 1, wherein the said rhodium foam was formed
comprising:
transferring the said solid product into an alumina crucible wetting the solid with acetonitrile to form uniform solution, heating the crucible at a rate of 5°K /min, subjecting the crucible to the step of cooling to ambient temperature.
6. The method as claimed in claim 5, wherein the temperature of the furnace was increased from room temperature to a pre-determined temperature.
7. The method as claimed in claim 5, wherein the furnace temperature was kept at a predetermined value for about 2hrs.
8. The method as claimed in claim 5, wherein the compound was cooled to ambient temperature at the rate of 10°C/min.

Documents:

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Patent Number

279100

Indian Patent Application Number

2271/MUM/2012

PG Journal Number

02/2017

Publication Date

13-Jan-2017

Grant Date

11-Jan-2017

Date of Filing

08-Aug-2012

Name of Patentee

THE SECRETARY, DEPARTMENT OF ATOMIC ENERGY

Applicant Address

O.Y.C. BUILDING, CHARTRAPATHI SHIVAJI MAHARAJ MARG, MUMBAI 400 001, MAHARASHTRA, INDIA

Inventors:

#	Inventor's Name	Inventor's Address
1	M. JAYAKUMAR	C/O. CHEMISTRY GROUP, INDIRA GANDHI CENTRE FOR ATOMIC RESEARCH, KALPAKKAM 603 102, INDIA
2	T. G. SRINIVASAN	C/O. CHEMISTRY GROUP, INDIRA GANDHI CENTRE FOR ATOMIC RESEARCH, KALPAKKAM 603 102, INDIA
3	P. R. VASUDEVA RAO	C/O. CHEMISTRY GROUP, INDIRA GANDHI CENTRE FOR ATOMIC RESEARCH, KALPAKKAM 603 102, INDIA
4	K. A. VENKATESAN	C/O. CHEMISTRY GROUP, INDIRA GANDHI CENTRE FOR ATOMIC RESEARCH, KALPAKKAM 603 102, INDIA

PCT International Classification Number

B01J23/46

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA