WO2009156997A1

WO2009156997A1 - Catalytic reduction of water

Info

Publication number: WO2009156997A1
Application number: PCT/IL2009/000635
Authority: WO
Inventors: Boris Rybtchinski; Haim Weissman
Original assignee: Yeda Research And Development Co. Ltd.
Priority date: 2008-06-26
Filing date: 2009-06-25
Publication date: 2009-12-30

Abstract

The present invention relates to methods and compositions for producing hydrogen from water involving reacting a dithionite salt in the presence of an effective amount of metal catalyst nanoparticles.

Description

CATALYTIC REDUCTION OF WATER

FIELD OF THE INVENTION

[001] The present invention relates to methods and compositions for producing hydrogen from water involving reacting a dithionite salt in the presence of an effective amount of metal catalyst nanoparticles.

BACKGROUND OF THE INVENTION

[002] Catalytic hydrogen production from water under mild conditions is one of the main objectives of a vast research effort aimed at the development of alternative fuels. Generally, catalytic water reduction requires at least three components: hydrogen evolving catalyst, an electron relay, and a sacrificial electron donor. In photodriven systems, a photosensitizer is also needed. It is widely recognized that simplification of the water-reducing catalytic systems is highly desirable.

[003] The increasing demand for hydrogen arises the imminent paradigm shift to a hydrogen- based energy economy, such as in hydrogen fuel cells. This shift approaches as the worldwide need for more electricity increases, greenhouse' gas emission controls tighten, and fossil fuel reserves wane. Hydrogen-based economy is the only long-term, environmentally benign alternative for sustainable growth. Over the last few years it is becoming more apparent that the emphasis on cleaner fuel will lead to use of hydrogen in a significant way. Providing that renewable energy sources, such as hydroelectricity or solar energy, are used to produce hydrogen through decomposition of water, there are no environmental threats produced by the hydrogen economy.

[004] This invention is directed to a readily available electron donor combined with a catalyst in a simple binary system that produces hydrogen under mild conditions. The catalytic system of this invention utilizes a low-cost inorganic reductant (sodium dithionite) and platinum nanoparticles to catalytically produce hydrogen from water. SUMMARY OF THE INVENTION

[005] In one embodiment, the present invention provides a method for the generation of hydrogen gas from a degassed aqueous solution comprising mixing a catalytic metal nanoparticles and a reductant in said degassed aqueous solution in an inert atmosphere.

[006] In one embodiment, this invention is directed to a composition for generating hydrogen (H₂) from water, comprising an aqueous solution, a reductant and a catalytic metal, wherein said composition is under inert atmosphere.

BRIEF DESCRIPTION OF THE DRAWINGS

[007] The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which:

[008] Figure 1 is an illustration of a vial with average volume of 4.80 mL with 13mm Mininert^® caps, where the catalytic reaction for hydrogen evolution is conducted.

[009] Figure 2 is an illustration of a calibration curve for hydrogen determination by GC.

[0010] Figure 3 depicts a graph of hydrogen evolution at room temperature versus turnover number (TON). Reaction conditions: 2.0 mL of double distilled water solution containing 20 nmol (10^~5 M) platinum atoms as platinum nanoparticles, 12 μmol (6-10^"3 M) of sodium dithionite and 120 μmol (6-10^"2M) of sodium bicarbonate.

[0011] Figure 4 depicts hydrogen evolution at 52°C versus turnover number (TON) with and without sodium dithionite. SBC=sodium bicarbonate. Reaction conditions: 2.0 mL of water solution containing 20 nmol (10^'5 M) platinum atoms as platinum nanoparticles, 12 μmol (6-10^"3 M) sodium dithionite and 120 μmol (6-10^"2 M) of sodium bicarbonate at the beginning of the reaction, followed by venting/reagent addition cycles after 75 h. . [0012] It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0013] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the present invention.

[0014] hi one embodiment, this invention provides a composition for generating hydrogen (H₂) from water, comprising an aqueous solution, a reductant and a catalytic metal, wherein said composition is under inert atmosphere.

[0015] This invention provides, in one embodiment, a composition for the generation of hydrogen (H₂), deuterium (D₂), tritium (T₂) gas or combination thereof, comprising a degassed aqueous solution, a reductant and a catalytic metal, wherein said composition is under inert atmosphere and wherein said aqueous solution comprises water (H₂O), deuterium oxide (D₂O), tritium oxide (T₂O) solution or combination thereof.

[0016] hi one embodiment, the composition of this invention is for the generation of H₂. In one embodiment, the composition of this invention is for the generation of hydrogen, hydrogen isotope or combination thereof, hi another embodiment the composition is for the generation of D₂. hi another embodiment the composition is for the generation of T₂. In another embodiment, the composition is for the generation of H-D. In another embodiment, the composition is for the generation of H-T.

[0017] hi one embodiment, the compositions and methods of this invention comprise a catalytic metal. In another embodiment, the catalytic metal of the present invention facilitate the production of hydrogen from an aqueous solution, upon the reaction of the catalytic metal and the reductant with said solution, hi another embodiment, the catalytic metal of the present invention facilitate the production of hydrogen isotope from an aqueous solution, upon the reaction of the catalytic metal and the reductant with said solution; wherein said solution comprises isotopic water.

[0018] In one embodiment, the composition and methods of this invention make use of an aqueous solution. In another embodiment, the aqueous solution comprises certain chemicals to any type of water in order to increase the impurity of the liquid. Non-limiting examples of water types include, fresh, tap, distilled, marine and water adjusted to comprise a high chloride concentration.

[0019] In one embodiment, the hydrogen or hydrogen isotope is generated from an aqueous solution, wherein, the aqueous solution comprises water or isotopic water or combination thereof. In another embodiment, the aqueous solution of this invention is buffered. In another embodiment, the buffer is sodium bicarbonate or phosphate. In another embodiment, the buffer . is sodium bicarbonate. In another embodiment, the buffer is phosphate.

[0020] In another embodiment, the buffered pH of the aqueous solution is from 6-11. In another embodiment, the buffered pH is between 6-7. In another embodiment, the buffered pH is between 7-8. In another embodiment, the buffered pH is between 7-9. In another embodiment the buffered pH is between 8-9. In another embodiment, the pH is between 9-10. In another embodiment, the buffered pH is 8.

[0021] In another embodiment, the aqueous solution of this invention is non-buffered. In another embodiment, the non-buffered pH is from 6-11. In another embodiment, the non- buffered pH is between 6-7. In another embodiment, the non-buffered pH is between 7-8. In another embodiment, the non-buffered pH is between 7-9. hi another embodiment the non- buffered pH is between 8-9. In another embodiment, the non-buffered pH is between 9-10. hi another embodiment, the non-buffered pH is 8.

[0022] hi one embodiment, a variety of non-aqueous solvents may also provide suitable sources of hydrogen or isotopic hydrogen atoms. These solvents may include an alcohol or an isotopic hydrogen atom sources such as deuturated and/or tritiated alcohols, acetonitrile, other nitriles, formamide, other amides, furans, pyroles, pyridine(s), and other compounds, which can undergo reductive decomposition to yield hydrogen or isotopic hydrogen atoms such as hydrogen sulfide and other sulfides. The solvents may be diluted or suspended in an aqueous medium containing either non-isotopic or isotopic water and other solute components as mentioned above.

[0023] In one embodiment, the compositions and methods of this invention comprise a catalytic metal In another embodiment, the catalytic metal is one of group Vm or group IVA. In another embodiment, the catalytic metal of this invention is palladium or platinum. In another embodiment, the catalytic metal is platinum. In another embodiment, the catalytic metal is palladium, platinum, iron, cobalt, nickel, ruthenium, rhodium, osmium, iridium, titanium, zirconium, hafnium or alloys thereof. The catalytic metal may also be a composite of a substrate consisting of platinum, palladium, rhodium, ruthenium, iridium, osmium, nickel, cobalt, iron, zirconium, titanium, platinum, hafnium, or alloys thereof.

[0024] In another embodiment, the catalytic metal is generated by reduction of an oxide of the catalytic metal. In another embodiment, the catalytic metal is deposited on activated carbon. In another embodiment, the catalytic metal is a pure metal.

[0025] In another embodiment, the form of the catalytic metal is a wire, gauze, powder, foil, spheres, granules or nanoparticles. In another embodiment, the form of the catalytic metal is nanoparticles. In another embodiment, the size of the nanoparticles is between about 1-100 nm. In another embodiment, the size of the nanoparticles is between about 1-25 nm. In another embodiment, the size of the nanoparticles is between about nanoparticles are 25-50 nm. In another embodiment, the size of the nanoparticles is between about 50-75 nm. In another embodiment, the size of the nanoparticles is between about 75-100 nm. In another embodiment, the size of the nanoparticles is between about 1-50 nm. In another the size of the nanoparticles is between about 50-100 nm. tn another embodiment, the size of the nanoparticles is about 4.7 nm. In one embodiment, the size of the nanoparticles is between about 1-10 nm. In one embodiment, the size of the nanoparticles is between about 1-5 nm

[0026] In one embodiment, the nanoparticles vary in terms of size, or in another embodiment, shape, or in another embodiment, composition, or any combination thereof, within a composition for use according to the methods of this invention. Such differences in the respective nanoparticles used in a particular composition or according to the methods of this invention may be confirmed via electron microscopy, or in another embodiment, by scanning electron microscopy (SEM), or in another embodiment, by tunneling electron microscopy (TEM), or in another embodiment, by optical microscopy, or in another embodiment, by atomic absorption spectroscopy (AAS)₅ or in another embodiment, by X-ray powder diffraction (XRD), or in another embodiment, by X-ray photoelectron spectroscopy (XPS), or in another ^• embodiment, by atomic force microscopy (AFM), or in another embodiment, by ICP (inductively coupled plasma).

[0027] In one embodiment, the larger is the surface area of the catalytic metal mixture exposed to water, thus the higher the rate of the reaction (i. e. larger amount of the metal reacts with water in unit time), and the higher the yield of the reaction (i.e. larger amount of the metal reacts with water).

[0028] hi one embodiment, the metal nanoparticles are recovered, or in another embodiment, recycled, or in another embodiment, regenerated and/or further reused after the catalytic reaction, using a composition of this invention, and/or according to the methods of this invention. In one embodiment the metal catalyst is recovered as a metallic bulk. In another embodiment, the metal nanoparticles are recovered by washing.

[0029] In one embodiment, the washing of the nanoparticles may be accomplished with water, or any polar solvent.

[0030] hi one embodiment, polyacrilic acid stabilizes the metal catalyst and prevents aggregation.

[0031] hi another embodiment, the nanoparticles are stabilized with polyacrylic acid. In another embodiment, the average molecular weight of the polyacrylic acid is between about 1000- 4,000,000. hi another embodiment, the average molecular weight of the polyacrylic acid is about 2100. In another embodiment, the average molecular weight of the polyacrylic acid is about 1800. In another embodiment, the average molecular weight of the polyacrylic acid is about 130,000. In another embodiment, the average molecular weight of the polyacrylic acid is about 450,000. hi another embodiment, the average molecular weight of the polyacrylic acid is about 1,250,000. hi another embodiment, the average molecular weight of the polyacrylic acid is about 3,000,000. hi another embodiment, the average molecular weight of the polyacrylic acid is about 4,000,000.

[0032] In one embodiment, the compositions and methods of this invention comprise a catalytic metal in an aqueous solution. In another embodiment, the concentration of the catalytic metal, as per metal atom, in the aqueous solution is between H0^"5M - 1-10^"7 M. In another embodiment, the concentration of the catalytic metal in the aqueous solution is between 1 ^• 10^"5 M - 1 ^• 10^"δ M, In another embodiment, the concentration of the metal catalyst in the aqueous solution is between 1 ^• 10^"6 M - 1 ^• 10^"7 M_. In another the concentration of the metal in the aqueous solution catalyst is between H(T⁴M - HO^"5 M.

[0033] In one embodiment, the compositions and methods of this invention comprise a reductant. In another embodiment, the reductant of this invention is a hypophosphite salt, a thionite salt, amines, or mixtures thereof, hi another embodiment, the reductant is sodium dithionite.

[0034] In one embodiment, the compositions and methods of this invention comprise a reductant in an aqueous solution. In another embodiment, the concentration of the reductant in the aqueous solution is between 1-10^"3 M - 1-10^"4 M. In another embodiment, the concentration of the reductant in the aqueous solution is between 1-10^"3 M - HO M. In another embodiment, the concentration of the reductant in the aqueous solution is between 1-10^" M - 1-10^" M. In another embodiment, the concentration of the reductant in the aqueous solution is between HO-²M - HO-⁴ M.

[0035] hi one embodiment, the catalytic metal and the reductant are present in a ratio of between about 1:1200 to about 1:120 by molar ratio. In another embodiment of the invention, tiie catalytic metal and the reductant are present in a ratio of between about 1:1200 to about 1:1000 by molar ratio. In another embodiment of the invention, the catalytic metal and the reductant are present in a ratio of between about 1:1000 to about 1:800 by molar ratio. In another embodiment of the invention, the catalytic metal and the reductant are present in a ratio of between about 1:800 to about 1:600 by molar ratio. Ih another embodiment of the invention, the catalytic metal and the reductant are present in a ratio of between about 1 :600 to about 1 :400 by molar ratio. In another embodiment of the invention, the catalytic metal and the reductant are present in a ratio of between about 1:400 to about 1:100 by molar ratio, hi accordance with another embodiment of the invention, the catalytic metal and the reductant are present in an approximately 1 : 1 ratio by molar ratio.

[0036] hi one embodiment, the terms "a" or "an" as used herein, refer to at least one, or multiples of the indicated element, which may be present in any desired order of magnitude, to suit a particular application, as will be appreciated by the skilled artisan, hi one embodiment, the term "a nanoparticle" refers to two or more kinds of nanoparticles, which differ in terms of their composition, or in one embodiment, size, or in one embodiment, surface modification, or a combination thereof, or other qualitative differences as will be understood by one skilled in the art. In some embodiments, the compositions and methods of this invention may comprise and/or make use of multiple kinds of nanoparticles for catalytic reduction of water, deuterium oxide, tritium oxide to hydrogen, deuterium, tritium, respectively.

[0037] This invention provides, in one embodiment, a method for the generation of hydrogen gas (H₂) from a degassed aqueous solution comprising mixing a catalytic metal and a reductant in said degassed aqueous solution in an inert atmosphere.

[0038] This invention provides, in one embodiment, a method for the generation of D₂ or T₂ gas from a degassed deuterium oxide solution, tritium oxide solution or combination thereof comprising mixing a catalytic metal and a reductant in said degassed solution in an inert atmosphere.

[0039] In one embodiment, the method and compositions of this invention comprise generation of hydrogen under an inert atmosphere. In another embodiment, the inert atmosphere comprises nitrogen, argon, helium or any combination thereof. In another embodiment, the inert atmosphere is under nitrogen.

[0040] hi one embodiment, the method of this invention comprises mixing a catalytic metal and a reductant. In another embodiment, the mixing of a catalytic metal and a reductant in a degassed aqueous solution is conducted at a temperature of between about 0-100 degrees Celsius. In another embodiment, the mixing is conducted at a temperature of between about 20- 80 degrees Celsius, hi another embodiment, the mixing is conducted at a temperature of between about 40-60 degrees Celsius. In another embodiment, the mixing is conducted at a temperature of about 50 degrees Celsius.

[0041] hi one embodiment, the method of this invention comprises mixing a catalytic metal and a reductant. In another embodiment, the mixing of a catalytic metal and a reductant hi a degassed aqueous solution is conducted at a temperature a buffered or non-buffered pH between about 6-11. hi another embodiment, the mixing of the aqueous solution is conducted at a buffered or non-buffered solution of pH between about 6-7. hi another embodiment, the mixing of the aqueous solution is conducted at a buffered or non-buffered solution of pH between about 7-8. In another embodiment, the mixing of the aqueous solution is conducted at a buffered or non-buffered solution of pH between about 7-9. In another embodiment, the mixing of the aqueous solution is conducted at a buffered or non-buffered solution of pH between about 8-9. In another embodiment, the mixing of the aqueous solution is conducted at a buffered or non- buffered solution of pH between about 9-10. In another embodiment, the mixing of the aqueous solution is conducted at a buffered or non-buffered solution of pH about 8.

[0042] In one embodiment, the chemical reactions of the instant invention are additionally affected by temperature and pH. Accordingly, as would be understood by a skilled in the art, the temperature or pH of the metal-catalyst reaction may be increased or decreased in such a way so as to produce hydrogen at a predetermined or desired rate.

[0043] In one embodiment, the method of this invention comprises catalytic generation of hydrogen from an aqueous solution. In another embodiment, the catalytic reaction provides a turnover of between 10-150 per metal atom. In another embodiment, the catalytic reaction provides a turnover of between 50-100 per metal atom. In another embodiment, the catalytic reaction provides a turnover of between 60-80 per metal atom. In another embodiment, the catalytic reaction provides a turnover of between 40-60 per metal atom. In another embodiment, the catalytic reaction provides a turnover of between 100-150 per metal atom.

[0044] In one embodiment, the method of this invention comprises catalytic generation of hydrogen from an aqueous solution by mixing a catalytic metal and a reductant. In another embodiment the mixing is conducted for between about 24 h-180 h. In another embodiment the mixing is conducted for about 24 h. In another embodiment the mixing is conducted for between about 24 h-48 h. In another embodiment the mixing is conducted for between about 10 h - 60 h.

[0045] In one embodiment, the compositions and methods of this invention make use of a reductant. m another embodiment, the reductant is added in one step to the aqueous solution. In another embodiment, the reductant is added stepwise. In another embodiment, the reductant is added stepwise wherein each portion is added upon completion of the reductant in the solution.

[0046] In one embodiment, the methods of this invention comprise mixing a catalytic metal and a reductant in a degassed aqueous solution. In another embodiment, the mixing is carried out at low pressures. In another embodiment, the pressure is between about 0.5 to about 5 atmospheres. In another embodiment, the pressure is about 1 atmosphere.

[0047] The term "catalyst," as used herein, refers to a substance or mixture of substances that can increase or decrease the rate of a chemical reaction without being consumed in the reaction.

[0048] The term "inert atmosphere", as used herein refers to a nonreactive gas atmosphere, such as nitrogen, argon or helium; used to blanket reactive liquids in storage, to purge process lines and vessels of reactive gases and liquids, and to cover a reaction mix in a partially filled vessel.

[0049] In one embodiment, this invention provides methods and compositions for the generation of hydrogen or isotopic hydrogen. The generated hydrogen is used to generate electricity in a fuel cell and provide access to useful alternative fuel systems. In another embodiment, the hydrogen generated by the methods and compositions of this invention is used as a chemical in forming products and in chemical processes. For example, the generated

^■ hydrogen can be used-in the manufacture of ammonia, nitrates, amines and alcohols (e.g., methanol), as well as in the hydrogenation of organic compounds. The generated hydrogen also can be used in steel making and other metal industries, the gasification and liquification of coal, the production of protein foods, and in total water management programs.

[0050] The proposed mechanism for the reaction involves hemolytic dissociation of the dithionate anion to two SO^2" radical species that are able to directly transfer an electron to the metal nanoparticles. The accumulated electrons on the metal surface reduce in turn surface bound protons by a process that eventually evolves gaseous hydrogen.

[0051] The following examples are presented in order to more fully illustrate the preferred embodiments of the invention. They should in no way be construed, however, as limiting the broad scope of the invention.

EXAMPLES

General Information

[0052] Reaction mixture preparations were performed in a glove box (MBraun, LABmaster) under a nitrogen atmosphere. Unless otherwise indicated, all starting materials were obtained from commercial suppliers and were used without further purification. In all experiments we used double distilled water that was degassed by freeze-pump-thaw technique prior to use. The experiments were conducted in 4.80 mL vials equipped with 13mm-425thead Mininert^® cap outfitted with a septum and a valve as illustrated in Fig. 1.

EXAMPLE l

Measurement of Hydrogen Gas Evolution

[0053] Hydrogen gas evolution were measured with HP 6890 GC instrument, utilizing thermal conductivity detector in the negative mode and helium as a carrier gas. The column used was 5'Xl/8" stainless 45/60 Carboxen 1000 (Supelco). Hydrogen concentrations were determined utilizing a calibration curve built from external hydrogen standards in the range 1.8- 10^"2-5.7- 10^'1 μmol/mL (Fig. 2). Each sample measurement was validated by injection of a known volume of hydrogen gas to verify the calibration curve.

EXAMPLE 2

Generation of Hydrogen by the Catalytic Reduction of Water

In a system containing 2 mL of an aqueous solution of 1-10^"5 M Pt atoms as PAA@Pt-NP, 6.0-10^'3 M sodium dithionite and 6-10^'2 M sodium bicarbonate, 1.4 μmol of hydrogen were generated at room temperature during 180 h, corresponding to 80 turnovers per platinum atom (TON=SO)₅ (Fig. 3).

EXAMPLE 3

Improvement of the Catalytic Turnover Number (TON)

[0054] Improving the turnover number (TON)s was achieved using moderate heating and replenishing of the sodium dithionite (SDT) (Fig. 4). When the system described in Example 2 was heated to 52⁰C₅ 1.2 μmol (TON=60) of hydrogen were observed after 23 h, corresponding to a turnover frequency (TOF) of 2.6. In the following 24 h₅ 0.21 μmol of H₂ (TON=I 0.5) evolved (TOF=0.46), and the system ceased to evolve H₂ after additional 24 h. The H₂ production was restored following the addition of SDT and sodium bicarbonate. Stepwise addition is required since initial high concentrations of SDT result in decreased catalytic activity due to bimolecular decomposition of SDT.

[0055] While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

Claims

What is claimed:

1. A composition for generating hydrogen (H₂) from water, comprising an aqueous solution, a reductant and a catalytic metal, wherein said composition is under inert atmosphere.

2. The composition of claim 1, wherein said aqueous solution is buffered.

3. The composition of claim 2, wherein said buffered solution is at pH of about 8.

4. The composition of claim 2, wherein the buffer is sodium bicarbonate.

5. The composition of claim 2, wherein the buffer is phosphate.

6. The composition of claim 1, wherein the aqueous solution is non-buffered solution.

7. The composition of claim 1 wherein said catalytic metal is palladium or platinum.

8. The composition of claim 1 wherein said catalytic metal is or platinum.

9. The composition of claim 1 wherein said catalytic metal is in a form of nanoparticles.

10. The composition of claim 8, wherein the nanoparticles are stabilized with polyacrylic acid.

11. The composition of claim 1, wherein the reductant is a dithionite salt.

12. The composition of claim 11 , wherein the reductant is sodium dithionite.

13. A method for the generation of hydrogen gas from a degassed aqueous solution comprising mixing a catalytic metal and a reductant in said degassed aqueous solution in an inert atmosphere.

14. The method of claim 13, wherein said aqueous solution is buffered.

15. The method of claim 14, wherein said buffered solution is at pH of about 8.

16. The method of claim 14, wherein the buffer is sodium bicarbonate.

17. The method of claim 14, wherein the buffer is phosphate.

18. The method of claim 1 , wherein the aqueous solution is non-buffered solution.

19. The method of claim 1 , wherein said catalytic metal is palladium or platinum.

20. The method of claim 1 , wherein said catalytic metal is or platinum.

21. The method of claim 1 , wherein said catalytic metal is in a form of nanoparticles.

22. The method of claim 21, wherein the nanoparticles are stabilized with polyacrylic acid.

23. The method of claim 13, wherein the reductant is a dithionite salt.

24. The composition of claim 24, wherein the reductant is sodium dithionite.

25. The method of claim 13, wherein the mixing is conducted at a temperature of between about 20-80 degrees Celsius.

26. The method of claim 13, wherein the mixing is conducted at a temperature of between about 40-60 degrees Celsius.