CATALYTIC SYSTEM FOR STORING AND RELEASING OF HYDROGEN FROM LIQUID ORGANIC HYDROGEN CARRIERS

Abstract

The present invention is directed to a catalytic system which can be used to hydrogenate and dehydrogenate a liquid organic hydrogen carrier (LOHC) compound. The catalytic system is composed of a special type of catalyst, a special type of solvent, and an LOHC compound. It can be used to store and release hydrogen upon demand, e.g. for usage in fuel cells of electrically propelled vehicles. Likewise, an apparatus comprising the inventive catalytic system and its use is contemplated.

Claims

1. Catalytic system for hydrogenation and dehydrogenation of a liquid organic hydrogen carrier comprising a complex comprising a tridentate ligand of the general formular D.sup.1-E-D.sup.2 and a transition metal, wherein E is covalently bonded to D.sup.1 and D.sup.2, and is complexing the transition metal, and D.sup.1 comprises a donor center E for complexing the transition metal, and D.sup.2 comprises a donor center E for complexing the transition metal, and E, E and E is an element selected from the group consisting of P, N, O, C, As, S, Ge, Se, Si, B, Al, Sb, characterized in that, the catalytic system comprises an ionic liquid and a liquid organic hydrogen carrier compound.

2. Catalytic system according to claim 1, wherein the liquid organic hydrogen carrier comprises a hydrocarbon aromatic compound.

3. Catalytic system according to claim 1, wherein the liquid organic hydrogen carrier comprises a heteroaromatic compound.

4. Catalytic system according to claim 1, wherein the liquid organic hydrogen carrier comprises compounds from the group of ketones, esters, carboxylic acids, CO.sub.2.

5. Catalytic system according to claim 1, wherein the transition metal is an element selected from the group consisting of Ru, Mn, Fe, Ir, Os, Mo, Rh, Pd, Pt, Ni, Cu, Co, W.

6. Catalytic system according to claim 1, wherein the tridentate ligand of the general formular D.sup.1-X-D.sup.2 comprises the following complexing centers for EEE in its structure: PNP, NCN, NNN, PCP, POP, SNS, SNP, CNC.

7. Catalytic system according to claim 1, wherein the ionic liquid cation is selected from (imid) azolium, ammonium, phosphonium, pyrrolidinium, piperidinium, sulfonium, pyridinium and the ionic liquid anion is selected from the group consisting of are carboxylates, halides, phosphates, bis(trifluoromethanesulfonyl)imide, triflate, sulfates, borates, nitrates.

8. Catalytic system according to claim 1, wherein the catalytic system is a homogeneous liquid solution.

9. Catalytic system according to claim 1, wherein the catalytic system is a heterogenous mixture.

10. Apparatus for producing electricity comprising a fuel cell and a catalytic system according to claim 1.

11. Use of a catalytic system of claim 1 for providing hydrogen to a fuel cell for producing electricity.

Description

EXAMPLES

[0069] Dehydrogenation under batch conditions:

Example 1

[0070] For dehydrogenation of isopropanol in a batch reactor, 0.013 mmol of a carbonylhydrido (tetrahydroborato) [bis(2-diphenylphosphinoethyl)amino] ruthenium (II) Pincer-type catalyst is dissolved in 1 mL of the ionic liquid 1-butyl-1-methylpiperidinium bis(trifluoromethanesulfonyl)imide and heated to 100 C. under stirring (typically 700 rpm) in a two-necked round-bottomed flask. Then, 2 ml of isopropanol is added to the mixture. After 2 hours of reaction, the conversion of isopropanol was 9%, corresponding to a turnover number of 380 and a turnover frequency of 190 h.sup.1. Isopropanol conversion is determined by .sup.1H and .sup.13C NMR. H.sub.2 is detected using gas chromatography.

Example 2

[0071] 0.003 mmol of a carbonylhydrido (tetrahydroborato) [bis(2-diphenylphosphinoethyl)amino] ruthenium (II) Pincer-type catalyst is added to 3 mL of the ionic liquid 1-butyl-3-methylimidazolium acetate and heated to 95 C. and stirred (typically 700 rpm) in a two-necked round-bottomed flask. 2 mL of formic acid is added. After 18 h of reaction full conversion is obtained, corresponding to a turnover number of 16750 and a turnover frequency of 930 h.sup.1. Formic acid conversion is determined by .sup.1H and .sup.13C NMR. H.sub.2 is detected using gas chromatography.

Example 3

[0072] Hydrogenation in a high-pressure reactor.

[0073] A solution containing 0.002 mmol of the carbonyldihydrido [bis(2-di-i-propylphosphinoethyl)amine] ruthenium (II) Pincer-type catalyst and 15 mL of the ionic liquid 1-ethyl-3-methylimidazolium acetate is heated to 80 C. and stirred (typically 700 rpm) in an autoclave. Then, the autoclave is loaded with a feed gas containing 30 bar hydrogen and 30 bar CO.sub.2. Formic acid production is determined by .sup.1H and .sup.13C NMR. The maximum turnover number obtained was 32411 and a turnover frequency of 900 h.sup.1 after two loads of 30:30 bar CO.sub.2/H.sub.2 and a total of 36 hours.

Example 4

[0074] Hydrogenation-dehydrogenation cycle:

[0075] The formic acid obtained in solution as described in Example 3, is reversibly converted to H.sub.2 and CO.sub.2. After the hydrogenation step, the residual gas is released and the autoclave is heated until the dehydrogenation temperature (80 C.) under stirring (typically 700 rpm). During the dehydrogenation step, the autoclave is left open under stirring to allow the release of H.sub.2 and CO.sub.2. Formic acid production and consumption is determined by 1H and 13C NMR. No visible deactivation of the system was observed in four different experiments of 10-13 cycles each. The system performs at least 13 cycles of hydrogenation/dehydrogenation with a maximum TON of 51000 using 3 mL of the ionic liquid 1-ethyl-3-methylimidazolium acetate and 0.002 mmol of the carbonyldihydrido [bis(2-di-i-propylphosphinoethyl)amine] ruthenium (II) Pincer-type catalyst.

Example 5

[0076] Dehydrogenation under continuous-flow conditions:

[0077] 0.02 mmol of the carbonylhydrido (tetrahydroborato) [bis(2-diphenylphosphinoethyl)amino] ruthenium (II) Pincer-type catalyst is dissolved in 4 mL of the ionic liquid 1-butyl-3-methylimidazolium acetate and heated to 80-95 C. and stirred (typically 700 rpm) in a three-necked round-bottomed flask. Then, formic acid is added by means of a syringe pump at a rate of 2-10 mL/h. The system consumed 15 liters of formic acid, reflected in a TON of 18000000 with an average TOF of 8000 h.sup.1 at 95 C. after 112 days.

Example 6

[0078] SILP system for dehydrogenation in a fixed bed reactor:

[0079] A typical 1 wt % Ru/SiO.sub.2 SILP catalyst is prepared by dissolving 0.3 mol of the carbonylhydrido (tetrahydroborato) [bis(2-diphenylphosphinoethyl)-amino] ruthenium (II) Pincer-type catalyst and 0.4 mL of the ionic liquid tributylmethylphosphonium bis(trifluoromethanesulfonyl)imide in 15 ml of dichloromethane. Then, 4 g of the solid support SiO.sub.2 is added and stirred (typically 300 rpm) for 15 minutes before removing the solvent under reduced pressure, resulting in the SILP catalyst. In a typical experiment, 4 g of the SILP catalyst is placed in the reactor tube (height 20 cm, diameter 2.5 cm, height of catalytic bed 2 cm) and the reactor heated to a temperature in the range 80-140 C. under a flow of nitrogen gas at 1 bar. Isopropanol is then pumped to an evaporator at 30 g/h, and the vapor is admitted to the reactor. The SILP catalyst described above was active for at least 100 hours affording 3-5% isopropanol conversion (TOF up to 70 h.sup.1).