ITFI20080160A1 - CATALYSTS BASED ON HIGH PERFORMANCE NOBLE METALS ALLOYS FOR AMMONIA ELECTION - Google Patents
CATALYSTS BASED ON HIGH PERFORMANCE NOBLE METALS ALLOYS FOR AMMONIA ELECTION Download PDFInfo
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- ITFI20080160A1 ITFI20080160A1 IT000160A ITFI20080160A ITFI20080160A1 IT FI20080160 A1 ITFI20080160 A1 IT FI20080160A1 IT 000160 A IT000160 A IT 000160A IT FI20080160 A ITFI20080160 A IT FI20080160A IT FI20080160 A1 ITFI20080160 A1 IT FI20080160A1
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- 239000003054 catalyst Substances 0.000 title claims description 40
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 title claims description 23
- 229910000510 noble metal Inorganic materials 0.000 title claims description 21
- 229910021529 ammonia Inorganic materials 0.000 title claims description 10
- 229910045601 alloy Inorganic materials 0.000 title claims description 9
- 239000000956 alloy Substances 0.000 title claims description 9
- 229910052751 metal Inorganic materials 0.000 claims description 22
- 239000002184 metal Substances 0.000 claims description 22
- 238000000034 method Methods 0.000 claims description 18
- 229910052697 platinum Inorganic materials 0.000 claims description 16
- 239000002904 solvent Substances 0.000 claims description 16
- 230000015572 biosynthetic process Effects 0.000 claims description 15
- 229910052741 iridium Inorganic materials 0.000 claims description 14
- 150000003839 salts Chemical class 0.000 claims description 13
- 239000000203 mixture Substances 0.000 claims description 12
- 239000002253 acid Substances 0.000 claims description 11
- 238000002360 preparation method Methods 0.000 claims description 11
- 239000000084 colloidal system Substances 0.000 claims description 10
- 238000009835 boiling Methods 0.000 claims description 7
- 238000006056 electrooxidation reaction Methods 0.000 claims description 7
- 238000010992 reflux Methods 0.000 claims description 6
- 238000003756 stirring Methods 0.000 claims description 6
- 229910052737 gold Inorganic materials 0.000 claims description 4
- 238000010438 heat treatment Methods 0.000 claims description 4
- 239000002105 nanoparticle Substances 0.000 claims description 3
- 229910052763 palladium Inorganic materials 0.000 claims description 3
- 238000001035 drying Methods 0.000 claims description 2
- 238000001914 filtration Methods 0.000 claims description 2
- 238000002955 isolation Methods 0.000 claims description 2
- 238000001465 metallisation Methods 0.000 claims description 2
- 229910001092 metal group alloy Inorganic materials 0.000 claims 1
- MTHSVFCYNBDYFN-UHFFFAOYSA-N diethylene glycol Chemical compound OCCOCCO MTHSVFCYNBDYFN-UHFFFAOYSA-N 0.000 description 24
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 23
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical compound OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 description 12
- 239000000725 suspension Substances 0.000 description 10
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 description 9
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 9
- 239000000446 fuel Substances 0.000 description 7
- 229920005862 polyol Polymers 0.000 description 7
- 150000003077 polyols Chemical class 0.000 description 7
- 150000002739 metals Chemical class 0.000 description 6
- ZIBGPFATKBEMQZ-UHFFFAOYSA-N triethylene glycol Chemical compound OCCOCCOCCO ZIBGPFATKBEMQZ-UHFFFAOYSA-N 0.000 description 6
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 5
- 230000000694 effects Effects 0.000 description 5
- 239000001257 hydrogen Substances 0.000 description 5
- 229910052739 hydrogen Inorganic materials 0.000 description 5
- 239000002245 particle Substances 0.000 description 5
- 239000002243 precursor Substances 0.000 description 5
- 238000003786 synthesis reaction Methods 0.000 description 5
- 238000002441 X-ray diffraction Methods 0.000 description 4
- 238000006243 chemical reaction Methods 0.000 description 4
- 238000000151 deposition Methods 0.000 description 4
- 230000008021 deposition Effects 0.000 description 4
- 239000010411 electrocatalyst Substances 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- PEDCQBHIVMGVHV-UHFFFAOYSA-N Glycerine Chemical compound OCC(O)CO PEDCQBHIVMGVHV-UHFFFAOYSA-N 0.000 description 3
- 229910000580 Lr alloy Inorganic materials 0.000 description 3
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 3
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- 229910052799 carbon Inorganic materials 0.000 description 3
- 239000007800 oxidant agent Substances 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical class O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- SVTBMSDMJJWYQN-UHFFFAOYSA-N 2-methylpentane-2,4-diol Chemical compound CC(O)CC(C)(C)O SVTBMSDMJJWYQN-UHFFFAOYSA-N 0.000 description 2
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 2
- 229910002621 H2PtCl6 Inorganic materials 0.000 description 2
- DNIAPMSPPWPWGF-UHFFFAOYSA-N Propylene glycol Chemical compound CC(O)CO DNIAPMSPPWPWGF-UHFFFAOYSA-N 0.000 description 2
- 239000003610 charcoal Substances 0.000 description 2
- 238000004090 dissolution Methods 0.000 description 2
- 239000002082 metal nanoparticle Substances 0.000 description 2
- BDAGIHXWWSANSR-UHFFFAOYSA-N methanoic acid Natural products OC=O BDAGIHXWWSANSR-UHFFFAOYSA-N 0.000 description 2
- YPFDHNVEDLHUCE-UHFFFAOYSA-N propane-1,3-diol Chemical compound OCCCO YPFDHNVEDLHUCE-UHFFFAOYSA-N 0.000 description 2
- 229910052707 ruthenium Inorganic materials 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- 150000005846 sugar alcohols Polymers 0.000 description 2
- OSWFIVFLDKOXQC-UHFFFAOYSA-N 4-(3-methoxyphenyl)aniline Chemical compound COC1=CC=CC(C=2C=CC(N)=CC=2)=C1 OSWFIVFLDKOXQC-UHFFFAOYSA-N 0.000 description 1
- 102100034013 Gamma-glutamyl phosphate reductase Human genes 0.000 description 1
- 101001133924 Homo sapiens Gamma-glutamyl phosphate reductase Proteins 0.000 description 1
- 229910000575 Ir alloy Inorganic materials 0.000 description 1
- -1 Ketjen Black Chemical compound 0.000 description 1
- 229910001260 Pt alloy Inorganic materials 0.000 description 1
- 229910002848 Pt–Ru Inorganic materials 0.000 description 1
- 238000003991 Rietveld refinement Methods 0.000 description 1
- UWHCKJMYHZGTIT-UHFFFAOYSA-N Tetraethylene glycol, Natural products OCCOCCOCCOCCO UWHCKJMYHZGTIT-UHFFFAOYSA-N 0.000 description 1
- HSFWRNGVRCDJHI-UHFFFAOYSA-N alpha-acetylene Natural products C#C HSFWRNGVRCDJHI-UHFFFAOYSA-N 0.000 description 1
- 238000005267 amalgamation Methods 0.000 description 1
- 229910052787 antimony Inorganic materials 0.000 description 1
- 229910021383 artificial graphite Inorganic materials 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
- 150000003841 chloride salts Chemical class 0.000 description 1
- 238000000970 chrono-amperometry Methods 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 230000005611 electricity Effects 0.000 description 1
- 125000002534 ethynyl group Chemical group [H]C#C* 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 235000019253 formic acid Nutrition 0.000 description 1
- 239000010931 gold Substances 0.000 description 1
- 229940051250 hexylene glycol Drugs 0.000 description 1
- 229920000554 ionomer Polymers 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 239000003273 ketjen black Substances 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 229910001510 metal chloride Inorganic materials 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 229910021382 natural graphite Inorganic materials 0.000 description 1
- 150000002823 nitrates Chemical class 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 229910000069 nitrogen hydride Inorganic materials 0.000 description 1
- 238000005580 one pot reaction Methods 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- KDLHZDBZIXYQEI-UHFFFAOYSA-N palladium Substances [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 description 1
- 238000004917 polyol method Methods 0.000 description 1
- 238000000634 powder X-ray diffraction Methods 0.000 description 1
- 229960004063 propylene glycol Drugs 0.000 description 1
- 239000002296 pyrolytic carbon Substances 0.000 description 1
- 238000002407 reforming Methods 0.000 description 1
- 229930195734 saturated hydrocarbon Natural products 0.000 description 1
- 238000005063 solubilization Methods 0.000 description 1
- 230000007928 solubilization Effects 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
- H01M4/90—Selection of catalytic material
- H01M4/92—Metals of platinum group
- H01M4/921—Alloys or mixtures with metallic 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
- B01J23/48—Silver or gold
-
- 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
- B01J35/00—Catalysts, in general, characterised by their form or physical properties
- B01J35/40—Catalysts, in general, characterised by their form or physical properties characterised by dimensions, e.g. grain size
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
- H01M4/90—Selection of catalytic material
- H01M4/92—Metals of platinum group
- H01M4/925—Metals of platinum group supported on carriers, e.g. powder carriers
- H01M4/926—Metals of platinum group supported on carriers, e.g. powder carriers on carbon or graphite
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Organic Chemistry (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Catalysts (AREA)
Description
Descrizione dell’invenzione dal titolo: Description of the invention entitled:
"Catalizzatori a base di leghe di metalli nobili ad alta prestazione per l’elettroossidazione di ammoniaca†"High-performance catalysts based on noble metal alloys for the electro-oxidation of ammonia⠀
Campo dell’invenzione Field of invention
La presente invenzione si riferisce alla preparazione di elettrocatalizzatori a base di leghe di metalli nobili e loro impiego in apparecchiature elettrochimiche. The present invention relates to the preparation of electrocatalysts based on noble metal alloys and their use in electrochemical equipment.
Stato dell’arte State of the art
Le celle a combustibile sono dispositivi elettrochimici che convertono l’energia chimica direttamente in elettricità . In tali celle, un combustibile (generalmente idrogeno, alcoli o idrocarburi saturi) e un ossidante (in genere l’ossigeno deH’aria) sono alimentati all’anodo e al catodo. Teoricamente, una cella a combustibile può produrre energia^elettrica finché un combustibile e un ossidante sono inviati agli elettrodi. In realtà , la degradazione dLuno o più componenti limita l’utilizzo pratico della maggior parte delle celle a combustibile. Fuel cells are electrochemical devices that convert chemical energy directly into electricity. In these cells, a fuel (generally hydrogen, alcohols or saturated hydrocarbons) and an oxidant (usually oxygen from the air) are fed to the anode and cathode. Theoretically, a fuel cell can produce electrical energy as long as a fuel and an oxidizer are sent to the electrodes. In fact, the degradation of one or more components limits the practical use of most fuel cells.
Negli ultimi anni, una particolare attenzione à ̈ stata posta all’elettroossidazione dell’ammoniaca come veicolo per la produzione di importanti quantità di idrogeno. Infatti, l’ammoniaca può essere considerata un eccellente carrier di idrogeno. L’ammoniaca liquida contiene 1.7 volte più idrogeno e possiede una densità di energia 50 volte superiori a quella contenuta dall’idrogeno liquido per un dato volume. La decomposizione dell’ammoniaca attraverso l’elettroossidazione in solvente alcalino a bassi potenziali à ̈ una reazione priva di prodotti quali NOxe COx; infatti gli unici prodotti della reazione sono l’azoto e l’acqua. Per questo motivo, tale reazione può essere utiilizzata vantaggiosamente come carrier di idrogeno. In recent years, particular attention has been paid to the electro-oxidation of ammonia as a vehicle for the production of significant quantities of hydrogen. In fact, ammonia can be considered an excellent hydrogen carrier. Liquid ammonia contains 1.7 times more hydrogen and has an energy density 50 times higher than that contained by liquid hydrogen for a given volume. The decomposition of ammonia through electro-oxidation in an alkaline solvent at low potential is a reaction without products such as NOx and COx; in fact the only products of the reaction are nitrogen and water. For this reason, this reaction can be used advantageously as a hydrogen carrier.
Elettrocatalizzatori comunemente usati per l’elettroossidazione di ammoniaca includono il Platino (Pt) e elettrocatalizzatori a base di Pt modificati con metalli nobili. Leghe di Pt-lr nano particolate sono note ed à ̈ stato mostrato che la presenza di Ir ne migliora le prestazioni per l’elettroossidazione di ammoniaca. Leghe nanoparticolate di metalli nobili possono essere preparate mediante la cosiddetta sintesi poliolica. Commonly used electrocatalysts for ammonia electrooxidation include Platinum (Pt) and Pt-based electrocatalysts modified with noble metals. Particulate nano Pt-lr alloys are known and it has been shown that the presence of Ir improves its performance for the electrooxidation of ammonia. Nanoparticulate alloys of noble metals can be prepared by the so-called polyol synthesis.
US 6,551,960 B1 descrive la preparazione di catalizzatori metallici supportati per l’uso nel reforming del metanolo. Pt e Ru sono preferibilmente descritti e i catalizzatori sono preparati formando specie solubili dei metalli in un polialcol a riflusso e supportate su carbone attivo. US 6,551,960 B1 describes the preparation of supported metal catalysts for use in methanol reforming. Pt and Ru are preferably described and the catalysts are prepared by forming soluble species of the metals in a refluxed polyalcohol and supported on activated carbon.
US 2003/0104936A1 fornisce un metodo per la produzione di catalizzatori metallici nanoparticolati comprendente i seguenti passaggi: US 2003 / 0104936A1 provides a method for the production of nanoparticulate metal catalysts comprising the following steps:
a) Solubilizzazione di uno o più cloruri metallici in un solvente contenente almeno un polialcol, tipicamente glicol etilenico contenente meno del 10% di acqua; b) formazione di una sospensione colloidale di nanoparticelle di catalizzatore non protetto mediante innalzamento del pH della soluzione, tipicamente a 10 o superiore, ed innalzamento delle temperatura, tipicamente 125°C o superiore; c) aggiunta del supporto elettroconduttore alla sospensione colloidale; a) Solubilization of one or more metal chlorides in a solvent containing at least one polyalcohol, typically ethylene glycol containing less than 10% of water; b) formation of a colloidal suspension of unprotected catalyst nanoparticles by raising the pH of the solution, typically to 10 or higher, and raising the temperature, typically 125 ° C or higher; c) adding the electroconductive support to the colloidal suspension;
d) deposizione, delle nanoparticelle metalliche di catalizzatore non protetto sulle particelle del supporto mediante abbassamento del pH della sospensione, tipicamente a pH 6.5 o inferiore, mediante aggiunta di HN03. d) deposition of the metal nanoparticles of unprotected catalyst on the particles of the support by lowering the pH of the suspension, typically to pH 6.5 or lower, by adding HN03.
US 2004/0087441 A1 descrive un metodo per la produzione di catalizzatori metallici nanoparticolati a base di Pt di formula PtX dove X Ã ̈ scelto nel gruppo consistente in Ru, Ir, Os, Sn, Sb, Au, WOXicomprendente i seguenti passaggi: a) fornire precursori metallici che contengano ioni Pt e X; US 2004/0087441 A1 describes a method for the production of Pt-based nanoparticulate metal catalysts of the formula PtX where X is selected from the group consisting of Ru, Ir, Os, Sn, Sb, Au, WOXic comprising the following steps: a) providing metal precursors that contain Pt and X ions;
b) aggiunta dei precursori metallici ad una soluzione di glicole etilenico il cui pH Ã ̈ stato basificato, tipicamente a pH fra 8 e 12 per addizione-di NaOH, per formare una soluzione colloidale; b) addition of the metal precursors to an ethylene glycol solution whose pH has been basified, typically at a pH between 8 and 12 by addition of NaOH, to form a colloidal solution;
c) innalzamento della temperatura per produrre la riduzione dei precursori metallici e formazione delle nano particelle di catalizzatore a base di Pt e Ir; c) raising the temperature to produce the reduction of the metal precursors and formation of the catalyst nano particles based on Pt and Ir;
d) formazione e simultanea deposizione del catalizzatore nano particolato su supporto poroso elettroconduttore mediante addizione del supporto alla soluzione colloidale. d) formation and simultaneous deposition of the nano particulate catalyst on a porous electroconductive support by adding the support to the colloidal solution.
US 2006/0094597 A1 descrive un metodo per la produzione di catalizzatori supportati a base di leghe di metalli nobili, preferibilmente Pt-Ru, comprendente due passaggi di riduzione sequenziali. In un primo passaggio il precursore del primo metallo (M1, meno nobile come Ru) à ̈ aggiunto alla sospensione di supporto poroso elettroconduttore in solvente poliossidrilato (ad es. glicol etilenico) ed à ̈ attivato per innalzamento delle temperatura fra 80 e 160°C. In un secondo passaggio il precursore di un secondo (o terzo) metallo (M2, metallo nobile come Pt, Pd, Au e miscele) à ̈ aggiunto alla miscela di M1 e la temperatura à ̈ ulteriormente innalzata fra 160 e 300 °C. US 2006/0094597 A1 describes a method for the production of supported catalysts based on noble metal alloys, preferably Pt-Ru, comprising two sequential reduction steps. In a first step, the precursor of the first metal (M1, less noble like Ru) is added to the suspension of porous electroconducting support in a polyhydric solvent (e.g. ethylene glycol) and is activated by raising the temperature between 80 and 160 ° C . In a second step the precursor of a second (or third) metal (M2, noble metal such as Pt, Pd, Au and mixtures) is added to the mixture of M1 and the temperature is further raised between 160 and 300 ° C.
Esiste la necessità di migliorare l'efficienza e l’attività dei catalizzatori per l’elettrossidazione d’ammoniaca da impiegare all’anodo di celle a combustibile. Maggior efficienza del catalizzatore significa minor quantità di catalizzatore a base di metalli nobili. There is a need to improve the efficiency and the activity of the catalysts for the electrioxidation of ammonia to be used at the anode of fuel cells. Greater catalyst efficiency means less noble metal-based catalyst.
Una delle fasi più importanti nella sintesi dei polioli à ̈ che ad una temperatura minore del punto di ebollizione del poliolo, il sale del metallo forma una soluzione colloidale, prima di essere ridotto a metallo a temperature più alte. I “metal blacks†così chiamati possono poi essere utilizzati come catalizzatori oppure essere depositati su un materiale di supporto con alta area superficiale. Nella preparazione di catalizzatori bimetalllici, la deposizione dei due metalli che devono essere in contatto nella fase colloidale mista à ̈ un passaggio molto importante. Nel caso particolare di catalizzatori bimetallici a base di Pt e Ir la preparazione mediante sintesi poliolica come nota allo stato dell’arte produce catalizzatori di scarsa efficienza a causa della perdita di Ir e Pt nelle acque madri del colloide. Esiste quindi anche la necessità di migliorare le metodologie di preparazione di detti catalizzatori. One of the most important steps in the synthesis of polyols is that at a temperature below the boiling point of the polyol, the salt of the metal forms a colloidal solution, before being reduced to metal at higher temperatures. The so called â € œmetal blacksâ € can then be used as catalysts or be deposited on a support material with a high surface area. In the preparation of bimetallic catalysts, the deposition of the two metals that must be in contact in the mixed colloidal phase is a very important step. In the particular case of bimetallic catalysts based on Pt and Ir, the preparation by means of polyol synthesis as known in the state of the art produces catalysts of poor efficiency due to the loss of Ir and Pt in the mother liquors of the colloid. There is therefore also the need to improve the methods of preparation of said catalysts.
Sommario dell’invenzione Summary of the invention
La presente invenzione fornisce un nuovo processo per la preparazione di materiali elettrocatalizzatori a base di leghe di metalli nobili, preferibilmente Pt-lr, supportati su materiale elettroconduttori mediante un processo poliolico caratterizzato dal fatto che le nanoparticelle metalliche che si formano dalla riduzione del colloide, sono depositate su un supporto conduttivo di carbone usando una sintesi " one-pot †a pH controllato mediante aggiunta di un acido debole. Detto processo consente di ottenere catalizzatori ad alto grado di amalgamazione caratterizzati da particelle di dimensioni inferiori a 10nm ed aventi alta prestazione per l’uso in celle a combustibile ed in particolare all’anodo per l’elettro-ossidazione di ammoniaca. The present invention provides a new process for the preparation of electrocatalyst materials based on noble metal alloys, preferably Pt-1r, supported on electroconductive material by means of a polyol process characterized in that the metal nanoparticles formed by the reduction of the colloid are deposited on a conductive carbon support using a "one-pot" synthesis at controlled pH by adding a weak acid. This process allows to obtain catalysts with a high degree of amalgamation characterized by particles smaller than 10nm and having high performance for the use in fuel cells and in particular at the anode for the electro-oxidation of ammonia.
Descrizione dettagliata dell’invenzione Detailed description of the invention
La presente invenzione riguarda un processo per la preparazione di catalizzatori nano particolati supportati a base di leghe di metalli nobili, preferibilmente Pt-lr, comprendente le seguenti fasi: The present invention relates to a process for the preparation of supported nanoparticulate catalysts based on noble metal alloys, preferably Pt-1r, comprising the following steps:
a) creazione di una miscela comprendente : a) creation of a mixture comprising:
- un supporto poroso elettroconduttore; - a porous electroconductive support;
- un solvente poliossidrilato altobollente; - a high boiling polyhydric solvent;
- due o più sali di metalli nobili. - two or more salts of noble metals.
b) formazione del colloide mediante riscaldamento della miscela a temperatura compresa fra 160 e 200 °C e misura del pH che da 2-3 sale fino a raggiungere il valore 5-7 che indica la completa formazione del colloide; b) formation of the colloid by heating the mixture at a temperature between 160 and 200 ° C and measuring the pH which rises from 2-3 until reaching the value 5-7 which indicates the complete formation of the colloid;
c) deposizione dei metalli sul supporto mediante aggiunta di un acido sotto vigorosa agitazione; c) metal deposition on the support by adding an acid under vigorous stirring;
d) riscaldamento della miscela a temperatura di riflusso del solvente poliossidrilato; d) heating the mixture to reflux temperature of the polyhydroxy solvent;
e) isolamento del prodotto mediante filtrazione ed essiccamento. e) isolation of the product by filtration and drying.
Secondo un aspetto preferito la creazione della miscela di cui alla fase a) Ã ̈ preparata sospendendo il supporto nel solvente poliossidrilato, a cui vengono aggiunte soluzioni dei sali di metalli nobili preventivamente solubilizzati nel solvente poliossidrilato. According to a preferred aspect, the creation of the mixture referred to in step a) is prepared by suspending the support in the polyhydric solvent, to which solutions of the noble metal salts previously solubilized in the polyhydric solvent are added.
Detti metalli nobili sono scelti nel gruppo consistente in: Pt, Ir, Pd, Ru, Ag, Au; preferibilmente Pt e Ir. Said noble metals are selected from the group consisting of: Pt, Ir, Pd, Ru, Ag, Au; preferably Pt and Ir.
Per un aspetto preferito detti due o più sali di metalli nobili sono scelti fra qualunque sale dei metalli elencati sopra che siano solubili in detto solvente poliossidrilato come ad esempio cloruri o nitrati. For a preferred aspect, said two or more salts of noble metals are selected from any salt of the metals listed above which are soluble in said polyhydric solvent such as for example chlorides or nitrates.
Il carico di metalli sul supporto à ̈ del 15% in peso o superiore; preferibilmente fra il 25% e il 30%. The load of metals on the support is 15% by weight or higher; preferably between 25% and 30%.
Secondo l'invenzione, il supporto poroso elettroconduttore à ̈ per esempio carbone attivo elettroconduttore come Ketjen Black, Vulcan XC-72R e acetilene nero; carbone per inchiostro trattato con agente ossidante, carbone pirolitico, grafite naturale, grafite artificiale; preferibilmente Vulcan XC-72R. According to the invention, the porous electroconductive support is for example electroconductive activated carbon such as Ketjen Black, Vulcan XC-72R and black acetylene; carbon for ink treated with oxidizing agent, pyrolytic carbon, natural graphite, artificial graphite; preferably Vulcan XC-72R.
Secondo l’invenzione, il solvente poliossidrilato alto bollente à ̈ un solvente il cui punto di ebollizione varia fra 200 a 285°C come glicole etilenico, glicole dietilenico, glicole trietilenico, 1,2 propilen glicol, 1,3 propilen glicol, tetraetilen glicole, glicerolo, esilen glicole; preferibilmente glicole dietilenico, glicole trietilenico. According to the invention, the high boiling polyhydric solvent is a solvent whose boiling point varies between 200 and 285 ° C such as ethylene glycol, diethylene glycol, triethylene glycol, 1,2 propylene glycol, 1,3 propylene glycol, tetraethylene glycol, glycerol, hexylene glycol; preferably diethylene glycol, triethylene glycol.
Secondo un aspetto preferito detto acido della fase c) à ̈ un acido debole di origine organica o inorganica ed à ̈ preferibilmente scelto nel gruppo consistente in acido acetico e acido formico; preferibilmente acido acetico. According to a preferred aspect, said acid of step c) is a weak acid of organic or inorganic origin and is preferably selected from the group consisting of acetic acid and formic acid; preferably acetic acid.
Detto acido à ̈ aggiunto in largo eccesso molare rispetto alle moli totali di metalli; preferibilmente l’acido aggiunto à ̈ in proporzione molare rispetto ai metalli 700:1 o inferiore. L’aggiunta à ̈ effettuata ad una velocità opportuna ad un’efficiente dispersione dell’acido nel colloide; tale velocità di addizione può variare a seconda dei mezzi usati per l'aggiunta e per la miscelazione e delle quantità di materiale. Indicativamente l'aggiunta può essere effettuata in un tempo variabile fra 5 e 60 min preferibilmente fra 10 e 30 min. Said acid is added in large molar excess with respect to the total moles of metals; preferably the added acid is in molar proportion with respect to metals 700: 1 or lower. The addition is carried out at a suitable speed for an efficient dispersion of the acid in the colloid; this speed of addition can vary according to the means used for the addition and mixing and the quantity of material. Indicatively, the addition can be carried out in a time varying between 5 and 60 minutes, preferably between 10 and 30 minutes.
La step di addizione dell’acido ad una fase critica della reazione, evitando la perdita di metallo nelle acque madri del colloide, migliora la deposizione dei colloidi metallici sul carbone e si riflette in una migliore prestazione del catalizzatore. The step of addition of the acid to a critical phase of the reaction, avoiding the loss of metal in the mother liquors of the colloid, improves the deposition of the metal colloids on the carbon and is reflected in a better performance of the catalyst.
Secondo l'invenzione la fase d) dì riflusso à ̈ mantenuta per un tempo compreso fra 15 e 45 minuti. According to the invention, the reflux phase d) is maintained for a time comprised between 15 and 45 minutes.
La presente invenzione riguarda catalizzatori supportati ottenibili mediante il processo di cui sopra; preferibilmente contenenti Pt o Ir ed in particolare preferibilmente a base di Pt e Ir. The present invention relates to supported catalysts obtainable by means of the above process; preferably containing Pt or Ir and in particular preferably based on Pt and Ir.
Per un aspetto preferito detti catalizzatori a base di Pt e Ir sono preparati a partire da sali metallici di Pt e Ir rispettivamente in proporzione molare variabile fra 0.10:0.90 e 0.30:0.70; preferibilmente fra 0.25:0.75 e 0.20:0.80. For a preferred aspect said catalysts based on Pt and Ir are prepared starting from metal salts of Pt and Ir respectively in a molar proportion varying between 0.10: 0.90 and 0.30: 0.70; preferably between 0.25: 0.75 and 0.20: 0.80.
La presente invenzione riguarda in particolar modo catalizzatori a base di Pt e Ir ottenuti mediante il processo sopradescritto utilizzando come sali metallici lrCI3.xH20 e H2PtCI6. The present invention relates in particular to catalysts based on Pt and Ir obtained by means of the process described above using lrCl3.xH20 and H2PtCl6 as metal salts.
Il carico metallico sul supporto à ̈ circa del 15% in peso o superiore, preferibilmente il Pt à ̈ presente al 20% in peso rispetto al peso del supporto. The metal load on the support is about 15% by weight or higher, preferably the Pt is present at 20% by weight with respect to the weight of the support.
I catalizzatori supportati a base di leghe di Pt e Ir nobili ottenuti mediante il processo sopra descritto hanno particelle di dimensioni medie inferiori a 10 nm, tipicamente 5-6 nm e sono caratterizzati da una superficie catalitica superiore a 40 m<2>/gNMtipicamente compresa fra 45 e 55m<z>/gNMThe supported catalysts based on noble Pt and Ir alloys obtained by the process described above have particles with an average size of less than 10 nm, typically 5-6 nm, and are characterized by a catalytic surface greater than 40 m <2> / gNM typically comprised between 45 and 55m <z> / gNM
La presente invenzione potrà essere meglio compresa alla luce dei seguenti esempi realizzativi. The present invention can be better understood in the light of the following embodiment examples.
ESEMPIO 1 - Preparazione del catalizzatore EXAMPLE 1 - Preparation of the catalyst
Carbone attivo Vulcan XC72 (1.283g) premacinato in un macinatore a palle ed à ̈ stato sospeso in 200ml di glicole dietilenico (>99%) e agitato a temperatura ambiente per 150 minuti, con agitatore meccanico in un apparato da riflusso. lrCI3.xH20 (MW 298.58) (0.1715g) à ̈ stato disciolto in 80ml di glicole dietilenico sotto agitazione e quindi aggiunto alla sospensione di carbone uitlizzando 120ml di glicole dietilenico per il lavaggio del recipiente di dissoluzione del sale di Ir. Vulcan XC72 activated carbon (1.283g) pre-ground in a ball grinder and was suspended in 200ml diethylene glycol (> 99%) and stirred at room temperature for 150 minutes, with a mechanical stirrer in a reflux apparatus. lrCI3.xH20 (MW 298.58) (0.1715g) was dissolved in 80ml of diethylene glycol under stirring and then added to the charcoal suspension using 120ml of diethylene glycol to wash the Ir salt dissolution vessel.
H2PtCl6(MW 409.79) (0.7995g) Ã ̈ stato disciolto in 80ml di glicole dietilenico sotto agitazione e quindi aggiunto alla sospensione di carbone utilizzando 120ml di glicole dietilenico .per il lavaggio del recipiente di dissoluzione del sale di.Pt. H2PtCl6 (MW 409.79) (0.7995g) was dissolved in 80ml of diethylene glycol under stirring and then added to the charcoal suspension using 120ml of diethylene glycol. To wash the Pt salt dissolution vessel.
La sospensione presenta un pH di circa 2-3 (misurato con cartina tornasole) e viene scaldata a 180°C e quando il pH si alza fino a 6 (misurato con cartina al tornasole) la formazione del colloide à ̈ finita. 100ml di acido acetico (>99%) sono aggiunti alla sospensione ad una velocità di circa 10ml al minuto mediante in imbuto gocciolatore sotto vigorosa agitazione. Il pH della sospensione rimane invariato attorno al valore 6 per tutta la durata dell’aggiunta. The suspension has a pH of about 2-3 (measured with litmus paper) and is heated to 180 ° C and when the pH rises to 6 (measured with litmus paper) the formation of the colloid is over. 100ml of acetic acid (> 99%) are added to the suspension at a rate of about 10ml per minute by means of a dropping funnel under vigorous stirring. The pH of the suspension remains unchanged around the value of 6 for the entire duration of the addition.
La miscela à ̈ quindi scaldata fino a riflusso e mantenuta sotto agitazione per 30 min. Il pH della sospensione rimane invariato attorno a 6 durante questa fase di riflusso. The mixture is then heated to reflux and kept under stirring for 30 min. The pH of the suspension remains unchanged around 6 during this reflux phase.
La miscela risultante à ̈ raffreddata e poi filtrata. Il solido à ̈ lavato con una soluzione EtOH/H20 deionizzata 50:50 e poi con abbondante H20 deionizzata. The resulting mixture is cooled and then filtered. The solid is washed with a 50:50 deionized EtOH / H20 solution and then with abundant deionized H20.
Il solido à ̈ asciugato all’aria sul filtro e poi macinato nel macinatore a palle (250 giri al min/15 min). The solid is air dried on the filter and then ground in the ball grinder (250 rpm / 15 min).
Sono stati preparati e ripetuti sia in piccola che in grande scala numerosi catalizzatori attraverso la procedura sopra riportata. Numerous catalysts were prepared and repeated both on a small and large scale through the above procedure.
La formazione della lega Pt-lr à ̈ stata valutata attraverso la diffrazione dei raggi X (XRD) dei catalizzatori. Per il raffinamento degli spettri XRD, à ̈ stato utilizzato programma Powdercell XRPD ( i risultati sono in accordo con un errore sulla terza cifra decimale, con quelli ottenuti con GSAS XRPD).Tutti i dati XRD confermano la presenza della lega Pt-lr entro l’errore sperimentale dell’ 0.3%. The formation of the Pt-lr alloy was evaluated by X-ray diffraction (XRD) of the catalysts. For the refinement of the XRD spectra, Powdercell XRPD program was used (the results are in agreement with an error on the third decimal place, with those obtained with GSAS XRPD) All XRD data confirm the presence of the Pt-lr alloy within Experimental error of 0.3%.
La Tabella 1 sintetizza i rilevanti risultati ottenuti per i catalizzatori Pt-lr preparati. L’attività elettrochimica à ̈ valutata in semicella atraverso esperimenti pontenziostatici condotti in 0.1M KOH e 1M NH3a 25°C.GIi “inks†sono preparati utilizzando lo ionomero della Tokuyama (A3, 5% in peso) mentre il carico di catalizzatore sull’elettrodo à ̈ uguale a 0.30mg/cm<2>· Table 1 summarizes the relevant results obtained for the prepared Pt-1r catalysts. The electrochemical activity is evaluated in the half-cell through pontentiostatic experiments conducted in 0.1M KOH and 1M NH3 at 25 ° C. GIi â € œinksâ € are prepared using the Tokuyama ionomer (A3, 5% by weight) while the catalyst load on the electrode is equal to 0.30mg / cm <2> ·
Tabella 1: Attività elettrochimica di massa normalizzata sulla massa totale di metallo nobile ricavata dalla cronoamperometria (determinata dopo 10minuti a potenzialele costante di 0.6V) dei catalizzatori Pt3lr/Vulcan con Pt(20% in peso) e lr(6.7% in peso) Table 1: Electrochemical activity of mass normalized on the total mass of noble metal obtained from the chronoamperometry (determined after 10 minutes at a constant potential of 0.6V) of the Pt3lr / Vulcan catalysts with Pt (20% by weight) and lr (6.7% by weight)
Sintesi N° Poliolo Quantità Attività Summary N ° Polyol Quantity Activity
preparata elettrochimica (mA/mgNM) electrochemical preparation (mA / mgNM)
1 Trietilen glicole 1.7 7.2 1 Triethylene glycol 1.7 7.2
2 Trietilen glicole 5 6.8 2 Triethylene glycol 5 6.8
3 Trietilen glicole 5 7,0 3 Triethylene glycol 5 7.0
La Tabella- 2 sintetizza tutti i risultati ottenuti utilizzando questa particolare sintesi dei polioli per la preparazione di catalizzatori Pt-lr per l’uso in un elettro lizzato re ad ammoniaca. Table 2 summarizes all the results obtained using this particular synthesis of polyols for the preparation of Pt-1r catalysts for use in an ammonia electrolyzer.
Tabella 2: Risultati relativi ai catalizzatori con il 20% in peso di Pt e il 6,7% in peso di Ir su Vulcan; Table 2: Results relating to catalysts with 20% by weight of Pt and 6.7% by weight of Ir on Vulcan;
Il diametro medio delle particelle à ̈ stato determinato attraverso il raffinamento di Rietveld degli The mean particle diameter was determined through Rietveld refinement of
spettri XRD. XRD spectra.
Attività Activity
Diametro Diameter
Numero elettrochimica Area stimata Poliolo medio delle Electrochemical number Estimated area Average polyol of
di test (mA/mgNM) [m<z>/gNWI] particelle[nm] of test (mA / mgNM) [m <z> / gNWI] particles [nm]
media ± dev. Std. mean ± dev. Std.
Trietilen glicole 3 7.0 ± 0.2 6 46 Triethylene glycol 3 7.0 ± 0.2 6 46
Dietilen -glicole 8;6 ± 0.4 5 Diethylene glycol 8; 6 ± 0.4 5
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US20040087441A1 (en) * | 2002-10-29 | 2004-05-06 | Christina Bock | Platinum based nano-size catalysts |
US20060094597A1 (en) * | 2004-10-29 | 2006-05-04 | Umicore Ag & Co. Kg | Method for manufacture of noble metal alloy catalysts and catalysts prepared therewith |
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US20040087441A1 (en) * | 2002-10-29 | 2004-05-06 | Christina Bock | Platinum based nano-size catalysts |
US20060094597A1 (en) * | 2004-10-29 | 2006-05-04 | Umicore Ag & Co. Kg | Method for manufacture of noble metal alloy catalysts and catalysts prepared therewith |
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