Catalyst Coating and Process for Production Thereof

a catalyst and catalyst technology, applied in the field of catalysts, can solve the problems of high electrolysis voltage, overpotential component of chlorine deposition, electrodes to evolve oxygen, etc., and achieve the effect of low overpotential and low electrolysis voltag

Inactive Publication Date: 2014-08-14
COVESTRO DEUTSCHLAND AG +1
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0017]It is an object of the present invention to provide an improved catalyst coating with electrocatalytically active components based on ruthenium oxide and titanium oxide and a process for production thereof, which overcomes the above disadvantages of the coatings known to date and, on application to an electrode, enables a lower overpotential in the evolution of chlorine, for example in chloralkali electrolysis or hydrochloric acid electrolysis. In addition, the catalyst coating should adhere firmly to the base metal and not be attacked chemically or electrochemically. With the catalyst coating, it should be possible to achieve a low electrolysis voltage even at low chloride concentrations.

Problems solved by technology

Disadvantages of these known electrodes when used in halide-containing electrolytes are the overpotential component for the chlorine deposition, which is still high, the tendency of the electrodes to evolve oxygen nonetheless, the high electrolysis voltage and the high demand for costly noble metal for production of the coating.
All these factors have an adverse effect on the economic viability of the known electrolysis process using such electrodes.
It is also known from the coatings from the prior art (DE 602005002661 T2) that the noble metals are eluted out of the coating with time under electrolysis conditions; long-term corrosion resistance is accordingly inadequate.
For the running of the electrolysis process, this means that no electrochemical operations take place any longer at this surface, which can cause a complete failure of the electrolysis cell with the associated adverse economic consequences.
Moreover, when an electrolyzer with noble metal-containing DSA electrodes is used in chloride-containing solutions for production of chlorine, it is observed that the side reaction of oxygen formation cannot be fully suppressed, as a result of which oxygen is found in the chlorine product gas.
The oxygen content means increased purification complexity for the chlorine gas and as a result likewise has adverse effects on the economic viability of the electrolysis.
Moreover, the sole use of noble metals as catalytic electrode material, because of the high cost thereof and diminishing availability thereof on the global market, likewise impairs the economic viability of known electrodes.
A disadvantage is that the electrodes thus coated still have a significant overpotential for the electrochemical chlorine production.
Likewise disadvantageous in the sol-gel synthesis is the use of very costly organic precursor compounds.

Method used

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Examples

Experimental program
Comparison scheme
Effect test

example 1

Comparative Example with Commercial Anodes for NaCl Electrolysis and Electrolysis Test

[0068]A titanium-standard expanded metal anode from De Nora for NaCl electrolysis, which had been equipped with a ruthenium oxide- and iridium oxide-containing catalyst coating, was used. The size of the anode in the laboratory cell used was 10 cm×10 cm; the anode support material contained titanium and had the form of an expanded metal, characterized by the mesh size of 8 mm, land width 2 mm and land thickness 2 mm. Between the anode space and cathode space, a DuPont Nafion 982 ion exchange membrane was used. The cathode used was a standard nickel cathode from Denora for NaCl electrolysis, which had been equipped with a ruthenium-containing coating. The electrode separation was 3 mm. Introduced into the anode space of the electrolysis cell was an NaCl-containing solution having a sodium chloride concentration of 210 g / l, a volume flow rate between 5 and 10 l / h and a temperature of 88° C. On the ca...

example 2

Comparative Example

[0069]A coating solution comprising 2.00 g of ruthenium(III) chloride hydrate (Ru content 40.5% by weight), 9.95 g of n-butanol, 0.94 g of conc. hydrochloric acid (37% by weight), 5.93 g of tetra-n-butyl titanate (Ti—(O-Bu)4) is made up. This is applied by brush to a sand-blasted expanded titanium metal with the same geometry as in Example 1 as a support. In the coating solution, the concentration of mineral acid is 27.3 mol % and the acid concentration thus totals 27.3 mol %. The ratio of the sum of the amounts of acid to the sum of the amounts of metal in the coating solution is 0.375.

[0070]Subsequently, the expanded metal is dried at 80° C. for 10 min and then sintered at 470° C. for 10 min. The application operation is repeated three times more, as are the drying and sintering. The last sintering operation is effected at 520° C. for 60 min. The areal ruthenium loading was determined from the consumption of the coating solution to be 20.8 g / m2, with a compositi...

example 3

Inventive Coating Production

[0071]Titanium sheets having a diameter of 15 mm (thickness 2 mm) were sand-blasted to clean and to roughen the surface and then etched in 10% oxalic acid at 80° C. (30 min), then cleaned with isopropanol.

[0072]Production of the coating solution: 4.00 g of titanium(IV) isopropoxide are added dropwise to an initial charge of 3.18 g of acetic acid while cooling in an ice bath with vigorous stirring, with at least 1 min of stirring time between two drops. The clear solution formed is then stirred while cooling for a further 12 h. To this is added dropwise a solution of 1.50 g of ruthenium(III) chloride hydrate (Ru content 40.35% by weight) in 29.74 g of 10% hydrochloric acid while cooling in an ice bath and stirring vigorously. Thereafter, the product is stirred for a further 96 h. In the coating solution prepared as described above, the concentration of organic acid is 34.3 mol %, the concentration of mineral acid 52.8 mol %, and the total acid concentratio...

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Abstract

A process for wet-chemical production of a catalyst coating on an electrically conductive support for electrodes for chloralkali or hydrochloric acid electrolysis with electrocatalytically active components based on noble metal oxides, in which the catalyst coating is produced by; producing a coating solution or dispersion comprising a precursor compound of a noble metal and/or a metal oxide of a noble metal, and a solvent or dispersant, with addition of one or more acids to the coating solution or dispersion, where the molar ratio of the total of the amounts of acid (in mol) present in the coating solution or dispersion to the sum of the amounts of the metals from the metal-containing components present in the coating solution or dispersion is at least 2:1; applying the coating solution or dispersion to the support; substantially freeing the layer applied of solvent or dispersant by drying; and subjecting the dried layer obtained to a thermal treatment to form the catalyst coating.

Description

FIELD OF THE INVENTION[0001]This application claims priority to the DE application 102013202143.7 filed Feb. 8, 2013.[0002]The invention relates to an improved catalyst coating with electrocatalytically active components based on ruthenium oxide and titanium oxide, especially for use in chloralkali or hydrochloric acid electrolysis for production of chlorine. The invention further relates to a production process for the catalyst coating and to a novel electrode.[0003]The present invention specifically describes a process for wet-chemical deposition of mixed oxide layers composed of ruthenium oxide and titanium oxide on a metallic support and the use thereof as electrochemical catalysts in chlorine production by electrolysis.[0004]The invention proceeds from electrodes and electrode coatings known per se, which are typically coated onto an electrically conductive support and comprise catalytically active components including, in particular, electrocatalytically active components base...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): C25B11/04C25B1/26
CPCC25B1/26C25B11/0484C25B1/34H01M4/0404H01M4/0471H01M4/8828H01M4/9016H01M4/9041H01M4/92Y02E60/50Y02E60/10C25B11/075C25B11/081C25B11/093C25B11/091
Inventor KINTRUP, JURGENBULAN, ANDREASHAMMARBERG, ELINSEPEUR, STEFANFRENZER, GERALDGROFRANK
Owner COVESTRO DEUTSCHLAND AG
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