WO2010020613A1 - Use of silicon-titanium mixed oxide powder as catalyst - Google Patents

Use of silicon-titanium mixed oxide powder as catalyst Download PDF

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Publication number
WO2010020613A1
WO2010020613A1 PCT/EP2009/060618 EP2009060618W WO2010020613A1 WO 2010020613 A1 WO2010020613 A1 WO 2010020613A1 EP 2009060618 W EP2009060618 W EP 2009060618W WO 2010020613 A1 WO2010020613 A1 WO 2010020613A1
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mixed oxide
silicon
oxide powder
titanium mixed
weight
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PCT/EP2009/060618
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French (fr)
Inventor
Reinhard Vormberg
Christian Schulze-Isfort
Kai Schumacher
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Evonik Degussa Gmbh
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Publication of WO2010020613A1 publication Critical patent/WO2010020613A1/en

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G23/00—Compounds of titanium
    • 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
    • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
    • B01J21/06—Silicon, titanium, zirconium or hafnium; Oxides or hydroxides thereof
    • B01J21/063—Titanium; Oxides or hydroxides thereof
    • B01J35/30—
    • B01J35/39—
    • B01J35/613—
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
    • C09C1/36—Compounds of titanium
    • C09C1/3607—Titanium dioxide
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/12—Surface area
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/12—Surface area
    • C01P2006/13—Surface area thermal stability thereof at high temperatures

Definitions

  • the invention relates to the use of a pyrogenic silicon- titanium mixed oxide powder as catalyst and catalyst support .
  • silicon-titanium mixed oxide powders as catalyst and catalyst support is known.
  • An important criterion is the very substantial retention of the properties of the powder during long-term use at high temperatures.
  • DE-A-4235996 discloses, for example, a pyrogenic silicon dioxide powder which has an Si ⁇ 2 content of 9.5% by weight and displays better thermal stability than a pyrogenic titanium dioxide powder.
  • a disadvantage is the limitation of the proportion of anatase which is important for catalytic reactions.
  • the proportion of the catalytically active anatase phase should not decrease during use at high temperatures.
  • use is made in the prior art of, for example, silicon-titanium mixed oxides obtained by precipitation (EP-A-1533027, EP-A-1719737) .
  • a disadvantage of the abovementioned disclosures is the fact that the photocatalytic activity of the silicon- titanium mixed oxide powder is significantly lower than that of AEROXIDE TiO 2 P25, Evonik Degussa, a pyrogenic titanium dioxide powder which is frequently used as standard for establishing the photocatalytic activity. It was therefore an object of the present invention to provide a silicon-titanium mixed oxide powder which has a high heat resistance in respect of the BET surface area and of the anatase content and a high, stable photocatalytic activity.
  • the invention provides for the use of a pyrogenic silicon- titanium mixed oxide powder which is present in the form of aggregated primary particles as catalyst or catalyst support, wherein the silicon-titanium mixed oxide powder has a proportion of Ti ⁇ 2 of from 94 to 99.5% by weight
  • Si ⁇ 2 of from 0.5 to 6% by weight, where the sum of the proportions of Ti ⁇ 2 and Si ⁇ 2, based on the silicon-titanium mixed oxide powder, is at least 99.5% by weight and the proportions of Ti ⁇ 2 and Si ⁇ 2 are distributed over the entire primary particle, a BET surface area of from 30 to 150 m 2 /g, an anatase content of from >80% to 95% based on the sum of rutile and anatase content, with the rutile and anatase regions of a primary particle being grown into one another, and a photon efficiency of at least 1.5%.
  • the term mixed oxide refers to the presence of Si-O-Ti bonds formed by intimate mixing of titanium dioxide and silicon dioxide at an atomic level.
  • the primary particles can also have regions of silicon dioxide alongside titanium dioxide. A few individual primary particles may sometimes also be present completely as titanium dioxide or silicon dioxide .
  • primary particles are smallest particles which cannot be divided further without breaking chemical bonds. These primary particles can grow together to form aggregates. Aggregates are characterized in that their surface area is smaller than the sum of the surface areas of the primary particles of which they are composed. The primary particles of the mixed oxide powder do not have an internal surface area.
  • Counting on transmission electron micrographs (TEM) in combination with EDX (Energy Dispersive X-ray Analysis) has shown that primary particles having Si-O-Ti bonds are present in a proportion of at least 80%, based on the total amount of the titanium mixed oxide. In general, the proportion is greater than 90%, in particular greater than 95%.
  • pyrogenic means that the silicon-titanium mixed oxide powders are obtained by means of flame hydrolysis and/or flame oxidation.
  • the particles are characterized in that they have virtually no internal surface area.
  • the pore volumes important for catalytic reactions are formed by the volume present between the aggregates.
  • the sum of the proportions of silicon dioxide and titanium dioxide in the mixed oxide powder used is, based on the total amount of the mixed oxide powder, at least 99.5% by weight. In addition, it can have traces of impurities from the starting materials and also impurities caused by the process. However, these impurities can be present in a maximum amount of 0.5% by weight, generally not more than 0.3% by weight.
  • the pyrogenic silicon-titanium mixed oxide powder used has a proportion of Ti ⁇ 2 of from 95 to 98% by weight and of Si ⁇ 2 of from 3 to 5% by weight.
  • the BET surface area of the powder used is determined in accordance with DIN 66131. In a preferred range, it has a BET surface area of from 50 to 100 m 2 /g.
  • the pyrogenic silicon-titanium mixed oxide powder used preferably has an anatase content of from 83% to 90%.
  • the pyrogenic silicon-titanium mixed oxide powder used has a photon efficiency of at least 1.5%, preferably from 1.5% to 2%.
  • the crystalline rutile and anatase in the primary particles of the pyrogenic silicon- titanium mixed oxide powder used can absorb light quanta, as a result of which an electron is raised from the valence band into the conduction band.
  • the energy difference between valence and conduction bands is 3.05 eV corresponding to an absorption at 415 nm
  • anatase the energy difference is 3.20 eV corresponding to an absorption at 385 nm.
  • the presence of rutile and anatase phases is important for a high photon efficiency.
  • the use of the pyrogenic silicon-titanium mixed oxide powder as catalyst or catalyst support has the following advantages : a) The BET surface area of the silicon-titanium mixed oxide powders decreases only slightly during heat treatment (800 0 C, 4h) even at a low silicon dioxide content. b) The anatase content remains virtually constant under these conditions. c) The photon efficiency of the silicon-titanium mixed oxide powders is high.
  • Pyrogenic silicon-titanium mixed oxide powders having the properties shown in Table 1 are prepared by means of known methods.
  • Example 7 shows a pyrogenic titanium dioxide as comparison. The powders are heat treated at 800 0 C for a period of 4 hours.
  • Ti ⁇ 2 and Si ⁇ 2 are determined by means of X-ray fluorescence analysis.
  • the BET surface area is determined in accordance with DIN 66131.
  • the proportion of the anatase phase is determined by X-ray diffraction.
  • the photon efficiency of the silicon-titanium mixed oxide powders is determined by means of fatty acid degradation.
  • methyl stearate dissolved in n-hexane is used. This is applied as a thin fat film to a layer of a silicon-titanium mixed oxide powder applied to a glass substrate.
  • a dispersion of in each case 120 mg of one of the powders 1 to 4 in 2 ml of isopropanol is prepared and applied to a glass area of 4 x 9 cm. The layers are subsequently heated at 100 0 C for 60 minutes in a muffle furnace.
  • a defined amount of a methyl stearate solution (5 mmol/1) in n-hexane is applied to the layers and is firstly radiated with 1.0 mW/cm 2 of UV-A light for 15 minutes.
  • about 500 ⁇ L of a methyl stearate solution (5 mmol/1) in n-hexane are in each case applied to the mixed oxide layers so that a concentration of about 0.5 mmol/1 based on the amount washed off (5 ml of n-hexane) is obtained.
  • the methyl stearate remaining on the mixed oxide layers is washed off using 5 ml of n-hexane and is determined quantitatively by means of gas chromatography.
  • the determination of the photon efficiency has an error of not more than 10%.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Environmental & Geological Engineering (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Geology (AREA)
  • Inorganic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Catalysts (AREA)

Abstract

Use of a pyrogenic silicon-titanium mixed oxide powder which is present in the form of aggregated primary particles as catalyst or catalyst support, characterized in that the silicon-titanium mixed oxide powder has a proportion of TiO2 of from 94 to 99.5% by weight SiO2 of from 0.5 to 6% by weight, where the sum of the proportions of TiO2 and SiO2, based on the silicon-titanium mixed oxide powder, is at least 99.5% by weight and the proportions of TiO2 and SiO2 are distributed over the entire primary particle, a BET surface area of from 30 to 150 m2/g, an anatase content of from >80% to 95% based on the sum of rutile and anatase content, with the rutile and anatase regions of a primary particle being grown into one another, and a photon efficiency of at least 1.5%.

Description

USE OF SILICON-TITANIUM MIXED OXIDE POWDERAS CATALYST
The invention relates to the use of a pyrogenic silicon- titanium mixed oxide powder as catalyst and catalyst support .
The use of silicon-titanium mixed oxide powders as catalyst and catalyst support is known. An important criterion is the very substantial retention of the properties of the powder during long-term use at high temperatures.
The retention of the BET surface area is of particular importance. DE-A-4235996 discloses, for example, a pyrogenic silicon dioxide powder which has an Siθ2 content of 9.5% by weight and displays better thermal stability than a pyrogenic titanium dioxide powder. A disadvantage is the limitation of the proportion of anatase which is important for catalytic reactions.
Furthermore, the proportion of the catalytically active anatase phase should not decrease during use at high temperatures. To ensure this, use is made in the prior art of, for example, silicon-titanium mixed oxides obtained by precipitation (EP-A-1533027, EP-A-1719737) .
A disadvantage of the abovementioned disclosures is the fact that the photocatalytic activity of the silicon- titanium mixed oxide powder is significantly lower than that of AEROXIDE TiO2 P25, Evonik Degussa, a pyrogenic titanium dioxide powder which is frequently used as standard for establishing the photocatalytic activity. It was therefore an object of the present invention to provide a silicon-titanium mixed oxide powder which has a high heat resistance in respect of the BET surface area and of the anatase content and a high, stable photocatalytic activity.
The invention provides for the use of a pyrogenic silicon- titanium mixed oxide powder which is present in the form of aggregated primary particles as catalyst or catalyst support, wherein the silicon-titanium mixed oxide powder has a proportion of Tiθ2 of from 94 to 99.5% by weight
Siθ2 of from 0.5 to 6% by weight, where the sum of the proportions of Tiθ2 and Siθ2, based on the silicon-titanium mixed oxide powder, is at least 99.5% by weight and the proportions of Tiθ2 and Siθ2 are distributed over the entire primary particle, a BET surface area of from 30 to 150 m2/g, an anatase content of from >80% to 95% based on the sum of rutile and anatase content, with the rutile and anatase regions of a primary particle being grown into one another, and a photon efficiency of at least 1.5%.
For the purposes of the present invention, the term mixed oxide refers to the presence of Si-O-Ti bonds formed by intimate mixing of titanium dioxide and silicon dioxide at an atomic level. In addition, the primary particles can also have regions of silicon dioxide alongside titanium dioxide. A few individual primary particles may sometimes also be present completely as titanium dioxide or silicon dioxide . For the purposes of the present invention, primary particles are smallest particles which cannot be divided further without breaking chemical bonds. These primary particles can grow together to form aggregates. Aggregates are characterized in that their surface area is smaller than the sum of the surface areas of the primary particles of which they are composed. The primary particles of the mixed oxide powder do not have an internal surface area. Counting on transmission electron micrographs (TEM) in combination with EDX (Energy Dispersive X-ray Analysis) has shown that primary particles having Si-O-Ti bonds are present in a proportion of at least 80%, based on the total amount of the titanium mixed oxide. In general, the proportion is greater than 90%, in particular greater than 95%.
For the purposes of the present invention, "pyrogenic" means that the silicon-titanium mixed oxide powders are obtained by means of flame hydrolysis and/or flame oxidation. The particles are characterized in that they have virtually no internal surface area. The pore volumes important for catalytic reactions are formed by the volume present between the aggregates.
The sum of the proportions of silicon dioxide and titanium dioxide in the mixed oxide powder used is, based on the total amount of the mixed oxide powder, at least 99.5% by weight. In addition, it can have traces of impurities from the starting materials and also impurities caused by the process. However, these impurities can be present in a maximum amount of 0.5% by weight, generally not more than 0.3% by weight. In a preferred embodiment, the pyrogenic silicon-titanium mixed oxide powder used has a proportion of Tiθ2 of from 95 to 98% by weight and of Siθ2 of from 3 to 5% by weight.
The BET surface area of the powder used is determined in accordance with DIN 66131. In a preferred range, it has a BET surface area of from 50 to 100 m2/g.
The pyrogenic silicon-titanium mixed oxide powder used preferably has an anatase content of from 83% to 90%.
Furthermore, the pyrogenic silicon-titanium mixed oxide powder used has a photon efficiency of at least 1.5%, preferably from 1.5% to 2%. The crystalline rutile and anatase in the primary particles of the pyrogenic silicon- titanium mixed oxide powder used can absorb light quanta, as a result of which an electron is raised from the valence band into the conduction band. In the case of rutile, the energy difference between valence and conduction bands is 3.05 eV corresponding to an absorption at 415 nm, while in the case of anatase the energy difference is 3.20 eV corresponding to an absorption at 385 nm. The presence of rutile and anatase phases is important for a high photon efficiency.
The use of the pyrogenic silicon-titanium mixed oxide powder as catalyst or catalyst support has the following advantages : a) The BET surface area of the silicon-titanium mixed oxide powders decreases only slightly during heat treatment (8000C, 4h) even at a low silicon dioxide content. b) The anatase content remains virtually constant under these conditions. c) The photon efficiency of the silicon-titanium mixed oxide powders is high.
Examples
Pyrogenic silicon-titanium mixed oxide powders having the properties shown in Table 1 are prepared by means of known methods. Example 7 shows a pyrogenic titanium dioxide as comparison. The powders are heat treated at 8000C for a period of 4 hours.
Figure imgf000006_0001
1) Heat treatment at 800 C, 4 hours; 2) PhEff = photon efficiency; 3) comparative example
The contents of Tiθ2 and Siθ2 are determined by means of X-ray fluorescence analysis. The BET surface area is determined in accordance with DIN 66131. The proportion of the anatase phase is determined by X-ray diffraction.
The photon efficiency of the silicon-titanium mixed oxide powders is determined by means of fatty acid degradation. For this purpose, methyl stearate dissolved in n-hexane is used. This is applied as a thin fat film to a layer of a silicon-titanium mixed oxide powder applied to a glass substrate. For this purpose, a dispersion of in each case 120 mg of one of the powders 1 to 4 in 2 ml of isopropanol is prepared and applied to a glass area of 4 x 9 cm. The layers are subsequently heated at 1000C for 60 minutes in a muffle furnace. A defined amount of a methyl stearate solution (5 mmol/1) in n-hexane is applied to the layers and is firstly radiated with 1.0 mW/cm2 of UV-A light for 15 minutes. For the determination, about 500 μL of a methyl stearate solution (5 mmol/1) in n-hexane are in each case applied to the mixed oxide layers so that a concentration of about 0.5 mmol/1 based on the amount washed off (5 ml of n-hexane) is obtained. After the end of the radiation, the methyl stearate remaining on the mixed oxide layers is washed off using 5 ml of n-hexane and is determined quantitatively by means of gas chromatography.
Comparison with a previously determined reference value determined by applying the defined amount of methyl stearate and immediate washing off of the layer of methyl stearate by means of n-hexane without prior radiation gives information on the photon efficiency of the layers.
The determination of the photon efficiency has an error of not more than 10%.

Claims

Claims :
1. Use of a pyrogenic silicon-titanium mixed oxide powder which is present in the form of aggregated primary particles as catalyst or catalyst support, characterized in that the silicon-titanium mixed oxide powder has a proportion of Tiθ2 of from 94 to 99.5% by weight
Siθ2 of from 0.5 to 6% by weight, where the sum of the proportions of Tiθ2 and Siθ2, based on the silicon-titanium mixed oxide powder, is at least 99.5% by weight and the proportions of Tiθ2 and Siθ2 are distributed over the entire primary particle, a BET surface area of from 30 to 150 m2/g, - an anatase content of from >80% to 95% based on the sum of rutile and anatase content, with the rutile and anatase regions of a primary particle being grown into one another, and a photon efficiency of at least 1.5%.
2. Use according to Claim 1, characterized in that the pyrogenic silicon-titanium mixed oxide powder used has a proportion of Tiθ2 of from 95 to 98% by weight and of Siθ2 of from 3 to 5% by weight.
3. Use according to Claim 1 or 2, characterized in that the pyrogenic silicon-titanium mixed oxide powder used has a
BET surface area of from 50 to 100 m2/g.
4. Use according to any of Claims 1 to 3, characterized in that the pyrogenic silicon-titanium mixed oxide powder used has an anatase content of from 83% to 90%. Use according to any of Claims 1 to 4, characterized in that the silicon-titanium mixed oxide powder used has a photon efficiency of from 1.7% to 2%.
PCT/EP2009/060618 2008-08-22 2009-08-17 Use of silicon-titanium mixed oxide powder as catalyst WO2010020613A1 (en)

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DE102008041470.0 2008-08-22

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5861132A (en) * 1994-08-31 1999-01-19 University Of Cincinnati Vapor phase flame process for making ceramic particles using a corona discharge electric field
KR20020058180A (en) * 2000-12-29 2002-07-12 조성종 Catalyst for removing dioxin and nitrogen oxides in flue gas and method for treating combustion exhaust gases using the same
EP1752216A1 (en) * 2005-08-09 2007-02-14 Degussa AG Use of a titanium dioxide - mixed oxide as a photocatalyst
EP1752215A1 (en) * 2005-08-09 2007-02-14 Degussa GmbH Photocatalyst

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4235996A1 (en) 1992-10-24 1994-04-28 Degussa Titanium dioxide mixed oxide produced by flame hydrolysis, process for its preparation and use
DE10352816A1 (en) 2003-11-12 2005-06-09 Sachtleben Chemie Gmbh Process for the preparation of a high-temperature stable, TiO 2 -containing catalyst or catalyst support
DE102005021623A1 (en) 2005-05-04 2006-11-09 Sasol Germany Gmbh Process for producing a temperature-stable TiO 2 / SiO 2 mixed oxide and its use as a catalyst support

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5861132A (en) * 1994-08-31 1999-01-19 University Of Cincinnati Vapor phase flame process for making ceramic particles using a corona discharge electric field
KR20020058180A (en) * 2000-12-29 2002-07-12 조성종 Catalyst for removing dioxin and nitrogen oxides in flue gas and method for treating combustion exhaust gases using the same
EP1752216A1 (en) * 2005-08-09 2007-02-14 Degussa AG Use of a titanium dioxide - mixed oxide as a photocatalyst
EP1752215A1 (en) * 2005-08-09 2007-02-14 Degussa GmbH Photocatalyst

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