EP1814660A1

EP1814660A1 - Use of titanium dioxide mixtures for producing catalysts

Info

Publication number: EP1814660A1
Application number: EP05815892A
Authority: EP
Inventors: Samuel Neto; Sebastian Storck; Jürgen ZÜHLKE; Frank Rosowski
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2004-11-18
Filing date: 2005-11-16
Publication date: 2007-08-08
Also published as: WO2006053732A1; CN101060927B; KR20070086369A; RU2007122282A; US20080064594A1; JP5174462B2; MX2007005850A; CN101060927A; JP2008520418A; KR101308197B1; TW200626232A; US7851398B2; TWI378823B; BRPI0517850A

Abstract

The invention relates to the use of titanium dioxide mixtures of the anatase form having defined physical properties for producing catalysts, which are particularly suitable for phthalic anhydride syntheses. The invention also relates to catalysts which contain titanium dioxide of the anatase form having defined physical properties.

Description

Use of titanium dioxide mixtures for the preparation of catalysts

description

The present invention relates to the use of titanium dioxide mixtures of the anatase form with defined physical properties for the preparation of catalysts which are particularly suitable for phthalic anhydride synthesis. Furthermore, the invention relates to catalysts which contain titanium dioxide mixtures of the anatase form with defined physical properties.

Catalysts for the production of phthalic anhydride, which consist of vanadium pentoxide and titanium dioxide, have long been known. Titanium dioxide in the anatase modification is the main constituent of the active composition of the phthalic anhydride catalysts and serves to support the catalytically active and selective vanadium pentoxide components.

DE-A 2 106 796 describes the preparation of supported catalysts for the oxidation of o-xylene to phthalic anhydride, wherein the titanium dioxide has a BET surface area of 15 to 100 m ² / g, preferably 25 to 50 m ² / g. Particularly suitable is a mixture of anatase of the BET surface area of 7 to 11 m ² / g and titanium dioxide hydrate of BET surface area> 100 m ² / g, wherein the components alone would not be suitable.

EP-A 522 871 describes a relationship between the BET surface area of the titanium dioxide and the catalyst activity. According to this document, the catalyst activity is when titanium dioxide having BET surface areas of below

10 m ² / g low. When using titanium dioxide with a BET surface area greater than 60 m ² / g, the life of the catalyst is reduced and the Phthalsäureanhydrid- yield drops sharply. BET surface areas are preferably from 15 to 40 m ² / g.

In order to improve the phthalic anhydride yield and the starting behavior of the catalysts, it has been the case in recent years to use activity-structured catalysts. The individual catalyst layers are structured so that in general the activity of the individual layers increases from the reactor inlet to the reactor outlet.

For example, EP-A 985 648 describes the preparation of phthalic anhydride by catalytic gas phase oxidation of o-xylene and / or naphthalene with a catalyst system which is structured so that the porosity of the catalyst and thus the activity from the reactor inlet to the reactor outlet increases quasi-continuously. The porosity is defined by the free volume between the coated moldings of the bed in the reaction tube. In the examples, the specific surface area of the active components changed by the variation of the specific surface of titanium dioxide, this was between 40 and 140 m ² / g.

According to the prior art summarized in EP-A1 063 222, the increase in activity can take place in very different ways:

(1) by a steady increase in the phosphorus content,

(2) by a steady increase in the active mass content,

(3) by a steady decrease in the alkali content, (4) by a steady decrease in the void space between the individual catalysts

(5) by a steady decrease in the content of inert substances or

(6) by steady increase in temperature

from the upper layer (reactor inlet) to the lower layer (reactor outlet). The BET surface area of the titanium dioxide should be between 10 and 60 m ² / g. In the examples of EP-A1 063 222, the BET surface area is constant at 22 m ² / g.

In multilayer catalyst systems, the decrease in the activity of the first catalyst layer with respect to the life of the catalyst has a negative effect. With aging, sales decline in the range of the first highly selective layer. The main reaction zone migrates deeper and deeper into the catalyst bed over the course of the catalyst life, i. The o-xylene or Naphthalinfeed is increasingly implemented only in the subsequent less selective layers. The result is reduced Phthalsäureanhydridausbeuten and an increased concentration of by-products or unreacted starting materials. In order to avoid the migration of the main reaction zone into the subsequent layers, the salt bath temperature can be raised steadily. As the catalyst life increases, however, this measure also leads to a reduction in the phthalic anhydride yield.

The object was therefore to show catalysts with improved properties, in particular with respect to the yield. Above all, it is intended to show oxidation catalysts, in particular phthalic anhydride catalysts having improved activity, selectivity and yield. The object further consisted of finding oxidation catalysts which, when used in an activity-structured multilayer catalyst system, combine the advantages thereof with those of a high service life and high selectivity in the first catalyst layers.

It has surprisingly been found that titanium dioxide (s) A in anatase modification, which has a BET surface area greater than 15 m ² / g and a hydrogen uptake for the reduction of Ti ⁴⁺ to Ti ³⁺ from 5 to 20 μmol / m ² , in admixture with one or more further titanium dioxide (s) B in anatase modification, which has a BET surface area of less than or equal to 15 m ² / g and a hydrogen uptake for the reduction of Ti ⁴⁺ Ti ³⁺ from 0.6 to 7 μmol / m ² , is particularly suitable for the preparation of catalysts.

Advantageous is the use of titanium dioxide (s) A, which has a BET surface area of 18 to 90 m ² / g, in particular from 18 to 55 m ² / g. Titanium dioxide A preferably has a hydrogen uptake for the reduction of Ti ⁴⁺ to Ti ³⁺ from 5 to 17 μmol / m ² .

Advantageous is the use of titanium dioxide (s) B ₁ which has a BET surface area of 3 to 15 m ² / g. Titanium dioxide B preferably has a hydrogen uptake for the reduction of Ti ⁴⁺ to Ti ³⁺ from 0.6 to 5 μmol / m ² .

The BET surface area of the titanium dioxide mixture of A and B advantageously has a value of from 5 to 50 m ² / g, in particular from 10 to 30 m ² / g.

The mixture is advantageously carried out with a ratio of titanium dioxide (s) A to titanium oxides (B) of from 0.5: 1 to 6: 1, in particular from 1: 1 to 5: 1.

Advantageously, no more than three titanium dioxides A and not more than three titanium dioxides B are mixed together. The titanium dioxide mixture used according to the invention particularly preferably consists of one titanium dioxide each from group A and B.

In particular, the titanium dioxide mixture used according to the invention is suitable for the preparation of catalysts which are used in an activity-structured at least two-phase, preferably at least three-layered catalyst system in the uppermost or the upper, in particular in the upper, catalyst entrance to the reactor entrance.

An activity-structured catalyst system is understood as meaning a system of different catalyst layers, the activity of the catalysts changing from one layer to the next. In general, preference is given to catalyst systems whose activity increases virtually continuously from the reactor inlet to the reactor outlet. However, one or more intermediate or intermediate catalyst layers which have a higher activity than the subsequent layers can be used.

When using the titanium dioxide mixture used according to the invention in a multilayer catalyst system, it is advantageous in the uppermost layer with a ratio of titanium dioxide (e) A to titanium dioxide (s) B of 0.8: 1 to 3: 1, in particular 1 : 1 to 2.5: 1 used. Titanium dioxide mixtures or pure titanium dioxides of the anatase modification can be used in the further layers. When using titanium dioxide mixtures, the ratio of A to B in the next lower layer is advantageously 2: 1 to 5: 1. The titanium dioxide mixture mentioned is particularly suitable for the preparation of oxidation catalysts for the synthesis of aldehydes, carboxylic acids and / or carboxylic acid anhydrides. In these catalytic gas phase oxidations of aromatic or heteroaromatic hydrocarbons such as benzene, o-, m- or p-xylene, naphthalene, toluene, Durol (1, 2,4,5-tetramethylbenzene) or ß-picoline (3-methylpyridine) are depending on Starting material, for example, benzaldehyde, benzoic acid, maleic anhydride, phthalic anhydride, isophthalic acid, terephthalic acid, pyromellitic anhydride or nicotinic acid obtained.

The titanium dioxide mixture mentioned is particularly suitable for the preparation of phthalic anhydride catalysts which are prepared in an activity-structured at least two-layer, preferably at least three-day catalyst system in the uppermost (in a two-layer catalyst system) or in the two uppermost or in the uppermost lysatorschicht used (in a three- or multi-layer catalyst system) wer¬ the. If appropriate, the catalyst top layer according to the invention may contain one or more catalyst layers as a precursor to said titanium dioxide mixture.

Furthermore, it has been found that benzaldehyde, benzoic acid, maleic anhydride, phthalic anhydride, isophthalic acid, terephthalic acid, pyromellitic anhydride or nicotinic acid can advantageously be prepared using the catalyst according to the invention, which is described below. For this purpose, a mixture of a gas comprising molecular oxygen, for example air, and the starting material to be oxidized is generally passed through tubes in which there is a charge of the catalyst according to the invention. Particularly advantageously, the oxidation is carried out using the catalyst according to the invention in an activity-structured catalyst system.

Suitable catalysts are oxidic supported catalysts. For the production of phthalic anhydride by gas phase oxidation of o-xylene or naphthalene or mixtures thereof are usually used spherical, annular or schalen¬ shaped carrier of a silicate, silicon carbide, porcelain, alumina, magnesia, tin dioxide, rutile, aluminum silicate, magnesium silicate ( Steatite), zirconium silicate or cersilicate or mixtures thereof. So-called coated catalysts in which the catalytically active composition has been applied to the carrier in the form of a dish have proven particularly useful. The catalytically active constituent used is preferably vanadium pentoxide. Furthermore, a small number of other oxidic compounds which, as promoters, influence the activity and selectivity of the catalyst, for example by lowering or increasing its activity, can be present in the catalytically active composition in small amounts. Such promoters are, for example, the alkali metal oxides, thallium (I) oxide, aluminum oxide, zirconium oxide, iron oxide, nickel oxide, cobalt baltoxid, manganese oxide, tin oxide, silver oxide, copper oxide, chromium oxide, molybdenum oxide, tungsten oxide, iridium oxide, tantalum oxide, niobium oxide, arsenic oxide, antimony oxide, cerium oxide and phosphorus pentoxide. The alkali metal oxides act, for example, as promoters which reduce the activity and increase the selectivity. Furthermore, organic binders, preferably copolymers, advantageously in the form of an aqueous dispersion, of vinyl acetate / vinyl laurate, vinyl acetate / acrylate, styrene / acrylate, vinyl acetate / maleate, vinyl acetate / ethylene and hydroxyethyl cellulose can be added to the catalytically active composition, with binder amounts of from 3 to 20 % By weight, based on the solids content of the solution of the active ingredient components, were used (EP-A 744 214). Organic binders are preferably used as described in DE-A 198 24 532. Is the catalytically active composition applied to the substrate without organic binders, coating temperatures above 15O ⁰ C is advantageous. In addition to the above binder, the surrounded angege¬ usable coating temperatures depending on ver¬ wendetem binder comprises between 50 and 45O ⁰ C (DE-A 2106796). The applied binders burn out after filling the catalyst and starting up the reactor within a short time. The binder additive has the advantage that the active material adheres well to the carrier, so that transport and filling of the catalyst are facilitated.

The catalyst for the Phthalsäureanhydrisynthese has on porous and / or non-porous support material advantageously 5 to 15 wt .-% based on the total catalyst, active composition, said active composition 3 to 30 wt .-% V ₂ O ₅ , 0 to 4 Wt .-% Sb ₂ O ₃ , 0 to 1, 0 wt .-% P, 0 to 1, 5 wt .-% alkali (calc. As the alkali metal) and the balance a mixture of titanium dioxide (s) A in anatase modification, which has a BET surface area of greater than 15 m ² / g and a hydrogen uptake for the reduction of Ti ⁴⁺ to Ti ³⁺ from 5 to 20 μmol / m ² , and titanium dioxide (e) B in anatase modification, which has a BET surface area of less than or equal to 15 m ² / g and a Wasserstoffauf¬ assumption for the reduction of Ti ⁴⁺ to Ti ³⁺ from 0.6 to 7 mol / m ² .

In a preferred embodiment, in the first, uppermost layer, the catalyst on carrier material has from 5 to 12% by weight, based on the total catalyst, of active composition, this active composition being from 3 to 20% by weight of V ₂ O ₅ , 0 to 4 Wt .-% Sb ₂ O ₃ , 0 to 0.5 wt .-% P, 0.1 to 1, 5 wt .-% alkali (calc. As the alkali metal) and the balance a mixture of titanium dioxide (e) A in Anatase modification which has a BET surface area of greater than 15 m ² / g and a hydrogen uptake for the reduction of Ti ⁴⁺ to Ti ³⁺ from 5 to 20 μmol / m ² , and titanium dioxide (e) B in anatase modification, which has a BET surface area of less than or equal to 15 m ² / g and a hydrogen uptake for the reduction of Ti ⁴⁺ to Ti ³⁺ from 0.6 to 7 μmol / m ² .

In general, multilayer catalyst systems are used in which the less active catalyst is placed in a fixed bed such that the reaction gas first with this catalyst and only then with the more active catalyst in the second layer comes into contact. If appropriate, pre-or intermediate-layer catalyst layers which have a higher activity than the subsequent catalyst layer can be used. Subsequently, the reaction gas comes into contact with the still more active catalyst layers. The differently active catalysts can be thermostated to the same or different temperatures.

Preferably, three- to five-day catalyst systems are used, in particular three- and four-layer catalyst systems. Particular preference is given to catalyst systems whose catalyst activity increases quasi-continuously from layer to layer.

In a preferred embodiment of an at least three-layer catalyst system, the catalysts for the synthesis of phthalic anhydride have the following composition:

for the first, uppermost layer (layer a), located towards the reactor entrance):

7 to 10 wt .-% of active material based on the total catalyst, this

Active material:

6 to 11% by weight vanadium (calculated as V ₂ O ₅ ) 0 to 3% by weight antimony trioxide

0.1 to 1% by weight of an alkali (calculated as alkali metal), in particular cesium oxide, and the remainder to 100% by weight of a mixture of titanium dioxide (s) A in anatase modification which has a BET surface area greater than than 15 m ² / g and a hydrogen uptake for the reduction of Ti ⁴⁺ to Ti ³⁺ from 5 to 20 μmol / m ² , and titanium dioxide (e) B in anatase modification, which has a BET surface area of less than or equal to 15 m ² / g and a hydrogen uptake for the reduction of Ti ⁴⁺ to Ti ³⁺ from 0.6 to 7 μmol / m ²

for the second, middle layer (layer b)): 7 to 12 wt .-% of active material based on the total catalyst, said

Active material:

5 to 13% by weight of vanadium (calculated as V ₂ O ₅ )

0 to 3 wt .-% antimony trioxide

0 to 0.4 wt .-% of an alkali (calculated as the alkali metal), in particular cesium oxide 0 to 0.4 wt .-% phosphorus pentoxide (calculated as P) and the remainder to 100 wt .-% titanium dioxide in anatase, given Where appropriate as in layer a)

for the third, lowest layer (layer c), located towards the reactor outlet): 8 to 12 wt .-% of active material based on the total catalyst, said

Active composition: 5 to 30% by weight of vanadium (calculated as V ₂ O ₅ ) 0 to 3 wt .-% antimony trioxide

0 to 0.3 wt .-% of an alkali (calculated as the alkali metal), in particular cesium oxide 0.05 to 0.4 wt .-% phosphorus pentoxide (calculated as P) and the balance to 100 wt .-% titanium dioxide, in particular in anatase modification, if appropriate as in layer a).

In a preferred embodiment of an at least four-layer catalyst system, the catalysts have the following composition:

- for the first layer (layer a), located towards the reactor entrance):

7 to 10 wt .-% active composition based on the total catalyst, die¬ se active composition:

From 6 to 11% by weight of vanadium (calculated as V ₂ O ₅ ) from 0 to 3% by weight of antimony trioxide contains from 0.1 to 1% by weight of an alkali (calculated as alkali metal), in particular cesium oxide, and the remainder to 100 % By weight of a mixture of titanium dioxide (s) A in anatase modification, which has a BET surface area of greater than 15 m ² / g and a hydrogen absorption for the reduction of Ti ⁴⁺ to Ti ³⁺ from 5 to 20 micromol / m ² has auf¬, and titanium dioxide (s) B in the anatase modification, the m a BET surface area of less than or equal to 15 ² / g and an absorption of hydrogen for the reduction of Ti ⁴⁺ to Ti ³⁺ 0.6 to 7 has μmol / m ²

for the second layer (layer b1)):

7 to 12% by weight of active composition based on the total catalyst, this active composition being:

4 to 15 wt% vanadium (calculated as V ₂ O ₅ ) 0 to 3 wt% antimony trioxide

0.1 to 1% by weight of an alkali (calculated as alkali metal), in particular cesium oxide 0 to 0.4% by weight of phosphorus pentoxide (calculated as P) and the remainder to 100% by weight of titanium dioxide in anatase modification Where appropriate as in layer a)

for the third layer (layer b2)):

5 to 15 wt% vanadium (calculated as V ₂ O ₅ ) 0 to 3 wt% antimony trioxide

0 to 0.4 wt .-% of an alkali (calculated as the alkali metal), in particular cesium oxide 0 to 0.4 wt .-% phosphorus pentoxide (calculated as P) and the remainder to 100 wt .-% titanium dioxide in anatase, given Where appropriate as in layer a) for the fourth layer (layer c, towards the reactor exit)): 8 to 12% by weight of active composition based on the total catalyst, this active compound being:

5 to 30 wt% vanadium (calculated as V ₂ O ₅ ) 0 to 3 wt% antimony trioxide

From 0.05 to 0.4% by weight of phosphorus pentoxide (calculated as P) and the remainder to 100% by weight of titanium dioxide in anatase modification, if appropriate as in layer a).

In general, the catalyst layers a), b1), b2) and / or c) can also be arranged so that they each consist of two or more layers. These interlayers advantageously have intermediate catalyst compositions.

Instead of layers of the different catalysts which are delimited against one another, a quasi-continuous transition of the layers and a quasi-uniform increase in the activity can be effected by forming a zone with a mixing of the following catalysts in the transition from one layer to the next layer performs.

The catalysts are filled in layers to react in the tubes of a Rohrbündelre¬ actuator. About the so-arranged catalyst bed, the reaction gas at salt bath temperatures of generally 300 to 45O ⁰ C, preferably 320 to 42O ⁰ C and more preferably 340 to 400 ⁰ C, passed. However, the different catalyst beds can also be thermostated to different temperatures.

The bed length of the first catalyst layer preferably accounts for more than 20 to 80% of the total catalyst fill level in the reactor. The bed height of the first two, or the first three catalyst layers advantageously makes up more than 60 to 95% of the total Katalysatorfüllhöhe. If appropriate, one or more catalyst layers, which preferably make up less than 20% of the total catalyst charge height, may be disposed upstream of the first catalyst layer mentioned. Typical reactors have a filling height of 250 cm to 350 cm. The Katalysator¬ layers can also be optionally distributed to several reactors.

The reaction gas (starting gas mixture) fed to the catalyst is generally accompanied by mixing a gas containing molecular oxygen, which may also contain suitable reaction moderators, such as nitrogen, and / or diluents, such as steam and / or carbon dioxide, besides oxygen the oxidized o-xylene or naphthalene produced. The reaction gas generally contains 1 to 100 mol%, preferably 2 to 50 mol%, and particularly preferably 10 to 30 mol% of oxygen. In general, the reaction gas is mixed with 5 to 140 g / Nm ³ gas, preferential Example 60 to 120 g / Nm ³ and more preferably 80 to 120 g / Nm ³ o-xylene and / or naphthalene loaded.

If desired, it is also possible to provide a downstream finishing reactor for producing phthalic anhydride, as described, for example, in DE-A 198 07 018 or DE-A 20 05 969. In this case, the catalyst used is preferably an even more active catalyst in comparison to the catalyst of the last layer.

The catalysts of the invention have the advantage of improved performance. This improvement can be observed even at high loadings with o-xylene and / or naphthalene, eg at 100 g / Nm ³ .

Examples

A. Preparation of the catalysts

A.1 Preparation of Inventive Catalyst System 1 (4-Layer Catalyst System)

Upper layer (a) 29.3 g anatase (BET-OF 7 m ² / g, H ₂ uptake: 4.9 μmol / m ² ), 69.8 g anatase (BET-OF 20 m ² / g, H ₂ Uptake: 7.7 μmol / m ² ), 7.8 g of V ₂ O ₅ , 1.9 g of Sb ₂ O ₃ , 0.49 g of Cs ₂ CO ₃ were suspended in 550 ml of deionized water and stirred for 18 hours. To this suspension was added 50 g of organic binder consisting of a copolymer of vinyl acetate and vinyl laurate in the form of a 50% by weight aqueous dispersion. The resulting suspension was then sprayed onto 1200 g of steatite (magnesium silicate) in the form of rings with an outer diameter of 7 mm, a length of 7 mm and a wall thickness of 1.5 mm and dried. The weight of the applied shell was 8% of the total weight of the finished catalyst. The catalytically active composition applied in this manner, after one hour of calcination at 450 ^° C., contained 7.1% by weight of vanadium (calculated as V ₂ O ₅ ), 1.8% by weight of anti-mon (calculated as Sb ₂ O) ₃ ), 0.36 wt% cesium (calculated as Cs). The BET surface area of the TiO ₂ mixture was 15.8 m ² / g.

Upper middle layer (b1) 24.6 g anatase (BET-OF 7 m ² / g, H ₂ uptake: 4.9 μmol / m ² ), 74.5 g anatase (BET-OF 20 m ² / g, H ₂ uptake: 7.7 μmol / m ² ), 7.8 g of V ₂ O ₅ , 2.6 g of Sb ₂ O ₃ , 0.35 g of Cs ₂ CO ₃ were suspended in 550 ml of deionized water and stirred for 18 h , To this suspension was added 50 g of organic binder consisting of a copolymer of vinyl acetate and vinyl laurate in the form of a 50% by weight aqueous dispersion. The resulting suspension was then sprayed onto 1200 g of steatite (magnesium silicate) in the form of rings with an outer diameter of 7 mm, a length of 7 mm and a wall thickness of 1.5 mm and dried. The weight of the applied shell was 8% of the total weight of the finished catalyst. The thus applied catalytically active material, ie the catalyst shell, comprised one hour calcination at 45O ⁰ C 7.1 wt .-% of vanadium (calculated as V ₂ O _5), 2.4 wt .-% antimony (calculated as Sb ₂ O ₃ ), 0.26 wt% cesium (calculated as Cs). The BET surface area of the TiO ₂ mixture was 16.4 m ² / g.

Lower middle layer (b2) 24.8 g anatase (BET-OF 7 m ² / g, H ₂ uptake: 4.9 μmol / m ² ), 74.5 g anatase (BET-OF 20 m ² / g, H ₂ uptake: 7.7 μmol / m ² ), 7.8 g of V ₂ O ₅ , 2.6 g of Sb ₂ O ₃ , 0.13 g of Cs ₂ CO ₃ were suspended in 550 ml of deionized water and stirred for 18 hours , This suspension were added 50 g of organic binder consisting of a copolymer of vinyl acetate and vinyl laurate in the form of a 50 wt .-% aqueous dispersion. The resulting suspension was then sprayed onto 1200 g of steatite (magnesium silicate) in the form of rings with an outer diameter of 7 mm, a length of 7 mm and a wall thickness of 1.5 mm and dried. The weight of the applied shell was 8% of the total weight of the finished catalyst. The catalytically active material applied in this manner, ie the catalyst shell, contained, after one hour of calcination at 450 ° C., 7.1% by weight of vanadium (calculated as V ₂ O ₅ ), 2.4% by weight of antimony (calculated as Sb ₂ O ₃ ), 0.10% by weight of cesium (calculated as Cs). The BET surface area of the TiO ₂ mixture was 16.4 m ² / g.

Lower class (c)

17.2 g anatase (BET-OF 7 m ² / g, H ₂ uptake: 4.9 μmol / m ² ), 69.1 g anatase (BET-OF 27 m ² / g, H ₂ uptake: 16.1 μmol / m ² ), 21.9 g of V ₂ O ₅ , 1.5 g of NH ₄ H ₂ PO ₄ were suspended in 550 ml of deionized water and stirred for 18 h. To this suspension was added 55 g of organic binder consisting of a copolymer of vinyl acetate and vinyl laurate in the form of a 50% by weight aqueous dispersion. The resulting suspension was subsequently sprayed onto 1200 g of steatite (magnesium silicate) in the form of rings with an outer diameter of 7 mm, a length of 7 mm and a wall thickness of 1.5 mm and dried. The weight of the applied shell was 8% of the total weight of the finished catalyst.

The catalytically active material applied in this manner, ie the catalyst shell, contained, after one hour of calcination at 450 ^° C., 20.00% by weight of vanadium (calculated as V ₂ O ₅ ), 0.38% by weight of phosphorus (calculated as P). The BET surface area of the TiO ₂ mixture was 20.9 m ² / g.

A.2 Preparation of the Inventive Catalyst System 2 (3-Layer Catalyst System)

Upper class (a)

34.3 g anatase (BET-OF 7 m ² / g, H ₂ uptake: 4.9 μmol / m ² ), 63.6 g anatase (BET-OF 20 m ² / g, H ₂ uptake: 7.7 μmol / m ² ), 7.74 g of V ₂ O ₅ , 2.58 g of Sb ₂ O ₃ , 0.48 g of Cs ₂ CO _{3 were} suspended in 650 ml of deionized water and stirred for 15 hours. To this suspension was then added 50 g of an aqueous dispersion (50% by weight) of vinyl acetate and vinyl laurate. Subsequently, the suspension was applied to 1200 g of steatite molded article (magnesium silicate) in the form of rings (7 × 7 × 4 mm, OD × L × ID) by spraying. The weight of the applied Aktivmassen¬ shell was 8% of the total weight of the finished catalyst. The catalytically active composition applied in this manner, after calcination at 400 ^° C. for ⁴ hours, contained 7.1% by weight of V ₂ O ₅ , 2.4% by weight of Sb ₂ O ₃ , 0.36% by weight of Cs. The BET surface area was 14.7 m ² / g. Middle class (b)

24.6 g anatase (BET-OF 7 m ² / g, H ₂ uptake: 4.9 μmol / m ² ), 54.9 g anatase (BET-OF 27 m ² / g, H ₂ uptake: 16 , 1 μmol / m ² ), 7.74 g of V ₂ O ₅ , 2.37 g of Sb ₂ O ₃ , 0.10 g of Cs ₂ CO ₃ wer¬ suspended in 650 ml of deionized water and stirred for 15 hours. 55 g of an aqueous dispersion (50% by weight) of vinyl acetate and vinyl laurate were subsequently added to this suspension. Subsequently, the suspension was applied to 1200 g of steatite molded article (magnesium silicate) in the form of rings (7 × 7 × 4 mm, OD × L × ID) by spraying. The weight of the applied Aktivmassen¬ shell was 9% of the total weight of the finished catalyst. The catalytically active composition applied in this manner after calcination at 400 ^° C. for ⁴ hours contained 8.6% by weight of V ₂ O ₅ , 2.6% by weight of Sb ₂ O ₃ , 0.10% by weight of Cs. The BET surface area was 20.8 m ² / g.

Undercoat (c) 24.6 g anatase (BET-OF 7 m ² / g, H ₂ uptake: 4.9 μmol / m ² ), 73.7 g anatase (BET-OF 30 m ² / g, H ₂ Uptake: 2.8 μmol / m ² ), 25.0 g of V ₂ O ₅ , 1.7 g of NH ₄ H ₂ PO ₄ were suspended in 650 ml of deionized water and stirred for 15 hours. To this suspension was then added 62 g of an aqueous dispersion (50% by weight) of vinyl acetate and vinyl laurate. Subsequently, the suspension was applied to 1200 g of steatite molded article (magnesium silicate) in the form of rings (7 × 7 × 4 mm, AD × L × ID) by spraying. The weight of the applied active mass shell was 10% of the total weight of the finished catalyst.

The catalytically active composition applied in this manner after calcination at 400 ^° C. for ⁴ hours contained 20.0% by weight of V ₂ O ₅ , 0.4% by weight of P. The BET surface area was 24.2 m ² / gA ²

A.3 Preparation of Comparative Catalyst System 3 (3-Layer Catalyst System)

Upper class (a)

46.0 g anatase (BET-OF 9 m ² / g, H ₂ uptake: 0.4 μmol / m ² ), 51, 9 g anatase (BET-OF 27 m ² / g, H ₂ uptake: 16 , 1 μmol / m ² ), 7.74 g of V ₂ O ₅ , 2.58 g of Sb ₂ O ₃ , 0.44 g of Cs ₂ CO ₃ wer¬ suspended in 650 ml of deionized water and stirred for 15 hours. To this suspension was then added 50 g of an aqueous dispersion (50% by weight) of vinyl acetate and vinyl laurate. Subsequently, the suspension was applied to 1200 g of steatite molded body (magnesium silicate) in the form of rings (7 × 7 × 4 mm, outside diameter (AD) × length (L) × inside diameter (ID)) by spraying. The weight of the applied active composition shell was 8% of the total weight of the finished catalyst. The catalytically active composition applied in this manner, after calcining at 400 ° C. for 4 hours, contained 7.1% by weight of V ₂ O ₅ , 2.4% by weight of Sb ₂ O ₃ , 0.33% by weight of Cs. The BET surface area was 18.4 m ² / g. Middle class (b)

21.5 g anatase (BET-OF 9 m ² / g, H ₂ uptake: 0.4 μmol / m ² ), 86.1 g anatase (BET-OF 27 m ² / g, H ₂ uptake: 16.1 μmol / m ² ), 14.2 g of V ₂ O ₅ , 1.7 g of NH ₄ H ₂ PO ₄ were suspended in 550 ml of deionized water and stirred for 15 hours. 55 g of an aqueous dispersion (50% by weight) of vinyl acetate and vinyl laurate were subsequently added to this suspension. Subsequently, the suspension was applied to 1200 g of steatite molded article (magnesium silicate) in the form of rings (7 × 7 × 4 mm, AD × L × ID) by spraying. The weight of the applied active mass shell was 9% of the total weight of the finished catalyst.

The catalytically active composition applied in this manner, after calcination at 400 ^° C. for ⁴ hours, contained 11.5% by weight of V ₂ O ₅ , 0.4% by weight of P. The BET surface area was 21. 3 m ² / g ,

Lower class (c)

24.6 g anatase (BET-OF 9 m ² / g, H ₂ uptake: 0.4 μmol / m ² ), 73.7 g anatase (BET-OF 30 m ² / g, H ₂ uptake: 2.8 μmol / m ² ), 25.0 g of V ₂ O ₅ , 1.7 g of NH ₄ H ₂ PO ₄ were suspended in 550 ml of deionized water and stirred for 15 hours. To this suspension was then added 62 g of an aqueous dispersion (50% by weight) of vinyl acetate and vinyl laurate. Subsequently, the suspension was applied to 1200 g of steatite molded article (magnesium silicate) in the form of rings (7 × 7 × 4 mm, AD × L × ID) by spraying. The weight of the applied active mass shell was 9% of the total weight of the finished catalyst. The catalytically active composition applied in this manner, after calcining at 400 ^° C. for ⁴ h, contained 20.0% by weight of V ₂ O ₅ , 0.4% by weight of P. The BET surface area was 19.9 m ² / g ,

A.4 Preparation of Comparative Catalyst System 4 (3-Layer Catalyst System)

Upper class (a)

34.3 g anatase (BET-OF 9 m ² / g, H ₂ uptake: 0.4 μmol / m ² ), 63.6 g anatase (BET-OF 20 m ² / g, H ₂ uptake: 1 , 5 μmol / m ² ), 7.74 g of V ₂ O ₅ , 2.58 g of Sb ₂ O ₃ , 0.48 g of Cs ₂ CO _{3 were} suspended in 650 ml of deionized water and stirred for 15 hours. To this suspension was then added 50 g of an aqueous dispersion (50% by weight) of vinyl acetate and vinyl laurate. Subsequently, the suspension was applied to 1200 g of steatite molded article (magnesium silicate) in the form of rings (7 × 7 × 4 mm, OD × L × ID) by spraying. The weight of the applied Aktivmassen¬ shell was 8% of the total weight of the finished catalyst. The catalytically active composition applied in this manner, after calcination at 400 ^° C. for ⁴ hours, contained 7.1% by weight of V ₂ O ₅ , 2.4% by weight of Sb ₂ O ₃ , 0.36% by weight of Cs. The BET surface area was 16.1 m ² / g. Middle class (b)

34.3 g anatase (BET-OF 9 m ² / g, H ₂ uptake: 0.4 μmol / m ² ), 102.9 g anatase (BET-OF 20 m ² / g, H ₂ uptake: 1 , 5 μmol / m ² ), 11, O g of V ₂ O ₅ , 3.7 g of Sb ₂ O ₃ , 2.3 g of NH ₄ H ₂ PO ₄ and 0.19 g of Cs ₂ CO ₃ were deionized in 650 ml Suspended water and stirred for 15 hours. 52 g of an aqueous dispersion (50% by weight) of vinyl acetate and vinyl laurate were subsequently added to this suspension. Subsequently, the suspension was applied to 1200 g of steatite molded article (magnesium silicate) in the form of rings (7 × 7 × 4 mm, AD × L × ID) by spraying. The weight of the applied active mass shell was 9% of the total weight of the finished catalyst. The catalytically active composition applied in this manner after calcination at 400 ^° C. for ⁴ hours contained 7.1% by weight of V ₂ O ₅ , 2.4% by weight of Sb ₂ O ₃ , 0.10% by weight of Cs, 0.4 wt.% P. The BET surface area was 17.3 m ² / g.

Lower class (c)

28.7 g anatase (BET-OF 9 m ² / g, H ₂ uptake: 0.4 μmol / m ² ), 86.2 g anatase (BET-OF 30 m ² / g, H ₂ uptake: 2.8 μmol / m ² ), 29.2 g of V ₂ O ₅ , 2.0 g of NH ₄ H ₂ PO ₄ were suspended in 650 ml of deionized water and stirred for 15 hours. To this suspension was then added 60 g of an aqueous dispersion (50% by weight) of vinyl acetate and vinyl laurate. Subsequently, the suspension was applied to 1200 g of steatite molded article (magnesium silicate) in the form of rings (7 × 7 × 4 mm, AD × L × ID) by spraying. The weight of the applied active mass shell was 10% of the total weight of the finished catalyst. The catalytically active composition applied in this manner, after calcination at 400 ^° C. for ⁴ hours, contained 20.0% by weight of V ₂ O ₅ , 0.4% by weight of P. The BET surface area was

24.8 m ² / g.

A.5 Preparation of the comparison catalyst system 5 according to WO 2004/103944 (catalyst 2) (4-layer catalyst system)

Upper class (a)

29.27 g anatase (TiO ₂ -I, BET-OF 9 m ² / g, H ₂ uptake: 0.4 μmol / m ² ), 69.80 g anatase

(TiO ₂ -2, BET-OF 20 m ² / g, H ₂ uptake: 1, 5 .mu.mol / m ² ), 7.83 g of vanadium pentoxide, 2.61 g of antimony oxide, 0.49 g of cesium carbonate were in 650 ml suspended deionized water and stirred for 18 hours to achieve a homogeneous distribution. 50 g of organic binder consisting of a copolymer of vinyl acetate and vinyl laurate in the form of a 50% strength by weight aqueous dispersion were added to this suspension. The suspension obtained was then sprayed onto 1200 g of steatite (magnesium silicate) in the form of rings (7 × 7 × 4 mm, (AD) × (L) × (ID)) and dried. The weight of the applied shell was 8% of the total weight of the finished catalyst. The catalytically active mass applied in this way, ie the catalyst shell, after one hour of calcination to 450 ⁰ C contained 7.12 wt .-% vanadium (calculated as V ₂ O ₅ ), 2.37 wt .-% antimony (calculated as Sb ₂ O ₃ ), 0.36 wt Cesium (calculated as Cs), 27.20% by weight of titanium dioxide (TiO ₂ -I) and 63.46% by weight of titanium dioxide (TiO ₂ -2).

Middle class (b1)

24.61 g anatase (TiO ₂ -I, BET-OF 9 m ² / g, H ₂ uptake: 0.4 μmol / m ² ), 74.46 g anatase (TiO ₂ -2, BET-OF 20 m ² / g, H ₂ uptake: 1.5 μmol / m ² ), 7.82 g of vanadium pentoxide, 2.60 g of antimony oxide, 0.35 g of cesium carbonate were suspended in 650 ml of deionized water and stirred for 18 hours to give to achieve a homogeneous distribution. 50 g of organic binder consisting of a copolymer of vinyl acetate and vinyl laurate in the form of a 50% strength by weight aqueous dispersion were added to this suspension. The suspension obtained was then sprayed onto 1200 g of steatite (magnesium silicate) in the form of rings (7 × 7 × 4 mm, (AD) × (L) × (ID)) and dried. The weight of the applied shell was 8% of the total weight of the finished catalyst. The catalytically active material applied in this manner, ie the catalyst shell, contained, after one hour of calcination at 450 ^° C., 7.12% by weight of vanadium (calculated as V ₂ O ₅ ), 2.37% by weight of antimony (calculated as Sb ₂ O ₃ ), 0.26 wt.% Cesium (calculated as Cs), 22.60 wt.% Titanium dioxide (TiO ₂ -I) and 67.79 wt.% Titanium dioxide (TiO ₂ -2).

Middle class (b2)

24.82 g anatase (TiO ₂ -I, BET-OF 9 m ² / g, H ₂ uptake: 0.4 μmol / m ² ), 74.46 g anatase

(TiO ₂ -2, BET-OF 20 m ² / g, H ₂ uptake: 1.5 μmol / m ² ), 7.82 g vanadium pentoxide, 2.60 g antimony oxide, 0.135 g cesium carbonate were dissolved in 650 ml deionized water Sus¬ suspended and stirred for 18 hours to achieve a homogeneous distribution. 50 g of organic binder consisting of a copolymer of vinyl acetate and vinyl laurate in the form of a 50% strength by weight aqueous dispersion were added to this suspension. The suspension obtained was then sprayed onto 1200 g of steatite (magnesium silicate) in the form of rings (7 × 7 × 4 mm, (AD) × (L) × (ID)) and dried. The weight of the applied shell was 8% of the total weight of the finished catalyst. The catalytically active material applied in this manner, ie the catalyst shell, contained, after one hour of calcination at 450 ^° C., 7.12% by weight of vanadium (calculated as V ₂ O ₅ ), 2.37% by weight of antimony (calculated as Sb ₂ O ₃ ), 0.10% by weight of cesium (calculated as Cs), 22.60% by weight of titanium dioxide (TiO ₂ -I) and 67.79% by weight of titanium dioxide (TiO ₂ -2).

Lower class (c)

17.23 g anatase (TiO ₂ -I, BET-OF 9 m ² / g, H ₂ uptake: 0.4 μmol / m ² ), 69.09 g anatase (TiO ₂ -3, BET-OF 27 m ² / g, H ₂ uptake: 2.8 μmol / m ² ), 21, 97 g of vanadium pentoxide, 1, 55 g of ammonium dihydrogen phosphate were suspended in 650 ml of deionized water and stirred for 18 hours in order to achieve a homogeneous distribution. This Suspension, 50 g of organic binder, consisting of a copolymer of vinyl acetate and vinyl laurate in the form of a 50 wt .-% aqueous dispersion zuge¬ give. The suspension obtained was then sprayed onto 1200 g of steatite (magnesium silicate) in the form of rings (7 × 7 × 4 mm, (AD) × (L) × (ID)) and dried. The weight of the applied shell was 8% of the total weight of the finished catalyst. The catalytically active material applied in this manner, ie the catalyst shell, contained, after one hour of calcination at 450 ^° C., 20.0% by weight of vanadium (calculated as V ₂ O ₅ ), 0.38% by weight of phosphorus (calculated as P), 15.73% by weight of titanium dioxide (TiO ₂ -I) and 62.90% by weight of titanium dioxide (TiO ₂ -3).

B Measurement of hydrogen consumption in the reduction of Ti ⁴⁺ to Ti ³⁺

200 mg of the TiO ₂ in the anatase modification were positioned as a powdery bed in the reactor. First, a pretreatment was carried out to remove adsorbed water. For this purpose, the sample was heated in helium at 20 K / min to 673 K and left for one hour at this temperature. After cooling to below 232 K and purging in helium, the experiment was carried out. The sample was heated with a ramp of 15 K / min to a final temperature of 1373 K in H ₂ / He stream (10% H ₂ in He, flow: 30 Nml / min). The hydrogen consumption was determined by gas chromatography (thermal conductivity detector) and then normalized to the amount / surface area of the sample.

C Oxidation of o-xylene to phthalic anhydride

C.1 3-layer catalyst

From bottom to top, 0.70 m each of the catalyst of the lower layer (c),

0.60 m of the catalyst of the middle layer (b) and 1.50 m of the catalyst of the upper layer (a) are introduced into a 3.85 m long iron tube with a clear width of 25 mm. The iron tube was surrounded by a salt melt for temperature control, a 2 mm thermal sleeve with built-in tension element was used for the catalyst temperature measurement. 4 Nm ^{3 of} air with loadings of 98.5% by weight of o-xylene from 0 to 100 g / Nm ³ were passed through the tube hourly from top to bottom. At 60-100 g of o-xylene / Nm ^3, the results summarized in Table 2 were obtained ("PSA yield" means the PSA obtained in percent by weight, based on 100% strength o-xylene).

C.2 4-Layer Catalyst From bottom to top, 0.70 m of the catalyst of the lower layer (c), 0.70 m of the catalyst of the middle layer 2 (b2), 0.50 m of the catalyst of the middle layer 1 (b1 ) and 1, 30 m of the catalyst of the upper layer (a) in a 3.85 m long Iron tube filled with a clear width of 25 mm. Otherwise, the experiment was carried out as indicated in C.1. The test results after activation are summarized in Table 1.

The following abbreviations were used:

HST hot spot temperature

OS upper class

SBT salt bath temperature PHD phthalide

PSA phthalic anhydride

Table 1: Results of the catalytic tests of the 4-layer catalysts

Table 2: Results of the catalytic tests of the 3-layer catalysts

Claims

claims

1. Use of one or more titanium dioxide (s) A in anatase modification, which has a BET surface area greater than 15 m ² / g and a hydrogen uptake for the reduction of Ti ⁴⁺ to Ti ³⁺ from 5 to 20 μmol / m ² in admixture with one or more further titanium dioxide (s) B in anatase modification, which has a BET surface area of less than or equal to 15 m ² / g and a hydrogen uptake for the reduction of Ti ⁴⁺ to Ti ³⁺ from 0.6 to 7 has μmol / m ² , for the preparation of catalysts.

2. Use according to claim 1, wherein A has a BET surface area of 18 to 90 m ² / g.

3. Use according to claim 1, wherein A has a hydrogen uptake for the reduction of Ti ⁴⁺ to Ti ³⁺ from 5 to 17 μmol / m ² .

4. Use according to claim 1, wherein B has a BET surface area of 3 to 15 m ² / g.

5. Use according to claim 1, wherein B has a hydrogen uptake for the reduction of Ti ⁴⁺ to Ti ³⁺ from 0.6 to 5 μmol / m ² .

6. Use according to claim 1, wherein titanium dioxide (s) A and titanium dioxide (s) B are used in a ratio of 0.5: 1 to 6: 1.

7. Use of titanium dioxide mixtures according to claims 1 to 6 for the preparation of oxidation catalysts for the synthesis of aldehydes, carboxylic acids and / or carboxylic acid anhydrides.

8. Use of titanium dioxide mixtures according to claims 1 to 6 for the preparation of production of oxidation catalysts for the synthesis of phthalic anhydride.

9. Use of titanium dioxide mixtures according to claims 1 to 6 for the production of catalysts, which are located in the upper layer of an activity-structured catalyst system.

10. Catalyst for the preparation of phthalic anhydride, the support material having 5 to 15 wt .-% based on the total catalyst, active composition, wherein the active composition 3 to 30 wt .-% V ₂ O ₅ , 0 to 4 wt .-% Sb ₂ O ₃ , 0 to 1, 0 wt .-% P, 0 to 1, 5 wt .-% alkali (calc. As the alkali metal) and the balance Titanium dioxide mixtures according to claims 1 to 6.

11. Catalyst system which has at least two catalyst layers arranged one above the other, wherein a catalyst according to claim 10 is used in the upper layer.

12. Catalyst system according to claim 11, which has at least three layers arranged one above the other, wherein

a) the catalyst of the upper layer on the carrier inlet towards the reactor inlet comprises 7 to 10% by weight, based on the total catalyst, of active compound, the active composition having from 6 to 11% by weight of V ₂ O ₅ , 0 to 3

% By weight of Sb ₂ O ₃ , 0.1 to 1% by weight of alkali (calculated as alkali metal) and the balance of titanium dioxide mixtures according to claims 1 to 6,

b) the next lower catalyst on support material has from 7 to 12% by weight, based on the total catalyst, of the active composition, the active compound comprising from 5 to 13% by weight of V ₂ O ₅ , 0 to 3% by weight. % Sb ₂ O ₃ , 0 to 0.4% by weight P, 0 to 0.4% by weight alkali (calc. As alkali metal) and the remainder titanium dioxide in anatase form, if appropriate as in layer a),

c) the next lower, to the reactor outlet catalyst located on Trä¬ germaterial 8 to 12 wt .-%, based on the total catalyst, Ak¬ tive mass, wherein the active material 5 to 30 wt .-% V ₂ O ₅ , 0 to 3% by weight of Sb ₂ O ₃ , 0.05 to 0.4% by weight of P, 0 to 0.3% by weight of alkali (calculated as the alkali metal) and the remainder being anatase titanium dioxide, if appropriate as in Layer a) contains.

13. Catalyst system according to claim 11, which has at least four layers arranged one above another, wherein

a) the catalyst of the upper layer on the carrier inlet toward the reactor inlet comprises 7 to 10% by weight, based on the total catalyst, of active compound, the active material having from 6 to 11% by weight of V ₂ O ₅ , 0 to 3 wt .-% Sb ₂ O ₃ , 0.1 to 1 wt .-% alkali (calc. As the alkali metal) and the remainder containing titanium dioxide mixtures according to claims 1 to 6,

b1) the next lower catalyst on support material has from 7 to 12% by weight, based on the total catalyst, of the active composition, the active composition comprising 4 to 15% by weight of V ₂ O ₅ , 0 to 3% by weight. % Sb ₂ O ₃ , 0.1 to 1% by weight of alkali (calculated as alkali metal), 0 to 0.4% by weight of P and the remainder being anatase titanium dioxide, if appropriate as in layer a), b2) the next lower catalyst on support material has from 7 to 12% by weight, based on the total catalyst, of the active composition, the active compound comprising 5 to 15% by weight of V ₂ O ₅ , 0 to 3% by weight. % Sb ₂ O ₃ , 0 to 0.4% by weight of alkali (calculated as alkali metal), 0 to 0.4% by weight of P and the remainder being titanium dioxide in anatase form, if appropriate as in layer a),

c) the next lower, to the reactor outlet catalyst located on Trä¬ germaterial 8 to 12 wt .-%, based on the total catalyst, Ak¬ tive mass, wherein the active material 5 to 30 wt .-% V ₂ O ₅ , 0 to 3 wt .-% Sb ₂ O ₃ , 0.05 to 0.4 wt .-% P and the remainder titanium dioxide in Anatas¬ form, optionally as in layer a) contains.

14. A process for the preparation of phthalic anhydride by gas phase oxidation of xylene, naphthalene or mixtures thereof in a tube bundle reactor, characterized in that xylene, naphthalene or mixtures thereof and a molecular oxygen-containing gas via a catalyst according to claim 10 or a catalyst system according to be passed to claims 11 to 13.