DE102008044890A1 - Catalyst for the catalytic gas-phase oxidation of aromatic hydrocarbons to aldehydes, carboxylic acids and / or carboxylic anhydrides, in particular to phthalic anhydride, and to processes for the preparation of such a catalyst - Google Patents

Abstract

The invention relates to a catalyst for the catalytic gas-phase oxidation of aromatic hydrocarbons to aldehydes, carboxylic acids and / or carboxylic anhydrides, in particular to phthalic anhydride, wherein the active composition vanadium oxide, preferably vanadium pentoxide, titanium dioxide, preferably in the anatase modification, and at least one Mischelementoxid of the silver defined elements, preferably vanadium and / or molybdenum and / or tungsten and / or niobium and / or antimony, and / or a mixed element oxide of vanadium with defined elements, preferably bismuth and / or molybdenum and / or tungsten and / or antimony and / or Niobium, and wherein in the preparation of the catalyst, in particular in the preparation of a catalyst suspension or a powder mixture required for the coating of a carrier, at least one Mischelementoxid of silver and / or vanadium and / or at least one precursor compound, in particular at least one mehrkerni ge precursor compound, at least one Mischelementoxides of silver and / or vanadium is used as a source of raw material.

Description

The catalytic gas phase oxidation of aromatic hydrocarbons such as benzene, xylene, naphthalene, toluene or durene in fixed bed reactors, preferably tube bundle reactors, has long been known and described many times in the literature. Become this way for example, benzoic acid, maleic anhydride, Phthalic anhydride, isophthalic acid, terephthalic acid and pyromellitic anhydride.

To is generally a mixture of a molecular oxygen containing gas, for example air, and the hydrocarbon to be oxidized, for example, o-xylene or naphthalene, by a variety of passed in a reactor arranged tubes in which a Bed of at least one catalyst is located.

to Temperature control or for the discharge of the exothermic Reaction resulting amount of heat are those with catalyst filled pipes from a heat transfer medium, for example, a molten salt, surrounded.

In spite of Such a temperature control may be in the catalyst bed for the formation of local temperature maxima ("hot spots") that lead to undesirable effects, such as total oxidation the starting material or the formation of difficult to separate by-products leading to a limited throughput of starting material can.

to Avoiding such hot spots has been done in practice, Catalysts with different activity and chemical Layer by layer in layers one above the other in the Reaction tubes to be arranged, according to the prior art in usually the catalyst in the range of the largest Temperature maximum has the lowest activity and the following in the direction of gas outlet catalyst layers increased Have activity.

in this connection so-called coated catalysts have proven that generally from an inert, non-porous carrier material exist on the at least one thin layer of the catalytic active mass is applied cup-shaped.

For the catalytic properties of the catalysts in question plays the composition of the catalytically active material is a crucial Role.

For the preparation of phthalic anhydride from o-xylene and / or Naphthalene by oxidation in the gas phase with molecular oxygen containing gases on a fixed bed catalyst have been used in the past proposed a variety of catalysts.

To The prior art contains virtually all industrially used Phthalic anhydride catalysts in their catalytic active compound the compounds titanium dioxide in the anatase modification and vanadium pentoxide and other components or promoters in usually small amounts to improve the activity of the Sales, yield, selectivity and Langzeitstabiltät the catalysts in question.

Such Additives are z. Cesium, antimony, phosphorus, boron, Molybdenum, tungsten, tin, bismuth, silver, niobium, iron, potassium, Rubidium, chromium and calcium.

It Thus, there is an effort through a targeted doping with different Substances performance and stability the PSA catalysts continue to increase. This means that in the Over time, more and more complicated catalyst formulations and combinations of different catalysts for solving these problems be developed.

Increasingly are also called "multilayer" catalysts used, due to their different composition the active mass in terms of activity and selectivity differ. In this case, in the catalyst bed several different catalysts arranged one after the other in layers, to perform various tasks depending on the location in the catalyst bed. It is essentially about the requirement, the exothermic Reaction at high throughputs of starting material, at the same time high selectivity and stability of the catalyst, sure to dominate.

EP A 21 325 describes catalysts for the production of phthalic anhydride their active material from 60 to 99% by weight of titanium dioxide, from 1 to 40% by weight of vanadium pentoxide and, based on the total amount of TiO ₂ and V ₂ O _5, up to 2% by weight of phosphorus and up to 1.5% by weight of % Rubidium and / or cesium, wherein the catalytically active material is applied in two layers on the support. The inner layer contains in this case 0 to 2.0 wt .-% phosphorus and no rubidium and / or cesium and the outer layer 0 to 0.20 wt .-% of phosphorus and 0.02 to 1.5 wt .-% rubidium and / or cesium. The catalytically active material of these catalysts can, in addition to the constituents mentioned, further substances, for. B. up to 10 wt .-% of an oxide of the metals molybdenum, tungsten, niobium, tin, silicon, antimony, hafnium. As inert carrier material steatite is used

EP A 286448 describes a process for the preparation of phthalic anhydride, in which two different catalysts are used with similar content of titanium dioxide and vanadium pentoxide. They differ essentially in that the catalyst additionally contains 2 to 5 wt .-% of a cesium compound, in particular cesium sulfate, but no phosphorus, tin, antimony, bismuth, tungsten or molybdenum compounds and the second catalyst additionally 0 , 1 to 3.0 wt .-% of a phosphorus, tin, antimony, bismuth, tungsten or molybdenum compound

US 4,864,036 relates to a catalyst for the production of phthalic anhydride, which is prepared in several steps. Here, in the first step, a compound of a metal of the 6th subgroup, preferably a molybdenum or tungsten compound, is applied to titanium dioxide in the anatase modification and subsequently calcined. Thereafter, in a second step, a vanadium compound is added to the calcined precursor and this precursor is calcined again.

GB 1140264 relates to an oxidation catalyst for aromatic and non-aromatic hydrocarbons to carboxylic acids, which consists of an inert, non-porous support and a 0.02 to 2 mm thick layer of active material, which in turn from 1 to 15% V ₂ O ₅ and 85 to 99 % Titanium dioxide, wherein the vanadium content of the total catalyst is in the range of 0.05 to 3%. It describes a catalyst in which the active material in addition to titanium dioxide and vanadium pentoxide additionally contains 0.1 to 3 wt .-% of at least one metal oxide from the group of silver, iron, cobalt, nickel, chromium, molybdenum or tungsten.

The EP 0447 267 describes a catalyst for preparing phthalic anhydride comprising as catalytically active composition: (A) 1 to 20 wt .-% V ₂ O ₅ and 99 to 80 wt .-% of a titanium dioxide in the anatase modification with a BET surface area of 10 to 60 m ² / g and (B), based on 100 parts by weight of this mixture (A), 0.05 to 1.2 parts by weight of at least one element from the group K, Cs, Rb and Tl as oxide and 0.05 to 2 parts by weight of silver, calculated as silver oxide.

EP 0522 871 B1 relates to a catalyst which, in addition to titanium dioxide and vanadium pentoxide, also contains 0.01 to 1% by weight of niobium as niobium pentoxide, 0.05 to 2% by weight of at least one element selected from potassium, cesium, rubidium or thallium as oxide, 0, 2 to 1.2 wt .-% of phosphorus as P2O5, and 0.55 to 5.5 wt .-% antimony oxide and 0.05 to 2 wt .-% silver as Ag2O, wherein a pentavalent antimony compound as a source of the antimony is used.

CN 1108996 relates to a catalyst with two layers based on titanium dioxide / V2O5 additionally containing at least one rare earth compound and at least one oxide of the elements antimony, phosphorus, zinc and silver, wherein the closer to the gas inlet layer additionally contains at least one alkali metal compound

Silver vanadium oxide compounds with an atomic ratio Ag: V <1 are known as silver bronzes. The use of silver vanadium bronzes as oxidation catalyst is well known in the literature.

DE 198 51 786 A1 describes a multimetal oxide of the general formula Ag _{starting from Mb} V ₂ O _x .cH ₂ O, where a has a value of 0.3 to 1.9, M is a metal selected from the group Li, Na, K, Rb, Cs Tl, Mg, Ca, Sr, Ba, Cu, Zn, Cd, Pb, Cr, Au, Al, Fe, Co, Ni and / or Mo, and b has a value of 0 to 0.5, where from the same or greater than 0.1. The use of the relevant multimetal oxides as precursor compounds for the preparation of precatalysts and catalysts for the gas phase oxidation of aromatic hydrocarbons is described.

In WO 2005/092496 A1 Finally, a catalyst for the preparation of aldehydes, carboxylic acids and / or carboxylic anhydrides is described, whose active material contains a phase A and a phase B in the form of three-dimensionally extended delimited areas, wherein the phase A is a silver Vanadiumo xid bronze and the phase B is a mixed element oxide phase based on titanium dioxide and vanadium pentoxide. The molar ratio of Ag: V in phase A is 0.15 to 0.95.

The described above, known in the art catalysts reach with different composition of the active mass either unsatisfactory selectivities, yields or Activities or have too little life on or but their industrial production is at a tremendous expense or costs associated.

It There is therefore a continuing need for catalysts with further improved selectivity and yield at the same time high raw material throughput and long service life, which industrial produced in an acceptable cost-benefit ratio can be.

Of the The present invention is therefore based on the object, an improved Catalyst for the gas phase oxidation of aromatic Hydrocarbons to aldehydes, carboxylic acids and / or Carboxylic anhydrides, especially to phthalic anhydride to develop with improved raw material throughput Selectivity combined with a long service life results. Next is the technical and economic effort for the large-scale production of the catalyst so low be held as possible.

These The object is achieved with the features of claim 1. Preferred embodiments are subject of the subclaims, their disclosure content expressly included in this description is included.

According to claim 1 is a catalytic gas phase oxidation catalyst from aromatic hydrocarbons to aldehydes, carboxylic acids and / or carboxylic acid anhydrides, especially to phthalic anhydride, in which the active composition is vanadium oxide, preferably vanadium pentoxide, Titanium dioxide, preferably in the anatase modification, and at least a mixed element oxide of silver with defined elements is preferred Vanadium and / or molybdenum and / or tungsten and / or niobium and / or antimony, and / or a mixed element oxide of vanadium with defined elements, preferably bismuth and / or molybdenum and / or tungsten and / or antimony and / or niobium. In the Production of the catalyst, in particular in the production of a Catalyst suspension or one for the coating of a Carrier needed powder mixture is at least a mixed element oxide of silver and / or vanadium and / or at least one precursor compound, in particular at least a polynuclear precursor compound, at least one Mixed element oxides of silver and / or vanadium as a source of raw material used.

It it was surprisingly found that the use of mixed element oxides, preferably of mixed metal oxides, of silver with z. Vanadium, Molybdenum, tungsten, niobium and / or antimony, and / or the use of mixed element oxides, preferably of mixed metal oxides, of vanadium with z. Bismuth, molybdenum, tungsten, niobium and / or antimony, or their precursor compounds as a source of raw material Preparation of the catalyst suspension or in the preparation of a powder mixture used for the coating process and / or as part of the active material of the catalysts in addition the components titanium dioxide and vanadium oxide a significant increase the selectivity.

The The reason for this is not clear, however suggests that the interaction of silver with the other catalytically active ingredients such as the titanium dioxide / vanadium oxide monolayer is much more effective and therefore the actual promoter effect of silver (suppression of total oxidation of organic Raw material to carbon oxides) comes to fruition.

In The technique is the use of silver as part of the active Mass often described. Here were as raw material source of the Silver for the preparation of the catalyst suspension in addition to silver oxide also corresponding salts such as silver nitrate, silver sulfate, silver halides, Silver sulfide, silver phosphate, silver salts of organic acids, Silver hydroxide, ammonium salts of silver and amine complexes of silver used. Most of these sources of raw materials are used when heating the catalyst mononuclear converted into silver oxide in the reactor and thus lie in the active mass as silver oxide before, while z. B. Silver phosphates and silver halides unchanged in the active mass and not in the thermal treatment be converted into silver oxide.

An essential aspect of the catalysts according to the invention is that conventional catalysts containing at least titanium dioxide and vanadium oxide in the active composition, as additional dopants mixing element oxides of silver with vanadium and / or other defined elements and / or Mischele containing at least one Mischelementoxid of silver and / or vanadium and / or a corresponding precursor compound of at least one of these mixing element compounds in the preparation of the catalyst suspension or in the preparation of a powder mixture used for the coating of the carrier ,

The The invention also expressly relates a method for producing the invention just described Catalysts in which a catalyst suspension or a Mixture of different components that produces at least Titanium dioxide in the anatase modification and a vanadium compound and at least one mixed element oxide of silver and / or vanadium with defined elements or a corresponding precursor compound contains at least one of these mixed element oxides as a source of raw material.

All Components are advantageous in aqueous medium with each other mixed and then by a spray process (preferably fluidized bed or drum method) on a ceramic Carrier applied. The mixed element oxide phase of silver and / or vanadium or their mixed element oxide precursor compounds are advantageous here directly with the catalyst suspension the main constituents titanium dioxide and vanadium oxide and others Promoters added and are generally not spatially separate phases to a phase consisting of titanium dioxide and vanadium oxide in front. Thus, all components of the catalyst suspension form one uniform phase, in addition to the components titanium dioxide and vanadium oxide also the relevant mixed element oxides and optionally further Contains components.

It But systems are also conceivable in which successively different Layers of different chemical composition on the inert Carrier be applied and wherein at least one layer at least one mixed element oxide of silver and / or vanadium Contains with defined elements. Here you can the individual coating layers of an inventive Catalyst also from a combination of inventive and non-inventive compositions consist.

As well The relevant elemental oxides can also be used alone or in combination with other compounds in one or more coating layers which are not containing titanium dioxide and / or vanadium oxide containing the active mass.

According to the invention thus catalysts or precursors for the production and production of catalysts for the gas phase partial oxidation of aromatic hydrocarbons containing a molar oxygen Realize gas from an inert, non-porous carrier material and one or more shell-like applied thereto Layer (s) are constructed, wherein at least one of these layers 0.01 to 15% by weight, based on the total weight of these layers, one or more of the above-mentioned mixed element oxides or their precursor compounds.

Furthermore becomes a concrete procedure for the production of Carboxylic acids and or carboxylic anhydrides by the partial oxidation of aromatic hydrocarbons in the gas phase with a molecular oxygen-containing gas at elevated temperature on a catalyst whose active mass cupped on an inert carrier material is applied, claimed, which is characterized in that to obtain a shell catalyst whose catalytically active composition on their total weight, 0.01 to 15% by weight of a mixed element oxide of silver with vanadium and / or a mixed element oxide of silver with other defined elements and / or 0.01 to 10 wt .-% of a Mixed element oxide of vanadium with bismuth and / or a mixed element oxide vanadium with other defined elements and simultaneously Titanium dioxide in the anatase modification and a vanadium compound (preferably V2O5), wherein the mixed element oxide compound (s) or their precursor compound (s) already for the production the catalyst suspension and / or the powder mixture, from which the active material after coating the carrier by thermal Treatment is formed, used or become.

in this connection at least one non-inventive coated catalyst, in its active mass as essential constituents vanadium oxide, in particular vanadium pentoxide, and titanium dioxide, in particular in the anatase modification, but none of the mixed element oxides mentioned below or their precursor compounds the oxidation of aromatic hydrocarbons to carboxylic acids and / or carboxylic acid anhydrides be absent or absent and in a combined bed (that is, in a single or multi-layer bed) Mixture) together with one or more of those described above catalysts of the invention are used.

For this purpose, the gaseous stream is preferably passed over a bed of at least two layers Catalysts, wherein the catalyst located closer to the gas inlet contains a catalyst according to the invention and the bed of the downstream catalyst contains at least one catalyst whose catalytically active material contains vanadium oxide and a titanium dioxide in the anatase modification, but no mixed element oxide of the silver with elements such. As vanadium, molybdenum, tungsten, niobium, antimony and / or no mixed element oxide of vanadium with elements such. Bismuth, molybdenum, tungsten, niobium, antimony.

It However, catalyst beds can also be present be used from at least two layers, all catalyst layers catalysts according to the invention. in this connection can be used according to the invention Catalysts by type and amount of the respective mixed element oxides differ in the active mass,

Preferably, at least a part, particularly preferably all catalyst layers used in the catalyst bed, including the catalysts according to the invention, should have a catalytically active composition comprising from 1 to 40% by weight of vanadium oxide (calculated as V ₂ O ₅ ), from 50 to 99% by weight of titanium dioxide ( calculated as TiO ₂ ), up to 1% by weight of an alkali metal compound (preferably a cesium compound, calculated as alkali metal), up to 1.5% by weight of a phosphorus compound (calculated as P) and up to 10% by weight of one Contains antimony compound (calculated as Sb ₂ O ₃ ).

According to one particularly advantageous embodiment, the inventive Catalysts preferably 0.01 to 15 wt .-% of at least one Mischelementoxids of the silver with at least one element from the group vanadium, Niobium, tantalum, titanium, zirconium, chromium, molybdenum, tungsten, Cerium, lanthanum, aluminum, boron, manganese, iron, cobalt, nickel, copper, Zinc, gold, cadmium, tin, lead, bismuth, antimony, arsenic, hafnium, Rhenium, ruthenium, rhodium and palladium, and / or preferably 0.01 to 10 wt .-% of at least one Mischelementoxids of vanadium with at least one element from the group of bismuth, antimony, niobium, tantalum, Titanium, zirconium, chromium, molybdenum, tungsten, cerium, lanthanum, Aluminum, boron, manganese, iron, cobalt, nickel, copper, zinc, gold, Cadmium, tin, lead, arsenic, hafnium, rhenium, ruthenium, rhodium and palladium.

Of the Content of mixed element oxides of silver with defined elements, especially with z. As vanadium and / or tungsten and / or molybdenum and / or niobium and / or antimony, in the active mass of catalysts lies in a preferred embodiment in an area from 0.01% to 15% by weight, in a further preferred embodiment in a range of 0.01 to 10 wt .-% and in a particularly preferred Embodiment in a range of 0.01 to 5 wt .-%. The content of mixed element oxides of vanadium with defined elements (except silver, see previous information regarding a mixed element oxide of silver with vanadium), in particular with z. As tungsten and / or molybdenum and / or niobium and / or Antimony, in the active mass of catalysts is in a preferred Embodiment in a range of 0.01 to 10% by weight and in a particularly preferred embodiment in one Range of 0.01 to 5 wt .-%.

In In a preferred embodiment, in a first, next to the gas inlet located catalyst layer Inventive catalyst used, wherein It is also the location with the highest hot spot. In the direction of gas outlet is at least one additional catalyst layer connected, which generally has a higher activity as the first catalyst layer and which is generally is a prior art catalyst. The catalyst according to the invention contains in this case at least one mixed element oxide of the silver, preferably silver vanadate, and preferably a mixed element oxide of vanadium, preferably bismuth vanadate.

It has also proved to be advantageous when in a multilayer Catalyst system with at least one of the hot spot catalyst layer in the direction of gas inlet upstream position, at least one of the catalyst layers from the gas inlet up to and including the location with the highest Hot Spot contains a catalyst according to the invention and for subsequent layers conventional, the Prior art catalysts are used and / or catalysts according to the invention with a reduced Content of the claimed mixed element oxides in the active composition be used.

In another particularly preferred embodiment, at least one of the catalyst layers located in front of the highest hotspot layer contains a mixed element oxide of silver, preferably a mixed element oxide of silver with molybdenum and / or tungsten, and more preferably a mixed element oxide of silver with vanadium the layer with the highest hot spot and the layers downstream therefrom do not contain mixed element oxide of the silver. The layer with the highest hot spot advantageously contains a mixed element oxide of the vanadium with bismuth. The gas outlet towards the hot spot Catalyst layer subsequent catalyst layers preferably correspond to the prior art and generally do not contain catalysts of the invention.

In a particularly preferred embodiment of the catalyst, the compounds AgVO ₃ and / or Ag ₂ MoO ₄ and / or Ag ₂ WO ₄ and / or BiVO _{4 are used} in the preparation of the catalyst suspension and / or are contained in the active material of the catalysts.

It is important to choose the content of acting as "promoters" Mischelementoxiden neither too small nor too large. If the content of mixed element oxides of silver is too small, the selectivity-enhancing effect does not fully take effect, whereas if the content of mixed element oxides of silver is too high, an increased activity can be observed, which leads to a reduced selectivity due to increased total oxidation to CO and CO ₂ ,

Farther it is advantageous catalysts of the invention especially in the closer to the gas inlet catalyst layers up to and including the highest level Hot spot to use, otherwise full selectivity-enhancing Effect can not be achieved, since already an essential part of the raw material was implemented.

One Excessive content of mixed element oxides of bismuth also has an effect negative for the selectivity of the catalyst and at the same time There may be an increase in the formation of by-products which a worse color stability of the desired Product cause phthalic anhydride. Too small a share on mixing element oxides of bismuth, however, leads to none significant increase in selectivity.

By the combination of at least two, but especially advantageous of several catalyst sites in one bed, of which at least one catalyst layer is an inventive Contains catalyst, can be a total of one achieve significantly higher yield than when used alone of multilayer catalyst systems with non-inventive Catalysts is the case.

in this connection In many cases, according to the prior art, the catalyst activity takes place from the first catalyst layer used at the gas inlet to the last step, the next to the Gaustritt lying position gradually to. The activity setting can be different by the Professional common methods are done. For example, done an increase in catalyst activity in the Layers from the gas inlet to the gas outlet by a stepwise Reduction of the alkali metal content in the active material, a Increase the average BET surface area the titanium dioxide used or an increase in the Active mass fraction of the total weight of the catalyst. It can also a combination of different activity-setting measures be used.

The catalysts of the invention contain advantageous at least one kind of titanium dioxide in the anatase modification in the active mass, at least one compound of vanadium (preferably V2O5), at least a mixed element oxide of silver and / or vanadium and optionally a compound of antimony, a compound of an alkali element and / or a phosphorus compound.

Of the Total content of titanium dioxide is 50 to 99 wt .-% in the active material of the catalysts of the invention and more preferably 80 to 99% by weight.

It can only use one kind of titanium dioxide in the anatase modification with defined physical properties or a mixture made of several titanium dioxides with different physical Properties for the preparation of the catalyst suspension and / or the active mass of the catalysts can be used.

The average BET surface area of the titanium dioxide of the catalysts according to the invention in the case of one or more titanium dioxide grades is advantageously 10-60 m ² / g and particularly advantageously 12-30 m ² / g, while the BET surface area of the individual grades is in the range from 3 to 300 m ² / g.

The average BET surface area of the titanium dioxide used is calculated from the quantity and BET surface area of the individual used varieties. It is preferred at least one variety Titanium dioxide used, whose average particle size in a range of 0.3 to 0.8 microns.

The content of vanadium oxide in the active composition (calculated as V2O5) is in a preferred range of 1 to 40 wt .-% and in a particularly preferred embodiment in a range of 1 to 20% by weight.

to Preparation of the catalysts of the invention Advantageously, the raw material sources vanadium pentoxide and / or Vanadium oxalate used. However, they are basically Other vanadium compounds such. B. ammonium metavanadate, Polyvanadic acid u. a. or a mixture of different ones Sources.

In usually these precursor compounds or raw material sources Vanadium in the thermal treatment of the catalyst or when heating the catalyst in the reactor in the presence of molecular Oxygen converted into vanadium pentoxide, so that in the active mass the vanadium is essentially pentavalent Oxidation stage is present.

Dependent from the position of the respective invention Catalyst in the catalyst bed have the active masses of these Catalysts in addition to titanium dioxide, vanadium oxide, one or more Mixed element oxides of silver and / or vanadium and in addition one or more elements from the group of alkali metals.

These are generally used as salts (eg, sulfates, carbonates, nitrates, Phosphates) are added to the catalyst suspension and are used in the Heating the catalyst converted to the corresponding oxides or are in the active mass (after the thermal treatment of the catalyst) continues unchanged.

Alkali metal compounds are used and improved for activity control simultaneously the selectivity of the catalysts.

In a preferred embodiment is the alkali metal content in the active mass in a range of 0 to 1.0 wt .-% and especially preferably in a range of 0 to 0.6 wt .-%. Especially advantageous is a soluble for the preparation of the catalyst suspension Cesium compound such as. As cesium sulfate used.

The catalysts according to the invention advantageously contain in particular in the active mass of the hot spot catalyst layer, In addition, an antimony compound as part of the active mass to Improvement of thermal stability. The content of Antimony in the active material is advantageously in a range of 0 to 10 wt .-% (calculated as Sb2O3) and particularly preferably in a range of 0 to 5 wt .-%, depending on the location of the catalyst in question throughout the catalyst bed and depending from the thermal load of the catalyst in question respective location.

When Starting materials for the preparation of the catalyst suspension or one needed for the coating of the carrier Powder mixtures of the catalysts according to the invention different antimony compounds such. B. antimony salts or antimony oxides are used in different oxidation states.

In a preferred embodiment of the invention Catalyst becomes antimony III oxide in the preparation of the catalyst suspension used.

Also can the catalysts of the invention contain a phosphorus compound in the catalytically active material or may be a phosphorus compound as a source of raw material in the production the catalyst suspension or one for the coating of the carrier powder mixture used. In a particularly advantageous embodiment of the invention Catalysts is the phosphorus content of the active material in a range of 0 to 1.5% by weight (calculated as P).

Especially advantageously increases in catalyst systems with multiple layers one or more of the invention and / or one or more catalysts not according to the invention in a bed of phosphorus content from the gas inlet to Gas outlet on. As a source of raw material for the catalysts of the invention is preferably ammonium dihydrogen phosphate.

Of further can in the active compositions of the invention Catalysts in small quantities a variety of other compounds be included as promoters reduce the activity or increase and / or affect the selectivity of the catalyst.

It is described in the literature that for activity control or for mitigation or avoidance tion of so-called "hot spots" (hot spots) in the art has begun to use multi-layer catalysts, which are arranged in layers, in particular with several superimposed catalyst layers, in the catalyst bed, which in the prior art usually the least active catalyst is closest to the gas inlet and the activity increases from layer to layer in the direction of gas leakage.

The Catalysts of the individual layers have different chemical Compositions, in turn, different activities and selectivity.

For the invention it is sufficient if in a multilayer catalyst system at least one layer of a catalyst according to the invention containing at least one of the respective mixed element oxides.

Prefers contains in particular the first location closest to you located to the gas inlet and also the location with the highest Hot spot is a catalyst according to the invention. In particular, it is advantageous if all the layers in the catalyst bed, starting from the gas inlet up to and including the situation with the highest hot spot according to the invention Catalysts included. The content and type of mixed element oxides of z. B. silver can in the various layers concerned vary. It is advantageous, even the other compositions adjust the active mass according to their location in the catalyst bed.

In a preferred embodiment contains in particular the location with the highest local temperature maximum Mixed element oxide of silver and / or a mixed element oxide of bismuth with vanadium.

Especially the use of a combination of the mixed element oxides of AgV03 and BiVO4 have been able to with the highest hot spot themselves in the catalysts of the invention as selectively increasing proved.

It was surprisingly found to be particularly advantageous if at least one of the active masses of the catalyst layers, going upstream towards the gas inlet in front of the Location with the highest hot spot, one opposite the location with the highest hot spot reduced salary Containing antimony in the active mass.

In a further advantageous embodiment of a catalyst with multiple layers in one or more beds, contains at least one catalyst layer which the Hot Spot catalyst layer is upstream, at least one Mischelementoxid of silver with the specified elements, especially advantageous with vanadium and / or molybdenum and / or tungsten.

In a particular embodiment of the invention Catalysts contains at least one of the layers from the gas inlet up to the location with the highest hot spot, a mixed element oxide of the silver, in particular a mixed element oxide of the silver with vanadium and / or molybdenum and / or tungsten, while the location with the highest hot spot, a mixed element oxide prefers of vanadium, in particular a mixed element oxide of vanadium with Bismuth, contains.

In another particularly preferred embodiment all layers from the gas inlet to the location with the highest Hot spot a mixed element oxide of silver and only the location with the highest hot spot an additional mixed element oxide Vanadium with bismuth.

Especially advantageous is the use of polynuclear Mischelementoxiden or their precursor compounds as a source in the preparation the catalyst suspension or one for the coating the carrier material used powder mixture.

moreover may also be mixed element oxides of silver for production the catalyst suspension and / or the active material are used, which is a smaller or larger atomic ratio to silver as it is in the case of AgVO3. Depending on which atomic ratio of the elements in the relevant Mixed element oxide is present, the amount of the mixed element oxide and / or their precursor compounds in the catalyst suspension or the powder mixture used for the coating be adapted to an optimal content of silver in the active To obtain mass of the finished catalyst.

It is advantageous if the described Mischelementoxidphase or their precursor compound is already formed before they the catalyst suspension or for the coating the carrier mixture used is added. However, one or more corresponding precursor compounds can also be used the catalyst suspension or the powder mixture are added, which then in the thermal treatment of the catalyst to the corresponding Mischelementoxiden be converted.

As previously described, not only in the integer molar ratio present mixed element oxides of silver with other elements and / or their precursor compounds as a source of raw material in the preparation of the catalyst suspension be used or in the active mass of the invention Catalysts are present, but also polynuclear or polynuclear mixed element oxides of silver with a large atomic deficit or surplus to silver. Depending on the general formula of the mixed element oxides or their silver component must then be the content of the relevant Mixed element oxide in the catalyst suspension and / or the active Mass be increased or decreased.

The two or more nuclear mixed element oxides of silver are represented by the general formula Ag _x M _y N _z O _n (Formula I) described according to claim 11:
In the mixed metal oxide of the formula I, x more preferably has a value of 0.1 to 5, the value of the variable y is preferably 0 to 0.3.

Particularly preferred are mixed metal oxides of the following general formula: Ag _x N _z O _n wherein
Ag = silver
x = a value from 0.1 to 5
N = an element of the group vanadium, molybdenum, tungsten, niobium, antimony
z = 1
n = a number which is determined by the valence and frequency of the elements other than oxygen in the formula I.

It is possible in principle and of the invention expressly includes that also in the production the catalyst suspension one or more precursor compounds the relevant mixed element oxides and / or their starting compounds be used and the catalysts of the invention with the relevant Mischelementoxiden only in the reactor by calcination at elevated temperature or during the heating-up period of the catalyst are formed in the reactor.

In a preferred embodiment of the catalyst leads in particular the use of mixed element oxides AgVO3, Ag2MoO4, Ag2WO4 and / or mixed element oxides of these elements with other atomic Conditions for improving the catalysts

It has now been found that the addition of mixed element oxides of silver preferably with z. As vanadium, tungsten and molybdenum, for Catalyst suspension instead of "mononuclear" silver compounds a significant improvement in selectivity pulls, compared to catalysts which have no silver in the active Have mass and / or in which silver as oxide (AgO or Ag2O) or as a salt (nitrate, phosphate, sulfate, chloride, ammonium salt, Salt of an organic acid) or as hydroxide or as amine complex of the catalyst suspension is added or in the active mass is contained. It is believed that silver in Form a mixed element oxide or a compound element compound more intensively participate in the catalytic process as in the form of a salt or a mononuclear oxide.

As an example, but not restricting, let's connect at this point AgVO3 as part of the catalysts of the invention mentioned as an additive in the preparation of the catalyst suspension or the active mass is used, wherein the active mass at least nor titanium dioxide in the anatase modification and a vanadium compound contains. Preferably, the inventive Catalyst also at least one compound of an element of first main group. Depending on the location of the invention Catalyst in the catalyst bed contains the inventive Catalyst also an antimony compound, especially Sb2O3 in the active composition and optionally a phosphorus compound

It was surprisingly found to be the case with multilayer catalysts of particular advantage in terms of increasing selectivity is at least one mixed element oxide of silver with vanadium and / or Tungsten and / or molybdenum or their precursor compounds to use in the preparation of the catalyst, wherein the inventive Catalyst advantageous in one or more catalyst layers of Gas entry up to and including the highest level Hot spot is used.

In a particularly preferred embodiment have a or more or all of said catalyst layers from the gas inlet up to and including the highest hot location Spot a mixed element oxide of silver with vanadium and / or tungsten and / or molybdenum from 0.01% by weight to 15% by weight, in particular from 0.01 to 10.0 wt .-% and particularly preferably from 0.01 to 5 Wt .-% in the active mass.

In a particular embodiment of the invention Catalyst is the silver vanadium Mischelementoxiden to compounds with a molar ratio of Ag: V of 1: 1, especially the mixed element oxide AgVO3. This is it not a so-called silver vanadium bronze, in which the atomic Ratio of Ag: V by definition is less than 1: 1.

Further it was found that the use of mixed element oxides of vanadium with bismuth, molybdenum, tungsten, antimony, arsenic, lead, tin, Zinc, copper, nickel, cobalt, iron, manganese, chromium, niobium, zirconium, Titanium, gold, rhenium, lantha, cerium, tantalum, rhenium as a source of raw materials in the catalyst preparation and / or as part of the active Mass causes an improvement in selectivity.

Especially has the use of bismuth vanadate as a source of raw material in the Preparation of the catalyst suspension or as part of the active Mass led to an improvement in selectivity. in this connection it is advantageous if the inventive Catalysts contain BiVO4 as a constituent of the active material in particular in one or more layers from the gas inlet up to and including the location with the highest hot spot.

The catalysts of the invention can besides at least titanium dioxide and vanadium oxide at the same time a mixed element oxide of silver with one or more of said Elements and at least one mixed element oxide of vanadium with a or more of said elements. In a special preferred embodiment are used for the production of Catalyst suspension of the catalysts of the invention Silver vanadate and bismuth vanadate are used and / or lie side by side in the active mass of the catalysts.

ever by location of the catalysts of the invention in the catalyst bed contain the inventive Catalysts additionally at least one alkali metal compound, preferably a cesium compound, an antimony compound, preferably antimony III oxide and optionally a phosphorus compound.

It not only in the integer atomic ratio present mixed element oxides of vanadium with other elements or their precursor compounds as a source of raw material the preparation of the catalyst suspension can be used or in the active composition of the catalysts of the invention but also two or more nuclear mixed element oxides vanadium with a large atomic surplus or excess on vanadium. Depending on the general formula of the mixed element oxides or their Vanadiumanteil must then the content of the respective Mischelementoxid increased in the catalyst suspension and / or the active mass or be humiliated.

The two or more nuclear mixed element oxides of vanadium are described by the following general formula according to claim 12: M _a N _b V _c O _d (formula II)

For the catalysts of the invention are advantageous so-called shell catalysts in which the catalytic active mass cup-shaped in one or more layers to a generally inert under the reaction conditions Carrier material, such as porcelain, magnesium oxide, tin dioxide, Silicon carbide, cerium silicate, magnesium silicate (steatite), zirconium silicate, Alumina, quartz, or mixtures of these supports is applied. In particular, support materials have turned out in the art Steatite or silicon carbide proven.

For the preparation of such coated catalysts is generally an aqueous and / or an or ganic solvent-containing solution or suspension (referred to herein as "catalyst suspension") of the active composition components and / or their precursor compounds on the support material in the fluidized bed process ( DE-A 2106796 ) is applied at elevated temperature until the desired amount of active mass in the total weight of the catalyst is reached. The coating of the inert, non-porous carrier material with the active ingredient components or their precursor compounds as a suspension or powder mixture can likewise be carried out in a heated coating drum at elevated temperatures.

There when spraying the catalyst suspension with the therein contained active composition components and / or their precursor compounds in the coating drum or during coating of the inert carrier material in the fluidized bed, in some cases high losses due to nebulization of the catalyst suspension and / or by partial abrasion of the already coated carrier occurred in the art was transferred to the catalyst suspension organic binders, preferably copolymers, advantageously in the form of a aqueous dispersion of vinyl acetate / vinyl laurate, vinyl acetate / acrylate, Styrene / acrylate, vinyl acetate / maleate and vinyl acetate / ethylene u. a, usually binder amounts of 10-20 Wt .-%, based on the solids content of the catalyst suspension be used. With the addition of one of the mentioned binders the coating temperature advantageously in a range of 50-450 ° C. The binders used decomposed after filling of the catalyst in the reactor usually already during the heating of the reactor to operating temperature or at the latest during commissioning of the catalyst and thereby become completely out of the catalyst away.

The here on the inert carrier material as a thin Shell remaining catalytically active components are considered called active mass. The components of the active mass can partially from those used in the catalyst suspension Components or raw material sources or precursor compounds differ, as these are partly due to the heat treatment the catalyst are chemically converted and mostly in the corresponding metal oxides are transferred.

It was now surprisingly found that the ability to perform the catalysts are not exclusively of the composition and amount of active mass (after heating or tempering) existing catalytically active compounds) of the catalysts depends, but in the catalyst suspension or for the Coating of the carrier used powder mixture used Raw material sources have a significant influence on the selectivity, Activity and lifetime of the catalysts have.

The The invention also relates to a process for the preparation of aldehydes, carboxylic acids and / or carboxylic acid anhydrides, where you have a gaseous stream that is an aromatic Contains hydrocarbon and a molecular oxygen containing gas at an elevated temperature with a catalyst defined above in contact.

The used as a source of raw material for the catalyst suspension Mixed element oxides can be prepared in various ways and the catalyst suspension as an isolated compound or Be buried directly as a reaction mixture. Likewise corresponding precursor compounds of the mixed metal oxides be added to the catalyst suspension. This is it advantageous to polynuclear mixing element compounds or Mischmetalloxidverbindungen, which generally have a different crystal structure than the corresponding present in the active composition thermally treated Mischelementoxide and also may contain water of crystallization.

to Preparation of the catalysts of the invention used mixed element oxides and / or their precursor compounds In many cases, the conversion is also advantageous a solution of a metal compound with a suspension a metal oxide at elevated temperatures in an aqueous medium or non-aqueous solvents. So can z. B. one for the invention Catalysts used silver vanadium oxide advantageous characterized be prepared that silver nitrate in aqueous solution at elevated temperatures with vanadium pentoxide in the corresponding desired atomic ratios is implemented. The resulting reaction mixture with the contained therein Mischmetallverbindung can be added directly to the catalyst suspension or the corresponding Mischmetallverbindung but also before isolated and optionally thermally treated.

In addition to water, polar organic solvents such as polyols, polyethers or amines can also be used as solvents. The reaction of a metal oxide or a plurality of metal oxides (such as vanadium pentoxide and molybdenum trioxide) with a silver compound and optionally another compound (such as a phosphorus compound) may generally be carried out at room temperature or elevated temperature. Preferably, the reaction is carried out at temperatures of 50 to 100 ° C and takes depending on starting materials used and reaction conditions for 20 minutes to 5 days.

The The mixed metal compound thus formed can be prepared from the reaction mixture isolated and optionally stored until further use or directly as a suspension solution of the catalyst suspension, which still contains at least titanium dioxide and a vanadium compound, be added. The product obtained and isolated by the reaction Mischmetallverbindung can also be added to the catalyst suspension before adding subjected to thermal treatment at elevated temperatures become a rearrangement of the crystal structure and a distance effect of crystal water.

in the Case of prior isolation of the mixed metal compound can this by filtering off the suspension and drying the obtained Solid, wherein the drying by various methods can be carried out. The drying becomes advantageous the mixed metal suspension by spray drying or freeze drying carried out.

alternative to the reaction in solution, the mixed metal compounds but also be generated by melting together, z. For example, that different finely mixed metal oxide powders in a solid state reaction reacted at elevated temperatures of 400 to 800 ° C. become.

The Components of the catalyst suspension are generally in the form of oxides and / or in the form of compounds, e.g. For example, salts, used, which on heating in the presence of oxygen convert to oxides. However, metal salts can also be used Phosphates or halides are added to the catalyst suspension, in the active mass of the catalyst even after a thermal Treatment unchanged.

The Preparation of the catalysts of the invention generally takes place via a preliminary stage of the finished Catalyst that can be stored as such. This acts it is an inert ceramic support on which the used in the catalyst suspension raw materials by means of a Spray applied and advantageous using an organic binder are fixed.

The active catalyst is usually formed by thermal treatment of this precursor or already during the heating of the catalyst in the reactor. In this case, the metal compounds used are usually converted into the corresponding metal oxides. For example, vanadium oxalate is decomposed and converted to V ₂ O ₅ . Also, other compounds contained in the catalyst suspension can be converted to their oxidic compounds upon heating of the catalyst. Thus it can be assumed that the ammonium dihydrogen phosphate is converted to P ₂ O ₅ and is present as such in the active composition. In the case that hydrous mixed metal oxides are prepared and used as a raw material source in the preparation of the catalyst suspension, it is generally assumed that they lose the water of crystallization during the thermal treatment of the catalyst and possibly change its crystal structure.

The Conversion of the raw material sources used in the catalyst suspension is preferably carried out at temperatures of 200 to 500 ° C. and more preferably in the range of 300 to 500 ° C.

The Form of the inert carrier material is not relevant crucial for the performance of the invention Catalysts, however, have become common in the art Spheres or rings proved to be advantageous moldings.

The Layer thickness of the active mass or the sum of the layer thicknesses the shells containing the active mass is generally 20-400 microns and varies depending on Location of the catalyst according to the invention in the catalyst bed.

It was further surprisingly found that a spatial Separation of the various components of the catalyst suspension of the mixed metal oxides used is generally not necessary to obtain improved catalysts. All in the catalyst suspension used components are generally associated with the corresponding Mischelementoxiden mixed or mixed and evenly mixed suspension applied to the inert carrier. However, catalysts are also conceivable in which different composite catalyst suspensions successively to the inert ceramic support are applied, wherein at least a layer of a catalyst according to the invention contains and thus an inventive improved catalyst is formed.

In addition, improved catalysts are conceivable in which a catalyst not according to the invention suspension containing at least titanium dioxide, a vanadium compound and advantageously also an alkali metal compound, first isolated and optionally thermally treated and then the resulting powder is generally mixed again with a powder (advantageously in water), which was previously obtained from a catalyst suspension consists of at least titanium dioxide, a vanadium compound and at least one mixed metal oxide or its precursor compound. This new catalyst suspension can be applied as a layer alone to an inert ceramic support or else used in combination with other coating layers according to the invention and / or not according to the invention.

The catalysts of the invention are generally for the partial gas phase oxidation of aromatic hydrocarbons to aldehydes, carboxylic acids and / or carboxylic anhydrides used. These catalysts are particularly suitable for the gas-phase oxidation of o-xylene and / or naphthalene to phthalic anhydride with a molecular oxygen-containing gas.

The catalysts of the invention can as already mentioned, for this purpose in a catalyst bed alone or in combination with others, different active Catalysts, for example, catalysts of the prior art (Vanadium pentoxide / anatase base without Mischmetalloxidkomponente) used become.

in this connection are the different inventive and not inventive Catalysts generally in separate catalyst beds used, which are arranged in at least one catalyst bed. Overall, the use of the invention is advantageous here Catalysts in the closest to the gas inlet Catalyst layers up to the location with the highest hot Spot.

The Use of the catalysts of the invention in the situation with the highest hot spot following Catalyst layers and closer to closer to the gas outlet although the catalyst layers also have a positive effect, but already a much lower positive effect regarding the selectivity as the use of the invention Catalysts to the closer to the gas inlet catalyst layers. The catalysts of the invention and / or their Precursor catalysts according to the invention In the reaction tubes, a reactor in layers are filled. The different layers can in this case from inventive and catalysts of the invention do not exist.

It is also conceivable, in one layer a bed of a Mixture of at least one inventive Catalyst and at least one non-inventive Catalyst to use and this bed alone or in combination with other catalyst layers of the invention and / or catalysts not according to the invention to use.

The Reaction tubes are in this case thermostated from the outside, which generally happens by means of a molten salt, which the pipes are washed around.

At the Heating the reactor with the newly filled with catalyst Reaction tubes and / or in the subsequent thermal Treatment of the catalyst arises from the precursor of the catalyst the actually active catalyst burned out by the organic binder and the respective ones used in the catalyst suspension Raw material sources generally into the corresponding oxidic Convert connections. In addition, depending on the nature of the Mischmetallverbindungen also their chemical composition and / or their crystalline structure change.

about consisting of such a thermally treated catalyst bed from at least one catalyst according to the invention is the reaction gas at temperatures of 250-550 ° C, especially at 330 to 500 ° C and at a Überduck of generally 0.1 to 2.5 bar, preferably 0.3 to 1.5 bar directed, with the space velocity generally 1000 to 5000 h (-1).

The reaction gas supplied to the catalyst is generally produced by mixing a molecular oxygen-containing gas, preferably air, which may contain, besides oxygen, still suitable reaction moderators and or diluents such as steam, nitrogen and / or carbon dioxide, with the aromatic hydrocarbon to be oxidized the molecular oxygen-containing gas generally 1 to 100 vol .-% and particularly preferably 10 to 30 vol .-% oxygen, 0 to 30 vol .-% water vapor, preferably 0 to 20 vol .-% water vapor and 0 to 50% by volume .-%, preferably 0 to 1 vol .-% carbon dioxide, the rest may contain nitrogen. For the formation of the reaction gas, the molecular oxygen-containing gas is generally mixed with 20 to 200 g per Nm ³ and be particularly preferably 60 to 120 g per Nm ^{3 of} the aromatic hydrocarbon to be oxidized.

at a preferred embodiment of the method for partial Oxidation of aromatic hydrocarbons to aldehydes, carboxylic acids and / or carboxylic anhydrides, which are particularly advantageous for the oxidation of o-xylene and / or napthhalin to phthalic anhydride the aromatic hydrocarbon first becomes on a bed of the invention Catalyst only partially reacted to a reaction mixture Starting material, intermediates and final product and this mixture reacted with at least one other catalyst, too may be according to the invention or the state of Technology may be appropriate catalyst.

The However, reaction can also be carried out with more than one reactor be, each reactor being different Reaction temperatures can be thermostated and at least a catalyst bed with at least one catalyst layer contains. It is sufficient for the invention Process here, if at least one of these reactors one layer having a catalyst according to the invention.

For contains the preparation of phthalic anhydride from o-xylene the partially reacted reaction gas after passing one or more Catalyst layers with catalyst according to the invention in addition to the desired product phthalic anhydride also a substantial amount of unreacted o-xylene and Intermediates such as o-tolualdehyde and o-toluic acid and Phthalide.

Subsequently As a rule, the product mixture is transferred without further separation passed at least one other catalyst layer, which in terms of their chemical composition and activity of the erfindungsge MAESSEN catalyst differs the complete implementation of the raw material or the oxidation the Unteroxidationsprodukte to ensure phthalic anhydride.

Farther is a separation of the unreacted o-xylene after it has passed through the catalyst bed with the inventive Catalyst conceivable before the reaction gas one or more is fed to further catalyst beds. However, such a variant is technically only with relatively large Effort feasible.

It is therefore preferred that the reaction mixture without successively Separation of starting materials or intermediates several catalyst layers passes through, wherein at least one of these catalyst layers, prefers the position (s) closer to the gas inlet, a bed of a catalyst according to the invention contains.

in the In general, the catalyst according to the invention together with at least one further or several catalyst layers used, wherein at least one of the catalyst layers from the gas inlet to including the location with the highest hot spot located catalyst layers a catalyst according to the invention which generally contains from 1 to 40% by weight of vanadium pentoxide, calculated as V2O5, 50 to 99% by weight of titanium dioxide, calculated as TiO 2, up to 1% by weight of an alkali metal compound, calculated as Alkali metal, preferably cesium, up to 1.5% by weight of one Phosphorus compound, calculated as P, up to 10% by weight of an antimony compound, calculated as Sb 2 O 3 and up to 15% by weight of at least one mixed element oxide of Silver with at least one of the elements previously described and / or up to 10% by weight of a mixed element oxide of vanadium with at least one of the elements previously described.

The Catalysts used in combination generally be used in layers that are closer to the gas outlet and follow the location with the highest hot spot mostly on non-inventive catalysts based on titanium dioxide / V205, but contain no mixed element oxides of silver and / or vanadium. It can, however, too exclusively catalysts according to the invention be used in all situations. Hereby differ in the Usually the catalysts in type and amount of active mass existing mixed metal oxides.

The in combination with the catalysts of the invention used non-inventive catalysts from the prior art usually have a titanium dioxide content of 60-99% by weight, a vanadium oxide content of 1 to 40 Wt .-%, an alkali metal content up to 1 wt .-%, a phosphorus content of up to 1.5% by weight and an antimony content of up to 10% by weight on.

unaffected The above-described compositions may include the active ones Compositions of the invention and / or not according to the invention Catalysts even small amounts of other oxidic compounds for activity and selectivity control included.

Examples

Preparation of the catalysts

The different components of the catalyst suspension are successively as solutions and / or as a powder in deionized water given and the resulting suspension advantageously at least 12 h stirred. As raw material sources for in the inventive Catalyst-containing components are advantageously titania in anatase modification, V2O5 or vanadyl oxalate, cesium sulfate, Ammonium dihydrogen phosphate, antimony trioxide, bismuth vanadate and silver vanadate, Silver molybdate, silver tungstate and / or other mixed metal oxides of silver and vanadium.

Subsequently becomes an organic binder in the form of an aqueous dispersion a vinyl acetate copolymer to the aqueous catalyst suspension given and the total of about 20 to 25% suspension even more Stirred for 30 minutes.

After that is an appropriate amount of the aqueous suspension, which the active substances and / or their precursor compounds and the organic binder, by spraying on the inert support (7 × 7 × 4 steatite rings mm or 8 × 6 × 5 mm dimension) is applied until a certain amount of the adhesive-containing suspension on the rings is applied, so that after calcination, in the examples indicated active mass results.

Of the Active mass fraction (proportion of catalytically active substances without binder) refers in each case to the proportion of catalytically active material on the total weight of the catalyst including the Carrier in the respective catalyst layer, determined according to Calcination for 4 h at 400 ° C.

Of the indicated content of phosphorus refers to those added in the catalyst suspension preparation Amount of a phosphorus compound. It is known to the person skilled in the art that the actual content of phosphorus in the active mass depending on how strong the TiO2 used with phosphorus compounds contaminated.

oxidation reaction

In a tubular reactor with a reaction tube of iron with an inner Diameter of 25 mm and a length of 3.7 m, which is lapped by a salt bath, the relevant multi-layered Catalyst system filled, wherein in the described Examples in each case the R1 layer closest to the gas inlet is located and the R4 location or the R5 location closest to Gas outlet is.

In the reaction tube was centrally arranged a thermal sleeve of 2 mm with built-in tension element for temperature measurement. 4 Nm ^{3 of} air at a loading of about 30 to 70 g-xylene / Nm ³ air were passed through the reaction tube hourly from top to bottom at a salt bath temperature of 340-380 ° C.

to Determination of the catalytic performance data is from the reaction tube exiting reaction gas through an oil-cooled Condenser passed, in particular, the phthalic anhydride formed largely complete and by-products such as benzoic acid, Particulate maleic anhydride and phthalide only partially. The separated in the condensers raw PSA is using hot oil melted, collected, weighed and then the Content of phthalic anhydride determined by GC analysis.

The raw PSA yield given in the examples is calculated as follows: Crude PSA yield (wt%) = (amount of crude PSA (g) x purity of crude PSA (%)) / (feed of o-xylene (g) x purity of o-xylene (%))

The so determined yield of solid PSA is despite deduction of it containing by-products as raw PSA yield, since one as pure PSA in general after the thermal pretreatment and product obtained by distillation. This the expert is also familiar.

There the conversion of o-xylene in each case is close to 100% corresponds the thus determined crude yield directly with the selectivity of the catalyst system.

Example 1 (Comparative Example): Catalyst system A (4 layers)

This catalyst system is a multi-layer system with four different layers. The individual beds of this comparative catalyst contain no mixed element oxide of the silver. composition 1st position 2nd position 3rd location 4th position In% by weight (Hot spot) Length: 147 cm 45 cm 70 cm 70 cm V2O5 5.0 7.7 8.5 15.0 Sb2O3 2.5 2.2 2.4 0.5 BiVO4 0.31 - - - Cs 0.37 0.20 0.10 0.05 P 0.03 0.05 0.05 0.10 TiO2 Rest to 100% Rest to 100% Rest to 100% Rest to 100% Share AM 8.3 8.4 8.4 8.0

At a loading of 50 to 65 g of o-xylene per Nm ^{3 of} air and a total air flow of 4.0 Nm ³ per hour and 344 to 347 ° C SBT the catalyst system A described in Example 1 was tested.

In this case, an average raw PSA yield (based on 100% o-xylene purity) was achieved after the run-in phase of 113.4 wt .-% and the phthalide content in the crude PSA was 0.01 wt .-%. Example 2 (according to the invention): Catalyst system B (4 layers) composition 1st position 2nd position 3rd location 4th position In% by weight Hot Spot Length: 140 cm 45 cm 70 cm 70 cm V2O5 5.0 7.7 8.5 15.0 Sb2O3 2.5 2.2 2.4 0.5 BiVO4 0.31 - - - AgVO3 0.17 - - - Cs 0.40 0.20 0.10 0.05 P 0.03 0.05 0.05 0.10 TiO2 Rest to 100% Rest to 100% Rest to 100% Rest to 100% Share AM 8.6 8.4 8.4 8.0

At a loading of 58 to 63 g of o-xylene per Nm ^{3 of} air and a total air flow of 4.0 Nm ³ per hour and 346 to 352 ° C SBT the catalyst system B described in Example 2 was tested. In this case, an average raw PSA yield (based on 100% o-xylene purity) was achieved after the run-in phase of 114.0 wt .-% and the phthalide content in the crude PSA was 0.06 wt .-%. Example 3 (according to the invention): Catalyst system C (4 layers) composition 1st position 2nd position 3rd location 4th position In% by weight (Hot spot) Length: 140 cm 45 cm 70 cm 70 cm V2O5 5.0 7.7 8.5 15.0 Sb2O3 2.5 2.2 2.4 0.5 BiVO4 0.31 - - - AgVO3 0.34 - - - Cs 0.42 0.20 0.10 0.05 P 0.03 0.05 0.05 0.10 TiO2 Rest to 100% Rest to 100% Rest to 100% Rest to 100% Share AM 8.7 8.4 8.4 8.0

At a loading of 58 to 65 g of o-xylene per Nm ^{3 of} air and a total air flow of 4.0 Nm ³ per hour and 346 to 347 ° C SBT the catalyst system C described in Example 3 was tested. In this case, an average raw PSA yield (based on 100% o-xylene purity) was achieved after the run-in of 115.3 wt .-% and the phthalide content in the crude PSA was 0.04 wt .-%. Example 4 (Inventive): Catalyst System D (4 layers) composition 1st position 2nd position 3rd location 4th position In% by weight (Hot spot) Length: 145 cm 45 cm 70 cm 70 cm V2O5 5.0 7.7 8.5 15.0 Sb2O3 2.5 2.2 2.4 0.5 BiVO4 0.31 - - - Ag2WO4 0.39 - - - Cs 0.40 0.20 0.10 0.05 P 0.03 0.05 0.05 0.10 TiO2 Rest to 100% Rest to 100% Rest to 100% Rest to 100% Share AM 8.7 8.4 8.4 8.0

At a loading of 57 to 69 g of o-xylene per Nm ^{3 of} air and a total air flow of 4.0 Nm ³ per hour and 346 to 348 ° C SBT the catalyst system D described in Example 4 was tested. In this case, an average raw PSA yield (based on 100% o-xylene purity) was achieved after the run-in phase of 113.9 wt .-% and the phthalide content in the crude PSA was 0.02 wt .-% on average. Example 5 (according to the invention): Catalyst system E (4 layers) composition 1st position 2nd position 3rd location 4th position In% by weight (Hot spot) 8 × 6 × 5 mm 7 × 7 × 4 mm 7 × 7 × 4 mm 7 × 7 × 4 mm Length: 140 cm 45 cm 70 cm 70 cm V2O5 5.0 7.7 8.5 15.0 Sb2O3 2.5 2.2 2.4 0.5 BiVO4 0.31 - - - Ag2MoO4 0.16 - - - Cs 0.40 0.20 0.10 0.05 P 0.03 0.05 0.05 0.10 TiO2 Rest to 100% Rest to 100% Rest to 100% Rest to 100% Share AM 8.6 8.4 8.4 8.0

At a loading of 52 to 62 g of o-xylene per Nm ^{3 of} air and a total air flow of 4.0 Nm ³ per hour and 347 to 348 ° C SBT the catalyst system E described in Example 5 was tested. In this case, an average raw PSA yield (based on 100% o-xylene purity) was achieved after the break-in of 114.2 wt .-% and the phthalide content in the crude PSA was an average of 0.01 wt .-%. Example 6 (Comparative Example): Catalyst System F (5 layers) composition 1st position 2nd position 3rd location 4th position 5th position In% by weight (Hot spot) Length: 45 cm 95 cm 50 cm 65 cm 70 cm V2O5 5.0 5.0 7.7 8.5 15.0 Sb2O3 2.5 2.5 2.2 2.4 0.5 BiVO4 0.31 0.31 - - - Cs 0.36 0.42 0.21 0.10 0.05 P 0.03 0.03 0.05 0.05 0.10 TiO2 Rest to 100% Rest to 100% Rest to 100% Rest to 100% Rest to 100% Share AM 8.8 7.8 8.4 8.4 8.0

At a loading of 58 to 61 o-xylene per Nm ^{3 of} air and a total amount of air of 4 Nm ³ per hour and 350 to 354 ° C SBT, the catalyst system F described in Example 6 was tested. Here, an average raw PSA yield (based on 100% o-xylene purity) of 113.1 wt .-% was achieved after the run-in phase and the phthalide content in the crude PSA was 0.01 wt .-%. Example 6 (Inventive): Catalyst System G (5 layers) composition 1st position 2nd position 3rd location 4th position 5th position In% by weight (Hot spot) Length: 50 cm 90 cm 45 cm 70 cm 70 cm V2O5 4.0 5.0 7.7 8.5 15.0 Sb2O3 0.2 2.5 2.2 2.4 0.5 BiVO4 - 0.31 - - - AgVO3 - 0.17 - - - Cs 0.28 0.40 0.21 0.10 0.05 P - 0.03 0.05 0.05 0.10 TiO2 Rest to 100% Rest to 100% Rest to 100% Rest to 100% Rest to 100% Share AM 6.9 7.8 8.4 8.4 8.0

At a loading of 58 to 75 g of o-xylene per Nm ^{3 of} air and a total amount of air of 4 Nm ³ per hour and 348 to 350 ° C SBT the catalyst system G described in Example 6 was tested. In this case, an average raw PSA yield (based on 100% o-xylene purity) of 114.8 wt .-% was achieved after the run-in phase and the phthalide content in the raw PSA was 0.03 wt .-%. Table 1: Performance data of the catalysts of the invention catalyst system Salt bath temperature ° C ∅ crude PSA yield (after break-in phase) (% by weight) ∅ phthalide content in crude PSA (wt%) A (comparison) 344-347 113.4 0.01 B 346-352 114.0 0.06 C 346-347 115.3 0.04 D 346-348 113.9 0.02 e 347-348 114.2 0.01 F (comparison) 350-354 113.1 0.01 G 348-350 114.8 0.03

Out Comparing Examples 2 to 5 and Comparative Example 1 It can be seen that the use of mixed element oxides of the Silver as a source of raw material for the preparation of a catalyst suspension for a catalyst in the first closest to the gas inlet catalyst layer to a significant increase in selectivity leads.

Out Comparing Example 7 with Comparative Example 6 seen that the use of silver vanadate in the active Mass of the hot spot catalyst layer even when used in at least one of the first catalyst layer subsequent catalyst layer a Improve the selectivity.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - EP 21325A [0013]
• EP 286448A [0014]
• - US 4864036 [0015]
• GB 1140264 [0016]
• EP 0447267 [0017]
• - EP 0522871 B1 [0018]
• - CN 1108996 [0019]
• - DE 19851786 A1 [0021]
• WO 2005/092496 A1 [0022]
• - DE 2106796 A [0101]

Claims (38)

Catalyst for catalytic gas phase oxidation from aromatic hydrocarbons to aldehydes, carboxylic acids and / or carboxylic acid anhydrides, especially to phthalic anhydride, in which the active compound vanadium oxide, preferably vanadium pentoxide, titanium dioxide, preferably in the anatase modification, and at least one mixed element oxide of the silver with defined elements, preferably vanadium and / or Molybdenum and / or tungsten and / or niobium and / or antimony, and / or a mixed element oxide of vanadium with defined elements, preferably bismuth and / or molybdenum and / or tungsten and / or Antimony and / or niobium, and being in the production the catalyst, in particular in the preparation of a catalyst suspension or one needed for the coating of a carrier Powder mixture, at least one mixed element oxide of the silver and / or of the vanadium and / or at least one precursor compound, in particular at least one polynuclear precursor compound, at least one Mischelementoxides of silver and / or vanadium used as a source of raw materials. Catalyst according to claim 1, characterized in that the active composition is from 0.01 to 15% by weight, preferably from 0.01 to 10 Wt .-%, most preferably 0.01 to 5 wt .-%, of a Mischelementoxides of the silver. Catalyst according to claim 1 or 2, characterized in that the at least one mixed element oxide of the silver is a mixed element oxide with at least one further element from the group of vanadium, Molybdenum, tungsten, niobium, tantalum, chromium, titanium, manganese, Iron, cobalt, nickel, copper, zinc, cadmium, gold, tin, zirconium, Antimony, arsenic, cerium, lanthanum, bismuth, hafnium, lead, boron, aluminum, Ruthenium, rhenium, palladium, rhodium. Catalyst according to one of claims 1 to 3, characterized in that the active mass 0.01 to 10 wt .-%, preferably 0.01 to 5 wt .-%, of a Mischelementoxides of vanadium having. Catalyst according to one of claims 1 to 4, characterized in that the at least one mixing element oxide of the vanadium a Mischelementoxid with at least one other Element from the group of bismuth, antimony, molybdenum, tungsten, Chromium, lanthanum, cerium, iron, manganese, niobium, tantalum, rhenium, cobalt, Nickel, copper, zinc, gold, cadmium, lead, tin, boron, titanium, zirconium, Hafnium, aluminum, arsenic, ruthenium, rhodium, palladium. Catalyst according to one of claims 1 to 5, characterized in that the vanadium oxide content of the active composition 1 to 40 wt .-%, calculated as V ₂ O ₅ , and the titanium dioxide content of the active material 50 to 99 wt .-%, calculated as TiO ₂ , is. Catalyst according to one of claims 1 to 6, characterized in that the active composition 0 to 10 wt .-% of an antimony compound, calculated as Sb ₂ O ₃ , and / or 0 to 1 wt .-% of a compound of at least one element of the Group of lithium, sodium, potassium, rubidium, cesium, each calculated as alkali metal, and / or 0 to 1.5 wt .-% of a phosphorus compound, calculated as P comprises. Catalyst according to one of claims 1 to 7, characterized in that the active material comprises AgVO ₃ and / or Ag ₂ MoO ₄ and / or Ag ₂ WO ₄ and / or BiVO ₄ . Catalyst according to claim 8, characterized in that a predetermined amount of AgVO ₃ and / or Ag ₂ MoO ₄ and / or Ag ₂ WO ₄ and / or BiVO ₄ and / or at least one precursor compound of these compounds used in the preparation of the catalyst as a raw material source is. Catalyst according to one of claims 1 to 9, characterized in that as a source of raw material in the Preparation of the catalyst used mixed element oxides and / or Mixed element oxide precursor compounds of mixed element oxide or the mixed element oxides of silver and / or vanadium prior to their use as a source of raw material in catalyst production during their production be isolated from the reaction mixture or the reaction mixture in question used directly as a source of raw material in catalyst production becomes. Catalyst according to one of claims 1 to 10, characterized in that the mixed element oxide of silver has the following formula (I) below: Ag _x M _y N _z O _n (Formula I) where Ag = silver x = 0.01 to 100, in particular 0.1 to 10, M = an element selected from the group Li, Na, K, Rb, Cs, P, Mg, Ca, Sr, Ba, Tl, y = 0 to 1 N = at least one element selected from the group V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Co, Rh, Ni, Pd, Cu, Au, Zn, Cd, Sn , Pb, B, Al, Bi, Sb, As, Ti, Zr, Hf, Ce, La z = 1 O = oxygen n = a number which is determined by the valency and frequency of the elements other than oxygen in the formula I. . Catalyst according to one of claims 1 to 11, characterized in that the mixed element oxide of vanadium has the following formula (II): M _a N _b V _b O _d (formula II) where M = at least one element selected from the group consisting of Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Co, Rh, Ni, Pd, Cu, Au, Zn, Cd, Sn, Pb, B, Al, Bi, Sb, As, Ti, Zr, Hf, Ce, La a = 0.01 to 100 N = at least one element selected from the group Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba , TI, P b = 0 to 1, V = vanadium c = 1 O = oxygen d = a number which is determined by the valency and frequency of the elements other than oxygen in the formula II. Catalyst according to one of claims 1 to 12, characterized in that as vanadium source for the preparation of the catalyst V ₂ O ₅ and / or vanadium oxalate and / or V ₆ O ₁₃ and / or NH ₄ VO ₃ and / or polyvanadic acid is used, wherein at least a portion of the vanadium is present in the active composition after the thermal treatment of the catalyst as vanadium pentoxide. Catalyst according to one of claims 1 to 13, characterized in that for the preparation of the catalyst at least one kind of titanium dioxide is used in the anatase modification and is present as such in the active composition, the average BET surface area calculated from quantitative and surface ratios of the individual varieties, the total titanium dioxide is between 10 and 60 m ² / g. Catalyst according to claim 14, characterized in that in the active composition, a mixture of several different titanium dioxide varieties is used in the anatase modification, wherein at least one titanium dioxide variety in the anatase modification has an average particle size of 0.3 microns to 0 , 8 .mu.m and a BET surface area of 13 to 60 m ² / g and wherein at least one further titanium dioxide variety in the anatase modification has a BET surface area of 2 to 15 m ² / g. Catalyst according to one of claims 1 to 15, characterized in that the for producing a catalyst suspension or one for the coating of a carrier required powder mixture used antimony compound and / or the antimony compound present in the active mass of the catalyst is an antimony-III-oxide and / or antimony-V-oxide. Catalyst according to one of claims 1 to 16, characterized in that the catalyst of at least three layers, wherein the antimony content of at least one of Hot spot catalyst layer in the direction of gas inlet upstream layer by 20 to 100% over the antimony content of the hot spot Catalyst layer is reduced. Catalyst according to one of claims 1 to 17, characterized in that the active material of the catalyst after tempering of the catalyst at 400 ° C over a defined, preferably several, in particular lasting about 4 hours period has the following composition: vanadium: 1-40% by weight (calculated as V ₂ O ₅ ) Titanium dioxide: 50-99% by weight (calculated as TiO ₂ ) AgxMyNzOn: 0.01-15% by weight (calculated as AgxMyNzOn) MaNbVcOd: 0-10% by weight (calculated as MaNbVcOd) Alkali metal: 0-1.0% by weight (calculated as alkali metal) antimony: 0-10% by weight (calculated as Sb ₂ O ₃ ) Phosphorus: 0-1.5% by weight (calculated as P) Catalyst according to claim 18, characterized in that the active material of the catalyst after tempering of the catalyst at 400 ° C over a defined, preferably several, in particular in about 4 hours lasting period has the following composition: vanadium oxide 1-20% by weight (calculated as V ₂ O ₅ ) Titanium dioxide: 80-99% by weight (calculated as TiO ₂ ) silver vanadate: 0-5% by weight (calculated as AgVO ₃ ) Silver tungstate: 0-5% by weight (calculated as Ag ₂ WO ₄ ) silver molybdate: 0-5% by weight (calculated as Ag ₂ MoO ₄ ) bismuth vanadate: 0-3 wt% (calculated as BiVO ₄ ) cesium: 0-1 wt% (calculated as Cs) antimony: 0-5% by weight (calculated as Sb ₂ O ₃ ) Phosphorus: 0-1.5% by weight (calculated as P) wherein at least one mixed element oxide of the silver and / or bismuth vanadate is part of the active material of the catalyst. Catalyst according to one of claims 1 to 19, characterized in that the active mass of the catalyst after tempering the catalyst at at least 400 ° C and a period of at least 4 h, a share of 2 to 25 Wt .-% of the total weight of the catalyst. Catalyst according to one of claims 1 to 20, characterized in that the layer thickness of the active Mass on an inert support material 20 to 400 microns is and the catalytically active mass to an inert, non-porous support is applied, it being preferably steatite carriers, in particular steatite rings, is. Catalyst according to one of claims 1 to 21, characterized in that at least two different Layers cupped on a preferably inert carrier wherein at least one of the layers of titanium dioxide, Vanadium oxide and a mixed element oxide of silver and / or vanadium contains Catalyst according to one of claims 1 to 22, characterized in that at least two different Layers cupped on a preferably ceramic Carrier are applied, wherein at least one layer at least titanium dioxide and vanadium oxide and at least one other Layer at least one silver and / or Vandadium Mischelementoxid with or without additional titanium dioxide and vanadium oxide. Catalyst according to one of claims 1 to 23, characterized in that in at least one catalyst layer from the gas inlet to the location with the highest hot spot a shell catalyst is used whose active material is a mixed element oxide of the silver according to claim 11 and / or a mixed element oxide of vanadium according to claim 12 and in which catalyst as a source of raw material for the preparation of the catalyst, a mixed element oxide of silver and / or vanadium and / or a precursor compound of a Mixed element oxide of silver and / or vanadium was used, and in which catalyst in at least one catalyst layer from the location with the highest hot spot to the location at Gas outlet a shell catalyst for the oxidation of aromatic Hydrocarbons used in its active mass contains as essential constituents vanadium pentoxide and titanium dioxide. Catalyst according to one of claims 1 to 24, characterized in that the binder for the production at least one catalyst layer, an organic polymer or copolymer, in particular a vinyl acetate copolymer, which is particularly useful in Form of an aqueous dispersion is used. Catalyst according to one of claims 1 to 25, characterized in that the catalytically active Mass, based on their total weight, 0.01 to 15 wt .-% of a Mischelementoxids of silver with vanadium and in which the ratio Ag: V of greater than 0.95 (> 0.95): 1 to 10: 1. Precursor for a catalyst, in particular for a catalyst according to any one of the claims 1 to 26, characterized by an inert, non-porous Carrier material and one or more shell-shaped layers applied thereto, wherein at least one layer at least a precursor compound of a mixed element oxide of the general Formula I according to claim 11, or the formula 11 according to claim 12, Titanium dioxide and a vanadium compound, and wherein this precursor compound in the thermal treatment the precursor of the catalyst in a Mischelementoxid of silver or vanadium is converted. Precursor for a catalyst, in particular for a catalyst according to any one of the claims 1 to 26, characterized in that at least two different Layers cupped on a preferably ceramic Carrier are applied, wherein at least one layer at least titanium dioxide and a vanadium compound and at least another layer at least one precursor compound a mixed element oxide with or without additional titanium dioxide and with or without an additional vanadium compound, and wherein this precursor compound in the thermal Treatment of the catalyst in a mixed element oxide of silver or vanadium converts. Process for the preparation of a catalyst according to one of claims 1 to 26, characterized in that a powder or a suspension, especially an aqueous one Suspension comprising at least titanium dioxide, a vanadium compound and at least one compound element compound of the silver and / or Vanadium and / or at least one precursor compound a compound element compound of silver and / or vanadium contains, is manufactured and on an inert carrier is applied. Process for the preparation of a precursor of a Mischelementoxids or a mixed element oxide according to claim 11, characterized in that that in a liquid, preferably water, suspended Metal oxide N, preferably vanadium pentoxide and / or molybdenum trioxide and / or tungsten trioxide, and / or a dissolved metal compound N, preferably ammonium metavanadate, with a suspension or solution, preferably an aqueous solution, a silver compound and optionally a solution or suspension of an oxide a metal compound M is heated and the reaction product is isolated and used as a raw material source for a catalyst becomes. Method according to claim 30, characterized in that that the resulting reaction mixture or the isolated reaction product for the preparation of catalysts or for the preparation of precursors of catalysts for the gas phase oxidation of aromatic Hydrocarbons is used. Process for the preparation of a precursor of a Mischelementoxids or a mixed element oxide according to claim 12, characterized in that that in a liquid, preferably water, a suspended and / or dissolved vanadium compound, preferably vanadium pentoxide and / or ammonium vanadate and / or vanadium (IV, V) oxide, with a Solution or a suspension, preferably an aqueous one Solution, a salt or an oxide of a metal compound M, preferably bismuth and / or molybdenum and / or tungsten and / or Niobium and / or antimony and optionally a solution of a Salt or a suspension of an oxide of a metal N, heated and the reaction product is isolated or as a reaction mixture is used as a raw material source for a catalyst. Method according to claim 32, characterized in that that the isolated reaction product and / or the resulting reaction mixture for the preparation of catalysts or for the preparation of precursors of catalysts for the gas phase oxidation of aromatic Hydrocarbons is used. A process for preparing a mixed element oxide according to claim 11, characterized in that at least one metal oxide N, preferably vanadium pentoxide and / or molybdenum trioxide and / or tungsten trioxide, and / or at least one metal salt N with an oxide or a salt of silver, preferably AgO and / or Ag ₂ O and optionally an oxide or a salt of a metal M, is mixed in dry form or in solution and the mixture is optionally heated after prior drying at temperatures of 200 to 900 ° C over a defined period of time and the reaction product as a source of raw material is used for a catalyst. A method according to claim 34, characterized that the reaction product or the resulting reaction mixture for the preparation of catalysts or for the preparation of precursors of catalysts for the gas phase oxidation of aromatic Hydrocarbons is used. Process for the preparation of a mixed element oxide according to claim 12, characterized in that at least one salt or an oxide of vanadium, preferably vanadium pentoxide and / or Ammonium vanadate and / or vanadium (IV, V) oxide, with at least one Oxide and / or a salt of a metal M, preferably bismuth oxide, and optionally an oxide or a salt of a metal N, in dry form or mixed in solution and the mixture if necessary after previous drying then at temperatures from 200 to 900 ° C over a defined period of time heated and the reaction product as a source of raw material for a catalyst for the gas phase oxidation of aromatic Hydrocarbons is used. A process for the preparation of aldehydes, carboxylic acids and / or carboxylic anhydrides by partial oxidation of aromatic hydrocarbons at elevated temperature on a catalyst, the catalytically active material is applied to an inert, non-porous support, characterized in that a shell catalyst whose catalytically active material, based on their total weight, 0.01 to 15% by weight of a mixed element oxide of silver with vanadium and / or molybdenum and / or tungsten and / or niobium and / or antimony and / or 0.01 to 10% by weight of a mixed element oxide of Vanadium with bismuth and / or molybdenum and / or niobium and / or antimony and simultaneously titanium dioxide and a vanadium compound, preferably V ₂ O ₅ , wherein the Mischelementoxid connec tion (s) or their precursor compound (s) in the preparation of the catalyst suspension and / or the powder mixture is used for the later active composition, in the presence or absence of at least one we Iterener shell catalyst containing in its active material as essential constituents vanadium pentoxide and titanium dioxide in the anatase modification used. Process for the preparation of a catalyst according to one of claims 1 to 26, characterized in that the catalytically active mass or in the catalyst suspension or in the powder mixture compounds contained in the fluidized bed or preferably applied in a fluidized bed to the inert carrier will or will be.