EP2355925A1

EP2355925A1 - Method for activating a catalyst

Info

Publication number: EP2355925A1
Application number: EP09744070A
Authority: EP
Inventors: Inga Walzel; Gerhard Mestl
Original assignee: Sued Chemie AG
Current assignee: Sued Chemie IP GmbH and Co KG
Priority date: 2008-10-22
Filing date: 2009-10-22
Publication date: 2011-08-17
Also published as: WO2010046110A1; DE102008052712A1

Abstract

The present invention relates to a method for activating a catalyst, to a catalyst activated according to the claimed method, to the use of said catalyst for producing formaldehyde, and to a reactor containing the catalyst treated according to the invention.

Description

Method of activating a catalyst

The present invention relates to a method for activating a catalyst, a catalyst activated according to the method of the invention, the use of this catalyst for the production of formaldehyde and a reactor containing the catalyst treated according to the invention.

Heterogeneously catalyzed oxidation reactions are of particular importance to the chemical industry as they are used for large scale, selective production of numerous end products from inexpensive and abundant raw materials (e.g., alcohols).

Typically, in so-called heterogeneous catalysis, two

Types of (solid) catalysts distinguished (J. Weitkamp and R. glasses in: Winnacker / Küchler "Chemical Engineering: Processes and Products", Volume 1, Chapter 5, Wiley-VCH, 2004):

On the one hand, there are so-called "supported catalysts", too

Coat or coating catalysts, which are understood as solid catalysts, which are prepared by coating a (typically non-porous) carrier body with a porous layer containing the actually catalytically active species.

In contrast, in the so-called. "Supported catalysts" by impregnation, the catalytically active species (eg, noble metals, such as Pd, Pt, Au, Ag, etc.) as a solution {reducible) compound of these species dispersed on a porous support, such as SiO ₂ , Al ₂ O ₃ , TiO ₂ , ZrO ₂ , etc.) applied. In the case of the supported catalysts produced by the impregnation process, there are usually chemical-physical interactions between the support and active species, which have a decisive influence on the catalytic process.

In contrast to supported catalysts in which the active elements are dispersed in the porous support - optionally also in an outer shell (= shell catalyst) arranged on the support - the carrier supports only the structural support , In the supported catalyst, the typically non-porous support body is enveloped by a layer containing the active species.

In the present case, the term "catalyst" is understood to mean both of the abovementioned (solid) catalyst types.

An important heterogeneously catalyzed oxidation reaction is the partial oxidation of methanol to formaldehyde (so-called Formox process). In addition to the coupled dehydrogenation and oxidation of silver contacts, partial oxidation with excess air on porous solid catalysts of iron molybdate is customary for large-scale production. As a possible side reaction, the total oxidation of methanol may occur.

In the industry today are usually

Iron molybdate full catalysts used, which, however, have only a small active surface in relation to their active mass. Next molybdenum-vanadium-iron or vanadium-iron catalysts for the partial oxidation of methanol to formaldehyde are known.

The atomic ratios between molybdenum or vanadium and iron vary considerably in the catalysts known from the prior art. Some of the active components may be further partially replaced by so-called promoters such as titanium, antimony, tin, nickel, chromium, cerium, aluminum, calcium, magnesium, niobium, silver and / or manganese in metallic form or in the form of compounds.

No. 3,975,302 describes an Fe / Mo catalyst prepared by the impregnation process for the oxidation of methanol to formaldehyde (generally referred to as the Formox process). Accordingly, iron and molybdenum are dissolved as MoO ₄ ^{2 "} and Fe ³⁺ salts in a solvent such as water and then applied to a porous support having a BET surface area of 1 to 20 m ² / g Catalyst for the oxidation of methanol to formaldehyde, which is prepared by impregnation in the fluidized bed process.

No. 5,217,936 describes a catalyst for the preparation of aldehydes from the corresponding alcohols, in particular formaldehyde from methanol, the catalytically active composition being applied to a monolithic carrier. In addition to molybdenum oxide, the active species may also contain oxides of chromium, vanadium, aluminum, iron, tungsten, manganese and mixtures thereof. To enhance binding of the active mass to the monolithic carrier, the active species may contain a binder. As a suitable binder, silicon dioxide and titanium dioxide are specified. DE 10 2004 014 918 describes a catalyst having a silver vanadium oxide phase and a promoter phase based on titanium dioxide and vanadium pentoxide, which is suitable for the preparation of aldehydes, carboxylic acids and carboxylic anhydrides from aromatic or heteroaromatic hydrocarbons by gas phase oxidation. The catalyst is preferably formed as a shell catalyst, wherein the two phases are arranged as concentric shells on an inert support.

In WO 2005/037427 a catalyst bed of a physical mixture of catalytically active and catalytically inactive moldings is described, wherein the catalytically inactive moldings have rounded edges on the outer friction surfaces. If the catalyst bed is used for the oxidation of methanol to formaldehyde, for example Eisenmolybdate can be used as catalytically active species.

Another important heterogeneously catalyzed

Oxidation reaction is the oxidation of propylene to acrolein and / or acrolein to acrylic acid, thus using so-called acrylic acid or acrolein catalysts. In SOHIO Acrolein process, for example, propylene is reacted in air at 300- 360 ⁰ C and a pressure of 0.2 MPa on a Bi ₂ O ₃ -MoO ₃ catalyst. Nowadays, especially the multi-component catalysts below are used. Examples of multi-component acrolein catalysts are Bi ₉ PMo ₁₂ O ₅₂ -SiO ₂ , Fe _4.5 Bi ₄ . ₅ PMOi ₂ O ₅₂ -SiO ₂ , K ₀ (Ni, Co) 9Fe ₃ BiPMOi ₂ O _x -SiO ₂ and (Na, K) ₀₁ (Ni, Mg _J Zn) ₀ Fe _C Bi _C jWeMOi ₂ Ox-SiO ₂ Examples of multi-component acrylic acid catalysts are PMOi ₂ O _x -SiO ₂ , Va (PJ _b MOi ₂ O _x -SiO ₂ and Cu _a V _b (Sn, Sb) _c W _d Mθi ₂ 0x -SiO ₂ . The previously known from the prior art catalysts, especially for the production of formaldehyde or acrolein or acrylic acid, require the (high-temperature) activation before delivery to the customer or the installation in the reactors or catalyst systems in the final

Destination. Catalysts which have already been activated or calcined prior to transport, redeployment or the like are very sensitive, in particular with regard to the abrasion resistance of the catalytically active layer, which entails various disadvantages: on the one hand, the high abrasion results in a loss of more expensive, catalytic On the other hand, abrasion leads to the development of dust, which has negative effects on the health of the persons in contact with the catalyst. Another aspect is that a large proportion of dust in the reactor inhibits the passage of the substances to be reacted and it can even lead to constipation in severe cases.

There was therefore a need for improved activatable

Catalysts and / or catalyst systems, in particular for the oxidation of methanol to formaldehyde or of propylene to acrolein, which do not have the aforementioned disadvantages and, however, at the same time have good activity and selectivity with respect to the reaction to be catalyzed.

The object of the present invention was therefore to provide an improved process for the activation of catalysts which have a particularly high abrasion resistance after activation, but at the same time have good activity and selectivity for the end product, for example formaldehyde or acrolein or acrylic acid. The object is achieved by a method for activating a catalyst comprising the steps of

a) heating a catalyst to a temperature of 160 0C to 200 ⁰ C at a gas flow of 0.1 Nm ³ to 10 Nm ³ ;

b) heating the catalyst from 160 ⁰ C to 200 ⁰ C to a temperature of 300 ⁰ C to 350 ⁰ C at a gas flow of 0.1 Nm ³ to 10 Nm ³ and maintaining the temperature for a period of 1 to 84 hours;

c) heating the catalyst from 300 ⁰ C to 350 ⁰ C to a temperature of 390 ⁰ C to 430 ⁰ C at a gas flow of 0.1 Nm ³ to 10 Nm ³ and maintaining the temperature for a period of 1 to 84 hours.

The process is preferably carried out in the reactor in which the reaction to be catalyzed also takes place. In other words, in the present case, this is an in-situ activation.

The present invention further relates to a catalyst which has been activated according to the process of the invention and to the use of such a catalyst for the synthesis of formaldehyde or acrolein or acrylic acid.

Finally, the present invention relates to a shell-and-tube reactor containing the catalyst activated according to the process of the invention.

The term "catalyst" is, as generally explained above, in the context of the present invention, any solid catalyst understood that the skilled person as for the method according to the invention is known. However, preference is given to using catalysts which are suitable for the production of formaldehyde in the process according to the invention. It is understood that analogous systems for acrolein / acrylic acid synthesis in further preferred embodiments can also be used.

The catalysts preferred according to the invention are particularly preferably catalysts which are suitable for the conversion of methanol to formaldehyde, most preferably catalysts which contain molybdenum, iron and / or vanadium as active components.

In the following, the catalysts which are most suitable for the process according to the invention with respect to the formaldehyde synthesis are described in more detail:

As the active component of the invention most preferred catalysts are preferably oxides of molybdenum and / or vanadium and iron and / or their mixed oxides (such as Fe ₂ (MoO ₄ J ₃ ) or compounds which can be converted into the corresponding oxides or mixed oxides, such as For example, acetates, oxalates, acetylacetonates, citrates, nitrates, chlorides, phosphates, sulfates or ammonium compounds of iron or molybdenum and vanadium used.

In a particularly preferred embodiment, the active component is a non-stoichiometric iron-molybdenum mixed oxide which does not have the composition Fe ₂ (MoO ₄ ) 3. Mo: Fe ratios of 0.5 to 12 are preferred. Mo: Fe ratios of 0.75 to 10 are particularly preferred.

Other optional compounds that may be included in the active component are metallic or metal oxide Components or compounds which can be converted into the corresponding oxides or mixed oxides, and which are familiar to the expert with regard to the use of the catalyst for the oxidation of methanol to formaldehyde as so-called promoters. Non-limiting examples are compounds of the

Titans, antimony, tin, nickel, cerium, aluminum, calcium, magnesium, chromium, niobium, silver and / or manganese, which can partially replace Fe, V and Mo.

If the catalyst - in a particularly preferred

Embodiment - contains at least one promoter compound, this is preferably selected from the group consisting of Li, Na, K, Cs, Rb, Ca, Sr, Ba, P, Sb, Bi, Cu, Ag, Au, Su, Ce and mixtures thereof ,

Further, the catalysts most preferred for the process of the invention are supported catalysts. This applies, for example, in particular both for the formaldehyde as well as for the acrolein / acrylic acid synthesis.

The supported catalyst which is preferred for the process according to the invention particularly preferably comprises a (catalytically) inert support structure. As a material for the inert carrier structure, it is possible in principle to use all inert materials familiar to the person skilled in the art. Preferably, however, the material should be substantially non-porous.

Substantially non-porous means that the material used in the context of the present invention is a BET

Surface (determined according to DIN 66131) of less than about 1 m ² / g. The pore volume of the inert, substantially non-porous material is preferably less than 0.1 ml / g, also determined according to DIN 66133. The material density is preferably in the range of 2.0 to 4.5 g / cm ³ , particularly preferably in the range of 2.3 to 3.5 g / cm ³ .

Non-limiting examples of suitable and preferred materials for the support structure of the preferred catalysts according to the invention are magnesium silicate (steatite), quartz (SiO ₂ ), porcelain, magnesium oxide, tin dioxide, silicon carbide, rutile, alumina (Al ₂ O ₃ ), zirconium silicate, aluminum silicate, cersilicate or mixtures thereof and metals or alloys such as stainless steel. Carrier structures of steatite are particularly preferred.

Particular preference is given to using hollow rings or rings which are known to the person skilled in the art as inert carrier structures and which permit a flow rate adapted to the reaction in the reactor. Such support structures are described, for example, in WO 2007/059974, EP 1 127 618 A1 or WO 2005/037427 A1, to the disclosure content of which reference is made here in their entirety.

The preferred carrier structures form less easily locally ordered dense packages when loading the reactor, but rather are arranged irregularly, with more turbulence arising in the gas stream through the catalyst bed, which is a slight onset of overheating (formation of so-called "hotspots"), especially in the oxidation reacting methanol to formaldehyde both in the molding as well as in the reactor, as typically occurs, for example, in monoliths, such as according to US 5,217,936th The reduction of overheating also leads to an extension of the life of the catalyst.

On the inert carrier structure, in preferred embodiments, at least one carrier layer consists of Particles of a metal oxide of a main group metal, an early transition metal or a lanthanum applied. These can, as already mentioned above, be applied either in the form of their powders (as suspension) and / or also as sols.

Depending on the sol, the solids content is between 10 and 50% by weight, for example SiO ₂ sols having 20 to 40% by weight, ZrO ₂ sols having 10 to 20% by weight, CeO ₂ sols having 15 to 20% by weight. 25% by weight solids content and 10% to 20% by weight TiO ₂ sols

Solid content preferred. TiO ₂ sols or TiO ₂ powders are very particularly preferred in the context of the invention. Particularly preferred is a preparation using a powder suspension of the carrier oxide plus a proportion of 0.05 wt .-% to 5 wt .-% of a sol of the same carrier oxide.

In a preferred embodiment according to the invention, the integral pore volume (determined by Hg porosimetry, DIN 66133) of the carrier layer is between about 100 and 800 mm ³ / g, preferably between about 200 and 700 mm ³ / g, more preferably between about 250 and 600 mmVg , The mean pore radius determined by this method is preferably between about 50 and 1000 nm, preferably between about 100 and 700 nm, more preferably between about 150 and 500 nm.

According to a very particularly preferred embodiment of the invention, the sol has a particle size of 1 to 100 nm, preferably from 2 to 50 nm, particularly preferably <40 nm. The determination of these particle sizes was carried out according to ASTM B822-97. Alternatively, ISO 13320-1 can also be used.

Preferred oxides used as support material are characterized by the following properties of their particle size distribution: dio: 0.1 to 2.5, preferably 0.1 to 0.3; d ₅₀ : 0.15 to 20, preferably 0.15 to 1; d ₉₀ : 0.5 to 40, preferably 0.5 to 2.5.

The catalyst to be activated is heated according to step a) of the inventive method to a temperature of 160 ⁰ C to 200 ⁰ C, preferably to a temperature of 170 ⁰ C to 190 ⁰ C, more preferably to a temperature of 175 ⁰ C to 185 0C and most preferably to a temperature of 180 ^° C.

The heating can be done by any method that suits the

A person skilled in the art is known to be suitable for the purpose according to the invention, but is preferably carried out with the aid of a gas stream which has previously been heated to the desired temperature. Any gas which is known to the person skilled in the art as suitable for the purpose according to the invention can be used as the gas.

Preferably, however, the gas is selected from the group consisting of air and the noble gases (inert gases) such as nitrogen, argon, helium, neon, krypton, xenon and mixtures thereof, with a mixture of air and nitrogen being particularly preferred. Further, it is preferable that the gas is mixed with an alcohol, which is more preferably methanol. In other developments of the invention, the alcohol is ethanol, which is particularly preferably mixed with water. Very particular preference is given to mixtures of air, inert gas and methanol, wherein the inert gas in one of the most preferred embodiments is nitrogen.

The alcohol, which is preferably methanol, is preferably present in the gas or gas mixture

Concentration of 0.1 to 10 vol .-%, more preferably 1 to 5% by volume. It is also preferred that with increasing the activity of the according to the invention Process treated catalyst, the alcohol content is gradually increased.

The alcohol content is preferably increased in the steps of 1 to 2% by volume per minute, more preferably 10 minutes. Particular preference is given, for example, to an increase starting from an initial concentration of 4% by volume, in each case 1% by volume, to a final concentration of max. 10 vol. -%.

According to the inventive method, the temperature of step b) and / or c) for a period of at least 1 to a maximum of 84 hours, preferably for a period of at least 2 to a maximum of 72 hours, more preferably for a period of at least 3 to a maximum of 48 Hours and most preferably held for a period of at least 6 to a maximum of 24 hours. A hold time of 6 hours, 12 hours or 18 hours is particularly preferred.

It is possible that the temperature in step b) and step c) is maintained for the same period of time, but the holding time of step b) and step c) can also be of different lengths. Furthermore, according to the method of the invention, it is possible to combine any temperature encompassed by the method according to the invention with any holding time encompassed by the method according to the invention.

According to the process of the invention, the gas stream in steps a), b) and / or c) is preferably 1 Nm ³ to 5 Nm ³ , more preferably 1.5 Nm ³ to 4 Nm ³ , more preferably 2 Nm ³ to 3, 5 Nm ³ and most preferably 3 Nm ³ . It is possible according to the inventive method that the gas stream of the individual steps a), b) and c) different or equal is selected. In the case of a tube bundle reactor, it is preferred that the gas flows are the same for each individual tube, but it is also possible that different gas flows are used for each tube. Further, according to the method of the invention, it is possible to combine any temperature encompassed by the method according to the invention with any holding time and gas stream included in the method according to the invention.

The present invention further relates to a

A catalyst which has been activated by a process as described in more detail above.

Furthermore, the present invention relates to the use of an activated according to the inventive catalyst for the production of formaldehyde.

This relates in particular to the use of a catalyst activated in accordance with the process according to the invention in a shell-and-tube reactor.

Preference is given to conventional tube bundle reactors, as described, for example, in EP 1837072 A1, with 5000 to 30,000 tubes having an internal diameter of preferably 21 mm to 30 mm, preferably 21 and 25 mm and a length of 1.8 m to 6 m 1.8 to 2.5 m. These tube bundle reactors are preferably cooled by means of a coolant, which are preferably heat transfer oils or molten salts. The invention will now be explained in more detail with reference to the following non-limiting example and with reference to a figure.

Show it:

1: the formaldehyde yield during a long-term

Stress tests at 100% methanol conversion, and

Fig. 2: the temperature profile during activation.

methods

According to the following physical

Determination methods used to characterize the catalyst:

1. Test for determining the adhesion of the active material ("abrasion test"):

The adhesion of the active material is investigated in a device of the company ERWEKA, type TAR 10. For this purpose, a total of 50 g of catalyst at a rotational speed of 75 revolutions / min is rotated a total of 10 times (= 10 revolutions of the drum). It is then determined the abrasion as the ratio of the loose, no longer bound to the carrier body coating to the total applied coating.

2. BET surface area:

The determination is made according to the BET method according to DIN 66131; a publication of the BET method can also be found in J. Am. Chem. Soc. 60, 309 (1938). 3. Pore radius distribution:

The pore radius distribution is determined by means of mercury porosimetry according to DIN 66133; maximum pressure: 2,000 bar, Porosimeter 4000 (Porotec, DE), according to the manufacturer.

4. Determination of particle sizes (particle sizes):

The particle sizes are determined by the laser diffraction method using a Fritsch Particle Sizer Analysette 22 Economy (Fritsch, DE) according to the manufacturer's instructions, also with regard to the sample pretreatment: The sample is homogenized in deionized water without addition of auxiliaries and ultrasonically for 5 minutes treated. The specified D values are based on the sample volume.

embodiment

Preparation of the active component

Ammonium heptamolybdate and ferric nitrate were purchased from Merck KGAa, Darmstadt, Eisenmolybdat from Süd-Chemie Catalysts Italia. Commercially available titanium dioxides were used. The BET surface areas of the titanium dioxides ranged from 21 m ² / g to 101 m ² / g, and the pH values obtained when slurrying the suspensions ranged from 3.89 to 7.62.

The pH values of the titanium dioxide suspensions were determined with a glass electrode by slurrying 9 g of the respective oxide in 400 ml of distilled water at room temperature and stirring for 12 hours. Impregnation of titanium dioxides

The impregnation was carried out by means of the spreading method (solid wetting)

This method assumes that the released enthalpy of uniform distribution of iron molybdate on the surface of titanium dioxide is greater than the enthalpy of clustering (reduction of surface free energy). The higher the temperature, the greater the risk of sintering, which can be far below the melting temperature of the active component. Typically, the surface diffusion of metal atoms can already be used at the Hüttig temperature (T _H ύttig = 0.3 T _Schm eiz) and that of metal agglomerates at the Tammann temperature (T _Tamm nn = 0.5 Tmezzle).

For the realization of the embodiments, a temperature between the Hüttig- and the Tammann temperature was chosen. The in situ annealing in the tubular reactor was carried out at 43O ⁰ C for 48 hours.

The amount of iron molybdate calculated for a monolayer was mixed with the respective titanium dioxide powder. The TiO ₂ used particularly preferably has a BET surface area of> 20 m ² / g and <50 m ² / g. Therefore, it was necessary to impregnate 250 g of TiO ₂ and 40.68 g of iron molybdate.

The coating composition thus obtained was applied in the form of thin layers at a temperature between 60 to 8O ⁰ C on the steatite bodies in the fluidized bed. The layer thickness of the catalytically active material was up to 300 microns. The same applies, of course, for a subsequent Impregnation of a previously applied to the carrier molding TiO ₂ layer.

catalyst test

1. Activation

Step a:

After introduction into a tube reactor, the catalyst was heated at 16O ⁰ C under 0.3 Nm ^{3 of} air for 3 hours.

Step b) Subsequently, the catalyst was heated to 330 ⁰ C under 0.3 Nm ^{3 of} air (per 1 tube) and calcined for 18 hrs.

Step c)

Subsequently, the catalyst was heated to 430 ⁰ C and calcined for 48h under a stream of 0.3 Nm ^{3 of} air.

2. Catalysis

For starting up the catalyst activated as above, N ₂ was first added to flow N ₂ [Nm ³ / h] NTP 0.112, then air to air [Nm ³ / h] NTP 0.081 and finally MeOH to methanol flow (gas) [Nm ³ / h ] 0.017 and equilibrated for one hour. Here, usually a hotspot (the maximum of the curve) developed as shown in FIG. After equilibration, the test was started.

The catalysis test listed below was carried out in a tube reactor with 21 mm inner diameter and a length of 100 mm at 290 ⁰ C average catalyst temperature. Formaldehyde, methanol, dimethyl ether and water were determined by gas chromatography, CO and CO ₂ by IR measurements.

The inventively activated catalyst of the embodiment was tested for the evaluation of its activity and selectivity in the oxidation of methanol to formaldehyde.

The following Table 1 summarizes the experimental results of the catalytic test with the inventively activated catalyst together.

Table 1: Results

FIG. 1 shows the yield of formaldehyde over a reaction time of 2400 hours. The formaldehyde yield remained virtually constant over the entire reaction time and is evidence of the extraordinary long-term stability of a catalyst activated by the process according to the invention.

Claims

claims

1. A method for activating a catalyst for the

Oxidation of methanol to formaldehyde or for the oxidation of propylene to acrolein / acrylic acid comprising the steps of

a) heating a catalyst to a temperature of 160 ⁰ C to 200 ⁰ C in the presence of a gas stream of 0.1 Nm ³ to 10 Nm ³ ;

b) heating the catalyst from 160 ⁰ C to 200 ⁰ C to a temperature of 300 ⁰ C to 350 ⁰ C at a gas flow of 0.1 Nm ³ to 10 Nm ³ and maintaining the temperature for a period of 1 to 84 hours -

2. The method according to claim 1, wherein the temperature in step b) and / or c) for a period of at least

2 to a maximum of 72 hours.

3. The method according to claim 2, wherein the temperature in step b) and / or c) for a period of at least

3 to a maximum of 48 hours.

4. The method according to any one of claims 1 to 3, wherein the

Gas stream in step a), b) and / or c) 1 Nm ³ to 5 Nm ³ .

5. The method according to any one of claims 1 to 4, wherein the gas is air.

6. The method according to any one of claims 1 to 4, wherein the gas is a mixture of methanol, air and inert gas.

A process according to claim 6, wherein the inert gas is nitrogen.

8. The method according to any one of claims 6 or 7, wherein the proportion of methanol is from 0.1 to 10 vol .-%.

9. The method according to claim 8, wherein the proportion of methanol is 1 to 5 vol .-%.

10. The method according to any one of claims 1 to 9, wherein the catalyst contains molybdenum, iron and / or vanadium.

11. The method according to claim 10, wherein molybdenum, iron and / or vanadium are present as oxide.

12. The method according to any one of claims 1 to 11, wherein the catalyst contains at least one promoter compound.

13. The method according to any one of claims 1 to 12, wherein the catalyst contains at least one oxide selected from the group consisting of TiO ₂ , SiO ₂ , Al ₂ O ₃ , MgO, ZrO ₂ , and their mixed oxides.

14. The method according to claim 13, wherein the promoter compound is selected from the group consisting of Li, Na, K, Cs, Rb, Ca, Sr, Ba, P, Sb, Bi, Cu, Ag, Au, Su, Ce and Mixtures thereof.

15. The method according to any one of claims 1 to 14, wherein the

Catalyst comprises an inert support structure.

16. The method according to claim 15, wherein the support structure is nonporous.

17. The method according to claim 15 or 16, wherein the material of the support structure is selected from magnesium silicate (steatite), quartz (SiO ₂ ), porcelain, magnesium oxide, tin dioxide, silicon carbide, rutile, alumina (Al ₂ O ₃ ), zirconium silicate, aluminum silicate, Cersilicate, or mixtures thereof, and metals or alloys.

18. Catalyst for the oxidation of methanol to formaldehyde or for the oxidation of propylene to

Acrolein / acrylic acid activated by a process according to any one of claims 1 to 17.

19.Use of a catalyst according to claim 18 for the production of formaldehyde or acrolein / acrylic acid.

20.Use of a catalyst according to claim 18 or 19 in a tube bundle reactor.