The present invention relates to the preparation of vanadium based catalyst. In particular, the invention is based on a solid state process for the preparation of vanadium pentoxide supported on a metal oxide catalyst carrier.

The conventional method used to produce a vanadium based catalysts comprises liquid impregnation of a catalyst car ^¬ rier such as titanium oxide with ammonium meta vanadate or vanadyl oxalate dissolved in water followed by calcination of the impregnated carrier to form vanadium pentoxide as layer on the carrier surface. A further method of introducing the vanadium pentoxide on or into a metal oxide carrier is carried out by means of solid state process. This method is simpler as pretreatment of the carrier and the active phase can be avoided when mixing fine vanadium pentoxide powder with the catalyst carrier metal oxide. Since vanadium pentoxide is rather mobile, it will disperse substantially homogeneous on surface of the carrier material and perform a solid state impregnation of the car ^¬ rier material when heated to temperature above 500°C. A dis ^¬ advantage of the solid state process is the high temperature necessary to anchor vanadium pentoxide to the catalyst carrier metal oxide. Sintering of the vanadium pentoxide par ^¬ ticles causes a change in the grain size, and the grain size of V205 increases with increasing the sintering temperature. This invention provides a solid state method for the prepa ^¬ ration of a catalyst comprising vanadium pentoxide supported on a metal oxide catalyst carrier with reduced sintering by addition of an anti-sintering agent during anchoring of the vanadium pentoxide particles to the carrier.

The term "solid state method" or "solid state process" as used hereinbefore and in the following shall be understood in context with present invention that the process or method of coating or impregnating a catalyst carrier material with vanadium pentoxide is carried out in the dry state by thermal spreading and anchoring without use of a liquid or solvent.

Thus, this invention provides a method for the preparation of a catalyst comprising vanadium pentoxide supported on a metal oxide catalyst carrier comprising the steps of a) providing particles of crystalline vanadium pentoxide and particles of a metal oxide catalyst carrier; b) solid state mixing the particles and dispersing the va ^¬ nadium pentoxide particles on surface of the metal oxide carrier particles; and c) anchoring the dispersed vanadium pentoxide particles on surface of the metal oxide carrier particles by calcination at a temperature above 500°C, characterized in that sintering of the vanadium pentoxide particles is suppressed by addition of an anti-sintering metal oxide component during the anchoring in step c) .

The particle size of the vanadium pentoxide particles is preferably between 0.5 and 10 ym, preferably between 2 and 5 ym, to obtain effective distribution and mixing of the carrier particles and the vanadium pentoxide particles. The thus prepared mixture is heated to a temperature of above 500°C, preferably between 550 to 650°C, whereby the vanadium pentoxide particles are effectively dispersed and anchored on surface of the carrier material.

In a specific embodiment, the carrier metal oxide is titania.

Vanadium pentoxide catalysts supported on titania show a very high efficiency in the selective catalytic reduction of nitrogen oxides. The supported V205/Ti02 catalysts possess high oxidation activity and are useful for the removal of hydrocarbons, in particular halogenated hydrocarbons like dioxins from power plant and waste incineration plant emis- sions.

To prevent sintering of the catalyst carrier particles, it is preferred to stabilize the metal oxide carrier with tung ^¬ sten oxide and/or silica.

In stationary applications, the vanadium pentoxide catalyst prepared by the method according to the invention can be used in particle form in fixed bed manner. In automotive applications, the catalyst will typically be applied on a monolithic substrate. For these applications, the metal oxide supported vanadium pentoxide catalyst can be coated on the substrate by use of a washcoat containing the catalyst .

When preparing a washcoat, the prepared supported vanadium pentoxide catalyst is milled or agglomerated to a required particle size and suspended in an organic solvent, optionally with addition of binders, viscosity improvers, foaming agents or other processing aids as known in the art. The thus prepared washcoat is coated on a monolithic sub ^¬ strate in known manner. The coated monolithic substrate is subsequently calcined in an inert atmosphere followed by a calcination sequence in air. The monolithic substrate can consists of corrugated non- woven fibers, preferably comprising glass fibers.

In a further embodiment, the monolithic substrate consists of ceramic extrudates, preferably extrudates of cordierite or silicon carbide.

A further application of the supported vanadium pentoxide catalyst prepared by a method according to the invention is in the manufacture of a full body catalyst by preparing a paste and extruding the past into the full body monolithic catalyst .

Example 2 parts of V205 were mixed thoroughly with 98 parts of either pure Ti02 (mixture 1) or Ti02 modified with 10% W03 (mixture 2) by dry milling with Zr02 beads. Each of the physical mixtures was calcined in static air for 4 h at 575°C. After calcination the surface area of mixture 1 is 48.2 m ² /g and of mixture 2 61.3 m ² /g.