Metal Doped Zeolite and Process for its Preparation

Abstract

The present invention relates to a metal-doped or metal-exchanged zeolite, respectively, wherein the doping metal is present in the zeolite in the form of individual atoms i.e. as monomeric and/or dimeric species. The invention further relates to a process for the preparation of such a metal-exchanged zeolite. Said metal-doped zeolites are useful, in particular, for the reduction of nitrogen oxides.

1 . Metal-exchanged zeolite, wherein the replacement metal is present in the zeolite as a monomeric and/or as a dimeric species. 
   
   
       2 . Zeolite according to  claim 1 , characterized in that the zeolite is selected from the zeolites of the structural types AEL, BEA, CHA, EUO, FAO, FER, KFI, LTA, LTL, MAZ, MOR, MEL, MTW, LEV, OFF, TON and MFI. 
   
   
       3 . Zeolite according to  claim 2 , characterized in that the zeolite is selected from the zeolites with the structural types BEA, MFI, FER, MOR, MTW, ERI. 
   
   
       4 . Zeolite according  claim 2 , characterized in that the pore size of the zeolites is 0.4 to 1.5 nm. 
   
   
       5 . Zeolite according to  claim 4 , characterized in that the replacement metal is catalytically active. 
   
   
       6 . Zeolite according to  claim 5 , characterized in that the replacement metal is selected from the group consisting of Fe, Co, Ni, Ag, Cu, V, Rh, Pd, Pt, Ir. 
   
   
       7 . Zeolite according to  claim 6 , characterized in that the replacement metal is selected from the group consisting of Fe, Co, Ni, Cu. 
   
   
       8 . Zeolite according to  claim 6 , characterized in that the replacement metal is present in a quantity of 1 to 5 wt.-% calculated as metal oxide relative to the total weight of the zeolite. 
   
   
       9 . Zeolite according to  claim 8 , characterized in that more than 50% of the exchangeable sites of the zeolite skeleton are occupied by the replacement metal. 
   
   
       10 . Process for the preparation of a metal-exchanged zeolite according to one of the previous claims, wherein firstly an aqueous suspension of a zeolite is prepared in a sealable reaction vessel, further comprising the steps of
 a) increasing the pH of the suspension to a value in the range from 8 to 10, and setting the oxygen level of the reaction vessel to a value of <10%,   b) reducing the pH to a value in the range from 1.5 to 6,   c) adding a metal salt and reacting over a period of 1 to 15 hours,   d) filtering off and washing the metal-exchanged zeolite.   
   
   
       11 . Process according to  claim 10 , characterized in that the suspension contains 5 to 25 wt.-% zeolite. 
   
   
       12 . Process according to  claim 11 , characterized in that the increase in pH in step a) takes place by adding ammonia in the form of ammonia water. 
   
   
       13 . Process according to  claim 12 , characterized in that the molar ratio of ammonia to zeolite has a value of 0.01 to 0.1. 
   
   
       14 . Process according to  claim 13 , characterized in that the pH is reduced in step b) by adding a mineral acid. 
   
   
       15 . Process according to  claim 14 , characterized in that the pH is set to a value in the range from 1.5 to 3. 
   
   
       16 . Process according to  claim 14 , characterized in that, after reducing the pH, the suspension is heated to a temperature in the range from 80 to 100° C. 
   
   
       17 . Process according to  claim 16 , characterized in that, during the exchange reaction in step c), the oxygen level in the reaction vessel is set to <5%. 
   
   
       18 . Process according to  claim 17 , characterized in that the zeolite obtained after step d) is dried at a temperature of >100° C. 
   
   
       19 . Process according to  claim 17 , characterized in that the process is carried out several times. 
   
   
       20 . Process according to  claim 18 , characterized in that the dried zeolite is calcined at a temperature of 400 to 600° C. 
   
   
       21 . Process according to  claim 20 , characterized in that the calcination takes place under inert gas. 
   
   
       22 . Metal-exchanged zeolite in which the metal is present as a monomeric and/or as dimeric species, obtainable by the process according to  claim 10 .