Bimetallic catalyst for the treatment of water containing nitrates

Abstract

A catalyst which, by means of a reduction reaction at ambient temperature, permits the elimination of nitrates and nitrites in waters. The catalyst comprises a combination of a noble metal and a non-noble metal supported on or incorporated into the structure of a support which, in elemental and anhydrous form, has the formula XYMgAl, in which X is at least one noble metal, Y is at least one non-noble metal, Mg is magnesium and Al is aluminium, the Mg and Al preferably forming the structure of a hydrotalcite or a mixed oxide deriving from a hydrotalcite.

1 . A bimetallic catalyst for the treatment of waters containing nitrates, comprising a support and at least one noble metal and at least one non-noble metal, characterized in that the support, in elemental and anhydrous form, has a composition corresponding to the formula  
       XYMgAl,  
       wherein 
 X is at least one noble metal;  
 Y is at least one non-noble metal;  
 Mg is magnesium;  
 Al is aluminium.  
 
     
     
         2 . A catalyst in accordance with  claim 1 , characterized in that Mg and Al form a hydrotalcite structure.  
     
     
         3 . A catalyst in accordance with  claim 1 , characterized in that the noble metal is selected from among Pd, Pt, Ru, Ir and Rh.  
     
     
         4 . A catalyst in accordance with  claim 1 , characterized in that the noble metal is present in the form of noble metal oxide, in a proportion referring to the total weight of the catalyst of 0.1 to 30% by weight, preferably from 0.5 to 15% by weight.  
     
     
         5 . A catalyst in accordance with  claim 1 , characterized in that the noble metal is Pd.  
     
     
         6 . A catalyst in accordance with  claim 1 , characterized in that the non-noble metal is selected from among Cu, Sn, Zn, In, Ni, Ag, Fe or Co.  
     
     
         7 . A catalyst in accordance with  claim 1 , characterized in that the non-noble metal is present in the form of non-noble metal oxide, in a proportion referring to the total weight of the catalyst of 0.5 to 10% by weight.  
     
     
         8 . A catalyst in accordance with  claim 1 , characterized in that the non-noble metal is Cu.  
     
     
         9 . A catalyst in accordance with  claim 2 , characterized in that the metals are incorporated into the hydrotalcite structure by impregnation.  
     
     
         10 . A catalyst in accordance with  claim 2 , characterized in that the metals have been incorporated into the hydrotalcite structure during the synthesis stage of the hydrotalcite.  
     
     
         11 . A catalyst in accordance with  claim 2 , characterized in that at least one non-noble metal is incorporated into the hydrotalcite structure during the synthesis stage of the hydrotalcite and in that at least one noble metal is incorporated by impregnation in a stage subsequent to the synthesis stage.  
     
     
         12 . A catalyst in accordance with  claim 1 , characterized in that the Mg and Al are present in the form of aluminium and magnesium oxides starting from a precursor of hydrotalcite by calcination in air at temperatures between 350 and 800° C., for a period of between 1 and 20 hours.  
     
     
         13 . A catalyst in accordance with  claim 12 , characterized in that at least one noble metal and at least one non-noble metal is incorporated into the structure of the hydrotalcite precursor during the synthesis stage of the hydrotalcite.  
     
     
         14 . A catalyst in accordance with  claim 13 , characterized in that at least one non-noble metal or metals are incorporated into the structure of the precursor during the synthesis stage of the hydrotalcite in order to form oxides of Mg/Al/non-noble metal, and in that at least one noble metal has been incorporated by impregnation in a stage subsequent to the synthesis stage.  
     
     
         15 . A process for treating waters to eliminate nitrates present in liquid phase therein, said process comprising treating said liquid phase with a catalyst in accordance with  claim 1 .  
     
     
         16 . A process in accordance with  claim 15 , characterized in that the reducing agent is selected among hydrogen, formic acid, hydrocarbons and combinations thereof.