Preparation of Diesel Oxidation Catalyst Via Deposition of Colloidal Nanoparticles

Abstract

The present invention relates to a process for preparing a catalyst, at least comprising the steps of adding a protecting agent to an aqueous solution of a metal precursor to give a mixture (M1), adding a reducing agent to mixture (M1) to give a mixture (M2), adding a support material to mixture (M2) to give a mixture (M3), adjusting the pH of mixture (M3), and separating the solid and liquid phase of mixture (M3). Furthermore, the present invention relates to the catalyst as such and its use as diesel oxidation catalyst.

1 . A process for preparing a catalyst, at least comprising the steps:
 (1) adding a protecting agent to an aqueous solution of a metal precursor to give a mixture (M1),   (2) adding a reducing agent to mixture (M1) to give a mixture (M2),   (3) adding a support material to mixture (M2) to give a mixture (M3),   (4) adjusting the pH of mixture (M3),   (5) separating the solid and liquid phase of mixture (M3).   
     
     
         2 . The process of  claim 1 , wherein the protecting agent is selected from soluble homo- and co-polymers having one or more amino, amido, carboxylic, aldehydic, or hydroxyl groups, and organic molecules having one or more amino, amido, carboxylic, aldehydic, or hydroxyl groups and mixtures thereof. 
     
     
         3 . The process of  claim 1 , wherein the protecting agent is selected from poly(vinylalcohol), poly(vinylpyrrolidone), poly-(ethyleneimine), poly(acrylic acid), carbohydrates or alkali metal citrates. 
     
     
         4 . The process of  claim 1 , wherein the metal precursor is selected from metal salt of platinum, palladium, rhodium, gold and silver or mixtures thereof. 
     
     
         5 . The process of  claim 1 , wherein the reducing agent is selected from alkali metal borohydrides, hydrazine, formaldehyde, alkali metal citrates, amino borane complexes, gaseous hydrogen and carbon monoxide. 
     
     
         6 . The process of  claim 1 , wherein the support material is selected from aluminum oxide, silicon oxide, cerium oxide, zirconium oxide, titanium oxide, magnesium oxide alone or as mixtures and/or solid solutions from these support materials. 
     
     
         7 . The process of  claim 1 , wherein in step (4) the pH is adjusted to a value in the range from 2 to 7. 
     
     
         8 . The process of  claim 1 , wherein in step (5) the solid and liquid phase of mixture (M3) are separated by filtration or evaporation of the solvent. 
     
     
         9 . A catalyst obtainable by a process according to  claim 1 . 
     
     
         10 . The catalyst according to  claim 9 , comprising platinum and palladium as metals, wherein after treatment of the catalyst at 800° C. for 12 h in an oxidizing atmosphere (10% H 2 O in air), no less than 36% of the metal particles have an average diameter below 22 nm. 
     
     
         11 . The catalyst according to  claim 9 , comprising platinum and palladium as metals, wherein after treatment of the catalyst at 800° C. for 12 h in an oxidizing atmosphere (10% H 2 O in air), no less than 90% of the metal particles are constituted by both Pt and Pd. 
     
     
         12 . A process for oxidizing diesel exhaust wherein the diesel exhaust is brought into contact with a catalyst according to  claim 9 .