ZIRCONIA-BASED COMPOSITIONS FOR USE IN PASSIVE NOx ADSORBER DEVICES

Abstract

A passive NO X adsorbent includes: palladium, platinum or a mixture thereof and a mixed or composite oxide including the following elements in percentage by weight, expressed in terms of oxide: 10-90% by weight zirconium and 0.1-50% by weight of least one of the following: a transition metal or a lanthanide series element other than Ce. Although the passive NO X adsorbent can include Ce in an amount ranging from 0.1 to 20% by weight expressed in terms of oxide, advantages are obtained particularly in the case of low-Ce or a substantially Ce-free passive NOx adsorbent.

1 - 20 . (canceled) 
     
     
         21 . A passive NOx adsorbent comprising: palladium, platinum or a mixture thereof and a mixed or composite oxide comprising the following elements in percentage by weight, expressed in terms of oxide: 10-90% by weight zirconium; and 0.1-50% by weight of least one of the following: a lanthanide series element other than Ce, comprising Pr; and a transition metal comprising at least one of the following metals selected from W, Mn, and Fe. 
     
     
         22 . A passive NOx adsorbent according to  claim 21  further comprising at least one of Y, La and Nd as said lanthanide series element other than Ce. 
     
     
         23 . A passive NOx adsorbent according to  claim 21 , comprising Mn as said transition metal in an amount of 0.1 to 20% by weight and Pr as said lanthanide series element other than Ce in an amount of 0.5 to 30% by weight, wherein a total amount of Pr and Mn is not more than 50% by weight. 
     
     
         24 . A passive NOx adsorbent according to  claim 23  further comprising at least one of W and Fe as said transition metal. 
     
     
         25 . A passive NOx adsorbent according to  claim 23  further including at least one of Y, La and Nd as said lanthanide series element other than Ce. 
     
     
         26 . A passive NOx adsorbent according to  claim 23  further comprising an element from Group 14 of the Periodic Table in an amount ranging from 0.1 to 20% by weight expressed in terms of oxide. 
     
     
         27 . A passive NOx adsorbent according to  claim 21  comprising Ce in an amount ranging from 0.1% to not more than 20% by weight expressed in terms of oxide. 
     
     
         28 . A passive NOx adsorbent according to  claim 21  comprising Ce in an amount ranging from 0.5 to not more than 5% by weight expressed in terms of oxide. 
     
     
         29 . A passive NOx adsorbent according to  claim 21  with the proviso that the passive NOx adsorbent is substantially free of Ce. 
     
     
         30 . A passive NOx adsorbent according to  claim 21  with a minimum fresh NOx storage capacity of 7.5 μmol/g after 5 minutes at 120° C. 
     
     
         31 . A passive NOx adsorbent according to  claim 21  with a minimum aged NOx storage capacity of 5 μmol/g after 5 minutes at 120° C. 
     
     
         32 . A passive NOx adsorbent according to  claim 21  in which the mixed or composite oxide includes Mn as said at least one transition metal and optional Ce, with a minimum fresh NOx storage capacity of at least 40 μmol/g after 5 minutes at 120° C. 
     
     
         33 . A passive NOx adsorbent according to  claim 21  in which the mixed or composite oxide includes Mn as said at least one transition metal and optional Ce, with a minimum aged NOx storage capacity of at least 19 μmol/g after 5 minutes at 120° C. 
     
     
         34 . A passive NOx adsorbent according to  claim 21  in which the mixed or composite oxide includes Mn as said at least one transition metal, with a minimum fresh NOx storage capacity of at least 50 μmol/g after 5 minutes at 120° C. 
     
     
         35 . A passive NOx adsorbent according to  claim 21  in which the mixed or composite oxide includes Mn as said at least one transition metal, with a minimum aged NOx storage capacity of at least 45 μmol/g after 5 minutes at 120° C. 
     
     
         36 . A monolithic substrate supporting a washcoat, said washcoat comprising said passive NOx adsorbent according to  claim 21 . 
     
     
         37 . A passive NOx adsorbent according to  claim 21  in combination with a Selective Catalytic Reduction catalyst. 
     
     
         38 . A method for reducing nitrogen oxides (NOx) present in a lean gas stream comprising at least one of nitric oxide (NO) and nitrogen dioxide (NO 2 ), comprising the steps of:
 (i) providing the passive NOx adsorbent according to  claim 21  in the lean gas stream;   (ii) adsorbing NOx from the lean gas stream on or in the passive NOx adsorbent at a temperature below 200° C.;   (iii) thermally net desorbing NOx from the passive NOx adsorbent in the lean gas stream at 200° C. and above;   (iv) catalytically reducing the NOx on a downstream catalyst situated downstream of the passive NOx adsorbent, with at least one of the following reductants: a nitrogenous reductant, a hydrocarbon reductant, hydrogen and a mixture thereof.   
     
     
         39 . A method according to  claim 38  wherein the lean gas stream emanates from a gasoline fueled or diesel fueled engine.