hmmm... It seems like I brought you on a wrong track with the word "catalytic"...
If I remember correctly, they basically will make use of the different sizes of nitrogen and oxygen molecules. If you push bleed air towards a filter with holes of a size between N2 and O2 molecules, only the N2 molecules will be able to pass the filter. On top of that, some fancy surface treatment will help this filter function... Not to many similarities to the device in our cars, I am afraid...
PickyPerkins: Don`t tell the FAA about your idea with the fuel vapours in the bleed air - they will immediately ground you...
