The palladium based three way catalyst may be palladium or palladium with {HEAD ~ another noble metal} like {TAIL ~ rhodium} 
The palladium based three way catalyst may be palladium or palladium with { HEAD ~ another noble metal } like { TAIL ~ rhodium }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL