O3 catalyst comprising of {HEAD ~ a mixture} of from 2.5 to 7.5% wt of Cr2 O3, 5 to 17.5% wt of Al2 O3 and {TAIL ~ 75 to 85% wt} of a Zn ZSM 5 zeolite or a Zn ZSM 5 zeolite/asbestos 
of from
O3 catalyst comprising of { HEAD ~ a mixture } of from 2.5 to 7.5 % wt of Cr2 O3 , 5 to 17.5 % wt of Al2 O3 and { TAIL ~ 75 to 85 % wt } of a Zn ZSM 5 zeolite or a Zn ZSM 5 zeolite / asbestos
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH