Preferred catalyst comprises potassium antimonate together with potassium sulfate and {HEAD ~ minor amounts} of {TAIL ~ zinc sulfate} and cupric sulfate  
of
Preferred catalyst comprises potassium antimonate together with potassium sulfate and { HEAD ~ minor amounts } of { TAIL ~ zinc sulfate } and cupric sulfate
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH