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