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