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