Preferred for the heteropolyacid is {HEAD ~ at least one type} selected from among silicomolybdic acid, {TAIL ~ phosphorotungstic acid}, silicotungstic acid, phosphoromolybdic acid and silicotungstomolybdic acid 
selected from among
Preferred for the heteropolyacid is { HEAD ~ at least one type } selected from among silicomolybdic acid , { TAIL ~ phosphorotungstic acid } , silicotungstic acid , phosphoromolybdic acid and silicotungstomolybdic acid
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH