A comparative study between transition-metal-substituted Keggin-type tungstosilicates supported on anatase leaf as catalyst for synthesis of symmetrical disulfides

Transition-metal-substituted  (TMS)  polyoxometalates  of  the  general  formula  [SiW9M3O39], (where M = first row transition metal), has been synthesized and supported on anatase by sol–gel method under oil-bath condition. The tetrabutylammonium (TBA) salts of the Keggin-type polyoxotungstates  [SiW9M3O39],  (M = VII, CrII, MnII,  FeII CoII  and NiII),  proved  to  be  green, reusable,  and  highly  efficient  catalysts  for  the  oxidation  of  thiols  and  dithiols  into  the corresponding disulfides using hydrogen peroxide as an oxidizing reagent. This article will be focused on  the discovery of other  transition metal substituted silicotungstate structures with a potential  for  homogeneous  and  heterogeneous  oxidation  catalysis. We  will  focus  on  red/ox active  3d  metals  (e.g.  Fe2+,  Cr2+).The  catalytic  activity  of  these  transition-metal-substituted polyoxometalates  (TMSPOMs) was  strongly  influenced by  the  type of  transition metal  in  the TMSPOMs. Among them, the (TBA7SiV3W9O40) catalytic system showed the highest activity. Nanoparticle  (TBA7SiV3W9O40-TiO2)  has  been  synthesized  by  sol–gel method  under  oil-bath condition  at  100  °C.  The  materials  were  characterized  by  IR,  XRD,  TEM  and  UV–vis techniques.