Insights into the Nature of the Active Sites of Tin‐Montmorillonite for the Synthesis of Polyoxymethylene Dimethyl Ethers (OME)

In this study,we reportthat intercalationof tin into montmor-illoniteclay (Sn-MMT)boostscatalyticactivityfor the synthesisof polyoxymethylenedimethylethers,a promisingdieselfueladditive.This increasein activityis attributedto the formationof a hierarchicalcatalystdisplayinghighsurfaceareawithaccessibleBrønstedand Lewisacid sites.Extensivecharacter-izationsuchas MAS-NMR,XRD and in-situDRIFTSconfirmedthat tin insertioninducedreorganizationof the clay layersintoa disorganizedhouse-of-cardsstructure.It also revealedthat tinresidedbetweenthe clay layersas defectiveSnO2nanocrystalsstabilizedby the negativechargeof MMT.The sourceof acidityin Sn-MMTwas studiedby comparingit withtwo similarmaterials,namelySn(OH)4, and thermallytreatedSn-MMT.Lowactivitymeasuredfor isolatedhydroxylatedSnO2nanoparticlesillustratesthe importanceof havingclayand tin in closeproximity.Meanwhile,deactivationuponthermaltreatmentoccurredvia sinteringof the tin phaseand diffusionof theprotonsinsidethe layers.Sn-MMTacidityis attributedto thecombinationof SiOHAl groups,formedas a by-productofSnO2crystallization,and undercoordinatedSn surfacesites,stabilizedby the negativechargeof MMT.