Aldose to ketose isomerization is one of the key steps forconverting cellulosic biomass to platform chemicals such as HMF.Epimerization, which involves alteration of stereochemistry at specificstereocenters, on the other hand, is the key to generatingnon-naturally abundant forms of sugars. Sn-Beta zeolite has beenshown to be an effective catalyst for these transformations. Numerousexperimental and computational studies point to the openhydrolyzed Sn site to be responsible for the catalytic activity. However,the role of the silanol group adjacent to the active Sn site remainsunclear. In this work, we employ density functional calculationsto elucidate the role of the silanol group in the isomerizationand epimerization of open chain form of glucose. We find that thesilanol group plays an important role in the isomerization reaction,wherein hydride transfer and subsequent proton transfer occurs ina single step with a lower energy of activation. Epimerization, onthe other hand, proceeds via mechanism similar to the B�lik mechanismand has a lower activation barrier when silanol group does notparticipate directly in the transition state.

Role of silanol group in Sn-Beta zeolite activity for isomerization and epimerization of glucose

247th National Meeting (2014)

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