Formation of Surface Alkoxy Species with Carbenium-Ion-Like Properties

Formation of Surface Alkoxy Species with Carbenium-Ion-Like Properties 

So far, fewer than 10 types of carbenium ions have been reported to be persistent species formed upon adsorption of olefins or alcohols on acidic zeolites. Instead, surface alkoxy (alkoxide) species with carbenium-ion-like properties are suggested to act, most likely, as catalytic intermediates in reactions catalyzed by acidic zeolites. Various groups have observed that, upon adsorption of olefins or alcohols on acidic zeolites, alkoxy species are formed the observations are based on both in situ and ex situ A MAS NMR spectroscopy (49,50,71-80). 

In Table 2, the A chemical shifts of the carbon atoms of alkoxy species attached to zeolite framework oxygen atoms are summarized. In general, the spins of surface alkoxy species are characterized by relatively long T times (2-5 s), an efficient CP, and broad spinning sideband patterns. The adsorption and 

MAS NMR Chemical Shifts of Surface Alkoxy Species Observed upon the Adsorption of Alkenes or Alcohols on Acidic Zeolites 

Surface alkoxy species Chemical shift (ppm) Adsorbate Zeolite References 

The chemical shift for the carbon atoms attached to zeolite framework oxygen. 

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