Enhanced <SUP>29</SUP>Si spin-lattice relaxation and observation of three dimensional lattice connectivity in zeolites by two-dimensional <SUP>29</SUP>Si MASS NMR

It is shown that considerable sensitivity enhancement is achieved in the 29Si MASS NMR spectra of highly siliceous zeolites by pretreating the material with oxygen. The presence of adsorbed molecular oxygen in zeolite channels promotes an efficient 29Si spin lattice relaxation via a paramagnetic interaction between the lattice 29Si T-site and the adxorbed oxygen on zeolite channels. This affords an efficient 2-D data collection and leads to increased sensitivity. The utility of this method is demonstrated in a two-dimensional COSY-45 NMR experiment of a high silica zeolte ZSM-5