NisNa 64H 6(sio2)1 O6(A102)8 6 Ni 3Na2 4 3 0 2 ) 3&4102)56 Ni20Na16(Si02) 136(402)56 Ni~1Na24(Si02)1o6(A102)s6

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The acid-base properties of silica-magnesia gels have been examined by an i.r. spectroscopic study of the adsorption of ammonia and pyridine and by a study of the cationic exchange capacity of the gels. The basic properties appear to be related to the presence either of hexacoordinated magnesium atoms or OH groups, the latter being located on tetracoordinated magnesium atoms or on neighbouring silicon atoms. The basic centres are related to hexacoordinated magnesium atoms or to OH groups located on neighbouring tetracoordinated magnesium atoms. The acidic centres appear to result from the existence of structural Lewis sites which are formed during magnesium insertion into the network.