Dependence of ethene dimerization activity and selectivity on Ni I in ion-exchange vs. framework sites in SAPO-5 and SAPO-11 materials

Abstract

Dehydrated nickel containing silicoaluminophosphates SAPO-11 and SAPO-5 materials are catalytically active for ethene dimerization. There is a striking difference between the catalytic activity due to nickel(I) species in ion-exchange and in framework positions. Both the ethene dimerization activity and the selectivity for the formation of n-butenes is dependent on the location (ion-exchange vs. framework site) of the nickel(I) species and on the channel size (10-ring vs. 12-ring) of the supporting materials. EPR studies show an isolated nickel(I) species A (g∥= 2.489 and g⊥= 2.108) which transfers to species E (g1= 2.680, g2= 2.474 and g3= 1.961) after ethene adsorption. This species has been assigned to an NiI–(C2D4)n complex. Subsequently, after heating to 353 K, species B1 (g1= 2.720, g2= 2.259 and g3= 1.996), B2 (g1= 2.363, g2= 2.174 and g3= 2.067) and B3 (g∥= 2.052 and g⊥= 2.007), depending of the type of SAPO material, are observed with simultaneous butene formation, detected by gas chromatography. Electron spin-echo modulation analysis allows the assignment of B1, B2 and B3 to NiI–C4D8 complexes with different geometries.