COMPARED FORMATION OF LIGHT PRODUCTS IN N-ALKANE CRACKING IN SAPO-37 AND SI-AL FAUJASITES - ENERGY GRADIENT SELECTIVITY

The selectivity to light hydrocarbons (C-2, C-3) in the cracking of al kanes expressed by the C-2/C-4 or C-3/C-4 ratios is the highest for ze olites with a heterogeneous distribution of charges. This energy gradi ent selectivity concept found for Si-Al zeolites is shown to extend to Sapo-37. The two ratios are lower for the template-free Sapo-37 pretr eated at 873 K and having isolated SiO4 tetrahedra in the framework. A t higher pretreatment temperature or/and high Si content (Si atomic ra tio > 0.125) the production of light hydrocarbons is increased in the heterogeneous energy gradient present in the cage, related to the pres ence of silicon islands.