Modification of Non-template Synthesized Ferrierite/ZSM-35 forn-Butene Skeletal Isomerization to Isobutylene

Abstract

Non-template synthesized ferrierite/ZSM-35 has been successfully modified by removal of non-shape selective acid sites and lowering of the number of acid sites. Modified materials were extensively studied by XRD, FT-IR, NMR, XPS, ammonia TPD, and kinetic evaluations for skeletal isomerization ofn-butene to isobutylene. Removal of non-shape selective acid sites from non-template synthesized ferrierite/ZSM-35 greatly suppresses butene dimerization reactions. These non-shape selective acid sites are located inside larger internal pores (as compared to the zeolitic pores) and on the surface of non-template synthesized ferrierite/ZSM-35 materials due to their lower crystallinity. Such non-shape selective acid sites were removed via framework dealumination of the surface with acid treatment. Lowering of the number of acid sites of non-template synthesized ferrierite/ZSM-35 decreases interactions of butene intermediates on adjacent acid sites and was achieved via framework dealumination by steaming. Steaming of non-template synthesized ferrierite/ZSM-35 at higher temperatures or higher steam pressures produces more dealumination and, accordingly, further lowering of the number of acid sites. The presence of Na+/K+ions gives more resistance to framework dealumination during steaming and the same potential for removing strong and weak acid sites. However, steaming of ferrierite/ZSM-35 of hydrogen form leads to removal of greater amounts of strong acid sites than weak acid sites. Studies have shown that steaming of non-template synthesized ferrierite/ZSM-35 of Na+/K+forms followed by NH4+ion exchange and acid washing is an effective modification procedure. Catalytic performances for such modified materials are very similar to those for template-synthesized materials, with respects to yields, selectivities, and catalytic stability.