SYNTHESIS AND CHARACTERIZATION OF THE LARGE-PORE MOLECULAR-SIEVE SAPO-46

Synthesis of a novel large-pore SAPO-46 molecular sieve has been descr ibed. The effect of the organic template (di-n-propylamine) and silica concentration in the synthesis gel on the crystallinity and phase pur ity of SAPO-46 was studied. Samples were characterized by X-ray diffra ction (XRD), magic-angle spinning (MAS) NMR spectroscopy, FTIR spectro scopy, thermal analysis (TG and DTA), chemical analysis, scanning elec tron microscopy and EDAX microprobe analysis, SAPO-46 had a lower ther mal stability than SAPO-5, SAPO-37 and MgAPO-36. Silicon substitution for phosphorus at crystallographically distinct sites has been suggest ed to cause the creation of two different silicon environments in SAPO -46. The extent of silicon substitution was large and temperature-prog rammed desorption (TPD) of ammonia has shown high concentration of ac id sites. SAPO-46 showed high activity for alkylation of toluene with methanol that was comparable with that of ZSM-5, but showed no para se lectivity. However, as the reaction proceeded, para selectivity develo ped due coking at the pore mouth.