TEAOH‐Templated SAPO‐34 Zeolite with Different Crystallization Processes and Silicon Sources: Crystallization Mechanism and MTO Performance

Abstract

SAPO‐34 zeolites were synthesized by one‐, two‐, and three‐stage crystallization processes with fumed silica (FS), acidic silica sol (AS), basic silica sol (BS) and tetraethoxysilane (TEOS) as silicon sources. Properties of samples were characterized by XRD, SEM, EDX, N2‐adsorption/desorption, NH3‐TPD and 29Si NMR. In contrast with one‐ and two‐stage processes, the three‐stage one favors the formation of SAPO‐34s with higher purity, higher Si/Al ratio, smaller crystallite/crystal size, better dispersion and more acidic sites. Crystallization mechanism was proposed. It is supposed that three‐stage process favors the formation of high supersaturated SBUs (secondary building units) and CBUs (composite building units) before nucleation. Thus massive nuclei are formed during nucleation and well‐dispersed small size SAPO‐34 crystals are formed in three‐stage process. Three‐stage SAPO‐34s are longer catalytic lifetime and better olefin selectivity in MTO process. TEOS‐3 has the best MTO performance. It was found that acidity of sample and mesopores in 2–4 nm range have little effect on the MTO performance of SAPO‐34. Catalytic lifetime and olefin selectivity are mainly depending on the size of crystallites, the dispersity of crystallites, and the purity of SAPO‐34.

Synthesis of SAPO-34 Nanoplates with High Si/Al Ratio and Improved Acid Site Density

“…Both the Si/Al ratio and Si incorporation, however, were found to show opposite behavior. These observations can also be understood by considering that many researchers get SAPO-5 and amorphous phases with thick gel systems [46,47]. The SAPO-5 is a low Si phase, and the amorphous phase forms with segregated Si in the system.…”

Exclusive SAPO-seeded synthesis of ZK-5 zeolite for selective synthesis of methylamines

“…Fig. 1c shows the 29 Si MAS NMR spectrum of ZK-5, in which the signals at −110 and −104 ppm can be assigned to Q 4 and Q 3 , respectively, and those at −99 and −94 ppm can be assigned to Q 2 . 18,19 The 27 Al MAS NMR spectrum of ZK-5 (Fig.…”

“…Considering that the Fig. 1 Experimental and simulated XRD patterns (a), SEM image (b), 29 Si MAS NMR spectrum (c), and 27 Al MAS NMR spectrum of the as-synthesized ZK-5 (d); N 2 adsorption (•) and desorption (○) isotherms of H-ZK-5 (e); TG curve of the as-synthesized ZK-5 (f ). Seeds.…”

“…After heating for 1 and 2 d, the intensity of the diffraction peaks of CHA is significantly enhanced, indicating an obvious growth of CHA crystals. The intensity of these diffraction peaks is gradually weakened and the peaks of the KFI phase emerge along with the heating time To further ascertain the state of the SAPO-34 seed in the initial mixture, we conducted 27 Al, 29 Si, and 31 P MAS NMR analyses on the SAPO-34 crystals and the initial mixture containing the SAPO-34 seed prior to loading into an autoclave. The corresponding spectra are shown in Fig.…”

Synthesis of SAPO‐34 Zeolite from Laponite and Its Application in the MTO Reaction

“…Zeolites have been widely applied in the chemical industry benefiting from their uniform molecular sized pores, excellent catalytic activity and great stability , . Silicoaluminophosphate zeolite SAPO‐34 with CHA topological structure has been proven to be the best catalyst for the production of ethylene and propylene in the methanol to olefins (MTO) reaction because of its shape selectivity and moderate strength of acidity .…”