Synthesis of tri-level hierarchical SAPO-34 zeolite with intracrystalline micro–meso–macroporosity showing superior MTO performance

Abstract

‡ These authors contributed equally. Electronic Supplementary Information (ESI) available: [TG curves and the detailed MTO results over SAPO-34 catalysts, etc. are provided in the supporting information.]. SeeHierarchically porous zeolites with different level of porosity have emerged as an important class of materials because of their enhanced mass transport and improved catalytic performance. Silicoaluminophosphate zeolite SAPO-34 is one of the best catalysts for methanol-to-olefin (MTO) conversion, but suffers from rapid deactivation due to the narrow 8-ring pore openings. To overcome the inherent diffusion bottleneck and improve the MTO performance, in this work, tri-level hierarchically porous SAPO-34 zeolite with intracrystalline micro-meso-macroporosity has been first synthesized by an Alrich method coupled with the use of polyethylene glycol 2000 polymer under hydrothermal conditions. The as-synthesized hierarchically porous SAPO-34 catalysts exhibit superior catalytic performance in MTO reaction with about six-times prolonged catalytic lifetime and nearly 5% improvement of selectivity for ethylene and propylene than the conventional microporous SAPO-34.Tri-level hierarchically porous SAPO-34 zeolite with intracrystalline micro-meso-macropore structure has been synthesized exhibiting remarkably enhanced performance in methanol-to-olefin reaction.

Performance of Methanol-to-Olefins Catalytic Reactions by the Addition of PEG in the Synthesis of SAPO-34

“…However, a slight decrease can be seen in the concentration of the strong acid sites with the addition of PEG, which is the same result that was reported in Ref. [31]. Therefore, the longer the chain of PEG is, the fewer strong acid sites will occur.…”

“…The BET specific surface areas, micropore surface areas, and micropore volumes of the samples are listed in Table 1. It can be observed that all the samples present type I isotherms according to the IUPAC classification [31,32]. With the addition of PEG, the external surface area of the samples increased, but the micropore surface area almost have no change.…”

Mesoporogen‐Free Synthesis of Hierarchical SAPO‐34 with Low Template Consumption and Excellent Methanol‐to‐Olefin Conversion

“…The microporous sample S M ‐4.0 and hierarchical samples S H ‐4.0, S H ‐3.0, S H ‐2.0, and S H ‐1.6 displayed characteristic type‐I N 2 adsorption–desorption isotherms (Figure a). Compared with sample S M ‐4.0, an apparent uptake near the saturation pressure in the isotherms of all hierarchical SAPO‐34 samples was observed, which was attributed to the presence of voids between the stacked nanometer‐sized crystals and the existence of mesopores or macropores in the hierarchical SAPO‐34 crystals . This was in accordance with the SEM and TEM images.…”

“…Notably, the nanometer‐sized hierarchical catalyst S H ‐3.0 had the longest catalytic lifetime of 366 min and the highest selectivity of ethylene plus propylene of up to 85.4 %, which were much higher than those of the microporous catalyst S M ‐4.0 (126 min, 79.7 %) and other hierarchical catalysts S H ‐4.0 (326 min, 84.9 %), S H ‐2.0 (326 min, 82.4 %), and S H ‐1.6 (306 min, 78.1 %). The MTO catalytic performance of the catalyst S H ‐3.0 was the highest level reported for MTO reactions under similar conditions . More importantly, under the same catalytic conditions (450 °C, WHSV=4 h −1 ) as our previous work, the S H ‐3.0 catalyst possessed more than 40 % decreased consumption of organic template and 0.7 % enhanced selectivity of ethylene and propylene (the detailed catalysis results of our previous work are shown in Table and Figure S10 in the Supporting Information) …”

Performance Enhanced SAPO-34 Catalyst for Methanol to Olefins: Template Synthesis Using a CO2-Based Polyurea

“…Methanol to lower olefins reaction is a critical process for conversion of nonoil resources to chemicals through methanol, and light olefins especially ethylene and propylene have been widely applied in polymerization reaction and petrochemical industry [1][2][3][4][5][6]. Several types of molecular sieves for the MTO reaction have been intensively studied, and the most typically are SAPO-34 [7,8], ZSM-5 [9][10][11], and SSZ-13 [12][13][14]. Among these catalysts, SAPO-34 has drawn the most attention due to its special framework with a CHA cage (9.4 Å) and 8-ring pore openings (0.38 Å 0.38 Å) [15], as well as mild acidity [16][17][18] which result in excellent catalytic performance [3,[19][20][21].…”