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

Abstract

Introducing mesopores into the channels and cages of conventional micropores CHA (Chabazite) topological structure SAPO-34 molecular sieves can effectively improve mass transport, retard coke deposition rate and enhance the catalytic performance for methanol to olefins (MTO) reaction, especially lifetime and olefins selectivity. In order to overcome the intrinsic diffusion limitation, a novel CO2-based polyurea copolymer with affluent amine group, ether segment and carbonyl group has been firstly applied to the synthesis of SAPO-34 zeolite under hydrothermal conditions. The as-synthesized micro-mesoporosity SAPO-34 molecular sieve catalysts show heterogeneous size distribution mesopores and exhibit slightly decrease of BET surface area due to the formation of defects and voids. Meanwhile, the catalysts exhibit superior catalytic performance in the MTO reaction with more than twice prolonged catalytic lifespan and improvement of selectivity for light olefins compared with conventional microporous SAPO-34. The methodology provides a new way to synthesize and control the structure of SAPO-34 catalysts.

A Review on CO2‐Based Polyureas and Polyurea Hybrids

“…As compared with conventional microporous SAPO-34, the asprepared catalyst exhibited superior catalytic performances (higher selectivity and prolonged catalytic lifetime) in the transformation of methanol to olefin. [76] Besides, the CO 2 -based PUas can also be applied as adhesives. The polycondensation of TAEA with urea led to highly-branched PUas (HBPUas) (a M n of 1976 ~17460 Da, a M w of 2895 ~39865 Da, a PDI of 1.5 ~8.6), which could serve as aldehyde-free wood adhesive resins (Scheme 24).…”

“…used PUa produced from polycondensation of TTD and CO 2 as the structure directing agent or mesoporogen to synthesize a micro‐mesoporosity molecular sieve (SAPO‐34), the addition of PUa made SAPO‐34 exhibited a center‐hollowed cubic‐like morphology with heterogeneous size distribution mesopores, and led to the formation of defects, voids and a decreased acidity. As compared with conventional microporous SAPO‐34, the as‐prepared catalyst exhibited superior catalytic performances (higher selectivity and prolonged catalytic lifetime) in the transformation of methanol to olefin [76] …”

Down the Microporous Rabbit Hole of Silicoaluminophosphates: Recent Developments on Synthesis, Characterization, and Catalytic Applications

“…Traditionally SAPO materials are synthesized hydrothermally, where an aqueous gel is formed from aluminum, phosphorus, and silicon precursors and a structure directing agent (SDA) . The initial acidity helps decompose the precursors into MO 4 tetrahedra within the gel, which combine to give small oligomers, that later form the framework. − The SDA, typically an amine or ammonium ion (though alternatives have been investigated − ), serves as a template for the framework to form around; thus, SDA choice helps dictate the SAPO structure that will be formed. One can rationalize that small SDAs, such as isopropylamine, form systems with small pores, while larger SDAs such as a tetrapropylammonium form larger pored systems.…”

Conversion of Methanol to Olefins over Modified OSDA-Free CHA Zeolite Catalyst

“…The chabazite (CHA) framework contains narrow eight-member ring openings and a large cage that enhances olefin selectivity with minimal aromatics. − Different modifications and synthesis methods of CHA zeolite have been studied. These modifications are either by in situ modifications , or by post-modifications .…”