Article pubs.acs.org/IECR
Preparation and Characterization of High-Performance Perfluorosulfonic Acid/SiO2 Nanofibers with Catalytic Property via Electrospinning Pei-Pei Lu, Zhen-Liang Xu,* Hu Yang, and Yong-Ming Wei State Key Laboratory of Chemical Engineering, Membrane Science, Engineering R&D Lab, Chemical Engineering Research Center, East China University of Science, Technology (ECUST), 130 Meilong Road, Shanghai 200237, China S Supporting Information *
ABSTRACT: Polymer nanofiber-supported perfluorosulfonic acid (PFSA)/SiO2 catalysts are successfully fabricated by electrospinning method from polymer/nanoparticle suspensions. This kind of catalyst has a large number of active acid sites and high specific surface area up to 85.6 m2/g. Scanning electron microscope images reveal that the catalysts present high porosity and inner-connected porous structure which varies much with SiO2 loading. Nitrogen adsorption−desorption measurements demonstrate a wide distribution of pore sizes inside the composites. Catalysts of different compositions are evaluated in esterification in a batch reactor under various conditions, and the results indicate that those of 20 wt % PFSA loading have the best activity of unit PFSA. Supporting PFSA by a nanofibrous matrix enhances liquid holdups inside the catalysts and offers accessibility of the acid sites, and therefore improves the activity of the catalysts. Moreover, these catalysts allow recovery at high percentages and regeneration with high activity. from 5 to 20 wt %.10 They reported that 5 and 13 wt % Nafion/ SiO2 catalysts had similarly high activity, but an even higher Nafion content (20 wt %) did not further improve the catalytic activity. Immobilization of PFSA resin on porous SiO2 particles has achieved great success in many heterogeneous reactions in view of the improvement of surface acid sites. However, these PFSA/SiO2 composite catalysts are either brittle or discontinuous in formation with aggregations from several to several tens of nanometers,2,11 which causes difficulties in packing and retrieval. Moreover, to reduce the external and internal diffusion resistances during the reaction, high stirring speed and small catalyst diameter are requied.11 These drawbacks slow down the development of PFSA as a catalyst in industry applications. This paper focuses on an innovative PFSA/SiO2 composite, of which the PFSA/SiO2 catalyst is immobilized on a continuous electrospun nanofiber support. Previous research provides evidence that the electrospun nanofiber is an ideal catalyst support due to the high SSA which is appropriate for attachment of nanoparticles, ions, and functional groups, and the inner-connected structure which offers enough mechanical strength as a support matrix.12,13 Besides, the highly porous structure ensures the permeability of the support matrix and the accessibility of the acid sites, providing distinct advantages for reducing the pressure drop and, if designed suitably, avoiding the transfer resistance inside the matrix.14,15 In our previous works, PFSA resin was successfully immobilized on nanofibers by an electrospinning method from polymer solutions16 or polymer/CaCO3 suspensions.17
1. INTRODUCTION Perfluorosulfonic acid (PFSA) resin has been used as a heterogeneous acid catalyst for a range of reactions;1 however, in nonpolar solvents or for gas phase reactions the activity is limited due to the extremely low surface area of the polymer beads (
