Polymeric ionic liquid forms of PEI microgels as catalysts for hydrogen production via sodium borohydride methanolysis

Abstract

• Ionic liquid (IL) forms of polyethyleneimine (PEI) as metal free catalyst for H 2 . • NaBH 4 methanolysis via PEI-X (X:Anion) catalyst for green H 2 production. • Highly reusable IL colloidal polymeric catalyst with low Ea in H 2 generation. • Green energy carrier, H 2 release from NaBH 4 via highly regenerable PEI-X catalyst. Ionic liquid (IL) forms of polyethyleneimine (PEI) microgels were prepared using anion exchange and direct acid treatment techniques employing tetrafluoroborate (TFB) and hexafluorophosphate (HFP) anions as well as their corresponding acids, tetrafluoroboric acid (TFBA) and hexafluorophosphoric acid (HFPA), respectively. Then, these polymeric ionic liquids (PIL) of PEI microgels were used as metal-free catalysts for hydrogen (H 2 ) production from sodium borohydride (NaBH 4 ) solution in methanol (methanolysis). The parameters affecting H 2 production rates such as the types of anions, the methods of PIL preparation, temperature, reusability, and regeneration of PEI-based microgels were investigated. In the dehydrogenation reaction of NaBH 4 in methanol catalyzed by PEI-based PIL microgels, the lowest Ea value in the temperature range of −10–40 °C was calculated as 16.0 ± 0.8 kJ/mol for PEI-HFP PIL microgel, prepared by anion exchange method. The reusability studies of PEI-TFB PIL microgels revealed that the catalytic activity was decreased to 89 ± 5% after 5 consecutive use with 100% conversions for every use. Additionally, independent of the anion exchange methods, PEI-based PIL microgels afford catalytic H 2 production from NaBH 4 methanolysis in a wide range of temperatures including subzero temperatures with facile regenerations by the treatments with TFBA and HFPA resulting in 100% recovery of catalytic activities at each regeneration. The metal-free PIL form of PEI microgel catalyst renders much better catalytic performances and advantages than metal nanoparticle-based catalysts for green H 2 production offering viable alternatives in industrial application.