An alternative to metal catalysts: Poly(4-vinyl pyridine)-based polymeric ionic liquid catalyst for H2 generation from hydrolysis and methanolysis of NaBH4

Abstract

Monodispersed p(4-VP) (poly(4-vinyl pyridine)) polymeric particles were synthesized via self-emulsion polymerization and modified with 1,2-dibromobutane 1,4-dibromobutane and 1,6-dibromobutane, to obtain polymeric ionic liquid (PIL) particles of poly(4-vinyl pyridine)-dibromoethane (p(4-VP)++C2), poly(4-vinyl pyridine)-dibromobuthane (p(4-VP)++C4), and poly(4-vinyl pyridine)-dibromohexane (p(4-VP)++C6) particles. Highly monodispersed p(4-VP), p(4-VP)++C2, p(4-VP)++C4 and p(4-VP)++C6 particles were obtained with the sizes of 335 ± 10, 451 ± 17, 432 ± 13 and 443 ± 24 nm, and the zeta potential values of 6.3 ± 0.6, 31.2 ± 2.1, 33.3 ± 1.0 and 35.5 ± 1.1 mV. PIL-metal composites of p(4-VP)++C6-Co p(4-VP)++C6-Ni and p(4-VP)++C6-Fe particles were prepared by reducing CoCl2, NiCl2 and FeCl3 metal salts loaded into p(4-VP)++C6 microgels and then reducing with NaBH4. The prepared PIL-metal composites and PIL particles were used as catalysts in H2 generation from the hydrolysis and methanolysis of NaBH4. It was found that the prepared PIL-metal composites (e.g., p(4-VP)++C6-Co) showed better catalytic performances than PIL particles (e.g., p(4-VP)++C6) for the hydrolysis reaction of NaBH4 whereas, PIL catalytic performances were much better than PIL-metal composites for the methanolysis of NaBH4. Various parameters affecting the hydrolysis and methanolysis reactions of NaBH4 such as the types of PIL/PIL-metal particle, the amount of PIL particles, the amount of NaBH4 and temperature were investigated. A very high hydrogen generation rate (HGR) value for the methanolysis reaction of 500 mM NaBH4 catalyzed by 50 mg p(4-VP)++C6 at 25 °C was calculated as 9125 ± 177 mL H2 (g of catalyst min)−1. Furthermore, very low activation energy (Ea), 13.78 ± 0.23 kJ mol−1 was calculated for the methanolysis of NaBH4 catalyzed by p(4-VP)++C6 at temperatures in the range of 0–40 °C.