Very fast H2production from the methanolysis of NaBH4by metal-free poly(ethylene imine) microgel catalysts

Abstract

The polyethyleneimine (PEI) microgels prepared via microemulsion polymerization are protonated by hydrochloric acid treatment (p-PEI) and quaternized (q-PEI) via modification reaction with methyl iodide and with bromo alkanes of different alkyl chain lengths such as 1-bromoethane, 1-bromobutane, 1-bromohexane, and 1-bromooctane. The bare p-PEI and q-PEI microgels are used as catalysts directly without any metal nanoparticles for the methanolysis reaction of sodium borohydride (NaBH4). Various parameters such as the protonation/quaternization reaction on PEI microgels, the amount of catalyst, the amount of NaBH4, and temperature are investigated for their effects on the hydrogen (H2) production rate. The reaction of self-methanolysis of NaBH4 finishes in about 32.5 min, whereas the bare PEI microgel as catalyst finishes the methanolysis of NaBH4 in 22 min. Surprisingly, it is found that when the protonated PEI microgels are used as catalyst, the same methanolysis of NaBH4 is finished in 1.5 min. The highest H2 generation rate value is observed for protonated PEI microgels (10 mg) with 8013 mL of H2/(g of catalyst.min) for the methanolysis of NaBH4. Moreover, activation parameters are also calculated with activation energy value of 23.7 kJ/mol, enthalpy 20.9 kJ/mol, and entropy −158 J/K.mol. Copyright © 2016 John Wiley & Sons, Ltd.