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

Abstract

Summary 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.

Surface‐modified carbon black derived from used car tires as alternative, reusable, and regenerable catalysts for H 2 release studies from sodium borohydride methanolysis

“…The corresponding reaction mechanism catalyzed by CB‐PEI‐HCl is demonstrated in Figure . It is apparent that the higher the number of protonated amine groups on the modified CB, the better the catalytic performances of the catalyst …”

“…So, increasing the amount of catalyst increases the reaction rate, while decreasing HGR validates that there is an inverse relation between reaction rate and HGR. To minimize the weighing mistake and make a comparison with the similar studies in the literature that generally reports the use of 50 mg of catalyst, this amount of catalyst is also used in rest of studies …”

“…NaBH 4 concentration also plays a significant role in H 2 production reactions from NaBH 4 methanolysis . Therefore, using five different NaBH 4 concentrations, 25, 62.5, 125, 250, and 500 mM in 20 mL ethanol and using 50 mg CB‐PEI‐HCl catalyst, H 2 release studies from NaBH 4 hydrolysis is carried out.…”

“…It is apparent that the higher the number of protonated amine groups on the modified CB, the better the catalytic performances of the catalyst. 11,25,37,38 The reaction mechanism for NaBH 4 methanolysis catalyzed by CB-PEI-HCl is shown Figure S3.…”

“…This reaction can offer numerous advantages such as faster reaction kinetics, lower Ea, and ability to generate H 2 at subzero temperatures even in the presence of metal‐free catalysts with readily regeneration capabilities . Amidst the solvents, methanol provides some accountable advantages over hydrolysis, as H 2 release from NaBH 4 methanolysis can be conveniently run at low temperatures (T < 0°C) efficiently, eg, −20°C, abiding by the following equation: …”