Highly regenerable ionic liquid microgels as inherently metal-free green catalyst for H2 generation

Polymeric ionic liquid (PIL) microgel of poly([2-(methacryloyloxy)ethyl]trimethylammonium chloride) (p(MTMA)) was synthesized by using an inverse suspension polymerization technique. The anion-exchanged PIL microgels via chloride replacement from p(MTMA) were prepared as p(MTMA)-potassium thiocyanate (p(MTMA)-KSCN), p(MTMA)-sodium tetrafluoroborate (p(MTMA)-NaBF4), and p(MTMA)-sodium dicyanamide (p(MTMA)-NaN(CN)(2)) microgels by treatment with corresponding salts of potassium thiocyanate (KSCN), sodium tetrafluoroborate NaBF4, and sodium dicyanamide NaN(CN)(2) in aqueous media. The prepared microgels were found to be efficient metal-free catalysts, and their catalytic activity in H-2 production from the methanolysis of NaBH4 was investigated. Moreover, various parameters affecting H-2 production such as the effect of microgel size, the concentration of NaBH4, the effect of the anion in the microgel, the reusability of the microgel, and temperature were investigated. The Ea value calculated for the methanolysis reaction of NaBH4 catalyzed by p(MTMA) microgels was found as 24.1 +/- 0.7kJmol(-1) ranging from -15 to 45 degrees C, and this Ea value is lower than some Ea values for the same reaction. Interestingly, 10-time successive use of p(MTMA) microgel as catalyst in NaBH4 methanolysis reduced its catalytic activity to 49%, whereas the anion-exchanged forms of p(MTMA) microgel, p(MTMA)-KSCN, p(MTMA)-NaBF4, and p(MTMA)-NaN(CN)(2) only reduced their catalytic activity to 89, 86, and 79%, respectively, after 10 consecutive uses. Therefore, these anion-exchanged microgel catalysts are highly efficient in comparison with virgin p(MTMA) microgels for regenerable H-2 generation from the methanolysis of NaBH4.