Catalytic activity of metal‐free amine‐modified dextran microgels in hydrogen release through methanolysis of <scp> NaBH ₄ </scp>

Abstract

Polymeric microgels were prepared from dextran (Dex) by crosslinking linear natural polymer dextran with divinyl sulfone (DVS) with a surfactant-free emulsion technique resulting in high gravimetric yield of 78.5 ± 5.3% with wide size distribution. Dex microgels were chemically modified, and then used as catalyst in the methanolysis of NaBH4 to produce H2. The chemical modification of Dex microgel was done on epichlorohydrin (ECH)-reacted Dex microgels with ethylenediamine (EDA), diethylenetriamine (DETA), and triethylenetetraamine (TETA) in dimethylformamide (DMF) at 90°C for 12 hours. The modified dextran-TETA microgels were protonated using treatment with hydrochloric acid (HCl) and m-Dex microgels-TETA-HCl was found to be a very efficient catalyst for methanolysis of NaBH4 to produce H2. The effects of reaction temperature and NaBH4 concentration on H2 generation rates were investigated and m-Dex microgels-TETA-HCl catalyst possessed excellent catalytic performances with 100% conversion and 80% activity at end of 10 consecutive uses and was highly re-generatable with simple HCl treatment. Interestingly, m-Dex microgels-TETA-HCl catalyst can catalyze NaBH4 methanolysis reaction in a mild temperature range 0 to 35°C with Ea value of 30.72 kJ/mol and in subzero temperature range, −20 to 0°C with Ea value of 32.87 kJ/mol, which is comparable with many catalysts reported in the literature.