Enhanced catalytic performance in hydrogen generation from NaBH_4 hydrolysis by super porous cryogel supported Co and Ni catalysts

摘要

The neutral 3-D superporous cryogel is prepared from a poly(acrylamide) (p(AAm)) hydrogel network modified with an amidoximation reaction to induce chemical changes to produce superporous ami-doximated-p(AAm) (amid-p(AAm)) cryogel. The newly-formed strongly ionizable matrices can readily absorb metal ions such as Co(Ⅱ) and Ni(Ⅱ) enabling in situ preparation of corresponding metal nano-particles by NaBH_4 treatments. It is found that the superporous amid-p(AAm)-Co cryogel composite is very effective as a catalyst for H_2 generation from hydrolysis of NaBH_4 in alkaline medium. Furthermore, it is demonstrated that the metal ion loading capacity and catalytic activity of superporous amid-p(AAm)-Co cryogel composites increased with 2nd and 3rd Co(Ⅱ) ion loading and reduction cycles. The hydrogen generation rate of p(AAm)-Co metal composites is increased to 1926.3 ± 1.1 from 1130.2 ± 1.5 (mL H_2) (min)~(-1) (g of M)~(-1). The effect of various parameters such as porosity, metal type, the number of reloading and reduction cycles of the metal ion, and temperature are investigated for the hydrolysis of NaBH_4. The kinetic parameters such as energy, enthalpy and entropy are determined as Ea = 39.7 ± 0.2 kJ mol~(-1), ΔH = 37.2 ± 0.1 kJ mol~(-1) and ΔS = -171.9 ± 0.5 J mol~(-1) K~(-1), respectively.