Kinetic studies of reversible hydrogen storage over sodium phenoxide-cyclohexanolate pair in aqueous solution

Abstract

Abstract With reduced dehydrogenation enthalpy change and reduced dehydrogenation temperature compared with its phenol-cyclohexanol pair, sodium phenoxide-cyclohexanolate pair developed recently is promising for large-scale energy storage and long-distance hydrogen transportation. In the present work, we investigate the kinetic behavior of the pair in the hydrogenation and dehydrogenation in water over three commercial catalysts. It is shown that 5% Ru/Al2O3 and 5% Pt/C perform well in the hydrogenation and dehydrogenation, respectively. Kinetic analyses show that the hydrogenation of sodium phenoxide is of first-order with respect to H2 pressure and zero-order to the concentration of sodium phenoxide in the presence of Ru/Al2O3 catalyst. >99% conversion of cyclohexanol and >99% selectivity to phenoxide can be achieved in the dehydrogenation catalyzed by Pt/C catalyst and in the presence of NaOH at 100 °C, where cyclohexanone was observed as an intermediate. According to the kinetic analysis, the hydrogenation of sodium phenoxide may undergo the hydrolysis and hydrogenation pathway. For the dehydrogenation, an intermediate, i.e., cyclohexanone, was detected and two possible pathways are proposed accordingly.