Highly loaded well dispersed stable Ni species in NiXMg2AlOY nanocomposites: Application to hydrogen production from bioethanol

Abstract

Inexpensive NiXMg2AlOY nanocomposites with high Ni content (Ni wt% >40%) are developed as efficient catalysts for the sustainable hydrogen production from a mixture of ethanol and water at low temperature. The NiXMg2AlOY nanocomposites are composed of small and uniform nanoparticles (4–6nm) of NiO, Ni–Mg–(Al)–O and/or MgO. The strong interactions existing between Ni2+ cations and Mg2+ and/or Al3+ cations either in the Ni–Mg–(Al)–O solid solution and/or at the interface of nanoparticles of NiO and/or Ni–Mg–(Al)−O make the catalyst highly active and stable. The behavior of the solids is analyzed in the presence of low and high concentrations of ethanol while maintaining a H2O/EtOH molar ratio of 3. The NiXMg2AlOY catalysts are shown to be efficient toward H2 production between 250 and 650°C. In the presence of low concentration of ethanol, on the highly loaded Ni compound (Ni12Mg2AlOY), total conversion of ethanol is obtained at 250°C without formation of CO and carbon, and at 300°C a H2 yield of 3molmolEtOH−1 is obtained without the formation of CO, exhibiting a remarkable stability with the time on stream even if some carbon is formed. In high concentration of ethanol, total conversion of ethanol is obtained at 450°C on the highly loaded Ni compound (Ni12Mg2AlOY). In such conditions, a stable co-generation of carbon nanofibrous materials which amount increases with Ni content is also obtained. The catalytic stability is related to the type and morphology of the carbon species formed. The correlations among the catalyst properties, the catalytic performances and the characterizations are thoroughly discussed.