Hydrogen production by oxidative ethanol reforming on Co, Ni and Cu ex-hydrotalcite catalysts

Five Co, Ni and Cu oxides derived from hydrotalcite-like precursors (ex-LDHs) were prepared and tested in the oxidative steam reforming reaction of ethanol under autothermal conditions. Highly crystalline LDH-precursors were obtained using urea hydrolysis method and both the precursors and the calcined ex-LDH oxides were characterized with several physical and chemical techniques. It has been shown that the particle size of the segregated active metal oxide decreases upon increasing the crystallinity of the LDH-precursor. Moreover, these small particle sizes favour the strong interactions between active metals and the amorphous matrix of Al-modifying cations, which cause a high stabilization of the active metal phases.All the ex-LDH catalysts (Co–Zn–Al, Co–Mg–Al, Co–Al, Ni–Mg–Al and Cu–Mg–Al) were tested in the oxidative steam reforming of ethanol with EtOH/H2O molar ratio (nH2O/nEtOH)(nH2O/nEtOH) of 2.28 and O2/EtOH molar ratio (nO2/nEtOH)(nO2/nEtOH) of 0.36, at temperatures of 848–898–948 K. All ex-LDH catalysts, apart from Cu-catalyst, reached the full ethanol conversion in the temperature range, and H2 and CO2 were the main reaction products. Thus, high absolute H2 production values of 14.5 L(STP) h−1 gcat−1 at 848 K with CoZnAl ex-LDH catalyst and nearly 18 L(STP) h−1 gcat−1 at 948 K with CoAl and CoMgAl catalysts were reached, which means H2 selectivity values of 85% at 848 K and 89% at 948 K, respectively.

Research highlights
► Highly crystalline LDH-precursors determine the stabilization of the active metal oxide phases.
► Hydrogen production rates as high as 14.5 L(STP)·h−1g−1cat at 848 K are reached using a CoZnAl ex-LDH catalyst.
► The highest H2 production rate (nearly of 18 L(STP)·h−1g−1cat) is obtained at 948 K on the CoMgAl ex-LDH catalyst.
► H2 selectivities values of 85% at 848 K and 89% at 948 K are reached on CoZnAl and CoMgAl catalysts, respectively.