Hydrogen from steam reforming of ethanol in low and middle temperature range for fuel cell application

A series of well crystallized Ni-Co-Zn-Al LDHs materials has been prepared by the urea hydrolysis method as precursors of mixed oxide catalysts for the Ethanol Steam Reforming (ESR) reaction. The calcination of the layered precursors gives rise to high surface area mixed oxides, mainly a mixture of rock-salt phase (NiO), wurtzite phase (ZnO) and spinel phase. Both precursors and mixed oxides have been throughtfully characterized and the steam reforming of ethanol has been investigated over the calcined catalysts in flow reactor and in-situ FT-IR experiments. The data here reported provide evidence of the good catalytic activity of Co-Zn-Al and Co-Ni-Zn-Al catalysts prepared from hydrotalcite-like LHD precursors for ethanol steam reforming. At 823 K the most active Co/Ni catalyst containains a predominant spinel phase with composition near Zn0.58Ni0.42[Al0.44Co0.56]2O4 and small amounts of NiO and ZnO. On the other side, at 873 K the selectivity to hydrogen increases with cobalt content. In particular, the presence of cobalt increases selectivity to H2 and CO2 and decreases selectivity to methane in the low temperature range 720–870 K. The most selective catalyst is the Ni-free Co-Zn-Al mixed oxide essentially constituted by a single spinel type phase Zn0.55Co0.45[Al0.45Co0.55]2O4. Cobalt catalysts appear consequently to behave better than nickel based catalysts in this temperature range. The key feature for high selectivity to hydrogen is proposed to be associated to a stability of a relatively high oxidation state at the catalyst surface, the most relevant selectivity determining step being constituted by the evolution of surface acetate species. In fact, over oxidized catalyst surface the acetate species evolve producing carbon dioxide and hydrogen while over a more reduced surface they evolve giving rise to methane and COx. Water is supposed to have the main role of allowing surface sites to stay in an unreduced state at least in the temperature range 720–870 K.

Download Full-text

Comparative Study of Ni-W /CeO2, Ni-W /y-Al2O3 and Ni-W /HT Catalysts for H2 Production by Steam Reforming of Bioethanol

Quimica Hoy ◽

10.29105/qh2.1-88 ◽

2011 ◽

Vol 2 (1) ◽

pp. 3

Author(s):

Paz Hernández ◽

Arturo Fernández ◽

Sarah Messina

Keyword(s):

Catalytic Activity ◽

Fuel Cell ◽

Hydrogen Production ◽

Comparative Study ◽

Steam Reforming ◽

Carbon Deposition ◽

Nickel Content ◽

H2 Production ◽

Good Stability ◽

Steam Reforming Of Ethanol

Ni-W catalysts supported on CeO2,Al2O3 and hydrotalcite (HT) were studied in the steam reforming of ethanol at 500-650ºC. The CeO2 and HT were synthesized by impregnation and direct coprecipitation methods, respectively. Commercial Al2O3 was used. Nickel content was varied from 10, 15 and 30% with 1% W. The catalyst that presented the highest catalytic activity and selectivity to hydrogen was 10% Ni-W/HT. Conversion to ethanol was 100% and selectivities to H2, CH4, CO2 and CO were 75, 5.78, 0.37 and 18.85%, respectively, at a temperature of 500 ºC. Moreover, these catalysts showed good stability with respect to carbon deposition and low selectivity towards C2H4 production. These are desirable features for catalysts to be used in hydrogen production for fuel cell applications.

Download Full-text