Comparative study of NiLaZr and CoLaZr catalysts for hydrogen production by ethanol steam reforming: Effect of CO2 injection to the gas reactants. Evidence of Rh role as a promoter

The catalytic performance of trimetallic oxides MeLaZr (Me: Ni, Co) was evaluated in the steam reforming of ethanol for hydrogen production. Rh doped and non doped catalysts were prepared by the pseudo sol–gel like method, characterized by X-ray diffraction (XRD), thermo-programmed reduction (TPR), micro-homogeneity analysis (TEM-EDXS), specific surface areas (BET). A phase-segregation process takes place during the calcination for both trimetallic systems leading to the formation of La2Zr2O7 pyrochlore-type compound in coexistence with the Me-oxide. NiLaZr and CoLaZr catalysts show high activity and high selectivity for hydrogen production. Addition of Rh promotes reducibility at lower temperatures for both trimetallic catalysts and remarkably improves the activity and selectivity for H2. The H2 selectivity is lowered by CO2 injection because of the increase of the rate of the reverse WGSR and/or methanation reaction. The CH4 selectivity is lowered by the dry reforming reaction. The key-role played by oxycarbonate species formed during the reforming tests leads to a highly efficient gasification of carbon deposits by the Boudouard reaction.

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► NiLaZr and CoLaZr catalysts displayed high activity for the ethanol steam reforming.
► Trimetallic oxides show high selectivity for hydrogen production.
► Rh doped catalysts improves the activity and selectivity for hydrogen production.
► The injection of CO2 to the reactant gas decreases the hydrogen selectivity.
► Oxycarbonate species leads to a highly efficient carbon gasification.