The effect of ZnO addition on Co/C catalyst for vapor and aqueous phase reforming of ethanol
•ZnO addition to Co/C increased COX selectivity for vapor phase ethanol reforming.•ZnO facilitated Co oxidation in vapor phase ethanol reforming at 250 °C.•Metallic Co quickly oxidizes in aqueous phase ethanol reforming regardless of ZnO.•ZnO primarily enhanced H2O activation.•Cobalt oxidation state is closely related to both support and reaction conditions.
The effect of ZnO addition on the oxidation behavior of Co along with catalytic performance in vapor and aqueous phase reforming of ethanol were investigated on Co supported on carbon black (XC-72R). Carbon was selected to minimize the support interactions. Effect of ZnO addition during both vapor and aqueous phase reforming were compared at 250 °C. ZnO addition inhibited the reduction of cobalt oxides by H2 and created surface sites for H2O activation. During vapor phase reforming at 450 °C the redox of cobalt, driven by steam oxidation and H2 reduction, trended to an equilibrium of Co0/Co2+. ZnO showed no significant effect on cobalt oxidation, inferred from the minor changes of C1 product yield. Surface sites created by ZnO addition enhanced water activation and oxidation of surface carbon species, increasing CO2 selectivity. At 250 °C cobalt reduction was minimal, in situ XANES demonstrated that ZnO addition significantly facilitated oxidation of Co0 under vapor phase reforming conditions, demonstrated by lower C1 product yield. Sites introduced by ZnO addition improved the COx selectivity at 250 °C. Both Co/C and Co-ZnO/C rapidly oxidized under aqueous phase reaction conditions at 250 °C, showing negligible activity in aqueous phase reforming. This work suggests that ZnO affects the activation of H2O for Co catalysts in ethanol reforming.
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Journal: Catalysis Today - Volume 233, 15 September 2014, Pages 38–45