Hydrogen production by bioethanol partial oxidation over Ni based catalysts

•The effect of Ni loading on ethanol partial oxidation reaction is studied.•xNiAlZn catalysts exhibit high activity and high H2 and CO selectivity.•Stability of catalysts was tested for 100 h at 700 °C without remarkable degradation.•Ni loading have an important effect on the product distribution.•Observed catalyst activity was in line with its enhanced structural properties.

The xNiAlZn catalysts with different Ni loading (x = 5, 10 and 20 wt%) and nearly constant Al/Zn weight ratio (Al/Zn = 0.73) were prepared by the citrate method and characterized by different techniques – SBET, TPR, XRD, XPS, and TEM. The influence of parameters, such as reaction temperature, oxygen-to-fuel molar ratio, and Ni loading on hydrogen production was investigated. The catalysts were active in the partial oxidation of ethanol at atmospheric pressure in the temperature range 600–750 °C. The conversion was always complete at temperatures above 600 °C, regardless of the changes in other reaction conditions. A syngas is produced which can be used in solid oxide fuel cell applications. Selectivity to hydrogen and CO increased with increasing temperature and decreased with increasing Ni loading. The highest selectivity (S) was obtained over 5NiAlZn. At 700 °C this sample showed S(H2) of 90%, S(CO) of 92%, and only small amounts of byproducts such as CO2 and CH4 were detected. Morphological and structural modifications in the catalysts under reaction conditions, determined by the amount of nickel, were closely related to the activity of the samples. The effect of the parameters on side reactions and distribution of byproducts were also discussed. During 100 h time-on-stream, ethanol conversion and selectivity to H2 and CO over 5NiAlZn and 10NiAlZn remained unchanged demonstrating stable performance of the catalysts. Additionally, the stability of the Ni catalyst was studied by means of simulated start–stop operation cycles during the partial oxidation reaction to simulate thermal cycles during the solid oxide fuel cell lifetime. With increasing number of thermal cycles a slight decline in ethanol conversion was observed and the selectivity to hydrogen and CO decreased. By using a molar ratio oxygen/ethanol of 0.75 a syngas with high selectivity to H2 and CO was obtained.

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