Stable hydrogen production from ethanol through steam reforming reaction over nickel-containing smectite-derived catalyst.
Bottom Line: The former is initially active, but significant catalyst deactivation occurs during the reaction due to carbon deposition.Side reactions of the decomposition of CO and CH4 are the main reason for the catalyst deactivation, and these reactions can relatively be suppressed by the use of the Ni-containing smectite.The Ni-containing smectite-derived catalyst contains, after H2 reduction, stable and active Ni nanocrystallites, and as a result, it shows a stable and high catalytic performance for the steam reforming of ethanol, producing H2.
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Hydrogen production through steam reforming of ethanol was investigated with conventional supported nickel catalysts and a Ni-containing smectite-derived catalyst. The former is initially active, but significant catalyst deactivation occurs during the reaction due to carbon deposition. Side reactions of the decomposition of CO and CH4 are the main reason for the catalyst deactivation, and these reactions can relatively be suppressed by the use of the Ni-containing smectite. The Ni-containing smectite-derived catalyst contains, after H2 reduction, stable and active Ni nanocrystallites, and as a result, it shows a stable and high catalytic performance for the steam reforming of ethanol, producing H2.
Mentions: Steam reforming of ethanol was carried out at 500 °C over the Ni catalysts prepared, which were compared to the total conversion and H2 yield at the initial stage (after 5 min) and at the later stage (after 200 min) (Figure 2). For a comparison, the catalytic performance of SM support was also measured. At the initial stage, a supported Ni catalyst of Ni35/SM gave the highest catalytic performance in both ethanol conversion and H2 yield among the catalysts used, but a remarkable catalyst deactivation was observed after 200 min. For the smectite-derived SM(Ni35) catalyst, however, initial conversion and H2 yield were lower than those of Ni35/SM, but, at the later stage of the reaction, higher catalytic performance was obtained despite the lower amount of surface Ni sites determined by CO chemisorption (Entries 1, 4 in Table 1). These results indicate that the durability of the Ni catalyst was improved by using a Ni-containing smectite as a precursor. After 200 min of reaction, the highest H2 yield was achieved over SM(Ni35) catalyst. It should be mentioned that an Al2O3-surpported catalyst of Ni35/Al2O3 gave a high conversion even after a long-time reaction, but the main carbon-containing product changed from CO2 to ethylene, which should be produced by the dehydration of ethanol on the acid sites of Al2O3 support, but not on Ni particles. Namely, undesired side reactions occurred, and so, Ni35/Al2O3 was losing its activity for the desired H2 production by the steam reforming of ethanol, as shown in Figure 2. The total ethanol conversion and H2 yield were plotted against the amount of exposed Ni sites measured by CO chemisorption in Figure 3. A clear correlation between the amount of surface Ni and either conversion or H2 yield was observed at the initial stage, meaning that the initial reaction rate simply depended on the amount of active sites, and these catalysts lost their activity after 200 min of reaction to a similar extent (Figure 3a). However, the extent of catalyst deactivation was relatively lower in the case of using SM(Ni35) compared with the other catalysts prepared by impregnation. That is, the durability of the catalyst was improved by using the Ni-containing smectite as the precursors.