Abstract
The present work concerns the characterization of trimetallic nickel catalysts, NiMoRe (Nickel/Molybdenum/Rhenium), NiMoCu (Nickel/Molybdenum/Copper) and NiMoCo (Nickel/Molybdenum/Cobalt), supported on gadolinia-doped ceria and the evaluation of their catalytic performance in the auto-thermal reforming of ethanol to hydrogen. Catalysts have been prepared by wet impregnation and characterized by XRD, SEM-EDX, TG-DSC, TEM, CHNS, H2-TPR and micro-Raman spectroscopy. The resistance of Ni-alloy catalysts to the carbon deposition and sulfur poisoning has been studied. All catalysts show a similar behavior in the auto-thermal reforming reaction: 100% of ethanol conversion and high selectivity to syngas products, up to 77 vol.%. At 800 °C the coke deposition is very low (less than 0.34 wt%). Sulfur content affects the selectivity and the activity of the catalysts, especially towards the coke formation: high sulfur content promotes the ethylene formation, therefore the amount of coke deposited on spent catalyst increases. NiMoCu seems to be the trimetallic catalyst less sensitive to this aspect.
Highlights
The world’s increasing energy demands makes today biomass an attractive energy source, based on the minimizing of CO2 emissions and the global warming reduction purposes
For NiMoCo/gadolinium-doped ceria (GDC) it is possible to observe that the activation temperature (T = 650 ◦ C) is not suitable to obtain a complete reduction of the catalyst
The higher selectivity to CO at 800 ◦ C observed for NiMoRe/GDC and NiMoCo/GDC is ascribable to the occurrence of reverse water gas shift reaction (RWGS, CO2 + H2 ⇔ CO + H2 O), which is favored at temperatures higher than 700 ◦ C
Summary
The world’s increasing energy demands makes today biomass an attractive energy source, based on the minimizing of CO2 emissions and the global warming reduction purposes. Nickel is a cost effective alternative solution to the more expensive noble metals, but its activity, in all the dehydrogenation/hydrogenation reactions, must be protected from coke deactivation and sintering phenomena [7,11,12] In this context, the correct selection of the support, as well as the presence of promoter elements, are fundamental aspects to be considered [17,18]. Ghani et al studied the ATR of crude glycerol over modified ceria-zirconia-supported nickel catalyst with the presence of promoters (Ca, Mg and Gd) [19] They demonstrated that the Ni/CeZr catalyst promoted with calcium exhibited the highest activity with hydrogen selectivity of c.a. 80%. Ethanol conversion and products distribution have been measured and analyzed
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