CeO2-, ZrO2-, and La2O3-supported Rh-Pt catalysts were tested to assess their ability to catalyze the steam reforming of ethanol (SRE) for H2 production. SRE activity tests were performed using EtOH:H2O:N2 (molar ratio 1:3:51) at a gaseous space velocity of 70,600 h −1 between 400 and 700 °C at atmospheric pressure. The SRE stability of the catalysts was tested at 700 °C for 27 h time on stream under the same conditions. RhPt/CeO2, which showed the best performance in the stability test, also produced the highest H2 yield above 600 °C, followed by RhPt/La2O3 and RhPt/ZrO2. The fresh and aged catalysts were characterized by TEM, XPS, and TGA. The higher H2 selectivity of RhPt/CeO2 was ascribed to the formation of small (~5 nm) and stable particles probably consistent of Rh-Pt alloys with a Pt surface enrichment. Both metals were oxidized and acted as an almost constant active phase during the stability test owing to strong metal-support interactions, as well as the superior oxygen mobility of the support. The TGA results confirmed the absence of carbonaceous residues in all the aged catalysts.

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The integration of H2 production and purification is an essential step in the development of sustainable power generation in proton exchange membrane fuel cells. Thence, coupling of steam reforming of ethanol (SRE) and carbon monoxide removal was evaluated for further hydrogen production in fuel cells. Firstly, SRE on RhPt/CeO2-SiO2 catalyst was carried out at 700 °C, displaying a stable product distribution for 120 h. Then, CO removal from the actual post-reforming stream was evaluated over several AuCu/CeO2 catalysts with different Au:Cu weight ratios (1:0, 3:1, 1:1, 1:3, and 0:1). The role of each active metal was identified: Au favors CO conversion by the formation of carbon intermediates, and Cu improves CO2 selectivity due to its redox properties. A 1:1 Au:Cu weight ratio on the AuCu/CeO2 catalyst at 210 °C favors complete CO removal from the post-reforming stream, achieving fuel-cell grade hydrogen production. However, 25% of H2 was loss during the CO removal step, which is very high compared to studies with synthetic feeds. These high H2 loss would be the result of a complex network of reactions occurring during the real post-reforming cleaning. Characterization tests allowed us to identify that CeO2, combined with the Cu redox properties, favors water decomposition and CO conversion. Likewise, catalyst reduction might favor Au-Cu alloy formation due to the similar crystal lattice. Finally, stability tests showed that Au1.0Cu1.0/CeO2 catalyst is susceptible to rearrangement due to the cumulative oxidation of its surface during operation. Nonetheless, periodic insitu reduction treatment contributes to the Au-Cu alloy formation and stabilization, maintaining high activity and mitigating H2 loss. Indeed, Au1.0Cu1.0/CeO2 catalyst was active for 95 h when reduced every 24 h, achieving fuel-cell grade hydrogen with a minimum of 14% H2 loss.

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Abstract:The steam reforming of ethanol (SRE) on a bimetallic RhPt/CeO 2 catalyst was evaluated by the integration of Response Surface Methodology (RSM) and Aspen Plus (version 9.0, Aspen Tech, Burlington, MA, USA, 2016). First, the effect of the Rh-Pt weight ratio (1:0, 3:1, 1:1, 1:3, and 0:1) on the performance of SRE on RhPt/CeO 2 was assessed between 400 to 700 • C with a stoichiometric steam/ethanol molar ratio of 3. RSM enabled modeling of the system and identification of a maximum of 4.2 mol H 2 /mol EtOH (700 • C) with the Rh 0.4 Pt 0.4 /CeO 2 catalyst. The mathematical models were integrated into Aspen Plus through Excel in order to simulate a process involving SRE, H 2 purification, and electricity production in a fuel cell (FC). An energy sensitivity analysis of the process was performed in Aspen Plus, and the information obtained was used to generate new response surfaces. The response surfaces demonstrated that an increase in H 2 production requires more energy consumption in the steam reforming of ethanol. However, increasing H 2 production rebounds in more energy production in the fuel cell, which increases the overall efficiency of the system. The minimum H 2 yield needed to make the system energetically sustainable was identified as 1.2 mol H 2 /mol EtOH. According to the results of the integration of RSM models into Aspen Plus, the system using Rh 0.4 Pt 0.4 /CeO 2 can produce a maximum net energy of 742 kJ/mol H 2 , of which 40% could be converted into electricity in the FC (297 kJ/mol H 2 produced). The remaining energy can be recovered as heat.

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