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Promoting the selectivity of Pt/m-ZrO2 ethanol steam reformi


Martinelli, Michela; Garcia, Richard; Watson, Caleb; Cronauer, Donald; Kropf, A.; Jacobs, Gary


The steam reforming of ethanol reaction was investigated on unpromoted, potassium and ru-bidium promoted Pt/m-ZrO2 catalysts. Evidence from in-situ DRIFTS characterization indicates that ethanol dissociates to ethoxy species, which undergo oxidative dehydrogenation to acetate followed by acetate decomposition. The acetate decomposition pathway depends on catalyst composition. The decarboxylation pathway tends to produce higher overall hydrogen selectivity and is the most favoured route at high alkali loading (2.55 wt.% K and higher or 4.25 wt.% Rb and higher). On the other hand, decarbonylation is a significant route for the undoped catalyst or when a low alkali loading (e.g., 0.85%K or 0.93%Rb) is used, thus lowering the overall H2 selectivity of the process. Results of in-situ DRIFTS and temperature-programmed reaction of ESR show that alkali doping promotes forward acetate decomposition while exposed metallic sites tend to fa-cilitate decarbonylation. In previous work, 1.8 wt.% Na was found to hinder decarbonylation completely. Because 1.8 wt.% Na is atomically equivalent to 3.1 wt.% K and 6.7 wt.% Rb, the results show that less K (2.55% K) or Rb (4.25% Rb) is needed to suppress decarbonylation; that is, more basic cations are more efficient promoters for improving the overall hydrogen selectivity of the ESR process.



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