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Catalysts 2017, 7(5), 148; doi:10.3390/catal7050148

Methanol Steam Reforming: Na Doping of Pt/YSZ Provides Fine Tuning of Selectivity

Center for Applied Energy Research, University of Kentucky, 2540 Research Park Dr., Lexington, KY 40511, USA
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Academic Editor: Morris D. Argyle
Received: 14 March 2017 / Revised: 10 April 2017 / Accepted: 3 May 2017 / Published: 10 May 2017
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Abstract

In this work, we found that sodium doping can be used to improve CO2 selectivity for supported Pt catalyst during methanol steam reforming. These materials are usually very active in the low temperature range; however, they are characterized by high selectivity of CO, which is a poison in downstream polymer electrolyte membrane fuel cells (PEM-FC) application. With Na doping, we found that CO2 selectivity was higher than 90% when 2.5 wt.% of sodium was added to Pt/YSZ. We have speculated that the different product distribution is due to a different reaction pathway being opened for CH3OH decomposition. Methanol decarbonylation was favored when Na was absent or low, while a formate decarboxylation pathway was favored when Na content reached 2.5 wt.%. The proposal is rooted in the observed weakening of the C-H bond of formate, as demonstrated in in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and kinetic isotope effect (KIE) experiments for the water-gas shift reaction conducted at low temperature. When adsorbed methoxy, produced when methanol is dissociatively adsorbed, was converted in the presence of H2O in DRIFTS spectroscopy, formate species were prevalent for a 2% Pt–2.5% Na/YSZ catalyst, while only a minor contribution was observed for 2% Pt/YSZ. Moreover, the formate produced on Na-doped Pt/YSZ exhibited ν(CH) stretching bands at low wavenumber, consistent with C–H bond weakening, thus favoring dehydrogenation (and decarboxylation). It is proposed that when Na is present, formate is likely an intermediate, and because its dehydrogenation is favored, selectivity can be fine-tuned between decarbonylation and decarboxylation based on Na dopant level. View Full-Text
Keywords: methanol steam reforming (MSR); yttrium stabilized zirconia (YSZ); Na doping; DRIFTS; methoxy; formate methanol steam reforming (MSR); yttrium stabilized zirconia (YSZ); Na doping; DRIFTS; methoxy; formate
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Martinelli, M.; Jacobs, G.; Graham, U.M.; Davis, B.H. Methanol Steam Reforming: Na Doping of Pt/YSZ Provides Fine Tuning of Selectivity. Catalysts 2017, 7, 148.

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