Abstract
The catalytic performances of Ru/ceria-based catalysts in the CO preferential oxidation (CO-PROX) reaction are discussed here. Specifically, the effect of the addition of different oxides to Ru/CeO2 has been assessed. The Ru/CeO2-MnOx system showed the best performance in the 80–120 °C temperature range, advantageous for polymer-electrolyte membrane fuel cell (PEMFC) applications. Furthermore, the influence of the addition of different metals to this mixed oxide system has been evaluated. The bimetallic Ru–Pd/CeO2-MnOx catalyst exhibited the highest yield to CO2 (75%) at 120 °C whereas the monometallic Ru/CeO2-MnOx sample was that one with the highest CO2 yield (60%) at 100 °C. The characterization data (H2-temperature programmed reduction (H2-TPR), X-ray diffraction (XRD), N2 adsorption-desorption, diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), X-ray photoelectron spectroscopy (XPS)) pointed out that the co-presence of manganese oxide and ruthenium enhances the mobility/reactivity of surface ceria oxygens accounting for the good CO-PROX performance of this system. Reducible oxides as CeO2 and MnOx, in fact, play two important functions, namely weakening the CO adsorption on the metal active sites and providing additional sites for adsorption/activation of O2, thus changing the mechanism from competitive Langmuir–Hinshelwood into non-competitive one-step dual site Langmuir–Hinshelwood/Mars–van Krevelen. As confirmed by H2-TPR and XPS measurements, these features are boosted by the simultaneous presence of ruthenium and palladium. The strong reciprocal interaction of these metals between them and with the CeO2-MnOx support was assumed to be responsible of the promoted reducibility/reactivity of CeO2 oxygens, thus resulting in the best CO-PROX efficiency at low temperature of the Ru-Pd/CeO2-MnOx catalyst. The higher selectivity to CO2 found on the Ru–Pd system, which reduces the undesired H2 consumption, represents a promising result of this research, being one of the key aims of the design of CO-PROX catalysts.
Highlights
The modern energy crisis and urgent development of green technologies and energies have driven in the last decade intensive research in fuel cell technologies both for stationary and mobile uses
The characterization data (H2 -temperature programmed reduction (H2 -TPR), X-ray diffraction (XRD), N2 adsorption-desorption, diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), X-ray photoelectron spectroscopy (XPS)) pointed out that the co-presence of manganese oxide and ruthenium enhances the mobility/reactivity of surface ceria oxygens accounting for the good CO preferential oxidation (CO-PROX) performance of this system
On the basis of the above considerations, here we report a study of the catalytic performance in the PROX reaction of Ru supported on ceria and ceria-mixed oxide catalysts
Summary
The modern energy crisis and urgent development of green technologies and energies have driven in the last decade intensive research in fuel cell technologies both for stationary and mobile uses. Polymer-electrolyte membrane fuel cells (PEMFC), which work in the 80–100 ◦ C temperature range, are among the most promising devices for automotive purposes [1]. The hydrogen used as fuel in PEMFC is currently produced by steam reforming of hydrocarbons or alcohols and a subsequent water–gas shift reaction. Catalysts 2018, 8, 203 been investigated to purify H2 from traces of CO including: catalytic methanation [3], membrane separation [4] and preferential oxidation of CO in excess of hydrogen (CO-PROX reaction) [5,6,7]. The catalyst of this process must be highly selective towards the first reaction. The use of a reducible/active support, such as cerium oxide or iron oxide, resulted in remarkably low-temperature
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