Enhancement of activity of PtRh nanoparticles towards oxidation of ethanol through modification with molybdenum oxide or tungsten oxide

Abstract

Electrocatalytic systems utilizing carbon (Vulcan)-supported PtRh nanoparticles (PtRh/Vulcan) admixed with either molybdenum oxide or tungsten oxide were tested and compared during electrooxidation of ethanol. The systems' performance was diagnosed using electrochemical techniques such as voltammetry and chronoamperometry. The proposed electrocatalytic materials were also characterized with X-ray diffraction (XRD), transmission and scanning electron microscopies (TEM and SEM), as well as SEM-coupled energy dispersive X-ray spectroscopy (SEM-EDX). For both systems containing molybdenum and tungsten oxides, enhancements in catalytic activities (relative to the behavior observed at bare PtRh/Vulcan nanoparticles) were found during ethanol electrooxidation at room temperature (22°C). Further, it was from chronoamperometric current (density)-time responses that anodic electrocatalytic currents measured at 0.3 V (vs. RHE) were more than 20% higher in the case of the MoO 3 -containing PtRh/Vulcan system relative to that utilizing WO 3 . The diagnostic "CO-stripping" experiments were consistent with the view that addition of molybdenum oxide or tungsten oxide to PtRh/Vulcan tended to shift potential for the oxidation of inhibiting CO-adsorbate ca. 80 or 40 mV towards less negative values in comparison to the analogous but oxide-free system. The fact that carbon (Vulcan)-supported PtRu nanoparticles exhibited higher electrocatalytic reactivity observed phenomena may be attributed to specific interactions between noble metal centers and the oxides in addition to chemical reactivity of metal oxo groups in the vicinity of PtRh/ Vulcan at the electrocatalytic interface.

PtIr–WO3 nanostructured alloy for electrocatalytic oxidation of ethylene glycol and ethanol

“…The presence of transition metal oxides in the neighborhood of catalytic sites of noble metal catalysts results in an increasing population of –OH groups at low potentials, thereby mitigating CO poisoning of catalytically active platinum centers, possibly facilitating the cleavage of C–H bonds as well as in a weakening of C–C bonds. This assumption is in accord with reports in which a significant improvement in oxidation of small organic molecules with metal oxides (e.g., WO 3 , MoO 3 , TiO 2 , ZrO 2 , V 2 O 5 , and CeO 2 ) modified by Pt-based alloy catalysts has been observed [ 8 , 9 , 39 – 43 ].…”

“…In addition, the onset potentials of ethanol and ethylene glycol oxidation shift toward more negative values which is especially pronounced in the case of ethylene glycol oxidation. This can be explained by the fact that transition metal oxides (e.g., WO 3 and related compounds) are known to activate interfacial water molecules (from –OH groups on WO 3 ) at lower potentials which, in turn, promote the removal of poisoning species from the noble metal catalyst [ 8 , 9 , 14 , 54 – 60 ].…”

“…In the initial phase of the chronoamperometric experiments, it is likely that a higher number of free active sites are available for adsorbed ethanol or ethylene glycol molecules (fast kinetic rate reaction), and during the next few minutes (rate determining step), the amount of free catalyst sites is limited by poisoning by intermediate species, such as CO, CH x , CH 3 CHO, CH 3 COOH (for ethanol oxidation), glycol aldehyde, glycolate, glyoxylate, oxalate, and glycolate (for ethylene glycol). In this regard, the improvement of catalytic properties observed by introduction of WO 3 on Pt-based nanoparticles surface can be associated with the oxophilic nature of tungsten oxide providing hydroxyl groups (–OH) on the oxide surface at lower potential, which promotes electrooxidation of the surface CO-poisoning intermediates species [ 8 , 9 , 54 – 60 ].

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“…The catalyst layer was fabricated through modification of the working electrode by immobilization of PtIr/C nanoparticles. WO 3 modification of the PtIr/C catalyst was in accordance with the procedure described in our previous papers [ 8 , 9 ]. Briefly, a solution of tungstic acid was prepared by passing an aqueous solution of 0.05 mol dm −3 Na 2 WO 4 through a proton exchange resin.…”

Tungsten(VI) Oxide Supported Rhodium(0) Nanoparticles Used as Catalyst in Hydrogenation of Benzene at Room Temperature

“…Since tungsten(VI) oxides are simply prepared and provide high chemical stability [11] they are widely used in many catalytic reactions such as oxidative desulfurization [12], dehydration of 2-Butanol [13], pentane isomerization [14], acetalization [15]. Recently, the promoting effect of WO 3 on noble NPs used as catalysts in ethanol [16,17], methanol [18] and CO [19] oxidations have been confirmed. On the other hand, tungsten(VI) oxides are considered to be used in hydrogenation reactions because the dissociation of H 2 molecules to H δ+ ionic species could easily be stabilized on WO 3 structure [17].…”