Replacing Platinum with Tungsten Carbide (WC) for Reforming Reactions: Similarities in Ethanol Decomposition on Ni/Pt and Ni/WC Surfaces

Abstract

Selective reforming of biomass-derived oxygenates to produce hydrogen or syngas (H 2 þ CO) offers an attractive route for biomass utilization. As reported previously, the Ni/Pt(111) bimetallic surface, with one monolayer of Ni residing on top of Pt(111), showed enhanced activity in oxygenate reforming. However, the Ni/Pt(111) structure is not stable at high temperatures because of diffusion of Ni into bulk Pt. In the current study we explore the possibility of replacing the Pt substrate with tungsten monocarbide (WC) to prevent the diffusion of monolayer Ni into the bulk. We report a combined study using density functional theory (DFT), temperature programmed desorption (TPD), and high resolution electron energy loss spectroscopy (HREELS) to compare the reforming reaction of ethanol on Ni/Pt and Ni/ WC surfaces. Strong similarities are observed in the reaction pathways of ethanol on monolayer Ni/Pt and Ni/WC, demonstrating the feasibility to replace Pt with WC and to use monolayer Ni/WC as active and less expensive reforming catalysts.

Decomposition pathways of C2 oxygenates on Rh-modified tungsten carbide surfaces

“…The presence of the weak shoulder attributed to the O-H stretching mode indicates that at least a fraction of ethanol adsorbed molecularly, but also that a significant amount adsorbed dissociatively. This was consistent with earlier work of dissociative adsorption of methanol [5] and ethanol [7] on WC. Upon heating to 200 K, the vibrational peaks decreased uniformly.…”

“…Table 1 shows the binding energy of ethanol and ethoxy on these surfaces. The binding energies of both species were consistent with previous studies in the case of WC [7] and Rh [27]. Also, binding energies followed the same trend of WC N Rh/WC N Rh observed for methanol and methoxy [6].…”

“…This trend is similar to that observed for ethanol on Ni/WC [7]. The activity and selectivity towards these reactions were quantified using procedures described previously [7]. Table 3 shows the total activity, the sum of ethanol undergoing different pathways, and selectivity to each pathway.…”

“…This shift in desorption products indicates that the Rh-modified surface is more active to C-H, and C-C bond scission than clean WC. This trend is similar to that observed for ethanol on Ni/WC [7]. The activity and selectivity towards these reactions were quantified using procedures described previously [7].…”

“…Depositing one monolayer (ML) of Pt, Ni, or Rh completely shifted the selectivity of methanol decomposition to C-H cleavage, producing CO and H 2 [5,6]. In the case of ethanol on WC and Ni/WC, ethylene was produced on WC, and CO was produced on Ni/WC [7].…”