Understanding Active Sites in the Water–Gas Shift Reaction for Pt–Re Catalysts on Titania

Abstract

Pt–Re clusters supported on titania have shown promise as catalysts for the low temperature water–gas shift reaction. However, the enhanced activity of the bimetallic Pt–Re catalyst versus pure Pt is not well understood. In this work, exclusively bimetallic clusters were grown on TiO2(110) by vapor-deposition of Pt on 2 ML Re clusters and Re on 2 ML Pt clusters. Temperature programmed desorption experiments with CO were used to determine the concentration of Re at the surface, given that CO dissociates on Re but not on Pt. Deposition of 2 ML Pt on 2 ML Re resulted in Re core–Pt shell structures, whereas deposition of low coverages (<0.5 ML) of Re on 2 ML Pt resulted in complete diffusion of Re into the Pt clusters. Both of these Pt on Re bimetallic clusters are thermodynamically favored by the lower surface free energy of Pt compared to Re, and both are also more active than pure Pt clusters in the WGS reaction. Postreaction XPS experiments indicate that Re in the Pt on Re clusters is not oxidized under WGS conditions (130–190 °C). Furthermore, preoxidized Pt–Re clusters exhibit lower activity than both pure Pt and the unoxidized Pt–Re clusters, demonstrating that ReO x does not provide active sites in the WGS reaction. Density functional theory calculations show that CO binds less strongly to the Pt on Re surface alloy compared to pure Pt, and infrared absorption–reflection spectroscopy studies on a Pt–Re surface alloy confirm that the coverage of CO after WGS reaction is lower on the Pt–Re alloy surface. Thus, decreased CO poisoning on Pt–Re could explain the higher WGS activity of the bimetallic clusters.

Towards the rational design of Pt-based alloy catalysts for the low-temperature water-gas shift reaction: from extended surfaces to single atom alloys

“…2a , the core–shell structured PtRe is about 65.4 fold more active than the Pt metal, which is consistent with the experimental observation in the literature. 31 In contrast, the PtCuPt subsurface alloy is inactive as compared to the Pt metal, which is quite different from the conclusion in a previous theoretical study. 29 It is worth noting that in the BEEF-vdW calculations, the CO adsorption energy on PtCuPt is 0.25 eV lower than that on Pt, which is close to the corresponding result from PW91 reported in the literature (0.33 eV), 29 as well as the values from PBE (0.20 eV), xPBE (0.24 eV), and vdW-DF (0.31 eV) calculations in the present work (see Table S10 † for more details).…”

A review of recent advances in water-gas shift catalysis for hydrogen production

“…The results showed that pre-oxidized clusters had lower activity in comparison to both unoxidized Pt-Re and pure Pt, which indicated that ReO x sites are not active in the WGS reaction. Reduced CO poisoning in Pt-Re clusters demonstrated a higher WGS activity of the bimetallic clusters [42]. Synergistic effects at the interface of the metal-carbide are reported to cause a chemical activity enhancement for pure Pt, TiC, and MoC [43].…”

“…Recently, Pt-Re bimetallic clusters on TiO 2 support were reported to be a superior catalyst than Pt cluster alone for the low-temperature WGSR [42]. In order to understand the impact of both the Pt-Re clusters composition as well as Re oxidation, Duke et al investigated a model system with bimetallic clusters grown on the surface of a rutile TiO 2 (110).…”

How Do Structurally Distinct Au/α‐Fe2O3 Interfaces Determine Surface OH/H2O reactivity, Intermediate Evolution, and Product Formation in Low‐temperature Water‐gas Shift Reaction?

“…Early researchers imply that the dissociation of H 2 O and the desorption of intermediate species could be the rate‐determining steps for the target reaction. Instead, the more recent observations made by Williams et al .…”

“…The typical one is the water gas shift (WGS) reaction, to which close attention is paid to minimizing the CO concentration in the processes of reforming fossil fuels . To design a high‐performance catalyst for the WGS reaction at low temperatures, a number of factors have been widely investigated, including strong metal‐support interaction, substrate morphology effect, and state of precious metal . However, establishing the structure‐performance correlation is still ambiguous especially for the complexity of catalyst surface structures, which asks for further mechanistic study on some carefully designed model catalysts where their catalyst surface structures can be clearly identified to understand the reaction process in depth.…”