Stable and Efficient Pt–Re/TiO₂ catalysts for Water‐Gas‐Shift: On the Effect of Rhenium

Abstract

The catalytic performance of Pt–Re/TiO2 catalysts, that is, activity and stability, in single‐stage water gas shift reactions was investigated by studying the influence of preparation strategies, Pt/Re molar ratios, and metals contents. Results show that sequential impregnation of Re precursor prior to Pt precursor without intermediate pretreatment is the optimum preparation strategy. The Pt/Re ratio of unity with 0.5 wt. % Pt content resulted in the most significant effect on activity and stability. In situ characterizing of both monometallic and the optimal bimetallic Pt–Re catalysts by means of CO chemisorption, H2 temperature programmed reduction, and FTIR spectroscopy under the reaction conditions provided evidence that Re increases the activity by enhancing the activation of water. No evidence was found for any direct influence of Re on the properties of Pt in the catalyst under the reaction conditions.

Elucidation of the roles of Re in steam reforming of glycerol over Pt–Re/C catalysts

“…This synergy allows for higher turnover of glycerol (or CO for WGS). This is also in agreement with previous reports that Re in an oxidized state (e.g., ReO x ) could provide sites for CO oxidation [32] and water activation [19].…”

“…ReO x was also proposed to be present as a redox center to enhance the WGS activity, in which ReO x could be reduced by CO (generating CO 2 ) and re-oxidized by H 2 O (forming H 2 ) [19]. We recently studied the catalytic performances of activated carbon-supported Pt and Pt-Re catalysts for glycerol aqueous-phase reforming (APR) [5,16,20].…”

Density Functional Theory and Reaction Kinetics Studies of the Water–Gas Shift Reaction on Pt–Re Catalysts

“…Several recent reports have indicated that the presence of Re has a beneficial role in the activity of Pt‐based catalysts in the LT‐WGS reaction 17. Although only a few experimental studies have been performed to understand the role of Re, they agree that Re provides an additional reaction pathway to activate H 2 O 17a. e, h In these studies, however, Pt and Re atoms are supported on titania and zirconia, which are promoters for Pt‐catalyzed LT‐WGS reactions themselves, and therefore their presence might obscure the isolation of the Re effect on the WGS reactions.…”

In SituStudies of Carbon Monoxide Oxidation on Platinum and Platinum–Rhenium Alloy Surfaces

“…A number of other studies have also demonstrated that Pt-Re/TiO 2 has greater activity for the WGS reaction compared to Pt/TiO 2 due to dissociation of water on ReO x . [26][27][28][29][30] Furthermore, density functional theory (DFT) calculations for the WGS reaction on Pt 3 Re(111) report that the active Pt-Re site is likely to contain partially oxidized ensembles. 31 It has also been proposed that Re-OH formation promotes hydrogenolysis of glycerol through direct activation of C-OH bonds.…”