(15a) In-Situ ATR IR Study on the Mechanism of Aqueous Phase Reforming of Polyols and Sugars

Aqueous phase reforming (APR) is a promising process for the production of hydrogen from biorenewable resources. In principle, a variety of polyols and sugars can be converted in this process, but it has been reported that the reaction becomes less reactive with increasing size of the feed molecule.

In this study, in situ attenuated total reflectance infra-red (ATR-IR) spectroscopy is used to study APR reactions on Pt/γ-Al₂O₃. Using this approach, surface species on a catalyst layer can be probed while reducing the strong signals from water in many important regions of IR spectrum. We demonstrate that a sequential pretreatment of degassed H₂O, O₂-saturated H₂O, and H₂-saturated H₂O is most effective for cleaning 5 wt% Pt/γ-Al₂O₃ prior to in-situ studies on the APR reaction of glycerol, sorbitol, and glucose. In the first step of APR, the reactant is converted into CO in bridging and linearly bound coordination on the surface of the Pt particles. The subsequent water gas shift (WGS) reaction is significantly faster for CO on bridging sites. Kinetic studies on the conversion of different oxygenates are discussed. In particular, it is shown how the size of the oxygenate molecules affects the rate of formation of surface bound carbon monoxide and how co-adsorbed surface species affect WGS activity.