Elucidation of mechanistic and kinetic aspects of water–gas shift reaction on supported Pt and Au catalysts via transient isotopic techniques

With growing interest in hydrogen fuel cell applications, novel and robust water–gas shift (WGS) industrial catalysts are required with high activity, preferably at low-temperatures (T<250 °C). Supported Pt and Au on reducible metal oxides appear very promising candidates for such applications. Towards this goal, the need for in-depth investigations of the actual mechanism(s) and micro-kinetics of potential catalytic systems and the need to obtain intrinsic correlations between site reactivity and chemical composition (quality and quantity) of the active adsorbed phase are imperative. The use of in situ kinetics coupled with spectroscopic measurements (operando methodology) fulfils these requirements. Steady state isotopic transient kinetic analysis (SSITKA) used in the operando mode coupled with other transient isotopic experiments can sensitively probe the chemical nature and surface composition of the active reaction intermediates. Rival mechanisms (“redox” versus “associative with –OH group regeneration”) can also be screened and kinetic parameters (e.g. rate constants) can be obtained through advanced micro-kinetic modelling of the transient isotopic responses of both gaseous and adsorbed species. The mechanisms of the WGS reaction on supported Pt (or Au) metal catalysts on the basis of recent DFT computations and experimental investigations, and the application of SSITKA-operando (FTIR-Mass Spectroscopy) methodology with a focus on its advantages and limitations are presented through several case studies.