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Three structurally distinct interfaces, i. e. Au/α-Fe2O3-THB-Air, Au/α-Fe2O3-HS-Air, and Au/α-Fe2O3-QC-Air, with the major substrate facet being {113}, {001}, and {012} respectively, were controllably prepared. The low temperature water gas shift (WGS) reaction (100-260 °C) was applied to these unique systems to reveal how these structurally distinct interfaces can impact on the reaction behavior. With the detailed performance evaluation plus the characterizations of CO-TPSR, XPS, and in situ-FTIR in particular, the correlations between the evolution of different intermediates and the distinct catalytic behaviors have been established. The substrate facet structure and the Au entity largely determine the form and reactivity of surface OH/ H2O species which in turn determine the formation of different intermediates and eventually the product formation. The Au/α-Fe2O3-THB-Air is enriched with oxygen vacant sites, favorable for dissociative adsorption of H2O, carboxyl intermediate formation and H2 production. The Au/α-Fe2O3-HS-Air is enriched with surface lattice oxygen, favorable for molecular adsorption of H2O, formate intermediate formation, and CO2 production. The Au/α-Fe2O3-QC-Air interface is enriched with surface Fe sites, favorable for dissociative adsorption of H2O and evolution of stable carboxyl intermediate as well as isolated OH species at low reaction temperatures. The findings are informative to control the interfacial structure for the WGS and other reactions. [ABSTRACT FROM AUTHOR]

Highlights: [•] WGS reaction mechanism on Pt/Ce1−x Ti x O2−δ was studied by SSITKA-operando methodology. [•] WGS on Pt/Ce0.8Ti0.2O2−δ at 300°C largely follows both the “redox” and “associative formate” mechanisms. [•] CeO2-doped (Zr4+, La3+ and Ti4+) largely affects the concentration of active C-pool and H-pool on Pt/CeO2-doped catalyst. [•] The extent (Δx, nm) of a reactive zone around Pt nanoparticles strongly depends on the dopant. [•] A very good correlation between the active C-pool and the specific WGS reaction rate as a function of dopant exists. [ABSTRACT FROM AUTHOR]

Platinum nanoparticles (dPt = 1.0–1.2 nm) supported on single CeO2 and La2O3 metal oxides and Ce0.8La0.2O2−δ solid solution were prepared to investigate for the first time the effect of La3+-doping of ceria on important mechanistic and kinetic aspects of the water-gas shift (WGS) reaction, namely: (i) the concentration and chemical structure of active adsorbed reaction intermediates present in the C-path and H-path of WGS at 250 and 300 °C, () the chemical nature of inactive species formed during WGS, and () the prevailing mechanistic path among “redox” and “associative” both proposed in the literature. For this, steady-state isotopic transient kinetic analysis () experiments coupled with in situ DRIFTS and mass spectrometry were performed to follow the H-path (use of D2O) and C-path (use of 13CO) of the WGS. In addition, other transient isotopic experiments using methodology (use of and mass spectrometry) were designed to follow with time on stream the reactivity toward water of the various adsorbed species formed under WGS. It is proposed that on Pt/Ce1−xLaxO2−δ (x=0.0, 0.2 and 1.0) the WGS reaction follows both the “redox” and “associative” mechanisms but the extent of participation of each mechanism to the overall WGS reaction rate depends on the support chemical composition. The WGS kinetic rate (μmol CO g−1 s−1) increased by a factor of 2.0 and 2.8 at 300 °C on 0.5 wt% Pt supported on Ce0.8La0.2O2−δ compared to CeO2 and La2O3, respectively. This was explained by (i) the larger concentration of active surface intermediates formed around each Pt nanoparticle (larger extent of reactive zone) a(ii) the higher reactivity of sites (k, s−1) responsible for CO2 and H2 formation on Pt/Ce0.8La0.2O2−δ compared to Pt/CeO2 and Pt/La2O3. Active OH groups is suggested to be formed on defect sites (Ce3+□s) of Ce0.8La0.2O2−δ as a consequence of the introduction of La3+ into the ceria lattice, the latter enhancing the concentration of labile oxygen and its surface mobility, important characteristics of the “redox” mechanism. [Copyright &y& Elsevier]

Abstract: A series of x wt.% Pt/CeO2 catalysts (x =0.1–2.0) was prepared to investigate for the first time the effect of Pt particle size on important kinetic and mechanistic aspects of the water–gas shift (WGS) reaction, namely the concentration (μmolg−1) and chemical structure of active adsorbed reaction intermediates present in the “carbon-path” and “hydrogen-path” of the WGS reaction at 300°C. For this, steady-state isotopic transient kinetic analysis (SSITKA) coupled with in situ DRIFTS and mass spectrometry experiments was performed using D2O and 13CO. Α novel transient isotopic experiment performed allowed to quantify the initial transient rates of reactions of adsorbed formate (–COOH) and CO by water, based on which it was concluded that formate should not be considered as an important intermediate. According to the present work, it is proposed that the WGS reaction on ceria-supported Pt at 300°C occurs largely via the “redox” mechanism, and to a lesser extent via the “associative formate with –OH group regeneration” mechanism. The TOF (s−1) of WGS was found to vary only slightly with Pt particle size (1.3–8.0nm), while the specific reaction rate based on the length of periphery of Pt–CeO2 interface (μmolcm−1 s−1) was found to significantly increase with increasing platinum loading and mean particle size in the 250–300°C range. [Copyright &y& Elsevier]

A detailed kinetic and mechanistic study of the water¿gas shift (WGS) reaction on a 0.5wt% Pt/TiO2 catalyst has been carried out. The dependence of kinetic reaction rate on the partial pressures of reactants (CO, H2O) and products (H2, CO2), and the concentration and chemical structure of active and inactive reaction intermediates that are found in the ¿hydrogen-path¿ and ¿carbon-path¿ of the reaction have been investigated in the 200¿270°C range. The most likely mechanistic pathway of the WGS reaction over the present catalytic system is discussed. It has been found that the reaction rate increases with an increase in the concentration of CO or H2O in the feed stream, while it decreases significantly with the addition of H2 in the feed stream. On the contrary, the kinetic reaction rate was found to be practically independent on the concentration of CO2 in the feed stream. The experimental reaction rates that were estimated were fitted to an empirical power-law rate expression from which the kinetic reaction orders with respect to CO, H2O, CO2, and H2 were estimated to be 0.5, 1.0, ¿0.0, and ¿0.7, respectively. An apparent activation energy of 10.8kcal/mol was also estimated. The formation of formate and carbonate surface species over the TiO2 support under WGS reaction conditions was proved via SSITKA¿DRIFTS experiments. However, these reaction intermediates must be considered as inactive (spectator) species for the steady-state WGS reaction. Additional transient experiments that involved 18O-isotope provided strong support for the red-ox mechanism as the prevailing one on the present Pt/TiO2 catalyst, where labile oxygen and oxygen vacancies of TiO2 near the metal¿support interface can participate in the reaction path of the WGS reaction. [Copyright &y& Elsevier]

Chemisorption and reactivity of the molecules involved in the water-gas shift (WGS) reaction on gold/ceria catalyst have been studied at 90 and 300 K by FTIR spectroscopy. Forward and reverse WGS reaction at 300 K and up to 573 K have been investigated, too. The FTIR results show that gold causes a strong modification of the surface properties of the support. The nanosized metallic gold particles in close contact with defective ceria play an essential role for the genesis of high catalytic activity in WGS reaction at low temperature and appear to be of crucial importance in explaining the remarkably high stability of this catalytic system. An electronic interaction between small gold metallic nanoparticles and ceria has been evidenced. [Copyright &y& Elsevier]