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Operando-SSITKA (Mass spectrometry-DRIFTS) and other isotopic experiments were employed to investigate the steam reforming of acetol on 10-wt% Ni/La2O3-Al2O3 at 500 °C. A large concentration (1 1) participates in the reaction path of H2 formation, while a significantly larger amount (H-content larger than 1.4 mmol H g−1) appeared as inactive species. The nature of the majority of active intermediates comprised of -CHx and -CxHy formed on both the Ni and support phases, and which are associated with a small mean rate constant (kapp = 0.075 min−1) towards H2(g) formation (D2O-SSITKA).

• Carbon-coated Al 2 O 3 influences Co dispersion and morphology of 20 wt% Co/γ -Al 2 O 3. • Lower rates for H 2 chemisorption and smaller θ H at 100 °C with smaller Co particles. • Similar θ CO and θ CHx (d Co ∼ 10 nm) but larger θ CxHy (inactive) for d Co ∼ 7 nm. • Similar TOF and TOF ITK (s−1) for Co/γ -Al 2 O 3 with d Co in the ∼7–10 nm range. • d Co ~ 7 nm promotes similar reactivity CO-s for CH 4 formation as opposed to d Co ∼ 10 nm. Two commercial Co-based catalysts supported on carbon-coated and uncoated γ-Al 2 O 3 (during Co deposition) of different Co particle size (∼7 and 10 nm) and surface structure were investigated to address the effect of preparation route on important kinetic parameters of the methanation reaction (5 vol% CO, H 2 /CO = 2, P = 1.1 bar) by advanced transient isotopic and operando DRIFTS experiments. 13CO-SSITKA-Mass Spectrometry experiments performed at 230 °C and after 32 h on TOS, showed that the surface coverage (θ CO) and mean residence time (τ CO , s) of reversibly adsorbed CO-s are not influenced by the different preparation route, while θ CHx , TOF CH4 (s−1) and the τ CHx (s) related to the active carbonaceous species were slightly increased with increasing Co particle size (in the 7–10 nm range). On the other hand, the kinetic rates of CO conversion and CH 4 production (μmol g−1 s−1) were found to increase with decreasing Co particle size. The TOF CH4,ITK (s−1) estimated on the basis of the measured active CH x -s and CO-s species was found very similar for the two Co particle sizes. The effective rate constant of hydrogenation of CH x -s (k eff , s−1) after short time on stream (1 h) was found to increase with increasing Co particle size as the result of the different preparation route applied. Transient isothermal hydrogenation (TIH) experiments following the 13CO-SSITKA-MS gas switch measured the concentration of inactive CH x (C β) species formed after 32 h of reaction and which were found to be readily hydrogenated at 230 °C. Temperature-programmed hydrogenation (TPH) experiments estimated the concentration of other types of inactive carbonaceous species (C γ), which were hydrogenated at elevated temperatures (250–600 °C). The amounts of C β and C γ species were found to significantly increase with increasing Co particle size, and their kinetics of hydrogenation was dependent of Co particle size. These results provided evidence for the lower deactivation rate observed under industrial FTS conditions over the Co/γ-Al 2 O 3 (carbon-coated) catalyst. Operando SSITKA-MS-DRIFTS studies followed by transient isothermal hydrogenation coupled with kinetic modeling highlighted the influence of Co particle size on the relative reactivity (k eff) of two different types of adsorbed CO-s towards hydrogen. Catalyst characterization was performed by HAADF-STEM, H 2 -TPR and transient hydrogen chemisorption at 100 °C followed by TPD. [ABSTRACT FROM AUTHOR]

A series of Pt/Ce x Zr 1-x O 2-δ (x = 0.4–0.6) solids were synthesized and evaluated for the SCR of NO under lean burn conditions (2.5 vol% O 2 ) using C 3 H 6 and H 2 as reducing agents. SSITKA-Mass Spectrometry, SSITKA-DRIFTS and other in situ DRIFTS experiments were conducted for the first time to gather fundamental information in explaining the remarkable H 2 /C 3 H 6 synergy effect towards steady-state selective reduction of NO into N 2 at T > 400 °C. In particular, the chemical structure of adsorbed active and inactive (spectator) NO x species formed under C 3 H 6 -SCR, H 2 -SCR and H 2 /C 3 H 6 -SCR of NO and the surface coverage and site formation of active NO x were probed. The Pt/Ce 1-x Zr x O 2-δ catalysts present significant differences in their H 2 -SCR performance (NO conversion and N 2 -selectivity) in the low-temperature range of 120–180 °C but practically the same catalytic behavior at higher temperatures. It was proved that the active NO x of the H 2 -SCR path reside within a reactive zone around each Pt nanoparticle which extends to less than one lattice constant within the support surface. The chemical structure of the active intermediate was proved to be the chelating nitrite , whereas nitrosyl, monodentate and bidentate nitrates were considered as inactive species (spectators). It was illustrated for the first time that the presence of 15 vol% H 2 O in the H 2 -SCR feed stream applied over the 0.1 wt% Pt/Ce 0.5 Zr 0.5 O 2 catalyst results in a 25% decrease in the concentration of active NO x , thus partly explaining the drop in activity observed when compared to the H 2 -SCR in the absence of H 2 O. A remarkable activity and N 2 -selectivity enhancement was observed at T > 400 °C when both H 2 and C 3 H 6 reducing agents were used compared to H 2 -SCR or C 3 H 6 -SCR alone. This synergy effect was explained to arise mainly because of the increase of θ Η by the presence of –CH x species derived from adsorbed propylene decomposition on Pt, which block sites of oxygen chemisorption, and of the increase of surface oxygen vacant sites that promote the formation of a more active chelating nitrite (NO 2 − ) species compared to the case of H 2 -SCR. [ABSTRACT FROM AUTHOR]

A series of 0.5 wt% Pt/Ce 0.5 La 0.5 O 2 − δ (Ce:La = 1:1) catalysts, the supports of which were prepared by different methods, namely: (i) sol–gel using citrate or oxalate as complexing agent, (ii) pechini, and (iii) urea co-precipitation, were investigated for the first time towards the water–gas shift (WGS) reaction in the 250–350 °C range and 1 atm total pressure. Towards a better understanding of the effect of support synthesis method on the intrinsic kinetic rate of WGS expressed per gram of catalyst (μmol CO g −1 s −1 ) or per length of the perimeter of Pt-support interface (μmol CO cm −1 s −1 ), a suite of various characterisation methods such as: in situ Raman, temperature-programmed techniques (TPD-H 2 , TPD-NH 3 , TPD-CO 2 ), powder XRD, and oxygen storage capacity (OSC) measurements were applied. The intrinsic kinetic rate of WGS (μmol CO g −1 s −1 ) was correlated with the concentration of the active “carbon-containing” (C-pool) and “hydrogen-containing” (H-pool) reaction intermediates formed within a reactive zone (Δ x , Å) around each Pt nanoparticle (1.2–1.5 nm), parameters that were estimated via SSITKA and non steady-state transient isotopic and titration with water operando experiments. The urea co-precipitation method (U) resulted in the formation of a Ce 1 − x La x O 2 − δ solid solution with different composition (Ce:La atom ratio) than that formed by the other synthesis methods, which may be the main reason for Pt/Ce 0.5 La 0.5 O 2 − δ (U) to exhibit the highest by far CO conversion and kinetic rate towards the WGS compared to the other supported Pt catalysts. The same method (U) resulted in the formation of La 2 O 3 as opposed to the other methods. However, this was not considered as the main reason for explaining the higher activity of Pt supported on Ce 0.5 La 0.5 O 2 − δ (U) compared to the other carriers. The Ce 0.5 La 0.5 O 2 − δ (U) was also found to possess the highest surface acidity and basicity compared to the other supports but lower OSC (μmol g −1 ) (by more than 30% in the 250–550 °C range) than Ce 0.5 La 0.5 O 2 − δ prepared by the citrate sol–gel method, in harmony with the lower content of O vacancies in Ce 0.5 La 0.5 O 2 − δ (U) as evidenced by Raman studies. Transient DRIFTS formate (HCOO–) decomposition kinetic experiments towards CO 2 and H 2 formation have illustrated the importance of the presence of Pt and support composition. [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 20 wt% Co-0.05 wt% Pt/γ-Al2O3 catalyst was investigated to obtain a fundamental understanding of the effect of CO partial pressure (constant H2 partial pressure) on important kinetic parameters of the methanation reaction (x vol% CO/25 vol% H2, x = 3, 5 and 7) by performing advanced transient isotopic and operando diffuse reflectance infrared Fourier transform spectroscopy–mass spectrometry (DRIFTS-MS) experiments. Steady State Isotopic Transient Kinetic Analysis (SSITKA) experiments conducted at 1.2 bar, 230 °C after 5 h in CO/H2 revealed that the surface coverages, θCO and θCHx and the mean residence times, τCO, and τCHx (s) of the reversibly adsorbed CO-s and active CHx-s (Cα) intermediates leading to CH4, respectively, increased with increasing CO partial pressure. On the contrary, the apparent activity (keff, s−1) of CHx-s intermediates, turnover frequency (TOF, s−1) of methanation reaction, and the CH4-selectivity (SCH4, %) were found to decrease. Transient isothermal hydrogenation (TIH) following the SSITKA step-gas switch provided important information regarding the reactivity and concentration of active (Cα) and inactive -CxHy (Cβ) carbonaceous species formed after 5 h in the CO/H2 reaction. The latter Cβ species were readily hydrogenated at 230 °C in 50%H2/Ar. The surface coverage of Cβ was found to vary only slightly with increasing CO partial pressure. Temperature-programmed hydrogenation (TPH) following SSITKA and TIH revealed that other types of inactive carbonaceous species (Cγ) were formed during Fischer-Tropsch Synthesis (FTS) and hydrogenated at elevated temperatures (250–550 °C). The amount of Cγ was found to significantly increase with increasing CO partial pressure. All carbonaceous species hydrogenated during TIH and TPH revealed large differences in their kinetics of hydrogenation with respect to the CO partial pressure in the CO/H2 reaction mixture. Operando DRIFTS-MS transient isothermal hydrogenation of adsorbed CO-s formed after 2 h in 5 vol% CO/25 vol% H2/Ar at 200 °C coupled with kinetic modeling (H-assisted CO hydrogenation) provided information regarding the relative reactivity (keff) for CH4 formation of the two kinds of linear-type adsorbed CO-s on the cobalt surface. [ABSTRACT FROM AUTHOR]