Realistic <i>Operando‐</i>DRIFTS Studies on Cu/ZnO Catalysts for CO<sub>2</sub> Hydrogenation to Methanol – Direct Observation of Mono‐ionized Defect Sites and Implications for Reaction Intermediates

Krossing, Ingo; Fehr, Samuel M.; Nguyen, Karin

doi:10.1002/cctc.202101500

Cited by 25 publications

(20 citation statements)

References 110 publications

(228 reference statements)

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“…Irrespective of the true kind of active sites for the conversion of CO 2 to CH 3 OH, various theoretical and experimental studies suggest formate or hydrocarboxyl species as reactive surface intermediates. − They undergo stepwise hydrogenation, leading finally to this alcohol. Using diffuse reflectance infrared Fourier transform spectroscopy, we identified formate species (Figure S15) on the surface of the spent sample (after 188 h on the CO 2 hydrogenation stream at 20 bar).…”

Section: Resultsmentioning

confidence: 99%

Revealing Origins of Methanol Selectivity Loss in CO₂ Hydrogenation over CuZn-Containing Catalysts

et al. 2022

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CO2 hydrogenation to methanol (CH3OH) is widely accepted to proceed through two parallel reactions: (i) CH3OH formation and (ii) the reverse water gas shift (RWGS) reaction to CO. The latter reaction causes the loss of CH3OH selectivity. Our spatially resolved analysis of rates of product formation over a classical CuZnAlO x catalyst in a broad range of CO2 conversion degrees (from 0 to 90% of equilibrium conversion) suggests revisiting this concept. In comparison with the RWGS reaction, CH3OH decomposition to CO mainly contributes to the loss of CH3OH selectivity with a rising degree of CO2 conversion. Separate CH3OH decomposition tests in a broad range of experimental conditions proved that this side reaction is accelerated by H2O but negatively affected by H2 and rising total pressure. Moreover, the decomposition should occur on other sites rather than those participating in CH3OH synthesis from CO2 and can be practically suppressed above certain partial pressures of CH3OH and H2O due to site saturation. The sites responsible for the hydrogenation of CO2 to CH3OH, however, are not saturated. Thus, this product can be further produced in downstream catalyst layers. As this concept is valid for several CuZn-based catalysts, we provide fundamentals for the design of selective CH3OH synthesis catalysts and for optimizing reaction conditions. Operating under conditions, where the undesired CH3OH decomposition reaction is hindered, enabled us to achieve 93% CH3OH selectivity at 19% CO2 conversion (55% equilibrium conversion) at 50 bar and 200 °C using a feed with the ratio of H2/CO2 of 3.

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Section: Resultsmentioning

confidence: 99%

Revealing Origins of Methanol Selectivity Loss in CO₂ Hydrogenation over CuZn-Containing Catalysts

et al. 2022

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“…S6 †). 69,70 Therefore, the decrease in Cu dispersion is exclusively related to the oxidation of the catalyst.…”

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confidence: 99%

Dynamics of the Cu/CeO₂catalyst during methanol steam reforming

Jin

Wang

et al. 2022

Catal. Sci. Technol.

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“…Figure 6 displayed the spectra obtained during the switch over both catalysts. The bands at 1590 and 1352 cm −1 were related to the asymmetric and symmetric vibrations of formate species formed in unlabeled CO 2 /H 2 reactants over both Cu/BaTiO 3 and Cu/BaTiO 2.8 H 0.2 catalysts [21a,22] . After switching CO 2 /H 2 /Ar to 13 CO 2 /He/H 2 , the intensity of the unlabeled formate species at ~1590 cm −1 decreased with simultaneous appearance and increase of the labeled species characterized by the new band at ~1537 cm −1 .…”

Section: Resultsmentioning

confidence: 94%

Significant Roles of Surface Hydrides in Enhancing the Performance of Cu/BaTiO_2.8H_0.2 Catalyst for CO₂ Hydrogenation to Methanol

He,

Li,

Lei

et al. 2023

Angew Chem Int Ed

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Tuning the anionic site of catalyst supports can impact reaction pathways by creating active sites on the support or influencing metal‐support interactions when using supported metal nanoparticles. This study focuses on CO2 hydrogenation over supported Cu nanoparticles, revealing a 3‐fold increase in methanol yield when replacing oxygen anions with hydrides in the perovskite support (Cu/BaTiO2.8H0.2 yields ~146 mg/h/gCu vs. Cu/BaTiO3 yields ~50 mg/h/gCu). The contrast suggests that significant roles are played by the support hydrides in the reaction. Temperature programmed reaction and isotopic labelling studies indicate that BaTiO2.8H0.2 surface hydride species follow a Mars van Krevelen mechanism in CO2 hydrogenation, promoting methanol production. High‐pressure steady‐state isotopic transient kinetic analysis (SSITKA) studies suggest that Cu/BaTiO2.8H0.2 possesses both a higher density and more active and selective sites for methanol production compared to Cu/BaTiO3. An operando high‐pressure diffuse reflectance infrared spectroscopy (DRIFTS)‐SSITKA study shows that formate species are the major surface intermediates over both catalysts, and the subsequent hydrogenation steps of formate are likely rate‐limiting. However, the catalytic reactivity of Cu/BaTiO2.8H0.2 towards the formate species is much higher than Cu/BaTiO3, likely due to the altered electronic structure of interface Cu sites by the hydrides in the support as validated by density functional theory (DFT) calculations.

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Realistic Operando‐DRIFTS Studies on Cu/ZnO Catalysts for CO₂ Hydrogenation to Methanol – Direct Observation of Mono‐ionized Defect Sites and Implications for Reaction Intermediates

Cited by 25 publications

References 110 publications

Revealing Origins of Methanol Selectivity Loss in CO₂ Hydrogenation over CuZn-Containing Catalysts

Revealing Origins of Methanol Selectivity Loss in CO₂ Hydrogenation over CuZn-Containing Catalysts

Dynamics of the Cu/CeO₂catalyst during methanol steam reforming

Significant Roles of Surface Hydrides in Enhancing the Performance of Cu/BaTiO_2.8H_0.2 Catalyst for CO₂ Hydrogenation to Methanol

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Realistic Operando‐DRIFTS Studies on Cu/ZnO Catalysts for CO2 Hydrogenation to Methanol – Direct Observation of Mono‐ionized Defect Sites and Implications for Reaction Intermediates

Cited by 25 publications

References 110 publications

Revealing Origins of Methanol Selectivity Loss in CO2 Hydrogenation over CuZn-Containing Catalysts

Revealing Origins of Methanol Selectivity Loss in CO2 Hydrogenation over CuZn-Containing Catalysts

Dynamics of the Cu/CeO2catalyst during methanol steam reforming

Significant Roles of Surface Hydrides in Enhancing the Performance of Cu/BaTiO2.8H0.2 Catalyst for CO2 Hydrogenation to Methanol

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Realistic Operando‐DRIFTS Studies on Cu/ZnO Catalysts for CO₂ Hydrogenation to Methanol – Direct Observation of Mono‐ionized Defect Sites and Implications for Reaction Intermediates

Revealing Origins of Methanol Selectivity Loss in CO₂ Hydrogenation over CuZn-Containing Catalysts

Revealing Origins of Methanol Selectivity Loss in CO₂ Hydrogenation over CuZn-Containing Catalysts

Dynamics of the Cu/CeO₂catalyst during methanol steam reforming

Significant Roles of Surface Hydrides in Enhancing the Performance of Cu/BaTiO_2.8H_0.2 Catalyst for CO₂ Hydrogenation to Methanol