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CO2 trapping and methanation allow to reduce greenhouse gas emissions and recycle CO2 into a sustainable fuel, provided renewable H2 is employed. Microwave (MW)-based reactors provide an efficient means to use electrical energy for upgrading chemicals, since MW can selectively heat up the load placed in the reactor and not the reactor itself. In this study, CO2 capture and methanation were investigated using solid adsorbents (ZrO2 and Fe3O4), microwave absorbers (SiC and Fe3O4) and Ru/SiO2 as CO2 the methanation catalyst. The sorption and catalyst beds were located in a domestic MW oven that was used to trigger CO2 desorption and methanation in the presence of H2. The working Fe-based structure turned out to be a mixture of FeO and Fe, which allowed for MW absorption and local heating; it also acted as a CO2 sorbent and reverse water–gas shift catalyst. Various reactor configurations were used, leading to different performances and selectivity to CO and CH4. To the best of our knowledge, this is the first report of its kind showing the potential of using inexpensive microwave technology to readily convert trapped CO2 into valuable products. [ABSTRACT FROM AUTHOR]

Cu/ZrO2 is a promising catalyst for the hydrogenation of CO2 to methanol. Reaction pathways involving formates or hydroxycarbonyls have been proposed. We show here that three different types of formates can be observed under reaction conditions at 220 °C and 3 bar, one being located on metallic Cu and two others being bound to ZrO2. The surface concentrations of formates were determined through calibration curves and their reactivity measured during chemical transient experiments. The Cu‐bound formate represented only about 7 % of surface formates, but exhibited a higher reactivity and was found to be the only formate that could account for all the production of methanol. Copper is thus not there only to activate H2, but also bears other crucial intermediates. This work reemphasizes that fully quantitative IR analyses and transient methods are required to unravel the role of surface species. [ABSTRACT FROM AUTHOR]

Cu/ZrO2 is a promising catalyst for the hydrogenation of CO2 to methanol. Reaction pathways involving formates or hydroxycarbonyls have been proposed. We show here that three different types of formates can be observed under reaction conditions at 220 °C and 3 bar, one being located on metallic Cu and two others being bound to ZrO2. The surface concentrations of formates were determined through calibration curves and their reactivity measured during chemical transient experiments. The Cu‐bound formate represented only about 7 % of surface formates, but exhibited a higher reactivity and was found to be the only formate that could account for all the production of methanol. Copper is thus not there only to activate H2, but also bears other crucial intermediates. This work reemphasizes that fully quantitative IR analyses and transient methods are required to unravel the role of surface species. [ABSTRACT FROM AUTHOR]

Cu/ZrO2 is a promising catalyst for the hydrogenation of CO2 to methanol. Reaction pathways involving formates or hydroxycarbonyls have been proposed. We show here that three different types of formates can be observed under reaction conditions at 220 °C and 3 bar, one being located on metallic Cu and two others being bound to ZrO2. The surface concentrations of formates were determined through calibration curves and their reactivity measured during chemical transient experiments. The Cu‐bound formate represented only about 7 % of surface formates, but exhibited a higher reactivity and was found to be the only formate that could account for all the production of methanol. Copper is thus not there only to activate H2, but also bears other crucial intermediates. This work reemphasizes that fully quantitative IR analyses and transient methods are required to unravel the role of surface species. [ABSTRACT FROM AUTHOR]

Cu/ZrO2 is a promising catalyst for the hydrogenation of CO2 to methanol. Reaction pathways involving formates or hydroxycarbonyls have been proposed. We show here that three different types of formates can be observed under reaction conditions at 220 °C and 3 bar, one being located on metallic Cu and two others being bound to ZrO2. The surface concentrations of formates were determined through calibration curves and their reactivity measured during chemical transient experiments. The Cu‐bound formate represented only about 7 % of surface formates, but exhibited a higher reactivity and was found to be the only formate that could account for all the production of methanol. Copper is thus not there only to activate H2, but also bears other crucial intermediates. This work reemphasizes that fully quantitative IR analyses and transient methods are required to unravel the role of surface species. [ABSTRACT FROM AUTHOR]

The surface species formed during the hydrogenation of CO2 with H2 over a ZrO2-supported Cu catalyst were investigated by operando diffuse reflectance FT-IR spectroscopy at 220 °C and 3 bar. The reactivity of two different formates located on zirconia could be unraveled. The data pointed to ZrO2 hydroxyl groups at 3755 cm−1 as the sites on which carbonates and then formates were hydrogenated to methoxy species. Formate hydrogenation appeared as the slowest step. The most reactive ZrO2-bound formates exhibited a rate constant of reaction about 65 times higher than that of the slower formate. [ABSTRACT FROM AUTHOR]

Fully quantitative analyses of DRIFTS data are required when the surface concentrations and the specific rate constants of reaction (or desorption) of adsorbates are needed to validate microkinetic models. The relationship between the surface coverage of adsorbates and various functions derived from the signal collected by DRIFTS is discussed here. The Kubelka-Munk and pseudoabsorbance (noted here as absorbance, for the sake of brevity) transformations were considered, since those are the most commonly used functions when data collected by DRIFTS are reported. Theoretical calculations and experimental evidence based on the study of CO adsorption on Pt/Si[O.sub.2] and formate species adsorbed on Pt/Ce[O.sub.2] showed that the absorbance (i.e., = log 1/R', with R' = relative reflectance) is the most appropriate, yet imperfect, function to give a linear representation of the adsorbate surface concentration in the examples treated here, for which the relative reflectance R' is typically > 60%. When the adsorbates lead to a strong signal absorption (e.g., R' < 60%), the Kubelka-Munk function is actually more appropriate. The absorbance allows a simple correction of baseline drifts, which often occur during time-resolved data collection over catalytic materials. Baseline corrections are markedly more complex in the case of the other mathematical transforms, including the function proposed by Matyshak and Krylov (Catal. Today 1995, 25, 1-87), which has been proposed as an appropriate representation of surface concentrations in DRIFTS spectroscopy.

The reactivity of the surface species present over a 2%Pt/CeO2 catalyst during the reserve water-gas-shift (RWGS) reaction is investigated by a detailed operando spectrokinetic analysis. The reactivity of the surface species was monitored by DRIFT spectroscopy (DRIFTS) and mass spectrometry (MS) using steady-state isotopic transient kinetic analysis (SSITKA) technique.