In Situ Control of the Adsorption Species in CO₂ Hydrogenation: Determination of Intermediates and Byproducts

Abstract

CO 2 hydrogenation over catalysts is a potentially exciting method to produce fuels while closing the CO 2 cycle and mitigating global warming. The mechanism of this process has been controversial due to the difficulty in clearly identifying the species present and distinguishing which are reaction intermediates and which are byproducts. We in situ manipulated the independent formation and hydrogenation of each adsorption species produced in CO 2 hydrogenation reaction over Ru/Al 2 O 3 using operando diffuse reflectance infrared Fourier transformation spectroscopy (DRIFTS) and executed a novel iterative Gaussian fitting procedure. The adsorption species and their role in the CO 2 hydrogenation reaction have been clearly identified. The adsorbed carbon monoxide (CO*) of four reactive structures was the key intermediate of methane (CH 4) production. Bicarbonate (HCO 3 − *), formed on the metal−support interface, appeared to be not only the primary product of CO 2 chemisorption but also a reservoir of CO* and consisted of the dominate reaction steps of CO 2 methanation from the interface to the metal surface. Bidentate formate (Bi-HCOO − *) formed on Ru under a certain condition, consecutively converting to CO* to merge into the subsequent methanation process. Nonreactive byproducts of the reaction were also identified. The evolution of the surface species revealed the essential steps of the CO 2 activation and hydrogenation reactions which were inevitably initiated from HCO 3 − * to CO* and finally from CO* to CH 4 .

Solvent‐ and Catalyst‐Free Carbon Dioxide Capture and Reduction to Formate with Borohydride Ionic Liquid

“…The peak at =1680 cm −1 increased during the first 20 min, then decreased gradually to zero. The peaks at =1712 cm −1 increased over the first 50 min, then decreased until equilibrium was reached after 2 h. From these trends, the peaks at =1680 and 1712 cm −1 are assigned to the C=O stretching of CO 2 δ − and HCOO − , respectively . The peak at =1604 cm −1 developed at the same rate as the peak at =1680 cm −1 .…”

Hydrothermal Synthesis of Ruthenium Nanoparticles with a Metallic Core and a Ruthenium Carbide Shell for Low-Temperature Activation of CO2 to Methane

“…S13), we can conclude that a direct CO2 hydrogenation path to CH4 takes place on the Ru@C-EDTA-20 sample, while contribution of a RWGS reaction mechanism occurs on the Ru/C sample in the presence of Ru 0 , in agreement to previous studies. 35,[37][38][39][40][41][42] Moreover, the fact that 13 CH4 is not observed in the isotopic studies of the Ru@C-EDTA-20 sample allows to discard the co-existence of Ru 0 species on the catalyst surface or, if present, it should be in a very low amount, being the activity ascribed predominately to the presence of RuC species. Based on it, a core shell structure containing a metallic core and an upper shell of ruthenium carbide and carbon species can be proposed in our catalysts.…”

Identifying Reaction Species by Evolutionary Fitting and Kinetic Analysis: An Example of CO2 Hydrogenation in DRIFTS

“…In comparison, ex situ HCOO − * hydrogenation on Al 2 O 3 produced noticeable gaseous CO above 200°C, which was represented by the occurrence of the rotational-vibrational peaks centered at 2142 cm −1 (Figure S2e), and invariant adsorbed CO 2 *, which was represented by OCO symmetric stretching and resonance at 1387 and 1288 cm −1 , respectively ( Figure S2f) 14 The main contribution of this work is the methodology of decoupling the peaks and understanding their meaning via the BEGF program. The initial values of peak positions in BEGF were taken from the IR bands of the samples of carbonates and bicarbonates ( Figure S5).…”

“…(3) the centroid of a given peak is identical for all spectra; (4) peak evolution directly gives the kinetics of the species; (5) manual intervention is not needed; and 6 14…”