In Situ IR Study of Transient CO₂ Reforming of CH₄ over Rh/Al₂O₃

Abstract

The CO2−CH4 reaction on Rh/Al2O3 was studied by in situ infrared spectroscopy coupled with pulse and step transient techniques. Steady-state isotopic 13CO transient studies at 773 K and 0.1 MPa show that the formation of gaseous 13CO2 closely follows that of linear 13CO, indicating that linear CO is an active adsorbate. Pulsing CH4 into CO2 flow and step switching from He to CO2/CH4 flow showed that the formation of H2 led that of CO, revealing that the first step of the reaction sequence is the decomposition of CH4 into *CH x species and hydrogen. Hydrogen activated adsorbed CO2 to produce linear CO. The linear CO was found to be the major species on Rh/Al2O3 during the reaction by in situ infrared spectroscopy. The accumulation of the linear CO on Rh0 sites revealed that the surface of Rh crystallites on Al2O3 remained in a reduced state throughout the study. The O2 pulse into CO2/CH4 resulted in (i) a total oxidation of CH4 to CO2 and H2O and then (ii) a net increase in the formation of the desired products, CO/H2, at a ratio of 1:1, revealing the promotion of the CO2−CH4 reaction. These are the first reported results on the enhancement of the CO and H2 formation rate via the pulse addition of oxygen into the CO2−CH4 reaction. The difference in product formation can be explained by two different types of adsorbed oxygen: one responsible for total oxidation and the other responsible for partial oxidation. The net increase in CO and H2 formation from the O2 pulse further suggests that combining mixed reforming of CH4 with CO2/O2 and selective poisoning of the total oxidation sites would enhance the selectivity and rate of CO/H2 formation.

Investigation on Reverse Water–gas Shift over La2NiO4 Catalyst by Cw-cavity Enhanced Absorption Spectroscopy During CH4/CO2 Reforming

“…20 s) was observed, which suggested the existence of CHO radical as an intermediate of CH 4 /CO 2 reforming. Stevens et al [29] verified the existence of CHO species (2038-2019 cm )1 band) on Rh/Al 2 O 3 catalyst by means of in situ IR spectroscopy technique. They considered that CH 4 reacted with adoxygen to form the ad-CH x O species, and then CH x O on the active sites further decomposed into adsorbed OH and CH x species.…”

Quantitative analysis of the reactivity of formate species seen by DRIFTS over a Au/Ce(La)O2 water–gas shift catalyst: First unambiguous evidence of the minority role of formates as reaction intermediates

“…The operando DRIFTS-SSITKA method used in the present study uses a single catalytic bed, which allows DRIFTS characterization of the surface of the very same catalyst that is responsible for the catalytic activity measured at the cell exit by gas chromatography or mass spectrometry [8]. This methodology is a powerful tool for an in-depth investigation of catalysts under reaction conditions, similar to the method developed earlier for transmission FTIR by Chuang et al [31,32].…”

Isotopic and kinetic assessment of the mechanism of reactions of CH4 with CO2 or H2O to form synthesis gas and carbon on nickel catalysts

“…Kinetic isotope effects on 7 wt% Ni/MgO-A were measured for CO 2 reforming from forward rates of CH 4 -CO 2 and CD 4 -CO 2 mixtures at 873 K, 25 methane, and 25 kPa water. Both CH 4 -CO 2 and CH 4 -H 2 O reactions showed normal kinetic isotopic effects (Fig.…”