“…This shows that the formation of CO 2 occurs mainly at the surface of the catalyst, and that the contribution of the gas-phase reactions for the CO 2 production was small. This is in agreement with results previously reported by Lacombe et al 9 Methane conversion versus residence time over a temperature range of 600−900 °C at t c = 45 mg s/cm 3 . 10 Outlet CO 2 concentration versus residence time over a temperature range of 600−900 °C at t c = 45 mg s/cm 3 .…”
A complete kinetic study of the partial oxidation of methane has been performed in a "catalytic jet-stirred reactor". The main goal of this study was to elucidate the interactions between gas-phase reactions and surface reactions and to propose a detailed heterogeneous-homogeneous mechanism. The catalyst used in this study was lanthanum oxide (La 2 O 3 ). Various kinetic parameters were considered, including the temperature, the residence time, the contact time, and the amount of catalyst. The results revealed a complex behavior. In this first part of the study, the experimental results are given and discussed.
“…This shows that the formation of CO 2 occurs mainly at the surface of the catalyst, and that the contribution of the gas-phase reactions for the CO 2 production was small. This is in agreement with results previously reported by Lacombe et al 9 Methane conversion versus residence time over a temperature range of 600−900 °C at t c = 45 mg s/cm 3 . 10 Outlet CO 2 concentration versus residence time over a temperature range of 600−900 °C at t c = 45 mg s/cm 3 .…”
A complete kinetic study of the partial oxidation of methane has been performed in a "catalytic jet-stirred reactor". The main goal of this study was to elucidate the interactions between gas-phase reactions and surface reactions and to propose a detailed heterogeneous-homogeneous mechanism. The catalyst used in this study was lanthanum oxide (La 2 O 3 ). Various kinetic parameters were considered, including the temperature, the residence time, the contact time, and the amount of catalyst. The results revealed a complex behavior. In this first part of the study, the experimental results are given and discussed.
“…Lanthanum oxides are widely employed as catalysts or catalyst supports in various reactions, particularly in oxidative coupling of methane − which leads to direct formation of C 2 products. Numerous gas-phase studies have been performed on the formation, dissociation, structures, and spectra of lanthanum oxide clusters, ,− whereas there are a very limited number of studies on their reactivity. , We have explored the reactivity of lanthanum oxide cluster anions with butane previously, and hydrogen atom abstraction (HAA) from butane by (La 2 O 3 ) 1–3 O – clusters can be identified due to the presence of O •– radicals within these clusters .…”
Lanthanum oxide cluster cations are prepared by laser ablation and reacted with alkane molecules (n-butane and methane) in a fast flow reactor under thermal collision conditions. A reflectron time-of-flight mass spectrometer is used to detect the cluster distributions before and after the reactions. Hydrogen atom abstraction (HAA) from n-butane by (La 2 O 3 ) N + (N = 1−8, N ≠ 6) is observed, while the HAA from methane is only observed for (La 2 O 3 ) 5 + . The experimentally determined rate constants for HAA vary significantly with the cluster sizes. Density functional theory (DFT) calculations are performed to study the structures and reactivity of (La 2 O 3 ) N + (N = 1−6) clusters. The DFT results suggest that the experimentally observed C−H bond activation by (La 2 O 3 ) N + is facilitated by oxygen-centered radicals. The position of oxygen-centered radicals binding onto the clusters can heavily influence the reactivity in C−H bond activation. This gasphase study improves our understanding about the chemistry of oxygen-centered radicals.
“…Herein, we present the first example of oxide cluster anion, La 6 O 10 À that can activate methane at ambient conditions, and hope that this study can improve our understanding about the mechanisms of thermal methane activation on surfaces. Lanthanum oxide-based catalysts are among the first reported for oxidative coupling of methane [10] that leads to direct formation of C 2 products. The oxygen-centered radical (denoted as O À· ) is proposed to be one important type of the reactive centers on lanthanum oxide surfaces to activate methane.…”
The first example of a metal oxide cluster anion, La6 O10 (-) that can activate methane under ambient conditions is reported. This reaction is facilitated by the oxygen-centered radical (O(-⋅) ) and follows the hydrogen atom transfer mechanism. The La6 O10 (-) has a high vertical electron detachment energy (VDE=4.06 eV) and a high symmetry (C4v ).
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