In Situ Spectroscopic Investigation of Low-Temperature Oxidation of Methane over Alumina-Supported Platinum during Periodic Operation

Abstract

Methane oxidation over Pt/Al 2 O 3 at transient inlet-gas conditions was studied in situ using synchronous EDXAS, FTIRS and mass spectrometry. The employed combination of experimental techniques allows for simultaneous analysis of, respectively, the electronic state of platinum, surface coverage of reaction intermediates/products and catalytic activity/selectivity.By cycling of the feed gas composition between net-oxidizing and net-reducing conditions the activity for methane oxidation can be increased as compared to continuous net-oxidising conditions. Using the white-line area of time-resolved XANES spectra, a quantitative estimation of the surface O/Pt ratio indicates the formation of an inhomogeneous surface oxide on the platinum crystallites during reaction. The obtained temporary high activity can be explained ⇤ To whom correspondence should be addressed 1 through Langmuir-Hinshelwood kinetics and may result either from the formation of a partially oxidized platinum surface that is more effective for methane dissociation or, more likely, from a period with more reactive chemisorbed oxygen prior to oxide formation.

Determination of Kinetic Parameters for Methane Oxidation over Pt/-Al2O3 in a Fixed-Bed Reactor

“…Dynamic operation can increase the average conversion of methane compared to steady state conversion [5]. According to Carlsson,et al [6], the differences in the reaction conversion are caused by differences in the catalyst state.…”

Unsteady-state operation of supported platinum catalysts for high conversion of methane

“…As shown in Figure 2, the introduction of the lean/rich phase is always accompanied by a temporary maximum in methane conversion for the alumina containing catalysts, which can be explained based on the sensitivity of the methane oxidation reaction to the surface O/Pt ratio [18], and by achieving an optimal adsorbate composition on the platinum surface through pulsing which leads to high methane conversion [13]. The electronic state of platinum is dependent on the oxidizing/reducing character of the feed.…”

“…However, no such state was reported at the switches from oxidizing to reducing conditions [22]. Furthermore, Becker et al also discussed formation of more reactive chemisorbed oxygen on the platinum surface before oxide formation, as a probable cause of the temporary increased activity at the switches [18].…”

“…In these cases temporary high activity is observed during the switch from net-reducing to net-oxidising conditions and vice versa. For methane oxidation over alumina supported platinum this temporary high activity has been shown to stem either from the formation of a partially oxidized platinum surface that is more e↵ective for dissociation of methane or, more likely, from a period with more reactive chemisorbed oxygen prior to oxide formation [17,18]. We mention that unsteady-state operation of the exhaust temperature also can be used to enhance the methane conversion over alumina supported platinum [19].…”

Dynamic Behavior of Reverse Flow Reactor for Lean Methane Combustion

“…Capturing methane emissions means two things: global warming potential reduction up to 87% and potential thermal energy generation. Oxidation of lean methane concentrations smaller than 1%-v can be conducted over appropriate catalysts, such as Pt or Pd active site [2].…”