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Title: Catalytic oxidation of methane over ZrO{sub 2}-supported Pd catalysts

Abstract

The catalytic oxidation of methane has been examined in an integral reactor over Pd/ZrO{sub 2} catalysts in this study in order to determine how various preparation pretreatment and reaction variables influence activity. The conversion of methane versus temperature data indicate that mild oxidative and reductive treatments enhance the activity of a 5 wt% Pd/ZrO{sub 2} catalyst while a higher-temperature reductive pretreatment produces a less efficient catalyst. Increasing the Pd loading from 0.1 to 10 wt% improves catalytic performance while higher loadings yield negligible improvement. Decay studies were performed on a 5 wt% Pd/ZrO{sub 2} catalyst and compared to those of an optimized Pd/Al{sub 2}O{sub 3} catalyst. Under the conditions used in this study, the activity of the Pd/ZrO{sub 2} catalyst remains fairly constant over a 50-hr period while the Pd/Al{sub 2}O{sub 3} catalyst initially exhibits an increase in activity but then a decrease after approximately 16 hr. At 250 C the Pd/ZrO{sub 2} converts 56% of the methane to CO{sub 2} and H{sub 2}O after approximately 45 hr while the Pd/Al{sub 2}O{sub 3} catalytically oxidizes only 32% of the methane under the same conditions. An optimized Pd/ZrO{sub 2} catalyst achieves a methane conversion of 100% below 300 C, which ismore » 40 C lower than that obtained using the optimized Pd/Al{sub 2}O{sub 3} catalyst. The 5 wt% Pd/ZrO{sub 2} CH{sub 4}-oxidation catalyst also was characterized using X-ray photoelectron spectroscopy before and during heating in vacuum at 180 C and after treatment in a 2:1 mixture of O{sub 2} and CH{sub 4} at 180 C and 100 Torr for 45 min. The near-surface region of the as-entered catalyst consists mostly of ZrO{sub 2} and PdO along with some Pd metal. Some of the PdO is reduced to Pd metal at 180 C, which is near the onset temperature for methane oxidation, and the Pd signal is diminished probably due to agglomeration of the Pd. Exposure of the catalyst to a 100 Torr mixture of 2:1 O{sub 2} and CH{sub 4} at 180 C for 45 min results in the formation of adsorbed CH{sub x}, CO and CO{sub 3}{sup {minus}2} and/or HCO{sub 3}{sup {minus}} species. These data suggest that the CH{sub 4} hydrogen bonds are first broken to form an adsorbed carbon species, which reacts with surface oxygen to form an adsorbed CO. This CO then reacts to form a surface carbonate or bicarbonate species which decomposes to form CO{sub 2}.« less

Authors:
;  [1]
  1. Univ. of Florida, Gainesville, FL (United States). Dept. of Chemical Engineering
Publication Date:
OSTI Identifier:
328293
Resource Type:
Journal Article
Journal Name:
Journal of Catalysis
Additional Journal Information:
Journal Volume: 182; Journal Issue: 1; Other Information: PBD: 15 Feb 1999
Country of Publication:
United States
Language:
English
Subject:
03 NATURAL GAS; METHANE; OXIDATION; PALLADIUM; CATALYTIC EFFECTS; CHEMICAL PREPARATION; CATALYSTS; CATALYST SUPPORTS; CARBON DIOXIDE; WATER VAPOR; TEMPERATURE DEPENDENCE

Citation Formats

Epling, W S, and Hoflund, G B. Catalytic oxidation of methane over ZrO{sub 2}-supported Pd catalysts. United States: N. p., 1999. Web. doi:10.1006/jcat.1998.2341.
Epling, W S, & Hoflund, G B. Catalytic oxidation of methane over ZrO{sub 2}-supported Pd catalysts. United States. doi:10.1006/jcat.1998.2341.
Epling, W S, and Hoflund, G B. Mon . "Catalytic oxidation of methane over ZrO{sub 2}-supported Pd catalysts". United States. doi:10.1006/jcat.1998.2341.
@article{osti_328293,
title = {Catalytic oxidation of methane over ZrO{sub 2}-supported Pd catalysts},
author = {Epling, W S and Hoflund, G B},
abstractNote = {The catalytic oxidation of methane has been examined in an integral reactor over Pd/ZrO{sub 2} catalysts in this study in order to determine how various preparation pretreatment and reaction variables influence activity. The conversion of methane versus temperature data indicate that mild oxidative and reductive treatments enhance the activity of a 5 wt% Pd/ZrO{sub 2} catalyst while a higher-temperature reductive pretreatment produces a less efficient catalyst. Increasing the Pd loading from 0.1 to 10 wt% improves catalytic performance while higher loadings yield negligible improvement. Decay studies were performed on a 5 wt% Pd/ZrO{sub 2} catalyst and compared to those of an optimized Pd/Al{sub 2}O{sub 3} catalyst. Under the conditions used in this study, the activity of the Pd/ZrO{sub 2} catalyst remains fairly constant over a 50-hr period while the Pd/Al{sub 2}O{sub 3} catalyst initially exhibits an increase in activity but then a decrease after approximately 16 hr. At 250 C the Pd/ZrO{sub 2} converts 56% of the methane to CO{sub 2} and H{sub 2}O after approximately 45 hr while the Pd/Al{sub 2}O{sub 3} catalytically oxidizes only 32% of the methane under the same conditions. An optimized Pd/ZrO{sub 2} catalyst achieves a methane conversion of 100% below 300 C, which is 40 C lower than that obtained using the optimized Pd/Al{sub 2}O{sub 3} catalyst. The 5 wt% Pd/ZrO{sub 2} CH{sub 4}-oxidation catalyst also was characterized using X-ray photoelectron spectroscopy before and during heating in vacuum at 180 C and after treatment in a 2:1 mixture of O{sub 2} and CH{sub 4} at 180 C and 100 Torr for 45 min. The near-surface region of the as-entered catalyst consists mostly of ZrO{sub 2} and PdO along with some Pd metal. Some of the PdO is reduced to Pd metal at 180 C, which is near the onset temperature for methane oxidation, and the Pd signal is diminished probably due to agglomeration of the Pd. Exposure of the catalyst to a 100 Torr mixture of 2:1 O{sub 2} and CH{sub 4} at 180 C for 45 min results in the formation of adsorbed CH{sub x}, CO and CO{sub 3}{sup {minus}2} and/or HCO{sub 3}{sup {minus}} species. These data suggest that the CH{sub 4} hydrogen bonds are first broken to form an adsorbed carbon species, which reacts with surface oxygen to form an adsorbed CO. This CO then reacts to form a surface carbonate or bicarbonate species which decomposes to form CO{sub 2}.},
doi = {10.1006/jcat.1998.2341},
journal = {Journal of Catalysis},
number = 1,
volume = 182,
place = {United States},
year = {1999},
month = {2}
}