Isotopic homogenization and scrambling associated with oxygen isotopic exchange on hot platinum: studies on gas pairs (O-2, CO2) and (CO, CO2)

Prasanna, K and Bhattacharya, SK and Ghosh, Prosenjit and Mahata, Sasadhar and Liang, Mao-Chang (2016) Isotopic homogenization and scrambling associated with oxygen isotopic exchange on hot platinum: studies on gas pairs (O-2, CO2) and (CO, CO2). In: RSC ADVANCES, 6 (56). pp. 51296-51303.

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Abstract

The catalytic exchange between O-2 and CO2 on hot platinum leads to isotope scrambling in CO2 and homogenization of the oxygen isotopes in the two phases (O2 and CO2) even though the two gases could be widely different in isotope ratios from each other (e.g., about 45 parts per thousand in delta O-18) before the exchange. After the exchange, the d(18)O values of the gases become close to each other (within 2 parts per thousand) depending on the time and temperature. The clumped-isotope analysis of the post-exchange CO2 samples shows that the Delta(47) values (relative to the pre-exchange values) decrease with increase in temperature from near zero (at similar to 25 degrees C) to about similar to 0.8 +/- 0.1 parts per thousand (at similar to 700 degrees C). The low value of -0.8 parts per thousand equals the values typically obtained for pure CO2 heated to 1000 degrees C inside quartz tubes suggesting a scrambled state. If the catalytic exchange between CO2 and O-2 is associated with isotopic scrambling (or random mixing) a microscopic mechanism of isotopic mixing can be inferred. It seems that CO2 and O-2 dissociate in the adsorbed state on platinum (or quartz surfaces) and the product CO molecules and O atoms mix uniformly while doing a random walk on the hot surface and produce two reservoirs (CO and O) where the three oxygen isotopes are randomly distributed. This can produce the observed internal isotopic scrambling in CO2 when CO and O recombine to form CO2 molecules on the platinum surface and desorb. Experiments using CO-CO2 gas pairs over hot platinum also show homogenization showing exchange of CO as a molecular entity and supporting the suggested mechanism.

Item Type:	Journal Article
Publication:	RSC ADVANCES
Publisher:	ROYAL SOC CHEMISTRY
Additional Information:	Copy right for this article belongs to the ROYAL SOC CHEMISTRY, THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND
Department/Centre:	Division of Mechanical Sciences > Centre for Earth Sciences Division of Mechanical Sciences > Divecha Centre for Climate Change
Date Deposited:	08 Jul 2016 05:36
Last Modified:	08 Jul 2016 05:36
URI:	http://eprints.iisc.ac.in/id/eprint/54169

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