skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: CO 2 coverage on Pd catalysts accelerates oxygen removal in oxy-combustion systems
Oxy-combustion systems result in enriched CO 2 in exhaust gases; however, the utilization of the concentrated CO 2 stream from oxy-combustion is limited by remnant O 2 . CH 4 oxidation using Pd catalysts has been found to have high O 2 -removal efficiency. Here, the effect of excess CO 2 in the feed stream on O 2 removal with CH 4 oxidation is investigated by combining experimental and theoretical approaches. Experimental results reveal complete CH 4 oxidation without any side-products, and a monotonic increase in the rate of CO 2 generation with an increase in CO 2 concentration in the feed stream. Density-functional theory calculations show that high surface coverage of CO 2 on Pd leads to a reduction in the activation energy for the initial dissociation of CH 4 into CH 3 and H, and also the subsequent oxidation reactions. A CO 2 -rich environment in oxy-combustion systems is therefore beneficial for the reduction of oxygen in exhaust gases.  more » « less
Award ID(s):
1729787 1931610 1806147
PAR ID:
10402910
Author(s) / Creator(s):
; ; ;
Date Published:
Journal Name:
Physical Chemistry Chemical Physics
Volume:
25
Issue:
8
ISSN:
1463-9076
Page Range / eLocation ID:
6527 to 6536
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; (, Angewandte Chemie International Edition)
    Abstract Direct synthesis of CH3COOH from CH4and CO2is an appealing approach for the utilization of two potent greenhouse gases that are notoriously difficult to activate. In thisCommunication, we report an integrated route to enable this reaction. Recognizing the thermodynamic stability of CO2, our strategy sought to first activate CO2to produce CO (through electrochemical CO2reduction) and O2(through water oxidation), followed by oxidative CH4carbonylation catalyzed by Rh single atom catalysts supported on zeolite. The net result was CH4carboxylation with 100 % atom economy. CH3COOH was obtained at a high selectivity (>80 %) and good yield (ca. 3.2 mmol g−1catin 3 h). Isotope labelling experiments confirmed that CH3COOH is produced through the coupling of CH4and CO2. This work represents the first successful integration of CO/O2production with oxidative carbonylation reaction. The result is expected to inspire more carboxylation reactions utilizing preactivated CO2that take advantage of both products from the reduction and oxidation processes, thus achieving high atom efficiency in the synthesis. 
    more » « less
  2. ; ; ; (, ChemPhysChem)
    Abstract Herein, we report on the synthesis of ultrasmall Pd nanoclusters (∼2 nm) protected by L‐cysteine [HOCOCH(NH2)CH2SH] ligands (Pdn(L‐Cys)m) and supported on the surfaces of CeO2, TiO2, Fe3O4, and ZnO nanoparticles for CO catalytic oxidation. The Pdn(L‐Cys)mnanoclusters supported on the reducible metal oxides CeO2, TiO2and Fe3O4exhibit a remarkable catalytic activity towards CO oxidation, significantly higher than the reported Pd nanoparticle catalysts. The high catalytic activity of the ligand‐protected clusters Pdn(L‐Cys)mis observed on the three reducible oxides where 100 % CO conversion occurs at 93–110 °C. The high activity is attributed to the ligand‐protected Pd nanoclusters where the L‐cysteine ligands aid in achieving monodispersity of the Pd clusters by limiting the cluster size to the active sub‐2‐nm region and decreasing the tendency of the clusters for agglomeration. In the case of the ceria support, a complete removal of the L‐cysteine ligands results in connected agglomerated Pd clusters which are less reactive than the ligand‐protected clusters. However, for the TiO2and Fe3O4supports, complete removal of the ligands from the Pdn(L‐Cys)mclusters leads to a slight decrease in activity where the T100%CO conversion occurs at 99 °C and 107 °C, respectively. The high porosity of the TiO2and Fe3O4supports appears to aid in efficient encapsulation of the bare Pdnnanoclusters within the mesoporous pores of the support. 
    more » « less
  3. ; ; (, Journal of The Electrochemical Society)
    To cut CO2emissions, we propose to directly convert shale gas into value-added products with a new H2/O2co-transport membrane (HOTM) reactor. A Multiphysics model has been built to simulate the membrane and the catalytic bed with parameters obtained from experimental validation. The model was used to compare C2 yield and CH4conversion rate between the membrane reactor and the state-of-the-art fixed-bed reactor with the same dimensions and operating conditions. The results indicate that (1) the membrane reactor is more efficient in consuming CH4for a given amount of fed O2. (2) The C2 selectivity of the membrane reactor is higher due to the gradual addition of O2into the reactor. (3) The current proposed membrane reactor can have a decent proton molar flux density but most of the proton molar flux will contribute to producing H2O on the feed side under the current operating conditions. The paper for the first-time projects the performance of the membrane reactor for combined H2O/H2removal and C2 production. It could be used as important guidance for experimentalists to design next generation natural gas conversion reactors. 
    more » « less
  4. ; ; ; ; ; (, Journal of Physics D: Applied Physics)
    Abstract In this work, we investigated atmospheric pressure plasma jet (APPJ)-assisted methane oxidation over a Ni-SiO 2 /Al 2 O 3 catalyst. We evaluated possible reaction mechanisms by analyzing the correlation of gas phase, surface and plasma-produced species. Plasma feed gas compositions, plasma powers, and catalyst temperatures were varied to expand the experimental parameters. Real-time Fourier-transform infrared spectroscopy was applied to quantify gas phase species from the reactions. The reactive incident fluxes generated by plasma were measured by molecular beam mass spectroscopy using an identical APPJ operating at the same conditions. A strong correlation of the quantified fluxes of plasma-produced atomic oxygen with that of CH 4 consumption, and CO and CO 2 formation implies that O atoms play an essential role in CH 4 oxidation for the investigated conditions. With the integration of APPJ, the apparent activation energy was lowered and a synergistic effect of 30% was observed. We also performed in-situ diffuse reflectance infrared Fourier-transform spectroscopy to analyze the catalyst surface. The surface analysis showed that surface CO abundance mirrored the surface coverage of CH n at 25 °C. This suggests that CH n adsorbed on the catalyst surface as an intermediate species that was subsequently transformed into surface CO. We observed very little surface CH n absorbance at 500 °C, while a ten-fold increase of surface CO and stronger CO 2 absorption were seen. This indicates that for a nickel catalyst at 500 °C, the dissociation of CH 4 to CH n may be the rate-determining step in the plasma-assisted CH 4 oxidation for our conditions. We also found the CO vibrational frequency changes from 2143 cm −1 for gas phase CO to 2196 cm −1 for CO on a 25 °C catalyst surface, whereas the frequency of CO on a 500 °C catalyst was 2188 cm −1 . The change in CO vibrational frequency may be related to the oxidation of the catalyst. 
    more » « less
  5. ; ; ; ; (, Proceedings of the National Academy of Sciences)
    Carbon dioxide (CO 2 ) supersaturation in lakes and rivers worldwide is commonly attributed to terrestrial–aquatic transfers of organic and inorganic carbon (C) and subsequent, in situ aerobic respiration. Methane (CH 4 ) production and oxidation also contribute CO 2 to freshwaters, yet this remains largely unquantified. Flood pulse lakes and rivers in the tropics are hypothesized to receive large inputs of dissolved CO 2 and CH 4 from floodplains characterized by hypoxia and reducing conditions. We measured stable C isotopes of CO 2 and CH 4 , aerobic respiration, and CH 4 production and oxidation during two flood stages in Tonle Sap Lake (Cambodia) to determine whether dissolved CO 2 in this tropical flood pulse ecosystem has a methanogenic origin. Mean CO 2 supersaturation of 11,000 ± 9,000 μ atm could not be explained by aerobic respiration alone. 13 C depletion of dissolved CO 2 relative to other sources of organic and inorganic C, together with corresponding 13 C enrichment of CH 4 , suggested extensive CH 4 oxidation. A stable isotope-mixing model shows that the oxidation of 13 C depleted CH 4 to CO 2 contributes between 47 and 67% of dissolved CO 2 in Tonle Sap Lake. 13 C depletion of dissolved CO 2 was correlated to independently measured rates of CH 4 production and oxidation within the water column and underlying lake sediments. However, mass balance indicates that most of this CH 4 production and oxidation occurs elsewhere, within inundated soils and other floodplain habitats. Seasonal inundation of floodplains is a common feature of tropical freshwaters, where high reported CO 2 supersaturation and atmospheric emissions may be explained in part by coupled CH 4 production and oxidation. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email