“…Repeating the CO-TPD experiments after different sputtering times shows that the amount of CO 2 increases with increasing reduction, while the yield for C 2 H 2 remains constant (within a few percent); see Table . This result may indicate an additional route for CO reaction (besides the coupling to acetylene) on defected surfaces; the Boudouard reaction (2CO(a) → CO 2 (g) + C(a); (a) for adsorbed, (g) for gas) is a likely pathway 12b 2 TPD following CO adsorption at 300 K on UO 2 - x ( x ≈ 0.3) (111) single crystal. 3 HRXPS U 4f lines of Ar + -sputtered UO 2 thin film before (a) and after (b−d) reaction with CO at the indicated exposures in langmuirs (1 L = 10 -6 Torr s).
1 Product Yield (%) during TPD Following CO and (CO + 3H 2 ) Adsorption at 300 K over “Reduced” UO 2 - x (111) Surface a productCO + trace H 2 CO + 3H 2 C 2 13 (5) 10 (0.1) CO 20 13 CO 2 54 40 H 2 O 13 37 b a The numbers in parentheses are for the acetylene/ethylene ratios.
…”
Section: Resultsmentioning
confidence: 99%
“…The UO 2 (111) single crystal surface was cleaned prior to all experimentation with several cycles of annealing to 800 K and Ar + sputtering; surface stoichiometry (or substoichiometry) was analyzed by XPS while surface order was checked by low energy electron diffraction (LEED) with the latter showing a sharp hexagonal structure (Figure ). The UO 2 thin film (about 1000 Å thick), prepared by sputter deposition on a Mo substrate,12a was cleaned using a similar method but with annealing temperatures not exceeding 600 K to maintain the integrity of the thin film. The defected surfaces (UO 2 - x ) were obtained with extended periods of Ar + sputtering and analyzed by HRXPS at BNL or by XPS at UA.…”
While coupling reactions of carbon-containing compounds are numerous in organometallic chemistry, they are very rare on well-defined solid surfaces. In this work we show that the reductive coupling of two molecules of carbon monoxide to C2 compounds (acetylene and ethylene) could be achieved on oxygen-defected UO2(111) single crystal and thin film surfaces. This result allows in situ electron spectroscopic investigation of a typical organometallic reaction such as carbon coupling and extends it to heterogeneous catalysis and solids. By using high-resolution photoelectron spectroscopy (HRXPS) it was possible to track the changes in surface states of the U and O atoms as well as identify the intermediate of the reaction. Upon CO adsorption U cations in low oxidation states are oxidized to U4+ ions; this was accompanied by an increase of the O-to-U surface ratios. The HRXPS C 1s lines show the presence of adsorbed species assigned to diolate species (-OCH=CHO-) that are most likely the reaction intermediate in the coupling of two CO molecules to acetylene and ethylene.
“…Repeating the CO-TPD experiments after different sputtering times shows that the amount of CO 2 increases with increasing reduction, while the yield for C 2 H 2 remains constant (within a few percent); see Table . This result may indicate an additional route for CO reaction (besides the coupling to acetylene) on defected surfaces; the Boudouard reaction (2CO(a) → CO 2 (g) + C(a); (a) for adsorbed, (g) for gas) is a likely pathway 12b 2 TPD following CO adsorption at 300 K on UO 2 - x ( x ≈ 0.3) (111) single crystal. 3 HRXPS U 4f lines of Ar + -sputtered UO 2 thin film before (a) and after (b−d) reaction with CO at the indicated exposures in langmuirs (1 L = 10 -6 Torr s).
1 Product Yield (%) during TPD Following CO and (CO + 3H 2 ) Adsorption at 300 K over “Reduced” UO 2 - x (111) Surface a productCO + trace H 2 CO + 3H 2 C 2 13 (5) 10 (0.1) CO 20 13 CO 2 54 40 H 2 O 13 37 b a The numbers in parentheses are for the acetylene/ethylene ratios.
…”
Section: Resultsmentioning
confidence: 99%
“…The UO 2 (111) single crystal surface was cleaned prior to all experimentation with several cycles of annealing to 800 K and Ar + sputtering; surface stoichiometry (or substoichiometry) was analyzed by XPS while surface order was checked by low energy electron diffraction (LEED) with the latter showing a sharp hexagonal structure (Figure ). The UO 2 thin film (about 1000 Å thick), prepared by sputter deposition on a Mo substrate,12a was cleaned using a similar method but with annealing temperatures not exceeding 600 K to maintain the integrity of the thin film. The defected surfaces (UO 2 - x ) were obtained with extended periods of Ar + sputtering and analyzed by HRXPS at BNL or by XPS at UA.…”
While coupling reactions of carbon-containing compounds are numerous in organometallic chemistry, they are very rare on well-defined solid surfaces. In this work we show that the reductive coupling of two molecules of carbon monoxide to C2 compounds (acetylene and ethylene) could be achieved on oxygen-defected UO2(111) single crystal and thin film surfaces. This result allows in situ electron spectroscopic investigation of a typical organometallic reaction such as carbon coupling and extends it to heterogeneous catalysis and solids. By using high-resolution photoelectron spectroscopy (HRXPS) it was possible to track the changes in surface states of the U and O atoms as well as identify the intermediate of the reaction. Upon CO adsorption U cations in low oxidation states are oxidized to U4+ ions; this was accompanied by an increase of the O-to-U surface ratios. The HRXPS C 1s lines show the presence of adsorbed species assigned to diolate species (-OCH=CHO-) that are most likely the reaction intermediate in the coupling of two CO molecules to acetylene and ethylene.
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