行政院國家科學委員會補助專題研究計畫 □ 成 果 報 告
■期中進度報告
含 OH 或 NH2端基分子鍵結於銅的結構、反應和 CO2的作用 研究(第 1 年)
計畫類別：■ 個別型計畫 □ 整合型計畫 計畫編號：NSC 97-2113-M-006-004-MY2
執行期間：2008 年 08 月 01 日至 2010 年 07 月 31 日
計畫主持人：林榮良 共同主持人：
計畫參與人員：
成果報告類型(依經費核定清單規定繳交)：■精簡報告 □完整報告
本成果報告包括以下應繳交之附件：
□赴國外出差或研習心得報告一份
□赴大陸地區出差或研習心得報告一份
□出席國際學術會議心得報告及發表之論文各一份
□國際合作研究計畫國外研究報告書一份
處理方式：除產學合作研究計畫、提升產業技術及人才培育研究計畫、
列管計畫及下列情形者外，得立即公開查詢
□涉及專利或其他智慧財產權，□一年□二年後可公開查詢
執行單位：國立成功大學化學系
附件一
Introduction
Hydrogen sulfide or carbon dioxide produced in refineries, petrochemical plants, natural gas processing plants, and other industries are often removed by amine treating in which alkanolamines, such as monoethanolamine, diethanolamine, and methyldiethanolamine, are most commonly used. Monoethanolamine (HOCH2CH2NH2) investigated in the present study possesses two reactive centers of OH and NH2. Adsorbed bifunctional molecules can show versatile bonding coordination, for example, monodentate forms through ligation with either a functional group with the surface or bidentate forms bonded with both functional groups.1 The design and construction of these anchored systems relate to fundamental surface processes and provide the basis for potential applications as chemical sensors, especially in the case of monodentate species.1
It has been reported that on Cu(100) precovered with oxygen ethanol molecules decompose by dehydrogenation, forming ethoxide intermediate.2 This surface species is stable up to ～350 K and transforms into CH3CHO and H2 at higher temperatures. In the system of dimethylamine on Cu(110) in the presence of surface atomic oxygen, (CH3)2N is suggested to be the reaction intermediate generated through N-H bond scission.3 On O/Ag(110), ethylamine is shown to dissociate by sequentially losing amino’s hydrogen to form adsorbed CH3CH2N.4 This intermediate continues to deprotonate, generating CH3CN and H2 between 300 and 400 K.
Surface reactions of monoethanolamine on mordenites with a high acid-site density and on Ni(100) have been reported.5,6 Adsorption of monoethanolamine at the Brønsted acid sites produces the corresponding ammonium (HOCH2CH2NH3+
), which decomposes into H2O, NH3, and C2H4 at a temperature higher than 673 K.5 Dissociation of monoethanolamine on Ni(100) generates H2, CO, and N2 between 250 and 550, 330–550, and 800–1100 K, respectively, with atomic carbon left on the surface.6 Reports of HOCH2CH2NH2 reactions on single-crystal surfaces are scarce. It is interesting to study the adsorption and reactions of monoethanolamine on surfaces with different structures, in terms of bonding geometry, reaction pathway, surface intermediate, and product distribution, and compare to those of monofunctional molecules with OH or NH2. In the present research, the surface chemistry of HOCH2CH2NH2 on O/Cu(100) is investigated with reflection–absorption infrared spectroscopy (RAIRS) and temperature-programmed reaction/desorption (TPR/D).
Experimental Section
All of the experiments were performed in an ultrahigh vacuum (UHV) apparatus, equipped with an ion gun for sputtering, a differentially pumped mass spectrometer for TPR/D, four-grid spherical retarding field optics for low-energy electron diffraction (LEED), an Auger electron spectrometer with cylindrical mirror analyzer, and a Fourier transformed infrared spectrometer for RAIRS.
Reactions of HOCH2CH2NH2 on O/Cu(100)
Figure 1 shows the TPR/D spectra of the products from HOCH2CH2NH2 reactions on O/Cu(100) at 0.5 L exposure. In addition to the ions indicated in this figure, other ions, such as m/z ) 14, 15, 31, 32, 34, 38, 39, 41, 42, 43, 44, 45, 46, 52, and 56 amu, etc., were also investigated,
but without a desorption feature detected. Therefore, formation of possible reaction products containing N-C-C, C-C-O, or N-C-C-O (other than HOCH2-CH2NH2) as a backbone can be ruled out. The desorption features at 394 K is attributed to H2; 526 K to N2; 290 K to H2O; 334 and 418 K to HCN; 339 K to H2CO; 365 K to HOCH2CH2NH2. The identification of H2O (m/z) 17 and 18 amu), HCN (m/z) 26 and 27 amu), and H2CO (m/z ) 28, 29, and 30 amu) is based on the detected fragmentation patterns that are similar to the NIST reference spectra8 or to those measured using our own spectrometer. The 28 amu desorption state (526 K) may result from N2, C2H4, or CO. Formation of ethylene is first excluded, because no fragments of 26 and 27 amu are detected at this temperature. Variation of the Auger peak intensities of HOCH2CH2NH2 with temperature has been studied and is shown in Figure 2. It is found that the N signal decreases significantly as the temperature is increased from 450 to 600 K, in contrast to the comparable C intensity in this temperature range. Although the possibility of CO formation can not be completely ruled out, this result strongly supports that the desorption state of 28 amu at 526 K is mainly due to N2. The carbon signal is still present at 980 K after the desorption of all of the reaction products. In the previous study of NH3 reaction on preoxidized Ag(110), N2 was found to evolve at 530 K from recombination of surface atomic nitrogen.9 The reaction route from HOCH2CH2NH2 to H2CO and HCN involves dehydrogenation and C-C bond rupture. The HCN desorption with two maximum rates of 334 and 418 K implies that they arise from two different surface intermediates. On Ni(100), the gaseous reaction products of HOCH2CH2NH2 are H2, CO, and N2, without forming H2CO or HCN.6 The nickel surface is more reactive toward breaking the C-N bond and dehydrogenation of HOCH2CH2NH2, as compared to Cu(100). On oxygen-precovered Cu(110) and Ag(110), the only carbon-containing product generated from CH3CH2OH reaction is acetaldehyde.10 Reaction of CH3CH2NH2 on O/Ag(110) produces CH3CN.4 These two reactions only involve loss of hydrogen, and the C-C bonds remain intact. In comparison to our case, substitution of one hydrogen at β-carbon by a reactive center indeed can alter the reaction pathways. On the surfaces of Ag and Cu with adsorbed CH3CH2O, ethanol can be regenerated in the presence of surface atomic hydrogen via a recombinative route.10 Hydrogenation is also observed for CH3CH2NH on Ag(110).4 A similar process can explain the HOCH2CH2NH2 desorption state at 365 K observed in Figure 2. Ethylene glycol (HOCH2CH2OH) reactions on O/Cu(110) and O/Ag(110) have been investigated previously.11–13 On both surfaces, the two OH groups can be oxidized to evolve glyoxal ((CHO)2). Furthermore, recombinative HOCH2CH2OH formation and C-C breakage generating CH2O and adsorbed HCOO are also reported on Ag(110).12
200 300 400 500 600
x 1/2 x 1/5
Ion Intensity (arb. units)
Temperature (K)
m/z 2
28
18 17
27 26
29 30
0.5L HOCH
2CH
2NH
2/O/Cu(100)
x 1/5
x 1/3 394 (H
2)
(N2) 526
290 (H
2O)
(HCN) 334 418 (HCN)
339 (H
2CO) 365K (HOCH
2CH
2NH
2)
240 280 320 360 400 520
HOCH2CH2NH2/O/Cu(100)
dN(E)/dE (arb. units)
Kinetic Energy (eV)
C N O
185K
300K
450K
600K
800K 980K
Fig. 1: Temperature-programmed reaction/desorption spectra of a O/Cu(100) surface after dosing 0.5 L HOCH2CH2NH2 at 120 K.
Fig. 2: Auger electron spectra taken after exposing 1 L of HOCH2CH2NH2 to O/Cu(100) at 120 K and flashing the surface to the temperatures indicated.
References
1) Meeker, K.; Ellis, A. B. J.Phys. Chem. B 1999, 103, 995-1001.
2) Sexton, B. A. Surf. Sci. 1979, 88, 299-318.
3) Carley, A. F.; Davies, P. R.; Edwards, D.; Jones, R. V.; Parsons, M. Topics in Catal. 2005, 36, 21-32.
4) Thornburg, D. M.; Madix, R. J. Surf. Sci. 1990, 226, 61-76
5) Pirngruber, G. D.; Eder-Mirth, G.; Lercher, J. A. J. Phys. Chem. B 1997, 101, 561-568.
6) Madix, R. J.; Yamada, T.; Johnson, S. W. Appl. Surf. Sci. 1984, 19, 43-58.
7) Wuttig, M.; Franchy, R.; Ibach, H. Surf. Sci. 1989, 213, 103.
8) Standard Reference Database 69, NIST (National Institute of Standards and Technology) Chemistry WebBook, 2005.
9) Madix, R. J.; Thornburg, D. M. Surf. Sci. 1989, 220, 268-294.
10) Wachs, I. E.; Madix, R. J. Appl. Surf. Sci. 1978, 1, 303-328.
11) Bowker, M.; Madix, R. J. Surf. Sci. 1982, 116, 549-572.
12) Capote, A. J.; Madix, R. J. Surf. Sci. 1989, 214, 276-288.
13) Armand, J. C.; Robert, J. M. J. Am. Chem. Soc. 1989, 111, 3570-3577
