Bebensee, F.

Chen, J.

Nefedov, A.

Wöll, C.

Yang, C.

English

KITopen

KIT – University of the State of Baden-Wuerttemberg and National Research Center of the Helmholtz Association  CO2 adsorption on CeO2(110) single crystal surface  Chengwu Yang,1,2 Alexei Nefedov,1 Fabian Bebensee,1 Jun Chen,1 Christof Wöll1 Motivation  Carbon dioxide studies were motivated by not only the mitigation of this greenhouse gas but also the potential utilization of CO2 as a feedstock for the chemical industry.1 Ceria, as one of the most reducible metal oxide, provides the basis for extensive catalytic applications due to oxygen vacancy defects can be rapidly formed and eliminated, giving it a high “oxygen storage capacity”. It has proven to be a highly active catalyst for CO2 reduction to methanol recently.2 The fundamental research which take a surface science approach on CO2 adsorption and reaction at well-defined single crystal surface is really desired for understanding the processes occurring on high surface-area CeO2 catalysts under reaction conditions.3   Very recently we succeeded in probing the oxygen vacancies on bulk single crystal CeO2(111) surface with CO by using UHV-IRRAS.4 Here we report the results of CO2 adsorption onto pristine and defective CeO2(110) single crystal surfaces, which is more reactive than the CeO2(111) surface, characterized by using x-ray photoelectron spectroscopy (XPS) and near edge x-ray absorption fine structure spectroscopy (NEXAFS), which proves the feasibility of this method to characterize the electronic, structural and chemical properties of surface species of ceria.  References [1]  M. Aresta (Ed.), Carbon Dioxide as Chemical Feedstock, Wiley-VCH, New York, 2010. [2]  J. Graciani, et al., Science, 2014, 345, 546. [3]  U. Burghaus, Progress in Surface Science, 2014, 89, 161. [4]  C. Yang, L. Yin, F. Bebensee, M. Buchholz, H. Sezen, S. Heissler, J. Chen, A. Nefedov, H. Idriss, X. Gong,       C. Wöll, Physical Chemistry Chemical Physics, 2014, 16, 24165. 1Institute of Functional Interfaces  2Helmholtz Research School „Energy-related catalysis“ Experimental                Figure 1. Ball-and-stick model of the CeO2(110) surface (a) side view and (b) top view, red – oxygen, white – cerium. The NEXAFS and XPS measurements were carried out in our own UHV-apparatus on the HE-SGM beamline at BESSY II. CeO2 single crystal was mounted on the sample holder with electron beam heating. Cooling was made with copper braids connected to the sample holder and a liquid helium cryostat. The CeO2(110) single crystal surface was prepared by repeated cycles of sputtering with 1 keV Ar+ and annealing at 800 K for 15 min in an O2 atmosphere of 1×10-5 mbar for forming a stoichiometric surface, or alternately without O2 to create a reduced one. For temperature monitoring, a K-type thermocouple was directly attached on the sample surface.   NEXAFS measurements only were performed after desired Ce oxidation state as judged by XPS. Exposure to 5 Langmuir CO2 at sample temperatures typically below 120 K was achieved by backfilling the analysis chamber up to 10-9 mbar. Typical base pressures during acquisition of NEXAFS and XP spectra were 2 × 10-10 mbar. NEXAFS and XP spectra after CO2 exposure were firstly recorded at low temperature. And then the sample temperature was elevated to a set of given temperatures and acquire the spectra there to monitor their evolution during thermal desorption process. NEXAFS/XPS Endstation at HE-SGM Beamline. CO2 on Reduced Surface Conclusions (a) (b) 285 290 295 300 305 310-4048121620242832120 K300 K200 K*(CO32-)  Intensity (a.u.)Photo Energy (eV) 30o 55o 90oC K-edge*(CO32-)538 536 534 532 530 5280.04.0x1058.0x1051.2x1061.6x1062.0x1062.4x106CO32- Intensity (a.u.)Binding Energy (eV) 150 K 200 K 250 K 300 K 400 K 500 KO1sPhysisorbed CO2Lattice O130 125 120 115 110 1050.02.0x1054.0x1056.0x1058.0x1051.0x1061.2x106  Intensity (a.u.)Binding Energy (eV) 150 K 500 KCe4d Reoxidation285 290 295 300 305 31001020304050*(C=O)in HCOO-*(CO32- and HCO3-)*(CO32- and HCO3-)300 K200 K150 K120 K  Intensity (a.u.)Photo Energy (eV) 30o 55o 90oC K-edge538 536 534 532 530 5280.05.0x1051.0x1061.5x1062.0x1062.5x1063.0x106/HCOO-CO32-Lattice OPhysisorbed CO2  Intensity (a.u.)Binding Energy (eV) 150 K 200 K 250 K 300 K 400 KO1s270 280 290 300 310 320 3300.40.60.81.01.2*(CO32-)  Intensity (a.u.)Photo Energy (eV) 1L CO2 at 300 K C K-edgeThird order excitation at the Ce MIV and MV edges536 534 532 530 528 5260.02.0x1054.0x1056.0x1058.0x1051.0x106  Intensity (a.u.)Binding Energy (eV) O1s130 125 120 115 110 10501x1052x1053x1054x105  Intensity (a.u.)Binding Energy (eV) Ce4dCO2 on Oxidized Surface CO2  dosed at RT on Reduced Surface 130 125 120 115 110 1050.04.0x1058.0x1051.2x1061.6x106  Intensity (a.u.)Binding Energy (eV) 150 K 300 KCe4d296 294 292 290 288 286 2840.04.0x1058.0x1051.2x1061.6x1062.0x106CO32-C1s  Intensity (a.u.)Binding Energy (eV) 150 K 200 K 250 K 300 K 400 K 500 K296 294 292 290 288 286 2840.05.0x1041.0x1051.5x1052.0x1052.5x1053.0x105  Intensity (a.u.)Binding Energy (eV) Ce4d296 294 292 290 288 286 284 2820.02.0x1054.0x1056.0x1058.0x1051.0x106HCOO-CO32-  Intensity (a.u.)Binding Energy (eV) 150 K 200 K 250 K 300 K 400 KC1sFigure 2. NEXAFS spectra at the C K-edge and C1s, O1s, Ce4d core level XP spectra following the adsorption of 5 Langmuirs of CO2 at 120 K and annealed as indicated on reduced CeO2(110) surface. Figure 4. NEXAFS spectra at the C K-edge and C1s, O1s, Ce4d core level XP spectra following the adsorption of 5 Langmuirs of CO2 at 120 K and annealed as indicated on oxidized CeO2(110) surface. Figure 3. Raw NEXAFS spectrum at the C K-edge and C1s, O1s, Ce4d XP spectra following the adsorption of 1 Langmuir of CO2 at room temperature on reduced CeO2(110) surface.   Stoichiometric CeO2(110) Surface                   CO2 adsorbs on reduced CeO2(110) surface mainly as carbonate and weakly bound      physisorbed CO2 below 150 K. The formation of a carboxylate intermediate is not      really evident. The physisorbed CO2 completely desorbs by 200 K.   However, on oxidized CeO2(110) surface carboxylate and bicarbonate were detected,      which possibly originate from CO2 react with surface hydroxylate group and        adsorbed atomic hydrogen.   CO2 even can be adsorbed at room temperature on reduced surface and act as an      oxidizing agent to partially reoxidized the reduced CeO2(110) surface. Contact: Christof Wöll, Institute of Functional Interfaces (IFG), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany. Christof.woell@kit.edu. Chengwu Yang would like to gratefully acknowledge the Helmholtz Research School Energy-Related Catalysis for financial support. 

CO₂ adsorption on CeO₂(110) single crystal surface

https://publikationen.bibliothek.kit.edu/220098082/3816704

CO₂ adsorption on CeO₂(110) single crystal surface

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