Bebensee, Fabian

Dohalek, Zdenek

Ge, Qingfeng

Nefedov, Alexei

Wang, Yuemin

Wöll, Christof

Yang, Chengwu

Yu, Xiaojuan

Zhang, Zhengrong

KITopen

KIT – University of the State of Baden-Wuerttemberg andNational Research Center of the Helmholtz AssociationmonolayerXiaojuan Yu,a Chengwu Yang,a Fabian Bebensee,a Alexei Nefedov,a Zhengrong Zhang,bQingfeng Ge,c Zdenek Dohálek,d Yuemin Wang,a,* Christof Wöll aFormaldehyde Adsorption on Rutile TiO2(110) Surface Probed by IR SpectroscopyaInstitute of Functional Interfaces, Karlsruhe Institute of Technology, Germany bDepartment of Physics, Baylor University, USAcDepartment of Chemistry and Biochemistry, Southern Illinois University, USAdFundamental and Computational Sciences Directorate, Institute for Interfacial Catalysis, Pacific Northwest National Laboratory, USA*Email: yuemin.wang@kit.eduTitanium dioxide (TiO2) is one of the most important metal oxides used in catalysis andphotocatalysis. Understanding the surface chemistry of formaldehyde (CH2O) on thismaterial is of particular interest because CH2O is a key species (reagent, intermediate,or product) in numerous catalytic and photocatalytic reactions such as methanolsynthesis, methanol oxidation and hydrocarbon production. Here, we present athorough surface science study on the interaction of formaldehyde (CH2O) with therutile TiO2(110) surface using a novel ultra-high vacuum infrared reflection-absorptionspectroscopy (UHV-IRRAS) apparatus.CH2O adsorption on TiO2(110) ： Multilayers UHV-FTIR(Bruker Vertex 80v)XPS, UPS and AES analyzer(VG Scienta R4000) Analysis chamberDistribution chambersPreparation chamberwith LEED, AES, TDSand effusion cellsmodes gas multilayer2n2 3471.7 3416n2+n5 3000.1 29922n3 2999.5 -nas(CH2), n4 2843.3 2887ns(CH2), n1 2782.5 2826n3+n5 2719.2 2724n(C=O), n2 1746.1 1731d(CH2), n3 1500.0 1500w(CH2), n5 1249.3 1248t(CH2), n6 1167.1 1179[110]_[110][001][110]_[110][001]CH2O adsorption on TiO2(110) ： Monomers ParaformaldehydeIntroductionIRRAS thermal desorption dataCH2O adsorption at 65 KMode assignment:Isolated CH2O monomerUHV-IRRAS apparatusIRRAS- Measurements:p- and s-polarized light incident along [1-10] directionp- and s-polarized light incident along [001] direction Pressure: ≤ 8×10-11 mbar Reflection mode  Grazing Incidence (80°) p- and s-polarized lightDioxymethylene Paraformaldehyde (POM) is formed viacoupling reactions of CH2O monomersat Ti5c sites. The POM chain is oriented primarilyalong the [001] direction in a slightlydisordered configuration. Dioxymethylene (DOM) was detectedas minority species formed via reactionof Ti5c-bound CH2O monomers withsurface O-atoms.Conclusions CH2O adsorption at 65 K leads to the formation of multilayer CH2O, which desorbscompletely upon heating to 120 K. The CH2O monomer was identified after submonolayer adsorption at 45-60 K, in whichCH2O is bound to the surface Ti5c sites via s-donation in a tilted geometry. Upon heating, the CH2O monomers polymerize to form paraformaldehyde (POM) chains,oriented primarily along the Ti5c rows ([001] direction). Dioxymethylene was detected as minority species formed via reaction of Ti5c-bound CH2Omonomers with surface O-atoms.［1］ H. Qiu, H. Idriss, Y. Wang, C. Wöll. J. Phys. Chem. C. 112 (2008) 9828–9834. ［2］ K. Zhu, Y. Xia, M. Tang, Z.-T. Wang, I. Lyubinetsky, Q. Ge, Z. Dohnálek, K. T. Park, Z. Zhang. J. Phys. Chem. C. 119 (2015) 18452.［3］ K. Zhu, Y. Xia, M. Tang, Z.-T. Wang, B. Jan, I. Lyubinetsky, Q. Ge, Z. Dohnálek, K. T. Park, Z. Zhang. J. Phys. Chem. C. 119 (2015) 14267–14272.［4］ Z. Zhang, M. Tang, Z.-T. Wang, Z. Ke, Y. Xia, K.T. Park, I. Lyubinetsky, Z. Dohnálek, Q. Ge. Top. Catal. 58 (2014) 103–113 .［5］ X. Yu, Z. Zhang, C. Yang, F. Bebensee, S. Heißler, A. Nefedov, M. Tang, Q. Ge, L. Chen, B. D. Kay, Z. Dohnálek, Y. Wang, C. Wöll.  J. Phys. Chem. C. 120 (2016) 12626-12636.References:Acknowledgements:The funding from the “Science and Technology of Nanosystems” Programme (Project No. 432202) is gratefully acknowledged . X.Y. andC.Y. are grateful for PhD fellowship donated by the China Scholarship Council (CSC). C.Y. thanks the Helmholtz Research School“Energy-related catalysis” for financial support.[110]_[110][001]ν(C=O) : 1709 cm-1 (exp.)1695 cm-1 (DFT)Strategy to overcome challenge of low reflectivity:• Attach spectrometer directly to UHV chamber.• Do not introduce any additional optical element.• Minimize mechanical vibrations,- crucial for time-resolved experiments.Additional features of “THEO”:• Allows transmission measurements on powder samples. • Cooling to 100 K (LN2) or 60 K (LHe); • Heating up to 1200 K.• Equipped for XPS, UPS, AES, LEIS, and LEED.70 K120 K0 100 200 300 400 500 600HCHO Desorption Rate (a.u.)Temperature (K)0 200 400 600 800C2H4 Desorption Rate (a.u.)Temperature (K)0 100 200 300 400 500 600HCHO Desorption Rate (a.u.)Temperature (K)0 200 400 600 800C2H4 Desorption Rate (a.u.)Temperature (K)TPD: CH2O adsorption on TiO2(110) at 80 KCH2O on reduced TiO2(110) CH2O on oxidized TiO2(110)0.75 L24 LVOmonomerdimerSTM0.07 ML CH2O at 45 K77 % isolated monomers at Ti5c sites23 % dimers at Ti5c sitesν(C-O) : 1075 cm-1 (exp.)1077, 818 cm-1 (DFT)ν(C-O) : 1164, 1109 cm-1 (exp.)1158, 1120 cm-1 (DFT)CH2O polymerization at the Ti5C rows CH2O monomer in η1(O) configuration CH2O dimer paraformaldehyde dioxymethyleneCH2O adsorption at 65 K Intermolecular interaction: dipole-dipole attractions between polar carbonyl groups  Fermi resonance: n2 + n5 combination mode and n4 mode, same symmetry (B1)aa bb*n2 = 1727 cm-1: O2c-bound CH2O at the second-layer

Formaldehyde adsorption on rutile TiO₂(110) surface probed by IR spectroscopy

https://publikationen.bibliothek.kit.edu/1000056903/3871003

Formaldehyde adsorption on rutile TiO₂(110) surface probed by IR spectroscopy

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