SYNTHESIS AND CHARACTERIZATION OF SILICA THIN FILMS Department of Chemistry and Biochemistry North Dakota State University Mindika Tilan Nayakasinghe

Objective To deposit Mo clusters on synthesized 2D-Zeolite like thin film to study Hydrodesulfurization

Hydrodesulfurization Motivation Hydrodesulfurization Hydrodesulphurization is the process of removing sulfur compounds form natural gas and form refined petroleum products. Example: C2H5SH + H2 C2H6 + H2S Catalyst

Main HDS catalysts are based on MoS2 (Molybdenum Disulfide) Other catalysts RhS2 Binary combinations of Co and Mo (Cobalt modified MoS2 catalyst) Metal disulfides are supported on materials with high surface area. Support allows the catalyst to be more widely distributed. Zeolite structure Ref: M. M. J. Treacy , C. J. Dawson , V. Kapko , I. Rivin , Flexibility mechanisms in ideal zeolite frameworks , DOI: 10.1098/rsta.2012.0036

Project Structure Synthesis of crystalline Silica films Thiophene adsorption of Silica thin films Synthesis of 2D Zeolite like thin films and characterization by LEED, AES, XPS and XRD Deposition of Mo clusters on 2D Zeolite like films Thiophene adsorption on Silica supported Mo model catalyst

Preparation of Thin Silica Films on Mo(112)

Synthesis of crystalline Silica films Clean Mo(112) substrate Do several cycles of Ar ion sputtering followed by annealing Oxidize the substrate Oxygen anneal for 10 minutes with the surface at 850 K (PO2= 1x10-8 mbar) Dose Silicon on oxidized substrate P= 3-5 x 10-10 mbar Ultra high vacuum chamber Oxidize Si dosed substrate to form Silica thin films

Step1: Cleaning process- AES Results Auger process Ionization of the atom Vacuum level hν hν hole Relaxation and Auger electron emission Vacuum level Auger electron Auger electron spectrum of Mo(112) substrate as received Auger electron spectrum of Mo(112) substrate after cleaning hole

Top view of Mo(112) surface LEED….. Electron diffraction by a layer of atoms LEED pattern of Mo(112) as received Top view of Mo(112) surface LEED pattern of Mo(112) after cleaning Ref: (1) Tetsuhiro Kinoshita, Seigi Mizuno, Surface Science 605 (2011) 1209–1213

Step2: Oxidation of Mo(112) Substrate LEED pattern of Mo(112) after cleaning LEED pattern of Mo(112) after oxidation Auger electron spectrum of Mo(112) substrate after oxidation

X-ray photoelectron spectra obtained for Oxidized Mo(112) XPS Results (a) (b) Binding energy/ eV X-ray photoelectron spectra of, (a) Oxygen and (b) Mo Ref: Moulder J,F; Stickle W,F; Sobol P,E; Bomben K,D; Hand Book of X-ray Photoelectron Spectroscopy. X-ray photoelectron spectra obtained for Oxidized Mo(112)

Step 3: Si dosing and Oxidation Metal Doser Dose Si by home made metal doser. Take AES to confirm the presence of Silicon. Oxygen annealing. Take AES and calculate Si/Mo ratio. Repeat the procedure until a monolayer or slightly less than a monolayer of silica layer is obtained.

Characterization by XPS X-ray photoelectron spectra of Silicon Ref: Moulder J,F; Stickle W,F; Sobol P,E; Bomben K,D; Hand Book of X-ray Photoelectron Spectroscopy.

Si/Mo ratio and Coverage AES results Silica Mo (f) (e) (d) (c) Si/Mo ratio and Coverage (b) Curve Si/ Mo ratio Coverage Mo(112) - (a) 0.1175 0.26 ML (b) 0.2463 0.54 ML (c) 0.3042 0.66 ML (d) 0.3775 0.82 ML (e) 0.4235 0.92 ML (f) 0.4594 1.00 ML (a) Mo(112) substrate 50 100 150 200 First dose of Silicon after oxidation electron energy (eV) AES spectra of SiO2 films on Mo(112) with different SiO2 coverages

Characterization of thin silica films by LEED Top view and side view of (A) Mo(112), (B) Mo(112)-c(2 × 2)-[SiO4] surface Ref: M. S. Chen, A. K. Santra, and D. W. Goodman; J. Phys. Chem. B 2004, 108, 17940-17945 LEED pattern obtained for Mo(112) Oxidized Mo(112) LEED pattern for silica thin film on Mo(112)

Future Work…… Experiment with Water Experiment with CO Experiment with Thiophene Mo(112)-c(2X2)- [SiO4] Zeolite thin film on Mo(112) Mo deposited Zeolite thin film

Acknowledgements Dr.Uwe Burghaus Dr. Ashish Chakradhar Nilushni Sivapragasam The donors of the American Chemical Society and Petroleum Research Fund are acknowledged for the support of this research