Postdoc Emre Emmez, Chemical Physics - Structure and Reactivity, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany

Adsorption on Metal-Supported Sheet-Like Silica Films: Surface and “Sub-surface” Chemistry

Recent progress in fabrication of well-defined, ultrathin silica films on metal surfaces opened up new possibilities for “surface-science” studies of silica-based materials [1]. In this study, we addressed adsorption properties of silica sheet-like films grown on Ru(0001) by using infrared reflection-absorption spectroscopy (IRAS) and temperature programmed desorption (TPD). As the performance of silica in catalysis is primarily determined by surface hydroxo species, we first studied adsorption of water. Hydroxo species in the form of isolated silanols (Si-OH) were observed upon water exposures at low temperatures and subsequent heating above 200 K. Most of the hydroxyl groups are thermally stable up to ~ 900 K.

Isotopic experiments showed that surface hydroxyls are formed exclusively from the adsorbed water molecules, and they do not undergo considerable scrambling with the lattice oxygen atoms upon heating. Steps on a silica sheet and/or “holes” in these ultrathin films are proposed as active sites for hydroxylation. The acidic properties of silanols were studied with adsorption of CO and NH3 as weak and strong bases, respectively [2]. Adsorption of gases such as CO as well as H2 at elevated pressures reveal a much more complex response which involves gas transport through the pores, associated with structural defects in the silica film, chemisorption and diffusion across the Ru(0001) surface underneath the silica film [3].

The results revealed some similarities as well as differences between behavior of metal-supported silica film and graphene with respect to the intercalation of molecules into the interface. Such a hybrid system, which would combine a robust molecular-sieve membrane and a chemically active metal underneath, could become interesting materials for technological applications, in particular in catalysis and sensors.

References

[1] Shaikhutdinov, S. and Freund, H.-J., Advanced Materials, (2013). 25: p. 49-67

[2] Yang, B.; Emmez, E.; Kaden, W.E.; Boscoboinik, J.A.; Sterrer, M.; Shaikhutdinov, S. and Freund, H.-J., Journal of Physical Chemistry C, (2013). 117: p. 8336-8344

[3] Emmez, E.; Yang, B.; Shaikhutdinov, S. and Freund, H.-J., The Journal of Physical Chemistry C, (2014). 118: p. 29034-29042

Host: Associate professor Jeppe Vang Lauritsen, Interdisciplinary Nanoscience Center, Aarhus University