Paper HC+SS-ThM4
Oxide Formation on Ir(100) Studied by in-Situ Surface X-ray-Diffraction

Thursday, October 25, 2018, 9:00 am, Room 201A

Methane (CH₄) conversion into higher added value hydrocarbons is done through a number of complex catalytic steps, and has been studied for many years [1]. The initial and often rate limiting step in the reaction is the dissociation of the molecule on the metal catalyst surface. Because alkane C–H bonds are among the least reactive known, no process for direct conversion of CH₄ into methanol (CH₃OH) has so far been developed.

IrO₂(1 10) surface grown on Ir(100) has shown facile dissociation of CH₄ at liquid nitrogen temperatures [2], as well as oxidizing H₂ to -OH [3]: two steps that could have importance for the development of a new direct methane-to-methanol catalysts.

In this contribution we will present recent results from in-situ Surface X-ray Diffraction (SXRD) recorded at beamline ID03 at the ESRF from the oxidation of a Ir(100) surface. We find that the Ir(100) surface oxidizes into a bulk oxide at a temperature of 775 K and a pressure of 5 mbar of O₂ similar to what observed in [2], forming a predominantly rutile IrO₂(110) oriented surface. Our study also demonstrates that lowering the partial O₂ pressure or the temperature results in the formation of a number of different Ir sub-oxides similar to the ones found for Ir(111) [4], and the structures formed will be discussed in this contribution.

[1] D. M. Bibby, C.D. Chang, R.F. Howe and S. Yurchak, Eds. Methane Conversion, Vol. 36 of Studies in Surface

Science and Catalysis (Elsevier, Amsterdam, 1988).

[2] Z. Liang, T. Li, M. Kim, A. Asthagiri, and J. F. Weaver, Science 356 (2017) 299.

[3] Li, T., Kim, M., Liang, Z. et al. Top Catal (2018) 61: 397

[4] Y. B. He, A. Stierle, W. X. Li, A. Farkas,N. Kasper, and H. Over, J. Phys. Chem. C 112 (2008) 11946.