An important goal in surface science is to provide fundamental information on gas-surface interactions for the design of cheaper and more efficient catalysts. For this purpose, the required minimum knowledge is the composition of a catalyst for a certain reaction under realistic reaction conditions. Although this information seems trivial it is surprisingly difficult to obtain due to the complex structural nature of a real catalyst and the sometimes high temperatures and pressures under reaction conditions.

 

In the case of the complete oxidation of methane using Pd as the catalyst, pure Pd metal, Pd surface oxides and bulk PdO have all been reported to be most efficient to convert CH4 into CO2 and H2O [1-5]. This highlights the complexity of catalysis even for a relatively simple catalytic reaction.

 

In order to shed some light on the state of Pd during complete methane oxidation, we have performed in-situ Surface X-Ray Diffraction (SXRD) over a Pd(100) surface in a realistic reaction environment combined with DFT calculations. Our study demonstrates that significant roughening of the surface occur during the reaction, which increases the active surface area and thus affects the overall reactivity. Nevertheless, our study strongly suggests that the Pd metal is the most active phase for the full oxidation of methane.

 

[1] R. Burch, P. K. Loader, and F. J. Urbano, Catalysis Today 27 (1996) 243.

[2] R. F. Hicks, H. H. Qi, M. L. Young, and R. G. Lee, J. Catal. 122 (1990) 280.

[3] M. Lyubovsky and L. Pfefferle, Catalysis Today 47 (1999) 29.

[4] S. Oh, P. J. Mitchell, and R. Siewert, J. Catal. 123 (1991) 287.

[5] J. G. McCarthy, Catalysis Today 26 (1995) 283.