Structure sensitivity of CO oxidation over rhodium. Reply to comments by Fisher, Peden, Oh and Goodman

Abstract

We recently published a letter [1] where we drew attention to the structure sensitivity of CO oxidation at rhodium single crystal surfaces. Fisher, Peden, Oh and Goodman, (previous letter, hereafter referred to as FPOG) have commented on some aspects of our work, in particular claiming to have noted the phenomenon of structure sensitivity in this reaction in previous studies [25]. They also criticise certain aspects of our interpretation. The clear message from the studies of FPOG is that CO oxidation is structure insensitive on rhodium and this is demonstrated by these extracts from the abstracts of their papers: "The C 0 / 0 2 reaction was found to be insensitive to the structure o f the surface, as evidenced by the identical rates, activation energies and partial pressure dependencies measured on the two single crystal surfaces" [Rh(111)and(100), ref.[3], our italics]. "The specific rates and the partial pressure dependencies determined for the single crystals are in excellent agreement with results obtained previously for high surface area supported catalysts, demonstrating the structure insensitivity o f this reaction" [ref. [5], our italics]. "...the kinetics of the CO-NO reaction, unlike the C 0 / 0 2 reaction kinetics, are sensitive to changes in the catalyst surface characteristics" [ref. [2], our italics]. In none of their abstracts do they mention the structure sensitivity of the reaction, so it is not appropriate for FPOG to claim that they said that the CO oxidation reaction was structure sensitive all along. The objective of our letter was to show that the reaction is unequivocally structure sensitive under some conditions, and to delineate and explain these. We did state, incorrectly, that CO oxidation results from single crystal planes had not been directly compared previously; we recognise that FPOG did make such a comparison and we apologise for our error. The FPOG papers together represent a valuable study of CO oxidation and evidence is presented which shows structure sensitivity under some conditions, however the authors largely ignore or misinterpret this. Ref. [3] claims that the reaction is structure insensitive, while noting some deactivation at high oxygen pressures