Boreskov Institute of Catalysis of the Siberian Branch of Russian ...

PP-II-4in range 0-1. In our case n O2 ≈ -0.6 – this can be explained only by blocking of the rhodiumsurface by low-reactive oxide.The activation energy was found to decrease in range 300-400 K from 33 to 23 kcal/mol.In this temperature range, according to [1], the apparent activation energy is close toactivation energy of CO desorption. Indeed, our TDS experiments give the E CO = 23-29 kcal/mol. The decreasing of the apparent activation energy can be explained by changingof the atomic oxygen reactivity at higher coverages, observed as in [1] as well as in ourexperiments [2].The activation energy E r of CO ads +O ads step can be found by analyzing the rate of reactionin 550-800 K range [1]. In this range the surface is covered be oxygen (not by CO ads ),therefore r~exp(Е СО – Е r ). The determined by this way Е r =21÷25 increases when R increases– this definitely points to formation of low-reactive oxide on the rhodium surface.Thus, we found, that at high ratios R=р(O 2 )/p(CO)>10 and temperature range 300-800 K,the oxide layer forms on the surface of the Rh(410). This leads to decreasing of the catalyticactivity of the rhodium surface.Acknowledgements: This work was supported by the RFBR Grant # 08-03-00454, 08-03-00825, INTAS # 05-109-5039.References1. T. Engel, G. Ertl, J. Chem. Phys. 69(3) 19782. V.V. Gorodetskii, A.A. Sametova, A.V. Matveev, N.N. Bulgakov, Chemical Physics, 2 (2007) 30280