The Kinetics of CO Oxidation on RuO₂(110): Bridging the Pressure Gap

Abstract

The steady-state rate r CO 2 of CO2 formation from CO + O2 on an epitaxially grown RuO2(110) single-crystal surface was recorded as a function of the partial pressures in the 10-7−10-6 mbar range. The RuO2(110) surface exposes singly coordinatively unsaturated “Ru-cus” sites and 2-fold coordinatively unsaturated “Ru-bridge” sites. Normally, the Ru-bridge sites are saturated by oxygen (O-bridge) which can be replaced by CO. The stage of the surface was controlled by vibrational spectroscopy (HREELS), and analysis of the kinetic data was based on previous information about the structural and adsorptive properties of this surface. Measurements of the rate as a function of temperature up to ≈350 K in a 1:1 mixture of CO and O2, each with 10-7 mbar partial pressure, revealed most remarkable agreement with data reported by Zang and Kisch13 with small supported RuO2 particles prepared from aqueous solution for 1 bar total pressure. Under these conditions of temperature and ratio of partial pressures the reaction will essentially proceed between CO and O species adsorbed at Ru-cus. The total pressure becomes largely insignificant: whereas the pressure changes by 10 orders of magnitude, r CO 2 is estimated to vary only within 1 order of magnitude so that the pressure gap is bridged here.

Catalytically active states of Ru(0001) catalyst in CO oxidation reaction

“…It should be noted that in surface science experiments, carried out at temperature and pressure conditions far from the realistic ones, no reduction of the RuO 2 (110) was observed even in extreme excess of CO, i.e. CO:O 2 pressure ratios of 10 [7].…”

“…Judging from the relative weight of the 'surface oxide' O 1s component, about 80% of the surface should be covered with RuO 2 islands at 590 K. Note that the RuO 2 bridge-O component at 528.7 eV is very weak, probably due to its continuous consumption during the reaction, in accordance with the mechanism suggested in ref. 7,9. The reaction rate can be reverted back and forth by decreasing-increasing the temperature in the range 550-600 K, which does not affect visibly the catalyst surface composition.…”

“…The rutile RuO 2 (110) surface consists of alternating rows of six-fold and unsaturated five-fold oxygen coordinated Ru atoms, the latter, called cus-Ru, playing a prominent role as active sites in CO oxidation. The inspired UHV surface science and theoretical studies of CO oxidation reaction on a model RuO 2 (110) single crystal surface reached the consensus that the elementary reaction steps involve CO and O adsorption on the cus-Ru, followed by reaction between cus-CO and cus-or bridge O atoms [5][6][7][8][9]. However, the RuO 2 (110) surface is an idealised case of an active Ru catalyst, which has been prompted by the parallel studies focused on the oxidation mechanism of the Ru(0001) surface and the stability of the Ru oxidation states at different partial pressures and temperatures [10][11][12][13][14][15][16].…”

Oxidation of the Ru(0001) surface covered by weakly bound, ultrathin silicate films

“…To compare with pure silicate films, the aluminosilicate film with Al 0. 25 Unless stated, the spectra were taken in ~ 10 -4 mbar O 2 ambient at varying temperature.…”

Adsorption of Methane and Ethane on RuO2(110) Surfaces

“…Recently, the RuO 2 (110) surface, prepared by exposing Ru(0001) to high doses of O 2 at elevated sample temperatures [3][4][5], has been found to exhibit high catalytic activity for CO oxidation [3,4,6]. The stoichiometric RuO 2 (110) surface is characterized by two different, coordinatively unsaturated surface atoms organized in rows along [001]: (i) twofold coordinated oxygen atoms (O-bridge) and (ii) fivefold coordinated Ru atoms (Ru-cus).…”