Geometric and electronic structure of Au on Au/CeO₂catalysts during the CO oxidation: Deactivation by reaction induced particle growth

Abstract

Abstract. Changes of the geometric and electronic structure of gold on Au/CeO 2 catalysts induced by different pre-treatments (oxidative and reductive) and by the CO oxidation reaction at 80°C were followed by operando XANES / EXAFS measurements. The results showed that i) oxidative pre-treatment (O 2 ) leads to larger Au nanoparticles than reductive pre-treatment (CO), that ii) Au is predominantly metallic during CO oxidation, irrespective of the preceding pre-treatment, and that iii) there is a reaction induced Au particle growth. Correlations with the activity of the respective catalysts and its temporal evolution give insights into the origin of deactivation of these catalysts under reaction conditions, in particular on reaction induced changes in the Au particle size.

Selective CO Methanation on Highly Active Ru/TiO2 Catalysts: Identifying the Physical Origin of the Observed Activation/Deactivation and Loss in Selectivity

“…10a) reaching 3.7×10 -6 mol g Ru -1 s -1 after 800 min on stream, equivalent to a total deactivaton of 47%, which is of similar order of magnitude as in the absence of water (44%). 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 In previous studies on Ru/Al 2 O 3 and Ru/zeolite catalysts we had observed that the addition of up to 15% water vapor to the reaction gas mixture, using an identical feed gas, resulted in a slight decrease in the catalytic activity, both for the initial and final activity for COmethanation, while CO 2 methanation was fully suppressed 13 . Using a low-CO reformate (SR-ref 100), the selectivity was below 100%, except for very small Ru NPs.…”

“…Water was added by bubbling the dry gas mixture through a water bath at fixed temperature (for more information see ref. 13 ). We observed an almost similar reaction behavior in the presence of water as in the absence of water (see Fig.…”

Chemical and Electronic Changes of the CeO2 Support during CO Oxidation on Au/CeO2 Catalysts: Time-Resolved Operando XAS at the Ce LIII Edge

“…The trend in the chemical state of the Au NPs fits well to that of the ceria support, with a highly oxidized Ce(IV) state after O400 pretreatment and a partly reduced ceria support after (reductive) H400 pretreatment. For a more detailed discussion on the nature of the Au species in the Au/CeO2 catalysts upon different pretreatments we refer to our previous publications [30,35,46]. .…”

“…This is discussed in more detail in the Supporting Information. Looking at the oxidation state of the catalyst, the previous experiments at the Au LIII edge had shown In the inset we additionally show XANES date collected at the Au L III edge at (11919 eV) after oxidative (O400-blue spectrum) and reductive (H400-red spectrum) pretreatments, which were taken from [30,35], respectively, together with spectra from Au 2 O 3 and a Au foil (dashed line: Au 2 O 3 , dashed dotted line: Au metal foil) used as reference materials. Note that a different catalyst was used in these measurements, with a Au loading of 2.5 wt.%, but otherwise rather similar properties as in the present study.…”

Ag/CeO2 Composites for Catalytic Abatement of CO, Soot and VOCs

“…As a rule, two main types of effective catalysts for total oxidation of VOCs are developed, including supported metals (e.g., Au, Pt, Pd, Ag) [125][126][127][128][129][130] and transition metal oxides (CeO 2 , MnO 2 , Co 3 O 4 ) [130][131][132][133]. The combination of noble metal and transition metal oxide used as a support or modifier is promising to increase the effectiveness of catalytic composites [134][135][136].…”