Journal of Catalysis 185, 333–344 (1999) Article ID jcat.1999.2519, available online at http://www.idealibrary.com on Characterization of Spent MnO 2 /CeO 2 Wet Oxidation Catalyst by TPO–MS, XPS, and S-SIMS Safia Hamoudi, Fa¨ ı¸ cal Larachi, 1 Alain Adnot, and Abdelhamid Sayari Department of Chemical Engineering and CERPIC, Universit´ e L aval, Ste-Foy, Q u ´ ebec G1K 7P4, Canada Received October 15, 1998; revised January 27, 1999; accepted April 13, 1999 The surface modifications of MnO 2 /CeO 2 catalyst during cata- lytic wet oxidation reaction were shown to be mainly due to car- bonaceous deposits. Detailed characterization of the deposits was carried out using temperature-programmed oxidation coupled with mass spectrometry detection (TPO–MS), X-ray photoelectron spec- troscopy, (XPS) and static secondary ion mass spectrometry (S- SIMS). The TPO–MS provided evidence that the nature of the car- bonaceous deposits was dependent on the reaction temperature and time. The XPS investigation revealed the complex chemical compo- sition of the organic material on the catalyst surface. The C1s region exhibited aromatic/graphitic, aliphatic, and oxygen-bearing carbon. The relative contribution of the aromatic/graphitic carbon increased with reaction time. The O1s region was composed of a strong sig- nal attributable to the inorganic oxides and signals with moderate intensity stemming from adsorbed water, surface hydroxyl, and or- ganic oxygen from alcohols or esters in agreement with the C1s peak reconstruction. The static SIMS analysis confirmed the exis- tence of long aliphatic chains on the catalyst surface, together with aromatics of low polycondensation level indicating a low level of graphitization of the deposits. c  1999 Academic Press Key Words: oxidation; wastewater; oxide catalyst; carbonaceous deposit; deactivation; XPS; TPO; SIMS. INTRODUCTION Catalyticwet oxidation (CWO) isa subcriticalabatement method that uses dissolved molecular oxygen to catalyti- cally destroy target organic pollutants contained in waste- water streams.Ideally,provided that temperature and pres- sure are sufficiently high, any organic species undergoes complete mineralization. The use of solid catalysts not only allowsoxidative treatmentsto be accomplished under mod- erate severity (90–150 ◦ C; 0.1–2 MPa O 2 ) (1) but also offers a versatile process wherein the catalyst, unlike a homoge- neous one, may be easily recovered and eventually reused. CWO involvingsolidcatalystshasthereforeattractedatten- tion as an alternate method for cleaning wastewaters, and 1 To whom correspondence should be addressed. E-mail: flarachi@ gch.ulaval.ca. various solid catalysts have been tested on model pollutant solutions (2–5). Previousworkonheterogeneouslycatalyzedoxidationof phenolicsolutionsrevealed the formation ofcarbonaceous polymeric deposits on the catalysts surface during the reac- tion (4, 6, 7). This resulted in catalyst deactivation via phys- ical blockage of active sites by these high-molecular-weight carbonaceous materials. However, despite the fact that the simultaneousformation ofheavypolymericproductsin wet oxidation is clearly evidenced, their chemical nature, their mechanism of formation, and their deactivating mode are still unclear or unknown. Hence, the understanding of the chemical composition of these surface species is a prereq- uisite for avoiding, or at least delaying, their formation. Amongthe numerousmethodsemployed to characterize carbonaceous deposits that are frequently encountered in the petroleum refining processes, temperature-program- med oxidation (TPO) is among the most commonly used techniques (8–10). In this bulk technique, an oxygen-con- taininginert gasflowsover a deactivated (coked) catalyst at a program-controlled increasing temperature. By monitor- ing the gas-phase composition versus time, information on the nature and the reactivity of the carbonaceous deposits can be obtained. Indeed, in TPO, oxygen is consumed via different reactions: carbon atoms are converted to carbon dioxide, hydrogen atoms to water, and eventually metals to oxides. The position of the oxidation peaks provides infor- mation on the temperature required for the depositsto burn off and thus on how easily the catalyst can be regenerated. X-ray photoelectron spectroscopy (XPS) has been suc- cessfully employed to provide useful surface analysis of nearly every type of material (11). Thus, it seemed worth- while to use this technique to probe the nature of the car- bonaceous deposits formed during CWO. Static secondary ion mass spectrometry (S-SIMS) can also provide valuable information on the nature of chemisorbed species (12–14) and deactivating carbonaceous layers on catalyst surfaces (15).The advantagesofthistechnique lie in itshigh sensitiv- ityanddetailedmolecularstructuralinformation.SIMSand XPS,therefore,make it possible to studythe outermost lay- ers of the catalyst surface with a low detection limit, giving 333 0021-9517/99 $30.00 Copyright c  1999 by Academic Press All rights of reproduction in any form reserved.