ORIGINAL PAPER Hysteresis Phenomena on Pt- and Pd-Diesel Oxidation Catalysts: Experimental Observations H. Dubbe 1 • G. Eigenberger 1 • U. Nieken 1 Ó Springer Science+Business Media New York 2016 Abstract In Diesel Oxidation Catalysts (DOC) platinum (Pt), palladium (Pd), or a combination of both (alloyed or multilayered) are the typical active components. During lightoff/lightout experiments, hysteresis phenomena of CO, NO, and HC conversion have repeatedly been reported and attributed to thermal effects, to surface coverage effects and/or to noble metal oxidation. A detailed understanding of the causes of these hysteresis phenomena will be crucial, especially for modeling purposes. The present contribution provides detailed experimental evidence on single com- ponent conversion as well as on the mutual influence of CO, NO, and HC on the respective conversion for close to commercial Pt- and Pd-only catalysts under isothermal conditions. It will be shown, that hysteresis effects on Pd- only catalysts mostly vanish after one lightoff. Contrarily, on Pt-only catalysts, a cyclic, stationary conversion hys- teresis during lightoff/lightout experiments is observed for CO and NO. C 3 H 6 -only however does not show this phe- nomenon whereas small hysteresis in conversion can be observed in combination with CO and/or NO. Keywords NO oxidation Á Hysteresis Á Deactivation Á Reactivation Á Platinum Á Palladium 1 Introduction The Diesel Oxidation Catalyst (DOC) is a key element in typical diesel exhaust treatment systems. Typical catalysts are platinum (Pt), palladium (Pd), or a combination of both (Pt/Pd, e.g. alloyed, multilayered). During lightoff/lightout experiments, hysteresis phenomena of CO, NO, and HC conversion have repeatedly been reported and attributed to thermal effects [1], to noble metal oxidation [2] and to surface coverage effects [3]. The present work’s goal is to present detailed experimental evidence on single compo- nent conversion as well as on the mutual influence of CO, NO, and HC on the respective conversion for Pt-only, and Pd-only catalysts under isothermal conditions. 2 Experimental Setup Model DOCs provided by Umicore AG&Co.KG with a close to commercial composition (Me-c-Al 2 O 3 , 400cpsi, 6,5mil) have first been hydrothermally degreened (24 h at 550 °C, 10 % H 2 O in air). Thin slices (30 mm 9 37 mm 9 1,4 mm) of the catalyst have then been tested in a metallic flat-bed reactor. The special reactor set-up, described in more detail in Ref. [4], provides isothermal conditions which were checked by thermocouple measurements in the catalyst channels. Experiments with the empty flat-bed reactor showed no measurable catalytic activity. After reducing the catalyst with hydrogen, temperature ramp experiments were conducted according to Fig. 1. A permanent feed of 5 % H 2 O, 7 % CO 2 , and 5 % O 2 in N 2 was used during the experiments at a space velocity of 40.000 h -1 . Noxious substance concentrations have been chosen as 800 ppm CO, 500 ppm NO, and 300 ppm C 3 H 6 . Experiments with one, two and all three substances have been conducted with both Pt and Pd catalysts to illuminate the individual behavior as well as the mutual inhibition effects. At the beginning of each experiment the catalyst is pretreated under reducing atmosphere (1 h at 350 °C, 3 % & H. Dubbe hendrik.dubbe@icvt.uni-stuttgart.de 1 Institute of Chemical Process Engineering, University of Stuttgart, Boeblinger Str. 78, 70199 Stuttgart, Germany 123 Top Catal DOI 10.1007/s11244-016-0589-8