Micromonoliths coated with Pt/Al 2 O 3 catalyst for the simultaneous combustion of H 2 , CO and CH 4 : Effect of the catalytic layer thickness and thermal conductivity Oscar. H. Laguna 1* , Oihane Sanz 2 , Miguel A. Centeno 1 , Mario Montes 2 , José A. Odriozola 1 1 Instituto de Ciencia de Materiales de Sevilla (Centro Mixto CSIC – Universidad de Sevilla) Avda. Américo Vespucio 49, CP:41092 – Seville (Spain) 2 Applied Chemistry Department, Chemistry Faculty of the University of the Basque Country (UPV/EHU), Donostia- San Sebastián (Spain) *olaguna@us.es Highlights  The micromonoliths achieve the total conversion of the mixture: H 2 /CO/CH 4 .  Heterogeneity of the axial thermal is controlled by catalytic layer thickness.  The thermal conductivity decreases with the loading of catalyst. 1. Introduction Within the fuel processors technology, the enhancement of the thermal efficiency is one of the challenges that have to be overcome in order to make this a competitive technology [1]. Among the different approaches for designing more efficient fuel processors, the use of the off-gas of the fuel cells for producing heat through a combustion reaction results interesting not only from an energetic point of view, but also from the environmental one because the use of an usually discarded stream that is released to the atmosphere, would reduce the environmental impact of this technology. The produced heat by the combustion of the off-gas of the fuel cell can be transferred by means of a heat-exchanger to the endothermic steps of the overall process. In the present work we study the combustion of a ternary mixture of fuels (H 2 , CO, and CH 4 ) usually present in the fuel cell off-gas. For this a Pt/Al 2 O 3 catalyst is used. This catalyst has been structured in metallic micromonoliths (stainless steel FeCrAlloy®) with 1350 cpsi (cells per square inch), modifying the amount of loaded catalyst. The catalytic performance of the monoliths during the combustion has been tested and compared with that of the powder catalyst. Additionally, axial thermic profiles under specific conditions of the combustion reaction have been measured for the more active monoliths, in order to establish the relationships between the amount of catalyst and the creation of hot spots in the structured systems. 2. Methods Firstly, for the synthesis of the catalysts, alumina PURALOX® (SCFa140/L3 - Sasol) was calcined at 900 ºC during 6 h. Then, a 2 wt.% of Pt was deposited over the calcined alumina by the incipient wetness impregnation method. The obtained solid was dried at 120 ºC during 12 h and finally calcined at 500 ºC during 6 h. As for the structured systems, cylindrical micromonoliths were manufactured (diameter =1.7 cm; height = 3.0 cm, and geometric exposed area 540 cm 2 , using FeCrAlloy ® [2]. Different loadings of catalyst were deposited over micromonoliths using the washcoating method (50, 100, 250 and 550 mg of catalyst that correspond to 0.1, 0.2, 0.5 and 1.0 mg/cm 2 of coating densities respectively). Monoliths have been labelled as M0.1, M0.2, M0.5 and M1.0 respectively. The catalytic activity measurements were carried out in a Microactivity Reference PID Eng&Tech ® system over the dried slurry (the solid obtained after the drying and calcination of the slurry) and the micromonoliths. Concerning the mixture feed, 200 and 500 mL/min total flows (composed by 2 Vol.% H 2 , 2 Vol.% CO, 2 Vol.% CH 4 , balanced with air) were used. The products of the reaction were followed by on-line gas chromatography (Varian ® CP-4900). For the measurement of the temperature profiles, a K-type thermocouple was placed at different axial positions along the center of the monoliths for measuring the temperature differences (ΔT) between the axis and the external reactor wall due to the combustion. An additional K-type thermocouple was employed for the control of the