Structured reactors for kinetic measurements in catalytic combustion

Two types of laboratory structured reactors, which closely resemble industr ial monolith catalysts, are theoretically and experimentally investigated f or measurements of catalytic combustion kinetics under severe conditions: t he annular reactor, consisting of a ceramic tube externally coated with a t hin catalyst layer and coaxially placed in a slightly larger quartz tube; a nd the metallic plate-type reactor, consisting of an assembled packet of me tallic slabs coated with a ceramic catalytic layer. After a brief description of an active coating deposition method suitable t o provide structured reactors with adequate characteristics, a mathematical model analysis of the annular reactor aimed at the design of the optimal c onfiguration for kinetic investigations is first presented. The resulting a dvantages, including: (i) negligible pressure drops; (ii) minimal impact of diffusional Limitations in high temperature - high GHSV experiments; (iii) effective dissipation of reaction heat are then experimentally demonstrate d for the case of CH4 combustion over a PdO/gamma -Al2O3 catalyst with high noble metal loading (10% w/w of Pd). The feasibility of near-isothermal operation with the metallic plate-type r eactor by an extremely effective dissipation of reaction heat through prope r selection of highly conductive support materials and of the geometry of t he metallic slabs is finally discussed and experimentally demonstrated for the case of combustion of CO at high concentrations over a PdO/gamma -Al2O3 (3% w/w of Pd) catalyst. (C) 2001 Elsevier Science B.V, All rights reserve d.