Structured reactors for kinetic measurements in catalytic combustion

Two types of laboratory structured reactors, which closely resemble industrial monolith catalysts, are theoretically and experimentally investigated for measurements of catalytic combustion kinetics under severe conditions: the annular reactor, consisting of a ceramic tube externally coated with a thin catalyst layer and coaxially placed in a slightly larger quartz tube; and the metallic plate-type reactor, consisting of an assembled packet of metallic slabs coated with a ceramic catalytic layer. After a brief description of an active coating deposition method suitable to provide structured reactors with adequate characteristics, a mathematical model analysis of the annular reactor aimed at the design of the optimal configuration for kinetic investigations is first presented. The resulting advantages, 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 demonstrated 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 reactor by an extremely effective dissipation of reaction heat through proper selection of highly conductive support materials and of the geometry of the 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 reserved.