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A Silicon Microreactor for in-Situ Spectroscopic Analysis of Working Nsr Catalysts

Chung Kwang Tan and Chelsey D. Baertsch. Purdue University, School of Chemical Engineering, Forney Hall of Chemical Engineering, 480 Stadium Mall Drive, West Lafayette, IN 47907-2100

The design and fabrication of a novel microreactor system for in-situ structure, surface, reactivity, and thermal analysis of a monolithic Pt/Ba-Al2O3 NOX storage-reduction (NSR) catalytic converter will be presented. The microreactor is a silicon based Microelectromechanical System (MEMS) fabricated using technology available in the microprocessor fabrication industry. NSR catalyst technologies are being developed to enable diesel engines to meet stringent environmental regulations for total NOX emissions. NSR catalysts such as Pt/Ba-Al2O3 operate with two main cycles including storage of the NOX pollutants in an oxygen rich capture phase followed by release and reduction of the trapped NOX species in a reductive regeneration phase. Previous literature studies on NSR catalysts have focused on determining mechanistic models and reaction rates based on kinetic studies of either model or supported catalysts, without spectroscopic analysis of surface species during NSR reactions. The complexity of this transient process and the monolithic reactor geometry pose challenges for in-situ spectroscopic analysis using conventional reactors and spectroscopic cells.

A new microsystem will be presented which will enable quantitative analysis of the type and concentration of surface species present in real time during quantified NSR reactions, in a geometry identical to a commercial monolith and along the monolith reaction channel, and with simultaneous temperature measurement. The silicon microreactor contains 16 parallel channels (400 Ám x 400 Ám x 30 mm each) with on-chip heaters and temperature sensors spaced down the length of the channels at 5 mm intervals. Fast, spatially resolved Fourier-Transform Infrared (FTIR) analysis is used in this study to quantify the surface species (adsorbed carbonates, nitrates, and nitrites, etc.) along the catalytic converter channel at 500 Ám intervals and up to 1600 Hz sampling rates. Gold-coated optical channels are integrated with path lengths near 20 mm to enable simultaneous product gas analysis for quantitative reactivity assessment. This high speed FTIR technique allows analysis of the transient processes occurring during capture and regeneration cycles of the NSR catalyst. Further, this microfabricated system will also allow determination of the temperature of the catalyst as a function of length along the channel with a degree of accuracy never before reported to aid in the development of NSR reactor models.