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The heat and mass transfer characteristics of a monolith reactor influence both its light-off performance and the steady-state temperature and concentration profiles. The transient behavior of an adiabatic monolith reactor is bounded by two limiting channel geometries: (a) cylindrical passages and (b) slits confined between parallel plates. These geometries represent extremes in heat/mass transfer characteristics for monolith channels and, therefore, allow the analysis of light-off behavior for the practical range of geometries and process conditions in automobile exhausts. Also, these two geometries allow an analytical solution for the velocity, concentration and temperature profiles in the gas phase. This study analyzes the light-off performance of monolith reactors with comparable voidage and surface area using automotive exhaust oxidation kinetics. The energy balance for the solid walls includes all three modes of heat transport: convection, conduction and radiation.

Platinum Group Metal (PGM) use is dominated by the automotive industry. The PGM market is sensitive to shifts in the drivers for emission control and the delicate supply-demand balance. Technology shifts in the emission control industry are particularly impactful because of the automotive market's dominance and the consequent ability to significantly affect metal prices. On the supply side, evolving ore ratios of platinum, palladium and rhodium, production ramp-up times, geopolitical factors, and labor relations contribute to a challenging production environment. This is mitigated by a growing above-ground supply from spent autocatalysts. The availability of spent autocatalyst is critical to alleviate the pressure on primary supply and is especially important in light of the hurdles primary PGM producers face. This paper reviews technology developments, legislative drivers, and consumer trends in the automotive industry and their impact on PGM demand.