Precious Metal Catalyst Mechanism and Reactor Kinetics Modeling

2 Precious Metal Catalyst Mechanism and Reactor Kinetics Modeling 

The reaction mechanism is an important and open question in CPO research. Direct and indirect mechanisms were proposed, as summarized in a review paper by York et al. in 2003.63 Some authors support the direct mechanism whereas some find evidence for the indirect mechanism. Others advocate for a mechanism in between. Professor Schmidt s group reported extensive fundamental studies on CPO reaction mechanism.64 For CPO reaction, the direct mechanism assumes that H2 and CO are primary reaction products formed by POX in the presence of gas phase 02. This can be shown by the following equation, with competitive formation of H20 and C02 included (0 x 2, 0 y 1)  

The indirect mechanism postulates a two-zone model with strongly exothermic CH4 combustion to H20 and C02 (Eq. 3.6) at the catalyst entrance, followed by strongly endothermic steam (see Eq. 3.3) and C02 reforming downstream (Eq. 3.7)  

Two approaches are typically adopted in literature for mechanistic studies.64 One is to compare reactor exit data obtained from realistic methane CPO experiments with numerical simulations derived from reaction mechanism assumption. For the other approach, well-defined isothermal low-pressure or diluted conditions different from technical applications are employed. Mechanistic conclusions are drawn based on experimental product distribution under those conditions. 

In the mechanistic studies conducted by Horn et al.,64 methane CPO reactions were run under as close to industrial conditions as possible. A high-resolution (=300/rm) spatial profiling technique was developed to measure the temperature and species profiles along the centerline of the catalyst bed. The unprecedented high-resolution data make it possible to accurately speculate reactions occurring along the catalyst bed (10mm) in a very short contact time. It was revealed that for Rh-supported CPO catalysts, H2 and CO are formed in both the initial 0-2-mm 

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