Strategy to enhance selectivity in a two-step reaction using the R1-R2-D
An analytically derived criterion for R1-R2 phenomenon is combined with
the Weisz criterion for R1-D phenomenon to allow the development of
assignment criteria for the overall controlling factors in R1-R2-D
phenomena. The overall assignment criteria are found to be dependent on
the internal effectiveness factors η_1 and η_2, as well as the rate of
the individual reactions at the surface of the catalyst particle.
Applying the developed criteria to a two-step methanol oxidation
reaction suggests that the selectivity of the formaldehyde intermediate
species can be enhanced at high reaction temperature when catalysts are
specifically designed to enhance the rate of formaldehyde formation.
However, CO formation needs to be suppressed to enhance selectivity
towards formaldehyde at moderately low temperature. This
reaction-diffusion theoretical framework provides guidance for the
development of highly selective catalyst for two-reactions-in-series
systems and can be extended for higher-number multiple reactions in
series and in parallel.