ABSTRACT
An efficient catalyst transforms reactants into desired products at a high rate. Much progress is made toward the atomic design of the active site, where the actual turnover occurs. The active site is an atomic or molecular assembly with the right geometric and electronic structure to selectively transform molecules. Biology is often remarkably efficient at this, guiding novel enzymatic and bio-inspired routes in heterogeneous catalysis. For complex transformations, several reaction steps may be needed, and one objective in catalyst design is to reduce their number, so as to increase the overall yield and selectivity. Facile, controlled access toward the active sites is desirable, and the final products need to be removed from the sites as quickly as possible. This avoids further conversion into undesired products and speeds up the entire process. Reactants may have to collide multiple times with the sites before a reaction occurs by an activated process. These boundary conditions mean that an optimal distribution and connectivity of the active sites over space is required to maximize the overall process efficiency. Catalysis engineering therefore involves not only the design of the catalyst site, as important as it may be, but also the design of the ‘‘network’’ linking feed and product streams. Designing this network is the topic of this chapter: What is the optimal road network, and what should these ‘‘nano-roads’’ look like?
