Dynamic site‐interconversion reduces the induction period of methanol‐to‐olefin conversion

Reaction–diffusion coupling across the catalyst pore, grain, pellet, and reactor bed has been studied using a particle‐resolved transient microkinetic model applied to temperature‐programmed desorption and step‐response studies of methanol and dimethyl ether conversion over ZSM‐5 catalysts, respectively. An evolution of desorption across scales is provided. Five models (coverage, anomalous diffusion, mass transfer, fixed site‐interconversion, and dynamic site‐interconversion) are investigated to describe the 44‐min induction period in the first step‐response cycle and the 95% reduction in subsequent step‐response cycles. The reduction is due to dynamic autocatalytic interconversion across three active site‐ensembles. The first active site‐ensemble retains the kinetic function of the first step response cycle while the second and third active site‐ensembles adopt a new kinetic function mediated by surface methoxy species and adsorbed water. The dynamic site‐interconversion mechanism reduces the induction period, increases the reaction efficiency, and describes the formation of primary olefins.