Understanding the entanglement between diffusion and reaction by probing the mobility of ketene in chabazites

• The diffusion and reaction of ketene in chabazite are intrinsically entangled. • Ketene can be protonated to acylium ion or surface acetate during diffusion. • The co-feeding of water, methanol, and DME modulated ketene diffusion differently. • 2D free energy surfaces obtained by deprojection techniques can disentangle reaction and diffusion in zeolite. In zeolite catalysis, diffusion and reaction are generally viewed as separate processes that independently affect catalytic performance due to the significant variation in timescales for diffusion and reaction. Nevertheless, this study reveals that reaction and diffusion can be intertwined, a phenomenon hitherto unexplored. In particular, we highlight this complex relationship for ketene intermediates in chabazite topologies, where the diffusion properties of ketene are notably affected by the reactivity with Brønsted acid sites (BAS) and guest molecules present in the zeolite pores. Ketene is an important intermediate in zeolite catalyzed methanol-to-hydrocarbons and CO x -to-hydrocarbons conversion and its diffusion and reaction behavior directly impacts the catalytic performance. Our ab initio molecular dynamics simulations reveal that ketene diffusion is significantly facilitated by hydrogen bonding interactions with BAS during the diffusion through the 8-ring windows of chabazite, and that ketene can also readily react with other guest species along the diffusion pathway. This entanglement between reaction and diffusion can be attributed to the high activity of ketene, resulting in a strong competition between reaction and diffusion, which cannot be viewed as two independent processes. Therefore, our findings concerning the complex interconnection between diffusion and reaction not only contribute to the fundamental understanding of ketene chemistry in chabazite but also have important consequences for other fields of catalysis involving highly active intermediates.