Active-site proximity across length scales: From molecular tethers to process integration

Modern heterogeneous catalysis increasingly emphasizes the control of active-site identity, distribution, and proximity to steer catalytic reactions and promote cooperative interactions. In this Review, we examine active-site proximity as a catalyst-design strategy for cooperative and multifunctional catalysis, beginning with surface-tethered catalytic sites and then extending these ideas to broader non-tethered catalytic systems across length scales. First, we revisit foundational strategies for controlling site arrangement and local microenvironments in tethered and surface-anchored architectures, highlighting how these parameters govern reactant adsorption, activation, and sequential transformation. Particularly, we emphasized analysis of amine-functionalized silica surfaces and related systems for multifunctional CO 2 capture and conversion, where discrete yet proximally controlled sites can enhance selectivity and efficiency. We then extend these design principles to broader catalytic platforms in which proximity is essential, including metal-metal synergy, bifunctional metal-acid catalysis, tandem and cascade transformations, chemical looping, and membrane catalysis.