Mordenite (MOR), the workhorse of industrial shape-selective catalysis, possesses a unique framework topology that sets it apart from every other commercial zeolite. Built from silica and alumina tetrahedra linked through signature four-membered rings (4-MR), MOR assembles into a layered architecture that stacks to form one-dimensional 12-membered ring (12-MR) elliptical channels (0.65 × 0.70 nm) intersected by 8-membered ring (8-MR) side pockets (~0.26 nm). This channel geometry — pure 1D, no cage, no supercage — confers extraordinary thermal stability, acid resistance, and water tolerance, while simultaneously imposing severe diffusion constraints that define both its catalytic brilliance and its Achilles' heel. This article provides a comprehensive structural analysis of MOR zeolite, tracing how every atomic-level feature — from the elusive 4-MR building unit to the spatial distribution of Brønsted acid sites at 8-MR windows — governs its performance in catalytic cracking, isomerization, biomass conversion, and emerging applications. The review culminates in a critical assessment of how modern synthesis strategies (desilication, seed-directed growth, heteroatom substitution) are engineering MOR beyond its natural limitations.
Keywords: Mordenite; MOR zeolite; one-dimensional channels; four-membered ring; 12-membered ring; shape-selective catalysis; thermal stability; Brønsted acidity
In the pantheon of commercial zeolites — ZSM-5, Y, Beta, MCM-41 — mordenite (MOR) occupies a paradoxical position: universally deployed yet structurally underappreciated. First described by Smith and Wadsley in 1948 and first synthesized by Hale and Minato in 1959, MOR has powered fluid catalytic cracking (FCC) units, hydrocracking reactors, and toluene disproportionation plants for over six decades. Yet unlike ZSM-5, whose MFI topology is taught in every catalysis textbook, MOR's structural elegance remains largely invisible to the broader catalytic community.
This is a profound oversight. MOR's framework is a masterclass in structural minimalism: no supercages, no intersecting 3D channels, no secondary porosity — just a clean, robust, one-dimensional channel running through the crystal like a molecular highway. This simplicity is precisely what gives MOR its legendary thermal stability (>1000°C), steam resistance, and coke tolerance — properties that no other medium-pore zeolite can match.
This article dissects MOR from the atomic level up, revealing how its structure dictates every aspect of its catalytic behavior.
