Ruthenium-catalyzed ammonia decomposition: from interfacial microenvironment design to standardized performance benchmarking

Low volumetric energy density of H 2 makes storage and transport prohibitively expensive, constraining the hydrogen economy. Ammonia (17.6 wt% H 2 ), served by mature global infrastructure, is a practical carbon-free carrier. Ruthenium catalysts set the kinetic benchmark for on-demand H 2 release via ammonia decomposition; their scarcity demands strategies that maximize atom utilization—driving a shift from empirical screening to mechanism-guided design. This review organizes recent progress along two interdependent axes: support-mediated microenvironment modulation and active-center regulation. Tailored matrices—carbons, metal oxides, composites, nitrides, and porous frameworks—regulate Ru dispersion, interfacial charge redistribution, and defect chemistry. Local-environment tuning through size control, low-coordination B5 ensembles, nanoconfinement, and alloying reshapes the energy landscape for N–H cleavage and N 2 recombination. This review integrates three elements that are usually treated separately: coupled support–active-site design, an evidence-constrained mapping of catalyst strategies to elementary steps, and condition-specific performance benchmarking with explicit provenance and normalization boundaries. For 5 wt% Ru/g-C 3 N 4 –AR, the reported 99.01% NH 3 conversion at 500 °C and 18,000 mL g cat −1 h −1 corresponds to a mass-balance-consistent H 2 production rate of 19.8904 mmol g cat −1 min −1 . Because a measured Ru loading and a defensible numerical site count were not available from the supplied primary record, neither a Ru-mass-normalized rate nor a site TOF is assigned. Across the reviewed studies, GHSV, WHSV, F/W, absolute flow, reactor mode, and activity denominators are retained rather than collapsed into nominally common metrics. The resulting framework connects mechanistic evidence to auditable catalyst/condition bundles without implying direct rankability where experimental bases differ.