Local Mo6+ Coordination and Textural Accessibility, Rather than Bulk Phase, Correlate with the Peroxidase-Mimetic Reactivity of CoMoO4 Nanopowders

Whether the bulk crystallographic phase determines the H2O2 reactivity of oxide nanopowders has direct implications for catalyst design. Three glycine–nitrate-derived CoMoO4 nanopowders—as-synthesized, calcined at 450 °C (both β-CoMoO4 by XRD), and calcined at 1000 °C (α-CoMoO4)—were studied by ATR-FTIR spectroscopy, the Briggs–Rauscher (BR) oscillatory reaction, cyclic voltammetry (CV), and electrochemical impedance spectroscopy. Deconvolution of the Mo–O stretching region with a uniform Voigt line shape resolves octahedral (α-type) and tetrahedral (β-type) Mo6+ components in both β-classified powders, indicating short-range coordination heterogeneity not detected by XRD. In the BR reaction (n = 3), the 450 °C powder suppresses oscillations at ≤0.002 g, whereas the as-synthesized powder still oscillates at 0.040 g (slope of the τosc decrease is 5172 ± 406 s g−1), and the bulk-α 1000 °C powder is about four times less active per gram than the as-synthesized powder. CV supports the highest activity of the 450 °C powder. A semi-quantitative descriptor, Φ = ρα × SBET, combining the FTIR α-type band-area fraction with the BET surface area, identifies the most active powder but does not discriminate between the two less active ones. Within this series, bulk phase identity alone does not predict peroxidase-mimetic activity.