Spatially resolved NMR is employed to quantitatively map the temperature of a solid catalyst under operating conditions during H(2) oxidation with O(2) over Pt/γ-Al(2)O(3). As this new non-invasive in situ technique utilizes the (27)Al NMR signal of the solid phase, it is suitable for catalyst temperature mapping in both liquid- and gas-phase heterogeneous catalytic processes.