The diffusion coefficients of Mo-V (as MoCl5) at 300 K in solutions of poly(acrylic acid) in dimethylformamide (DMF) have been measured by two-dimensional spatial-spectral electron spin resonance imaging (2D ESRI), at polymer contents of 5%, 10%, and 15% w/w in the solvent. The concentration dependence of the diffusion coefficients is consistent with the free volume theory. The central position of molybdenum complexes in redox and acid-base catalysis, together with the possibilities opened by this study, suggest that the method of ESRI based on Mo-V could become important for measuring transport properties and spatial characteristics of reactions in heterogeneous catalysis. Further developments of the approach taken in this study are discussed.