Near-infrared imaging of 2D and 3D spatial resolutions allowed access to behavior of flowing gases and catalyst activity by measuring spatial distribution of composition and temperature in packed beds of low light scattering, subject to wall effects, and nonisothermal conditions. Water vapor was used as tracing species owing to high absorption coefficient in the near-infrared spectrum. Heterogeneous distribution of activity, flow maldistribution, and dynamic lags between the local mixing zones were observed and quantified. The uneven distribution of concentration and temperature highlighted the importance of mass and heat transport at gas–solid boundaries. The spatial resolution of near-infrared imaging was of importance to give reliable profiles of physical data, and dispersion coefficients and local activity were cited as examples of acceptable validation. The results were a proven stage for further developments, particularly those anticipated with infrared technology. However, key to that would be the development of affordable tunable lasers, optical accessories, and focal planar array sensors of similar sensitivities to those available in the near-infrared spectrum, allowing the technique to be applied to packed beds and other nontransparent reactive media.