Magnetic resonance imaging (MRI) is a powerful technique to characterize reactors during operating catalytic processes. However, MRI studies of heterogeneous catalytic reactions are particularly challenging because the low spin density of reacting and product fluids (for gas phase reactions) as well as magnetic field inhomogeneity, caused by the presence of a solid catalyst inside a reactor, exacerbate already low intrinsic sensitivity of this method. While hyperpolarization techniques such as parahydrogen induced polarization (PHIP) can substantially increase the NMR signal intensity, this general strategy to enable MR imaging of working heterogeneous catalysts to date remains underexplored. Here, we present a new type of model catalytic reactors for MRI that allow the characterization of a heterogeneous hydrogenation reaction aided by the PHIP signal enhancement, but also suitable for the imaging of regular nonpolarized gases. These catalytic systems permit exploring the complex interplay between chemistry and fluid-dynamics that are typically encountered in practical systems, but mostly absent in simple batch reactors. High stability of the model reactors at catalytic conditions and their fabrication simplicity make this approach compelling for in situ studies of heterogeneous catalytic processes by MRI.Catalytic processes (e. g., hydrogenation, reforming, oxidation, etc.) are at the cornerstone of chemical and petrochemical industry [1] and, to make these processes more sustainable, control over reaction selectivity, conversion rates, mass and heat transport inside the working reactor (that is under operando conditions) is required. Magnetic resonance imaging (MRI) is a tool applicable to operando studies that provide information for example about the distribution of liquids in the catalyst pellet during hydrogenation of α-methylstyrene [2] or heptene, [3] the coke profiles within a catalyst pellet, [4] the flow of water [5] or propane [6] through a packed bed, the structure of a porous medium and the water flow during the deposition of fines, [7] or the velocities of particles in a fluidized bed. [8][9][10] MRI of reactors utilizing gases are not as developed as studies of liquids because the spin density in the gas phase is ca. 3 orders of magnitude lower relative to the condensed phase, which significantly limits the deployment of MRI for studying gases. [11] Nevertheless, a recent report showed that the distribution of the reactants and products inside a monolith type reactor can be measured even in the gas phase during ethylene hydrogenation reaction using two different catalyst supports, thereby revealing an effect of the support on the mass and heat transport. [12] Overall, to date, there are only a handful of MRI studies of the gas phase reactions with regular non-hyperpolarized gases. [13,14] The limitation of low NMR sensitivity spurs the implementation of hyperpolarization techniques, which can potentially increase the intensity of NMR signals by up to several orders of magnitude, including spin-ex...
