The application of neutron imaging to examine ethene hydrogenation over a carbon-supported palladium catalyst

The combination of a heterogeneous catalyst operating within a defined reactor comes within the domain of reaction engineering, which takes cognisance of combined roles for both the catalyst and the reactor to define the overall operational system. One technique which is demonstrating much promise in investigating reaction engineering issues is neutron imaging. The technique is skewed towards monitoring hydrogen and hydrogenous species so, with hydrogen being ubiquitous in industrial organic chemistry and the penetrating power of the neutrons, neutron imaging can monitor hydrogen concentrations distributed throughout steel reactors whilst the reaction is taking place. In this way, neutron imaging can be used to assess the homogeneity of active catalyst beds and, additionally, determine how hydrogen is being partitioned throughout the catalyst bed as a function of time-on-stream. These are important parameters in the reaction engineering of catalytic systems involving transformations of hydrogen containing species. The article commences by reviewing the handful of existing neutron imaging studies in this field, then progresses to describe the application of the neutron imaging technique to investigate ethene hydrogenation over a 5 wt% Pd/C powder catalyst at 333 K and ambient pressure in a rectangular stainless-steel reactor. Modulations of the incident gas stream are seen to lead to spatially resolvable fronts moving across the bed and illustrate the diffusion of reagents from the reactor inlet across to the reactor exit. Thus, the investigation reveals spatially and temporally resolved elementary reactions that contribute to the hydrogenation process.