Magnetic resonance imaging is a particularly valuable technique for studying heterogeneous catalytic processes in the reactor environment because it has the potential to characterise hydrodynamics and chemical composition at different spatial locations within the reactor. Here we report recent developments in: (i) temperature mapping in a trickle-bed reactor with an accuracy of +/- 2.0 degrees C, (ii) imaging of local gas and liquid flow velocities in a fixed-bed reactor during trickle-flow with a measurement accuracy of 5% and 7%, respectively, and (iii) quantitative mapping of chemical composition within the bed to an accuracy of <2.5%. The ability to measure local reaction rate enables us to calculate a local rate-based selectivity to specific products within the reactor. (C) 2009 Elsevier B. V. All rights reserved.