Abstract The improved mass transfer and reduced macroscopic backmixing of segmented flow regimes in mini and microchannels favour its application in three-phase reaction processes. Therefore, industrial available and standardised catalyst particles or pellets may benefit from these microfluidic phenomena if they are packed into inert minichannels. Such packings form the key components of composite minichannel reactors. In order to evaluate this reactor concept, hydrodynamic phenomena, mass transfer, and pressure drop will be examined for a reactor consisting of a ceramic minichannel packing with a hydraulic diameter of 1.0mm and dumped spherical catalyst particles of 0.8mm in diameter. The experimental data, achieved in a setup combining hydrodynamic observation and chemical reaction, were used to derive universal applicable correlations to predict mass transfer coefficients and friction factors from Reynolds, Schmidt, and Sherwood numbers. The work concludes with an extensive comparison of composite minichannel reactors with conventional multiphase reactors and developing packed-bed reactors in terms of mass transfer capability, power consumption, and contacting efficiency. At identical power consumption, the investigated composite minichannel reactor offered a remarkably higher overall mass transfer rate for the gaseous compound than conventional trickle-bed, slurry bubble column, or slurry stirred tank reactors. Similar rates or even higher rates were achieved in miniaturised packed-bed reactors with particles less than 1.0mm in diameter. Consequently, it is expected that structured and miniaturised packed-bed reactors are a promising concept to intensify multiphase reaction processes, e.g. by switching from batch to continuous processing.