Suspended catalyst particles in two phase slug flow could be an alternative technique for using heterogeneous catalysts in microreactors. which has so far mainly been restricted to immobilised solid catalysts, either in micro-fixed-beds or catalytically coated wall reactors. The hydrodynamic and particle behaviour in slug flow was analysed using fluorescent particles and particles of typical catalyst supports in various biphasic liquid-liquid systems. Typically, the circulations only encompassed the anterior section of the slug and depended on the properties of the liquid-liquid system and, in particular, on the slug velocity. Silicon dioxide or aluminum oxide particles suspended in the aqueous phase follow the internal circulation streamlines almost exactly, while carbon-based particles suspended in the continuous organic phase formed a contiguous cap around the rear end of the dispersed aqueous slug. The principle of suspension catalysis was demonstrated experimentally for a heterogeneous catalytic transfer hydrogenation of m-nitrotoluene with aqueous potassium formate. (C) 2010 Elsevier B.V. All rights reserved.