In fundamental heterogeneous catalyst development, testing is usually performed with rather small amounts of catalyst. Transferring the results in terms of performance and catalyst lifetime to industrial relevant pilot-scale is hardly feasible. Thus, a new modular test system has been developed which allows large-scale testing of heterogeneous catalysts in fixed-bed or slurry mode, enabling a wide range of test conditions with regard to particle size, gas composition, pressure, and reaction temperature. The test system has been used for higher alcohol synthesis and one-step dimethyl ether synthesis.