A novel microreactor that allows for mixed, slurry-phase batch experiments to be conducted at temperatures to 445 degrees C and pressures of 13.8 MPa is reported. The reactor uses a glass insert to isolate the reaction mixture from the catalytically active reactor walls and a vortex mixer to promote gas liquid solid mixing and requires only 150 mu L of reaction mixture to operate. The rapid heating and cooling (to 445 degrees C and back to room temperature in under 30 min) afforded by the small size makes this reactor ideal for fast catalyst-screening studies. The utility of the reactor is demonstrated through a study of the hydro conversion of diphenylmethane (DPM) at 445 degrees C and 13.8 MPa and the hydrodeoxygenation of 4-methylphenol (4-MP) at 375 degrees C and 4.8 MPa, both conducted using an unsupported MoS2 catalyst. A high-speed video is used to identify 2000 rpm as the optimum mixing speed for the microreactor. Conversion data for DPM and 4-MP in the microreactor is used to determine rate constants for the reactions and, hence, quantify MoS2 catalytic activity and thermal/reactor wall activity. The MoS2 activity is found to be in good agreement with published stirred batch reactor results using the same catalyst.