What is a fixed bed reactor and where is it used?

A fixed bed reactor contains stationary solid catalyst particles through which reactant fluid flows. The catalyst remains in place (not suspended or fluidized). Characteristics: high catalyst loading, good for high-throughput gas-phase reactions, temperature gradients possible (radial and axial), and pressure drop increases with smaller particles. Applications: ammonia synthesis, methanol synthesis, catalytic reforming, and hydroprocessing. May use multiple beds with intermediate heating/cooling for temperature control.