The flow around a single spherical VPO particle (d p = 5 mm) in a rectangular channel (see Figure , top right) coupled with reaction inside the catalyst is calculated for particle Reynolds numbers ranging from 50 to 1, 500. According the findings of , the sphere is placed 5d p from the inlet and the size of the box is chosen to be 15d p × 15d p × 20d p (Height x Width x Length) to guarantee a solution being independent from the domain size.