[curious stackhouse]

Am involved in the design of a trickle bed reactor for desulphurisation of diesel.The catalyst involved is a mix of Nickle and molybednum.I have calculated the volume of catalyst required from the kinetics of the reaction and realised I need three consecutive beds in the reactor column because of the large quantity required.My question... 1) Is it necessary to place some inert material substance on top ot the catalyst like they do on fixed beds. 2)What is the most suitable inert substance? 3)What volume of inert substance say alumina beads should be on each bed, what determines the volume, 4)Is it safe to assume that the catalyst and innert substance account for 80% of the total reactor volume and use this to get the total reactor volume?