A device for the intimate mixing of solid particles and a gaseous medium within a gas-solid fluidized bed, comprising a plurality corrugated and/or ribbed planar stanchions arranged in alternating intersecting planes that provide a plurality of open spaces between or adjacent the alternating intersecting planar stanchions. The element has a three-dimensional lattice configuration and the corrugated and/or ribbed planar stanchions are formed from metal having peaks and valleys or ribs, such that the peaks and valleys or ribs are angled at less than 90 degrees from the fall-line of the planar stanchion when assembled into the element. The angled peaks and valleys or ribs form channels that enhance lateral movement of catalyst particles into the spaces between the stanchions to provide improved vapor/solids mixing and contact.