A support structure for securing a catalyst structure comprising a multiplicity of longitudinally disposed channels for passage of a flowing gas mixture within a reactor, said support structure being comprised of a monolithic open celled or honeycomb-like structure formed by thin strips or ribs of high temperature resistant metal or ceramic which abuts against one end of the catalyst structure, and extends in a direction perpendicular to the longitudinal axis of the catalyst structure to essentially cover an end face (at either the inlet end or outlet end or both) of the catalyst structure with the support structure being secured on its periphery to the reactor wall. The strips or ribs making up the support structure are bonded together to form a unitary structure having cellular openings at least as large as the catalyst structure channel openings. The cellular openings in the support structure are also positioned to be in fluid communication with the channels of the catalyst structure thus affording essentially unaltered gas flow from the catalyst structure through the support structure.