Alumina heat transfer solids are admixed with a catalyst, or catalysts, and used in conducting high temperature fluidized bed reactions, particularly in a process for the production of hydrogen and carbon monoxide from a low molecular weight hydrocarbon by contact with a fluidized bed of catalyst and said heat transfer solids at high temperature in the presence of oxygen, or steam, or both oxygen and steam. The particulate heat transfer solids are characterized as having a performance index, PI, greater than 20, preferably greater than 40, as characterized by the formula PI=[(i).times.(ii).times.(iii).times.(iv)].sup.-1 where (i) the peripheral outer surface of the particle contains