In one aspect, the invention includes a reactor apparatus for pyrolyzing a hydrocarbon feedstock, said apparatus including: a reactor component comprising a refractory material in oxide form, the refractory material having a melting point of no less than 20600C and which remains in oxide form when exposed to a gas having carbon partial pressure of 10-22 bar and oxygen partial pressure of 10-10 bar, at a temperature of 12000C; wherein said refractory material has no less than 4 vol% formed porosity, measured at 200C, based upon the bulk volume of said refractory material. In another embodiment, the refractory material has total porosity in the range of from 4 to 60 vol%.