A particulate, precalcined low silica content zirconia, especially one stabilized with yttria, is useful as a catalyst support or as a heat transfer solids component for conducting chemical reactions at high temperature, in oxidizing, reducing or hydrothermal conditions, especially in syn gas operations. An admixture of precalcined particulate low silica content zirconia, particularly a low silica content yttria-stabilized zirconia, is employed in a preferred embodiment as a heat transfer solid, in concentrations ranging generally from about 10 wt. % to about 99.9 wt. %, with a particulate catalyst, notably a nickel-on-alumina catalyst, in concentration ranging generally from about 0.1 wt. % to about 90 wt. %. Such an admixture provides a particularly useful catalytic contact mass in high temperature oxidizing, reducing and hydrothermal environments, notably in conducting synthesis gas generation operations. This type of bed promotes continuous, highly efficient heat and mass transfer within the reacting gas phase. The presence of the heat transfer solid as a bed component maintains excellent bed fluidization characteristics, suppressing the normal tendency of the catalyst to sinter or agglomerate; tendencies which promote defluidization of the bed. Moreover, the heat transfer particles of the bed are highly attrition resistant, and are chemically compatible with the catalyst particles of the admixture.