In a process for dehydrogenating cyclohexylbenzene and/or alkyl-substituted cyclohexylbenzene compounds, a dehydrogenation catalyst comprising at least one Group 10 metal compound on a support is heated in the presence of hydrogen from a first temperature from 0° C. to 200° C. to a second, higher temperature from 60° C. to 500° C. at a ramp rate no more than 100° C./hour. The dehydrogenation catalyst is contacted with hydrogen at the second temperature for a time from 3 to 300 hours to produce an activated dehydrogenation catalyst. A feed comprising cyclohexylbenzene and/or an alkyl-substituted cyclohexylbenzene compound is then contacted with hydrogen in the presence of the activated dehydrogenation catalyst under conditions effective to produce a dehydrogenation reaction product comprising biphenyl and/or an alkyl-substituted biphenyl compound.