The reaction of AsPh3 with Ni/Al2O3 at 100 to 200 degreesC under 6 to 30 bars of hydrogen has been followed by kinetic analysis of both the consumption of AsPh3 and the evolution of benzene and cyclohexane as well as magnetic and XRD measurements of the metallic and intermetallic phase(s). The reaction proceeds via complete hydrogenolysis of the As-Ph bonds, with final formation of a well-characterized NiAs alloy (XRD). The mechanism of alloy formation is complex: at low coverage of the nickel surface, stepwise hydrogenolysis of the As-Ph bonds leads to the formation of the surface organometallic fragments Ni-s[AsPhx](y) (kinetic studies and analytical data). Further hydrogenolysis of these fragments progressively leads to the formation of arsenic "adatoms" which quickly migrate inside the nickel particles to form NiAs0.45 amorphous intermetallic phases (XRD and magnetic measurements). The reaction then proceeds slowly up to the As/Ni ratio of unity with formation of the crystalline NiAs "nickeline" phase (XRD). (C) 2001 Academic Press.