A route for cleaving the C–O aryl ether bonds of p-substituted H–, CH 3 –, and OH– diphenyl ethers has been explored over Ni/SiO 2 catalyst at very mild conditions (393K, 0.6MPa). The C–O bond of diphenyl ether is cleaved by parallel hydrogenolysis and hydrolysis (hydrogenolysis combined with HO * addition) on Ni. The rates as a function of H 2 pressure from 0 to 10MPa indicate that the rate-determining step is the C–O bond cleavage on Ni surface. H * atoms compete with the organic reactant for adsorption leading to a maximum in the rate with increasing H 2 pressure. In contrast to diphenyl ether, hydrogenolysis is the exclusive route for cleaving a C–O bond of di-p-tolyl ether to form p-cresol and toluene. 4,4′-Dihydroxydiphenyl ether undergoes sequential surface hydrogenolysis, first to phenol and OC 6 H 4 OH * (adsorbed), which is then cleaved to phenol (C 6 H 4 OH * with added H * ) and H 2 O (O * with two added H * ) in a second step. Density function theory supports the operation of this pathway. Notably, addition of H * to OC 6 H 4 OH * is less favorable than a further hydrogenolytic C–O bond cleavage. The TOFs of three diaryl ethers with Ni/SiO 2 in water follow the order 4,4′-dihydroxydiphenyl ether 69molmolNi Surf-1h-1>diphenyl ether 26molmolNi Surf-1h-1>di-p-tolyl ether 1.3molmolNi Surf-1h-1, in line with the increasing apparent activation energies, ranging from 4,4′-dihydroxydiphenyl ether (93kJmol −1 )<diphenyl ether (98kJmol −1 )<di-p-tolyl ether (105kJmol −1 ).