Catalytic hydrogenolysis of a gamma-acetylated dimer lignin model compound is effected using a Ru-xantphos catalyst. Mechanistic investigations show mono-aryl degradation products are generated from the beta-O-4 substrate as well as a terminal alkene ketone dimer (bis-aryl) that further dimerizes to a tetra-aryl product. Preliminary results using an acetylated kraft lignin as a substrate are also discussed.