Nickel phosphide catalysts supported on activated carbon were tested for the conversion of cellulose in water. High sorbitol yields of over 60 % were obtained with high cellulose conversions at 503 K and 5 MPa of H2. It is interesting that an amorphous nickel phosphide phase is generated from a crystalline phase during the increase in temperature and that the amorphous phase is responsible for the high yield of sorbitol. The optimization of the reaction parameters indicates that the increase of the amorphous part in the cellulose is the key to obtaining high yields of sorbitol. A phase change of the nickel phosphide is observed, which can be correlated to the change in catalytic activity.