A novel approach to the synthesis of unsupported nickel phosphide catalysts using nickel thiophosphate as precursor

Abstract Nickel thiophosphate, NiPS 3 synthesized at room temperature using a soft chemistry approach (a-NiPS 3 ) has been successfully used as precursor for low-temperature preparation of unsupported nickel phosphide. Using Raman spectroscopy and EXAFS, comparison with a well-crystallized NiPS 3 reference (c-NiPS 3 ) first confirmed that nickel thiophosphate can be effectively obtained at low temperatures of preparation. In situ XRD diffraction and EXAFS showed that Ni 2 P was obtained by the reduction of a-NiPS 3 at a temperature as low as 573 K. For c-NiPS 3 , slower kinetics of reduction first led to the formation of an intermediate richer phosphorus-containing nickel phosphide phase, Ni 5 P 4 at a temperature of reduction of 623 K while Ni 2 P started being formed at 773 K. Under hydrodesulfurization (HDS) thiophene catalytic conditions (613 K, 2.8 mol% thiophene/H 2 ), a-NiPS 3 was decomposed into a mixture of Ni 2 P and Ni 5 P 4 while c-NiPS 3 was converted into Ni 5 P 4 . Both nickel phosphide catalysts exhibit much higher activities compared to a MoS 2 reference. Ni 5 P 4 exhibited a specific activity (per gram of catalyst) seven times as high as for MoS 2 .