Low-temperature synthesis of rhodium phosphide on alumina and investigation of its catalytic activity toward the hydrodesulfurization of thiophene

Abstract In this study, the low-temperature synthesis of rhodium phosphide (Rh 2 P) on alumina (Al 2 O 3 ) using triphenylphosphine (TPP) as a phosphorus (P) source and its catalytic activity toward hydrodesulfurization (HDS) were investigated to prepare a highly active HDS catalyst. TPP was more easily reduced than phosphate, and Rh 2 P was formed in the P(T)/Rh/Al 2 O 3 catalyst prepared from TTP at lower temperature as compared with the temperature required by Rh-P(A)/Al 2 O 3 catalyst prepared from a phosphate precursor. However, after reduction at a low temperature (450 °C), excess P covered the surface of Rh 2 P. The optimal reduction temperature for HDS rate of the P(T)/Rh/Al 2 O 3 catalyst (650 °C) was lower than that of the Rh-P(A)/Al 2 O 3 catalyst (800 °C). Furthermore, this temperature was slightly higher than the optimal reduction temperature for CO uptake (600 °C). These results are explained as follows: HDS rate is increased by both elimination of excess P on the active sites at higher reduction temperatures and enhancement of the crystallinity of Rh 2 P. Furthermore, because the particle size of the P(T)/Rh/Al 2 O 3 catalyst (ca. 1.2 nm) was substantially smaller than that of the Rh-P(A)/Al 2 O 3 catalyst, the P(T)/Rh/Al 2 O 3 catalyst exhibited greater HDS rate compared with the Rh-P(A)/Al 2 O 3 catalyst.