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

•The formation temperature of Rh2P can be remarkably decreased through the use of triphenylphosphine as a P source.•After reduction at lower temperatures (below 450 °C), excess P covered the surface of Rh2P.•The P(T)/Rh/Al2O3 catalyst exhibited higher hydrodesulfurization activity than the Rh-P(A)/Al2O3 catalyst.•Small Rh2P particle can be prepared from triphenylphosphine.

In this study, the low-temperature synthesis of rhodium phosphide (Rh2P) on alumina (Al2O3) 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 Rh2P was formed in the P(T)/Rh/Al2O3 catalyst prepared from TTP at lower temperature as compared with the temperature required by Rh-P(A)/Al2O3 catalyst prepared from a phosphate precursor. However, after reduction at a low temperature (450 °C), excess P covered the surface of Rh2P. The optimal reduction temperature for HDS rate of the P(T)/Rh/Al2O3 catalyst (650 °C) was lower than that of the Rh-P(A)/Al2O3 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 Rh2P. Furthermore, because the particle size of the P(T)/Rh/Al2O3 catalyst (ca. 1.2 nm) was substantially smaller than that of the Rh-P(A)/Al2O3 catalyst, the P(T)/Rh/Al2O3 catalyst exhibited greater HDS rate compared with the Rh-P(A)/Al2O3 catalyst.

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