Formation of active sites and hydrodesulfurization activity of rhodium phosphide catalyst: Effect of reduction temperature and phosphorus loading

• The Rh-1.5P catalyst exhibited the highest activity among the investigated catalysts.
• Rh2P was easily formed in catalysts with a higher P loading.
• Higher P loadings and higher reduction temperatures led to aggregation of Rh species.
• RhP2 exhibits lower catalytic activity than Rh2P.
• High HDS activity was caused by small Rh2P formation at lower reduction temperature.

Effects of reduction temperature and phosphorus loading on rhodium phosphide (Rh2P) formation and on the catalytic activity of Rh-xP catalysts for hydrodesulfurization (HDS) were investigated to prepare highly active HDS catalysts. Analysis of the Rh-xP catalysts showed that a suitable P loading for HDS activity is 1.5 wt%—four times greater than that of an Rh catalyst. Temperature-programmed reduction and X-ray diffraction analyses of the Rh-xP catalysts showed that Rh2P is readily formed in catalysts with higher P loading. In contrast, the results of transmission electron microscopy observation and CO adsorption experiments indicated that the Rh2P particle size increased with increasing P content. Thus, the high HDS activity of the Rh-1.5P catalyst was explained by the formation of small Rh2P at a relatively low reduction temperature (550 °C).

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