Preparation of Highly Active Noble Metal Phosphide Catalysts: Effect of Precursors on the Formation of the Active Phase and Hydrodesulfurization Activity

Abstract

The effect of precursors on the active phase formation and hydrodesulfurization activities of noble metal phosphide catalysts was examined. The maximum activities of PdP and RhP catalysts prepared from acetylacetonato (acac) complex were observed at lower reduction temperatures than those for catalysts prepared from chlorides (Cl). The PdP catalyst prepared from acac also showed higher activity than that obtained from Cl. However, this trend was not observed in the RhP catalyst. The characterization results revealed that the higher activity of the PdP catalyst prepared from the acac is due to the highly dispersed Pd 4.8 P.The combustion of organic sulfur compounds in fuels used for boilers and engines results in the formation of sulfur oxides (SO X ). It is well known that SO X causes air pollution, acid rain, and the deactivation of automotive catalysts. Clean fuels are produced by the petroleum industry using hydrodesulfurization (HDS) processes. Recently, the development of new HDS catalysts that exhibit higher activity than commercial CoMo/ Al 2 O 3 catalysts have been claimed to produce cleaner fuels with low sulfur content. We reported that Rh 2 P and Pd 4.8 P showed higher catalytic activity than Ni 2 P and other NM X P Y (Ru and Pt).10 On the other hand, supported Pt catalysts prepared from acetylacetonato (acac) complexes have higher HDS activity than supported Pt catalysts prepared from other precursors.15 Thus, it may be possible to prepare highly active NM X P Y catalysts from acac complexes. In this study, the effect of precursors on the formation of NM X P Y (Pd 4.8 P and Rh 2 P) and its catalytic activity was examined in order to develop a new highly active HDS catalyst.Silica (SiO 2 , 295 m 2 g ¹1 ) was used as the catalyst support. P-added NM (NMP) catalysts were prepared using a previously described impregnation method. 10,12 The chloride precursors, RhCl 3 ¢3H 2 O and PdCl 2 , were dissolved in water and a 1.0 mol L ¹1 HCl solution, respectively. Ammonium dihydrogenphosphate (NH 4 H 2 PO 4 , AHP) was used for the preparation of NMP(Cl) catalysts. After impregnation, the catalysts were dried at 110°C for 24 h followed by heat treatment at 450°C in N 2 for 1 h to decompose the salts. The sieved catalysts (3042 mesh granules) were calcined in air at 500°C for 4 h (10°C min ¹1 ). The NMP(acac) catalysts were prepared using the same procedure but with acac complexes ([Rh(C 5 H 8 O 2 ) 3 ] and [Pd(C 5 H 7 O 2 ) 2 ]) dissolved in acetylacetone. In addition, triphenylphosphine ((C 6 H 5 ) 3 P, TPP) was used as the P precursor for the preparation of the NMP(acac) catalysts, because AHP does not dissolve in acetylacetone.The HDS of thiophene was performed using a fixed bed flow reactor under atmospheric pressure. The sieved catalyst (0.1 g) was treated in He at 500°C for 1 h, followed by reduction with H 2 at 350700°C for 1 h prior to the reaction. The HDS reaction was carried out using a mixture of H 2 and vaporized thiophene at 0°C, which was introduced into the quartz reactor at 350°C. The W/F of the...

Noble Metal Phosphides as New Hydrotreating Catalysts: Highly Active Rhodium Phosphide Catalyst

“…55) Reduction temperature is one of the important factors in the reducibility of phosphate and the formation of phosphide. Figure 1 shows the temperature programmed reduction (TPR) profiles of 1. in the TPR profile of P/SiO2 catalyst 57) . Furthermore, two peaks at approximately 50 and above 650 occurred for the physically mixed Rh/SiO2 and P/SiO2 catalysts, in which the Rh2O3 hardly interacted with the phosphate 58) .…”

Platinum Group Metal Phosphides as Efficient Catalysts in Hydroprocessing and Syngas-Related Catalysis

“…The development of the noble metal phosphide catalysts for hydrotreating catalysts shows that Rh 2 P displays the highest activity in the HDS and HDO reactions. The main factors affecting the activity of Rh 2 P are the preparation pathway and precursors, reduction temperature, and support material as shown by the broad investigations by Kanda et al [29][30][31][32][33][34]43,52]. For deoxygenation reactions, cooperative mechanisms of multifunctional or adjacent sites are discussed as a major motive.…”

“…A sample reduced at 550 • C with 1.5 wt % P loading has an average particle diameter of 6.4 nm, while a sample with 3.0 wt % has an average particle diameter of 8.8 nm. Kanda et al [32] also compared the use of acetylacetonato (acac) precursors and triphenylphosphine (TPP) with the use of chloride and phosphate precursors for the preparation of Rh 2 P and Pd 4.8 P on SiO 2 . When the acac precursor and TPP are employed, slightly lower reduction temperatures are needed for the formation of the phosphides.…”

“…Further investigations have shown that Rh 2 P has a higher activity in the HDS of thiophene than all the other PGM phosphides [29]. Due to the higher intrinsic activity of the Rh 2 P catalyst, different publications have focused on the application of Rh 2 P as a catalyst material for hydrotreating reactions [27][28][29][30][31][32][33][34]43,47,52], for the hydrogen evolution reaction [53], and for the hydroformylation [35]. Reviews focusing on the metal phosphides in general and their applications as catalyst materials can be found elsewhere [24][25][26]49,54,55].…”

Formation of Rh₂P Supported on Na-form Zeolites and Catalytic Activity for Hydrodesulfurization

“…These peaks could be divided into two parts; 180-500 (in the case of Rh _ P/ NaMOR catalyst, 200-500 ) and above 500 . The former was attributed to the reduction of phosphates interacting with Rh species 14) . The latter was attributed to the reduction of phosphates weakly interacting with Al by existing sodium species 12) .…”