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

Abstract

The effects of zeolite structure on rhodium phosphide (Rh2P) formation, dispersion and hydrodesulfurization (HDS) activity were investigated. TPR showed that the order of maximum peak temperature for phosphates reduction was Na-beta NaMFI NaMOR. The XRD patterns of reduced catalysts revealed that the order of Rh2P formation temperature agreed with that of phosphate reducibility. CO uptake of NaMOR-supported catalyst was much lower than those of other zeolite-supported catalysts. These results suggested that since the NaMOR support had a one-dimensional channel, the phosphates and Rh species did not easily diffuse into the micropores. The order of thiophene HDS conversion was NaMFI Na-beta NaMOR. The order of average particle size of Rh2P calculated from TEM images was NaMOR Na-beta ≈ NaMFI. Since formation of Rh2P on the Na-beta needed high reduction temperature, the beta structure might be partially collapsed. Well-dispersed Rh2P was formed on NaMFI at lower reduction temperature, so that this catalyst exhibited the highest HDS activity among the zeolite-supported catalysts.

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.…”

“…Sawada et al [33,34] prepared Rh 2 P catalysts supported on SiO 2 , Al 2 O 3 , and different zeolites (Na-beta, Na-MFI, Na-MOR) for the HDS of thiophen via the incipient wetness impregnation method. Sawanda et al [33] investigated the effect of Na doping on the formation of Rh 2 P. The addition of Na to samples lowers the required reduction temperature of the samples supported on zeolites or Al 2 O 3 by weakening the interactions between the Al and the phosphate precursor [33].…”

“…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].…”

“…A moderate P loading of 1.5 wt % leads to the formation of well-dispersed Rh 2 P at moderate temperatures without the drawback of excess P covering or sintering due to the high reduction temperature. Sawanda et al [33,34] investigated the HDS of thiophene with Rh 2 P supported on zeolites. In the first investigation [10,33] the effect of adding Na to the Rh 2 P catalysts supported on MFI zeolite, SiO 2 , and Al 2 O 3 on the HDS of thiophene was studied.…”

“…Sawanda suggested that the addition of Na decreases the interaction between the Al and the phosphate and thus enhances the reducibility of the phosphate species to Rh 2 P and increases the activity of the catalysts. In a subsequent investigation [34], different Na-form zeolites (Na-beta, NaMFI, NaMOR) were used as supports for the Rh 2 P catalyst and tested in the HDS of thiophen. The order of the thiophene conversion values is NaMFI (~35%) > Na-beta (~17%) » NaMOR (~8%) under identical reaction conditions (fixed-bed reactor, 0.1 g catalyst, 350 • C, 0.1 MPa, H 2 /thiophene = 30, W/F = 37.9 g h mol −1 ).…”