Characterization of Silica-Supported Molybdenum and Tungsten Phosphide Hydroprocessing Catalysts by 31P Nuclear Magnetic Resonance Spectroscopy

On the surface sites of MoP/SiO2 catalyst under sulfiding conditions: IR spectroscopy and catalytic reactivity studies

“…The XRD pattern of bulk MoP (Fig. 1e) gives several peaks at 27.6, 31.8, 42.8, 57.0, 64.6, 67.2, and 74.0 • , similar to the standard pattern from the powder diffraction file (PDF) [24] as well as that reported in the literature [6,7,14,15,19]. The diffraction patterns for MoP/SiO 2 samples with 25 and 35 wt% Mo exhibit similar peaks of bulk MoP, confirming the successful preparation of MoP on the silica support.…”

“…More recently, transition metal phosphides prepared by temperature-programmed reduction (TPR) were reported to have high catalytic activity for both HDN [6][7][8][9][10][11][12][13][14][15][16][17][18] and HDS [10][11][12][13][14][15][16][17]19,20]. Among these phosphide catalysts, molybdenum phosphides (MoP, MoP/SiO 2 , and MoP/ Al 2 O 3 ) [6][7][8][9]14,15,[17][18][19] received the most attention.…”

“…The HDN and HDS activities of Mo nitride and carbide catalysts are initially high but decline with time in the presence of sulfur-containing compounds, which was explained mainly by the irreversible sulfidation of these catalysts [21][22][23] under reaction conditions. However, it is interesting to note that molybdenum phosphide catalysts show quite stable activities in hydrotreating reactions in the presence of sulfur-containing feedstock, and in some cases even exhibit increased activities with reaction time [7,8,14,15,18,19]. For example, Stinner et al [7] reported that pure MoP shows a decrease in activity in the presence of H 2 S in the HDN of o-propylaniline, but the activity increases to a higher level than that at the beginning of the reaction when H 2 S is removed.…”

“…Although XAFS [14], NMR [15], and XPS [19] studies provided some useful information on the chemical states of P and Mo atoms in molybdenum phosphides, a key question still remains: what are the chemical properties of the surface sites of a nonpassivated or fresh MoP catalyst? Meanwhile, the number of active sites on phosphide catalysts has typically been estimated by CO chemisorption [9,14,15,19]. But little is known about the sites where CO adsorbs on phosphide catalysts.…”

Effects of Support on Formation of Active Sites and Hydrodesulfurization Activity of Rhodium Phosphide Catalyst

“…This observation indicates that Rh2P is difficult to form on Al2O3 compared with SiO2 and TiO2. The peak temperature in the TPR spectra of MoP/Al2O3 occurred at about 800 to 900 27) , higher than that observed for MoP/SiO2 (550 ) 25) . Furthermore, phosphorus reacts with the surface of Al2O3 to form AlPO4 in Ni2P/ Al2O3 catalyst 22) .…”