Molybdenum Phosphide Catalysts Research Articles

Preparation, Characterization, and Performance of Alumina-Supported Nanostructured Mo−Phosphide Systems

A series of γ-Al2O3-supported molybdenum phosphide catalysts containing fixed Mo-loading (9.9 wt %) and variable P amounts (1.5−9.6 wt %) were prepared by temperature-programmed reduction (TPR) from their oxide precursors in hydrogen. The effect of the P/Mo atomic ratio on the structure of the molybdenum phosphide materials was studied by SBET, XRD, HRTEM, TPD−NH3, H2 chemisorption, XPS, and 31P- and 27Al-MAS NMR techniques. The reactions involved in the transformation of oxide precursor to Mo−phosphide were followed by TPR. Specific surface areas of samples subjected to reduction at 1123 K were rather high (210−263 m2 g-1). These catalysts were tested in the gas-phase hydrodesulfurization (HDS) of dibenzothiophene (DBT) at 553 K and 3.4 MPa. All Mo−phosphide catalysts were more active than a molybdenum sulfide sample with the same Mo-loading. The Mo−phosphide catalysts with P/Mo ratios of 1 and 1.1 were found to be the most active among the catalysts studied. The activity drop observed for higher P-loadi...

Fractal Dimension of MoP−Al2O3 Catalysts and Their Activity in Hydrodesulfurization of Dibenzothiophene

Alumina-supported molybdenum phosphide catalysts were prepared by temperature-programmed reduction at 823 and 1123 K under a H2 flow. The catalysts were characterized by physicochemical and spectroscopy techniques. Molybdenum and phosphorous concentration, as well as reduction temperature, emerged as two parameters which influence directly on the morphological and structural aspects of MoP particles at the alumina surface. 95Mo NMR evidences the formation of metallic molybdenum and molybdenum phosphide where molybdenum has a metallic character. The fractal dimension of the catalyst was correlated linearly with the performance in the catalysis of hydrodesulfurization of dibenzothiophene.

Selective Hydrogenation of Acetonitrile over Molybdenum Phosphide Catalysts

Abstract A series of molybdenum phosphide catalysts were prepared from initial Mo/P molar ratios ranging from 0.6 to 2.6. The catalytic activity of the catalysts for the selective hydrogenation of acetonitrile was studied. The catalysts with initial Mo/P ratios > 1.0 have high selectivity for ethylamine (80%–90%), and for the catalysts with Mo/P ratios

Hydrodesulfurization of dibenzothiophene over alumina-supported nickel molybdenum phosphide catalysts

The activity of nickel molybdenum phosphide catalysts was studied for the hydrodesulfurization of dibenzothiophene at 573 K and total pressure of 2.0 MPa. The Al 2O 3-supported NiMo phosphide catalysts were prepared by successive and simultaneous methods. The effect of the reduction temperature on the catalyst activity was also studied. The simultaneous preparation was determined to be the best method for the preparation of the active supported catalyst for dibenzothiophene HDS. The 623 K-reduced catalyst had the highest HDS rate of the catalysts. Nickel migrated from the inside to the surface during the reaction and promoted the HDS activity. The active species in the dibenzothiophene HDS and the oxidation states of Mo, Ni and P in the catalyst before and after reaction and of S after the reaction were studied on the basis of an XPS analysis.

Synthesis, Characterization, and Hydrodesulfurization Properties of Silica-Supported Molybdenum Phosphide Catalysts

Silica-supported molybdenum phosphide (MoP/SiO2) catalysts have been prepared and characterized by X-ray diffraction (XRD), pulsed chemisorption (CO and O2), scanning and transmission electron microscopy (SEM and TEM, respectively), and X-ray photoelectron spectroscopy (XPS). XRD and TEM analysis of MoP/SiO2 catalysts confirmed the presence of MoP crystallites dispersed on the surface of the silica support, while SEM energy dispersive X-ray microanalysis indicated the bulk composition of the supported MoP particles to be 12.7 atom% Mo and 14.1 atom% P. XPS analysis of a passivated 25 wt% MoP/SiO2 catalyst indicated the presence of two kinds of Mo species as well as phosphide and phosphate species at the catalyst surface. Thiophene hydrodesulfurization (HDS) activities were measured for 15 and 25 wt% MoP/SiO2 catalysts, and for a sulfided Mo/SiO2 catalyst with a Mo loading similar to that of the lower loading MoP catalyst. The 15 wt% MoP/SiO2 catalyst, when pretreated only by degassing in flowing He, was nearly four times more active than the sulfided Mo/SiO2 catalyst after 150 h on-stream. Following an initial decline in HDS activity during the first 3 h of measurement, the MoP/SiO2 catalyst displayed an unusual trend of HDS activity that increased monotonically as a function of time on-stream.

XAFS Characterization of Highly Active Alumina-Supported Molybdenum Phosphide Catalysts (MoP/Al2O3) for Hydrotreating

Alumina-supported molybdenum phosphide (MoP/Al2O3) catalysts were prepared by temperature-programmed reduction of supported phosphate precursors in H2 at 0.083 K s-1 to 1123 K. The catalysts had excellent activity in the simultaneous hydrodenitrogenation (HDN) of quinoline and hydrodesulfurization (HDS) of dibenzothiophene at realistic conditions [P = 3.1 MPa (450 psig) and T = 643 K (370 °C)]. The catalysts surpassed the performance of a sulfided commercial Ni−Mo−S/Al2O3 catalyst in both HDN and HDS. X-ray absorption fine structure (XAFS) analysis of the supported samples indicated the presence of dispersed species retaining metallic bonding with a characteristic Mo−P distance of 0.243 nm but showing considerable attenuation in Mo−Mo linkages.

Formation, Structure, and HDN Activity of Unsupported Molybdenum Phosphide

A molybdenum phosphide catalyst was prepared from an aqueous solution of (NH4)6Mo7O24·4H2O and (NH4)2HPO4 by precipitation, calcination, and subsequent reduction in H2 at 923 K. Raman spectroscopic measurements revealed that the aqueous solution contained MoO42−, HPO42−, and P2Mo5O6−23 anions. Powder XRD measurements showed that pure molybdenum phosphide had formed after precipitation and reduction with H2. MoP crystallizes in the tungsten carbide structure in which each Mo atom is trigonal-prismatically coordinated by six P atoms. The molybdenum phosphide was tested for catalytic activity in the HDN reaction of o-propylaniline at 643 K and 3.0 MPa. The intrinsic HDN activity of the surface Mo atoms of MoP was about 6 times higher than that of Mo edge atoms in γ-Al2O3-supported MoS2. Their selectivity is comparable to that of an Ni-promoted MoS2 catalyst.