Nature of active sites in Ni2P hydrotreating catalysts as probed by iron substitution

Abstract

A series of NiFeP/SiO 2 catalysts with different Ni:Fe molar ratios (1:0, 3:1, 1:1, 1:3, 0:1) was investigated for the hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene.The Fe component is a good probe for active sites because Ni 2 P and Fe 2 P adopt the same hexagonal crystal structure, yet Fe 2 P is completely inactive for HDS. X-ray diffraction analysis and FTIR spectroscopy of adsorbed CO indicated the formation homologous alloys. At 3.1 MPa and 613 K (340 o C) the activity of the alloys was similar to that of Ni 2 P, which was very high. There was also unprecedented selectivity towards direct desulfurization (DDS). A reconstruction of the NiFe phase occurred to expose more Ni sites, likely driven by the formation of surface Ni-S bonds as observed by EXAFS. The analysis showed that Ni(2) pyramidal sites responsible for hydrogenation were largely replaced by Fe. This left behind Ni(1) tetrahedral sites which favor DDS and explains the reactivity results.

Development of nickel based catalysts for the transformation of natural triglycerides and related compounds into green diesel: a critical review

“…Another alternative is the use of carbides, nitrides and phosphides of the aforementioned metals instead of the sulfides. It is well known that the supported carbides, nitrides and phosphides of the early transition metals, exhibiting an activity similar to noble metals, are quite promising catalysts for the hydrotreatment of petroleum fractions and may substitute the conventional NiMo, CoMo and NiW sulfided catalysts [200][201][202][203][204]. Their high intrinsic activity is due to the introduction of nitrogen, carbon or phosphorus into the lattice of the metal resulting to an increase in the delectron density and of the lattice parameter a 0 as well [205].…”

Hydrodesulfurization of dibenzothiophene, 4,6-dimethyldibenzothiophene, and their hydrogenated intermediates over bulk tungsten phosphide

“…The most active (Ni 2 P) and the second most active catalyst (WP) possess different structures. The crystal structure of Ni 2 P is the same as that of Fe 2 P, and the hexagonal unit cell contains one Ni atom in tetrahedral coordination and another Ni atom in square-pyramidal coordination [7]. Tungsten phosphide, on the other hand, adopts the orthorhombic manganese phosphide (MnP) structure, which is closely related to the hexagonal NiAs structure, but in which lattice distortions accompany the formation of chains of phosphorus atoms [8].…”

“…They are covalent compounds, in which the electron density is shared between the metal and phosphorus atoms [4]. The order of overall activity of the transition-metal phosphides in the simultaneous HDS of dibenzothiophene (DBT) and hydrodenitrogenation (HDN) of quinoline is Fe 2 P < CoP < MoP < WP < Ni 2 P, based on comparison with an equal number of sites as determined by CO chemisorption [5][6][7]. The most active (Ni 2 P) and the second most active catalyst (WP) possess different structures.…”

Solvothermal synthesis of nickel‐tungsten sulfides for 2‐propanol dehydration

“…In the last years, it has been of great importance to obtain a cleaner environment and a more suitable production of petroleum derivatives; this is the main reason of an indefinite number of studies looking for selective catalysts for hydrotreating processes (Zhao et al, 2015). In the last decade, the use of Ni-W catalysts has grown in hydrotreating processes, especially when it is desired to hydrogenate aromatics compounds.…”