Tuning of structural and optical properties with enhanced catalytic activity in chemically synthesized Co-doped MoS2 nanosheets

Molybdenum disulfide (MoS2) nanosheets, due to having a highly active nature, being low cost and having unique physical and chemical properties, have shown their efficacy in the catalytic reduction of nitroarenes. Doping of transition metal ions in molybdenum disulfide (MoS2) nanosheets is a well-known strategy to enhance their catalytic efficiency for the reduction of nitroarenes, however, finding the optimum dopant amount is still a subject of ongoing research. Herein, we have synthesized few-layered cobalt (Co) doped MoS2 nanosheets with different cobalt content (2%, 4%, 6% and 8%) through the solvothermal approach, taking sodium molybdate dihydrate (Na2MoO4·2H2O), thiourea (CH4N2S) and cobalt acetate tetrahydrate [Co(CH3COO)2·4H2O] as precursors and their catalytic performance has been affirmed by monitoring the reduction of p-nitrophenol by NaBH4 in real time using UV-visible absorption spectroscopy. The 6% Co doped MoS2 nanosheets have exhibited superior catalytic activity with a pseudo-first order rate constant of 3.03 × 10-3 s-1 attributed to the abundant defects in the active edge sites having a dominant metallic 1T phase with Co ion activated defective basal planes, sulphur (S) edges, synergistic structural and electronic modulation between MoS2 and Co ions and enhanced electron transfer assisted through redox cycling in the active sites. An attempt has also been made to study the manipulation of structural and optical properties with cobalt doping in MoS2 nanosheets to establish a correlation between the catalytic efficiency and dopant content. This study demonstrates that proper tuning of Co doping in MoS2 nanosheets paves the way in searching for a potential alternative of a noble metal catalyst for the catalytic reduction of nitroarenes.

Transition Metal Phosphides for the Catalytic Hydrodeoxygenation of Waste Oils into Green Diesel

Recently, catalysts based on transition metal phosphides (TMPs) have attracted increasing interest for their use in hydrodeoxygenation (HDO) processes destined to synthesize biofuels (green or renewable diesel) from waste vegetable oils and fats (known as hydrotreated vegetable oils (HVO)), or from bio-oils. This fossil-free diesel product is produced completely from renewable raw materials with exceptional quality. These efficient HDO catalysts present electronic properties similar to noble metals, are cost-efficient, and are more stable and resistant to the presence of water than other classical catalytic formulations used for hydrotreatment reactions based on transition metal sulfides, but they do not require the continuous supply of a sulfide source. TMPs develop a bifunctional character (metallic and acidic) and present tunable catalytic properties related to the metal type, phosphorous-metal ratio, support nature, texture properties, and so on. Here, the recent progress in TMP-based catalysts for HDO of waste oils is reviewed. First, the use of TMPs in catalysis is addressed; then, the general aspects of green diesel (from bio-oils or from waste vegetable oils and fats) production by HDO of nonedible oil compounds are presented; and, finally, we attempt to describe the main advances in the development of catalysts based on TMPs for HDO, with an emphasis on the influence of the nature of active phases and effects of phosphorous, promoters, and preparation methods on reactivity.

Preparation and Catalytic Performance of Metal-Rich Pd Phosphides for the Solvent-Free Selective Hydrogenation of Chloronitrobenzene

A facile synthesis method of palladium phosphide supported on the activated carbon was developed. The effects of Pd precursors for phosphatization, phosphatization temperature, and the ratio of hypophosphite/Pd on the generation of palladium phosphide were investigated, and a generation mechanism of the Pd3P crystal structure is proposed. The results demonstrate that only PdO, rather than Pd or PdCl2, can transform into Pd phosphide without damage to the activated carbon. The penetration of P into the Pd particle can dramatically improve the dispersion of Pd species particles on the activated carbon. The generation of Pd phosphide greatly depends on the phosphatization temperature and the ratio of hypophosphite/Pd. An intact Pd3P crystal structure was obtained when the ratio of hypophosphite/Pd reached 32 and the phosphatization temperature was above 400 °C. The Pd3P supported on the activated carbon exhibited superior catalytic performance in terms of the hydrogenation of halonitrobenzenes to haloanilines because it had few L acids and B acids sites and could not generate deficient-electron active hydrogen atoms as electrophiles.

Semimetallic MoP2: an active and stable hydrogen evolution electrocatalyst over the whole pH range

Developing efficient non-precious metal hydrogen evolution reaction (HER) electrocatalysts is a great challenge for sustainable hydrogen production from water. In this communication, for the first time, semimetallic MoP2 nanoparticle films on a metal Mo plate (MoP2 NPs/Mo) are fabricated through a facile two-step strategy. When used as a binder-free hydrogen evolution cathode, the as-prepared MoP2 NPs/Mo electrode exhibits superior HER catalytic activity at all pH values. At a current density of 10 mA cm(-2), the catalyst displays overpotentials of 143, 211 and 194 mV in 0.5 M H2SO4, 1.0 M phosphate buffer solution and 1.0 M KOH, respectively. Furthermore, it exhibits excellent stability over a wide pH range. Thus, this in situ route opens up a new avenue for the fabrication of highly efficient, cost-effective and binder-free non-precious catalysts for water splitting and other electrochemical devices.

Nickel and cobalt phosphides as effective catalysts for oxygen removal of dibenzofuran: role of contact time, hydrogen pressure and hydrogen/feed molar ratio

The catalytic activity of nickel and cobalt phosphides, with a metal loading of 5 wt.%, supported on silica was investigated in the hydrodeoxygenation reaction (HDO) of dibenzofuran (DBF) as a model oxygenated compound at different contact times, H₂ pressures and H₂/DBF molar ratios.

Thiophene Adsorption and Activation on MoP(001), γ-Mo2N(100), and Ni2P(001): Density Functional Theory Studies

The adsorption and dissociation of thiophene on the MoP(001), gamma-Mo(2)N(100), and Ni(2)P(001) surfaces have been computed by using the density functional theory method. It is found that thiophene adsorbs dissociatively on MoP(001), while nondissociatively on gamma-Mo(2)N(100) and Ni(2)P(001). On MoP(001), the dissociation of the C-S bonds is favored both thermodynamically and kinetically, while the break of the first C-S bond on gamma-Mo(2)N(100) has an energy barrier of 1.58 eV and is endothermic by 0.73 eV. On Ni(2)P(001) there are Ni(3)P(2)- and Ni(3)P-terminated surfaces. On the Ni(3)P(2)-terminated surface, the dissociation of the C-S bonds of adsorbed thiophene is endothermic, while it is exothermic on the Ni(3)P-terminated surface.