Promotion of Niobium Oxide Sulfidation by Copper and Its Effects on Hydrodesulfurization Catalysis

Abstract

Niobium sulfide (NbS2) has shown a promising performance in versatile applications, but its formation from Nb oxide is thermodynamically limited, which hinders its usage. We predicted, based on thermodynamic calculations, and experimentally verified that the addition of copper (Cu) to niobium promotes Nb oxide sulfidation at practical temperatures. A series of bimetallic bulk NbCu structures at varying Cu/Nb molar ratios were synthesized via a coprecipitation technique. X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (TPR) results revealed that copper facilitated sulfidation and reduction of niobium oxide. The synthesized NbCu catalysts were evaluated in hydrodesulfurization (HDS) of dibenzothiophene (DBT) at 325 °C and 3 MPa. Copper promotes sulfidation but does not change the turnover frequency of surface NbS2 and behaves as a spectator. The optimal Cu/Nb molar ratio was found to be 0.3, below which there is not enough Cu to ensure maximum sulfidation and above which copper segregates to the catalyst surface and blocks NbS2 active sites. The weight-based sulfur-removal activity of the optimal catalyst was doubled in the presence of copper. This study demonstrates that the bimetallic Earth-abundant NbCu catalyst could be a promising candidate for hydrotreating catalysis. Since Cu-promoted NbS2 was determined to be more active than molybdenum sulfide per mass and surface area, the copper addition may be recommended for thermodynamically limited niobium oxide sulfidation to promote NbS2 formation as a potential alternative to MoS2 for a variety of emerging applications with transition-metal sulfides. The study also demonstrates that the concept of promotion in catalysis can be extended to the assisted increase of the number of active sites, with no effect on their performance during catalysis.

Recent Insights in Transition Metal Sulfide Hydrodesulfurization Catalysts for the Production of Ultra Low Sulfur Diesel: A Short Review

“…Another method for achieving high surface areas and improve the dispersion is the use of organic templates. This section deals with the hydrodesulfurization activity of the catalysts synthesized using various organic templates such as polyethylene glycol [157][158][159][160], polivinylpyrrolidone (PVP) [161], pluronic 123 (P123) [162], tetrabutylammonium bromide [163], or biotemplates [164]. The use of templates could improve morphology, thermal stability, and the formation of active NiMoS/CoMoS phases [157].…”

“…As described in the previous sections, promoters increase the formation of the active phase. Indeed, the Cu promoted NbS 2 catalyst was more active than molybdenum sulfide per mass [162].…”

Layered Nano‐Mosaic of Niobium Disulfide Heterostructures by Direct Sulfidation of Niobium Carbide MXenes for Hydrogen Evolution

“…The Nb 2 O 5 reflections remain even when the treatment is extended to 60 min at 700 °C (Figure 1B), indicating that the oxide neither decomposes nor is further converted during the treatment with H 2 S. Once Nb 2 O 5 is formed, its sulfidation is thermodynamically unfavored at 700 °C, requiring higher temperatures than Nb 2 C to form NbS 2 . [ 46 ] This can explain the absent Nb 2 O 5 signal in the Nb 2 C‐H 2 S900‐60′ sample: the higher temperature efficiently removes surface functionalities. Besides, H 2 S decomposition is favored above 900 °C, leading to a more significant amount of H 2 that helps to reduce oxygenated groups.…”

A Tandem 0D/2D/2D NbS2 Quantum Dot/Nb2O5 Nanosheet/g‐C3N4 Flake System with Spatial Charge–Transfer Cascades for Boosting Photocatalytic Hydrogen Evolution

“…[ 12 ] The peaks in the O 1s region (Figure 3e) at 530.1 and 531.4 eV indicate the presence of the NbO bond and oxygen from the precursor of niobium oxalate, respectively. [ 12,29,30 ] The peaks in the S 2p region (Figure 3f) at 162.6 and 163.8 eV are attributed to S 2p 3/2 and S 2p 1/2 in NbS 2 , respectively. [ 29,31 ] The above XPS results strongly indicate the successful construction of tandem 0D/2D/2D NbS 2 quantum dot/Nb 2 O 5 nanosheet/g‐C 3 N 4 flake, which is beneficial to form plentiful spatial charge–transfer cascades to markedly improve the photocatalytic H 2 evolution activity.…”