Study of the Promotion Effect of Citric Acid on the Active NiMoS Phase in NiMo/Al₂O₃ Catalysts

Abstract

A series of NiMo/Al2O3 catalysts were prepared using an aqueous solution containing Ni and Mo salts and citric acid (CA). Hydrodesulfurization (HDS) of dibenzothiophene (DBT) and hydrogenation (HYD) of biphenyl showed that both HDS and HYD activities of NiMo/Al2O3 catalysts were enhanced with addition of CA. The promotion effect of CA can be attributed to a morphology control of the MoS2 phase and an increase of the NiMoS phase. Transmission electron microscopy analysis indicates that CA has a minor effect on MoS2 dispersion but increases its mean stacking degree, with 3-layer dominating. X-ray photoelectron spectroscopy analysis confirmed the increase of the NiMoS phase. A preferential complexation between Ni and CA was supported by the fact that the catalyst prepared by reacting Ni with CA before Mo in the impregnation solution had the best catalytic activity and CA has no promotion effect within the monometallic Mo/Al2O3 catalyst.

Fabrication of well-structured NiMo hydrodesulfurization catalysts using electropositive Mo-based nanoparticles

“…[25][26][27][28][29] Some researchers attribute the promoting effects of complexing agents to the morphology control of the MoS 2 phase. 17 Pimerzin et al concluded that polyethylene glycol probably hinders the aggregation of active species during the drying process and increases the number of active sites. 25 Li et al further suggests that the isolating effect of organic agents is possibly owed to carbon species derived from the pyrolysis of citric acid on the surface of alumina, which inhibits the agglomeration and increases the dispersity of active metal.…”

“…The electrical properties of the precursor species and the support surface actually play a crucial role in the formation and distribution of the active species. 16 The Mo precursors are generally polyoxomolybdate anions (POMs) such as Mo 7 O 24 6− , 17 P 2 Mo 5 O 231 6− , 18,19 Mo 4 (Hcitrate) 2 O 11 4− , 20 and [Mo 2 O 4 (C 2 O 4 ) 2 (H 2 O) 2 ] 2− . 21 The typical impregnation solutions are acidic conditions with pH 4–6, where POMs are electronegative, e.g.…”

The Influence of Metal–Support Interactions on the Performance of Ni-MoS2/Al2O3 Catalysts for Dibenzothiophene Hydrodesulfurization

“…The current focus of research on MSIs encompasses two key aspects: the adjustment of the support [17,[19][20][21][22][23] and the modification of the preparation method [15,[24][25][26][27]. Several studies have highlighted the direct influence of support characteristics on the strength of MSIs [28], consequently impacting catalyst performance.…”

Hydrotreatment of FCC Gasoline Catalyzed by CoMo Bifunctional Catalysts: The Effects of Acidity on Catalytic Performance

“…Currently, hydrodesulfurization (HDS) has still been widely regarded as an effective process to remove sulfur compounds from FCC gasoline in refineries. The core of the deep HDS process is highly efficient catalysts. , Normally, conventional HDS catalysts with Co- or Ni-promoted MoS 2 are mainly dispersed on γ-Al 2 O 3 , exhibiting good HDS activity but usually cause a great loss of research octane number (RON). ,− It is known that FCC gasoline contains 20–50 vol % olefins, which are one of the main RON contributors. The RON loss during the hydrotreating process of FCC gasoline is mainly owing to olefin hydrogenation (HYDO) into saturated hydrocarbons .…”

“…The core of the deep HDS process is highly efficient catalysts. 6,7 Normally, conventional HDS catalysts with Co-or Ni-promoted MoS 2 are mainly dispersed on γ-Al 2 O 3 , exhibiting good HDS activity but usually cause a great loss of research octane number (RON). 1,8−10 It is known that FCC gasoline contains 20−50 vol % olefins, which are one of the main RON contributors.…”