Analysis of the role of citric acid in the preparation of highly active HDS catalysts

Hydrodesulfurization, Hydrodenitrogenation and Hydrodearomatization over CoMo/SAPO-11-Al₂O₃ Catalysts

“…High dispersion of Mo also led to smaller length and higher stacking number of CoMoS active slabs. These findings agree well with previous reports of sulfided CoMo/Al2O3 catalyst 16) .…”

Improvement of HDS catalysts through the modification of the oxidic precursor with 1,5-pentanediol: Gas phase sulfidation and thiophene conversion

“…Recently Costa et al showed, mainly by Raman spectroscopy, that addition of triethyleneglycol (TEG) on dried CoMo and CoMoP catalysts leads to a change in the dispersion of the supported entities even if no bulk oxide (MoO 3 , CoMoO 4 , Co 3 O 4 ) was evidenced on the starting oxidic precursor [9]. They proposed that the TEG-based aqueous solution acts as a solvent via a redissolution/redispersion phenomenon inducing, for CoMo oxidic precursors, the transformation of non-well-defined oxomolybdate species into AlMo 6 After sulfidation, we can see that the modification of CoMoRef by C 5 diol provokes an enhancement of the molybdenum and cobalt sulfidation degree. For Mo, while we cannot detect any modification of the nature of the supported species we can imagine that this higher sulfidation degree could be due to a decrease in the Moealumina interaction induced by the impregnation of the C 5 diol solution.…”

“…Among them the use of Keggin or Anderson based heteropolyanions was proposed several years ago to prepare impregnating solutions instead of the classical ammonium heptamolybdate precursor [2,3]. Improvements have also been obtained through the addition of organic agents to the impregnating solution prepared with [4,5] or without [6] heteropolyanions. More recently the modification of dried or calcined oxidic precursors by organic molecules was shown to improve HDS catalytic performances [7e10].…”

“…In our laboratory TGA (thioglycolic acid) [7,8], also described as a sulfiding agent [15], was used to impregnate a commercial CoMo/Al 2 O 3 oxidic precursor. Recently due to its low cost and availability, citric acid has attracted much attention for the preparation of fresh catalysts [4,6,11]. Through the formation of Mo and/or Co complexes with the chelating agents, the improved HDS catalytic activities have been ascribed to (i) a decrease of the interaction between metals and the support [16e21] and/or to a lower formation of cobalt aluminate [2], (ii) an improvement of the Mo and/or Co dispersion [2,12,13,22e26], and (iii) the modification of the sulfidation of Co and Mo atoms (delay of Co sulfidation) [7,8,27e35].…”

Influence of the support on the catalytic performance of Mo, CoMo, and NiMo catalysts supported on Al2O3 and TiO2 during the HDS of thiophene, dibenzothiophene, or 4,6-dimethyldibenzothiophene

“…The first two peaks, 2190 and 2158 cm −1 , correspond to CO interacting with Al 3+ and OH's in the alumina support respectively [46,47]. CO adsorbed on Mo-S sites in the Mo-and S-edge, respectively [48][49][50][51][52][53], showing that the supported MoS 2 crystallites expose both types of edges after the sulfidation procedure [54,55]. It is evident, however, that the main contribution comes from Mo sites on the Mo-edges.…”