Thiophene Hydrodesulfurization Activity Research Articles

Support effect in the hydrodesulfurization of thiophene over rhodium sulfide

The effect of support on thiophene hydrodesulfurization activity over rhodium sulfide was studied. The loading was 5 wt% and the supports were (surface areas SBET in m2 g−1 in parenthesis): C (1100), Nb2O5 (99), ZrO2 (108), TiO2 (140), SiO2 (289), MgO (300) and 11 Al2O3 (77–279). The activity at 400 °C decreased in the order (relative activity in parenthesis): C (4.44), Al2O3 (0.98–0.32), Nb2O5 (0.54), ZrO2 (0.50), TiO2 (0.48), SiO2 (0.26), MgO (0.19), commercial CoMo/Al2O3 (1.00). The activity did not correlate with SBET, point of zero charge PZC of the support and the ratio S/Rh in the presulfided catalysts. The broad range of activities of Rh/Al2O3 illustrate that secondary factors such as SBET, texture, PZC, impurities and additives might be as important as the principal type of the support.

Synthesis, Characterization, and Thiophene Hydrodesulfurization Activity of Novel Macroporous and Mesomacroporous Carbon

Two different types of macroporous and mesomacroporous carbons have been synthesized using the templating method with polystyrene (PS) and SBA-15/PS (1:4) as templates. These synthesized carbon materials were exact replicas of the templates and showed a small window in the large pores of macroporous carbon in addition to mesophase in mesomacroporous carbon. Materials were characterized using X-ray diffraction (XRD), nitrogen adsorption-desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), Fourier transform infrared (FT-IR), and CO chemisorption. Mo, Co, and CoMo catalysts were prepared by supporting the aforementioned metals on optimized macroporous and mesomacroporous carbon, while commercial activated carbon (Darco G-60) and alumina (γ-Al2O3) supported catalysts were used for comparison purposes. Thiophene hydrodesulfurization of these catalysts showed that mesomacroporous carbon supported catalysts had superior activity and selectivity compared to the others, which might be due to its better metal dispersion and bimodal porosity which made transport easier and minimized channel blocking.

Effect of High Pressure Sulfidation on the Structure of Sulfide Sites of Hydrotreatment Catalysts

The effect of high-pressure sulfidation on (Co)Mo/Al2O3 catalysts was studied by means of IR spectroscopy of adsorbed CO and thiophene hydrodesulfurization (HDS). A new IR cell, called CellEx, was designed in order to characterize catalysts sulfided in situ under H2S/H2 flow with pressure varying from 0.1 up to 4.0 MPa. On Mo/Al2O3, high sulfidation pressure changes neither the HDS rate nor the MoS2 site concentration. Conversely on CoMo catalyst, sulfidation under high pressure leads to a marked increase of the thiophene HDS activity and of the Co-promoted site concentration as well as to some changes in the local structure of CoMoS sites. Study of CoMo catalyst, in the new IR cell, CellEX that allows in situ sulfidation under high-pressure, shows that sulfidation pressure increases HDS activity in parallel to the CoMoS concentration.

The influence of reducing and sulfiding conditions on the properties of unsupported MoS 2-based catalysts

Unsupported MoS 2 catalysts were obtained from the decomposition of ammonium tetrathiomolybdate (ATM) at variable temperatures (400–700 °C) and under different gas compositions, from pure H 2S to pure H 2. The catalysts were further studied in the non-promoted state or promoted by Ni and Co. Catalytic activity and selectivity were studied in the model reaction of thiophene hydrodesulfurization (HDS). Surface areas, crystalline phase and particle size distributions were determined by Brunauer–Emmet–Teller (BET), X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. A comparison of average values calculated from these techniques has enabled the understanding of the morphology of the solids. The catalysts were characterized before and after catalytic tests by X-ray photoelectron spectroscopy (XPS), laser Raman spectroscopy (LRS) and temperature-programmed reduction (TPR). Comparison of catalytic activity trends with the results of the characterizations show that over-stoichiometric sulfur, present in the fresh catalysts in the form of edge-located S 2 2 - species, plays a key role for the activity of unsupported MoS 2 and for its ability to be promoted. Direct hydrogenation (HYD) of thiophene to butane occurs presumably with the participation of –SH groups, produced from the opening of S–S bridges by hydrogen. Whatever the gas atmosphere, any treatment leading to the removal of over-stoichiometric sulfur leads to a decrease in HYD selectivity. Thus, very similar catalytic properties were observed for MoS 2 annealed at 700 °C in pure H 2, H 2S or N 2 gases. Ni and Co introduced by means of reflux with acetylacetonates, gave identical promotion trends for all the MoS 2 samples. The solids treated in pure H 2S could not take up promoter atoms at the edges, whereas for the H 2-reduced samples high promotion levels were achieved. The degree of stacking does not seem to have a significant impact on the thiophene HDS activity and selectivity of the unsupported MoS 2 catalysts.

Sulfidation of an aluminum-nickel-molybdenum catalyst and its activity in thiophene hydrodesulfurization

We consider the interaction of H2S with the molybdenum component of the catalyst using an Mo7O24H12 cluster as an example. At 200–300°C, SH groups substitute for OH groups of the molybdenum component. Intense reduction of the molybdenum component starts at 300°C. The reaction of hydrogen with the molybdenum component at 300°C generates Mo-H hydride groups, Mo5+ ions, and anionic vacancies; these vacancies are filled in by sulfur anions produced by the dissociation of hydrosulfuric acid. An NiMoO4 crystal phase is reduced and completely sulfided at 300°C. Mo7O24H12 clusters are sulfided only partially; complete substitution by sulfur does not occur in them even at 600–650°C. We consider the thiophene hydrodesulfurization scheme on molybdenum oxysulfide in the presence of nickel, as well as the scheme of this reaction on MoS2 in the absence of nickel. We conclude that hydrodesulfurization and hydriding occur at the same sites. Catalytically active surface sites in Mo7OxSy + Ni, MoS2 + Ni, and MoS2 structures are alike. A common feature of these structures is the existence of Mo-H− and MoSH− basic sites. The difference between them lies in the nature of proton-donor sites: in MoS2, proton donors are Mo-S-H+ groups, whereas in nickel-containing structures, nickel crystallites reacting with hydrogen are generators of protons and hydride ions.

Effect of the activation process on thiophene hydrodesulfurization activity of activated carbon-supported bimetallic carbides

The effect of passivation and presulfidation after carbiding of activated carbon-supported Fe–Mo, Co–Mo and Ni–Mo catalysts on their thiophene HDS activity was evaluated. Catalytic precursors were prepared by co-impregnation of the support with solutions of ammonium heptamolybdate and the promotor nitrates or sulfates. Carbiding was achieved by means of the carbothermal method, employing pure H 2 as reductant and the support as the carbon source. Carbided samples were submitted to one out of three types of procedures before HDS tests: (a) passivation at room temperature followed by presulfiding; (b) presulfiding (no passivation); and (c) neither passivation nor sulfiding before HDS. Samples of passivated catalysts prepared from the sulfates of Fe, Co or Ni contained variable amounts of sulfur, as shown by XPS and elemental analysis, while XRD showed only metals and mixed Fe 3Mo 3C or η-M 6Mo 6C 2 (M Co, or Ni) phases. The nitrate-derived catalysts only presented β-Mo 2C and metals (XRD). Sulfur containing catalysts showed high initial activities although deactivate strongly during the first 40 min on the reaction stream, while the unsulfided nitrate-derived samples showed a more stable behavior and lower activities during the 2–3 h of testing. In general, samples submitted to passivation followed by presulfiding showed the higher steady state activities and those neither passivated nor sulfided were the less active. The results show the benefits of a passivating treatment on these carbon-supported catalysts, and point out to the importance of sulfided surface phases in HDS on carbides of transition metal catalysts.

Study on hydrodesulfurization of thiophene over Mo/Al 2O 3 catalyst presulfided by thiosulfate ammonium

Ammonium thiosulfate as a novel sulfiding agent was used for presulfidation of hydrodesulfurization (HDS) catalysts. The presulfided Mo/Al 2O 3 catalysts with different molar ratios of S/Mo were prepared by impregnating Mo/Al 2O 3 catalysts with an aqueous solution of ammonium thiosulfate, followed by drying. Their characteristics of crystal phases, activation, and surface compositions were examined by X-ray diffraction, thermogravimetric analysis, and X-ray photoelectron spectroscopy. The S 2− and S 6+ in ammonium thiosulfate play different roles during the activation of presulfided catalysts. The S 2− sulfides Mo and S 6+ reacts with Al 2O 3 support, decreasing the interaction of support with the active metal. The collaboration between S 2− and S 6+ ions improves the sulfidation of MoO 3. The best HDS performance was observed for the presulfided catalyst with S/Mo = 3. Its thiophene HDS activity is 17% higher than that of Mo/Al 2O 3 catalyst sulfided with H 2S.

Effect of Thermal Treatment under Nitrogen on the Ammonium Thiosulfate-Presulfidized Mo/Al2O3 Catalyst

A series of Mo/Al2O3 catalysts were presulfidized with (NH4)2S2O3 aqueous solution, dried at ambient temperature, and thermally treated in N2 flow. The catalysts were characterized by X-ray diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, thermogravimetry-mass spectrometry, and sulfur analysis. Thermal pretreatment in N2 had a significant effect on the catalytic performance of the (NH4)2S2O3-presulfidized Mo/Al2O3 for the hydrodesulfurization (HDS) of thiophene. The sample pretreated at 80 °C in N2 flow and activated at 200 °C in H2 gave the highest thiophene conversion. This is due to that the modification of the Al2O3 support by sulfate ions weakened the interaction of Mo species with the support, which increased its sulfidization to form a highly active multilayer Type II MoS2 structure. In contrast, N2 thermal treatment obove 200 °C led to the decomposition of (NH4)2S2O3 and decreased the sulfiding degree, which resulted in the formation of a less active single layer Type I MoS2 structure with a low activity for thiophene HDS.

High surface area MoO3/TiO2 hydrodesulfurization catalysts

MoO3/TiO2 catalysts were prepared by conventional impregnation of TiO2 supports with surface areas of 140, 230 and 407 m2g−1. The loading of MoO3 was 2–32wt.%. According to the point of zero charge, the supports were saturated with a molybdena monolayer at approximately 12, 24 and 14 wt.%, respectively. Activity in hydrodesulfurization of thiophene increased up to the loading of ∼20 wt.%, and then decreased for all the three supports.

Highly active Mo/Al2O3 hydrodesulfurization catalyst presulfided with ammonium thiosulfate

Abstract Ammonium thiosulfate ((NH 4 ) 2 S 2 O 3 ) was used as an ex situ sulfiding agent to pretreat Mo/Al 2 O 3 catalyst through impregnation. After H 2 activation, Mo/Al 2 O 3 presulfided with (NH 4 ) 2 S 2 O 3 exhibits much higher catalytic activity in thiophene hydrodesulfurization (HDS) than Mo/Al 2 O 3 in situ sulfided by dimethyl disulfide. Through (NH 4 ) 2 S 2 O 3 presulfidation, Al 2 O 3 support is modified by sulfate groups, leading to a decrease of interaction between Mo and support; this promotes the formation of multi-layer type II MoS 2 that contributes to the high HDS activity of the ex situ presulfided Mo/Al 2 O 3 catalyst.

Synthesis, characterization and hydrotreating performance of supported tungsten phosphide catalysts

Supported tungsten phosphide catalysts were prepared by temperature-programmed reduction of their precursors (supported phospho-tungstate catalysts) in H2 and characterized by X-ray diffraction (XRD), BET, temperature-programmed desorption of ammonia (NH3-TPD) and X-ray photoelectron spectroscopy (XPS). The reduction-phosphiding processes of the precursors were investigated by thermogravimetry and differential thermal analysis (TG-DTA) and the suitable phosphiding temperatures were defined. The hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) activities of the catalysts were tested by using thiophene, pyridine, dibenzothiophene, carbazole and diesel oil as the feedstock. The TiO2, γ-Al2O3 supports and the Ni, Co promoters could remarkably increase and stabilize active W species on the catalyst surface. A suitable amount of Ni (3%–5%), Co (5%–7%) and V (1%–3%) could increase dispersivity of the W species and the BET surface area of the WP/γ-Al2O3 catalyst. The WP/γ-Al2O3 catalyst possesses much higher thiophene HDS and carbazole HDN activities and the WP/TiO2 catalyst has much higher dibenzothiophene (DBT) HDS and pyridine HDN activities. The Ni, Co and V can obviously promote the HDS activity and inhibit the HDN activity of the WP/γ-Al2O3 catalyst. The G-Ni5 catalyst possesses a much higher diesel oil HDS activity than the sulphided industrial NiW/γ-Al2O3 catalyst. In general, a support or promoter in the WP/γ-Al2O3 catalyst which can increase the amount and dispersivity of the active W species can promote its HDS and HDN activities.

Hydrodesulfurization of thiophene on carbon nanofiber supported Co/Ni/Mo catalysts

Co, Mo, NiMo and CoMo catalysts supported on alumina, fishbone and platelet carbon nanofibers (CNFs) have been prepared. The dispersion of the oxide phases was qualitatively studied and compared using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The reducibility of the catalysts was studied by temperature programmed reduction (TPR). Hydrodesulfurization (HDS) of thiophene was used as a model reaction to compare the activity of different catalysts. The activity tests showed that the alumina supported catalysts exhibited higher activity compared to the corresponding CNF supported catalysts, and the NiMo catalysts were more active than the corresponding CoMo catalysts. The thiophene HDS activity was correlated with the dispersion of the molybdenum species and the reducibility of different catalysts. Interestingly, the CNF supported Co catalysts have higher thiophene HDS activity than the CNF supported Co(Ni)Mo catalysts.

Effect of the type of precursor and the synthesis method on thiophene hydrodesulfurization activity of activated carbon supported Fe-Mo, Co-Mo and Ni-Mo carbides

In this work it is studied the effect of the type of precursor (sulfate vs. nitrate of promotor) and the synthesis method (conventional vs. carbothermal carbiding) on the thiophene hydrodesulfurization (HDS) activity of activated carbon supported Fe-Mo, Co-Mo and Ni-Mo carbides. Catalytic precursors were prepared by co-impregnation of the support with solutions of ammonium heptamolybdate and the promotor salt. Conventional carbiding consists of a temperature-programmed treatment under a CH 4/H 2 (1:4) atmosphere, while the carbothermal method employs pure H 2. The passivated carbided solids were characterized by XRD and XPS. The presence of metals and Fe 3Mo 3C or M 6Mo 6C 2 phases (M = Co or Ni) in samples from sulfate precursors and of β-Mo 2C and metals in those from nitrate precursors was verified by XRD, whereas XPS showed the presence at the surface of Mo δ+ (0 ≤ δ ≤ 2), Mo 4+, Mo 6+, Fe 3+, Co 2+, Ni 0 and Ni 2+ species. The bimetallic carbides obtained from sulfate precursors retained sulfur on the surface, as shown by signals in the S 2p region, at 169 and 162 eV, assigned to S 2− and SO 4 2−, respectively. Prior to the catalytic reaction, the passivated carburized forms of carbon supported catalysts were presulfided in situ. The catalytic activity of carbides was strongly influenced by the type of precursor and slightly by the synthesis method. The activity of carbides obtained by the carbothermal method and with sulfate precursors was greater than that of the solids obtained by the conventional method and with nitrate precursors. The carbides obtained from nitrates showed increased catalytic activity when presulfided, suggesting that the carbides with sulfided surfaces or mixed carbo-sulfide species could be the active phase in HDS on carbide catalysts. The catalysts derived from sulfates showed higher activity than those obtained from nitrates, even without presulfiding, suggesting that sulfide from the precursor sulfate results in more active species than those obtained after presulfiding.

Support effect with rhenium sulfide catalysts

The well known support effect observed for molybdenum sulfide has been studied with rhenium sulfide, which was reported to be a very active hydrotreating catalyst. Solids containing from 0.8 to 4 rhenium atoms per nm 2 have been prepared on titania, zirconia and γ-alumina supports and sulfided using N 2-H 2S (15%) or H 2-H 2S (15%) mixtures. The catalytic activity in thiophene hydrodesulfurization (HDS) has been evaluated and additional information about the structure over the different supports has been obtained by XPS and HRTEM.

Effect of the electronic properties of Mo sulfide phase on the hydrotreating activity of catalysts supported on Al2O3, Nb2O5 and Nb2O5/Al2O3

Activity in thiophene hydrodesulfurization (HDS) and in the three routes of 2,6-dimethylaniline (DMA) decomposition was examined on Mo sulfide catalysts supported on Al 2 O 3 , Nb 2 O 5 and Nb 2 O 5 -Al 2 O 3 . Catalysts activity is enhanced when Mo phase is deposited on niobium-containing support. For HDS and for the hydrogenation route of DMA decomposition, the niobium-containing support strongly contributes to the catalyst activity whereas the activity of the Mo phase per Mo atom decreases with the increase of niobium amount in the support. By contrast, as for the DMA route, which leads to xylene formation (XYL), the activity of the Mo sulfide phase per Mo atom is strongly enhanced. The electronic properties of the MoS 2 phase were studied by means of IR spectroscopy of CO adsorption. Comparison of v(CO/Mo) wavenumbers reveals an upward shift when Mo sulfide phase is deposited on Nb-containing support. The modification of the electronic properties of the sulfide phase is related to an interaction Mo-Nb either through the formation of a mixed Mo-Nb sulfide phase, or through the interaction MoS 2 slabs - support whose strength depends on the support acidity. Hence, the beneficial effect for xylene formation route is attributed to a decrease of the electron density of the Mo sulfide phase that should strengthen the DMA adsorption on the sulfide phase.

Characterization and hydrodesulfurization activity of CoMo catalysts supported on boron-doped sol–gel alumina

Abstract A series of hydrodesulfurization (HDS) catalysts was prepared by impregnation of Co and Mo on sol–gel B–Al2O3 supports with B/Al ratios of 0, 0.02, 0.04, 0.08, 0.20, 0.32, 0.49, and 0.61. The thiophene HDS and dibenzothiophene (DBT) HDS activities were both maximal for the catalyst with B/Al = 0.04, with respective values 70 and 42% higher than those for an industrial reference catalyst. These maxima in HDS activity correlated with the previously reported presence of isolated BO4 surface species. These BO4 species were responsible for a local maximum in the acidity of the B–Al2O3 supports when B/Al = 0.04. In contrast, the formation of mixed oxides (A9B2 and A2B) or B2O3 that also resulted in enhanced acidity of the B–Al2O3 supports had a detrimental effect on the HDS activity. The 4,6-dimethyldibenzothiophene (4,6-DMDBT) HDS activity over the CoMo/B–Al2O3 catalysts decreased when the B/Al ratio was increased. This was attributed to the strong direct desulfurization character of the CoMo catalysts supported on the B–Al2O3 supports, because high hydrogenation ability toward the C C double bonds is essential prior to sulfur removal from 4,6-DMDBT. The excellent performance in the thiophene and DBT HDS of the CoMo/B–Al2O3 catalysts is particularly useful for ultra-deep HDS of light fractions.

Thiophene hydrodesulfurization activity of alumina supported heteropoly compounds: nickel effect

Hydrotreating nickel tungsten catalysts have been prepared by impregnation of g-alumina with solutions of H3PW12O40 acid and its Ni salt. It is shown that the initial heteropolyanion, its lacunar analog, nickel substituted heteropolyanion and other new formed phases are present on the surface. The thiophene conversion is related to the presence of mixed NiWS phase and to the close cooperation between WS2 and NiSx phases.

Highly active ReS2/γ-Al2O3 catalysts: Effect of calcination and activation over thiophene hydrodesulfurization

The effect of activation conditions on alumina-supported rhenium sulfide catalysts on their activity for thiophene hydrodesulfurization has been studied. The results showed that activation using H2S/N2 leads to ReS2/γ-Al2O3 catalysts with a higher activity than an industrial NiMo catalyst. Characterization by temperature-programmed reduction and X-ray photoelectron spectroscopy revealed that the higher activity of the catalysts activated by H2S/N2 is associated with a higher sulfur content and probably related to different ReSx phases.

Effect of aluminum modification on catalytic performance of Pt supported on MCM-41 for thiophene hydrodesulfurization

The catalytic activities and properties of platinum supported on siliceous MCM-41 and Al-modified MCM-41, such as Al-incorporated MCM-41 (AlMCM-41) and alumina-modified MCM-41 (Al 2O 3-MCM-41), for the hydrodesulfurization (HDS) of thiophene were investigated. Al 2O 3-MCM-41 was prepared by an impregnation method using aluminum nitrate (Al(NO 3) 3·9H 2O) aqueous solution. Pt/Al 2O 3-MCM-41 catalyst showed high and stable activity for HDS of thiophene and this activity was remarkably higher than that of a commercial CoMo/Al 2O 3 HDS catalyst. The catalysts were characterized by XRD, hydrogen adsorption, ammonia-TPD, 2-propanol dehydration, cumene cracking and FT-IR. Dispersion of platinum on Al 2O 3-MCM-41 was remarkably higher than on MCM-41 or on AlMCM-41. It was revealed that the acidity of Al 2O 3-MCM-41 was higher than that of MCM-41 or of AlMCM-41. Furthermore, it was observed that there exist Brønsted acid sites on Al-modified MCM-41. FT-IR spectra of thiophene adsorbed on Al-modified MCM-41 support indicates that thiophene molecules interact with Brønsted acid sites on Al-modified MCM-41. It was found that the HDS activity of Pt/quartz mixed mechanically with Al-modified MCM-41 catalyst was higher than that calculated. This suggests that there exists spillover hydrogen on supported Pt catalysts in the HDS of thiophene. Results revealed that the high activity of Pt/Al 2O 3-MCM-41 catalyst for HDS reaction is due to good harmony of high dispersion of Pt particles and Brønsted acidity of the support.

Effect of lanthanum addition on the thiophene hydrodesulfurization activity over Al-MCM-41 supported molybdenum catalysts

A series of Al-MCM-41 modified with 1–7% lanthanum were used as supports to prepare the Mo/La–Al-MCM-41 catalysts containing 10 wt.% molybdenum. The supports and catalysts were characterized with XRD, BET, XPS, TPD, TEM and SEM, and their catalytic activities were tested for thiophene hydrodesulfurization. The La addition did not cause any significant collapse of the structure and morphology of Al-MCM-41 samples, and increased the acidity of Al-MCM-41 samples. The Mo/La–Al-MCM-41 catalysts showed higher thiophene HDS activity than non-modified catalysts. The La-modified catalysts showed an enhanced butene selectivity but a decreased tetrahydrothiophene selectivity, indicating that the La–Al-MCM-41 supports contained a larger amount of acid sites.