B. Pawelec

Retracted article: Towards near zero-sulfur liquid fuels: a perspective review

We, the named authors, hereby wholly retract this Catalysis Science & Technology article, due to significant similarity with previously published work. Signed: B. Pawelec, R. M. Navarro, J. M. Campos-Martin and J. L. G. Fierro, October 2012. Retraction endorsed by Jamie Humphrey, Editor, Catalysis Science & Technology.

SBA-15 Mesoporous Silica as Catalytic Support for Hydrodesulfurization Catalysts—Review

SBA-15 is an interesting mesoporous silica material having highly ordered nanopores and a large surface area, which is widely employed as catalyst supports, absorbents, drug delivery materials, etc. Since it has a lack of functionality, heteroatoms and organic functional groups have been incorporated by direct or post-synthesis methods in order to modify their functionality. The aim of this article is to review the state-of-the-art related to the use of SBA-15-based mesoporous systems as supports for hydrodesulfurization (HDS) catalysts.

Aromatics hydrogenation on silica-alumina supported palladium-nickel catalysts

Abstract Nickel- and palladium–nickel catalysts supported on silica–alumina have been studied in the simultaneous hydrogenation of naphthalene and toluene. These catalysts were characterised by means of X-ray diffraction, CO chemisorption, temperature-programmed reduction, NH 3 temperature-programmed desorption, diffuse reflectance spectroscopy, Fourier transform infrared spectroscopy of adsorbed CO and X-ray photoelectron spectroscopy techniques. All the catalysts studied showed higher initial intrinsic activity in the hydrogenation of toluene than of naphthalene. Regarding the hydrogenation of toluene, the 1Pd–8Ni/SA sample displayed the strongest resistance to deactivation by coke precursors as compared with the Ni-free 1Pd/SA catalyst. For the 1Pd–8Ni catalyst, the characterisation data pointed not only to a high degree of reducibility of nickel but also the greatest exposure of Pd species. Both findings appear to be related to the development of nickel hydrosilicate species at the support interface. Indeed, a better resistance towards deactivation was obtained by Pd incorporation and by increasing Ni-loading.

Dibenzothiophene hydrodesulfurization on silica-alumina-supported transition metal sulfide catalysts

Unpromoted and Pt, Pd, Ni and Ru-promoted molybdenum catalysts supported on amorphous silica-alumina (ASA) were characterized in the hydrodesulfurization of dibenzothiophene, and their activities were compared with a commercial PtASA catalyst. The catalytic activity was found to increase in the following order: commercial PtASA ⪢ PtMo ≈ NiMo ≈ RuMo > PdMo ≈ Mo ≈ ASA. Characterization of the catalysts by XPS, TPR, and FTIR spectroscopy of adsorbed NO and pyridine confirmed that incorporation of 16.1 wt.-% Mo, minimized to a large extent the metal-support interaction, and decreased the acidity of the catalysts; although for the Ni-catalyst, the formation of Ni aluminate (and silicate) was not prevented. The incorporation of promoters enhanced molybdenum surface exposure and decreased the reduction temperature of MoO3; and for the Ni-promoted catalyst, increased the amount of sulfidable Ni species. Pd was not very effective as a promoter due to its poor dispersion, and the presence of a low percentage of active sites in the PdMo catalyst. For binary samples, a correlation was found to exist between the dispersion of MoS2 phases, the number of active sites titrated by NO, and the HDS activity of the sulfided samples.

DEEP HYDRODESULFURIZATION OF DBT AND DIESEL FUEL ON SUPPORTED PT AND IR CATALYSTS

Abstract Deep hydrodesulfurization (HDS) of dibenzothiophene (DBT) and diesel fuel (0.08 wt.−% S) has been carried out on Pt and Ir supported on amorphous silica-alumina (ASA) and on a stabilized HY zeolite under standard industrial conditions. The effect of temperature, two different supports and feedstocks on HDS and hydrogenation (HYD) product selectivities are investigated. Normalized activity data indicate that in the HDS of DBT and of diesel fuel, the platinum catalysts are much more active than the iridium counterparts. In HDS of diesel fuel (at 623 K), both Pt HY and Pt ASA are a little more active than a commercial Co-Mo Al 2 O 3 catalyst. The normalized activity in the HDS of DBT (593 K) increases in the following order: Pt HY > Pt ASA ⪢ Ir HY > Ir ASA , and in the HDS of diesel fuel (623 K), increases according to: Pt HY ⪢ Pt ASA ⪢ Ir HY > Ir ASA . All spent catalysts were characterized by X-ray photoelectron spectroscopy (XPS). In view of their superior performance, both platinum catalysts were characterized by FTIR spectroscopy of CO probe.

Regeneration of Ni-USY catalysts used in benzene hydrogenation

Abstract The structural and morphological changes of the metal phases which occur during regeneration in hydrogen and air/hydrogen cycles have been studied for Ni-USY catalysts which had been deactivated during the hydrogenation of benzene. Independent of nickel loading in the zeolite, regeneration in hydrogen alone was not sufficient to restore the initial activity. Regeneration in air/hydrogen cycles was more successful for catalysts with higher Ni loadings, but structural transformations of the metal particles occurred during the oxidative regeneration process. Temperature programmed reduction (TPR), photoelectron spectroscopy (XPS) and FTIR of adsorbed CO have been used to identify these modifications.

Relationship between reduced nickel and activity for benzene hydrogenation on Ni-USY zeolite catalysts

Abstract Nickel-containing ultrastable Y zeolites (Ni x USY, x = 0.76–9.01) have been prepared with variable amounts of nickel and tested for the reaction of benzene hydrogenation. All catalysts were prereduced at 673 and 873 K and then tested for the reaction in the temperature range 373–423 K, but only those with the highest nickel content appeared active. The hydrogen-prereduced catalysts have been characterized by X-ray photoelectronspectroscopy (XPS) and Fourier-transform infrared (FT-IR) of chemisorbed carbon monoxide. Both techniques revealed that only the catalysts x = 4.98 and 9.01 show Ni 0 clusters after reduction, in the other preparations with lower nickel contents, the Ni 2+ ions appear to be strongly stabilized by the zeolite lattice. The large XPS Ni/Si intensity ratios found on the x = 4.98 and 9.01 zeolites indicate that the NiO clusters are located at the outer surface and the large cavities of the zeolite. This same finding was confirmed by the appearance of an infrared band at 2100 cm −1 of chemisorbed carbon monoxide on degassed zeolites. All data support the previous conclusion that the hydrogenation of benzene is proportional to the extent of nickel reduction, and hence to the number of reduced nickel atoms.

Silica–alumina-supported transition metal sulphide catalysts for deep hydrodesulphurization

Abstract Deep hydrodesulphurization (HDS) of dibenzothiophene (DBT) and gas-oil has been carried out on amorphous-silica–alumina (ASA)-supported transition metal sulphides (TMS) under conditions which approach industrial practice. The activity and selectivity of the binary Ni-, Ru- and Pd-promoted Mo catalysts were compared with the monometallic ones (Ru, Ir, Pd, Ni, Mo on ASA). For both HDS of DBT and gas-oil, the observed activity trends were similar; thus, all catalysts were more active with model feed than with gas-oil, and less active than commercial CoMo/Al 2 O 3 . The binary catalysts showed larger activity than monometallic ones, with Ni–Mo catalyst being more effective than Ru–Mo or Pd–Mo. For Ni–Mo sample, the X-ray photoelectron and temperature-programmed reduction techniques confirmed that incorporation of Mo minimises metal–support interaction, although the formation of nickel hydrosilicate was not prevented. The consecutive impregnation of calcined Mo/ASA catalyst with precursor solution followed by calcination enhances molybdenum surface exposure in binary samples. As a consequence, the temperature of reduction of MoO 3 to molybdenum suboxides is decreased.

Dibenzothiophene hydrodesulfurization on HY-zeolite-supported transition metal sulfide catalysts

Noble and semi-noble metals (Pt, Pd, Ru, Ir, Ni) were incorporated on a HY zeolite support, and tested in the hydrodesulfurization (HDS) of dibenzothiophene (DBT). Under steady-state conditions, the intrinsic activity of the catalysts was found to display the following order of reactivity: Ir>Pt>Pd≫Ni. While deactivation on Ir, Pt and Pd catalysts was very low, the significant differences in the activity of Ni and Ru zeolites could be attributed to catalyst deactivation. Temperature-programmed reduction studies revealed that noble metals were reduced at moderately low temperatures, whereas Ni catalyst was much more difficult to reduce as a consequence of the much stronger interaction with the zeolite substrate. For the most active Pt/HY and Ir/HY zeolites, photoelectron spectra of the used catalysts revealed that Pt is in metallic state (100% Pt°) and Ir is present as a mixture of metal (62% Ir°) and sulfide.

Evaluation of silica-alumina-supported nickel catalysts in dibenzothiophene hydrodesulphurisation

Abstract The influence of both the nickel–support interaction and the Pd promotion on the activity and thiotolerance during the hydrodesulphurisation (HDS) of dibenzothiophene (DBT) was studied in a variety of amorphous silica-alumina-supported nickel catalysts (Ni/ASA). The catalysts were characterized by means of X-ray diffraction (XRD), N 2 adsorption–desorption measurements, temperature-programmed reduction (TPR), temperature-programmed desorption (TPD) of NH 3 , CO chemisorption and X-ray photoelectron spectroscopy (XPS) techniques. In the low-nickel-content catalysts, a difficulty in reducing the Ni 2+ –support phase was observed, whereas in the high nickel-content catalysts a major reducible NiO phase was developed. Catalysts containing low amounts of nickel exhibited higher activity and selectivity toward ring-opening (RO) products than those containing higher nickel loadings. The larger ring-opening activity and the greater resistance to deactivation of the low nickel-loading catalysts appear to be related to the morphology of the nickel phases at the catalyst surface, consisting of very small Ni clusters separated by non-reduced Ni 2+ species. The high activity of the catalysts in the ring-opening reaction can be explained assuming that non-reduced Ni 2+ species might to force DBT adsorption on Ni 0 phase via CC bonds perpendicular to the surface. In addition, the greater resistance of the catalysts to deactivation was related to H 2 S adsorption on Ni 2+ species, thus maintaining Ni 0 locations available for performing the ring-opening reaction.