Yuji Yoshimura

Support effect on the catalytic activity and properties of sulfided molybdenum catalysts

The effect of the support on the catalytic activity and properties of molybdenum sulfide catalysts was investigated in order to obtain the fundamental information necessary for designing better hydrotreating catalysts. The catalytic activity for each catalyst was evaluated using model test reactions under high hydrogen pressure. The order of supports for hydrogenation (HYD) of 1-methylnaphthalene was A12O3 > TiO2 > MgO > SiO2, while that for hydrocracking (HYC) of diphenylmethane and hydrodesulfurization (HDS) of dibenzothiophene was TiO2 > SiO2 > A12O3 > MgO. Characterization of catalysts clarified that the catalytic activities depend on the structure and properties of the metal oxide which is the precursor of the active sulfide species. Formation of highly dispersed two-dimensional polymolybdate structures, which were observed on the A12O3 and the TiO2 supports, were the most favorable for high HYD activity. In contrast, the data indicate that the enhancement of HYC activity requires an electronegative form of the molybdenum species on which Bronsted acid sites can be formed under the reaction condition. HDS of DBT can be catalyzed on both kinds of active sites, although the product distribution is different.

Catalytic Cracking of Naphtha to Light Olefins

A catalytic process that produces light olefins from naphtha was developed to improve the yield of the conventional steam cracker. In laboratory-scale tests, a newly developed zeolite-based catalyst at a reaction temperature of 650 °C produced an ethylene-plus-propylene yield of about 60%, which is about 10% higher than the conventional process operated at around 820 °C. A feasibility study carried out for a catalytic cracking process using the developed catalyst, that cracks 3 000 tons-naphtha/day, indicated an energy saving of about 20% compared with the conventional process.

New generation of titanium dioxide support for hydrodesulfurization

Mesoporous titanium oxide with a high specific surface area of 120 m 2 /g prepared by a novel method developed by Chiyoda was used for supporting molybdenum sulfide. In order to examine the influence of the surface area on the properties of the molybdenum sulfide phase, two different samples of titanium oxide were studied, a commercial one with a surface area of 72 m 2 /g and that prepared by Chiyoda. Molybdenum was deposited on the TiO2 supports by incipient wetness impregnation with ammonium heptamolybdate in one or two steps depending on the Mo loading. Some samples were also prepared by impregnation of ammonium heptamolybdate basified by ammonia. Raman spectroscopy and XPS were used to examine the nature of the molybdate phase and its dispersion in the oxidic state. HREM and XPS were used for studying the sulfided state. As expected, the maximum amount of well-dispersed molybdenum is higher on the Chiyoda support than on the reference support with a lower surface area. The catalytic properties of the catalysts were studied in dibenzothiophene conversion. For the Chiyoda support, the catalytic activity varied linearly with the Mo loading up to 6–7 Mo/nm 2 then became nearly constant for the higher loadings. Much higher activities (six times, expressed per gram of catalyst) were obtained compared to molybdenum sulfide supported on alumina.

Confirmation of sulfur tolerance of bimetallic Pd–Pt supported on highly acidic USY zeolite by EXAFS

The sulfur tolerance (i.e., degree of sulfidation) of Pd and Pt in sulfided bimetallic Pd–Pt catalysts (Pd : Pt mole ratio of 4 : 1) supported on USY (ultrastable Y) zeolites (SiO2/Al2O3 = 10.7, 48, and 310) was investigated using an extended X‐ray absorption fine structure (EXAFS) method. The sulfidation of the catalysts was done in a 1000 ppm H2S–2% H2/N2 stream at 573 K for 0.5 h. In the Fourier transforms of Pd K‐edge and Pt LIII‐edge EXAFS spectra, both of the peaks due to metallic Pd and to metallic Pt for the Pd–Pt/USY (SiO2/Al2O3 = 10.7) catalyst remained most after sulfidation. Further, the results of the Fourier transforms confirmed that the sulfur tolerance of both Pd and Pt decreased with increasing SiO2/Al2O3 ratio, suggesting that Pd and Pt become sulfur‐tolerant when Pd–Pt bimetallic particles are supported on highly acidic USY zeolite.

Sulfur-tolerant Pd-Pt/Yb-USY zeolite catalysts used to reformulate diesel oils

Abstract Bimetallic Pd-Pt catalysts supported on ytterbium-modified ultrastable Y (USY) zeolite showed excellent hydrodesulfurization (HDS) and hydrodearomatization (HDA) activity as well as high stability when used to reformulate hydrotreated diesel oils; sulfur decreased from 263 to −1 . Modification of USY zeolite with ytterbium by impregnation decreased the number of strong acidic sites, while it increased the dispersion of the Pd-Pt phases, thus, possibly contributing to the increase in the nitrogen- and sulfur-tolerance and stability of Pd-Pt/Yb-USY zeolite catalysts.

Control of hydrodesulfurization and hydrodearomatization properties over bimetallic Pd–Pt catalysts supported on Yb-modifed USY zeolite ☆

Abstract Increasingly stringent regulations on the removal of aromatic and sulfur compounds in diesel fuel require the development of new catalysts and processes. Here, control of hydrodesulfurization (HDS) and hydrodearomatization (HDA) properties was studied by preparing bimetallic Pd–Pt catalysts supported on ytterbium-modified ultrastable Y (USY) zeolite by impregnation and subsequent calcination under different temperatures. Catalytic performances of the prepared catalysts, such as HDS of 4,6-dimethyldibenzothiophene (4,6-DMDBT) and HDA of tetralin, were investigated in a high-pressure continuous-flow reactor. With changing calcination temperature, the HDS activity is only slightly affected, although the maximum HDS conversion was obtained at 300°C. In contrast, the HDA activity decreased significantly, with hydrogenation selectivity remaining relatively constant as confirmed by the weak variation of the trans-decalin to cis-decalin ratio. A low calcination temperature of 200°C simultaneously favored both deep HDS and deep HDA, whereas a high calcination temperature of 500°C favored selective HDS reactions with minimal HDA reactions (i.e. saving of expensive hydrogen). These results clearly indicate that the selectivity of HDS to HDA can be controlled by simply changing the calcination temperature of Pd–Pt/Yb/USY zeolite catalysts.

Preparation of nickel-tungstate catalysts by a novel impregnation method

Abstract Nickel-tungstate/γ-alumina (NiW) catalysts were prepared by an incipient wetness impregnation method using citric acid as a complexing agent. Citric acid has been used by our research group in preparing cobalt-molybdate and nickel -molybdate catalysts. The extended X-ray absorption fine structure (EXAFS) data of the impregnating solutions indicated that citric acid contributes to the formation of polytungstate anions that are smaller than the dodecatungstate ions formed when conventional ammoniacal solutions are used. Sulfided NiW catalysts prepared by using citric acid showed higher hydrogenation activity and hydrogenation selectivity than NiW catalysts prepared using the conventional ammoniacal solutions.

Molybdate catalysts prepared by a novel impregnation method: Effect of citric acid as a ligand on the catalytic activities

Abstract Molybdate, nickel-molybdate and cobalt-molybdate/γ-alumina catalysts were prepared by an impregnation method using citric acid as well as ammonia as ligands. Molybdenum structures in the impregnating solutions and on the sulfided catalysts were characterized by EXAFS and XPS. Agglomerated molybdenum octahedra existed in the impregnating solutions containing citric acid, in contrast to the monomeric molybdenum tetrahedra obtained when using ammonia. The nickel-molybdenum catalyst prepared by using citric acid was inferior to the one prepared by using ammonia in terms of both hydrogenation and HDN activities, which might be due to a decrease in the amount of active Ni-Mo-S phase. On the other hand, the cobalt-molybdenum catalyst prepared using citric acid was superior to the one prepared using ammonia in terms of HDS activity. A decrease in the lateral size of MoS2-like crystallites might attribute to an increase in the HDS activity.

EXAFS study on Pd–Pt catalyst supported on USY zeolite

Abstract Local structure around Pd and Pt in the bimetallic Pd–Pt catalysts supported on ultra stable Y (USY) zeolite (SiO2/Al2O3=680) was investigated by an extended X-ray absorption fine structure (EXAFS) method during oxidation, reduction, and sulfidation. The Pt L III-edge EXAFS spectra showed that a new bond that was significantly different from Pt–Pt to Pt–Pd metallic bonds was formed in the bimetallic Pd–Pt (4:1) reduced catalysts supported on USY zeolite. This new bond may reflect the ionic properties of Pt through the Pt–Pd interaction. Furthermore this new bond survived sulfidation indicating that the bond has a cationic property and sulfur-tolerance property. The Pt–Pd ionic interaction in these catalysts allows some of the Pd metal to survive as metallic phase. The existence of this metallic phase under sulfidation condition may result in high activity of Pd–Pt (4:1) catalyst supported on USY zeolite in the aromatics hydrogenation.

Cracking of n-Butane Over Alkaline Earth-Containing HZSM-5 Catalysts

The effect of alkaline earth modification on HZSM-5 was investigated by catalytic cracking of n-butane under non-oxidative and oxidative conditions. The yields of aromatic products were low compared with that obtained using the non-modified HZSM-5, and higher yields of ethylene and propylene were observed with Mg-, Ca-, and Ba-ZSM-5. The NH3-TPD spectra of these catalysts show that the strong acid sites were transformed to weak acid sites. The dehydrogenation cracking was considered to occur at the acid sites modified with the alkaline earth elements because the ethylene/ethane ratio and the C2/other products ratio were high using the alkaline earth-containing HZSM-5. It is suggested that the suppression of hydrogen transfer reaction and the stimulation of dehydrogenation cracking were the major cause of the improvement of olefin yield in the cracking.