Suehiko Yoshitomi

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.

Hydrogenation of tetralin over sulfided nickel-tungstate/alumina and nickel-molybdate/alumina catalysts

Abstract Nickel-tungstate/alumina (NiW/Al2O3) and nickel-molybdate/alumina ( NiMo Al 2 O 3 ) catalysts were prepared using an incipient wetness impregnation method with citric acid as a complexing agent. The hydrogenation activity of both sulfided catalysts was measured in a continuous-flow reactor as well as in a batch tube-bomb reactor with tetralin as an aromatic compound. Activity and stability of both sulfided catalysts were then compared in detail. The hydrogenation activity of the two catalysts depended on the partial pressure of the hydrogen sulfide (H2S) in the reaction atmosphere, where dimethyl disulfide (DMDS) was added to control its pressure. The sulfided NiW/Al2O3 catalyst was advantageous in hydrogenating tetralin under low H2S partial pressure, and the structure of the sulfide phases was quite stable in the reducing atmosphere which was measured by XPS and EXAFS methods. On the other hand, the sulfided NiMo Al 2 O 3 catalyst was advantageous in hydrogenating tetralin under high H2S partial pressure, where the hydrogenation activity of both catalysts were inhibited by H2S. The sulfided NiMo Al 2 O 3 catalyst under low H2S partial pressure was less stable than the sulfided NiW/Al2O3 catalyst due to structural changes of the active phases, such as migration of the Ni species into γ-Al2O3 to form the NiAl2O4 phase and sintering of the MoS2-like phase as confirmed by an XPS and an EXAFS. The superiority of the sulfided NiW/Al2O3 catalyst over the sulfided NiMo Al 2 O 3 catalyst was indicated in deep hydrogenation of low-sulfur feedstocks.

DEACTIVATION OF HYDROTREATING MOLYBDATE CATALYSTS BY METAL DEPOSITION

Abstract Nickel-molybdate and cobalt-molybdate catalysts were used for hydrotreating coal-derived oils and a petroleum vacuum gas oil. The metallic components deposited on the spent catalysts were characterized to reveal their inhibitory effects on hydrogenation and hydrocracking activities. Inhibition by typical metal components, such as Na, K, Mg, Ca, Fe, Ti, Ni and V, were also evaluated by doping such metals on the catalysts. Inhibitory effects of alkali and alkaline earth metals on hydrogenation and hydrocracking activities were significant, and their effects decreased in the following order for both catalytic activities; KNaCaMg. Deposition of V, Fe and Ti resulted in an increase in hydrocracking, but a decrease in hydrogenation. The effect of these metals decreased in the following order: VFeTi. Data from X-ray photoelectron spectroscopy, X-ray diffraction and extended X-ray absorption fine structure showed that alkali and alkaline earth metals not only segregated on the catalyst surface to cover the active sites but also caused the lateral growth of MoS 2 -like structures, and that some of these metals formed double oxides with molybdenum after the oxidative regeneration. The neutralization of acidity was significant for these basic metals. On the other hand, V, Fe and Ti tended not only to disperse the MoS 2 -like species but also to increase the catalyst acidity through the formation of an acidic double oxide with molybdenum/alumina support.

Application of zeolite-based catalyst to hydrocracking of coal-derived liquids

Abstract Y-zeolite supported catalysts were applied to the hydrocracking of coal-derived liquids. By the introduction of two-stage upgrading consisting of hydrotreating and hydrocracking, Wandoan coal-derived middle distillate was hydrocracked over NiMo/Y-zeolite, producing a high gasoline fraction yield. Zeolite supported catalysts gave little hydrocracked compounds in the hydroprocessing of coal-derived heavy oils, even after hydrotreatment. The reaction inhibitors which seriously poison the active sites of zeolites were found to be small nitrogen-containing molecules. In the hydroprocessing of coal-derived heavy oils, zeolite supported catalysts were inferior to alumina supported catalysts. This is due to the high hydrocracking but low hydrogenation activity of zeolite supported catalysts.

Dual-functional Ni-Mo sulfide catalysts on zeolite-alumina supports forhydrotreating and hydrocracking of heavy oils

Ni-Mo sulfide catalysts supported on the mixtures of γ-Al 2 O 3 and HY zeolite with various ratios were prepared and tested in the hydroprocessing reactions of heavy oils to reveal the roles of the dual-functions of hydroprocessing catalysts. Hydrogenation activity solely functioned for the hydrodesulfurization and hydrodearomatization of heavy feedstocks with high nitrogen contents, typically oil sand bitumen and coal-derived oils. For other feedstocks, the dual-functionality played important roles not only in hydrocracking but also in hydrodenitrogenation. The optimum balance of the hydrogenation/hydrocracking activities greatly depend on the feedstock properties. Pre-hydrotreatment which reduced the concentration of heavy nitrogen-containing materials was effective for maximizing the dual-functionality.

Hydrogenation active sites of molybdenum sulfide catalysts enhanced by Ni and Co organometallics

Abstract Organometallic complexes of Ni or Co were doped on a MoO 3 /Al 2 O 3 catalyst to enhance the hydrogenation (HY) activity of molybdenum sulfide catalysts and to help understand the nature of the HY active sites. The HY activity increased with increasing doping with the organometallics. The HY activity of nickel phthalocyanine Ni(Pc)-MoO 3 /Al 2 O 3 catalysts were much higher than those of conventionally prepared NiO-MoO 3 /Al 2 O 3 catalysts. XAFS, FT-IR, and thermal analysis revealed that the Ni(Pc) structure on the catalysts was fairly stable during calcination and presulfiding. These results indicated that the Ni(Pc) structure on the catalysts is effective for the formation of the HY active sites. Since there is no direct bond between Mo in MoS 2 and Ni in Ni(Pc), hydrogen spillover seems to play an important role in enhancing the HY activity of the catalysts.

Correlation Between Catalytic Activities and Surface Properties of Ni-Mo Sulfide Catalyst. (II). Support Effect.

Two series of Ni-Mo catalysts were prepared using Al2O3 and TiO2 supports. Ni/ (Ni+Mo) ratio of the catalysts was varied, while a total metal loading of Ni and Mo was kept constant. Sulfiding conditions were optimized to give superior catalytic activities. After sulfiding, model test reactions were carried out to evaluate hydrogenation (HY), hydrocracking (HC) and hydrodesulfurization (HDS) activities of the sulfide catalysts.The highest HY activities of Al2O3 and TiO2 supported catalysts were obtained when the Ni/ (Ni+Mo) ratios were 0.25 and 0.12, respectively, showing different interaction between support and active metals. XPS measurements revealed that the atomic ratio of active metal sulfide {NiS/ (NiS+MoS2)}, which gave the highest HY activities, was 0.2 on both supports. This indicates that sulfided active metals such as NiS or MoS2 play an important role for the formation of HY active sites.Both catalysts supported on Al2O3 and TiO2 showed the highest HDS activities when the NiS/ (NiS+MoS2) ratio was 0.4. This ratio is different from that obtained in HY measurements. While HC activities of the two series of sulfide catalysts decreased with increasing of Ni loading.These results clealy show that HY, HC and HDS active sites of Ni-Mo sulfide catalysts are different each other and that proper selection of each active metal loading is required for preparing highly selective catalysts.

Stereoselective addition of phenols to dimethyl acetylenedicarboxylate adsorbed on alumina

Although phenols react with dimethyl acetylenedicarboxylate (DMAD) to give a mixture of both cis- and trans-addition products, the reaction with DMAD adsorbed on alumina gives cis-addition products stereoselectively.