Ryuichiro Iwamoto

Influence of phosphorus on the properties of alumina-based hydrotreating catalysts

On the basis of numerous patents, phosphorus is classified as a second promotor in molybdenum-containing hydrotreating catalysts, which are used for preparing clean-burning fuels. Notwithstanding the substantial work on the influence of phosphorus in catalysts, its role is still a matter of debate, as critically discussed in this review. Preparation of the catalysts, which consists of mixing the selected ingredients (P, Mo, Co, or Ni and alumina) to form solids that meet specific requirements (e.g., specific surface area, dispersion, and loading of the elements), has been extensively examined. The review includes data concerning adsorption (competitive or sequential) of phosphorus oxo-species on alumina. Several states have been identified (e.g., monophosphate, polyphosphate, Al or Ni phosphate, and “Mo–P” heteropoly compounds) on the basis of data characterizing reference compounds and the combined use of techniques such as extended X-ray absorption fine structure, X-ray photoelectron, solid state nuclear magnetic resonance, and vibrational (infrared and Raman) spectroscopies. Texture, thermal stability, and acidity measurements complement the spectroscopic information. Large differences in acidity are reported that might be attributed both to the nature of the catalysts and to the methods of measurement. It is often claimed that the addition of phosphorus does not induce enough acidity to promote hydrogenolysis during catalysis. The dispersion of the elements in the oxide-form catalysts depends not only on the phosphorus content but also on the preparation conditions. Large amounts of phosphorus favor the agglomeration of metal oxides. However, no clear conclusion can be proposed for the influence of phosphorus on the dispersion of the sulfide phases or their sulfur contents. In general, the catalytic influence of phosphorus strongly depends on its content, with an effect that is usually negative at high loadings. Phosphorus shows no effect or only a very small positive effect on hydrodesulfurization of thiophene, and the most significant positive effects have been reported primarily for hydrodenitrogenation reactions. However, the effect of phosphorus depends on the nature of the reactants and intermediates, and different active sites are involved in the various hydrotreating reactions. Structural models of phosphorus-containing hydro-treating catalysts and the main influences of phosphorus on the states of the other elements on the alumina surface are presented.

Effect of cobalt on the sulfiding temperature of CoOMoO3/Al2O3 studied by temperature programmed sulfiding

Abstract The effect of cobalt on the sulfiding temperature of CoO MoO 3 /Al 2 O 3 was investigated by means of temperature programmed sulfiding (TPS). MoO 3 supported on alumina transforms into MoS 2− x by sulfidation via formation and subsequent hydrogenation of Mo oxi-sulfide or MoS 3 . The temperature of which the Mo oxi-sulfide or MoS 3 phase are hydrogenated (Ps temperature) decreased with increasing amount of cobalt in the CoO MoO 3 /Al 2 O 3 catalysts. A decrease in the Ps temperature was also observed in the case of ‘ Co/Al+ Mo/Al catalysts’ which were prepared by mechanical mixing of CoO/Al 2 O 3 and MoO 3 /Al 2 O 3 . On the other hand, the Ps temperature did not change by mechanical mixing of bulk CoO and the MoO 3 /Al 2 O 3 catalyst. The cobalt adsorption test suggested that the cobalt species preferably interact with the molybdenum species during impregnation. It was concluded that the well dispersed cobalt species have a capability to provide spillover hydrogen to accelerate the hydrogenation of the Mo oxi-sulfide. Furthermore, a correlation between the Ps temperature and HDS activity for light gas oil was obtained. This result suggests that the cobalt species facilitate the hydrogenation of sulfur atoms adsorbed on the HDS active sites (coordinatively unsaturated Mo sites) by supplying spillover hydrogen and consequently accelerate the HDS reaction.

Genesis, characterizations and HDS activity of Mo-P-aluminabased hydrotreating catalysts prepared by a sol-gel method

Mo oxide-P oxide-Aluminum catalysts with a wide range of P loading (0–14wt%) were prepared by a sol-gel method to elucidate the role of phosphorous on the textural, structural and catalytic properties of Mo based catalysts. Two different Mo loadings (expected ∼20 and ∼30wt%Mo) and two kinds of P precursors (phosphoric acid, phosphorus pentoxide) were examined. The structural properties of dried and calcined forms were studied by means of various characterization techniques. Specific surface area (S.S.A.) of catalysts were decreased proportional to the P loading in every series. Especially, the S.S.A. in the series of P2O5 precursor decreased drastically above 7.7wt%P loading. XRD measurements revealed that excess loading of Mo and P within the alumina framework provokes aggregation of bulk MoO3 (above 6.8wt%P in the series of 30wt%Mo for H3PO4 precursor and above 5.5wt%P in the series of P2O5 precursor). From IR measurements, it was found that P and Mo atoms interact with equivalent sites of alumina. From NMR measurements, predominant formation of Mo-P heteropoly complex were observed in the drying step. P interacted strongly not only with alumina framework but also with P itself. P2O5 prefers to polymerize by calcination. It was also found that Mo enhanced the interaction of P with alumina through the formation of P-Mo heteropoly complex. Water extraction tests revealed that Mo and P interacts strongly with the alumina framework. The HDS activity was not promoted by P while excess P decreased HDS activity with the formation of bulk MoO3.

Genesis, structural, and catalytic properties of Ni-Mo-P-alumina based hydrotreating catalysts prepared by a sol-gel method

Ni oxide-Mo oxide-P oxide-Alumina with wide range of P loading (from 1 to 10 wt% P) were prepared by a sol-gel method to elucidate the role of P on the genesis, structural, and catalytic properties of Ni-Mo based hydrotreating catalysts. Specific surface area of catalysts decreased gradually in proportion to the P loading from ∼500 to 260 m2/g. X-ray powder diffraction revealed that both small and large amounts of P within the alumina framework provoke aggregation of Mo related species. 27Al-NMR indicated that a part of octahedral aluminium sites is highly distorted in the presence of Ni, Mo and P. From 31P-NMR measurements, predominant formation of polymeric P oxospecies and AlPO4 was observed after the calcination step. Thiophene HDS activity gave a maximum at 2 wt% of P due to an increase in Mo dispersion. However, large amount of P has a negative effect on HDS activity due to the formation of bulk MoO3. Butane formation during thiophene HDS decreases with P addition which may indicate the segregation of Ni from MoS2.

Effect of P on the Sulfidability of NiMo/Alumina Based Hydrotreating Catalysts Prepared by a Sol-Gel Method

Abstract Effect of P on the sulfidability of Ni-Mo/Alumina based hydrotreating catalysts prepared by a sol-gel method was investigated by using XPS and bulk chemical analysis. In MoO3- P2O5-Alumina (Mo-P-Alumina) catalysts, the sulfidability of Mo species strongly depended on the Mo and P content. At low Mo loading (17 wt% of Mo), the addition of P did not affect the Mo sulfidability which was estimated by measurement of bulk S/Mo atomic ratio after thiophene HDS reaction. On the other hand, the presence of P decreased the S/Mo ratio from 2 to 1 at higher Mo loading (26 wt% of Mo). XPS of high Mo loading catalysts suggested that a part of P is associated with Mo species through oxygen atoms. Strong P-O-Mo bond may prevent exchanging oxygen by sulfur atom during the sulfidation procedure. On the other hand, in NiO- P2O5-Alumina (Ni-P-Alumina) catalysts, the addition of P increased the sulfidability of Ni species from 78 to 93 %. It is considered that the strong interaction between P oxo-species and alumina (i.e. the formation of A1PO4) prevents the formation of stable nickel aluminate. In Ni-Mo-P-Alumina catalysts, the sulfidability of Mo also decreased with P addition as in the case of Mo-P-Alumina catalysts. However, the Ni species in Ni-Mo-Alumina was completely sulfided and less depends on the P addition. It is suggested that the Ni species are predominantly associated with Mo species rather than with Alumina in Ni-Mo-Alumina.

Active Sites of Novel Iron Supported Y-Type Zeolite

Abstract A novel iron supported Y-type zeolite prepared by treating NH 4 Y with ferric nitrate solution under low pH condition (FeHY) showed high activity for toluene disproportionation in the coexistence of H 2 S and H 2 . Active sites of FeHY for toluene disproportionation were investigated by elucidating function of iron cluster and zeolite separately. The activity of FeHY was significantly decreased by potassium ion exchanging (K/FeHY). Ultra stable Y-type zeolite (USY) also showed low activity. However, catalyst prepared by mixing K/FeHY and USY mechanically showed extremely higher activity than the sum of both catalysts. It was suggested that the active sites of FeHY are Bronsted acid sites in zeolite framework and that iron clusters supply spillover hydrogen to prevent zeolite from deactivation due to coke deposition.

Reduction and sulfidation properties of iron species in Fe-treated Y-zeolites for hydrocracking catalysts

Abstract Temperature programmed reduction (TPR) and temperature programmed sulfiding (TPS) were used to characterize reduction and sulfiding properties of Fe-treated Y-zeolites, which were prepared by treating NH4Y-zeolite with an aqueous ferric nitrate solution (Fe-treatment). It was demonstrated that three types of the Fe-species are present in the Fe-treated Y-zeolites: ion-exchanged type species, small Fe-oxide clusters, and Fe oxides without interaction with the zeolite framework (including aggregated ferric oxide), the proportion of which is dependent on the extent of the Fe-treatment. The small Fe-oxide clusters, which are probably situated inside the supercages through a coordination with the framework oxygen atoms, are responsible for high activity for toluene disproportionation. A realistic production control for the active Fe-treated Y-zeolite catalyst has been achieved for the first time by using the TPR and TPS techniques.

New Method of Modifying Y-type Zeolite—Fe Supported Zeolite

An iron supported Y-type zeolite which was prepared from modifying NH4Y with ferric nitrate solution showed high activity for toluene disproportionation under the flow of H 2 S/H 2 . Detailed investigations found that preparation conditions such as temperature and Fe 3+ concentration significantly affect catalytic activity. The catalyst which was prepared by modifying NH 4 Y with 0.25M Fe(NO 3 ) 3 solution at 323K showed the highest activity among the tested samples.