The catalytic activity of partially reduced Pt/MoO3 for alkane isomerization was investigated. The surface area of Pt/MoO3 was markedly enlarged by H2 reduction to a maximum after reduction at 673 K for 12 h. Enlargement of the surface area was caused by formation of pores with diameters of 0.6-3 nm. The catalytic activity of partially reduced Pt/MoO3 for heptane isomerization increased with reduction temperature, and reached a maximum at 723 K. The catalytic activity for 2-propanol dehydration was very similar to that of heptane isomerization. The isomerization and dehydration activities of partially reduced Pt/Na-MoO3 rapidly decreased with increasing content of Na. In contrast, the hydrogenation of cyclohexene was promoted on catalysts containing Na. The isomerization and dehydration activities were related to the number of acid sites, determined by NH3-TPD. Therefore, the isomerization activity of partially reduced Pt/MoO3 depends on the activity as an acid catalyst. H2 reduction at 673 K enlarged the surface areas of H1.55MoO3 and Pt/MoO3, but not the surface area of MoO3. H1.55MoO3 and Pt/MoO3 reduced at 673 K had comparable activity for pentane isomerization, and were much more active than MoO3 reduced at 673 K, even after considering the differences in surface areas. Molybdenum oxyhydride, MoOxHy, was formed after the decomposition of hydrogen molybdenum bronze in the reduction of H1.55MoO3 and Pt/MoO3. On the other hand, MoO3 was reduced to MoO2 without the formation of hydrogen bronze. These results show that surface area and isomerization activity were improved by the formation of MoOxHy from HxMoO3.
Behavior and mechanisms of degradation of thermosetting plastics used as FRP-matrix and GFRP in liquid environments are reviewed based on our experimental findings. The forms of chemical degradation were classified into three types, 'surface reaction type,' 'corrosion layer forming type' and 'penetration type.' The mechanism of each type is dependent on the chemical structures of the resin, the reactivity between resins and liquids, and the diffusivity of liquid in the resins. The corrosion rate was defined as change of corrosion thickness with immersion time in the 'surface reaction' and 'corrosion layer forming type' corrosion. By applying the concept of corrosion rate, the residual thickness of the non-corroded region after corrosion could be predicted. For 'surface reaction' and 'corrosion layer forming type' corrosion, a life-prediction method was proposed using the master curve focused on retention of flexural strength after corrosion. For 'penetration type corrosion,' the weight change was important to predict the initiation of decrease in mechanical strength.
Introduction of the legal requirement for <10-ppm sulfur in diesel fuels is intended to help reduce diesel exhaust emissions, such as nitrogen oxide and particulate matter, as well as CO2 emissions depending on the improvement of mileage. Development of highly active HDS catalysts for five years has resulted in new CoMo HDS catalysts for the production of ultra-low sulfur diesel fuels. The developed catalyst, C-606A, has three times higher HDS activity compared with the conventional CoMoP/Al2O3 catalyst, which enables <10-ppm sulfur content in products using a commercial diesel hydrotreater designed to produce 500-ppm sulfur diesel fuels. The new catalysts were prepared by coimpregnation using an aqueous solution containing Co, Mo, orthophosphoric acid and carboxylic acid on a support consisting of HY-Al2O3. After impregnation, these catalysts were air-dried only without calcination. The new catalyst preparation method could increase the formation of the active phase, Co-Mo-S phase, and provide more highly active Co-Mo-S Type II, which is located at the edges of the MoS2 multi-layers. Based on the environmental and economical advantages, Cosmo Oil Co., Ltd. has utilized C-606A in all diesel hydrotreaters at its refineries. High catalyst performance has been demonstrated for each application. This HDS catalyst technology is expected to be introduced worldwide to encourage energy conservation, minimum capital investment, and reduction of CO2 emissions.
The present study investigated the structure of Co species formed during the preparation of Co/SiO2 Fischer-Tropsch synthesis (FTS) catalysts with an aqueous Co nitrate solution modified with chelating agents (NTA and CyDTA), to clarify the origin of the promotion effects. Diffuse reflectance FTIR measurements showed that both NTA and CyDTA complexes formed in the impregnating solution are preserved on the SiO2 surface. These complexes were interacted with OH groups on SiO2 surface. During the subsequent drying step, some of the NTA-Co2+ complex were decomposed, whereas the CyDTA-Co2+ complex was completely preserved. Both types of complex are combusted during the calcination step at ca. 100 K higher temperature compared with Co nitrate. Furthermore, the combustion temperature was higher for the CyDTA-Co2+ complex than the NTA-Co2+ complex. After the calcination step, Co3O4 and α-Co2SiO4-like structures with smaller cluster sizes were observed by Co K-edge EXAFS when modified with NTA and CyDTA, respectively. The FTS activity of the NTA-modified catalyst strongly depends on the calcination temperature. Higher FTS activities were obtained only when the catalyst was calcined above the combustion temperature of the NTA complex. Therefore, the interactions between the chelating agents, Co2+ and the SiO2 surface during the preparation steps is the crucial factor for the promotion effect of NTA. Modification with NTA results in moderate interactions with Co2+ and the SiO2 surface, leading to the higher FTS activity.
Photochemical and enzymatic synthesis of malic acid from pyruvic acid and HCO3- was studied with malic enzyme (ME) and NADP+ photoreduction with ferredoxin-NADP+-reductase (FNR) by visible light photo-sensitization of the chlorophyll derivative, zinc chlorin-e6 (ZnChl-e6), in the presence of NADH as an electron-donating reagent and methylviologen (MV2+) as an electron-relay reagent. NADPH was produced by irradiation of the reactant solution containing NADH, ZnChl-e6, MV2+, NADP+ and FNR in Bis-Tris buffer (pH 8.0). After 180-min irradiation, 8.3 mmol·dm-3 NADPH was produced under the optimum conditions with 10 mmol·dm-3 of NADP+. The reduction ratio of NADP+ to NADPH was about 83%. Malic acid was produced by irradiation with visible light (>390 nm) of the reactant solution containing NADH, ZnChl-e6, methylviologen (MV2+), pyruvic acid, NaHCO3, NADP+, ferredoxin-NADP+-reductase (FNR) and ME. Malic acid production was 2.0 mmol·dm-3 after 3-h irradiation under the optimum conditions with NADH, ZnChl-e6, MV2+, FNR, pyruvic acid, NaHCO3, NADP+ and ME. The ratio of HCO3- and pyruvic acid to malic acid was about 20% under the optimum conditions.
Hydrocracking (HC) catalysts consisting mainly of silica-alumina and a small amount of ultra stable Y type (USY) zeolite were prepared with silica-alumina powders of different mean particle sizes, and the effects of particle size on the pore structure and HC catalytic performance were investigated. The structures of the macropores depended on the average particle size of the silica-alumina powder, with larger particle size resulting in larger mean pore diameter. The HC activities of prepared catalysts for straight run vacuum gas oil were also evaluated. Up to 300 nm, larger pore size led to higher HC activity, but pore size larger than 400 nm led to lower HC activity. These results suggest that there is an optimum macropore diameter for HC activity. Smaller macropore size provided higher middle distillate selectivity. This result suggests that the smaller macropores allow middle distillate oil molecules to escape easily, and avoid secondary cracking. These results indicate that selecting the optimum silica-alumina particle size for high diffusivity in HC catalysts is important to enhance catalytic activity without loss of middle distillate selectivity.
Combustion catalysts free from precious metals, such as platinum, for removal of volatile organic compounds were investigated. Common metal oxides (titanium(IV) oxide (TiO2), alumina and silica) were selected as candidates for a catalyst for combustion of toluene at low concentrations. Complete conversion of toluene was not achieved even at 500°C without catalysts, although the ignition point of toluene is 480°C. TiO2 exhibited the highest activity for combustion of toluene among representative metal oxides. Toluene was almost quantitatively converted to carbon dioxide (>99% yield) over TiO2 under the condition of appropriate contact time at 500°C.