Akira Obuchi

Performance of platinum-group metal catalysts for the selective reduction of nitrogen oxides by hydrocarbons

Abstract The performances of platinum-group metals, platinum, iridium, palladium, rhodium and ruthenium supported on γ-alumina, as catalysts for the selective reduction of nitrogen oxides by hydrocarbons were investigated. Platinum and rhodium had high nitric oxide conversion activities both in model mixtures and in real diesel exhaust gases, especially at relatively low temperatures between 200 and 350°C. It was confirmed that the platinum-rhodium and platinum catalysts have higher activity and durability than a catalyst composed of copper supported on ZSM-5 under real diesel exhaust conditions. The platinum-containing catalysts, however, produced more nitrous oxide than nitrogen. It is expected that platinum-group metal catalysts will be able to be used for practical purposes if once their selectivity toward nitrogen is improved.

Improvement of Pt catalyst for soot oxidation using mixed oxide as a support

Catalytic activity of pt catalysts for soot oxidation was studied using temperature programmed reactions. the activity of pt loaded over tio2-sio2 (pt/tio2-sio2) showed higher activity than other pt/mox systems (mox = tio2, zro2, sio2, al2o3. tio2-zro2. tio2-al2o3, zro2-sio2, zro2-al2o3, sio2-al2o3). the activity was highest when the molar ratio of tio2/(tio2 + sio2) ranged from 0.4 to 0.7. the effect of pretreatment with a gas containing low so2 concentrations on the activity was compared for pt/sio2, pt/tio2 and pt/tio2-sio2. in the case of pt/tio2-sio2, the activity was markedly promoted by the pretreatment whereas no variation in the activity was observed for pt/sio2. the difference in the behavior towards the so, pretreatment was attributed to property difference in the supports for sulfate accumulation. the high activity of pt/tio2-sio2 was also confirmed under practical conditions with a diesel engine exhaust using a catalyst-supported diesel particulate filter (dpf). (c) 2003 elsevier science b.v. all rights reserved.

Selective reduction of nitric oxide with propene over platinum-group based catalysts : studies of surface species and catalytic activity

The reduction of nitric oxide by propene in the presence of oxygen over platinum-group metals supported on TiO2, ZnO, ZrO2, and Al2O3 has been investigated by combined diffuse reflectance FT-IR spectroscopy and catalytic activity studies under flow reaction conditions at 523–673 K and atmospheric pressure. The catalytic activity for the selective reduction of nitric oxide and the intensity of the IR bands due to reaction species depended strongly on the nature of the support, type of supported metal, reaction time and temperature. The main surface species detectable by IR were adsorbed hydrocarbons (2900–3080 cm−1), isocyanate (2180, and 2232–2254 cm−1), cyanide (2125 cm−1), nitrosonium (1901 cm−1), CO2 (2343–2357 cm−1), CO (2058 cm−1) and carbonate (1300–1650 cm−1) species. In the case of rhodium containing catalysts, when supported on Al2O3, they exhibited both the highest concentration of surface species and the highest activity for nitric oxide reduction and selectivity to nitrogen. The catalytic activity and the IR intensities of the nitrosonium and isocyanate bands increased with reaction temperature, reached their maximum between 570 and 620 K, and then decreased at higher temperatures. The IR band intensities due to nitrogen containing surface species were found to be strongly correlated to the activity for nitric oxide conversion and only slightly related to the selectivity to dinitrogen.

Carbon oxidation with platinum supported catalysts

Abstract The effect of the support oxide, Pt precursor and reactant gas composition on the catalysis of soot oxidation was investigated using carbon black as a model soot and simulated exhaust gases. The Pt precursors used were Pt(NH3)4(OH)2, H2PtCl6·6H2O, Pt(NH3)4(NO3)2, and Pt(NH3)4Cl2. The support metal oxides used were SiO2, Al2O3, and ZrO2. Pt/SiO2 prepared from Pt(NH3)4(OH)2 showed the highest carbon oxidation activity. It had much higher activity in the condition of N2+O2+H2O+NO+SO2 than without NO and SO2.

Decomposition of nitrous oxide over supported rhodium catalysts and dependency on feed gas composition

Abstract The catalytic decomposition of nitrous oxide to nitrogen and oxygen was studied overRh/ZnO, Rh/CeO 2 , Rh/ZSM-5, Cu ZSM-5 and Co Al CO 3 HT (hydrotalcite). The effects of metal loading and calcination conditions upon the catalytic performance were examined on Rh/ZnO. A 0.5 wt.% Rh/ZnO catalyst was found to be the most active catalyst, whose reaction rate was 4.0 × 10 4 μmol(N 2 O) · g −1 · h −1 under the conditions of 950 ppm N 2 O and 5% O 2 at 300°C. The oxidized Rh/ZnO showed a higher activity than that calcined in a reducing atmosphere. The TEM and EDX observations revealed the formation of particles of ca. 50Ain diameter. They consisted of rhodium and zinc oxides as major and minor components, respectively. The activities of all these catalysts decreased when NO 2 and H 2 O were added to the feed.

Oxidation of carbon black over various Pt/MOx/SiC catalysts

Abstract Catalytic activities of various Pt/MOx/SiC systems for carbon oxidation under simulated diesel exhaust gas were investigated in temperature-programmed reactions. When Pt/MOx (MOx=TiO2, ZrO2, Al2O3) was loaded onto silicon carbide (SiC), the oxidation activities became higher than those of Pt/MOx alone or other Pt/MOx/SiC systems (MOx=Ta2O5, WO3, Nb2O5, SnO2, SiO2, CeO2, MoO3, V2O5). Among them, Pt/TiO2/SiC exhibited the highest activity. We discuss the activity of MOx=TiO2, ZrO2, and Al2O3 in connection with NO oxidation activity, adsorption of sulfate onto the support, Pt dispersion, and specific surface area of the catalyst. Furthermore, we investigated the catalytic performance of Pt/TiO2/SiC in more detail under isothermal conditions and in a staged arrangement.

An exploratory study of diesel soot oxidation with NO2 and O2 on supported metal oxide catalysts

Abstract A number of supported metal oxide catalysts were screened for their catalytic performance for the oxidation of carbon black (CB; a model diesel soot) using NO 2 as the main oxidant. It was found that contact between the carbon and catalyst was a key factor in determining the rate of oxidation by NO 2 . Oxides with low melting points, such as Re 2 O 7 , MoO 3 and V 2 O 5 showed higher activities than did Fe 3 O 4 and Co 3 O 4 . The activities of MoO 3 and V 2 O 5 on various supporting materials were also examined. MoO 3 /SiO 2 was the most active catalyst among the supported MoO 3 examined, whereas, V 2 O 5 /MCM-41 showed the highest activity among the supported V 2 O 5 . Different performances of the supported MoO 3 catalysts were explained by the interaction of MoO 3 with the supports: a strong MoO 3 /support interaction may result in a poor mobility of MoO 3 and a poor activity for oxidation of carbon by NO 2 . The high activity of V 2 O 5 /MCM-41 was associated with its catalysis of the oxidation of SO 2 by NO 2 to form SO 3 , which substantially promotes oxidation of carbon by NO 2 . Addition of transition metal oxides or sulfates to supported MoO 3 and V 2 O 5 was also investigated. Combining MoO 3 or V 2 O 5 with CuO on SiO 2 , adding VOSO 4 to MoO 3 /SiO 2 or MoO 3 /Al 2 O 3 and adding TiOSO 4 or CuSO 4 to V 2 O 5 /Al 2 O 3 improved the catalytic performance.

Catalytic performance of Pt supported on various metal oxides in the oxidation of carbon black

Abstract The effect of support materials for Pt catalysts on the oxidation of carbon black, a model diesel-exhaust soot was examined. Among eight kinds of Pt-supported metal oxides (Ta2O5, Nb2O5, WO3, SnO2, SiO2, TiO2, Al2O3 and ZrO2), Pt/Ta2O5 showed the highest activity towards the oxidation of carbon black in a model diesel exhaust, containing O2, H2O, NO and SO2 in N2. Pt catalysts supported on other non-basic metal oxides such as Nb2O5, WO3, SnO2 and SiO2 showed similar high activities. The high activity for these catalysts was attributed to their non-basicity and negligible affinity toward SO3 (or H2SO4), which results in less poisoning of the supported Pt and also in a smooth supply of SO3 to the carbon surface, which is oxidized by NO2 with a catalysis of SO3.

A practical scale evaluation of catalysts for the selective reduction of NOx with organic substances using a diesel exhaust

Abstract Several promising catalysts for the selective reduction of NOx with organic compounds were made into large scale samples (cylindrical, o = 118 mm, length = 50 mm), either as washcoated honeycomb monoliths (400 cell/in2) or as packings of pellets with a diameter of 2–3 mm. These samples were tested under diesel exhaust gas conditions with the SV = 16 400 h−1, in the temperature range from 200 to 460°C. When propylene was used as a reducing agent, Pt/Al2O3, Pt-ZSM-5 and Au/Al2O3 + Mn2O3 showed high catalytic activities in the low temperature range from 200 to 250°C. Cu-ZSM-5 (propylene as a reductant), Co/Al2O3 (methanol) and Ag/Al2O3 (ethanol) showed high activities at temperatures >350°C. Except for the manifestation of differences in the activity among catalysts, the general behaviors of these catalysts, such as the active temperature range, selectivity to N2O and emission of non-reacted or or incompletely oxidized reductants, were similar to that shown when model gas mixture systems were used.

Synergistic catalysis of carbon black oxidation by Pt with MoO3 or V2O5

Abstract A series of SiO2-supported MoO3, V2O5, and Pt catalysts were prepared for the study of model soot oxidation with simulated diesel exhaust gas. Composite samples of Pt with the metal oxides demonstrated higher oxidation activities than the single-component SiO2-supported MoO3, V2O5 or Pt catalysts in the absence of SO2 in the reactant gas. Based on the effects of NO2 on carbon oxidation, a synergistic reaction mechanism was suggested to explain the effects of combining Pt with the oxides: Pt catalyzes the oxidation of NO with gas phase O2 to NO2, while MoO3 and V2O5 catalyze the oxidation of carbon with NO2. Finally, the effects of SO2 on the carbon oxidation reaction were examined and discussed.