Junko Uchisawa

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.

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.

Screening of Catalysts for Acrylonitrile Decomposition

The catalytic decomposition of acrylonitrile over various metal components (Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn, Ga, Pd, Ag, and Pt) supported on several metal oxides (Al2O3, SiO2, TiO2, ZrO2, and MgO) and ZSM-5 was studied. The most promising catalyst was Cu-ZSM-5, which exhibited 100% conversion and at least 80% N2 selectivity above 350 °C.

The effect of layering of functionally different catalysts for the selective reduction of NOx with hydrocarbons

Abstract The performance of double-layered catalysts composed of a layer of Pt/SiO2 and a layer of H-ZSM-5 or Al2O3 wash-coated over the Pt/SiO2 layer for the selective reduction of NOx with hydrocarbons, was examined. Under synthetic gas conditions, the double-layered catalysts showed higher activity than did Pt/SiO2 without the secondary layer, the performance of H-ZSM-5 as an upper layer being better than that of Al2O3. Under practical, diesel exhaust-gas conditions, the combination of Pt/SiO2 with H-ZSM-5 was superior to a single layer of Pt-ZSM-5. The reaction scheme for the double-layered catalysts and factors affecting performance are discussed.

Morphology of active species of Ag/ZrO2 for low-temperature soot oxidation by oxygen

The catalytic oxidation of carbon black, a model soot, over Ag/ZrO2 was studied. Transmission electron microscopy observations revealed that Ag nanoparticles with sizes of 2–10 nm on the catalysts presented 3–10 wt% Ag loading. Temperature-programmed reaction and transient activity measurements of carbon black oxidation revealed that the oxidation rate also increased with an increasing number of Ag nanoparticles on the catalysts up to 5 wt% Ag loading. The catalytically active Ag species thus was concluded to be nanoparticles with sizes of 2–10 nm.

Method for selective removal of supported platinum particles from external zeolite surfaces: characterisation of and application to a catalyst for the selective reduction of nitrogen oxide by hydrocarbons

Abstract A method for selectively removing Pt particles supported on H–ZSM-5 (Pt/H–ZSM-5) from the external surfaces of zeolite crystals was investigated, using a reagent system composed of halogen–tetraethylammonium halide–organic solvent. The influence of the nature of the halogen and the treatment time on the quantity of Pt removed was studied. After treatment of the Pt/H–ZSM-5, the characterisation by hydrogen chemisorption, XPS and TEM indicated that the method is suitable for preparing a zeolite material that contains exclusively Pt particles confined in the grain boundaries of zeolite crystals (enveloped Pt). As an example of its application, the catalytic activity for the reduction of nitrogen oxides (NO x ) with n -dodecane in the presence of oxygen was studied. The results indicate a beneficial effect of removing Pt from the outermost surface of Pt/H–ZSM-5, with an increase in the selectivity of NO x reduction to N 2 from 25 to 45% at the maximum of NO x conversion. This effect was mainly attributed to the hindered access of the bulky hydrocarbon molecules to the enveloped Pt, thus favouring the reaction of the hydrocarbon with NO 2 formed by the oxidation of NO on the Pt sites.

Study on the catalytic oxidation of soot from diesel engines

Abstract The influence of contact between carbon black(CB), a model soot, and solid catalysts on the catalytic oxidation of CB was investigated under simulated gaseous conditions. Water condensation was found to have a big promotive effect on the carbon oxidation. The effect of reactant gas composition on the catalytic reaction was also studied for KVO 3 /SiC. The results showed that during the reaction process KVO 3 partly changes into K 2 SO 4 and V 2 O 5 which are more stable and catalytically active under simulated gaseous conditions. Based on these results, a large number of single or mixed sulfates were screened. Most of them were found to be active for carbon oxidation. Among them, mixed sulfates containing vanadium were most active.

Characterization of Cu species on SiO2 and ZSM-5 by temperature-programmed reduction by ammonia

We studied the temperature-programmed reduction by NH3 (NH3-TPR) as a supplement to the temperature-programmed reduction by H2 (H2-TPR) for the characterization of supported Cu species. The NH3-TPR profile of Cu/SiO2, which contained only bulk CuO, exhibited two peaks for N2 formation in equal amounts, suggesting stepwise reduction of the bulk CuO. In contrast, the H2-TPR profile exhibited only one H2 consumption peak. We also studied Cu-NaZSM-5 samples with various Cu and Na loadings. The Cu ions on ZSM-5 were reduced to Cu+ but no further. Kinetic analysis revealed that the NH3-TPR profile exhibited peaks for separate reductions of isolated and binuclear Cu2+ ions. Thus, we found NH3-TPR to be useful for detailed analysis of the reducibility of Cu2+ to Cu+ in zeolite pores.

Formation of nitroethylene during selective catalytic reduction of NO2 by C2H4 over H-ferrierite

Nitroethylene, formed during the selective catalytic reduction (SCR) of NO2 by C2H4 over H-ferrierite, was determined to be an intermediate in SCR due to its decomposition behavior in forming N2.