Kouji Yokota

Effect of the addition of transition metals to Pt/Ba/Al2O3 catalyst on the NOx storage-reduction catalysis under oxidizing conditions in the presence of SO2

Abstract The NO x storage-reduction catalysis under oxidizing conditions in the presence of SO 2 has been investigated on Pt/Ba/Fe/Al 2 O 3 , Pt/Ba/Co/Al 2 O 3 , Pt/Ba/Ni/Al 2 O 3 , and Pt/Ba/Cu/Al 2 O 3 catalysts compared with Pt/Ba/Al 2 O 3 , Pt/Fe/Al 2 O 3 , Pt/Co/Al 2 O 3 , Pt/Ni/Al 2 O 3 , Pt/Cu/Al 2 O 3 and Pt/Al 2 O 3 catalysts. The NO x purification activity of Pt/Ba/Fe/Al 2 O 3 catalyst was the highest of all the catalysts investigated in this paper after an aging treatment. That of the aged Pt/Ba/Co/Al 2 O 3 and Pt/Ba/Ni/Al 2 O 3 catalysts was essentially the same as that of the aged Pt/Ba/Al 2 O 3 catalyst, while that of the aged Pt/Ba/Cu/Al 2 O 3 and Pt/Cu/Al 2 O 3 catalysts was substantially lower than the others. The Fe-compound on the aged Pt/Ba/Fe/Al 2 O 3 catalyst has played a role in decreasing the sulfur content on the catalyst after exposure to simulated reducing gas compared with the Pt/Ba/Al 2 O 3 catalyst without the Fe-compound. XRD and EDX show that the Fe-compound inhibits the growth in the size of BaSO 4 particles formed on the Pt/Ba/Fe/Al 2 O 3 catalyst under oxidizing conditions in the presence of SO 2 and promotes the decomposition of BaSO 4 and desorption of the sulfur compound under reducing conditions.

Effect of periodic operation over Pt catalysts in simulated oxidizing exhaust gas

Abstract The effect of periodic operation over Pt and Pt/Ba catalysts supported on γ-alumina under oxidizing conditions was investigated using simulated automotive exhaust gas from lean-burn combustion. The conversion of hydrocarbons and NOx was measured in cycled feedstream and steady feedstream under oxidizing conditions. The activities of the catalysts were improved in the cycled feedstream between oxidizing and reducing atmospheres under average oxidizing conditions. In particular, the NOx reduction on the Pt/Bt catalyst was higher than that on the Pt catalyst in the cycling operation. From the mass spectral analysis in streams of NO O2 C3H6 and NO O2 H2 (balance He) gas, it was found that NO was oxidized and stored on the Pt/Ba catalyst under oxidizing conditions, and that the stored NOx on the catalyst was subsequently reduced to N2 under reducing conditions.

ESR study of the deactivation of Cu-ZSM-5 in a net oxidizing atmosphere

A microscopic study of the deactivation of Cu-ZSM-5 was carried out. The activity of Cu-ZSM-5 for NOx reduction with hydrocarbons decreased when heated above 600°C in a simulated net oxidixing exhaust gas.27Al and29Si nuclear magnetic resonance results revealed that a dealumination of the zeolite occurs in the deactivated Cu-ZSM-5. Electron spin reonance (ESR) results indicated that aggregation of copper ions did not occur and copper remained as isolated ions in Cu-ZSM-5 even after the deactivation. The ESR spectra of dehydrated Cu-ZSM-5 suggested the migration of copper ions in the zeolite after the deactivation. To investigate the interactions between copper ions and NO/C3H6, the ESR spectra were measured after exposure to nitric oxide and propene. The ESR results indicated that the oxidation state and coordination structure of the copper ions were changed by the adsorption of nitric oxide or propene in active Cu-ZSM-5. On the other hand, no such reaction was observed in the deactivated Cu-ZSM-5. In the deactivated Cu-ZSM-5, copper ions remain atomically dispersed but cannot interact with nitric oxide or propene. In conclusion, the deactivation of Cu-ZSM-5 is suggested to occur through the migration of copper ions to sites where gas molecules like nitric oxide and propene cannot reach them. This migration is triggered by the dealumination of the zeolite.

Effect of the addition of Fe on catalytic activities of Pt/Fe/γ-Al2O3 catalyst

Abstract The catalytic activities of stoichiometric and lean mixture simulated exhaust from automotive engines have been investigated on bimetallic Pt/Fe/Al2O3 catalysts after the O2, O2–H2, and O2–H2–O2 treatments and compared to that of Pt/Al2O3 catalysts. The state of the Pt particles of the Pt/Fe/Al2O3 catalysts was also investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM). The activity of the Pt/Fe/Al2O3 catalyst was greater than that of the Pt/Al2O3 catalyst after the O2–H2–O2 treatment for the stoichiometric mixture. Also, the activity of the Pt/Fe/Al2O3 catalyst after the O2–H2 treatment was greater than that after the O2 and O2–H2–O2 treatments. Pt particles were found to react with Fe additives to form homogeneous Pt/Fe alloy particles on Al2O3 under reducing conditions. Also, the Pt/Fe alloy particles on Al2O3 were found to segregate into Pt and Fe2O3 and to form a Fe2O3 coverage layer on Pt particles so that Pt particles were prevented from sintering when heated at 800°C for a lean mixture. On the other hand, the activity of the Pt/Al2O3 catalyst was greater than that of the Pt/Fe/Al2O3 catalyst after the O2–H2–O2 treatment for lean mixture. The layer of Fe2O3 on Pt is responsible for the low activity.

Comparative NOx reduction behavior of Pt, Pd, and Rh supported catalysts in simulated exhaust gases as a function of oxygen concentration

NOx reduction activity on Pt and Pd catalysts had a maximum for S value as stoichiometry number at a fixed temperature, and the S value at the maximum NOx conversion increased with decreasing temperature. NOx conversion on Rh catalyst increased with decreasing S value, but independent of temperature. As for the effect of HC on NOx reduction behavior, it was concluded that, for Pt and Pd catalysts, HC adsorbs strongly on the catalysts surface to cause the self-inhibition. Increasing O2 concentration lead to oxidation of HC, but decreased the value of NO/O2 ratio. The balance point of the two factors generated a maximum NOx conversion. For Rh catalyst, the strongly adsorbed oxygen is more reactive with decreasing S value, and thus NOx conversion is increased.

Rh-free three-way catalysts for automotive exhaust control

Platinum (Pt), palladium (Pd) and rhodium (Rh) catalysts were evaluated on an engine dynamometer to examine the effects of air-fuel ratio (a/f), a/f amplitude and its frequency on the conversion efficiencies of NO-x, THC and CO. Under steady-state conditions, Rh is more suitable for NO-x conversion than Pt and Pd. The Pt and Pd catalysts give higher conversions in dynamic-states than in steady-states. With increasing a/f amplitude, a/f for the maximum NO-x conversion is shifted to rich side, while a/f for the maximum THC and CO conversions are shifted to lean side. At the stoichiometric point, both Pt and Pd show the maximum conversions for particular frequency and their frequencies are shifted to higher values with increasing a/f amplitude. If the a/f amplitude and the frequency are selected to be optimum, Pt and Pd may be used as three-way catalysts (twc). As a result of the durability test which was accomplished until 50000 km, Pd was promised as a main component of Rh-free twc. (Author/TRRL)