Hideaki Muraki

Nitric oxide reduction performance of automotive palladium catalysts

Reduction of nitric oxide over palladium catalysts under reducing conditions was examined by using cycled feeds and steady non-cycled feeds. The effects of lanthanum(III) oxide on the catalytic properties of α-alumina-supported palladium for the reduction of nitric oxide were studied by X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) and chemisorption of propene. The reduction of nitric oxide on palladium catalysts is significantly inhibited by hydrocarbon. However, the reduction activity is improved by both the periodic operation effect and the addition lanthana to the catalyst. The mechanism of the periodic operation effect is interpreted in terms of the strong adsorption of hydrocarbons. The addition of lanthana to the catalyst substantially moderated this hydrocarbon poisoning. The conversion of nitric oxide on the Pd/La2O3 catalyst with cycled feeds was similar to that on a rhodium catalyst. The XPS, TPR and hydrocarbon chemisorption studies showed that the presence of lanthana provided palladium oxide in a hardly-reduced state and suppressed the chemisorption of hydrocarbons on the palladium oxide.

Periodic operation effects in propane and propylene oxidation over noble metal catalysts

Abstract It had been observed that under cycling conditions, the catalytic activities of three-way automotive catalysts are superior to those under static conditions, and that catalyst performance depends on the cycling period and feedstream conditions. The oxidation of propylene and propane over platinum, palladium and rhodium catalyst under static and periodic conditions was therefore investigated. The results were as follows; (i) the order of catalytic acitivities was Pd>Pt>Rh for propylene—oxygen and Pt>Rh>Pd for propane-oxygen; (ii) the periodic operation effect is dependent on both catalyst species and reaction temperature; (iii) the optimum period for the maximum conversion decreases with increasing temperature; and (iv) from results of the partial reaction order and evolution pattern analysis, either hydrocarbons or oxygen self-poison the reaction on the catalysts. The order of sensitivity to self-poisoning corresponds to the order of the periodic operation effect.

Effect of lanthanum on the no reduction over palladium catalysts

Abstract A palladium-lanthanum (Pd-La) catalyst was found to be more active for NO reduction than a palladium (Pd) catalyst under the reducing conditions found in engine exhaust gas. Both the Pd-La and Pd catalysts had same activities for the NO reduction with CO. However, in the presence of hydrocarbons, the NO reduction activity of a Pd-La catalyst was much better than that of a Pd catalyst. The NO reduction of the Pd catalyst was significantly inhibited by hydrocarbons. The behavior of the adsorbed hydrocarbons on the both catalysts were studied by means of the transient response method. The hydrocarbon was more strongly adsorbed on the Pd catalyst than on the Pd-La catalyst. Also, the partial oxidation activity of hydrocarbon for the Pd-La catalyst was much better than that for the Pd catalyst. The presence of lanthanum in the Pd-La catalyst perhaps weakens the adsorption strength of hydrocarbons.

Effect of Severe Thermal Aging on Noble Metal Catalysts

Abstract Both sintering and activity behaviours over noble metal catalysts aged in oxidative atmospheres with various O 2 contents at 1100°C (or 1000° C) for 5 h were systematically characterized. With increasing O 2 contents, catalytic activities over aged Pt, Rh, and Pt/Rh catalysts decreased, and, in contrast, those over aged Pd and Pd/Rh catalysts increased. While, an order of sintering for the noble metal particles on aged catalysts agreed closely to that of the each percentage conversions as well as to that of vapour pressures of respective catalyst species, such as noble metals or their oxides. Selectivity profiles of the aged catalysts for converting NO and O 2 in a simulated exhaust gas were characteristic ones. It is confirmed through the above results that the performance of aged catalysts are tightly governed by the properties of noble metals and the selectivity data are also important for exploring the catalytic activities, in particular, over multi-functional catalysts such as automotive exhaust ones.

Periodic Operation Effects on Automotive Noble Metal Catalysts — Reaction Analysis of Binary Gas Systems

Catalytic activities and periodic operation effects in various binary gas systems (CO-O2, NO-CO, NO-H2, C3H6-O2, and C3H8-O2) over Pt, Pd, and Rh/α-Al2O3 were compared. In all reaction systems, periodic operation effects were found to some extent. That is, the conversion improved in the cycling feed compared to the static one. The periodic operation effects occurred most noticeably for catalysts having lower catalytic activity as a result of the difference of adsorption capability between the two reactants.

Steam reforming of n-heptane using a Rh/MgAl: I. Support and kinetics2O4 catalyst

Abstract A Rh/MgAl2O4 catalyst was found to be active for the steam reforming of n-heptane in the range 400–500°C. The MgAl2O4 support was prepared by calcining of a mixture of α-alumina and magnesia powders at 1420°C. The development of pore structure in MgAl2O4 support was examined with SEM, XRD and porosimetry before and during calcination. The pores are found to originate from voids among MgAl2O4 particles produced by solid reaction that magnesia was diffusing to alumina particles. Therefore, the pore size is able to control as a result of control of alumina particle size. In order to clarify the role of this support, a kinetic study on the reaction between n-heptane and steam was conducted at 500°C and 1 atm. The initial reaction rate, r0 (mol g−1h−1), obtained experimentally is best expressed by the following equation: r0=k(KP0C7H161+KP0C7H16)(K′P0H2O1+K′P0H2O) wherek (0.071 mol/g h) is the apparent rate constant, p0j are the partial pressures of reactantsj in the feed gas andK (111 atm−1) andK′ (0.712 atm−1) are the adsorption equilibrium constants for n-heptane and water, respectively. It is confirmed that steam reforming of n-heptane proceeds through the adsorption of n-heptane on rhodium metal and of steam on the support surface. The characteristics of the composition distribution of products shows that carbon monoxide is a primary product in the reaction system and both carbon dioxide and methane are the secondary products.

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)

A new catalyst system for endothermic gas production

Research has been conducted on a gas carburizing atmosphere system for better quality control and energy savings. In this paper a new and excellent catalyst for producing endothermic gas at low temperatures is introduced.The conventional endothermic gas catalysts, such as a nickel catalyst, are used in a space velocity (SV) of 400–600/hr at a high temperature (about 1100° C). The new catalyst can be used in a high space velocity of 6000–12000/hr at a lower temperature (about 950° C). The composition of the new catalyst is cobalt supported on an alumina magnesia spinel.The catalyst was examined under various severe conditions. As a result, the catalyst’s deterioration was almost never observed under normal operating conditions (SV: 12000/hr, 930° C). The durability tests using various practical reforming furnaces were successfully conducted from 6–16 months. The higher efficiency and lower operating temperature of this new process results in an electrical energy savings of about 40%.