Tatsuo Miyadera

Alumina-supported silver catalysts for the selective reduction of nitric oxide with propene and oxygen-containing organic compounds

The selective catalytic reduction of nitric oxide with propene and oxygen-containing organic compounds over several alumina-supported metal catalysts was investigated. Alumina-supported silver catalysts showed high activities in the presence of water and excess oxygen, while water vapor significantly decreased the activities of alumina and Co/Al2O3 which were highly active in the absence of water. It was also found that oxygen-containing organic compounds such as ethanol and acetone were more effective than propene in reducing nitric oxide over Ag/Al2O3 in the presence of water and excess oxygen.

Selective catalytic reduction of NOx with CH3OH, C2H5OH and C3H6 in the presence of O2 over Ag/Al2O3 catalyst: Role of surface nitrate species

The involvement of the reaction of surface nitrate [NO3−(ads)] species with different reductants (C3H6, C2H5OH and CH3OH) in the selective catalytic reduction of nitrogen oxides (NOx) over a Ag/Al2O3 catalyst has been studied by in situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and temperature-programmed desorption (TPD). When an NO/O2 mixture was exposed to a Ag/Al2O3 catalyst at 150 °C, three kinds of nitrate species (bridging, monodentate and bidentate) were observed by DRIFT. The thermal stability of the monodentate NO3−(ads) species was higher than that of the bridging and bidentate NO3−(ads) species, which was confirmed by DRIFT and TPD measurements. The monodentate NO3−(ads) species reacted effectively with C2H5OH and CH3OH in the presence of O2 to form surface isocyanate [NCO(ads)] species at 250 °C, whereas the bridging and bidentate NO3−(ads) species reacted minimally. All NO3−(ads) species were largely unreactive with C3H6 in the presence of O2 at temperatures below 250 °C. On the other hand, the order of reactivity in the reduction of NOx at temperatures below 350 °C was in good agreement with that of both the reactivity of the monodentate NO3−(ads) species and the ease of NCO(a) formation (C2H5OH>CH3OH>C3H6). Based on these findings, the involvement of the reactivity of NO3−(ads) species and the formation of NCO(ads) species in the selective reduction of NOx are discussed.

Hydrogen-transfer hydrodehalogenation of aromatic halides with alcohols in the presence of noble metal catalysts

Abstract Catalytic hydrodehalogenation of aromatic halides was carried out in an alcohol solution containing base compounds in the presence of carbon-supported noble metal catalysts. It was found that dechlorination of 1,2,4-trichlorobenzene to benzene effectively occurred in a 2-propanol solution of a base compound such as NaOH or KOH in the presence of Rh/C or Pd/C at temperatures below 65°C. When deuorium-labeled 2-propanol, CD 3 CD(OD)CD 3 , was used as a solvent, 1,2,4-trichlorobenzene was dechlorinated to give benzene containing D atoms with high yield, indicating that the hydrodechlorination reaction includes hydrogen-transfer from 2-propanol to chlorobenzenes. Iodo-, bromo- and fluoro-benzenes were also readily dehalogenated in the catalytic system.

Reactivity of surface isocyanate species with NO, O2 and NO+O2 in selective reduction of NOχ over Ag/Al2O3 and Al2O3 catalysts

Reactivity of surface isocyanate (NCO(a)) species with NO, O2 and NO+O2 in selective reduction of NOχ over Ag/Al2O3 and Al2O3 catalysts was studied by a pulse reaction technique and an in situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The NCO(a) species on Ag/Al2O3 reacted with O2 or NO+O2 mixture gas to produce N2 effectively above 200°C, while the reaction of NCO(a) with NO hardly produced N2 even at 350°C. In the case of Al2O3 alone, less N2 was detected in the reaction of NCO(a) with NO+O2, indicating that silver plays an important role in the N2 formation from NCO(a). These behaviors of the reactivity of NCO(a) species with reactant gases were in good agreement with the changes in NCO(a) bands shown by in situ DRIFT measurements. Based on these findings, the role of NCO(a) species in the selective reduction of NOχ on Ag/Al2O3 and Al2O3 catalysts is discussed.

Characterization of highly active silver catalyst for NOx reduction in lean-burning engine exhaust

A new Ag/Al2O3 catalyst for removing NOx in lean exhaust gas was developed. Oxidized Ag/Al2O3 catalyst is highly active for reduction of NOx with ethanol and propene, whereas reduced Ag/Al2O3 catalyst is less active for these reactions. Selectivity to N2 is also high on the oxidized Ag/Al2O3 compared to that on the reduced Ag/Al2O3. XRD and SEM studies of these two types of Ag catalysts suggest that oxidation induces an interaction between Ag and the support, where the particles are grown in large size. In contrast, the metallic Ag particles are finely dispersed by the reduction process. Although dispersion of Ag particles is decreased by the oxidation process, the catalytic activity is increased. This suggests that the Ag-alumina sites created in the high temperature oxidizing environment are active in catalytic reduction of NOx.

Selective reduction of NOx by ethanol on catalysts composed of Ag/Al2O3 and Cu/TiO2 without formation of harmful by-products

Abstract An attempt was made to remove by-products such as NH 3 , CH 3 CN, HCN, CO and CH 3 CHO which are produced from the reduction of lean NO x by ethanol over an alumina-supported silver catalyst. The efficiency of titania-supported noble metals, vanadium oxide, tungsten oxide, and copper sulfate for the removal of these compounds was examined. It was found that NH 3 , CH 3 CN, and HCN were easily oxidized to NO x and that the reduction of NO x to N 2 by these nitrogen-compounds did not occur effectively on noble metal catalysts. Among the tested catalysts, CuSO 4 /TiO 2 was the most effective for simultaneously removing NH 3 , CH 3 CN, and HCN and reducing NO x to N 2 by using these nitrogen-compounds. Lean NO x were reduced to N 2 by ethanol effectively and the concentration of nitrogen-containing by-products was lowered over the composite catalyst, Ag/Al 2 O 3 +CuSO 4 /TiO 2 . However, in addition to CuSO 4 /TiO 2 , Pt/TiO 2 was required to remove harmful compounds completely. Consequently, a three-component composite catalyst, Ag/Al 2 O 3 +CuSO 4 /TiO 2 +Pt/TiO 2 , has been employed in reducing lean NO x by ethanol. This composite catalyst has proved to be quite effective even in the presence of water vapor in that it can reduce lean NO x to N 2 by ethanol effectively and sufficiently lower the concentrations of all harmful by-products.

Catalytic dechlorination of aromatic chlorides with noble-metal catalysts under mild conditions: approach to practical use

Abstract Catalytic dechlorination of aromatic chlorides was carried out in a solution of NaOH in 2-propanol with a carbon-supported Rh-based catalyst (Rh-Pt/C) at temperatures below 35°C. It was found that the dechlorination rate of aromatic chlorides (chlorobenzene, p -chlorotoluene, and 4-chlorobiphenyl) is strongly dependent upon the substituents. The dechlorination rate is hardly affected by the presence of water (ca. 10%), even under aerobic conditions, although the catalytic activity is suppressed significantly in the presence of acetone (ca. 5%). The catalyst life was evaluated both in a batch system and in a continuous-flow system. The catalytic activity gradually decreased, probably because of an accumulation of NaCl on the catalyst surface. The deactivated catalyst could be reactivated by washing it with water.

Selective reduction of nitric oxide with ethanol over an alumina-supported silver catalyst

Abstract Nitric oxide was effectively reduced by ethanol over an alumina-supported silver catalyst in the presence of excess oxygen and water vapor. In this reduction, though NO was mainly converted to N2, there was also a substantial amount of nitrogen-containing by-products such as N2O, NH3, CH3CN, HCN. There was also a very small amount of by-products — HNCO and NH4OCN (and/or urea, an isomer). The effects of silver content of the catalysts, water vapor, space velocity, and ethanol concentration on the reduction of NO were studied. The mechanism for the formation of nitrogen-containing compounds was also examined on the basis of the reactions of model compounds and the analyses of the products.

Infrared study of catalytic reduction of lean NOx with alcohols over alumina-supported silver catalyst

Two intense IR absorption bands due to surface isocyanate (-NCO) species have been observed at 2262 and 2232 cm−1 when an alumina-supported silver catalyst is exposed to a mixture of NO, O2 and ethanol at 150°C and subsequently heated to > 300°C in vacuum. The intensity of the isocyanate band is hardly affected by the water existing in the mixture. Methanol is less reactive than ethanol for the formation of isocyanate species. The reaction mechanism of catalytic reduction of lean NOx with alcohols is discussed based on these IR spectroscopic findings.

In situ diffuse reflectance infrared Fourier transform spectroscopy study of surface species involved in NOx reduction by ethanol over alumina-supported silver catalyst

Abstract In situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy has been used to investigate the surface species involved in NOx reduction by ethanol over alumina-supported silver catalyst. The experiments were carried out in dynamic conditions (under reaction mixture flow and reaction temperature) at atmospheric pressure. The DRIFT measurements were combined with gas chromatography (GC) analysis to monitor the N2 formation under reaction mixture and when the reaction mixture flow was switched to He followed by heating the catalyst under He flow (mixture, 250°C→He, 250°C→heating under He). A parallelism has been observed between the isocyanate band change and N2 formation during the step change experiment using an initial C2H5OH/NO/O2/He reaction mixture. Furthermore, the isocyanate species (NCO) were found to be generated from the decomposition of adsorbed organic nitro compounds formed under both ethanol/NO/O2/He and ethanol/NO/He and reaction mixtures. The role of oxygen in NOx reduction process was determined by comparing the result of different step-change experiment using an initial reaction mixture containing oxygen and without oxygen.