Yuji Ukisu

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.

Surface isocyanate intermediate formed during the catalytic reduction of nitrogen oxide in the presence of oxygen and propylene

IR spectroscopic measurements have revealed that an IR band ascribable to adsorbed isocyanate species grows up when alumina-supported Cu-Cs oxide catalyst is exposed to a mixture of NO, O2 and C3H6 at room temperature and subsequently heated to 400 °C in vacuum. The species produces N2, CO2 and CO in the ratio of ca. 2:1:1 in the presence of NO at 350°C. Alumina and alumina-supported Cu oxide catalyst are less active for the formation of isocyanate species.

Possible role of isocyanate species in NOx reduction by hydrocarbons over copper-containing catalysts

The behavior of an isocyanate intermediate (-NCO) formed during NOx reduction has been studied on alumina-supported CuCs oxide catalyst in the presence of oxygen and hydrocarbons (propene, acetylene, propane and n-heptane) using infrared spectroscopy. While a reaction involving NO, O2 and acetylene needs some heat treatment to produce the isocyanate species on the catalyst, no heat treatment is required in the NO/O2/propene or n-heptane system. No isocyanate intermediate is formed in a NO/O2/propane system by an ordinary procedure. Adsorbed water on the catalyst surface is found to suppress the formation of the isocyanate species. This inhibition effect is smaller in the acetylene or n-heptane containing system than in the propene containing system. The role of isocyanate species is discussed with reference to results for the practical reduction of NOx.

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.

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.

Catalytic dechlorination of polychlorinated biphenyls with carbon-supported noble metal catalysts under mild conditions

Polychlorinated biphenyls (PCBs) were effectively dechlorinated to biphenyl and phenylcyclohexane using a 2-propanol solution of sodium hydroxide in the presence of carbon-supported noble metal catalysts (Pd/C, Rh/C) at the temperatures below 82°C. Total amounts of the dechlorinated aromatic products and chlorine ions after the complete dechlorination were in good agreement with theoretical ones. It was postulated that the dechlorination reaction includes hydrogen transfer from 2-propanol to PCBs.

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.

Activity enhancement of copper-containing oxide catalysts by addition of cesium in the reduction of nitric oxide

Catalytic reduction of nitric oxide in the presence of propylene and oxygen over alumina and copper-containing oxide catalysts has been studied. The optimum temperature for this reaction is dependent upon the composition of the catalysts: ≈ 640 K on Cu-Cs/Al2O3, ≈ 680 K on Cu/Al2O3, and ≈ 780 K on Al2O3. IR spectroscopic measurements show that an isocyanate (−NCO) intermediate formed on Cu-Cs/Al2O3 is more reactive with NO to give N2 than the intermediate produced on Al2O3 and Cu/Al2O3. Electron donation from Cs to Cu may activate the intermediate.