Yusaku Takita

Catalytic activity of transition metal ion exchanged Y zeolites in the reduction of nitric oxide with ammonia

Catalytic reduction of nitric oxide with ammonia was studied over transition metal ion exchanged Y zeolites (MeY). Among various catalysts used, Cu(II)Y was found to be of particular interest, exhibiting low temperature activity coupled with an unusual activity-temperature profile. In the binary metal ion exchanged systems, where one of the component ions was fixed as Cu(II), promoting effects of the second ionic species were observed. This seems to be correlated with the oxidation potential of the second ion. Both NH3 and NO were adsorbed considerably on Cu(II)Y, suggesting that the NONH3 reaction proceeds between adsorbed molecules. Further, from the measurement of reaction kinetics, the mechanism was proposed to be a Langmuir-Hinshelwood type of reaction of NO and NH3 coordinated to Cu(II) ions.

Oxyhydrative scission of olefins: I. Oxidation of lower olefins

Abstract A new type of oxidation of C 2 -C 5 olefins leading to the oxidative scissions of carbon skeletons was examined on the V 2 O 5 -MoO 3 catalyst in the presence of water vapor. Acetic acid and acetaldehyde and acetic acid and propionic acid were selectively formed from C 2 -C 4 and C 5 olefins, respectively. The reaction was found to go through consecutive multisteps. Taking into account the similarities between the present oxidation and the oxyhydration reaction, it was concluded that the reaction comprises the oxyhydration of olefins to form ketones and the subsequent oxidative scission of the ketones to acids and aldehydes, thus best being named “oxyhydrative scission.” The reaction scheme was discussed in comparison with mechanisms for other types of olefin oxidation reactions.

Oxyhydrative scission of olefins: II. Examination of reaction mechanism

Abstract In the presence of water vapor and gaseous oxygen, lower olefins such as n -butenes are subject to oxidative scission over V 2 O 5 MoO 3 catalysts at 170–250 °C to form carboxylic acids and/or aldehydes. To examine the mechanism of this reaction, the effects of the acid-base character of catalysts and the feed of water vapor and gaseous oxygen on the reaction were investigated. The results show that, while acidic sites of catalysts, water vapor, and gaseous oxygen are all necessary for the reaction, water vapor in particular plays an important role, the cut of its feed causing a total loss of reactivity of olefins at temperatures below 250 °C. Results also show that the reaction proceeds consecutively through the oxyhydrative scission mechanism previously proposed; an olefin is hydrated on an acidic site of the catalyst to form an alcohol followed by oxidation to a ketone and oxidative scission to the final products. The oxidation of C 5 ketone isomers indicates that the last step, the oxidative scission of ketones, follows Popoffs law. In addition, reactivity orders of assumed intermediates show that, of the multiple reaction steps, the oxidative scission step is rate determining in propylene oxidation, while this step is faster than others in butene oxidation.

Oxyhydrative scission of olefins: III. An extension to various olefins and ketones

Abstract In an attempt to extend the oxyhydrative scission reaction which is typical with n-olefins, three olefins and four ketones with various structures have been subjected to oxidation over a V2O5-MoO3 ( V Mo = 9 1 ) catalyst in the presence of water vapor. Styrene was selectively oxidized at 453–533 K to benzaldehyde and benzoic acid in conformity with the proposed scission scheme. Cyclohexene and l-chloro-2-butene, however, were subjected to dehydrogenation and dehydrochlorination, respectively, at 423–533 K in preference to the scission reaction. Methylvinylketone underwent scission reaction to form acetic acid and carbon oxides at 423–473 K. 2-Chloro-3-butanone showed high reactivity even at 393 K and produced acetic acid very selectively; one of the expected scission products, acetylchloride, was hydrolyzed to acetic acid. Cycloketones, i.e., cyclopentanone and cyclohexanone, however, were oxidized only to carbon oxides. On the basis of these results the oxyhydrative scission mechanism and the requirements of reactants for it are discussed.