Vapor phase hydroformylation of ethene over Co/SiO2 promoted by noble metals: dynamic in situ diffuse reflectance FT-IR study of surface species

An in situ diffuse reflectance FT-IR technique was employed to investigate the active surface species and the reaction mechanism of the oxygenate formation in the vapor phase hydroformylation of ethene on Co/SiO₂ promoted with various noble metals such as Ir, Rh, Pt, Re, Ru, and Pd. Co(A)/SiO₂ and Ir(CO)/SiO₂ which were derived from cobalt(II) acetate and Ir₄(CO)₁₂, respectively, were quite inactive in the reaction, and showed only quite small peaks of adsorbed CO under the conditions of 1.1 MPa of C₂H₄/CO/H₂ at 298 K. In contrast, Co(A)-Ir(CO)/SiO₂, which were very active in the reaction, exhibited strong absorption bands of linear and bridged CO species. At 423–463 K, propanal adsorbed on the catalyst and acyl species which is suggested as the intermediate for the formation of propanal were also observed on this catalyst. By exposing CO preadsorbed on this catalyst to C₂H₄/H₂ at 289 K and 0.1 MPa, the intensity of the linear CO band decreased, and the bands of propanal and acyl species emerged simultaneously, whereas that of the bridged CO band remained constant after the initial drop. These results suggested that the oxygenates are formed via the CO insertion into adsorbed ethyl species, and linear CO species plays a major role in the CO insertion on these noble metal-promoted cobalt catalysts.     

Synthesis and properties of N,N'-unsymmetrical dialkyl-3,4:9,10-perylenebis(dicarboximide)s

N,N'- Unsymmetrical dialkyl-3,4:9,10-perylenebis(dicarboximide)s (in which alkyl = methyl, ethyl, propyl, butyl, isobutyl, pentyl, hexyl and octyl) were prepared by the condensation of N-alkyl-3,4:9,10-perylene-tetracarboxylic monoanhydride monoimide with the appropriate alkyl-amines. The properties of these derivatives as pigments were tested and their thermal stability measured.     

Synthesis and properties of N-alkyl-N′-aryl-3,4:9,10-perylenebis(dicarboximide)

N′-Alkyl-N′-aryl-3,4:9,10-perylenebis(dicarboximide) (alkyl = isobutyl, pentyl, hexyl, octyl, etc.; aryl = phenyl, p-tolyl, p-methoxyphenyl, etc.) were prepared by the condensation of N-alkyl-3,4:9,10-perylene-tetracarboxylic monoanhydride monoimide with arylamines (aniline, p-toluidine, p-anisidine, o-phenylenediamine, etc.). The properties of these derivatives as pigments were tested, and also the thermal stability of 3,4:9,10-perylenebis(dicarboximide) derivatives was measured.     

A new scaling algorithm for the maximum mean cut problem

We present a new scaling algorithm for the maximum mean cut problem. The mean of a cut is defined by the cut capacity divided by the number of arcs crossing the cut. The algorithm uses an approximate binary search and solves the circulation feasibility problem with relaxed capacity bounds. The maximum mean cut problem has recently been studied as a dual analogue of the minimum mean cycle problem in the framework of the minimum cost flow problem by Ervolina and McCormick. A networkN=(G, lower, upper) with lower and upper arc capacities is said to be -feasible ifN has a feasible circulation when we relax the capacity bounds by ; that is, we use (lower(a)- , upper(a)+) bounds instead of (lower(a), upper(a)) bounds for each arca A. During an approximate binary search we maintain two bounds,LB andUB, such thatN is LB-infeasible andUB-feasible, and we reduce the interval size (LB, UB) by at least one-third at each iteration. For a graph withn vertices, m arcs, and integer capacities bounded byU, the running time of this algorithm is O(mn log(nU). This time bound is better than the time achieved by McCormick and Ervolina under thesimilarity condition (that is,U=O(n^o(1))). Our algorithm can be naturally used for the circulation feasibility problem, and thus provides a new scaling algorithm for the minimum cut problem.Research supported by a grant-in-aid of the Ministry of Education, Science and Culture of Japan.     

New catalytic technologies in Japan

Recent trends in R&D of catalytic technology in Japan (cleaner and more efficient production, environmental catalysts, and recycling processes) are overviewed and examples of recent achievements are listed. Examples are then described as zeolite-catalyzed organic reactions recently commercialized and expected to be commercialized: hydration of cyclohexene, synthesis of pyridine derivatives and gas-phase Beckmann rearrangement of cyclohexanone oxime. Finally, as an example of environmental catalysts, the NO_x storage–reduction type three-way automobile catalyst, is introduced.     

Heterogeneous Catalysis by Heteropoly Compounds of Molybdenum and Tungsten

Heteropolyanions are polymeric oxoanions which are formed by the condensation of more than two different oxoanions [Eq. (1)l. Polyanions consisting of one kind of oxoanion are called isopolyanions [Eq. (2)]. Acidic elements such as Mo, W, V, Nb, and Ta are present as oxoanions in aqueous solutions and polymerize to form polyanions at low pH. Free acids (or acid forms) of these species are called heteropoly and isopoly acids, respectively. Here, the term “heteropoly compounds” is used for heteropoly acids and their salts.     

Recent progress in the practical applications of heteropolyacid and perovskite catalysts: Catalytic technology for the sustainable society

Recent progresses in practical applications of (i) supported heteropolyacid and (ii) Pd/perovskite catalysts are described. (i) Two industrial catalytic processes, ethyl acetate and acetic acid syntheses both from ethylene, utilize silicotungstic acid, alone and together with Pd, respectively, carefully supported on silica, and exhibit high performance from green chemical and economical viewpoints. The layer structure of heteropolyacid on silica and physical properties of silica are among the key factors of the high performance. (ii) Pd/perovskite catalyst is applied for the treatment of automotive emission, where the catalyst life is very much elongated by embedding Pd into the perovskite lattice and hence resulted in much reduced usage of Pd. These are good examples of green catalytic technology that will contribute to the sustainable society.     

Relative rates of various steps of NO–CH4–O2 reaction catalyzed by Pd/H-ZSM-5

Reaction mechanism of the reduction of nitrogen monoxide by methane in an oxygen excess atmosphere (NO–CH₄–O₂ reaction) catalyzed by Pd/H-ZSM-5 has been studied at 623–703 K in the absence of water vapor, in comparison with the mechanism for Co-ZSM-5. Kinetic isotope effect for the N₂ formation in NO–CH₄–O₂ vs. NO–CD₄–O₂ reactions was 1.65 at 673 K and decreased with a decrease in the reaction temperature. In addition, H–D isotopic exchange took place significantly in NO–(CH₄+CD₄)–O₂ reaction. These results are in marked contrast with the case of Co-ZSM-5, for which the C–H dissociation of methane is the only rate-determining step, and show that the C–H dissociation is slow but not the only rate-determining step in the case of Pd/H-ZSM-5.

A reaction scheme was proposed, in which the relative rates of the three steps ((i)–(iii) below) vary depending on the reaction conditions.

Further, in contrast to Co-ZSM-5, NO_x–CH₄–O₂ reaction was much slower than CH₄–O₂ reaction for Pd/H-ZSM-5; the presence of NO_x retards the reaction of CH₄ over the latter catalyst, while it accelerates the reaction over the former. It is suggested that CH₄ is activated directly by the Pd atoms in the case of Pd/H-ZSM-5, but by NO₂ strongly adsorbed on Co ion for Co-ZSM-5. The reaction order of the NO–CH₄–O₂ reaction with respect to NO pressure was consistent with this mechanism; 1.05 for Pd/H-ZSM-5 and 0.11 for Co-ZSM-5.