http://libir.tmu.edu.tw/bitstream/987654321/43034/1/4.pdf

Review of second-order models for adsorption systems.

ion. The oxidative addition mechanism was originally proposed22i because of the lack of a strong rate dependence on polar factors and on the acidity of the medium. Later, however, the electrophilic substitution mechanism also was proposed. Recently, the oxidative addition mechanism was confirmed by investigations into the decomposition and protonolysis of alkylplatinum complexes, which are the reverse of alkane activation. There are two routes which operate in the decomposition of the dimethylplatinum(IV) complex Cs2Pt(CH3)2Cl4. The first route leads to chloride-induced reductive elimination and produces methyl chloride and methane. The second route leads to the formation of ethane. There is strong kinetic evidence that the ethane is produced by the decomposition of an ethylhydridoplatinum(IV) complex formed from the initial dimethylplatinum(IV) complex. In D2O-DCl, the ethane which is formed contains several D atoms and has practically the same multiple exchange parameter and distribution as does an ethane which has undergone platinum(II)-catalyzed H-D exchange with D2O. Moreover, ethyl chloride is formed competitively with H-D exchange in the presence of platinum(IV). From the principle of microscopic reversibility it follows that the same ethylhydridoplatinum(IV) complex is the intermediate in the reaction of ethane with platinum(II). Important results were obtained by Labinger and Bercaw62c in the investigation of the protonolysis mechanism of several alkylplatinum(II) complexes at low temperatures. These reactions are important because they could model the microscopic reverse of C-H activation by platinum(II) complexes. Alkylhydridoplatinum(IV) complexes were observed as intermediates in certain cases, such as when the complex (tmeda)Pt(CH2Ph)Cl or (tmeda)PtMe2 (tmeda ) N,N,N′,N′-tetramethylenediamine) was treated with HCl in CD2Cl2 or CD3OD, respectively. In some cases H-D exchange took place between the methyl groups on platinum and the, CD3OD prior to methane loss. On the basis of the kinetic results, a common mechanism was proposed to operate in all the reactions: (1) protonation of Pt(II) to generate an alkylhydridoplatinum(IV) intermediate, (2) dissociation of solvent or chloride to generate a cationic, fivecoordinate platinum(IV) species, (3) reductive C-H bond formation, producing a platinum(II) alkane σ-complex, and (4) loss of the alkane either through an associative or dissociative substitution pathway. These results implicate the presence of both alkane σ-complexes and alkylhydridoplatinum(IV) complexes as intermediates in the Pt(II)-induced C-H activation reactions. Thus, the first step in the alkane activation reaction is formation of a σ-complex with the alkane, which then undergoes oxidative addition to produce an alkylhydrido complex. Reversible interconversion of these intermediates, together with reversible deprotonation of the alkylhydridoplatinum(IV) complexes, leads to multiple H-D exchange

Activation of c-h bonds by metal complexes

Cigarette smoke contains two very different populations of free radicals, one in the tar and one in the gas phase. The tar phase contains several relatively stable free radicals; we have identified the principal radical as a quinone/hydroquinone (Q/QH2) complex held in the tarry matrix. We suggest that this Q/QH2 polymer is an active redox system that is capable of reducing molecular oxygen to produce superoxide, eventually leading to hydrogen peroxide and hydroxyl radicals. In addition, we have shown that the principal radical in tar reacts with DNA in vitro, possibly by covalent binding. The gas phase of cigarette smoke contains small oxygen- and carbon-centered radicals that are much more reactive than are the tar-phase radicals. These gas-phase radicals do not arise in the flame, but rather are produced in a steady state by the oxidation of NO to NO2, which then reacts with reactive species in smoke such as isoprene. We suggest that these radicals and the metastable products derived from these radical reactions may be responsible for the inactivation of alpha 1-proteinase inhibitor by fresh smoke. Cigarette smoke oxidizes thiols to disulfides; we suggest the active oxidants are NO and NO2. The effects of smoke on lipid peroxidation are complex, and this is discussed. We also discuss the toxicological implications for the radicals in smoke in terms of a number of radical-mediated disease processes, including emphysema and cancer.

Free-radical chemistry of cigarette smoke and its toxicological implications.

Although technological practice should minimize environmental impact, this is not always economically feasible. During the past decade, for example, there has been increasing global concern over th...

CO2 Reforming of CH4

A review of the production of activated carbons from agricultural residues is presented. The effects of various process parameters on the pyrolysis stage are reviewed. Influences of activating conditions, physical and chemical, on the active carbon properties are discussed. Under certain process conditions several active carbons with BET surface areas, ranging between 250 and 2410 m 2 /g and pore volumes of 0.022 and 91.4 cm 3 /g, have been produced. A comparison in characteristics and uses of activated carbons from agricultural residues with those issued from tires, and commercial carbons, have been made. A review is carried out of the reaction kinetic modelling, applied to pyrolysis of agricultural wastes and activation of their pyrolytic char.

Agricultural residues as precursors for activated carbon production—A review

Etude de la pyrolyse avec adjonction permanente d'eau. Etude des composes formes ainsi que de l'aire superficielle du charbon actif

Preparation of activated carbon by thermal decomposition of used automotive tires

Reaction mechanism for styrene synthesis over polynaphthoquinone

Oxidative coupling of methane over Y2O3CaO catalysts

Infrared studies of the adsorption and the catalysis of hydrogen chloride on alumina and on silica

The surface structure, the environment and the distribution of the active sites of fixed Mo catalysts were spectroscopically investigated and compared with those of conventional catalysts made by an impregnation method. The fixed catalysts were found to have the tetrahedral dioxostructure of six-valent molybdenum with coordination unsaturation, uniformly and atomically populated at silica or alumina surface, in a different environment from that of the impregnation catalysts. Such properties of molybdenum are thought to be essential factors for catalytic action in the abstraction of a hydrogen atom(hydride) from the C—H bond of a reactant. There are three different types of molybdenum species in the impregnation silica catalysts.

Sadao Ogasawara

Papers

Preparation of activated carbon by thermal decomposition of used automotive tires

Reaction mechanism for styrene synthesis over polynaphthoquinone

Oxidative coupling of methane over Y2O3CaO catalysts

Infrared studies of the adsorption and the catalysis of hydrogen chloride on alumina and on silica

Spectroscopic study on the surface structure and environment of fixed Mo catalysts prepared by use of Mo(π-C3H5)4