http://www1.udel.edu/chem/polenova/PDF/Polyoxometalates/POMs_Catalysis_NMR_ChemRev1998.pdf

Catalysis by Heteropoly Acids and Multicomponent Polyoxometalates in Liquid-Phase Reactions

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

UV-Visible ار راد ن .د TiO2 ( تیفرظ راون مان هب نورتکلا یاراد یژرنا زارت لماش VB و ) رگید زارت ی یژرنا اب ( ییاناسر راون مان هب نورتکلا زا یلاخ و رتلااب VB یم ) .دشاب ت ود نیا نیب یژرنا توافت یژرنا فاکش زار ، پگ دناب هدیمان یم .دوش هک ینامز زا نورتکلا لاقتنا VB هب VB یم ماجنا دریگ ، TiO2 اب ودح یژرنا بذج د ev 2 / 3 ، نورتکلا تفج کی دیلوت یم هرفح .دیامن و نورتکلا هرفح ی نا اب هدش دیلوت یم کرتشم حطس هب لاقت ثعاب دناوت شنکاو ماجنا اه یی ددرگ . TiO2 دربراک ،دراد یدایز یاه هلمج زا یم ناوت اوه یگدولآ هیفصت یارب (CO2) و بآ و ... نآ زا هدافتسا درک .

Advanced Nanoarchitectures for Solar Photocatalytic Applications

Ordered mesoporous materials in catalysis

The open literature concerning chemical and mechanistic aspects of the selective catalytic reduction of NO by ammonia (SCR process) on metal oxide catalysts is reviewed. Catalytic systems based on supported V2O5 (including the industrial TiO2-supported V2O5–WO3 and/or V2O5–MoO3 catalysts) and catalysts containing Fe2O3, CuO, MnOx and CrOx are considered. The results of spectroscopic studies of the adsorbed surface species, adsorption–desorption measurements, flow reactor and kinetic experiments are analyzed. The proposed reaction mechanisms are described and critically discussed. Points of convergence and of disagreement are underlined.

Chemical and mechanistic aspects of the selective catalytic reduction of NOx by ammonia over oxide catalysts: A review

Mukaiyama-aldol reactions of carbonyl compounds with silyl enol ethers were well catalyzed on siliceous mesoporous materials (MCM-41). The reactivity of acetals was much higher than that of aldehyde. The reactions proceeded selectively at 273–298 K on the catalyst of 30 mg per mmol of the substrate.

Selective Aldol Reactions of Acetals on Mesoporous Silica Catalyst.

Proton exchanged ultrastable Y-type zeolite showed a pronounced catalytic activity for the formation of acetone directly from propene and water. The formation rate of acetone was higher or comparable to those on MoO3-based catalysts in the oxidation of propene by oxygen to produce acetone.

One-Step Formation of Acetone from Propene and Water on Ultrastable Y- Type Zeolite Catalyst.

Conversion of No to Nh3 Using C3h6 Over Tio2-Supported Ag Catalysts in the Presence of a Large Excess of Oxygen and Water Vapor: Turning Hazardous Waste into a Resource

Catalysts for the NO to NH3 reaction in the presence of 10% O2 and 10% H2O were investigated on a TiO2(rutile) support. The activity sequence of the various metals supported...

Catalysts for selective conversion of nitric oxide to ammonia (NTA) with propene in the presence of large excess oxygen and water vapor

The reaction of Ag2O with NO has been studied in the range 333–473 K with flow and batch reactors. The reaction products are Ag[NO2], Ag[NO3], Ag, and NO2. A change in the products with reaction times reveals that [AgNO2] is the primary product by reaction (i), Ag2O + NO → Ag[NO2]+ Ag, and then decomposes to Ag[NO3] with the evolution of NO by reaction (ii), 2 Ag[NO2]→ Ag[NO3]+ Ag + NO. When Ag[NO2] is a starting material, reaction (iii), Ag[NO2]→ Ag + NO2, occurs together with (ii). Reaction (i) occurs mainly at ⩽353 K and the reaction order with respect to [NO] is close to unity. Reactions (ii) and (iii) proceed at 353 K and are inhibited by NO. At 453 K in the flow system, Ag[NO3] reacts further with NO through (iv), Ag[NO3]+ NO → Ag + 2NO2. In the static system, on the other hand, (iv) does not proceed. This difference is suggested to result from NO2 inhibition of reaction (iv).

Masakazu Iwamoto

Papers

Selective Aldol Reactions of Acetals on Mesoporous Silica Catalyst.

One-Step Formation of Acetone from Propene and Water on Ultrastable Y- Type Zeolite Catalyst.

Conversion of No to Nh3 Using C3h6 Over Tio2-Supported Ag Catalysts in the Presence of a Large Excess of Oxygen and Water Vapor: Turning Hazardous Waste into a Resource

Catalysts for selective conversion of nitric oxide to ammonia (NTA) with propene in the presence of large excess oxygen and water vapor

Reaction of silver(i) oxide with nitrogen monoxide