Pt y Pd soportado en carbón activado para la oxidación de 5-hidroximetilfurfural a ácido 2,5-furanodicarboxílico (original) (raw)
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Effect of Pt:Pd ratio on CO and hydrocarbon oxidation
For several reasons, typical diesel oxidation catalysts (DOCs) contain a mixture of Pt and Pd and in this study, the effect of the Pt:Pd ratio on a DOC’s ability to oxidize CO and different hydrocarbon types was investigated. The concentrations and types of pollutant species were used to simulate those found in low temperature combustion (LTC) engine exhaust. Representative hydrocarbon species were selected; C2H4 (short-chain alkene), C2H6 (short-chain alkane), C6H14 (long-chain alkane) and C7H8 (aromatic). Two types of experiments were performed, one in which the oxidation of each hydrocarbon or CO reactant was examined individually (simple feed conditions), and the second in which all reactants were added together (full feed conditions). Under the simple feed conditions, CO and C2H6 oxidation increased with increasing Pd content, while C2H4 and C6H14 oxidation improved with higher Pt content. When the full mixture of CO and hydrocarbons was used, hydrocarbon oxidation light off consistently followed that of CO, regardless of the Pt:Pd ratio, due to strong inhibition by CO. The best CO oxidation activity was observed over the Pd-only catalyst, and performance over the bimetallic samples was a function of both CO inhibition and Pt:Pd ratio. More specifically, as Pd content increased, CO inhibition was dampened, and as Pt content increased its inherent activity toward alkene oxidation became significant. Since inhibition is a function of the Pt/Pd content and the individual metals have different inherent activities toward the oxidation of different hydrocarbons, results obtained from the experiments with the simple feed could not be directly correlated to those from the experiments with the mixture of hydrocarbons.
Theoretical studies of the oxidative addition of PhBr to Pd(PX3)2 and Pd(X2PCH2CH2PX2) (X=Me, H, Cl)
Journal of Organometallic Chemistry, 2007
The density functional theory calculations were used to study the influence of the substituent at P on the oxidative addition of PhBr to Pd(PX 3) 2 and Pd(X 2 PCH 2 CH 2 PX 2) where X = Me, H, Cl. It was shown that the C ipso-Br activation energy by Pd(PX 3) 2 correlates well with the rigidity of the X 3 P-Pd-PX 3 angle and increases via the trend X = Cl < H < Me. The more rigid the X 3 P-Pd-PX 3 angle is, the higher the oxidative addition barrier is. The exothermicity of this reaction also increases via the same sequence X = Cl < H < Me. The trend in the exothermicity is a result of the Pd(II)-PX 3 bond strength increasing faster than the Pd(0)-PX 3 bond strength upon going from X = Cl to Me. Contrary to the trend in the barrier to the oxidative addition of PhBr to Pd(PX 3) 2 , the C ipso-Br activation energy by Pd(X 2 PCH 2 CH 2 PX 2) decreases in the following order X = Cl > H > Me. This trend correlates well with the filled d p orbital energy of the metal center. For a given X, the oxidative addition reaction energy was found to be more exothermic for the case of X 2 PCH 2 CH 2 PX 2 than for the case of PX 3. This effect is especially more important for the strong electron donating phosphine ligands (X = Me) than for the weak electron donating phosphine ligands (X = Cl).
A Mechanistic Investigation of Oxidative Addition of Methyl Iodide to [Tp*Rh(CO)(L)]
Inorganic Chemistry, 2002
Palladium atoms (vapor) have been cocondensed at low temperature with a series of al kyl ha? ides. Oxidative addition to form RMX occurs. Trapping experiments, free radical scavenging experiments, and decomposition product distributions suggest that the metal atom C-X bond insertion occurs directly fi a caged radical pair. dapendent on M, ligands attached to M, and on the nature of-X-Y. Even a simple change from one alkyl halide (X-Y) to another can cause a change in mechanism. 4 Thus, steric effects, reaction centers involved, and solvent effects are all important. Our study of the mechanism of oxidative addition to palladium atoms was undertaken for several reasons: Cl) it represents an example of a sterically unhindered metal center; (2) solvent effects and ligand effects would be eliminated; (3) the results may have imp1 ications regarding oxidative addition to surface metal atoms; (4) we have already obtained substantial chemical information about RPdXcompoundsthat can be formed in this way,5*6 and thereby have developed broad knowledge in this area. R-X + Pd atoms -f R-P&x R = CH3, C2H5, (CH3)3C, (.cH~)~ccH~. CF~. C~FS X = Br, I Results Iso'lable RPdX Species Previous work in our laboratory showed the compounds (CF3PdI)n, (C2F5PdI),, and (n-C3F-,Pdi)n are stable, albeit reactive. compounds which can be prepared by codeposi tion of Pd vapor with the respective RfI substrate.5y7 A search for other products was made, in particular PdI2 and gaseous coupling and disproportionation products, RfF and RfRf. discussed later). For the analogous C2F51-Pd system, again no gaseous. products, C2F6. C2F4, or $F,O, were observed. The yields of C2F6PdI were quite high (66% and 49%), but still significant amounts of Pd12 (17% and 6%) were formed. These experiments do point out that RPdX can be formed directly without formation of gaseous decomposition products. Therefore, in cases where gaseous products are formed, they probably come from decomposition of RPdX rather than from the process of formation of .WdX.
Journal of Organometallic Chemistry, 2004
The reactions of compound [Pt(dba) 2 ] with ligands RCHNCH 2 CH 2 NMe 2 (1a-1f) in which R is a fluorinated aryl ring produced activation of C-F bonds when two fluorine atoms are present in the ortho positions of the aryl ring or activation of C-H bonds for ligands containing only one fluoro substituent in ortho. Both C-F and C-H bond activation are favoured by an increase of the degree of fluorination of the ring. Further reaction with lithium halides produced cyclometallated platinum (II) compounds [PtX(Me 2 NCH 2 CH 2 NCHR)] (X = Br, Cl) (2) containing a terdentate [C,N,N 0 ] ligand. The obtained compounds were fully characterized including a structure determination for [PtCl{Me 2 NCH 2 CH 2 NCH(2,4,5-C 6 HF 3 )}] (2d 0 ).
Inorganic Chemistry, 2013
The initial aim of the present work was the synthesis of the axial disuccinato Pt(IV) derivative of [PtCl 2 (cis-1,4-DACH)] (Kiteplatin, 1 in ) (DACH = diaminocyclohexane), which contains an isomeric form of the diamine ligand present in oxaliplatin (i.e., 1R,2R-DACH). The interest in this compound stems from its activity on several cisplatin and oxaliplatin-resistant cell lines. Oxidation of 1 with hydrogen peroxide affords cis,trans,cis-[PtCl 2 (OH) 2 (cis-1,4-DACH)] (2) which was treated with succinic anhydride in suitable solvents. To our surprise, in dimethylformamide (DMF) (50−70°C or under light irradiation) or in dimethylsulfoxide (DMSO) (under light irradiation) the formation of the succinato complex cis,trans,cis-[PtCl 2 {OC(O)CH 2 CH 2 C(O)-OH} 2 (cis-1,4-DACH)] (3) was accompanied by reduction to 1. It was found that solvolysis of 2 and formation of a μ-oxo dinuclear species is the key step. The dinuclear species can then undergo reduction to a 1:1 mixture of 1 and 2 with concomitant elimination of oxygen (1/2 O 2 in the form of H 2 O 2 ). The whole process is fostered by heat and/or light, which could favor solvolysis of 2 as well as decomposition of hydrogen peroxide to water and oxygen so preventing the reoxidation of 1 to 2. Because of its peculiar behavior, compound 5 could be exploited also for the development of a technology for water splitting.
Formation of PCDD/Fs from oxidation of 2-monochlorophenol over an Fe2O3/silica surface
Chemosphere, 2012
The role of iron in surface-mediated formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) from 2-chlorophenol (2-MCP) was investigated over the temperature range of 200 to 550°C under oxidative conditions. In order to compare and contrast with previous work on copper and ferric oxide-mediated pyrolysis of 2-MCP, identical reaction conditions were maintained (50 ppm 2-MCP, model fly-ash particles containing 5% Fe 2 O 3 on silica). Observed products included dibenzo-p-dioxin (DD), 1-monochlorodibenzo-p-dioxin (1-MCDD), dibenzofuran (DF), 4,6-dichlorodibenzofuran (4,6-DCDF), 2,4-and 2,6-dichlorophenol, 2,4,6trichlorophenol, quinone, catechol, chloro-o-quinone, chlorocatechol and polychlorinated benzenes. Yields of DD and 1-MCDD were 2 and 5 times higher than under pyolysis conditions, respectively. Although 4,6-DCDF was the major PCDD/F product formed with a yield that was 2.5x greater than under pyrolysis, the yield of non-chlorinated DF, which was the dominant PCDD/F product under pyrolysis, decreased by a factor of 3. Furthermore, the ~2x higher yield of PCDDs under oxidative conditions resulted in a PCDD to PCDF ratio of 0.75 compared to a relatively low ratio of 0.39 previously observed under pyrolytic conditions.