Dispersion, catalyst incorporation

Kim et al.32 reported the preparation, characterization, and catalytic performance of a finely dispersed and thermally stable nickel catalyst incorporated into mesopo-rous alumina. Mesoporous alumina catalysts that incorporate Ni (Ni-alumina) with different Ni/Al molar ratios were synthesized by a one-step sol-gel method using lauric acid as a template. The prepared Ni-alumina catalysts showed a relatively high surface area with a narrow pore size distribution after calcination at 700 °C these effects were independent of the Ni/Al molar ratio. The Ni-alumina catalysts were found to be highly active in the POX of methane. The deactivation of catalysts examined in this work was not due to catalyst sintering, but mainly to carbon deposition. 

Dispersancy Incorporating dispersancy into OCP VI improvers is considerably more difficult than the case with free-radical solution chemistry, as described for PMAs. Direct copolymerization of the preferred N- or O-containing monomers is not practical since these Lewis bases will complex, and thus poison, the acidic Ziegler-Natta catalysts. The only option identified so far is to use an amount of catalyst in excess of that complexed by the polar monomer, as described for N-vinylimidazole [24] or V-vinyl succinimide [25]. 

Zeolite catalysts incorporated or encapsulated with transition metal cations such as Mo, or Ti into the frameworks or cavities of various microporous and mesoporous molecular sieves were synthesized by a hydrothermal synthesis method. A combination of various spectroscopic techniques and analyses of the photocatalytic reaction products has revealed that these transition metal cations constitute highly dispersed tetrahedrally coordinated oxide species which enable the zeolite catalysts to act as efficient and effective photocatalysts for the various reactions such as the decomposition of NO into N2 and O2 and the reduction of CO2 with H2O into CH3OH and CH4. Investigations on the photochemical reactivities of these oxide species with reactant molecules such as NOx, hydrocarbonds, CO2 and H2O showed that the charge transfer excited triplet state of the oxides, i.e., (Mo - O ), - O ), and (Ti - O ), plays a significant role in the photocatalytic reactions. Thus, the present results have clearly demonstrated the unique and high photocatalytic reactivities of various microporous and mesoporous zeolitic materials incorporated with Mo, V, or Ti oxide species as well as the close relationship between the local structures of these transition metal oxide species and their photocatalytic reactivities. 

These examples demonstrate the interest of conducting polymers as matrices to disperse active electrocatalysts, so that a detailed investigation of their electroformation and of the catalyst incorporation process was undertaken at the molecular level, using in situ" U V-visible Reflectance Spectroscopy (UVERS). 

The catalyst for the second stage is also a bifimctional catalyst containing hydrogenating and acidic components. Metals such as nickel, molybdenum, tungsten, or palladium are used in various combinations and dispersed on sofid acidic supports such as synthetic amorphous or crystalline sihca—alumina, eg, zeofites. These supports contain strongly acidic sites and sometimes are enhanced by the incorporation of a small amount of fluorine. 

PtWZ (Std) to obtain a reference catalyst. Prior to reaction, all samples were calcined for one hour at the chosen temperature (1096 K for WZ, Pt/Al203 and Pt/WZ (Std), and 773 K for Pt/WZ (acac)) and subsequently reduced for 1 h under a H2 flow of. 5 liter/ min g at 623 K. The choice of temperature for the second calcination cycle of the Pt/WZ (acac) sample is not in any way arbitrary. The idea is to use a non-aqueous scheme to keep the incorporation of moisture to a minimum, and a calcination temperature low enough to guarantee better metal dispersions. 

Incorporation into a Polymer Layer In recent years a new electrode type is investigated which represents a layer of conducting polymer (such as polyaniline) into which a metal catalyst is incorporated by chemical or electrochemical deposition. In some cases the specific catalytic activity of the platinum crystallites incorporated into the polymer layer was found to be higher than that of ordinary dispersed platinum, probably because of special structural features of the platinum crystallites produced within the polymer matrix. A variant of this approach is that of incorporating the disperse catalyst directly into the surface layer of a solid polymer electrolyte. 

The dispersion of Pt(0) inside the functionalized resins was carried out by two main routes. The first is based on impregnation of the resin with a mesitylene solution of Pt nanoclusters (Solvated Pt Atoms) obtained via MVS. The second procedure, called Chemical Incorporation and Reduction (CIR), implies the immobilization of convenient molecular Pt precursors (i.e. [Pt(NH3)4]Cl2) in the pre-swollen resins, followed by chemical reduction of the metal center. Among the Pt catalysts obtained by the CIR procedure only Pt/CF3 exhibits a high conversion of the... 

In Sn/V/Nb/Sb/O catalysts, different compoimds form (10) mtile Sn02 (also incorporating Sb, Sb/Nb mixed oxide and non-stoichiometric mtile-type V/Nb/Sb/O the latter segregates preferentially at the smface of the catalyst. Tin oxide (cassiterite) provides the matrix for the dispersion of the active components therefore, a variation of the value of x in Sn/V/Nb/Sb x/0.2/1/3 catalysts imphes a... 

Pristine CNTs are chemically inert and metal nanoparticles cannot be attached [111]. Hence, research is focused on the functionalization of CNTs in order to incorporate oxygen groups on their surface that will increase their hydrophilicity and improve the catalyst support interaction (see Chapter 3) [111]. These experimental methods include impregnation [113,114], ultrasound [115], acid treatment (such as H2S04) [116— 119], polyol processing [120,121], ion-exchange [122,123] and electrochemical deposition [120,124,125]. Acid-functionalized CNTs provide better dispersion and distribution of the catalysts nanoparticles [117-120],... 

The factors 4 and 4 accormt for the heterogeneity of the interface. The interfacial flux conditions. Equations (6.56) and (6.57), can be straightforwardly applied at plain interfaces of the PEM with adjacent homogeneous phases of water (either vapor or liquid). However, in PEFCs with ionomer-impregnated catalyst layers, the ionomer interfaces with vapor and liquid water are randomly dispersed inside the porous composite media. This leads to a highly distributed heterogeneous interface. An attempt to incorporate vaporization exchange into models of catalyst layer operation has been made and will be described in Section 6.9.4. 

Carbon supported powdered palladium catalysts have been widely used in the chemical industry. In addition to activity and selectivity of those catalysts, the recovery rate of the incorporated precious metal has a major impact on the economic performance of the catalyst. In this study, the effects of catalyst age, oxidation state of the incorporated metal and temperature treatment on the palladium leaching resistance as well as on activity and dispersion of carbon supported palladium catalysts were investigated. 

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