Adsorbed precursors

IR spectra of adsorbed precursors on alumina were recorded before and after solvent removal with a Bruker lFS-66v spectrometer with a resolution of 4 cm. ... 

When a supported metal on an oxide is prepared from an adsorbed precursor incorporating a noble metal bonded to an oxophilic metal, the result may be small noble metal clusters, each more-or-less nested in a cluster of atoms of the oxophilic metal, which is cationic and anchored to the support through metal-oxygen bonds [44,45]. The simplest such structure is modeled on the basis of EXAFS data as Re4Pt2, made from Re2Pt(CO)i2 (Fig. 6) [45]. 

For metal atoms the state of lowest Gibbs Free Energy is achieved when they are organized in a macroscopic polyhedron. High dispersion on a support requires strong chemical interaction between metal and support, conventionally called chemical anchoring The formation of solid particles either from the vapor or from an adsorbed precursor is dominated by two kinetic processes ... 

The interplay of these two basic rates determines the size of the resulting particles. For instance, the reason that snow flakes reach sizes of several cm at lower latitudes but arrive as extremely small crystals, called diamond dust in Antarctica, is that the nuclei that are formed in a cloud, will grow during their voyage to earth by adsorbing water molecules. Obviously, this growth will be more important in the moist atmosphere at low latitudes than in the extremely dry atmosphere above Antarctica. The same interplay of nucleation and growth determine the size of metal particles that are formed on a support by chemical reduction of adsorbed precursors, such as metal ions. Here... 

Adsorption-desorption of CO. CO adsorption is monomolecular. On all the Pt metals except Ir it proceeds through the pre-adsorbed ("precursor ) state [17, 93], The activation energy is practically zero and the initial sticking coefficient is high (0.5-1.0). Oxygen does not inhibit CO adsorption [55, 94], The sticking coefficient is weakly dependent on the surface concentration of CO. During the adsorption on Ru and Ir, surface carbides can form. 

Gas-Surface Reactions Proceeding via a Strongly Adsorbed Precursor. 471... 

The deposition process is illustrated in the left part of Fig. 5. The precursor gases are sprayed on the surface by the nozzle , where they are adsorbed. In a second step, the incoming ion beam decomposes the adsorbed precursor gases. Then the volatile reaction products desorb from the surface and are removed through the vacuum system, while the desired reaction products remain fixed on the surface as a thin film. The deposited material is not fully pure however, because organic contaminants as well as Ga ions (from the ion beam) are inevitably included in the deposited film [23],... 

Apparent from Fig. 24 is the self-similarity of the curves for molecular adsorption and dissociative adsorption which Nolan et al. argues provides strong evidence that both processes occur via a similar initial step, specifically, a molecularly adsorbed precursor. Further, the adsorption probability at 71 = 77 K appears to scale with normal energy, mirroring the normal energy scaling of the dissociative probability curve. 

Surface-bound methoxy, CH3O, is an intermediate in a variety of surface processes in catalysis and electrocatalysis involving methanol. The chemistry of methoxy on Pt(lll) and the Sn-alloys had been elusive because of the difficulty of cleanly preparing adsorbed layers of methoxy. One approach is to use the thermal dissociation of an adsorbed precursor, methyl nitrite (CH O-NO), to produce methoxy species on such surfaces at temperatures lower than required for methoxy formation from methanol [58, 59]. The methoxy intermediate is strongly stabilized (to 300 K) against thermal decomposition on both Sn/Pt(lll) alloys, whereas on Pt(lll), dissociation occurs below 140 K. There is a high selectivity to formaldehyde, CHjO, on both alloys, i.e., methoxy disproportionates to make equal amounts of formaldehyde and methanol. The two Sn/Pt(lll) alloys do not form CO and products characteristic of methoxy decomposition on Pt(l 11). 

Preparation of MejC by Adsorption of Metal Hydroxide Ammoniates This method requires an excess of ion-exchange groups compared to the number of the supported metal ions and thus relies on the utilization of oxidized carbon materials. Reduction of adsorbed precursors in H2 at 100-300 °C results in the generation of very fine metal particles, their size being 1.5-2.5nm for... 

If the adsorbed precursor (or successor) state concentrations are insufficient to allow analytical detection, resort must be made to less direct methods to diagnose electrochemical inner-sphere pathways. Three such methods are ... 

Fig. 1 shows the decomposition of monometallic ruthenium precursors, impregnated (b) and adsorbed (e), and monometallic platinum adsorbed precursors (f) supported on zirconia. These results are compared to those obtained for bimetallic precursors prepared either by... 

There is a serious obstacle on a path leading to building such advanced models, namely the absence of a generally accepted concept of how free radicals react with surfaces of different nature. Does this interaction always proceed as a direct collision or in some cases it is proceeded by more or less stable adsorbed precursor What properties of the solid surface—local or collective—are responsible for directions and rates of such reactions to a greater extent Which approaches are more fruitful for evaluation of kinetic parameters in this case What experimental information could be relevant and helpful for building more adequate models and for a more precise evaluation of kinetic parameters What type of experimental data should be employed to examine the efficiency of such models ... 

Introduction FIBID can be employed to realize the localized maskless deposition of both metal and insulator materials. In the FIBID process, the precursor gas is first sprayed and then adsorbed locally on the sample surface using a fine nozzle. The injecting ion beam decomposes the adsorbed precursor gases. The desired reaction products would be fixed on the surface and form a thin film. 

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