Potential-Programmed Reduction

Y. Jiang, I.V. Yentekakis, and C.G. Vayenas, Potential-programmed reduction A new technique for investigating chemisorption on catalysts supported on solid electrolytes, J. Catal. 148, 240-251 (1994). 

The creation of two types of chemisorbed oxygen on Pt and Ag surfaces subject to NEMCA conditions is clearly shown by cyclic voltammetry (Fig. 5.27)319,50,52 or by the similar Potential-Programmed-Reduction (PPR)... 

The promotional index, Pip [Eq. (2)]. After the establishment, via the use of surface spectroscopy (XPS [87,88], UPS [89], TPD [90], PEEM [91], STM [92], work function measurements [93]) but also electrochemistry (cyclic voltammetry [90], potential programmed reduction [94], AC impedance spectroscopy [43,95]), that electrochemical promotion is due to the potential-controlled migration (reverse spillover or backspillover) [13] of promoting ionic species (0 , Na", H, F ) from the solid electrolyte to the gas-exposed catalyst surface, it became clear that electrochemical promotion is functionally very similar to classical promotion and that the promotional index PI, already defined in Eq. (2), can be used interchangeably, both in classical and in electrochemical promotion. 

In addition to solid electrolyte potentiometry, the techniques of cyclic voltammetry" and linear potential sweep have also been used recently in solid electrolyte cells to investigate catalytic phenomena occurring on the gas-exposed electrode surfaces. The latter technique, in particular, is known in catalysis under the term potential-programmed reduction (PPR). With appropriate choice of the sweep rate and other operating parameters, both techniques can provide valuable kinetic" and thermodynamic information about catalytically active chemisorbed species and also about the NEMCA effect," as analyzed in detail in Section III. 

Copper and zinc containing mesoporous molecular sieves AIMCM-41 have been studied by MAS NMR, electron spin resonance, nitrogen and carbon monoxide adsorption and temperature programmed reduction. AlMCM-41 materials with ns,/nAi = 15, 30 and x have been synthesized in the presence of copper and zinc Carbon monoxide adsorption shows the presence of Cu ions after mild activation, but Zn ions have not been detected indicating that only a ZnO phase is formed Temperature programmed reduction reveals the presence of CuO clusters of various size depending on the on the ns./n ij ratio and the zinc concentration The results of this study allow the preparation of mesoporous molecular sieves with remarkable redox properties, which are potential model catalyst for methanol synthesis... 

For each program review cycle, the scope and schedule of response actions proposed at individual sites should be adjusted to maximize the potential risk reduction to be achieved with available resources. Response actions are prioritized to address near-term human health or environmental concerns. Key elements of this program management plan include ... 

The classical procedure for the activation of an electrode surface is to obtain a surface roughness by cycles of oxydation and reduction. This type of activation is easy to apply but does not give an opportunity to produce well-defined surfaces, whereas deposition of an SERS-active metal on an inert electrode offers the possibility of achieving the enhancement effect as well as controlling the surface structure. Some potential programs useful for the activation of the electrode surface are depicted in Fig. 1. 

Composites containing different types of guests (metal or alloy particles, oxides, sulfides, complexes, polymers) in the cavities of zeolite hosts are prepared for various appHcations in materials research and catalysis. Except for quality assessment by detection of extra-zeolite material after synthesis or thermal treatments, photoemission plays a largely auxiliary role in this area, cooperating with bulk techniques such as X-ray absorption, UV-Vis, IR of probe molecules, and temperature-programmed reduction. The attention drawn to the significance of intra-zeolite potentials by XPS studies [12] has, however, contributed to the elaboration of a new theory of metal-support interactions [18,19]. 

Oxide Growth Kinetics and Mechanism. Formation of oxide films by potentiostatic polarization and their characterization by CV enables distinction of various oxide states as a function of the polarization conditions, here Ep, tp and T. This method allows precise determination of the thickness of oxide films with accuracy comparable to the most sensitive surface science techniques 4-7J1-20), CV may be considered the electrochemical analog of temperature programmed desorption, TPD, and one may refer to it as potential programmed desorption, PPD. Theoretical treatment of such determined oxide reduction charge densities by fitting of the data into oxide formation theories leads to derivation of important kinetic parameters of the process as a function of the polarization conditions. The kinetics of electro-oxidation of Rh at the ambient temperature were studied and some representative results are reported in ref 24. The present results are an extension of the previous experiments and they involve temperature dependence studies. 

A novel voltammetric technique based on the simultaneous dynamic potential control of both the disk and the ring electrodes of an RRDE is presented. The method of dual cyclic voltammetry has proven to be an especially promising method for studying the mechanisms of electrochemical processes. The new 3D representation of the data can be effectively used in order to reveal the formation of electroactive species at the disk electrode. By using appropriate potential programs, the selectivity and sensitivity of RRDE systems can be significantly increased. The results of some selected e>q)eriments have been discussed and some drawbacks of the technique have been pointed out. Numerical simulations have been carried out in order to study the cross-talk effects, and a method has been suggested for their reduction. 

The feedback approach can also be used to study the O2 reduction reaction at a substrate in alkaline media. Oxygen is generated at a An tip by oxidation of OH" and reduced at the substrate. There is a drift in the tip current due to the formation of an anodic film on the tip in the potential range where the oxidation of OH occurs. This drift is alleviated by applying a periodic potential program to the An tip, which resulted in a stable, steady-state tip current. Kinetic parameters can then be determined from SECM approach curves. Similarly, the behavior of the product, O2, from O2 reduction at the tip in 02-saturated 10 M NaOH solution can be investigated as a function of substrate potential. ... 

Liu, B., Bard, A.J. Scanning electrochemical microscopy. 45. Study of the kinetics of oxygen reduction on platinum with potential programming of the tip. J. Phys. Chem. B 2002, 106,12801-12806. 

Liu B and Bard A J (2002) Scanning Electrochemical Microscopy Study of the Kinetics of Oxygen Reduction on Platinum with Potential Programming of the Tip, J. Phys. Chem. B, 106, pp. 12801-12806. 

Silica-alumina l-gels have been prepared with a variety of compositions the addition of A1 reduces the adsorption capacity, the total surface area and the microporosity o j the gels. This can be explained if the adsorption or incorporation of A1 reduces the charge on the silica sol-gel partlcle and enhances their adhesion. The gels readily allowed ion-exchange with Cu and temperature-programmed reduction and X-ray photoelectron spectroscopy has been used to probe the environment of these cations in model precursors of heterogeneous catalysts. The potential of this approach for the analysis of solutions is considered. 

Potential tax incentives. In an effort to promote pollution prevention, taxes may eventually need to be levied to encourage waste generators to consider reduction programs. Conversely, tax breaks could be developed for corporations that utilize pollution-prevention methods to foster pollution prevention. 

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