Kinetics clean single-crystal

Kinetics of Structure Insensitive Reactions Over Clean Single Crystal Surfaces... 

The above described experiments over atomically clean single crystal catalysts have been extended to studies of the kinetics of various catalytic reactions over chemically modified catalysts. Examples are recent studies Into the nature of poisoning by sulfur of the catalytic activity of nickel, ruthenium, and rhodium toward methana-tlon of CO (11,12) and CO2 (15). ethane (12) and cyclopropane (20) hydrogenolysls, and ethylene hydrogenation (21). 

Kinetics over the Mo(lOO) Crystal Surface. We have studied the hydrodesulfurization of thiophene over the initially clean Mo(lOO) single crystal surface in the temperature range 520K - 690K and at reactant pressures of 100 Torr < P(H ) 800 Torr and 0.1 Torr P(Th) < 10 Torr. Under these conditions the reaction is catalyzed at a constant rate for a period of approximately one hour after which the rate begins to decrease with time. The rates reported here are all initial rates of reaction calculated from data collected in the period over which they remain constant. 

HoUoway PH, Hudson JB (1974) Kinetics of the reaction of oxygen with clean nickel single crystal surfaces 1. Ni(lOO) surface. Surf Sci 43 123... 

Microbalances have been used to measure adsorption kinetics under a wide variety of conditions. Several authorshave studied adsorption on single crystal surfaces of semiconductors under ultra high vacuum conditions and utilising ion bombardment to obtain a clean surface. Gulbransen et al and Walker et have made a special study of microbalance operation at high temper-... 

Surface science techniques have been used to obtain vital information about reactions at a molecular scale [4]. We have employed a molecular beam reactor and STM to obtain kinetic and topographic data. The reaction is carried out on an atomically clean Pd (110) single crystal, under ultra high vacuum (UHV) conditions. Thus when O2 and / or CO are... 

Kinetic isotope effect studies under ultra-clean conditions on single-crystal surfaces... 

The synthesis of methanol from C0(+C02) and H2 was also attempted by Campbell and co-workers (102) over a Cu(l 11) surface and over well-defined Cu overlayers on a ZnO(OOOl) single-crystal surface. They could set an upper limit of < 2 x 1012 molecules/cm2/s on the methanol production rate at temperatures up to 600 K and pressures up to 1500 torr. These limits are consistent with expectations based on (extrapolated) kinetics for high-surface-area Cu/ZnO catalysts. Their results also showed that C02 has extremely low reactivity for oxidation of the clean Cu(l 11) surface (102), and they argue that it is very unlikely that significant oxygen concentrations exist on the Cu(lll)-like surfaces of practical catalysts under methanol synthesis conditions (102, 103). 

Figure 7.4 (A) Polarization curves for O2 reduction on platinum monolayers (PIml) on Ru(OOOI), lr(111), Rh(111), Au(111), and Pd(111) surfaces in 02-saturated 0.1 M HCIO4 solution on a disk electrode. The rotation rate is 1600 rpm, and the sweep rate is 20 mV s (50 mV s for R(111)) y= current density, RHE = reversible hydrogen electrode. (Reprinted with permission from Ref. 6) (B) kinetic currents (yi< square symbols) at 0.8 V for O2 reduction on the platinum monolayers supported on different single-crystal surfaces in 02-saturated 0.1 M HCIO4 solution and calculated binding energies of atomic oxygen (BEO filled circles) as functions of calculated d-band center (fd cp relative to the Fermi level) of the respective clean Pt monolayers. Labels (1) PtMi/Ru(0001),(2) RMi/lrOU). (3) PtMi/Rh(111),(4) PtMi/Au(111), (5) Pt(111), (6) PtML/Pd(111). Reprinted with permission from Ref. 22.

ORR at the Pt(hk/)-CUupd Interfaces Studies of the kinetics of the ORR on platinum single-crystal electrodes modified by U PD metal ad-atoms are of interest primarily from a fundamental science perspective. Since it is possible to begin the experiment with a clean Pt(hkl) surface in which the ORR is well known, the change in both rate and reaction pathway with the addition of another metal to the surface, usually in a highly structured manner, can provide some insight into the ORR on metals that are otherwise difficult to study, for example, Cu, Pb, and Bi. Only the results... 

Electrocatalysts for the Oxygen Reaction, Core-Shell Electrocatalysts, Fig. 2 Kinetic currents (jk) at 0.8 V versus REE for ORR on the PtML supported on different single-crystal surfaces in a 0.1 M HCIO4 solution as functions of calculated d-band center (ej-ep relative to the Fermi level) of the respective clean E ml- The current data for Pt( 111) is taken from Ref [22] and included for comparison... 

Courtesy of Edmond E. Bisson and Donald H. Buckley The following tables give coefficients of kinetic sliding friction for single crystals—metals and non-metals. Metals Coefficient of Friction In Vacuum, Metal Atomic Plane In Air, 20"C Clean ... 

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