Liquid-solid interface, hydrogen

Figure Al.7.14. 3.4 mn x 3.4 mn STM images of 1-docosanol physisorbed onto a graphite surface in solution. This image reveals the hydrogen-bonding alcohol molecules assembled in lamellar fashion at the liquid-solid interface. Each bright circular region is attributed to the location of an individual hydrogen...

The effects of transfer of atoms by tunneling may play an essential role in a number of phenomena involving the transfer of atoms and atomic groups in the condensed phase. One may expect that these effects may exist not only in the proton transfer reactions considered above but also in such processes as the diffusion of hydrogen atoms and other light ions (e.g., Li+) in liquids, tunnel inversion and isomerization in some molecules, quantum diffusion of defects and light atoms in the electrode at cathodic incorporation of the ions, ion transfer across the liquid/solid interface, and low-temperature chemical reactions. 

It is thus found convenient that, in all liquid-solid interfaces, there will be present different (apolar (dispersion) forces + polar (hydrogen-bonding) electrostatic forces). Hence, all liquids and solids will exhibit y of different kinds as shown... 

The well-known DLVO theory of colloid stability (10) attributes the state of flocculation to the balance between the van der Waals attractive forces and the repulsive electric double-layer forces at the liquid—solid interface. The potential at the double layer, called the zeta potential, is measured indirectly by electrophoretic mobility or streaming potential. The bridging flocculation by which polymer molecules are adsorbed on more than one particle results from charge effects, van der Waals forces, or hydrogen bonding (see COLLOIDS). 

Ti + state. Though it has been impossible to monitor this state at the liquid-solid interface, the Ti + concentration decreases during hydrogen producing illumination in water vapor. One would expect an increase in Ti + upon illumination if photopopulation of this electron trap state controlled the reaction rate. 

The solubilities of gases in solid metals are much lower than liquid metals. Figure 10.18 shows the solubility of hydrogen in copper and copper-aluminum alloys. Because of the lower solubility in the solid, gas bubbles are released at the liquid-solid interface as the metal freezes. With long dendrites the gas bubbles are trapped and the result is gas porosity. 

C L and CH represent the dissolved hydrogen concentrations at the gas-liquid (saturation) and liquid-solid interfaces, respectively. The analytical expression of the particle scale apparent reaction rate r as a function of has... 

Due to its many advantages, STM at the liquid-solid interface [27] has provided detailed insight into the molecule-substrate (epitaxy [60]) and molecule-molecule interactions (e.g. hydrogen bonding, metal complexation) responsible for the ordering of molecules on the atomically flat surface. It is possible to induce chemical reactions at the liquid-solid interface, via external stimuli (e.g. light), or by manipulation with the STM tip, where the location and orientation of functional groups could be controlled [27]. 

Figure 9 compares the oxygen and hydrogen density profiles for the interface between pure water and rigid mercury (solid lines taken from Ref. 40) and water and liquid mercury (short dashes taken from Ref. 78). The features of the water density profiles at the liquid/liquid interface are washed out considerably relative to those at the liquid/solid interface. However, in the first layer this effect is almost entirely due to the roughness of the mercury surface not all mercury atoms at the interface are in the same plane (at z = 0) but cover a range of approximately 1.3 A (see Figure 1 in... 

Ref. 78). The width is larger than the width of the oxygen and hydrogen peaks near the solid surface. Consequently, in order to compare the liquid/liquid with the liquid/ solid interface, the density distribution near the rigid surface can be convoluted with a width function w(z) due to the mercury motion according to... 

Transition of the four different states of hydrogen, as described in Chapter 4.4, occurs at the gas-solid and liquid-solid interface as illustrated below ... 

Hydrogen is generated by thermal decomposition or hydrolysis. For thermal decomposition some doped-catalytic reagents are applied to reduce the decomposition temperature to practical levels. Hydrolysis uses catalysts to generate hydrogen under ambient conditions. [See Chapter 6.5 for thermal decomposition and Chapter 6.8 for hydrolysis]. In these reactions, the aid of surface reactants is needed to liberate hydrogen at the gas-solid or liquid-solid interfaces. 

The most catalytic or noncatalytic processes involving reactions in multiphase systems. Such processes include heat and mass transfer and other diffusion phenomena. The applications of these processes are diverse and its reactors have their own characteristics, which depends on the type of process. For example, the hydrogenation of vegetable oils is conducted in a liquid phase slurry bed reactor, where the catalyst is in suspension, the flow of gaseous hydrogen keeps the particles in suspension. This type of reaction occurs in the gas-liquid-solid interface. 

The mathematical model was constracted on the basis of a three-phase plug-flow reactor model developed by Korsten and Hoffmaim [63]. The model incorporates mass transport at the gas-liquid and liquid-solid interfaces and uses correlations to estimate mass-transfer coefficients and fluid properties at process conditions. The feedstock and products are represented by six chemical lumps (S, N, Ni, V, asphaltenes (Asph), and 538°C-r VR), defined by the overall elemental and physical analyses. Thus, the model accounts for the corresponding reactions HDS, HDN, HDM (nickel (HDNi) and vanadium (HDV) removals), HD As, and HCR of VR. The gas phase is considered to be constituted of hydrogen, hydrogen sulfide, and the cracking product (CH4). The reaction term in the mass balance equations is described by apparent kinetic expressions. The reactor model equations were built under the following assumptions ... 

---