Adsorption, acetylene

Aeetylacetone, 32 248-249 hydrogenation, 32 259-262 Acetylcholine esterase, 20 344, 367 Acetylene adsorption complexes, 31 6-7 potential dependence, 30 258 catalytic oxidation of, for oxygen manufacture, 3 107... 

Fig. 7.3. Perspective view of ethylidyne on Pt(l 11), the stable structure reached after acetylene adsorption with hydrogen addition...

Clearly the situation of acetylene adsorption on Si(100) is a complex problem, presumably related to the higher potential reactivity and capacity for bonding of the C=C species. Fortunately, the situation for ethylene appears to be more straightforward, and it seems to be the interaction of Si(100) with C=C species that underpins most of the potential applications in creating suitable inorganic/organic electronic interfaces [126]. 

Silvestrelli, P. L., Pulci, O., Palummo, M., Del Sole, R. and Ancilotto, F. First-principles study of acetylene adsorption on Si(100) The end-bridge structure. Physical Review 68, 235306... 

C-Tracer studies of acetylene adsorption on alumina- and silica-sup-ported palladium [53,65], platinum [66] and rhodium [53] show the coexistence of at least two adsorbed states, one of which is retained on the surface, the other being reactive undergoing molecular exchange and reaction with hydrogen. Acetylene adsorption exhibits the same general characteristics as those observed with ethylene (see Sect. 3.2). However, there are important differences. The extent of adsorption and retention is substantially greater with acetylene than with ethylene. Furthermore, the amounts of acetylene retained by clean and ethylene-precovered sur-... 

The greater amount of retention observed with acetylene than with ethylene has been ascribed to the ability of the former to polymerise extensively. The existence of surface polymers following acetylene adsorption on alumina- and silica-supported platinum [60], evaporated palladium films [154] and silica-supported rhodium [67] has been demonstrated by thermal desorption studies. 

This postulate has several implications regarding the mechanism of alkyne hydrogenation these will be discussed in Sect. 4.3. It should be noted, however, that there is as yet little or no direct evidence for structure L, although analogous structures are known to exist with organometallic complexes [161], Such a structure is also consistent with the positive surface potentials observed for acetylene adsorption on evaporated nickel films [88]. 

Fig. 27. 14C-acetylene adsorption isotherm on palladium—silica at 20°C (O) and the 14C-ethylene adsorption isotherm on an acetylene-precovered palladium—silica catalyst... 

Theoretical and Experimental NMR techniques provide powerful tools for the investigation of heterogeneous catalysis. Recent advances in in situ NMR techniques are summarized, as are advances in theoretical methods. The utility of our combined theoretical/experimental approach is illustrated by studies of the pentamethylbenzenium cation and the 1,3-dimethylcyclopentenyl cation in zeolite HZSM-5, acetylene adsorption on MgO, and the isopropyl cation on frozen SbF5. We also discuss the role of the basicity of adsorbates in the formation of stable carbenium ions on zeolites. 

For selective acetylene adsorption from other hydrocarbons (e.g., ethylene and ethane), NiCl2 supported on alumina or silica can form reversible jr-complexation bonds with acetylene but not olefins. Pure component acetylene-ethylene ratios of up to 3 were obtained (Kodde et al., 2000). The bonding between acetylene and NiCl2 is reasonably understood (Huang and Yang, 1999). 

Acetylene adsorption, selective, 117 Acoustic cavitation, nanostructured catalysts, 19 Activated alumina commercial, 93 commercial use, 80 pore size distribution, 89 Activated carbon... 

Table 3 Bonding Characteristics of Several Acetylene Adsorption Sites on Pt(lll)...

The IR spectra of methylacetylene adsorbed on zeolites are similar to those of acetylene. Adsorption bands at 3250 (with a shoulder at 3150 cm-i) are assigned to the C-H---0 complexes and are characterized by frequency shifts of 85 cm ( 185 cm"i for the shoulder) relative to the gas-phase frequency, which agrees with the corresponding frequency shifts found for the acetylene adsorption. 

Acetylene adsorption was IR spectroscopically studied by Howard and Kadir [833], who dealt with the uptake of this unsaturated compound into silver-exchanged zeoHte A. They could evidence the formation of acetylides and the formation of two different adsorption complexes of n-bonded acetylene, indicated by bands at 1955 and 1912 cm for CjHj and 1740 and 1710 cm for CjDj imder an adsorbate pressure of 13.3 kPa. 

Fig. 7 ReaxFF RD simulations of acetylene adsorption and decomposition on a 468-atom nickel particle [not shown] (a) after 1 ns a limited number of structured rings have formed and (b) after 2 ns of ReaxFF RD simulations a clear ring pattern formation appears. Simulations were performed using the parallel protot3 pe reaxFF implementation from collaboration with H.M. Aktulga and A. Grama at Purdue, and A.C.T van Duin at Penn State...

Figure 15 (a) A cross-sectioned capsule of sublimed 2 with two molecules of methane embedded in the cavity. Reproduced with permission from Ref. 89. Copyright 2005 the Royal Society of Chemistry, (b) Acetylene adsorption (circles) and desorption (triangles) isotherms at room temperamre show a large hysteresis loop. (Reproduced from Ref. 90. Wiley-VCH, 2006.)... 

Padin, J., and Yang, R.T., Tailoring new adsorbents based on pi-complexation Cation and substrate effects on selective acetylene adsorption, Ind. Eng. Chem. Res., 36(10), 4224-4230 (1997). 

---