Surface catalyzed chemistry

Gellman, A. J. (2000). Transition states for surface-catalyzed chemistry. Acc. Chem. Res. 33, 19. 

The impact on negative-CA resists of airborne base contamination differs qualitatively from their positive tone counterparts. Suppression of acid-catalyzed chemistry at the surface of a negative resist results in some film erosion at the top of the exposed fields and in some cases an apparent loss of photosensitivity, but in general the reUef images formed exhibit the expected cross-sectional profile. This is in sharp contrast with the typical behavior seen with positive-tone CA resists, where suppression of acid-catalyzed chemistry at the surface causes an insoluble surface skin. 

This sort of analysis could be extended to any metal-catalyzed chemistry in which a large runaway chiral excess is induced in the product by way of a small chiral excess of the molecules that serve as ligands to the metal. It is only necessary that the D,L-metal center be kinetically slower and thermodynamically more stable than the d,d- or L,L-complexes in order that any small e.e. of a chiral ligand be translated into chiral dominance of the reaction product. That the initial e.e. resulting in chiral takeover within a reacting system can be induced by asymmetric mineral surfaces indicates that a general chemical route to the asymmetry of life may exist. 

The rapid development of the chemistry of transition metal complexes containing terminal carbene (A) or carbyne (B) ligands (7) has been followed more recently by much research centered on bridged methylene compounds (C) (2). The importance of /t-methylidyne complexes, whether in recently established binuclear examples (D), the well-known trinuclear derivatives (E), or the unusual complexes (F), has also become apparent. All are based on one-carbon (C,) fragments, and considerable interest is centered on their possible significance as models for intermediates in surface-catalyzed reactions between carbon monoxide and hydrogen (Fischer -Tropsch reactions) and related processes. These topics have been extensively ... 

The surface chemistry of carborane (C2B10H12) and decaborane (B10H14) on Pt(lll) has been studied with reflection absorption infrared spectroscopy (RAIRS), temperature programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). It is found that the Pt surface catalyzes the release of hydrogen from both molecules at temperatures much lower than their thermal decomposition temperatures. The thermal degradation of these two molecules was found to occur in stages as shown by the TPD results. From XPS data, it was concluded that boron remains on the surface up to very high temperatures. 

Third, and not least, the mechanistic features of the Fischer-Tropsch hydrocarbon synthesis mirror a plethora of organometallic chemistry. More precisely Molecular models have been invoked that could eventually lead to more product selectivity for eq. (1). Although plausible mechanistic schemes have been considered, there is no way to define precisely the reaction path(s), simply because the catalyst surface reactions escape detection under real process conditions (see Section 3.1.1.4). Nevertheless, the mechanism(s) of reductive hydrocarbon formation from carbon monoxide have strongly driven the organometallic chemistry of species that had previously been unheard of methylene (CH2) [7-9] and formyl (CHO) [10] ligands were discovered as stable metal complexes (Structures 1-3) only in the 1970s [7, 8]. Their chemistry soon explained a number of typical Fischer-Tropsch features [11, 12]. At the same time, it became clear to the catalysis community that molecular models of surface-catalyzed reactions cannot be... 

Combining concepts of surface coordination chemistry with established models of lattice statistics and activated complex theory, Wieland et al. (8) proposed a general rate expression for the proton-catalyzed dissolution of oxide minerals ... 

A number of hydrogen-transfer reactions involving carbonyl groups are known in organic chemistry however, these are for the most part limited to liquid-phase, homogeneously catalyzed systems. In this paper there is described a vapor-phase surface-catalyzed reaction which like the liquid-phase aluminum alkoxide catalyzed reductions of Meerwein-Ponndorf-Verley (J) will selectively reduce a carbonylic group in conjugation with a carbon-carbon double bond. 

The presence of solution or solvent can appreciably perturb the chemistry of surface-catalyzed reactions compared to their ultra-high vacuum or vapor-phase counterparts. Polar solvents, such as water, are able to stabilize charged intermediate and transition-state species at the surface that are unstable (or less stable) as gas-phase adsorbates, thus altering both the thermodynamics (i.e., reaction energy) and kineties (i.e., activation barrier) for specific reaction steps. This can influence the activity, as well as the selectivity of the overall catalytic system, and thus control aqueous-phase electrocatalysis. Thiel and Madey [36] and Henderson [37] present exceptional reviews that describe in... 

Sun, W.-J. Zhao, H.-X. Cui, F.-J. Li, Y.-H. Yu, S.-L. Zhou, Q. Qian, J.-Y. Dong, Y. D-isoascorbylpalmitate Lipase-catalyzed synthesis, structural characterization and process optimization using response surface methodology. Chemistry Central Journal, 2013, 7, 114-127. 

Catalyzed by Silica Supported Transition Metal Hydrides, Science 276,99,1997 b) J. Corker, F. Lefebvre, C. Lecuyer, V. Dufaud, F. Quignard, A. Choplin, J. Evans, J.-M. Basset - Catalytic Cleavage of the C-H and C-C Bond of Alkanes by Surface Organometallic Chemistry An EXAFS and IR Characterization of a Zr-H Catalyst, Science 271, 966, 1996. 

Two other significant conclusions can be made from this study i) the observed reaction between SiH4 and UF5 was most likely surface catalyzed and ii) UF and HF show fundamentally different reactivity towards partially fluorinated silane derivatives. Evidence for the first conclusion was obtained from reactions involving either SiH4 or UFg and reactor walls preconditioned with UF5 or SiH4, respectively, which proceeded in a very similar fashion to the bulk reactions between the two species. The latter reactions proceeded at or below ambient temperature whether the two species were mixed directly in the gas phase or first condensed together at -196 before warming up to ambient temperature, which supports the apparently active role of the reactor walls in the system s chemistry. 

Another facet of surface organometallic chemistry involves modelling of the mechanisms of surface reactions on the basis of the reactivity of molecular models. For example, the reactivity of metal-imine complexes of molybdenum is considered by CHAN, who proposes elementary steps constituting the catalytic cycle of the surface-catalyzed alkene ammoxidation reaction, which is of great industrial importance. HERRMANN provides some very fine examples of molecular models of the rhenium oxide catalysts used commercially in the alkene metathesis reaction. 

Chemistry. Successful electroless plating depends on the optimized interaction of five separate complex chemical solutions (1) to clean, roughen, and catalyze the surface before plating. These steps are critical for formation of an adherent continuous electroless coating, and for optimum durabHity after electrolytic plating. 

Wachtershanser has also suggested that early metabolic processes first occurred on the surface of pyrite and other related mineral materials. The iron-sulfur chemistry that prevailed on these mineral surfaces may have influenced the evolution of the iron-sulfur proteins that control and catalyze many reactions in modern pathways (including the succinate dehydrogenase and aconitase reactions of the TCA cycle). 

Cu and Ag on Si(lll) surfaces. In the last example, we come back to surfaces. It is well known (44-46) that Cu catalyzes the formation of dimethyl-dichlorosilane from methylchloride and solid silicon, which is a crucial technological step in the synthesis of silicone polymers. Even today, the details of the catalytic mechanism are unclear. Cu appears to have unique properties for example, the congener Ag shows no catalytic activity. Thus, the investigation of the differences between Cu and Ag on Si surfaces can help in understanding the catalytic process. Furthermore, the bonding of noble metal atoms to Si surfaces is of great importance in the physics and chemistry of electronic devices. 

---