The structural sensitivity of the water-gas shift (WGS) reaction (CO + H20 --* H, + CO, ) over metallic copper is addressed here by comparing its kinetics over the atomically clean Cu(ll0) surface with prior results for Cu(ll1). The surfaces were prepared and characterized with UHV surface analysis (AES, LEED. XPS), then transferred to an attached microreactor for medium-pressure [ l O -l O O O Torr (1 Torr = 101 325/760 Pa)] kinetic measurements and finally returned to UHV for post-reaction surface analysis. For both surfaces, the rate is nearly first-order in H, O pressure and zero-order in CO. Depending upon the temperature, Cu(ll0) is four-to ten-fold more active than the more densely packed Cu(ll1) surface. The apparent activation energy is also ca. 7 kcal mol-' (1 cal = 4.184 J) lower on Cu(ll0). This is attributed to a lower barrier for 0-H bond cleavage in the rate-determining step: i.e. the dissociative adsorption of water. Strong evidence for a 'surface redox' mechanism involving oxygen adatoms is provided by comparing the known kinetics of reverse WGS with the rate of dissociative C02 adsorption on Cu(ll0). A potential-energy diagram is presented which explains the known kinetics and energetics for the elementary steps as occurring in the forward or reverse direction, as well as the overall WGS reaction on clean Cu(ll0). The influence of adsorbed Cs on the reaction kinetics is also presented, and compared to earlier results on Cs/Cu(lll). In both cases, Cs strongly accelerates the reaction. In the case of Cu(llO), the rate-determining step is even changed. The reaction mechanism involves Cs . CO, , a and Cs -0,.

The development of 'user-friendly' surface analytical instrumentation has expanded the application of x-ray photoelectron spectroscopy (XPS) towards softer and more complex composite materials. However, the knowledge of fundamental phenomena in practical, interdisciplinary applications is dearly needed. In the case of polymers and polymer-based or -reinforced composites, the analytical problems are not only related to detection limits and resolution; indeed, the effects of contamination and experimental artefacts on interpretation of the carbon signal are often the more crucial challenge.As a biopolymer, natural cellulose fibres provide an interesting model system for polymer studies. Numerous published XPS studies on lignocelluloses highlight both the possibilities and the problems of the surface analytical probes in analysis of air-exposed organic materials.We report XPS experiments of cellulosic natural fibre materials, discussing the effects of sample storage, UHV exposure, radiation doses, charging and data analysis. Based on a large body of experimental data we also propose that clean paper specimens could be used as an in-situ reference in polymer studies.

The interactions of benzene with the clean and Bi-dosed Pt(lll) surface have been studied between 110 and 850 K with a combination of thermal desorption mass spectroscopy (TDS), X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES). Below ~350 K, benzene adsorbs molecularly. The first monolayer saturates at a coverage of 0.16 (molecules per Pt atom). About 55% of this dehydrogenates upon heating to liberate H2 in a series of steps between 450 and 800 K. This leaves residual carbon on the surface in a graphitic overlayer. The remaining benzene desorbs molecularly at ~505 K (Eá qí 30.8 kcal/mol) and 350 K (E¿ =* 21 kcal/mol). Substantial isotopic scrambling is seen in TDS from coadsorbed mixtures of C6H6 and C6D6. The activation energies for dehydrogenation of perdeuterated benzene are ~1.2

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This paper combines theoretical considerations with experimental evidence to explain the behavior of cellulose when exposed to different media. The observations are explained based on the amphiphilic character of the cellulose molecule and fundamental physicochemical phenomena. Nanofibrillated cellulose was chosen to demonstrate the phenomena since due to its high surface area the effects at issue are pronounced. X-Ray photoelectron spectroscopy and contact angle measurements were used to demonstrate the chemical and energetical changes taking place on the cellulose surface, and atomic force microscopy was used to follow nanoscale structural changes. Due to its hydrophilicity cellulose is well dispersed in water. However, when exposed to non-polar media like air or organic solvents cellulose undergoes partly irreversible reorganization like aggregation or surface passivation in order to find the energetically most favorable state. We show that when NFC is dried directly from water it aggregates strongly and accumulates a very high amount of non-cellulosic material on the surface. Very similar effects also occur when using non-polar media like toluene. Hence, both the reactivity and nanoscale structure are lost. In contrast, NFC retains its reactivity and nano-scaled structure in amphiphilic media like dimethyl acetamide as is confirmed with a simple silylation reaction. We conclude that the interfacial phenomenon is general for cellulosic material but has the most practical impact on applications of nanoscaled cellulose or ultrathin cellulose films.

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We show a simple method toward nanoscale cilia-like structures, i.e., functional hairy surfaces, upon topochemically functionalizing nanorods of cellulose nanocrystals (CNCs) with thiol end groups (CNC-SHs), which leads to their immobilization onto a gold surface from one end, still allowing their orientational mobility. CNCs having a lateral dimension of 3-5 nm and length of 50-500 nm incorporate the native crystalline structure with hydrogen-bonded cellulose chains in the parallel configuration. This facilitates asymmetric, selective chemical modification of the reducing ends through reductive amination. Successful thiol functionalization is demonstrated using cryo transmission electron microscopy based on selective attachment of silver nanoparticles to the CNC-SH ends to form Janus-like colloidal rod-sphere adducts. The extent of thiol modification of CNC-SHs is quantified using X-ray photoelectron spectroscopy. The promoted binding of CNC-SHs on gold surfaces is shown by atomic force microscopy and quartz crystal microbalance, where the high dissipation suggests pronounced orientational mobility due to flexible joints at one rod end onto the surfaces. That the joints are flexible is also shown by the bending and realignment of the CNC-SH rods using a receding triple-phase evaporation front of a drying drop of water. The ability of the hairy surface to size-selectively resist particle binding was also investigated. As the CNCs are piezoelectric and allow magnetic functionalization by nanoparticles, we foresee a general platform for nanosized artificial cilia for fluid manipulation and controlled adsorption/desorption.