We report here the results of electrochemical studies on CO2 electroreduction at multilayered catalyst composed of the monatomic layer of copper covering palladium overlayers (0.8-10 monolayers) deposited on the well-defined Au(111) surface. These multilayered systems were obtained by successive underpotential deposition steps: Pd on Au(111) as well as Cu on Pd/Au(111). Low index orientation of Au substrate was chosen to compare Pd overlayers with bulk Pd(111), which is known to reduce CO2 to CO adsorbates in acidic solutions. The process of CO2 electroreduction was studied by using classical transient electrochemical methods. Catalytic activity of bare Pd layers was investigated in acidic and neutral solutions. In the latter case, much higher activity of Pd overlayers was observed. The results showed that the palladium layer thickness significantly changed the catalytic activities of both bare Pd overlayers and the one Cu monolayer covered electrodes toward CO2 electroreduction. Results show that catalytic activity can be finely tuned by using the multilayered near-surface-alloy approach.

The functionalized carbon nanostructure, nitrogen and sulfur co-doped iron-containing highly porous carbon gel (obtained via carbonization of corresponding organic gel) is considered here as a non-precious metal catalyst for the electroreduction of carbon dioxide in neutral solution (potassium bicarbonate at pH = 6.8). Various electrochemical measurements (performed in distinct modes and under different conditions) have been utilized to comment about the catalyst performance and the reaction mechanism, in particular about the reaction products and the relative contribution from hydrogen evolution. At low overpotentials, the carbon dioxide reduction is favored over the hydrogen evolution reaction. Combination of conventional (stationary) stripping-type and hydrodynamic (rotating ring-disk electrode) voltammetric approaches has been demonstrated to function as an unique electroanalytical tool here. The CO 2 -reduction products can be identified as adsorbates (oxidative stripping voltammetry) or monitored continuously (electrooxidation) at the Pt ring electrode. Finally, the results of both electrochemical diagnostic and parallel gas chromatographic analytical measurements are consistent with the view that, in the examined range of the potentials, CO is the main CO 2 -reduction product. The electrochemical reduction of carbon dioxide (CO 2 ) permits, in principle, selective generation of carbon-based fuels (or syngas) and, indirectly, lowering population of one of green-house gases in the atmosphere. Due to existence of two strong C=O bonds in the CO 2 molecule, its electroreduction requires high overpotentials, and the low reaction efficiency still remains fundamental problem limiting practical applications. 1-3During recent years, various catalysts, including noble and non-noble transition metals, as well as their numerous coordination compounds, have been considered as catalysts for CO 2 electroreduction. [4][5][6][7][8][9][10] It has been demonstrated that selectivity of the process depends largely on the activating adsorptive (CO 2 ) phenomena and the affinity of catalytic centers to adsorbed carbon monoxide intermediate. 11 Depending on the strength of adsorption and according to the Sabatier principle, CO may be further protonated or hydrogenated to CHO adsorbate. This step is often considered as the rate-determining one during the hydrocarbon formation.12 It should be noted here that, for example, copper is capable of successfully catalyzing electroreduction of CO 2 to multicarbon products, 13-15 palladium induces the reaction mainly to CO and H 2 and only small amounts of formate. 2,[16][17][18][19] Another important practical issue is related to the need of lowering costs of catalysts by substituting the noble metals with inexpensive abundant elements. There has been growing interest in catalysts based on nanostructured carbons that include the metal-free Ndoped systems and the metal-containing carbons. [20][21][22][23][24][25][26] For example, the biomimetic centers containing metallic moieties in the vi...

Small (4 nm) nanoparticles with a narrow size distribution, exceptional surface purity, and increased surface order, which exhibits itself as an increased presence of basal crystallographic planes, can be obtained without the use of any surfactant. These nanoparticles can be used in many applications in an as-received state and are threefold more active towards a model catalytic reaction (oxidation of ethylene glycol). Furthermore, the superior properties of this material are interesting not only due to the increase in their intrinsic catalytic activity, but also due to the exceptional surface purity itself. The nanoparticles can be used directly (i.e., as-received, without any cleaning steps) in biomedical applications (i.e., as more efficient drug carriers due to an increased number of adsorption sites) and in energy-harvesting/data-storage devices.

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The real composition of nanostructure strongly determines its properties. Especially, in some cases the bulk composition of material could be different than the surface composition due to the surface segregation. Surface segregation is a common process caused by different surface energy of elements. Moreover the surface (in the sense of first atomic layer) composition is very important knowledge in many science fields e.g. semiconductors functionalization, environmental protection or pollution remediation. One of such a surface science is heterogeneous catalysis. In this field surface composition is extremely important because chemical reaction occurs only at catalyst surface. The X-ray Photoelectron Spectroscopy is surface sensitive technique, which could determine samples' composition. In this method, depending on the material, major amount of signal is collected from the first 5 nm of the sample. Nevertheless for nanostructures like core-shell nanoparticles such an XPS analysis is more challenging due to the diameter of nanoparticles which is usually around 5 nm. Although with more complex analysis, which includes Inelastic Mean Free Path model for each element building nanoparticle, we can more effectively describe observed segregation [1]. Figure1. XPS quantitative analysis for Pt-Rh nanoparticles in function of nominal platinum content. Two data sets are shown black line-determined from higher energetic Pt 4f doublet and red line-determined from higher energetic Pt 4d doublet. Increased Pt content in topmost layer can be observed. In this report we determined composition and described surface segregation in bimetal alloy-PtRh nanoparticles. We determined surface composition using monochromatic XPS measurement and we compared it with total composition obtained by ICP-MS (Inductively Coupled Plasma-Mass Spectrometry). Thanks to determining the actual surface composition in this material we could properly correlate catalytic properties of this material to Rhodium content on the surface. Our results demonstrate the strength of X-ray Photoelectron Spectroscopy technique in such interdisciplinary studies.

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The paper presents selected methods of assessment of tooth preparation based on the literature, among others, computer software cooperating with scanners, e.g. Preppr, DentSim, PREPassistant, E4D Compare, PrepCheck and Simodont Dental Trainer. During tooth preparation for prosthetic restorations, it is necessary to create sufficient space, which will allow the technician to construct an aesthetic and durable restoration. Hard tissues should be prepared very sparingly, while at the same time providing retention and stabilization as well as marginal integration for future restoration. The anatomy of the occlusal surface should be preserved, and the axial walls reduced to the proper thickness to obtain an optimal degree of convergence angle, which equals 6 o. The most common errors in tooth preparation for crowns are inadequate reduction of the occlusal surface, the lack of functional cusp bevel and incorrect finish line width. The occlusal surface is excessively reduced on average by 15%, whereas the width of the finish line on the vestibular surface is about 28% too small. The results of the convergence angle measurement exceed three times the recommended values in the literature, which can adversely affect the retention of restoration.

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