Brolly good MOFs: A new series of hydrophobic isoreticular porous Zr oxide dicarboxylate MOFs have been prepared (see picture, Zr blue polyhedra, O red, C black). They have a one‐dimensional pore ...system, a rare combination of Lewis acidity and hydrophobic character, and a higher hydrothermal and mechanical stability than their UiO MOF polymorph counterparts.
A careful choice of the surface coverage of iron phthalocyanine (FePc) on Ag (110) around the single monolayer allows us to drive with high precision both the long-range supramolecular arrangement ...and the local adsorption geometry of FePc molecules on the given surface. We show that this opens up the possibility of sharply switching the catalytic activity of FePc in the oxygen reduction reaction and contextual surface oxidation in a reproducible way. A comprehensive and detailed picture built on diverse experimental evidence from scanning tunnelling microscopy, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy, coupled with density functional theory calculations, sheds new light on the nature of the catalytically active molecule-surface coordination and on the boundary conditions for its occurrence. The results are of relevance for the improvement of the catalytic efficiency of metallo-macrocycles as viable substitutes for platinum in the cathodic compartment of low-temperature fuel cells.
In this contribution we evaluated the effect of synthesis procedure (complexing molecule, calcination temperature) and doping on the properties and catalytic performance of SrTiO
3
. Focusing on ...preparation we compared two complexants: citric acid and glycine calcinating the catalysts at 700 and 850 °C. Moreover, we doped the perovskite substituting Sr with K and Ti with Mn. The obtained catalysts have been characterized by X-Ray diffraction, X-Ray photoelectron spectroscopy, BET, scanning electron microscopy, energy dispersive X-Ray analysis, temperature programmed reduction. To evaluate the effect of upon mentioned aspects on the catalytic activity, the following reactions have been considered: CO oxidation, CO assisted NO reduction, soot oxidation. The obtained results underline the deep effect of dopants, with particular reference to Mn, on the catalytic performance.
The adsorption of formic acid and sodium formate on the stoichiometric anatase (101) surface has been studied by means of density functional calculations with a slab geometry. On the clean surface, ...the most stable adsorption structure for HCOOH is a molecular monodentate configuration, hydrogen bonded to a surface bridging oxygen, while for HCOONa a dissociated bridging bidentate geometry is preferred. The bidentate chelating structure is energetically unstable for both the acid and the salt. On the hydrated surface, both HCOOH and HCOONa preferentially form an inner-sphere adsorption complex. HCOOH maintains a monodentate coordination, but, due to the interaction with a nearby water molecule, it becomes dissociated, while HCOONa again prefers a bridging bidentate structure. The energies for adsorption from an aqueous solution are estimated to be 0.30 and 0.79 eV for HCOOH and HCOONa, respectively.
SrTi
0.7
Co
0.3
O
3
, SrTi
0.7
Cu
0.3
O
3
, SrTi
0.7
Co
0.15
Cu
0.15
O
3
were prepared by the “citrate route” and characterized (XRD, XPS, SEM, TPR). Their reactivity with respect to CO oxidation and ...NO reduction was investigated and compared with that of CuO/SrTi
0.7
Co
0.3
O
3
nanocomposite. High conversions were obtained in CO oxidation (90 % at 350 °C for SrTi
0.7
Co
0.3
O
3
). Only CuO/SrTi
0.7
Co
0.3
O
3
was observed to be active in NO reduction (100 % at 350 °C).
Graphical Abstract
Iron(II) phthalocyanine (FePc) self-assembly on Ag(110) has been studied in ultrahigh-vacuum conditions at room temperature by means of scanning tunneling microscopy (STM) and density functional ...theory (DFT) calculations. For submonolayer to monolayer coverage, FePc molecules lie parallel to the Ag(110) surface, arranged in rows running along the 001 direction. Two similar yet distinct ordered phases are formed, the c(10 × 4) and p(10 × 4) superstructures. The latter is characterized by two equivalent equilibrium configurations of the constituent FePc units, that interconvert by means of a concerted transformation wherein molecules belonging to adjacent rows collectively rotate in opposite directions around the molecular axis perpendicular to the surface. The FePc adsorption site for both superstructures and the transition mechanism between the two configurations in the p(10 × 4) phase have been inferred from high resolution STM images and rationalized by means of DFT calculations. In the case of multilayer films a (1 ± 4, 4 ∓3) phase is observed, whose stacking geometry has been revealed by STM analysis. The p(10 × 4)/c(10 × 4) → (1 ± 4, 4 ∓3) coverage-dependent transformation is analyzed by DFT calculations, and shown to be driven by the overlayer−substrate interaction. The inclusion of the dispersion contribution to this interaction is found to be essential to correctly reproduce the observed phenomenon.
Thermal self-assembly of C60 on (1 × 2)-Pt(110) following room-temperature deposition has been studied by means of scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and ...density functional theory (DFT) calculations. Two distinct C60 chemisorption phases have been identified and characterized as a function of the annealing temperature. After a thermal treatment at 700 K, islands of a C60 quasi-hexagonal lattice form. These islands are characterized by the highest surface density so far reported for a two-dimensional surface-supported fullerene phase (the surface area per molecule is 87.0 Å2), with intermolecular nearest-neighbor distances equal to 9.6 ± 0.1 Å. Embedded nanowires of fullerene dumbbell dimers (with an intermolecular distance equal to 9.2 ± 0.1 Å) occasionally nucleate within this high-density phase following a “molecular zip” mechanism. Highly site selective chemisorption driven by the particularly strong overlayer−substrate bonding is proposed to be responsible for the first reported example of surface-templated chemical bond formation between fullerene molecules. After annealing at 850 K, an oblique C60 chemisorption phase forms. This is characterized by a tetramolecular basis associated to each lattice point of the two-dimensional superstructure and by a peculiar bright−dim contrast in STM images acquired at positive sample bias values. The combination of high-resolution STM images with LEED data and DFT calculations leads to the conclusion that the (1 × 2) substrate reconstruction is lifted at the fullerene−platinum interface and also provides a detailed description of the molecular bonding sites and orientations found within the phase. It is proposed that the main factor ruling the interconversion of chemisorption phases is the variation of substrate atom mobility as a function of temperature.
The molecular adsorption of some probe molecules (CO, H2O, and H2S) on a 5-fold-coordinated Ti Lewis acid site of the TiO2 rutile (110) surface is studied within the density functional theory. The ...substrate is modeled with a small Ti7O9 cluster terminated with pseudo-hydrogens. This is found to describe the electronic and structural properties of the clean surface in good agreement with both experimental and periodic slab calculations. Adsorption energies (6.7, 19.3, and 7.0 kcal/mol for CO, H2O, and H2S, respectively) and adsorbate stretching frequencies compare favorably with available experimental data. The agreement is particularly good for the C−O stretching frequency shift (+56 cm-1), as was found in previous investigations carried out with the same theoretical approach on other oxides. In contrast, the HOH scissoring mode is poorly reproduced, suggesting that molecularly adsorbed H2O is actually involved in weak bonds with other adsorbed species. This agrees with predictions of very recent slab calculations by Lindan et al. (Phys. Rev. Lett. 1998, 80, 762). Differences with respect to calculations carried out by embedding the cluster in point-charge arrays are discussed.
Brolly good MOFs: A new series of hydrophobic isoreticular porous Zr oxide dicarboxylate MOFs have been prepared (see picture, Zrblue polyhedra, Ored, Cblack). They have a one-dimensional pore ...system, a rare combination of Lewis acidity and hydrophobic character, and a higher hydrothermal and mechanical stability than their UiO MOF polymorph counterparts.
The interaction of single C60 molecules with the (1 × 2)-Pt(110) surface has been studied by scanning tunneling microscopy and density functional theory (DFT) calculations on slab models. Molecules ...are observed to be frozen at room temperature and are found to be almost exclusively in the same configuration. Extensive DFT calculations show that this configuration is the global energy minimum, suggesting that adsorbed molecules have enough rototranslational freedom to escape from the numerous local minima. The adsorption energy (3.81 eV) is the strongest ever found for C60, and it is roughly proportional to the number of the Pt and C atoms at contact distance. Analysis of DFT results shows that the surface−adsorbate interaction is covalent in nature. A minority fraction of C60 molecules appear to be adsorbed on surface defects. A careful investigation of their registry and height with respect to the regularly adsorbed units leads to an indirect structural characterization of the nanopits which act as their adsorption sites.
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