Infrared spectrometric studies of the surface basicity of metal oxides and zeolites using adsorbed probe molecules

Machine learning methods can be useful for materials discovery; however certain properties remain difficult to predict. Here, the authors present a universal machine learning approach for modelling the properties of inorganic crystals, which is validated for eight electro…

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Universal fragment descriptors for predicting properties of inorganic crystals

Nanoscale structural information underlies research aimed at fabricating catalysts in a more controlled way. Surface science methods can provide that information, but the complexity of heterogeneous systems in general hinders the application of these methods to their full potential. In the last decades, a solution to this problem has been found in the use of model systems, ranging from well-defined single crystals of the supported phase to films or particles of that phase on flat or spherical model supports. In this paper, we review the literature on the latter model systems, that is, particles on a model support. Attention is payed to both preparation and use of such model systems.

https://pure.tue.nl/ws/files/1495087/617871.pdf

Surface Science Approach to Modeling Supported Catalysts

The specific heat C of a sintered polycrystalline sample of MgB 2 with a bulk superconducting transition temperature T c =36.7 K is measured as a function of the temperature (2–300 K) and magnetic field (0–16 T), together with magnetic properties (normal-state susceptibility, superconducting-state magnetization, etc.). The Sommerfeld constant γ =0.89±0.05 mJ/K 2 /gat (2.7 mJ/K 2 /mol) is determined in the normal state above H c2 . The normal- and superconducting-state entropies are equal at T c . Several moments of the PDOS are obtained from the lattice specific heat. We report bulk values for: the thermodynamic critical field, B c (0)=0.26 T; the slope of the upper critical field, (d B c2 /d T ) T c =0.56 T/K; the Ginzburg–Landau parameter, κ =38; the coherence length, ξ ≅5 nm; the lower critical field, B c1 ≅0.018 T; the London penetration depth, λ (0)≅180 nm. These results characterize MgB 2 as a type-II superconductor. The nearly quadratic dependence of C ( T ) versus T at T ≪ T c , its non-linear field dependence, and the discrepancy between the electron–phonon coupling constant λ ep as determined by the renormalization of the electron density of states ( λ ep ≅0.6) and by McMillan's equation for isotropic superconductors ( λ ep ≅1.1), are inconsistent with a single isotropic gap. In addition to high phonon frequencies, anisotropy or two-band gap structure may explain why the critical temperature of this superconductor is high in spite of its low condensation energy, which does not exceed 1/16 of that of YBa 2 Cu 3 O 7 and 1/4 of that of Nb 3 Sn.

Specific heat in the superconducting and normal state (2–300 K, 0–16 T), and magnetic susceptibility of the 38 K superconductor MgB2: evidence for a multicomponent gap

The adsorption of pyridine, carbon dioxide (CO2), and formic acid (HCOOH) on various types of surface sites of ZrO2, vacant sites (for example:  bare surface Zr4+O2- ions), and those modified by terminal (t-) and bridged (b-) OH as well as t- and b-methoxy (OCH3) groups, has been studied by infrared (IR) spectroscopy. The selective reaction of CO2 with the t-OH group at 213 K and the adsorption of pyridine to replace the t-OH group on ZrO2 at 373−573 K confirms that t-HO−Zr site possesses acidic and basic properties. Moreover, the nucleophilic substitution adsorption of pyridine occurs more actively at the t-HO−Zr site than that at the vacant t-site on ZrO2. At 523 K, HCOOH reacts with basic t-OH or t-OCH3 species before the b-OH or b-OCH3 species. The selective reaction of HCOOH with t- and b-OCH3 groups on ZrO2 disappears at 573 K. The high activity of t-HO−Zr sites is attributed to relatively stronger Lewis acidic sites generated by releasing t-OH groups in the adsorption, and is also related to the hi...

D. Defourneau

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