This paper reports the effects of substrate roughness on the odd-even effect in n-alkanethiolate self-assembled monolayers (SAMs) probed by vibrational sum frequency generation (SFG) spectroscopy. By fabricating SAMs on surfaces across the so-called odd-even limit, we demonstrate that differentiation of the vibrational frequencies of CH from SAMs derived from alkyl thiols with either odd (SAM) or even (SAM) numbers of carbons depends on the roughness of the substrate on which they are formed. Odd-even oscillation in SFG susceptibility amplitudes was observed for spectra derived from SAM and SAM fabricated on flat surfaces (RMS roughness = 0.4 nm) but not on rougher surfaces (RMS roughness = 2.38 nm). In addition, we discovered that local chemical environments for the terminal CH group have a chain-length dependence. There seems to be a transition at around C, beyond which SAMs become "solid-like".

It is well recognized that both alkali and alkali earth metals have a poisoning effect on selective catalytic reduction (SCR) catalyst. In this study, the different poisoning effects of K and Mg on Mn/TiO 2 catalyst were investigated. It was found that the deactivation effect of K was much stronger than that of Mg. The effect of K or Mg addition on the physicochemical properties of Mn/TiO 2 catalyst was investigated based on N 2 adsorption, XRD, XPS, H 2 -TPR, NH 3 -TPD, and NO-TPD techniques. The results indicated that the addition of K or Mg on Mn/TiO 2 catalyst would decrease its specific area, promote the crystallization of TiO 2 , and lead to a decrease of Mn 4+ and surface chemisorbed oxygen. Furthermore, the presence of K or Mg on Mn/TiO 2 catalyst would lead to the drop of reducibility and the adsorption capacity of NH 3 and NOx species. In addition, the adsorption behavior of NH 3 and NOx and their surface reactions over the fresh and poisoned Mn/TiO 2 catalysts were investigated by in situ DRIFT study. It was found that the NH 3 −SCR reaction over Mn/TiO 2 −Mg was mainly controlled by the L−H mechanism (≤150 °C) and E−R mechanism (>200 °C), while the NH 3 −SCR reaction over Mn/TiO 2 −K mainly followed the E−R pathway. The deactivation of Mn/TiO 2 −Mg mainly resulted from the inhibited adsorption and oxidation of NO, and the seriously suppressed adsorption of NH 3 species made a great contribution to the deactivation of Mn/TiO 2 −K.

Low-temperature scanning tunneling microscope investigations reveal that hexabromobenzene (HBB) molecules arrange in either hexagonally closely packed (hcp) [Formula: see text] or tetragonal [Formula: see text] structure on Au(111) dependent on a small substrate temperature difference around 300 K. The underlying mechanism is investigated by density functional theory calculations, which reveal that substrate-mediated intermolecular noncovalent C-Br···Br-C attractions induce hcp HBB islands, keeping the well-known Au(111)-22×√3 reconstruction intact. Upon deposition at 330 K, HBB molecules trap freely diffusing Au adatoms to form tetragonal islands. This enhances the attraction between HBB and Au(111) but partially reduces the intermolecular C-Br···Br-C attractions, altering the Au(111)-22×√3 reconstruction. In both cases, the HBB molecule adsorbs on a bridge site, forming a ∼15° angle between the C-Br direction and [112̅]Au, indicating the site-specific molecule-substrate interactions. We show that the competition between intermolecular and molecule-substrate interactions determines molecule packing at the subnanometer scale, which will be helpful for crystal engineering, functional materials, and organic electronics.

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