Interaction of adsorbates with clean and metal-covered oxide surfaces

Der rationale Ansatz, der einen tiefen Einblick in diese Systeme auf atomarer Ebene ermöglicht, ist die "Surface Science"-Untersuchung mit Hilfe von modernsten Oberflächen-Analysemethoden unter Ultrahochvakuum-Bedingungen. In dieser Arbeit wurden die Adsorptionen und Reaktionen einer Anzahl von Molekülen ($H_{2}$, $H_{2}O$, CO, $CO_{2}$, $CH_{2}O$, HCOOH, und $CH_{3}OH$) auf verschiedenen reinen und metall- bedeckten Oxid-Einkristalloberflächen (ZnO und $TiO_{2}$) durch kombinierte Techniken einschließlich hochauflösender Elektronen-Energieverlust-Spektroskopie (HREELS), Thermodesorptionsspektroskopie (TDS) und Beugung niederenergetischer Elektronen (LEED) untersucht. Basierend auf den detaillierten experimentellen Daten wurden wichtige Informationen über die strukturellen und elektronischen Eigenschaften sowie chemische Aktivitäten der perfekten, defekten und metallbedeckten Oxidoberflächen gewonnen.The physical and chemical properties of low dimensional systems such as thin films, nanoparticles and clean solid surfaces have attracted increasing research interest in the recent decades. The most popular way to get an atomic level insight into them is the surface science study using advanced surface analytical methods under ultrahigh vacuum (UHV) conditions. In this work, the adsorption and reactions of a number of molecules ($H_{2}$, $H_{2}O$, CO, $CO_{2}$, $CH_{2}O$, HCOOH, and $CH_{3}OH$) on clean and metal-covered single crystalline oxide surfaces (ZnO and $TiO_{2}$) were studied by combined techniques including high resolution electron energy loss spectroscopy (HREELS), thermal desorption spectroscopy (TDS) and low electron energy diffraction (LEED). On the basis of the detailed experimental data, important information has been obtained about the structural and electronic properties as well as chemical activities of perfect, defective and metal-covered oxide surfaces

Catalytic Hydrogenation of CO₂ to Methanol: A Review

High-efficiency utilization of CO2 facilitates the reduction of CO2 concentration in the global atmosphere and hence the alleviation of the greenhouse effect. The catalytic hydrogenation of CO2 to produce value-added chemicals exhibits attractive prospects by potentially building energy recycling loops. Particularly, methanol is one of the practically important objective products, and the catalytic hydrogenation of CO2 to synthesize methanol has been extensively studied. In this review, we focus on some basic concepts on CO2 activation, the recent research advances in the catalytic hydrogenation of CO2 to methanol, the development of high-performance catalysts, and microscopic insight into the reaction mechanisms. Finally, some thinking on the present research and possible future trend is presented

Catalytic Hydrogenation of CO2 to Methanol: A Review

High-efficiency utilization of CO2 facilitates the reduction of CO2 concentration in the global atmosphere and hence the alleviation of the greenhouse effect. The catalytic hydrogenation of CO2 to produce value-added chemicals exhibits attractive prospects by potentially building energy recycling loops. Particularly, methanol is one of the practically important objective products, and the catalytic hydrogenation of CO2 to synthesize methanol has been extensively studied. In this review, we focus on some basic concepts on CO2 activation, the recent research advances in the catalytic hydrogenation of CO2 to methanol, the development of high-performance catalysts, and microscopic insight into the reaction mechanisms. Finally, some thinking on the present research and possible future trend is presented

Tuning the reactivity of oxide surfaces by charge-accepting adsorbates

Bridging the materials and pressure gaps : The adsorption of CO on ZnO surfaces becomes much stronger in the presence of preadsorbed CO2 (see picture; O red, Zn gray, C green). The increased strength of the interaction between CO and polycrystalline ZnO powder originates from the formation of tridentate carbonate species on the mixed-terminated (1010) surfaces, which increase the Lewis acidity of neighboring Zn2+ cations. (Figure Presented).</p

Clarification of Active Sites at Interfaces between Silica Support and Nickel Active Components for Carbon Monoxide Methanation

Identification of active site is critical for developing advanced heterogeneous catalysis. Here, a nickel/silica (Ni/SiO2) catalyst was prepared through an ammonia-evaporation method for CO methanation. The as-obtained Ni/SiO2 catalyst shows a CO conversion of 96.74% and a methane selectivity of 93.58% at 623 K with a weight hourly space velocity of 25,000 mL&middot;g&minus;1&middot;h&minus;1. After 150 h of continuous testing, the CO conversion still retains 96%, which indicates a high catalyst stability and long life. An in situ vacuum transmission infrared spectrum demonstrates that the main active sites locate at the interface between the metal Ni and the SiO2 at a wave number at 2060 cm&minus;1 for the first time. The interesting discovery of the active site may offer a new insight for design and synthesis of methanation catalysts

A Bulk Boron-Based Photocatalyst for Efficient Dechlorination: K₃B₆O₁₀Br

Nanoparticles of a borate nonlinear optical material, K₃B₆O₁₀Br (KBB), have been fabricated and demonstrated excellent catalytic activity in UV-induced dechlorination of chlorophenols, which are typical persistent organic pollutants. The obtained dechlorination efficiency is 2 orders of magnitude higher than that of a commercial P25 TiO₂ catalyst under UV (λ > 254 nm) light irradiation. The noncentrosymmetric structure of KBB gives rise to an intrinsic large polarization effect as evidenced by Kelvin probe force microscopy, and the polarization promotes separation of photogenerated electron–hole pairs, leading to efficient cleavage of chlorophenols into small molecular fragments and dissociative Cl^– anions. This work suggests that nonlinear materials open a new window for designing efficient photocatalysts