Role Of Surface Hydroxyls Research Articles

The role of surface hydroxyls in the entropy-driven adsorption and spillover of H2 on Au/TiO2 catalysts

The role of surface hydroxyls in the entropy-driven adsorption and spillover of H2 on Au/TiO2 catalysts

The Role of Surface Hydroxyls in the Mobility of Carboxylates on Surfaces: Dynamics of Acetate on Anatase TiO2(101).

The dynamics of reactive intermediates are important in catalysis for understanding transient species, which can drive reactivity and the transport of species to reaction centers. In particular, the interplay between surface-bound carboxylic acids and carboxylates is important for numerous chemical transformations, including CO2 hydrogenation and ketonization. Here, we investigate the dynamics of acetic acid on anatase TiO2(101) using scanning tunneling microscopy experiments and density functional theory calculations. We demonstrate the concomitant diffusion of bidentate acetate and a bridging hydroxyl and provide evidence for the transient formation of molecular monodentate acetic acid. The diffusion rate is strongly dependent on the position of hydroxyl and adjacent acetate(s). A facile three-step diffusion process is proposed consisting of acetate and hydroxyl recombination, acetic acid rotation, and acetic acid dissociation. This study clearly demonstrates that the dynamics of bidentate acetate could be important in forming monodentate species, which are proposed to drive selective ketonization.

The role of surface hydroxyls on ZnZrOx solid solution catalyst in CO2 hydrogenation to methanol

ZnZrOx solid solution catalyst is an excellent catalyst in methanol synthesis from CO2 hydrogenation. It is still highly aspiration to make any further improvement in catalytic performance. In this work, ZnZrOx solid solution catalyst is prepared with different methods, resulting in different surface property. The ZnZrOx solid solution catalyst prepared by reflux ammonia (ZnZrOx-RA) exhibits higher methanol selectivity of 95.2% and CO2 conversion of 3.3% than that of the catalyst obtained via co-precipitation (ZnZrOx-CP) at 280 °C, 5 MPa. Subsequent kinetics analysis shows that ZnZrOx-RA, in comparison to ZnZrOx-CP, shows a decreased activation energy for methanol synthesis, an increased reaction order in H2, and a similar reaction order in CO2. Structural characterizations indicate that these two catalysts are in solid solution state, while ZnZrOx-RA possesses more Zn-OH species on the surface. The surface Zn-OH species enhance the activation and adsorption of CO2 and H2, and improve the generation and stability of HCOO* species, which promote CO2 hydrogenation to methanol.

A theoretical study of the atomic layer deposition of HfO2 on Si(1 0 0) surfaces using tetrakis(ethylmethylamino) hafnium and water

The atomic layer deposition (ALD) of hafnium oxide (HfO2) thin film has attracted considerable attention owing to its crucial role in downscaling semiconductor devices. Herein, we theoretically investigated the reaction mechanisms during the ALD of HfO2 thin film (HfO2–ALD) on silicon (Si) surface using tetrakis(ethylmethylamino) hafnium (TEMAH) and water. By using two surface models, fully and partially hydroxylated Si(100) surfaces, we demonstrated that controlling the concentration of hydroxyl groups on the surface is important to enhance the activity for ligand-exchange reactions (LERs) of TEMAH and thereby effectively promote HfO2–ALD. During the precursor pulse, LERs on the fully hydroxylated Si(100) surface easily convert TEMAH into an unsaturated Hf atom with a low energy barrier of 25.8 kJ/mol, while mono(ethylmethylamino) hafnium (MEMAH) is obtained as the final product on the partially hydroxylated Si(100) surface with an energy barrier of 61.3 kJ/mol. The remaining ligand of the adsorbed MEMAH can be removed via LER with water during the water pulse. This work not only provides a better understanding of the conversion of TEMAH into a Hf atom on the hydroxylated Si(100) surface but also offers us more insights into the role of surface hydroxyls in the formation of HfO2 thin films.

The role of surface hydroxyls on the radiolysis of gibbsite and boehmite nanoplatelets

Understanding mechanistic pathways to radiolytic hydrogen generation by metal oxyhydroxide nanomaterials is challenging because of the difficulties of distinguishing key locations of OH bond scission, from structural interiors to hydroxylated surfaces to physi-sorbed water molecules. Here we exploited the interface-selectivity of vibrational sum frequency generation (VSFG) to isolate surface versus bulk hydroxyl groups for gibbsite and boehmite nanoplatelets before and after 60Co irradiation at dose levels of approximately 7.0 and 29.6 Mrad. While high-resolution microscopy revealed no effect on particle bulk and surface structures, VSFG results clearly indicated up to 83% and 94% radiation-induced surface OH bond scission for gibbsite and boehmite, respectively, a substantially higher proportion than observed for interior OH groups by IR and Raman spectroscopy. Electron paramagnetic spectroscopy revealed that the major radiolysis products bound in the mineral structures are trapped electrons, O, O2− and possibly F-centers in gibbsite, and H, O and O3− in boehmite, which persist on the time frame of several months. The entrapped radiolysis products appear to be highly stable, enduring re-hydration of particle surfaces, and likely reflect a permanent adjustment in the thermodynamic stabilities of these nanomaterials.

The Role of Surface Hydroxylation, Lattice Vacancies and Bond Covalency in the Electrochemical Oxidation of Water (OER) on Ni-Depleted Iridium Oxide Catalysts

Abstract The usage of iridium as an oxygen-evolution-reaction (OER) electrocatalyst requires very high atom efficiencies paired with high activity and stability. Our efforts during the past 6 years in the Priority Program 1613 funded by the Deutsche Forschungsgemeinschaft (DFG) were focused to mitigate the molecular origin of kinetic overpotentials of Ir-based OER catalysts and to design new materials to achieve that Ir-based catalysts are more atom and energy efficient, as well as stable. Approaches involved are: (1) use of bimetallic mixed metal oxide materials where Ir is combined with cheaper transition metals as starting materials, (2) use of dealloying concepts of nanometer sized core-shell particle with a thin noble metal oxide shell combined with a hollow or cheap transition metal-rich alloy core, and (3) use of corrosion-resistant high-surface-area oxide support materials. In this mini review, we have highlighted selected advances in our understanding of Ir–Ni bimetallic oxide electrocatalysts for the OER in acidic environments.

CO oxidation over Au/TiO2 catalyst: Pretreatment effects, catalyst deactivation, and carbonates production

A commercially available Au/TiO2 catalyst was subjected to a variety of thermal treatments in order to understand how variations in catalyst pretreatment procedures might affect CO oxidation catalysis. Catalytic activity was found to be inversely correlated to the temperature of the pretreatment. Infrared spectroscopy of adsorbed CO experiments, followed by a Temkin analysis of the data, indicated that the thermal treatments caused essentially no changes to the electronics of the Au particles; this, and a series of catalysis control experiments, and previous transmission electron microscopy (TEM) studies ruled out particle growth as a contributing factor to the activity loss. Fourier transform infrared (FTIR) spectroscopy showed that pretreating the catalyst results in water desorption from the surface, but the observable water loss was similar for all the treatments and could not be correlated with catalytic activity. A Michaelis–Menten kinetic treatment indicated that the main reason for deactivation is a loss in the number of active sites with little changes in their intrinsic activity. In situ FTIR experiments during CO oxidation showed extensive buildup of carbonate-like surface species when the pretreated catalysts were contacted with the feed gas. A semi-quantitative infrared spectroscopy method was developed for comparing the amount of carbonates present on each catalyst; results from these experiments showed a strong correlation between the steady-state catalytic activity and amount of surface carbonates generated during the initial moments of catalysis. Further, this experimental protocol was used to show that the carbonates reside on the titania support rather than on the Au, as there was no evidence that they poison Au–CO binding sites. The role of the carbonates in the reaction scheme, their potential role in catalyst deactivation, and the role of surface hydroxyls and water are discussed.

On the role of surface hydroxyls during the Cr/SiO 2-catalyzed polymerization of ethylene

The onset of polymerization of ethylene over a 0.5% chromium supported on silica catalyst was studied using a diffraction-type IR spectrophotometer. Detailed investigations emphasizing the hydroxyl region of the IR spectrum suggested the importance of silanol groups in the processes of reaction initiation, termination, and catalyst deactivation. The formation of chromium-bound hydroxyls and their role in catalyst deactivation were suggested.

Role of surface hydroxyls in the nucleation of sputtered tantalum films

Role of surface hydroxyls in the nucleation of sputtered tantalum films