Complexity of Intercalation in MXenes: Destabilization of Urea by Two-Dimensional Titanium Carbide.

MXenes are a new class of two-dimensional materials with properties that make them important for applications that include batteries, capacitive energy storage, and electrocatalysis. These materials can be exfoliated and delaminated to create high surface areas with interlayers accessibility. Intercalation is known to be possible, and it is critical for many applications including electrochemical energy storage, water purification, and sensing.

A high precision gas flow cell for performing in situ neutron studies of local atomic structure in catalytic materials.

Gas-solid interfaces enable a multitude of industrial processes, including heterogeneous catalysis; however, there are few methods available for studying the structure of this interface under operating conditions. Here, we present a new sample environment for interrogating materials under gas-flow conditions using time-of-flight neutron scattering under both constant and pulse probe gas flow. Outlined are descriptions of the gas flow cell and a commissioning example using the adsorption of N by Ca-exchanged zeolite-X (NaCaAlSiO,x ≈ 38).

Diphosphine-Protected Au Nanoclusters on Oxide Supports Are Active for Gas-Phase Catalysis without Ligand Removal.

Investigation of atomically precise Au nanoclusters provides a route to understand the roles of coordination, size, and ligand effects on Au catalysis. Herein, we explored the catalytic behavior of a newly synthesized Au(L) nanocluster (L = 1,8-bis(diphenylphosphino) octane) with in situ uncoordinated Au sites supported on TiO, CeO, and AlO. Stability of the supported Au nanoclusters was probed structurally by in situ extended X-ray absorption fine structure (EXAFS) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and their ability to adsorb and oxidize CO was investigated by IR absorption spectroscopy and a temperature-programmed flow reaction.

Dehydrogenation of methanol to formaldehyde catalyzed by pristine and defective ceria surfaces.

We have explored the dehydrogenation of methoxy on pristine and defective (111), (100), and (110) ceria surfaces with density functional methods. Methanol conversion is used as a probe reaction to understand structure sensitivity of the oxide catalysis. Differences in reaction selectivity have been observed experimentally as a function of crystallographically exposed faces and degree of reduction.

Understanding catalyst behavior during in situ heating through simultaneous secondary and transmitted electron imaging.

By coupling techniques of simultaneous secondary (SE) and transmitted electron (TE) imaging at high resolution in a modern scanning transmission electron microscope (STEM), with the ability to heat specimens using a highly stable MEMS-based heating platform, we obtained synergistic information to clarify the behavior of catalysts during in situ thermal treatments. Au/iron oxide catalyst 'leached' to remove surface Au was heated to temperatures as high as 700°C. The Fe2O3 support particle structure tended to reduce to Fe3O4 and formed surface terraces; the formation, coalescence, and mobility of 1- to 2-nm particles on the terraces were characterized in SE, STEM-ADF, and TEM-BF modes.

Hierarchically superstructured prussian blue analogues: spontaneous assembly synthesis and applications as pseudocapacitive materials.

Hierarchically superstructured Prussian blue analogues (hexacyanoferrate, M=Ni(II) , Co(II) and Cu(II) ) are synthesized through a spontaneous assembly technique. In sharp contrast to macroporous-only Prussian blue analogues, the hierarchically superstructured porous Prussian blue materials are demonstrated to possess a high capacitance, which is similar to those of the conventional hybrid graphene/MnO2 nanostructured textiles. Because sodium or potassium ions are involved in energy storage processes, more environmentally neutral electrolytes can be utilized, making the superstructured porous Prussian blue analogues a great contender for applications as high-performance pseudocapacitors.

Thiolate ligands as a double-edged sword for CO oxidation on CeO2 supported Au25(SCH2CH2Ph)18 nanoclusters.

The effect of thiolate ligands was explored on the catalysis of CeO2 rod supported Au25(SR)18 (SR = -SCH2CH2Ph) by using CO oxidation as a probe reaction. Reaction kinetic tests, in situ IR and X-ray absorption spectroscopy, and density functional theory (DFT) were employed to understand how the thiolate ligands affect the nature of active sites, activation of CO and O2, and reaction mechanism and kinetics. The intact Au25(SR)18 on the CeO2 rod is found not able to adsorb CO.

Identifying active functionalities on few-layered graphene catalysts for oxidative dehydrogenation of isobutane.

The general consensus in the studies of nanostructured carbon catalysts for oxidative dehydrogenation (ODH) of alkanes to olefins is that the oxygen functionalities generated during synthesis and reaction are responsible for the catalytic activity of these nanostructured carbons. Identification of the highly active oxygen functionalities would enable engineering of nanocarbons for ODH of alkanes. Few-layered graphenes were used as model catalysts in experiments to synthesize reduced graphene oxide samples with varying oxygen concentrations, to characterize oxygen functionalities, and to measure the activation energies for ODH of isobutane.

Ionic liquid derived carbons as highly efficient oxygen reduction catalysts: first elucidation of pore size distribution dependent kinetics.

Metal-free N-doped carbons with controllable pore texture were derived from carbonization of ionic liquid and served as catalysts for oxygen reduction reaction (ORR) with an activity comparable to that of Pt/C. The investigation shows that both the ORR activity and kinetics are strongly correlated with the pore size distribution.

Structure of Au15(SR)13 and its implication for the origin of the nucleus in thiolated gold nanoclusters.

Au15(SR)13 is the smallest stable thiolated gold nanocluster experimentally identified so far, and its elusive structure may hold the key to the origin of the nucleus in the formation of thiolated gold nanoclusters. By an extensive exploration of possible isomers by density functional theory, we arrive at a novel structure for Au15(SR)13 with high stability and whose optical absorption characteristics match those of the experiment. Different from the previous structures and the prevailing working hypothesis about the construction of thiolated gold nanoclusters, the Au15(SR)13 model features a cyclic [Au(I)-SR] pentamer interlocked with one staple trimer motif protecting the tetrahedral Au4 nucleus, together with another trimer motif.

Oxygen-functionalized few-layer graphene sheets as active catalysts for oxidative dehydrogenation reactions.

Nanostructured graphitic forms of carbons have shown intersting potential for catalysis research and are ideal candidates to substitute the conventional metal-oxide catalysts because they can be easily disposed, which enables a greener, more sustainable catalytic process. Few-layer graphene and its functionalized form offer the opportunity to investigate the nature of graphitic active sites for oxidation reactions in well-defined carbon-based catalysts. In this paper, we report the utilization of oxygen-functionalized few-layer graphene sheets containing variable amounts of oxygen in the heterogeneous catalytic oxidative dehydrogenation (ODH) reaction of isobutane at 400ºC.

Oxygen vacancy-assisted coupling and enolization of acetaldehyde on CeO2(111).

The temperature-dependent adsorption and reaction of acetaldehyde (CH(3)CHO) on a fully oxidized and a highly reduced thin-film CeO(2)(111) surface have been investigated using a combination of reflection-absorption infrared spectroscopy (RAIRS) and periodic density functional theory (DFT+U) calculations. On the fully oxidized surface, acetaldehyde adsorbs weakly through its carbonyl O interacting with a lattice Ce(4+) cation in the η(1)-O configuration. This state desorbs at 210 K without reaction.

Novel MEMS-based gas-cell/heating specimen holder provides advanced imaging capabilities for in situ reaction studies.

In prior research, specimen holders that employ a novel MEMS-based heating technology (Aduro™) provided by Protochips Inc. (Raleigh, NC, USA) have been shown to permit sub-Ångström imaging at elevated temperatures up to 1,000°C during in situ heating experiments in modern aberration-corrected electron microscopes. The Aduro heating devices permit precise control of temperature and have the unique feature of providing both heating and cooling rates of 10⁶°C/s.

Support Shape Effect in Metal Oxide Catalysis: Ceria-Nanoshape-Supported Vanadia Catalysts for Oxidative Dehydrogenation of Isobutane.

The support effect has long been an intriguing topic in catalysis research. With the advancement of nanomaterial synthesis, the availability of faceted oxide nanocrystals provides the opportunity to gain unprecedented insights into the support effect by employing these well-structured nanocrystals. In this Letter, we show by utilizing ceria nanoshapes as supports for vanadium oxide that the shape of the support poses a profound effect on the catalytic performance of metal oxide catalysts.

Dynamics of phenanthrenequinone on carbon nano-onion surfaces probed by quasielastic neutron scattering.

We used quasielastic neutron scattering (QENS) to study the dynamics of phenanthrenequinone (PQ) on the surface of onion-like carbon (OLC), or so-called carbon onions, as a function of surface coverage and temperature. For both the high- and low-coverage samples, we observed two diffusion processes; a faster process and nearly an order of magnitude slower process. On the high-coverage surface, the slow diffusion process is of long-range translational character, whereas the fast diffusion process is spatially localized on the length scale of ∼4.

A solid molecular basket sorbent for CO2 capture from gas streams with low CO2 concentration under ambient conditions.

In this paper, a solid molecular basket sorbent, 50 wt% PEI/SBA-15, was studied for CO(2) capture from gas streams with low CO(2) concentration under ambient conditions. The sorbent was able to effectively and selectively capture CO(2) from a gas stream containing 1% CO(2) at 75 °C, with a breakthrough and saturation capacity of 63.1 and 66.

Interaction of Gold Clusters with a Hydroxylated Surface.

We explore the interaction between gold nanoclusters and a fully hydroxylated surface, Mg(OH)2's basal plane, by using a density functional theory-enabled local basin-hopping technique for global-minimum search. We find strong interaction of gold nanoclusters with the surface hydroxyls via a short bond between edge Au atoms and O atoms of the -OH groups. We expect that this strong interaction is ubiquitous on hydroxylated support surfaces and helps the gold nanoclusters against sintering, thereby contributing to their CO-oxidation activity at low temperatures.

Low-temperature exfoliation of multilayer-graphene material from FeCl3 and CH3NO2 co-intercalated graphite compound.

Microwave induced rapid decomposition of nitromethane at low temperature exfoliates the graphene sheets from the FeCl(3) and CH(3)NO(2) co-intercalated graphite compound without creating many defects and functional groups. This approach provides a scalable method for high-quality graphene materials via low-temperature exfoliation of graphite under mild chemical conditions.

Synthesis of silica supported AuCu nanoparticle catalysts and the effects of pretreatment conditions for the CO oxidation reaction.

Supported gold nanoparticles have generated an immense interest in the field of catalysis due to their extremely high reactivity and selectivity. Recently, alloy nanoparticles of gold have received a lot of attention due to their enhanced catalytic properties. Here we report the synthesis of silica supported AuCu nanoparticles through the conversion of supported Au nanoparticles in a solution of Cu(C(2)H(3)O(2))(2) at 300 °C.

Probing defect sites on CeO2 nanocrystals with well-defined surface planes by Raman spectroscopy and O2 adsorption.

Defect sites play an essential role in ceria catalysis. In this study, ceria nanocrystals with well-defined surface planes have been synthesized and utilized for studying defect sites with both Raman spectroscopy and O(2) adsorption. Ceria nanorods ({110} + {100}), nanocubes ({100}), and nano-octahedra ({111}) are employed to analyze the quantity and quality of defect sites on different ceria surfaces.

Behavior of Au species in Au/Fe2O3 catalysts characterized by novel in situ heating techniques and aberration-corrected STEM imaging.

The recent advent of a novel design of in situ heating technology for electron microscopes has permitted unprecedented control of elevated temperature studies of catalytic materials, particularly when coupled with the sub-Angström imaging performance of a modern aberration-corrected scanning transmission electron microscope (STEM). Using micro-electro-mechanical-systems (MEMS)-based Aduro heating chips from Protochips, Inc. (Raleigh, NC, USA) allows nearly instantaneous heating and cooling of catalyst powders, avoiding effects of temperature ramping as experienced with standard heating stages.

Temperature evolution of structure and bonding of formic acid and formate on fully oxidized and highly reduced CeO2(111).

Adsorption of formate on oxide surfaces plays a role in water-gas shift (WGS) and other reactions related to H(2) production and CO(2) utilization. CeO(2) is of particular interest because its reducibility affects the redox of organic molecules. In this work, the adsorption and thermal evolution of formic acid and formate on highly ordered films of fully oxidized CeO(2)(111) and highly reduced CeO(x)(111) surfaces have been studied using reflection absorption infrared spectroscopy (RAIRS) under ultra-high vacuum conditions, and the experimental results are combined with density functional theory (DFT) calculations to probe the identity, symmetry, and bonding of the surface intermediates.

Open-cage fullerene-like graphitic carbons as catalysts for oxidative dehydrogenation of isobutane.

We report herein a facile synthesis of fullerene-like cages, which can be opened and closed through simple thermal treatments. A glassy carbon with enclosed fullerene-like cages of 2-3 nm was synthesized through a soft-template approach that created open mesopores of 7 nm. The open mesopores provided access to the fullerene-like cages, which were opened and closed through heat treatments in air and inert gas at various temperatures.

Evolution of gold structure during thermal treatment of Au/FeOx catalysts revealed by aberration-corrected electron microscopy.

High-resolution aberration-corrected electron microscopy was performed on a series of catalysts derived from a parent material, 2 at.% Au/Fe(2)O(3) (WGC ref. no.