Dendrimer-Stabilized Metal Nanoparticles as Efficient Catalysts for Reversible Dehydrogenation/Hydrogenation of N-Heterocycles
Not Available
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Engineering topics
Ralston, Walter T.
Publications and source records attributed to Ralston, Walter T..
Fluorinated End-Groups in Electrolytes Induce Ordered Electrolyte/Anode Interface Even at Open-Circuit Potential as Revealed by Sum Frequency Generation Vibrational Spectroscopy
Fluorine-based additives have a tremendously beneficial effect on the performance of lithium-ion batteries, yet the origin of this phenomenon is unclear. This study shows that the formation of a solid-electrolyte interphase (SEI) on the anode surface in the first five charge/discharge cycles is affected by the stereochemistry of the electrolyte molecules on the anode surface starting at open-circuit potential (OCP). This study shows an anode-specific model system, the reduction of 1,2-diethoxy ethane with lithium bis(trifluoromethane)sulfonimide, as a salt on an amorphous silicon anode, and compares the electrochemical response and SEI formation to its fluorinated version, bis(2,2,2-trifluoroethoxy) ethane (BTFEOE), by sum frequency generation (SFG) vibrational spectroscopy under reaction conditions. The SFG results suggest that the —CF 3 end-groups of the linear ether BTFEOE change their adsorption orientation on the a-Si surface at OCP, leading to a better protective layer. Finally, supporting evidence from ex situ scanning electron microscopy and X-ray photoelectron spectroscopy depth profiling measurements shows that the fluorinated ether, BTFEOE, yields a smooth SEI on the a-Si surface and enables lithium ions to intercalate deeper into the a-Si bulk.
36 MATERIALS SCIENCE↗
In Situ Spectroscopic Investigation into the Active Sites for Crotonaldehyde Hydrogenation at the Pt Nanoparticle–Co 3 O 4 Interface
The hydrogenation of crotonaldehyde by platinum nanoparticles supported on cobalt oxide was used as a reaction to probe the effect of the interface between the two materials on the activity and selectivity of the catalyst. Four potential products can be formed by this reaction: propylene, butyraldehyde, crotyl alcohol, and butanol. When Pt nanoparticles are supported on SiO 2 , an inert support, only propylene and butyraldehyde are formed. However, when Pt is supported on cobalt oxide, the alcohols make up roughly 40% of the total activity, indicating that cobalt oxide plays a pivotal role in the reaction, much like other active supports such as TiO 2 . To elucidate the mechanism of alcohol formation, in situ sum frequency generation vibrational spectroscopy (SFG) and ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) were utilized to probe the reactant adsorption and intermediate formation and the chemical state of the materials under working catalytic conditions. The SFG data indicate that crotonaldehyde adsorbs on the oxide surface, likely through the aldehyde oxygen as well as on the Pt surface through the alkene group. AP-XPS results show that the surface of the Co 3 O 4 support becomes partially reduced under the reaction conditions and Pt exists in its metallic state. Taking these results together, we propose in this paper that the crotonaldehyde adsorbs at reduced oxide surface sites and that this adsorption mode is responsible for the production of alcohol products. A platinum nanoparticle density dependence study was also undertaken to change the abundance of interface sites and study their effect on the reaction. The selectivity between the two alcohol products was altered as a function of the Pt nanoparticle density: higher selectivity toward butanol and lower selectivity toward crotyl alcohol was obtained with increasing density, while propylene and butyraldehyde selectivities were constant with respect to density. Finally, on the basis of the data presented, we propose that butanol is preferentially formed at the metal–oxide interface, while crotyl alcohol is formed at oxide surface sites by reaction with spillover hydrogen.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Metal Nanoparticles Catalyzed Selective Carbon–Carbon Bond Activation in the Liquid Phase
Not Available
36 MATERIALS SCIENCE↗
Soft X-ray spectroscopy studies of adsorption and reaction of CO in the presence of H 2 over 6 nm MnO nanoparticles supported on mesoporous Co 3 O 4
MnO nanoparticles (6 nm) were supported on mesoporous spinel Co 3 O 4 and studied using ambient pressure X-ray photoelectron spectroscopy (APXPS) and in situ X-ray absorption spectroscopy (XAS) during hydrogenation of CO. The nature and evolution of surface adsorbed species as well as the oxidation states of the metal oxide surfaces were evaluated under oxidizing, reducing, and H 2 + CO (2:1) reaction atmospheres. From APXPS, MnO nanoparticle surfaces were found to be progressively reduced in H 2 atmospheres with increasing temperature. Surface adsorbed CO was found to be formed at the expense of lattice O under H 2 + CO reaction conditions. In situ XAS indicated that the dominant oxide species were Co(OH) 2 , Co (II) oxides, MnO, and Mn 3 O 4 under reaction conditions. In situ XAS also indicated the formation of gas phase CO 2 , the disappearance of lattice O, and the further reduction of Mn 3 O 4 to MnO upon prolonged reaction in H 2 + CO. Mass spectroscopy measurements showed the formation of CO 2 and hydrocarbons. Finally, the spent catalyst was investigated using scanning transmission X-ray microscopy and (scanning) transmission electron microscopy; the catalyst grains were found to be homogeneous.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Corrosion behavior of mesoporous transition metal nitrides
Transition metal nitrides (TMN) have many desirable characteristics such as high hardness and good thermal stability under reducing conditions. This work reports an initial survey of the chemical stability of mesoporous TMNs (TM=Nb, V, Cr and Ti) in water at 80 °C at neutral, acidic and alkaline pH. The mesoporous TMNs had specific surface areas of 25–60 m{sup 2}/g with average pore sizes ranging from 10 to 50 nm. The high surface areas of these materials enhance the rate of corrosion per unit mass over that of a bulk material, making detection of corrosion much easier. The products were characterized by Rietveld refinement of powder X-ray diffraction (PXRD) patterns and by scanning electron microscopy (SEM). Several nitrides have corrosion rates that are, within error, not distinguishable from zero (±1 Å/day). Of the nitrides examined, CrN appears to be the most corrosion resistant under acidic conditions. None of the nitrides studied are corrosion resistant under alkaline conditions. - Graphical abstract: Corrosion behavior of mesoporous transition metal nitrides (TM=Nb, V, Cr and Ti) in acidic and alkaline solutions at 80 °C for 2 weeks. Display Omitted - highlights: • Corrosion rates of mesoporous transition metal nitrides in aqueous solution is reported. • The mesoporous TMNs had surface areas of 25–60 m{sup 2}/g. • CrN is the most corrosion resistant under the conditions studied.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Mesoporous VN prepared by solid-solid phase separation
We recently reported a simple route to prepare mesoporous, conducting nitrides from Zn containing ternary transition metal oxides. Those materials result from the condensation of atomic scale voids created by the loss of Zn by evaporation, the replacement of 3 oxygen anions by 2 nitrogen anions, and in most cases the loss of oxygen to form water on the reduction of the transition metal. In this report, we present a different route to prepare mesoporous VN from K containing vanadium oxides. In this case, ammonolysis results in a multiphase solid product that contains VN, and other water soluble compounds such as KOH or KNH{sub 2}. On removing the K containing products by washing with degassed water, only mesoporous VN remains. VN materials with different pore sizes (10 nm-20 nm) were synthesized at 600 Degree-Sign C by varying the reaction time, while larger pores are obtained at higher temperatures (50 nm at 800 Degree-Sign C). - Graphical Abstract: The synthesis process of mesoporous VN from solid-solid separation. Highlights: Black-Right-Pointing-Pointer Mesoporous VN has been prepared by solid-solid phase separation. Black-Right-Pointing-Pointer Mesoporous VN was characterized by Rietveld refinement of PXRD, SEM and nitrogen physisorption. Black-Right-Pointing-Pointer VN materials with different pore sizes (10 nm-50 nm) were synthesized.
36 MATERIALS SCIENCE↗