The non-oxidative dehydrogenation of ethanol to acetaldehyde has long been considered as an important method to produce acetaldehyde and clean hydrogen gas. Although monometallic Cu nanoparticles have high activity in the non-oxidative dehydrogenation of ethanol, they quickly deactivate due to sintering of Cu. Herein, we show that adding a small amount of Ni (Ni 0.01 Cu-Ni 0.001 Cu) into Cu to form highly dilute NiCu alloys dramatically increases the catalytic activity and increases their long-term stability. The kinetic studies show that the apparent activation energy decreases from ~70 kJ/mol over Cu to ~45 kJ/mol over the dilute NiCu alloys. The improved performance is observed both for nanoparticles and nanoporous NiCu alloys. The improvement in the long-term stability of the catalysts is attributed to the stabilization of Cu against sintering. Our characterization data show that Ni is atomically dispersed in Cu. The comparison of the catalytic performance of highly dilute alloy nanoparticles with nanoporous materials is useful to guide the design of novel mesoporous catalyst architectures for selective dehydrogenation reactions.

Understanding photochemical processes on nanomaterials is key to developing effective photocatalysts. Herein, methanol oxidation and reduction is used to probe the thermal and photochemical properties of rutile titania nanowires grown using a hydrothermal method. The presence of oxygen vacancy defects leads to methoxy formation and subsequent disproportionation to formaldehyde and methanol at 700 K. Methane and dimethyl ether are also produced in minor quantities. Oxygen adatoms enhance the formation of methoxy, which led to an increase in the disproportionation products and dimethyl ether at high temperature and a decreased amount of methane. The thermal reactivity of the nanowires parallels that of rutile TiO2(110) single crystals. Photo-oxidation of methoxy using UV light produced formaldehyde and methyl formate. These product yields were enhanced on nanowires with oxygen adatoms, but a majority of methoxy (∼70%) is not photoactive. In contrast, all methoxy is photo-oxidized on rutile TiO2(110) when O-adatoms are present. This difference indicates that holes created in the nanowires during UV excitation do not migrate to most of the methoxya required step for methoxy photo-oxidation. This lack of activity could be due to either trapping of holes in the material or different binding of the inactive methoxy. These studies demonstrate that while charge carriers can be efficiently created in nanowires differences in chemical properties can suppress photo-oxidation.

Many application-relevant properties of nanoporous metals critically depend on their multiscale architecture. For example, the intrinsically high step-edge density of curved surfaces at the nanoscale provides highly reactive sites for catalysis, whereas the macroscale pore and grain morphology determines the macroscopic properties, such as mass transport, electrical conductivity, or mechanical properties. In this work, we systematically study the effects of alloy composition and dealloying conditions on the multiscale morphology of nanoporous copper (np-Cu) made from various commercial Zn-Cu precursor alloys. Using a combination of X-ray diffraction, electron backscatter diffraction, and focused ion beam cross-sectional analysis, our results reveal that the macroscopic grain structure of the starting alloy surprisingly survives the dealloying process, despite a change in crystal structure from body-centered cubic (Zn-Cu starting alloy) to face-centered cubic (Cu). The nanoscale structure can be controlled by the acid used for dealloying with HCl leading to a larger and more faceted ligament morphology compared to that of HPO. Anhydrous ethanol dehydrogenation was used as a probe reaction to test the effect of the nanoscale ligament morphology on the apparent activation energy of the reaction.

In situ and ex situ X-ray photoelectron spectroscopy and electron-microscopy reveal that the stability of nanoporous NiCu alloy catalysts for non-oxidative ethanol dehydrogenation improves by generating kinetically trapped Ni²⁺ subsurface states.

3D nanoporous metals made by alloy corrosion have attracted much attention due to various promising applications ranging from catalysis and sensing to energy storage and actuation. In this work we report a new process for the fabrication of 3D open nanoporous metal networks that phenomenologically resembles the nano-Kirkendall hollowing process previously reported for Ag/Au nanowires and nanoparticles, with the difference that the involved length scales are 10–100 times larger. Specifically, we find that dry oxidation of Ag70Au30 bulk alloy samples by ozone exposure at 150 °C stimulates extremely rapid Ag outward diffusion toward the gas/alloy-surface interface, at rates at least 5 orders of magnitude faster than predicted on the basis of reported Ag bulk diffusion values. The micrometer-thick Ag depleted alloy region thus formed transforms into a 3D open nanoporous network morphology upon further exposure to methanol–O2 at 150 °C. These findings have important implications for practical applications of alloys, for example as catalysts, by demonstrating that large-scale compositional and morphological changes can be triggered by surface chemical reactions at low temperatures, and that dilute alloys such as Au97Ag3 are more resilient against such changes.

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To improve the understanding of catalytic processes, the surface structure and composition of the active materials need to be determined before and after reaction. Morphological changes may occur under reaction conditions and can dramatically influence the reactivity and/or selectivity of a catalyst. Gold‐based catalysts with different architectures are currently being developed for selective oxidation reactions at low temperatures. Specifically, nanoporous Au (npAu) with a composition of Au 97 ‐Ag 3 is obtained by dealloying a Ag 70 ‐Au 30 bulk alloy. Recent studies highlight the efficiency of npAu catalysts for methanol oxidation as well as the importance of the residual Ag in the catalytic process. Ozone is used to activate the catalysts before methanol oxidation. In this work, we studied the morphological and compositional changes occurring at the surface of Au‐based catalysts of different compositions. To get better insight of the Ag distribution within the Au backbone, we first analysed nanoporous Au catalysts (composition: Au 97 ‐Ag 3 ) by atom probe tomography (APT). APT is a powerful technique to characterize the composition and 3D structure of materials at the atomic‐scale, but the presence of pores make the analysis and reconstruction difficult. New developments in sample preparation are required, and we were able to successfully image npAu samples by atom probe tomography and analyse the segregation of Ag atoms in the npAu sample ( Fig. 1 ). Complimentary experiments were performed on a bulk sample of the same composition, and XPS and APT experiments confirm the surface segregation of Ag (as silver oxide species) after ozone treatment, which is then reduced after exposing the catalyst to reaction conditions. Further experiments were performed on bulk Ag 70 ‐Au 30 samples which were exposed to ozone and reaction conditions. Ozone induces the segregation of Ag at the surface, which forms a distinct black layer of silver oxides. Below this oxide, a homogeneous Ag‐depleted region (Ag 56 ‐Au 44 ) can be observed, and extends over a depth of a few μm (the depth depends on the duration of the ozone treatment). As it can be seen on Fig. 2 , this region undergoes severe morphological changes, and the bulk sample becomes porous. FIB cross‐section analysis proves the segregation behaviour and long‐range diffusion of Ag in bulk samples, as compared to the nanoscale‐segregation observed by APT, correlating previous observations by E‐TEM. The nanoconfinement induced by the specific architecture of the nanoporous sample is then responsible of the long term stability and efficiency of the catalyst. This study highlights the importance of ozone treatment in the segregation of Ag at the surface, which can dramatically influence the local chemistry and morphology of a catalyst. The combination of APT, FIB/SEM and XPS allows studying the surface and subsurface compositional and morphological changes of the sample after various physicochemical treatments, and also allows the segregation behaviour of Ag in different Au‐based catalysts to be correlated.