8 research outputs found
Recommended from our members
Conversion of γ-Valerolactone to Ethyl Valerate over Metal Promoted Ni/ZSM-5 Catalysts : Influence of Ni0/Ni2+ Heterojunctions on Activity and Product Selectivity
Promoter (Cr, Mo and W) modified Ni/ZSM-5 catalysts were explored in the vapor phase conversion of γ-valerolactone (GVL) to ethyl valerate (EV; gasoline blender) at atmospheric pressure. Among the three different promoters (Cr, Mo and W) tested the Mo-modified catalyst was found to be the best candidate. In addition, this catalyst was found to be stable up to 50 h reaction time with an insignificant decrease in activity. The good catalytic performance is related to an optimal ratio of acid and hydrogenation functions provided by Ni2+ and Ni0, respectively. In situ FTIR spectroscopic studies revealed a strong adsorption of GVL on all catalysts which quickly reacts with dosed ethanol by formation of EV, most pronounced on the Mo-modified catalyst, while VA was identified as side product. These findings suggest the preferred GVL ring opening by cracking the C−O bond on the methyl side of the GVL molecule on this type of catalysts leading to pentenoic acid as intermediate, which is quickly hydrogenated and esterified. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA
Impact of surface defects on LaNiO3 perovskite electrocatalysts for the oxygen evolution reaction
Perovskite oxides are regarded as promising electrocatalysts for water splitting due to their cost-effectiveness, high efficiency and durability in the oxygen evolution reaction (OER). Despite these advantages, a fundamental understanding of how critical structural parameters of perovskite electrocatalysts influence their activity and stability is lacking. Here, we investigate the impact of structural defects on OER performance for representative LaNiO3 perovskite electrocatalysts. Hydrogen reduction of 700¿°C calcined LaNiO3 induces a high density of surface oxygen vacancies, and confers significantly enhanced OER activity and stability compared to unreduced LaNiO3; the former exhibit a low onset overpotential of 380 mV at 10 mA¿cm-2 and a small Tafel slope of 70.8 mV¿dec-1. Oxygen vacancy formation is accompanied by mixed Ni2+/Ni3+ valence states, which quantum-chemical DFT calculations reveal modify the perovskite electronic structure. Further, it reveals that the formation of oxygen vacancies is thermodynamically more favourable on the surface than in the bulk; it increases the electronic conductivity of reduced LaNiO3 in accordance with the enhanced OER activity that is observed.Peer ReviewedPostprint (author's final draft
Oxygen-deficient photostable Cu2O for enhanced visible light photocatalytic activity
Oxygen vacancies in inorganic semiconductors play an important role in reducing electron-hole recombination, which may have important implications in photocatalysis. Cuprous oxide (Cu2O), a visible light active p-type semiconductor, is a promising photocatalyst. However, the synthesis of photostable Cu2O enriched with oxygen defects remains a challenge. We report a simple method for the gram-scale synthesis of highly photostable Cu2O nanoparticles by the hydrolysis of a Cu(i)-triethylamine [Cu(i)-TEA] complex at low temperature. The oxygen vacancies in these Cu2O nanoparticles led to a significant increase in the lifetimes of photogenerated charge carriers upon excitation with visible light. This, in combination with a suitable energy band structure, allowed Cu2O nanoparticles to exhibit outstanding photoactivity in visible light through the generation of electron-mediated hydroxyl (OH) radicals. This study highlights the significance of oxygen defects in enhancing the photocatalytic performance of promising semiconductor photocatalysts.V. B. thanks the Australian Research Council (ARC) for a
Future Fellowship (FT140101285) and funding support
through an ARC Discovery (DP170103477). ARC is also
acknowledged for DECRA Fellowships to E. D. G.
(DE170100164) and J. v. E. (DE150100427) and a Future
Fellowship to N. C. (FT1401000834). M. S. acknowledges RMIT
University for an Australian Postgraduate Award (APA). A. E. K.,
E. D. G., P. R. and R. R. acknowledge RMIT University for Vice
Chancellor Fellowships. V. B. recognizes the generous support
of the Ian Potter Foundation toward establishing an Ian Potter
NanoBioSensing Facility at RMIT University. The authors
acknowledge the support from the RMIT Microscopy and
Microanalysis Facility (RMMF) for technical assistance and
providing access to characterization facilities. This work was
also supported by the ARC Centre of Excellence for Nanoscale
BioPhotonics (CE140100003)
Nanowire Morphology of Mono- and Bidoped α‑MnO<sub>2</sub> Catalysts for Remarkable Enhancement in Soot Oxidation
In the present work,
nanowire morphologies of α-MnO<sub>2</sub>, cobalt monodoped
α-MnO<sub>2</sub>, Cu and Co bidoped α-MnO<sub>2</sub>, and Ni and Co bidoped α-MnO<sub>2</sub> samples were prepared
by a facile hydrothermal synthesis. The structural, morphological,
surface, and redox properties of all the as-prepared samples were
investigated by various characterization techniques, namely, scanning
electron microscopy (SEM), transmission and high resolution electron
microscopy (TEM and HR-TEM), powder X-ray diffraction (XRD), N<sub>2</sub> sorption surface area measurements, X-ray photoelectron spectroscopy
(XPS), hydrogen-temperature-programmed reduction (H<sub>2</sub>-TPR),
and oxygen-temperature-programmed desorption (O<sub>2</sub>-TPD).
The soot oxidation performance was found to be significantly improved
via metal mono- and bidoping. In particular, Cu and Co bidoped α-MnO<sub>2</sub> nanowires showed a remarkable improvement in soot oxidation
performance, with its <i>T</i><sub>50</sub> (50% soot conversion)
values of 279 and 431 °C under tight and loose contact conditions,
respectively. The soot combustion activation energy for the Cu and
Co bidoped MnO<sub>2</sub> nanowires is 121 kJ/mol. The increased
oxygen vacancies, greater number of active sites, facile redox behavior,
and strong synergistic interaction were the key factors for the excellent
catalytic activity. The longevity of Cu and Co bidoped α-MnO<sub>2</sub> nanowires was analyzed, and it was found that the Cu/Co bidoped
α-MnO<sub>2</sub> nanowires were highly stable after five successive
cycles and showed an insignificant decrease in soot oxidation activity.
Furthermore, the HR-TEM analysis of a spent catalyst after five cycles
indicated that the (310) crystal plane of α-MnO<sub>2</sub> interacts
with the soot particles; therefore, we can assume that more-reactive
exposed surfaces positively affect the reaction of soot oxidation.
Thus, the Cu and Co bidoped α-MnO<sub>2</sub> nanowires provide
promise as a highly effective alternative to precious metal based
automotive catalysts
A spatially orthogonal hierarchically porous acid–base catalyst for cascade and antagonistic reactions
Complex organic molecules are of great importance to research and industrial chemistry and typically synthesized from smaller building blocks by multistep reactions. The ability to perform multiple (distinct) transformations in a single reactor would greatly reduce the number of manipulations required for chemical manufacturing, and hence the development of multifunctional catalysts for such one-pot reactions is highly desirable. Here we report the synthesis of a hierarchically porous framework, in which the macropores are selectively functionalized with a sulfated zirconia solid acid coating, while the mesopores are selectively functionalized with MgO solid base nanoparticles. Active site compartmentalization and substrate channelling protects base-catalysed triacylglyceride transesterification from poisoning by free fatty acid impurities (even at 50 mol%), and promotes the efficient two-step cascade deacetalization-Knoevenagel condensation of dimethyl acetals to cyanoates