Preface

Click on the DOI link to access the article (may not be free).Energy and environmental issues are of great concerns for the public and will keep increasing in the next few decades. The demand for clean energy sources in our current society also increases with large-scale economic developments and population growth. It is crucial to build clean energy systems

The influence of water vapour on the photocatalytic oxidation of cyclohexane in an internally illuminated monolith reactor

This paper discusses effects of humidity on photocatalytic cyclohexane oxidation performed in an internally illuminated monolith reactor equipped with an immobilised layer of approximately 3 μm titania (Hombikat uv100). Using dry nitrogen containing 10–20% of oxygen, cyclohexanone is produced with high selectivity (>90%) over cyclohexanol. The photocatalytic monolith deactivates within 80 min of operation. Regeneration of activity of such deactivated monolith is possible by air treatment at 450 °C. When the applied nitrogen/oxygen gas is humidified, stable ketone production rates are obtained around 5 × 10−6 mol h−1 at an optimised relative humidity of 65%. Ketone over alcohol selectivity is lower in humidified conditions, the ratio of the cyclohexanol/cyclohexanone production rates increases from 0.4 to 1.0 as a function of increasing humidity from 30% to 90%. Rapid transients in water vapour content lead to relatively slow changes in concentration of in situ produced cyclohexanone and cyclohexanol. The observation of these changes is used to explain the effect of humidity on reactor performance

Investigation of the Deactivation Phenomena Occurring in the Cyclohexane Photocatalytic Oxidative Dehydrogenation on MoOx/TiO2 through Gas Phase and in situ DRIFTS Analyses

In this work, the results of gas phase cyclohexane photocatalytic oxidative dehydrogenation on MoOx/SO4/TiO2 catalysts with DRIFTS analysis are presented. Analysis of products in the gas-phase discharge of a fixed bed photoreactor was coupled with in situ monitoring of the photocatalyst surface during irradiation with an IR probe. An interaction between cyclohexane and surface sulfates was found by DRIFTS analysis in the absence of UV irradiation, showing evidence of the formation of an organo-sulfur compound. In particular, in the absence of irradiation, sulfate species initiate a redox reaction through hydrogen abstraction of cyclohexane and formation of sulfate (IV) species. In previous studies, it was concluded that reduction of the sulfate (IV) species via hydrogen abstraction during UV irradiation may produce gas phase SO2 and thereby loss of surface sulfur species. Gas phase analysis showed that the presence of MoOx species, at same sulfate loading, changes the selectivity of the photoreaction, promoting the formation of benzene. The amount of surface sulfate influenced benzene yield, which decreases when the sulfate coverage is lower. During irradiation, a strong deactivation was observed due to the poisoning of the surface by carbon deposits strongly adsorbed on catalyst surface

Silver Nanocubes Coated in Ceria:Core/Shell Size Effects on Light-Induced Charge Transfer

Plasmonic sensitization of semiconductors is an attractive approach to increase light-induced photocatalytic performance; one method is to use plasmonic nanostructures in core@shell geometry. The occurrence and mechanism of synergetic effects in photocatalysis of such geometries are under intense debate and proposed to occur either through light-induced charge transfer (CT) or through thermal effects. This study focuses on the relation between the dimensions of Ag@CeO2 nanocubes, the wavelength-dependent efficiency, and the mechanism of light-induced direct CT. A 4-mercaptobenzoic acid (4-MBA) linker between core and shell acts as a Raman probe for CT. For all Ag@CeO2 nanocubes, CT increases with decreasing excitation wavelength, with notable increase at and below 514 nm. This is fully explainable by CT from silver to the 4-MBA LUMO, with the increase for excitation wavelengths that exceed the Ag/4-MBA LUMO gap of 2.28 eV (543 nm). A second general trend observed is an increase in CT yield with ceria shell thickness, which is assigned to relaxation of the excited electron further into the ceria conduction band, potentially producing defects

Bimetallic Cu-based hollow fibre electrodes for CO2 electroreduction

The electrochemical reduction of CO2 represents an attractive alternative to both, satisfy the increasing energy demand, and to help closing the carbon cycle. However, the energy required for CO2 activation and the subsequent multiple number of proton-coupled electron transfer steps involved, makes this process very challenging. Besides, catalytic material limitations are hampering the application of this technology in the short term. Consequently, in this work we synthesise, characterise and preliminarily evaluate bimetallic Cu-based hollow fibre electrodes with a compact three-dimensional geometry to overcome mass transfer limitations and to enhance the electrochemical conversion of CO2. The Cu hollow fibres are functionalised with Au in an attempt to tune the binding energy of the CO* intermediate, which appears to be key in the reduction of CO2. The Cu fibres are also functionalised with Ni, aiming to decrease the reaction overpotential, resulting in beneficial energy efficiency. The so prepared Cu-based porous hollow fibre electrodes are obtained by spinning and electrodeposition procedures. The materials are then characterised by scanning electron microscopy, energy dispersive X-ray spectroscopy, Xray diffraction analyses and cyclic voltammetry tests. Finally, preliminary results of CO2 electroreduction in a divided three-electrode cell are reported. The results show the potential of highly active, bimetallic hollow fibre-based electrocatalysts for enhanced conversion of CO2 into value-added products, and deposition of particles should be performed with acre, not to effect pore characteristics and thus mass transfer properties.I. M-G would like to thank the Spanish Ministry of Economy and Competitiveness (MINECO) for the Early Stage Researcher Contract, including the Research Stay grant (EEBB-I-17-12382) as well as the postdoctoral period of the predoctoral contract (BES-2014-070081). I. M-G, J. A and A. I gratefully acknowledge financial support from the MINECO through the projects CTQ2013-48280-C3-1-R and CTQ2016-76231-C2-1-R, as well as Ramón y Cajal programme (RYC-2015-17080). G. M also acknowledges NanoNextNL, a micro and nanotechnology consortium of the Government of the Netherlands and 130 partners