Gold nanocatalyst is a potential catalyst for CO preferential oxidation (PROX) reaction. However, with the increase of reaction temperatures, CO conversion and CO2 selectivity in PROX reaction will decrease due to the enhanced competition oxidation of hydrogen, which leads to a narrow temperature window.
It’s still a challenge to completely remove CO at a wide temperature window and meanwhile maintain superior stability in CO-PROX reaction.
Recently, Prof. LI Can’s group and Prof. HUANG Jiahui’s group from theDalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS) developed a photoexcited deposition of metal oxide (PDMO) method to improve the performance of the CO-PROX reaction.
The researchers developed a unique and visualized strategy to selectively modify the interfacial region of Au/TiO2 catalyst by a PDMO method based on the photocatalytic reactions induced by the surface plasmon resonance (SPR) of gold NPs. Au/TiO2 catalyst is a well-known gold nanocatalyst and also a representative plasmonic photocatalyst.
They modified the interface of Au/TiO2 catalyst, and eliminated CO in a very wide temperature range, which exhibited superior performance in CO-PROX reaction. Meanwhile, the decorated PbO2 also improved the long-term stability of Au/TiO2 even in a harsh condition.
“This study is promising for gold catalysts to remove the trace CO from H2 for proton-exchange membrane fuel cells and offers an elaborate interface modification method to design highly efficient gold-based catalysts,” said Prof. HUANG.
This work was supported by the National Natural Science Foundation of China, National Key R&D Program of China, and the Strategic Priority Research Program of the CAS.
Featured image: Structure characterization and catalytic performance of prepared catalysts (Image by HONG Feng and WANG Shengyang)
Janus structure is composed of two or more components with different (usually opposite) physical and chemical properties. Janus nanoparticles possess multiple surface structures that are anisotropic in shape, composition, and surface chemistry.
Janus nanoreactors have been applied in the fields like catalysis, biomedicine, as well as energy storage and conversion. However, it remains a challenge to construct Janus nanoreactors with stable interfacial structure.
Recently, a research team led by Prof. LIU Jian from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences, in collaboration with Prof. HU Ming from East China Normal University, reported a novel and simple strategy for the synthesis of dual-component Janus nanoreactor with asymmetric structure to realize bifunction of photocatalytic water oxidation/reduction.
“We mimics the concepts of compartmentalization used by nature to design PBA-TiO2 Janus photocatalysts for coordinating incompatible chemical transformations,” said Prof. LIU.
In the synthesis process, the partial dissociation of the PBA cube was induced by mild etching. The unsaturated metal sites on the PBAs could form the chemical bond with oxygen ions and Ti4+, inducing heterogeneous nucleation of TiOx on the surface of the PBA single crystals.
Free-standing flowers assembled by TiO2 nanoflakes took root in the PBA single crystals. The PBA-TiO2 Janus nanoreactor gradually emerged and the asymmetric dual-components of nanoreactor possessed a synergistic effect due to the presence of the interfacial structure.
The formed interfacial structure could promote the fast charge transport and effectively inhibit the photogenerated electron and hole recombination. The photocatalytic activity of PBA-TiO2 Janus nanoreactor for water oxidation/reduction was significantly higher than that of pure TiO2 and PBA catalysts.
The above work was supported by the National Natural Science Foundation of China, and Dalian National Laboratory for Clean Energy (DNL) Cooperation Fund, Chinese Academy of Sciences.
Featured image: A: schematic illustration of the synthetic strategy for the PBA-TiO2 Janus nanoreactor. B: TEM images of the as-prepared PBA-TiO2 Janus nanoreactors. C: comparison of photocatalytic H2 evolution and O2 evolution rate of TiO2, PBA, PBA-TiO2 Janus nanoreactors and PBA-TiO2 (mix) samples under light irradiation (Image by SHI Chunjing)
Efficient autoxidation chain reactions demonstrated for the substance group of saturated hydrocarbons
Thuwal/Helsinki/Leipzig. Alkanes, an important component of fuels for combustion engines and an important class of urban trace gases, react via another reaction pathways than previously thought. These hydrocarbons, formerly called paraffins, thus produce large amounts of highly oxygenated compounds that can contribute to organic aerosol and thus to air pollution in cities. An international research team has now been able to prove this through laboratory experiments with state-of-the-art measurement technology at the University of Helsinki and the Leibniz Institute for Tropospheric Research (TROPOS) in Leipzig.
The results of this interdisciplinary work provide crucial information about oxidation processes both in combustion engines and in the atmosphere – with direct implications for engine efficiency and the formation of aerosols, especially in cities, the research team writes in the journal Communications Chemistry, an open-access journal published by the Springer-Nature publishing group.
Oxidation processes play a major role both in the atmosphere and in combustion. A chain reaction called autoxidation is enabled by high engine temperatures. But it also acts as an important source of highly oxygenated compounds in the atmosphere that form organic aerosol, as researchers from Finland, Germany and the USA demonstrated in 2014. Autoxidation is one reason for ageing processes of organic compounds by oxygen from the air. It contributes to the spoilage of food and wine.
This chain reaction is initiated by the formation of peroxy radicals (RO2). The propensity of organic compounds to undergo such multistep autoxidation determines the ignition timing of fuels in engines and, on the other hand, the potential for the formation of low-volatility condensable vapours and consequently organic aerosol in the atmosphere. The extent to which multistep autoxidation takes place depends on the molecular structure of the organic compounds and the reaction conditions. Determining the different reaction pathways of peroxy radicals, which are important intermediates in all oxidation reactions, is crucial for the formation of the different reaction products and their key properties, which can ultimately affect both human health and the climate.
Since peroxy radicals are very reactive, their chemical reactions take place very quickly and individual reaction steps were thus overlooked for a long time. The discovery of highly oxygenated organic molecules (HOMs) seven years ago was only possible due to advances in measurement techniques. A special mass spectrometer (Chemical Ionisation – Atmospheric Pressure Interface – Time of Flight (CI-APi-TOF) mass spectrometer), that can monitor the very short-lived compounds, was used now to measure the radicals and oxidation products of alkanes. “Until now, there have been no studies on HOM formation from alkanes because it was assumed that their structure would be unfavourable for autoxidation,” reports Dr. Torsten Berndt from TROPOS. Methane, an important greenhouse gas, belongs to the group of alkanes. But the most important fossil fuels of the world economy from crude oil and natural gas also consist of alkanes: these include propane, butane, pentane, hexane, heptane and octane. New findings about the oxidation behaviour of this group of substances therefore have great relevance in many areas.
To gain a deeper insight into alkane autoxidation, experiments were carried out in the free-jet flow reactor at TROPOS in Leipzig in addition to experiments in Helsinki. The experimental set-up is optimised so that the gases do not come into contact with the walls during the reaction in order to exclude interferences of the results by wall processes. During the experiments, almost all reactive intermediates, RO2 radicals and their reaction products could be directly monitored. The interdisciplinary cooperation of researchers from combustion chemistry and atmospheric chemistry proved to be very useful, because in the combustion processes analogous processes take place as in the atmosphere, only at a higher temperature. “As a result, it became visible that not only isomerisation reactions of RO2 radicals but also of RO radicals are responsible for the build-up of higher oxidised products. The study made it possible to identify with the alkanes the last and perhaps most surprising group of organic compounds for which autoxidation is important”, Torsten Berndt concludes.
Even at high concentrations of nitrogen oxides, which otherwise quickly terminate autoxidation reactions, the alkanes apparently produce considerable amounts of highly oxidised compounds in the air. The new findings allow for a deeper understanding of autoxidation processes and give rise to further investigations on isomerisation reactions of RO radicals.
Featured image: The team succeeded in proving this process in laboratory experiments using a special flow apparatus at TROPOS in Leipzig, which allows interference-free investigations of gas phase reactions at atmospheric pressure. Photo: Tilo Arnhold, TROPOS
Wang, Z.; Ehn, M.; Rissanen, M.P.; Garmash, O.; Quéléver, L.; Xing, L.; Monge-Palacios, M.; Rantala, P.; Donahue, N.M.; Berndt, T.; Sarathy, S.M.: Efﬁcient alkane oxidation under combustion engine and atmospheric conditions. Communications Chemistry (2021) 4:18. https://doi.org/10.1038/s42004-020-00445-3