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Copper-based catalysts enable the hydrogenation of CO 2 to methanol (MeOH). Selective MeOH synthesis requires the interaction of copper with a metal oxide support to facilitate CO 2 adsorption and hydrogenation. Here, we systematically appraise the role of ZnO, ZrO 2 and CeO 2 in Cu-based catalysts for low-pressure (1 bar) MeOH synthesis. During temperature-programmed desorption (TPD) of CO 2 , the bare ZnO, ZrO 2 , and CeO 2 exhibited desorption events at both low (70–100 °C) and high (400–700 °C) temperatures, also observed when combining each support with copper. Investigations in a packed bed reactor showed suppressed CO by-production over Cu-ZrO 2 , leading to a 1.5-fold improvement as compared to Cu-ZnO. Upon Cu-CeO 2 , CO 2 was prone to undergo reduction to CO and desorb, resulting in a MeOH yield 9 times lower than over Cu-ZrO 2. Experiments aiming at intermittent operation with successive start-ups and shut-downs showed that the performance of Cu-ZrO 2 catalyst remained stable, whilst Cu-ZnO deteriorated monotonically, ascribed to sintering driven by OH and H 2 O species. In situ infrared spectroscopy demonstrated that methanol synthesis over Cu-ZnO progresses via a single pathway with formate species, whilst parallel formate and bicarbonate pathways were demonstrated over Cu-ZrO 2. Unlike Cu-ZnO, the formation of bicarbonate over Cu-ZrO 2 allows surface OH species to participate in MeOH synthesis, which we link to the superior performance and stability of Cu-ZrO 2. [Display omitted] • ZnO, ZrO 2 , and CeO 2 supports essential in facilitating CO 2 adsorption. • Cu-ZrO 2 most selective towards methanol synthesis. • Cu-CeO 2 favours reduction of CO 2 to CO via reverse water gas shift pathway. • Cu-ZrO 2 stable over successive start-up and shut-down, whilst Cu-ZnO deteriorates. • Formate and bicarbonate pathways over Cu-ZrO 2 , unlike Cu-ZnO, improving stability. [ABSTRACT FROM AUTHOR]

CO 2 capture and utilisation (CCU) is a promising strategy to effectively mitigate the adverse greenhouse effects caused by CO 2 emissions at an industrial scale. Through a process intensification strategy known as integrated CO 2 capture and utilisation (ICCU), CO 2 capture and catalytic CO 2 conversion can be achieved in a single process with the use of dual function materials (DFMs), which are both CO 2 sorbents and CO 2 conversion catalysts. Given the significantly different operating conditions of ICCU from conventional catalytic CO 2 hydrogenation, the catalytic mechanism of DFMs, especially during CO 2 hydrogenation, needs to be thoroughly investigated. In this study, the relationship between the nature of the Ni/carbonate interfaces and the performance of Ni-based DFMs over ICCU cycles is systematically investigated. A series of Ni/alkaline earth carbonate DFMs were synthesised with varying Ca:Mg ratios to simulate different metal-carbonate model interfaces. At 400 °C, CH 4 formation with nearly 100% CH 4 selectivity was achieved on Ni/CaCO 3 over 15 ICCU cycles. In general, Ni/CaCO 3 interfaces correspond to higher CO 2 conversion and higher CH 4 selectivity than Ni/MgCO 3 interfaces. Such trend may be attributed to the higher surface basicity of CaO and the higher thermal stability of CaCO 3. As a consequence, the hydrogenation of the Ni/CaCO 3 interface proceed via the formate pathway, in which carbonates are consecutively converted to surface formates, methoxyl, methyl species and eventually desorb as methane. This reaction model is applicable to the hydrogenation of both surface carbonate and bulk carbonates, although the former proceeds with much faster kinetics. On the weakly alkaline Ni/MgCO 3 interface, MgCO 3 preferentially decomposes to form gaseous CO 2 , which is subsequently hydrogenated via the reverse-water-gas-shift pathway, with CO as the key reaction intermediate. Interestingly, in situ infrared spectroscopy shows similar surface significant species during the direct hydrogenation of DFMs and during the conventional catalytic hydrogenation of molecular CO 2 , suggesting that the catalytic mechanisms during the two operating regimes are highly correlated. [Display omitted] • Novel Ni/carbonate dual function materials for CO 2 capture and hydrogenation. • Different hydrogenation behaviour and pathway on Ni/CaCO 3 and Ni/MgCO 3 interfaces. • Two reaction regimes proposed during hydrogenation of Ni/CaCO 3. • Suitable basic sites and metal-support interaction favours the hydrogenation. • Correlation between ICCU cycles and those of conventional CO 2 hydrogenation. [ABSTRACT FROM AUTHOR]

The millimeter-wave (mmWave) band will be used for the fifth-generation communication systems. In this paper, 60-GHz mmWave channel measurements and modeling are carried out for indoor office environments. The rotated directional antenna-based method and uniform virtual array-based method are adopted and compared to investigate the 60-GHz channel in a 3-D space, simultaneously covering azimuth and coelevation domains. The multipath component parameters including power, delay, azimuth, and elevation angles are estimated with the space-alternating generalized expectation–maximization estimation algorithm, and then processed with the K-means clustering algorithm. An extended Saleh–Valenzuela model with both delay and angular cluster features is used to characterize the measured channel, and the intercluster and intracluster parameters are extracted. We find that the azimuth departure angles are diverse and highly related to the antenna position and measurement environment, while the elevation departure angles are more related to the antenna height difference and confined in a relatively small direction range. The azimuth angle spread is much larger than the elevation angle spread either in global level or in cluster level. The results agree with the studies in the literature and channel models in IEEE standards. [ABSTRACT FROM PUBLISHER]

The interuser interference between wireless body area networks worn by two moving persons in an indoor environment at 60 and 2.45 GHz is experimentally investigated. Both omnidirectional antennas (monopoles) and directional antennas (horns) were used in the measurements. The interference power-level variation and carrier-to-interference ratio (CIR) were measured and characterized. Median interference power-level reduction of nearly 20 dB was achieved in all measured channels by adopting 60-GHz radio transmissions compared to 2.45 GHz, both with omnidirectional on-body antennas. A further 20 dB of interference-level reduction was achieved at 60 GHz by adopting directional antennas confining the radiated wave along the body surface. Level crossing rates for interference power variation using omnidirectional antennas range from 2.7 to 7.2 \texts^-1 at 2.45 GHz and 32–64 \texts^-1 at 60 GHz for static to progressively more dynamic links, whereas the corresponding range using 60-GHz directional antennas is reduced to 39–54 \texts^-1. The median improvement in the instantaneous CIR for the chest-head channel between 60 and 2.45 GHz was approximately 30 dB. The measured interference power level and CIR, in dB, were found to satisfactorily fit the normal distribution according to the normalized root-mean-square error-based fit metric. [ABSTRACT FROM PUBLISHER]

Variation of on-body millimetre-wave propagation channels with body movements has been studied experimentally. A statistical description of the propagation channel is presented, including path-loss probability distributions, level-crossing rates and average fade durations. The median path losses for the considered practical links with omnidirectional monopole antennas lied within the range of 55-88 dB. The signal variation was found to consist of two superimposed variations, in general: the long-term and short-term fadings, but was dominated by the much stronger long-term fading. The use of a simple two-state Markov process model to describe on-body communication links is also proposed and its limitations are discussed. [ABSTRACT FROM AUTHOR]

Measurements of on-body dynamic propagation channels have been performed at 60 GHz using dual-polarized scalar horn antennas. Comparison of the statistics of the measured signals showed that the choice of polarization (vertical or horizontal) does not affect the path losses significantly, and the relative polarization of the two antennas depends on their placement on the body. In volatile links, such as those from the wrist to other parts of the body, random movements equalize the differences between different polarization configurations. These depolarization effects can be exploited to improve link performance through the use of receive diversity with maximal ratio combining. More advanced multiple-input multiple-output diversity methods are found to produce only marginally better performance compared to receive maximal ratio combining. [ABSTRACT FROM PUBLISHER]

The configurational disorder of high entropy oxides (HEOs) promotes the reversible exsolution–redissolution of constituent metal species. This unique feature could be exploited to facilitate cyclic lattice oxygen storage and exchange. Herein, we report an in situ generated, halite-structured (MgCoNiMnFe)O x HEO, which simultaneously functions as a redox catalyst and an oxygen carrier for dry reforming of methane in a chemical looping process (CL–DRM). Accordingly, the (MgCoNiMnFe)O x /ZrO 2 HEO catalyst exhibits outstanding DRM activity, syngas selectivity and cyclic stability compared to medium-entropy oxides and bimetallic oxides over 100 CL–DRM cycles at 800 °C. XRD analysis verified the entropy-mediated preservation of the alloy/HEO/ZrO 2 catalytic structure over CL–DRM cycles. XAFS studies revealed the reversible and cyclic evolution–dissolution of Ni, Fe, Co over redox cycles. The exsolved NiFeCo nanoalloy exhibited high efficiency in activating CH 4. This study has demonstrated the potential applications of HEO-based catalysts in efficient chemical looping processes. [Display omitted] • Formation of a single halite-phase high entropy oxide containing Fe2+ and Mn2+. • Durable high-performance catalyst for chemical looping dry reforming of methane. • Dynamic evolutions of high entropy oxides over chemical looping cycles. • NiFeCo nanoalloys facilitating methane activation. [ABSTRACT FROM AUTHOR]