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Interfaces of mixed oxide are often considered the primary catalytic sites, yet the functionalities of the surrounding environments are less understood. Composite oxides, particularly ZnO‐Cr2O3, show high activity and selectivity for syngas conversion, with ZnO dissociating H2 to hydrides and Cr2O3 activating CO. However, hydrides on ZnO cannot remain stable at temperatures above room temperature. Focusing on the puzzlingly high performance despite ZnO's inability to stabilize active hydrides at reaction temperatures (300–400 °C), we clarified the roles of each phase using models of Cr2O3/ZnO and ZnO/Cr2O3. Cr2O3 clusters on ZnO effectively stabilize and store hydrides, significantly enhancing syngas conversion compared to individual oxides or ZnO/Cr2O3. An acetate/ketene pathway on Cr2O3/ZnO was identified, driven by the unique role of Cr2O3 clusters in regulating local hydride and CO coverages, unlike other routes observed on ZnO/Cr2O3. These insights advance the understanding of the active structures and functionalities of mixed oxides in catalysis. [ABSTRACT FROM AUTHOR]

The limited surface coverage and activity of active hydrides on oxide surfaces pose challenges for efficient hydrogenation reactions. Herein, we quantitatively distinguish the long-puzzling homolytic dissociation of hydrogen from the heterolytic pathway on Ga2O3, that is useful for enhancing hydrogenation ability of oxides. By combining transient kinetic analysis with infrared and mass spectroscopies, we identify the catalytic role of coordinatively unsaturated Ga3+ in homolytic H2 dissociation, which is formed in-situ during the initial heterolytic dissociation. This site facilitates easy hydrogen dissociation at low temperatures, resulting in a high hydride coverage on Ga2O3 (H/surface Ga3+ ratio of 1.6 and H/OH ratio of 5.6). The effectiveness of homolytic dissociation is governed by the Ga-Ga distance, which is strongly influenced by the initial coordination of Ga3+. Consequently, by tuning the coordination of active Ga3+ species as well as the coverage and activity of hydrides, we achieve enhanced hydrogenation of CO2 to CO, methanol or light olefins by 4-6 times. Zhu et al. report a quantitative and time-resolved analysis of hydrogen activation on Ga2O3, specifically shedding light on the long-standing puzzle of homolytic dissociation as opposed to the heterolytic pathway on oxides. [ABSTRACT FROM AUTHOR]

The metal-support interfaces between metals and oxide supports have long been studied in catalytic applications, thanks to their significance in structural stability and efficient catalytic activity. The metal-rare earth oxide interface is particularly interesting because these early transition cations have high electrophilicity, and therefore good binding strength with Lewis basic molecules, such as H2O. Based on this feature, here we design a highly efficient composite Ni-Y2O3 catalyst, which forms abundant active Ni-NiOx-Y2O3 interfaces under the water-gas shift (WGS) reaction condition, achieving 140.6 μmolCO gcat−1 s−1 rate at 300 °C, which is the highest activity for Ni-based catalysts. A combination of theory and ex/in situ experimental study suggests that Y2O3 helps H2O dissociation at the Ni-NiOx-Y2O3 interfaces, promoting this rate limiting step in the WGS reaction. Construction of such new interfacial structure for molecules activation holds great promise in many catalytic systems. Developing effective and stable catalytic interfaces in the medium temperature region is a practical route to replace the existing water gas shift (WGS) process. Here the authors designed a composite Ni-Y2O3 catalyst achieving the highest WGS activity for Ni based catalysts. [ABSTRACT FROM AUTHOR]

Benefiting from a non-zero value of the linewidth enhancement factor which leads to a variety of dynamics different from any other lasers, the broad bandwidth of chaos can be easily generated. There are several applications in chaotic laser, such as broadband random-bit generation, ranging, and secured communications. In the past two decays, most studies of the chaos generations focused on the nonlinear dynamics of the traditional continuous wave (cw) injection and dynamical pulse and sine wave injection. In this work, we study chaos generation utilizing an optically square-wave-injected semiconductor laser with tunable duty cycle. By injecting a slave laser with periodic optical square-wave at specific parameters, chaos oscillation and chaos pulsing can be generated individually. Compared with continuous wave injection with the same injected conditions, the chaos oscillation generated by square-wave injection shows larger bandwidth and more complex behaviors. Furthermore, if the operating variables are adjusted to the center of the chaos area in the dynamical mapping, the waveforms of power spectra of the generated chaos are much smoother and broader. In this paper, the distribution map of chaos oscillation and pulsing oscillation are investigated. When the duty cycle is operated at high level, chaos oscillation is observed. On the other hand, if we operate the condition at high repetition rate and strong injection strength, nonlinear dynamics is driven into the chaos pulsing states and the bandwidth of chaos pulsing is two times larger than chaos oscillation which is operated in week injection strength. The three parameters, duty cycle, repetition rate, and injection strength, all play important roles in chaos generation utilizing optical square-wave injection system. [ABSTRACT FROM AUTHOR]

Recently, nonlinear dynamics of the optically dynamical injection systems are of interested. Potential applications in microwave photonics such as broadband microwave frequency comb generation are demonstrated through an optically pulse-injected semiconductor laser. To the best of our knowledge, most studies focused on the nonlinear dynamics of the traditional continuous wave injection and dynamical pulse and sine wave injection. Nonlinear characteristics of the semiconductor laser subject to optical square wave injection are investigated the first time. In this work, nonlinear dynamics and characteristics of a semiconductor laser subject to optical square wave injection are investigated numerically. The periodic optical square waveforms for injection are generated from a laser (master laser) by using an external EO modulator on a laser (master laser). Under proper operational conditions, namely the repetition frequency and injection strength of the injected light, harmonic and sub-harmonic frequency-locked states with different locking ratios are observed at the output of the injected laser (slave laser). By examination of the electrical power spectra and time series generated from both the injection waveform and injected laser output, all optical frequency conversion are observed. The peaks of the injected laser output are induced by the injected square wave with repetition frequency of 1 GHz. The existence and enhancement of high-order harmonics lays on the foundation of frequency conversion. When applying a stronger injection level to the semiconductor laser, the conversion ratio can be continuously tuned to a higher value. As the result, the conversion ratio of 23 times is achieved due to the effect of bandwidth broadening in optical injection system. The proposed scheme possesses the advantages of low cost, compact, less system complexity, and more flexibility in frequency tuning which also shows the potential of high frequency microwave signal generation. [ABSTRACT FROM AUTHOR]

As the water-gas shift (WGS) reaction serves as a crucial industrial process, strategies for developing robust WGS catalysts are highly desiderated. Here we report the construction of stabilized bulk-nano interfaces to fabricate highly efficient copper-ceria catalyst for the WGS reaction. With an in-situ structural transformation, small CeO2 nanoparticles (2–3 nm) are stabilized on bulk Cu to form abundant CeO2-Cu interfaces, which maintain well-dispersed under reaction conditions. This inverse CeO2/Cu catalyst shows excellent WGS performances, of which the activity is 5 times higher than other reported Cu catalysts. Long-term stability is also very solid under harsh conditions. Mechanistic study illustrates that for the inverse CeO2/Cu catalyst, superb capability of H2O dissociation and CO oxidation facilitates WGS process via the combination of associative and redox mechanisms. This work paves a way to fabricate robust catalysts by combining the advantages of bulk and nano-sized catalysts. Catalysts with such inverse configurations show great potential in practical WGS applications. Cu-CeO2 has been considered as promising alternative to Cu-Zn-Al catalyst for water-gas shift (WGS) reaction, but it still suffers from low activity caused by Cu sintering. Here, the authors develop inverse CeO2/Cu catalyst with remarkable activity and stability in WGS via construction of stabilized bulk-nano interfaces. [ABSTRACT FROM AUTHOR]