Synthesis Chemistry and Properties of Ni Catalysts Fabricated on SiC@Al2O3 Core-Shell Microstructure for Methane Steam Reforming

Heat and mass transport properties of heterogeneous catalysts have significant effects on their overall performance in many industrial chemical reaction processes. In this work, a new catalyst micro-architecture consisting of a highly thermally conductive SiC core with a high-surface-area metal-oxide shell is prepared through a charge-interaction-induced heterogeneous hydrothermal construction of SiC@NiAl-LDH core-shell microstructures. Calcination and reduction of the SiC@NiAl-LDH core-shell results in the formation of Ni nanoparticles (NPs) dispersed on SiC@Al2O3, referred to as Ni/SiC@Al2O3 core-shell catalyst. The Ni/SiC@Al2O3 exhibit petal-like shell morphology consisting of a number of Al2O3 platelets with their planes oriented perpendicular to the surface, which is beneficial for improved mass transfer. For an extended period of methane-stream-reforming reaction, the Ni/SiC@Al2O3 core-shell structure remained stable without any significant degradation at the core/shell interface. However, the catalyst suffered from coking and sintering likely associated with the relatively large Ni particle sizes and the low Al2O3 content. The synthesis procedure and chemistry for construction of supported Ni catalyst on the core-shell microstructure of the highly thermal conductive SiC core, and the morphology-controlled metal-oxide shell, could provide new opportunities for various catalytic reaction processes that require high heat flux and enhanced mass transport

Morphology Controlled Synthesis of γ-Al₂O₃ Nano-Crystallites in Al@Al₂O₃ Core–Shell Micro-Architectures by Interfacial Hydrothermal Reactions of Al Metal Substrates

Fine control of morphology and exposed crystal facets of porous γ-Al2O3 is of significant importance in many application areas such as functional nanomaterials and heterogeneous catalysts. Herein, a morphology controlled in situ synthesis of Al@Al2O3 core–shell architecture consisting of an Al metal core and a porous γ-Al2O3 shell is explored based on interfacial hydrothermal reactions of an Al metal substrate in aqueous solutions of inorganic anions. It was found that the morphology and structure of boehmite (γ-AlOOH) nano-crystallites grown at the Al-metal/solution interface exhibit significant dependence on temperature, type of inorganic anions (Cl−, NO3−, and SO42−), and acid–base environment of the synthesis solution. Different extents of the electrostatic interactions between the protonated hydroxyl groups on (010) and (001) facets of γ-AlOOH and the inorganic anions (Cl−, NO3−, SO42−) appear to result in the preferential growth of γ-AlOOH toward specific crystallographic directions due to the selective capping of the facets by adsorption of the anions. It is hypothesized that the unique Al@Al2O3 core–shell architecture with controlled morphology and exposed crystal-facets of the γ-Al2O3 shell can provide significant intrinsic catalytic properties with enhanced heat and mass transport to heterogeneous catalysts for applications in many thermochemical reaction processes. The direct fabrication of γ-Al2O3 nano-crystallites from Al metal substrate with in-situ modulation of their morphologies and structures into 1D, 2D, and 3D nano-architectures explored in this work is unique and can offer significant opportunities over the conventional methods

Morphology Controlled Synthesis of γ-Al2O3 Nano-Crystallites in Al@Al2O3 Core–Shell Micro-Architectures by Interfacial Hydrothermal Reactions of Al Metal Substrates

Fine control of morphology and exposed crystal facets of porous γ-Al2O3 is of significant importance in many application areas such as functional nanomaterials and heterogeneous catalysts. Herein, a morphology controlled in situ synthesis of Al@Al2O3 core–shell architecture consisting of an Al metal core and a porous γ-Al2O3 shell is explored based on interfacial hydrothermal reactions of an Al metal substrate in aqueous solutions of inorganic anions. It was found that the morphology and structure of boehmite (γ-AlOOH) nano-crystallites grown at the Al-metal/solution interface exhibit significant dependence on temperature, type of inorganic anions (Cl−, NO3−, and SO42−), and acid–base environment of the synthesis solution. Different extents of the electrostatic interactions between the protonated hydroxyl groups on (010) and (001) facets of γ-AlOOH and the inorganic anions (Cl−, NO3−, SO42−) appear to result in the preferential growth of γ-AlOOH toward specific crystallographic directions due to the selective capping of the facets by adsorption of the anions. It is hypothesized that the unique Al@Al2O3 core–shell architecture with controlled morphology and exposed crystal-facets of the γ-Al2O3 shell can provide significant intrinsic catalytic properties with enhanced heat and mass transport to heterogeneous catalysts for applications in many thermochemical reaction processes. The direct fabrication of γ-Al2O3 nano-crystallites from Al metal substrate with in-situ modulation of their morphologies and structures into 1D, 2D, and 3D nano-architectures explored in this work is unique and can offer significant opportunities over the conventional methods

Core–Shell Metal–Ceramic Microstructures: Mechanism of Hydrothermal Formation and Properties as Catalyst Materials

Unique metal–ceramic composites with core–shell microarchitecture (γ-Al₂O₃@Al and spinel-MeAl₂O₄@Al, Me = Zn, Ni, Co, Mn, and Mg) were obtained by a simple hydrothermal surface oxidation (HTSO) of Al metal particles in an aqueous solution of heterometal ions at elevated temperatures (393–473 K). The reactions afforded self-constructed core–shell microarchitecture with Al core encapsulated by the high-surface-area γ-Al₂O₃ or spinel metal aluminates (MeAl₂O₄) shell with various surface morphologies, compositions, and excellent physicochemical properties. Extensive experimental and theoretical investigation with period 3–6 metal elements (Na⁺, Ca²⁺, Sr²⁺, Ba²⁺, K⁺, Fe³⁺, Cu²⁺, Zn²⁺, Ni²⁺, Co²⁺, Mn²⁺, and Mg²⁺) at various metal concentrations and temperatures revealed that the heterogeneous self-construction of spinel-MeAl₂O₄@Al primarily depends on two intrinsic properties of the additive metal ions: (i) thermodynamic stability constant of the metal hydroxide complex and (ii) size of the metal ion. The spinel-MeAl₂O₄@Al microstructures formed with a limited number of hetero metal ions (Me = Zn²⁺, Ni²⁺, Co²⁺, Mn²⁺, and Mg²⁺) with (i) moderate rates of the hydroxide formation with compatible kinetics to the hydrolysis of aluminum on the Al surface and (ii) small size of additive metal ions enough for diffusion through the shell layer. As heterogeneous catalyst substrates, these metal–ceramic composites delivered markedly enhanced catalytic performance at intensive reaction conditions because of their facile heat transfer and superior physicochemical surface properties. The performance and effects of the core–shell metal–ceramic composites were demonstrated using Rh catalysts supported on MgAl₂O₄@Al. The Rh/MgAl₂O₄@Al catalyst was utilized for the endothermic glycerol stream reforming (C₃H₈O₃ + 3H₂O ⇄ 3CO₂ + 7H₂, Δ<i>H</i>₀²⁹⁸ = 128 kJ mol^–1), exhibiting markedly greater catalytic performance than the conventional Rh/MgAl₂O₄ under intensive reaction conditions attributed to significantly facilitated heat transport through the core–shell metal–ceramic microstructures

Impedance Characterization and Modeling of Subcellular to Micro-sized Electrodes with Varying Materials and PEDOT:PSS Coating for Bioelectrical Interfaces

Electrode-to-cell/tissue interfaces with high biocompatibility, low impedance, and long-term chemical and mechanical stability are of paramount importance in numerous biological and biomedical applications. For meticulous monitoring of biological parameters, there is a rapidly growing interest in sensing at subcellular levels with radically improved spatiotemporal resolution, which necessitates ultra-miniaturized electrodes with significant reduction in electrode contact sizes. Such aggressive electrode downsizing inevitably impacts the electrochemical interfaces, with the consequences still poorly understood. This paper reports the first systematic analysis of the interfacial electrochemical impedance spectroscopy of electrodes comprising a variety of biocompatible electrode materials consisting of gold (Au), platinum (Pt), indium tin oxide, and titanium nitride (TiN) coated with/without an organic polymer, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), with electrode diameters (D) ranging from millimeter to subcellular ( 200 μm, the effect is lessened due to the dominance of solution, or bulk electrolyte, and routing resistance. The low interfacial impedance of PEDOT:PSS-coated electrodes makes them promising candidates for next-generation bioelectrical interfaces with subcellular spatial resolution.ISSN:2637-611

A Digital Power Amplifier With Built-In AM–PM Compensation and a Single-Transformer Output Network

This article presents a digital power amplifier (DPA) with a built-in AM–PM compensation technique and a compact single-transformer footprint. The AM–PM distortion behavior of the current-mode/voltage-mode power amplifiers (PAs) is detailed and an AM–PM compensation technique for both modes is introduced. The proposed design utilizes one current-mode DPA as the main path PA and a class-G PA voltage-mode digital PA as the auxiliary path PA, combined through a single-transformer footprint. It provides enhanced linearity through built-in adaptive biasing and hybrid current-/voltage-mode Doherty-based power combining. As a proof of concept, a 1.2–2.4-GHz wideband DPA is implemented in the Globalfoundries 45-nm CMOS SOI process. The measurements show a 37.6% peak drain efficiency (DE) at 1.4 GHz, and 21.8-dBm saturated output power (Psat) and 1.2×/1.4× power back-off (PBO) efficiency enhancement, compared to the ideal class-B at 3 dB/6 dB PBO at 1.2 GHz. This proposed digital PA supports 20-MSym/s 64-QAM modulation at 14.8-dBm average output power and 22.8% average PA DE while maintaining error vector magnitude (EVM) lower than −23 dB without any phase predistortion. To the best of our knowledge, this is the first demonstration of hybrid current–voltage-mode Doherty power combining on a single-footprint transformer over a broad bandwidth (BW).ISSN:2644-134

An Evaluation of Orbital Angular Momentum Multiplexing Technology

This paper reports our investigation of wireless communication performance obtained using orbital angular momentum (OAM) multiplexing, from theoretical evaluation to experimental study. First, we show how we performed a basic theoretical study on wireless OAM multiplexing performance regarding modulation, demodulation, multiplexing, and demultiplexing. This provided a clear picture of the effects of mode attenuation and gave us insight into the potential and limitations of OAM wireless communications. Then, we expanded our study to experimental evaluation of a dielectric lens and end-to-end wireless transmission on 28 gigahertz frequency bands. To overcome the beam divergence of OAM multiplexing, we propose a combination of multi-input multi-output (MIMO) and OAM technology, named OAM-MIMO multiplexing. We achieved 45 Gbps (gigabits per second) throughput using OAM multiplexing with five OAM modes. We also experimentally demonstrated the effectiveness of the proposed OAM-MIMO multiplexing using a total of 11 OAM modes. Experimental OAM-MIMO multiplexing results reached a new milestone for point-to-point transmission rates when 100 Gbps was achieved at a 10-m transmission distance