Frequency- and Amplitude-Dependent Transmission of Stress Waves in Curved One-Dimensional Granular Crystals Composed of Diatomic Particles

We study the stress wave propagation in curved chains of particles (granular crystals) confined by bent elastic guides. We report the frequency- and amplitude-dependent filtering of transmitted waves in relation to various impact conditions and geometrical configurations. The granular crystals studied consist of alternating cylindrical and spherical particles pre-compressed with variable static loads. First, we excite the granular crystals with small-amplitude, broadband perturbations using a piezoelectric actuator to generate oscillatory elastic waves. We find that the linear frequency spectrum of the transmitted waves creates pass- and stop-bands in agreement with the theoretical dispersion relation, demonstrating the frequency-dependent filtering of input excitations through the diatomic granular crystals. Next, we excite high-amplitude nonlinear pulses in the crystals using striker impacts. Experimental tests verify the formation and propagation of highly nonlinear solitary waves that exhibit amplitude-dependent attenuation. We show that the wave propagation can be easily tuned by manipulating the pre-compression imposed to the chain or by varying the initial curvature of the granular chains. We use a combined discrete element (DE) and finite element (FE) numerical model to simulate the propagation of both dispersive linear waves and compactly-supported highly nonlinear waves. We find that the tunable, frequency- and amplitude-dependent filtering of the incoming signals results from the close interplay between the granular particles and the soft elastic media. The findings in this study suggest that hybrid structures composed of granular particles and linear elastic media can be employed as new passive acoustic filtering materials that selectively transmit or mitigate excitations in a desired range of frequencies and amplitudes.     

Investigation of the Support Effect in Atomically Dispersed Pt on WO3−x for Utilization of Pt in the Hydrogen Evolution Reaction

Single‐atom catalysts (SACs) have attracted growing attention because they maximize the number of active sites, with unpredictable catalytic activity. Despite numerous studies on SACs, there is little research on the support, which is essential to understanding SAC. Herein, we systematically investigated the influence of the support on the performance of the SAC by comparing with single‐atom Pt supported on carbon (Pt SA/C) and Pt nanoparticles supported on WO_3?x (Pt NP/WO_3?x). The results revealed that the support effect was maximized for atomically dispersed Pt supported on WO_3?x (Pt SA/WO_3?x). The Pt SA/WO_3?x exhibited a higher degree of hydrogen spillover from Pt atoms to WO_3?x at the interface, compared with Pt NP/WO_3?x, which drastically enhanced Pt mass activity for hydrogen evolution (up to 10 times). This strategy provides a new framework for enhancing catalytic activity for HER, by reducing noble metal usage in the field of SACs.     

Two‐Dimensional Infrared Correlation Spectroscopy and Principal Component Analysis on the Carbonation of Sterically Hindered Alkanolamines

Despite the academic and industrial importance of the chemical reaction between carbon dioxide (CO₂) and alkanolamine, the delicate and precise monitoring of the reaction dynamics by conventional one‐dimensional (1D) spectroscopy is still challenging, due to the overlapped bands and the restricted static information. Herein, we report two‐dimensional infrared correlation spectroscopy (2D IR COS) and principal component analysis (PCA) on the reaction dynamics of a sterically hindered amine, 2‐[(1,1‐dimethylethyl)amino]ethanol (TBAE) and CO₂. The formation of carbonate rather than carbamate species, which contribute to the unusual high working capacity of ～1 mole CO₂ per mole of TBAE at 40 °C, occurs through deprotonation of the hydroxyl group, protonation on the nitrogen atom of the amino group, and formation of a carbonate species due to the steric hindrance of the tert‐butyl group. In particular, PCA captures the chemical transition into a carbonate species and the main contributions of ${\nu _{{\rm{CO}}_2 } }$ , ${\nu _{{\rm{OH}}} }$ , ${\nu _{{\rm{C - N}}} }$ , and ${\nu _{{\rm{C}} = {\rm{O}}} }$ bands to the carbonation, while 2D IR COS verifies the interrelation of four bands and their changes. Therefore, these results provide a powerful analytic method to understand the complex and abnormal reaction dynamics as well as the rational design strategy for the CO₂ absorbents.