Ultrahigh Metal Content Carbon-Based Catalyst for Efficient Hydrogenation of Furfural: The Regulatory Effect of Glycerol.

The development of high-content non-noble metal nanocatalysts is important for multiphase catalysis applications. However, it is a challenge to solve the agglomeration in the preparation of high-content metal catalysts. In this paper, a carbon-based catalyst (Co@CN-G-600) with 71.28 wt % cobalt metal content was prepared using a new strategy of gas-phase carbon coating assisted by glycerol. The core of this strategy is to maintain the spacing of metallic cobalt by continuous replenishment of dissociated ligands during pyrolysis over gas-phase glycerol. This approach is also applicable to other non-noble metals. When Co@CN-G-600 was further used as a catalyst for the selective hydrogenation of furfural (FF) to prepare furfuryl alcohol (FOL), the yield of FOL was >99.9% under mild conditions of 80 °C, compared to only 8.23% catalytic yield at up to 130 °C for Co@CN-600 without glycerol. The excellent catalytic performance mainly lies in the fact that the introduction of glycerol modulates the size effect, electronic effect, and acidic site intensity of the high-content Co catalyst, which promotes the activation of FF and hydrogen. Meanwhile, the optimized specific surface area and pore structure by glycerol improve the accessibility of high-density active sites and promote more efficient mass transfer. In addition, the introduction of glycerol produced a graphitic carbon layer encapsulation structure relative to Co@CN-600, which substantially improved the cycling stability of the catalyst. This study resolves the paradox of high content and high dispersion of non-noble metal catalysts in the synthesis process and provides a general pathway and example for the preparation of stable high-content metal catalysts.

On the propagation of long thickness-stretch waves in piezoelectric plates.

We study the propagation of thickness-stretch waves in a piezoelectric plate of polarized ceramics with thickness poling or crystals of class 6 mm whose sixfold axis is along the plate thickness. For device applications we consider long waves with wavelengths much longer than the plate thickness. A system of two-dimensional equations in the literature governing thickness-stretch, extensional, and symmetric thickness-shear motions of the plate is further simplified. The equations obtained can be used to analyze piezoelectric plate acoustic wave devices operating with thickness-stretch modes.

An analysis of thickness-shear vibrations of doubly-rotated quartz crystal plates with the corrected first-order Mindlin plate equations.

The Mindlin plate equations have been widely used in the analysis of high-frequency vibrations of quartz crystal resonators with accurate solutions, as demonstrated by the design procedure based on analytical results in terms of frequency, mode shapes, and optimal parameters for the AT-cut quartz crystal plate, which is the core element in a resonator structure. Earlier studies have been focused on the AT-cut (which is one type of rotated Y-cut) quartz crystal plates because it is widely produced and has relatively simple couplings of vibration modes at thickness-shear frequencies of the fundamental and overtone modes. The simplified equations through the truncation, correction, and modification of the Mindlin plate equations have been widely accepted for practical applications, and further efforts to expand their applications to similar problems of other material types, such as doubly-rotated quartz crystals, with the SC-cut being a typical and popular one, are also naturally expected. We have found out that the Mindlin plate theory can be truncated and corrected for the SC-cut quartz crystal plates in a manner similar to the AT-cut plates. The analytical results show that the corrected Mindlin plate equations are equally accurate and convenient for obtaining essential design parameters of resonators for the thickness-shear vibrations of SC-cut quartz crystal plates.

An analysis of nonlinear vibrations of coupled thickness-shear and flexural modes of quartz crystal plates with the homotopy analysis method.

We investigated the nonlinear vibrations of the coupled thickness-shear and flexural modes of quartz crystal plates with the nonlinear Mindlin plate equations, taking into consideration the kinematic and material nonlinearities. The nonlinear Mindlin plate equations for strongly coupled thickness- shear and flexural modes have been established by following Mindlin with the nonlinear constitutive relations and approximation procedures. Based on the long thickness-shear wave approximation and aided by corresponding linear solutions, the nonlinear equation of thickness-shear vibrations of quartz crystal plate has been solved by the combination of the Galerkin and homotopy analysis methods. The amplitude frequency relation we obtained showed that the nonlinear frequency of thickness-shear vibrations depends on the vibration amplitude, thickness, and length of plate, which is significantly different from the linear case. Numerical results from this study also indicated that neither kinematic nor material nonlinearities are the main factors in frequency shifts and performance fluctuation of the quartz crystal resonators we have observed. These efforts will result in applicable solution techniques for further studies of nonlinear effects of quartz plates under bias fields for the precise analysis and design of quartz crystal resonators.