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Catalytic properties of Pt catalysts supported on mesoporous silica (Pt/m-SiO2) have been studied in enantioselective hydrogenation of ethyl pyruvate. The influences of pore structure of mesoporous silica (m-SiO2), type of chiral modifier, and H2 pressure on the catalytic performance have been investigated by using various m-SiO2 supports and cinchona alkaloids and by varying H2 pressure. The use of MCM-41, SBA-15, KIT-6, and MCF reveals that characteristic pore structure and size of m-SiO2 supports significantly affect both activity and enantioselectivity. A facile diffusion of chiral modifier through large mesopores of MCF support enables Pt/MCF to exhibit excellent performance. A comparison of the efficiency of cinchona alkaloids-modified Pt catalysts shows that QN and QD lead to higher performance than CD and CN at ambient H2 pressure. The influence of cinchona alkaloids on enantioselectivity noticeably depends on H2 pressure. Cinchona alkaloid-modified Pt/m-SiO2 exhibit superior enantioselectivity to the corresponding Pt/Al2O3 under various H2 pressures. These results imply that m-SiO2 is a promising support and that fine control of pore structure can further improve catalytic performance of Pt/m-SiO2 in heterogeneous enantioselective hydrogenation.

Heterogeneous enantioselective catalysis is an attractive approach to produce enantiopure chemicals, which are key intermediates for pharmaceutical products. Herein, mesocellular silica foams (MCFs) functionalized by primary, secondary, and tertiary amine groups were used as supports for Pt nanoparticles. The catalytic performances of the Pt/amine-functionalized MCFs were evaluated for the enantioselective hydrogenation of methyl pyruvate in the presence of cinchonidine. Compared to Pt/MCF, the Pt/amine-functionalized MCFs exhibited enhanced activity and enantioselectivity. Particularly, 0.5 wt% Pt/NH 2-MCF showed a superior performance than 5 wt% Pt/Al2O3, a highly efficient catalyst in the enantioselective hydrogenation of α-keto esters, despite a 10 times lower Pt loading. Furthermore, the Pt/NH2-MCF yielded 100% conversion and 96% ee at 0.1 MPa H2 pressure during nine successive cycles, thus showing high reusability. The excellent performance of the Pt/amine-functionalized MCFs is attributed to the formation of electron-deficient Pt species through strong interactions between the Pt nanoparticles and amine groups.

Heterogeneous enantioselective catalysis is considered a promising strategy for the large-scale production of enantiopure chemicals. In this work, polymer-capped Pt nanocatalysts having a uniform s...

Mesocellular silica foams (MCFs) with different pore size were synthesized and used as supports for Pt catalysts for enantioselective hydrogenation of ethyl pyruvate. The influences of the pore size of MCFs, the amount of Pt loading and H2 pressure on catalytic performance of cinchonidine-modified Pt/MCFs were investigated. Both activity and enantioselectivity of the Pt/MCF catalyst increased with the increase in the pore size. These results were attributed to the fact that the larger mesopores facilitate intraparticle diffusion of bulky chiral modifier molecules and generate more chirally modified Pt sites. The performances of Pt/MCFs were compared to those of Pt supported on non-porous silica (Pt/SiO2) and commercial Pt/Al2O3 catalysts. The 1 wt% Pt/MCFs showed superior performance than the 1 wt% Pt/SiO2 and the commercial 1 wt% Pt/Al2O3 catalysts. Furthermore, the 0.6 wt% Pt/MCF exhibited higher activity and enantioselectivity than the commercial 5 wt% Pt/Al2O3, one of the most efficient heterogeneous catalysts for this reaction, in spite of a considerably less Pt loading. At optimized reaction conditions, the Pt/MCF catalyst gave enantiomeric excess of 96% at 100% conversion. They also maintained high enantioselectivity during 10 successive reaction cycles, exhibiting high reusability.

This paper presents a complete noncontact fatigue crack visualization technique based on nonlinear ultrasonic wave modulation and investigates the main source of nonlinear modulation generation. Two distinctive frequency input signals are created by two air-coupled transducers and the corresponding ultrasonic responses are scanned using a 3D laser Doppler vibrometer. The effectiveness of the proposed technique is tested using aluminum plates with different stages of fatigue crack formation such as micro and macro-cracks. Furthermore, the main source of nonlinear modulation is discussed based on the visualization results and the microscopic images.

Rotating shafts in drop lifts of manufacturing facilities are susceptible to fatigue cracks as they are under repetitive heavy loading and high speed spins. However, it is challenging to use conventional contact transducers to monitor these shafts as they are continuously spinning with a high speed. In this study, a noncontact crack detection technique for a rotating shaft is proposed using air-coupled transducers (ACTs). (1) Low frequency (LF) and high frequency (HF) sinusoidal inputs are simultaneously applied to a shaft using two ACTs, respectively. A fatigue crack can provide a mechanism for nonlinear ultrasonic modulation and create spectral sidebands at the modulation frequencies, which are the sum and difference of the two input frequencies Then LF and HF inputs are independently applied to the shaft using each ACT. These three ultrasonic responses are measured using another ACT. (2) The damage index (DI) is defined as the energy of the first sideband components, which corresponding to the frequency sum and difference between HF and LF inputs. (3) Steps 1 and 2 are repeated with various combinations of HF and LF inputs. Crack existence is detected through an outlier analysis of the DIs. The effectiveness of the proposed technique is investigated using a steel shaft with a real fatigue crack.

This paper presents a fatigue crack detection technique based on visualization of nonlinear ultrasonic wave modulation produced by a fatigue crack. When distinctive low frequency (LF) and high frequency (HF) inputs are generated and applied to a structure, the presence of a fatigue crack can provide a mechanism for nonlinear ultrasonic modulation and create spectral sidebands around the frequency of the HF signal. In this study, the two input signals are created by two air-coupled transducers (ACT), and the corresponding ultrasonic responses are scanned over a target specimen using a 3D laser Doppler vibrometer (LDV). The crack-induced spectral sidebands are isolated using a combination of linear response subtraction (LRS), and continuous wavelet transform (CWT) filtering. Then, the extracted spectral sideband components are visualized near the fatigue crack. The effectiveness of the proposed non-contact scanning technique is tested using an aluminum plate with a real fatigue crack.