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The dynamic formation of alginate droplets containing Lactobacillus buchneri cells by the microtube dripping method was investigated experimentally. Supermacroporous cell-entrapped cryogel beads were then fabricated via cryo-cross-linking of these cell-loaded droplets under freezing conditions and used as the biocatalysts for the synthesis of phenyllactic acid by bioconversion. The evolution of the interface, the dripping velocity, the microthread length, and the droplet diameter during the formation process of cell-loaded droplets were studied by the high-speed imaging method together with computational fluid dynamics modeling. The results showed that the formation and detachment of cell-loaded droplets were controlled by the interaction of the gravity, the surface tension, and the viscous drag forces. With the increase of the microtube size from 0.5 to 2.2 mm, the length of the microthread, the dripping velocity and the mean diameter of the cell-loaded droplets increased by 5.9, 3.7, and 1.7 times, respectively. There is a good agreement between the simulation and experimental results regarding the dynamic performance of the formation and detachment of cell-loaded droplets. The cell-entrapped cryogel beads prepared by the microtube dripping and cryo-cross-linking methods have narrow diameter distributions, macroporous structures, and high porosity of 88.1%. These beads had remarkable biocatalysis ability for the synthesis of phenyllactic acid by conversion of the substrate phenylpyruvic acid. Compared with the free cells, cell-entrapped cryogel beads had the high biotransformation ratio of about 95.9% after recycled for two times, indicating that these beads could be employed as a new class of biocatalysts for the production of phenyllactic acid and thus have potential application in bioconversion processes. [ABSTRACT FROM AUTHOR]

Pt- and Pd-promoted CexZr1-xO2 mixed oxides were characterized and investigated for passive NOx adsorber applications. X-ray diffraction analysis revealed a phase transition from tetragonal to cubic with increasing cerium content in CexZr1-xO2, while H2 and CO chemisorption data in all cases indicated average Pt and Pd particle sizes of close to 2 nm. H2-temperature programmed reduction (TPD) measurements revealed a shift of the Pt reduction peak to higher temperature with increasing Ce content, consistent with a corresponding increase in the degree of Pt oxidation. According to microreactor data, doping Ce into the ZrO2 lattice resulted in a significant improvement in low temperature (80-160 °C) NOx storage efficiency. Diffuse reflectance infrared Fourier transform spectroscopy measurements on Pt/CexZr1-xO2 showed that as Ce content increased, relatively more nitrite species were generated during NOx storage. However, oxidation of nitrite to nitrate during subsequent NOx-TPD increasing the concentration of more thermally stable nitrate also correlated with increased Ce content. The use of Pd as a promoter resulted in decreased NOx storage efficiency compared to Pt, although low-temperature NOx desorption behavior was improved. This is attributed to decreased formation of nitrate during NOx storage compared to that of Pt, as well as the lower activity of Pd for oxidation of nitrite to nitrate during subsequent NOx-TPD. To achieve more balanced NOx storage and desorption behavior, Ce0.2Zr0.8O2 was promoted with both Pt and Pd, resulting in superior overall NOx performance relative to its Pt and Pd analogues. After hydrothermal aging at 750 °C for 16 h, the copromoted sample still maintained excellent NOx adsorption-desorption performance. [ABSTRACT FROM AUTHOR]