Transformation of sodium bicarbonate and CO2 into sodium formate over NiPd nanoparticle catalyst

The present research systematically investigated, for the first time, the transformation of sodium bicarbonate and CO2 into sodium formate over a series of Ni based metal nanoparticles (NPs). Ni NPs and eight NiM (M stands for a second metal) NPs were prepared by a facile wet chemical process and then their catalytic performance were evaluated in sodium bicarbonate hydrogenation. Bimetallic NiPd NPs with a composition of 7:3 were found to be superior for this reaction, which are more active than both pure Ni and Pd NPs. Hot filtration experiment suggested the NPs to be the truly catalytic active species and kinetic analysis indicated the reaction mechanism to be different than most homogeneous catalysts. The enhanced activity of the bimetallic nanoparticles may be attributed to their smaller size and improved stability

Catalytic transfer hydrogenolysis as an efficient route in cleavage of lignin and model compounds

Cleavage of aromatic ether bonds through hydrogenolysis is one of the most promising routes for depolymerisation and transformation of lignin into value-added chemicals. Instead of using pressurized hydrogen gas as hydrogen source, some reductive organic molecules, such as methanol, ethanol, isopropanol as well as formates and formic acid, can serve as hydrogen donor is the process called catalytic transfer hydrogenolysis. This is an emerging and promising research field but there are very few reports. In this paper, a comprehensive review of the works is presented on catalytic transfer hydrogenolysis of lignin and lignin model compounds aiming to breakdown the aromatic ethers including α-O-4, β-O-4 and 4-O-5 linkages, with focus on reaction mechanisms. The works are organised regarding to different hydrogen donors used, to gain an in-depth understanding of the special role of various hydrogen donors in this process. Perspectives on current challenges and opportunities of future research to develop catalytic transfer hydrogenolysis as a competitive and unique strategy for lignin valorisation are also provided

Efficient algorithm for general polygon clipping

International audienceWe present an efficient algorithm to determine the intersection of two planar general polygons. A new method based on rotation angle is proposed to obtain the classification of an edge with respect to a polygon. The edge candidates can be determined efficiently by a 1-dimensional range searching approach based on an AVL tree (a balanced binary search tree). The simplicial chain is used to represent the general polygons, and to determine the classification of polygon edges. Examples are given to illustrate the algorithm

Dielectric response of soft mode in ferroelectric SrTiO3

We report far-infrared dielectric properties of powder form ferroelectric SrTiO3. Terahertz time-domain spectroscopy (THz-TDS) measurement reveals that the low-frequency dielectric response of SrTiO3 is a consequence of the lowest transverse optical (TO) soft mode TO1 at 2.70 THz (90.0 1/cm), which is directly verified by Raman spectroscopy. This result provides a better understanding of the relation of low-frequency dielectric function with the optical phonon soft mode for ferroelectric materials. Combining THz-TDS with Raman spectra, the overall low-frequency optical phonon response of SrTiO3 is presented in an extended spectral range from 6.7 1/cm to 1000.0 1/cm.Comment: 14 pages; 4 figure

Production of Terephthalic Acid from Corn Stover Lignin

Funneling and functionalization of a mixture of lignin-derived monomers into a single high-value chemical is fascinating. Herein, we report a three-step strategy for the production of terephthalic acid (TPA) from lignin-derived monomer mixtures, in which redundant, non-uniform substitutes such as methoxyl groups are removed and the desired carboxyl groups are introduced. The strategy starts with hydro-treating of corn stover-derived lignin oil over supported molybdenum catalyst to selectively remove methoxyl groups. The generated 4-alkylphenols are converted into 4-alkylbenzoic acids via carbonylation with carbon monoxide. Co-Mn-Br catalyst then oxidizes various alkyl chains into carboxyl groups, transforming the 4-alkylbenzoic acids mixture into a single product: TPA. Based on this route, the overall yields of TPA based on lignin content of corn stover could reach 15.5 wt%, and importantly, TPA with >99% purity was obtained simply by first decanting the reaction mixture, followed by washing the solid product with water

All-optical active THz metasurfaces for ultrafast polarization switching and dynamic beam splitting.

Miniaturized ultrafast switchable optical components with an extremely compact size and a high-speed response will be the core of next-generation all-optical devices instead of traditional integrated circuits, which are approaching the bottleneck of Moore's Law. Metasurfaces have emerged as fascinating subwavelength flat optical components and devices for light focusing and holography applications. However, these devices exhibit a severe limitation due to their natural passive response. Here we introduce an active hybrid metasurface integrated with patterned semiconductor inclusions for all-optical active control of terahertz waves. Ultrafast modulation of polarization states and the beam splitting ratio are experimentally demonstrated on a time scale of 667 ps. This scheme of hybrid metasurfaces could also be extended to the design of various free-space all-optical active devices, such as varifocal planar lenses, switchable vector beam generators, and components for holography in ultrafast imaging, display, and high-fidelity terahertz wireless communication systems

Manifestation of PT symmetry breaking in polarization space with terahertz metasurfaces

By utilizing the vector nature of light as well as the inherent anisotropy of artificial meta-atoms, we investigate parity time symmetry breaking in polarization space using a metasurface with anisotropic absorption, whose building blocks consist of two orthogonally orientated meta-atoms with the same resonant frequency but different loss coefficients. By varying their coupling strength, we directly observe a phase transition in the eigenpolarization states of the system, across which the long axis of the eigenpolarization ellipses experience a sudden rotation of 45°. Despite the lack of rotational symmetry of the metasurface, precisely at the phase transition, known as the exceptional point, the eigenmodes coalesce into a single circularly polarized state. The PT symmetric metasurfaces are experimentally implemented at terahertz frequencies