Effect of Cesium and Phosphate Addition to Mo/V/W Mixed Oxide Catalysts for the Gas Phase Oxidation of Methacrolein to Methacrylic Acid

The present study investigates modified Mo/V/W mixed oxides as a possible alternative for state of the art heteropoly acid catalysts (HPA) in the partial oxidation of methacrolein (MAC) to methacrylic acid (MAA). Even though HPAs show an excellent activity and MAA selectivity, their long-term stability is unsatisfying, rendering the catalyst inoperable after runtimes of roughly 6 months. Mo/V/W mixed oxides consisting of M1 and a hexagonal (Mo,V,W)O$_{x}$-phase (h-phase) in varying proportions were modified by impregnation with aqueous solutions containing cesium and phosphate ions. All samples were characterized with respect to specific surface area, crystallinity, elemental and phase composition. The catalytic performance in the oxidation of MAC to MAA was investigated using a continuously operated reaction unit with tubular fixed bed reactor. Impregnation with cesium and phosphate ions and subsequent heating triggers the transformation of the mixed oxide into a Keggin-type HPA, whereby the h-phase is more reactive than M1. The transformation into HPA is accompanied by a change in the catalytic properties, i.e., the selectivity to MAA is considerably improved. Compared to HPA synthesized directly, however, the HPA samples obtained by transformation of mixed oxides exhibit no advantages, be it with respect to activity, MAA selectivity or stability

Compound interaction screen on a photoactivatable cellulose membrane (CISCM) identifies drug targets

Identifying the protein targets of drugs is an important but tedious process. Existing proteomic approaches enable unbiased target identification but lack the throughput needed to screen larger compound libraries. Here, we present a compound interaction screen on a photoactivatable cellulose membrane (CISCM) that enables target identification of several drugs in parallel. To this end, we use diazirine-based undirected photoaffinity labeling (PAL) to immobilize compounds on cellulose membranes. Functionalized membranes are then incubated with protein extract and specific targets are identified via quantitative affinity purification and mass spectrometry. CISCM reliably identifies known targets of natural products in less than three hours of analysis time per compound. In summary, we show that combining undirected photoimmobilization of compounds on cellulose with quantitative interaction proteomics provides an efficient means to identify the targets of natural products

Quantifying Concentration Polarization – Raman Microspectroscopy for In-Situ Measurement in a Flat Sheet Cross-flow Nanofiltration Membrane Unit

In this work, the concentration polarization layer (CPL) of sulphate in a cross-flow membrane system was measured in-situ using Raman microspectroscopy (RM). The focus of this work is to introduce RM as a new tool for the study of mass transfer inside membrane channels in reverse osmosis (RO) and nanofiltration (NF) generally. Specifically, this work demonstrates how to use RM for locally resolved measurement of sulphate concentration in a cross-flow flat-sheet NF membrane flow cell with channel dimensions similar to commonly applied RO/NF spiral wound modules (channel height about 0.7 mm). Concentration polarization profiles of an aqueous magnesium sulphate solution of 10 gsulphate·L−1 were obtained at operating pressure of 10 bar and cross-flow velocities of 0.04 and 0.2 m·s−1. The ability of RM to provide accurate concentration profiles is discussed thoroughly. Optical effects due to refraction present one of the main challenges of the method by substantially affecting signal intensity and depth resolution. The concentration profiles obtained in this concept study are consistent with theory and show reduced CPL thickness and membrane wall concentration with increasing cross-flow velocity. The severity of CP was quantified to reach almost double the bulk concentration at the lower velocity

Interplay of Electronic and Steric Effects to Yield Low‐Temperature CO Oxidation at Metal Single Sites in Defect‐Engineered HKUST‐1

In contrast to catalytically active metal single atoms deposited on oxide nanoparticles, the crystalline nature of metal‐organic frameworks (MOFs) allows for a thorough characterization of reaction mechanisms. Using defect‐free HKUST‐1 MOF thin films, we demonstrate that Cu$^{+}$/Cu$^{2+}$ dimer defects, created in a controlled fashion by reducing the pristine Cu2$^{+}$/Cu$^{2+}$ pairs of the intact framework, account for the high catalytic activity in low‐temperature CO oxidation. Combining advanced IR spectroscopy and density functional theory we propose a new reaction mechanism where the key intermediate is an uncharged O$_{2}$ species, weakly bound to Cu$^{+}$/Cu$^{2+}$. Our results reveal a complex interplay between electronic and steric effects at defect sites in MOFs and provide important guidelines for tailoring and exploiting the catalytic activity of single metal atom sites

Spectroscopic Investigation of Bianthryl‐Based Metal–Organic Framework Thin Films and Their Photoinduced Topotactic Transformation

Metal organic frameworks MOFs have gained a large amount of interest because of their periodic and modular structure. These features allow easy prediction of the physical and chemical properties of an organic chromophore, acting as a linker in the MOF. In the present work, a bianthryl BA chromophore, equipped with metal coordinating carboxylate groups, is studied to construct a photoluminescent Zn BA surface anchored MOF SURMOF thin film. The Zn BA SURMOF, in response to prolonged UV light irradiation under ambient conditions, exhibits prominent changes in the ground and excited state optical properties, without losing its crystalline structure. A detailed spectroscopic study using UV vis, infra red, Raman, and electron paramagnetic resonance EPR reveals that in the presence of O2 a photoinduced topotactic transformation is initiated by the formation of singlet oxygen, which then reacts with the BA linkers to form endoperoxid

Liquid Wells as Self-Healing, Functional Analogues to Solid Vessels

Liquids are traditionally handled and stored in solid vessels. Solid walls are not functional, adaptive, or self-repairing, and are difficult to remove and re-form. Liquid walls can overcome these limitations, but cannot form free-standing 3D walls. Herein, a liquid analogue of a well, termed a “liquid well” is introduced. Water tethered to a surface with hydrophobic–hydrophilic core–shell patterns forms stable liquid walls capable of containing another immiscible fluid, similar to fluid confinement by solid walls. Liquid wells with different liquids, volumes, and shapes are prepared and investigated by confocal and Raman microscopy. The confinement of various low-surface-tension liquids (LSTLs) on surfaces by liquid wells can compete with or be complementary to existing confinement strategies using perfluorinated surfaces, for example, in terms of the shape and height of the confined LSTLs. Liquid wells show unique properties arising from their liquid aggregate state: they are self-healing, dynamic, and functional, that is, not restricted to a passive confining role. Water walls can be easily removed and re-formed, making them interesting as sacrificial templates. This is demonstrated in a process termed water-templated polymerization (WTP). Numerical phase-field model simulations are performed to scrutinize the conditions required for the formation of stable liquid wells