Operando Spectroscopic Studies of Cu–SSZ-13 for NH3–SCR deNOx Investigates the Role of NH3 in Observed Cu(II) Reduction at High NO Conversions

The small pore zeolite chabazite (SSZ-13) in the copper exchanged form is a very efficient material for the selective catalytic reduction by ammonia (NH 3 ) of nitrogen oxides (NOx) from the exhaust of lean burn engines, typically diesel powered vehicles. The full mechanism occurring during the NH 3 –SCR process is currently debated with outstanding questions including the nature and role of the catalytically active sites. Time-resolved operando spectroscopic techniques have been used to provide new level of insights in to the mechanism of NH 3 –SCR, to show that the origin of stable Cu(I) species under SCR conditions is potentially caused by an interaction between NH 3 and the Cu cations located in eight ring sites of the bulk of the zeolite and is independent of the NH 3 –SCR of NOx occurring at Cu six ring sites within the zeolite

In situ X-ray Diffraction Computed Tomography studies examining the thermal and chemical stabilities of working Ba0.5Sr0.5Co0.8Fe0.2O3-δ membranes during oxidative coupling of methane

In this study we present the results from two in situ X-ray diffraction computed tomography experiments of catalytic membrane reactors (CMRs) using Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) hollow fibre membranes and Na-Mn-W/SiO2 catalyst during the oxidative coupling of methane (OCM) reaction. The negative impact of CO2, when added to the inlet gas stream, is seen to be mainly related to the C2+ yield, while no evidence of carbonate phase(s) formation is found during the OCM experiments. The main degradation mechanism of the CMR is suggested to be primarily associated with the solid-state evolution of the BSCF phase rather than the presence of CO2. Specifically, in situ XRD-CT and post-mortem SEM/EDX measurements revealed a collapse of the cubic BSCF phase, formation of secondary phases, which include needle-like structures and hexagonal Ba6Co4O12, and formation of a BaWO4 layer, the latter being a result of chemical interaction between the membrane and catalyst materials at high temperatures

Detection of Key Transient Cu Intermediates in SSZ-13 During NH₃-SCR deNOₓ by Modulation Excitation IR spectroscopy

The small pore zeolite Cu-SSZ-13 is an efficient material for the standard selective catalytic reduction of nitrogen oxides (NOₓ) by ammonia (NH₃). In this work, Cu-SSZ-13 has been studied at 250 °C under high conversion using a modulation excitation approach and analysed with phase sensitive detection (PSD). While the complementary X-ray absorption near edge structure (XANES) spectroscopy measurements showed that the experiments were performed under cyclic Cu^{+}/Cu^{2+} redox, Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) experiments provide spectroscopic evidence for previously postulated intermediates Cu–N([double bond, length as m-dash]O)–NH_{2} and Cu–NO_{3} in the NH_{3}-SCR deNO_{x} mechanism and for the role of [Cu^{2+}(OH^{−})]^{+}

An amphipathic helix in Brl1 is required for nuclear pore complex biogenesis in S. cerevisiae

The nuclear pore complex (NPC) is the central portal for macromolecular exchange between the nucleus and cytoplasm. In all eukaryotes, NPCs assemble into an intact nuclear envelope (NE) during interphase, but the process of NPC biogenesis remains poorly characterized. Furthermore, little is known about how NPC assembly leads to the fusion of the outer and inner NE, and no factors have been identified that could trigger this event. Here, we characterize the transmembrane protein Brl1 as an NPC assembly factor required for NE fusion in budding yeast. Brl1 preferentially associates with NPC assembly intermediates and its depletion halts NPC biogenesis, leading to NE herniations that contain inner and outer ring nucleoporins but lack the cytoplasmic export platform. Furthermore, we identify an essential amphipathic helix in the luminal domain of Brl1 that mediates interactions with lipid bilayers. Mutations in this amphipathic helix lead to NPC assembly defects, and cryo-electron tomography analyses reveal multilayered herniations of the inner nuclear membrane with NPC-like structures at the neck, indicating a failure in NE fusion. Taken together, our results identify a role for Brl1 in NPC assembly and suggest a function of its amphipathic helix in mediating the fusion of the inner and outer nuclear membranes.publishedVersio

An amphipathic helix in Brl1 is required for nuclear pore complex biogenesis in S. cerevisiae

The nuclear pore complex (NPC) is the central portal for macromolecular exchange between the nucleus and cytoplasm. In all eukaryotes, NPCs assemble into an intact nuclear envelope (NE) during interphase, but the process of NPC biogenesis remains poorly characterized. Furthermore, little is known about how NPC assembly leads to the fusion of the outer and inner NE, and no factors have been identified that could trigger this event. Here, we characterize the transmembrane protein Brl1 as an NPC assembly factor required for NE fusion in budding yeast. Brl1 preferentially associates with NPC assembly intermediates and its depletion halts NPC biogenesis, leading to NE herniations that contain inner and outer ring nucleoporins but lack the cytoplasmic export platform. Furthermore, we identify an essential amphipathic helix in the luminal domain of Brl1 that mediates interactions with lipid bilayers. Mutations in this amphipathic helix lead to NPC assembly defects, and cryo-electron tomography analyses reveal multilayered herniations of the inner nuclear membrane with NPC-like structures at the neck, indicating a failure in NE fusion. Taken together, our results identify a role for Brl1 in NPC assembly and suggest a function of its amphipathic helix in mediating the fusion of the inner and outer nuclear membranes

Spatial control of nucleoporin condensation by fragile X-related proteins

Nucleoporins (Nups) build highly organized nuclear pore complexes (NPCs) at the nuclear envelope (NE). Several Nups assemble into a sieve-like hydrogel within the central channel of the NPCs. In the cytoplasm, the soluble Nups exist, but how their assembly is restricted to the NE is currently unknown. Here, we show that fragile X-related protein 1 (FXR1) can interact with several Nups and facilitate their localization to the NE during interphase through a microtubule-dependent mechanism. Downregulation of FXR1 or closely related orthologs FXR2 and fragile X mental retardation protein (FMRP) leads to the accumulation of cytoplasmic Nup condensates. Likewise, models of fragile X syndrome (FXS), characterized by a loss of FMRP, accumulate Nup granules. The Nup granule-containing cells show defects in protein export, nuclear morphology and cell cycle progression. Our results reveal an unexpected role for the FXR protein family in the spatial regulation of nucleoporin condensation

Atomic spectrometry update: Review of advances in the analysis of metals, chemicals and materials

There has been a large increase in the number of papers published that are relevant to this review over this review period. The growth in popularity of LIBS is rapid, with applications being published for most sample types. This is undoubtedly because of its capability to analyse in situ on a production line (hence saving time and money) and its minimally destructive nature meaning that both forensic and cultural heritage samples may be analysed. It also has a standoff analysis capability meaning that hazardous materials, e.g. explosives or nuclear materials, may be analysed from a safe distance. The use of mathematical algorithms in conjunction with LIBS to enable improved accuracy has proved a popular area of research. This is especially true for ferrous and non-ferrous samples. Similarly, chemometric techniques have been used with LIBS to aid in the sorting of polymers and other materials. An increase in the number of papers in the subject area of alternative fuels was noted. This was at the expense of papers describing methods for the analysis of crude oils. For nanomaterials, previous years have seen a huge number of single particle and field flow fractionation characterisations. Although several such papers are still being published, the focus seems to be switching to applications of the nanoparticles and the mechanistic aspects of how they retain or bind with other analytes. This is the latest review covering the topic of advances in the analysis of metals, chemicals and materials. It follows on from last year's review1-6 and is part of the Atomic Spectrometry Updates series

Identification of Structure-activity Relationships in Molybdenum and Iron containing Zeolites used in Methane Dehydroaromatisation and NOx Reduction

In order to design an optimal catalyst, it is important to correlate different chemical species with their activity. This thesis is focused on structure-activity relationship studies of M/zeolite catalysts (where M = Mo or Fe) for methane dehydroaromatisation (MDA) and selective catalytic reduction with ammonia (NH3-SCR). MDA is of great industrial interest as it converts methane directly into light hydrocarbons and aromatics - precursors for the chemical industry. Mo-containing medium pore H-ZSM-5 zeolite is a promising catalyst; nonetheless, the rapid material deactivation compromises its commercialisation. In order to shed light on the MDA catalyst working mechanism, the evolution of Mo species in Mo/H-ZSM-5 has been investigated by means of synchrotron-based X-ray absorption/diffraction techniques under operando and in situ conditions. The results reveal that in contact with methane, initial tetrahedral Mo-oxo species attached to the zeolite are fully carburised to MoxCy which show to be highly active for MDA. Evidences of detachment of MoxCy from the zeolite and subsequent sintering bring new insights regarding catalyst deactivation. The effect of zeolite acidity and topology on MDA has been also investigated by comparing the performance of catalysts based on Silicalite-1 (a pure siliceous analogue of the H-ZSM-5 presenting no Brønsted acidity) and small pore H-SSZ-13. These studies reveal that Brønsted acidity is not necessary for the aromatisation to occur and puts the traditionally accepted bifunctional mechanism into question. Mo/H-SSZ-13 presented different product distribution due to the shape selectivity of small pores towards lighter hydrocarbons. Finally, NH3-SCR is a process used to reduce NOx into N2 and H2O; among others, Fe/zeolites present good catalytic performance. High energy resolution fluorescence detected X-ray absorption and X-ray emission spectroscopic experiments under in situ standard NH3-SCR conditions were performed to determine that octahedral isolated species on Fe/H-ZSM-5 showed greater activity

Determination of Molybdenum Species Evolution during Non‐Oxidative Dehydroaromatization of Methane and its Implications for Catalytic Performance

Mo/H‐ZSM‐5 has been studied using a combination of operando X‐ray absorption spectroscopy and High Resolution Powder Diffraction in order to study the evolution of Mo species and their location within the zeolite pores. The results indicate that after calcination the majority of the species present are isolated Mo‐oxo species, attached to the zeolite framework at the straight channels. During reaction, Mo is first partially carburized to intermediate MoCxOy species. At longer reaction times Mo fully carburizes detaching from the zeolite and aggregates forming initial Mo1.6C3 clusters; this is coincident with maximum benzene production. The Mo1.6C3 clusters are then observed to grow, predominantly on the outer zeolite surface and this appears to be the primary cause of catalyst deactivation. The deactivation is not only due to a decrease in the amount of active Mo surface but also due to a loss in shape‐selectivity which leads to an increased carbon deposition at the outer shell of the zeolite crystals and eventually to pore blockage