On the synthesis and performance of hierarchical nanoporous TS-1 catalysts

Hierarchical TS-1 zeolite was successfully prepared using chitosan as a sacrificial template. The X-ray diffraction showed that the presence of chitosan with the synthesis precursor had no deleterious effect on the crystallinity and phase purity of this zeolite. X-ray absorption spectroscopy at the Ti K-edge, FTIR and Raman spectroscopies revealed the titanium ions in the zeolite structure have predominantly tetrahedral coordination. However, it appears that the higher chitosan content in the synthesis gel imparted some hydrophilic character to the TS-1 system. Furthermore, the technique adopted for the preparation of the synthesis gel – e.g partially dried or fully dried – appears to affect the amount of framework titanium in the zeolite structure. The calcined form of the chitosan templated TS-1 zeolites exhibited higher cyclohexene conversion compared to the TS-1 material synthesised without this template, but these catalysts showed lower selectivity for cyclohexene epoxide

Activation of Copper Species on Carbon Nitride for Enhanced Activity in the Arylation of Amines

We report the promoting effect of graphitic carbon nitride in Cu-catalyzed N-arylation. The abundance of pyridinic coordination sites in this host permits the adsorption of copper iodide from the reaction medium. The key to achieving high activity is to confine active Cu species on the surface, which is accomplished by introducing atomically-dispersed metal dopants to block diffusion into the bulk. The alternative route of incorporating metal during the synthesis of graphitic carbon nitride is ineffective as Cu is thermodynamically more stable in inactive subsurface positions. A combination of X-ray absorption, X-ray photoelectron, and electron paramagnetic resonance spectroscopy, density functional theory, and Kinetic Monte Carlo simulations is employed to determine the location and associated geometry as well as the electronic structure of metal centers. N-arylation activity correlates to the surface coverage by copper, which varies during the reaction due to an interplay between site formation via adsorption from the reaction medium and deactivation by diffusion into the bulk of the material, and is highest when an Fe dopant is used that hinders movement through the lattice

Measurement of hadronic event shapes in high-p T multijet final states at √s = 13 TeV with the ATLAS detector

A measurement of event-shape variables in proton-proton collisions at large momentum transfer is presented using data collected at s = 13 TeV with the ATLAS detector at the Large Hadron Collider. Six event-shape variables calculated using hadronic jets are studied in inclusive multijet events using data corresponding to an integrated luminosity of 139 fb−1. Measurements are performed in bins of jet multiplicity and in different ranges of the scalar sum of the transverse momenta of the two leading jets, reaching scales beyond 2 TeV. These measurements are compared with predictions from Monte Carlo event generators containing leading-order or next-to-leading order matrix elements matched to parton showers simulated to leading-logarithm accuracy. At low jet multiplicities, shape discrepancies between the measurements and the Monte Carlo predictions are observed. At high jet multiplicities, the shapes are better described but discrepancies in the normalisation are observed. [Figure not available: see fulltext.

Measurement of the azimuthal anisotropy of charged-particle production in Xe+Xe collisions at sNN =5.44 TeV with the ATLAS detector

This paper describes the measurements of flow harmonics v2-v6 in 3μb-1 of Xe+Xe collisions at sNN=5.44 TeV performed using the ATLAS detector at the Large Hadron Collider (LHC). Measurements of the centrality, multiplicity, and pT dependence of the vn obtained using two-particle correlations and the scalar product technique are presented. The measurements are also performed using a template-fit procedure, which was developed to remove nonflow correlations in small collision systems. This nonflow removal is shown to have a significant influence on the measured vn at high pT, especially in peripheral events. Comparisons of the measured vn with measurements in Pb+Pb collisions and p+Pb collisions at sNN=5.02 TeV are also presented. The vn values in Xe+Xe collisions are observed to be larger than those in Pb+Pb collisions for n=2, 3, and 4 in the most central events. However, with decreasing centrality or increasing harmonic order n, the vn values in Xe+Xe collisions become smaller than those in Pb+Pb collisions. The vn in Xe+Xe and Pb+Pb collisions are also compared as a function of the mean number of participating nucleons, (Npart), and the measured charged-particle multiplicity in the detector. The v3 values in Xe+Xe and Pb+Pb collisions are observed to be similar at the same (Npart) or multiplicity, but the other harmonics are significantly different. The ratios of the measured vn in Xe+Xe and Pb+Pb collisions, as a function of centrality, are also compared to theoretical calculations

Measurements of inclusive and differential cross-sections of combined t t ¯ γ and tWγ production in the eμ channel at 13 TeV with the ATLAS detector

Abstract: Inclusive and differential cross-sections for the production of top quarks in association with a photon are measured with proton-proton collision data corresponding to an integrated luminosity of 139 fb−1. The data were collected by the ATLAS detector at the LHC during Run 2 between 2015 and 2018 at a centre-of-mass energy of 13 TeV. The measurements are performed in a fiducial volume defined at parton level. Events with exactly one photon, one electron and one muon of opposite sign, and at least two jets, of which at least one is b-tagged, are selected. The fiducial cross-section is measured to be 39.6−2.3+2.7 fb. Differential cross-sections as functions of several observables are compared with state-of-the-art Monte Carlo simulations and next-to-leading-order theoretical calculations. These include cross-sections as functions of photon kinematic variables, angular variables related to the photon and the leptons, and angular separations between the two leptons in the event. All measurements are in agreement with the predictions from the Standard Model

Measurements of the production cross-section for a Z boson in association with b -jets in proton-proton collisions at s = 13 TeV with the ATLAS detector

Abstract: This paper presents a measurement of the production cross-section of a Z boson in association with b-jets, in proton-proton collisions at s = 13 TeV with the ATLAS experiment at the Large Hadron Collider using data corresponding to an integrated luminosity of 35.6 fb−1. Inclusive and differential cross-sections are measured for events containing a Z boson decaying into electrons or muons and produced in association with at least one or at least two b-jets with transverse momentum pT> 20 GeV and rapidity |y| < 2.5. Predictions from several Monte Carlo generators based on leading-order (LO) or next-to-leading-order (NLO) matrix elements interfaced with a parton-shower simulation and testing different flavour schemes for the choice of initial-state partons are compared with measured cross-sections. The 5-flavour number scheme predictions at NLO accuracy agree better with data than 4-flavour number scheme ones. The 4-flavour number scheme predictions underestimate data in events with at least one b-jet

Performance of the missing transverse momentum triggers for the ATLAS detector during Run-2 data taking

Abstract: The factor of four increase in the LHC luminosity, from 0.5 × 1034 cm−2s−1 to 2.0 × 1034cm−2s−1, and the corresponding increase in pile-up collisions during the 2015–2018 data-taking period, presented a challenge for the ATLAS trigger, particularly for those algorithms that select events with missing transverse momentum. The output data rate at fixed threshold typically increases exponentially with the number of pile-up collisions, so the legacy algorithms from previous LHC data-taking periods had to be tuned and new approaches developed to maintain the high trigger efficiency achieved in earlier operations. A study of the trigger performance and comparisons with simulations show that these changes resulted in event selection efficiencies of > 98% for this period, meeting and in some cases exceeding the performance of similar triggers in earlier run periods, while at the same time keeping the necessary bandwidth within acceptable limits