Advances in sample environments for neutron scattering for colloid and interface science

This review describes recent advances in sample environments across the full complement of applicable neutron scattering techniques to colloid and interface science. Temperature, pressure, flow, tensile testing, ultrasound, chemical reactions, IR/visible/UV light, confinement, humidity and electric and magnetic field application, as well as tandem X-ray methods, are all addressed. Consideration for material choices in sample environments and data acquisition methods are also covered as well as discussion of current and potential future use of machine learning and artificial intelligence.

Neutron Scattering Studies of Heterogeneous Catalysis

Understanding the structural dynamics/evolution of catalysts and the related surface chemistry is essential for establishing structure-catalysis relationships, where spectroscopic and scattering tools play a crucial role. Among many such tools, neutron scattering, though less-known, has a unique power for investigating catalytic phenomena. Since neutrons interact with the nuclei of matter, the neutron-nucleon interaction provides unique information on light elements (mainly hydrogen), neighboring elements, and isotopes, which are complementary to X-ray and photon-based techniques. Neutron vibrational spectroscopy has been the most utilized neutron scattering approach for heterogeneous catalysis research by providing chemical information on surface/bulk species (mostly H-containing) and reaction chemistry. Neutron diffraction and quasielastic neutron scattering can also supply important information on catalyst structures and dynamics of surface species. Other neutron approaches, such as small angle neutron scattering and neutron imaging, have been much less used but still give distinctive catalytic information. This review provides a comprehensive overview of recent advances in neutron scattering investigations of heterogeneous catalysis, focusing on surface adsorbates, reaction mechanisms, and catalyst structural changes revealed by neutron spectroscopy, diffraction, quasielastic neutron scattering, and other neutron techniques. Perspectives are also provided on the challenges and future opportunities in neutron scattering studies of heterogeneous catalysis.

Past, present and future-sample environments for materials research studies in scattering and spectroscopy; a UK perspective

Small angle x-ray scattering and x-ray absorption fine structure are two techniques that have been employed at synchrotron sources ever since their inception. Over the course of the development of the techniques, the introduction of sample environments for added value experiments has grown dramatically. This article reviews past successes, current developments and an exploration of future possibilities for these two x-ray techniques with an emphasis on the developments in the United Kingdom between 1980-2020.

Bulk and Confined Benzene-Cyclohexane Mixtures Studied by an Integrated Total Neutron Scattering and NMR Method

Herein mixtures of cyclohexane and benzene have been investigated in both the bulk liquid phase and when confined in MCM-41 mesopores. The bulk mixtures have been studied using total neutron scattering (TNS), and the confined mixtures have been studied by a new flow-utilising, integrated TNS and NMR system (Flow NeuNMR), all systems have been analysed using empirical potential structure refinement (EPSR). The Flow NeuNMR setup provided precise time-resolved chemical sample composition through NMR, overcoming the difficulties of ensuring compositional consistency for computational simulation of data ordinarily found in TNS experiments of changing chemical composition—such as chemical reactions. Unique to the liquid mixtures, perpendicularly oriented benzene molecules have been found at short distances from the cyclohexane rings in the regions perpendicular to the carbon–carbon bonds. Upon confinement of the hydrocarbon mixtures, a stronger parallel orientational preference of unlike molecular dimers, at short distances, has been found. At longer first coordination shell distances, the like benzene molecular spatial organisation within the mixture has also found to be altered upon confinement.

Applications of pair distribution function analyses to the emerging field of non-ideal metal-organic framework materials

Pair distribution function, PDF, analyses are emerging as a powerful tool to characterize non-ideal metal-organic framework (MOF) materials with compromised ordering. Although originally envisaged as crystalline porous architectures, MOFs can incorporate defects in their structures through either chemistry or mechanical stress, resulting in materials with unpredicted novel properties. Indeed, a wide variety of current non-ideal MOFs have disorder in their structures to some extent, thereby often lacking crystals. Typically, PDF experiments are performed using high-energy synchrotron X-rays or neutrons to achieve a superior high atomic resolution in short times. The PDF technique analyses both Bragg and diffuse scattering signals simultaneously, without being restricted to crystalline materials. This characteristic makes PDF analyses a powerful probe to address the structural characterization of non-ideal MOF materials both at the local and intermediate range scales, including under in situ conditions relevant to MOF synthesis, activation and catalysis.

Low-field NMR relaxation-exchange measurements for the study of gas admission in microporous solids

Understanding the uptake and storage of gases by microporous materials is important for our future energy security. As such, we demonstrate here the application of two-dimensional NMR relaxation experiments for probing the admission and corresponding exchange dynamics of methane within microporous zeolites. Specifically, we report low-field (12.7 MHz) 1H NMR relaxation-exchange correlation measurements of methane within commercial LTA zeolites (3A and 4A) at 25 and 35 bar and ambient temperature. Our results demonstrate the clear identification of bulk-pore and pore-pore exchange processes within zeolite 4A, facilitating the calculation and comparison of effective exchange rate dynamics across varying diffusion length scales and gas pressures. Additional data acquired for zeolite 3A reveals the sensitivity of NMR relaxation phenomena to size-exclusive gas admission phenomena, illustrating the potential of benchtop NMR protocols for material screening applications.

In situ high-pressure 13C/1H NMR reaction studies of benzyl alcohol oxidation over a Pd/Al2O3 catalyst

We report in situ high-pressure NMR kinetic studies of catalytic oxidations inside heterogeneous catalysts exploiting distortionless enhancement by polarisation transfer (DEPT) ¹³C NMR.