The role of steric effects and acidity in direct synthesis of iso-paraffins from syngas on cobalt zeolite catalysts

This study focuses on the effects of the localization of Co species, zeolite structure, and acidity on the performance of Co bifunctional catalysts promoted with Pt for the direct synthesis of iso-paraffins from syngas. ZSM-5, MOR, and BEA were chosen as zeolites with different structures and pore diameters. The catalysts were prepared either by incipient wetness impregnation or by the mechanical mixing of the zeolite with a conventional silica-supported Co catalyst. The increase in the pore size and open character of the zeolite structure from ZSM-5 to BEA resulted in a higher fraction of Co located inside the pores of the catalysts prepared by impregnation. The catalytic performance was affected strongly by the zeolite acidity, pore structure, and Co distribution between the pores and the external surface. The selectivity to short-chain iso-paraffins is affected principally by the zeolite acidity, whereas the selectivity to long-chain branched hydrocarbons mostly depends on steric effects

Probing the acid sites of zeolites with pyridine: quantitative AGIR measurements of the molar absorption coefficients

This study presents a detailed methodology, which combines high-precision thermogravimetry and FTIR spectroscopy, aiming to establish the most accurate and reliable means of measuring the molar absorption coefficients of adsorbed species. As the integrated molar absorption coefficients of Py complexes with Brønsted and Lewis acid sites, ɛ(Py-B) and ɛ(Py-L), are determined and the validity of the Beer-Lambert-Bouguer law for IR characterisation of solid acids is demonstrated, this work is setting a benchmark for the quantitative acidity measurements in zeolites and related materials. The following values of ɛ(Py-B) have been obtained at 150°C (band at ~1545 cm-1): 1.09±0.08 cm μmol-1 for ZSM-5; 1.12±0.16 cm μmol-1 for BEA; 1.29±0.04 cm μmol-1 18 for MOR and 1.54±0.15 cm μmol-1 for FAU. The value of ɛ(Py-L) (band at ~1455 cm-1 19 , which refers to different cations) measured at the same temperature is 1.71±0.1 cm μmol-1 20 . Values of ɛ(Py-B) depend on the zeolite structure, in contrast to that for ɛ(Py-L). Clear correlations are presented between the temperature of the FTIR measurements and ɛ values for Py complexes and other species, which decrease by ~10% as the temperature increases by 100oC. In addition, the effects of key experimental procedures, instrumentation design and sample preparation are established and quantified

Transalkylation of Toluene with 1,2,4-Trimethylbenzene over Large Pore Zeolites

Using industrially relevant operating parameters, the transalkylation of 1,2,4-trimethylbenzene (TMB) with toluene was studied. The effect of acidity and structure, increased reaction pressure, and very low levels of Pt impregnation have been investigated over both H-form and Pt-loaded zeolites: Beta, MOR, and Y. A fixed bed reactor was used at WHSV of 5 h–1, 400 °C, and a 50:50 wt % toluene:TMB ratio with the order of activity after 50 h TOS of Y > Beta ≫ MOR at 1 bar. At elevated pressure (10 bar), all catalysts showed better performance with significant improvement in MOR as pore blockage reduced and the order of activity was Beta > MOR > Y. Incorporation of Pt (0.08 wt %) further improved the activity of all catalysts with the highest conversion after 50 h TOS over Beta (62 wt %) where Beta and MOR yielded similar levels of xylenes (40 wt %). All catalysts were further optimized for activity while maintaining the desired stability and highest xylenes yield

Structural features and stability of Spanish sepiolite as a potential catalyst

Abstract Sepiolite-based catalysts loaded with potassium hydroxide were prepared via the wet impregnation and ion-exchange methods and evaluated as catalysts in base-assisted reactions, such as transesterification of renewable oils. The structural features of these catalysts were characterised in detail by variable-temperature in situ X-ray diffraction, N2 adsorption-desorption, scanning electron microscopy with energy-dispersive X-ray analysis and in situ FTIR spectroscopy. Although a high yield of fatty acid methyl esters was achieved in transesterification reactions in the presence of K-containing sepiolite, this system showed significant deactivation due to its structural degradation and loss of the active component during the reaction and regeneration cycles. This work demonstrates for the first time how the thermal and structural stability of sepiolite based systems can affect their performance, which is an essential issue that has not been sufficiently addressed in recent research related to the catalytic applications of these materials

Magnesium oxide loaded mesoporous silica: Synthesis, characterisation and use in removing lead and cadmium from water supplies

Water pollution by potentially toxic elements such as cadmium (Cd) and lead (Pb) is a persistent problem in many parts of the world. It continues to have profound implications for drinking water supplies, wastewater discharge and environmental quality of rivers and lakes. Treatment is routinely needed but is not always accessible or practical for a given location or situation, hence new treatment options are the focus of much research. Nanotechnology has great potential to enhance water purification and decontamination efficiency. Nanomaterials have been shown to efficiently remove organic and inorganic pollutants, including metals, from contaminated waters but they can have a tendency to flocculate and thereby lose removal efficiency. Research aimed at stabilising nanoparticles into matrices such as silica offers a way forward. In this study, mesoporous silica (mSiO2, also referred to as MCM-41) was prepared and loaded with magnesium oxide nanoparticles (MgO-NP) to form a MgO-silica composite (MgO-mSiO2) and characterised using UV–Vis, FTIR, XRD, BET, and SEM techniques. The MgO-NP, mSiO2 and MgO-mSiO2 were then evaluated for their Cd and Pb removal capacity across varying conditions of pH, metal concentration, adsorbent: solution volume ratio and contact time. Sorption data were evaluated using the Freundlich, Langmuir and Temkin isotherm models. The MgO-mSiO2 was found to have a very high sorption capacity across the conditions tested, with >99% Cd removal across pH range 3–9 and >99% Pb removal across pH range 5–9. When tested at pH 6–7, the MgO-mSiO2 achieved nearly 100% adsorption efficiencies across the contact times tested (15–180 min)

Catalytic performance of microporous materials for the production of renewable fuels

ETS-10, zeolite A and sepiolite based nano-structured materials were prepared and modified with potassium containing compounds using ion-exchange or impregnation and evaluated as basic catalysts for transesterification of vegetable oils using microwave heating. The structural features of these catalysts were characterised in detail by the variable temperature in situ X-ray diffraction, N2 adsorption–desorption, scanning electron microscopy with energy dispersive X-ray analysis and in situ FTIR spectroscopy using adsorption–desorption of acetylene as a basic probe in order to evaluate their structure–catalytic performance relationship in the methanolysis of triglycerides. A wide range of parameters were utilised in order to optimise the reaction conditions. Although a high yield of fatty acid methyl esters with almost 100% selectivity can be achieved in transesterification reactions in the presence of K-containing sepiolite, this system shows significant deactivation due to its structural degradation and loss of the active component during the reaction and regeneration cycles. In contrast, zeolite KA and ETS-10, which are thermally stable crystalline materials, demonstrated no decrease in their activity for up to four reaction runs, and therefore can be used as effective solid basic catalysts in this reaction. Here we explore for the first time how the thermal and structural stability of the supported clay can affect its activity, an essential issue which has not been sufficiently studied in the recent research related to the biofuel production over solid catalysts

On the enhancing effect of Ce in Pd-MOR catalysts for NOx CH4-SCR: a structure-reactivity study

The effect of palladium and cerium species on the selective catalytic reduction (SCR) of NOx using methane as reductant (NOx CH4-SCR) has been investigated using Pd-HMOR and PdCe-HMOR system. The catalysts have been characterised by H2-TPR, DRS UV–Vis, TEM/EDS and FTIR using CO and pyridine as probe molecules. The oxidation of NO and CH4-SCR catalytic tests have been conducted using monometallic and bimetallic formulations. Above 0.3 wt.% Pd, the increase in Pd loading leads to a decrease in NOx selectivity towards N2, with the formation of N2O, and a decrease in the CH4 selectivity towards SCR, due to CH4 direct combustion. H2-TPR and FTIR-CO studies indicate that palladium is stabilised as Pd2+ in ion-exchange position, probably in two different sites within the MOR framework. The addition of cerium to Pd-HMOR enhances its catalytic performance for NOx CH4-SCR. With 1 wt.% Ce, both NOx conversion into N2 and CH4 selectivity towards SCR have increased. Small CeO2 clusters interacting with palladium are likely to play a major role in this catalytic reaction. The number of such species increases up to Ce loading of ca. 2 wt.%. However, above 3 wt%, NOx conversion values decrease with Ce loading, which is attributed to the formation of bulk CeO2 species not interacting with palladium

Stoichiometric methane conversion to ethane using photochemical looping at ambient temperature

Methane activation and utilization are among the major challenges of modern science. Methane is potentially an important feedstock for manufacturing value-added fuels and chemicals. However, most known processes require excessive operating temperatures and exhibit insufficient selectivity. Here, we demonstrate a photochemical looping strategy for highly selective stoichiometric conversion of methane to ethane at ambient temperature over silver–heteropolyacid–titania nanocomposites. The process involves a stoichiometric reaction of methane with highly dispersed cationic silver under illumination, which results in the formation of methyl radicals. Recombination of the generated methyl radicals leads to the selective, and almost quantitative, formation of ethane. Cationic silver species are simultaneously reduced to metallic silver. The silver–heteropolyacid–titania nanocomposites can be reversibly regenerated in air under illumination at ambient temperature. The photochemical looping process achieves a methane coupling selectivity of over 90%, a quantitative yield of ethane of over 9%, high quantum efficiency (3.5% at 362 nm) and excellent stability

eXtended Reality (XR) virtual practical and educational eGaming to provide effective immersive environments for learning and teaching in forensic science

Online virtual learning resources have been available for learning and teaching in forensic science for some years now, but the recent global COVID-19 related periods of irregular lockdown have necessitated the rapid development of these for teaching, learning and CPD activities. However, these resources do need to be carefully constructed and grounded in pedagogic theory to be effective. This article details eXtended Reality (XR) learning and teaching environments to facilitate effective online teaching and learning for forensic geoscientists. The first two case studies discussed in this article make use of Thinglink software to produce virtual learning and teaching XR resources through an internet system, which was delivered to undergraduate students in 2021. Case one details an XR virtual laboratory-based XRF equipment resource, providing a consistent, reliable and asynchronous learning and teaching experience, whilst the second case study presents an XR virtual learning applied geophysics resource developed for a 12-week CPD training programme. This programme involves recorded equipment video resources, accompanying datasets and worksheets for users to work through. Both case studies were positively received by learners, but there were issues encountered by learners with poor internet connections or computer skills, or who do not engage well with online learning. A third case study showcases an XR educational forensic geoscience eGame that was developed to take the user through a cold case search investigation, from desktop study through to field reconnaissance and multi-staged site investigations. Pedagogic research was undertaken with user questionnaires and interviews, providing evidence that the eGame was an effective learning and teaching tool. eGame users highly rated the eGame and reported that they raised awareness and understanding of the use of geophysics equipment and best practice of forensic geoscience search phased investigations. These types of XR virtual learning digital resources, whilst costly to produce in terms of development time and staff resource, provide a complementary virtual learning experience to in-situ practical sessions, and allow learners to asynchronously familiarise themselves with equipment, environments and techniques resulting in more efficient use of in situ time. The XR resources also allow learners to reinforce learning post in-situ sessions. Finally, XR resources can provide a more inclusive and authentic experience for learners who cannot attend or complete work synchronously

Chemically and thermally stable silica nanowires with a β-sheet peptide core for bionanotechnology

Background: A series of amyloidogenic peptides based on the sequence KFFEAAAKKFFE template the silica precursor, tetraethyl orthosilicate to form silica-nanowires containing a cross-β peptide core. Results: Investigation of the stability of these fibres reveals that the silica layers protect the silica-nanowires allowing them to maintain their shape and physical and chemical properties after incubation with organic solvents such as 2-propanol, ethanol, and acetonitrile, as well as in a strong acidic solution at pH 1.5. Furthermore, these nanowires were thermally stable in an aqueous solution when heated up to 70 °C, and upon autoclaving. They also preserved their conformation following incubation up to 4 weeks under these harsh conditions, and showed exceptionally high physical stability up to 1000 °C after ageing for 12 months. We show that they maintain their β-sheet peptide core even after harsh treatment by confirming the β-sheet content using Fourier transform infrared spectra. The silica nanowires show significantly higher chemical and thermal stability compared to the unsiliconised fibrils. Conclusions: The notable chemical and thermal stability of these silica nanowires points to their potential for use in microelectromechanics processes or fabrication for nanotechnological devices