Probing the dynamics and structure of confined benzene in MCM-41 based catalysts

A combination of Molecular Dynamics (MD) simulations and Quasielastic Neutron Scattering (QENS) experiments has been used to investigate the dynamics and structure of benzene in MCM-41 based catalysts. QENS experiments of benzene as both an unconfined liquid and confined in the catalyst Pt/MCM-41 find that the mobility of benzene decreases upon confinement as shown by the decreased diffusion coefficients. Complementary MD simulations on benzene in MCM-41 show agreement with the QENS experiments when using a novel fully flexible model of MCM-41. Structural information from the MD simulations show that benzene in MCM-41 has a significantly different structure from that of the bulk liquid; with benzene molecules closer together and no prefered orientation

Effects of surfactant on morphology, chemical properties and catalytic activity of hydroxyapatite

Hydroxyapatite (HAP) was synthesised in the presence of surfactants and tested as a catalyst in CO oxidation. XRD confirmed that the characteristic HAP crystal phase was practically unaffected by the addition of surfactant. The surfactant altered both the Ca/P ratio and particle size of HAP. Catalyst tests showed that the activity of HAP increased for preparations using TWEEN, PEG and PVA. The temperature for 50% conversion, T50, values decreased from 340 °C for unmodified HAP, to 320 °C for TWEEN and to 315 °C for both PEG and PVA. This enhanced activity is rationalised by the higher BET surface areas and acid site densities in the surfactant-modified preparations: these increased from 52 m2 g−1 for HAP to 69, 76 and 68 m2 g−1, and from 101 μmol g−1 for HAP to 110, 170 and 126 μmol g−1 for TWEEN, PEG and PVA, respectively. These findings demonstrate that HAP i.e. without the addition of precious metals to either the surface or framework, is an active CO catalyst and that the straightforward inclusion of surfactant during preparation can optimise the catalytic performance

Ethanol Steam Reforming over Ni/ZSM-5 Nanosheet for Hydrogen Production

Compared to reforming reactions using hydrocarbons, ethanol steam reforming (ESR) is a sustainable alternative for hydrogen (H2) production since ethanol can be produced sustainably using biomass. This work explores the catalyst design strategies for preparing the Ni supported on ZSM-5 zeolite catalysts to promote ESR, specifically, two-dimensional ZSM-5 nanosheet and conventional ZSM-5 crystal were used as the catalyst carriers and two synthesis strategies, i.e., in situ encapsulation and wet impregnation method, were employed to prepare the catalysts. Based on the comparative characterization of the catalysts and comparative catalytic assessments, it was found that the combination of the in situ encapsulation synthesis and the ZSM-5 nanosheet carrier was the effective strategy to develop catalysts for promoting H2 production via ESR due to the improved mass transfer (through the 2-D structure of ZSM-5 nanosheet) and formation of confined small Ni nanoparticles (resulted via the in situ encapsulation synthesis). In addition, the resulting ZSM-5 nanosheet supported Ni catalyst also showed high Ni dispersion and high accessibility to Ni sites by the reactants, being able to improve the activity and stability of catalysts and suppress metal sintering and coking during ESR at high reaction temperatures. Thus, the Ni supported on ZSM-5 nanosheet catalyst prepared by encapsulation showed the stable performance with ~88% ethanol conversion and ~65% H2 yield achieved during a 48-h longevity test at 550 °C. Keywords: ZSM-5 nanosheet; In situ encapsulation; Ni catalyst; Ethanol steam reforming of (ESR); Hydrogen (H2) production

Unraveling the H2 promotional effect on the Palladium catalysed CO oxidation using a combination of temporally and spatially resolved investigations

The promotional effect of H2 on the oxidation of CO is of topical interest and there is debate over whether this promotion is due to either thermal or chemical effects. As yet there is no definitive consensus in the literature. Combining spatially resolved mass spectrometry and X-ray absorption spectroscopy (XAS) we observe a specific environment of the active catalyst during CO oxidation, having the same specific local coordination of the Pd in both the absence and presence of H2. In combination with Temporal Analysis of Products (TAP), performed under isothermal conditions, a mechanistic insight into the promotional effect of H2 was found, providing clear evidence of non-thermal effects in the hydrogen promoted of oxidation of carbon monoxide. We have identified that H2 promotes the Langmuir Hinshelwood mechanism and we propose this is linked to the increased interaction of O with the Pd surface in the presence of H2. This combination of spatially resolved MS and XAS and TAP studies has provided previously unobserved insights into the nature of this promotional effect

Coupling non-thermal plasma with Ni catalysts supported on BETA zeolite for catalytic CO2 methanation

Catalytic carbon dioxide (CO2) methanation is a promising and effective process for CO2 utilisation and the production of CH4 as an alternative to using natural gas. Non-thermal plasma (NTP) activation has been proven to be highly effective in overcoming the thermodynamic limitation of reactions under mild conditions and intensifying the CO2 hydrogenation process greatly. Herein, we present an example of NTP-assisted catalytic CO2 methanation over Ni catalysts (15 wt%) supported on BETA zeolite employing lanthana (La) as the promoter. It was found that a NTP-assisted system presents remarkable catalytic performance in catalytic CO2 methanation without an external heat source. Significantly, the use of Na-form BETA zeolite and the addition of La (i.e. 15Ni–20La/Na-BETA catalyst) resulted in an improvement in CO2 conversions, surpassing the 15Ni/H-BETA catalyst, i.e. a seven-fold increase in the turnover frequency, TOF (1.45 s−1vs. 0.21 s−1), and selectivity towards CH4 (up to ca. 97%). In addition, the developed catalyst also exhibited excellent stability under NTP conditions, i.e. a stable performance over a 15 h longevity test (with a TOF of 1.44 ± 0.01 s−1). Comparative in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) characterisation of the developed catalysts revealed that the introduction of La2O3 to the Ni catalyst provides more surface hydroxyl groups, and hence enhances CO2 methanation. Additionally, by analysing the surface species over 15Ni–20La/Na-BETA comparatively under thermal and NTP conditions (by in situ DRIFTS analysis), it is proposed that both the Langmuir–Hinshelwood and Eley–Rideal mechanisms co-exist in the NTP system due to the presence of dissociated H species in the gas phase. Conversely, for the thermal system, the reaction has to go through reactions between the surface-dissociated H and carbonate-like adsorbed CO2via the Langmuir–Hinshelwood mechanism. The current mechanistic understanding of the NTP-activated system paves the way for the exploration of the reaction mechanisms/pathways of NTP-assisted catalytic CO2 methanation

Catalytic decomposition of NO2 over a copper-decorated metal-organic framework by non-thermal plasma

Efficient catalytic conversion of NO2 to non-harmful species remains an important target for research. State-of-the-art deNOx processes are based upon ammonia (NH3)-assisted selective catalytic reduction (NH3-SCR) over Cu-exchanged zeolites at elevated temperatures. Here, we describe a highly efficient non-thermal plasma (NTP) deNOx process catalyzed by a Cu-embedded metal-organic framework, Cu/MFM-300(Al), at room temperature. Under NTP activation at 25°C, Cu/MFM-300(Al) enables direct decomposition of NO2 into N2, NO, N2O, and O2 without the use of NH3 or other reducing agents. NO2 conversion of 96% with a N2 selectivity of 82% at a turnover frequency of 2.9 h−1 is achieved, comparable to leading NH3-SCR catalysts that use NH3 operating at 250°C–550°C. The mechanism for the rate-determining step (NO→N2) is elucidated by in operando diffuse reflectance infrared Fourier transform spectroscopy, and electron paramagnetic resonance spectroscopy confirms the formation of Cu2+⋯NO nitrosylic adducts on Cu/MFM-300(Al), which facilitates NO dissociation and results in the notable N2 selectivity

Atomically dispersed copper sites in a metal-organic framework for reduction of nitrogen dioxide

Metal–organic framework (MOF) materials provide an excellent platform to fabricate single-atom catalysts due to their structural diversity, intrinsic porosity, and designable functionality. However, the unambiguous identification of atomically dispersed metal sites and the elucidation of their role in catalysis are challenging due to limited methods of characterization and lack of direct structural information. Here, we report a comprehensive investigation of the structure and the role of atomically dispersed copper sites in UiO-66 for the catalytic reduction of NO2 at ambient temperature. The atomic dispersion of copper sites on UiO-66 is confirmed by high-angle annular dark-field scanning transmission electron microscopy, electron paramagnetic resonance spectroscopy, and inelastic neutron scattering, and their location is identified by neutron powder diffraction and solid-state nuclear magnetic resonance spectroscopy. The Cu/UiO-66 catalyst exhibits superior catalytic performance for the reduction of NO2 at 25 °C without the use of reductants. A selectivity of 88% for the formation of N2 at a 97% conversion of NO2 with a lifetime of >50 h and an unprecedented turnover frequency of 6.1 h–1 is achieved under nonthermal plasma activation. In situ and operando infrared, solid-state NMR, and EPR spectroscopy reveal the critical role of copper sites in the adsorption and activation of NO2 molecules, with the formation of {Cu(I)···NO} and {Cu···NO2} adducts promoting the conversion of NO2 to N2. This study will inspire the further design and study of new efficient single-atom catalysts for NO2 abatement via detailed unravelling of their role in catalysis