Abstract
The synergistic interaction among different components in complex catalysts is one of the crucial factors in determining catalytic performance. Here we report the interactions among the ...three components in controlling the catalytic performance of Cu–ZnO–ZrO
2
(CZZ) catalyst for CO
2
hydrogenation to methanol. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements under the activity test pressure (3 MPa) reveal that the CO
2
hydrogenation to methanol on the CZZ catalysts follows the formate pathway. Density functional theory (DFT) calculations agree with the in situ DRIFTS measurements, showing that the ZnO–ZrO
2
interfaces are the active sites for CO
2
adsorption and conversion, while the presence of metallic Cu is also necessary to facilitate H
2
dissociation and to provide hydrogen resource. The combined experiment and DFT results reveal that tuning the interaction between ZnO and ZrO
2
can be considered as another important factor for designing high performance catalysts for methanol generation from CO
2
.
·Vapor phase diffusion is a simple approach to prepare continuous gradients for TLC.·UV illumination and diffuse reflectance provide a means to evaluate gradient shape.·Gradient shape depends on ...silane concentration, exposure time, and humidity.·Gradient direction influences the retention behavior of the analytes.·New selectivities are achieved using continuous stationary phase gradients
A new, versatile, and straightforward vapor phase deposition (VPD) approach was used to prepare continuous stationary phase gradients (cSPGs) on silica thin-layer chromatography (TLC) plates using phenyldimethylchlorosilane (PDCS) as a precursor. A mixture of paraffin oil and PDCS was placed at the bottom of an open-ended rectangular chamber, allowing the reactive silanes to evaporate and freely diffuse under a controlled atmosphere. As the volatile silane diffused across the length of the TLC plate, it reacted with the surface silanol groups thus functionalizing the surface in a gradient fashion. Characterization of the gradient TLC plates was done through UV visualization and diffuse reflectance spectroscopy (DRS). Visualizing the fluorescent gradient plates under UV radiation shows the clear presence of a gradient with the side closest to the vapor source undergoing the most modification. More quantitative characterization of the shape of the gradient was provided by DRS. The DRS showed that the degree of modification and shape of the gradient was dependent on the concentration of silane, VPD time, and relative humidity. To evaluate the chromatographic performance, a mixture of three aromatic compounds (acetaminophen (A), aspirin (As), and 3-hydroxy-2-naphthoic acid (3H)) was spotted on the high (GHP) and low phenyl (GLP) ends of the gradient TLC plates and the results compared to the separations carried out on unmodified and uniformly modified plates. The GHP TLC plates showed retention factors (Rf) of 0.060 ± 0.006, 0.391 ± 0.006, and 0.544 ± 0.006, whereas the unmodified plate displayed Rf values of 0.059 ± 0.006, 0.092 ± 0.003, and 0.037 ± 0.002 for the analytes A, As, and 3H, respectively. From the Rf values, it was observed that each modified plate exhibited different selectivity for the analytes. The GHP TLC plates exhibited better separation performance, and improved resolution compared to the GLP, unmodified, and uniformly modified plates. Overall, VPD is a new, cost-effective method for creating a gradient on the stationary phase which has the potential to advance chromatographic separation capabilities.
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•Operando UV–Vis diffuse reflectance spectroscopy and chemometrics could distinguish the reaction phases of the methane dehydroaromatization process.•Upon activation in CO, the ...spectral component for the activation phase was removed.•During the active period, typical hydrocarbon pool intermediates could be observed.•Deactivation is governed by the built-up of polyaromatic coke species.•Catalyst preparation only impacts the dispersion of the molybdenum active phase, but not the spectral components.
Methane Dehydroaromatization (MDA) is proposed as a possible way to valorize stranded natural gas, e.g., arising during crude oil drilling. In this study, we used operando UV–Vis Diffuse Reflectance Spectroscopy (DRS) in combination with Multivariate Curve Resolution Alternating Least Squares (MCR-ALS) to distinguish the MDA reaction phases of activation, induction, and deactivation. We identified three spectral components, which describe these distinct reaction phases. When the catalyst was activated in CO, two spectral components alone sufficiently described the operando UV–Vis DRS data. We further found that the preparation method of the Mo/ZSM-5 catalyst has little influence on the observed spectral features. However, the different preparation methods impact the dispersion of Mo, resulting in faster deactivation for the catalyst with more Mo-clusters compared to the catalyst with a higher Mo dispersion. This study shows that operando UV–Vis DRS in combination with the MCR-ALS methodology is a powerful analytical tool to disentangle and study the three MDA reaction phases.
Sc2-xLaxGe2O7 (0.00 ≤ x ≤ 2.00) ceramics were synthesized by the solid-state method and their structural, vibrational, and optical properties were investigated by XRD, Raman scattering, infrared and ...diffuse reflectance spectroscopies. Phase-pure Sc2Ge2O7 is monoclinic, belonging to the C2/m (#12) space group, while La2Ge2O7 belongs to the triclinic P1̅ (#2) space group, which was confirmed by second harmonic generation measurements. It was verified that the solid solubility was attained at two distinct compositional ranges. For 0.00 <x ≤ 0.04, the monoclinic structure incorporates La3+ ions, while in the range of 1.80 ≤ x < 2.00, Sc3+ replaces La3+ into the triclinic space group. The results from vibrational spectroscopic data were essential to observe the crystal phase evolution as the optical phonon modes change, tracking gradually the structural modifications observed through the analysis of 22 different chemical compositions. In addition, the resulting compositional effects on the band gap energies of the pyrogermanate series showed values that varied between 5.75 (pure La2Ge2O7) and 6.00 eV (pure Sc2Ge2O7).
•The monoclinic-triclinic phase transformation in Sc2-xLaxGe2O7 ceramics is reported.•A complete solid solubility was attained at two distinct compositional ranges.•Raman spectroscopy was employed to track gradually the structural changes observed.•Diffuse reflectance spectroscopy unveiled the resulting compositional effects on the bandgap energies.•Vegard’s Law described the pyrogermanate system in terms of the crystal structure mismatch.
We report three electrically conductive metal-organic frameworks (MOFs) based on a tetrathiafulvalene linker and La
3+
. Depending on the solvent ratios and temperatures used in their solvothermal ...synthesis, these MOFs crystallize with different topologies containing distinct π-π stacking sequences of the ligand. Notably, their transport properties correlate rationally with the stacking motifs: longer S S contact distances between adjacent ligands coincide with lower electrical conductivities and higher activation energies. Diffuse reflectance spectroscopic measurements reveal ligand-based intervalence charge transfer bands in each phase, implicating charge delocalization among mixed-valent tetrathiafulvalene units as the dominant mode of transport. Overall, these frameworks demonstrate how tuning the intermolecular interactions in MOFs serves as a route towards controlling their physical properties.
We report three electrically conductive metal-organic frameworks (MOFs) based on a tetrathiafulvalene linker and La
3+
.
The maximization of the numbers of exposed active sites in supported metal catalysts is important to achieve high reaction activity. In this work, a simple strategy for anchoring single atom Fe on ...SBA-15 to expose utmost Fe active sites was proposed. Iron salts were introduced into the as-made SBA-15 containing the template and calcined for simultaneous decomposition of the iron precursor and the template, resulting in single atom Fe sites in the nanopores of SBA-15 catalysts (SAFe-SBA). X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy (UV–vis DRS), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and extended X-ray absorption fine structure (EXAFS) imply the presence of single atom Fe sites. Furthermore, EXAFS analysis suggests the structure of one Fe center with four O atoms, and density functional theory calculations (DFT) simulate this structure. The catalytic performances of SAFe-SBA were evaluated in Fenton-like catalytic oxidation of p-hydroxybenzoic acid (HBA) and phenol. It was found that the single atom SAFe-SBA catalysts displayed superior catalytic activity to aggregated iron sites (AGFe-SBA) in both HBA and phenol degradation, demonstrating the advantage of SAFe-SBA in catalysis.
Delicate modulations of CO2 activation and charge carrier separation/migration are challenging, yet imperative to augment CO2 photoreduction efficiency. Herein, by supporting diethylenetriamine ...(DETA)‐functionalized Cd0.8Zn0.2S nanowires on the exterior surface of hollow Co9S8 polyhedrons, hierarchical Co9S8@Cd0.8Zn0.2S‐DETA nanocages are fabricated as an S‐scheme photocatalyst for reducing CO2 and protons to produce syngas (CO and H2). The amine groups strengthen adsorption and activation of CO2, while the “nanowire‐on‐nanocage” hierarchical hollow heterostructure with an S‐scheme interface boosts separation and transfer of photoinduced charges. Employing Co(bpy)32+ as a cocatalyst, the optimal photocatalyst effectively produces CO and H2 in rates of 70.6 and 18.6 µmol h−1 (i.e., 4673 and 1240 µmol g−1 h−1), respectively, affording an apparent quantum efficiency of 9.45% at 420 nm, which is the highest value under comparable conditions. Ultraviolet photoelectron spectroscopy, Kelvin probe, and electron spin resonance confirm the S‐schematic charge‐transfer process in the photocatalyst. The key COOH* species responsible for CO2‐to‐CO reduction is detected by in‐situ diffuse reflectance infrared Fourier transform spectroscopy and endorsed by density functional theory calculations, and thus a possible CO2 reduction mechanism is proposed.
Hierarchical Co9S8@Cd0.8Zn0.2S‐diethylenetriamine (DETA) hybrid nanocages are created by supporting DETA‐functionalized Cd0.8Zn0.2S nanowires on the exterior surface of hollow Co9S8 polyhedrons and they are applied as an S‐scheme photocatalyst for efficient syngas production from CO2 and protons, yielding a superior apparent quantum efficiency of 9.45% at 420 nm.
Photosynthetic conversion of CO2 into fuel and chemicals is a promising but challenging technology. The bottleneck of this reaction lies in the activation of CO2, owing to the chemical inertness of ...linear CO2. Herein, we present a defect‐engineering methodology to construct CO2 activation sites by implanting carbon vacancies (CVs) in the melon polymer (MP) matrix. Positron annihilation spectroscopy confirmed the location and density of the CVs in the MP skeleton. In situ diffuse reflectance infrared Fourier transform spectroscopy and a DFT study revealed that the CVs can function as active sites for CO2 activation while stabilizing COOH* intermediates, thereby boosting the reaction kinetics. As a result, the modified MP‐TAP‐CVs displayed a 45‐fold improvement in CO2‐to‐CO activity over the pristine MP. The apparent quantum efficiency of the MP‐TAP‐CVs was 4.8 % at 420 nm. This study sheds new light on the design of high‐efficiency polymer semiconductors for CO2 conversion.
Defects that overcome deficiency: A steam engineering strategy was developed to construct carbon vacancies (CVs) in a melon‐based carbon nitride polymer matrix. The CVs in the material effectively promoted the activation of CO2 while prolonging the charge lifetime of the carbon nitride polymer, thus promoting CO2 reduction (see picture).
Currently, selective catalytic reduction (SCR) of NOx with NH3 in the presence of SO2 by using vanadium-free catalysts is still an important issue for the removal of NOx for stationary sources. ...Developing high-performance catalysts for NOx reduction in the presence of SO2 is a significant challenge. In this work, a series of Fe2O3-promoted halloysite-supported CeO2–WO3 catalysts were synthesized by a molten salt treatment followed by the impregnation method and demonstrated improved NOx reduction in the presence of SO2. The obtained catalyst exhibits superior catalytic activity, high N2 selectivity over a wide temperature range from 270 to 420 °C, and excellent sulfur-poisoning resistance. It has been demonstrated that the Fe2O3-promoted halloysite-supported CeO2–WO3 catalyst increased the ratio of Ce3+ and the amount of surface oxygen vacancies and enhanced the interaction between active components. Moreover, the SCR reaction mechanism of the obtained catalyst was studied using in situ diffuse reflectance infrared Fourier transform spectroscopy. It can be inferred that the number of Brønsted acid sites is significantly increased, and more active species could be produced by Fe2O3 promotion. Furthermore, in the presence of SO2, the Fe2O3-promoted halloysite-supported CeO2–WO3 catalyst can effectively prevent the irreversible bonding of SO2 with the active components, making the catalyst exhibit desirable sulfur resistance. The work paves the way for the development of high-performance SCR catalysts with improved NOx reduction in the presence of SO2.
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