Topics in Catalysis最新文献

The conversion of reactants, reaction rate referred to catalyst mass, and turnover frequency (TOF) are values typically employed to compare the activity of different catalysts. However, experimental parameters have to be chosen carefully when systems of different complexity are compared. In order to characterize UHV-based model systems, we use a highly sensitive sniffer setup which allows us to investigate the catalytic activity by combining three different measurement modes: temperature-programmed desorption, continuous flow, and pulsed-reactivity experiments. In this article, we explore the caveats of quantifying catalytic activity in UHV on the well-studied and highly defined reference system of CO oxidation on Pt(111), which we later compare to the same reaction on Pt₁₉ clusters deposited on Fe₃O₄(001). We demonstrate that we can apply fast heating ramps for TOF quantification, thus inducing as little sintering as possible in the metastable clusters. By changing the reactant ratio, we find transient reactivity effects that influence the TOF, which should be kept in mind when comparing catalysts. In addition, the TOF also depends on the surface coverage that itself is a function of temperature and pressure. At a constant reactant ratio, in the absence of transient effects, however, the TOF scales linearly with total pressure over the entire measured temperature range from 200 to 700 K since the reaction rate is dependent on both reactant partial pressures with temperature-dependent reaction order. When comparing the maximum TOF at this particular reactant ratio, we find a 1.6 times higher maximum TOF for Pt₁₉/Fe₃O₄(001) than for Pt(111). In addition, pulsed-reactivity measurements help identify purely reaction-limited regimes and allow for a more detailed investigation of limiting reactants over the whole temperature range.

The potential of silica (SiO₂)-based materials in environmental remediation and energy production, particularly in the conversion of methane (CH₄) with carbon dioxide (CO₂) to fuels (synthesis gas, mixture of carbon monoxide and hydrogen) via dry reforming of methane (DRM), cannot be overemphasized. In this study, the significance of fibrous SiO₂ in minimizing waste and optimizing resource utilization through the exploration of CO₂ applications, its environmental consequences, the assessment of commercialization prospects, and the role of silica-based materials in environmental remediation are comprehensively presented. Analysis of research documents spanning from 1995 to 2022 is presented with an examination of 3122 Keywords Plus (ID) and 1211 Author's Keywords from these publications, which revealed trending themes, major funding institutions, prolific countries, notable authors, and leading journals. The findings underscore China’s dominance as the most productive country in terms of publications and citations (101, 2127), closely trailed by Iran (55, 688), India (47, 675), the USA (39, 864), Japan (26, 342), France (21, 425), Germany (18, 816), Spain (17, 309), South Korea (16, 239), and Malaysia (12, 282). The investigation inveils that implementing renewable energy-powered direct air capture demands a comprehensive strategy, addressing the potential negative impacts of SiO₂ nanoparticles and their interaction with biological components and environmental elements. This study elucidates the potential applications and commercialization prospects for fibrous SiO₂ materials, especially their incorporation into carbon capture and utilization technologies, thereby expanding the range of carbon–neutral solutions.

In this study, an anionic dye, Reactive Black 5 (RB5), was subjected to sonophotocatalytic treatment process with the aim of establishing the effectiveness of the prepared ZnO incorporated activated red mud (ZnO/ARM) as a viable sonophotocatalyst. ZnO/ARM was prepared by impregnation method at different weight ratios (0.25:1, 0.5:1, 0.75:1 and 1:1) with the ZnO/ARM at weight ratio of 0.75:1 proving to be the best sonophotocatalyst. The prepared sonophotocatalysts were characterized by X-ray diffractometer for crystal phase studies, Brunauer–Emmett–Teller for surface area studies, Fourier transform infrared for surface functional groups studies, SEM–EDX for surface morphological and elemental studies, diffuse reflectance spectroscopy and photoluminescence for sonophotocatalyst band-gap studies while parametric and kinetic studies of the removal of RB5 from the simulated wastewater were conducted to confirm its effectiveness under simultaneous application of a transducer bath-type sonicator (35 kHz) and a UV-C (254 nm) lamp. The influence of the solution pH, concentration and catalyst dosage were manipulated throughout this study to investigate the sonophotodegradation kinetics and synergistic effects on the RB5 degradation. Experimental results confirmed that the sonophotocatalytic degradation rate of 20 ppm RB5 was most effective under acidic medium (66.7%) as compared to alkaline medium (46.1%) due to an excess of positive charge in the ZnO/ARM surface which favours a strong electrostatic interaction with SO₃⁻ groups of the dye resulting in a higher degradation rate (0.0156 min⁻¹). Under alkaline conditions, the catalytic activity of ZnO/ARM was attenuated by the higher negative charge which promoted the repulsion of the dye from ZnO/ARM surfaces leading to a lower degradation rate of 0.01 min⁻¹. The accelerated photo induced electron–hole transfer and separation, decreased recombination rate and band energy matching, enhancing the photocatalytic performance of ZnO/ARM composite.

Graphical Abstract

Abstract

MnO_X-Na₂WO₄/SiO₂ catalyst exhibited notable C₂ selectivity/yield in the oxidative coupling of methane (OCM), a promised green chemistry reaction. Nevertheless, the reaction mechanism of this catalyst remains a subject of contention, particularly regarding the role of Na₂WO₄ in the activation. In this study, in situ characterizations of a TiO₂-modified MnO_X-Na₂WO₄/SiO₂ catalyst are conducted by XRD and XPS correlating to the OCM reaction condition, focusing on the simultaneous phase transition of catalyst components within its activation temperature zone. The online MS along with XPS/XRD coupled activity study confirm that transition from Mn³⁺ to Mn²⁺ stands as a pivotal factor influencing the reactivity. In situ XRD further revealed that in this narrow temperature window there is a particular three-step Na₂WO₄ phase change, ending as molten salt, right before the substantial Mn³⁺ to Mn²⁺ transfer initiated. In addition, the rarely observed Na₂WO₄ behavior as molten salt is observed by in situ XPS with rapid spectra collected during an on-stage heating process. These comprehensive in situ catalyst characterizations, covering the extensive structure–activity relationship from solid state to partial molten salt condition, supply new important evidence of the active oxygen transfer pathway from Na₂WO₄ to Mn species which provides a key to understand the activation mechanism of MnO_X-Na₂WO₄/SiO₂ catalyst in OCM.