Topics in Catalysis最新文献

Beech-wood lignin, derived from the wood of beech trees (genus Fagus), is a lignin-rich biomass with significant potential for valorization. Beech forests are prevalent in temperate regions worldwide, and beech wood possesses desirable properties for various applications, including the construction industry, furniture-making, and pulp production. The oxidative depolymerization of hardwood lignin is a sustainable approach to converting complex lignin structures into high-value aromatic compounds. In this study, the depolymerization of hardwood lignin was optimized using a Box-Behnken design (BBD) quadratic regression model to maximize monomer yields. The model demonstrated high predictive accuracy, with significant alignment between predicted and actual results, indicating its reliability in optimizing reaction conditions. Key operating parameters – temperature, pressure, and reaction time—were systematically varied, and the optimal conditions for monomer yield were found to be 191 °C, 5 bar O₂ pressure, and 25 min. Under these conditions, the primary monomers obtained included syringaldehyde (5.78 wt%) and vanillin (2.31 wt%), along with smaller quantities of acetovanillone, acetosyringone, syringol, and guaiacol. The reducing ability of the resulting monomers was investigated using density functional theory calculations, where electron, hydrogen-atom, and hydride donation ability were determined. Finally, size-exclusion chromatography confirmed the effective breakdown of lignin, showing distinct differences between blank and oxidized samples. This study highlights the effectiveness of oxidative depolymerization under controlled conditions for converting hardwood lignin into valuable aromatic compounds, with the BBD model playing a crucial role in optimizing the process for efficient lignin valorization.

Cyclic voltammetry (CV) is a fundamental electrochemical technique for studying catalytic surfaces, while IrO₂ serves as the gold standard for the oxygen evolution reaction in green hydrogen production. In this study, we simulated theoretical CV on IrO₂ surfaces with different orientations and compared the results with experimental data. Our findings reveal that in heterogeneous electrocatalysis, a single redox couple can manifest as multiple redox peaks, and conversely, a single redox peak may relate to multiple redox couples. This complexity arises from the interplay between surface structure and adsorbate coverage. We discuss strategies to enhance the accuracy and reliability of theoretical CV simulations, emphasizing the importance of comparing to high-quality experimental data from surfaces with low roughness and minimal pseudocapacitance. This integrated approach bridges theory and experiment, paving the way for improved predictions of catalytic activity and for the rational design of enhanced electrocatalysts for sustainable energy applications.

Molecular solar thermal (MOST) systems combine the conversion, storage and release of solar energy using switchable photoisomers. Isomerization of azaborinines (BN-benzenes) to their Dewar isomers (BN-Dewar) yields BNB/BND couples, representing a relatively new class of MOST systems with promising properties for energy storage. However, so far only homogeneous catalysts are available for triggering energy release, which does not allow for a straightforward catalyst-photoisomer separation. In this work, we investigate the heterogeneously catalyzed energy release of two different BNB/BND-based MOST systems, namely 1-(tert-butyldimethylsilyl)-2-mesityl-1,2-dihydro-1,2-azaborinine/2-(tert-butyldimethylsilyl)-3-mesityl-2-aza-3-borabicyclo[2.2.0]hex-5-ene (BNB1/BND1) and 1-(tert-butyl)-2-mesityl-1,2-dihydro-1,2-azaborinine/2-(tert-butyl)-3-mesityl-2-aza-3-borabicyclo[2.2.0]hex-5-ene (BNB2/BND2), using Au(111) as a potential catalytic material. We used highly oriented pyrolytic graphite (HOPG) as inert reference surface. In our study, we combined photochemical infrared reflection absorption spectroscopy (PC-IRRAS) with density functional theory (DFT). We show that Au(111) is active in releasing the energy stored in a BNB/BND MOST system. However, the catalytic activity is strongly dependent on the substituents. Although the activity of the Au catalyst is too low to be implemented in applications, our study provides proof of principle that a heterogeneously catalyzed approach is applicable.

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Against the backdrop of accelerated industrialization and urbanization, the combustion of fossil fuels has led to a significant increase in air pollutant emissions in the environment. Due to its excellent catalytic activity and environmental characteristics, cerium-based catalysts are widely used in flue gas denitrification in coal-fired power plants, steel manufacturing, and chemical industries. This article systematically analyzes different types of cerium-based oxide catalysts and elucidates their excellent performance and reaction mechanism in SCR (Selective Catalytic Reduction) reactions. Meanwhile, this article further investigates the influence of preparation methods of cerium-based catalysts on their catalytic performance. Intended to provide valuable resources for the development of cerium-based catalysts with better performance. In addition, this article explores the effects of metals and sulfur dioxide on the activity of cerium-based catalysts and improves their anti-poisoning performance through methods such as metal doping and structural optimization. Finally, to improve the application of cerium-based catalysts in various fields, three suggestions have been put forward. Future research should focus on analyzing the intermediates of NH₃ denitrification reaction, exploring the synergistic mechanism between active substances and additives or carriers at low temperatures, and simulating poisoning reactions in real applications. I hope to provide broad ideas and application prospects for the innovative development of cerium-based catalysts with better comprehensive performance.

The growing interest in sustainable development and circular economy has contributed with developing environmentally friendly technologies for recovering critical and strategic minerals (CSM). In this study, molecular modeling was employed to simulate the formation of peptide-metal biocomposites as an eco-friendly approach to recover CSM by adsorption. The molecular interactions involved in the adsorption of glutathione (GSH), which is a three-amino acid peptide (γ-l-glutamyl-l-cysteinylglycine), onto the surfaces of particles of palladium (Pd), platinum (Pt) and gold (Au) were simulated. The modeling process was performed in several steps, comprising the molecular structure construction (with the software Avogadro), the molecular volume (with spartan’20), the volume of control (with Packmol.exe), the molecular interaction in the volume of control (with Tinker9), and the visualization of adsorbed molecules (with VMD). The adsorption conditions for simulations were temperature of 298 K, pressure of 1 atm, and pH 7 for the neutralized form of GSH. The number of peptides adsorbed, counted with VMD, was determined with the criterion that peptides located at 3.5 Å or less away from the surface of metals were considered adsorbed. The Langmuir isotherm fitted better the simulation data for three metals than Freundlich isotherm, and the calculated maximum adsorption capacity of Pd, Pt and Au was 72, 42, and 46 mg of GSH/g of metal, respectively. The adsorption energy of GSH on Pd, Pt and Au surfaces was calculated simulating the interactions among the chemical species present in the control volume and doing an energy balance. This adsorption energy ranged from − 27 to − 4 kcal/mol was in accordance close proximity to data reported in the literature for the adsorption energy of peptides with the three metals tested, confirming that the modeling procedure developed in this research is appropriate for calculating main adsorption parameters of peptide adsorption on metal surfaces.

Mixing dopants into oxide catalysts can improve their catalytic activity, as shown in the dramatic boost of the NH₃ selective catalytic reduction (SCR) activity on vanadia catalysts upon doping by tungsten. Here, we employ first-principles calculations to study the influence of selected dopants (Ce, Zr, Nb, Mo, and W) in vanadia on the SCR activity in terms of dopant concentration, distribution, and species. We demonstrate how the dopants affect the stoichiometry of the catalyst and thus finetune the local electron distribution and polarization in the catalytic layer. In addition, we address the relation between dopant concentration and the population of the active vanadyl configuration on the surface. Finally, we propose the generalized surface stoichiometry of the doped vanadia catalysts as a descriptor for the SCR catalytic activity, which promises to be instrumental in identifying oxide catalysts with improved properties also for other important catalytic reactions.

Graphical Abstract

The present study bridges the gap between academic research on monolayer-type catalysts and industrial high-performance catalysts. It investigates industrial high-performance oxidation catalysts for o-xylene to phthalic anhydride conversion. The optimization of the active mass shell thickness enhances pore utilization and thus allows improving catalyst selectivity and activity without influence of diffusion limitation. A design of experiments study focusing on the optimization of the elemental catalyst composition reveals that optimal catalysts require surface VO₄ and SbO₄ monolayer coverages far beyond typical monolayer catalysts as studied in academic literature. The statistical data evaluation shows that optimum element ratios in these catalysts are far from any known stoichiometric compounds. Hence, the role of the well-known antimony promoter cannot be explained by literature concepts like site isolation or mixed oxide formation. Comprehensive analysis of surface evolution during catalyst calcination and equilibration, combined with DFT studies, provides a detailed understanding of surface species formation and stability: the Sb promoter in such catalysts is not located at the outermost catalyst surface. It is incorporated into the surface of anatase maybe in form of VSbO_x dimers. This yields catalysts which activate at higher rates during equilibration, and which are characterized by higher activity without sacrificing selectivity. The Cs promoter can readily be used to tune catalyst activity to the task of the catalyst layer within the graded bed, but it also affects selectivity. By shedding some light onto this complex interplay between the active component V, and the promoting elements, Sb and Cs, in determining catalyst activity and selectivity, and demonstrating the benefits of an Sb-doped anatase support, this study opens new avenues for catalyst optimization and design in the industrial, selective o-xylene oxidation reaction.

Boron-based materials have emerged as a leading catalyst family for the oxidative dehydrogenation of light alkanes. These materials operate via a mixed mechanism involving both surface reactions and gas-phase radical propagation steps. Despite high performance, selectivity to olefin products at industrially-relevant conversions continues to limit viability of these materials. In this perspective, we focus on understanding the contribution of the surface towards observed reactivity. Combining computational, reaction, and spectroscopic evidence we propose that the oxidized surface is primarily activating propane, rather than propylene. However, the stronger C–H abstracting species generated on the oxidized boron surface lead to the formation of both i- and n-propyl radicals with the latter ones reducing the propylene selectivity. Improving the selectivity and activity of the surface species is a promising route to drive these materials towards industrial viability.