Search Results (465)

An efficient catalyst for the reaction of ethanol–acetaldehyde into 1,3-butadiene (EATB) is prepared through the grafting of zirconia into a zeolite Beta lattice. The grafting is achieved through the dealumination of a zeolite framework by acid treatment followed by zirconia impregnation, leading to the substitution of aluminum in the zeolite framework by zirconia. The catalyst with zirconia grafted into the zeolite framework promotes desirable catalyst properties like high zirconium dispersion, stability, and the close proximity of Lewis acid, Bronsted acid, and medium basic sites. The phase, the coordination of zirconia, the location of the active center and the cooperative synergism were elucidated through various characterization techniques, including X-ray diffraction, Raman spectroscopy, N₂ adsorption, UV–vis spectroscopy, XPS, ²⁹Si MAS NMR, NH₃-TPD, Py-IR, CO-IR and CO₂-TPD. The catalytic results show that a suitable phase and content of zirconia were needed to improve the ethanol–acetaldehyde conversion, butadiene selectivity and catalyst stability. Among the catalysts, m+t-ZrO_x-Beta-H₂O-9020 (m = monoclinic, t = tetragonal ZrO₂ phase) achieved the best butadiene selectivity of 82–73% at the conversion of 100–66%, run over 200 h. The results allow us to propose a Lewis acid–medium basic pairing for the Si–O–Zr–O–Si group, where the adjacent Si-OH is the active center for reactions. Full article

Zeolites, both natural (e.g., clinoptilolite) and synthetic (e.g., FAU, ZSM-5), provide robust, tunable platforms for the removal of air pollutants and process-stream contaminants via adsorption and catalysis. This author-led article integrates experimental and theoretical insights on the adsorption of odorous compounds and ammonia (NH₃) and the catalytic abatement of nitrogen oxides (NOx) and nitrous oxide (N₂O), highlighting how topology, acidity, and metal speciation jointly control performance. Representative theoretical results show that adsorption on Brønsted acid sites is significantly more favorable (≈−1.1 eV for NH₃ and −0.37 eV for acetaldehyde) than on Na⁺ sites (≈0.02 eV and 1.22 eV, respectively), demonstrating the critical role of acid site distribution in adsorption selectivity. We dissect structure–function relationships encompassing pore size and connectivity, Si/Al ratio, Brønsted/Lewis site distribution, hydrophilicity/hydrophobicity, and the role of water, with emphasis on hierarchical porosity to alleviate transport limitations. Metal exchange and surface functionalization are discussed as levers to tailor adsorption strength and redox activity, supported by density functional theory (DFT) analyses and reaction pathways. We propose practical design descriptors (acid strength metrics, metal nuclearity, and confinement factors) that enable faster iteration of zeolite architecture for targeted separations and reactions. Sustainability considerations include the use of abundant natural zeolites, low-energy regeneration, stability under humid, mixed-stream conditions that minimize pressure drop and waste. The article closes with a forward look at data-guided optimization to accelerate “engineering zeolites” for durable, selective, and energy-efficient clean-air and process-intensification applications. Full article

Ni/Siral catalysts with different Si/Al ratios were prepared by incipient wetness impregnation (IWI) to assess the impact of support composition on Ni²⁺ speciation and ethylene oligomerization (EO) performance. The catalysts were characterized by X-ray photoelectron spectroscopy (XPS), H₂ temperature-programmed reduction (TPR), X-ray diffraction (XRD), NH₃ temperature-programmed desorption (TPD), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) with energy-dispersive X-ray (EDX) analysis, and diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS). The EO catalysts were tested in a fixed-bed reactor at 225 °C under 11 bar ethylene and at 120 °C under 26 bar ethylene. Ni/Siral-70 was the most active catalyst investigated, but Ni/Siral-30 also exhibited good performance. The active sites were inferred to be isolated Ni²⁺ ions on amorphous SiO₂-Al₂O₃ containing interstitial Al³⁺ ions that enhance Brønsted acidity; Ni/Siral-70 displayed the highest concentration of these sites based on CO DRIFTS. Formation of NiAl₂O₄ surface species limited the activity of Ni/Siral-30 and especially Ni/Siral-5. The catalysts were also tested using a simulated ethane oxidative dehydrogenation (ODH) product stream containing 44% ethylene, 44% ethane, 4.5% methane, 2% H₂, 4.5% CO₂, 0.9% propylene, and 0.1% CO. The simulated ODH mixture gave lower EO conversion than 50/50 ethylene/N₂ at 225 °C and 11 bar over Ni/Siral-30, consistent with catalyst poisoning. In contrast, EO conversion over the Ni/Siral-70 catalyst was unaffected under these conditions. Catalyst testing at 120 °C and 26 bar revealed catalyst poisoning by feed impurities for both catalysts. Low-temperature/high-pressure EO activity was not recovered by simple thermal regeneration of Ni/Siral-30 at 300 °C. Full article

In order to address corrosion and pollution problems of liquid acids and limitations of traditional solid acids, sulfated MOF-808-SO₄ catalysts were developed by creating unsaturated sites in MOF-808 for sulfate grafting with ligand defect engineering. Characterization verified framework integrity, successful sulfate coordination, and maintenance of high surface areas and tunable porosity. Temperature-programmed desorption of ammonia (NH₃-TPD) establishes a clear consistent trend between defect density and the concentration as well as the strength of acid sites, indicating that a higher degree of ligand deficiency promotes the formation of more abundant and stronger acid centers. For esterification of acetic acid with n-butanol, the catalyst prepared by replacing 40 mol% of BTC with BDC achieved ≥99% conversion of acetic acid under mild conditions of 2.0 wt% catalyst loading and 1:2 alcohol/acid molar ratio at 120 °C for 6 h, outperforming conventional solid acids. This performance stems from high-density strong Brønsted acid sites strongly coordinated at defects and an open pore structure facilitating diffusion. The catalyst was easily recovered by ethanol washing and maintained stable activity over five cycles without loss of catalytic capability. This work suggests defect engineering as an effective strategy for tuning acidity and catalytic performance in MOF-based solid acids for green esterification. Full article

In this work, the activity of vanadium-doped and undoped phosphomolybdic acids with general formulae H_3+nPMo_12−nV_nO₄₀ (n = 0, 1, 2, and 3) was evaluated in the acetalization of furfural with alkyl alcohols. The main focus was to assess how vanadium charge affects the catalytic activity of phosphomolybdic acid and to link these effects to changes in structural properties. The main reaction parameters, such as charge and concentration of the catalyst, temperature, time, type of alcohol and aldehyde, and charges of vanadium and of H⁺ ions, were studied. Various Brønsted acids (sulfuric, p-toluenesulfonic, undoped, and doped phosphomolybdic acids) were evaluated on the condensation reactions of furfural with methyl alcohol. Notably, H₄PMo₁₁VO₄₀ was the most active and selective catalyst for the formation of methyl acetal furfural. Water has a leveling effect on the strength of these acids. Nonetheless, under reaction conditions, the presence of vanadium affected their acidity strength, and it was possible to verify that the vanadium-monosubstituted phosphomolybdic acid was the strongest. The superior performance of H₄PMo₁₁VO₄₀ was attributed to its additional acidity, resulting from the presence of very strong Brønsted acid sites (H⁺) and Lewis acid sites, due to the inclusion of V⁵⁺ ions in its structure. The novelty of this work is the assessment of vanadium-doped phosphomolybdic acids in the homogeneous phase in the condensation reactions of furfural with various alcohols and of methyl alcohol with various aldehydes. Full article

In this work, the ability of a series of imidazolium-based ionic liquids (ILs) to depolymerize Kraft lignin through acid hydrolysis was evaluated. ILs featuring two-, four-, and six-carbon alkyl chains combined with [Cl⁻], [BF₄⁻] and [CH₃COOH⁻] anions were studied to determine the influence of cation and anion structure. The twelve ILs were synthesized and characterized by FT-IR and ¹H/¹³C NMR spectroscopy. Results indicate that both the anion and cation significantly affect depolymerization efficiency; specifically, longer alkyl chain lengths correlated with higher conversion percentages. Anion efficacy followed the order: [Cl⁻] > [CH₃COOH⁻] > [BF₄⁻]. Furthermore, reaction temperature did not show a significant impact on conversion within the studied range. Spectroscopic data suggest that bond dissociation follows a Brønsted acid-catalyzed mechanism, evidenced by the reduction of phenolic components and guaiacyl/syringyl units in the recovered lignin samples. Full article

Making 1 $\mathrm{k}$$\mathrm{t}$ of cheese produces 9 $\mathrm{k}$$\mathrm{t}$ of cheese whey permeate, a waste with 5% lactose, which is either discarded or dried for animal feed. One pathway to add value to this waste is to convert it to lactic acid (LA), a monomer for polylactic acid, the largest bioplastic produced in the world. Lactose hydrolyses to glucose and galactose. While Brønsted acidity enhances lactose hydrolysis, Lewis acidity favours the formation of lactic acid. For the first time, we tested both industrial whey permeate and purified lactose as feedstocks for LA over a heterogeneous catalyst–Er₂O₃/Al₂O₃. LA Yield from whey permeate reached 14%, while the maximum yield with purified lactose was 22%. LA yield was invariant with respect to mixing speed while increasing temperature accelerates the time it takes to reach quasi-equilibrium. Yield was also independent of pressure with either air, He, N₂, or H₂ in the vapour space above the liquid phase in the autoclave. LA yield over spent catalyst with fresh lactose was only 11%, which indicates that the catalyst deactivates. Based on XRF analyses, the Er₂O₃ mass fraction dropped from 15% to 5%, with 6.4% leaching into the aqueous phase after the first step but only 0.8% after the second test. Full article

First-principles calculations are employed to systematically investigate the dynamic evolution from Al(O_h) to Al(T_d) in zeolites induced by proton–cation exchange (Cu⁺, Li⁺, Na⁺, NH₄⁺). The protons directly bonded to Al(O_h) are found to be essential for structural stability. Single cation exchange preserves the six-coordinated Al(O_h), while double exchange triggers spontaneous conversion to four-coordinated Al(T_d), accompanied by stepwise detachment of two water molecules. Different cations exhibit variations in spatial occupation patterns and water-binding strength. The coordination effect of metal cations and the hydrogen bonding effect of NH₄⁺ dominate the transformation of the aluminum coordination configurations. Protons directly bonded to Al(O_h) serve as strong Brønsted acid sites. Single exchange indirectly reduces the activity of adjacent protons, whereas double exchange eliminates Al–O–H bonds to stabilize Al(T_d). This work reveals a cooperative mechanism among cation species, exchange number, water binding, and electronic coupling that controls the Al(O_h) to Al(T_d) transformation, providing a theoretical basis for activating Al species and for designing high-performance catalysts with controlled acid site distributions via ion exchange. Full article

Considering the expanded interest in reducing organic solvents in synthesis, surfactants and surfactant-based catalysis have been used to carry out various organic transformations in water. In recent years, the integration of Lewis and Brønsted acid catalysis with micellar systems has gained considerable attention as a powerful approach to enhance reaction efficiency while minimizing the environmental impact of synthetic processes. In this article, we depict the most recent advances in the water-interceded synthesis of different organic systems by utilizing different surfactant-type catalysts, which are important structural motifs in pharmaceuticals, agrochemicals and functional materials. Further, these methods incorporate green reaction media, mild reaction conditions, and a great yield of product with high purity in a shorter interval of time. Understanding the scope and impact of this area, authors have made efforts to collect and compile the data that indicates many named reactions, such as Friedlander annulation, aldol condensation, the Biginelli reaction, the Mannich reaction, Suzuki–Miyaura cross-coupling, etc., now take place using surfactant-based catalysts. Full article

The ethylene aromatization (ETA) reaction is a pivotal route for non-petroleum-based aromatics production, yet a systematic understanding of its thermodynamic constraints and kinetic modulation remains elusive. Herein, an integrated thermodynamic and kinetic study is presented to elucidate the temperature-dependent reaction pathways over metal oxide-modified HZSM-5 catalysts. Thermodynamic calculations reveal that while oligomerization, cyclization, and the hydrogen transfer (HT) pathway are exothermic, the aromatics-generating dehydrogenation (DH) pathway is endothermic. Crucially, despite the general thermodynamic penalty imposed by elevated temperatures on most elementary steps, the overall ethylene aromatization reaction retains a strong driving force, underscoring the dehydrogenation pathway as the thermodynamic and kinetic key to aromatic selectivity. Experimentally, it is demonstrated that modifying HZSM-5 with ZnO, Ga₂O₃, and ZnGa₂O₄ effectively tunes the Lewis-to-Brønsted acid (L/B) ratio. A strong linear correlation is established between the L/B ratio and the apparent activation energy, with a higher L/B ratio significantly lowering the activation barrier. This synergistic effect optimally promotes the dehydrogenation pathway, suppresses alkane by-product formation, and maximizes aromatic yield within an optimal temperature window of 470–520 °C. The findings provide a fundamental and practical framework for the rational design of high-efficiency ethylene aromatization catalysts and the optimization of process conditions via targeted acid site engineering. Full article

The transition to renewable carbon resources has positioned lignocellulosic biomass as a key feedstock for sustainable fuel and chemical production; however, its intrinsic recalcitrance limits efficient conversion. Dilute acid pretreatment functions as a homogeneous Brønsted acid catalytic system that selectively depolymerizes hemicellulose and disrupts lignin–carbohydrate complexes, while competing with consecutive sugar dehydration reactions, thereby enhancing downstream processing. This review presents a feedstock-specific analysis of acid catalyzed biomass deconstruction across agricultural residues, woody biomass, and energy crops, with xylose yield employed as a kinetically and mechanistically relevant descriptor of catalytic performance. By correlating proton activity, reaction severity, diffusion constraints, lignin chemistry, and mineral interference with observed conversion behavior, the work establishes a structure–reactivity–performance framework for biomass dependent hydrolysis. Particular attention is given to competing dehydration and condensation pathways that reduce pentose selectivity and generate fermentation inhibitors. The analysis identifies optimal severity windows for maximizing catalytic efficiency while suppressing degradation reactions and provides guidance for feedstock-tailored pretreatment and next-generation acid catalytic systems and reactor configurations in integrated biorefineries. Full article

Ammonia decomposition represents a promising route for CO₂-free hydrogen production; however, the development of efficient and stable catalysts remains a critical challenge. In this work, a series of Al-based mixed-oxide catalysts (AlM, where M = Ni, Co, Ce) were synthesized via co-precipitation and systematically investigated to elucidate the relationship between physicochemical properties and catalytic performance in ammonia decomposition. Comprehensive characterization by X-ray diffraction (XRD), N₂ physisorption (BET), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDX), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and pyridine-adsorbed Fourier transform infrared spectroscopy (FTIR-Py) revealed significant variations in surface area, morphology, dispersion, and acidity as a function of the incorporated metal. Among the investigated catalysts, the AlNi system exhibited superior activity, achieving the highest ammonia conversion over the studied temperature range. This enhanced performance is attributed to its high specific surface area, homogeneous mesoporous structure, and a balanced distribution of Lewis/Brønsted acid sites, which promote effective ammonia adsorption, activation and decomposition. Kinetic analysis further confirmed the favorable reaction pathway on AlNi, as evidenced by its lower apparent activation energy and higher pre-exponential factor compared to the other materials. The results demonstrate a clear correlation between surface acidity, textural properties, and catalytic performance, highlighting the pivotal role of AlM interactions in governing ammonia decomposition. These findings provide valuable insights for the rational design of efficient catalysts for hydrogen production from ammonia. Full article

Here, we report a highly efficient and stable catalytic system based on monometallic oxides supported on HY zeolites for the catalytic oxidation of chlorobenzene (CB). Among the transition and rare-earth metal oxides screened, the 30Cu/HY catalyst demonstrates exceptional performance, achieving near 100% CB conversion at 300 °C (500 ppm CB, 10,000 h⁻¹) alongside outstanding 24 h continuous stability without deactivation. Quantitative Py-IR analysis reveals that this superior activity is fundamentally driven by extensive solid-state ion exchange, forming robust Lewis acid centers (Cu-Y structures) that synergize with zeolitic Brønsted acid sites to efficiently polarize and cleave C-Cl bonds. Through an integrated approach combining in situ DRIFTS, real-time mass spectrometry, TGA, and NLDFT pore size analysis, we elucidate that the exceptional deep-oxidation capability of Cu/HY continuously mineralizes carbonaceous intermediates. This property minimizes coke deposition (2.91 wt%) and preserves the hierarchical pore architecture, preventing the coverage of active sites and severe pore blockage by partially oxidized intermediates (such as phenolic, aldehydic, and quinonic species) and stable carbonate species responsible for the deactivation of other metal oxides. These insights provide a mechanistic framework for the rational design of robust, chlorine-resistant catalysts for the sustainable abatement of persistent organic pollutants. Full article

Ammonia decomposition represents a promising route for carbon-free hydrogen production, provided that efficient and cost-effective catalysts are developed. In this study, lanthanum-based mixed oxide catalysts (LaNi, LaCo, and LaCe) were synthesized via a controlled co-precipitation method and systematically evaluated for catalytic ammonia decomposition under atmospheric pressure in the temperature range of 350–500 °C. Comprehensive characterization combining N₂ physisorption, XRD, SEM–EDX, TGA–DTG, XPS, and FTIR-pyridine adsorption revealed pronounced structure–property relationships. LaNi exhibited the highest surface area (31.11 m²·g⁻¹), well-developed mesoporosity, and a balanced Lewis/Brønsted acidity (C_L/C_B ≈ 0.82), leading to superior catalytic performance with NH₃ conversion reaching ~48% at 500 °C (GHSV = 50 h⁻¹). LaCo showed intermediate activity (~30% conversion), while LaCe displayed limited performance (<13%), most likely due to its dense morphology and low surface accessibility. Increasing gas hourly space velocity resulted in decreased ammonia conversion for all catalysts, highlighting the critical role of residence time. These findings demonstrate that the catalytic efficiency of lanthanum-based systems is governed by the synergistic interplay between surface area, mesoporous architecture, and acidity distribution, with LaNi emerging as the most promising catalyst among the investigated materials. Full article

Carbon dioxide (CO₂) capture is a cornerstone of global carbon neutrality, yet the high energy penalty associated with solvent regeneration—particularly for monoethanolamine (MEA) systems—remains a major barrier to its sustainable deployment. This study presents a sustainable and high-performance catalytic solution using micro-sized iron oxyhydroxide (β-FeOOH). Characterized by a high specific surface area ($287 m²/g) and a synergistic distribution of abundant Lewis and Brønsted acid sites, the β-FeOOH catalyst significantly enhances CO₂ desorption kinetics. Experimental results demonstrate that the incorporation of β-FeOOH into a 30 wt% MEA solution increases the CO₂ desorption rate by 10.9% while simultaneously lowering the regeneration temperature from the conventional 120 °C to 85 °C. Such a reduction in thermal requirements offers a pathway to utilize low-grade industrial waste heat, drastically improving the process’s energy efficiency. Furthermore, the catalyst exhibited remarkable cyclic stability over ten consecutive cycles, maintaining its structural integrity and catalytic activity. These findings highlight β-FeOOH as an eco-friendly, cost-effective, and robust catalyst that aligns with the principles of green chemical engineering, offering a scalable strategy to enhance the sustainability of carbon capture operations. Full article