Search Results (517)

The global depletion of fossil resources, combined with accelerating climate change and environmental concerns, is driving intensive research into alternative, sustainable sources of energy and raw materials. Particular attention is being paid to lignocellulosic biomass as the most abundant and renewable organic resource. The catalytic conversion of biomass-derived carbohydrates into high-value-added products (fuels and chemicals) aligns with the principles of sustainable development and offers a viable alternative to petroleum-based feedstocks. This review provides a product-oriented perspective on the deep valorization of carbohydrates, focusing on catalytic strategies that enable the production of renewable fuels and chemicals. It highlights two key stages in the valorization of lignocellulosic biomass: (1) the acid-catalyzed conversion of carbohydrates into platform molecules (furfural, 5-hydroxymethylfurfural, and levulinic acid); and (2) the selective hydrogenation and hydrogenolysis of these intermediates to obtain target end products. These target products fall into two major categories: (i) biofuels and fuel additives; and (ii) green chemicals, such as solvents, pharmaceuticals, agrochemicals, cosmetics, and intermediates for the synthesis of biobased polymeric materials, including polyesters, resins, and polyurethanes. Particular emphasis is placed on recent advances in the development of heterogeneous catalysts. Solid acid catalysts used in the synthesis of platform molecules are discussed, along with ruthenium-based catalysts employed in the subsequent hydrogenation and hydrogenolysis steps. Recent efforts toward integrating both catalytic stages into a single one-pot processes using bifunctional metal–acid catalysts and dual catalytic systems based on ruthenium are also reviewed, as they represent a promising route to simplify biomass valorization schemes and improve product selectivity toward fuels and chemicals. Full article

The conversion of cellulosic biomass into renewable chemicals can serve as a sustainable resource for levulinic acid (LA) production. LA yield is significantly influenced by reaction temperature, reaction time, substrate concentration, active sites, catalyst amount, catalyst porosity, and durability. Beyond the features of the catalyst, such as acidity, porosity, functional groups, and catalytic efficiency, the contact between the solid acid catalyst and the solid substrate is of vital importance. Solid-based catalysts show remarkable catalytic activity for cellulose-derived LA production, thanks to the incorporation of functional groups. For a solid carbon-based catalyst to be effective, a synergistic interaction between the binding domain (functional groups capable of anchoring cellulose to the catalyst surface, such as chloride groups, COOH, or OH) and the hydrolysis domain (due to their ability to cleave glycosidic bonds, such as in SO₃H) is essential. As a relatively new market niche, carbon-based catalyst supports are projected to reach a market value of nearly USD 125 million by 2030. This review aims to highlight the advantages and limitations of carbon-based materials compared to conventional catalysts (including metal oxides or supported noble metals, among others) in features like catalytic activity, thermal stability, and cost, examine recent advancements in catalyst development, and identify key challenges and future research directions to enable more efficient, sustainable, and scalable processes for LA production. The novelty of this review lies in its focus on carbon-based catalysts for LA production, emphasizing their physical and chemical characteristics. Full article

The production of biodiesel from microalgae presents a sustainable and renewable solution to the growing global energy demands, with catalysts playing a critical role in optimizing the transesterification process. This study examines the emerging catalysts and innovative techniques utilized in converting microalgal lipids into fatty acid methyl esters, emphasizing their impact on reaction efficiency, yield, and environmental sustainability. Sulfuric acid demonstrates excellent performance in in situ transesterification, while NaOH/zeolite achieves high biodiesel yields using ultrasound- and microwave-assisted methods. Metal oxides such as CuO, NiO, and MgO supported on zeolite, as well as ZnAl-layered double hydroxides (LDHs), further enhance reaction performance through their high activity and stability. Enzymatic catalysts, particularly immobilized lipases, provide a more environmentally friendly option, offering high yields (>90%) and the ability to operate under mild conditions. However, their high cost and limited reusability pose significant challenges. Ionic liquid catalysts, such as tetrabutylphosphonium carboxylate, streamline the process by eliminating the need for drying and lipid extraction, achieving yields as high as 98% from wet biomass. The key novelty of this work lies in its detailed focus on the use of ionic liquids and nanocatalysts in microalgae-based biodiesel production, which are often underrepresented in previous reviews that primarily discuss homogeneous and heterogeneous catalysts. Full article

Esterification is a key transformation in the production of lubricants, pharmaceuticals, and fine chemicals. Conventional processes employing homogeneous acid catalysts suffer from limitations such as corrosive byproducts, energy-intensive separation, and poor catalyst reusability. This review provides a comprehensive overview of heterogeneous catalytic systems, including ion exchange resins, zeolites, metal oxides, mesoporous materials, and others, for improved ester synthesis. Recent advances in membrane-integrated reactors, such as pervaporation and nanofiltration, which enable continuous water removal, shifting equilibrium and increasing conversion under milder conditions, are reviewed. Dual-functional membranes that combine catalytic activity with selective separation further enhance process efficiency and reduce energy consumption. Enzymatic systems using immobilized lipases present additional opportunities for mild and selective reactions. Future directions emphasize the integration of pervaporation membranes, hybrid catalyst systems combining biocatalysts and metals, and real-time optimization through artificial intelligence. Modular plug-and-play reactor designs are identified as a promising approach to flexible, scalable, and sustainable esterification. Overall, the interaction of catalyst development, membrane technology, and digital process control offers a transformative platform for next-generation ester synthesis aligned with green chemistry and industrial scalability. Full article

In the field of green chemistry, the development of more sustainable and cost-efficient methods for synthesizing primary amines is of paramount importance, with catalyst research being central to this effort. This work presents a facile, aqueous-phase synthesis of highly active cobalt catalysts (Co-Ph@SiO₂(x)) via pyrolysis of silica-supported cobalt–phenanthroline complexes. The optimized Co-Ph@SiO₂(900) catalyst achieved exceptional performance (>99% conversion, >98% selectivity) in the reductive amination of acetophenone to 1-phenylethanamine using NH₃/H₂. Systematic studies revealed that its exceptional performance originates from the in situ pyrolysis of the cobalt–phyllosilicate complex. This process promotes the uniform distribution of metal cobalt nanoparticles, simultaneously enhancing porosity and imparting bifunctional (acidic and basic) properties to the catalyst, resulting in outstanding catalytic activity and selectivity. The catalyst demonstrated broad applicability, efficiently converting diverse ketones (aryl-alkyl, dialkyl, bioactive) and aldehydes (halogenated, heterocyclic, biomass-derived) into primary amines with high yields (up to 99%) and chemoselectivity (>40 examples). This sustainable, non-noble metal-based catalyst system offers significant potential for industrial primary amine synthesis and provides a versatile tool for developing highly selective and active heterogeneous catalysts. Full article

Biodiesel, a renewable and environmentally friendly alternative to fossil fuels, has attracted significant attention due to its potential to reduce greenhouse gas emissions. However, high production costs and complex processing remain challenges. Heterogeneous catalysts have shown promise in overcoming these barriers by offering benefits, such as easy separation, reusability, low-cost raw materials, and the ability to reduce reaction times and energy consumption. This review evaluates key classes of heterogeneous catalysts, such as metal oxides, ion exchange resins, and zeolites, and their performance in transesterification and esterification processes. It highlights the importance of catalyst preparation methods, textural properties, including surface area, pore volume, and pore size, activation techniques, and critical operational parameters, like the methanol-to-oil ratio, temperature, time, catalyst loading, and reusability. The analysis reveals that catalysts supported on high surface area materials often achieve higher biodiesel yields, while metal oxides derived from natural sources provide cost-effective and sustainable options. Challenges, such as catalyst deactivation, sensitivity to feedstock composition, and variability in performance, are discussed. Overall, the findings underscore the potential of heterogeneous catalysts to enhance biodiesel production efficiency, although further optimization and standardized evaluation protocols are necessary for their broader industrial application. Full article

The sludge produced by the Fenton process contains mixed-valence iron particulates (hereafter called Fenton wastes). Using a solvothermal method, we fabricated a new heterogeneous photo-Fenton catalyst using Fenton wastes and metal–organic frameworks (MOFs). Nanoporous metal carboxylate (MIL-88) MOF impregnated with Fenton waste was functionalized using 2,5-dihydroxyterephthalic acid (x-HO-MIL-88-C, x, concentration of the 2,5-dihydroxyterephthalic acid). The efficiency of x-HO-MIL-88-C was examined under visible light radiation using methylene blue (MB) as an index pollutant. We observed the best catalytic performance for MB degradation by 4-HO-MIL-88-C. In the photo-Fenton process, the simultaneous presence of singlet oxygen, superoxide, and hydroxyl radicals is confirmed by free radical quenching and electron spin resonance spectral data. These free radicals associate with holes in the non-selective degradation of MB. The 4-HO-MIL-88-C catalyst shows good stability and reusability, maintaining over 80% efficiency at the end of five consecutive cycles. This work opens up a new path for recycling Fenton wastes into usable products. Full article

A novel metal–organic framework based on zinc ions, designated as Zn-URJC-12, has been synthesized and applied for the first time in the cycloaddition reaction between carbon dioxide and epoxides. This MOF is constructed from two different organic linkers: 5-aminoisophthalic acid and 4,4′-biphenyldicarboxylic acid. The framework features –NH₂ functional groups coordinated to Zn(II) centers, as confirmed by single-crystal X-ray diffraction analysis. Zn-URJC-12 demonstrates exceptional chemical stability in polar organic solvents, such as methanol, while maintaining thermal stability up to 250 °C. The material exhibits high catalytic efficiency in the cycloaddition of CO₂ with epoxides, achieving yields of 100% and 76% for propylene oxide and allyl glycidyl ether, respectively. Additionally, Zn-URJC-12 maintains its structural integrity and catalytic performance during five successive reaction cycles. These findings underscore Zn-URJC-12 as a promising heterogeneous catalyst for the valorization of CO₂ into cyclic carbonates. Full article

2,5-Furandicarboxylic acid (FDCA) is a bio-based platform chemical with high potential to replace terephthalic acid in polymer production, particularly for polyethylene furanoate (PEF), a biopolymer with superior thermal and barrier properties. This study investigates the selective oxidation of 5-hydroxymethylfurfural (HMF) into FDCA using nickel-based heterogeneous catalysts, aiming at a cost-effective and sustainable alternative to noble metal catalysts. A series of nickel oxide catalysts were synthesized and screened. The NiOx catalyst synthesized without thermal treatment via Route B showed the best performance, achieving a FDCA yield of 11.77%, selectivity of 27.41%, and concentration of 0.9 g/L under preliminary conditions. Reaction kinetics revealed that the controlled addition of NaClO enhanced FDCA yield by 2.28 times. Optimization using a 2³ factorial design identified the optimal conditions as 6% (w/v) catalyst concentration, 25 °C, and a NaClO:HMF molar ratio of 12:1, leading to 34.14% yield and 42.57% selectivity. The NiOx catalyst maintained its activity over five successive cycles, indicating good recyclability. Moreover, NiOx demonstrated catalytic activity with crude HMF derived from glucose dehydration, confirming its practical applicability. These results support the potential of nickel-based catalysts in sustainable FDCA production, contributing to the advancement of bio-based polymer synthesis. Full article

The electrochemical oxidation of biomass-derived 5-hydroxymethylfurfural (HMF) coupled with water electrolysis for green hydrogen production is a promising strategy to address energy crises and environmental pollution. Despite the suitable adsorption energy for HMF due to their partially filled d-band electronic structures, Ni- or Co-based oxides/hydroxides still face challenges in insufficient activity and stability. In this study, a porous heterogeneous nickel cobalt oxide/hydroxide growth on nickel foam (NF), which is defined as NF@NiCo-H/O, was developed via immersion in concentrated alkali solution. Compared with the single-component NiCo oxides, the NF@NiCo-H/O catalyst exhibits a lower application potential of only 1.317 V, 1.395 V, and 1.443 V to achieve current densities of 20, 50, and 100 mA cm⁻², respectively, in an alkaline solution containing HMF. Additionally, it demonstrates rapid reaction kinetics with a Tafel slope of 27.6 mV dec⁻¹ and excellent cycling stability. Importantly, the presence of more high-valent Ni³⁺-O species on the catalyst surface contributes to its exceptional selectivity for 2,5-furandicarboxylic acid (86.7%), Faradaic efficiency (93.1%), and conversion rate (94.4%). This catalyst provides some theoretical guidance for the development of biomass electrooxidation catalysts for sustainable energy and chemical production. Full article

Biochar-based materials have gathered increasing attention as sustainable catalysts for carbon dioxide (CO₂) valorization, offering a green alternative to traditional metal-based systems. Produced from renewable biomass through pyrolysis, biochar possesses key features—such as high surface area, rich porosity and tunable surface chemistry—that make it particularly suited for heterogeneous catalysis. This review highlights recent advances in the use of biochar-derived catalysts for key CO₂ conversion reactions, focusing on cycloaddition to epoxides, dry reforming of methane and catalytic biomass upgrading. Emphasis is given to the role of biochar’s origin and preparation methods, which critically influence its structure, surface functionality and catalytic performance. Feedstocks rich in mineral content or oxygenated groups, for instance, can enhance CO₂ activation and product selectivity. Furthermore, tailored modifications—such as doping with heteroatoms or supporting metal nanoparticles—further boost catalytic activity and stability by tuning acid–base behavior, while maintaining low toxicity and cost-effectiveness. Compared to conventional catalysts, biochar-based systems offer advantages in low cost, recyclability and resistance to deactivation. Challenges remain in standardizing production methods, controlling structural variability, minimizing metal leaching and scaling up. This review presents biochar as a versatile, renewable platform for CO₂ utilization, highlighting the importance of rational design, feedstock selection and functionalization strategies for developing efficient, sustainable catalytic systems, in line with green chemistry and circular economy principles. Full article

The site-directed immobilization of enzymes has demonstrated significant potential in industrial applications due to its ability to minimize enzyme heterogeneity and maximize retained activity. However, existing approaches often require the introduction of unnatural amino acids or excessive specific ligase to achieve this goal. In this study, a self-catalyzed protein capture system (i.e., the SnoopCatcher/SnoopTag pair) was utilized for the directed immobilization of lipase on magnetic carriers. By tagging the Pseudomonas fluorescens lipase (PFL) with a SnoopTag at the C-terminal, the fused lipase PFL-SnoopTag (PSNT) readily conjugated with the SnoopCatcher partner via a spontaneously formed isopeptide bond between them. Novel magnetic particles functionalized by SnoopCatcher proteins were prepared using a co-precipitation method, achieving a loading capacity of around 0.8 mg/g carrier for the SnoopCatcher. This functionalized magnetic carrier enabled the site-directed immobilization of lipase PSNT at 81.4% efficiency, while the enzyme loading capacity reached 3.04 mg/g carriers. To further assess the practical performance of site-directed immobilized lipases, they were applied in biodiesel production and achieved a yield of 88.5%. Our results demonstrate a universal platform for the site-directed immobilization of enzymes with high performance, which offers significant advantages, e.g., single-step purification and catalyst-free immobilization of engineered enzymes, as well as easy recovery, highlighting its potential for industrial applications. Full article

Copper complexes have attracted significant interest for catalyzing oxidative dehydrogenative carboxylation of alkanes to form esters. Here, we report a heterogeneous catalyst, in which copper complexes are immobilized on coal-bearing kaolin for the synthesis of allylic esters via C(sp³)-H bond activation through cross-dehydrogenation coupling reactions between cyclic alkanes and aromatic carboxylic acids. Systematic optimization of reaction conditions—including catalyst loading, copper content, oxidant, temperature, and reaction time—resulted in a high yield of 71% of allylic ester, comparable to homogeneous transition metal catalysts. The catalyst is easily recoverable via centrifugation and retains its activity over five consecutive reuse cycles. This system demonstrates broad substrate compatibility with various aromatic carboxylic acids and cyclic alkanes. Beyond offering an efficient and reusable catalytic route for allylic ester synthesis, this work highlights the potential of coal-bearing kaolin as a sustainable support material for transition metal catalysis and provides an environmentally benign method for activating inert C(sp³)–H bonds. Full article

The transition from fossil resources to renewable raw materials derived from lignocellulosic waste is crucial for economic and environmental sustainability. Advancing toward a bio-based economy necessitates the development of innovative heterogeneous catalysts. This study explores the use of modified sugarcane bagasse biochar, embedded with ruthenium and iron particles, as a green catalyst for converting levulinic acid (LA) to γ-valerolactone (GVL). The efficiency of both raw and modified biochar in the LA to GVL conversion process, utilizing formic acid (FA) exclusively as the hydrogen source, was systematically assessed through characterization techniques, including XRD, TGA, XPS, and SEM/EDS. The gelification method using alginate enhanced the ruthenium and iron content on the surface of the biochar. The results demonstrate that the modified material has significant potential for efficient LA-to-GVL conversion, achieving a yield of 73.0 ± 9.2% under optimized conditions (0.5 g of BC₅₀₀Fe/3%Ru at 180 °C for 3 h, with 4 mmol LA, 8 mmol FA, and 10 mL of water). Iron on the biochar surface facilitated the formation of adsorption sites for LA, supporting the notion of this novel catalyst for LA conversion in an aqueous medium in the presence of FA. This research underscores the potential of this green catalyst in advancing sustainable biomass conversion and contributes to the ongoing shift towards a bio-based economy. Full article

Mixed oxides were obtained via calcination at 550 °C from layered double hydroxides (LDHs), which were synthesized in a previous study via co-precipitation and co-precipitation followed by hydrothermal treatment using aluminum residues as the source of this element. After characterization, these oxides (Mg-Al-_LDH-CP and Mg-Al-_LDH-H, named according to the synthesis methods of the precursor LDHs) were applied as heterogeneous catalysts in the methyl transesterification of ethyl acetate (EA). The formation of mixed oxides was confirmed by the absence of basal peaks associated with the layered LDH structure in the XRD analysis, due to calcination. Further characterization revealed that Mg-Al-_LDH-CP exhibited the highest number of acidic sites, while Mg-Al-_LDH-H had the highest number of basic sites. The transesterification activity was evaluated in the reaction between ethyl acetate (EA) and methanol (MeOH). The best result, obtained under a molar ratio of 1:5:0.005 (EA:MeOH:catalyst) at 120 °C, was a 63% conversion after 360 min of reaction for the Mg-Al-_LDH-CP catalyst, which had a higher number of acidic sites and fewer basic sites. Additionally, the catalysts demonstrated robustness, maintaining catalytic activity over four cycles without a significant decrease in performance. These results indicate the feasibility of using mixed oxides derived from LDH, synthesized from aluminum residues, as heterogeneous catalysts in transesterification reactions, highlighting their potential for advancing more sustainable catalyst development. Full article