In the permanent research on sustainable processes, chemists are now looking for clean, safe and simple processes for producing chemicals.
Following the Green Chemistry principles established 25 years ago, each step in the procedure deserves to be studied in pursuit of these greener requirements.
- The use of renewable substrates is important for facing the depletion of fossil resources. Biomass is thus an important renewable source that has to be studied. Indeed, many platform molecules can be obtained from this resource and represent a short-carbon-cycle alternative.
- Energy savings have to be pursued. Catalysis is, in this respect, an interesting aspect in terms of gains in energy consumption. These energy gains are not to be neglected.
- Safer processes have to be found. Organic solvent-free processes are interesting solvent-sober protocols since they diminish some of the hazards involved due to the handling of organic solvents.
This work will present recent results concerning the use of polyoxometalates (POMs) grafted onto a solid support and their use as catalysts to valorize biomass. These POMs contained molybdenum and vanadium metals.
Simple protocols for the synthesis of these catalytic materials and their characterisation will be presented. Improvements compared to the literature will be emphasised.
Valuable natural substrates such as terpenes will be presented, and mechanistic conclusions will be given.

Biomass serves as an essential renewable energy source for the production of clean hydrogen (Hâ‚‚) and bio-oil due to the ongoing global shift toward sustainable alternatives. The thermochemical methods of pyrolysis and gasification demonstrate potential for biomass conversion into valuable fuels which align with the European Green Deal and other sustainability goals across the world. These technologies face limiting technical and economic barriers because of catalyst performance problems, which affect cost efficiency and longevity. The authors introduce a new strategy using optimized biomass-based catalytic systems supported by progressive catalyst formulation techniques with life cycle analysis and predictive AI methods. Engineered biomass-derived catalysts possess excellent catalytic characteristics alongside advanced selectivity and superior environmental capabilities compared to traditional catalysts, as revealed by the experimental findings. A day-to-day LCA assessment shows that incorporating these catalysts leads to reduced carbon emissions throughout hydrogen and bio-oil production procedures. AI-based optimization techniques help forecast catalyst performance in different operational conditions to enable engineers to design highly stable catalytic systems. Experimental tests show that biomass-derived catalysts increase industrial output alongside sustainable processing capabilities. Economic analysis benefits from these catalysts when scaled up for industrial production. This strategy stands as a core contribution to achieving a clean energy future because it helps decrease fossil fuel usage and supports worldwide carbon emission reductions.

Black liquor, a by-product of the pulp and paper industry, is the main source of industrial lignin. Its conventional use as fuel for energy recovery underutilizes its potential and contributes to greenhouse gas emissions. Lignin, an aromatic polymer, can replace fossil fuel-based products like hydrogels, biosensors, and carbon fibers. The phenolic hydroxyl group of lignin is particularly important, as it plays a key role in determining lignin's functionality for various applications, including its antioxidant, adhesive, and polymer-stabilizing properties. Accordingly, this study employed a Box–Behnken design with 29 experimental trials to assess how pH, temperature, residence time, and acid concentration influence the total phenolic content (TPC) of lignin extracted via acid precipitation. Within the examined ranges, TPC values varied from 305.72 to 521.78 mg/g GAE, with the highest TPC achieved at pH 3, 70°C, 20% w/v Hâ‚‚SOâ‚„, and 1.5 h. In contrast, the lowest TPC occurred at pH 6, 25°C, 10% w/v Hâ‚‚SOâ‚„, and 1.5 h. A regression model and response surface methodology (RSM) were employed to analyze the data, and the model’s significance was confirmed by ANOVA (p < 0.05), despite a moderate F value (2.7257). The model showed good explanatory power (R² = 0.73, R²-adj = 0.43) and an insignificant lack of fit (p = 0.3704), suggesting it accurately captured the effects of the independent variables on TPC. The linear terms for pH and temperature were statistically significant, indicating that reducing pH and increasing temperature strongly enhance TPC. Interaction profiles and three-dimensional response surfaces revealed that acid concentration and residence time also affected TPC, with optimal conditions identified at 20% w/v H₂SO₄ and 1.5 h. These findings demonstrate that the careful optimization of process parameters can substantially improve lignin’s phenolic properties, thereby guiding more efficient, sustainable strategies for lignin valorization.

Sawdust is a plentiful source of lignocellulosic biomass, offering a sustainable alternative to fossil raw materials for the production of aromatics, fuels, and chemicals. Lignin, a key component of lignocellulosic biomass, serves as a renewable feedstock that can be depolymerized into aromatics suitable for use as octane enhancers or as precursors for high-value products. Additionally, lignin's multiple hydroxyl groups enable the synthesis of diverse polymers with potential industrial applications. This study investigates the extraction of lignin from Chlorophora excelsa sawdust using organosolv technology. The sawdust was collected and characterized, revealing a composition of 41.15% cellulose, 28.63% hemicellulose, and 26.13% lignin. The organosolv pretreatment process was conducted at temperatures of 100°C, 120°C, 140°C, 160°C, 180°C, and 200°C for 1 hour and 30 minutes. The sawdust was mixed with an ethanol–water solution (60:40 w/w) at a solid-to-liquid ratio of 1:10 (w/w), with 20% sulfuric acid as a catalyst. The highest lignin yield of 49.81% was achieved at 160°C, while the yields at 100°C, 120°C, 140°C, 180°C, and 200°C were 14.58%, 27.29%, 28.37%, 29.57%, and 24.48%, respectively. FTIR analysis confirmed that the lignin produced at 160°C contained multiple hydroxyl functional groups. Additionally, FTIR spectroscopy indicated chemical homogeneity across the extracted lignin samples. Elemental analysis using the Walkley–Black method, flame photometry, atomic absorption spectrometry, and wet digestion revealed the carbon, sodium, sulfur, and nitrogen contents of the lignin as 60.00%, 0.02%, 0.88%, and 0.40%, respectively. The bulk density, ash content, and moisture content of the extracted lignin were determined to be 0.264 g/cm³, 0.95%, and 1.88%, respectively.

Agricultural byproducts such as banana peel and corn husk are cost-effective and abundant sources of lignocellulosic biomass, offering significant potential for producing value-added biological and biochemical products. Chemical composition analysis shows that banana peels contain 13–15% hemicellulose, while corn husks contain 40–50%, making them valuable sources of xylans, particularly for Xylo-oligosaccharide production. This study explored the enzymatic hydrolysis of xylans from banana peels and corn husks using xylanase concentrations ranging from 2 to 10 mg/mL at 55 °C for 30 minutes. Samples were prepared as untreated samples or autoclaved (121 °C, 15 min). Reducing sugar concentrations were positively correlated with xylanase concentration, with the highest levels observed at 10 mg/mL. For banana peels, the maximum reducing sugar concentrations were 3.47 mg/mL for untreated samples and 3.93 mg/mL for autoclaved samples, while corn husks yielded 3.35 mg/mL and 2.88 mg/mL, respectively. Notably, banana peels exhibited higher reducing sugar values compared to corn husks, and autoclaved samples consistently outperformed untreated ones within each biomass type. Thin-layer chromatography (TLC) confirmed that the hydrolysis products of both untreated and autoclaved samples from banana peels and corn husks consisted of Xylo-oligosaccharides, including xylobiose through xylohexaose. The presence of these oligosaccharides highlights the efficiency of enzymatic hydrolysis in breaking down xylans into functional biomolecules. These findings emphasize the potential of banana peels and corn husks as sustainable and economical raw materials for Xylo-oligosaccharide production, contributing to the valorization of agricultural waste. This approach aligns with the principles of green biotechnology, supporting the development of renewable resources and advancing waste-to-value strategies for biotechnological applications.

Introduction

Developing new chemical processes based on sustainable feedstocks is essential for reducing the dependence on fossil resources, lowering greenhouse gas emissions, and fostering a more sustainable chemical industry [1]. Among these chemicals, gluconic acid is one of the most important products derived from glucose, due to its biodegradability, biocompatibility, and widespread applications in the pharmaceutical, food, construction, and cleaning industries [2]. The oxidation of glucose to gluconic acid has been extensively investigated using biochemical processes, as well as homogeneous and heterogeneous catalysis. Among these methods, heterogeneous catalysis offers significant advantages in terms of recyclability and process integration [3].

In the present work, the synthesis of gluconic acid from glucose is investigated, using hydrogen peroxide as the oxidant and gold-supported catalysts. An initial catalyst screening was conducted under standard reaction conditions (80 °C, 30 min), followed by an optimization study to evaluate the influence of key reaction parameters.

Experimental

The method followed for the synthesis of all mesoporous silicas (SBA-15, MCM-41, HMS-2, HMS-3, HMS-5) was based on self-assembly processes and the sol-gel method. Au modification was achieved via a polyvinyl alcohol (PVA)-protected method with in situ parallel reduction by using NaBH₄ as a reducing agent. All synthesized catalysts were fully characterized regarding their physicochemical properties. Glucose oxidation reaction was carried out in a batch, stirred, autoclave reactor (C-276 Parr Inst., USA). The reaction products were analyzed by ion chromatography (ICS-5000, Dionex, USA). The stability of the materials after the reaction was evaluated using ICP-AES analysis of the liquid phase.

Results and Discussion

Τhe results indicated that all synthesized catalysts exhibited excellent stability, with no detectable leaching of Au. Notably, the 1Au/TiO₂ and 1Au/SBA-15 catalysts demonstrated the most promising performance, achieving glucose conversions of 69% and 67%, respectively, along with a gluconic acid selectivity exceeding 22 %.

To tackle the critical issue of reducing greenhouse gas emissions, renewable fuels such as biofuels present an attractive alternative to fossil fuels due to their lower toxicity, renewability, biodegradability, and cleaner combustion [1,2]. This study focuses on developing cost-effective and innovative catalysts, specifically glasses (ceramics) derived from the Na₂O-V₂O₅-(Al₂O₃)-P₂O₅-Nb₂O₅ system [3], for the pyrolytic deoxygenation of long-chain fatty acids into alkanes. Stearic acid was selected as a model compound to investigate the thermal decomposition of fatty acids and assess the catalytic performance of oxide glass (ceramic) catalysts, with additional experiments conducted on oleic acid and palmitic acid to extend the study. The tested catalysts varied in V₂O₅ content, ranging up to 70 mol% V₂O₅, with commercially available V₂O₅ used as a standard reference material. Catalytic activity was evaluated using thermogravimetric analysis/differential scanning calorimetry (TG/DSC), while coupled thermogravimetry–infrared spectroscopy (TG-IR) and simultaneous thermal analysis–quadrupole mass spectrometry (STA-QMS) provided comprehensive insights into the decomposition mechanisms. The results indicated that catalysts with a higher V₂O₅ content (≥ 55 mol%) significantly enhanced the thermal decomposition of fatty acids. This study highlights that oxide glasses (ceramics) are efficient catalysts for fatty acid decarboxylation, offering a combination of thermal and chemical stability, cost-effective and straightforward synthesis, and the flexibility to fine-tune catalyst properties through simple compositional adjustments, which is crucial for industrial applications.

This work is supported by the Croatian Science Foundation under projects IP-2018–01–5425 and DOK-2021–02–9665 and partially funded by the European Union – NextGenerationEU.

[1] Mulyatun, M. et al. Catal. Lett. 154, 4837–4855 (2024).

[2] Chen, B., et al., Appl. Catal. B: Environ. 338, 123067 (2023).

[3] Pisk, J. et al. J. Non-Cryst. Solids 626, 122780 (2024).

Gamma Valerolactone (GVL) is an important chemical derived from the hemicellulose in biomass whose applications span across the solvent, biofuel and polymer industries. A domino reaction selectively producing GVL from furfural makes it a highly desirable transformation. In this regard, finely dispersed copper nanoparticles immobilized on zirconia-modified montmorillonite K10 clay were synthesized and examined to achieve high selectivity for GVL. The catalysts were well characterized by employing various techniques, such as PXRD, TEM, FESEM, N₂ sorption, NH₃-TPD, TGA, ICP-OES, FTIR, pyridine IR and XPS. A detailed investigation of the co-operative effect of the active sites responsible for achieving the maximum selectivity towards GVL was carried out. An intrinsic interplay between the lower particle size of copper (metal centers), the Lewis acidity (zirconia sites) and the Brönsted acidic (MMT) sites was found. Further active site masking and reaction intermediates were tested to identify and prove the synergistic effect of the active sites in the reaction pathway. To achieve the highest yield, a response surface methodology using a Central Composite Design model was formulated. Under the optimized reaction conditions, the catalyst demonstrated 99.9% furfural conversion and a high GVL selectivity of 98%, the highest obtained so far in the literature. The catalyst remained highly stable over four reaction cycles with a marginal decrease in its activity and was regenerated via an autogenous solvothermal treatment in between each cycle. Spent catalyst characterizations revealed that its structural integrity and physicochemical properties were retained.

Hydrothermal carbonization (HTC) is a thermochemical treatment involving the use of subcritical water, which acts not only as solvent but also exploits its acidity as a catalyst, promoting carbonization reactions in biomass. In this study, HTC is proposed as a mild pre-treatment for enhancing the combustion properties of bamboo species, focusing on reductions in fouling and particulate matter emissions through selective solubilization of the ashes. Bamboo is one of the fastest-growing plants, and it can suitably grow on poor soils, such as marginal lands, making it a promising feedstock for biorefineries, even under Mediterranean climate conditions. In this context, optimization of the HTC treatment was carried out with the aim of maximizing the ash removal and at the same time preventing the solubilization of C5 and C6 structural carbohydrates. Several HTC tests were performed using a 300 mL Parr reactor, varying the reaction temperature (160-180-200 °C) and the reaction time (1-4-8 hours), with a biomass loading of 10 wt%. The macrostructural composition of the raw bamboo and the solids recovered from the HTC tests was determined, along with the chemical composition of their ashes. Moreover, physicochemical characterization of the corresponding mother liquors was carried out to obtain useful information about their valorization. The results indicate that the mildest HTC reaction conditions (160 °C, 1 hour) could effectively solubilize certain critical inorganic elements (mainly K, Mg, and P) while preserving the macrostructural components of the pre-treated solid, thus resulting in them being more easily exploitable for energy uses. The use of carboxylate-based chelating agents to improve ash solubilization is in progress, enhancing HTC further as a mild pre-treatment for bamboo species. Remarkably, this approach could be appropriate for the development of a better-integrated biorefinery scheme, requiring the best fractionation/exploitation of each biomass component.

Metallic and semiconducting fractions of single-walled carbon nanotubes (SWCNTs) attract attention from researchers because they have unique catalytic properties. The catalytic properties of sorted fractions are very important. They are needed to control the properties of metallic and semiconducting SWCNTs. For these reasons, it is important to develop and investigate the sorting process of SWCNTs. The sorting process of SWCNTs leads to metallic and semiconducting SWCNTs, as well as single-chirality samples. They possess new unique physical features, as revealed with a microscopic and spectroscopic techniques. Filled SWCNTs are important materials. Methods of obtaining sorted and filled SWCNTs are currently being developed. They allow for obtaining high-quality samples that are clean from impurities with controlled properties. In this work, the metallic fractions of nickelocene-filled SWCNTs were obtained, and the sorting process was investigated with optical absorption spectroscopy (OAS). It was demonstrated that the sorting process of 1.4 nm diametermixed-metallicity SWCNTs leads to obtaining pure metallic SWCNTs. The OAS spectrum of the nickelocene-filled SWCNTs shows the characteristic peaks of the metallic SWCNTs. These peaks correspond to electronic transitions between the first van Hove singularities of metallic SWCNTs. This confirms the purity of the samples and their applicability for catalysis.