Green synthesis of gamma-valerolactone (GVL) through hydrogenation of biomass-derived levulinic acid using non-noble metal catalysts : A critical review

The distinct physicochemical properties and renewable origin of gamma-valerolactone (GVL) have provided opportunities for diversifying its applications, particularly as a green solvent, excellent fuel additive, and precursor to valuable chemicals. Among the related publications found in the SCOPUS database (≈172 in the last 10 years), we focused our effort to review the conversion of levulinic acid (LA) to GVL over non-noble metal catalysts and the corresponding mechanisms (≈30 publications) as well as the applications of GVL as a solvent, fuel additive, and platform chemical (≈30 publications) mostly in the last five years (some preceding publications have also been included due to their relevance and importance in the field). The use of non-noble metals (e.g., Cu and Zr) presents a greener route of GVL synthesis than the conventional practice employing noble metals (e.g., Pd and Ru), in view of their higher abundance and milder reaction conditions needed (e.g., low pressure and temperature without H 2 involved). The significance of the catalyst characteristics in promoting catalytic transfer hydrogenation of LA to GVL is critically discussed. Structural features and acid-base properties are found to influence the activity and selectivity of catalysts. Furthermore, metal leaching in the presence of water in catalytic systems is an important issue, resulting in catalyst deactivation. Various endeavors for developing catalysts using well-dispersed metal particles along with a combination of Lewis acid and base sites are suggested for efficiently synthesizing GVL from LA

A sustainable biochar catalyst synergized with copper heteroatoms and CO2 for singlet oxygenation and electron transfer routes

We have developed a wood waste-derived biochar as a sustainable graphitic carbon catalyst for environmental remediation through catalytic pyrolysis under the synergistic effects between Cu heteroatoms and CO2, which for the first time are found to significantly enhance the oxygen functionalities, defective sites, and highly ordered sp2-hybridized carbon matrix. The copper-doped graphitic biochars (Cu-GBCs) were further characterized by XRD, FTIR, Raman, XPS, etc., revealing that the modified specific surface area, pore structure, graphitization, and active sites (i.e., defective sites and ketonic group) on the Cu-GBCs corresponded to the synergistic Cu species loading and Cu-induced carbon-matrix reformation in CO2 environment during pyrolysis. The catalytic ability of Cu-GBCs was evaluated using the ubiquitous peroxydisulfate (PDS) activation system for the removal of various organic contaminants (i.e., rhodamine B, phenol, bisphenol A, and 4-chlorophenol), and gave the highest degradation rate of 0.0312 min-1 in comparison with those of pristine GBCs and N2-pyrolyzed Cu-GBCs ranging from 0.0056 to 0.0094 min-1. The synergistic effects were attributed to the encapsulated Cu heteroatoms, evolved ketonic groups, and abundant unconfined π electrons within the carbon lattice. According to scavenger experiments, ESR analysis, and two-chamber experiments, selective and sustainable non-radical pathways (i.e., singlet oxygenation and electron transfer) mediated by the Cu-induced metastable surface complex were achieved in the Cu-GBC/PDS system. This study offers the first insights into the efficacy, sustainability, and mechanistic roles of Cu-GBCs as an emerging carbon-based catalyst for green environmental remediation

Nanomaterials for sustainable remediation of chemical contaminants in water and soil

Rapid growth in population, industry, urbanization and intensive agriculture have led to soil and water pollution by various contaminants. Nanoremediation has become one of the most successful emerging technologies for cleaning up soil and water contaminants due to the high reactivity of nanomaterials (NMs). Numerous publications are available on the use of NMs for removing contaminants, and the efficiencies are often improved by modifications of NMs with polymers, clay minerals, zeolites, activated carbon, and biochar. This paper critically reviews the current state-of-the-art NMs used for sustainable soil and water remediation, focusing on their applications in novel remedial approaches, such as adsorption/filtration, catalysis, photodegradation, electro-nanoremediation, and nano-bioremediation. Insights into process performances, modes of deployment, potential environmental risks and their management, and the consequent societal and economic implications of using NMs for soil and water remediation indicate that widespread acceptance of nanoremediation technologies requires not only a substantial advancement of the underpinning science and engineering aspects themselves, but also practical demonstrations of the effectiveness of already recognized approaches at real world in-situ conditions. New research involving green nanotechnology, nano-bioremediation, electro-nanoremediation, risk assessment of NMs, and outreach activities are needed to achieve successful applications of nanoremediation at regional and global scales

Ball-milled, solvent-free Sn-functionalisation of wood waste biochar for sugar conversion in food waste valorisation

A solvent-free ball milling protocol was investigated for synthesizing sustainable Sn-functionalized biochars for glucose isomerization to fructose. Raw wood biomass (W) and its derived biochars pyrolyzed at low (LB, 400 °C) and high (HB, 750 °C) temperatures were investigated as catalyst supports. This study emphasized that the interactions between Sn and the carbonaceous supports were related to the surface chemistry of the catalysts. Functional group-enriched surfaces provide more active sites for anchoring Sn, resulting in a high loading on the biochar support. Sn was primarily bound with W via surface complexation or precipitation, while it mainly interacted with LB and HB via physical adsorption. The annealing temperature was another critical factor that affected the concentrations and nature of the species of loaded Sn. Catalytic conversion experiments indicated that SnW annealed at 750 °C exhibited the best fructose yield (12.8 mol%) and selectivity (20.2 mol%) at 160 °C in 20 min. The catalytic activity was correlated to the amount and nature of active Sn sites. Reusability tests revealed a noticeable increase in product selectivity compared to pristine materials, despite a compromise in product yield. This study elucidated the roles of the carbon support and annealing temperature for synthesizing biochar-supported catalysts, highlighting a simple and green approach for designing effective solid catalysts for sustainable biorefineries

Valorization of lignocellulosic fibres of paper waste into levulinic acid using solid and aqueous Brønsted acid

International audienc

Organic Acid-Regulated Lewis Acidity for Selective Catalytic Hydroxymethylfurfural Production from Rice Waste: An Experimental–Computational Study

International audienc

Graphite oxide- and graphene oxide-supported catalysts for microwave-assisted glucose isomerisation in water

Graphite (G), graphite oxide (GIO), and graphene oxide (GO) were evaluated for the first time as carbonaceous supports to synthesise heterogeneous Lewis acid catalysts, via simple AlCl3 pretreatment followed by one-step thermal modification. The GIO- and GO-supported Al catalysts were active towards catalytic isomerisation of glucose in water as the greenest solvent. The highest fructose yield of 34.6 mol% was achieved under microwave heating at 140 °C for 20 min. The major active sites were characterised as amorphous Al hydroxides (e.g., β-Al(OH)3, γ-Al(OH)3, and γ-AlO(OH)) with octahedral coordination, as revealed by 27Al NMR, XPS, SEM, TEM-EDX, Raman, ESR, and XRD analyses. The transformation of octahedral Al to pentahedral/tetrahedral coordination was observed when the activation temperature increased. Oxygen-containing functional groups on the GIO and GO surfaces, e.g., C-O-C, -OH, and -COOH, contributed to the formation of microwave-absorbing active sites. In contrast, the G-supported catalyst may contain microwave-transparent Al hydroxides, accounting for its low catalytic activity under microwave irradiation. This study elucidates the significance of the surface chemistry of carbonaceous supports in generating active species for a Lewis acid-driven reaction. The revealed intertwined relationships among modification conditions, physicochemical properties, and catalytic performance will be useful for designing effective carbon-supported catalysts for sustainable biorefinery

Study of glucose isomerisation to fructose over three heterogeneous carbon-based aluminium-impregnated catalysts

Driven by the worldwide demand for sustainable resources and renewable energy, the synthesis of bio-based platform chemicals has attracted broad interest. The isomerisation of glucose to fructose acts as a critical intermediate step among many chemical synthesis routes. In this study, biochar (BC), graphitic oxide (GIO), and graphene oxide (GO) were used as carbon supports to synthesize Al-impregnated heterogeneous catalysts, which were then used for glucose isomerisation under microwave heating in the water at 140 °C. The kinetics model with parameters was used to reveal the interplay of the active sites and compare the activity of the three carbon-based catalysis systems. Catalyst characterisation results showed effective aluminium (Al) impregnation onto the three types of catalysts, and it was found that GIO-Al200 and GO-Al200 showed comparable catalytic activity (fructose yield of 34.3–35.0%) for glucose isomerisation. At the same time, BC-Al200 exhibited slightly lower catalytic activity (fructose yield of 29.4%). The conversion kinetics suggested similar catalytic mechanisms on the three catalysts while BC-Al200 manifested slower kinetics, possibly implying higher activation energy. The fructose selectivity decreased with increasing time due to the formation of side products, yet BC-Al200 resulted in less carbon loss than GIO-Al200 and GO-Al200, probably attributed to its lower catalytic activity and higher pH buffering capacity. A green synthesis route of this study promotes biomass valorisation and makes engineered biochar a promising carbon-based catalyst for sustainable biorefinery