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Methylcyclohexane (MCH) dehydrogenation is an equilibrium-limited reaction that requires high temperatures (>300 °C) for complete conversion. However, high-temperature operation can degrade catalytic activity and produce unwanted side products. Thus, a hybrid zeolite membrane (Z) is prepared on the inner surface of a tubular support and used it as a wall in a membrane reactor (MR) configuration. Pt/C catalysts is packed diluted with quartz sand inside the Z-coated tube and applied the MR for MCH dehydrogenation at low temperatures (190-250 °C). Z showed a remarkable H 2 -permselectivity in the presence of both toluene and MCH, yielding separation factors over 350. The Z-based MR achieved higher MCH conversion (75.3% ± 0.8% at 220 °C) than the conventional packed-bed reactor (56.4% ± 0.3%) and the equilibrium state (53.2%), owing to the selective removal of H 2 through Z. In summary, the hybrid zeolite MR enhances MCH dehydrogenation at low temperatures by overcoming thermodynamic limitations and improves the catalytic performance and product selectivity of the reaction., (© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)

Preserving ultrasmall sizes of metal particles is a key challenge in the study of heterogeneous metal-based catalysis. Confining the ultrasmall metal clusters in a well-defined crystalline porous zeolite has emerged as a promising approach to stabilize these metal species. Successful encapsulation can be achieved by the addition of ligated metal complexes to zeolite synthesis gel before hydrothermal synthesis. However, controlling the metal particle size during post-reduction treatment remains a major challenge in this approach. Herein, an in situ incorporation strategy of pre-made atomically precise gold clusters within Na-LTA zeolite was established for the first time. With the assistance of mercaptosilane ligands, the gold clusters were successfully incorporated within the Na-LTA without premature precipitation and metal aggregation during the synthesis. We have demonstrated that the confinement of gold clusters within the zeolite framework offers high stability against sintering, leading to superior CO oxidation catalytic performance (up to 12 h at 30 °C, with a space velocity of 3000 mL g -1 h -1 ).

The sustainable utilization of biochar produced from biomass waste could substantially promote the development of carbon neutrality and a circular economy. Due to their cost-effectiveness, multiple functionalities, tailorable porous structure, and thermal stability, biochar-based catalysts play a vital role in sustainable biorefineries and environmental protection, contributing to a positive, planet-level impact. This review provides an overview of emerging synthesis routes for multifunctional biochar-based catalysts. It discusses recent advances in biorefinery and pollutant degradation in air, soil, and water, providing deeper and more comprehensive information of the catalysts, such as physicochemical properties and surface chemistry. The catalytic performance and deactivation mechanisms under different catalytic systems were critically reviewed, providing new insights into developing efficient and practical biochar-based catalysts for large-scale use in various applications. Machine learning (ML)-based predictions and inverse design have addressed the innovation of biochar-based catalysts with high-performance applications, as ML efficiently predicts the properties and performance of biochar, interprets the underlying mechanisms and complicated relationships, and guides biochar synthesis. Finally, environmental benefit and economic feasibility assessments are proposed for science-based guidelines for industries and policymakers. With concerted effort, upgrading biomass waste into high-performance catalysts for biorefinery and environmental protection could reduce environmental pollution, increase energy safety, and achieve sustainable biomass management, all of which are beneficial for attaining several of the United Nations Sustainable Development Goals (UN SDGs) and Environmental, Social and Governance (ESG)., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Utilizing renewable energy to hydrogenate carbon dioxide into fuels eliminates massive CO 2 emissions from the atmosphere and diminishes our need for using fossil fuels. This review presents the most recent developments for designing heterogeneous catalysts for the hydrogenation of CO 2 to formate, methanol, and C 2+ hydrocarbons. Thermodynamic challenges and mechanistic insights are discussed, providing a strong foundation to propose a suitable catalyst. The main body of this review focuses on nanostructured catalysts for constructing efficient heterogeneous systems. The most important factors affecting catalytic performance are highlighted, including active metals, supports and promoters that can potentially be used. The summary of the results and the outlook are presented in the final section. During the past few decades, heterogeneous CO 2 hydrogenation has gained much attention and made tremendous progress. Thus, many highly efficient catalysts have been studied to discover their active sites and provide mechanistic insights. This paper summarizes recent advances in CO 2 hydrogenation and its conversion into various hydrocarbons such as formate, methanol, and C 2+ products. As for formate production, Au and Ru nanocatalysts show superior activity. However, considering the catalyst cost, Cu-based catalysts have an excellent prospect for methanol production, among other catalysts. Ultra-small nanoparticles and nanoclusters appear promising to provide highly active cost-effective catalysts. A growing number of researchers are investigating the possibility of directly synthesizing C 2+ products through CO 2 hydrogenation. The major challenge in producing heavy hydrocarbons is breaking the ASF limitations, which have been achieved over bifunctional catalysts using zeolites. Using suitable support and promoter can lead to a superior activity, ascribed to structural, electronic, and chemical promotional effects., (© 2023 The Authors. ChemPlusChem published by Wiley-VCH GmbH.)

Biogas is an environmentally friendly and sustainable energy resource that can substitute or complement conventional fossil fuels. For practical uses, biogas upgrading, mainly through the effective separation of CO 2 (0.33 nm) and CH 4 (0.38 nm), is required to meet the approximately 90-95% purity of CH 4 , while CO 2 should be concomitantly purified. In this study, a high CO 2 perm-selective zeolite membrane was synthesized by heteroepitaxially growing a chabazite (CHA) zeolite seed layer with a synthetic precursor that allowed the formation of all-silica deca-dodecasil 3 rhombohedral (DDR) zeolite (with a pore size of 0.36 × 0.44 nm 2 ). The resulting hydrophobic DDR@CHA hybrid membrane on an asymmetric α-Al 2 O 3 tube was thin (ca. 2 μm) and continuous, thus providing both high flux and permselectivity for CO 2 irrespective of the presence or absence of water vapor (the third largest component in the biogas streams). To the best of our knowledge, the CO 2 permeance of (2.9 ± 0.3) × 10 -7 mol m -2 s -1 Pa -1 and CO 2 /CH 4 separation factor of ca. 274 ± 73 at a saturated water vapor partial pressure of ca. 12 kPa at 50 °C have the highest CO 2 /CH 4 separation performance yet achieved. Furthermore, we explored the membrane module properties of the hybrid membrane in terms of the recovery and purity of both CO 2 and CH 4 under dry and wet conditions. Despite the high intrinsic membrane properties of the current hybrid membrane, reflected by the high permeance and SF, the corresponding module properties indicated that high-performance separation of CO 2 and CH 4 for the desired biogas upgrading was achieved at a limited processing capacity. This supports the importance of understanding the correlation between the membrane and module properties, as this will provide guidance for the optimal operating conditions.

Development of non-noble metal cluster catalysts, aiming at concurrently high activity and stability, for emission control systems has been challenging because of sintering and overcoating of clusters on the support. In this work, we reported the role of well-dispersed copper nanoclusters supported on TiO 2 in CO oxidation under industrially relevant operating conditions. The catalyst containing 0.15 wt% Cu on TiO 2 (0.15 CT) exhibited a high dispersion (59.1%), a large specific surface area (381 m 2 /g Cu ), a small particle size (1.77 nm), and abundant active sites (75.8% Cu 2 O). The CO oxidation activity measured by the turnover frequency (TOF) was found to be enhanced from 0.60 × 10 -3 to 3.22 × 10 -3 mol CO ·mol Cu -1 ·s -1 as the copper loading decreased from 5 to 0.15 wt%. A CO conversion of approximately 60% was still observed in the supported cluster catalyst with a Cu loading of 5 wt% at 240 °C. No deactivation was observed for catalysts with low copper loading (0.15 and 0.30 CT) after 8 h of time-on-stream, which compares favorably with less stable Au cluster-based catalysts reported in the literature. In contrast, catalysts with high copper loading (0.75 and 5 CT) showed deactivation over time, which was ascribed to the increase in copper particle size due to metal cluster agglomeration. This study elucidated the size-activity threshold of TiO 2 -supported Cu cluster catalysts. It also demonstrated the potential of the supported Cu cluster catalyst at a typical temperature range of diesel engines at light-load. The supported Cu cluster catalyst could be a promising alternative to noble metal cluster catalysts for emission control systems., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

MFI type zeolites with 10-membered-ring pores (ca. 0.55 nm) have the ability to separate p-xylene (ca. 0.58 nm) from its bulkier isomers. Here, we introduced non-zeolitic micropores (ca. 0.6-1.5 nm) and mesopores (ca. 2-7 nm) to a conventional microporous MFI type zeolite membrane, yielding an unprecedented hierarchical membrane structure. The uniform, embedded non-zeolitic pores decreased defect formation considerably and facilitated molecular transport, resulting in high p-xylene perm-selectivity and molar flux. Specifically, compared to a conventional, crack network-containing MFI membranes of similar thickness (ca. 1 μm), the mesoporous MFI membranes showed almost double p-xylene permeance (ca. 1.6±0.4×10 -7  mol m -2  s -1  Pa -1 ) and a high p-/o-xylene separation factor (ca. 53.8±7.3 vs. 3.5±0.5 in the conventional MFI membrane) at 225 °C. The embedded non-zeolitic pores allowed for decreasing the separation performance degradation, which was apparently related to coke formation., (© 2020 Wiley-VCH GmbH.)

Efficient conversion of food waste to value-added products necessitates the development of high-performance heterogeneous catalysts. This study evaluated the use of Al 2 O 3 as a low-cost and abundant support material for fabricating Lewis acid catalysts, i.e., through the in-situ doping of Cu, Ni, Co, and Zr into Al 2 O 3 followed by calcination. The characterisation results show that all catalysts were mainly amorphous. In particular, adding the transition metals to the Al 2 O 3 matrix resulted in the increase of acidity and meso-/micro-pores. The catalysts were evaluated in the conversion of glucose, which can be easily derived from starch-rich food waste (e.g., bread waste) via hydrolysis, to fructose in biorefinery. The results indicate that the Ni-doped Al 2 O 3 (Al-Ni-C) achieved the highest fructose yield (19 mol%) and selectivity (59 mol%) under heating at 170 °C for 20 min, of which the performance falls into the range reported in literature. In contrast, the Zr-doped Al 2 O 3 (Al-Zr-C) presented the lowest fructose selectivity despite the highest glucose conversion, meaning that the catalyst was relatively active towards the side reactions of glucose and intermediates. The porosity and acidity, modified via metal impregnation, were deduced as the determinants of the catalytic performance. It is noteworthy that the importance of these parameters may vary in a relative sense and the limiting factor could shift from one parameter to another. Therefore, evaluating physicochemical properties as a whole, instead of the unilateral improvement of a single parameter, is encouraged to leverage each functionality for cost-effectiveness. This study provides insights into the structure-performance relationships to promote advance in catalyst design serving a sustainable food waste biorefinery., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Mesoporous ZSM-5 (MFI) zeolite was synthesized by using bacterial cellulose-derived activated carbon (BC-AC500) with a high surface area as a hard template. Different ratios of BC-AC500 and zeolite precursor gel were prepared in a Teflon-lined autoclave and crystallized at 180 °C for 48 h in a rotating oven. The physicochemical properties of the samples were characterized by x-ray diffraction (XRD), scanning/transmission electron microscopies (SEM/TEM), and N 2 physisorption techniques. It was found that the mesoporous ZSM-5 zeolites have a specific surface area of 184-190 m 2 /g, a high mesopore volume of 0.120-0.956 ml/g and a wide pore size distribution ranging from 5 to 100 nm with a maximum at approximately 25.3 nm. The successfully made mesoporous ZSM-5 was tested as an adsorbent for formaldehyde adsorption in batch mode. The mesoporous ZSM-5 zeolite made from bacterial cellulose-derived activated carbon showed significantly faster adsorption kinetics than conventional ZSM-5 (0.0081 vs. 0.0007 g/mg min, respectively). The prepared material has an adsorption capacity of 98 mg/g and is highly reusable. The reported mesoporous ZSM-5 zeolites can be deployed for the rapid removal of toxic organics from wastewater when urgently needed, e.g., under breakthrough conditions., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Lignocellulosic wastes constitute a significant portion of the municipal solid waste, which should be valorised for the synthesis of value-added chemicals to achieve circular bioeconomy. This study evaluates the use of γ-valerolactone (GVL) and acetone as green co-solvents to produce levulinic acid (LA) from lignocellulosic paper towel waste at different temperatures using dilute H 2 SO 4 . At the highest reaction temperature (200 °C), H 2 O-only system achieved ~15 Cmol% of LA at maximum. while GVL/H 2 O and acetone/H 2 O co-solvent systems enhanced the depolymerisation of paper towel waste and the subsequent conversion to LA, with the highest yield amounted to ~32 Cmol%. Acetone/H 2 O solvent system generated ~17 Cmol% LA at a lower temperature (180 °C), while higher temperature induced polymerisation of soluble sugars and intermediates, hindering further conversion to LA. In contrast, the availability of soluble sugars was higher in the GVL/H 2 O system, which favoured the production of LA at higher temperatures., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Metal clusters and nanoparticles, which have been used to tune the acidity of zeolite support, are beneficial for promoting the catalytic performance of various reaction processes, including biomass conversion. However, catalytic instabilities resulting from metal coalescence, sintering and leaching are major problems that need to be resolved. Therefore, metal encapsulation within the zeolite structure has been proposed as a feasible solution for this issue, particularly for biomass conversions that require high temperatures. In this current review, recent developments in metal confinement techniques are described along with experimental examples of biomass upgrading reactions. The present and future perspectives of zeolite-encapsulated metal catalysts in biomass conversions are also given., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

The secondary growth methodology to form zeolite membranes has stringent requirements for homogeneous epitaxial intergrowth of the seed layer and limits the number of accessible high-quality zeolite membranes. Despite previous reports on hetero-epitaxial growth, high-performance zeolite membranes have yet to be reported using this approach. Here, the successful hetero-epitaxial growth of highly siliceous ZSM-58 (DDR-type zeolite) films from a SSZ-13 (CHA-type zeolite) seed layer is reported. The resulting membranes show excellent CO 2 perm-selectivities, having maximum CO 2  /N 2 and CO 2  /CH 4 separation factors (SFs) as high as about 17 and 279, respectively, at 30 °C. Furthermore, the hybrid membrane maintains the CO 2 perm-selectivity in the presence of water vapor (the third main component in both cases), that is, CO 2  /N 2 SF of about 14 and CO 2  /CH 4 SF of about 78, respectively, at 50 °C (a representative temperature of both CO 2 -containing streams)., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

CO 2 capture is projected as one of the pragmatic approaches to deal with the global warming phenomenon. Adsorption-based CO 2 capture is considered an economically attractive option to reduce CO 2 emission. The success of the adsorption-based capture primarily relies on adsorbents and thus a variety of adsorbents have been investigated in the literature. We here report a high surface area (210.2 m 2 /g) exfoliated Ni-Al LDH nanoplatelet as a promising candidate for CO 2 capture at an intermediate temperature of 200 °C applicable to integrated gasification combined cycle (IGCC) and sorption enhanced water gas shift (SEWGS) reactions. The materials were well characterized by PXRD, TGA, FTIR, TEM, ICP-OES, and N 2 adsorption surface area, and pore size distribution techniques. A unique nanoflower morphology comprising of exfoliated LDH platelets of ca. 5 layer thickness was obtained. The CO 2 capture capacity (0.66 mmol/g) of the exfoliated Ni-Al LDH nanoplatelet is comparable to that of the widely reported Mg-Al LDH-derived mixed oxides and MgO-based adsorbents. Provided that Ni-Al and other transition metal LDH materials are known to exhibit superior catalytic properties for CO 2 methanation, this work could pave the way for development of dual-functional materials for CO 2 capture and conversion., (Copyright © 2019 Elsevier B.V. All rights reserved.)

-While sulfate radical (SO 4 - )-based processes are useful to degrade acetaminophen (ACE), studies of using peroxymonosulfate (PMS) to degrade ACE are quite limited. In addition, although Co is validated as the most effective metal for activating PMS, very few Co catalysts have been developed and investigated for activating PMS to degrade ACE. Since carbon is a promising substrate to support Co nanoparticles (NPs) to form Co/carbon composite catalysts, most existing carbon substrates require delicate fabrications. As biochar is an easy-to-obtain but versatile carbon material, pyrolysis of Co/lignin affords an advantageous Co-impregnated biochar (CoIB) as an attractive catalyst for PMS activation. Specifically, as CO 2 substitutes N 2 as a reaction medium for pyrolysis of Co/lignin, the syngas production from pyrolysis can be substantially improved and a magnetic CoIB is afforded. This CoIB consists of evenly-distributed Co nanoparticles (NPs) impregnated in carbon matrices of biochar, and possesses several superior characteristics, such as high porosity, large surface area and magnetism, enabling CoIB a promising catalyst for activating PMS to degrade ACE. CoIB also shows a much higher catalytic activity of PMS activation than CoIBN 2 , and Co 3 O 4 for degrading ACE. CoIB is also recyclable for activating PMS to effectively degrade ACE for multiple cycles. The ACE degradation pathway by this CoIB-activated PMS is proposed according to the degradation products. These findings validate that CoIB is assuredly an advantageous heterogeneous catalyst, which can be easily prepared from pyrolysis of Co/lignin in CO 2 with concomitant enhanced syngas production for effectively activating PMS to degrade ACE., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

The adsorption characteristics of four aromatic hydrocarbons (i.e., benzene, toluene, xylene, and styrene) onto ground-activated carbon were investigated both independently and as a mixture of the four at <10 Pa partial pressures (e.g., 0-100 ppm concentration range). The maximum sorption capacities for benzene, toluene, styrene, and xylene were measured both as a sole component and as a mixture (at 10 Pa). In the former, the values were approximately 123, 184, 272, and 238 mg g -1 , respectively. In contrast, the latter values were 5, 52, 222, and 248 mg g -1 respectively, showing dramatic reduction in lighter compounds (below C7) relative to heavier ones (above C8). The mechanistic detail of sorption has been explained in terms of Henry's law and Langmuir, Freundlich, Dubinin-Radushkevich, and Elovich isotherm models. The linearized Langmuir adsorption isotherm analysis showed three sorption pressure regions: low (<1 Pa, retrograde), intermediate (1-4 Pa), and high (4-10 Pa). As such, the outcome of this study offers a unique opportunity to acquire detailed information on the dramatic and dynamic effects of the sorptive interaction between competing sorbates, along with a common sorption process between sorbent and sorbate at 298 K., (Copyright © 2019 Elsevier Inc. All rights reserved.)

In this work, the degradation of cefalexin, norfloxacin, and ofloxacin was examined via various advanced oxidation processes (AOPs). Direct photolysis by ultraviolet (UV) and vacuum ultra violet (VUV) was less effective for the degradation of fluoroquinolone antibiotics such as norfloxacin and ofloxacin than that of cefalexin. Both hydrogen peroxide (H 2 O 2 ) and potassium persulfate (K 2 S 2 O 8 ) assisted UV/VUV process remarkably enhanced fluoroquinolone degradation. The addition of K 2 S 2 O 8 was superior to H 2 O 2 under VUV irradiation, with the best removal efficiency of norfloxacin and ofloxacin being almost 100% within 3 min in the presence of VUV/K 2 S 2 O 8 . The ofloxacin degradation rate was accelerated as concentrations of H 2 O 2 and K 2 S 2 O 8 was increased to 3 mM, but the degradation rate was slightly decreased with excess H 2 O 2 (>3 mM). The performance of modified VUV processes (i.e., VUV/H 2 O 2 and VUV/K 2 S 2 O 8 ) was inhibited at highly alkaline condition (pH 11). The co-existence of halides (Cl - and Br - ) enhanced antibiotics degradation via the modified VUV processes, but the reaction was almost unaffected in the presence of single halides. This study demonstrated that modified VUV processes (especially VUV/K 2 S 2 O 8 ) are efficient for eliminating fluoroquinolone antibiotics from water, which can be considered as a clean and green method for the treatment of antibiotics-containing industrial wastewater., (Copyright © 2019 Elsevier B.V. All rights reserved.)

A new and environmentally benign photocatalyst is introduced in this study, which was synthesized via incipient wetness impregnation onto MIL-47(V) using an ethanolic Fe(III) chloride solution. The resultant materials were characterized by XRD, FE-SEM, and HR-TEM analyses. The photocatalytic capability of Fe/MIL-47 towards removal of methylene blue (MB) was evaluated in comparison to MIL-53(Al), Cu/MIL-47, and Fe/zeolite-Y. The unmodified MIL-47 achieved 55% MB removal after 20-min exposure to UV/H 2 O 2 , through photodegradation as the dominant mechanism. Incorporation of Fe species into MIL-47 significantly increased the MB removal rate by 2.4-fold and accomplished nearly complete removal (98.2%) in 60 min, outcompeting the performance of Cu/MIL-47 and Fe/zeolite-Y. Based on the results of XRD, the impregnation of Fe retained the crystalline characteristics of MIL-47. The significance of temperature, catalyst dose, pH, and molar ratio of H 2 O 2 :MB was also evaluated in governing the photocatalytic activity of Fe/MIL-47. The reusability of Fe/MIL-47 was evidenced through its repetitive uses in MB photodegradation. The current work highlighted the potential of Fe impregnation for modification of MOFs in order to fabricate highly efficient and water-stable heterogeneous photocatalyst for degradation of organic pollutants. With the use of an economical and environmentally safe reagent (i.e., Fe), robust photocatalyst can exhibit high sustainability to warrant clean environmental remediation., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Nanotechnology is currently one of the highest priority research fields in many countries due to its immense potentiality and economic impact. Nanotechnology involves the research, development, production, and processing of structures and materials on a nanometer scale in various fields of science, technology, health care, industries, and agriculture. As such, it has contributed to the gradual restructuring of many associated technologies. However, due to the uncertainties and irregularities in shape, size, and chemical compositions, the presence of certain nanomaterials may exert adverse impacts on the environment as well as human health. Concerns have thus been raised about the destiny, transport, and transformation of nanoparticles released into the environment. A critical evaluation of the current states of knowledge regarding the exposure and effects of nanomaterials on the environment and human health is discussed in this review. Recognition on the potential advantages and unintended dangers of nanomaterials to the environment and human health is critically important to pursue their development in the future., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

This study aimed to produce a high-value platform chemical, hydroxymethylfurfural (HMF), from food waste and evaluate the catalytic performance of trivalent and tetravalent metals such as AlCl 3 , CrCl 3 , FeCl 3 , Zr(O)Cl 2 , and SnCl 4 for one-pot conversion. Starchy food waste, e.g., cooked rice and penne produced 4.0-8.1 wt% HMF and 46.0-64.8 wt% glucose over SnCl 4 after microwave heating at 140 °C for 20 min. This indicated that starch hydrolysis was effectively catalyzed but subsequent glucose isomerization was rate-limited during food waste valorization, which could be enhanced by 40-min reaction to achieve 22.7 wt% HMF from cooked rice. Sugary food waste, e.g., kiwifruit and watermelon, yielded up to 13 wt% HMF over Sn catalyst, which mainly resulted from naturally present fructose. Yet, organic acids in fruits may hinder Fe-catalyzed dehydration by competing for the Lewis sites. In contrast, conversion of raw mixed vegetables as cellulosic food waste was limited by marginal hydrolysis at the studied conditions (120-160 °C and 20-40 min). It is interesting to note that tetravalent metals enabled HMF production at a lower temperature and shorter time, while trivalent metals could achieve a higher HMF selectivity at an elevated temperature. Further studies on kinetics, thermodynamics, and reaction pathways of food waste valorization are recommended., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

This study aimed to maximize the valorization of bread waste, a typical food waste stream, into hydroxymethylfurfural (HMF) by improving our kinetic understanding. The highest HMF yield (30mol%) was achieved using SnCl 4 as catalyst, which offered strong derived Brønsted acidity and moderate Lewis acidity. We evaluated the kinetic balance between these acidities to facilitate faster desirable reactions (i.e., hydrolysis, isomerization, and dehydration) relative to undesirable reactions (i.e., rehydration and polymerization). Such catalyst selectivity of SnCl 4 , AlCl 3 , and FeCl 3 was critical in maximizing HMF yield. Higher temperature made marginal advancement by accelerating the undesirable reactions to a similar extent as the desirable pathways. The polymerization-induced metal-impregnated high-porosity carbon was a possible precursor of biochar-based catalyst, further driving up the economic potential. Preliminary economic analysis indicated a net gain of USD 43-236 per kilogram bread waste considering the thermochemical-conversion cost and chemical-trading revenue., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

This study aimed to transform food waste into a value-added chemical, hydroxymethylfurfural (HMF), and unravel the tangled effects induced by the metal catalysts on each single step of the successive conversion pathway. The results showed that using cooked rice and bread crust as surrogates of starch-rich food waste, yields of 8.1-9.5% HMF and 44.2-64.8% glucose were achieved over SnCl4 catalyst. Protons released from metal hydrolysis and acidic by-products rendered Brønsted acidity to catalyze fructose dehydration and hydrolysis of glycosidic bond. Lewis acid site of metals could facilitate both fructose dehydration and glucose isomerization via promoting the rate-limiting internal hydride shift, with the catalytic activity determined by its electronegativity, electron configuration, and charge density. Lewis acid site of a higher valence also enhanced hydrolysis of polysaccharide. However, the metals also catalyzed undesirable polymerization possibly by polarizing the carbonyl groups of sugars and derivatives, which should be minimized by process optimization., (Copyright © 2016 Elsevier Ltd. All rights reserved.)