Oxidation of bio-renewable glycerol to value-added chemicals through catalytic and electro-chemical processes

Due to its unique structure, characteristics, and bio-availability, glycerol transformation into value-added chemicals has been in the spotlight in recent years. This study provides a comprehensive review and critical analysis on catalytic and electro-chemical oxidation of glycerol into commodity chemicals, which have broad applications to the pharmaceutical, polymer, and food industries. Various synthesis methods (e.g. impregnation, sol-immobilization, incipient wetness, and deposition precipitation) for the preparation of the catalysts are discussed. Catalytic performance of mono-, bi-, multi-, and non-metal supported catalysts on carbon black, activated carbon, graphene, single- or multi wall-carbon nano-tubes, layered-double hydroxides, metal oxides, and polymers are evaluated. Among the methods, sol-immobilization is highly commended since fine metal NPs could be homogeneously distributed on the support, reported as an effective factor for controlling the selectivity of the desired product. In particular, the environmentally benign novel polymeric structures, illustrate significant breakthroughs in production of commodity chemicals compared to the conventional materials. Homogeneous oxidation of glycerol by enzymes and microorganisms also displayed acceptable performance particularly in production of DHA, but at the expense of long reaction time. Unlike the homogenous and heterogeneous catalytic processes, electro-chemical oxidation could be tuned for high product selectivity by controlling the nature, composition and structure of the electro-catalyst as well as the electrode potential. Most importantly, combination of electro-chemical oxidation of glycerol with oxygen or water reduction process in full- and electrolysis-cells, respectively could be the ultimate goal in this field. Simultaneous generation of value-added chemicals and electrical energy would have significant economical and environmental merits compared to the conventional processes. The current state-of-the-art of the glycerol oxidation process and recommendations for further research are also included.

  1. Talebian-Kiakalaieh, A., Amin, N., Rajaei, K. and Tarighi, S. (2018). Oxidation of bio-renewable glycerol to value-added chemicals through catalytic and electro-chemical processesApplied Energy, 230, pp.1347-1379.

DOI : https://doi.org/10.1016/j.apenergy.2018.09.006

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Constructing bio-templated 3D porous microtubular C-doped g-C3N4withtunable band structure and enhanced charge carrier separation

For the first time, the bio-templated porous microtubular C-doped (BTPMC) g-C3N4with tunable band structure was successfully prepared by simple thermal condensation approach using urea as precursors and kapok fibre which provides a dual function as a bio-templates and in-situ carbon dopant. Prior to the thermal condensation process, the impregnation strategies (i.e. direct wet and hydrothermal impregnation) of urea on the treated kapok fibre (t-KF) were compared to obtained well-constructed bio-templated porous microtubular C-doped g-C3N4. The details on a physicochemical characteristic of the fabricated samples were comprehensively analyze using X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), Field-emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), N2 adsorption-desorption, Thermogravimetric (TGA), and UV–vis spectroscopy. Our finding indicated that the hydrothermal impregnation strategy resulted in well-constructed microtubular structure and more carbon substitution in sp2-hybridized nitrogen atoms of g-C3N4 as compared to the direct wet impregnation. Also, compared to pure g-C3N4, the fabricated BTPMC g-C3N4 exhibited extended photoresponse from the ultraviolet (UV) to visible and near-infrared regions and narrower bandgap. The bandgap easily tuned with the increased t-KF loading in urea precursor which responsible for in-situ carbon doping. Moreover, as compared to pristine g-C3N4, dramatic suppression of charge recombination of the BTPMC g-C3N4 was confirmed through photoluminescence, photocurrent response, and electrochemical impedance spectroscopy. The resultants BTPMC g-C3N4 possesses more stable structure, promoted charge separation, and suitable energy levels of conduction and valence bands for photocatalysis application.

  1. Mohamed, M., M. Zain, M., Jeffery Minggu, L., Kassim, M., Saidina Amin, N., W. Salleh, W., Salehmin, M., Md Nasir, M. and Mohd Hir, Z. (2018). Constructing bio-templated 3D porous microtubular C-doped g-C 3 N 4 with tunable band structure and enhanced charge carrier separation. Applied Catalysis B: Environmental, 236, pp.265-279.

DOI : https://doi.org/10.1016/j.apcatb.2018.05.037

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Cold plasma dielectric barrier discharge reactor for dry reforming of methane over Ni/ɤ-Al2O3-MgO nanocomposite

Dry reforming of methane (DRM) to syngas in a dielectric barrier discharge (DBD) plasma reactor over Ni-loaded ɤ-Al2O3-MgO nanocomposite catalysts has been investigated. The catalysts are prepared by modified incipient wetness impregnationmethod, assisted by cold plasma treatment. The samples are characterized by XRD, N2 adsorption-desorption, H2-TPR, CO2-TPD, FESEM and EDX. The performance of the catalyst for DRM is evaluated at various specific input energy (SIE J ml−1) and gas hourly space velocity (GHSV, h−1). The maximum conversion achieved are 74.5% and 73% for CH4 and CO2 respectively, over 10% Ni/ɤ-Al2O3-MgO at specific input energy (SIE) = 300 J ml−1 and gas hourly space velocity (GHSV) = 364 h−1. The main reaction products are H2 (29.5%), CO (30.5%) with H2/CO = 1 inferring RWGS reaction is suppressed for 12 h operation time. The enhanced conversion and yield are due to the strong metal-support interaction, high Lewis basicity and stable 10% Ni/ɤ-Al2O3-MgO catalyst as well as the plasma-catalyst interface. The energy efficiency (EE) of the plasma-catalytic DRM is higher (0.117 mmol kJ−1) compared to plasma only (0.087 mmol kJ−1) demonstrating the synergy between catalyst and plasma. The reaction mechanism is also proposed to postulate the steps involved in the DRM.

  1. Khoja, A., Tahir, M. and Amin, N. (2018). Cold plasma dielectric barrier discharge reactor for dry reforming of methane over Ni/ɤ-Al 2 O 3 -MgO nanocomposite. Fuel Processing Technology, 178, pp.166-179.

https://doi.org/10.1016/j.fuproc.2018.05.030

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Esterification of Levulinic Acid to Levulinate Esters in the Presence of Sulfated Silica Catalyst

Levulinic acid (LA) is one of biomass derived building block chemicals with various applications. Catalytic esterification of LA with alkyl alcohol produces levulinate ester which can be applied as fragrance, flavouring agents, as well as fuel additives. In this study, a series of sulfated silica (SiO2) catalyst was prepared by modification of SiO2 with sulfuric acid (H2SO4) at different concentrations; 0.5 M to 5 M H2SO4. The catalysts were characterized, and tested for esterification of LA with ethanol to ethyl levulinate (EL). The effect of various reaction parameters including reaction time, catalyst loading and molar ratio of LA to ethanol on esterification of LA to EL were inspected. The catalyst with high concentration of acid sites seemed suitable for LA esterification to EL. Among the sulfated SiO2 catalysts tested (0.5 M-SiO2, 1 M-SiO2, 3 M-SiO2 and 5 M-SiO2), 3 M-SiO2 exhibited the highest performance with the optimum EL yield of 54% for reaction conducted at reflux temperature for 4 h, 30% 3 M-SiO2 loading and LA to ethanol molar ratio of 1:20. Besides, the reusability of 3 M-SiO2 catalyst for LA esterification with ethanol was examined for five cycles. Esterification of LA with methanol and 1-butanol were also carried out for methyl levulinate (ML) and butyl levulinate (BL) productions with 69% and 40% of ML and BL yields, respectively. This study demonstrates the potential of sulfated SiO2 catalyst for levulinate ester production from LA at mild process condition.

DOI: 10.17576/jsm-2018-4706-08

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Synthesis of hierarchical ZnV2O6 nanosheets with enhanced activity and stability for visible light driven CO2 reduction to solar fuels

Hierarchical nanostructures have lately garnered enormous attention because of their remarkable performances in energy storage and catalysis applications. In this study, novel hierarchical ZnV2O6 nanosheets, formulated by one-step solvothermal method, for enhanced photocatalytic CO2 reduction with H2O to solar fuels has been investigated. The structure and properties of the catalysts were characterized by XRD, FESEM, TEM, BET, UV–vis, Raman and PL spectroscopy. The hierarchical ZnV2O6nanosheets show excellent performance towards photoreduction of CO2 with H2O to CH3OH, CH3COOH and HCOOH under visible light. The main product yield, CH3OH of 3253.84 μmol g-cat−1 was obtained over ZnV2O6, 3.4 times the amount of CH3OH produced over the ZnO/V2O5 composite (945.28 μmol g-cat−1). In addition, CH3OH selectivity of 39.96% achieved over ZnO/V2O5, increased to 48.78% in ZnV2O6nanosheets. This significant improvement in photo-activity over ZnV2O6 structure was due to hierarchical structure with enhanced charge separation by V2O5. The obtained ZnV2O6 hierarchical nanosheets exhibited excellent photocatalytic stability for selective CH3OH production.

  1. Bafaqeer, A., Tahir, M. and Amin, N. (2018). Synthesis of hierarchical ZnV2O6 nanosheets with enhanced activity and stability for visible light driven CO2 reduction to solar fuelsApplied Surface Science, 435, pp.953-962.

DOI: https://doi.org/10.1016/j.apsusc.2017.11.116

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Optimization Studies of Oil Palm Empty Fruit Bunch Liquefaction for Carbon Cryogel Production as Catalyst in Levulinic Acid Esterification

Liquefaction of oil palm empty fruit bunch (EFB) using 1-butyl-3-methylimidazolium chloride was investigated in this study. The experiments were designed based on central composite by response surface methodology (RSM). The optimum conditions for the predicted liquefied EFB yield of 80.97 wt% was obtained at the temperature of 151.9 °C, a reaction time of 112.78 min and a ratio (Ionic liquid to EFB) of 4.27. The Regression coefficient (R2) for the model was 0.90 indicating a high correlation between observed and predicted values. The liquefied EFB mixture was used in the preparation of carbon cryogel via a sol-gel poly-condensation reaction and calcination process. The presence of sulfuric acid during the gel synthesis promoted an active site on the gel linkage and surface. The carbon cryogel prepared was tested as catalyst in an esterification reaction. The conversion of levulinic acid and yield of ethyl levulinate were reported as 58.7% ansd 57.2 mol%, respectively.

  1. Mohammad Zainol, M., Saidina Amin, N. and Asmadi, M. (2018). OPTIMIZATION STUDIES OF OIL PALM EMPTY FRUIT BUNCH LIQUEFACTION FOR CARBON CRYOGEL PRODUCTION AS CATALYST IN LEVULINIC ACID ESTERIFICATIONJurnal Teknologi, 80(2).
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Tailoring performance of La-modified TiO2 nanocatalyst for continuous photocatalytic CO2 reforming of CH4 to fuels in the presence of H2O

Photo-induced CO2 reforming of CH4 in the presence of H2O over La-modified TiO2nanoparticles in a continuous flow photoreactor has been investigated. The structure and properties of the catalyst samples, synthesized by a sol-gel method, were systematically characterized by XRD, Raman, SEM, TEM, CO2-TPD, TGA, N2-sorption, XPS, UV–Vis DRS and PL spectroscopy. The crystallite size was reduced while, BET surface area and basicity were increased due to the presence of La2O3. The La-modified TiO2 nanocatalysts were tested under different catalyst loading, irradiation time, reaction temperature and type of reductants. The main products detected over La/TiO2 catalysts during photo-induced CO2-CH4 reaction system were CO, H2 and C2H6. The amount of CO produced over 5 wt.% La/TiO2 was 9.6 fold more the amount of CO produced by pure TiO2. When H2O was added to the CO2-CH4 reaction system, the yield of CO increased 37 fold higher over 5 wt.% La/TiO2compared to TiO2. The enhanced photocatalytic performances can be attributed to the synergistic effect of La2O3 for CO2 adsorption with hindered charge recombination rate by La3+ and appropriate redox potentials. The photocatalytic turnover productivity (PTOP), calculated for the first time, presented amounts of products evolved with the photon energy consumption. The highest PTOP number achieved for CO production using the CO2-CH4-H2O reaction system was 3.83 fold higher than PTOP achieved in CO2-CH4 reaction system. However, PTOP for the production of H2 and C2H6 in CO2-CH4 system was 1.2 and 2.1 fold higher than the CO2-CH4-H2O reaction system, respectively. The stability test revealed prolonged life time of La/TiO2 in cyclic runs for dynamic CO2-CH4 conversion to fuels in the presence of H2O than using only CO2-CH4 reaction system. Therefore, CO2-CH4 could efficiently be converted to fuels over a La/TiO2 catalyst while the addition of H2O could promote both photoactivity and stability.

  1. Tahir, B., Tahir, M. and Amin, N. (2018). Tailoring performance of La-modified TiO 2 nanocatalyst for continuous photocatalytic CO 2 reforming of CH 4 to fuels in the presence of H 2 OEnergy Conversion and Management, 159, pp.284-298. DOI : https://doi.org/10.1016/j.enconman.2017.12.089
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Reduction of CO2 emission by INCAM model in Malaysia biomass power plants during the year 2016

As the world’s second largest palm oil producer and exporter, Malaysia could capitalize on its oil palm biomass waste for power generation. The emission factors from this renewable energy source are far lower than that of fossil fuels. This study applies an integrated carbon accounting and mitigation (INCAM) model to calculate the amount of CO2 emissions from two biomass thermal power plants. The CO2emissions released from biomass plants utilizing empty fruit bunch (EFB) and palm oil mill effluent (POME), as alternative fuels for powering steam and gas turbines, were determined using the INCAM model. Each section emitting CO2 in the power plant, known as the carbon accounting center (CAC), was measured for its carbon profile (CP) and carbon index (CI). The carbon performance indicator (CPI) included electricity, fuel and water consumption, solid waste and waste-water generation. The carbon emission index (CEI) and carbon emission profile (CEP), based on the total monthly carbon production, were determined across the CPI. Various innovative strategies resulted in a 20%-90% reduction of CO2 emissions. The implementation of reduction strategies significantly reduced the CO2 emission levels. Based on the model, utilization of EFB and POME in the facilities could significantly reduce the CO2 emissions and increase the potential for waste to energy initiatives.

Amin, N. and Talebian-Kiakalaieh, A. (2018). Reduction of CO 2 emission by INCAM model in Malaysia biomass power plants during the year 2016Waste Management, 73, pp.256-264.

DOI : 10.1016/j.wasman.2017.11.019

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Thermo-kinetic assessment of glucose decomposition to 5-hydroxymethyl furfural and levulinic acid over acidic functionalized ionic liquid

Decomposition of biomass feedstock is a promising technique for producing versatile chemicals such as 5-hydroxymethyl furfural (5-HMF) and levulinic acid (LA). Glucose, the model compound of cellulose, is one of the most important starting components for bio-based chemical synthesis. Herein, the kinetics of glucose decomposition catalyzed by an acidic functionalized ionic liquid, 1-sulfonic acid-3-methyl imidazolium tetrachloroferrate ([SMIM][FeCl4]) was studied in the temperature range of 110–170 °C. A simplified kinetic model was developed based on pseudo-homogeneous first-order reactions. The kinetic model consists of four main key steps: (1) dehydration of glucose to 5-HMF; (2) degradation of glucose to humins; (3) rehydration of 5-HMF to LA; and (4) degradation of 5-HMF to humins. The proposed model was in a good agreement with the experimental results. The evaluated activation energies for glucose decomposition to 5-HMF and 5-HMF decomposition to LA were 37 and 30 kJ·mol−1, respectively. The first-order rate constants were also used to calculate the thermodynamic activation parameters. The kinetic and thermodynamic parameters obtained can be applied to provide insights on the biomass decomposition to 5-HMF and LA using acidic ionic liquid.

  1. Ramli, N. and Amin, N. (2018). Thermo-kinetic assessment of glucose decomposition to 5-hydroxymethyl furfural and levulinic acid over acidic functionalized ionic liquidChemical Engineering Journal, 335, pp.221-230.
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Synergistic effects of 2D/2D ZnV2O6/RGO nanosheets heterojunction for stable and high performance photo-induced CO2 reduction to solar fuels

Highly photo-stable and efficient 2D/2D zinc vanadium oxide-reduced graphene oxide (ZnV2O6/RGO) nanosheets heterojunction was fabricated by the one-pot solvothermal method. The structures and properties of the catalysts were analyzed by XRD, FE-SEM, EDX, TEM, BET, UV–vis, Raman and PL spectroscopy. The 2D/2D ZnV2O6/RGO catalyst shows excellent performance towards CO2 photo-reduction with H2O to CH3OH, CH3COOH and HCOOH under visible light. The yield of the main product CH3OH of 5154 μmol g-cat−1, obtained over ZnV2O6/4%RGO, was 1.6 times the amount of CH3OH produced over the pure ZnV2O6 (3254 μmol g-cat−1) and a 5.5-fold higher than that of the ZnO/V2O5 composite (945 μmol g-cat−1). In addition, CH3OH selectivity of 39.96% achieved over the ZnO/V2O5 composite increased to 68.89% in ZnV2O6/4%RGO. The continuous and selective production of CH3OH was detected over the entire irradiation time in ZnV2O6 and ZnV2O6/4%RGO samples, whereas the yield of products gradually decreased in ZnO/V2O5. The significant improvement in photo-activity over 2D ZnV2O6 structure was due to the hierarchical structure with enhanced charges separation. A combined 2D/2D ZnV2O6/RGO nanosheets prevailed as a promising strategy to ameliorate the photocatalytic performance of ZnV2O6 nanosheets due to efficient trapping and transport of electrons by RGO. The synergistic effects in ZnV2O6/RGO 2D/2D nanosheets exhibited excellent photocatalytic stability, which prevailed even after 32 h of operation time for selective and continuous CH3OH production. A proposed photo-induced reaction mechanism, corroborated with the experimental data, was also deliberated.

Bafaqeer, A., Tahir, M. and Amin, N. (2018). Synergistic effects of 2D/2D ZnV2O6/RGO nanosheets heterojunction for stable and high performance photo-induced CO2 reduction to solar fuelsChemical Engineering Journal, 334, pp.2142-2153.

DOI : 10.1016/j.cej.2017.11.111

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