Prof. Ir. Dr. Nor Aishah Saidina Amin

The synthesis of ethyl levulinate, a fuel additive, by catalytic esterification of levulinic acid with ethanol over carbon cryogel has been investigated. The carbon cryogel catalyst, coupled with a large surface area and strong acidity, has been identified as an effective carbon-based catalyst for obtaining high ethyl levulinate yield of 86.5 mol%. The pseudo-homogeneous kinetic model is adopted to evaluate the different reaction orders. The first-order pseudo-homogeneous model is considered most suitable (R² > 0.98) while the selection of kinetic model is also clarified and supported by the linearity of the parity plot. The activation energy of the esterification reaction is estimated to be 20.2 kJ/mol. Based on the thermodynamic activation parameters, the reaction is classified as endergonic and more ordered. The results from this study could provide valuable information for reactor modeling and simulation purposes in the future.

1. Zainol, M., Amin, N. and Asmadi, M. (2018). Kinetics and thermodynamic analysis of levulinic acid esterification using lignin-furfural carbon cryogel catalyst. Renewable Energy, 130, pp.547-57.
2. DOI :https://doi.org/10.1016/j.renene.2018.06.085

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-C₃N_4, 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

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

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 fuels. Applied Surface Science, 435, pp.953-962.

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

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 O. Energy Conversion and Management, 159, pp.284-298. DOI : https://doi.org/10.1016/j.enconman.2017.12.089

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 2016. Waste Management, 73, pp.256-264.

DOI : 10.1016/j.wasman.2017.11.019

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 liquid. Chemical Engineering Journal, 335, pp.221-230.