Prof. Ir. Dr. Nor Aishah Saidina Amin

Abstract:

The successful production of higher hydrocarbons from methane depends on the stability or the oxidation rate of the intermediate products. The performances of the BZSM-5 and the modified BZSM-5 catalysts were tested for ethylene conversion into higher hydrocarbons. The catalytic experiments were carried out in a fixed-bed micro reactor at atmospheric pressure. The catalysts were characterized using XRD, NH₃-TPD, and IR for their structure and acidity. The result suggests that BZSM-5 is a weak acid. The introduction of copper into BZSM-5 improved the acidity of BZSM-5. The conversion of ethylene toward higher hydrocarbons is dependent on the acidity of the catalyst. Only weaker acid site is required to convert ethylene to higher hydrocarbons. The loading of Cu on BZSM-5 improved the selectivity for higher hydrocarbons especially at low percentage. The reactivity of ethylene is dependent on the amount of acidity as well as the presence of metal on the catalyst surface. Cu1%BZSM-5 is capable of converting ethylene to higher hydrocarbons. The balances between the metal and acid sites influence the performance of ethylene conversion and higher hydrocarbon selectivity. Higher loading of Cu leads to the formation of CO_x.

1. Ramli Mat, Nor Aishah Saidina Amin, Zainab Ramli and Wan Azli Wan Abu Bakar. (2006). Ethylene Conversion to Higher Hydrocarbon over Copper Loaded BZSM-5 in the Presence of Oxygen. Journal of Natural Gas Chemistry, 15, 259-265, Science Press.

Abstract:

A dual-bed catalytic system is proposed for the direct conversion of methane to liquid hydrocarbons. In this system, methane is converted in the first stage to oxidative coupling of methane (OCM) products by selective catalytic oxidation with oxygen over La-supported MgO catalyst. The second bed, comprising of the HZSM-5 zeolite catalyst, is used for the oligomerization of OCM light hydrocarbon products to liquid hydrocarbons. The effects of temperature (650–800 °), methane to oxygen ratio (4–10), and SiO₂/Al₂O₃ ratio of the HZSM-5 zeolite catalyst on the process are studied. At higher reaction temperatures, there is considerable dealumination of HZSM-5, and thus its catalytic performance is reduced. The acidity of HZSM-5 in the second bed is responsible for the oligomerization reaction that leads to the formation of liquid hydrocarbons. The activities of the oligomerization sites were unequivocally affected by the SiO₂/Al₂O₃ ratio. The relation between the acidity and the activity of HZSM-5 is studied by means of TPD-NH₃ techniques. The rise in oxygen concentration is not beneficial for the C₅₊ selectivity, where the combustion reaction of intermediate hydrocarbon products that leads to the formation of carbon oxide (CO+CO₂) products is more dominant than the oligomerization reaction. The dual-bed catalytic system is highly potential for directly converting methane to liquid fuels.

1. Nor Aishah Saidina Amin and Sriraj Ammasi (2006). Dual-bed Catalytic System for Direct Conversion of Methane to Liquid Hydrocarbons. Journal of Natural Gas Chemistry, 15, 191-202, Science Press.

Abstract:

The present investigation focuses on the synergistic effect of catalyst basicity and reducibility on the catalytic activity of binary and ternary CeO₂-based catalysts in the CO₂ oxidative coupling of methane (CO₂ OCM). Proper amount of medium and strong basic sites together with lower amount of very strong basic sites are identified as pertinent factors in increasing the catalytic performance. The CO₂-TPD and H₂-TPR studies indicate synergistic effect between the catalyst basicity and reducibility for the 12.8CaO–6.4MnO/CeO₂ ternary metal-oxide catalyst in enhancing the CO₂ OCM performance.

1. Istadi and Nor Aishah Saidina Amin (2006). Synergistic Effect of Catalyst Basicity and Reducibility on Performance of Ternary CeO₂-based Catalyst for CO₂ OCM to C₂ Journal of Molecular Catalysis A: Chemical, 259, 61 – 66, Elsevier.

Abstract:

Carbon dioxide rather than oxygen seemed to be an alternative oxidant for the catalytic reaction of methane to produce C₂hydrocarbons via oxidative coupling of methane (CO₂ OCM). The proper amount of medium and strong basic sites and the reducibility of the catalyst enhanced the CH4 conversion and C₂ hydrocarbon yield, which may be due to the synergistic effect among CeO₂, CaO and MnO in the catalyst. The C₂ hydrocarbons selectivity and yield of 75.6% and 3.9%, respectively were achieved over the 12.8CaO-6.4MnO/CeO₂ catalyst. The catalyst showed a good stability for 20 h time on stream in the CO₂OCM process.

1. Nor Aishah Saidina Amin and Istadi (2006). Selective Conversion of Methane to C₂ Hydrocarbons using Carbon Dioxide as an Oxidant over CaO-MnO/CeO₂ Studies in Surface Science & Catalysis, 159, 213-216, Elsevier B.V.

Abstract:

Methane conversion to higher hydrocarbons in the presence of oxygen was studied over W/HZSM-5-based catalysts. W–H₂SO₄/HZSM-5 catalyst containing octahedral coordinated tungsten species showed the highest activity. Over 2% W–H₂SO₄/HZSM-5 catalyst, the methane conversion reached ≈20% with the average aromatic yield being 9% after 200 min of time on stream. In addition, the results of methane conversion in non-oxidative condition showed that the catalytic activity was drastically reduced with time on stream. Consequently, it can be concluded that the durability of the catalysts was enhanced in the presence of suitable amount of O₂.

1. Nor Aishah Saidina Amin and Soon Ee Pheng (2006). Methane Conversion to Higher Hydrocarbons Over W/HZSM-5-based Catalysts in the Presence of Oxygen. Catalysis Communications, 7, 403-407, Elsevier.

Abstract:

The optimization of process parameters and catalyst compositions for the CO₂oxidative coupling of methane (CO₂-OCM) reaction over CaO–MnO/CeO₂ catalyst was developed using Response Surface Methodology (RSM). The relationship between the responses, i.e. CH₄ conversion, C₂ hydrocarbons selectivity or yield, with four independent variables, i.e. CO₂/CH₄ ratio, reactor temperature, wt.% CaO and wt.% MnO in the catalyst, were presented as empirical mathematical models. The maximum C₂ hydrocarbons selectivity and yields of 82.62% and 3.93%, respectively, were achieved by the individual-response optimization at the corresponding optimal process parameters and catalyst compositions. However, the CH₄ conversion was a saddle function and did not show a unique optimum as revealed by the canonical analysis. Moreover pertaining to simultaneous multi-responses optimization, the maximum C₂ selectivity and yield of 76.56% and 3.74%, respectively, were obtained at a unique optimal process parameters and catalyst compositions. It may be deduced that both individual- and multi-responses optimizations are useful for the recommendation of optimal process parameters and catalyst compositions for the CO₂-OCM process.

1. Istadi and Nor Aishah Saidina Amin (2006). Optimization of Process Parameters and Catalyst Compositions in Carbon Dioxide Oxidative Coupling of Methane over CaO-MnO/CeO₂ Catalyst using Response Surface Methodology. Fuel Processing Technology, 87 (5), 449-459, Elsevier.