Bio-oils are becoming alternatives to fossil fuels in view of the ever rising global energy demands, greenhouse emissions, and crude oil shortage. Bio-oils extracted from lignocellulosic biomass are composed of multicomponent molecules extracted from lignin, cellulose, and hemicellulose. The lignin component of lignocellulose is a promising renewable feedstock for the production of a number of chemicals and fuels. Lignin has an advantage over its counterparts hemicellulose and cellulose considering that bio-oils extracted from lignin can be upgraded to higher quality transportation fuels. This is in view of the high stability of the lignin aromatic structures with reference to resonance stabilization.
Fast pyrolysis has been an extensively applied method for converting lignin into bio-oil. Unfortunately, the potential of the resulting bio-oil is limited by the presence of a number of oxygenated functional groups, which in consequence lead to undesirable physicochemical attributes including low thermal and chemical stability, low heating values, easy corrosiveness and high density. In addition, lignin-extracted bio-oils are incompatible with either direct use or in combination with a petroleum fraction. This has forced researchers to look for alternative strategies which can enhance the commercial viability of lignin-extracted bio-fuels for use as a transportation fuel.
One method to remove chemically bonded oxygen from lignin-extracted oil and therefore enable the use of lignin-extracted bio-fuels is through catalytic hydrodeoxygenation processes. However, the direct application of catalysts in such processes is associated with numerous challenges owing to the complex nature of its oxygenated aromatic elements such as anisole, furan, benzofuran, and phenols. In order to overcome these issues, heterogeneous catalysts are attracting much attention, containing both a metal centre for the hydrogenation of the acidic support and an aromatic ring for the deoxygenation. While noble metals such as platinum, palladium, and ruthenium have been used in this process, their application is limited by the high cost and scarcity of these noble metals. Therefore, researchers have focused their attention on transition metal based catalysts including cobalt, nickel, iron, and copper-nickel.
Putla Sudarsanam and Suresh Bhargava at the Centre for Advanced Materials and Industrial Chemistry, School of Science, RMIT University in Australia in collaboration with Murtala Ambursa, Lee Hwei Voon, and Sharifah Bee Abd Hamid at the University of Malaya investigated the preparation, characterization and catalytic application of bimetallic Cu-Ni catalysts supported on Ti-MCM-41 for the hydrodeoxygenation of guaiacol. Their research work is published in the journal Fuel Processing Technology.
The authors prepared Cu-Ni catalysts supported on either Ti-MCM-41 or pure MCM-41 and compared their catalytic efficiencies for the hydrodeoxygenation of guaiacol. They performed the catalytic experiments in an autoclave reactor and investigated the effect of hydrogen pressure on guaiacol conversion as well as product selectivity.
Through the catalytic activity investigation, the authors observed that the CuNi/Ti-MCM-41 catalysts had a higher catalytic performance in guaiacol conversion as well as cyclohexane selectivity as opposed to a CuNi/MCM-41 catalyst. The high catalytic activity of the CuNi/Ti-MCM-41 catalyst was as a result of the cooperative function of the larger surface area, hexagonal pore geometry, medium-sized mesopores, adequate acidic sites, and excellent redox attributes. For this reason, Ti-MCM-41 is an efficient catalyst support for the hydrodeoxygenation of oxygenated elements to saturated hydrocarbons.
The research team also found that increased hydrogen pressures improved the guaiacol conversion and selectivity of the oxygenated compounds to hydrocarbons over the Ti-MCM-41 supported CuNi catalyst, increasing the impact of these catalysts within this important field of research.
Murtala M. Ambursa, Putla Sudarsanam, Lee Hwei Voon, Sharifah Bee Abd Hamid, Suresh K. Bhargava. Bimetallic Cu-Ni catalysts supported on MCM-41 and Ti-MCM-41 porous materials for hydro-deoxygenation of lignin model compound into transportation fuels. Fuel Processing Technology, volume 162 (2017), pages 87–97.
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