Hydrodeoxygenation of Lignin Monomer Guaiacol Over Supported Bimetallic Nickel-Iron Catalysts to Produce Valuable Chemicals

Munagala, Meghana and Shee, Debaprasad (2018) Hydrodeoxygenation of Lignin Monomer Guaiacol Over Supported Bimetallic Nickel-Iron Catalysts to Produce Valuable Chemicals. Masters thesis, Indian Institute of Technology Hyderabad.

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Abstract

Upgradation of Lignin derived bio-oil and Liginin depolymerization stream to chemicals of industrial importance by catalytic hydrodeoxygenation (HDO) has garnered a lot of attention in many research studies. However, development of suitable catalysts with superior catalytic activity for deoxygenation, less H2 requirments and are also inexpensive is a challenging task. In this present work, we screened bimetallic nickel-iron (Ni-Fe) catalysts supported on zirconia (ZrO2) of varying Ni to Fe mole ratio synthesized by co-impregnation method with an aim to develop a novel inexpensive catalyst for guaiacol HDO. All the synthesized catalysts were analysed using characterization techniques such as BET, XRD (powder), H2-TPR, UV-vis, FTIR and pyridine-FTIR. We have investigated the effect of reaction parameters on product distribution and conversion of guaiacol over a wide range of reaction temperature (523 to 623 K), initial hydrogen pressure (0 to 40 bar H2), catalyst loading (0 to 1 % (wt/v)), varying Ni to Fe mole ratio and total metal loading (2 to 7 wt%) and optimized all these parameters. Bimetallic 5Ni1Fe1/ZrO2 catalyst demonstrated superior catalytic activity than monometallic 5Ni1Fe0/ZrO2 and 5Ni0Fe1/ZrO2 with 60% selectivity to phenol and this can be attributed to the synergistic effects of Ni and Fe in bimetallic catalyst. Phenol was found to be major primary product upon which it is further transformed to cyclohexanol, cyclohexanone, cyclohexane, benzene and cresols with varying selectivities depending upon the active metal species dispersed on the catalyst surface. 5Ni1Fe0/ZrO2 catalyst exhibited a higher affinity for aromatic ring hydrogenation and there by yielding cyclohexane as major product whereas on the other hand 5Ni0Fe1/ZrO2 yielded phenol as major product. Upon increaing the Fe content in bimetallic Ni-Fe catalysts resulted in decreased selectivity towards ring hydrogenation products and thus demonstrating the ability of Fe to suppress the ring hydrogenation reactions as reported in the literature earlier. Upon studying the time distribution of products of guaiacol HDO under broad range of reaction parameters with catalysts of varying Ni to Fe mole ratio, we have come up with possible reaction pathways involved in guaiacol HDO and reaction mechanism for HDO of guaicol has been proposed.

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