Abstract
Valorization of lignin into aromatics has driven researchers for decades. In this research, niobium was deposited on oyster shells (OSNC) and carbon rods (CRNC) and tested as a catalyst for depolymerization of lignin. Catalysts (2%, 5%, and 8% loading) were synthesized via wet impregnation. Batch experiments were performed at 95 °C, using 8 g of lignin, and 1 g of catalyst. Our research indicates that niobium supported catalysts are effective in partial oxidation of lignin. Maximum vanillin concentration for OSNC was found to be 86.25 mg L−1 (0.1 wt%) at 5% niobium whereas, as for CRNC, maximum vanillin concentration was found to be 139.40 mg L−1 (0.17 wt%) at 2% niobium loading. Addition of hydrogen peroxide into the batch reactor decreased the concentration of vanillin production.
Highlights
Use of lignocellulosic feedstocks as precursors for the production of chemicals and value-added products have generated a significant interest lately [1,2,3,4,5]
Villar et al [32] investigated oxidation of hardwood kraft lignin under alkaline conditions using CuSO4, CoCl2, and Co(II) salen catalysts and reported that the yields of aldehydes did not increase when copper (II) and cobalt (II) loading increased perhaps due to subsequent oxidation of the reaction products
Vanillin yield from the softwoods were 3.1% to 4.4% with respect to lignin, while hardwood lignin yielded 1.2% of vanillin and 2.5% of syringaldehyde
Summary
Use of lignocellulosic feedstocks as precursors for the production of chemicals and value-added products have generated a significant interest lately [1,2,3,4,5]. Oxidation of lignin into desired chemicals requires a selective catalyst that would minimize secondary oxidation reactions. Application of niobium as an effective and selective catalyst for several oxidation reactions has been well documented [17,18,19]. As a result, supported niobium catalysts have been employed in hydrogenation, methylisobutyl ketone synthesis, metathesis, and hydrotreating reactions [20]. Supported-carbon catalysts have been used by several researchers for a variety of applications, including oxidation reactions [30,31]. Niobium impregnated on an oyster shell and carbon rods were synthesized as catalysts for use in lignin oxidation
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