Value addition of lignin to zingerone using recyclable AlPO4 and Ni/LRC catalysts

Abstract

Value-addition of lignin to chemicals and medicinal compounds is highly desirable for bio-refineries and chemical industries. We present a simple and intriguing two-step method for synthesizing zingerone from vanillin. The first step was to make dehydrozingerone via aldol condensation of vanillin and acetone in the presence of an AlPO4 catalyst. At 120 °C for 24 h, this catalyst showed outstanding activity, with 99% selectivity of dehydrozingerone. Second, utilizing lignin residual carbon assisted Ni nanocatalyst (Ni/LRC), the dehydrozingerone was transformed into targeted zingerone by selective hydrogenation of the C–C double bond. The reaction parameters significantly influenced the formation of both dehydrozingerone and zingerone. The Physico-chemical properties of both the catalysts (AlPO4 and Ni/LRC) were thoroughly investigated by NH3 and CO2 TPD, Py-FTIR, XRD, N2 adsorption–desorption, 27Al, and 31P MAS NMR and FT-IR analysis. Interestingly, both AlPO4 and Ni/LRC catalysts were effectively recovered and reused for 10 cycles without apparent loss in catalytic activity for their respective reactions. Zingerone was eventually synthesized directly from lignin for the first time, with yields of 9.25 wt% on initial lignin intake.