Enhanced catalytic performance of transition metal-doped Co/TiO2 for continuous-flow synthesis of borneol from isoborneol

Abstract

Borneol, a pharmaceutically important monoterpenoid, has emerged as a key ingredient in modern medicinal formulations. Here, we report a highly efficient heterogeneous catalytic system using transition metal-doped Co/TiO₂ catalysts for the continuous-flow isomerization of isoborneol to borneol. Through systematic screening of bimetallic combinations, we demonstrate that Cu and Ni dopants synergistically enhance the redox properties of Co species, particularly improving hydrogenation–dehydrogenation efficiency in the isomerization of isoborneol. The optimized 1Cu–3Co/TiO₂ catalyst (Cu : Co = 1 : 3 mass ratio) enabled a two-stage continuous-flow system, achieving 58% molar yield of borneol with <0.4% camphor byproduct formation after solvent removal. Remarkably, the catalyst maintained >99% metal retention during a total of 200 h of continuous reaction. This work not only provides fundamental insights into promoter effects in bimetallic catalysis but also establishes a commercially viable platform for continuous production of high-purity botanical therapeutics.