Calcination-driven structure–activity relationship of SnO₂–ZrO₂ mixed oxide catalysts for highly selective transfer hydrogenation of cinnamaldehyde to cinnamyl alcohol

We report the cost-effective SnO₂–ZrO₂ (1:1) mixed oxide catalysts by co-precipitation and calcined at different temperatures (400–800 °C) to explore the impact of calcination-driven structural changes on selective transfer hydrogenation (TH) reaction of cinnamaldehyde (CAL) with some lower alcohols to cinnamyl alcohol (COL). We also compared the activity of pure SnO₂ and ZrO₂. We systematically characterised the catalysts using a range of analytical techniques. In addition to optimising calcination temperature, this work provides new insight into the decisive role of Lewis acidity, in which synergistic interactions between Sn 4+ –Zr 4+ cations coordinate crystallinity and surface area, thereby modulating structural and catalytic properties. The TH reaction of CAL with isopropyl alcohol (IPA) using the SZ-6 (600°C) catalyst displayed superior activity, with 87.5% conversion and 96% selectivity toward COL. Good performance is due to a small crystallite size (16.3 nm), a high surface area (81.5 m 2 /g), strong acidity (314 µmol/g), optimal synergism/Lewis acidity, and a stable tetragonal phase of SZ-6. Turnover frequency (TOF) calculations based on acidic sites and catalyst mass further confirmed its high intrinsic activity. The SZ-6 catalyst demonstrated good stability over five consecutive cycles. The deactivation behaviour was systematically analysed using XRD, BET, and SEM.