Solid base catalysts for pentaerythritol synthesis: Activity, stability, and recyclability of catalysts based on alkali and alkaline earth metals

The substitution of homogeneous bases with solid basic catalysts is highly desirable for the synthesis of pentaerythritol (penta), as liquid alkalis generate waste, accelerate reactor corrosion, and require extensive separation steps to isolate pure penta. This study investigates the catalytic activity of alkali and alkaline earth metals Ca, Na, and Mg supported on SnO 2 , TiO 2 , and γ-Al 2 O 3 for the conversion of formaldehyde and acetaldehyde to penta. Reaction parameters including temperature, feed ratios, reaction time, and catalyst loading were examined to find optimized conditions to maximize penta selectivity. Among the tested systems, 22% Mg/γ-Al 2 O 3 catalyst demonstrated the best performance, achieving 76% penta selectivity at 49% formaldehyde conversion under the following conditions: 90 °C, a 5:1 M ratio of formaldehyde to acetaldehyde, 0.2 g catalyst and 15 min reaction time. However, the leaching of Mg was siginficant. Mg on γ-Al 2 O 3 with different Mg loadings were evaluated, showing that 9 wt% Mg/γ-Al 2 O 3 catalyst exhibited the least amount of leaching, from 9 for fresh catalyst to 7.5 wt% Mg for spent catalyst (after reaction at 70 °C) and a penta selectivity of 61%, albeit at a slightly lower formaldehyde conversion of 41%. However, the accumulation of formate species on catalyst surface was observed with DRIFT spectroscopy, which resulted in deactivation of the catalyst. The catalyst partially regained the activity when recycled in multiple cycles after regeneration of spent catalyst. These findings highlight the potential of Mg-based solid catalysts for pentaerythritol synthesis, while also underscoring the need for further research to enhance catalyst stability and recyclability for industrial applications.