Amine-functionalised framework NH-MIL-101(Al) was synthesized using a solvothermal and microwave method and characterized by PXRD, FT-IR, TGA, SEM-EDX, and BET surface area analysis. The desolvated framework, in the presence of co-catalyst tetrabutylammonium bromide (TBAB), acted as an excellent heterogeneous catalyst for the solvent-free cycloaddition of carbon dioxide (CO) with epoxides, affording five-membered cyclic carbonates. Using styrene oxide, the NH-MIL-101(Al)/TBAB system showed more than 99% conversion, affording 96% yield and 99% selectivity with a turn over frequency of 23.5 h. This validated the synergistic effect of the quaternary ammonium salt during CO cycloaddition. The catalyst could be recycled at least five times without a noticeable loss in activity, while leaching test showed no leached Al ions throughout the reaction. Thorough analysis of the reaction parameters showed that the optimum conditions for obtaining the maximum yield and highest selectivity were 120 °C and 18 bar of CO for 6 h. The outstanding conversion and selectivity were maintained for a range of aliphatic and aromatic epoxides, corroborating the duel benefit of the micro-mesoporous system with amine functionality, which offered easy access for reactant molecules with diverse sizes, and provided inspiration for future CO cycloaddition catalytic systems. We also propose a rationalized mechanism for the cycloaddition reaction mediated by NH-MIL-101(Al) and TBAB based on literature precedent and experimental outcome.

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Rhodium hydrotalcite (Rh‐HT), a heterogeneous catalyst was synthesized, characterized and investigated for CO2 hydrogenation. The catalyst was effectual for the CO2 hydrogenation and selective formation of formic acid at a moderate temperature and was efficiently recycled up to 5 times without any significant loss in activity. A TON of 15840 for formic acid was selectively obtained at 50 bar pressure (1:1, p/p, CO2 and H2) and 60 °C temperature in a mixture of methanol:water (5:1 v/v, 60 mL) as a solvent in 24 h with no additional base. The effect of various reaction parameters was investigated for the reaction rate and CO2 conversion. The formic acid formation rate follows the 1st order kinetic trend regarding the catalyst amount and partial pressure. The determined activation parameters from the temperature dependence rate of formic acid were Ea=33.5 ± 2.5 kJmol−1, ΔH#=30.9 ± 2.5 kJmol−1, ΔS#=‐275 ± 5 Jdeg−1mol−1. The presence of water as a solvent together with methanol have effectively enhanced the performance of the catalyst. The mechanistic routes for CO2 hydrogenation to formic acid are proposed and discussed by the kinetic and experimental observations.