Understanding the role of acid sites of Zinc Aluminophosphate catalysts in eco-friendly synthesis of carbamates

Abstract

Aluminophosphate and metal incorporated aluminophosphates have been synthesized at ice-cold temperature by simple co-precipitation method in the absence of a templating agent. Surface and bulk properties of synthesized materials were studied by different characterization techniques. The materials were found to be X-ray amorphous. N₂ adsorption-desorption studies exhibited the existence of microporous structure and uniform narrow slit type of pores on the materials. The catalytic activity of the synthesized material was tested in phosgene free synthesis of carbamates from corresponding amines and dimethyl carbonate (DMC) through a greener route. Metal incorporated Aluminophosphates indicated excellent catalytic activity compared to pure aluminophosphates. Zinc aluminophosphate catalyst exhibited 83% carbamate yield with 100% selectivity towards the formation of carbamate. The excellent catalytic activity of Zinc aluminophosphate with 94% amine conversion is attributed to its surface properties mainly moderate acid strength. The incorporated metal plays a vital role in the structural and textural properties of aluminophosphates. A systematic study was conducted to correlate the catalytic activity and surface properties of metal aluminophosphates. Reaction conditions were optimized to obtain a better yield through phosgene free eco-friendly routes using different amines. The catalyst was found to be recyclable for 5 cycles in the desired reaction without a reduction in conversion and selectivity.